JPH0813505B2 - Method for producing laminated stretched film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for producing a laminated stretched film by coextrusion co-stretching of a polyester and an ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH), The obtained stretched film is excellent in transparency, oxygen barrier property, strength, and the like, and thus various foods, for example, pickles, pudding, miso, snacks, biscuit, oil confectionery, dried bonito, rice cake, carbonated beverages, oils. Mainly used for packaging such as.

B. Conventional Technology Polyester film has excellent physical properties such as Young's modulus, tensile strength, heat resistance, and transparency, and is utilized for various packaging applications by taking advantage of these characteristics. On the other hand, EVOH is widely used as a food packaging material because of its excellent gas barrier properties against oxygen, carbon dioxide, helium and the like, and the aroma retaining property against various odors. A biaxially stretched film composed of polyester, adhesive resin, and EVOH that makes use of these characteristics has the condition that it can be a food packaging material with excellent mechanical strength, gas barrier properties, transparency, and heat resistance. .

In general, a polyester can be easily obtained as a raw material for stretching, and by applying a stretching operation, a high-quality film having very few thickness unevenness after stretching can be obtained. On the other hand, EVOH is a highly crystalline material, and the raw material before stretching is also crystallized. Therefore, after stretching, there is a strong tendency for the film to have large unevenness in thickness. As a method of biaxially stretching a laminate containing EVOH, which is difficult to uniformly stretch, a method of laminating with a stretchable thermoplastic film such as polyester and co-stretching has been already proposed. For example, JP-A-51-6276
This is the issue. When such a dry laminating method or an extrusion laminating method is used, EVOH is crystallized due to heating during lamination, and thus the stretchability of the laminate is deteriorated, and there are problems such as cost up due to the complicated laminating process. is there. Therefore, in order to solve these problems, as a method for producing a laminate containing EVOH as a barrier layer,
In recent years, the co-extrusion method has been widely adopted.

Since the polyester film has excellent dimensional stability at high temperatures, it has excellent high-speed bag-making properties. However, in the case of a co-stretched film of a polyester layer / EVOH layer, since it is desired to use it as it is without losing the effect of stretch orientation and crystallization of EVOH, it is below the melting point of EVOH and co-stretched of the polyester layer / EVOH layer. The idea of heat-treating a film is disclosed in JP-A-52-110781, JP-A-53-147773,
55-139263 etc.

C. Problems to be Solved by the Present Invention In the case of a polyester film, it was necessary to heat-treat the polyester at 200 ° C. or higher and below the melting point of the polyester in order to impart heat resistance as described above. However, when this temperature is applied to the co-stretched film of the polyester layer / EVOH layer, it exceeds the melting point of EVOH, and the EVOH layer has no orientation effect and extremely low crystallinity. For this reason, the co-stretched film of polyester layer / EVOH layer is a film with excellent gas barrier properties, which is an excellent feature, and also has three layers of polyester layer / adhesive resin layer / EVOH layer with EVOH layer on the surface. In the case of the film having the constitution, the surface of the melted EVOH is roughened like a crater. There has been a demand for a technique that takes advantage of the heat resistance of the polyester film and further improves the gas barrier property by the orientation and crystallization of EVOH. The present invention solves exactly this point.

D. Means for Solving the Problems In the present invention, a raw fabric having a constitution of at least five layers of polyester layer / adhesive resin layer / EVOH layer / adhesive resin layer / polyester layer is biaxially stretched and then heat treated. In this case, the following conditions are adopted, which is a method for producing a laminated stretched film.

0.5≤X≤5 (I) EVOH melting point + 40 ° C ≤ T <Polyester melting point ... (II) 8 seconds ≤ t ≤ 25 seconds (III) E. More Detailed Description of the Invention First, it is important for the present invention to have a layer structure in which EVOH is not present on the surface. When EVOH layer / adhesive resin layer / polyester layer has EVOH on the surface, film surface roughness such as crater occurs on the surface of EVOH layer. However, like the present invention, polyester layer / adhesive resin layer / EVOH layer / adhesive resin layer /
This problem can be solved by using a polyester layer and completely covering the EVOH layer with the polyester layer. It is considered that this is because generation of a small amount of volatile matter from the surface of the melted EVOH can be suppressed by coating with a polyester layer. In the present invention, if necessary, further addition of other layers to the inner and outer layers, and optionally to the intermediate layer (by coextrusion, extrusion laminating, dry laminating, etc.) may be added to the five-layer structure.

Furthermore, regarding the thickness configuration of the polyester layer and the EVOH layer, the tension during the heat treatment of the polyester layer keeps the tension state of the EVOH layer in order to support the molten EVOH layer during the heat treatment and prevent the molecular flow between layers. It is important to satisfy the formula (I) because it is necessary to hold. The preferred range is 1 ≦ X ≦ 3.

If the thickness ratio exceeds the upper limit value and the polyester layer becomes too thick, it becomes difficult to obtain a film having an excellent barrier effect, and conversely, if the thickness ratio falls below the lower limit value and the EVOH layer becomes too thick, the stretching becomes difficult. It is difficult to do so, and the EVOH intramolecular flow is likely to occur, the orientation state of EVOH disappears at high temperature, and the barrier property deteriorates.

It is important that the heat treatment temperature satisfies the formula (II). If the heat treatment temperature (T) is lower than the melting point of EVOH + 40 ° C., the heat treatment effect of the polyester is insufficient, and if the heat treatment temperature (T) is higher than the melting point of the polyester, the polyester is melted and the shape of the film is impaired. The preferred range is EVOH melting point + 45 ° C ≤ T ≤ polyester melting point -5 ° C.
Is. The melting point here is the differential thermal analysis curve (DSC)
The main endothermic peak point of (scanning speed 10 ° C / min).

Furthermore, the advantage of heat treatment in this temperature range is that it relates to interlayer adhesion. Polyester layer / EVOH
There have been few adhesive resins with excellent layer adhesiveness, which has been a problem so far. However, it was confirmed that heat treatment of the EVOH layer in a semi-molten state can give excellent interlayer strength in terms of adhesiveness. In the prior art, since the heat treatment is performed at a temperature equal to or lower than the melting point of the EVOH layer, sufficient adhesive strength could not be obtained, but the present invention could solve this problem.

Next, it is important that the heat treatment time satisfies the formula (III). By satisfying the formula (III), it is possible to simultaneously satisfy the heat resistance improvement of the polyester by heat treatment and the retention of the EVOH orientation effect. If the heat treatment time (t) exceeds 25 seconds, EVOH undergoes molecular flow, and the orientation structure imparted by stretching is lost, resulting in insufficient barrier properties of the film. Also, t is 8
If it is less than a second, the barrier property, the dimensional stability at high temperature, and the interlayer adhesive force will be poor. The preferred range is 12 seconds ≤ t ≤ 20 seconds. The heat treatment is performed by blowing hot air or using an infrared lamp.

Furthermore, in the present invention, the effect of the present invention is increased when the EVOH layer at the time of heat treatment is 20 μm or less. In other words, when heat-treating the coextrusion biaxially stretched film of polyester layer / adhesive resin layer / EVOH layer / adhesive resin layer / polyester layer, the part near the surface of the EVOH layer is a solid polyester layer through the adhesive resin. EVOH melts because it is supported, but the flow of EVOH molecules is suppressed. However, since the suppression effect decreases toward the center of the EVOH layer, if the EVOH becomes too thick, molecular flow occurs and the orientation effect of EVOH molecules is lost. Therefore, as a result of various studies on this point, it was found that a more preferable laminated stretched film can be obtained when the thickness of the EVOH layer during heat treatment is 20 μm or less. The more preferable thickness of the EVOH layer is 15 μm or less. The lower limit value of the EVOH layer is not particularly limited, but it is not preferable that the EVOH layer is too thin from the viewpoint of gas barrier property, so it is preferable to set it to 2 μm or more.

The polyester resin used in the present invention may be a biaxially stretchable saturated polyester, and includes ordinary polyesters for film forming homopolymers, copolymers, polymer mixtures and the like. The most suitable is polyethylene terephthalate (PET). Here, PET is mainly composed of ethylene glycol and terephthalic acid, and 80 mol% or more, preferably 90 mol% or more of the acid component is terephthalic acid, and 80 mol% or more, preferably 90 mol% of the glycol component. The above is a polyester resin that is ethylene glycol,
Other acid components include phthalic acid, naphthalene 1,4- or
Aromatic dicarboxylic acids such as 2,6-dicarboxylic acid, diphenyl ether 4,4'-dicarboxylic acid, diphenyl dicarboxylic acid and diphenoxyethane dicarboxylic acid, adipic acid, sebacic acid, azelaic acid and decane 1,10-
Examples thereof include fatty acid dicarboxylic acids such as dicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. These can be used alone or in admixture of two or more kinds with terephthalic acid in the range of less than 20 mol% of the acid component.

Other glycol components include propylene glycol, trimethylene glycol, tetramethylene glycol, diethylene glycol, polyethylene glycol,
Aliphatic glycols such as polypropylene glycol, polytetramethylene glycol, hexamethylene glycol, dodecamethylene glycol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, 2,2-bis (4'-β-hydroxy) Examples include ethoxyphenyl) propane and other aromatic diols. These glycols can be included in amounts of less than 20 mol% within the glycol component.

The polyester resin used in the present invention may be copolymerized with a polyfunctional component such as trimethylolpropane, pentaerythritol, trimellitic acid, and trimesic acid in an amount of 5 mol% or less, preferably less than 3 mol%. In addition, colorants, antioxidants, anti-UV agents, antistatic agents, antibacterial agents,
Additives such as lubricants can be contained in appropriate amounts as necessary.

The intrinsic viscosity of the polyester used in the present invention is
From the viewpoint of mechanical properties of the obtained molded product, it was mixed in a mixed solvent with a phenol / tetrachloroethane weight ratio of 50/50 (30
It is desirable to have a value at 0.5 ° C.) of 0.55 dl / g or more. When it is necessary to prevent drawdown in coextrusion of a sheet, a pipe or the like or to have a low temperature impact resistance of the final molded product, a polyester of 0.8 dl / g or more may be preferable. From the viewpoint of the molding method and the physical properties, if there is no particular advantage in increasing the viscosity, 0.55 to 0.8 dl / g of polyester may be used.

Adhesive resin for both polyester and EVOH
Since it adheres during coextrusion and covers the difficulty of stretching EVOH with polyester, there is enough adhesive force to transmit stretching stress, and the molded product after secondary processing is actually used. Sometimes it is necessary to have an adhesive strength that does not cause problems. Examples of these include carboxyl group-modified polyolefin and carboxyl group-modified ethylene-
Ethyl acrylate copolymer, carboxyl group-modified ethylene-vinyl acetate copolymer, modified styrene-butadiene copolymer, latex, polyacrylate, polyurethane, and aluminum element and monocarboxylic acid described in JP-A-59-115327. An acid-bonded polyester or the like can be used. The term "carboxyl modified" as used herein means modified with an unsaturated carboxylic acid or an anhydride thereof (eg, maleic anhydride, acrylic acid). These adhesive resins preferably have a melting point lower than that of EVOH and higher than room temperature.

The EVOH used in the present invention mainly means a copolymer obtained by saponifying a copolymer of ethylene and vinyl acetate. From the viewpoint of gas barrier properties, thermal stability, co-stretchability, etc., the ethylene content is 20 to 60 mol%, preferably
25 to 45 mol%. From the viewpoint of gas barrier property, the degree of saponification of vinyl acetate component is 95% or more, preferably 98%.
That is all. Further, especially for improving the stretchability, a third component other than the ethylene and vinyl alcohol units can be contained within a range that does not significantly affect the barrier property and the moldability. It is also possible to mix and use two or more kinds of EVOH resins having different compositions within the range of not impairing transparency and gas barrier property. Such polyester, adhesive resin, EVOH
The multi-manifold merging method T-die method, the feed block merging method T-die method, and the inflation method may be used as the co-extrusion method according to the present invention. EV for co-extrusion
The OH may contain a small amount of water, for example, 0.01 to 0.03%.

The unstretched raw fabric of the film used in the present invention is required to satisfy the formula (I) as described above, but it is preferable that the total thickness is 50 to 2000 μm, more preferably 50 to 1000 μm. is there. If the total thickness is less than 50μ, it is easy to tear during stretching, 1000μ
If it exceeds, the rapid cooling becomes difficult and the crystallinity increases, so that the stretching tension becomes large and uniform stretching becomes difficult. Further, the thickness of the EVOH layer of the unstretched raw fabric is preferably 20 to 200 μ, and more preferably 40 to 100 μ. The thickness of the polyester layer (total layer) is
20-950μ, more preferably 20-300μ is suitable, and the thickness of the adhesive resin layer (each layer) is 10-300μ, further 10-100
μ is preferred.

Furthermore, it is desirable that the thickness ratio of the polyester layers (thin polyester layer / thick polyester layer) is 1/3 or more. If the thickness ratio of the polyester layers is less than 1/3, the obtained biaxially stretched film will curl, which will cause problems in handling the film itself, and also the work of post-processing such as lamination of the sealing layer and printing. Tends to be difficult to do.

Next, with regard to the two-stretching condition, a magnification in the range of 2 to 4.5 times, preferably 2.5 to 4 times in each direction is desirable. The ratio of vertical stretching ratio / horizontal stretching ratio is 0.5 to 2, preferably 0.7.
~ 1.3. Simultaneous or sequential stretching can be adopted as the biaxial stretching. The suitable temperature for stretching is 75 ° C to 130 ° C.
Although various types of stretching devices and heat treatment devices can be used, it is possible to use the stretching device and heat treatment device that are usually used in the production of a polyethylene terephthalate biaxially stretched film.

The total thickness of the film after biaxial stretching is 10-80μ or even 15
~ 30μ, polyester layer thickness (total thickness) is 4 ~ 60
μ, further 10 to 20μ, thickness of adhesive resin layer (each layer) is 1
It is preferably -15 μm, and more preferably 1-10 μm. EV
The thickness of the OH layer is as described above.

The stretched film thus obtained has transparency, oxygen barrier property,
Since it is excellent in strength and the like, it is mainly used for packaging various foods such as miso, pickles, snacks, biscuits, oil confectionery, dried bonito, and rice cake.

 Hereinafter, the present invention will be described in detail with reference to Examples.

 The method of measuring the measured values described in the examples is as follows.

1. Oxygen permeation amount; after humidity control for 14 days under conditions of 20 ℃ and 85% pH, M
Using OX-TRAN100 manufactured by odern Controls, 20 ° C, 85% pH
It was measured at.

2. Adhesive strength: After humidity control at 20 ° C. and 65% for 14 days, it was measured by T-type peeling at a tensile speed of 250 mm / min using an autograph manufactured by Shimadzu Corporation.

F. Examples Example 1 EVOH with an ethylene content of 31 mol% and a saponification degree of 99.5% (melting point
181 ℃) and [η] = 0.65 PET (melting point 260 ℃), and
PET / PE using a modified polyester (melting point 100 ° C) in which aluminum element and benzoic acid are bonded as an adhesive resin
The modified polyester / EVOH / modified polyester / PET was coextruded to prepare a stretching original fabric having a structure of 65 μ / 22 μ / 54 μ / 22 μ / 65 μ. Using this, biaxial stretching was performed at 90 ° C. by a simultaneous method at a stretching ratio of 3.3 × 3.3 times. As a stretching machine, a testing machine manufactured by Toyo Seiki Seisakusho was used. After stretching, hot air is blown in the stretched state using the same device, and the surface temperature is 230 ° C, 1
After heat treatment for 5 seconds, the sample was removed. The characteristics of the stretched film are shown in Table 1. A film having excellent appearance, dimensional stability, and oxygen gas barrier property was obtained as compared with Comparative Examples described later. The interlayer adhesive strength between the PET layer and the EVOH layer was better than that shown in Comparative Example 5.

Example 2. Using the raw fabric shown in Example 1, biaxial stretching was performed by the sequential method and the same heat treatment was performed. An excellent stretched film similar to the simultaneous method was obtained.

Comparative Examples 1 to 8 As shown in Table 1, in the case of a stretched film produced under conditions in which the thickness constitution and the heat treatment conditions are different from those of the present invention,
Nothing satisfying all of appearance, size, stability, and oxygen gas barrier property has been obtained.

Examples 3 and 4 EVOH having an ethylene content of 27 mol% and a saponification degree of 99.5% (melting point
191 ° C.), PET used in Example 1, and a maleic anhydride modified ethylene-vinyl acetate copolymer (vinyl acetate content 29 mol%) as an adhesive resin, and a maleic anhydride modified amount of 1.1.
Mol%) (melting point 40 ° C.) was used to carry out the same test as in Example 1. The results are shown in Table 1. A film having excellent appearance, dimensional stability and oxygen gas barrier property was obtained.
The interlayer adhesion was also higher than that of Comparative Example 5.

G. Effect of the Invention According to the present invention, it is possible to obtain a laminated stretched film having excellent heat resistance and gas barrier properties, and further having an excellent appearance.

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29L 9:00 (72) Inventor Satoshi Kawai 1621 Sakazu, Kurashiki City, Okayama Prefecture Kuraray Co., Ltd. Akira Wataya Examiner Hiro (56) Reference JP 62-113526 (JP, A) JP 61-290047 (JP, A) JP 56-60248 (JP, A) JP 55-139263 (JP, A)

Claims (2)

[Claims] 1. A biaxially stretched raw material having a constitution of at least five layers of polyester layer / adhesive resin layer / ethylene-vinyl alcohol copolymer layer / adhesive resin layer / polyester layer, and then when heat treated, A method for producing a laminated stretched film, characterized in that the following conditions are adopted. 0.5 ≦ X ≦ 5 (I) Melting point of ethylene-vinyl alcohol copolymer + 40 ° C. ≦ T
<Melting point of polyester ℃ …… (II) 8 seconds ≤ t ≤ 25 seconds …… (III) 2. The thickness of the ethylene-vinyl alcohol copolymer layer after biaxial stretching is 2 to 20 .mu.m.
The method for producing a laminated stretched film according to item.