JPH0247495B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low-foaming moldable styrenic resin sheet containing a rubber component so as to have a specific bending strength. Currently, various synthetic resin sheets are used as food storage containers, and most of these are formed into desired shapes by air pressure forming and/or vacuum forming. Among these synthetic resin sheets for manufacturing food storage containers, expanded polystyrene sheets (generally abbreviated as PSP) have a beautiful pearlescent appearance, are rich in heat insulation, and It is widely used because it is lightweight. However, this expanded polystyrene sheet
Because of the lack of toughness, the wall thickness must be increased in order to create a container that requires strength. Increasing the wall thickness creates a new problem in that the container becomes bulky and increases the cost of transporting the container. Also,
When using expanded polystyrene sheets, reinforcing ribs may be provided on the container wall to increase the strength of the product container. Expanded polystyrene sheets are inferior to other synthetic resin sheets in their moldability, especially in so-called "shaping", so they are often used in product containers.
The disadvantage is that it is difficult to form reinforcing ribs with an excellent appearance. The inventors of the present invention have developed a method for producing polystyrene foam without sacrificing its beautiful appearance, heat insulation properties, etc., which are the characteristics of foamed polystyrene sheets.
The present invention was completed as a result of intensive studies aimed at providing a container-forming sheet that eliminates the disadvantages of lack of toughness, excessive bulk, poor moldability, etc. . That is, the gist of the present invention is to blend a styrene resin containing a rubber component in the range of 1.5 to 8% by weight with a chemical foaming agent and extrude it into a sheet shape, so that the foaming ratio is 1.1 times or more. Less than 1.5 times thicker
The present invention relates to a styrenic resin sheet for molding, which is in the range of 0.1 to 1 mm and has a bending strength of 5 or more as measured in accordance with JIS P8115. In the present invention, the styrenic resin containing a rubber component within the above range may include a polymer blend of a rubber component and a styrene resin that does not contain a rubber component, or a rubber component grafted with a monomer constituting the styrene resin. Also included are graft (co)polymers. The rubber component refers to natural rubber, synthetic rubber derived from conjugated dienes, and other substances exhibiting rubber-like behavior. Specifically, for example, natural crepe rubber, polybutadiene, butadiene-styrene copolymer rubber (SBR), butadiene-acrylonitrile copolymer rubber (NBR), polyisoprene,
Polyisobutylene, isoprene-isobutylene copolymer rubber, polychloroprene, ethylene-propylene copolymer rubber, ethylene-propylene-diene monomer ternary copolymer rubber, styrene-butadiene block copolymer rubber, ethylene-vinyl acetate Examples include copolymer rubber, alkyl acrylate (co)polymer rubber, alkyl methacrylate (co)polymer rubber, and the like. The styrene resin refers to polystyrene, a copolymer containing styrene as a main component, and a monomer copolymerizable with the polystyrene. Such monomers include α
-Methylstyrene, P-methylstyrene, 2,4
- Dimethylstyrene, acrylonitrile, methacrylonitrile, acrylic acid alkyl esters, methacrylic acid alkyl esters, and the like. Note that the graft (co)polymer is produced by producing (polymerizing) the rubber component during the production of styrenic resin.
It can be obtained by (co)polymerizing the monomers in the system. The rubber component contained in styrene resin is 1.5~
It is necessary that the content be in the range of 8% by weight. When the rubber component is less than 1.5% by weight, the folding strength of the sheet becomes weak, and when it is more than 8% by weight, the appearance of the sheet becomes poor and the desired sheet cannot be obtained. The styrenic resin sheet for molding according to the present invention is
It is a sheet formed by blending a chemical foaming agent with a styrene resin containing the above-mentioned rubber component, and does not include a sheet stretched in biaxial directions. Chemical blowing agents include low-boiling hydrocarbon compounds that vaporize at the sheeting temperature of styrene resins containing rubber components, such as propane, butane, pentane, petroleum ether, etc.; Organic blowing agents that decompose to generate gas at temperature, such as azobisisobutyronitrile, azodicarbonamide, dinitrosopentamethylenetetramine, benzenesulfonylhydrazide, P-P'-oxybisbenzenesulfonylhydrazide. , trihydrazinotriazine, N,
Examples include N'-dinitroso-N,N'-dimethylterephthalamide and azobishexahydrobenzonitrile. However, it is not limited to these examples. When forming a styrene resin containing a rubber component into a sheet, various types and amounts of additives such as nucleating agents, dyes and pigments, stabilizers,
Lubricants, fillers, etc. can be added. A T-die is preferably used to add a chemical foaming agent to a styrene resin containing a rubber component and extrude it into a sheet. The styrenic resin sheet for molding according to the present invention is
The foaming ratio is within the range of 1.1 times or more and less than 1.5 times. If the expansion ratio is less than 1.1 times, the resin sheet will not have an improved appearance or heat insulation properties, which is not preferable. When the foaming ratio is greater than 1.5 times,
This is not desirable because the resin sheet is bulky, and
If it is larger than 2.1 times, the toughness will not be improved either.
The amount of the foaming agent added may be adjusted so that the foaming ratio of the resin sheet falls within the above range. The styrenic resin sheet for molding according to the present invention is
The thickness is in the range of 0.1 to 1.0 mm. Thickness is 0.1mm
If it is smaller, the resin sheet will be too thin,
It is not preferred because it is not suitable for molding various containers. If the thickness is greater than 1.0 mm, the rib structure for reinforcing the container wall cannot be accurately formed on the product container when forming the desired container by air pressure forming and/or vacuum forming. Otherwise, the object of the present invention, which is to reduce the bulk, is not achieved, which is not preferable. The styrenic resin sheet for molding according to the present invention is
It is made into a sheet so that the folding strength measured in accordance with JIS P8115 is 5 or more. JIS
The folding strength measured in accordance with P8115 represents the repeated bending strength of the resin sheet, and the higher this value, the greater the folding strength. In this case, the test piece is prepared by cutting out the resin sheet along the extrusion direction. If the bending strength is less than 5, the resin sheet has poor toughness and is not practical as a molding sheet, which is not preferable.
In order to make the bending strength of the resin sheet 5 or more, the blending amount of the rubber component, the foaming ratio of the resin sheet, the thickness, etc. may be adjusted within the above ranges. The styrenic resin molding sheet according to the present invention is
It has the following characteristics and has extremely high industrial utility value. (1) The resin sheet according to the present invention has a foaming ratio of
The resin sheet itself is 1.1 times or more and less than 1.5 times (significantly lower than conventional sheets) and has a thickness of 0.1 to 1 mm, so it has excellent rigidity and good "shaping" during molding. And the bulk of the sheet molded product is also small. (2) Since the resin sheet according to the present invention is made of styrene-based resin containing a rubber component in a specific proportion, even if the foaming ratio is low and the thickness is thin, it has significantly greater toughness than conventional foam sheets. Are better. (3) Since the resin sheet according to the present invention has excellent toughness, there is no need to supplement the strength with sheet thickness unlike conventional foam sheets, and therefore the resulting molded product is not bulky. The cost of transporting molded products becomes cheaper. (4) Since the resin sheet according to the present invention has good "shaping" during molding, it is easy to provide ribs on the wall surface of the molded product to increase the strength of the molded product, and the ribs improve the aesthetic appearance of the molded product. can be increased. (5) Since the resin sheet according to the present invention is foamed, it has a beautiful appearance, good heat insulation properties, and light weight, which are the characteristics of conventional foamed polystyrene sheets. Hereinafter, the present invention will be explained in detail based on examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Examples 1 to 5, Comparative Examples 1 to 3 General-use polystyrene (Mitsubishi Monsanto Chemical Co., Ltd.)
manufactured by Dialex HH-102) and styrene.
Butadiene block copolymer (manufactured by Phillips Petroleum Co., Ltd., KR-03, rubber component approximately 22%)
A total of 100 parts by weight was weighed so as to have the ratio shown in the table, 0.1 part by weight of dioctyl phthalate was added as a spreading agent for the chemical blowing agent, and the mixture was stirred and mixed using a ribbon blender for 20 minutes. Next, 0.15 parts by weight of azodicarbonamide as a chemical blowing agent was added to this mixture, and the mixture was further stirred and mixed for 20 minutes. This mixture is kneaded using a normal extruder,
A non-stretched, low-foam sheet with a thickness of approximately 0.3 mm and a foaming ratio of approximately 1.25 times was created by extruding it into a sheet through a T-die. The properties of these sheets were measured as follows and are shown in Table 1. (1) Folding strength Measured in accordance with JIS P8115. (2) Appearance of Sheet The sheet was visually observed and rated as ◎ (extremely good), 〇 (good), △ (poor), and × (extremely poor).

[Table] From Table 1, the following is clear. (a) When the rubber component is less than 1.5% by weight (Comparative Examples 1 and 2), the appearance of the sheet is excellent, but the folding strength is extremely poor. (b) When the rubber component is more than 8% by weight (Comparative Example 3), the folding strength is improved, but the sheet becomes rough on the surface and has an extremely poor appearance. (c) On the other hand, the rubber component contained in the sheet
When the amount is in the range of 1.5 to 8% by weight, the folding strength is excellent, the appearance has a beautiful pearlescent luster, and the surface of the sheet is not rough. Examples 6-8, Comparative Examples 4-5 General-purpose polystyrene (Dialex HH102)
and high-impact polystyrene (Mitsubishi Monsanto Chemical
A total of 100 parts by weight of Dialex HT-190 (manufactured by Co., Ltd.) was weighed so that the content of the rubber component contained in the base resin was 3% by weight, 0.1 part by weight of dioctyl phthalate was added thereto, and a ribbon blender was used. The mixture was stirred and mixed for 20 minutes. Next, azodicarbonamide was added to this mixture in the proportions shown in Table 2, and each
Stir and mix for 20 minutes. This mixture is kneaded using a normal extruder,
It was extruded into a sheet through a T-die to create unstretched, low-foam sheets with a thickness of 0.3 mm and different expansion ratios. The foaming ratio of the obtained sheet was calculated using the following formula from the specific gravity measured in accordance with ASTM D792, and is shown in Table 2. Expansion ratio=specific gravity of unfoamed raw material sheet/specific gravity of foamed sheet The appearance of the obtained sheet was observed with the naked eye in the same manner as in the previous example. The determination results are shown in Table 2.

【table】

[Table] The following is clear from Table 2. (b) When the foaming ratio is smaller than 1.1 (Comparative Example 4), only a few air bubbles are scattered on the sheet,
Does not exhibit a pearlescent appearance. (b) When the foaming ratio is greater than 2.1 times (Comparative Example 5), the sheet will have excessive air bubbles, the surface of the sheet will be rough, and the appearance will be poor. (c) On the other hand, the foaming ratio of the sheet is 1.1 to 2.1.
Those within twice the range have a beautiful pearlescent appearance and do not cause roughness on the sheet surface.

Claims (1)

[Claims] 1 A styrene resin containing a rubber component in the range of 1.5 to 8% by weight is blended with a chemical foaming agent and extruded into a sheet, with a foaming ratio of 1.1 times or more and less than 1.5 times and a thickness of 0.1 to 1 mm. range and JIS
A styrenic resin sheet for molding, characterized by having a folding strength of 5 or more as measured in accordance with P8115.