JPS63272548A - Manufacture of laminating oriented film - Google Patents

Abstract

PURPOSE:To enhance heat resistance and gas barrier characteristics by biaxially orientating a raw fabric constituted of at least five layers consisting of a polyester layer/a bonding resin layer/ an ethylene-vinyl alcohol copolymer layer/a bonding resin layer/ a polyester layer and then heat treating under given conditions. CONSTITUTION:A raw fabric constituted of at least five layers consisting of a polyester layer/a bonding resin layer/an EVOH layer/a bonding resin layer/a polyester layer is biaxially oriented. It is important that the thickness constitution over the polyester layer and the EVOH layer should satisfy the Formula I. It is also important that the heat treatment temperature should satisfy the Formula II and the heat treatment time should satisfy the Formula III. A good laminated extensible film is manufactured by making the thickness of the EVOH layer at the time of heat treatment as 2-20 mu. Saturated polyester which can be oriented biaxially can be used as the polyester resin to be utilized and polyethylene terephthalate is most suitable. Also, the melting point of the bonding resin should be lower than that of the EVOH, and should preferably be higher than the room temperature.

Description

Detailed Description of the Invention A. Industrial Application Field The present invention relates to a method for producing a laminated stretched film by coextrusion and co-stretching of polyester and ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH). The obtained stretched film has transparency and oxygen barrier properties of 1 strength, so it can be used in various foods, such as pickles, etc.
Mainly used for packaging pudding, miso, snacks, biscuits, oil confections, bonito flakes, mochi, carbonated drinks, oils, etc.

B. Prior Art Polyester films are known for their 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, EVOH is
It has excellent gas barrier properties against oxygen, carbon dioxide, and helium, and has excellent aroma retention properties against various fruits, and is widely used as a food packaging material. A biaxially oriented film made of polyester, &i-adhesive resin, and EVOH that takes advantage of the characteristics of both of them has mechanical strength, gas barrier properties, transparency,
Polyester, which has the conditions to be used as a food packaging material with excellent heat resistance, can generally be easily obtained into a nearly amorphous raw material for stretching, so by adding a stretching operation,
A high quality film with extremely little thickness unevenness after stretching can be obtained. On the other hand, EVOH is highly crystalline, and the original film before stretching is also crystallized, so after stretching, there is a strong tendency to form a film with large thickness unevenness. EVOH is difficult to stretch uniformly.
As a method for biaxially stretching a laminate containing a polyester film, a method has already been proposed in which the film is laminated with a stretchable thermoplastic film such as polyester and then co-stretched. For example, JP-A-51
-6276, etc. 0 When such dry lamination method or extrusion lamination method is used, crystallization of EVOH progresses due to heating during lamination.
Therefore, there are problems such as deterioration in the stretchability of the laminate and increased costs due to the complication of the lamination process. 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.

Polyester film has excellent dimensional stability at high temperatures, and therefore 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 the EVO:E without losing its stretching orientation and crystallization effects, the polyester layer/EVOH The idea of heat-treating the co-stretched film of the layers was introduced in JP-A-52-11078/1.
, Japanese Patent Publication No. 53-147773. % Kaisho 55-13926
Proposed for 3rd prize.

C9 Problems to be Solved by the Present Invention In the case of polyester films, in order to impart heat resistance as described above, it was necessary to heat-treat the polyester at a temperature of 200° C. or higher but below the melting point of the polyester. However, when this temperature is applied to a polyester layer/EVOH layer co-stretched film, it exceeds the melting point of EVOH, and the EVOH layer has no orientation effect and has an extremely low degree of crystallinity. For this reason, the polyester layer IE
The VOH layer co-stretched film has insufficient gas barrier properties, which is its excellent feature, and furthermore, the EV
Polyester layer with OH layer on the surface/adhesive resin layer/I
In the case of a film with a three-layer structure of VOH layers, the melted EV
Crater-like film surface roughness occurs on the OH surface. Taking advantage of the heat resistance of polyester film, further EV
There has been a desire for a technology that takes advantage of the effect of improving gas barrier properties due to the orientation and crystallization of OH. The present invention solves exactly this problem.

Means for solving the D0 problem The present invention consists of a polyester layer/adhesive resin layer/EVOH layer/
When biaxially stretching and then heat-treating a raw fabric having at least five layers of adhesive resin layer/polyester layer,
This is a method for producing a laminated stretched film characterized by adopting the following conditions.

0.5≦X≦5 ・・・・・・・・・
... (1) Melting point of EVOH + 40℃≦T Melting point of polyester ... (II) 8 seconds≦t≦25 seconds
°°°°゛°°°°°゛ (2) First, the present invention
It is important to have a layer structure that does not have OI (OI) on the surface.E
EV on VOH layer/adhesive resin layer/polyester layer
If the structure is such that OH is on the surface, a crater-like roughness will occur on the surface of the EVOH layer. This problem can be solved by completely covering the EVOH layer with a polyester layer. This is thought to be because the generation of trace amounts of volatile matter from the surface of the molten EVOH can be suppressed by covering it with the polyester layer. In the present invention, other layers may be added to the five-layer structure as necessary to the inner and outer layers, and in some cases to the intermediate layer (by coextrusion, extrusion lamination, dry lamination, etc.).In addition, there is also a polyester layer. Regarding the thickness structure of the EVOH layer,
In order to prevent molecular flow between the layers, it is important that the tension during heat treatment of the polyester layer satisfies formula (1), as it is necessary to firmly maintain the tension state of the EVOH layer. 0 The preferred range is 1≦X≦3 It is.

If the thickness ratio exceeds the upper limit and the polyester layer becomes too thick, it will be difficult to obtain a film with excellent barrier effect.On the other hand, if the thickness ratio falls below the lower limit and the EVOH layer becomes too thick, the stretching will be difficult. In addition, EVOH intramolecular flow tends to occur, and the orientation state of EVOH disappears at high temperatures, resulting in a decrease in clear properties.0 Regarding the heat treatment temperature, it is important to satisfy formula (I [)]. If the heat treatment temperature (T) is less than the melting point of EVOH + 40°C, the heat treatment effect of the polyester will be insufficient, and if it is higher than the melting point of the polyester, the polyester will melt and the shape of the film will be damaged, which is inappropriate. A preferred range is EVOH melting point +45°C≦T≦polyester melting point -5°C. Note that the melting point here refers to the main endothermic peak point of the differential thermal analysis curve (DSC) (scanning speed 103 fmin).

Furthermore, the advantage of heat treatment in this temperature range is that it relates to interlayer adhesion.0 Polyester layer/EVO
There are few adhesive resins with excellent adhesive properties for the H layer, which has been a problem up until now. However, it was confirmed that heat-treating the EVOH layer in a semi-molten state can provide excellent glabellar strength in terms of adhesiveness. In the prior art, EVO
Since the heat treatment was performed at a temperature below the melting point of the H layer, sufficient adhesive strength could not be obtained, but this problem was solved by the present invention. is important. By satisfying the formula (2), it is possible to simultaneously improve the heat resistance by heat treatment of polyester and maintain the alignment effect of EVOH. If the heat treatment time (1) exceeds 25 seconds, EVOH causes molecular flow, and the oriented structure imparted by stretching is lost, resulting in insufficient barrier properties of the film. If t is less than 8 seconds, the barrier properties, dimensional stability at high temperatures, and interlayer adhesion will be poor. A preferred range is 12 seconds≦t≦20 seconds. Note that the heat treatment is performed by blowing hot air, using an infrared lamp, or the like.

Furthermore, in the present invention, the EVOH layer during heat treatment is 20μ
The following will increase the effects of the present invention. In other words, when a coextruded biaxially stretched film of polyester layer/adhesive resin layer/EVOI (layer/adhesive resin layer/polyester layer) is heat-treated, the portion near the surface of the EVOH layer is
EVOH melts because it is supported by a solid polyester layer via an adhesive resin, but the 70-
is suppressed. However, this suppressing effect decreases closer to the center of the EVOH layer, so if the thickness of EVOH becomes too thick, molecular flow will occur and the orientation effect of EVOH molecules will be lost.

Therefore, as a result of various studies on this point, we found that the EV during heat treatment
It has been found that a more preferable laminated stretched film can be obtained when the thickness of the OH layer is 20 μm or less. EV
A more preferable thickness of the OH layer is 15 μm or less.

There is no particular limit to the lower limit of the EVOH layer, but from the viewpoint of gas barrier properties, it is not preferable to make it too thin, so it is better to have a thickness of 2μ or more.

The polyester resin used in the present invention may be any biaxially stretchable saturated polyester, and includes polyesters such as ordinary homopolymers, copolymers, and monopolymer polymers for film forming. The most suitable is polyethylene terephthalate (PET). Here, PET is mainly composed of ethylene glycol and terephthalic acid, and has an acid content of 80 moles or more.

Preferably, the polyester resin contains 90 moles or more of terephthalic acid, 80 moles or more of the glycol component, preferably 90 moles or more of ethylene glycol, and other acid components include heptalic acid, naphthalene 1,4-1
or 2,6-dicarboxylic acid, diphenyl ether 4.4
Aromatic dicarboxylic acids such as -dicarboxylic acid, cyphenyl dicarboxylic acid and diphenoxyethane dicarboxylic acid, fatty acid dicarboxylic acids such as adipic acid, sepatenoic acid, azelaic acid and decane 1.1°-dicarboxylic acid.

Examples include 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 moles of the acid component.

Other glycol ingredients include propylene glycol,
trimethylene glycol, tetramethylene glycol,
Aliphatic glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, hexamethylene glycol, dodecamethylene glycol and neobentyl glycol, alicyclic glycols such as cyclohesane dimetatool, 2.2 Examples include -bis(4'-β-hydroxyethoxyphenyl)propane and other aromatic diols. These glycols can be contained in an amount of 20 mole or more in the glycol component. The polyester resin used in the present invention includes trimethylolpropane, pentaerythritol, trimellitic acid,
Polyfunctional components such as trimesic acid may be copolymerized to less than 5 molar proportions, preferably less than 3 molar proportions. Additionally, additives such as colorants, antioxidants, ultraviolet inhibitors, antistatic agents, antibacterial agents, lubricants, and the like can be contained in appropriate amounts as required.

The intrinsic viscosity of the polyester used in the present invention is determined from the viewpoint of mechanical properties of the obtained molded product in a mixed solvent of phenol/tetrachloroethane with a weight ratio of 50150 (3
It is desirable to have a value of 0.55 d12/f' or more at 0°C). When it is necessary to prevent drawdown during coextrusion of sheets, pipes, etc., or when low-temperature impact resistance of the final molded product is required, polyester of 0.8 dllf 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
A polyester of dl/y may be used.

The adhesive resin adheres to both polyester and EVOH during coextrusion, and in order to cover the difficulty of stretching EVOH with polyester, it has adhesive strength sufficient to transmit stretching stress, and It is necessary that the molded product after secondary processing has enough adhesion strength to cause no problems when actually used. Examples of these include carboxyl group-modified polyolefin, carboxyl group-modified ethylene-ethyl acrylate copolymer, carboxyl group-modified ethylene-vinyl acetate copolymer, modified styrene-butadiene copolymer, latex, polyacrylate, polyurethane, Further, a polyester containing an aluminum element and a monocarboxylic acid described in JP-A-59-115327 can be used. Note that carboxyl modification herein means modification with an unsaturated carboxylic acid or its anhydride (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 refers to 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 from 20 to 60 mmol, preferably from 25 to 45 mmol. 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, a third component other than the six-metal, ethylene, and vinyl alcohol units that particularly improve stretchability may be included within a range that does not significantly affect the barrier properties and moldability. Furthermore, two or more EVOH resins having different compositions may be used in combination as long as transparency and gas barrier properties are not impaired. These polyesters
Multilayering is performed by coextrusion using an adhesive resin and EVOH, and the coextrusion method according to the present invention can be any of the multi-manifold merging T-die method, the feedbook merging method 2 T-die method, and the inflation method. But that's fine.

Further, the EVOH during coextrusion may contain a small amount of water, for example, about 0.01 to 0.03%.

The unstretched original film used in the present invention needs to satisfy formula (1) as described above, but it is preferable that the total thickness is 50 to 2000μ, more preferably 50 to 1000μ. be. If the total thickness is less than 50 μm, it is easy to tear during stretching, and if it exceeds 1000 μm, rapid cooling becomes difficult, and the degree of crystallinity increases, causing the stretching tension to increase and making uniform stretching difficult. In addition, the EVOI of the unstretched original fabric (layer thickness is 20 to 20
It is suitable that it is 0μ, and more preferably 40 to 100μ.

The thickness of the polyester layer (total layer) is preferably 20 to 950μ, more preferably 20 to 300μ, and the thickness of the adhesive resin layer (each layer) is 10 to 300μ, more preferably 10 to 10μ.
0μ is suitable.

Furthermore, the ratio of the thicknesses of the polyester layers (ratio of thin polyester layer/thick polyester layer) is preferably 1/3 or more. If the thickness ratio of the polyester layers is less than 1/3, the obtained biaxially stretched film will curl, causing problems in handling the film itself, and will also cause problems during post-processing such as lamination of the seal layer and printing. It tends to be difficult to do.

Next, regarding the second stretching conditions, it is desirable to have a magnification in the range of 2 to 4.5 times, preferably 2.5 to 4 times, in each direction. Further, the vertical stretch ratio/horizontal stretch ratio is 0.5 to 2, preferably 0.7 to 1.3. Further, as the biaxial stretching, simultaneous or sequential stretching can be adopted.

The suitable temperature for stretching is 75°C to 130°C. Although various types of stretching equipment and heat treatment equipment can be used, it is possible to use the stretching equipment and heat treatment equipment that are normally used in the production of polyethylene tele-7 tallate biaxially stretched film.

The total thickness of the film after biaxial stretching is 10 to 80 μm, and even 15 to 30 μm, and the total thickness of the polyester layer is
The thickness of the adhesive resin layer (each layer) is preferably 1 to 15 microns, more preferably 1 to 10 microns. The thickness of the EVOR layer is as described above.

The obtained stretched film has excellent transparency, oxygen barrier properties, strength, etc., so it can be used in various foods such as miso,
It is mainly used for packaging pickles, snacks, biscuits, oil confections, dried bonito flakes, mochi, etc.

In the following Examples, the present invention will be explained in detail.Methods for measuring the measured values described in Examples are as follows.

1. Oxygen permeation rate: After 14 days of humidity control under 20°C and 185°C conditions, OX manufactured by Modern Cor+ytrols
- Measured at 20'C, 85%) using TRANloo.

2. Adhesive strength: After 14 days of humidity control at 20°C and 65cm.

Tensile speed 2501o using autograph manufactured by Takasugi Seisakusho
Measurement was performed using T-peel at a distance of 11/1 m.

F, Examples Example 1 EVO containing ethylene [31 mole, degree of saponification 99.5%
PET with R (melting point 181°C) and [η] = 0.65
(melting point: 260°C) and modified polyester (melting point: 100°C) in which aluminum element and benzoic acid are bonded as adhesive resin.
Perform OH/modified polyester/PETO coextrusion, 6
Original fabrics for stretching were prepared with a configuration of 5μ/22μ, 154μ/22μ/65μ. Using this, biaxial stretching was carried out at 90° C. in a simultaneous method at a stretching ratio of 3.3×3.3 times. As the stretching machine, a testing machine manufactured by Toyo Seiki Urasaku Shin was used. Using a post-stretching device, hot air was blown into the stretched state to perform heat treatment at a surface temperature of 230° C. for 15 seconds, and then the sample was removed. Table 1 shows the properties of the stretched film. Superior appearance, dimensional stability, and oxygen gas barrier compared to the comparative example described below.
A film with properties was obtained. In addition, PET layer and EV
The interlayer adhesive strength of the OR layer was better than that shown in Comparative Example 5.

Example 2 Using the original film shown in Example 1, biaxial stretching was carried out by the sequential method and a similar heat treatment was performed to obtain an excellent stretched film similar to that obtained by the zero simultaneous method.

Comparative Examples 1 to 8 As shown in Table 1, in the case of stretched films produced with thickness structure and heat treatment conditions different from those of the present invention, appearance, dimensions, stability, and oxygen gas barrier properties were all improved. I haven't found anything satisfying.

Examples 3 and 4 EVO with ethylene content of 27 mol% and saponification degree of 99.5%
H (melting point 191°C) and PET used in Example 1 and maleic anhydride-modified ethylene-vinyl acetate copolymer (vinyl acetate content 29 mol%, maleic anhydride modified amount 1.1 mol width) as the adhesive resin. (melting point: 40°C), the same test as in Example 1 was conducted. The results are shown in Table 1. A film with excellent appearance, dimensional stability, and oxygen gas barrier properties was obtained. The interlayer adhesive strength was also higher than that of Comparative Example 5.

Margin G9 Below Effects of the Invention According to the present invention, it is possible to obtain a laminated stretched film that has excellent heat resistance and gas barrier properties, and has a crushed appearance.

Claims (2)

[Claims] (1) biaxially stretching a raw fabric having a composition of at least five layers: polyester layer/adhesive resin layer/ethylene-vinyl alcohol copolymer layer/adhesive resin layer/polyester layer;
A method for producing a laminated stretched film, characterized in that the following conditions are adopted during subsequent heat treatment. 0.5≦X≦5...(I) Melting point of ethylene-vinyl alcohol copolymer +40℃≦T<melting point of polyester℃...(II)
8 seconds≦t≦25 seconds...(III) (X: total thickness of polyester layer of raw fabric/thickness of ethylene-vinyl alcohol copolymer layer of raw fabric T: heat treatment temperature (
℃) t: Heat treatment time (seconds) (2) The method for producing a laminated stretched film according to claim 1, wherein the ethylene-vinyl alcohol copolymer layer has a thickness of 2 to 20 μm after biaxial stretching.