Study On Application And Modification Properties Of New Mold Rubber

Silicone mold rubber had been largely applied to replace plaster, metal and wood due to its high precision of complex mode, which possessed good simulation, mold release, excellent flexibility, simple and inexpensive. Therefore, it had become one of the important materials in mold making. At present, it had been widely used in culture stones, photo-electric equipments, domestic appliances, automobile parts, toys and so on, which has always been paid close attention to.However, the mold rubber, especially in hot and humid conditions, had many deficiencies such as large mold shrinkage, large corner deviation, poor strength, low dimensional stability etc, which led to short lifetime during the production process. For these reasons, the organic/inorganic hybrid modification techniques were used in this paper. In order to prolong the useful lifetime of mold rubber, the rubber blends technology, plasma-coated composite modification and thermoplastic elastomer alternative technologies were used to improve dimensional stability, heat resistance and mechanical property,Following four aspects were included in this paper:(1) Bis(2-hydroxyethyl) methyl ammonium lauryl was selected to modify Namontmorillonite(Na-MMT) to prepare organic montmorillonite(OMMT). The silicone rubber mold rubber was prepared through OMMT and waterborne polyurethane(WPU) organic/inorganic hybrid modification. The physical and mechanical properties of mold rubber were also tested. Results showed that the OMMT interlayer spacing increased 1.4~3.6 times compared with that of Na-MMT. The compatibility of rubber mixing is better. When WPU/OMMT content is 3%, the dimensional stability, thermal stabilityof mold rubber had been significantly improved. Compared with pure RTV, the tensile strength, elongation at break and tear strength of RTV/WPU/OMMT-3 were increased by 175%, 164%, 133%, respectively. At room temperature to 120 ℃, the linear expansion coefficient and volume expansion coefficient were reduced by 59% ~ 75% and 68% ~ 92%, respectively.(2) The ground glass fiber powder(MG) was organic modified by silane coupling agent(KH560) and the organic grinding glass fiber powder(OMG) was prepared. The silicone mold rubber was prepared by EP/OMG. The physical and mechanical properties were tested. Results showed that the surface modification had obvious effects for KH560 to MG. When the EP/OMG mass fraction was 3%, the dimensional stability and thermal stability of mold rubber had been improved. The tensile strength, elongation at break and tear strength of RTV/EP/OMG-3 were increased by 150%,140%, 152% respectively compared with that of pure RTV mold rubber. At room temperature~120 ℃, the linear expansion coefficient and volume expansion coefficient were reduced by 37%~52% and 55%~73%,respectively. Meanwhile, the acid and alkali resistance performance was also improved.(3) The surface of RTV/OMG compositewas cured by different plasma. The fluorine- silicon antifouling coating was sprayed to prepared new mold rubber. The surface modification effects of O2, N2 and air plasmas were compared. The physical and mechanical properties of mold rubber were tested. Results showed that the hydrophilic modified effect of O2 plasma wfas better than that of N2 and air plasma. The best time for treatment was 3min. Compared with pure RTV, the dimensional stability and thermal stability of P-RTV/OMG-3 had been improved. Results showed that the maximum tensile strength was 4.7MPa,the elongation at the break was 1020% and the tear strength was 44 k N/m. In the range of room temperature~120 ℃, the linear expansion coefficient and volume expansion coefficient were 1.12 × 10-3 K-1 ~ 1.48 × 10-3 K-1 and 0.81 × 10-3K-1 ~ 5.4 × 10-3K-1, which were reduced by 13% ~ 41% and 27 % ~ 80% respectively.(4) The TPE/OMMT composites were prepared by melt blending. The dimensional stability, thermal stability and other physical and mechanical properties for the composites were tested. Results showed that the exfolication of OMMT occurred in TPE matrix. The composites were transformed from thermal contraction mode to the expansion mode, and dimensional stability was excellent. When 1% of OMMT was added, the tensile strength of the compositewas 10.9MPa,the elongation at the break was 1313.6% and the tear strength was 73 k N/m. These mechanical properties were much better than that of pure RTV. Therefore, TPE/OMMT composites were expected to replace RTV as mold rubber.