JP2934286B2 - Polystyrene sheet for forming drawn containers - Google Patents

Description

The present invention relates to a polystyrene sheet for forming a drawn container having barrier properties, heat resistance, and oil resistance.
More specifically, the present invention relates to a polystyrene-based sheet which is excellent in food preservability and microwave resistance and is particularly applied to the field of food packaging containers as a molding sheet for cup-shaped or bowl-shaped containers and trays.

[Conventional technology]

Conventionally, polystyrene foam containers (PSP), laminated products of PSP and polystyrene or high-impact polystyrene (HIPS) films, and polystyrene-based sheets such as general-purpose polystyrene (GP) sheets have been used as one of the methods for producing molded polystyrene containers. Is drawn by a vacuum forming method or a pressure forming method.

However, the polystyrene sheet molded container manufactured in this manner has the following problems.

A) The gas permeability of oxygen, water vapor, etc. was high, and the preservability of the contents was significantly insufficient.

(B) Heat resistance and oil resistance were insufficient, and when the contents in the tray were warmed in a microwave oven, troubles such as deformation and attack by oil frequently occurred.

In order to solve these problems, measures for improving heat resistance and oil resistance by laminating a film having a low gas permeability, blending another polymer with polystyrene, or copolymerizing are being studied.

[Problems to be solved by the invention]

However, none of them satisfies all of the transmittance of oxygen, water vapor, gas, etc., heat resistance and oil resistance, and has not been put to practical use due to a large increase in cost.

[Means and actions for solving the problem]

The present inventors have conducted extensive studies to provide a polystyrene sheet for drawn containers having a high gas barrier property, heat resistance, and oil resistance.As a result, a coating film of a specific vinylidene chloride-based copolymer resin latex was obtained. The present inventors have found that polystyrene-based sheets exhibit excellent performance, and have accomplished the present invention.

That is, the present invention relates to a sheet having a polystyrene-based resin as a base resin and having at least one surface having a coating film of a vinylidene chloride-based copolymer resin latex having a thickness of 3 to 40 μm.
The vinylidene chloride copolymer resin latex has a vinylidene chloride unit content of 88 to 93% by weight, a relative crystallinity of 0.90 to 1.35, and a tensile breaking elongation at 80 ° C of 80%. The above is a polystyrene sheet for forming a drawn container, wherein the crystal melting peak temperature in DSC is 120 to 170 ° C.

The feature of the present invention is that by specifying the structure and physical properties of the coating film of the vinylidene chloride-based copolymer resin latex, both the workability of drawing and the barrier property, heat resistance, and oil resistance imparting properties to the product container are provided. The point is to have a good balance.

Polystyrene resin used in the present invention, styrene,
A polymer having a styrene-based vinyl monomer such as methyl styrene or dimethyl styrene as a main constituent unit, and a copolymer with another vinyl monomer such as acrylic acid, methacrylic acid or an alkyl ester thereof, acrylonitrile, acrylamide, etc. It may be a polymer. Sheets can be manufactured according to conventional methods.

The vinylidene chloride-based copolymer resin latex used in the present invention is an aqueous dispersion of a resin obtained by emulsifying and copolymerizing vinylidene chloride and a vinyl monomer. The vinylidene chloride unit content must be 88 to 93% by weight. is there. If the content is less than 88% by weight, high crystallinity cannot be obtained, and the barrier properties, heat resistance and oil resistance are insufficient. On the other hand, if it exceeds 93% by weight, on the contrary, the crystallinity is too high, and the coating film has no practical flexibility and cannot be drawn.

The vinylidene chloride copolymer resin latex used in the present invention must have a relative crystallinity of 0.90 to 1.35 described later. If the relative crystallinity is less than 0.90, the barrier properties, heat resistance and oil resistance are insufficient, and if it exceeds 1.35, drawing cannot be performed.

The vinylidene chloride-based copolymer resin latex used in the present invention must have a breaking elongation at 80 ° C. described later of 80% or more. If it is less than 80%, it will not be able to follow the deformation at the time of drawing, causing breakage of the coating film and peeling from the base polystyrene sheet. The latex needs to have a crystal melting peak temperature in DSC of 120 to 170 ° C. which will be described later. If the crystal melting peak is lower than 120 ° C., the heat resistance is insufficient and the composition does not have microwave resistance. On the other hand, when the temperature exceeds 170 ° C., deformation cannot be followed during container molding.

The polystyrene-based sheet for a drawn container of the present invention is produced by a method of forming a coating film of a vinylidene chloride-based copolymer resin latex on at least one surface of a polystyrene-based resin sheet (hereinafter abbreviated as a base sheet). As a method for forming a coating film, a normal coating method such as an air knife or a bar coater is used, and the coating film is dried by hot air or the like. Latex may be directly applied to the substrate sheet and dried, or latex may be applied to a film of polystyrene or HIPS in advance and dried, and then laminated on the substrate sheet by a method such as fusion lamination to obtain the sheet of the present invention. In application, it is also preferable to perform a corona discharge treatment on the base sheet or apply an anchor agent. The coating film of the vinylidene chloride-based copolymer resin latex may be formed on any one side, both sides, or the sandwich side of the polystyrene sheet for forming a drawn container of the present invention.

The polystyrene sheet for forming a drawn container according to the present invention is a composite sheet having a thickness of 0.1 to 4 mm having a coating film of a vinylidene chloride copolymer resin latex having a thickness of 3 to 40 μm on at least one surface of an expanded polystyrene sheet or a non-expanded polystyrene sheet. It is. Formability is poor when the sheet thickness is less than 0.1 mm or more than 4 mm. When the base sheet is a foamed polystyrene sheet, it is preferably adjusted to a sheet of the present invention having a thickness of 2 to 3 mm, and when it is a non-expanded polystyrene sheet, it is preferably adjusted to a sheet of the present invention having a thickness of 0.15 to 0.5 mm. If the coating thickness of the vinylidene chloride copolymer resin latex is less than 3 μm, the barrier properties
Heat resistance and oil resistance are insufficient, and even if the thickness exceeds 40 μm, a large improvement in the performance is not recognized, but rather, the film formation state is deteriorated. 5
2525 μm is preferred. The most preferred range of the composition and physical properties of the latex is a vinylidene chloride unit content of 89 to 92% by weight, a relative crystallinity of 1.00 to 1.30, and a tensile elongation at break at 80 ° C.
The crystal melting peak temperature in DSC is more than 150%, 130-165 ° C.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to examples. Evaluation methods and measurement methods in the examples were based on the following methods.

(1) Vinylidene chloride unit content of vinylidene chloride-based copolymer resin latex Chlorine content of dry resin obtained by coagulation of vinylidene chloride-based copolymerized resin latex with methanol was determined by baking method of oxygen flask of Shni-ger. It was shown by the converted vinylidene chloride content from the amount.

(2) Relative crystallinity A vinylidene chloride-based copolymer resin latex (50% solids) was applied on a biaxially oriented polypropylene film having a thickness of 22 μm with a Mayer bar, and dried at 75 ° C. for 2 minutes to obtain a thickness of 10 μm.
μm, and the coated film was peeled off from the biaxially stretched polypropylene film and aged at 40 ° C. for 36 hours. Then, the red color of 1150 to 900 cm ⁻¹ was measured with an infrared spectrophotometer (Nihon Bunko Kogyo IR-G). The external absorption spectrum was taken, and the ratio of the absorbance at ₁₀₄₆ cm ^-1 to 1070 cm ^-1 (A ₁₀₄₆ / A ₁₀₇₀ ) was defined as the relative crystallinity.

(3) Tensile breaking elongation at 80 ° C A vinylidene chloride-based copolymer resin latex (50% solids) was applied on a 22 µm thick biaxially oriented polypropylene film using a Mayer bar, and dried at 75 ° C for 23 minutes. 20μ thickness
m, and the coating was peeled off from the biaxially oriented polypropylene film and aged at 40 ° C. for 36 hours.
m, cut out to a width of 15 mm, 2 at 80 ° C in a tensile tester
After holding for minutes, the tensile elongation at break was measured in an atmosphere at 80 ° C.

Tensile conditions: gripping interval: 50 mm Peeling speed: 1,000 mm / min (4) Crystal melting peak by DSC Using the same coating film as used for the measurement of tensile elongation at break, a differential scanning calorimeter (DT-Shimadzu Corporation) 15 ℃ at 30B)
The temperature of the endothermic peak at a heating rate of 1 min was measured.

(5) Formability Cracking and peeling of the coating film during drawing were observed.異常 indicates that no abnormality was observed, and X indicates cracking or peeling.

(6) Food preservability Store the contents of commercially available cup noodles (without soups and individual packaging) in a draw-formed container, seal the aluminum lid, and store in a 40 ° C, 90% RH atmosphere for one month. Left for a while.な い indicates that no abnormality was observed, and × indicates that the soup was dissolved due to moisture absorption.

(7) Microwave oven properties Four commercially available croquettes were packed in a draw-formed container, covered with a stretch film made of vinyl chloride, and treated in a microwave oven (National NE-M315) for 1 minute to warm the croquettes. At this time, 異常 indicates that no abnormality was observed in the container, and X indicates that the container was deformed or the bottom surface was damaged.

The following is used as an abbreviation for the resin composition in the examples.

VDC: vinylidene chloride MA: methyl acrylate MMA: methyl methacrylate BA: n-butyl acrylate AN: acrylonitrile AA: acrylate MAA: methacrylate HEA: 2-hydroxyethyl acrylate Example 1 and Comparative Examples 1 5 Apply various vinylidene chloride-based copolymer resin latexes shown in Table 1 to the thickness shown in Table 1 with a Mayer bar on one side of a 2.5 mm thick PSP sheet (expansion ratio 7 times)
For 3 minutes.

Thereafter, the polystyrene sheet was aged at 40 ° C. for 36 hours, and then vacuum-molded (heater temperature: 180 ° C.) into the shape shown in FIG. . Table 1 shows the results.

Example 2 and Comparative Examples 6 to 7 The vinylidene chloride copolymer latex used in Example 1 was applied to a corona discharge treated surface of a 30 μm thick HIPS film with a Mayer bar, and dried at 75 ° C. for 3 minutes. 15μ thickness
m of the coating film was formed. After aging the film at 40 ° C. for 36 hours, the PSP sheet used in Example 1 and the H
The polystyrene sheet was obtained by laminating the IPS surface (untreated surface). The polystyrene sheet was vacuum-formed in the same manner as in Example 1 with the coating film as the outer surface, and the food preservability was evaluated. Table 2 shows the results.

Example 3 and Comparative Examples 8 to 10 The polystyrene-based sheet of Example 1 was vacuum-formed into the shape shown in FIG. 2 with the coating surface inside, and the microwave resistance was evaluated. Table 3 shows the results.

Examples 4 to 5 and Comparative Example 11 After a corona discharge treatment on both sides of a GP sheet having a thickness of 150 μm, various vinylidene chloride copolymer resin latexes shown in Table 4 were applied to both sides of the sheet with a Meyer bar to a thickness of 13 μm each. A coating was formed (drying at 75 ° C. for 2 minutes each). The polystyrene sheet is pressure-formed into a shape shown in FIG.
° C), and the microwave resistance was evaluated. Table 4 shows the results.

[Effect of the Invention] The polystyrene sheet for forming a drawn container of the present invention has barrier properties, heat resistance and oil resistance, has excellent moldability, forms a uniform coating film on the container surface, and has good food preservability. It is.

[Brief description of the drawings]

1 and 2 are perspective views of containers manufactured in Examples and Comparative Examples. FIG. 1 is a cup-shaped container, and FIG. 2 is a tray-shaped container.

Claims (1)

(57) [Claims] 1. A composite sheet having a thickness of 0.1 to 4 mm having a coating film of a vinylidene chloride copolymer resin latex having a thickness of 3 to 40 μm on at least one surface of a sheet using a polystyrene resin as a base resin. The vinylidene copolymer resin latex has a vinylidene chloride unit content of 88 to 93% by weight, a relative crystallinity of 0.90 to 1.35, a tensile breaking elongation of 80% or more at 80 ° C, and a crystal melting peak temperature in DSC. A polystyrene sheet for forming a drawn container, characterized in that the temperature is from 120 to 170 ° C.