JP3065678B2 - Heat-shrinkable multilayer barrier film and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention has excellent gas barrier properties and is mainly used for various packaging materials (mainly household wrap films, non-shrink wrapping films utilizing barrier properties, shrink wrapping films, laminates) TECHNICAL FIELD The present invention relates to a heat-shrinkable multilayer film useful for a film and other uses and a method for producing the same, and more specifically, to a gas barrier (mainly O ₂ , CO ₂ ) mainly composed of a polymer mainly composed of an ethylene-vinyl alcohol copolymer. ₂ Other gas barrier properties.
The present invention relates to a heat-shrinkable multilayer film including a specific polymer layer mainly composed of thermoplastic polyester as another layer, and a method for producing the same.

[0002]

2. Description of the Related Art Various film packaging methods, such as household wrap packaging, overlap packaging, twist packaging, bag packaging, skin packaging, shrink packaging, stretch packaging, etc., make use of the characteristics of the film. The method has been adopted. Among them, shrink wrapping is characterized by its beautiful appearance, enhanced product value, sanitary contents and easy visual quality confirmation, and quick and tight fixation of irregular or multiple products. It is often used for packaging foods and sundries because of its ability to be packaged.However, on the other hand, films that have excellent gas barrier properties in order to suppress deterioration Mainly, it is required for packaging of chemicals and also electronic parts. In general, the packaged object often does not generate heat. In the case of a heat-shrinkable film, it is also desired that the film has a low-temperature shrinkability that does not cause a dimensional change in the distribution process including storage.

Conventionally, as a heat-shrinkable polymer film,
Films mainly using polyvinyl chloride, polypropylene, polyethylene, etc. are known, but these films are inferior in gas barrier properties, and in heat-shrinkable films using polyvinyl chloride, they are used in combination. Plasticizers and heat stabilizers are not preferred in terms of hygiene, and disposal and incineration are problematic in terms of environmental conservation and hygiene.

On the other hand, polymers having excellent gas barrier properties include a vinylidene chloride-based polymer and an ethylene-vinyl alcohol-based copolymer. Usually, a large amount of a plasticizer or a stabilizer is added in order to give stretchability, and these are not preferable in terms of hygiene and have problems of odor and discoloration. In addition, in some cases, in a multilayer film, these additives may be transferred to an adjacent layer, and the barrier properties may become unstable with time. Furthermore, as with the above-mentioned polyvinyl chloride, disposal and incineration are environmental protection and
There is a problem in hygiene. On the other hand, the latter ethylene-vinyl alcohol-based copolymer does not have the above-mentioned environmental health problems of the former and has a better gas barrier property during drying than the former. Have been.

However, in addition to the crystalline nature of the ethylene-vinyl alcohol copolymer itself,
Due to the presence of strong hydrogen bonds, the film exhibits necking-like (combined with extremely thick and thin portions) stretching during stretching, and has poor stability and is easily broken. There was a problem that the film-forming properties were extremely poor, and it was particularly difficult to impart a stretch orientation required as a heat-shrinkable film. Also, the obtained film has poor shrinkage (especially low-temperature shrinkage) as a shrink film, and there is a problem when a high shrinkage is required in practical use.

To solve this problem, Japanese Patent Laid-Open Publication No.
No. 1 discloses a saponified ethylene vinyl acetate copolymer,
Although a method of improving stretchability by containing a specific amount of water in accordance with the ethylene content is disclosed, troubles such as generation of bubbles during coextrusion molding and breakage of the film during stretch film formation are solved. Adjustment of the water content to avoid is complicated, and lowering the gas barrier property is inevitable by adding more water. In addition, before stretching, it is difficult to uniformly control the amount of water serving as a plasticizer throughout the entire surface during stretching, or in the case of tubular stretching, it is difficult to keep the internal pressure constant. There are drawbacks that are difficult to do. Further, if the moisture is removed, the above-mentioned shrinkability is inferior. Also, JP-A-2-251418 discloses that a saponified ethylene vinyl acetate copolymer is extruded into a tube by coextrusion molding as an inner surface layer, and cooling water is brought into direct contact with the saponified ethylene vinyl acetate copolymer. A method is disclosed in which a relatively large amount (5 to 15% by weight) of water is contained by quenching to improve stretchability. However, since a saponified ethylene vinyl acetate copolymer layer is present on the surface layer,
There is a danger that quality will deteriorate due to external influences, especially the gas barrier properties will decrease. In addition, the inclusion of a relatively large amount of water itself lowers the gas barrier properties. However, in order to cover this, heat treatment is performed at a relatively high temperature (140 to 160 ° C.). Since the orientation is relaxed, a practical heat-shrinkable film cannot be obtained. Further, the shrinkage as a shrink film is also poor.

JP-A-53-138468 discloses a laminated film obtained by co-extruding a saponified ethylene-vinyl acetate copolymer with an inflation-capable thermoplastic resin (eg, polyethylene, nylon 6, ionomer, etc.). Immediately in the circumferential direction depending on the gas pressure, 1.2 to 3.
A method of obtaining a blown film by blowing 5 times is disclosed. However, in this method, it is difficult to give a high degree of orientation, and in the ordinary one-stage inflation method, intermolecular flow is likely to occur during stretch film formation, which is necessary for realizing practical heat shrinkability. It is difficult to provide a proper molecular orientation. Further, after laminating a film made of saponified ethylene vinyl acetate copolymer and another stretchable thermoplastic film (for example, polyolefin resin, vinyl chloride resin, polyester resin, acrylonitrile copolymer, etc.), Although there is a method of performing biaxial stretching (Japanese Patent Application Laid-Open No. 51-6267), stretchability is insufficient, and a highly shrinkable film has not been obtained. Also, a method has been proposed in which a saponified ethylene-vinyl acetate copolymer film is combined with an unstretched or uniaxially stretched polyester film and then stretched (Japanese Patent Laid-Open No. 55-86722). In order to obtain a highly stretched film for each of the layers constituting the multilayer, the optimum extrusion conditions, stretching conditions, etc. for each resin are different, so that uneven thickness, puncture, delamination, and whitening occur during stretching film formation. For example, it is not always possible to obtain satisfactory stretch film forming properties, and as a result, it is difficult to obtain a practical heat-shrinkable film. Other methods are disclosed in JP-A-62-103140 and JP-A-6-103140.
JP-A-2-113526 and JP-A-1-97623
Japanese Patent Application Laid-Open Publication No. H11-163,086 discloses a technique relating to co-extrusion co-stretching of a multilayer stretched film having a constitution of polyester / adhesive resin / ethylene-vinyl alcohol copolymer / adhesive resin / polyester. In order to smooth out unevenness in thickness and thickness, the raw material molding conditions for obtaining a multi-layer stable flow during co-extrusion are specified, which are inadequate as in the methods described above, and It is difficult to obtain a typical heat-shrinkable film, particularly a film excellent in low-temperature shrinkability.

[0008]

As described above, there is no particular problem in environmental hygiene such as disposal and incineration, and the gas barrier film has excellent stretch film forming property and heat shrinkability, and excellent mechanical properties and optical properties. The development of is strongly desired.

[0009]

Means for Solving the Problems That is, at least one
The layer (A) mainly composed of an ethylene-vinyl alcohol-based copolymer and the other layer (B) have a Vicat softening point of a resin constituting the layer, and the above-mentioned layer (A) constitutes the layer (A). (B) Vicat of the resin constituting the layer (B) including at least one thermoplastic polyester-based polymer layer having a value equal to or higher than the glass transition point of the main resin and equal to or lower than the Vicat softening point of the main resin. 3 from softening point
A heat-shrinkable multilayer film characterized in that the heat-shrinkage rate at a temperature higher by 0 ° C. is at least 20% in at least one direction of vertical and horizontal.

[0010] The production method is such that at least one layer of a polymer layer (A) mainly composed of an ethylene-vinyl alcohol copolymer and another layer (B) have a Vicat softening point of a resin constituting the layer. The resin (A) constituting the layer (A) has a glass transition point which is equal to or higher than the glass transition point of the main resin and the V of the main resin.
The polymer of each layer is melted in a respective extruder, co-extruded with a multilayer die and quenched so as to have a structure including at least one layer of a thermoplastic polyester-based polymer layer having a value equal to or lower than the icat softening point. After cooling and solidifying at least the (B) layer so as to maintain a substantially amorphous state to obtain a multilayer film raw material, the raw material film is heated to obtain a Vicat softening point of a resin constituting the layer (B). A stretching temperature within a temperature range of 20 ° C. or lower and a melting point of a resin as a main component of the layer (A) and a stretching ratio of at least 5 to 50 in at least one direction.
It is to stretch twice.

Hereinafter, the present invention will be described in detail. The polymer layer (A) of the present invention has a role as a main gas barrier layer, and has physical properties due to external direct heat, physical and chemical actions, and the like. In order to avoid deterioration and make the stretching orientation effect described later more effective, preferably at least one
The layers are arranged. The ethylene-vinyl alcohol copolymer serving as a main component of the layer (A) is prepared by converting an ethylene-vinyl acetate copolymer having an ethylene content of 15 to 80 mol% to a saponification degree of 80 mol% or more. A copolymer obtained by adding a -OH group derived from a copolymer obtained by saponification or another copolymer is used. In this case, those having an ethylene content of less than 15 mol% are inferior in melt moldability and stretch film forming properties, while those having an ethylene content of more than 80 mol% are insufficient in gas barrier properties. Further, it is preferable that the film has low-temperature shrinkability as much as possible.However, this low-temperature shrinkage is affected by the characteristics of the resin constituting the multilayer, the effect of the combination of the layer configurations of the multilayer configuration, and the stretching temperature during film formation. Affected strongly. Therefore, in order to provide low-temperature shrinkage, a material having a low Vicat softening point is preferable, but in consideration of gas barrier properties, the ethylene content is 20 to 55 mol%, and the saponification degree of the vinyl acetate component is 90% or more. Preferably, it is 95% or more. In addition, at least one kind of resin which can be mixed is used as a component within a range that does not significantly impair the barrier property.
The inner layer (A) may be mixed within a range not exceeding 0 wt%, and the mixed resin mainly composed of the ethylene-vinyl alcohol copolymer may constitute the inner layer (A). The amount is preferably 4
0 wt% or less, more preferably 30 wt% or less, still more preferably 20 wt% or less.

[0012] Examples of the resin to be mixed are those having an ethylene content different from that of the ethylene-vinyl alcohol copolymer mainly used, or ethylene-vinyl alcohol copolymers of a group having a high ethylene content other than those described above. And partially saponified products thereof, polyamide-based polymers, polyester-based copolymers, ethylene-vinyl ester copolymers, ethylene-aliphatic unsaturated fatty acid copolymers, and ethylene-aliphatic unsaturated fatty acid ester copolymers Coalescing,
Ionomer resins, styrene-conjugated diene block copolymers, those obtained by hydrogenating at least a part of the block copolymer, or modifying these polymers to obtain, for example, a monomer having a carboxylic acid group as a polar functional group. In addition to those obtained by grafting a body, or ethylene and carbon monoxide, or a copolymer further containing a vinyl acetate component, or those obtained by converting at least a part of the resin to a hydroxyl group, other ethylene-based resins, Propylene resins and the like can be mentioned, and at least one kind is selected from these.
The barrier property of the layer (A) is usually about 200 cc [25.4 μ / m ² · 24 hr · atm in oxygen permeability.
(25 ° C., 65% RH)], but preferably 100 cc [25.4 μ / m ² · 24 h
r.atm].

Next, as another layer of the polymer layer (A), the film of the present invention contains at least one polymer layer (B) mainly composed of thermoplastic polyester.
The Vicat softening point of the resin constituting the layer (B) is (A)
It has a value equal to or higher than the glass transition point of the main resin constituting the layer and equal to or lower than the Vicat softening point of the main resin. By satisfying this requirement, a particularly excellent stretched product which is a main object of the present invention is achieved. In addition to simultaneously achieving both film properties and heat shrinkage, particularly low-temperature shrinkage, a gas barrier film having excellent mechanical properties and optical properties has been completed.

This is because the ethylene-vinyl alcohol copolymer, which is the main constituent of the polymer layer (A), is essentially a crystalline resin, and its stretching mainly involves the orientation and crystallization of the amorphous part. Although it is preferable to crystallize in addition to molecular orientation from the viewpoint of gas barrier properties, excessive crystallization not only impairs shrinkage but also significantly deteriorates transparency. On the other hand, by combining a polymer layer mainly composed of the specific thermoplastic polyester of the present invention having excellent mechanical properties and optical properties and itself having excellent stretchability, stretchability, especially Since the low-temperature stretchability is remarkably improved, a large number of crystal nuclei due to molecular orientation are generated in the ethylene-vinyl alcohol-based copolymer by stretching, and as a result, a large number of microcrystals that do not adversely affect the heat shrinkage and transparency. It is thought that mechanical properties are also improved with the formation of gas barrier properties and an increase in tie molecules.

If the Vicat softening point of the resin constituting the polymer layer (B) mainly composed of thermoplastic polyester is lower than the glass transition point of the resin constituting the polymer layer (A), the resin is stretched. The film properties tend to decrease, and it is easy to cause necking, film breakage, thickness unevenness, etc., making it difficult to give an effective orientation to the (A) layer. In addition to poor thermal characteristics, problems such as insufficient heat shrinkage tend to occur. On the other hand, if the Vicat softening point of the resin constituting the layer (B) exceeds the Vicat softening point of the resin constituting the main layer constituting the layer (A), the stretching temperature becomes too high, and at the same time the film-forming stability deteriorates. At the same time, slip between molecules in the layer (A) becomes relatively large, and it becomes difficult to provide effective orientation. The resulting film is also inferior in low-temperature shrinkage in combination with the shrinkage performance of both layers, and the (A) layer tends to be too short in shrinkage. This causes a problem that the zigzag whitening phenomenon easily occurs during thermal contraction.

The Vicat softening point of the resin constituting the layer (B) is preferably from 40 ° C. to 120 ° C., more preferably from 60 ° C. to 110 ° C. Here Vic
The at softening point is determined according to ASTM D1525-76 (Rate
B, load 1 kg), and usually has a value equal to or higher than the glass transition point for the same resin.

The glass transition point in the present invention is defined by DSC
It refers to the value measured by the method (heating rate: 10 ° C./min). As the thermoplastic polyester constituting the main component of the polymer layer (B), heat-sealing properties when the layer (B) is disposed on the surface layer, and interlayers when the layer (B) is disposed adjacent to the layer (A). In consideration of the adhesiveness, etc., it is not particularly limited, but is preferably a copolymerized polyester, more preferably a copolymerized polyester having a low crystallinity and a low crystalline melting point, and still more preferably a substantially noncrystalline copolymerized polyester. It is. Further, there is a copolymer obtained by copolymerizing a component having a higher barrier property (for example, a mixed copolymer of an aromatic monomer as an alcohol component). Specifically, for example, when alcohol is used as a copolymer component, ethylene glycol is generally used, but propylene glycol, 1,4-butanediol, and 1,5-pentanediol are used as other copolymer components. , 1,6-hexanediol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol, cyclohexane dimethanol, xylylene glycol, or at least one other diol selected from known compounds. A combination with one of the diols, or one containing the other diol based on any one of the above diols without ethylene glycol may be used.

On the other hand, as an acid component of the copolymer, terephthalic acid is generally used. In addition, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, other aromatic compounds, or an ester having an aromatic ring as an ester. Dicarboxylic acid having a substituent that does not contribute to the chemical reaction. Also, succinic acid,
At least one selected from adipic acid, sebacic acid, other aliphatic dicarboxylic acids, and the like, or other known ones
May contain some dicarboxylic acids.

Either the alcohol component or the acid component may be used, or both may be used as appropriate. Examples of preferred combinations include, for example, ethylene glycol as a main component and 1,4-
Examples include those containing 40 mol% or less of cyclohexanedimethanol and copolymerized using terephthalic acid as an acid component. In that case, the more preferable ratio of the copolymerization is about 20 to 40 mol%, more preferably about 25 to 36 mol% of 1,4-cyclohexanedimethanol. Preferred is
Among them, the raw material has a crystallinity (measured by a wide-angle X-ray diffraction method) of 30% or less, more preferably 10% or less, and further preferably substantially amorphous. In addition, the blend of the other resins is the same as in the case of the layer (A) (both in amount and type.
However, the main resin of the layer (A) is also added).

The greatest feature of the film of the present invention is that the adhesiveness between the layer (A) and the layer (B) is excellent.
It is advantageous for stretchability and practicality as a film.
Further, the film of the present invention has a heat shrinkage at a temperature 30 ° C. higher than the Vicat softening point of the resin constituting the layer (B) in at least one direction of the warp and weft, preferably at least 30%. Having. Here (B)
The reason for defining the heat shrinkage of the film at a temperature 30 ° C. higher than the Vicat softening point of the resin constituting the layer is that the (B) layer provides the main stretching orientation for developing the heat shrinkability of the film. Thus, the point that the shrinkage characteristic of the film is relatively strongly affected by the Vicat softening point of the resin constituting the layer (B), and the shrinkage characteristic in practical use is (B)
This is because it can be almost expressed by shrinkage characteristics at a temperature 30 ° C. higher than the Vicat softening point of the resin constituting the layer. If the heat shrinkage is less than 20%, the fit after shrinkage will be insufficient, which will cause wrinkles and lumps after packaging. In the distribution process including storage,
Stability that does not cause dimensional change is required as much as possible, and the shrinkage onset temperature of the film is 45 ° C. or higher, preferably 55 ° C.
It is desirable that this is the case. However, the shrinkage onset temperature of the film refers to the temperature at which the heat shrinkage becomes 5%.

The polymer layers (A) and (B) of the present invention comprise:
As long as each does not impair its original properties, plasticizer,
Antioxidants, surfactants, coloring agents, UV absorbers, lubricants, may contain inorganic fillers and the like, and one or both sides of the surface of the film of the present invention is antifogging, antistatic,
In order to impart adhesion, lubricity, etc., surface modification such as corona treatment or plasma treatment as group (1), or coating treatment with surfactant, antifogging agent, antistatic agent, etc. as group (2) The treatment may be performed, or an adhesive and a pressure-sensitive adhesive known as group (3) may be treated in the same manner. For example, group (2) includes polyhydric alcohol partial fatty acid esters such as sorbitan fatty acid esters, glycerin fatty acid esters, and polyglycerin fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyethylene glycol fatty acid esters, and polyoxyethylene. Sorbitan fatty acid esters, ethylene oxide adducts such as polyoxyethylene glycerin fatty acid esters, alkylamines, alkylamides, alkylethanolamines,
Amines such as alkylethanolamides, amides, polyalkylene glycols, granidine derivatives, phosphate-containing anionic activators, sulfonate derivatives, quaternary ammonium salts, pyridinium salts, imidazoline derivatives, polyvinyl alcohol, acrylic acid-based Examples include hydrophilic polymers, polymers having a pyrrolidium ring in the main chain, silica sol, alumina sol, and the like. Group (3) includes mineral oil, liquid polybutene, oils and fats not included in the former, and other viscous liquids. (500 centipoise or more), and these are used alone or in combination as appropriate. or,
Each of the above-mentioned treatments or the additives of each group may be freely combined.

The film of the present invention comprises at least two layers each comprising at least one layer of each of the polymer layers (A) and (B).
(B), (A) / (B) / (A), (B) / (A) /
(B), (B) / (A) / (B) / (A), (A) /
(B) / (A) / (B) / (A), (B) / (A) /
(B) / (A) / (B) and the like, but it is preferable that the (A) layer is arranged as an internal layer. When each of the (A) layer and the (B) layer has two or more layers, the resins constituting those layers may be the same or different. The layer (B) may be a multilayer of a polymer mainly composed of different thermoplastic polyesters, for example, (B ₁ ) / (B ₂ ), and the same applies to the layer (A). Further, if necessary, depending on use conditions, an adhesive layer made of another known adhesive resin may be provided in some cases in order to improve the adhesive strength between the respective layers. As the resin used for such an adhesive layer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, or ethylene and the above copolymer A multi-component copolymer composed of at least two kinds of free combinations of monomers, or a partially saponified ethylene-vinyl acetate copolymer, an ethylene-carbon monoxide-vinyl acetate copolymer, a thermoplastic resin Polyurethane, known acid-modified polyolefin and the like are used.

Further, another layer composed of another known thermoplastic resin may be disposed on the surface layer for further improving the sealing property. These include, for example, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer (for example, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, etc.), ethylene-aliphatic Unsaturated carboxylic acid ester copolymer (for example, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid ester copolymer, etc.), polypropylene-based polymer, polybutene-
1. Ethylene polymers (linear low-density polyethylene consisting of ordinary low-density, medium-density, high-density polyethylene and ethylene-α-olefin copolymer having a density of 0.880 to 0.935 g / cm ³ , ultra-low-density polyethylene Etc.), ethylene-α olefin copolymers or softer polymers composed of different α-olefin copolymers, ion-crosslinkable copolymers, block copolymers of vinyl aromatic hydrocarbons and conjugated diene derivatives, and Derivatives, crystalline 1.2 polybutadiene and the like can be mentioned, and at least one of them is used. Further, a layer composed of these resins is a layer (A),
The inner layer of the layer (B) or the layer between the layers (A) and (B) may be arranged, and the above-mentioned adhesive layer may be similarly provided between the layers. These may be freely combined according to the purpose.

The heat-shrinkable multilayer film of the present invention has an overall thickness of 5 to 100 microns, more preferably 7 to 80 microns. If the thickness is less than 5 microns, the film tends to have insufficient stiffness and is easily torn, causing problems in workability at the time of packaging. In addition, the thickness of the inner layer (A) as a main gas barrier layer is reduced, and the film is practically usable. Cause trouble. On the other hand, if it exceeds 100 microns, the film becomes too stiff and has problems such as poor fit and sealability. In addition, the responsiveness of shrinkage may be poor, or the overall shrinkage force may be too strong, resulting in impaired finish. The thickness of the inner layer (A) according to a preferred embodiment is 0.7 to 20 microns in total, preferably 1.0 to 15 microns. If the thickness is less than 0.7 μm, the probability of occurrence of pinholes due to foreign substances such as gel may increase, and the quality of gas barrier properties may deteriorate due to the influence of thickness unevenness. On the other hand, if it is 20 microns or more, the cost is increased due to the use of a high-priced resin, or the performance is excessive. In addition, a problem occurs in the stretchability.

The total thickness of the layer (B) is appropriately selected according to various constitutions of the heat-shrinkable multilayer film of the present invention.
(A) 0.3 to 20, preferably 0.5 to 20, more preferably 0.7 to 20, as a ratio to the total thickness of the layer.
More preferably, it is 1.0 to 20. The lower limit is limited by stretchability (stability, expandability of stretch condition range).

Next, a method for producing the multilayer film of the present invention will be described. First, a polymer layer (A) mainly composed of an ethylene-vinyl alcohol-based copolymer and a glass transition point of a resin mainly composed of thermoplastic polyester and having a Vicat softening point whose main component constitutes the layer (A). The polymer of each layer constituting the multilayer film including the above and the polymer layer (B) having a Vicat softening point of the same main resin or lower is melted by a respective extruder, co-extruded with a multilayer die, rapidly cooled, At least the layer (B) is cooled and solidified so as to maintain a substantially amorphous state to obtain a raw multilayer film.

Quenching at the time of co-extrusion at least (B)
Maintaining the layer in a substantially amorphous state is for facilitating subsequent stretching film formation, and is important for imparting effective molecular orientation and achieving uniformity in thickness. When the layer (B) is composed of a mixed resin, at least the main component of the thermoplastic polyester is kept in an amorphous state. The extrusion method is not particularly limited, and a multilayer T-die method, a multilayer circular method, or the like can be used, and the latter is preferable.

The multilayer film raw material thus obtained is heated to a temperature at least 20 ° C. lower than the Vicat softening point of the resin constituting the layer (B) and the resin constituting the main component constituting the layer (A). The stretching is performed at a stretching temperature equal to or lower than the melting point. Here, the stretching temperature is the average value of the surface temperature of the film in the flow direction from the start of stretching to the end of stretching (stretching start point,
The average value of the film surface temperature at the stretching end point and the intermediate point between the stretching start point and the stretching end point. ).

When the stretching temperature exceeds the melting point of the resin constituting the layer (A), breakage is liable to occur, and it is difficult to provide an effective orientation, and the resulting film has poor mechanical properties. In addition, the heat shrinkability is impaired. On the other hand, when the stretching temperature is lower than the temperature lower by 20 ° C. than the Vicat softening point of the resin constituting the layer (B), the stretching stress becomes too high, so that breakage easily occurs, and thickness unevenness and whitening phenomenon easily occur. Become. The preferred stretching temperature is in the range of not less than 15 ° C. lower than the Vicat softening point of the resin constituting the layer (B), and not more than the Vicat softening point of the main resin constituting the layer (A).

The stretching is performed in at least one direction at an area stretching ratio of 5 to 50 times, preferably 8 to 36 times, and is appropriately selected according to the required heat shrinkage rate depending on the application. As a stretching method, a roll stretching method, a tenter method, a bubble method, etc.
Although there is no particular limitation, a method of forming a film by simultaneous biaxial stretching is preferable. Further, if necessary, post-treatment, for example, heat setting, lamination with other kinds of films or the like may be performed, and further, before or after stretching, a modification treatment is freely performed with an energy beam such as an electron beam or ultraviolet ray. May be.

The film of the present invention is mainly used for packaging materials,
Although it is particularly suitable for shrink wrapping, it is a film that can be used as a wrap film for home use or business use by taking advantage of its excellent gas barrier properties. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

The measurement and evaluation methods in the present invention and examples are described below. (1) Crystallinity The raw material resin was sufficiently annealed to obtain an equilibrium state, which was determined by a wide-angle X-ray diffraction method. The X-ray apparatus is Rotorflex RV-200B (Rigaku Electric Co., Ltd.)
Acceleration voltage: 50 KV, using a monochromator)
Tube current: 160 mA (target: Cu), 2θ: 5
Performed at ~ 36 °. In addition, for simplicity, wide-angle X
A sample whose crystallinity is fixed by X-ray diffraction is determined by the density method (JIS
K7112-D method) or DSC method (JIS K)
7122) to obtain a calibration curve, and the unknown sample may be determined by a density method or a DSC method. (2) Vicat softening point The raw material resin is sufficiently heated and melted and then rapidly cooled to an amorphous state at least when the raw material resin is a thermoplastic polyester to prepare a sample having a thickness of 3 ± 0.2 mm.
It was measured by D1525-76 (Bate: B, load 1 kg). (3) Glass transition point Using a sample (about 10 mg) obtained in the same manner as in the above (2), the glass transition point was measured at a heating rate of 10 ° C./min in a nitrogen stream by a DSC method. (4) Melting point After the temperature was once raised to 290 ° C. under the conditions of (3) by DSC, the temperature was lowered to room temperature or lower at a rate of 20 ° C./min, and the temperature was raised again at 10 ° C./min for measurement. The main endothermic peak temperature at that time was defined as the melting point. (5) Film surface temperature Using a contact-type surface thermometer using an iron-constantan type thermocouple, bring the thermocouple tip into contact with the film surface,
The indicated value after seconds was defined as the film surface temperature. (6) Film-forming stability The continuous stability of the film (continuous stability of the stretched bubble) and the unevenness of the thickness of the completed film were evaluated when the film was heated and stretched by a predetermined method.

Symbol Scale ：: The stretching pattern of the film (stretched bubble) hardly fluctuates, and the continuous stability is good. ：: Film thickness unevenness is within ± 15%. Δ: The stretching start position is slightly unstable. Within ± 25% exceeding thickness unevenness ± 15%.

X: Film breakage, bubble puncture frequently occurred. Alternatively, even if stretching is possible, the variation of the stretching start position is large, and the thickness unevenness exceeds ± 25%. (7) Heat shrinkage rate A 100 mm square film sample is placed in an air oven type constant temperature bath set at a predetermined temperature, and is allowed to shrink freely.
After processing for one minute, the shrinkage of the film was determined and expressed as a percentage of the value divided by the original dimension. In the case of uniaxial stretching, the average was taken in the stretching direction, and in the case of biaxial stretching, which is a preferred embodiment, the average in the vertical and horizontal directions was used. However, the predetermined temperature is defined as (B) of the present invention.
The temperature is 30 ° C. higher than the Vicat softening point of the resin constituting the layer. (8) Measured according to HAZE ASTM-D-1003-52. (9) Tensile modulus was performed in accordance with ASTM-D-882-67, and was expressed as a value obtained by converting stress at 2% elongation to 100%. (10) O ₂ TR (oxygen permeability) unit: cc / m ² · 2
It was measured by the method of 4 hr · atm ASTM D3985.

The resins used in Examples and Comparative Examples are described below. a ₁ : ethylene-vinyl alcohol copolymer (ethylene content: 44 mol%, saponification degree: 99% or more,
MFR (210 ° C., 2160 g); 3.5, glass transition point; 55 ° C., Vicat softening point; 150 ° C., melting point;
5 ° C.) a ₂ ; same as above (ethylene content: 38 mol%, saponification degree: 99% or more;
MFR (210 ° C., 2160 g); 3.2, glass transition point; 58 ° C., Vicat softening point; 154 ° C., melting point;
6 ° C.) a ₃ ; same as above (ethylene content: 29 mol%, degree of saponification: 99% or more;
MFR (210 ° C., 2160 g); 3.2, glass transition point; 62 ° C., Vicat softening point; 175 ° C., melting point;
0 ° C.) b _1; terephthalic acid as a main component as an acid component, the diol component is 1,4-cyclohexane dimethanol 30 molar <br/>% and ethylene glycol 70 mol% from the consisting copolymerized polyester (Vicat softening point; 82 ° C., crystallinity: 0% (amorphous)) b ₂ ; 85 mol% of terephthalic acid, 15 mol% of isophthalic acid as an acid component, and ethylene glycol 9 as a diol component
Copolymerized polyester consisting of 8 mol% and diethylene glycol 2 mol% (Vicat softening point; 75 ° C., crystallinity: 20%, melting point: 230 ° C.) b ₃ ; 85 mol% of terephthalic acid and 10 mol% of isophthalic acid as acid components adipic acid 5 mol%, 98 mol% di-ol component of ethylene glycol, diethylene glycol 2 mol% than consisting copolymerized polyester (Vicat softening point; 67 ° C., crystallinity; 10%, mp: 180 ° C.) b _4; acid Copolymerized polyester composed of 80 mol% of terephthalic acid, 20 mol% of isophthalic acid, 97 mol% of tetramethylene glycol and 3 mol% of ethylene glycol as components (Vicat softening point: 40 ° C., crystallinity: 15%, melting point;
193 ° C.) b ₅ ; conventional film-forming polyethylene terephthalate (Vicat softening point; 71 ° C., crystallinity; 45%, melting point: 263 ° C.) b ₆ ; 85 mol% of terephthalic acid and 15 mol% of isophthalic acid as acid components A copolymer polyester comprising a diol component of ethylene glycol (Vicat softening point; 70 ° C., crystallinity: 17%, melting point: 220 ° C.) c ₁ ; ethylene-vinyl acetate copolymer (vinyl acetate content: 15% by weight, Vicat softening point; 6
7 ° C., MFR (190 ° C., 2160 g); 2) c ₂ ; maleic anhydride-modified ethylene-vinyl acetate copolymer (vinyl acetate content; 28% by weight, Vicat softening point; 5)
2 ° C, MFR (190 ° C, 2160g); 3)

[0036]

Example 1 Ethylene-vinyl alcohol copolymer; a
₁ (ethylene content; 44 mol%, degree of saponification: 99% or more, MFR (210 ° C., 2160 g); 3.5, glass transition point; 55 ° C., Vicat softening point; 150 ° C., melting point;
165 ° C.) the (A) layer, the terephthalic acid as a main component as an acid component, consisting of 30 mole% of ethylene glycol 70 mol% of the diol component is 1,4-cyclohexanedimethanol copolymer polyester; b ₁ (Vicat softening point ;
82 ° C., crystallinity: 0% (amorphous)) as a (B) layer, and extruded using an annular multilayer die so that the layer arrangement becomes three layers (B) / (A) / (B). After that, the mixture was quenched and solidified with a refrigerant to produce a tubular raw material having a thickness of 200 mm and a thickness of 320 μm and uniform thickness accuracy for each layer. At that time,
A mixed solution (50:50 by weight) of mineral oil and diglycerin / monooleate was sealed in the tube, and the inner surface was coated by squeezing with a nip roll. The thickness of each layer is 128 μ / 6 in order from the outside of the tube.
4 μ / 128 μ. Then, the raw material is passed between two pairs of differential nip rolls, heated to 115 ° C. in a heating zone, and stretched in a stretching zone (under a multi-stage hood) under the same atmosphere, at a stretching ratio of 4.0 times and 4.0 times horizontally. The film was simultaneously biaxially stretched twice and cooled in a cooling zone with air at 20 ° C. to perform bubble stretching. The stretching temperature at this time was 105 ° C. The edges (both ends) of the obtained film were slit, and two films were wound into a roll by a winder.

The obtained film was a film of 8 μ / 4 μ / 8 μ in total in the same order as the above-mentioned raw material, with a total of 20 μ.
(Run-1) Next, using the same raw, changing the stretching temperature and stretching ratio, were subjected to stretching in the same manner as described above, each case rupture by puncture does not 殆 throat occurs, film stability It was good. (Run-2 to 5) Table 1 shows the layer structure, stretching conditions, physical property evaluation results, and the like of the obtained film.

As described above, the film of the present invention had extremely good film-forming stability at the time of stretching, and was excellent in gas barrier properties, optical properties, low-temperature shrinkage, mechanical properties, and the like. In addition, the interlayer adhesive strength was high, and peeling was impossible (cellophane tape was used). In the run ratios -1 and 2, stretching was performed at 167 ° C. and 74 ° C., respectively, using a tubular raw material having the same layer configuration as Run-1, but both punctures occurred frequently and were stable. It was difficult to perform film formation.

[0039]

[Table 1]

[0040]

Example 2 A film having the layer structure shown in Table 2 was obtained in the same manner as in Example 1. Table 2 shows the stretching conditions and physical property evaluation results. The stretched film-forming property was good, and the resulting film was also excellent in gas barrier properties, low-temperature shrinkage, and the like.

[0041]

Example 3 As an adhesive layer, ethylene-vinyl acetate copolymer; C ₁ (vinyl acetate content; 15% by weight, Vicat
Softening point; 67 ° C., MFR (190 ° C., 2160 g);
2) and maleic anhydride-modified ethylene-vinyl acetate copolymer: C ₂ (vinyl acetate content; 28% by weight, Vica
t softening point; 52 ° C, MFR (190 ° C, 2160 g);
Using 3), using three types of five-layer dies, the layer arrangement is (B)
A film having a layer configuration shown in Table 3 of / (adhesive layer) / (A) / (adhesive layer) / (B) was obtained in the same manner as in Example 1.

The film formation stability was good. Table 3 also shows the stretching conditions and the results of evaluation of the physical properties.

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

Example 4 A film having the layer constitution shown in Table 4 was obtained in the same manner as in Example 1. Table 4 shows the stretching conditions and physical property evaluation results.

[0046]

Comparative Example 1 Ethylene-vinyl alcohol copolymer; a
₁ (ethylene content: 44 mol%, degree of saponification: 99% or more, MFR (210 ° C., 2160 g); 3.5, glass transition point; 55 ° C., Vicat softening point; 150 ° C., melting point;
165 ° C.) to the (A) layer, terephthalic acid 80 as the acid component.
Mol%, isophthalic acid 20 mol%, a diol component consisting of tetramethylene glycol 97 mol% and ethylene glycol 3 mol%; b ₄ (Vica
t softening point: 40 ° C, crystallinity: 15%, melting point: 193
C) as the (B) layer, and a three-layer tubular raw material having a layer arrangement of (B) / (A) / (B) was prepared in the same manner as in Example 1. The thickness of each layer was the same as in Example 1, and the stretching was performed under the same conditions, but the stretching start position fluctuated.
Since puncture also occurred frequently, the stretching ratio was reduced to 3.2
The film was barely obtained with a width, width and 2.2 times. However, the thickness of the film was uneven (± 31%), and the heat shrinkage was about 15%.
%, Uneven wrinkles and undulations were observed.

[0047]

Comparative Example 2 Ethylene-vinyl alcohol copolymer; a
₂ (ethylene content; 38 mol%, degree of saponification: 99% or more, MFR (210 ° C, 2160 g); 3.2, glass transition point; 58 ° C, Vicat softening point; 154 ° C, melting point;
176 ° C. ) with layer (A), conventional film-forming polyethylene terephthalate: b ₅ (Vicat softening point; 71)
° C, crystallinity: 45%, melting point: 263 ° C)
Maleic anhydride-modified ethylene-vinyl acetate copolymer: c ₂ (vinyl acetate content; 28% by weight, Vic
at softening point: 52 ° C, MFR (190 ° C, 2160
g); 3), and the layer arrangement is (B) / (adhesive layer) /
(A) / (adhesive layer) / (B) is melt-combined in a die so that each layer has a thickness of 224 μm with a cooling roll adjusted to a temperature of 60 ° C. A stock was made. The thickness of each layer is 64 μ /
32 μ / 32 μ / 32 μ / 64 μ. Next, under the condition of the raw material, biaxial stretching was sequentially performed at 85 ° C. three times in the vertical direction and three times in the horizontal direction. As conditions, first, 9
The biaxial stretching was performed three times vertically at 5 ° C. and then three times horizontally at 130 ° C. Under the conditions, the stretching in the vertical direction was relatively smooth, but the film was torn when stretched in the horizontal direction. Because of the occurrence of many occurrences, the stretching speed was slowed down, and a film having a predetermined stretching ratio was barely obtained. However, local whitening was observed in the obtained film, and the heat shrinkage thereof was as low as about 13%. This is presumably because the crystallization progressed due to the long heat history including the stretching from the heating of the raw material necessary for stretching film formation, and the heat shrinkage decreased.

On the other hand, in the condition, the vertical,
In both cases, stretching could be performed relatively smoothly, but the heat shrinkage of the obtained film was as low as 9%, and the heat shrinkage of both films was at least 150 ° C., but the heat shrinkage was 2% or less. This was unsuitable as a heat-shrinkable film. As described above, according to the known prior art, it was difficult to obtain a film having excellent heat shrinkability as the object of the present invention. A ₁₁ in Table 4; (a ₁ : 90% by weight + b ₁ : 10% by weight) a ₁₂ ; (a ₁ : 80% by weight + b ₁ : 20% by weight) a ₁₃ ; (a ₁ : 80% by weight + SEBc: 20) (Weight%) SEBc: (hydrogenated butadiene block of styrene-butadiene block copolymer, acid modified (maleic anhydride 2 wt%), styrene content about 40 wt%, MFR (230 ° C., 2.16 kg) 1.
0) a ₁₄ ; (a ₁ : 80% by weight + EVOH note): 20% by weight) Note EVOH; (Saponified ethylene-vinyl acetate copolymer).
Ethylene content about 89 mol%, saponification degree 99% or more, MF
R (090 ° C., 2.16 Kg) 5) a ₁₅ ; (a ₁ : 80% by weight + EVC: 20% by weight) EVC; (Ethylene-vinyl acetate-carbon monoxide copolymer; MFR (190 ° C., 2.16 Kg) ) 3.5, melting point 6
(6 ° C.) a ₁₆ ; (a ₁ : 85% by weight + Ny 6: 15% by weight) Ny 6; (Relative viscosity 2.8 measured in a 6.98% nylon sulfuric acid solution (25 ° C.)) a ₁₇ ; (a ₁ : (85% by weight + Ny6 / 66: 15% by weight) Ny6 / 66; (copolymer nylon 6/66; nylon 6)
6 content; 15% by weight, relative viscosity measured in a 95% sulfuric acid solution (25 ° C. 3.0) a ₁₈ ; (a ₁ : 85% by weight + IR: 15 % by weight) IR; (ethylene-methyl methacrylate) An ester copolymer (methyl methacrylate content 20% by weight) neutralized with Mg ions by 30%, MFR (190 ° C, 2.
_{16Kg) 1.5) a 19; (} a 1: 70 by weight% + IR: 15 wt% + Ny6
/ 66: 15% by weight) IR and Ny6 / 66 are as described above (Run No. 2).
0, 21). b ₁₁ ; (b ₁ : 90% by weight + a ₁ : 10% by weight) (Vi
cat softening point; 87 ° C)

[0049]

[Table 4]

[0050]

Embodiment 5 In the same manner as in Embodiments 1 and 3,
A film having a layer configuration shown in Table 5 was obtained. Table 5 shows the stretching conditions and physical property evaluation results. RunNo. The crystallinity of each thermoplastic polyester layer after stretching film formation of Nos. 27 and 28 was 7% and 10%, respectively. (Measurement is performed by immersing the obtained film in methanol at room temperature or lower for 10 hours or more, then removing the thermoplastic polyester layer by air drying, measuring the density with a density gradient tube, and using a wide-angle X-ray diffraction method in advance. A sample having a fixed crystallinity was similarly measured by a density method to obtain a calibration curve.) Diglycerin monooleate of about 120 mg /
m ² of such that the coating amount is performed over the entire surface substantially uniformly coating process was evaluated suitability as wrap film, film of the present invention has a waist, good cut resistance, for less cling film comrades Workability was easy. Also, the self-adhesiveness was good, the film was not turned up by heat treatment in a microwave oven, there was no perforation or whitening phenomenon due to melting, and the suitability for a microwave oven was good. There were many points superior to the vinylidene chloride-based wrap used for comparison, and the odor barrier property when wrapped was also excellent.

Further, RunNo. The films of Nos. 27 and 28 were heat-treated at temperatures of 180 ° C. and 150 ° C., respectively, so that the crystallinity of the thermoplastic polyester layer of each film was 41% and 15%, respectively. )) The same evaluation as a wrap film was also performed on a film subjected to the same coating treatment, and it was found that the film had excellent cuttability, self-adhesiveness, suitability for a microwave oven, and the like.

The method for evaluating the suitability for lap is described below. Cutability: When a 300 mm wide film is cut with a saw-tooth cutter (a box for Saran Wrap ^R manufactured by Asahi Kasei Kogyo Co., Ltd.), there is no tear in the other direction during the cutting, and the cut is smooth along the saw teeth almost without waste. Those that could be cut were rated good. Adhesion: A Setomono cup (diameter: about 60 mm) was wrapped with a 200 mm x 200 mm film, and a visual judgment was made after 24 hours of close contact. Suitability for microwave oven: About 40 g of pork belly was wrapped in a film and processed for 3 minutes using a microwave oven with a rated high-frequency output of 600 W, and changes in the film were visually determined.

[0053]

[Table 5]

[0054]

As described above, the heat-shrinkable multilayer barrier film of the present invention has, as a main gas barrier layer, a polymer layer mainly composed of an ethylene-vinyl alcohol copolymer having sufficient adaptability in terms of environmental hygiene. In relation to the ethylene-vinyl alcohol-based copolymer which is the main constituent of the polymer layer, by combining a polymer layer mainly composed of thermoplastic polyester having a specific Vicat softening point, an excellent stretched product is obtained. It is possible to simultaneously achieve film properties and heat shrinkage, especially low-temperature shrinkage, and is excellent not only in gas barrier properties but also in mechanical properties and optical properties, and is extremely useful mainly for use in various packaging materials.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FIB29L 9:00

Claims (2)

(57) [Claims] 1. At least one layer of a polymer layer (A) mainly composed of an ethylene-vinyl alcohol-based copolymer and another layer (B) of a resin Vica which constitutes the layer.
at least one layer of a thermoplastic polyester-based polymer layer having a t-softening point equal to or higher than the glass transition point of the main resin constituting the layer (A) and equal to or lower than the Vicat softening point of the main resin. Wherein the heat shrinkage of the resin constituting the layer (B) at a temperature 30 ° C. higher than the Vicat softening point is 20% in at least one of the vertical and horizontal directions.
A heat-shrinkable multilayer film characterized by the above. 2. At least one layer of a polymer layer (A) mainly composed of an ethylene-vinyl alcohol-based copolymer, and as another layer (B), Vica of a resin constituting the layer.
at least one layer of a thermoplastic polyester-based polymer layer having a t-softening point equal to or higher than the glass transition point of the main resin constituting the layer (A) and equal to or lower than the Vicat softening point of the main resin. The polymer of each layer is melted by a respective extruder, co-extruded with a multilayer die and quenched so that at least the layer (B) is solidified by cooling so that at least the layer remains substantially amorphous. After obtaining the raw film, the raw material is heated to a temperature not lower than 20 ° C. lower than the Vicat softening point of the resin constituting the layer (B) and not higher than the melting point of the main resin constituting the layer (A). A method for producing a heat-shrinkable multilayer barrier film, wherein the film is stretched in at least one direction at a stretching temperature in a range of 5 to 50 times in area stretching ratio.