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Nov 24, 2021
Silicone rubber has a variety of excellent properties, but its mechanical properties such as compressive strength and tearing strength are poor, and cannot meet the requirements of the process. Fillers need to be added to modify and strengthen it. When MQ silicone resin is used as a reinforcing filler, it can not only increase the strength of the rubber matrix, but also will not increase the viscosity of the system too fast to facilitate subsequent operations, and the prepared vulcanizate has better transparency.
The organic part of silicone resin can improve its compatibility with silicone rubber and play a role in tackifying; the energy-saving silicon-oxygen chain can improve the mechanical strength, cohesive strength, peeling strength and high temperature resistance of silicone rubber, and play a reinforcing role. Addition vulcanized silicone rubber is mainly composed of vinyl-containing raw rubber, reinforcing filler, hydrogen-containing silicone oil crosslinking agent and platinum catalyst. Under the action of the platinum catalyst, the vinyl-containing resin can chemically bond with the raw rubber through the hydrosilylation reaction with the SiH crosslinking agent, thereby forming a three-dimensional network structure for reinforcement. With the increase in the amount of MQ silicone resin, the hardness, tensile strength, tear strength, adhesive properties, and crosslinking density of silicone rubber gradually increase to the optimum value. The reason is that the molecular weight of MQ silicone resin is relatively small, the vinyl content is relatively high, the compatibility and dispersibility in silicone rubber are better, and it is chemically combined with silicone rubber. However, when the cross-linking density is too large, the distribution of cross-linking points is not uniform, resulting in stress concentration, and the silicone rubber becomes hard and brittle, and the silicone rubber is easily broken under the action of stress. The curing time is prolonged with the increase of the amount of MQ. This is due to the small molecule of MQ and the high vinyl content, which can preferentially react with hydrogen-based silicone oil, thereby delaying the reaction of silicone hydrogen and vinyl raw rubber until the MQ is consumed. As the amount of MQ resin increases, the dielectric constant of silicone rubber increases to its maximum value and approaches equilibrium. However, if the amount of MQ resin is too large, the cross-linking of the silicone rubber is excessive, which limits the activity of the polar groups and stabilizes the dielectric constant. However, the dielectric properties of silicone resin are still lower than that of general rubber.
Condensed vulcanized silicone rubber is mainly composed of silicone rubber containing terminal hydroxyl or alkoxy groups, reinforcing fillers, crosslinking agents and catalysts. After the catalyst or the moisture in the air, the crosslinking agent is hydrolyzed to generate silanol, which undergoes condensation reaction with the silanol of the raw rubber to form a three-dimensional network structure and vulcanize into an elastomer. When MQ silicone resin is mixed with silicone rubber, it can increase the viscosity and strengthen the silicone rubber, so that the silicone rubber has excellent mechanical properties. However, when exposed to electromagnetic radiation and vacuum ultraviolet radiation, the silicone rubber will age, deform, and crack, and its performance will change accordingly. Difference. The main reasons for the decrease in quality and performance of silicone rubber caused by irradiation are the escape of unreacted low-molecular substances in the vulcanized rubber under irradiation, the breaking of the macromolecular network structure, and the degradation or cross-linking of molecular chains. In order to make the silicone rubber resistant to radiation, you can add anti-radiation fillers, such as nano-TiO2.
2.3 Application of MQ resin in pressure sensitive adhesive
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 modification type, biodegradable type, functional type and other systems.
Since the solvent type contains a large amount of volatile organic compounds, during curing, the volatilization of the solvent can easily cause serious pollution to the environment. Nowadays, environmental protection has been paid more and more attention. The silicone pressure-sensitive adhesive industry is taking environmentally-friendly low-cost products as the mainstream of development, and new products such as biodegradable and radiation curing products are the research direction. MQ silicone resin is mainly used to increase viscosity and strengthen. The silanol or vinyl in MQ resin can respectively react with the hydroxyl group of silicone rubber or through the condensation reaction of hydrogen-containing siloxane and silicone rubber under the action of a catalyst. Silicone pressure sensitive adhesive.
The indicators to measure the adhesive performance of pressure-sensitive adhesives are tack T, adhesion A, cohesion C and keying K. To obtain pressure-sensitive adhesives with excellent performance , We must consider how to make the 4 kinds of adhesive force meet the following balance relationship: K ＞ C ＞ A ＞ T. The research shows that the ratio of silicone resin to rubber material has the greatest impact on the performance of pressure-sensitive adhesives. With the increase of the amount of silicone resin, the cohesive force of the pressure-sensitive adhesive increases, but the peeling force decreases; with the increase of the amount of silicone rubber, the initial adhesion increases. But the stickiness is reduced. This is because silicone rubber can increase the fluidity of the pressure-sensitive adhesive, thereby increasing the interfacial adhesion, and has a strong initial tack; the reduction in the amount of resin is not conducive to deep crosslinking, the reinforcing effect is not good, and the cohesion is reduced. The molecular weight of MQ resin has a greater impact on the adhesive performance of the pressure-sensitive adhesive, because the change of molecular weight causes the viscosity and cohesive strength of the pressure-sensitive adhesive to change. When the molecular weight is high, the pressure-sensitive adhesive has high cohesive strength and good stickiness; when the molecular weight is low, its bulk viscosity is low, which can improve the interfacial adhesion, but the polymer has low cohesive strength, and the cohesive failure is likely to occur during peeling. When the molecular mass distribution of MQ resin is wide, and the number average molecular mass is about 3000, it can be used to prepare pressure-sensitive adhesives. Nicolas studied the adhesion properties of acrylic adhesives to silicone elastomers containing different quality MQ silicone resins to adjust the mechanical properties of the tape (mainly peel strength). The results show that the amount of MQ silicone resin in the elastomer has a great influence on the performance of the modified tape, and controlling the surface properties of the elastomer is an effective way to adjust the peeling force.
2.4 Other applications
It can be used to prepare high temperature and strong alkali resistant organosilicon defoamer, which also has the advantages of non-toxicity and environmental protection. By adding high-viscosity hydroxy silicone oil and MQ silicone resin to synthesize a network polymer with a high degree of branching, so as to improve the high temperature resistance and strong alkali resistance of the defoamer. The MQ silicone resin containing SiH groups or aralkyl groups is used as a crosslinking agent. Under the action of platinum catalyst, a phenyl silicone resin-containing encapsulation material is synthesized with a silicone resin containing vinyl and high phenyl groups. The material is compatible and compatible. With good transparency, high hardness and high refractive index, it can be used for LED packaging and lens production. With MQ hydrogen-containing silicone oil and silyl enoate, under the catalysis of Pt, the hydrosilylation reaction occurs to obtain MQ resin-modified carboxyl silicone oil. It can be used in combination with amino silicone oil emulsion to give fabrics a better soft, smooth, and plump feel.