JPH11156932A - Process for producing biaxially stretched film of saponified ethylene-vinyl acetate copolymer - Google Patents

Abstract

[PROBLEMS] Biaxially stretched film of saponified ethylene-vinyl acetate copolymer excellent in continuous stretch processability (stable production), film thickness accuracy, gas barrier properties, film strength, boil resistance, etc. To provide a method of manufacturing. SOLUTION: In producing a biaxially stretched film of a saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 60 mol% and a degree of saponification of 90 mol% or more, the film is stretched in the machine (MD) direction. The water content of the saponified product is adjusted to be more than 3.5% by weight and less than 8% by weight and stretched at a temperature of 40 to 75 ° C.
Stretch in the direction D).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a biaxially stretched film of a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH).

[0002]

2. Description of the Related Art Conventionally, stretched EVOH films have been frequently used for various packaging applications by utilizing their gas barrier properties. As a method for producing such an EVOH film, E
Generally, a raw film is formed from a VOH (pellet) by a melt extruder or the like, and the raw film is uniaxially or biaxially stretched. In producing a stretched film of EVOH, the conditions at the time of stretching are important, and breakage occurs frequently during stretching, so that stable production cannot be performed, or the film thickness accuracy of the stretched film is poor, or desired physical properties cannot be obtained. Sometimes. In order to solve such disadvantages, Japanese Patent Publication No. Sho 59-1
Japanese Patent No. 3970 discloses a method in which the moisture content of a raw film before stretching is adjusted to 8 to 20%, first stretching is performed at 40 to 75 ° C, and then second stretching is performed at 85 to 140 ° C. But,
Japanese Patent Publication No. Sho 60-26697 describes a method in which a raw EVOH film having a specific gravity is adjusted to a water content of 3.5% or less and stretched at 50 to 130 ° C.

[0003]

However, according to detailed studies by the inventors, the former method allows continuous stretching of a film without breaking, but the film thickness accuracy of the obtained stretched film is poor. In the latter method, although a film having good physical properties can be obtained,
There is also a risk that stable production cannot be achieved due to breakage during stretching, and there is still room for improvement.

[0004]

The inventors of the present invention have conducted intensive studies in view of such circumstances, and have found that EVO having an ethylene content of 10 to 60 mol% and a saponification degree of 90 mol% or more.
In producing a biaxially stretched film of H, a vertical (machine;
2. The water content of the saponified product during stretching in the MD) direction is set to 3.
The above problem can be solved by adjusting the content to be more than 5% by weight and less than 8% by weight and stretching at a temperature of 40 to 75 ° C., and then stretching in the transverse (TD) direction. Have found that an EVOH biaxially stretched film having excellent boil resistance can be obtained, and have completed the present invention.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the production method of the present invention will be specifically described. The raw film (unstretched film) before biaxial stretching used in the present invention is obtained by forming EVOH into a film (film formation) by melt molding or the like.
As an ethylene content of 10 to 60 mol%, preferably 20 to 60 mol%, more preferably 25 to 55 mol%,
A vinyl acetate component having a degree of saponification of at least 90 mol%, preferably at least 95 mol% is used.
If the amount is less than 0 mol%, the water resistance becomes insufficient. On the other hand, if it exceeds 60 mol%, the gas barrier property decreases, which is not preferable.
On the other hand, if the saponification degree is less than 90 mol%, the water resistance becomes insufficient, which is not preferable.

[0006] The EVOH may be variously modified, if necessary, or may be a mixture of the modified EVOH and the EVOH. As the modified EVOH, for example, modified EVOH with propylene, isobutene, etc., having 3 carbon atoms
At least one α-olefin having from 30 to 30 carbon atoms or 3 carbon atoms
Saponified terpolymer comprising modified EVOH, modified EVOH obtained by graft polymerization of at least one α-olefin of at least 30 and ethylene and acrylic acid ester, and (meth) acrylate-ethylene-vinyl acetate Modified EVOH, a modified EVOH obtained by modifying the hydroxyl group of EVOH with a cyanoethyl group, a modified EVOH containing a polyester graft obtained by depolymerizing a polyester with vinyl alcohol, a vinyl acetate-ethylene-silicon-containing olefinically unsaturated monomer EVOH obtained by saponifying a monomeric copolymer, modified EVOH obtained by saponifying a terpolymer comprising a pyrrolidone ring-ethylene-vinyl acetate, acrylamide-
Modified EVOH obtained by saponifying a terpolymer of ethylene-vinyl acetate, modified EVOH obtained by saponifying a terpolymer of allyl acetate-ethylene-vinyl acetate, isopropenyl acetate-ethylene-acetic acid Modified EVO obtained by saponifying vinyl terpolymer
H, a modified EVOH in which a polyether component is added to the terminal of EVOH, a modified EVOH in which a polyether component is added in a graft form as a branch polymer of EVOH, a modified EVOH in which an alkylene oxide is added to EVOH,
And the like.

EVOH contains comonomer other than the above, such as α-olefins, unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides, anhydrides, unsaturated sulfonic acids or salts thereof. You can be there. In the present invention, the above E
Adjusting the water content of the raw EVOH film obtained from VOH to a range of more than 3.5% by weight and less than 8% by weight and further stretching at a temperature of 40 to 75 ° C. The method will be specifically described.

First, the moisture content of the raw film is adjusted to the above-mentioned range, but such adjustment is not particularly limited, and the raw film is adjusted by performing a humidity control operation immediately after the film is formed. be able to. As an example of the adjusting method, a method of dipping in hot water, a method of passing through a humidified atmosphere, and the like are selected. In the present invention, when the water content is 3.5% by weight or less, breakage occurs frequently during stretching, and stable production cannot be performed. Conversely, when the water content is 8% by weight or more,
The thickness accuracy of the obtained stretched film is inferior, and it is difficult to achieve the object of the present invention. The raw film having the adjusted water content is subjected to biaxial stretching. Such stretching may be performed simultaneously or sequentially, and is not particularly limited. In the present invention, the film is particularly effective for the sequential biaxial stretching method. And
The stretching method will be described in detail.

The raw film whose water content has been adjusted is subjected to a first (MD direction) stretching step. For the primary (MD direction) stretching, a known method can be used, but in the present invention, it is also necessary to adjust the temperature during stretching to 40 to 75 ° C. The stretching stress is too strong and the film breaks,
If the temperature exceeds ℃, not only the final film properties are reduced because the stretching orientation is difficult to obtain, but for example, when a roll-type stretching machine is used, the film is fused to a roll, and it is difficult to achieve the object of the present invention. Becomes Although the stretching ratio is not particularly limited, the raw film is stretched 3 to 6 times (more preferably 3.5 to 5 times) in the machine direction (MD) direction in such a temperature range.
).

The above-mentioned primary (MD) stretched EV
OH film is transverse (TD) under the condition of 70-140 ° C.
Although the stretching ratio is not particularly defined in the direction, the film is stretched 3 to 6 times (more preferably 3.5 to 5 times). Usually, it is performed by a tenter method in which the both ears of the film are clipped, but may be performed by a generally known method. Usually, heat setting is further performed. Heat fixation is 12 under tension
Heating the film at a temperature of 0 ° C. to 5 ° C. lower than the melting point of the film for several seconds to several minutes.

Thus, a biaxially stretched film of EVOH is obtained, and the EVO obtained by the method of the present invention is obtained.
The biaxially stretched film of H is often used not only as a single layer but also as a laminate having at least one such film. In the production of the laminate, a film obtained by the production method of the present invention, the other substrate is laminated on one or both sides of a layer of a resin molded product such as a sheet, as a lamination method, for example, A method of laminating the resin molded product and a film or sheet of another base material using a known adhesive such as an organic titanium compound, an isocyanate compound, or a polyester compound may be used.

Such other base films include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-propylene copolymer, ethylene- Acrylic ester copolymer, polypropylene, propylene-α-olefin (C 4-20
Α-olefins) copolymers, polyolefins such as polybutene and polypentene, and polyolefins in a broad sense, such as homo- or copolymers of these olefins, or homo- or copolymers of these olefins graft-modified with unsaturated carboxylic acids or esters thereof Resin, polystyrene resin, polyester,
Polyamide, copolymerized polyamide, polyvinyl chloride, polyvinylidene chloride, acrylic resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorinated polypropylene, E
VOH (two or more EVOH layers) and the like.
Paper, metal foil, uniaxially or biaxially stretched plastic film or sheet, woven fabric, nonwoven fabric, metal strip, wood surface, etc. can also be used.

As a layer structure of the laminate, a layer of the biaxially stretched film of EVOH is composed of I (I ₁ , I ₂ ,...), Another substrate,
For example, when the thermoplastic resin layer is II (II ₁ , II ₂ ,...), If it is in the form of a film or a sheet, not only a two-layer structure of I / II but also II / I / II, I / II _{/ I, I 1 / I 2} / II, I / II
Any combination such as ₁ / II ₂ , II ₂ / II ₁ / I / II ₁ / II ₂ is possible.

Thus, the biaxially stretched EVOH film of the present invention and the laminate thereof have excellent properties, that is, appearance properties, gas barrier properties, etc., and therefore, films and sheets for packaging foods, pharmaceuticals, agricultural chemicals, and industrial chemicals. It is very useful for applications such as tubes, bags, containers, and retort containers.

[0015]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” mean on a weight basis unless otherwise specified. Example 1 EVOH [ethylene content 32 mol%, saponification degree 99.
8 mol%] to the following single-screw extruder.

(Single screw extruder) Screw inner diameter 65 mm L / D 32 Screw compression ratio 3.2 T die Coat hanger type Die width 450 mm Extrusion temperature C1: 210 ° C, H: 220 ° C C2: 220 ° C, D: 220 ° C C3: 230 ° C, C4: 230 ° C, C5: 220 ° C,

The resin molded by the above extruder is heated at 25 ° C.
Quenched on a 600 mm diameter casting roll that has been cooled to a thickness of 220 µm.
I got Next, the obtained EVOH raw film was treated with 6
The film was immersed in warm water of 0 ° C. for about 10 seconds to adjust the water content of the film to 4.4%, and then continuously baked under the following conditions.
Axial stretching, heat setting, and humidity control were performed to obtain a biaxially stretched film of EVOH of the present invention.

[Primary stretching (longitudinal stretching) conditions] Stretching machine Roll stretching machine Stretching temperature 60 ° C. Longitudinal stretching ratio 3.6 times Film thickness after stretching 60 μm [Second stretching (lateral stretching) conditions] Stretching Machine Tenter type stretching machine Stretching temperature 90 ° C Lateral stretching ratio 3.9 times Film thickness after stretching 15 μm Film width after stretching 800 mm

[Heat setting condition] Temperature 160 ° C Time 5 seconds [Humidity control condition] Leave at 20 ° C and 65% RH for 7 days Water content after humidity control 2.5%

The obtained biaxially stretched EVOH film (the film after 3 hours of stretching treatment) was evaluated as follows with respect to film thickness accuracy (in the width direction), gas barrier properties, film strength, and boil resistance. Was. Further, the above stretching treatment was performed for 8 hours, the number of breaks at that time was examined, and the continuous stretching property was also evaluated.

(Film thickness accuracy) Film flow direction (MD)
The thickness was measured at 10 points each at a distance of 30 mm from the center to both sides perpendicular to the center, and the maximum value, minimum value, and average value were obtained. (Gas barrier property) The oxygen permeability (cc / m ² · day · atm) was measured under the conditions of 20 ° C and 65% RH. (Film strength) AS at 20 ° C. and 65% RH
According to TM-D-882 and 1922, the tensile strength (Ts; kg / mm ² ) in the longitudinal and transverse directions was measured. (Boil resistance) The surroundings were fixed with a frame in hot water of 95 ° C. 5
A 0 × 50 mm film was immersed for 30 minutes, the state of whitening was visually observed, and evaluated as follows. ○ −−− No change (no whitening is observed) △ −−− Partial whitening is observed × −−− Whitening is observed on the entire surface

Example 2 In Example 1, the raw film was heated at 70 ° C. for about 7 hours.
The film was immersed for 2 seconds to adjust the water content of the film to 7.1%, and the same procedure was performed except that the longitudinal (MD) stretching temperature was changed to 55 ° C. to obtain a biaxially stretched film of EVOH. An evaluation was performed.

Example 3 In Example 1, the raw film was passed through a humidified atmosphere at 90 ° C. for about 15 seconds, the water content of the film was adjusted to 6.0%, and the longitudinal (MD) stretching temperature was adjusted. Was changed to 65 ° C. to obtain a biaxially stretched film of EVOH, which was similarly evaluated.

Example 4 In Example 1, the raw film was heated in hot water at 65 ° C. for about 1 hour.
The film was immersed for 5 seconds, the moisture content of the film was adjusted to 7.5%, the longitudinal (MD) stretching temperature was changed to 55 ° C, and the longitudinal (M)
D) The stretching ratio is 4.0 times, and the transverse (TD) stretching ratio is 4.2.
A biaxially stretched film of EVOH was obtained in the same manner except that the number was doubled, and evaluated similarly.

Comparative Example 1 In Example 1, the raw film was heated for about 1 hour in 50 ° C. hot water.
A biaxially stretched EVOH film was obtained in the same manner except that the film was immersed for 0 second to adjust the water content of the film to 1.8%, and was similarly evaluated.

Comparative Example 2 In Example 1, the raw film was heated for about 1 hour in 75 ° C. hot water.
A biaxially stretched EVOH film was obtained in the same manner except that the film was immersed for 0 second to adjust the water content of the film to 10.2%, and evaluated similarly.

Table 1 shows the evaluation results of the examples and the comparative examples.

[Table 1] Film thickness accuracy Gas barrier properties Film strength Wheel resistance Continuous stretchability Maximum Minimum Average (times) Example 1 15.5 14.5 15.0 0.4 25/27 ○ 0 2 15.5 14.2 14.8 0.5 27/28 ○ 0 3 15.6 14.3 14.9 0.4 23/25 ○ 0 〃 4 13.7 12.5 13.1 0.5 28/30 ○ 0 Comparative Example 1 15.7 14.0 14.8 0.4 24/27 × 20 〃 2 17.0 13.2 15.1 0.6 17/18 △ 2 Note) Film strength is tensile strength ( kg / mm ² ), and the numerical values represent measured values in the vertical and horizontal directions, respectively, and the unit of gas barrier property is cc / m ² · day · atm.

[0028]

According to the present invention, since the raw EVOH film is stretched under specific conditions, it is excellent in continuous stretching processability, and furthermore, the film thickness accuracy, gas barrier property, film strength, and the like.
A biaxially stretched film having excellent boil resistance can be obtained, and a multilayer laminate having at least one stretched film is very useful, and is very useful as a packaging material for foods, pharmaceuticals, agricultural chemicals, industrial chemicals, and the like. Useful.

Claims (2)

[Claims] 1. A biaxially stretched film of a saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 60 mol% and a saponification degree of 90 mol% or more is stretched in a machine (MD) direction. The water content of the saponified product at that time was adjusted to be more than 3.5% by weight and less than 8% by weight, and stretched at a temperature of 40 to 75 ° C.
D) A method for producing a biaxially stretched film of a saponified ethylene-vinyl acetate copolymer, characterized by stretching in the direction. 2. The stretching ratio is 3 to 5 in the machine (MD) direction.
2. The method for producing a biaxially stretched film of saponified ethylene-vinyl acetate copolymer according to claim 1, wherein the ratio is 6 to 6 times in the transverse (TD) direction.