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Dec 18, 2020
Silicone pressure sensitive adhesive is a special adhesive composed of silicone resin (commonly used MQ silicone resin), silicone rubber, catalyst, crosslinking agent and other additives. Silicone pressure sensitive adhesives mainly include solvent type, high solid content type, solvent free type, emulsion type, radiation curing type, resin modified type, biodegradable type and functional type system.
Due to the large amount of volatile organic compounds (VOCs) in the solvent type, the solvent volatilization easily causes serious pollution to the environment during curing. Nowadays, environmental protection has been paid more and more attention. The silicone pressure sensitive adhesive industry is taking environmental protection and low-cost products as the development mainstream, and new products such as biodegradation and radiation curing are the research direction. MQ silicone resin mainly plays the role of tackifying and reinforcing. The silicone hydroxyl group or vinyl group in MQ resin can condense with the hydroxyl group of silicone rubber or through hydrogen containing siloxane and silicone rubber under the action of catalyst to prepare silicone pressure sensitive adhesive.
The adhesion properties of pressure-sensitive adhesives are stack T, adhesion a, cohesion c and keying K. in order to produce pressure-sensitive adhesives with excellent performance, it is necessary to consider how to make the four adhesion forces meet the following balance: k > C > a > t. The results show that the material ratio of silicone resin to rubber has the greatest influence on the properties of pressure-sensitive adhesive. With the increase of silicone resin content, the cohesion of pressure-sensitive adhesive increases, but the peeling force decreases; with the increase of silicone rubber content, the initial viscosity increases, but the holding viscosity decreases. This is because silicone rubber can increase the fluidity of pressure-sensitive adhesive, so as to increase the interfacial adhesion, and the initial viscosity is strong; the reduction of resin content is not conducive to deep cross-linking, and the reinforcement effect is poor, and the cohesion is reduced. The molecular weight of MQ resin has a great influence on the bonding performance of pressure-sensitive adhesive, because the change of molecular weight changes the viscosity and cohesive strength of pressure-sensitive adhesive. When the molecular weight is high, the pressure-sensitive adhesive has high cohesive strength and good viscosity; when the molecular weight is low, its bulk viscosity is low, which can improve the interfacial adhesion, but the polymer cohesion strength is low, and the cohesive failure occurs easily when peeling off. When the molecular weight distribution of MQ resin is wide and the number average molecular weight is about 3000, it can be used to prepare pressure sensitive adhesive. Nicolas studied the adhesion properties of acrylic adhesive to siloxane elastomers with different quality MQ silicone resin, so as to adjust the mechanical properties (mainly peel strength) of adhesive tape. The results show that the amount of MQ silicone resin in the elastomer has a great influence on the properties of the modified tape, and controlling the surface properties of the elastomer is an effective way to adjust the stripping force.
Other applications
It can be used to prepare silicone defoamer with high temperature resistance and strong alkali resistance. The defoamer also has the advantages of non-toxic and environmental protection. High branched network polymer was synthesized by adding high viscosity hydroxyl silicone oil and MQ silicone resin, so as to improve the high temperature and alkali resistance of defoamer. Using MQ silicone resin containing SIH group or aryl alkyl group as crosslinking agent and silicone resin containing vinyl group and high phenyl group under the action of platinum catalyst, the packaging material containing phenyl silicone resin is synthesized. The material has good compatibility, transparency, high hardness and high refractive index, which can be used for LED packaging and lens manufacturing. MQ resin modified carboxyl silicone oil was prepared by hydrosilylation of MQ hydrogenated silicone oil and silyl alkenyl ester under the catalysis of Pt. Its combination with amino silicone oil can give fabric a better softness, smoothness and fullness.