JPH0778144B2 - Foam sheets for food packaging containers, etc. - Google Patents

Description

TECHNICAL FIELD The present invention relates to a foamed sheet for food packaging containers and the like, and more specifically, a chilled food product and a frozen food product having excellent heat resistance and moldability and having little odor. , A foam sheet suitable for a packaging container for retort foods and the like.

[Conventional technology and problems]

Today, chilled foods, frozen foods, and retort foods are widely used as instant foods not only as mere preserved foods at the beginning but also because of the widespread use of microwave ovens and the variety of contents.

Conventionally, these food containers have been heat sterilized (120 ° C
Molded containers made of unfoamed polypropylene sheet or heat-resistant polyester are used because there is no inexpensive foam sheet in the world that can withstand (30 minutes or more). However, these unfoamed containers have problems in that the entire container becomes hot during microwave oven cooking and cannot be carried by hand, and in the case of polypropylene, the container is deformed.

On the other hand, as a resin having excellent heat resistance and moldability, a copolymer resin of polyphenylene ether and styrene and a mixed resin of polyphenylene ether and polystyrene are known, but foams thereof have hardly been put into practical use. One of the reasons for this is that we could not beat the cost competitiveness in the foam market, but the peculiar odor of this resin also plays a major role. This odor is quite fatal especially as a food packaging material.

[Means for solving problems]

By the way, polyphenylene ether has an odor peculiar to a polymer, and as a cause of this odor, a polymerization catalyst, an antioxidant, etc. are considered. As the odor component, an aldehyde-based or amine-based substance is shown, but the component directly related to the odor has not been clarified. In other words, the odor of polyphenylene ether is not the odor of a single component, but the complex odor generated from the complex component, so that it is very difficult to analyze the component.

On the other hand, it is impossible to eliminate the odor in the present polymerization of polyphenylene ether, and the odor can be suppressed by post-treatment such as vent extrusion or acid washing.
However, it is necessary to make the concentration of residual odor in the resin extremely low in order to obtain an odor level that can be used in food applications. Each odor component is considered to be in phase equilibrium with polyphenylene ether, but if it is in phase equilibrium, one odor component can be represented, although the odor is generated by the mixed component.

Therefore, as a result of earnestly examining various odor components and odors,
It was surprisingly found that toluene, which is not generally considered as an odor component, can be a representative characteristic value of polyphenylene ether odor.

When using a polyphenylene ether resin, the amount of the odorous component should be appropriately determined depending on the application. Even the currently marketed polyphenylene ether resin does not cause any problem when used at low temperature as an unfoamed container. However, when it is used as a heat-resistant foaming container, it is unusable because it is used at a high temperature of 100 ° C. or higher and the odor becomes extremely large due to expansion of the specific surface area due to foaming. Therefore, the vent extrusion of commercially available polyphenylene ether resin was repeated to measure the amount of toluene in the volatile components of the resin with reduced odor components, and at the same time, a sensory test was performed when it was used as a foaming container. It has been found that a foamed sheet that can be used as a food container can be obtained by suppressing the amount of toluene in the sex ingredient, and has completed the present invention.

That is, the first aspect of the present invention is that the amount of toluene in the volatile component is 5 p
A foamed sheet for a food packaging container or the like, which is obtained by mixing a mixed resin of polyphenylene ether and polystyrene suppressed to pm or less with a foaming agent under high temperature pressure and extruding into a low pressure zone. The amount of toluene was suppressed to 5 ppm, polyphenylene ether and styrene were both mixed with a foaming agent under high temperature and high pressure, and the foaming sheet for food packaging containers and the like was formed by extruding into a low pressure zone. .

In the present invention, the amount of toluene in the volatile component is 0.5 g of resin pellets (specific surface area 1 to 31 / mm) placed in 20 cc of a vial and aged in an oven at 150 ° C. for 1 hour to obtain the amount of toluene in the vial. Can be easily and accurately measured by measuring by gas chromatography.

Examples of the polyphenylene ether used in the present invention include poly (2,6-dimethylphenylene-1,4-ether) and poly (2-methyl-6-ethylphenylene-1,4).
-Ether), poly (2,6-diethylphenylene-1,4-
Ether), poly (2-methyl-6-n-propylphenylene-1,4-ether), poly (2-methyl-6-n)
-Butylphenylene-1,4-ether), poly (2-methyl-6-chlorophenylene-1,4-ether), poly (2-methyl-6-bromophenylene-1,4-ether), poly (2 -Ethyl-6-chlorophenylene-1,4
-Ether).

Examples of the copolymerized styrene or blended polystyrene used in the present invention include styrene, α-methylstyrene, 2,4-dimethylstyrene, monochlorostyrene, dichlorostyrene, p-methylstyrene and ethylstyrene. However, styrene is preferable in order to sufficiently exhibit the thermal stability of polyphenylene ether.

In any of the above polyphenylene ethers and (poly) styrenes, one or more compounds copolymerizable with each, such as acrylonitrile, methacrylonitrile, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate or the like, or Those obtained by copolymerizing two or more kinds are also included.

The ratio of polyphenylene ether to (poly) styrene of the foamed sheet of the present invention is 40 to 90% by weight of polyphenylene ether.
60 to 10 parts by weight of (poly) styrene is suitable for parts by weight. When the polyphenylene ether is less than 40 parts by weight, not only the heat resistance becomes insufficient, but also when both are kneaded into pellets, the pellets become cloudy due to insufficient dissolution of the polyphenylene ether, and extrusion is performed using this pellet. When foaming, bubble unevenness may occur in the foam.
If it exceeds 90 parts by weight, a general extruder cannot perform extrusion foaming due to insufficient temperature rise or overload. Even if extrusion foaming is possible, shearing heat is large and the resin temperature cannot be lowered, and a good foam cannot be obtained.

In the present invention, the amount of toluene in the volatile component is suppressed to 5 ppm or less, preferably 3 ppm or less. The method for suppressing the reduction is not particularly limited, and known methods such as venting and acid washing can be used. In the case of a mixed resin, either the polyphenylene ether before mixing or the mixed resin may be suppressed to the above value.

The foamed sheet of the present invention is obtained by kneading a copolymer resin of polyphenylene ether and styrene or a mixed resin of polyphenylene ether and polystyrene and a mixed resin with an extruder to form pellets, and after foaming agent is pressed into the pellets at high temperature and high pressure, and then kneaded. A method of adjusting the foaming optimum temperature and extruding into a low pressure zone (usually in the atmosphere) is suitable. By using the pre-pelletized material as the raw material in this way, especially when a mixed resin of polyphenylene ether and polystyrene is used, the mixing dispersibility of both is improved, and a foam having uniform cells with a high expansion ratio is obtained. Since the pellets obtained by kneading in this way have improved mixing and dispersibility, it is possible to further add polystyrene to the pellets within the above mixing ratio range. In this case, the amount of polystyrene added is preferably 150 parts by weight or less with respect to 100 parts by weight of the pellets. 150
If added in excess of parts by weight, bubble unevenness occurs.

As the foaming agent used in the present invention, a known foaming agent is used, but dichlorodifluoromethane (Freon 12),
Hydrocarbon-based blowing agents based on iso-butane are preferred. The latter is particularly suitable because there is no problem of environmental pollution or destruction. The hydrocarbon-based blowing agent containing iso-butane as a main component preferably has a composition of 50 to 100% by weight of iso-butane and 50 to 0% by weight of n-butane.

INDUSTRIAL APPLICABILITY The foamed sheet of the present invention has reduced heat odor and excellent heat resistance and moldability, and thus is suitably used for food containers (especially for retorts and microwave ovens) and applications where odor is not desired.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these.

Example 1 Commercially available polyphenylene ether-polystyrene blend resin "Cope Ace" (trade name, manufactured by Mitsubishi Gas Chemical Industry Co., Ltd., polyphenylene ether / polystyrene = 50)
/ 50) was vent-extruded with a twin-screw vent extruder, and the obtained pellets were heated at 150 ° C. for 1 hour and heated to measure the gas generated by gas chromatography.

Next, these pellets were mixed in a 40 to 50φ tandem extruder with 3 parts by weight of iso-butane as a foaming agent and 100 parts by weight of the resin, and extruded into a sheet form from a circular die having a diameter of 75φ.
A foamed sheet having a thickness of 1.5 mm, a width of mm and a foaming ratio of 10 times was obtained.

This foamed sheet was molded into a cup having a diameter of 150φ and a depth of 100, water was put in the container and boiled in a microwave for 3 minutes, and then the odor of the container and boiling water when taken out from the microwave was examined. The results are shown in Table 1. The odor was evaluated according to the following four grades.

◎: No abnormality ○: Slight odor △: Very bad odor ×: Strong odor Example 2 The same operation as in Example 1 was repeated except that a commercially available polyphenylene ether-polystyrene copolymer resin "Zylon" (trade name, manufactured by Asahi Chemical Industry Co., Ltd., polyphenylene ether / polystyrene = 50/50) was used. . The results are shown in Table 2.

[Operation / Effect] As described above, according to the present invention, heat resistance and moldability are excellent,
A foamed sheet with reduced odor is also provided.

Further, in the present invention, the odor of the polyphenylene ether-based copolymerization or blended resin can be determined using the amount of toluene that can be easily measured by gas chromatography as an index, so its practical significance is extremely large.

Claims (3)

[Claims] 1. A foamed sheet for food packaging containers, which is obtained by mixing a mixed resin of polyphenylene ether and polystyrene in which the amount of toluene in the volatile component is suppressed to 5 ppm or less with a foaming agent under high temperature pressure and extruding into a low pressure zone. . 2. A food packaging container or the like prepared by mixing a copolymerization resin of polyphenylene ether and styrene in which the amount of toluene in the volatile component is suppressed to 5 ppm with a foaming agent under high temperature and high pressure and extruding into a low pressure zone. Foam sheet. 3. The foamed sheet according to claim 1, wherein the amount of toluene in the volatile component is suppressed to 3 ppm or less.