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Sponge foam rubber products made from natural rubber as the main raw material have low density, good elasticity and other hot spots, and have remarkable sound absorption and shock absorption effects. They are widely used in sealing, shock absorption, noise reduction and other applications. In actual production, the shrinkage of natural rubber sponge products affects the service performance and life of finished products. Rubber products manufacturers need to take certain measures to improve the shrinkage of natural rubber sponge products.

1. Significance of improving the shrinkage of natural rubber sponge products

When the natural rubber sponge rubber is vulcanized at a certain temperature, the gas decomposed from the foaming agent will generate a certain pressure to make the rubber sponge; Sponge rubber will be in a relatively stable state under the support of gas pressure. However, with the continuous dissolution, permeation and diffusion of gas in natural rubber 2LLYY1022WFM, the internal gas pressure will decrease; When the pressure is reduced, the natural rubber sponge rubber will shrink during the foaming process, resulting in the poor stability of sponge products during storage and use.

2. Measures to reduce the shrinkage of natural rubber sponge products

When natural rubber is used to prepare sponge rubber, factors such as rubber variety, rubber content in formula, etc. will affect the shrinkage of foam rubber. Rubber product manufacturers can reduce the shrinkage of natural rubber sponge products from the following aspects.

(1) Control glue content

In actual production, the relatively large rubber content of natural rubber sponge foam products is beneficial to rubber foaming, but the larger the rubber content, the greater the possibility of shrinkage of the sponge rubber. Properly reducing the rubber content can reduce the rubber shrinkage. It should be noted that when the gum content of natural rubber sponge foam rubber is lower than 30%, it is difficult to foam the sponge rubber, so the gum content should not be too low. It is necessary to reasonably control the gum content of natural rubber sponge products.

(2) Use butadiene rubber with caution

Natural rubber sponge products are often used together with butadiene rubber in the production process. The permeability of gas in different rubber is different, and the permeability in butadiene rubber is the largest; Therefore, when NR/BR is used together, the greater the content of butadiene, the greater the shrinkage of sponge rubber. When blending butadiene rubber into natural rubber sponge products, the dosage must be reasonably controlled. If necessary, an appropriate amount of styrene butadiene rubber can be added to reduce the shrinkage of natural rubber/butadiene rubber sponge rubber.

When natural rubber/butadiene rubber is used together, the more butadiene is used, the greater the probability of roller stripping is. The proper use of styrene butadiene rubber can improve the process performance of the blend rubber to a certain extent.

(3) Rubber and plastic

The plastic has less permeability to gas and forms a rigid skeleton after being heated, plasticized and cooled during vulcanization. When using natural rubber to produce sponge foam rubber products, rubber product manufacturers can use plastic appropriately in the formula to effectively prevent shrinkage and reduce the shrinkage of natural rubber sponge rubber. Theoretically, adding about 20 phr of plastic in the formula of natural rubber sponge products can effectively avoid the shrinkage of rubber. It should be noted that the addition of plastic will lead to the increase of permanent deformation of sponge rubber, and the dosage should be reasonably controlled.

(4) Use resin

Thermoplastic resins such as phenolic resin and polymerized rosin can improve the rheological properties of the rubber compound, which is not only beneficial to the foaming process, but also has a certain reinforcement effect. It can improve the rigidity of natural rubber sponge products and reduce the shrinkage of sponge rubber compound. In actual production, phenolic resin has a high melting point and is difficult to disperse in natural rubber. It is recommended that phenolic resin be fully heated before use.

(5) Use recycled rubber

The experiment shows that the proper amount of recycled rubber mixed with natural rubber can reduce the swelling or shrinkage of rubber during processing, improve the accuracy of rubber processing technology, size and shape of finished products, and improve the shrinkage of natural rubber sponge products.