When using low-hardness rubber compound, it is often encountered that colorful patterns are formed on the surface of the rubber compound. Although this phenomenon will not affect the performance of the rubber compound, it will seriously affect the appearance of the rubber compound and cause trouble for customers.

Cause Analysis:

(1) Formula design

1. In general, the smaller the particle size of carbon black, the larger the specific surface area, the more by-products carried on the particles, and the greater the possibility that some by-products will be precipitated from the rubber compound due to the difference in solubility, resulting in overcolor. Like N220, N330 and other highly reinforced carbon blacks, the possibility of overcoloring is much greater than that of N660, N774, N990 and other carbon blacks. In addition, N550 and N774 appear reddish, and N330 is bluish.Inert fillers are added to the raw materials of EPDM rubber, and the inert fillers are preferably silicon powder. It can effectively absorb the number of functional groups on the surface of carbon black, and can react with hydroxyl, carbonyl and carboxyl groups on the surface of carbon black, and at the same time these functional groups are bound, thus preventing these functional groups from coming into contact with oxygen in the air and risking overtone formation under sunlight scattering.The carbon black of the raw material of EPDM rubber is selected as medium and low reinforced carbon black. Its function is that the number of functional groups carried on the surface of the medium and low reinforced carbon black is higher and the number of reinforced carbon black is less, that is, the number of surface hydroxyl groups, carboxyl groups and carbonyl groups At the same time, it is easy to mix with rubber during the production process, so as to avoid the risk of overcolor caused by functional groups and by-products on the surface of carbon black.In the preparation process, the medium and low reinforcing carbon black and the oil are added in stages, the purpose is to avoid the phenomenon of slippage during the mixing process, resulting in the rubber material not heating up normally.

2. The use of higher quality paraffin oil will reduce the risk of overcolor, such as high flash point and higher purity paraffin oil. In addition, oil-extended ethylene-propylene rubber can be used in formula design to relatively reduce the use of paraffin oil;

3. 4010NA (EPDM is generally not added, natural rubber is more), and additives such as petroleum resin will also have the problem of overcolor.

4. Paraffin oil, carbon black and some additives are not uniformly dispersed during rubber mixing.

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