JP2003105107A - Polyamide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyamide film suitable for use in packaging retort foods that does not show degraded strength even when subjected to a retort treatment at a temperature >135 deg.C. SOLUTION: This polyamide film comprises, as a main component, a polyamide resin having >=6 methylene chains in the minimum repeating unit of the molecular chain, and with a melting point of >=160 deg.C. The strength retention rate at break is >=70% in a 140 deg.C hot water treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyamide film having excellent hot water resistance. More specifically, the present invention relates to a polyamide film whose mechanical strength does not decrease even when subjected to a high temperature retort treatment.

[0002]

2. Description of the Related Art Polyamide film is superior to other films used for packaging foods, such as polypropylene film and polyethylene terephthalate film.
a) High tensile strength and high flexibility, b) Strong pinhole strength, c) Excellent flex fatigue resistance,
d) It has excellent wear resistance properties, e) It has many excellent features such as a wide temperature range that can be used from low temperatures to high temperatures.
Utilizing these characteristics, the polyamide film has been widely used mainly in the field of food packaging. In particular, its excellent mechanical strength and excellent heat resistance are suitable for packaging retort pouch foods and are indispensable as materials for transparent retort pouches and the like.

However, its hot water resistance is also limited, and when exposed to hot water or steam of about 135 ° C. in the conventional film, the mechanical strength such as tensile strength is lowered or the film is whitened. There was a problem of deterioration. Therefore, the heat resistance limit of the polyamide film when used under such conditions is at most about 130 ° C. even with the heat resistant water film currently on the market, and there is a problem that it cannot be used under high temperature conditions exceeding 135 ° C. . For this reason, conventionally, a protective layer made of polyethylene terephthalate is provided on a polyamide film which is a surface layer,
For example polyethylene terephthalate layer / polyamide layer /
A laminated film having a layer structure of a polypropylene layer has been proposed. Although the use of such a film can improve the hot water resistance to some extent by the effect of the protective layer, it is not an essential solution, and on the other hand, a new problem arises that the manufacturing cost is significantly increased. From such a background, development of a polyamide film for food packaging that can withstand retort treatment at high temperature has been strongly desired.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and provides a polyamide film suitable for packaging of retort foods, which does not decrease in strength even when subjected to retort treatment at a temperature exceeding 135 ° C. With the goal.

[0005]

The gist of the present invention is, however, that the main component is a polyamide resin having 6 or more methylene chains per repeating minimum unit of molecular chains and a melting point of 160 ° C. or more, and 140 ° C. The polyamide film has a breaking strength retention rate of 70% or more in the hot water treatment.

The present invention will be described in detail below. In the present invention, the polyamide resin having 6 or more methylene chains per repeating minimum unit of molecular chain and having a melting point of 160 ° C. or higher means, for example, NY66, NY11, NY12, NY6.
A polyamide resin such as 10, NY612. Alternatively, it refers to a polyamide resin that is a copolymer of a polyamide resin and another compound that is copolymerizable and has a weighted average of 6 or more methylene chains per repeating minimum unit of molecular chain and a melting point of 160 ° C. or higher.

Other copolymerizable compounds include, but are not limited to, aliphatic polyamides, aromatic polyamides, and polyamides obtained by copolymerizing terephthalic acid. Examples of polyamides include polyhexamethylene adipamide, nylon salts composed of aliphatic or aromatic diamines, and aliphatic or aromatic dicarboxylic acids. Representative examples of the diamines include ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, octamerenediamine,
Nonanediamine, decamethylenediamine, meta-xylylenediamine, para-xylylenediamine and the like, and typical examples of the dicarboxylic acid include adipic acid, sebacic acid, corkic acid, glutaric acid, azelaic acid, β
-Methyl adipic acid, terephthalic acid, isophthalic acid, decamethylenecarboxylic acid, dodecamethylenecarboxylic acid, pimelic acid and the like can be mentioned. The copolymer may be a binary copolymer, a ternary copolymer or more as long as the weighted average number of methylene chains per repeating unit of the molecular chain is 6 or more and the melting point is 160 ° C. or more.

A polyamide resin having 6 or more methylene chains per repeating minimum unit of molecular chain and a melting point of 160 ° C. or more can be mixed with a compatible polymer by using this as a main component. The main component preferably contains a polyamide resin having 6 or more methylene chains per repeating minimum unit of molecular chain and a melting point of 160 ° C. or more in an amount of 50 parts by weight or more in the film. Examples of compatible and miscible polymers include aliphatic polyamides, aromatic polyamides, amorphous polyamides, and the above-mentioned copolymerized polyamides.

Due to the modification, these polyamide resins are, apart from the above-mentioned compound groups, a lubricant, an antistatic agent, a pinhole resistance improving agent, and an antiblocking agent as long as they do not impair the properties of the obtained film. Various additives such as agents, dyes, pigments and inorganic fine particles may be blended.

The polyamide film according to the present invention is 140
The breaking strength retention rate by hot water treatment at 70 ° C. is 70% or more, preferably 80% or more, more preferably 90% or more. If it is 70% or less, delamination from the sealant film or the like and bag breakage are likely to occur and problems in use tend to occur.

It is desirable to add a specific antioxidant to the polyamide film according to the present invention, such as hindered phenol type, phosphorus type (phosphonite type), lactone type,
Examples include benzotriazole type. It is preferable to contain a hindered phenolic antioxidant. The hindered phenol-based antioxidant can be suitably used for generally known polyamide resins. Specifically, N, N '
-Hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester, 1,3 , 5-Trimethyl-2,4,6-tris (3,
5-di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (2,4-di-t-butylphenyl)
4,4'-biphenylylene diphosphonate, triethylene glycol bis-3- (3-t-butyl-4-hydroxy-5-methyl-phenyl) propionate and the like can be mentioned. Especially when used for food packaging, N, N'-hexamethylenebis (3,5-di-t-
Butyl-4-hydroxy-hydrocinnamamide), 3,5
-Di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester, 1,3,5-trimethyl-2,
At least one selected from the group consisting of 4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene
Certain compounds are preferred.

The content of the hindered phenolic antioxidant is preferably 0.01 part by weight or more, more preferably 0.1 part by weight or more, based on 100 parts by weight of the polyamide resin.
It is at least 03 parts by weight. The content of the hindered phenolic antioxidant is preferably 0.8 part by weight or less, more preferably 0.5 part by weight or less.

The antioxidant contained in the polyamide resin may be a single antioxidant or a combination of plural antioxidants, and there is no particular limitation as long as the ratio to the polyamide resin is within the above range. If the ratio of the antioxidant to 100 parts by weight of the polyamide-based resin is less than 0.01 parts by weight, the film strength such as tensile rupture strength after retort treatment will decrease, and the intended stretched film will not be obtained.
Further, if it is more than 0.5 parts by weight, the antioxidant is likely to bleed out on the surface of the film, which may impair the printability and adhesiveness of this surface, and if it is more than 0.8 parts by weight, this tendency becomes more prominent. It becomes noticeable and not practical. In particular, if the adhesiveness is impaired, delamination (also known as delamination) occurs at the adhesive surface between the polyamide film and the sealant film (for example, polypropylene film) laminated on it, which is fatal for packaging of retort foods. To be the target.

The polyamide film according to the present invention can be produced by various conventionally known methods using the polyamide resin composition containing the above-mentioned antioxidant as a film raw material. For example, in the case of the sequential biaxial stretching method, the film raw material is heated and melted by an extruder,
-Extrusion in the form of a film from a die and quenching 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. Further, this unstretched film, a film further stretched 2 to 4 times by a roll type longitudinal stretching machine, then stretched 3 to 5 times by a tenter type transverse stretching machine, and after heat treatment as desired, while slowly cooling this film, A biaxially stretched polyamide film can be produced by continuously winding.

The polyamide resin composition (film raw material) containing the above-mentioned antioxidant can be prepared by any method. For example, in the polyamide resin production system (polymerization system) A method of producing a polyamide-based resin containing an antioxidant by adding an agent, adding an antioxidant to a polyamide-based resin that does not contain an antioxidant, and using a powder mixer such as a Henschel mixer or a tumbler. A method of providing a uniform composition can be adopted.

The polyamide film according to the present invention can be produced not only by the tenter type sequential biaxial stretching method exemplified above, but also by other methods such as a tenter type simultaneous biaxial stretching method and a tubular method. The polyamide film produced in this manner may be subjected to a surface treatment such as corona treatment in order to improve printing ink coverage and adhesion to other films (for example, sealant film).

The polyamide film according to the present invention is used for retort food packaging for high temperature exposure or high temperature storage, such as miso, pickles, prepared foods, baby foods, tsukudani, konjac, chikuwa, kamaboko, seafood products, meatballs, hamburg, genghis khan. , Ham, sausage, other livestock products, toothpaste, pet food, pesticides, fertilizers, infusion packs, as well as semiconductor packaging, precision material packaging, medical treatment, etc.
It can be used for packaging industrial materials such as electronic, chemical and mechanical. There are various forms such as a bag, a lid material, a cup, a tube, and a standing pack.

[0018]

INDUSTRIAL APPLICABILITY The present invention has particularly remarkable effects as follows, and its industrial utility value is extremely large. (1) Since the polyamide film of the present invention is extremely excellent in hot water resistance, it does not decrease in strength even when subjected to a high temperature retort treatment, and is very suitable for retort food packaging applications. (2) Since the polyamide film of the present invention has excellent surface characteristics, it has good adhesiveness to a sealant film or the like and does not cause delamination (delamination) even when subjected to high temperature retort treatment. (3) Since the polyamide film according to the present invention does not need to be laminated with a special protective film or coated with a protective layer, the polyamide film can be produced easily and at low cost.

[0019]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but it goes without saying that the present invention is not limited to these examples. In the following examples, the breaking strength retention rate,
The presence or absence of delamination after the retort treatment was carried out and measured by the following methods, respectively, but it is not limited to this as long as the apparatus used is equivalent to these. Retort processing method From a polyamide film, a square sample film with a side length of 200 mm is cut out, and the entire circumference of this sample film has a square-shaped opening with a side length of 100 mm and silicon It was fixed with a mold provided with rubber packing material. The sample film fixed by this mold is subjected to retort treatment under the following conditions. 1) Processing equipment Retort kettle (manufactured by HISAKA) 2) Temperature and pressure inside the kettle: 130 ° C: Total pressure 2.7kg / cm2 (gauge pressure) Air partial pressure 1.0kg / cm2: 135 ° C: Total pressure 3.2 kg / cm2 (gauge pressure) Air partial pressure 1.0kg / cm2 140 ℃: Total pressure 3.7kg / cm2 (gauge pressure) Air partial pressure 1.0kg / cm2 145 ℃: Total pressure 4.2kg / cm2 (gauge pressure) ) Air partial pressure 1.0kg / cm2 3) Processing time Under any of the above conditions, 30 minutes 4) Number of sample films 5 pieces / pot

Method for measuring film breaking strength A polyamide film (before retort treatment) or a polyamide film treated under the above conditions (after retort treatment) was conditioned for 2 days at 23 ° C. and 50% relative humidity. After that, a rectangular measurement sample with a width of 10 mm and a length of 50 mm is cut out from these films, and this sample is subjected to the above temperature and humidity conditions using Autograph DS-100 manufactured by Shimadzu Corporation. A tensile test in the transverse stretching direction was performed at a speed of 50 mm / min, and the tensile strength at the time when the film broke was defined as the breaking strength (kg) of the film. In addition, this measurement is performed for 5 samples (5 measurements) for each example, and the average value of these is evaluated. In the breaking strength of the polyamide film manufactured under the same conditions, the breaking strength after retort treatment is evaluated by "breaking strength retention rate" defined by the following formula. Breaking strength retention rate = (Ft / Fto) × 100 (%) where Fto means breaking strength before retort treatment (kg) Ft means breaking strength after retort treatment (kg), respectively.

Delamination after retort treatment The film obtained by the method described in each of the following examples
Two-component urethane adhesive (AD90, manufactured by Toyo Morton Co., Ltd.)
0 / RT5) was used to dry laminate an unstretched polypropylene film (ZK-93, Toray Gosei Co., Ltd., thickness 70 μm) to prepare a laminated film. Next, this laminated film was subjected to aging at 40 ° C. for 3 days, then subjected to retort treatment according to the above-mentioned “method of retort treatment”, and the presence or absence of delamination after the retort treatment was visually determined.

Example 1 Polyhexamethylene adipamide (manufactured by Asahi Kasei Co., Ltd.)
100 parts by weight of N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) as an antioxidant (Irganox manufactured by Ciba-Geigy)
1098) was added to 0.02 parts by weight and blended by a tumbler, and the mixture composition was heated and melted at a temperature of 260 ° C. with a 65 mmφ extruder, and continuously extruded into a sheet form from a T-die. The surface of the cooling rotary drum was closely cooled by electrostatic pinning to obtain a substantially amorphous and non-oriented sheet having a thickness of 140 μm. This sheet was stretched 3 times in the longitudinal direction by a roll type longitudinal stretching machine, and this longitudinally stretched film was immediately introduced into a tenter type transverse stretching machine and stretched 3 times in the transverse direction, followed by heat setting treatment. A biaxially stretched polyamide film having a thickness of 15 μm was obtained. The breaking strength of each of the obtained biaxially stretched films was measured by the above method before and after the retort treatment. Further, the laminated film prepared from the obtained biaxially stretched film was examined for the presence of delamination after retort treatment according to the method described above. The results are shown in Table 1 together with the names and amounts of the antioxidants contained in polyhexamethylene adipamide.

Examples 2 to 4 In the example described in Example 1, the antioxidant and the amount thereof added per 100 parts by weight of polyhexamethylene adipamide were changed as shown in Table 1. A biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in the same example, and the breaking strength of the obtained biaxially stretched film was measured in the same manner as in the same example, and the presence or absence of delamination was examined.

Examples 5 and 6 In the example described in Example 1, 100 parts by weight of polyhexamethylene adipamide was added to polyhexamethylene adipamide.
51 to 80 parts by weight and 20 to 49 parts by weight of NOMIMIT 1020 (NY6) manufactured by Mitsubishi Engineering Plastics Co., Ltd., and the same except that the added antioxidant and its amount were changed as shown in Table 1. A biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in the example, and the breaking strength of the obtained biaxially stretched film was measured in the same manner as in the example, and the presence or absence of delamination was examined.

Example 7 In the example described in Example 1, 100 parts by weight of polyhexamethylene adipamide was added to 80 parts by weight of Mitsubishi Engineering Link Plastics Co., Ltd. NOVAMIT 2420 (NY66 / NY6 copolymer) and Mitsubishi Engineering Plastics ( Novamid 1020 manufactured by
(NY6) A biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in the same example except that 20 parts by weight and the added antioxidant and the amount thereof were changed as described in Table 1. With respect to the obtained biaxially stretched film, the breaking strength was measured in the same manner as in the example, and the presence or absence of delamination was examined.

Example 8 In the example described in Example 1, 100 parts by weight of polyhexamethylene adipamide was added to Showa Denko MGS Grilon C (N).
80 parts by weight of Y6 / NY12 copolymer) and 20 parts by weight of NOMIMIT 1020 (NY6) manufactured by Mitsubishi Engineering Plastics Co., Ltd., and the added antioxidant and its amount were changed as shown in Table 1. Otherwise in the same manner as in the example, a biaxially stretched polyamide film having a thickness of 15 μm was obtained, and the breaking strength of the obtained biaxially stretched film was measured in the same manner as in the example, and the presence or absence of delamination was examined.

Comparative Example 1-2 In the example described in Example 1, the antioxidant and the amount thereof added per 100 parts by weight of Novamid 1020 (NY6) manufactured by Mitsubishi Engineering Plastic Co., Ltd. are shown in Table 1. Same as in the same example except that
A 15 μm biaxially stretched polyamide film was obtained, and the breaking strength of the obtained biaxially stretched film was measured in the same manner as in the same example, and the presence or absence of delamination was examined.

The results of the above Examples and Comparative Examples are the same as the first example.
Shown in the table. In addition, the first showing the results of Examples and Comparative Examples
In the table, the abbreviations of the added compounds and the meanings of A to C are as follows. A: N, N'-hexamethylenebis (3,5-di-t-butyl-
4-hydroxy-hydrocinnamamide) (manufactured by Ciba-Geigy, Irganox 1098) B: 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester (manufactured by Ciba-Geigy, Irganox 1222) C: 1,3,5-toytyl-2,4,6-tris (3,5-di-t-
Butyl-4-hydroxybenzyl) benzene (Ciba-Geigy Co., Irganox 1330)

[0029]

[Table 1]

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08K 5/5333 C08K 5/5333 C08L 77/00 C08L 77/00 // B29K 77:00 B29K 77:00 B29L 7:00 B29L 7:00 F term (reference) 3E086 AA01 AB01 AC07 AC22 AD01 AD30 BA02 BA15 BA33 BB41 BB71 CA03 DA08 4F071 AA54 AA55 AA84 AC11 AC12 AC15 AE05 AF13 AH04 BB08 BC01 4F210 CL0 406026 001 HO06 QC06 A4 GG02

Claims (8)

[Claims] 1. A polyamide resin having 6 or more methylene chains per repeating minimum unit of a molecular chain and a melting point of 160 ° C. or more as a main component and having a breaking strength retention of 70% or more by hot water treatment at 140 ° C. Polyamide film characterized by 2. A polyamide film according to claim 1, which contains a hindered phenolic antioxidant. 3. The polyamide film according to claim 1, which contains 0.01 part by weight or more of a hindered phenolic antioxidant with respect to 100 parts by weight of the polyamide resin. 4. The polyamide film according to claim 1, which contains 0.8 parts by weight or less of a hindered phenolic antioxidant with respect to 100 parts by weight of the polyamide resin. 5. The polyamide film according to claim 1, wherein the polyamide resin having 6 or more methylene chains per repeating minimum unit of molecular chain is nylon 66. 6. The hindered phenolic antioxidant is N,
N'-hexamethylenebis (3,5-di-t-butyl-4-
Hydroxy-hydrocinnamamide), 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester, and 1,3,5-trimethyl-2,4,6-tris (3,5 The polyamide film according to any one of claims 2 to 5, which is at least one compound selected from the group consisting of -di-t-butyl-4-hydroxybenzyl) benzene. 7. The biaxially stretched polyamide film according to claim 1. 8. A polyamide film for packaging retort foods according to claim 1.