Polyamide-based resin film

Abstract

To provide a polyamide film which is excellent in heat resistance and bending resistance.SOLUTION: There are provided a polyamide-based resin film which contains polyamide (A), and a copolymer (B) including an ethylene unit, a vinyl acetate unit and a vinyl alcohol unit in a molecular chain, wherein a content of (B) to the total of (A) and (B) is 2 to 6 mass%; the polyamide-based resin film, wherein the polyamide (A) is polyamide 6; the polyamide-based resin film, wherein thermal shrinkage percentages of both of an MD and a TD of a film when being heat-treated at 150°C for 15 minutes according to JIS K 7133 are 2.0% or less; and the polyamide-based resin film, wherein an average value of the number of pinholes per 500 cm2 of the film after having been subjected to a 1,000-cycle flexural fatigue test using a Gelbo Flex Tester is 5 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyamide resin film. [Background technology]

[0002] Films made of a copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units and a polyamide, and having a high copolymer content, are used as food packaging films because of their excellent gas barrier properties and pinhole resistance. The consumption of food packaging films has been increasing rapidly due to the diversification of eating habits.

[0003] For example, Patent Document 1 discloses a film comprising 5 to 45% by mass of polyamide, 55 to 95% by mass of a partially saponified ethylene-vinyl acetate copolymer, and a metal salt of a higher fatty acid, and describes that the film has excellent pinhole resistance and flex resistance. However, the film in Patent Document 1 has problems in that the film shrinks when subjected to retort treatment and has low heat resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-253649 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a polyamide film having excellent heat resistance and flex resistance.

[0006] As a result of extensive research to solve these problems, the present inventors have found that the above object can be achieved by mixing a copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units in the molecular chain with a polyamide in a specific ratio and forming the mixture into a film, thereby arriving at the present invention. [Means for solving the problem]

[0007] That is, the gist of the present invention is as follows. <1> A polyamide-based resin film containing polyamide (A) and copolymer (B) containing ethylene units, vinyl acetate units, and vinyl alcohol units in the molecular chain, wherein the content of (B) relative to the total of (A) and (B) is 2 to 6 mass%. <2> Polyamide (A) is polyamide 6 <1> The polyamide resin film according to claim 1. <3> According to JIS K 7133, the heat shrinkage rate of the film in both MD and TD is 2.0% or less when heat treated at 150°C for 15 minutes. <1> or <2> The polyamide resin film according to claim 1. <4> After 1000 bending fatigue tests using a Gelbo flex tester, the film 2 The average number of pinholes per unit is 5 or less <1> ~ <3> The polyamide resin film according to any one of the preceding claims. [Effects of the Invention]

[0008] According to the present invention, a polyamide resin film having excellent heat resistance and flex resistance can be provided. The polyamide resin film of the present invention can be suitably used as a food packaging film for retort pouches. DETAILED DESCRIPTION OF THE INVENTION

[0009] The polyamide resin film of the present invention contains a polyamide (A) and a copolymer (B) containing ethylene units, vinyl acetate units and vinyl alcohol units in the molecular chain.

[0010] [Polyamide (A)] The polyamide (A) used in the present invention is a polymer having an amide bond formed from an amino acid, a lactam, or a diamine and a dicarboxylic acid.

[0011] Examples of the amino acid include 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and para-aminomethylbenzoic acid.

[0012] Examples of lactams include ε-caprolactam and ω-laurolactam.

[0013] Examples of diamines include tetramethylenediamine, hexamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- / 2,4,4-trimethylhexamethylenediamine, 5-methylnonamethylenediamine, 2,4-dimethyloctamethylenediamine, metaxylylenediamine, paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 3,8-bis(aminomethyl)tricyclodecane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, and bis(aminopropyl)piperazine.

[0014] Examples of dicarboxylic acids include adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 5-sodiumsulfoisophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, and diglycolic acid.

[0015] Examples of the polyamide (A) used in the present invention include polyamide 6, polyamide 66, polyamide 46, polyamide 69, polyamide 610, polyamide 612, polyamide 1010, polyamide 11, polyamide 12, polymetaxylylene adipamide (polyamide MXD6), polyamide 6T, polyamide 9T, polyamide 10T, and mixtures thereof. Among these, polyamide 6 is preferred because of its excellent balance between productivity and the resulting performance.

[0016] The relative viscosity of the polyamide (A) used in the present invention, measured using 96% by mass concentrated sulfuric acid as a solvent at a temperature of 25°C and a concentration of 1 g / dl, is preferably 2.5 to 4.0, more preferably 3.0 to 4.0.

[0017] The polyamide (A) can be produced by a known polycondensation method.

[0018] [Copolymer (B) containing ethylene units, vinyl acetate units, and vinyl alcohol units in the molecular chain] The copolymer (B) used in the present invention, which contains ethylene units, vinyl acetate units, and vinyl alcohol units in its molecular chain, is a copolymer containing at least ethylene units, vinyl acetate units, and vinyl alcohol units in its molecular chain, and may contain other monomer units. The other monomer units are preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably none, of the total monomer units in the copolymer (B). In the copolymer (B), the content of vinyl acetate groups relative to the total of vinyl acetate units and vinyl alcohol units is preferably 40% by mol or less, more preferably 30% by mol or less, and even more preferably 20% by mol or less. The content of vinyl alcohol units relative to the total of vinyl acetate units and vinyl alcohol units is preferably 0.5 to 50% by mol, more preferably 0.5 to 40% by mol, and even more preferably 1 to 30% by mol.

[0019] The melting point of the copolymer (B) containing ethylene units, vinyl acetate units, and vinyl alcohol units is preferably 80 to 150° C., more preferably 100 to 120° C. The melting point is measured using a differential scanning calorimeter by heating the material in a nitrogen atmosphere to 300° C. at a heating rate of 20° C. / min, holding the material at 300° C. for 5 minutes, lowering the material to 25° C. at a heating rate of 20° C. / min, further holding the material at 25° C. for 5 minutes, and then raising the material temperature again at a heating rate of 20° C. / min, and measuring the melting point at the top of the endothermic peak.

[0020] The copolymer (B) containing ethylene units, vinyl acetate units and vinyl alcohol units can be produced by hydrolyzing an ethylene-vinyl acetate copolymer.

[0021] An example of a commercially available copolymer (B) containing ethylene units, vinyl acetate units, and vinyl alcohol units is Mersen H manufactured by Tosoh Corporation.

[0022] The content of the copolymer (B) containing ethylene units, vinyl acetate units, and vinyl alcohol units in the film of the present invention must be 2 to 6 mass %, and preferably 3 to 5 mass %. If the content exceeds 2 mass %, bending resistance decreases, which is not preferable. On the other hand, if the content exceeds 6 mass %, heat resistance decreases, which is not preferable.

[0023] [Production of polyamide resin film] The polyamide resin film of the present invention can be produced by mixing polyamide (A) and copolymer (B) containing ethylene units, vinyl acetate units and vinyl alcohol units, and forming the mixture into a film.

[0024] The method for mixing the polyamide (A) and the copolymer (B) is not particularly limited, but an example is a method in which (A) and (B) are mixed in a tumbler.

[0025] The film-forming method is not particularly limited, but examples thereof include a method in which the mixture is melt-kneaded and extruded through a T-die to obtain an unstretched film, which is then allowed to absorb water and then stretched.

[0026] The melt-kneading may be carried out using either a single-screw extruder having one screw in the cylinder or a multi-screw extruder having multiple screws. The cylinder temperature is preferably set to 180 to 200°C near the start of kneading and to (the melting point of the polyamide used + 10°C) to (the melting point of the polyamide used + 30°C) near the outlet.

[0027] The unstretched film can be obtained by extruding the resin from a T-die, and then cooling and solidifying it on a rotating cooling drum by a known casting method such as air knife casting or electrostatic casting.

[0028] Before stretching, the unstretched film is preferably allowed to absorb water so that its moisture content is 2 to 10% by mass, more preferably 5 to 6% by mass. If the moisture content of the unstretched film is less than 2% by mass, the amount of water that acts as a plasticizer is small, which increases stress during stretching and may result in frequent breakage of the film. If the moisture content of the unstretched film exceeds 10% by mass, the film may have significant thickness variations. By adjusting the moisture content of the unstretched film to 2 to 10% by mass before stretching, it can be stretched with reduced stretching stress and the formation of numerous voids in the unstretched film can be prevented.

[0029] The water-absorbed unstretched film is preferably preheated before the stretching step. The preheating temperature is preferably (melting point of the polyamide used - 60°C) to (melting point of the polyamide used - 40°C). If the preheating temperature is less than (melting point of the polyamide used - 60°C), sufficient heat for stretching is not obtained, resulting in high stretching stress and frequent breakage of the film during production. On the other hand, if the preheating temperature is higher than (melting point of the polyamide used - 40°C), draw stretching occurs, and the resulting film may have uneven thickness.

[0030] The stretching method is not particularly limited, and examples thereof include a tubular method, a simultaneous biaxial stretching method, and a sequential biaxial stretching method. The stretching ratio in the machine direction (MD) and the stretching ratio in the transverse direction (TD) are preferably 2.5 to 3.5 times, and more preferably 3.0 to 3.3 times. If the stretching ratio is low, the unstretched film may not be sufficiently stretched, resulting in reduced mechanical strength. On the other hand, if the stretching ratio is high, orientation crystallization of the film may progress, resulting in frequent breakage of the film during production.

[0031] The stretched film is preferably heat-set at a temperature equal to or lower than the melting point of the polyamide used minus 10° C., and is preferably subjected to a relaxation treatment of 0 to 10% in both TD and MD.

[0032] The polyamide resin film of the present invention preferably contains a lubricant to improve slip properties. The lubricant may be either an inorganic lubricant or an organic lubricant, and examples thereof include silica, alumina, magnesium oxide, calcium silicate, and zeolite.

[0033] Furthermore, the polyamide resin film of the present invention may contain one or more additives such as antioxidants, ultraviolet absorbers, preservatives, antistatic agents, antiblocking agents, inorganic fine particles, etc., as needed.

[0034] The polyamide resin film of the present invention has excellent heat resistance and flex resistance, and can therefore be suitably used as a food packaging film for retort pouches. [Example]

[0035] The present invention will be specifically described below with reference to examples, but is not limited to these examples.

[0036] A. Evaluation Method The methods for evaluating various physical properties in the examples and comparative examples are as follows. (1) Heat shrinkage rate The heat shrinkage of the film in MD and TD was measured after heat treatment at 150°C for 15 minutes according to JIS K 7133. A film was deemed to have passed the test if both the heat shrinkage in MD and TD were 2.0% or less.

[0037] (2) Flexibility The obtained film was left for 2 hours in an environmental test room adjusted to 65% RH, and then subjected to a 1000-cycle flex fatigue test (torsion angle 440°, chuck distance 178 mm, diameter 89 mm) using a Gelbo Flex Tester (Tester Sangyo Co., Ltd., BE-1005). The number of pinholes in the film after the test was determined by counting the number of ink-permeated areas on filter paper. Measurements were carried out on three samples, and the number of pinholes was 500 cm 2 The average value per 500cm was calculated. 2 In this case, the test was considered passed.

[0038] B. Raw materials (1) Polyamide Polyamide 6: Unitika 1030BRF, melting point 220°C (2) A copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units in the molecular chain H-6051K: Tosoh Mersen H-6051K, melting point 110°C, copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units

[0039] (3) Lubricant SY-150: Syloid SY-150, silica, manufactured by Mizusawa Industrial Chemicals (4) Other resins Rexpearl: Rexpearl ET230X, ethylene-acrylic ester-maleic anhydride terpolymer manufactured by Japan Polyethylene Co., Ltd.

[0040] (5) Masterbatch A Masterbatch A was prepared by mixing 80 parts by mass of polyamide and 20 parts by mass of H-6051K and melt-kneading the mixture at 260°C using a TEM26-SS twin-screw extruder manufactured by Shibaura Machine Co., Ltd.

[0041] Example 1 90 parts by mass of polyamide 6 and 10 parts by mass of masterbatch A were mixed and extruded at 270°C in an extruder to obtain an unstretched film. The unstretched film was subjected to a water absorption treatment at 60°C for 1 minute to achieve a water absorption rate of 5%. Thereafter, the film was stretched 3.0×3.3 times at a stretching temperature of 170° C. using a simultaneous biaxial stretching machine, and then subjected to a 10% relaxation treatment in the TD at a heat setting temperature of 215° C. to obtain a stretched film.

[0042] Examples 2 and 3, Comparative Examples 1 to 3 The same procedure as in Example 1 was carried out except that the blending amounts were changed to those shown in Table 1, and an unstretched film was then produced, followed by a stretched film.

[0043] Comparative Example 4 95 parts by mass of polyamide 6 and 5 parts by mass of Rexpearl were mixed and formed into a film using an extruder at 270°C to obtain an unstretched film. The unstretched film was subjected to a water absorption treatment at 60°C for 1 minute to achieve a water absorption rate of 5%. Thereafter, an attempt was made to stretch the film 3.0x3.3x using a simultaneous biaxial stretching machine at a stretching temperature of 170°C, but wrinkles appeared in the unstretched film during the moisture content adjustment process, resulting in uneven stretching and frequent breakage, making it impossible to obtain a film.

[0044] Table 1 shows the blending ratios of raw materials and the constituent ratios and property values ​​of the obtained films in the examples and comparative examples.

[0045] [Table 1]

[0046] The films obtained in Examples 1 to 3 had excellent heat resistance, with a 150°C heat shrinkage rate (MD / TD) of 2.0% or less, and the average number of pinholes after a flexural fatigue test was 5 / 500 mm. 2 or less, and had excellent flex resistance.

[0047] The film obtained in Comparative Example 1 did not contain a copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units, and therefore the average number of pinholes after the flexural fatigue test was 5 / 500 mm. 2 The bending resistance was poor.

[0048] The film obtained in Comparative Example 2 had a content of copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units greater than the range specified in the present invention, and therefore had a heat shrinkage rate at 150°C in either MD or TD exceeding 2.0%, resulting in poor heat resistance.

[0049] The film obtained in Comparative Example 3 had a high content of copolymer containing ethylene units, vinyl acetate units, and vinyl alcohol units, so the 150°C heat shrinkage in MD and TD was large and could not be measured, and the heat resistance was poor.

Claims

1. The polymer contains a polyamide (A) and a copolymer (B) containing an ethylene unit, a vinyl acetate unit, and a vinyl alcohol unit in the molecular chain, A polyamide resin film in which the content of (B) relative to the total of (A) and (B) is 2 to 6 mass %.

2. 2. The polyamide resin film according to claim 1, wherein the polyamide (A) is polyamide 6.

3. 3. The polyamide resin film according to claim 1, wherein the heat shrinkage of the film in both MD and TD when heat treated at 150°C for 15 minutes in accordance with JIS K 7133 is 2.0% or less.

4. After 1000 bending fatigue tests using a Gelbo flex tester, the 500 cm ２ 3. The polyamide resin film according to claim 1, wherein the average number of pinholes per film is 5 or less.

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