JPS63125334A - Gas barriering multilayer film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer stretched film with excellent gas barrier properties.

Saponified ethylene/vinyl acetate copolymer (EVOH)
) is used as a gas barrier film in the form of an unstretched film. Since this film lacks water resistance, it is actually used by bonding it to a heat-resistant film such as polyolefin or polyester using an adhesive. However, since this is not very boil resistant,
Use is restricted. Therefore, various efforts have been made to improve these drawbacks, and a method of stretching EVOH has been proposed as one promising method. EVOH
has very poor stretchability, and can only be uniaxially stretched within a limited temperature range and at a limited stretching ratio; biaxial stretching is not possible. Moreover, even in -axial stretching, when the stretching ratio is as high as 8 times or more, the film becomes extremely easy to tear, and a single film is not usable. In addition, in order to improve this stretchability, a method has been proposed in which a stretchable film such as polypropylene (hereinafter abbreviated as PP) is laminated and stretched, but although this method allows uniaxial stretching, Since the adhesion between EVO)L and PP is poor, the films may peel off from each other, and if the stretching ratio is high, the EVOH layer may crack, resulting in poor gas barrier properties and poor quality. do not have.

A method of stretching EVOH in a water-containing state has also been proposed, but it is necessary to control the humidity to maintain the water content at a constant value. In addition, methods have been proposed to improve stretchability by adding plasticizers such as glycerin, but in all of these methods, although the stretching operation is performed, Because it is stretched, molecular orientation hardly occurs, so in terms of the degree of molecular orientation, it is essentially the same as an unstretched film.

Furthermore, this film has drawbacks such as a decrease in gas barrier properties due to water evaporation and bleed-out of plasticizer.

In view of such conventional drawbacks, the present inventors developed gv.

The present invention was arrived at as a result of research into a film that has excellent H gas barrier properties, as well as water resistance, boil resistance, and dimensional stability. That is, the technical configuration of the present invention is such that the ethylene content is 20 to 50 mol%, the degree of saponification is 90% or more, and the intrinsic viscosity is 0.07 to 0.17 l/
rt7) EVOHK, j-”lJ7 mido 5-4Qwt
An unstretched film made of a composition containing 1% of
．． 5 to 6 times, 2 to 8 times in the horizontal direction, and area magnification of 4 to 25
This is a gas barrier multilayer film which has another thermoplastic resin layer on at least one side of the film obtained by biaxially stretching the film to double its original size. The film has excellent gas barrier properties with an oxygen permeability of 35 cc/m2·24 hf or less at 20° C. and 100% RH.

Here, EVOH means ethylene content of 120 to 50 mol%,
Saponification degree of 90% or more, preferably ethylene content 25-4
It is a saponified ethylene/vinyl acetate copolymer with a saponification degree of 0 mol% and 95% or more.

If the ethylene content is less than 20 molar, the extrusion temperature cannot be raised to a high temperature, e.g., 260°C or higher, because it has poor melt extrudability, is easily colored when melt extruding the composition with polyamide, and is easily thermally decomposed. Therefore, a deep stretched film with good flatness suitable for stretching cannot be produced. On the other hand, ethylene is 50
If the composition exceeds molch, the melt extrudability of the composition is good, but
Poor gas barrier properties. If the degree of saponification is less than 90%, the biaxially stretched film lacks dimensional stability during heat treatment, tends to shrink due to heat, and has poor gas barrier properties. The EVOI of the present invention (as a composition) must have excellent melt extrudability and gas barrier properties. Considering this, a more preferred EVOH of the present invention has an ethylene content of 25 to 40 mol% and a degree of saponification. There are more than 95%.

The intrinsic viscosity of such an EVOH polymer influences the film formability, and in the present invention, the intrinsic viscosity is 0.07 to 0.171.
/? , preferably 0.09 to 0.151/f (15wt
% EVO (measured at 30'C in aqueous phenol)
H is preferably used.

Intrinsic viscosity is 0.071/? When the amount is less than 1, the castability of the unstretched film of the composition is poor, and an unstretched film with good flatness cannot be obtained, which tends to cause stretching unevenness.

On the other hand, if it exceeds 0.1711/l, the extrusion temperature of the composition needs to be on the high side, which causes thermal decomposition and coloring.

As the polyamide of the present invention, (1) nylon 6.11
．． (2) polyamides made from diamines and dibasic acids such as nylon 66.610, polyhexamethelene inphthalamide, and (8) the above (
Examples include various copolyamides made from the monomer groups 1) and (2), and (4) blends of two or more of the above polyamides. Especially nylon 6, poly(
Hexamethylene isophthalamide/terephthalamide (copolymerization molar ratio 10,010 to 50,150) is preferred.

Such polyamides are blended with EVOH at 5-4 Qwt%. In the blend composition of the present invention, the polyamide content does not significantly affect gas barrier properties and stretchability, i.e. less than 5wt% and 40wt%.
If the polyamide content exceeds 24%, the film's stretchability deteriorates and its gas barrier properties decrease, and the oxygen permeability exceeds 35 CC/rr1·24 hr, making it impossible to obtain a practical film.

In the present invention, from the point of view of gas barrier properties, it is thought that it is preferable to use a small amount of polyamide blended, but when the blend amount reaches 5 wt%, tearing occurs. In fact, it has the characteristic of being improved (compared to EVOHI O0% unstretched film). Further, when the blend amount reaches 10 wt%, sequential biaxial stretching can be performed,
The gas barrier properties are also excellent as described above. Of course, this composition can also be coaxially and biaxially stretched. However, if the blend amount exceeds 4 Qwt%, both the gas barrier properties and the stretchability will decrease at the same time, and furthermore, it will not be possible to obtain a practical gas barrier film due to other properties such as dimensional stability. The gas barrier film of the present invention is preferably provided by stretching to an area ratio of 4 to 25 times that of the film before stretching, and more preferably to an area ratio of 6 to 20 times. Although any stretching method may be used, biaxial stretching is superior to -axial stretching in terms of dimensional stability.

A stretched film made of a composition in which the polyamide of the present invention is blended with 5 to 40 wt% EVOH is oriented in the longitudinal direction (
Nx), the refractive index in the width direction (Ny) and thickness direction (Nz) is 0.040)lNx-Nyl≧Q, ((Nx+Ny)/2-NZ)>0.010, preferably 0.030>lNx- Nyl ≧0, C(Nx-N
It is important that y)/2-Nz)>o, ox 5.

The reason why the refractive index in each direction cannot be clearly indicated numerically is that the EVOH used is a copolymer and the refractive index is affected by the degree of saponification and ethylene content, and the type and amount of polyamide used in the blend. This is because it also differs depending on the To give an example of refractive index, ethylene is 38 mol%
, saponification degree of 99% or more, intrinsic viscosity o, 13 l/l E
In a film obtained by stretching an unstretched film made by blending 20 wt% of nylon 6 with VOH at 160°C by 2.5 times in length and 4.0 times in width, Nx = 1.536. Ny=1.545, Nz
=1.518.

1Nx-Nyl≧0.040, ((Nx-Ny)/2
-Nz) > 0.010, the anisotropy of the mechanical properties of the film is significant, and the film tends to tear, tear and curl when subjected to boiling treatment. On the other hand, 0.04
Even if 0>INX-NYI≧0((Nx-N)')
/2-Nz]≦0.010, it is not a poor gas barrier property, and cannot withstand boiling and retort processing.Usually, blended with polyamide such as nylon 6, which has poor gas barrier properties compared to EVO)1. It is thought that the gas barrier properties of the unstretched film would be significantly reduced if EVOH was used alone, but in the present invention, the EVOH composition is highly oriented and crystallized by stretching and subsequent heat setting. Therefore, the deterioration in gas barrier properties is considered to be practically negligible, and the water resistance and boil resistance are significantly improved to an extent that would not be expected from an unstretched film. In other words, a film made of EVOH alone has poor water resistance, poor flatness due to water absorption, and lacks shape retention when subjected to a boil test.
It has the disadvantage of becoming lumpy and turning white.

By laminating another thermoplastic resin on at least one side, preferably both sides, of the gas barrier film of the present invention, film properties other than the above-mentioned effects can be added. Of course, in such a laminated film, an adhesive layer may be provided between each film layer using an appropriate adhesive or an adhesive thermoplastic resin, or it may be directly laminated without providing such an adhesive layer. It can be anything.

The film properties added to such a laminated film vary depending on the type of thermoplastic resin to be laminated. For example, laminating polyolefin resin can significantly reduce water vapor permeability, and laminating polyolefin resin such as polyamide 6 By laminating them, impact resistance can be improved. Furthermore, when polyester is laminated, the heat resistance is significantly improved and it becomes possible to sufficiently withstand high-temperature retort processing.

Next, the above laminated film will be explained by giving two specific examples. One is a laminated film consisting of the EVOH composition of the present invention and a polyolefin, and one is a laminated film having an adhesive layer between each film layer.

That is, an unstretched or at least uniaxially stretched polyolefin layer (hereinafter referred to as layer B) can be provided on at least one side of the stretched film layer (hereinafter referred to as layer A) of the EVOH composition, and such a laminated film It can be obtained by extrusion laminating a polyolefin layer on a stretched film of the composition and then stretching it as necessary, or by coextruding it with an EVOH composition and stretching it.
Oxygen permeability at 00%RH is 35 cc/rIf・
24hr or less (preferably 30cc/rr!-24hr
r or less), water vapor permeability at 40°C is 30f/-・
It has a characteristic of being 24 hr (preferably 10 f/rl·24 hr or less). The preferable thickness structure of such a composite film is A:B layer 1:0.03-10 (more preferably l:0.05-5). With such a composite film, compared to a single-layer stretched EVOH composition film,
Water resistance and boiling resistance have been further improved, and it can withstand retort processing, and gas barrier properties are less likely to deteriorate even in high humidity environments. No more outbreaks. These characteristics are particularly remarkable in the case of a composite film having polyolefin layers (layer B) on both sides. The polyolefin used for the polyolefin layer (layer B) is (1) polypropylene, (2) a copolymer of propylene and an α-olefin such as ethylene or butene, and (8) an aliphatic material such as acrylic acid or maleic acid. Mono- or dicarboxylic acids or their acid anhydrides, salts,
Examples include modified polypropylene in which an ester or the like is grafted onto polypropylene or a copolymer thereof, and (4) blends of modified polypropylene with the aforementioned various polyolefins, copolymers of ethylene and polar monomers, and the like. (8) and (4) are preferred because they have particularly excellent adhesion to the EVOH composition layer (layer A). The thickness of layer A of the composite film is practically preferably 3 to 30 microns (preferably 5 to 20 microns). A: B layer 1: When the B layer is thinner than 0.03, the degree of improvement in gas barrier properties and flatness under high humidity is small. Conversely, if layer B is thicker than A:B=l:IQ, the composite film as a whole is too thick, and when a container such as a bag is made, it easily rips open, resulting in no impact resistance. In addition, the oxygen permeability and water vapor permeability are each 35 per sheet.
CIC/rl・24hr or less, 309/rl・24hr
The reason why it is limited to less than r is that the gas barrier property is necessary for use in food packaging which is prone to oxidative deterioration and moisture absorption, and if it is more than this, the food is susceptible to oxidative deterioration and moisture absorption. Furthermore, since the A layer has a higher stretching tension than polyethylene terephthalate, polypropylene, etc., the thicker the A layer, the greater the mechanical strength of the stretching machine is required, which is economically disadvantageous. Therefore, the gas barrier performance and handling of the film determine its thickness. That is,
If it is a single-layer stretched film with only layer A, the thickness is 8 to 30 μm (preferably 12 to 25 μm). If it is less than 8μ, there are disadvantages such as insufficient gas barrier properties, insufficient film stiffness, and wrinkles when laminated with other films. In addition, if the A layer in a composite film is less than 3 μm, the gas barrier performance will be insufficient, and if it exceeds 30 μm, the overall thickness of the composite film will become thicker, making it easier to cleave open when making bags and heat sealing. ), it has the disadvantage of poor impact resistance.

A stretched film of a composite film of such an EVOH composition, another thermoplastic resin, and a polyolefin can be prepared as a single film or a laminated film at a temperature of (Tm -5Q°C) to (Tm -
5°C) (where - is the melting point of the saponified material) in at least one direction. Tm is ethylene content, degree of saponification,
The temperature is about 155 to 185°C, depending on the intrinsic viscosity. In the case of biaxial stretching, it is 1.5 to 6 times (preferably 2 to 5 times) in the machine direction and 2 to 8 times (preferably 3 to 7 times) in the transverse direction.
(fold) made by stretching. Sequential biaxial stretching in the order of longitudinal stretching → transverse stretching is particularly preferred from the viewpoint of productivity, but transverse stretching → longitudinal stretching may also be used. Of course, simultaneous biaxial stretching is also possible. After biaxial stretching, further longitudinal stretching ((Tm-
50°C) to (Tm-5°C)] to further improve productivity, barrier properties, etc.
There is an advantage that the mechanical properties in the machine direction (MD) and the transverse direction (TD) are balanced, and anisotropy is reduced.

In the present invention, after stretching (Tm -40°C) to (T'm
-5℃) is preferable in order to maintain dimensional stability, water resistance, and boilability, and when tension heat treatment or dimensional stability is particularly important, relaxation heat treatment at 10 degrees or less is effective. . The longitudinal stretching temperature during biaxial stretching is (Tm-
40°C) to (Tm-10°C) is particularly preferred.

When the longitudinal stretching temperature is less than (Tm-50°C), l Nx
If -Nyl≧0.040, the film is likely to break during longitudinal stretching or break during the next transverse stretching. In the case of a laminated film with layer B, a film that is easily torn in the longitudinal direction is a film in which layer A is cracked. If the temperature exceeds (Tm - 5 DEG C.), adhesion of the film to the stretching roll becomes a problem, surface roughness occurs, and an opaque film is produced. This tendency is particularly noticeable in a laminated film with layer B. The stretching ratio is particularly preferably 1.5 to 3 times on the low temperature side near (Tm - 50°C), and 3 to 6 times on the high temperature side near (Tm - 5°C), to avoid problems during film formation such as film tearing. Stable film-forming properties can be obtained without causing any problems.

Laminated film A (7) in which layer B is provided on at least one side of layer A
), it is particularly preferable to stretch the film by a factor of 1.5 to 5 times (Tm-50°C) to (Tm-20°C). Stretching ratio is 1
．． When it is less than 5 times, uneven stretching occurs, and when it is more than 6 times, it tends to tear vertically, making it difficult to stretch horizontally. In the case of a laminated film with layer B, if the B layer is thick and the A layer is thin, if the B layer is thick and the A layer is thin, the B layer will act as a support and the film may not break, but the A layer may crack. , gas barrier properties are lost. In the case of other thickness ratios, film tearing occurs.

The transverse stretching temperature is (Tm-5Q°C) to (Tm-5°C) [preferably (Tm-40°C) to (Tm-IQ°C)]. If the stretching temperature is less than (Tm - 5Q °C), the film will break, and if it exceeds (Tm - 5 °C), it will be near the melting point, so [: (NX + N)') / 2 - NZ) ≦ 0.010
Tonashi, # due to the relaxed orientation, gas barrier properties, etc.
Ii characteristic value decreases. In particular, in the case of a film laminated with layer B, the transparency not only decreases markedly, but also the film sticks to the clips of a horizontal stretching machine (tentter), inhibiting the continuous chain. Kii when the lateral stretching ratio is less than 2 times.

Stretching unevenness occurs, and if the stretching exceeds 8 times, film tearing occurs. In particular, in a laminated film with layer B, when layer A is thinner than layer B, layer B acts as a support and layer A cracks even when the film barely breaks, resulting in a decrease in barrier properties.

When the biaxially stretched film is further longitudinally stretched, the stretching ratio needs to be 2 times or less. If it exceeds twice that, the mechanical properties tend to improve, but the gas barrier properties deteriorate.

Thus, the area after stretching is 4 to 25% of that of the unstretched film.
times (preferably 6 to 20 times). It is necessary to avoid combinations of stretching ratios that result in area ratios greater than this, as they may lead to film tearing or a decrease in gas barrier properties.

In the present invention, the temperature at which heat treatment is performed after stretching is (Tm-4
When the temperature is less than 0°C, the gas barrier properties and dimensional stability are not significantly different from those of unheated products, and are inferior to heat-treated products. (Tm-
Heat treatment at temperatures exceeding 5° C.) deteriorates gas barrier properties, transparency, and mechanical properties.

Next, a case where an adhesive layer is provided between each layer of the laminated film will be explained using a laminated film with polypropylene as an example. A composite layer A/C or C/A/C consisting of the EVO)L composition and an adhesive resin (abbreviated as CM) is extrusion laminated on a uniaxially stretched polypropylene film, and then the laminated film is in the direction perpendicular to the previous stretching direction at a temperature of (Trn-5Q°C) to (Tm-5°C) [
Preferably (Tm-40°C) to (Tm-10°C)] at 5
5 to 12 times, preferably 6 to 10 times), and then,
('I'm - 40°C (Tm -5°C), heat treated in the same way as when no adhesive layer is provided. As an example of c75, (8) and (
4) can be mentioned. Here, stretching at a higher temperature than (Tm-5℃) and heat treatment exceeding ('I'm-5℃) will damage the stretching orientation effect of the polypropylene layer.
This will lead to film tearing.

When layer C is further provided, the direction perpendicular to the initial stretching direction of layer A is (Tm -5Q°C) to (Tm -5°C) Te1.2
It is also possible to improve the anisotropy of the A layer by stretching it to 2 times.

The thickness of the final zero layer is 5μ or less per layer, preferably 2μ
It is as follows.

However, the EVOH composition of the present invention can be laminated with polyamides or polyesters other than the above-mentioned polyolefins as appropriate. In this case, the polyamide used in the above blend can be used, and the polyester used can be a saturated polyester consisting of a dicarboxylic acid and a diol. For example, as the dicarboxylic acid, terephthalic acid has a concentration of 90 mole or more, and other dicarboxylic acids include aromatic dicarboxylic acids such as inophthalic acid, phthalic acid, 2,6-7tale dicarboxylic acid, and adipic acid,
Examples include copolymerized aliphatic dicarboxylic acids with 6 to 18 carbon atoms such as sebacic acid in the required amount, and diols with 2 to 8 carbon atoms such as ethylene glycol and tetramethylene glycol are used as the diol component. I can give you things that I did. Typical examples include polyethylene terephthalate, polybutylene terephthalate, and copolymers thereof.

Next, the present invention will be described in detail with reference to examples. The physical properties were measured by the method described below.

Oxidation transmittance: After leaving the film at 20"C1100%RH, OXY-TRAN 100 (Mod
(manufactured by ErnControls). The unit is 1 sheet:): OO/i ・24 br
s thickness 0.1m J): cc/rl-24hr/
0.11111Q Water vapor transmission rate: Measured at 40°C using a high-speed moisture transmission rate meter (manufactured by HoneyWe 11). Unit is l sheet per F): f/rl・24hr
O-boil and retort test: After the film has been boiled (held in boiling water for 30 minutes) and retorted (held in a 110"C steam atmosphere for 30 minutes), the film is taken out and changes in the film are observed.

O: There are changes in flatness, transparency, etc. before and after treatment.
Δ: Film surface is uneven and has poor flatness, ×
: Those with extremely poor flatness, or those that cause layer peeling in composite films.

Stretchability: ◎: Uniformly stretched and very transparent, O
: Stretched uniformly and had good transparency; Δ: Slightly uneven stretching;

Charpy impact strength: A film with a width of 10 seconds + length and a length of 100 cm is set in a Charpy impact tester (newly manufactured by Toyo Seiki Co., Ltd.), and the impact rupture energy is measured according to JIS B-7722.

Example I Layer A: ethylene content 33 mol%, saponification degree 99%.

Intrinsic viscosity 0.1317V%m, p, 178°C oEv.

Blend of H and nylon 6 (20Wtl) OB layer: I
, I, 98%, modified polypropylene obtained by graft polymerizing Q, 5 wt % of maleic anhydride to polypropylene of [η] 2.2.

Each resin forming layer A and layer B was supplied to two extruders and melted at 250°C. In the cap, 3 of B/A/H
Laminated in layers and extruded through slits.

Casting was performed at 55°C. By adjusting the screw rotation speed of each extruder, the thickness ratio of A:B was changed to obtain an unstretched film. This unstretched film was stretched 3 times in the longitudinal direction at 140°C, stretched 5 times in the transverse direction at 160°C using a tenter, and subjected to a 2% relaxation heat treatment at 160°C. Products 11 to 4 of the present invention have a surface layer covered with a modified polyolefin, so they have poor moisture resistance, significantly improved gas barrier properties, and do not peel off due to the good adhesion of each layer even in a retort test. It has good flatness. Therefore, a single layer film cannot withstand a retort test, but by covering the surface layer with polyolefin, it can withstand a retort test. On the other hand, since layer A is thin in Mu 5, the water vapor permeability is excellent, but the gas barrier property is poor.

Moreover, since the unstretched film having the same thickness as A3 is not stretched, it not only has significantly poor transparency, gas release, and hardness, but also lacks shape retention when subjected to a retort test.

Also, when comparing the tensile strength, A3 had Mn18.3 and T
D24. Okf/-Ashi, A6 has Mn2.8. TD5
．． At 5kf/-, I63 is significantly superior mechanically.

9chi5JJQ AJil:xsuL/721t38-e/L/l,'7:
/'1cfl'191 or more, melting point 165℃, intrinsic viscosity 0
．． 151/1 EVOH and nine on 6 (y+r3.2)
A 15wt% blend of

8 layers: 9 layers used in Example 1.

A%B Two layers of resin are fed into two extruders, melted at 250°C, and A:B=l:1, in a polymer tube leading to the nozzle.
5, and extruded from a die to a thickness of 200μ and cast at 45°C. This film was sequentially biaxially stretched under the stretching conditions shown in Table 2. Under the stretching conditions of the present invention, uniform stretching can be achieved and a transparent composite film can be obtained.

On the other hand, 410, which has a low longitudinal stretching temperature, tends to easily break the film during transverse stretching. 1611 has a too high transverse stretching temperature and is easily torn during transverse stretching. No. 412 has too high a longitudinal stretching ratio, so it breaks during horizontal stretching, and No. 13 has a small horizontal stretching ratio, resulting in uneven stretching.

Example 3 Layer A: EVOH (used in Example 2) mixed with 15 wt bohexamethylene isophthalamide (ηr2.1).

8 layers: 0.5 wt of maleic anhydride in a polypropylene copolymer with an ethylene content of 2.5 wt% and [η] of 2.0.
% graft-polymerized modified polypropylene Margin 0 or less The three-layer laminate 7 of Example 1 was subjected to heat treatment at a relaxation rate of 3% within the range of (Tm-4Q°C) to (Tm-5°C) using a Lum extrusion device. A biaxially stretched film CB/A/B=5/1015μ) having a thickness of 20μ was wound up. As is clear from the results in Table 3, (Tm-40℃) to (Tm-5℃
) The barrier properties and dimensional stability will improve if the heat treatment is performed within the range. On the other hand, /I&18, in which the heat treatment temperature is too high, has poor transparency, barrier properties, and retortability.

Example 4 Using the unstretched film used in A1 of Example 1, Table 4
Simultaneous biaxial stretching was performed under the following conditions.

Margin Table 4 Below: After stretching, a 2% relaxation heat treatment was performed at 160°C. As shown in Table 4, at a stretching ratio of 130°C, 3. OX3.0x, 16
4 at 0℃. OX 4.0 times had good stretchability. On the other hand, stretching at 120°C was not possible due to the low temperature.

Example 5 Unstretched film used for A2 in Example 1 (thickness 450
μ, A:B layer 1:2), and 2
．． Stretched 5 times, then stretched 4 times in the transverse direction at 150℃ using a tenter.
．． It was stretched 0 times. Furthermore, 1.25 to 2 in the longitudinal direction at 140℃
．． It was stretched 25 times and subjected to relaxation heat treatment at 150°C for 2 times. As is clear from Table 5, the anisotropy of mechanical properties is improved by longitudinal re-stretching. Also, compared to A2°, which has the same thickness composition ratio as l623, the barrier properties are improved by re-longitudinal stretching (Table 5 shows that as the stretching ratio increases, the appearance increases, and the oxygen and water vapor permeability increases. However, this is because the film becomes thinner, and if the thickness is kept constant, the barrier properties will improve by re-stretching in the longitudinal direction)0, Example 6 Example as the resin for layer A and layer B Using the material used in 1, make an unstretched film with the thickness composition ratio shown in Table 6.
i), the film was stretched 2.5 times in the machine direction at 140° C., then stretched 4 times in the transverse direction at 150° C. using a tenter, and then subjected to tension heat treatment at 150° C., and properties were evaluated. 428 of the present invention
．． No. 29 has no problems in gas barrier properties and retortability. A3
0 indicates good gas barrier properties and water vapor barrier properties, but flatness is impaired in a retort test. A31 has insufficient gas barrier properties.

Margin below Example 7 Measured in Tetralin at 135°C [η12.3, I.

98% polypropylene (T = 160°C)
Melt extruded at 85℃ and cast at 45℃ to a thickness of 700mm
An unstretched film of μ was obtained. This film was stretched 5 times in the longitudinal direction at 130° C. using a roll-type longitudinal stretching machine to obtain a −axially stretched film (layer B).

On the other hand, Af'f! The composition of Example 1 was used as the resin I, the adhesive layer ◎ had an ethylene content of 3.3 wt%, [η]2
．． 0.5w of maleic anhydride to 0% propylene copolymer
A T-grafted modified polypropylene was prepared, and various three-layer films having a C/A/C structure were extruded and laminated onto the B layer at a melting temperature of 250°C.

Next, feed it into a tenter and as shown in Table 7, it will be 150~1
The film was stretched 4 to 7 times in the transverse direction at 75°C, subjected to a 5% relaxation heat treatment at 155°C, and the stretched film was wound up.

432.33 is transparent, has excellent gas barrier properties and water vapor barrier properties, and can withstand retort processing.

On the other hand, A34 has insufficient lateral stretching magnification, resulting in uneven stretching and p1 thickness unevenness, making it impractical. Since the transverse stretching temperature of A35 was much higher (Tm -5°C), film breakage occurred frequently during stretching, and only a cloudy film was obtained.

Table 7

Claims (1)

[Scope of Claims] Ethylene content of 20 to 50 mol%, degree of saponification of 90% or more, and intrinsic viscosity of 0.07 to 0.17 l/g
An unstretched film made of a composition of saponified ethylene/vinyl acetate copolymer mixed with 5 to 40 wt% of polyamide, with an area magnification of 1.5 to 6 times in the longitudinal direction, 2 to 8 times in the transverse direction, and an area magnification of A gas barrier multilayer film, which has another thermoplastic resin layer on at least one side of the film obtained by biaxially stretching the film so as to have a stretching ratio of 4 to 25 times.