Generally, a higher amount of carbon black is added to the rubber compound to increase the hardness, but this also leads to problems such as increased raw material viscosity and processing difficulties. Therefore, phenolic resin is used to increase hardness and stiffness.And it can make the viscosity of the raw material within an acceptable range. Linear phenolic resin is usually melt mixed in a roller. Unlike other processing aids, it can be condensed by adding methyl donors during the vulcanization process. For example, six times.

Reinforcing resin can provide good hardness and stiffness for rubber composition. Moreover, it has good compatibility with different types of rubber. And when added in an amount of 8-15%, a good reinforcing effect can be obtained. Methylene donor is generally preferably added in an amount of 7-15%, and it should be added at a lower temperature and in the final vulcanization stage.