JPH10329211A - Manufacture of biaxially oriented polyamide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a biaxially oriented polyamide film having excellent transparency, pinhole resistance, dimensional stability and producing efficiency. SOLUTION: An unoriented film formed by using resin composition obtained by mixing 90 to 99.9 wt.% of polyamide (A) and 10 to 0.1 wt.% of ethylene copolymer containing 95 to 60 wt.% of ethylene, 0.1 to 10 wt.% of maleic anhydride and 4.9 to 30 wt.% of lower alkyl ester of unsaturated carboxylic acid as material is water absorbed so that water content becomes 0.2 to 2.0 wt.%, and then biaxially oriented simultaneously in longitudinal and lateral directions in at an orienting temperature of a range of 70 to 120 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially stretched polyamide film having excellent transparency inherent in a polyamide film, excellent pinhole resistance and excellent dimensional stability.

[0002]

2. Description of the Related Art A biaxially stretched polyamide film has mechanical properties, thermal properties, gas barrier properties, wear resistance, and the like.
It has excellent impact resistance and pinhole resistance, and is widely used as a packaging material.

However, the pinhole resistance has a large temperature dependency, and when used at a low temperature such as 10 ° C. or less, the leakage of the filler due to the pinhole caused by dropping or piercing by the contents is caused. Such troubles may occur, which is a problem.

[0004] In order to solve such a problem, a resin composition obtained by mixing a polyamide and an ethylene copolymer comprising an alkyl ester of ethylene, maleic anhydride and an unsaturated carboxylic acid as a raw material is used. A biaxially stretched polyamide film having excellent pinhole resistance has been proposed (Japanese Patent Publication No. 7-15059). However, in the above polyamide film, since the transparency of the film is reduced, it is necessary to rapidly form an unstretched film or to perform low-temperature stretching to prevent a decrease in transparency. There is a problem that the uniformity of physical properties in the width direction of the film is impaired.

[0005]

SUMMARY OF THE INVENTION The present invention provides a biaxially stretched polyamide film having excellent transparency inherent in a polyamide film, excellent pinhole resistance even at a low temperature, and excellent production efficiency. To provide a way to do so.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve this problem. As a result, the present inventors have found that an ethylene copolymer having a specific composition is blended with polyamide and stretched under specific conditions. As a result, it has been found that uniformity of physical properties in the width direction and pinhole resistance at low temperatures can be improved without impairing the transparency of the film.

That is, the gist of the present invention is as follows.
Ethylene copolymer (B) comprising 90 to 99.9% by weight of polyamide (A), 95 to 60% by weight of ethylene, 0.1 to 10% by weight of maleic anhydride and 4.9 to 30% by weight of lower alkyl ester of unsaturated carboxylic acid An unstretched film formed by using a resin composition containing 10 to 0.1% by weight as a raw material is subjected to water absorption treatment so that the moisture content becomes 0.2 to 2.0% by weight, and the stretching temperature is set in a range of 70 to 120 ° C. A method for producing a biaxially stretched polyamide film, comprising simultaneously biaxially stretching in the longitudinal and transverse directions.

[0008]

Next, the present invention will be described in more detail. The polyamide in the present invention is a thermoplastic polymer compound having an amide bond (—CONH—) in its molecule, and is composed of polyε-capramide (nylon 6), polyhexamethylene adipamide (nylon 66), Methylene sebacamide (nylon 610), polyaminoundecamide (nylon 11), polylauramide (nylon 12), and copolymers thereof are included. Among these, nylon 6 can be mentioned as a polyamide suitable for the present invention.

In the present invention, the maleic anhydride component in the ethylene copolymer is 0.1 to 10% by weight, preferably 0.5 to 10% by weight.
~ 5.0 wt%, optimally 1.0-2.0 wt%.

When the amount of the maleic anhydride component is less than 0.1% by weight, the obtained copolymer has insufficient affinity for polyamide, and the transparency and pinhole resistance of the obtained biaxially stretched film are reduced. On the other hand, when the maleic anhydride component exceeds 10% by weight, a large amount of gel is generated at the time of melt extrusion, so that the pressure rise rate of the filter is increased, leading to a decrease in productivity.

As the lower alkyl ester of unsaturated carboxylic acid in the ethylene copolymer in the present invention, for example, n-butyl acrylate is suitable, and the component weight% is 4.9 to 30% by weight, preferably 10 to 20%. % By weight.

When the content of the lower alkyl ester component of the unsaturated carboxylic acid is less than 4.9% by weight, the effect of improving the pinhole resistance of the obtained copolymer is insufficient. The effect of improving pinhole resistance is saturated,
On the contrary, it is not preferable because the transparency is lowered.

Next, in the mixing ratio of the polyamide (A) and the ethylene copolymer (B) in the present invention, A is 90 to 99.9.
B is 10 to 0.1% by weight, more preferably 95 to 99.5% by weight, and B is 5 to 0.5% by weight with respect to% by weight. If B is more than 10% by weight, the transparency of the biaxially stretched film is impaired, the amount of gel formed during melting increases, the pressure rise rate of the filter decreases, and the production efficiency decreases. When the amount is less than 10% by weight, the pinhole resistance of the biaxially stretched film comprising the composition with the polyamide becomes insufficient.

The method for producing a biaxially stretched film in the present invention is not particularly limited, and a conventionally known method can be used. For example, after blending A and B in advance, melt-kneading with an extruder to obtain pellets, remelting the pellets, forming a film by a T-die method, an inflation method, etc., and manufacturing an unstretched film. Can be. Alternatively, an unstretched film can be produced by blending A and B, melt-kneading with an extruder, and then continuously forming a film.

In the present invention, the unstretched film has a water content of 0.2 to 2.0% by weight, preferably 0.4 to 1.5% by weight.
It is necessary to simultaneously stretch biaxially in the vertical and horizontal directions after the water absorption treatment so that If the water absorption is less than 0.2% by weight, the stretching stress increases, causing troubles such as cutting, and the operability decreases. If the water absorption is more than 2.0% by weight, the strength of the obtained stretched film decreases. And the thickness unevenness of the film in the width direction increases. On the other hand, if the water absorption is too large, the unstretched film being subjected to the water absorption treatment may be wrinkled or have troubles such as meandering of the film. In order to make the moisture content of the unstretched film 0.2 to 2.0% by weight, for example, the unstretched film may be subjected to a water immersion treatment in a water tank whose temperature is controlled at 10 to 30 ° C. for 20 seconds or less, preferably 5 to 15 seconds.

Prior to simultaneous biaxial stretching, the unstretched film subjected to the water-absorbing treatment has a temperature of 50 to 70 ° C., preferably 60 ° C.
Preheated near. If the preheating temperature is lower than 50 ° C, stretching becomes difficult, and if the preheating temperature is higher than 70 ° C, the transparency of the stretched film deteriorates.

In the present invention, it is necessary to stretch the unstretched film subjected to water absorption and pre-heat treatment at a temperature in the range of 70 to 120 ° C. If the stretching temperature is lower than 70 ° C., stretching and cutting tend to occur, and if it is higher than 120 ° C., the strength of the stretched film is reduced and the transparency of the film is undesirably reduced. The stretching is usually carried out simultaneously and biaxially at 2.0 to 4.0 times in the longitudinal and transverse directions. When the stretching ratio is less than 2.0 times, the strength of the obtained stretched film is low, and when the stretching ratio exceeds 4.0 times, stretching and cutting of the film tend to occur.

Next, the stretched film is heated at a temperature of 140 to 215 ° C.
Heat treatment. If the heat treatment temperature is lower than 140 ° C., the oblique difference in heat shrinkage becomes large, and if it is higher than 215 ° C., the pinhole resistance and transparency of the obtained stretched film are undesirably reduced. Normally, the heat treatment zone is constituted by a plurality of zones having different set temperatures, and it is necessary that all the heat treatment zones satisfy the above temperature range.

The thickness of the biaxially stretched film is suitably from 1 to 50 μm, usually from 10 to 30 μm. It should be noted that the pinhole resistance of the film is dependent on the thickness and tends to decrease when the film is too thick, so that care may be required in some cases.

In the present invention, the biaxially stretched film may be a single layer or a multi-layer film combined with another film. Further, in the present invention, the film may contain, if necessary, known additives such as an antioxidant, a crystal nucleating agent, a lubricant, and an antistatic agent.

[0021]

Next, the present invention will be described specifically with reference to examples. In addition, the measuring method used for evaluation of an Example and a comparative example is as follows.

(1) Repeated bending fatigue test Fed. Test Method Std. NO. 101C shown in MIL-B-131F
According to Method 2017, 5
After bending 1000 times at ℃, the number of pinholes generated in the film was counted. (2) Cloudiness Measured according to the JIS-K-6714 method. (3) Moisture content The unstretched film immediately before biaxial stretching was collected, placed in a weighing bottle, dried, and the moisture content was calculated from the weight change before and after drying. (4) Oblique Difference in Hot Water Shrinkage Ratio The difference in the hot water shrinkage ratio in the directions of 45 ° and 135 ° oblique to the width direction of the film was measured. Each of the measurement samples was cut into a film of 10 mm width x 100 mm length along the above directions and boiled in hot water at 100 ° C for 5 minutes.
The dimensions after being left at 20 ° C. × 65% RH for 2 hours were measured, and the shrinkage relative to the dimensions before the treatment was determined. (5) Evaluation of operability The state of occurrence of folding wrinkles and meandering of the unstretched film during the water absorption treatment, and the occurrence of tarmi of the stretched film were observed and evaluated according to the following criteria. A: Good without any problem. B: There are slight wrinkles and wrinkles in the stretched film, but there is no major problem. C: There was a production trouble due to the occurrence of stretching and cutting, and severe occurrence of wrinkles and wrinkles.

Example 1 Relative viscosity measured at 25 ° C. at a concentration of 1 g / dl in 96% concentrated sulfuric acid
97.5% by weight of 3.0 nylon 6 (Unitika A1030BRF), 83.4% by weight of ethylene, 1.6% by weight of maleic anhydride
And 2.5% by weight of an ethylene copolymer (a) composed of 15.0% by weight of n-butyl acrylate, and melt-kneaded with an extruder set at 250 ° C. to form pellets. Next, the pellet was melt-extruded from a T-die at 260 ° C.
It was cooled on a drum at 10 ° C. to obtain an unstretched film having a thickness of 150 μm. Next, the unstretched film was guided to a warm water bath at a temperature of 20 ° C., and after being subjected to a soaking treatment for 10 seconds, a speed of 108 m / min.
The preheating temperature is 60 ° C., the stretching temperature is 95 ° C., and the heat treatment temperature is 140 ° C. in the first set, 160 ° C. in the second set, and 190 ° C. in the third set.
C., a fourth set at 208.degree. C., and a fifth set at 211.degree. C. to obtain a biaxially stretched film having a thickness of 15 .mu.m. (The moisture content of the unstretched film before stretching is 0.4
%Met. ) Stretching is 3.3 times in the vertical direction and horizontal direction
The film was simultaneously biaxially stretched at a magnification of 3.0 times and subjected to a 5% relaxation treatment in the transverse direction in the heat treatment zone. Table 1 shows the performance of the obtained stretched film. The length of each zone of preheating, stretching and heat treatment is as follows.

Examples 2 to 5 Biaxially stretched films were obtained in the same manner as in Example 1 except that the conditions of the water immersion treatment were as shown in Table 1, except that the moisture content of the unstretched film before stretching was changed. Table 1 shows the performance of the obtained stretched film.

Comparative Examples 1 to 4 Biaxially stretched films were obtained in the same manner as in Example 1 except that the conditions of the water immersion treatment and the stretching temperature were changed as shown in Table 1. Table 1 shows the performance of the obtained stretched film.

[0026]

[Table 1]

[0027]

According to the present invention, it is possible to obtain a biaxially stretched polyamide film having excellent transparency inherent in a polyamide film, excellent pinhole resistance, dimensional stability, and excellent production efficiency. Can be. According to the present invention, the range of use of the polyamide film is widened, and its industrial value is extremely high.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 77:00 B29L 7:00 (72) Inventor Fumio Yamamoto 31-3 Uji Hinojiri, Uji-shi, Kyoto Unitika Uji Plastics Factory Co., Ltd. Inside

Claims (1)

[Claims] 1. Polyamide (A) 90 to 99.9% by weight, 95 to 60% by weight of ethylene, 0.1 to 10% by weight of maleic anhydride and lower alkyl ester of unsaturated carboxylic acid 4.9 to 30
Water-absorbing treatment of an unstretched film formed from a resin composition containing 10 to 0.1% by weight of an ethylene-based copolymer (B) consisting of 10% by weight as a raw material so that the moisture content becomes 0.2 to 2.0% by weight. And then simultaneously biaxially stretching the film in the longitudinal and transverse directions at a stretching temperature of 70 to 120 ° C.