JP2917401B2 - Biaxially stretched polyamide film with excellent hot water resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biaxially stretched polyamide film having excellent hot water resistance. More specifically, the present invention relates to a biaxially stretched polyamide film whose mechanical strength does not decrease even when subjected to a high-temperature retort treatment.

[Conventional technology]

The biaxially stretched polyamide film is a) higher in tensile strength and more flexible than other films used for packaging of foods and the like, for example, biaxially oriented polypropylene film and biaxially oriented polyethylene terephthalate film, b. ) It has many excellent features such as high piercing pinhole strength, c) excellent bending fatigue resistance, d) excellent wear resistance, and e) a wide usable temperature range from low to high temperatures.

Taking advantage of these features, biaxially stretched polyamide films have been widely used mainly in the field of food packaging. In particular, the excellent mechanical strength and the excellent heat resistance are suitable for packaging of retort foods and are indispensable as a material for transparent retort pouches and the like.

However, there is a limit to the hot water resistance, and the conventional film suffers from the problem of film deterioration such that when exposed to hot water or steam at about 130 ° C., the mechanical strength such as tensile strength is reduced or whitened. was there. Therefore, the heat resistance limit of the polyamide film when used under such conditions is at most about 125 ° C., and there is a problem that it cannot be used under high temperature conditions of 130 ° C. or more. For this reason, conventionally, a protective layer made of polyethylene terephthalate is provided on a polyamide film serving as a surface layer,
For example, polyethylene terephthalate layer / polyamide layer /
A laminated film having a layer configuration of a polypropylene layer has been proposed. Although the use of such a film can improve the hot water resistance to some extent due to the effect of the protective layer, it does not solve the problem essentially, and on the other hand, it raises a new problem that the production cost is significantly increased. Against this background, there has been a strong demand for the development of a biaxially stretched polyamide film for food packaging that can withstand retort treatment at high temperatures.

[Problems to be solved by the invention]

The present invention has solved the above-mentioned problems, without reducing the strength even under retort treatment at 130 ° C or higher,
An object of the present invention is to provide a biaxially stretched polyamide film suitable for packaging retort foods.

The present inventor has conducted intensive studies on the problems of the prior art, and as a result, the above problem was solved by a biaxially stretched polyamide film comprising a composition in which a specific compound was contained in a polyamide resin in a specific range as a deterioration inhibitor. The inventors have learned that the present invention can be solved and completed the present invention.

[Means for solving the problem]

The gist of the present invention is that N, N'-hexamethylenebis (3,5
-Di-tert-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-tert-butyl-4-hydroxy-benzylphosphonate-diethyl ester, and 1,3,5
-Trimethyl-2,4,6-tris (3,5-di-t-butyl-
A biaxial resin having excellent hot water resistance, comprising a polyamide resin composition containing one or more compounds selected from the group consisting of 4-hydroxybenzyl) benzene in the range of 0.01 to 0.5 part by weight. Exists in stretched polyamide film.

 Hereinafter, the present invention will be described in detail.

In the present invention, the term "polyamide resin" means a homopolymer of ε-caprolactam (homopolymer), a copolymer containing ε-caprolactam as a main component, and up to 2 to 10 mol% of another compound copolymerizable therewith. Copolymers, and mixtures of these homopolymers and / or copolymers with compatible polymers up to 5 to 20% by weight.

As the compound copolymerizable with ε-caprolactam,
Aliphatic or aromatic and diamines, and a nylon salt comprising an aliphatic or aromatic dicarboxylic acid, and typical examples of the diamines include ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, Octamylenediamine, decamethylenediamine, meta-xylylenediamine, para-xylylenediamine, and the like. Representative examples of the dicarboxylic acids include adipic acid, sebacic acid, corkic acid, glutaric acid, azelaic acid, and β-methyl. Adipic acid, terephthalic acid, isophthalic acid, decamethylenecarboxylic acid, dodecamethylenecarboxylic acid, pimelic acid and the like.

Examples of the polymer which is compatible with and can be mixed with the homopolymer and / or the copolymer include a polycondensate of the above diamine and the above dicarboxylic acid.

These polyamide-based resins, for modification, within the range not impairing the properties of the resulting film, apart from the compound group, a lubricant, an antistatic agent, an anti-blocking agent,
Various additives such as dyes, pigments and inorganic fine particles may be blended.

The biaxially stretched polyamide film according to the present invention comprises, as a deterioration inhibitor, the above-mentioned compound, that is, a group consisting of the following (A), (B), and (C), based on 100 parts by weight of the polyamide resin. It is necessary to comprise a polyamide resin composition containing one or more selected compounds in a range of 0.01 to 0.5 part by weight, preferably in a range of 0.03 to 0.2 part by weight.

 However, in the following formula, -Bt represents a t-butyl group.

(A) N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) (B) 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester (C) 1,3,5-trimethyl-2,4,6-tris (3,5-di-
t-butyl-4-hydroxybenzyl) benzene These compounds (deterioration inhibitors) to be contained in the polyamide resin may be used alone or in a combination of two or more. If the ratio to the polyamide resin is within the above range, there is no particular limitation. Absent.

If the ratio of the deterioration inhibitor to 100 parts by weight of the polyamide resin is less than 0.03 parts by weight, the deterioration prevention effect is small,
If the amount is less than 0.01 part by weight, the effect of preventing deterioration becomes insufficient. If this is retorted, the film strength such as tensile breaking strength is reduced, and the intended stretched film is not obtained. If the amount is more than 0.2 parts by weight, the deterioration inhibitor tends to bleed out on the surface of the film, and the printability and adhesiveness of the surface may be impaired. It is not a typical thing. In particular, when the adhesiveness is impaired, delamination (also referred to as delamination) occurs at the bonding surface between the polyamide film and the sealant film (for example, a polypropylene film) laminated therewith. It is fatal.

The biaxially stretched polyamide-based film according to the present invention can be produced by a conventionally known various method using a polyamide-based resin composition containing the above-mentioned deterioration inhibitor as a film raw material. For example, in the case of the sequential biaxial stretching method, the above-mentioned film raw material is heated and melted by an extruder, and T-
Extrusion in the form of a film from a die, quenching this on the surface of a casting roll using a known casting method such as electrostatic pinning, to obtain a substantially amorphous and non-oriented polyamide film, The film is stretched 2 to 4 times by a roll type longitudinal stretching machine, and then stretched 3 to 5 times by a tenter type transverse stretching machine. The obtained biaxially stretched film is subjected to a heat treatment as required. It can be manufactured by winding up.

The preparation of the polyamide-based resin composition (film raw material) containing the above-mentioned deterioration preventing agent can be performed by any method. For example, the deterioration preventing agent is added to the polyamide resin production system (polymerization system). A method of producing a polyamide resin containing a deterioration inhibitor at once, adding a deterioration prevention agent to a polyamide resin not containing a deterioration inhibitor, and using a powder mixer such as a Henschel mixer or a tumbler to obtain a homogeneous composition. Can be adopted.

The biaxially stretched polyamide-based film according to the present invention can be produced not only by the tenter-type sequential biaxial stretching method described above but also by other methods such as a tenter-type simultaneous biaxial stretching method and a tubular method.

The biaxially stretched film thus manufactured may be subjected to a surface treatment such as a corona treatment in order to improve the adhesion of the printing ink and the adhesion to another film (for example, a sealant film).

〔The invention's effect〕

The present invention has a particularly remarkable effect as follows, and its industrial utility value is extremely large.

(1) Since the biaxially stretched polyamide film of the present invention has extremely excellent hot water resistance, the biaxially stretched polyamide film does not lose its strength even when subjected to a high-temperature retort treatment and is extremely suitable for retort food packaging applications.

(2) Since the biaxially stretched polyamide film of the present invention has excellent surface properties, it has good adhesion to a sealant film and the like, and does not cause a delamination (delamination) phenomenon even when subjected to a high-temperature retort treatment. .

(3) Since the biaxially stretched polyamide film according to the present invention does not require a special protective film to be laminated or a protective layer to be applied and provided, the manufacturing method is simple and can be manufactured at low cost.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it is needless to say that the present invention is not limited to these Examples.

In the following examples, the retort treatment, the breaking strength of the film, and the presence or absence of delamination after the retort treatment were performed and measured by the following methods, respectively.

Method of retort treatment From the biaxially stretched film obtained by the method described in each of the following examples, cut out a square-shaped sample film having a side length of 200 mm, the entire circumference of the sample film, the length of one side It was fixed with a mold having a 100 mm square opening and having a silicone rubber packing material all around. The sample film fixed by this mold was retorted under the following conditions.

1) Processing equipment Retort pot (Hisaka Seisakusho) 2) Temperature and pressure in the pot 130 ° C: Total pressure 2.7kg / cm ² (gauge pressure) Air partial pressure 1.0kg / cm ² 135 ° C: All Pressure 3.2 kg / cm ² (gauge pressure) Air partial pressure 1.0 kg / cm ² 3) Processing time 30 minutes under any of the above conditions 4) Number of sample films 5 pieces / kettle Measuring method of film breaking strength For the biaxially stretched film obtained by the method described in each example (before retort treatment) or the biaxially stretched film treated under the above conditions (after retort treatment), 23
After conditioning for 2 days at 50 ° C and a relative humidity of 50%, a rectangular measurement sample of 10 mm width x 50 mm length was cut out of these films, and this sample was subjected to the above temperature and humidity conditions. Then, using an Autograph DS-100 manufactured by Shimadzu Corporation, a tensile test was performed in the transverse stretching direction at a speed of 50 mm / min, and the tensile strength at the time when the film broke was measured as the breaking strength of the film. (K
g). In addition, this measurement was performed about 5 samples (5 measurement) per one example, respectively, and evaluated by the average value of these.

Further, in the breaking strength of the biaxially stretched film manufactured under the same conditions, the breaking strength after the retort treatment was evaluated by “retention strength at break” defined by the following equation.

Breaking strength retention = (Ft / Ft _o ) × 100 (%) where Ft _o means breaking strength before retort treatment (kg) Ft means breaking strength after retort treatment (kg), respectively.

Delamination after retort treatment Unstretched polypropylene film is applied to a biaxially stretched film obtained by the method described in each of the following examples using a urethane-based two-part adhesive (AD900 / RT5, manufactured by Toyo Morton Co., Ltd.). (Toray Gosei Co., Ltd., ZK-93, thickness 70μm)
Was dry-laminated to prepare a laminated film. Next, after aging at 40 ° C. for 3 days, the laminated film was subjected to a retort treatment according to the above-mentioned “method of retort treatment”, and the presence or absence of delamination after the retort treatment was determined by visual observation.

Example 1 100 parts by weight of poly-ε-caprolactam having a relative viscosity of 3.7 (Novamid 1022 manufactured by Mitsubishi Kasei Co., Ltd.) was added as an anti-deterioration agent as N, N'-hexamethylenebis (3,5-di-t). −
0.1 part by weight of butyl-4-hydroxy-hydrocinnamamide (Ciba Geigy, Irganox 1098) was added and blended with a tumbler, and the mixture was heated and melted at 65 ° C. with an extruder at 65 ° C. at 260 ° C. Continuously extruded into a sheet form from a T-die, adhered to the surface of a cooling rotating drum with a surface temperature of 25 ° C. and rapidly cooled down by electrostatic pinning, and the thickness was 140 μm.
m was obtained. This sheet is stretched three times in the machine direction at a film temperature of 60 ° C. by a roll-type longitudinal stretching machine. The vertically stretched film is immediately led to a tenter-type transverse stretching machine, and the film temperature is raised to 70 ° C. Under the conditions, the film is stretched 3 times in the transverse direction, followed by a film temperature of 21.
A heat-setting treatment was performed at 0 ° C. to obtain a biaxially stretched polyamide film having a thickness of 15 μm. With respect to the obtained biaxially stretched film, the breaking strength before and after the retort treatment was measured by the above method. Further, the laminated film prepared from the obtained biaxially stretched film was examined for the presence or absence of delamination after the retort treatment according to the method described above.

The results are shown in Table 1 together with the names and amounts of the compounds (deterioration inhibitors) contained in poly-ε-caprolactam.

Examples 2 to 6, Comparative Examples 1 to 7 In the examples described in Example 1, compounds added per 100 parts by weight of poly-ε-caprolactam (deterioration inhibitor)
And the amount thereof were changed as described in Table 1, except that a biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in the same example.
The breaking strength was measured in the same manner as in the same example, and the presence or absence of delamination was examined.

 The results are also shown in Table 1.

In Table 1 showing the results of the examples and comparative examples, the abbreviations of the added compounds and the meanings of A to E are as follows.

A: N, N'-hexamethylenebis (3,5-di-t-butyl-
4-Hydroxy-hydrocinnamamide) (Irganox 1098, manufactured by Ciba-Geigy) B: 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester (Irganox 1222, manufactured by Ciba-Geigy) C: 1,3,5-Toytyl-2,4,6-tris (3,5-di-t-
Butyl-4-hydroxybenzyl) benzene (Irganox 1330, manufactured by Ciba-Geigy) D: 2- (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole (Tinuvin, manufactured by Ciba-Geigy)
320) E: Cuprous oxide-containing composition (fine powder comprising 9.3% by weight of cuprous oxide, 82.5% by weight of potassium iodide and 8.2% by weight of calcium stearate) From Table 1, the following is clear.

(1) The biaxially stretched film satisfying the requirements of the present invention is 13
Even when subjected to a retort treatment at a high temperature of 0 ° C. or more, the tensile strength at break does not decrease, and the adhesiveness to the sealant film is excellent, and the delamination phenomenon does not occur.

(2) The requirement of the present invention was not satisfied, and the addition of the deterioration inhibitor was too large (Comparative Examples 1 and 4) or small (Comparative Example 2,
3, 5), when other compounds not belonging to the specified group are added (Comparative Examples 6 and 7), the film does not simultaneously satisfy the retention of the tensile breaking strength and the prevention of the delamination phenomenon with the sealant film. .

Continuation of the front page (51) Int.Cl. ⁶ identification code FI C08L 77/00 C08L 77/00 // B29K 77:00 B29L 7:00 (58) Field surveyed (Int.Cl. ⁶ , DB name) C08J 5/00-5/02 C08J 5/12-5/22 C08L 77/00

Claims (1)

(57) [Claims] 1. N, N 'based on 100 parts by weight of a polyamide resin.
-Hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamide), 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester, 3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
A biaxially stretched polyamide film having excellent hot water resistance, comprising a polyamide resin composition containing one or more compounds selected from the group consisting of benzene in the range of 0.01 to 0.5 part by weight.