JPH08323910A - Laminated porous film and separator for non-aqueous solvent type battery composed thereof - Google Patents

Abstract

PURPOSE: To provide a lminated porous film excellent in dimensional stability, thrust strength and mechanical strength and usually having pores in an opened state to keep ion permeability or air permeability but taking in a non-aqueous solvent by heating to swell to close the pores and a separator for a non-aqueous solvent type battery formed from the porous film. CONSTITUTION: In a porous film wherein a support layer having pores composed of a crystalline resin or a non-crystalline resin and a porous layer having pares composed of a synthetic resin are laminated, the synthetic resin constituting the porous film layer is swollen by a non-aqueous solvent at temp. lower than the m.p. of the crystalline resin constituting the support layer or the glass transition point of the non-crystalline resin to close the pores of the porous film layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated porous membrane in which fine pores of a synthetic resin porous membrane are closed by swelling and a separator for non-aqueous solvent type batteries. More specifically, a porous membrane in which a support layer and a specific synthetic resin porous membrane layer are laminated (1)
Excellent dimensional stability, (2) piercing strength and (3) mechanical strength,
In addition, normally, the micropores penetrate and retain ion permeability or air permeability, but when heated, they can take in a nonaqueous solvent, swell and close the micropores, and a nonaqueous solvent type composed of the same. The present invention relates to a battery separator.

[0002]

2. Description of the Related Art Conventionally, various porous membranes have been developed,
It is used as a filter, electrolytic membrane, and separator for non-aqueous solvent batteries. In particular, as a separator of a non-aqueous solvent type battery, contact of positive and negative electrodes due to formation of dendritic lithium metal crystals (dendrites) during charging and discharging of a lithium secondary battery, contact of positive and negative electrodes due to contraction of the separator, and contact of separator It is necessary to have safety against overheating of the battery due to contact of the positive and negative electrodes due to electrode penetration that occurs due to insufficient puncture strength, but it is possible to achieve with the polyolefin single-layer porous membrane known so far. Was difficult.

Japanese Patent Laid-Open No. 2-77108 and Japanese Examined Patent Publication No. 4-38101 disclose the above-mentioned safety.
A separator comprising a laminate of a high-melting point polyolefin resin porous membrane layer and a low-melting point polyolefin resin porous membrane layer described in Japanese Patent Laid-Open Publication No. 2003-242242. That is, according to these inventions, even if an excessive current flows in the battery due to a short circuit, the polyolefin resin constituting the low melting point polyolefin resin porous film layer is melted by the heat generated at that time, The effect of blocking and sealing, stopping the flow of current and suppressing overheating, and stacking the high melting point polyolefin resin porous film layer to hold the low melting point polyolefin resin porous film layer that is melted and blocked, and re-establishing short circuit It is understood that it has the effect of preventing the occurrence.

However, the conventional polyolefin-based resin porous membrane and polyolefin-based resin laminated porous membrane separator (1) have low dimensional stability at high temperature and (2) low puncture strength, so that they can prevent contact between positive and negative electrodes. Is not enough. In order to suppress overheating due to contact between the positive and negative electrodes,
It is desired that the separator melts and blocks at a low temperature (about 100 to 140 ° C.), but in the conventional polyolefin-based separator, those having good puncture strength, tensile strength, and dimensional stability have a high blocking temperature and conversely block. Those with low temperature tended to be inferior in piercing strength, tensile strength and dimensional stability.

Further, in non-aqueous solvent type batteries such as lithium batteries and lithium ion batteries, it is necessary to tightly stack the positive electrode, the separator and the negative electrode in this order in order to have a high energy density. , (3)
Therefore, tensile strength is required for the non-aqueous solvent type battery separator.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies in view of the above circumstances, the present inventors have found that a support layer has a specific relationship with the melting point or glass transition point of the support layer and is capable of swelling. It was found that a laminated porous membrane having excellent dimensional stability and mechanical strength can be obtained by providing a specific synthetic resin porous membrane layer, which has led to the completion of the present invention.

That is, according to the first aspect of the present invention, a support layer (A ₁ ) having fine pores made of crystalline resin and a porous membrane layer (B) having fine pores made of synthetic resin are laminated. In the porous membrane, the synthetic resin constituting the porous membrane layer (B) is swollen by the non-aqueous solvent at a temperature lower than the melting point of the crystalline resin constituting the support layer (A ₁ ), so that the fineness of the porous membrane layer (B) becomes small. There is provided a laminated porous membrane characterized in that pores are closed.
According to a second aspect of the present invention, in a porous membrane in which a support layer (A ₂ ) having a fine pore made of an amorphous resin and a porous membrane layer (B) having a fine pore made of a synthetic resin are laminated. , The synthetic resin constituting the porous membrane layer (B) is swollen by the non-aqueous solvent at a temperature lower than the glass transition point of the amorphous resin constituting the support layer (A ₂ ) and the fineness of the porous membrane layer (B) is increased. There is provided a laminated porous membrane characterized in that pores are closed. Furthermore, according to a third aspect of the present invention, there is provided a separator for a non-aqueous solvent battery comprising the first or second laminated porous membrane of the present invention. Hereinafter, the present invention will be described in detail.

[Support layer (A ₁ ), (A ₂ )] The shape of the support layer (A ₁ ) or (A ₂ ) having pores that constitutes the laminated porous membrane of the present invention is a porous membrane layer. If the shape of the laminated porous membrane can be maintained when the synthetic resin constituting (B) is swollen, it may be in the form of a mesh such as a woven or non-woven fabric, or a porous membrane. In particular, the support layer of the present invention is preferably a porous film.

(Crystalline Resin) As the crystalline resin constituting the support layer (A ₁ ), a resin which does not melt at the temperature at which the porous membrane layer (B) swells may be appropriately selected. Preferably, it is a crystalline resin having a melting point of 160 ° C. or higher, such as polypropylene, poly-4-methylpentene-1,
Polyolefin resin such as poly-3-methylbutene, polyester resin such as polyethylene terephthalate and polybutylene terephthalate, nylon-6, nylon-1
1, polyamide resins such as 1, Nylon-12 and Nylon-66, polyphenylene sulfide, and polyether ether ketone. More preferably, it is a copolymer of polypropylene, poly-4-methylpentene-1, poly-3-methylbutene and monomers constituting them, or a mixture thereof. When the melting point of the crystalline resin is 160 ° C. or higher, the function of supporting the synthetic resin porous membrane layer (B) is easily maintained even at high temperatures, for example, overheating caused by contact between the positive and negative electrodes of the battery. Further, since it can withstand a high temperature when producing a laminated porous membrane, it can be heat treated at a high temperature, has more dimensional stability, and when used as a non-aqueous solvent type battery separator as described later. Also, the puncture strength and the tensile strength can be improved.

(Amorphous Resin) As the amorphous resin constituting the support layer (A ₂ ), a resin which does not show a clear crystal melting peak in the melting point measurement using DSC (Differential Scanning Calorimeter) Therefore, a resin that does not soften at the temperature at which the porous membrane layer (B) swells may be appropriately selected. An amorphous resin having a glass transition point of 140 ° C. or higher is preferable, and examples thereof include polycarbonate and polyetherimide. More preferably, it is polycarbonate. If the amorphous resin has a glass transition point of 140 ° C. or higher, as in the case of the crystalline resin constituting the support layer (A ₁ ), even at high temperature, for example, overheating caused by contact between positive and negative electrodes of a battery. The function of supporting the synthetic resin porous membrane layer (B) is easily retained. Further, since it can withstand a high temperature when producing a laminated porous membrane, it can be heat treated at a high temperature, has more dimensional stability, and when used as a non-aqueous solvent type battery separator as described later. Also, the puncture strength and the tensile strength can be improved.

[Synthetic Resin Porous Membrane Layer (B)] As the synthetic resin constituting the porous membrane layer (B), when the laminated porous membrane of the present invention is used as a non-aqueous solvent type battery separator,
Any resin can be used as long as it swells in a non-aqueous solvent and can close the fine pores of the porous membrane layer (B), and examples thereof include vinylidene fluoride resin, polysulfone, polyether sulfone, polyacrylonitrile, and polystyrene. A synthetic resin having a melting point or a glass transition point of 150 ° C. or higher is preferable, and examples thereof include vinylidene fluoride resin, polyether sulfone, polysulfone, and polyacrylonitrile.

Further, when the synthetic resin constituting the porous membrane layer (B) has a melting point or a glass transition point of 150 ° C. or higher, the synthetic resin takes in a non-aqueous solvent in a temperature range of 100 to 140 ° C. It is preferable to swell and block the porous membrane layer (B). In the laminated porous membrane of the present invention, since the mechanism for closing the fine pores of the porous membrane layer (B) is due to swelling, the pores are closed at a temperature lower than the melting point or glass transition point of the synthetic resin constituting the porous membrane layer (B). Will be done. In order to utilize the closing mechanism, the support layer (A ₁ ) made of the crystalline resin having pores or the support layer (A ₂ ) made of the amorphous resin having pores of the present invention is a porous membrane layer. In the case of, in comparison with a conventional separator comprising a laminate of a high melting point polyolefin resin porous membrane layer and a low melting point polyolefin resin porous membrane layer, a heat treatment for producing a porous membrane, that is, a resin is mixed with a plasticizer. Then, the film is formed, and heat treatment such as drying after extraction and heat setting after stretching can be performed at a higher temperature, so that it has excellent puncture strength, tensile strength and dimensional stability. When it is used as a separator for non-aqueous solvent type batteries, it swells at a temperature higher than 100 to 140 ° C. and closes the porous membrane layer (B). Takes longer, which reduces safety.

In the present invention, when the resin constituting the porous membrane layer (B) swells, the porous membrane layer (B) is closed. Swelling means that the synthetic resin absorbs the solvent, as is generally recognized. This is a phenomenon in which the volume increases. The swelling includes infinite swelling (dissolution) and finite swelling, but the infinitely swelling vinylidene fluoride resin or the like also has fine pores blocked even if it does not reach dissolution if the amount of solvent is small. The degree of swelling differs depending on the combination of the resin and the solvent forming the porous film (B), and therefore the combination of the porous film (B) and the solvent can be appropriately selected according to the application of the porous film and the operating temperature. Since there are various factors that affect swelling, the degree of swelling can be evaluated by fixing the non-aqueous solvent to be used according to the “temperature at which the swelling causes blockage” described below.

[Layered Structure] (Combination of Support Layer (A ₁ ) Made of Crystalline Resin and Porous Membrane Layer (B)) The layer structure of the laminated porous membrane according to the first aspect of the present invention is a support layer ( 2 of A ₁ ) / porous membrane layer (B)
Layer structure, three layers of porous membrane layer (B) / support layer (A ₁ ) / porous membrane layer (B) or support layer (A ₁ ) / porous membrane layer (B) / support layer (A ₁ ). Structure, etc., at least support layer (A ₁ ) /
Any multi-layer structure including the two-layer structure of the porous membrane layer (B) may be used. Further, the resin constituting the porous membrane layer (B) of the porous membrane layer (B) / support layer (A ₁ ) / porous membrane layer (B) may be the same or different, and the support layer (A ₁ ) / Porous membrane layer (B)
/ Resins constituting the support layer (A ₁ ) of the support layer (A ₁ ) may be the same or different. In order to improve the puncture strength, tensile strength and dimensional stability, it is preferable that both the resin constituting the support layer and the porous membrane layer have a high melting point or glass transition point, for example, vinylidene fluoride. 2 of a porous film layer (B) made of a resin and a porous film layer (A ₁ ) made of a polyolefin resin such as polypropylene, poly-4-methylpentene-1, poly-3-methylbutene
Examples include a single layer porous film and a three layer porous film. As a combination of these, for example, (vinylidene fluoride resin / polypropylene) two-layer porous membrane, (vinylidene fluoride resin / polypropylene)
Poly 4-methylpentene-1) two-layer porous membrane, (polypropylene / vinylidene fluoride resin / polypropylene) 3
3-layer porous membrane, (poly-4-methylpentene-1 / vinylidene fluoride resin / poly-4-methylpentene-1) 3-layer porous membrane, (poly-4-methylpentene-1 / vinylidene fluoride resin / polypropylene) 3 3-layer porous membrane, (vinylidene fluoride resin / polypropylene / vinylidene fluoride resin) 3-layer porous membrane, (vinylidene fluoride resin / poly 4-
Methyl pentene-1 / vinylidene fluoride resin) three-layer porous membrane. Among these, (vinylidene fluoride resin / polypropylene) two-layer porous membrane, (vinylidene fluoride resin / poly-4-methylpentene-1) two-layer porous membrane,
(Poly-4-methylpentene-1 / vinylidene fluoride resin / poly-4-methylpentene-1) three-layer porous membrane, (poly-4-methylpentene-1 / vinylidene fluoride resin / polypropylene) three-layer porous membrane More preferable.

(Combination of Support Layer (A ₂ ) Made of Amorphous Resin and Porous Membrane Layer (B)) The layer structure of the laminated porous membrane according to the second aspect of the present invention is the support layer (A ₂ ). / Two-layer structure of porous membrane layer (B), porous membrane layer (B) / support layer (A ₂ ).
At least a support layer (A ₂ ) / a porous film layer (B), such as a three-layer structure of / porous film layer (B) or support layer (A ₂ ) / porous film layer (B) / support layer (A ₂ ). The multi-layer structure may be included, including the two-layer structure of (1). The resin constituting the porous membrane layer (B) of the porous membrane layer (B) / support layer (A ₂ ) / porous membrane layer (B) may be the same or different, and the support layer (A ₂ ).
/ Porous membrane layer (B) / support layer (A ₂ ) support layer (A ₂ ).
The resins forming the may be the same or different. To improve piercing strength, tensile strength and dimensional stability,
It is preferable that both the resin constituting the support layer and the porous membrane layer have a high melting point or a high glass transition point. For example, the porous membrane layer (B) made of a vinylidene fluoride resin and the polycarbonate or polyetherimide. A two-layer porous film or a three-layer porous film together with a porous film layer (A ₂ ) made of an amorphous resin such as As a combination of these, for example, (vinylidene fluoride resin / polycarbonate) two-layer porous membrane, (polycarbonate / vinylidene fluoride resin /
Polycarbonate) 3-layer porous membrane, (polycarbonate /
Vinylidene fluoride resin / polyetherimide) 3-layer porous membrane, (vinylidene fluoride resin / polycarbonate /
Vinylidene fluoride resin) three-layer porous film. Among these, (vinylidene fluoride resin / polycarbonate) two-layer porous membrane and (polycarbonate / vinylidene fluoride resin / polycarbonate) three-layer porous membrane are more preferable.

[Average Porosity] The average porosity of the laminated porous membrane of the present invention is 30 to 65%, preferably 30 to 55%, more preferably 35 to 45%. Average porosity is 30%
If it is less than the above, the function as a porous membrane cannot be achieved, and when used as a separator for a non-aqueous solvent type battery, the amount of non-aqueous solvent absorbed and retained decreases, so that the electrical resistance of the separator increases and the performance as a battery decreases. To do. On the other hand, if the average porosity exceeds 65%, the mechanical strength such as piercing strength and tensile strength decreases.

[Average Pore Size] The average pore size of the laminated porous membrane of the present invention is 0.01 to 5 μm, preferably 0.05 to 3 μm.
More preferably, it is 0.1 to 1 μm. If the average pore size is less than 0.01 μm, the gas permeability or ion permeability will decrease, and when used as a separator for non-aqueous solvent type batteries, the electric resistance will increase and the function as a battery will not be sufficient. On the other hand, when the average pore size exceeds 5 μm, it becomes difficult to close the pores, and when it is used as a separator for a non-aqueous solvent type battery, an electrode active material such as carbon slid off from the electrode easily passes therethrough and a short circuit occurrence rate increases.

[Film Thickness] The laminated porous membrane of the present invention preferably has a thickness of 10 to 50 μm, more preferably 15 to 25 μm. If the thickness of the laminated porous film is less than 10 μm, the mechanical strength is not sufficient, and when used as a separator for a non-aqueous solvent type battery, a short circuit is likely to occur. On the other hand, if the thickness of the laminated porous film exceeds 50 μm, in the case of a wound battery, the volume ratio of the separator per battery is increased, which reduces the electrode area, which is not preferable because the battery capacity is reduced.

The thickness of the support layer (A ₁ ) or (A ₂ ), particularly, the crystalline resin or amorphous resin porous membrane is 5 to 47.
μm is preferable, and the range of 7 to 20 μm is more preferable. When the thickness of the support layer (A ₁ ) or (A ₂ ) is less than 5 μm, the porous membrane layer (B) does not have sufficient mechanical strength after swelling and clogging, and when used as a separator for a non-aqueous solvent battery. There is also a problem that a short circuit easily occurs.

The thickness of the porous membrane layer (B) is 3 to 45.
μm is preferable, and a range of 5 to 20 μm is more preferable. If the thickness of the porous membrane layer (B) is less than 3 μm, the swelling and blocking are not sufficient, and when used as a separator for non-aqueous solvent type batteries, overheating due to the occurrence of short circuit cannot be suppressed, and the electrodes pierce the separator. It is easy to short circuit again. The method for producing the laminated porous membrane of the present invention will be described below.

[Production Method] The support layer (A ₁ ) made of a crystalline resin, the support layer (A ₂ ) made of an amorphous resin, and the porous membrane layer (B) are produced by the support layer (A). ₁ ),
(A ₂ ) and the resin constituting the porous membrane layer (B) are mixed with a plasticizer to form a film, and then the plasticizer is extracted from the membrane with an extraction solvent to form a porous membrane. There are two ways.

For example, when the resin forming the porous membrane layer (B) is a vinylidene fluoride resin, it can be manufactured as follows.

The plasticizer for vinylidene fluoride resin is a plasticizer for vinylidene fluoride resin,
For example, adipic acid-propylene glycol type, adipic acid-1,3-butylene glycol type adipic acid type polyester, sebacic acid-propylene glycol type,
Sebacic acid-1,3-butylene glycol-based sebacic acid-based polyester, azelaic acid-propylene glycol-based, azelaic acid-1,3-butylene glycol-based azelaic acid-based polyester, aliphatic dibasic acid and glycol Examples of such aliphatic polyester plasticizers and phthalic acid diester plasticizers such as dioctyl phthalate are preferable, and adipic acid polyesters are particularly preferable from the viewpoint of compatibility with vinylidene fluoride resin. The amount of the plasticizer blended is 30 to 250 parts by weight with respect to 100 parts by weight of the vinylidene fluoride resin, taking porosity into consideration.
Preferably 40-170 parts by weight, more preferably 50-
It is 120 parts by weight.

The melting temperature of the resin composition during molding is 1
70-250 degreeC is preferable, More preferably, it is 180-2.
40 ° C. Extrusion preferably uses a T-die and has a thickness of 3
-45 μm, more preferably 5-20 μm.

The solvent for extracting the plasticizer from the film obtained above is not particularly limited as long as it does not dissolve the vinylidene fluoride resin and can dissolve the plasticizer. Examples include alcohols such as methanol and isopropyl alcohol, and examples of chlorinated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane.

The extraction method using the above solvent is carried out at a temperature of 10 to 1
It is left in an extraction solvent at 50 ° C, preferably 15 to 100 ° C, more preferably 20 to 50 ° C. Moreover, it is possible to accelerate the extraction by applying appropriate vibration. After extracting the plasticizer,
For drying the porous membrane, at a temperature of 50 to 150 ° C., 0.5 to
Heat treatment for 360 minutes.

When the resin constituting the support layer (A ₁ ) is a polyolefin resin, it can be manufactured as follows.

As the plasticizer for polyolefin resin,
A resin for plasticizing a polyolefin resin, for example, an aliphatic dibasic acid such as phthalic acid diester, azelaic acid-propylene glycol-based, azelaic acid-1,3-butylene glycol-based azelaic acid-based polyester, and glycol. Examples thereof include aliphatic polyesters, phosphoric acid esters, glycol esters, and epoxy compounds, and phthalic acid polyesters are particularly preferable from the viewpoint of compatibility with polyolefin resins. The amount of the plasticizer blended is 30 to 250 parts by weight, preferably 40 to 200 parts by weight, and more preferably 50 to 150 parts by weight, based on 100 parts by weight of the polyolefin resin, in consideration of the porosity.
Parts by weight.

The melting temperature of the resin composition during molding is 1
80-340 degreeC is preferable, More preferably, it is 200-2.
It is 70 ° C. Extrusion preferably uses a T-die and has a thickness of 3
-45 μm, more preferably 5-20 μm.

The solvent for extracting the plasticizer from the film obtained above is not particularly limited as long as it does not dissolve the polyolefin resin and can dissolve the plasticizer. Examples thereof include haloalkanes such as trichloromethane and trichloroethane, ketones such as acetone and methyl ethyl ketone, lower carboxylic acid esters such as ethyl acetate, lower alcohols such as methanol, and aromatic hydrocarbons such as toluene and xylene.

The above extraction method using a solvent is carried out at a temperature of 10 to 1
It is left in an extraction solvent at 50 ° C, preferably 15 to 100 ° C, more preferably 20 to 50 ° C. Moreover, it is possible to accelerate the extraction by applying appropriate vibration. After extracting the plasticizer,
For drying the porous membrane, at a temperature of 50 to 150 ° C., 0.5 to
Heat treatment for 360 minutes.

When the resin constituting the support layer (A ₂ ) is a polycarbonate resin, it can be manufactured as follows.

As the plasticizer for the polycarbonate resin,
A resin for plasticizing a polycarbonate resin, for example, an aliphatic dibasic acid such as phthalic acid diester, azelaic acid-propylene glycol-based, azelaic acid-1,3-butylene glycol-based azelaic acid-based polyester, and glycol. Examples of the aliphatic polyester, phosphoric acid ester, glycol ester, and epoxy compound are The amount of the plasticizer blended is 30 to 2 with respect to 100 parts by weight of the polycarbonate resin in consideration of the porosity.
The amount is 50 parts by weight, preferably 40 to 200 parts by weight, and more preferably 50 to 150 parts by weight.

The melting temperature of the resin composition during molding is 1
80-340 degreeC is preferable, More preferably, it is 200-2.
It is 70 ° C. Extrusion preferably uses a T-die and has a thickness of 3
-45 μm, more preferably 5-20 μm.

The solvent for extracting the plasticizer from the film obtained above is not particularly limited as long as it does not dissolve the polycarbonate resin and can dissolve the plasticizer. Examples thereof include lower alcohols such as methanol, ethanol and isopropyl alcohol.

The above extraction method using a solvent is carried out at a temperature of 10 to 1
It is left in an extraction solvent at 50 ° C, preferably 15 to 100 ° C, more preferably 20 to 50 ° C. Moreover, it is possible to accelerate the extraction by applying appropriate vibration. After extracting the plasticizer,
For drying the porous membrane, at a temperature of 50 to 150 ° C., 0.5 to
Heat treatment for 360 minutes.

The laminated porous membrane of the present invention may be laminated by a coextrusion method, a method of laminating each porous membrane formed in advance using a hot press, a heat roll or the like, or spot fusion. . When the support layer (A ₁ ) is other than the porous membrane layer, the support layer (A ₁ ) is added to the porous membrane (B) obtained by the above method.
_It is preferable to obtain a laminated porous membrane by the method of joining ₁ ).
On the other hand, when the support layer (A ₁ ) is a porous film, the coextrusion method is preferable in terms of the number of manufacturing steps.

For example, when the coextrusion method is adopted, the synthetic resin forming the support layer (A ₁ ) is a polyolefin resin, and the synthetic resin forming the porous membrane layer (B) is a vinylidene fluoride resin. Taking a laminated porous membrane as an example, it can be manufactured as follows.

The plasticizer can be selected from the above-mentioned polyolefin resin plasticizer and vinylidene fluoride resin plasticizer, and it is preferable to use the same plasticizer or a combination of plasticizers which can be extracted with the same solvent. The melting temperature of the resin composition during molding is 170 to 2 for both the polyolefin resin and the vinylidene fluoride resin.
The temperature is preferably 70 ° C, more preferably 180 to 260 ° C. Extrusion preferably uses a T-die to form a film. The solvent for extracting the plasticizer from the obtained film is not particularly limited as long as it does not dissolve the polyolefin resin and the vinylidene fluoride resin and can dissolve the plasticizer. Even if only the plasticizer of one synthetic resin is dissolved, a solvent that can remove the other plasticizer after removing the one plasticizer may be used. Extraction temperature is 1
It is left in an extraction solvent at 5 to 150 ° C, preferably 15 to 100 ° C, more preferably 20 to 50 ° C. Moreover, it is possible to accelerate the extraction by applying appropriate vibration. After extracting the plasticizer, the temperature is 50 to 150 ° C. for drying the porous membrane,
Heat treatment is performed for 0.5 to 360 minutes.

The laminated porous membrane is preferably uniaxially or biaxially stretched from the viewpoint of mechanical strength. Further, from the viewpoint of dimensional stability, it is preferable to perform the heat treatment after stretching at a temperature lower than the temperature at which the resin composition constituting each porous membrane layer melts. In order to improve the puncture strength, the tensile strength and the dimensional stability, it is preferable to increase the heat treatment temperature. From this point, both the resin constituting the support layer and the porous membrane layer have a melting point or a glass transition point. It is preferably high.

The laminated porous membrane of the present invention can be used as a separator for non-aqueous solvent type batteries, and the resin constituting the porous membrane layer (B) swellable with the following non-aqueous solvent may be appropriately selected and used. As the non-aqueous solvent used in the non-aqueous solvent type battery, for example, propylene carbonate, ethylene carbonate, a cyclic carbonic acid ester solvent such as butylene carbonate, γ-butyrolactone, a cyclic carboxylic acid ester solvent such as γ-valerolactone, dimethoxymethane, 1,2-
Chain ether solvents such as dimethoxyethane and 1,3-dimethoxypropane, tetrahydrofuran, 1,3-dioxolane, 2-methyltetrahydrofuran, 4-methyl-
Cyclic ether solvents such as 1,3-dioxolane, methyl formate, methyl acetate, chain carboxylic acid ester solvents such as methyl propionate, dimethyl carbonate, ethyl methyl carbonate, chain carbonic acid ester solvents such as diethyl carbonate, acetonitrile, sulfolane, One or a combination of two or more kinds of other organic solvents such as 3-methylsulfolane, dimethyl sulfoxide, N, N-dimethylformamide, N-methyloxazolidinone and the like can be mentioned. For example, when the porous membrane layer (B) is made of vinylidene fluoride resin, a combination of cyclic carbonic acid ester and chain ether or chain carbonic acid ester is preferable,
More preferred are combinations of propylene carbonate and 1,2-dimethoxyethane, propylene carbonate and dimethyl carbonate, propylene carbonate and diethyl carbonate, and propylene carbonate and ethylmethyl carbonate.

[0042]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited thereto. The measurements in Examples and Comparative Examples were based on the following methods.

[1. Average Pore Size] The average pore size is ASTM F-316-86 using a test piece with a measurement area of 20 mmφ.
It was determined by the half-dry method of ethanol according to

[2. Porosity] A sample (5 cm x 5 cm) was immersed in mineral oil (Aldrich) for 6 hours, and the weight (W2) after the surface mineral oil was sufficiently wiped off was measured. The pore volume (V1) was calculated from (W1) and the density (ρ) of the mineral oil by the following formula: V1 = (W2-W1) / ρ. The porosity (P) is calculated from the apparent volume (V2: a value calculated from thickness and dimensions) and the porosity volume (V1) by the following equation: P = V1
/ V2 × 100 (%).

[3. Measurement of temperature at which blockage occurs due to swelling] An electrolyte solution (propylene carbonate and 1,2-
After impregnating 1 mol / l lithium perchlorate dissolved in a 1: 1 mixed solvent of dimethoxyethane), 5c
The measurement cell was fixed by sandwiching it between two platinum electrodes of m ² .
A voltage of DC 4V was applied between the electrodes while heating the measurement cell, and the change in DC resistance (Ω · cm ² ) was measured from the circuit current. At this time, the temperature (Y ° C.) satisfying the following equation: (DC resistance at Y ° C.) / (DC resistance at 100 ° C.) = 2 was taken as the temperature at which the blockage due to swelling occurred.

[4. Melting Point Measurement of Crystalline Resin] The melting point was measured by a method based on ASTM-D3418 using a differential scanning calorimeter (DSC).

[5. Measurement of Tensile Strength and Elongation] Tensile strength and elongation measuring machine (Tensilon RTM-10 manufactured by Orientec Co., Ltd.)
(Type 0), a test piece of a laminated porous film having a width of 10 mm and a length of 100 mm was used, a chuck distance was 50 mm, and a pulling speed was 1
The breaking strength and the amount of elongation until breaking were measured under the condition of 00 mm / min, and the following formula: stress at break (MPa) = [strength at break (Kgf) / cross-sectional area (cm ² ) before tensile of test piece]. ×
From 0.0981, the stress at break and the following formula: elongation at break (%) = [elongation to break: displacement (mm) / 50
(Mm)] × 100, the elongation at break was determined.

[6. Measurement of puncture strength] Tensile strength and elongation measuring machine (Tensilon RTM-100 manufactured by Orientec Co., Ltd.)
53m to the sample fixing jig using the compression mode of
Set a circular test piece of mφ and R of the tip is 0.5 m
With a cone-shaped piercing jig of m, compression speed (piercing speed) 120
The puncture strength was measured in mm / min. The load when the test piece is broken by the piercing jig is defined as the breaking point load (gf), and the displacement amount of the piercing jig from the point where the piercing jig touches the test piece (origin of displacement) to the breaking Displacement at break (mm)
And The puncture strength (gf · mm) in the present invention means
It is the integrated value of the load at each displacement point from the origin of displacement to the break point.

[7. Measurement of heat shrinkage ratio] A laminated porous film as a sample is cut out into 100 mm x 100 mm and the temperature is 60 ° C
Was heat-treated in the oven for 1 hour. The rate of dimensional change in length before and after heat treatment was measured, and the following formula: Shrinkage (%) = {[(length of sample before heat treatment-length of sample after heat treatment)]
The shrinkage ratio was calculated as: ((length of sample before heat treatment)) × 100.

Example 1 As a resin constituting the layer B, 100 parts by weight of polyvinylidene fluoride (Kureha Chemical Industry Co., Ltd., trade name: KF, melting point 178 ° C.) was added to an adipic acid-based polyester plasticizer ( Fifty parts by weight of Asahi Denka Kogyo KK, trade name: PN-640 was melt-mixed at 240 ° C. using a twin-screw extruder and pelletized. Poly-4-methylpentene-1 (Mitsui Petrochemical Co., Ltd., trade name: TPX, melting point 235 ° C.) as a resin constituting the layer A
65 parts by weight of 100 parts by weight of adipic acid-based polyester plasticizer (manufactured by Asahi Denka Co., Ltd., trade name: PN-6
40) is melt mixed at 260 ° C. using a twin-screw extruder,
Pelletized. The pellets obtained are 370 mm wide and
It is melt-extruded from three extruders equipped with a T-die for layer co-extrusion to form a melt sheet consisting of A layer / B layer / A layer, which is cooled on a chill roll at 80 ° C. Got The obtained raw fabric is cut into 200 mm squares and 30 ° C
While applying ultrasonic waves in isopropyl alcohol, 5
Processed for a minute. After drying, the film was uniaxially stretched 1.5 times at room temperature and then heat-treated at 120 ° C. for 30 minutes to obtain a laminated porous film. When the cross section of the obtained laminated porous film was observed using a polarization microscope, the thickness of A layer / B layer / A layer was 8 μm / 9 each.
It was μm / 8 μm. In addition, Table 1 shows the physical properties of the laminated porous membrane obtained by the above-mentioned measuring method.

(Comparative Example 1) Polypropylene which does not swell in an electrolytic solution as a resin constituting the layer B (manufactured by Chisso Corporation,
Product name: Chisso Polypro, melting point: 165 ° C) 100 parts by weight of adipic acid-based polyester (Asahi Denka Kogyo Co., Ltd.)
70 parts by weight (trade name: PN-640 manufactured by the company) was melt-mixed at 240 ° C. using a twin-screw extruder and pelletized. A
Poly-4-methylpentene-1 as a resin constituting the layer
65 parts by weight of adipic acid polyester (manufactured by Asahi Denka Kogyo Co., Ltd., trade name: PN, manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: TPX, melting point 235 ° C.)
-640) was melt-mixed at 260 ° C. using a twin-screw extruder and pelletized. Width of the obtained pellets 370 mm
Of the three-layer coextrusion T-die for extrusion is melt-extruded to form a molten sheet of A layer / B layer / A layer, which is cooled on a chill roll at 80 ° C. to form a porous film. I got the original fabric. The obtained raw fabric is cut into 200 mm squares and 30
While applying ultrasonic waves in isopropyl alcohol at ℃,
It was treated for 5 minutes. After drying, the film was uniaxially stretched 1.5 times at room temperature and then heat-treated at 120 ° C. for 30 minutes to obtain a laminated porous film. When the cross section of the obtained laminated porous film was observed using a polarization microscope, the thickness of A layer / B layer / A layer was 8 μm /
It was 9 μm / 8 μm. In addition, Table 1 shows the physical properties of the laminated porous membrane obtained by the above-mentioned measuring method.

(Comparative Example 2) Polybutene-1 (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: Beaulon, melting point 123 ° C.) which does not swell in the electrolyte as the resin constituting the B layer 10
80 parts by weight of adipic acid-based polyester (manufactured by Asahi Denka Kogyo Co., Ltd., trade name: PN-640) per 0 parts by weight,
It was melt-mixed at 240 ° C. using a twin-screw extruder and pelletized. Poly-4-methylpentene-1 (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: TP) as a resin constituting the layer A
X, melting point 235 ° C.) 65 parts by weight of adipic acid polyester (trade name: PN-640, manufactured by Asahi Denka Kogyo Co., Ltd.) per 100 parts by weight is melt mixed at 260 ° C. using a twin-screw extruder. And pelletized. Width of the resulting pellets 3
It is melt-extruded from three extruders equipped with a 70 mm T-die for three-layer coextrusion to form a molten sheet of A layer / B layer / A layer, which is cooled on a chill roll at 80 ° C. to be porous. I got a membrane roll. The obtained raw fabric was cut into a 200 mm square and treated in isopropyl alcohol at 30 ° C. for 5 minutes while applying ultrasonic waves. After drying, 1.5 times 1 at room temperature
After axial stretching, heat treatment was performed at 60 ° C. for 30 minutes to obtain a laminated porous membrane. When the cross section of the obtained laminated porous film was observed using a polarization microscope, the thicknesses of A layer / B layer / A layer were 7.5 μm / 10 μm / 7.5 μm, respectively. In addition, Table 1 shows the physical properties of the laminated porous membrane obtained by the above measuring method.

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[Table 1]

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The laminated porous membrane of the present invention is excellent in dimensional stability and mechanical strength. Further, according to the separator for a non-aqueous solvent type battery of the present invention comprising the laminated porous film, the puncture strength and the tensile strength are excellent, and even if an excessive current flows in the battery due to a short circuit, The synthetic resin porous film capable of swelling due to the heat generated at that time swells by taking in the non-aqueous solvent, has the effect of blocking and sealing the pores at a relatively low temperature, stopping the flow of current, and suppressing overheating. Further, since the separator for a non-aqueous solvent type battery of the present invention is also excellent in dimensional stability, it is possible to prevent contact between the positive and negative electrodes due to contraction of the separator. Furthermore, since the separator for a non-aqueous solvent type battery of the present invention has excellent mechanical strength, it is possible to manufacture a non-aqueous solvent type battery without causing tearing of the separator.

Claims (11)

[Claims] 1. A porous membrane in which a support layer (A ₁ ) having fine pores made of a crystalline resin and a porous membrane layer (B) having fine pores made of a synthetic resin are laminated, and the support layer (A ₁ ) The synthetic resin constituting the porous membrane layer (B) is swollen by the non-aqueous solvent at a temperature lower than the melting point of the crystalline resin constituting the ( ₁ ) to close the fine pores of the porous membrane layer (B). Laminated porous membrane. 2. A support layer (in a porous membrane in which a support layer (A ₂ ) having pores made of an amorphous resin and a porous membrane layer (B) having fine pores made of a synthetic resin are laminated. (A ₂ ) that the synthetic resin forming the porous membrane layer (B) swells at a temperature lower than the glass transition point of the amorphous resin forming A ₂ ) by the non-aqueous solvent to close the fine pores of the porous membrane layer (B). A laminated porous membrane characterized by: 3. The laminated porous structure according to claim 1, wherein the support layer (A ₁ ) is a porous membrane layer made of a crystalline resin having a melting point of 160 ° C. or higher, and the melting point or glass transition point of the synthetic resin is 150 ° C. or higher. film. 4. The support layer (A ₂ ) has a glass transition point of 140.
The laminated porous membrane according to claim 2, which is a porous membrane layer made of an amorphous resin having a temperature of not less than 0 ° C, and a synthetic resin having a melting point or a glass transition point of not less than 150 ° C. 5. The support layer (A ₁ ) is a porous membrane layer made of a crystalline resin having a melting point of 160 ° C. or higher, the melting point or glass transition point of the synthetic resin is 150 ° C. or higher, and the temperature range 1
4. The laminated porous membrane according to claim 1 or 3, wherein the synthetic resin is swollen by a non-aqueous solvent at 00 to 140 ° C to close the fine pores of the porous membrane layer (B). 6. The support layer (A ₂ ) has a glass transition point of 140.
A porous film layer made of an amorphous resin having a temperature of 100 ° C or higher, the melting point or glass transition point of the synthetic resin being 150 ° C or higher, and the synthetic resin being swollen by a nonaqueous solvent in the temperature range of 100 to 140 ° C. The laminated porous membrane according to claim 2 or 4, wherein the fine pores of (B) are closed. 7. The crystalline resin forming the support layer (A ₁ ) is a polyolefin resin, and the synthetic resin forming the porous membrane layer (B) is a vinylidene fluoride resin. 5. The laminated porous membrane according to any one of 5 above. 8. The amorphous resin forming the support layer (A ₂ ) is a polycarbonate resin, and the synthetic resin forming the porous membrane layer (B) is a vinylidene fluoride resin. 6. The laminated porous membrane according to any one of 6. 9. The average porosity of the laminated porous membrane is 30 to 65%.
The laminated porous membrane according to any one of claims 1 to 8. 10. The laminated porous membrane has an average pore diameter of 0.01 to 5
The laminated porous membrane according to any one of claims 1 to 9, which has a thickness of µm. 11. A separator for a non-aqueous solvent type battery, comprising the laminated porous membrane according to any one of claims 1 to 10.