JPH0446979B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition for molding a foam, and more particularly to a rubber composition for molding a foam to obtain an ultrafine foamed rubber-like elastic body having properties such as rubber-like elasticity, vibration damping properties, and heat insulation properties. Conventionally, molding materials that are rubber-like elastic bodies have been manufactured for various purposes, but these molding materials cannot be said to have sufficient rubber-like elasticity, and the resulting molding It has been difficult to make materials have both vibration-proofing properties and heat-insulating properties. Further, foam molding compositions have also been proposed in which a nitrone compound-based, azobis-compound-based, or hydrazide compound-based blowing agent is blended into the rubber composition as required. However, even in this case, there are problems in that it is difficult to mix the blowing agent into the composition with good compatibility, and it is also difficult to control the expansion ratio of the blowing agent. is relatively large,
This results in a so-called sponge-like foamed molding material, which has the disadvantage that it is difficult to obtain a rubber sheet-like material that takes advantage of rubber elasticity and has the desired hardness. In addition, natural rubber latex and various emulsion-type molding materials that are difficult to form are also used, but in any case, molding materials with the desired rubber-like elasticity, vibration-proofing, and heat-insulating properties can be used for various purposes. It was difficult to obtain. Therefore, the present inventor conducted various studies in order to obtain a rubber sheet-like molding material that has rubber-like elasticity, vibration damping properties, and heat insulation properties, and developed a new foam structure that is completely different from conventional foam molding compositions. The present invention was completed by newly discovering a foam molding composition that can produce a finely foamed rubber-like elastic material. That is, in the present invention, one or more shell wall materials selected from the group of polyethylene, polyamide, polybutadiene, polyurethane resin, and polyvinylidene chloride resin are added to 100 parts by weight of rubber or rubber-like elastic material to obtain a rubber-like elastic body. The present invention relates to a rubber composition in which 1 to 30 parts by weight of microcapsules made of a thermoplastic material and containing a core material having a property of expanding the shell wall material by heat are blended into the shell wall material. The composition of the present invention uses the above-mentioned certain thermoplastic substance as the shell wall material, and further contains a certain amount of microcapsules having the property of expanding the shell wall material by heat as a core material, so that it can be heated and molded. As a result, the microcapsules expand to a certain degree and the core substance gasifies, leaving a fine hollow cell structure in the molding material, and the shell wall material of the microcapsules becoming integrated with the rubbery substance, resulting in an excellent It is possible to make rubber sheet-like molded products with specific characteristics. The rubber or rubber-like elastic material used in the present invention includes natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, nitrile-butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene, ethylene-propylene rubber, butyl rubber, urethane rubber, acrylic rubber,
Examples include polyepichlorohydrin rubber, propylene oxide rubber, ethylene-vinyl acetate copolymers, polyvinyl chloride, olefins, etc. Among these rubbers and rubber-like elastic substances, one can be selected depending on the characteristics required for the molded product. One type or a mixture of two or more types can be selected. Furthermore, conventionally used compounding agents such as fillers, softeners, antiaging agents, vulcanizing agents, or crosslinking agents can be added to these rubbers or rubber-like elastic substances. The composition of the present invention is a composition in which a certain amount of microcapsules are blended into these rubbers or rubber-like elastic substances, or if desired, further containing additives such as fillers and softeners. For the shell wall material, it is necessary to use one or more thermoplastics selected from the group mentioned above. When a thermoplastic or thermosetting substance other than these is used as the shell wall material, the shell wall material of the hollow cell is hard, so the hollow cell is difficult to deform due to external impact, and has sufficient rubber elasticity. The problem of not showing
This is because the heat treatment causes problems such as breakage of the molded product, which is not preferable. The core material of the microcapsule is one that has the property of thermally expanding the core material due to heat and causing the shell wall material to expand in volume accordingly, such as petroleum-based rubber, liquid, aromatic hydrocarbon-based compounds, etc. , other organic solvents, and organic and inorganic substances that generate decomposed gases such as carbon dioxide gas and nitrogen gas, such as sodium bicarbonate, sodium carbonate, ammonium carbonate, azide compounds, and hydrazide compounds. Specific examples of microcapsules containing such a core substance and having the above-mentioned thermoplastic substance as a shell wall material include Expancel (manufactured by Nippon Ferrite Co., Ltd.);
Microsphere F50, Microsphere
F60 (manufactured by Matsumoto Yushi Co., Ltd.) is exemplified. In the present invention, the amount of microcapsules required is 1 to 30 parts by weight per 100 parts by weight of the rubber or rubber-like elastic material.
When the amount of microcapsules blended is as small as less than 1 part by weight, the required rubber-like elasticity and
If vibration-proofing and heat-insulating properties cannot be obtained, and on the other hand, if the amount of microcapsules added exceeds 30 parts by weight, many hollow cells will be present in the molded product when the composition is molded. , rather than the hollow cells being compressed and deformed in response to an external impact, adjacent hollow cells shift relative to each other to absorb the impact force, so not only is the rubber-like elasticity insufficient; This is because it exhibits paper-like, relatively brittle properties, making it impossible to obtain rubber sheet-like properties with appropriate hardness. The amount of microcapsules blended into the composition is as follows:
Various changes can be made depending on the usage characteristics of the final molded product. The molding composition of the present invention as described above is specifically manufactured as follows. That is, a method is adopted in which rubber or rubber-like elastic material is mixed and kneaded with necessary fillers, softeners, anti-aging agents, etc. using a Banbury mixer, formed into a batch, and then mixed with microcapsules and a vulcanizing agent. .
Another method is to mix and knead rubber or rubber-like elastic material with fillers, softeners, anti-aging agents, microcapsules, vulcanizing agents, etc. using oven rolls. The rubber or rubber-like elastic material composition thus obtained is molded into an ultrafine foamed rubber-like elastic body by heat vulcanization or heat crosslinking.
For example, after molding with an injection molding machine, an extrusion molding machine, etc., adjusting the shape, heat treatment at about 100 to 180°C, forming a sheet using rolls such as a calendar roll, or various molding processes. There is a method of obtaining a desired rubber-like elastic body depending on the method. The heat treatment in all of these cases depends on the physical properties of the rubber or rubber-like elastic material, the vulcanizing agent,
Although various changes can be made depending on the properties of additives such as crosslinking agents and the properties imparted to the molded article, it can be carried out by mold heating, hot air heating vulcanization, etc. As described above, according to the present invention, it is possible to provide a rubber sheet-like molded product having very excellent properties in terms of rubber-like elasticity, vibration damping properties, heat insulation properties, etc. by foam molding by heating. It will be done.
The present invention also has the advantage that by appropriately changing the amount of microcapsules in the composition, rubber sheet-like molded articles having various properties can be obtained. The present invention will be described below in detail with reference to Examples, and the characteristics of molded articles obtained from the composition of the present invention will also be described, but the present invention is not limited to these Examples. Examples 1 to 5 After masticating natural rubber through a thin roll, styrene-butadiene rubber was mixed and kneaded, and zinc white, stearic acid, anti-aging wax, paraffin wax, white luster CC, and accelerator were sequentially mixed. A rubber compound was prepared and made into a master batch. Next, this masterbatch is divided into desired amounts, wound around a roll again, and a mixture of acrylonitrile and methyl methacrylate (F50), a mixture of vinylidene chloride, acrylonitrile, and methyl methacrylate (F60) is used as the shell wall material, and the core material is isobutane. A certain microcapsule and sulfur were mixed and dispersed in this order to obtain a moldable rubber composition. Table 1 shows the mixing ratio based on these ingredients. As a comparative example, a composition without microcapsules was also obtained in the same manner.

【table】

[Table] Using the composition obtained as described above, a molded material was obtained by air vulcanization. In other words, a 0.3mm thick sheet is rolled with liner cloth 70d at 80℃.
Rolled into nylon taffeta cloth with 210 threads and heated at 140℃
A molded product is obtained by processing with hot air for 10 minutes in a gear oven adjusted to . Table 1 shows the apparent specific gravity and hardness of these molded products. As is clear from these results, in the mixed system of styrene-butadiene and natural rubber, the apparent specific gravity of the molded product is lower than that of the molded product without microcapsules.
1.18, whereas the apparent specific gravity of the product containing microcapsules decreased as the amount of the microcapsules was increased, indicating favorable foaming. The foamed cells of the molded products using the compositions of Examples 1 to 5 were all extremely fine and uniform cells, and rubber sheet-like products with good rubber elasticity were obtained. Examples 6 to 9 Using chloroprene rubber as the rubber, after passing it through a roll and masticating it, magnesium oxide, stearic acid, dixie clay, SRF carbon, process oil, anti-aging agent RD, accelerator, and zinc white were mixed in order. This was used as a masterbatch as a rubber composition. Next, divide this masterbatch into desired amounts,
Microcapsules were again mixed in and dispersed using a roll to obtain a molding rubber composition. For comparison, a composition containing microcapsules and a composition containing an Asobis foaming agent instead of microcapsules were also produced. Table 2 shows these blending ratios.

【table】

[Table] Using the compositions obtained as described above, molded materials were obtained by air vulcanization and press vulcanization. The air vulcanization conditions were the same as those described in Examples 1 to 6 above. Press vulcanization was carried out as follows. That is, the compositions were dispensed into 21.0 mm sheets using rolls at 60° C., and molded sheets of 150 mm×120 mm were molded and vulcanized. The mold is 2 deep
mm, longitude 150mm, latitude 150mm internal capacity,
This mold was filled with the molded sheet and heated to 150°C.
Heat treatment was performed for 5 minutes using a hot press to obtain a molded product. Table 2 shows the apparent specific gravity and hardness of these molded products.
It was shown to. As is clear from these results, the change in apparent specific gravity of chloroprene rubber molded products is greater with increasing blending amount of microcapsules than in Comparative Example 2, which does not contain microcapsules. becomes smaller, indicating that foaming is effective. Also, its hardness is comparable. Furthermore, regarding Comparative Examples 3 and 4 in which conventionally used blowing agents were blended,
There was no change in apparent specific gravity during air vulcanization, and the desired foaming did not occur. The foamed cells of the molded products obtained from the compositions of Examples 6 to 9 were also extremely fine and uniform cells, and were in the form of a rubber sheet with good rubber elasticity.

Claims (1)

[Scope of Claims] 1. 100 parts by weight of rubber or rubber-like elastic material, and the shell wall material is made of one or more thermoplastic materials selected from the group of polyethylene, polyamide, polybutadiene, polyurethane resin, and polyvinylidene chloride resin, and A rubber composition for foam molding, characterized in that 1 to 30 parts by weight of microcapsules containing a core substance having a property of expanding the shell wall material by heat are blended into the shell wall material. 2. The rubber or rubber-like elastic substance is natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, nitrile-butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene, ethylene-propylene rubber, butyl rubber, urethane rubber, acrylic rubber, polyepichlorohydrin rubber , propylene oxide rubber, ethylene vinyl acetate copolymer, polyvinyl chloride, and polyolefin.