JPH0535070B2 - - Google Patents

Description

[Detailed description of the invention]

A. Field of Industrial Application The present invention relates to a packaging material with excellent hot water resistance and gas permeation resistance, and particularly to a packaging material for retorts. B. Conventional technology Conventionally, saponified ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH) has properties such as gas permeability, oil resistance,
It is widely known as a thermoplastic resin with excellent solvent resistance, and has been used in various packaging fields, particularly in films, sheets, containers, etc. for food packaging. However, EVOH is weak against water, and when it comes into contact with hot water, it swells, softens, and deforms.
It cannot be used for the outermost layer of packaging materials for foods that require boiling or retort sterilization, as well as for the inner layer of packaging materials for substances containing moisture. Furthermore, even if EVOH is in the intermediate layer, boiling or retort processing may cause problems such as deformation and protrusion of the container, wrinkles, and deterioration of the appearance of the end surface. Therefore, a satisfactory packaging material for retorts made of EVOH has not been obtained. C Problems to be Solved by the Invention The present invention aims to provide a packaging material for retorts that is free from the above-mentioned drawbacks and has excellent hot water resistance and gas permeation resistance. D. Means for Solving the Problems As a result of extensive research, the present inventors have discovered that the third component is a modified compound represented by the following general formula ().
By adding a hot water resistance improvement aid to EVOH as necessary and performing appropriate heat treatment, it is possible to
It was discovered that much superior hot water resistance can be obtained compared to EVOH, and the present invention was completed. (R ¹ is a lower alkylene group, R ² has 1 to 40 carbon atoms
(alkyl group) E Effects Laminated films, sheets, containers, etc. using modified EVOH according to the present invention have much better hot water resistance than those using conventional EVOH, and Gas permeability comparable to
It has aroma retention properties, oil resistance, etc., and is suitably used in various packaging fields, particularly in the food packaging field, and in the food packaging field that requires boiling or retort sterilization. F More detailed description of the invention The EVOH of the present invention is a saponified modified ethylene-vinyl acetate copolymer containing a third component represented by the following general formula (), with an ethylene content of 20 to 60 mol%, preferably It is preferable that the saponification degree of the vinyl acetate component of the copolymer is 20 to 55 mol %, the degree of saponification of the vinyl acetate component of the copolymer is 95 mol % or more, and the content of the third component is 0.5 to 5 mol %. A more preferred range of the third component is 0.5 to 3 mol%. (R ¹ is a lower alkylene group, R ² has 1 to 40 carbon atoms
(alkyl group) If the ethylene content is less than 20 mol%, not only will it be difficult to achieve the effects of the present invention, but gas permeation resistance at high humidity will be impaired. In addition, the ethylene content exceeds 60 mol% or the degree of saponification is
If it is less than 95 mol%, gas permeability will decrease. Furthermore, if the content of the third component is less than 0.5 mol %, the effects of the present invention will be difficult to achieve, and if it exceeds 5 mol %, the gas permeability will decrease, making it impossible to maintain the original characteristics of EVOH. The EVOH of the present invention can be industrially produced by a conventionally known method. That is, in the presence or absence of alcohol such as methanol, ethylene, vinyl acetate, and the substance represented by the above general formula () are mixed with a known radical polymerization initiator such as α,α'-azobisisobutyronitrile. The resulting copolymer is then saponified in an alcohol solvent using an alkali catalyst such as sodium hydroxide. As the third component, a substance represented by the above general formula () is used, including N-methoxymethylacrylamide, N-methoxyethyleacrylamide, N-methoxyethyleacrylamide,
-Ethoxymethylacrylamide, N-(n-propoxymethyl)acrylamide, N-isopropoxymethylacrylamide, N-(n-butoxymethyl)acrylamide, N-(n-butoxyethyl)acrylamide, N-isobutoxymethylacrylamide, etc. It is preferred, especially N-(n
-butoxymethyl)acrylamide is preferred.
The preferred carbon number of the lower alkylene group for R ¹ is 1 to 5
It is. Further, the alkyl group for R ² is a linear or branched alkyl group, and the alkyl group preferably has 1 to 20 carbon atoms. Although the modified EVOH of the present invention can be used alone as a packaging material, it is preferably used in a laminate with other thermoplastic resins. In this case, the EVOH layer is the inner layer,
It can be used regardless of whether it is an outer layer or an intermediate layer, and in particular, it can be boiled or retorted even when used in the outermost layer, something that conventional EVOH cannot match at all. As a method for forming the laminate, known methods such as coextrusion, co-injection, lamination, and solution coating can be applied. In this case, as an aid to improve the hot water resistance of EVOH, ammonium salts of strong acids such as ammonium chloride and ammonium sulfate, inorganic acids such as sulfuric acid and phosphoric acid, and organic acids such as oxalic acid, lactic acid, acetic acid and formic acid may be added to EVOH. It is mixed and heat treated. For individual melt molding, coextrusion, and coinjection,
[η] (intrinsic viscosity measured at 30°C in a mixed solvent of 85% by weight of phenol and 15% by weight of water) of EVOH is preferably 0.07 to 0.17/g. It is determined by viscosity compatibility. For solution coating, EVOH [η]
is preferably 0.03 to 0.12/g. From the viewpoint of workability in solution coating, it is preferable that the viscosity is low, but from the viewpoint of the mechanical properties of the coated film, if [η] is too low, it will be a practical problem. The various laminate containers obtained in this way are
Suitable for use as a packaging container for boiled or retort foods. The present invention will be explained in more detail with reference to examples below, but these examples are not intended to limit the present invention in any way. (% in the examples indicates weight % unless otherwise specified) G Examples Example 1 N-(n-butoxymethyl)acrylamide content 1 mol%, ethylene content 32 mol%, saponification degree of vinyl acetate component 99.2 Mol% modified EVOH {[η]=
0.1/g} was supplied to an extruder and melted into a film using a T-shaped die at 220°C to obtain a film with a thickness of 15 μm. This film was immersed in a 10% ammonium chloride aqueous solution at 50°C for 2 minutes, the surface was washed with water, dried at 80°C, and further heat-treated at 120°C for 15 seconds. -11,
(manufactured by Mitsui Polychemicals) was extrusion coated to a thickness of 50μ at 300°C to obtain a two-layer EVOH/polyethylene film. EVOH with this laminated film
A bag was prepared using the outer layer, and the oxygen permeability and hot water resistance were examined. Table 1 shows the results. Control example 1 Unmodified EVOH with an ethylene content of 32 mol% and a saponification degree of vinyl acetate component of 99.3 mol% {[η]=0.1/
A bag made of EVOH/polyethylene double-layer film was obtained in the same manner as in Example 1 using the same method as in Example 1, and the same experiment as in Example 1 was conducted. The results are shown in Table 1. Control Example 2 Modified EVOH with N-(n-butoxymethyl)acrylamide content of 1 mol%, ethylene content of 61 mol%, and saponification degree of vinyl acetate component of 99.2 mol% {[η]=
0.085/g} in the same manner as in Example 1.
Obtain an EVOH/polyethylene double layer film bag,
An experiment similar to Example 1 was conducted. The results are shown in Table 1.

[Table] Condition after immersion Example 2 Modified EVOH with N-ethoxymethylacrylamide content of 2 mol%, ethylene content of 35 mol%, and saponification degree of vinyl acetate component of 99.2 mol% {[η] = 0.07/
g} in a mixed solvent of n-propanol/water (55/45 weight ratio) (containing 0.5% ammonium chloride) at 60°C.
to obtain a solution with an EVOH concentration of 15%. Polypropylene (Noblen MA-6, manufactured by Mitsubishi Yuka)
After applying 10μ of urethane adhesive (AD-300, manufactured by Toyo Morton) to a stretch-blow-molded bottle with a volume of 0.5 mm and a body thickness of 0.6 mm, it was immersed in the above EVOH solution, dried at 80 °C, and then heated at 110 °C. Heat treatment was performed for 15 seconds to obtain a container having an EVOH coating layer with a thickness of 8 μm. Table 2 shows the results of examining the oxygen permeability, carbon dioxide gas permeability, and hot water resistance of this container. Control example 3 Modified EVOH with N-ethoxymethylacrylamide content of 5.5 mol%, ethylene content of 35 mol%, and saponification degree of vinyl acetate component of 99.2 mol% {[η] = 0.07
/g}, a bottle was obtained through the same operation as in Example 2, and the same experiment as in Example 2 was conducted. The results are shown in Table 2. Control example 4 Modified EVOH with an N-ethoxymethylacrylamide content of 2 mol%, an ethylene content of 15 mol%, and a saponification degree of vinyl acetate component of 99.3 mol% {[η] = 0.09/
g} using the same procedure as in Example 2 (however, the mixed solvent composition was n-propanol/water = 40/
60) A bottle was obtained and the same experiment as in Example 2 was conducted. The results are shown in Table 2.

[Table] Condition after immersion Example 3 N-isobutoxymethylacrylamide content 3
Mol%, modified EVOH with ethylene content of 40 mol% and saponification degree of vinyl acetate component of 99.3 mol% {[η] = 0.095
/g} as the intermediate layer, the inner and outer layers are polypropylene (Noblen MA-6, manufactured by Mitsubishi Yuka), and the adhesive layer is modified polypropylene (Admer QF500, manufactured by Mitsui Petrochemical). Obtained by coextrusion. This sheet was formed using solid-phase air pressure forming at a sheet temperature of 145℃ with an inner diameter of 100 mm and a depth of 100 mm.
A cylindrical cup of 100 mm and wall thickness of 0.5 mm was obtained. outer layer,
The thickness ratio of adhesive layer, intermediate layer, adhesive layer, and inner layer is 45:
It was 2.5:5:2.5:45. Table 3 shows the results of examining the oxygen permeability and hot water resistance of this cup. Control example 5 N-isobutoxymethylacrylamide content
Modified EVOH {[η]= 0.3 mol%, ethylene content 40 mol%, saponification degree of vinyl acetate component 99.3 mol%
0.095/g} was treated in the same manner as in Example 3 to obtain a cup, and the same experiment as in Example 3 was conducted. The results are shown in Table 3.

[Table] Condition after immersion Example 4 A bag with a size of 12 cm x 16 cm was made using the EVOH/polyethylene double layer film obtained in Example 1, filled with cooked curry sauce, heat sealed, and then autoclaved. Medium, heating water temperature 120℃
Retort sterilization treatment was performed for 30 minutes. When this was stored at room temperature, there was no change in color or taste even after 6 months. On the other hand, when a similar experiment was conducted using the two-layer film obtained in Comparative Example 1, the curry changed color and began to spoil after 4 days.

Claims (1)

[Claims] 1. The third component is represented by the following general formula (),
Saponification degree of vinyl acetate component of modified ethylene-vinyl acetate copolymer: 95 mol% or more, ethylene content: 20
A packaging material with excellent hot water resistance, comprising a saponified modified ethylene-vinyl acetate copolymer having a content of ~60 mol% and a third component content of 0.5~5 mol%. (R ¹ is a lower alkylene group, R ² has 1 to 40 carbon atoms
(alkyl group) 2) The packaging material having excellent hot water resistance according to claim 1, wherein the packaging material is a packaging material for a retort.