Century Creation (International) Co., Ltd

Composition of Rubber Sponge and Balance between Vulcanization and Foaming Rate


  All rubber, EVA (ethylene-vinyl acetate copolymer), high phenyl ethyl vinyl, and thermoplastic elastomer blended with rubber, can be used to make rubber sponge. In the selection, the processing performance shall be determined according to the comprehensive consideration, such as the use of the product, the physical and chemical performance index of the product, and the manufacturing method. Ordinary sponge mainly employs natural rubber, styrene-butadiene rubber, styrene-butadiene rubber, low-grade rubber, etc.. 

  Ordinary boots can adopt recycled rubber. Advanced tasteless insoles can use EVA/ rubber combination. Microporous soles can adopt EVA or high styrene with common rubber, while holes can adopt butyl rubber blended with PVC. And oil-resistant rubber, neoprene, butyl rubber/polyvinyl chloride (PVC), epoxidation of natural rubber and other D-shaped holes can be selected.

  For heat resistance and ozone aging resistance, EPDM and silicone rubber can be selected. The plastic/rubber are usually used in light (relative density less than 1) and high hardness (not less than 80) foam plastic plates with good bending resilience, and sBs or rubber alone is difficult to meet the requirements of composite materials.

  Natural rubber, styrene butadiene rubber, butadiene rubber as well as their blends with plastics are mostly used in the manufacture of civil sponge rubber products.

  Considering the service life, process and cost comprehensively, the ideal materials are EPDM and neoprene, which are used to make industrial sponge rubber products, and widely used in automobile, airplane, chemical industry, daily necessities and other industries for thermal insulation, sound insulation and shockproof materials, as well as cushion, mattress, medical machinery, sanitary products, sporting goods and so on. The foaming agent can be added to prepare raw rubber (such as urea, ammonium carbonate, azobisisobutyronitrile, etc.) or concentrated latex, which is sent into the air through a stirring drum, and then vulcanized.

  Balance between vulcanization speed of rubber sponge and foam

  Before the foam is vulcanized, a large amount of gas enters, rubber molecules are still in a free crosslinking state, and porosity is formed without being separated from the gas. The hole wall collapses or breaks under strong impact, and part of the gas is washed away by the rubber surface, thus causing insufficient foam and unsmooth surface, and forming nonuniform macropores and products with very thin skin. 

  When the sulfide is earlier than foaming and starts to decompose to generate gas foaming agent, the rubber has already produced certain crosslinking, and the contribution degree of the rubber increases. When the foaming agent is converted into gas, the rubber is foamed, difficult to foam and causes foaming, under the yoke of vulcanized rubber. The result is that the thick-skin pore products produced by sponge are with low foam content, high hardness and low elasticity. Therefore, it is very important to adjust the vulcanization speed. The proper sponge rubber density (foaming rate), water absorption rate (foaming rate increased, water absorption rate increased) and good states have great influence on skin.

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