10th International Conference on Surface Engineering (ICSE 2026)

As the type 45 steel rubber mold is easy to be contaminated and the fluororesin coated mold is expensive, this work aims to prepare the anti-sticking coating on rubber mold based on the sol-gel method, and investigate the anti-sticking performance and durability of the coating. The sol-gel coating was formulated with silica sol and methyl triethoxysilane (MTES) as the main raw materials, and air sprayed on the type 45 steel mold samples. A fluoroalkyl silane containing sol-gel coating and surface treatment by a fluoroalkyl silane coating were also prepared for comparison with the non-fluorine sol-gel coating. The anti-sticking property and durability of the coatings were investigated by rubber vulcanization tests. The changes of surface micro morphology and element composition of the samples with the number of vulcanization tests were studied by scanning electron microscope and energy dispersive spectrometer. The adhesion process of rubber on the coating surface were investigated. The results show that the sol-gel coating is composed of O, Si, C, and Ti, with good film forming property. Its vulcanization release force is about 20 N, similar to that of the PTFE coating. The element composition changes little after 10 vulcanization tests, indicating that it has good anti-fouling performance. The fluoroalkyl silane modified sol-gel coating is composed of O, Si, C, Ti, and F. The element F reduces the adhesion between the coating and the substrate, which may lead to cracking and spalling of the coating during the vulcanization tests. The fluoroalkyl silane surface treatment can reduce the surface energy and the release force, but the fluoroalkyl silane film is easy to stick to the rubber and pollutes the products. The sol-gel coating is more applicable to rubber molds compared with the fluoroalkyl silane modified sol-gel coating and fluoroalkyl silane surface treatment. The results of the durability test show that the type 45 steel surface becomes yellow after 100 vulcanization tests, with different brightness at different positions, and turns brown after 300 tests. However, the surface color of the sol-gel coating changes little after 200 vulcanization tests, turns light yellow after 300 tests, and becomes brown after 500 tests. The variation of Zn element mass content with the number of vulcanization tests indicates that the sol-gel coating can be used approximately 300 times more than the type 45 steel mold for rubber vulcanization, increasing the continuous service life of the mold 2~3 times. The adhesion and accumulation of rubber contaminants on the surface of the mold are related to the flow of rubber during vulcanization. In areas where the rubber flow speed is low, the micro morphology of rubber pollutants appears as a textured pattern. While in the high flow rate area, rubber pollutants initially appear as flakes, gradually thicken with increasing vulcanization times, and then crack along the flow direction, developing into blocks. The different micro morphology leads to the different appearance at different positions, and affects the surface quality of the rubber products. Thus, reducing the rubber flow will improve the surface brightness uniformity of the products. Although the service life of the sol-gel coating is shorter than that of the fluororesin anti-sticking coating, it has the advantages of environmentally friendly (does not contain toxic and refractory substances such as perfluorooctanoic acid), low film forming temperature, low carbon consumption, low cost, and easy to clean. The sol-gel coating has broad application prospects in rubber molds.

sol-gel method,coating,rubber mold,anti-sticking property,durability