JP4734396B2 - Laminated porous film, lithium battery separator and battery using the same - Google Patents

Description

  The present invention relates to a porous body, and the porous body can be used as a packaging product, a sanitary product, a livestock product, an agricultural product, a building product, a medical product, a separation film, a light diffusing plate, a reflective sheet, or a battery separator, and particularly various electronic devices. It is suitably used as a separator for a non-aqueous electrolyte battery such as a lithium ion secondary battery used as a power source.

  The polymer porous body with many fine communication holes is used for separation membranes used for the production of ultrapure water, purification of chemicals, water treatment, waterproof and moisture-permeable films used for clothing and sanitary materials, and batteries. It is used in various fields such as battery separators.

In particular, secondary batteries are widely used as power sources for portable devices such as OA, FA, household electric appliances, and communication devices. In particular, portable devices using lithium ion secondary batteries are increasing because they have a high volumetric efficiency when mounted on devices, leading to a reduction in size and weight of the devices.
On the other hand, large-sized secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage, and long-term storage. Therefore, the use of lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary battery, is expanding.

The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1 to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages.
As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of making more lithium ions exist is used, and organic carbonates such as polypropylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. in use. As a supporting electrolyte that becomes a lithium ion source in the solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.

  In the lithium ion secondary battery, a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit. Of course, the separator is required to have insulating properties due to its role. Moreover, it is necessary to have a microporous structure in order to provide air permeability as a lithium ion passage and a function of diffusing and holding the electrolyte. In order to satisfy these requirements, a porous film is used as a separator.

With the recent increase in battery capacity, the importance of battery safety has increased.
As a characteristic that contributes to the safety of the battery separator, there is a shutdown characteristic (hereinafter referred to as “SD characteristic”). This SD characteristic is a function of preventing the subsequent increase in temperature inside the battery because the micropores are closed when the temperature is about 100 to 140 ° C., and as a result, ion conduction inside the battery is blocked. When used as a battery separator, it is necessary to have this SD characteristic.

Another characteristic that contributes to safety is a breakdown characteristic (hereinafter referred to as “BD characteristic”). This BD characteristic is a function in which heat generation does not stop due to the development of the SD characteristic and the film does not break even when the temperature is higher (160 ° C. or higher) and the positive electrode and the negative electrode are kept separated. If it has BD characteristics, insulation can be maintained even at high temperatures, and a wide range of short-circuits between electrodes can be prevented, thereby preventing accidents such as ignition due to abnormal heat generation of the battery. Therefore, when it is used as a battery separator, it preferably has this BD characteristic, and the breakdown temperature (hereinafter referred to as “BD temperature”) is preferably higher.
Here, the “BD temperature” refers to the lowest temperature among the temperatures at which the film breaks when the laminated porous film of the present invention is put in a frame and heated in an oven.

Because of the excellent BD characteristics, dimensional stability during temperature rise is one of the important required characteristics. When the battery is abnormally heated, both electrodes are short-circuited due to a film breakage caused by the thermal contraction of the separator, and there is a risk of causing further heat generation, and further improvement in heat resistance is required.
On the other hand, it is desirable to have an appropriate shrinkage at a high temperature of about 100 ° C. for excellent SD characteristics. Since this is contrary to dimensional stability, it is extremely important to balance the shrinkage rate and the SD characteristics.

  In response to such a request, JP 2003-103624 A (Patent Document 1) provides ultra-high molecular weight polyethylene and a solvent in a kneaded and sheeted form, and after stretching, the solvent is extracted to stabilize the dimensions at 105 ° C. It has been proposed that a porous film with good properties can be obtained.

  Japanese Patent No. 3852492 (Patent Document 2) discloses a method for producing a battery separator, characterized in that a laminated film of polyethylene and polypropylene is made porous by changing the temperature in one axis direction and stretching in two stages. Has been proposed.

  On the other hand, various methods for obtaining a porous film by stretching a polypropylene sheet containing β crystals have been proposed. A feature of this method for producing a porous film is that a porous structure is obtained by using β crystals, and it is preferable that a lot of β crystals are contained in the sheet before stretching to obtain a porous structure. In addition, this method is a general biaxial stretching method, and is characterized in that productivity is very good as a method for obtaining a porous film.

  As an example, in Japanese Patent No. 1953202 (Patent Document 3), a porous resin film is obtained by forming a sheet of a resin composition containing a predetermined amount of a filler and a β-crystal nucleating agent in polypropylene and stretching the resin composition under specific stretching conditions. A method has been proposed. In addition, Japanese Patent No. 2509030 (Patent Document 4) proposes a microporous film of superpermeable polypropylene obtained by biaxial stretching from an original polypropylene film having a high β crystal content (K> 0.5). . In Japanese Patent No. 3443934 (Patent Document 5), a specific amide compound is contained in polypropylene, and crystallized under specific conditions to obtain a solidified product containing β crystals. A method for producing a film has been proposed.

JP 2003-103624 A Japanese Patent No. 3852492 Japanese Patent No. 1953202 Japanese Patent No. 2509030 Japanese Patent No. 3443934

However, the porous film manufactured by the manufacturing method of Patent Document 1 has a high thermal shrinkage rate at a temperature equal to or higher than the closed pore temperature. For example, as disclosed in Japanese Patent No. 3307231, the shrinkage rate at a high temperature such as 150 ° C. is high. It cannot be said that the stability is sufficient.
Furthermore, in this method, since the solvent contained in the entire porous membrane is removed by washing with an organic solvent for washing, a large amount of organic solvent is required, which is not preferable from an environmental viewpoint.
In addition, with respect to Patent Document 2, it is difficult to say that the manufacturing method requires strict control of manufacturing conditions and has good productivity. For example, when creating a laminated film before making it porous, film formation is performed while controlling the higher order structure with a high draft ratio, but it is very difficult to form a stable film with such a high draft ratio. Have difficulty. In addition, in order to develop a porous structure, it is necessary to perform multistage stretching at two stages, a low temperature region and a high temperature region, at a low stretching speed, and the stretching speed is greatly limited, resulting in extremely poor productivity. .
Furthermore, since the separator manufactured by the manufacturing method is manufactured by uniaxial stretching in the film flow direction, not only the dimensional stability in the direction perpendicular to the film flow direction is bad, but also the film flow direction. In addition, it is very weak against vertical tearing, and there is a problem that a tear is likely to occur in the flow direction.

  Moreover, the polypropylene porous film mentioned in the said patent documents 3-5 is superior to a polyethylene porous film in BD characteristic from the crystal melting temperature of a polypropylene being high. However, since the BD characteristic is adversely affected and the SD characteristic cannot be exhibited at all, there is a problem in securing the safety of the battery in order to use these porous films as a battery separator.

  This invention is made | formed in view of the said problem, and makes it the subject to provide the laminated porous film which has the outstanding shutdown characteristic, ensuring dimensional stability.

  In order to solve the above problems, the present invention provides a laminated porous film comprising an A layer mainly composed of a polypropylene resin and a B layer containing a polyethylene resin and having β activity. In the direction perpendicular to the flow direction of the laminated porous film, the shrinkage ratio after heating at 105 ° C. for 1 hour is 10% or less, and the flow direction of the laminated porous film and the flow direction A laminated porous film is characterized in that the ratio of shrinkage after heating for 1 hour at 105 ° C. in the vertical direction is 0.1 to 3.0.

The B layer includes a polyethylene resin and has a lower shutdown temperature (hereinafter referred to as “SD temperature”) than the A layer.
In the present invention, “SD temperature” refers to the lowest temperature at which micropores are blocked, and specifically, the air permeability after heating when the laminated porous film of the present invention is heated by the method described in the examples. Is the lowest temperature among the temperatures at which the air permeability before heating is 10 times or more.

Since at least one layer of the laminated porous film of the present invention has β activity, a fine porous layer can be provided and excellent air permeability characteristics can be exhibited.
In the laminated porous film of the present invention, the presence or absence of “β activity” is determined when a crystal melting peak temperature derived from β crystal is detected by a differential scanning calorimeter described later, or a wide angle X-ray diffraction measuring device described later. When a diffraction peak derived from the β crystal is detected by measurement using γ, it is determined to have β activity.
The β activity is measured in the state of the laminated porous film when the laminated porous film of the present invention is composed of only the A layer and the B layer and when another porous layer is laminated. is doing.

The laminated porous film preferably has the β activity by adding a β crystal nucleating agent to the resin composition of the A layer.
Further, it is preferable that a β-crystal nucleating agent is blended with the polypropylene-based resin so that the A layer has the β-activity, and the blending amount of the β-crystal nucleating agent is 100 parts by mass of the polypropylene-based resin. It is preferably 0.0001 to 5.0 parts by mass.

  The B layer preferably contains at least one compound selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, and a wax. .

The laminated porous film of the present invention is a laminated porous film in which at least two porous layers are laminated, and the shrinkage rate at a high temperature is controlled in a well-balanced manner.
Since one of the porous layers has an A layer mainly composed of a polypropylene resin and a B layer containing a polyethylene resin, the BD characteristics of a conventional laminated porous film made of a polypropylene resin are maintained. It has the SD characteristic that the hole is closed in an appropriate temperature range.
Furthermore, since the laminated porous film of the present invention has β activity, it has micropores, can ensure sufficient communication, and can maintain strength in the A layer, so that pin puncture strength And mechanical strength such as tear strength. Therefore, it is useful for battery separators from the viewpoint of structure maintenance and impact resistance.
The laminated porous film of the present invention has an air permeability at 25 ° C. of 10 to 1000 seconds / 100 ml or less, and an air permeability after heating at 135 ° C. for 5 seconds is 50000 seconds / 100 ml or more. It is characterized by that.

Hereinafter, embodiments of the laminated porous film of the present invention will be described in detail.
In the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. Although the content ratio of the components is not specified, the main component (when two or more components are the main components, the total amount thereof) is 50% by mass or more, preferably 70% by mass or more, particularly in the composition. It preferably includes 90% by mass (including 100%).
Further, when “X to Y” (X and Y are arbitrary numbers) is described, “X to Y” is intended unless otherwise specified, and “it is preferably larger than X and smaller than Y”. Includes intentions.

  The laminated porous film of the present embodiment is a laminated porous film in which at least two porous layers are laminated, and one of the two porous layers is an A layer mainly composed of a polypropylene resin. And the other layer is a B layer containing a polyethylene resin, and the laminated porous film has β activity.

The laminated porous film of the present invention is characterized by having the β activity.
The β activity can be regarded as an index indicating that the polypropylene resin has produced β crystals in the film-like material before stretching. If the polypropylene resin in the film-like material before stretching produces β crystals, fine pores are formed by subsequent stretching, so that a porous film having air permeability can be obtained.

The presence or absence of β activity of the laminated porous film can be determined by conducting a differential thermal analysis of the laminated porous film using a differential scanning calorimeter and detecting a crystal melting peak temperature derived from β crystals of polypropylene resin. Judgment is based on no.
Specifically, the laminated porous film is heated at a heating rate of 10 ° C./min from 25 ° C. to 240 ° C. for 1 minute with a differential scanning calorimeter, and then cooled from 240 ° C. to 25 ° C. at a cooling rate of 10 ° C. / When the temperature is lowered for 1 minute and held for 1 minute, and when the temperature is raised again from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./minute, the crystal melting peak temperature (Tmβ) derived from the β crystal of polypropylene is If detected, it is determined to have β activity.

In addition, the β activity of the laminated porous film is calculated by the following formula using the heat of crystal melting derived from the α crystal of the polypropylene resin (ΔHmα) and the heat of crystal melting derived from the β crystal (ΔHmβ). Yes.
β activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
For example, in the case of homopolypropylene, the heat of crystal melting derived from β crystal (ΔHmβ) detected mainly in the range of 145 ° C. or higher and lower than 160 ° C. and the α crystal derived from α crystal detected mainly at 160 ° C. or higher and 175 ° C. or lower. It can be calculated from the heat of crystal fusion (ΔHmα). Further, for example, in the case of random polypropylene copolymerized with 1 to 4 mol% of ethylene, the crystal melting heat amount (ΔHmβ) derived from the β crystal detected mainly in the range of 120 ° C. or more and less than 140 ° C., and mainly 140 It can be calculated from the crystal melting calorie (ΔHmα) derived from the α crystal detected in the range of from 0 ° C. to 165 ° C.

The β activity of the laminated porous film is preferably large, and the β activity is preferably 20% or more. More preferably, it is 40% or more, and particularly preferably 60% or more. If the laminated porous film has a β activity of 20% or more, it indicates that a large amount of β crystals of polypropylene resin can be produced in the film-like material before stretching, and fine and uniform pores are formed by stretching. Many layers are formed, and as a result, a laminated porous film having high mechanical strength and excellent air permeability can be obtained.
The upper limit of β activity is not particularly limited, but the higher the β activity, the more effective the effect is obtained.

The presence or absence of the β activity can also be determined by a diffraction profile obtained by wide-angle X-ray diffraction measurement of a laminated porous film subjected to a specific heat treatment.
Specifically, a wide-angle X-ray diffraction measurement was performed on the laminated porous film which was subjected to heat treatment at 170 to 190 ° C., which is a temperature exceeding the melting point of the polypropylene resin, and was slowly cooled to produce and grow β crystals. When the diffraction peak derived from the (300) plane of the β crystal of the resin is detected in the range of 2θ = 16.0 to 16.5 °, it is determined that there is β activity.
For details on the β crystal structure and wide-angle X-ray diffraction measurement of polypropylene resins, see Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and references cited therein. A detailed evaluation method of β activity will be described in Examples described later.

As a method for obtaining the β activity of the above-mentioned laminated porous film, a method in which a substance that promotes the formation of α crystals of the polypropylene resin in the resin composition of the A layer is not added, or described in Japanese Patent No. 3739481. Examples include a method of adding polypropylene that has been subjected to treatment for generating peroxide radicals, and a method of adding a β crystal nucleating agent to the resin composition of the A layer.
Among these, it is particularly preferable to obtain β activity by adding a β crystal nucleating agent to the resin composition of the A layer.
By adding a β crystal nucleating agent, it is possible to promote the generation of β crystals of polypropylene resin more uniformly and efficiently, and to obtain a lithium ion battery separator having a porous layer having β activity. it can.

  Below, the detail of the component of each layer which comprises the laminated porous film of this invention is demonstrated.

[Description of layer A]
First, the A layer will be described in detail below.
(Description of polypropylene resin)
Polypropylene resins contained in layer A include homopropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene. Alternatively, a random copolymer or block copolymer with an α-olefin such as 1-decene may be mentioned. Among these, homopolypropylene is more preferably used from the viewpoint of the mechanical strength of the laminated porous film.

Moreover, as a polypropylene resin, it is preferable that the isotactic pentad fraction (mmmm fraction) which shows stereoregularity is 80 to 99%. More preferably 83-99%, still more preferably 85-99%. If the isotactic pentad fraction is too low, the mechanical strength of the film may be reduced. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit that can be obtained industrially at the present time, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.
The isotactic pentad fraction (mmmm fraction) is the same direction for all five methyl groups that are side chains with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Means the three-dimensional structure located at or its proportion. Signal assignment of the methyl group region is as follows. It conforms to Zambelli et al (Macromolecules 8,687, (1975)).

  Polypropylene resin has a polydispersity (ratio of weight average molecular weight Mw and number average molecular weight Mn, expressed as Mw / Mn), which is a parameter indicating molecular weight distribution, of 1.5 to 10.0. Is preferred. More preferably, 2.0 to 8.0, and still more preferably 2.0 to 6.0 is used. This means that the smaller the Mw / Mn, the narrower the molecular weight distribution. However, if the Mw / Mn is less than 1.5, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially. . On the other hand, when Mw / Mn exceeds 10.0, low molecular weight components increase, and the mechanical strength of the laminated porous film tends to decrease. Mw / Mn is obtained by GPC (gel permeation chromatography) method.

  Further, the melt flow rate (MFR) of the polypropylene-based resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g / 10 minutes, and 1.0 to 10 g / 10 minutes. It is more preferable. When the MFR is less than 0.5 g / 10 min, the resin has a high melt viscosity at the time of molding and the productivity is lowered. On the other hand, if it exceeds 15 g / 10 minutes, the mechanical strength of the film is insufficient, and problems are likely to occur in practice. MFR is measured according to JIS K7210 under conditions of a temperature of 230 ° C. and a load of 2.16 kg.

(Description of β crystal nucleating agent)
Examples of the β crystal nucleating agent used in the present invention include those shown below, but are not particularly limited as long as they increase the formation and growth of β crystals of polypropylene resin, and two or more types are mixed. May be used.
Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by: a two-component compound comprising a component a which is an organic dibasic acid and a component b which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table; a cyclic phosphorus compound; Made of magnesium compound Such as the formation thereof.

  As specific examples of particularly preferable β crystal nucleating agents, β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of polypropylene resins to which β crystal nucleating agents are added include polypropylene manufactured by Aristech “Bepol B-022SP”, polypropylene manufactured by Borealis “Beta (β) -PP BE60-7032”, polypropylene manufactured by mayzo “BNX BETAPP-LN”, and the like. Specific types of other nucleating agents are described in JP-A No. 2003-306585, JP-A No. 06-228966, and JP-A No. 09-194650.

  The ratio of the β-crystal nucleating agent added to the polypropylene resin needs to be appropriately adjusted depending on the type of the β-crystal nucleating agent or the composition of the polypropylene-based resin. 0.0001 to 5.0 parts by mass of the agent is preferred. 0.001-3.0 mass parts is more preferable, and 0.01-1.0 mass part is still more preferable. If it is 0.0001 part by mass or more, β-crystals of polypropylene resin can be sufficiently produced and grown at the time of production to ensure sufficient β activity, and sufficient β activity is ensured even when a laminated porous film is formed. And desired air permeability and mechanical strength can be obtained. On the other hand, addition of 5.0 parts by mass or less is preferable because it is economically advantageous and there is no bleeding of the β crystal nucleating agent on the film surface.

It is important that the A layer is mainly composed of a polypropylene resin. Specifically, when a polypropylene resin and a β crystal nucleating agent are used, the total mass of the polypropylene resin and the β crystal nucleating agent is 70% by mass or more, preferably 80% by mass or more, based on the total mass of the A layer. Preferably it occupies 90 mass% or more.
The layer A may contain additives or other components that are generally blended in the resin composition within a range that does not impair the purpose of the present invention and the characteristics of the layer A as described above. Examples of the additive include recycling resin, silica, talc, kaolin, carbonic acid, etc., which are added for the purpose of improving / adjusting the processability, productivity, and various physical properties of the laminated porous film. Inorganic particles such as calcium, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents And additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents. Specifically, as antioxidants, copper halides, amine-based antioxidants such as aromatic amines, triethylene glycol bis [3- (3-t-butyl-5methyl-4-hydroxyphenyl) propionate] and the like And phenolic antioxidants. A commercially available product is “Irganox B225” (manufactured by Ciba Special). In addition, UV absorbers described in P178 to P182 of “Plastics compounding agents”, surfactants as antistatic agents described in P271 to P275, lubricants described in P283 to 294, etc. Is mentioned.

[Description of layer B]
Next, the B layer will be described.

  The B layer of the present invention is a porous layer containing a polyethylene resin. The layer B may have any structure / configuration as long as it has a large number of fine pores communicating in the thickness direction and is composed of a composition containing a polyethylene resin as described above. For example, a structure in which the fine pores are provided in a film-like material containing a polyethylene-based resin composition may be used, or particulate or fibrous fine objects may be aggregated to form a layer, A structure in which the gap is the fine hole may be used. The B layer of the present invention preferably has the former structure in which uniform fine pores can be formed and the porosity and the like can be easily controlled.

The thermal properties of a polyethylene resin, which is one of the compositions constituting the B layer, are important. That is, it is necessary to select the polyethylene resin so that the crystal melting peak temperature of the composition constituting the B layer is lower than the crystal melting peak temperature of the composition constituting the A layer. Specifically, the B layer is preferably a polyethylene resin having a crystal melting peak temperature of 100 ° C. or higher and 150 ° C. or lower.
This crystal melting peak temperature is a peak value of the crystal melting temperature when the temperature is raised from 25 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter in accordance with JIS K7121.

  Specific types of polyethylene resins include not only polyethylene resins such as low density polyethylene, medium density polyethylene, high density polyethylene, or linear low density polyethylene alone, but also ethylene propylene copolymers or polyethylene resins. A mixture with other polyolefin resin is mentioned. Among these, a polyethylene resin alone is preferable.

Density of the polyethylene resin is preferably 0.920~0.970g / cm ^3, more preferably 0.930~0.970g / cm ^3, 0.940~0.970g / cm ³ is more preferable. A density of 0.920 g / cm ³ or more is preferable because a first layer having an appropriate SD temperature can be formed. On the other hand, if it is 0.970 g / cm ³ or less, it is preferable in that a laminated porous film having a B layer having an appropriate SD temperature can be formed and that stretchability is maintained. The density can be measured according to JIS K7112 using a density gradient tube method.

Further, the melt flow rate (MFR) of the polyethylene resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g / 10 minutes, and 1.0 to 10 g / 10 minutes. It is more preferable. An MFR of 0.5 g / 10 min or more is preferable because the melt viscosity of the resin at the time of molding is sufficiently low, so that the productivity is excellent. On the other hand, if it is 15 g / 10 minutes or less, since it is close to the melt viscosity of the polypropylene resin to be mixed, dispersibility is improved, resulting in a homogeneous laminated porous film, which is preferable.
MFR is measured in accordance with JIS K7210 under conditions of a temperature of 190 ° C. and a load of 2.16 kg.

  The production method of the polyethylene resin is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. And a polymerization method using a single site catalyst.

  It is preferable to add a substance for promoting porosity to the B layer. Among them, the B layer preferably contains at least one compound selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax (X). preferable. By adding the compound (X), a porous structure can be obtained more efficiently, and the shape and diameter of the pores can be easily controlled.

  The modified polyolefin resin refers to a resin mainly composed of an unsaturated carboxylic acid or an anhydride thereof, or a polyolefin modified with a silane coupling agent. Examples of unsaturated carboxylic acids or anhydrides thereof include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid, citraconic anhydride, itaconic acid, itaconic anhydride, or monoepoxy compounds of these derivatives and the above acids. Examples include ester compounds, reaction products of a polymer having a group capable of reacting with these acids in the molecule and an acid. These metal salts can also be used. Among these, maleic anhydride is more preferably used. Moreover, these copolymers can be used individually or in mixture of 2 or more types, respectively.

  Examples of the silane coupling agent include vinyltriethoxysilane, methacryloyloxytrimethoxysilane, and γ-methacryloyloxypropyltriacetyloxysilane.

  In order to produce the modified polyolefin resin, for example, these modified monomers can be copolymerized in the stage of polymerizing the polymer in advance, or these modified monomers can be graft copolymerized with the polymer once polymerized. For modification, these modified monomers are used alone or in combination, and those having a content in the range of 0.1% by mass or more and 5% by mass or less are preferably used. Of these, those that have been graft-modified are preferably used.

  Examples of commercially available modified polyolefin resins include “Admer” (manufactured by Mitsui Chemicals) and “Modic” (manufactured by Mitsubishi Chemical).

Examples of alicyclic saturated hydrocarbon resins and modified products thereof include petroleum resins, rosin resins, terpene resins, coumarone resins, indene resins, coumarone-indene resins, and modified products thereof.
Examples of petroleum resins include aliphatic petroleum resins mainly containing C5 fraction, aromatic petroleum resins mainly containing C9 fraction, copolymer petroleum resins thereof, and alicyclic petroleum resins. . Examples of terpene resins include terpene resins and terpene-phenol resins from β-pinene, and examples of rosin resins include rosin resins such as gum rosin and wood rosin, and esterified rosin resins modified with glycerin and pentaerythritol. The alicyclic saturated hydrocarbon resin and the modified product thereof have relatively good compatibility when mixed with a polyethylene resin, but a petroleum resin is more preferable in terms of color tone and thermal stability, and a hydrogenated petroleum resin is used. More preferably.

  Hydrogenated petroleum resin is obtained by hydrogenating petroleum resin by a conventional method. Examples thereof include hydrogenated aliphatic petroleum resins, hydrogenated aromatic petroleum resins, hydrogenated copolymer petroleum resins and hydrogenated alicyclic petroleum resins, and hydrogenated terpene resins. Among hydrogenated petroleum resins, hydrogenated alicyclic petroleum resins obtained by copolymerizing and hydrogenating a cyclopentadiene compound and an aromatic vinyl compound are particularly preferable. Examples of commercially available hydrogenated petroleum resins include “ALCON” (manufactured by Arakawa Chemical Industries).

  The ethylene copolymer has an ethylene monomer unit content of 50% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more, and 95% by mass or less, preferably 90% by mass or less. More preferably, the content is 85% by mass or less. If the content of the ethylene monomer unit is within a predetermined range, a porous structure can be formed more efficiently.

  As the ethylene copolymer, those having an MFR (JIS K7210, temperature: 190 ° C., load: 2.16 kg) of 0.1 g / 10 min to 10 g / 10 min are preferably used. When the MFR is 0.1 g / 10 min or more, the extrudability can be maintained satisfactorily. On the other hand, when the MFR is 10 g / 10 min or less, the strength of the film is hardly lowered, which is preferable.

  The ethylene copolymer is “EVAFLEX EV40LX” (ethylene content 78 mol%, MFR 2.5 g / 10 min) as an ethylene-vinyl acetate copolymer, and “NUC copolymer” as an ethylene-acrylic acid copolymer (Japan). Unicar), Everflex-EAA (Mitsui / DuPont Polychemical), “REXPEARL EAA” (Nippon Ethylene), “ELVALOY” (Mitsui / DuPont Polychemical) as an ethylene- (meth) acrylic acid copolymer ), “REXPEARL EMA” (manufactured by Nippon Ethylene Co., Ltd.), “REXPEARL EEA” (manufactured by Nippon Ethylene Co., Ltd.) as an ethylene-ethyl acrylate copolymer, “Acryft” as an ethylene-methyl (meth) acrylic acid copolymer (Manufactured by Sumitomo Chemical Co., Ltd.), “Bondyne” (manufactured by Sumitomo Chemical Co., Ltd.), ethylene-methacrylic acid as an ethylene-vinyl acetate-maleic anhydride terpolymer Glycidyl copolymer, ethylene-vinyl acetate-glycidyl methacrylate terpolymer, and “bond first” (manufactured by Sumitomo Chemical Co., Ltd.) are commercially available as ethylene-ethyl acrylate-glycidyl methacrylate terpolymer. it can.

  For waxes, polar or nonpolar waxes, polypropylene waxes, polyethylene waxes and wax modifiers are included. Specifically, polar wax, nonpolar wax, Fischer-Tropsch wax, oxidized Fischer-Tropsch wax, hydroxy stearamide wax, functionalized wax, polypropylene wax, polyethylene wax, wax modifier, amorphous wax, carnauba wax , Castor oil wax, microcrystalline wax, beeswax, carnauba wax, castor wax, plant wax, candelilla wax, Japanese wax, ouricury wax, douglas fur bark wax, rice bran wax, jojoba wax, bay wax, montan wax, ozo Kelite wax, ceresin wax, petroleum wax, paraffin wax, chemically modified hydrocarbon wax, substituted amide wax, and combinations and derivatives thereof Body, and the like. Among these, paraffin wax, polyethylene wax, and microcrystalline wax are preferable from the viewpoint of efficiently forming a porous structure, and microcrystalline wax that can further reduce the pore diameter is more preferable from the viewpoint of SD characteristics. Examples of commercially available polyethylene wax include “FT-115” (manufactured by Nippon Seiwa), and examples of microcrystalline wax include “Hi-Mic” (manufactured by Nippon Seiwa).

  Of the compounds (X), alicyclic saturated hydrocarbon resins or modified products thereof, or waxes are more preferable as those having SD characteristics that work more effectively, and waxes are more preferable from the viewpoint of moldability.

In addition, the layer B may contain additives or other components that are generally blended in the resin composition in addition to polyethylene and a substance that promotes porosity. Examples of the additive include recycling resin, silica, talc, kaolin, carbonic acid, etc., which are added for the purpose of improving / adjusting the processability, productivity, and various physical properties of the laminated porous film. Inorganic particles such as calcium, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents And additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, and coloring agents.
Among them, the nucleating agent is preferable because it has an effect of controlling the crystal structure of the polyethylene resin and reducing the porous structure at the time of stretching and opening. Examples of commercially available products include “Gelall D” (manufactured by Shin Nippon Rika Co., Ltd.), “Adeka Stub” (manufactured by Asahi Denka Kogyo Co., Ltd.), and “IRGACLEAR D” (manufactured by Ciba Special Chemicals). Examples of commercially available master batches include “Rike Master” (manufactured by Riken Vitamin Co., Ltd.).

  In the B layer, a thermoplastic resin may be used as long as it does not impair the thermal characteristics of the laminated porous film, specifically, the SD characteristics, in addition to polyethylene and the compound (X) that promotes porosity. . Examples of other thermoplastic resins that can be mixed with the polyethylene resin include styrene resins such as styrene, AS resin, and ABS resin: polyvinyl chloride, fluorine resin, polyethylene terephthalate, polybutylene terephthalate, and polycarbonate. Or ester resins such as polyarylate; ether resins such as polyacetal, polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone or polyphenylene sulfide; polyamides such as 6 nylon, 6-6 nylon and 6-12 nylon Examples thereof include thermoplastic resins such as resins.

  Moreover, what is called rubber components, such as a thermoplastic elastomer, may be added to the resin composition which comprises B layer as needed. Examples of the thermoplastic elastomer include styrene / butadiene, polyolefin, urethane, polyester, polyamide, 1,2-polybutadiene, polyvinyl chloride, and ionomer.

  The compounding amount of the compound (X) is 1 mass as a lower limit with respect to 100 parts by mass of the polyethylene resin contained in the B layer when the interface between the polyethylene resin and the compound (X) is peeled to form micropores. Part or more, preferably 5 parts by weight or more, more preferably 10 parts by weight or more. On the other hand, the upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less. When the compounding amount of the compound (X) is 1 part by mass or more with respect to 100 parts by mass of the polyethylene-based resin, an effect of expressing a desired good porous structure is sufficiently obtained. Moreover, the more stable moldability is securable because the compounding quantity of compound (X) shall be 50 mass parts or less.

  In addition, the additive etc. generally mix | blended with a resin composition may be mix | blended with B layer in the range which does not impair the objective of this invention mentioned above and the characteristic of B layer. Specifically, it is the same as the example of the additive which can be mix | blended with A layer. Among them, the crystal nucleating agent is preferable because it has an effect of controlling the crystal structure of polyethylene and making the porous structure fine at the time of stretching and opening by adding.

[Description of laminated structure]
The laminated structure of the laminated porous film of the present invention will be described.
The present invention is not particularly limited as long as at least the A layer and the B layer which are basic structures exist. The simplest structure is a two-layer structure of an A layer and a B layer, and the next simple structure is a two-kind three-layer structure of both an outer layer and an intermediate layer, which are preferable structures. In the case of two types and three layers, it may be A layer / B layer / A layer or B layer / A layer / B layer. In addition, it is possible to adopt a form of three types and three layers in combination with layers having other functions as required. Further, the number of layers may be increased as necessary to 4 layers, 5 layers, 6 layers, and 7 layers.
Regarding the stacking ratio of the A layer and the B layer, the value of the A layer / B layer is preferably 0.05 to 20, more preferably 0.1 to 10, and 0.3 to 5. More preferably. By setting the value of A layer / B layer to 0.05 or more, the BD characteristics and strength of the A layer can be sufficiently exhibited. Moreover, by setting it to 20 or less, for example, when applied to a battery, SD characteristics can be sufficiently exhibited, and safety can be ensured. Moreover, when other layers other than B layer and A layer exist, 0.1-0.5 are preferable with respect to the total thickness 1 of other layers, and 0.1-0.3 are preferable. More preferred.

[Description of shape and physical properties of laminated porous film]
The form of the laminated porous film may be either flat or tube-like, but it is good in productivity because it can be taken as a product, and the inner surface can be treated such as a coat. From the viewpoint, a planar shape is more preferable.
The thickness of the laminated porous film of the present invention is preferably 50 μm or less, more preferably 40 μm or less, and still more preferably 30 μm or less. On the other hand, the lower limit is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. When used as a battery separator, if the thickness is 50 μm or less, the electrical resistance of the laminated porous film can be reduced, so that the battery performance can be sufficiently ensured. Further, if the thickness is 5 μm or more, substantially necessary electrical insulation can be obtained. For example, even when a large voltage is applied, short-circuiting is difficult and excellent safety is achieved.

The physical properties of the laminated porous film of the present invention can be freely adjusted by the composition of the A layer or the B layer, the number of laminated layers and the lamination ratio, combinations with layers having other properties, and the production method.
The lower limit of the SD temperature of the laminated porous film of the present invention is preferably 100 ° C or higher, more preferably 110 ° C, and still more preferably 120 ° C or higher. On the other hand, the upper limit is preferably 140 ° C. or lower. When SD characteristics are developed at 100 ° C. or lower, for example, when the laminated porous film of the present invention is used as a separator for a lithium ion battery and the battery is left in a car in summer, the temperature may be 100 ° C. depending on the location. Since it may rise to near, it is not preferable that the battery does not function in this state. On the other hand, a temperature higher than 140 ° C. is not sufficient in terms of ensuring safety as a battery.
Effective means to adjust the SD temperature include selecting a thermoplastic resin having a crystal melting peak temperature close to the desired SD temperature as the thermoplastic resin contained in the B layer, and increasing the layer ratio of the B layer. It is.

The laminated porous film of the present invention is also characterized by exhibiting BD characteristics at 160 ° C. or higher. That is, the BD temperature of the laminated porous film of the present invention is 160 ° C. or higher, preferably 180 ° C. or higher, more preferably 200 ° C. or higher. When the BD temperature is less than 160 ° C., there is no difference between the SD temperature and the BD temperature. For example, when the laminated porous film of the present invention is used as a separator for a lithium ion battery, it is possible to provide a battery with sufficiently secured safety. Can not. On the other hand, although there is no restriction | limiting in particular about the high temperature side of BD temperature, Preferably it is 300 degrees C or less.
As a means for adjusting the BD temperature, a means such as increasing the layer ratio of the A layer is effective.

  The laminated porous film of the present invention can be used as a separator for a non-aqueous electrolyte battery such as a lithium ion secondary battery used as a power source for various electronic devices.

(Air permeability at 25 ° C)
The laminated porous film of the present invention needs to have an air permeability at 25 ° C. of 1000 seconds / 100 ml or less, preferably 950 seconds / 100 ml or less, more preferably 900 seconds / 100 ml or less. By using 1000 sec / 100 ml or less, when used as a separator for a lithium ion battery, the battery performance can be excellent when used at room temperature.
Moreover, the low air permeability at 25 ° C. of the laminated porous film means that the charge can be easily transferred when used as a separator for a lithium ion battery, and is preferable because of excellent battery performance.
On the other hand, the lower limit is preferably 10 seconds / 100 ml or more, more preferably 50 seconds / 100 ml or more, still more preferably 100 seconds / 100 ml or more. If the air permeability at 25 ° C. is 10 seconds / 100 ml or more, troubles such as an internal short circuit can be avoided when used as a lithium ion battery separator.

(Air permeability after heating at 135 ° C for 5 seconds)
It is important that the laminated porous film of the present invention exhibits SD characteristics when used as a lithium ion battery separator. Accordingly, the air permeability after heating at 135 ° C. for 5 seconds needs to be 50000 seconds / 100 ml or more, preferably 75000 seconds / 100 ml or more. By setting the air permeation resistance after heating at 135 ° C for 5 seconds to 50000 seconds / 100ml or more, the holes are quickly closed when the battery runs out of heat, thus avoiding problems such as battery rupture. be able to.
In order to set the air permeability after heating at 135 ° C. for 5 seconds to 50000 seconds / 100 ml or more, it depends on the pore diameter and the porosity. Although not limited to the following contents, for example, the compound (X) is added to the polyethylene resin, and the kind and blending amount of the compound (X) is adjusted, or a crystal nucleating agent is added to the polyethylene resin. By miniaturizing the crystal, the air permeability after heating at 135 ° C. for 5 seconds can be controlled.
In the production method, the air permeability after heating at 135 ° C. for 5 seconds can be set to 50000 seconds / 100 ml or more by adjusting the stretching conditions.

(Porosity)
The porosity is an important factor for defining the porous structure, and is a numerical value indicating the proportion of the space portion in the film. In the laminated porous film of the present invention, the porosity is preferably 15% or more, more preferably 20% or more, still more preferably 30% or more, and particularly preferably 40% or more. On the other hand, the upper limit is preferably 80% or less, more preferably 70% or less, and even more preferably 65% or less. When the porosity is 15% or more, it is possible to obtain a laminated porous film having sufficient communication properties and excellent air permeability. Moreover, if the porosity is 80% or less, the mechanical strength of the laminated porous film can be sufficiently maintained, which is preferable from the viewpoint of handling.

(Shrinkage factor)
One of the features of the laminated porous film of the present invention is a well-balanced shrinkage rate.

The upper limit of the TD shrinkage ratio S _TD2 at 105 ° C. of the laminated porous film of the present invention is important to be 10% or less, preferably 9% or less, more preferably 8% or less. When the shrinkage ratio _STD2 of TD at 105 ° C. is larger than 10%, there is a risk of winding tightness and wrinkles occurring when the laminated porous film is dried in a rolled state when used as a lithium ion battery separator. . In addition, after winding with the electrode, if the shrinkage rate _SMD2 is high, the end of the electrode is strongly pressed against the separator, so that the separator is easily cracked and short-circuited easily.
On the other hand, the lower limit of the shrinkage rate S _TD2 is preferably 2% or more, and more preferably 2.3% or more. Since a certain amount of thermal shrinkage is required to show the SD characteristics, if the shrinkage rate _STD2 is 2% or more, sufficient SD characteristics can be obtained.

The upper limit of the shrinkage percentage _SMD2 at 105 ° C. of the laminated porous film of the present invention is preferably 10% or less, more preferably 8% or less, still more preferably 6% or less. If the shrinkage ratio _{SMD2 at} 105 ° C. is greater than 10%, the dimensional stability is poor, and there is a risk of wrinkling during drying or short circuit in the battery, which is not preferable.
On the other hand, the lower limit of the shrinkage rate _SMD2 is preferably 0% or more. When the shrinkage percentage _SMD2 is less than 0%, that is, when it expands, it is not preferable because winding displacement occurs during storage in the state of a roll, and wrinkles and breakage occur.

The upper limit of the ratio of MD and TD shrinkage _SMD2 / _STD2 at 105 ° C. of the laminated porous film of the present invention is 3.0 or less, preferably 2.5 or less, and more preferably 2.0 or less. On the other hand, the lower limit of _SMD2 / _STD2 is 0.1 or more, preferably 0.3 or more, and more preferably 0.5 or more.
For dimensional stability, it is preferable that the shrinkage rate is small for both MD and TD, but some degree of thermal shrinkage is necessary to develop SD characteristics, and the shrinkage rate in each direction is more isotropic. is required. If the S _MD2 / S _TD2 is less than 0.1, the TD shrinkage rate is too high, and if it is greater than 3.0, the MD shrinkage rate is too high. In either case, the anisotropy increases. It is not preferable.

It is preferable that shrinkage _| contraction rate _STD1 in 40 _degreeC of the laminated porous film of this invention is less than 1%. More preferably, it is less than 0.9%, More preferably, it is less than 0.8%. When the shrinkage ratio _{STD1 at} 40 ° C. is 1% or more, it is difficult to handle as a product because deformation occurs during transportation or storage.
On the other hand, the lower limit of the shrinkage rate S _TD1 is preferably 0% or more. When the shrinkage rate _STD1 is less than 0%, that is, when it expands, for example, a winding shift occurs during storage in the state of a roll, which is not preferable because wrinkles and breakage occur.

Moreover, it is preferable that shrinkage _| contraction rate _SMD1 in 40 degreeC of the laminated porous film of this invention is less than 1%. More preferably, it is less than 0.9%, More preferably, it is less than 0.8%. When the shrinkage rate at 40 ° C. is 1% or more, deformation occurs during transportation and storage, making it difficult to handle as a product.
On the other hand, the lower limit of the shrinkage rate _SMD1 is preferably 0% or more. When the shrinkage rate _SMD1 is less than 0%, that is, when it expands, for example, a winding shift occurs during storage in the state of a roll, which is not preferable because wrinkles and breakage occur.

The shrinkage ratio S _TD3 of TD at 150 ° C. of the laminated porous film of the present invention is 25% or less, more preferably 23% or less. If the _STD3 is greater than 25%, the electrodes separated by the separator come into contact with each other and short circuit when used as a lithium ion battery separator.
On the other hand, the lower limit of the shrinkage rate S _TD3 is preferably 0% or more. When the shrinkage rate _STD3 is less than 0%, that is, when it expands, when it is stored in the state of a scroll, winding deviation occurs, and wrinkles and breakage occur.

The MD shrinkage _SMD3 at 150 ° C. of the laminated porous film of the present invention is preferably 18% or less, more preferably 15% or less. When the shrinkage percentage _SMD3 is larger than 18%, it is not preferable because when the separator is used as a lithium ion battery separator, the separator is wound together with the wound body and may be short-circuited.
On the other hand, the lower limit of the shrinkage rate _SMD3 is preferably 0% or more. When the shrinkage percentage _SMD3 is less than 0%, that is, when it expands, when it is stored in the form of a roll, winding deviation occurs and wrinkles and breakage occur, which is not preferable.

  One effective means for reducing the shrinkage rate is to reduce the draw ratio. However, the reduction of the draw ratio is accompanied by other physical properties necessary for a lithium ion battery separator, such as a reduction in strength and elastic modulus. In particular, when the laminated porous film of the present invention is used for a separator for a lithium ion battery, the MD and the electrode are wound with a high tension, so that the MD has a high tensile elastic modulus so that winding does not occur. Is desirable. At this time, the tensile modulus of MD is preferably 500 MPa or more, and more preferably 700 MPa.

The laminated porous film of the present invention is characterized by lowering the shrinkage rate by adjusting the stretching conditions and at the same time ensuring an elastic modulus higher than necessary.
One method for increasing the tensile modulus of the laminated porous film is to align molecular chains along MD. In the laminated porous film of the present invention, as the degree of molecular chain orientation necessary for exhibiting a balanced property in shrinkage rate, tensile elastic modulus, etc., the azimuth angle (β) of (−113) plane by wide-angle X-ray diffraction measurement is used. ) _OMD / _OTD ( _OMD : integrated intensity of MD, _OTD : integrated intensity of _TD ) is calculated from the direction profile.
Here, the (−113) plane is a crystal lattice plane including a component in the molecular chain axis direction in an X-ray diffraction profile obtained by 2θ / θ scan, and is obtained around 2θ = 41 °. Also, O _MD and O _TD, as described in the measurement method described below, the θ apex of the diffraction peak of the (-113) plane is obtained, in 2 [Theta], and fixed samples, and the position of the counter, a sample film It is the integrated intensity calculated from the profile of the intensity distribution obtained when rotating in the azimuth (β) direction in the plane. In the same sample, if the volume of the sample irradiated with X-rays is constant with respect to the azimuth angle, the intensity distribution profile in the azimuth direction (-113) corresponds to the orientation distribution of crystal chains in the film plane. is doing. That, O _MD Out of the crystal chains within the film plane, the component oriented in the MD, O _TD corresponds to the component oriented in the TD. For example, if the O compared to O _{MD TD} is high enough, the crystal chains within the film plane is mainly correspond to be oriented in TD. Therefore, the magnitude of O _MD / O _TD can be said to be a measure showing how much the crystal chains in the film plane are oriented in the MD. That is, O _MD / O _TD is high for films highly oriented in _MD , while O _MD / O _TD is small for films mainly oriented in _TD .

The value of O _MD / O _TD in the laminated porous film of the present invention is preferably 5 or more. More preferably, it is 6 or more, More preferably, it is 7 or more. By setting the value of O _MD / O _TD to 5 or more, the tensile elastic modulus, tensile strength, and pin puncture strength of MD can be sufficiently ensured. On the other hand, the upper limit of the value of O _MD / O _TD is not particularly limited, but is preferably 12 or less, more preferably 10 or less. By setting the value of O _MD / O _TD to 12 or less, it is possible to sufficiently obtain the isotropy of the film and to sufficiently maintain the tear strength of TD.

  The laminated porous film of the present invention is preferably biaxially stretched. Biaxial stretching reduces the anisotropy, and a laminated porous film with a sufficient balance between handling and physical properties can be obtained.

  In the laminated porous film of the present invention, other physical properties can be freely adjusted by the composition of the resin composition constituting the A layer and the B layer, the layer configuration, the production method, and the like.

[Description of manufacturing method]
Next, although the manufacturing method of the laminated porous film of this invention is demonstrated, this invention is not limited only to the laminated porous film manufactured by this manufacturing method.
The manufacturing method of the laminated porous film of this invention is divided roughly into the following three by the order of porous formation and lamination.
(A) A layer porous film (hereinafter referred to as “porous film PP”) mainly composed of polypropylene resin and B layer porous film containing polyethylene resin (hereinafter referred to as “porous film PE”) And then laminating at least the porous film PP and the porous film PE.
(B) A film-like material containing a polypropylene resin as a main component (hereinafter referred to as “non-porous film-like material PP”) and a film-like material containing polyethylene resin (hereinafter referred to as “non-porous film-like material PE”). ) To produce a laminated non-porous film-like material comprising at least two layers, and then making the non-porous film-like material porous.
(C) One of the two layers of the A layer mainly composed of a polypropylene resin and the B layer containing a polyethylene resin is made porous, and then laminated with another non-porous film-like material. How to turn.

Examples of the method (a) include a method of laminating the porous film PP and the porous film PE and a method of laminating with an adhesive or the like.
As the above-mentioned method, a non-porous film-like material PP and a non-porous film-like material PE are respectively produced, and the non-porous film-like material PP and the non-porous film-like material PE are laminated with a laminate or an adhesive and then made porous. Examples thereof include a method or a method of forming a porous nonporous film by coextrusion and then making it porous.
Examples of the method (c) include a method of laminating the porous film PP and the nonporous film-like material PE, or the method of laminating the nonporous film material PP and the porous film PE, and a method of laminating with an adhesive or the like.
In the present invention, the method (b) is preferable from the viewpoint of simplicity of the process and productivity, and a method using coextrusion is more preferable.

The production method of the laminated porous film of the present invention can be classified by the method for forming the B layer separately from the above classification.
That is, when the A layer has β activity, micropores can be easily formed by stretching. On the other hand, as a method for making the layer B porous, a known method such as a stretching method, a phase separation method, an extraction method, a chemical treatment method, an irradiation etching method, a foaming method, or a combination of these techniques can be used. Of these, the stretching method is preferably used in the present invention.

The stretching method is a method in which a non-porous layer or a non-porous film-like material is formed using a composition in which a compound is mixed with a resin, and the interface between the resin and the compound is separated by stretching to form micropores. is there.
The phase separation method is a technique called a conversion method or a microphase separation method, and is a method of forming pores based on a phase separation phenomenon of a polymer solution. Specifically, it is roughly classified into (a) a method of forming micropores by phase separation of polymer, and (b) a method of forming pores while forming micropores during polymerization. As the former method, there are a solvent gelation method using a solvent and a hot melt rapid solidification method, and either method may be used.

In the extraction method, an additive that can be removed in a later step is mixed with the thermoplastic resin composition constituting the B layer, and after forming a nonporous layer or a nonporous film, the additive is extracted with a chemical or the like. This is a method for forming fine holes. Examples of the additive include a polymer additive, an organic additive, and an inorganic additive.
As an example using a polymer additive, a non-porous layer or a non-porous film-like material is formed using two types of polymers having different solubility in an organic solvent, and only one of the two types of polymers is used. A method of extracting the one polymer by immersing in a dissolving organic solvent is mentioned. More specifically, a method of forming a nonporous layer or a nonporous film made of polyvinyl alcohol and polyvinyl acetate, and extracting polyvinyl acetate using acetone and n-hexane, or a block or graft copolymer And a method of forming a non-porous layer or a non-porous film-like material by containing a hydrophilic polymer and removing the hydrophilic polymer with water.

As an example using an organic substance additive, a non-porous layer or a non-porous film-like material is formed by blending a substance soluble in an organic solvent in which the thermoplastic resin constituting the B layer is insoluble, There is a method of extracting and removing the substance by dipping.
Examples of the substance include higher aliphatic alcohols such as stearyl alcohol or seryl alcohol, n-alkanes such as n-decane or n-dodecane, paraffin wax, liquid paraffin, or kerosene. These include isopropanol, ethanol, It can be extracted with an organic solvent such as hexane. In addition, water-soluble substances such as sucrose and sugar can also be mentioned as the substances, and these have the advantage of reducing the burden on the environment because they can be extracted with water.

The chemical treatment method is a method of forming micropores by chemically cleaving the bond of the polymer substrate or conversely performing a bonding reaction. More specifically, a method of forming micropores by chemical treatment such as redox agent treatment, alkali treatment, acid treatment, and the like can be mentioned.
The irradiation etching method is a method of forming minute holes by irradiating with neutron beam or laser.
The fusion method is a method of using a polymer fine powder such as polytetrafluoroethylene, polyethylene, or polypropylene and sintering the polymer fine powder after molding.
Examples of the foaming method include a mechanical foaming method, a physical foaming method, and a chemical foaming method, and any of them can be used in the present invention.

  As a preferred embodiment of the method for producing a laminated porous film of the present invention, a resin composition containing a polypropylene resin having β activity as a main component, a resin containing a polyethylene resin, and further containing a compound (X) Using the composition, a laminated nonporous film-like material composed of at least two layers of A layer and B layer is prepared, and the laminated nonporous film-like material is stretched to form fine pores having connectivity in the thickness direction. A method for producing a laminated porous film characterized in that a large number of films are formed.

The production method of the laminated non-porous film is not particularly limited, and a known method may be used. For example, the resin composition is melted using an extruder, coextruded from a T die, and cooled and solidified with a cast roll. Is mentioned. Moreover, the method of cutting open the film manufactured by the tubular method and making it flat is also applicable.
Regarding the method of stretching the laminated nonporous film-like material, there are methods such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and biaxial stretching can be performed by combining these alone or in combination of two or more. preferable.

  More preferable embodiments include a resin composition mainly composed of a polypropylene resin having β activity that constitutes the A layer, a polyethylene resin that constitutes the B layer, and the compound (X). A laminated nonporous film-like material having a two-kind / three-layer structure is produced by coextrusion from a T die so that the resin composition is made porous by a stretching method. A method for producing a laminated porous film that becomes porous by stretching will be described below.

  The resin composition constituting the A layer preferably contains at least a polypropylene resin and a β crystal nucleating agent. These raw materials are preferably mixed using a Henschel mixer, a super mixer, a tumbler type mixer, etc., or after all ingredients are put in a bag and mixed by hand blending, then a single screw or twin screw extruder, a kneader, etc. Is pelletized after melt-kneading with a twin screw extruder.

  When preparing the resin composition constituting the B layer, the raw materials such as the polyethylene resin, the compound (X) and other additives as described in the description of the B layer, a Henschel mixer, a super mixer, a tumbler mixer, etc. After mixing by using, it is melt-kneaded with a single-screw or twin-screw extruder, a kneader or the like, preferably a twin-screw extruder, and then pelletized.

The pellets of the resin composition for the A layer and the pellets of the resin composition for the B layer are put into an extruder and extruded from a die for co-extrusion with a T die. The type of T-die may be a multi-manifold type for type 2 and 3 layers or a feed block type for type 2 and 3 layers.
The gap of the T die to be used is determined from the final required film thickness, stretching conditions, draft rate, various conditions, etc., but is generally about 0.1 to 3.0 mm, preferably 0.5. -1.0 mm. If it is less than 0.1 mm, it is not preferable from the viewpoint of production speed, and if it is more than 3.0 mm, it is not preferable from the viewpoint of production stability because the draft rate increases.

In extrusion molding, the extrusion processing temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition, but is generally preferably 150 to 300 ° C, and more preferably 180 to 280 ° C. In the case of 150 ° C. or higher, the viscosity of the molten resin is preferably sufficiently low and excellent in moldability. On the other hand, at 300 ° C. or lower, the deterioration of the resin composition can be suppressed.
The cooling and solidifying temperature by the cast roll is very important in the present invention, and β crystals in the film-like material before stretching can be generated and grown, and the ratio of β crystals in the film-like material can be adjusted. The cooling and solidification temperature of the cast roll is preferably 80 to 150 ° C, more preferably 90 to 140 ° C, and still more preferably 100 to 130 ° C. By setting the cooling and solidifying temperature to 80 ° C. or higher, the ratio of β crystals in the cooled and solidified film can be sufficiently increased, which is preferable. Further, it is preferable to set the temperature to 150 ° C. or lower because troubles such as the extruded molten resin sticking to and wrapping around the cast roll hardly occur and the film can be efficiently formed into a film.

It is preferable to adjust the β crystal ratio of the obtained film-like material before stretching to 30 to 100% by setting a cast roll in the temperature range. 40-100% is more preferable, 50-100% is still more preferable, and 60-100% is the most preferable. By setting the β crystal ratio of the film-like material before stretching to 30% or more, a porous film can be easily formed by a subsequent stretching operation, and a film having good air permeability can be obtained.
The β crystal ratio of the film-like material before stretching is detected when the film-like material is heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. The crystal melting calorie (ΔHmα) derived from the α crystal and the crystal melting calorie (ΔHmβ) derived from the β crystal are calculated by the following formula.
β crystal ratio (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100

  Next, the obtained laminated nonporous membrane is biaxially stretched. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In the case of producing a laminated porous film excellent in SD characteristics, which is the object of the present invention, sequential biaxial stretching is more preferred because the stretching conditions can be selected in each stretching step and the porous structure can be easily controlled. In addition, the extending | stretching to the take-up (flow) direction (MD) of a film-like thing is called "longitudinal stretching", and the extending | stretching to the perpendicular direction (TD) is called "lateral stretching."

When using sequential biaxial stretching, it is necessary to select the stretching temperature according to the composition of the resin composition to be used, the crystal melting peak temperature, the crystallinity, etc., but the control of the porous structure is easy, and the mechanical strength and shrinkage rate It is easy to balance with other physical properties. The stretching temperature in the longitudinal stretching is generally controlled in the range of 15 to 135 ° C, preferably 20 to 130 ° C.
The longitudinal draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, and still more preferably 4 to 7 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while suppressing breakage during stretching. On the other hand, the stretching temperature in transverse stretching is generally 80 to 150 ° C, preferably 90 to 140 ° C. The transverse draw ratio is preferably 1.1 to 10 times, more preferably 1.2 to 8 times, and still more preferably 1.4 to 7 times. By transversely stretching within the above range, the pore starting point formed by longitudinal stretching can be appropriately expanded, and a fine porous structure can be expressed. The stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1500 to 10,000% / min, and further preferably 2500 to 8000% / min.

  The laminated porous film thus obtained is preferably heat-treated at a temperature of about 100 to 150 ° C., preferably about 110 to 140 ° C. for the purpose of improving dimensional stability. During the heat treatment step, 1 to 25% relaxation treatment may be performed as necessary. The laminated porous film of the present invention can be obtained by uniformly cooling and winding after this heat treatment.

[Explanation of battery separator]
Next, a nonaqueous electrolyte battery containing the laminated porous film of the present invention as a battery separator will be described with reference to FIG.
Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the battery separator 10, and the outside is stopped with a winding tape to form a wound body. When winding in this spiral shape, the battery separator 10 preferably has a thickness of 5 to 40 μm, particularly preferably 5 to 30 μm. By making the thickness 5 μm or more, the battery separator is hardly broken, and by making the thickness 40 μm or less, it is possible to increase the battery area when wound in a predetermined battery can and to increase the battery capacity. it can.

  A wound body in which the positive electrode plate 21, the battery separator 10 and the negative electrode plate 22 are integrally wound is housed in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25. Next, the electrolyte is injected into the battery can, and after the electrolyte has sufficiently penetrated into the battery separator 10 or the like, the positive electrode lid 27 is sealed around the opening periphery of the battery can via the gasket 26, and precharging and aging are performed. A cylindrical non-aqueous electrolyte battery is manufactured.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used. The organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, esters such as dimethyl carbonate, methyl propionate or butyl acetate, and nitriles such as acetonitrile. 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane These may be used alone or in combination of two or more.
Among them, an electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.0 mol / L in a solvent obtained by mixing 2 parts by mass of methyl ethyl carbonate relative to ethylene carbonate 1 part by weight is preferred.

As the negative electrode, an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. Or a compound with a sulfide or the like.
When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  In this embodiment, as a negative electrode, a carbon material having an average particle size of 10 μm is mixed with a solution in which vinylidene fluoride is dissolved in N-methylpyrrolidone to form a slurry, and this negative electrode mixture slurry is passed through a 70-mesh net. After removing the large particles, uniformly apply to both sides of the negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm and dry, and then compression-molded with a roll press machine, cut, strip-shaped negative electrode plate and We use what we did.

  As the positive electrode, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, etc. are used as active materials. , These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.

In the present embodiment, a strip-like positive electrode plate produced as follows is used as the positive electrode. That is, lithium graphite oxide (LiCoO ₂ ) is added with phosphorous graphite as a conductive additive at a mass ratio of 90: 5 (lithium cobalt oxide: phosphorous graphite) and mixed, and this mixture and polyvinylidene fluoride are mixed with N -Mix with a solution dissolved in methylpyrrolidone to make a slurry. This positive electrode mixture slurry is passed through a 70-mesh net to remove large particles, and then uniformly applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press. After forming, it is cut into a strip-like positive electrode plate.

[Description of Examples]
Next, although an Example and a comparative example are shown and it demonstrates in detail about the laminated porous film of this invention, this invention is not limited to these.

Example 1
0.2 parts by weight of an antioxidant (Ciba Specialty Chemicals Co., Ltd., Irganox B225) and 100 parts by mass with respect to 100 parts by mass of a polypropylene resin (manufactured by Prime Polymer, Prime Polypro F300SV, MFR: 3 g / 10 min) As a nucleating agent, 0.2 part by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxylic acid amide is added, and the same direction twin screw extruder (caliber 40 mmφ, L / D = 32) manufactured by Toshiba Machine Co., Ltd. is used. A resin composition A1 that was melt-kneaded at 270 ° C. and processed into a pellet was obtained.
In addition, as a polyethylene resin, 80 parts by mass of high-density polyethylene (manufactured by Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min), microcrystalline wax (Nippon Seiwa Co., Ltd.) Made by Hi-Mic 1090), and 0.2 parts by weight of dibenzylidene sorbitol (manufactured by Shin Nippon Chemical Co., Ltd., Gelol D) as a nucleating agent, and melted at 230 ° C. using the same type of twin-screw extruder. A resin composition B1 kneaded and processed into a pellet was obtained.
Resin compositions A1 and B1 were extruded at 200 ° C. with separate extruders, co-extruded using a T-die for multilayer molding through a two-type three-layer feed block, and the film thickness ratio after stretching was A1 / B1 / A1 = 3/1/3, and then cooled and solidified with a cast roll at 125 ° C. to produce a laminated non-porous film having a thickness of 80 μm.
The laminated nonporous membrane was biaxially stretched sequentially at 110 ° C. 5 times in MD, then at 110 ° C. 2.4 times in TD, and then relaxed 22% in TD at 125 ° C. to obtain a laminated porous film. It was.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Example 2)
Resin compositions A1 and B1 were laminated in the same manner as in Example 1, and then cooled and solidified with a cast roll at 130 ° C. to produce a laminated nonporous film-like material having a thickness of 80 μm.
The laminated non-porous film was biaxially stretched sequentially at 93 ° C. to MD, then at 98 ° C. to TD, and then relaxed 18% to TD at 125 ° C. A film was obtained.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Comparative Example 1)
Resin compositions A1 and B1 were laminated in the same manner as in Example 1, and then cooled and solidified with a cast roll at 131 ° C. to produce a laminated non-porous film having a thickness of 80 μm.
The laminated non-porous membrane was biaxially stretched successively at 98 ° C. to MD, then at 108 ° C. twice to TD, and then relaxed 19% to TD at 125 ° C. to obtain a laminated porous film. Obtained.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

(Comparative Example 2)
The process was performed in the same manner as in Example 1 except that the stretching ratio was stretched 2.2 times to TD and then relaxed 15% to TD at 125 ° C.
Various characteristics of the obtained laminated porous film were measured and evaluated, and the results are summarized in Table 1.

  About the film of the obtained Example and the comparative example, various characteristics were measured and evaluated as follows.

(1) Layer ratio A cross section of the laminated porous film was cut out and observed with a scanning electron microscope (S-4500, manufactured by Hitachi, Ltd.), and the layer ratio was measured from the layer configuration and thickness.
(2) Thickness A thickness of 1/1000 mm was used to measure 30 in-plane thicknesses unspecified, and the average was taken as the thickness.
(3) Porosity A substantial amount W1 of the film was measured, and a mass W0 in the case of a porosity of 0% was calculated from the density and thickness of the resin composition, and calculated based on the following formula from these values.
Porosity (%) = {(W0−W1) / W0} × 100
(4) Shrinkage rate at 40 ° C. and 105 ° C. Cut the laminated porous film into a size of 150 mm in the measurement direction and 15 mm in the direction perpendicular to the measurement direction, and draw a marked line at an interval of 100 mm along the measurement direction, It was hung in a pre-baked baking test apparatus (Daiei Kagaku Seiki Seisakusho, DK-1M). After 1 hour, the sample was taken out, allowed to cool to room temperature, the length between the marked lines of the sample was measured with a metal scale, and the change before and after heating was taken as the shrinkage rate.
(5) Shrinkage at 150 ° C. The laminated porous film was cut into a size of 60 mm × 60 mm, and a marked line was drawn at an interval of 50 mm × 50 mm to obtain a measurement sample. This was sandwiched between glass plates having an area of 100 mm × 100 mm and a thickness of 5 mm and placed in a pre-baked baking test apparatus (Daiei Kagaku Seiki Seisakusho, DK-1M). After 1 hour, the sample was taken out and allowed to cool to room temperature while sandwiched between glasses, and then the length between the marked lines of the sample was measured with a metal scale, and the change before and after heating was taken as the shrinkage rate.
(6) Air permeability at 25 ° C. Air resistance (second / 100 ml) was measured in accordance with JIS P8117 in an air atmosphere at 25 ° C. For the measurement, a digital type Oken type air permeability dedicated machine (Asahi Seiko Co., Ltd.) was used.
(7) Air permeability after heating at 135 ° C. for 5 seconds A laminated porous film was cut into a 60 mm vertical x 60 mm horizontal square, and an aluminum with a circular hole of φ40 mm in the center as shown in FIG. 2 (A) A sheet (material: JIS A5052, size: 60 mm long, 60 mm wide, 1 mm thick) was sandwiched between two sheets, and the surrounding area was clipped as shown in FIG. ). Next, glycerin (manufactured by Nacalai Tesque, grade 1) was filled up to 100 mm from the bottom, and was fixed to the center of a 135 ° C. oil bath (manufactured by ASONE, OB-200A) with two aluminum plates. The film in the state was immersed and heated for 5 seconds. Immediately after heating, it is immersed in a separately prepared cooling bath filled with 25 ° C. glycerin and cooled for 5 minutes, and then washed with 2-propanol (manufactured by Nacalai Tesque, special grade) and acetone (manufactured by Nacalai Tesque, special grade). And dried in an air atmosphere at 25 ° C. for 15 minutes. The air permeability of the dried film was measured according to the method (6).
(8) Tensile modulus For the measurement, a tensile / compression tester (manufactured by Intesco, 200X type) was used. As the test piece, a laminated porous film cut out in a length of 200 mm in MD and a width of 5 mm in TD was used. The test piece was pulled under conditions of a distance between chucks of 150 mm and a crosshead speed of 5 mm / min. From the load applied to the load cell when the distance between the chucks was extended by 3%, the tensile elastic modulus was obtained from the following equation. The thickness of the sample was determined from the average value measured at three locations.
Tensile modulus (MPa) = {Load (kg) × 9.8 (m / s ² ) / Extension distance (mm)} / Cross sectional area (mm ² ) × Chuck distance (mm)
The average value of the tensile modulus measured at five points was taken as the tensile modulus.

  Further, the obtained film was evaluated for β activity and molecular orientation ratio as follows.

(9) Differential scanning calorimetry (DSC)
Using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, the film was heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min and held for 1 minute, and then from 240 ° C. to 25 ° C. The temperature was lowered at a cooling rate of 10 ° C./min, held for 1 minute, and further heated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min. The presence or absence of β activity was evaluated as follows depending on whether a peak was detected at 145 ° C. to 160 ° C., which is the crystal melting peak temperature (Tmβ) derived from the β crystal of polypropylene at the time of reheating.
○: When Tmβ is detected within the range of 145 ° C to 160 ° C (with β activity)
X: When Tmβ is not detected within the range of 145 ° C to 160 ° C (no β activity)
The β activity was measured with a sample amount of 10 mg under a nitrogen atmosphere.

(10) Wide-angle X-ray diffraction measurement The film was cut into a 60 mm long x 60 mm wide square and fixed as shown in FIGS.
The film in a state of being restrained by two aluminum plates is placed in a ventilation constant temperature thermostat (model DKN602, manufactured by Yamato Kagaku Co., Ltd.) having a set temperature of 180 ° C. and a display temperature of 180 ° C., and held for 3 minutes. The temperature was changed and gradually cooled to 100 ° C. over 10 minutes. When the display temperature reaches 100 ° C., the film is taken out and cooled in an atmosphere of 25 ° C. for 5 minutes while being restrained by two aluminum plates. Wide-angle X-ray diffraction measurement was performed on a circular portion having a diameter of 40 mm.
-Wide-angle X-ray measuring device: manufactured by Mac Science Co., Ltd. Model No. XMP18A
X-ray source: CuKα ray, output: 40 kV, 200 mA
Scanning method: 2θ / θ scan, 2θ range: 5 ° to 25 °, scanning interval: 0.05 °, scanning speed: 5 ° / min
About the obtained diffraction profile, the presence or absence of β activity was evaluated from the peak derived from the (300) plane of the β crystal of polypropylene as follows.
○: When a peak is detected in the range of 2θ = 16.0 to 16.5 ° (with β activity)
X: When no peak was detected in the range of 2θ = 16.0 to 16.5 ° (no β activity)
If the film piece cannot be cut into a 60 mm × 60 mm square, the sample may be prepared by adjusting so that the film is placed in a circular hole of φ40 mm in the center.

(11) Molecular orientation ratio Wide angle X-ray diffractometry (diffractometer method) The diffraction peak on the (−113) plane observed near 2θ = 41 ° is measured in the circumferential direction (azimuth angle) under the following measurement conditions: (Β direction) intensity distribution was measured.
・ Wide-angle X-ray measuring device: manufactured by Mac Science Co., Ltd. Model No. XMP18A
・ X-ray source: CuKα ray ・ Output: 40 kV, 20 mA
2θ / θ measurement: 2θ range: 35 ° to 55 °, scanning interval: 0.05 °, scanning speed: 1.5 ° / min
Orientation measurement: 2θ = 41 ° (fixed), β measurement range 0 to 180 °, 0.5 ° step scanning speed: 1.5 ° / min
・ Optical system: Pinhole optical system (2mmφ) manufactured by Rigaku Corporation
・ Goniometer: RINT200 Vertical goniometer ・ Detector: Scintillation counter ・ Divergent slit: 2 mmφ, 1 °
・ Light receiving slit: 4mmφ
・ Scattering slit: 1mmφ
・ Measuring method: reflection method ・ Sample stage: Multi-purpose sample stage for poles The film was aligned and cut out so that the thickness was about 1 mm, and the ends were fixed with a bond and used for measurement.
2. First, β = 0 ° is fixed to TD, and 2θ / θ scan is performed under the above conditions. Next, the position of the sample and the counter is fixed at θ, 2θ, which is the peak apex near 2θ = 41 °. Subsequently, the sample was scanned in the β direction under the above conditions to obtain the target X-ray intensity distribution.
3. Using the obtained β-direction profile, the integrated strength (O _MD ) in the vertical direction and the integrated strength (O _TD ) in the horizontal direction were determined by the following methods.
In the range of 3-10 to 180 °, smoothing was automatically performed by the weighted average method of the data diffraction program, and a baseline passing through the minimum intensity was drawn.
3-2 The integrated intensities O _MD and O _TD were calculated as the area of the part surrounded by the base line and the X-ray intensity curve in the following β range.
O _MD : 45 ≦ β ≦ 135 °, O _TD : 0 ≦ β ≦ 45 ° and 135 ≦ β ≦ 180 °
3-3 From this, O _MD / O _TD was calculated, and the obtained value was used as a measure of the orientation balance of crystal chains in the film plane.

Table 1 shows the physical property values obtained in each Example and Comparative Example.
The laminated porous films of the examples configured within the range specified in the present invention have superior dimensional stability and SD characteristics as compared with the films of the comparative examples configured within the range other than specified in the present invention. I understand.
On the other hand, it can be seen from Comparative Example 1 that when the value of the shrinkage ratio _SMD2 / _STD2 is large, the SD characteristics are not exhibited. Further, from Comparative Example 2, the dimensional stability is insufficient even when the SD characteristic is exhibited, which causes a battery safety problem such as an internal short circuit.
Among the examples, Example 1 is a more preferable embodiment from the viewpoint of tensile modulus.

  Since the laminated film of the present invention has excellent dimensional stability and SD characteristics, and has high air permeability, it is a packaging product, sanitary product, livestock product, agricultural product, building product, medical product, separation product. It can be used as a film, a light diffusing plate, a reflection sheet, or a battery separator, and can be suitably used as a lithium ion battery separator used as a power source for various electronic devices.

It is a partially broken perspective view of the lithium ion battery which has accommodated the separator for lithium ion batteries of this invention. It is a figure explaining the fixing method of the film in the air permeability and wide-angle X-ray-diffraction measurement after heating for 5 second at 135 degreeC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Battery separator 20 Lithium ion battery 21 Positive electrode plate 22 Negative electrode plate 31 Aluminum plate 32 Film 33 Clip 34 Film vertical direction 35 Film horizontal direction

Claims (10)

A laminated porous film having a layer A containing a polypropylene resin as a main component and a layer B containing a polyethylene resin and having β activity;
1) Shrinkage ratio _STD2 after heating for 1 hour at 105 ° C. in a direction perpendicular to the flow direction of the laminated porous film (TD) is 10% or less 2) Flow direction (MD) of the laminated porous film, And the ratio S _MD2 / S _TD2 of the shrinkage ratio after heating at 105 ° C. for 1 hour in the direction perpendicular to the MD (TD) is 0.1 to 3.0.
A laminated porous film characterized by the above. 2. The laminated porosity according to claim 1, wherein in the direction perpendicular to the flow direction of the laminated porous film (TD), the shrinkage ratio _STD1 after heating at 40 ° C. for 1 hour is less than 1%. the film. _3. The shrinkage ratio _STD3 after heating at 150 ° C. for 1 hour in a direction perpendicular to the flow direction of the laminated porous film (TD) is 25% or less. The laminated porous film described. In the flow direction (MD) of the laminated porous film,
1) Shrinkage percentage _MD1 after heating at 40 ° C for 1 hour is less than 1% 2) Shrinkage percentage _MD2 after heating at 105 ° C for 1 hour is 10% or less A laminated porous film according to any one of the above. The laminated porous film according to any one of claims 1 to 4, wherein a shrinkage ratio _SMD3 after heating for 1 hour at 150 ° C in a flow direction (MD) of the laminated porous film is 18% or less. Sex film. The molecular orientation ratio O _MD / O _TD determined by wide-angle X-ray diffraction measurement is 5 or more in the flow direction (MD) of the laminated porous film and the direction perpendicular to the MD (TD). The laminated porous film according to any one of claims 1 to 5.   The B layer contains at least one compound (X) selected from a modified polyolefin resin, an alicyclic saturated hydrocarbon resin or a modified product thereof, an ethylene copolymer, or a wax. The laminated porous film according to any one of claims 1 to 6.   8. The air permeability at 25 ° C. is 10 to 1000 seconds / 100 ml, and the air permeability after heating at 135 ° C. for 5 seconds is 50000 seconds / 100 ml or more. A laminated porous film according to any one of the above.   A separator for a lithium battery, comprising the laminated porous film according to any one of claims 1 to 8.   A battery comprising the lithium battery separator according to claim 9 incorporated therein.

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