JPS62113526A - Manufacture of multi-layer molded product and multi-layer orientated film - Google Patents

Abstract

PURPOSE:To obtain a multi-layer molded product, having no dry area, uniform in the thicknesses of respective layers and prominent in mechanical strength, gas barrier property, transparency and resistance to heat, by a method wherein the multi-layer molded product having the constitution of polyester/adhesive resin/ethylene vinyl alcohol copolymer/adhesive resin/polyester is extruded by co-extrusion under a condition satisfying a specified formula. CONSTITUTION:The copolymer of ethylene vinyl alcohol, which satisfies a formula 1 in the relation of the ratio of the thickness Lp of a polyester layer, thinner between an inner layer and an outer layer, to the thickness Le of ethylene vinyl alcohol copolymer or Lp/Le and the melt flow index Y (g/10min) of the ethylene vinyl alcohol copolymer, is employed. Further, co-extrusion is effected under a condition satisfying the formula 2 in the relation between respective melting ciscosities etaP, etaA, etaE and respective thicknesses LP, LA, LE of polyester, adhesive resin and the ethylene vinyl alcohol copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to a method for producing a coextruded multilayer molded product made of polyester and an ethylene-vinyl alcohol copolymer, and a multilayer stretched film by coextrusion and costretching. be.

B. Prior Art Polyester films have excellent physical properties such as Young's modulus, tensile strength, heat resistance, and transparency, and are used in various packaging applications by taking advantage of these characteristics.

On the other hand, 11 ethylene-vinyl alcohols (hereinafter E
VOH) has excellent gas barrier properties against oxygen, nitrogen, carbon dioxide, helium, etc. and aroma retention properties against various odors, and is widely used as a food packaging material. Polyester, adhesive resin, and EV that take advantage of the characteristics of both
O) The laminate having the structure i has the conditions that it can be used as a food packaging material having excellent mechanical strength, gas barrier properties, transparency, and heat resistance.

Generally, polyester can be easily obtained into a nearly amorphous raw fabric for secondary processing such as biaxial stretching or deep drawing. Therefore, by adding secondary processing, a high-quality molded product with extremely few spots can be obtained.

On the other hand, EVOH is highly crystalline, and the raw material for secondary processing also crystallizes, so that after secondary processing there is a strong tendency to produce molded products with large spots. In general, methods for obtaining laminates include, in the case of sheets and films, the dry laminating method in which each layer is formed and then laminated using an adhesive, the sandwich laminating method, and the method in which one of the layers is used as a base material and the other is extrusion laminated or There is a method of laminating layers using coats.

Among these lamination techniques, in lamination methods such as dry lamination, extrusion lamination, and solution coating, the crystallization of EVO:EI progresses due to heating, resulting in deterioration in the extensibility of the laminate and complication of the lamination process. There are problems such as increased costs. In order to solve these problems, the coextrusion method has recently been widely adopted as a method for producing laminates containing EVOH as a barrier layer. By combining the original fabric manufacturing conditions and secondary processing conditions in this coextrusion method without any problems,
For the first time, it is possible to obtain high-quality secondary processed products that were not available in the past. Even in the coextrusion method, in order to obtain a molded product that has a beautiful appearance, the thickness of each layer is uniform, and can be commercialized by secondary processing (e.g., biaxial stretching processing, deep drawing processing, etc.). K is subject to certain conditions. In order to obtain a raw fabric with uniform thickness distribution of each layer and excellent appearance and suitability for secondary processing, it is first necessary to optimize the thickness structure of each layer and the combination of raw material resins. Next, as conditions for coextrusion, it is necessary to control conditions such as extrusion temperature, die temperature, resin cooling temperature, cooling rate, etc. of each resin.

The reason why a molded product of good quality cannot be obtained after post-processing such as stretching or deep drawing is often due to defects in the coextruded sheet or film used for secondary processing. The details of these defects are as follows.

That is, an interfacial instability phenomenon occurs during coextrusion, resulting in a wavy appearance defect on the entire surface. In severe cases, the entire surface becomes severely uneven, and the layers bite into each other, resulting in holes and tears. Even in a state where the degree of appearance defect is small, the entire surface may have a sissy-like pattern with a fine pattern that is satin-like.

If such a coextruded product with poor appearance is subjected to deep drawing or co-stretching, the poor appearance will be further exacerbated and a net-like pattern will appear on the entire surface. Such wavy surface roughness and satin texture in coextrusion are related to the stability of multilayer flow. If the flow is unstable, it will appear as a wavy rough surface if the flow is severe, or as a matte finish or streaks if the flow is less severe.

C1 Problems to be Solved by the Invention The present inventors commercialized the product from a composition of polyester/adhesive resin/EVOH/adhesive resin/polyester by coextrusion processing and by biaxial stretching processing and deep drawing processing. In order to achieve this, we have conducted extensive research on a method for producing a good quality raw fabric that does not cause the above-mentioned problems, and have arrived at the present invention.

Means for Solving Problem D1 The key point of the technique according to the present invention is to obtain a stable flow in each layer after the merging of the five layers. In particular, in the feed block merging type T-die, after the five layers merge, the resin undergoes large deformation within the T-die and spreads in a five-layer state, and the multilayer flow is often disturbed during this time. Also, in multi-manifold merging type T-dies and inflation dies, the multi-layer flow may be disturbed in the transition state where the melting multi-layer flow exits the die and the pressure is released. Therefore, the most important point is how to stably extrude and draw the multilayer flow that has the final thickness. As a result of careful consideration of molding factors, raw fabric quality, and secondary processed product quality, certain limitations were found due to the ratio of the thickness of the inner or outer polyester layer to the thickness of the intermediate EVOH layer. By using EVOH with a melt flow index and controlling the viscosity ratio in the low shear rate region of each constituent resin and the combination of the thickness structure of each layer, we can obtain a raw fabric that does not cause instability for the first time. It has become clear that good molded products can be obtained even after processing. The gist is that a multilayer molded product having a composition of polyester/adhesive resin/ethylene vinyl alcohol copolymer/adhesive resin/polyester is coextruded under conditions that satisfy the following formula. This is a method for manufacturing a multilayer molded product.

(a) Thinner polyester f of the inner and outer layers
The thickness ratio LP/LE to f1o thickness LP and the thickness LE of the ethylene-vinyl alcohol copolymer, and the melt flow index Y (t
/10 minutes) is Y≦35 log (LP/LE
)+40.

(b) Furthermore, the melt viscosity ηP, η of each of the polyester, adhesive resin, and ethylene-vinyl alcohol copolymer
The relationship between A, ηE and each thickness LP, LA, LE is ηP/ηE≦2.1≦LP/LE≦20ηA/ηE≦
2. ＾≦L＾/Lg≦1.

Here, ηP...Temperature and shear rate during molding 50 sec
The viscosity (poise) of polyester ηE...at the temperature and shear rate of 50 sec during molding, the viscosity (poise) of the ethylene-vinyl alcohol copolymer ηA...at the temperature and shear rate of 5osec during molding,
Viscosity (poise) of the adhesive resin LP... Thickness of the thinner polyester layer in the original fabric LE... Thickness of the ethylene-vinyl alcohol copolymer layer in the original fabric LA... Thinner layer in the original fabric Thickness of adhesive resin layer E1 More detailed description of the invention First, the above formula will be explained. By using EVOH that satisfies the requirements in (a) and further satisfying the requirements in (b), it can be applied to a wide variety of coextrusion devices with different structures, and it can produce homogeneous coextrusion products with an extremely beautiful appearance. It is possible to obtain

(a) means: ■ Usable EVOH is especially polyester/EVO
It is influenced by the thickness ratio of H.

(2) The smaller the thickness ratio, the narrower the range of EVOH melt flow index, and it is necessary to use EVOH having a limited melt flow index.

That's what it means.

First, the Y value that regulates the range of EVOH that can be adopted will be explained. The upper limit of Y value is 35 log (LP/L
E) If it exceeds +40, the above-mentioned satin pattern, wavy surface roughness, etc. will occur.

On the other hand, EVOH (lower limit IC of IDY value) and Fi3F/
It is desirable that the time be 10 minutes or more. The reason for this is that when the Y value is less than 3, EVOH itself is difficult to gel, and the occurrence of fish eyes and streaks becomes noticeable. The upper limit is also preferably 351 og (LP
/LE)+35, and the preferable range of the Y value is 3≦Y≦351of (LP/LFt)+35. The reason why the MFI of 260°C was adopted here is that the resin temperature in the multilayer die used in coextrusion molding of polyester composition is around 260°C. The resin temperature in the multilayer gooey is approximately 240°C to 290°C, but based on the experimental results so far, by representing the MF'I of EVOH at 260°C, it is possible to sufficiently compare the EVO)I to be adopted. be. Using EVOH that satisfies the requirements of (a), various studies were conducted on the adhesive resin, the relative viscosity of polyester to EVOH, and the thickness ratio of each layer, and the requirements that led to the present invention are (b).

The condition (b) will be explained below.

“Although it is understood that coextrusion requires the use of raw materials with similar viscosities, in reality it is not clear under what conditions the viscosities should be compared.

The different thicknesses of the layers result in different distances from the die wall, making it difficult to define the viscosity.

The focus of this technology is on what viscosity and thickness structure should be in order to obtain a stable five-layer flow.

As a result of intensive studies by the present inventors, it has been found that by controlling the viscosity in the low shear region and the thickness structure of each layer as factors, a molded product of good quality can be obtained even after post-processing. The shear rate during molding changes depending on the temperature, channel shape, and resin flow rate. Temperature is defined as the temperature during molding.

5 Q sec was used as a representative low shear value. Comparing the viscosity at high shear (more than 100 sec) does not correspond well with the experimental results, so the unstable phenomenon of multilayer flow is more likely to occur at areas farther from the wall than at high shear (closer to the channel wall). In other words, it is necessary to compare the viscosity at the layer interface (approximately 0 shear at the midpoint between the walls, where the shear is lower than that at the wall). It was found that when the viscosity is higher in this low shear region than that of the adhesive layer or polyester layer, a molded product of good quality (free of matte finish, streaks, and unevenness) can be obtained more stably.

ηh/vE needs to be 2 or less, and ηP/ηE needs to be 2 or less. If this value exceeds 2, the satin pattern will become noticeable, and if it becomes more noticeable, a multilayered molded product will result in a phenomenon in which the layers bite into each other.

If the ratio of ηh/'Qn+17p/long is small, the pressure in each resin flow path may be unbalanced and stable laminar flow may not be obtained. Preferably, 1≦ηA/ηE≦2, Xun≦
ηP/ηE≦2.

Moreover, the values of ηA and ηE1ηP are not particularly specified, and are 5×102 to 5×102, which allow normal extrusion molding.
5×10 voice level (temperature is resin temperature and shear rate 5
KVOH used in the present invention mainly refers to a copolymer obtained by saponifying a copolymer of ethylene and vinyl acetate. From the viewpoints of gas barrier properties, thermal stability, co-stretchability, etc., the ethylene content is from 20 to 60 moles, preferably from 25 to 45 moles. From the viewpoint of gas barrier properties, the degree of saponification of the vinyl acetate component is 95% or more, preferably 98% or more. Furthermore, especially to improve stretchability, a third component other than ethylene and vinyl alcohol units can be included within a range that does not significantly affect barrier properties and moldability.

The polyester resin used in the present invention may be any biaxially stretchable polyester, and includes polyesters such as ordinary homopolymers, copolymers, and polymer mixtures for film forming. The most suitable is polyethylene terephthalate (P
ET). Here, PET is mainly composed of ethylene glycol and terephthalic acid, and 80 or more moles of the acid component, preferably 90 or more moles, is terephthalic acid, and 80 moles or more, preferably 90 moles or more of the glycol component is ethylene. It is a polyester resin that is glycol, and other acid components include phthalic acid, naphthalene 1,
Aromatic dicarboxylic acids such as 2,6-dicarboxylic acid, diphenyl ether 4,4'-dicarboxylic acid, diphenyldicarboxylic acid and diphenoxyethane dicarboxylic acid, adipic acid, sepatic acid, azelaic acid and decane 1,1 Examples include fatty acid dicarboxylic acids such as °-dicarboxylic acid and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. These can be used alone or in combination of two or more of them and mixed with terephthalic acid in an amount of less than 20 mole of the acid component.

Other glycol ingredients include propylene glycol,
trimetele/glycol, tetramethylene glycol,
Aliphatic glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, hexamethylene glycol, dodecamethidi/glycol and neobentyl glycol; alicyclic glycols such as cyclohexane dimetatool% 2,2-bis( Examples include 4'-β-hydroxyethoxyphenyl)propane and other aromatic diols. These glycols can be included in the glycol component in amounts of less than 20 moles.

The polyester resin used in the present invention includes trimethylolpropane, pentaerythritol, trimellitic acid,
A polyfunctional component such as trimesic acid may be copolymerized with less than 5 moles, preferably less than 3 moles. Additionally, appropriate amounts of additives such as colorants, antioxidants, ultraviolet inhibitors, antistatic agents, antibacterial agents, and lubricants may be contained as necessary.The intrinsic viscosity of the polyester used in the present invention is From the point of view of the mechanical properties of the molded product, in a mixed solvent of phenol/tetrachloroethane with a weight ratio of 50150 (30
It is desirable to have a value of 0.55 dllf or more in terms of temperature (°C). When it is necessary to prevent drawdown during coextrusion of sheets, nodules, etc., or when low-temperature impact resistance of the final molded product is required, a polyester having a ratio of 0.8 dt/i or more may be preferable. From the point of view of the molding method and physical properties, if there is no particular advantage of increasing the viscosity, 0.55 to 0.8 dl
lf polyester may be used.

Adhesive resin adheres to both polyester and EVOH during coextrusion, and because polyester overcomes the difficulty of stretching EVOH, it has sufficient adhesive strength to transmit stretching stress. Furthermore, it is necessary that the molded product after secondary processing has sufficient adhesive strength to cause no problems when actually used. Examples of these include carboxyl group-modified polyolefin, carboxyl group-modified ethylene-ethyl acrylate, etc. Copolymers, carboxyl group-modified ethylene-vinyl acetate copolymers, modified styrene/-butadiene copolymers, latex, polyacrylates, polyurethanes, and even aluminum elements and monocarboxylic acids described in JP-A-59-115327. A bonded polyester can be used. Carboxyl modification here means modification with an unsaturated carboxylic acid or its anhydride (eg maleic anhydride, acrylic acid).

Multilayering is performed by coextrusion using such polyester, adhesive resin, and EVO), and the coextrusion method according to the present invention includes multi-manifold confluence T-die method, feed block confluence T-die method, inflation Any law is fine.

During coextrusion, the relative viscosity relationship between the resins is also related to the relative thickness of each layer, and it is important to keep the interface as far away from the channel wall as possible. Therefore, in order to stabilize the laminar flow, the thickness ratio of each layer must also be incorporated into the element.

If it is smaller than h, it may be difficult to obtain a raw fabric with a good appearance during coextrusion. In particular, if the viscosity of the adhesive resin layer is high, problems tend to occur when this thickness ratio is small. Also LA
/LE does not need to exceed 1, and may be 1 or less in terms of cost and physical properties, and preferably 1/2 or less.

LP/Lg ranges from - to 20. If it is smaller than the size, it is difficult to obtain a raw fabric with a good appearance during coextrusion.

If it exceeds 20, it is difficult to obtain a molded product with sufficient barrier properties. In other words, the barrier properties of EVOH cannot be utilized. Preferably 1/3≦L p/
L is in the range of E≦10.

Furthermore, regarding the thickness structure, the ratio of the thicknesses of the polyester layers is not particularly limited when the sheet is cup-shaped, bottle-shaped, or has a thickness of 100 μm or more. In the case of a final molded product of 50μ or less, a thin polyester layer/thick polyester layer is used to prevent curling, causing problems in handling the film itself, and making it difficult to perform post-processing operations such as lamination printing of the seal layer. It is desirable that the ratio is 1/3 or more. In addition, after satisfying the conditions mentioned above,
A polyolefin layer or the like having a function as a heat-sealing layer may be added. Various molded products can be obtained by secondary processing the thus obtained coextrusion molded product. For example, (1) multilayer molded products (sheets, films, etc.) -
A multilayer co-stretched sheet or film obtained by stretching and heat treating in the axial or biaxial direction, (2) a multilayer rolled sheet or film obtained by rolling a multilayer molded product (sheet or film, etc.), (8) a multilayer molded product (
(4) Bottles and cup-shaped containers made from multilayer molded products (such as pipes) by stretch blow molding, etc. etc. can be obtained. There are no particular limitations on such secondary processing methods, and known secondary processing methods other than those mentioned above may also be employed.

Regarding the stretching conditions when co-stretching as secondary processing,
- In the case of axial stretching, the magnification is preferably in the range of 2 times to 6 times, and in the case of biaxial stretching, the magnification is in the range of 2 times to 4.5 times in each direction.

In the case of biaxial stretching, simultaneous or sequential stretching can be employed.

The suitable temperature for stretching is 75 to 130°C. Furthermore, it is possible to apply the stretching equipment and heat treatment equipment that are normally used in the production of biaxially stretched polyethylene terephthalate films.

Through such co-stretching, as is clear from Example 2 described below, the appearance is excellent (no surface roughness), the thickness of each layer is uniform, and mechanical strength, gas barrier properties, transparency, and heat resistance are achieved. A multilayer stretched film with excellent properties can be obtained. In addition, when obtaining a multilayer stretched film by co-stretching, it is necessary to satisfy the above-mentioned (a) and (b) as co-extrusion conditions, but among these conditions, LP/L
Regarding E, it is necessary to satisfy Buy≦LP/LE≦5.

Various molded products after secondary processing such as co-stretching or deep drawing processing such as vacuum-pressure forming have excellent transparency, oxygen barrier properties, strength, etc., and are suitable for various foods, such as pickles and puddings. , miso, snacks, biscuits, oil sweets, bonito flakes, mochi.

Mainly used for packaging carbonated drinks, alcoholic beverages, etc.

The present invention will be explained in detail in Examples below.

E Examples Example 1 Ethylene content 32 mole, degree of saponification of vinyl acetate component 9
EVO whose melt 70-index Y at 9.3 degrees, temperature 260 degrees Celsius, load 2160 degrees F is 11/10 minutes
H as the intermediate layer, maleic anhydride modified ethylene-vinyl acetate copolymer as the adhesive layer, PET (polyester consisting of ethylene glycol component and terephthalic acid component)
A multilayer sheet with inner and outer layers was coextruded.

The viscosity measured at 270℃ and 50sec-' is E
VOH……ηg-5X103 Poise adhesive resin……η
I = 2X103 poise PET…………ηp-1! lXl
It was 0'poise. Using these raw materials, a film was formed with a composition of polyester/adhesive resin/EV OH/adhesive resin/polyester under the following molding conditions. The extruder is
A size of 50φ is used for EVOH, 40φ for adhesive resin, and 65φ for polyester, and the feed block method is used for the die merging method. die temperature 265
℃, cooling roll 60℃, take-up speed 2m/min.
A sheet with a total layer thickness of approximately 500 μm was prepared. Results of measuring resin temperature at the die exit.

The temperature was 255°C to 270°C. Using these sheets, apply a vacuum pressure forming machine with a drawing ratio of 0.5 and a diameter of 75yxφ'.
A cup was made. The molding conditions at this time were a sheet surface temperature of 100 DEG C. and an air pressure of 20.degree. C. and 97.degree. The results are shown in Table 1.

Below is a blank Example 2 The intermediate layer was kVOH containing 32 moles of ethylene, 99.2 moles of saponification of the vinyl acetate component, and a temperature of 260°C. A multilayer sheet was coextruded using the same adhesive resin and PET as in Example 1.

The viscosity was measured under the conditions of 270°C and 50 seconds.

EVOH...ηE=1.5×103 poise.

Polyester/adhesive resin/EVOH/adhesive resin/
Imitation fc due to the composition of polyester.

Using the original fabric, sequential biaxial stretching was performed at 85° C. by 3 times in length and 3 times in width using a biaxial stretching machine manufactured by Toyo Seiki Seisakusho. Thereafter, heat treatment was performed at 170° C. for 20 seconds. The results are shown in Table 2.

The following margin comparison example 1 Co-extrusion using the method of Example 20 with a different thickness structure,
Table 3 shows the results of the stretching. The take of PE'1' alone is also shown in Table 3.
EV with a melt flow index of 25 r/l 0 min at a temperature of 260° C. and a load of 2160 f.
O) 93 mol of ethylene shown in Table 4 with i as the intermediate layer,
The adhesive layer is made of adhesive resin of 6.5 mol of vinyl acetate and 0.5 mol of methyl acrylate, and PET (polyester consisting of ethylene glycol component and terephthalic acid component) is used as the adhesive layer.
A coextrusion sheet of PET/adhesive resin/EV OH7 adhesive resin/PET was prepared as an outer layer. The molding conditions were the same as in Example 1. Table 5 shows the molding results.

Table 4 Effects of the G0 Invention The present invention produces polyester/EVO) 1/polyester with no surface roughness, uniform thickness of each layer, and excellent mechanical strength, gas barrier properties, transparency, and heat resistance. Multilayer molded products and multilayer stretched films can be obtained.

Claims (11)

[Claims] (1) In the original fabric having the structure of polyester/adhesive resin/ethylene-vinyl alcohol copolymer/adhesive resin/polyester, (a) the thickness L_P of the thinner polyester layer among the inner and outer layers; The thickness ratio L_P/L_E to the thickness L_E of the ethylene-vinyl alcohol copolymer and the temperature 26
Melt flow index Y (g/10
) is Y≦35log(L_P/L_E)+4
(b) Further, the melt viscosities η_P, η_ of each of the polyester, adhesive resin, and ethylene-vinyl alcohol copolymer are used.
The relationship between A, η_E and each thickness L_P, L_A, L_E is η_P/η_E≦2, 1/10≦L_P/L_E≦20
A method for producing a multilayer molded product, characterized in that coextrusion is carried out under conditions that satisfy η_A/η_E≦2 and 1/10≦L_A/L_E≦1. Here, η_P...Temperature and shear rate during molding 50 sec^
Viscosity (poise) of polyester at -^1 η_E...Temperature and shear rate during molding 50 sec^-^1
The viscosity (poise) of the ethylene-vinyl alcohol copolymer at
Viscosity (poise) of the adhesive resin in L_P...Thickness of the thinner polyester layer in the original fabric L_E...Thickness of the ethylene-vinyl alcohol copolymer layer in the original fabric L_A...Thinner in the original fabric Thickness of the adhesive resin layer on the side (2) The method for manufacturing a multilayer molded article according to claim 1, which satisfies 3≦Y≦35logX+35. (3) The method for producing a multilayer molded article according to claim 1, which satisfies 1/3≦L_P/L_E≦3. (4) Multilayer molding according to claim 1, wherein the polyester has an intrinsic viscosity [η] of 0.55 dl/g or more at 30°C of a mixed solvent of phenol/tetrachloroethane in a weight ratio of 50/50. How things are manufactured. (5) The method for producing a multilayer molded article according to claim 1, wherein the ethylene-vinyl alcohol copolymer has an ethylene content of 20 to 60 mol%. (6) In the original fabric having the structure of polyester/adhesive resin/ethylene-vinyl alcohol copolymer/adhesive resin/polyester, (a) the thickness L_P of the thinner polyester layer among the inner and outer layers; The thickness ratio L_P/L_E to the thickness L_E of the ethylene-vinyl alcohol copolymer and the temperature 26
Melt flow index Y (g/10
(b) Furthermore, the melt viscosity of each of the polyester, adhesive resin, and ethylene-vinyl alcohol copolymer is η_P, η_
The relationship between A, η_E and each thickness L_P, L_A, L_E is η_P/η_E≦2, 1/10≦L_P/L_E≦5η
A method for producing a multilayer stretched film, comprising coextrusion under conditions satisfying _A/η_E≦2, 1/10≦L_A/L_E≦1, and then stretching in at least one axis direction. Here, η_P...Temperature and shear rate during molding 50 sec^
Viscosity (poise) of polyester at -^1 η_E...Temperature and shear rate during molding 50 sec^-^1
The viscosity (poise) of the ethylene-vinyl alcohol copolymer at
Viscosity (poise) of the adhesive resin in L_P...Thickness of the thinner polyester layer in the original fabric L_E...Thickness of the ethylene-vinyl alcohol copolymer layer in the original fabric L_A...Thinner in the original fabric Thickness of the adhesive resin layer on the side (7) The method for producing a multilayer stretched film according to claim 6, which satisfies 3≦Y≦35logX+35. (8) The method for producing a multilayer stretched film according to claim 6, which satisfies 1/3≦L_P/L_E≦3. (9) The method for producing a multilayer stretched film according to claim 6, wherein the thickness ratio of the thinner polyester layer to the thicker polyester layer is 1/3 or more. (10) The intrinsic viscosity [η] at 30°C of the polyester mixed solvent with a weight ratio of phenol/tetrachloroethane of 50/50 is 0.55 to 0.9 dl/g. A method for producing a multilayer stretched film. (11) Claim 6, wherein the ethylene-vinyl alcohol copolymer has an ethylene content of 20 to 6.0 mol%.
A method for producing a multilayer stretched film as described in Section 1.