JPS6366335B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an extruded polystyrene foam sheet with improved secondary formability and a method for producing the same.
More specifically, the present invention relates to an extruded polystyrene resin foam sheet with improved secondary moldability that maintains good secondary foaming power over a long period of time, and a method for producing the same. Extruded polystyrene foam sheets made from polystyrene resins, such as polystyrene resins, maleic anhydride-styrene copolymer resins, AS resins, and ABS resins, have traditionally been used as raw materials for various molded products such as trays and containers. It is used. These extruded foam sheets are obtained by melt-mixing polystyrene resin, various additives such as a blowing agent and a nucleating agent in an extruder, and extruding and foaming the mixture into the atmosphere from a die at the tip of the extruder. This extruded foam sheet is suitably second-formed into a molded product having a predetermined shape by vacuum forming, press molding, etc., and then subjected to mass production. It is known that the secondary formability in this case largely depends on the secondary foaming power of the original extruded foam sheet. However, if such extruded polystyrene foam sheets are not subjected to secondary molding within a short period of time, at most two months after being manufactured, the secondary foaming power will be insufficient due to the loss of residual foaming agent. During secondary molding, the sheet is not expanded tightly into the mold quickly, resulting in poor moldability, making secondary molding practically difficult. Therefore, when an extruded polystyrene foam sheet is used as a raw material for secondary molding, there is a problem that the sheet cannot be kept in stock for a long period of time. This invention was made to solve these conventional problems, and when a small amount of superabsorbent resin is dispersed and added into the extruder during the production of conventional polystyrene extruded foam sheets, the resulting extruded foam This was achieved by discovering the unexpected fact that the secondary foaming power of the sheet was significantly improved. Thus, according to the present invention, there is provided an extruded polystyrene foam sheet with improved secondary moldability, which is made of a mixed resin composition in which a small amount of super absorbent resin is dispersed and blended into a polystyrene resin as a base resin. The super-absorbent resin of this invention means a resin known as a "super-absorbent resin" in the field of synthetic resins, and specifically refers to polyacrylate-based resins, vinyl alcohol-acrylic acid copolymer-based resins, etc. Resin, starch-acrylic acid graft copolymer resin, starch-acrylonitrile copolymer resin, polyvinyl alcohol resin, polyethylene glycol resin,
Examples include carboxymethylcellulose resin. Among these, it is preferable to use sodium polyacrylate, vinyl alcohol-acrylic acid copolymer resin, or starch-acrylic acid graft copolymer resin. Examples of these resins include Sunwet (trade name of Sanyo Chemical Industries, Ltd.), Aqua Keep (trade name of Seitetsu Kagaku Kogyo Co., Ltd.), Sumikagel (trade name of Sumitomo Chemical Industries, Ltd.), and PermaSoap (trade name of Kanebo NSC). It is available under names such as Aquaric (trade name of Nippon Shokubai Kagaku Kogyo Co., Ltd.). On the other hand, the polystyrene resin of the present invention includes various resins that are mainly composed of polystyrene units and are known for use in molding, and specifically include polystyrene resin, acrylonitrile-styrene (AS) resin, Examples include butadiene-styrene (ABS) resin, maleic anhydride-styrene copolymer resin, and the like. The foamed sheet of the present invention is an extruded foamed sheet made of a mixed resin in which a superabsorbent resin is dispersed and blended with the above-mentioned polystyrene resin. It is necessary to keep the content of the super absorbent resin in a small amount with respect to 100 parts by weight of the polystyrene resin, and it is usually 0.1 to 30 parts by weight. If it is less than 0.1 part by weight, the improvement in secondary foaming power is insufficient, and if it exceeds 30 parts by weight, extrusion moldability deteriorates and a uniform foam sheet cannot be formed. In terms of manufacturing and effectiveness, the content ratio of super absorbent resin is 0.5 to 100 parts by weight of polystyrene resin.
Preferably, the amount is 10 parts by weight. The foamed sheet of this invention is produced using a conventional extruder. Specifically, a mixed resin with the above blending ratio is melt-kneaded in an extruder together with various additives such as a foaming agent, a nucleating agent, and a spreading agent, and the melt is passed through a predetermined die at the tip of the extruder into a low-pressure region (usually is obtained by extrusion and foaming (in the atmosphere). As the blowing agent used at this time, it is usually appropriate to use a volatile blowing agent or gas such as a hydrocarbon type, halogenated hydrocarbon type, alcohol type, carbon dioxide type, nitrogen gas type, etc. Decomposed or reactive blowing agents can also be used. Nucleating agents such as talc, white carbon, zeolite, cyclodextrin, baking soda, and titanium oxide are used, and spreading agents include liquid paraffin, polybutene, polyethylene glycol, fatty acid glycol, fatty acids, water, and alcohol. Various materials are used that are liquid under normal pressure at temperatures below 80°C. Therefore, there is no problem even if the foamed sheet of the present invention contains these various additives. During the production, it is necessary to dry blend the polystyrene resin and the water-absorbing resin together with appropriate additives in advance, and then feed this into the extruder. In this case, the polystyrene resin may be in the form of powder, granules, or pellets, but the raw material superabsorbent resin is one that passes through a 35 mesh sieve (Taylor mesh; USA), preferably one that passes through a 60 mesh sieve. It is necessary to use powdered material. this is,
This is because polystyrene resins and superabsorbent resins are incompatible and cannot be sufficiently mixed by melt-kneading alone, which tends to make the surface and inner surface of the foam sheet non-uniform. When using a mixed resin that has been dry-blended in advance using powdered products that have passed through a 35-mesh sieve, the water-absorbing resin is maintained in a uniformly dispersed state in the polystyrene resin even during melt-kneading, and the resulting foamed sheet is A desired foamed sheet with a smooth and uniform surface and a water-absorbing resin evenly dispersed in the foamed sheet can be obtained. The extruded polystyrene foam sheet of the present invention thus obtained maintains its secondary foaming power for a longer period of time than conventional ones, and even after storage for a long period of time (at least two months or more), Good secondary formability such as vacuum forming and press forming. moreover,
The foamed sheet of this invention also has an improved foaming ratio compared to one obtained under similar conditions (other conditions such as the amount of foaming agent and amount of nucleating agent are the same) without dispersing and blending the water-absorbing resin. This also has the effect of saving on blowing agents. Therefore, from another point of view,
The present invention also provides a method for manufacturing a polystyrene resin foam sheet with improved expansion ratio, which comprises adding a small amount of super absorbent resin to the polystyrene resin during extrusion foam molding of the polystyrene resin. be. The reason why the extruded polystyrene foam sheet of the present invention maintains good secondary foaming power over a long period of time is unknown, but it is known that the residual foaming agent gas in the sheet decreases while it is left standing, compared to conventional foam sheets. Therefore, the super absorbent resin dispersed in the sheet of this invention absorbs moisture (water vapor) from the outside air at the same time as the residual gas decreases, and this water vapor and the reduced residual gas are combined. It is believed that these factors together maintain good foamability during secondary molding. The reason why the foaming ratio of the obtained foamed sheet itself is improved is also unknown, but it is thought that the dispersed superabsorbent resin may have acted as a kind of nucleating agent. In any case, the foamed sheet of the present invention has superior secondary foaming power compared to the conventional foamed sheet, and can be kept in stock for a long period of time, making it extremely useful industrially. EXAMPLES This invention will be explained below with reference to Examples, but the invention is not limited thereby. Example 1 100 parts of polystyrene with a melt index of 2.5, 0.1 part of polybutene, 1.0 part of talc, and 3 parts of sodium polyacrylate (Mesh 60; trade name Alonbis)
The components were uniformly mixed in advance using a blender. This was melted and mixed in an extruder with a diameter of 40 mm, and 5.0% by weight of butane was injected and mixed through an injection port provided in the middle of the extruder, and the mixture was extruded and foamed into the atmosphere through a ring mold with a diameter of 30 φ provided at the tip of the extruder. Thickness 1.98mm, width
A foamed sheet of 350 mm and a density of 0.0909 g/cm ³ was obtained. This sheet was then heated in an oven set at 110°C for 16 seconds, and the change in secondary foaming rate over time was measured. The results were as plotted with x in FIG. In this figure, the vertical axis represents the secondary foaming rate (%), and the horizontal axis represents the number of days elapsed. Example 2 Same as Example 1 except that the sodium polyacrylate in Example 1 was changed to 1.0 part of vinyl alcohol-acrylate copolymer powder (Meshyu 80; trade name Sumikagel S50) and the butane was changed to 4.8% by weight. A foam sheet was obtained in the same manner. This foam sheet has a thickness
It had a width of 2.02 mm, a width of 350 mm, and a density of 0.089 g/cm ³ . When this foamed sheet was subjected to the same measurements as in Example 1, the results were as plotted with ◯ in FIG. Example 3 A foamed sheet was obtained in the same manner as in Example 1, except that the polyacrylic acid soda was changed to 3 parts of starch-acrylic acid graft polymer resin (Mesh 80; trade name Sunwet IM300) and the butane was changed to 4.2% by weight. Ta. This foam sheet had a thickness of 1.94 mm, a width of 350 mm, and a density of 0.093 g/cm ³ . When this foamed sheet was subjected to the same measurements as in Example 1, the result was -1 as plotted with △ in Figures 1 and 2. Example 4 Example 3 except that 3 parts of starch-acrylic acid graft polymer resin was changed to 1 part and butane was changed to 4.8% by weight.
A foamed sheet was obtained in the same manner as above. This foam sheet had a thickness of 2.03 mm, a width of 350 mm, and a density of 0.089 g/cm ³ . When this foamed sheet was subjected to the same measurements as in Example 1, the results were as shown in -2 plotted with ▲ in FIG. Example 5 A foamed sheet was obtained in the same manner as in Example 3, except that 3 parts of the starch-polyacrylic acid copolymer was changed to 0.5 parts and butane was changed to 5.1% by weight. This foam sheet had a thickness of 2.03 mm, a width of 350 mm, and a density of 0.089 g/cm ³ . When this foamed sheet was measured in the same manner as in Example 1, the result was -3 as plotted in □ in FIG. Comparative Example 1 A foamed sheet was obtained in the same manner as in Example 1 except that butane was added in an amount of 5.7% by weight without adding a water-absorbing resin. This foam sheet has a thickness of 1.9mm, a width of 350mm, and a density of 0.095.
g/ ^cm3 . When this foamed sheet was subjected to the same measurements as in Example 1, the results were as compared with the dotted lines in FIGS. 1 and 2. Example 6 Injected gas amount (butane) to mixed resin 5.0
% by weight, and a predetermined proportion of starch-acrylic acid graft copolymer resin (mesh) as super absorbent resin.
Example 1 except using Sunwet IM300)
A foamed sheet was prepared in the same manner as above, and its properties and secondary foamability were measured. The results are shown in Table 1.

[Table] All parts in the examples indicate parts by weight. As shown in the above examples, the extruded polystyrene foam sheet of the present invention using a superabsorbent resin can exhibit superior secondary foaming power over a long period of time compared to a sheet that does not use a superabsorbent resin. I understand. Furthermore, as shown in Example 6, the foaming ratio of the extruded polystyrene foam sheet itself of the present invention is found to be significantly higher than that of the foam sheet that does not use a superabsorbent resin.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs respectively illustrating the secondary foaming rate of the polystyrene extruded foam sheet of the present invention together with comparative examples.

Claims (1)

[Scope of Claims] 1. A secondary moldable resin comprising a mixed resin in which 0.1 to 30 parts by weight of a super absorbent resin is dispersed and blended into a polystyrene resin as a base resin, based on 100 parts by weight of the polystyrene resin. Improved polystyrene extruded foam sheet. 2. The extruded foam sheet according to claim 1, comprising a mixed resin in which the super absorbent resin is blended in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the polystyrene resin. 3. The extruded foam sheet according to claim 1 or 2, wherein the super absorbent resin is sodium polyacrylate, vinyl alcohol-acrylic acid copolymer resin, or starch-acrylic acid graft copolymer resin. 4 Polystyrene resin and the polystyrene resin
0.1 to 30 parts by weight of super absorbent resin powder and optional additives such as a nucleating agent and a spreading agent are uniformly dry-blended per 100 parts by weight, and this mixture is fed into an extruder together with a foaming agent to knead and melt. 1. A method for producing an extruded polystyrene foam sheet with improved secondary moldability, which comprises extruding it from an extruder die. 5. The manufacturing method according to claim 4, wherein the super absorbent resin powder is a powder that passes through a 35 mesh sieve.