JPH0715059B2 - Polyamide film with excellent pinhole resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyamide film that retains the original transparency of a polyamide film and has excellent pinhole resistance even at low temperatures.

(Prior Art) Polyamide biaxially stretched film has not only general mechanical properties, thermal properties and barrier properties, but also excellent abrasion resistance, impact resistance and pinhole resistance, which are important in the packaging material field. Therefore, it is widely used mainly in the food packaging field.

(Problems to be solved by the invention) However, among the above characteristics, the pinhole resistance, which is most important in practical use, has a remarkable temperature dependence, and it has a significant temperature dependence. In use,
There were often problems such as leakage of fillers due to pinholes resulting from repeated bending fatigue, and their use was limited.

(Means for Solving Problems) As a result of investigations aimed at improving such drawbacks, the present inventors have found that
By adding a specific amount of an ethylene-based copolymer having a very limited composition and melt index, and limiting the thickness of the resulting film, the polyamide has excellent transparency while maintaining pin resistance at low temperatures. The inventors have found that the hole property is improved and arrived at the present invention.

That is, the present invention includes (a) polyamide 99.9 to 95 wt%, (b) ethylene 95 to 50 wt%, and maleic anhydride 0.1 to 10 wt%.
% And alkyl esters of unsaturated carboxylic acids 4.9-40w
A biaxially stretched film having a thickness of 1 to 50 μm, which is composed of a melt mixture of 0.1 to 5 wt% of an ethylene-based copolymer having a melt index of 0.1 to 60 g / 10 min and having a melt index of 5% at 5 ° C.
A polyamide film with excellent pinhole resistance, characterized in that the number of pinholes generated in the 1000 times repeated bending fatigue test is 10 or less and the haze value is 7% or less.

Next, the present invention will be described in detail.

The polyamide in the present invention is a linear polymer compound having an amide bond —CONH— in its molecule, such as polycaprolactam (nylon 6), polyhexamethyleneadipamide (nylon 66), polyhexamethylenesebacamide. (Nylon 610), polyaminoundecanoic acid (nylon
11), polylaurinlactam (nylon 12) and their copolymers. Polyamides suitable for the present invention include polycaprolactam (nylon 6) and polyhexamethylene adipamide (nylon 66).

The ethylene-based copolymer of the present invention is a ternary copolymer composed of ethylene, maleic anhydride and an alkyl ester of unsaturated carboxylic acid. Maleic anhydride is most suitable as a component that mainly imparts an affinity to polyamide.

The unsaturated carboxylic acid alkyl ester of the present invention is an unsaturated carboxylic acid esterified with an alkyl group having 1 to 4 carbon atoms. The unsaturated carboxylic acid referred to herein is an α, β-unsaturated monocarboxylic acid and dicarboxylic acid having 3 to 8 carbon atoms, and includes their metal salts and acid anhydrides. Examples of such an acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride and the like.

The main meaning of copolymerizing these alkyl esters of unsaturated carboxylic acids is to suppress the crystallinity of polyethylene and improve its impact characteristics, especially low temperature impact characteristics, and improve the transparency of polyethylene.

Preferred examples of the alkyl ester of unsaturated carboxylic acid in the present invention include methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate. Among them, ethyl acrylate can be mentioned, but ethyl acrylate is most preferable. preferable.

Next, the ratio of the maleic anhydride and the alkyl ester of unsaturated carboxylic acid of the present invention to the ethylene copolymer component is 0.1 to 10 w for maleic anhydride.
t%, preferably 0.5-5 wt%. Maleic anhydride
If it is less than 0.1 wt%, the affinity of the obtained copolymer with polyamide becomes insufficient, and the characteristic value of the present invention for the biaxially stretched film obtained from the melt mixture of the copolymer and polyamide ( The number of pinholes generated in a flex fatigue test 1000 times at 5 ° C was 10 or less, and the haze value was 7% or less).

On the other hand, when the maleic anhydride content exceeds 10 wt%, the melt viscosity of the obtained copolymer increases extremely, making it difficult to knead with the polyamide, and as a result, it is possible to obtain it from the melt mixture of the copolymer and the polyamide. With respect to the biaxially stretched film, the characteristic value targeted by the present invention cannot be obtained.

Next, for the alkyl ester of unsaturated carboxylic acid, refer to 4.
It is 9-40 wt%, preferably 10-35 wt%. When the alkyl ester of unsaturated carboxylic acid is less than 4.9 wt%, the impact property and the transparency improving effect of the obtained copolymer are not sufficient, and the biaxial stretching obtained from the melt mixture of the copolymer and polyamide is obtained. It is not possible to achieve the target property values of the invention for the film.

On the other hand, when the alkyl ester of unsaturated carboxylic acid exceeds 40% by weight, the resulting copolymer has good impact property and transparency improving effect, and the biaxial obtained from the melt mixture of the copolymer and polyamide is excellent. Although it is possible to sufficiently achieve the target characteristic value of the present invention for a stretched film, it becomes difficult to polymerize it using a normal polyethylene polymerization apparatus.

Further, the melt index of the ethylene-based copolymer is 0.1 g / 10 min-60 g / 10 min, preferably 1 g / 10 min-50 g /
10 minutes. When the melt index is less than 0.1 g / 10 minutes, the ethylene-based copolymer has too large a molecular weight, resulting in insufficient compatibility with the polyamide, and the biaxial obtained from the melt mixture of the copolymer and the polyamide. It is not possible to obtain the target characteristic value of the present invention for a stretched film. When the melt index is more than 60 g / 10 min, the impact properties and the transparency improving effect of the ethylene-based copolymer are not sufficient because the molecular weight is too small, and it is obtained from a melt mixture of the copolymer and polyamide. It is not possible to obtain the target characteristic value of the present invention for a biaxially stretched film.

As described above, a very special ethylene-based copolymer is essential to the present invention.

The mixing ratio of the polyamide of the present invention and the ethylene copolymer is such that the ratio of the ethylene copolymer to the polyamide is 0.1 to 5
wt%, preferably 0.5-3.5 wt%. When the content of the ethylene-based copolymer is less than 0.1 wt%, the haze value of the biaxially stretched film obtained from the melt mixture with polyamide is 7% or less among the characteristic values of the object of the present invention. The number of pinholes in the repeated bending fatigue test of 1000 pieces at 5 ° C exceeds 10, and the present invention cannot be achieved.

On the other hand, when the ethylene-based copolymer is more than 5 wt%,
Regarding the biaxially stretched film obtained from the molten mixture with polyamide, the number of pinholes generated in the flex fatigue test 1000 times at 5 ° C is 10 or less among the characteristic values of the object of the present invention, but it is cloudy. The value exceeds 7% and the present invention cannot be achieved.

2 from the melt mixture of polyamide and ethylene copolymer
The method for obtaining the axially stretched film is not particularly limited, and a generally known method can be used. For example, first, a polyamide and an ethylene copolymer are blended and then melt-kneaded with an extruder to obtain pellets of the melt mixture. Then, the pellets of this molten mixture are re-melted and formed into a film by a T-die method, an inflation method or the like to produce an unstretched film. Alternatively, the polyamide and the ethylene-based copolymer may be blended, melt-kneaded with an extruder, and then directly formed into a film by the above method to obtain an unstretched film. The unstretched film thus produced is sequentially or simultaneously biaxially stretched. The stretching temperature can be almost the same as in the case of polyamide film,
The temperature may be changed if necessary. If necessary, the stretching ratio can be 1.2 to 6 times in both the longitudinal and transverse directions. The biaxially stretched film thus obtained has a thickness of 1 to 50 µ, preferably 5 to 40 µ.

The pinhole resistance referred to in the present invention has thickness dependency, and becomes worse as the film becomes thicker. When the film thickness exceeds 50 μ, even if the ethylene-based copolymer is added, the number of pinholes generated by repeated bending fatigue at 5 ° C. exceeds 10 out of the target characteristic values of the present invention and the present invention is achieved. You cannot do it. If the film thickness is less than 1 μm, it cannot be used as a strength retaining material.

The biaxially stretched film of the present invention is optionally subjected to a heat treatment after stretching. Moreover, the biaxially stretched film of the present invention can be used as one layer of a composite film composed of two or more layers.

Further, if necessary, generally known additives such as an antioxidant, a crystal nucleating agent, a lubricant and an antistatic agent may be added to the film of the present invention.

Next, the method for measuring the characteristic value of the present invention will be described.

Repeated bending fatigue test Fed. Test Method Std. No. 101C shown in MIL-B-131F
According to Method 2017 of 5 ℃ with a so-called gel tester
The number of pinholes formed in the film after bending 1000 times below was taken as the value.

 Haze value Measured by the JIS-K-6714 method.

 Melt index Measured by JIS-K-6170 method.

(Function) In the present invention, by adding a very limited amount of an ethylene-based copolymer to polyamide and limiting the film thickness thereof, the polyamide film is resistant to low temperatures while maintaining excellent transparency. The pinhole property is remarkably improved. Although this principle is not known in detail, an ethylene copolymer in which a specific compound is copolymerized in a specific ratio and has a specific molecular weight to impart excellent impact properties and affinity for polyamide It is considered that the impact force applied to the film at the time of bending is dispersed by the ethylene-based copolymer by adding to the polyamide, and as a result, the occurrence of pinholes in repeated bending fatigue at low temperature is significantly reduced.

However, such pinhole resistance has a thickness dependency, and the thicker the film, the worse this property becomes. Therefore, the pinhole resistance limited by the present invention can be achieved only by adding a specific amount of the ethylene copolymer and limiting the film thickness within the range of the present invention.

In addition, the above ethylene-based copolymer has low crystallinity due to copolymerization and limitation of molecular weight and has good transparency, and even if it is added to polyamide, if the addition amount is below a certain ratio, It does not significantly impair transparency. Therefore, the above-mentioned ethylene copolymer is added in a specific amount, and the polyamide-based film of the present invention having a limited film thickness improves the pinhole resistance under low temperature while maintaining the excellent transparency of the polyamide film. It becomes possible.

(Example) Next, a specific description will be given with reference to Comparative Examples and Examples.
The present invention is not limited to these examples.

Comparative Example 1 Polycaprolactam having a relative viscosity of 3.0 measured at 25 ° C. in 96% concentrated sulfuric acid was melt extruded from a T die at 270 ° C. and cooled on a drum at 30 ° C. to obtain a 173 μ unstretched film. Subsequently, this film was simultaneously biaxially stretched 3.3 times in the machine direction and 3.5 times in the transverse direction at 80 ° C. to obtain a 15 μ biaxially stretched film.

Comparative Example 2 98 wt% of polycaprolactam of Comparative Example 1 and IV of Table 1
2 wt% of the ethylene copolymer was mixed and melt-kneaded into pellets with an extruder set at 250 ° C. Then, the pellets were extruded and stretched in the same manner as in Comparative Example 1 to obtain a 15 μ biaxially stretched film.

Example 1 98 wt% of polycaprolactam of Comparative Example 1 and VI to VI of Table 2
According to the method of Comparative Example 2 from 2 wt% of ethylene copolymer of I
A 15 μ biaxially stretched film was obtained.

Example 2 98 wt% of polycaprolactam of Comparative Example 1 and VIII to VIII of Table 3
According to the method of Comparative Example 2, a biaxially stretched film of 15 μ was obtained from 2 wt% of the ethylene copolymer of IX.

Comparative Example 3 According to the method of Comparative Example 2, a biaxially stretched film of 15 μm was obtained from 99.95 wt% of polycaprolactam of Comparative Example 1 and 0.05 wt% of ethylene copolymers VI to IX of Tables 2 and 3.

Comparative Example 4 According to the method of Comparative Example 2, a biaxially stretched film of 15 μm was obtained from 94 wt% of polycaprolactam of Comparative Example 1 and 6 wt% of ethylene-based copolymers VI to IX of Tables 2 and 3.

Comparative Example 5 An unstretched film of 690μ was obtained from 98 wt% of polycaprolactam of Comparative Example 1 and 2 wt% of ethylene copolymers of Tables 2 and 3 according to the method of Comparative Example 1. Subsequently, this film was stretched in the same manner as in Comparative Example 1 to obtain a 60 μ biaxially stretched film.

The characteristic values of the films of the above Comparative Examples and Examples are shown in Table 4.

As is clear from this table, only the film of the present invention has excellent pinhole resistance and transparency at low temperatures.

(Effect of the invention) According to the present invention, the intrinsic transparency of a polyamide film is impaired by adding a very limited amount of ethylene-based copolymer to polyamide in a specific amount and limiting the thickness of the obtained film. Without it, it becomes possible to improve the pinhole resistance under a low temperature which is practically important.

Further, according to the present invention, the range of use of the polyamide film, which has been limited so far, at a low temperature is greatly expanded.

Claims (3)

[Claims] 1. A polyamide 99.9 to 95 wt%;
Melt with ethylene 95〜50wt%, maleic anhydride 0.1〜10wt%, unsaturated carboxylic acid alkyl ester 4.9〜40wt%, melt index 0.1〜60g / 10min ethylene copolymer 0.1〜5wt% Mixture thickness 1-50
It is a biaxially stretched film of μ, and the number of pinholes in the 1000 times repeated bending fatigue test at 5 ° C is 10 or less, and the haze value is 7% or less. A polyamide film with excellent properties. 2. The polyamide film according to claim 1, wherein the polyamide is polycaprolactam or polyhexamethylene adipamide. 3. The polyamide film according to claim 1, wherein the alkyl ester of the unsaturated carboxylic acid of the ethylene copolymer is ethyl acrylate.