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-based, high-solid-content, solvent-free, emulsion, radiation-curable, resin-modified, biodegradable, and functional systems.
Because the solvent type contains a large amount of volatile organic compounds, the volatilization of the solvent is likely to cause serious pollution to the environment during curing. Nowadays, environmental protection has been paid more and more attention. The silicone pressure-sensitive adhesive industry is focusing on environmental protection and low-cost products, and researches on new products such as biodegradable and radiation curing. MQ silicone resin mainly plays the role of tackifying and reinforcing. The silicon hydroxyl group or vinyl group in MQ resin can react with the hydroxyl group of silicone rubber or the hydrogen-containing siloxane and silicone rubber under the action of catalyst, thereby preparing Silicone pressure-sensitive adhesive.
The indexes for measuring the adhesive properties of pressure-sensitive adhesives are tack T, adhesion A, cohesion C, and keying K, respectively. To produce pressure-sensitive adhesives with excellent performance, , We must consider how to make the four kinds of adhesive force meet the following equilibrium relationship: K> C> A> T. It is found that the ratio of silicone resin to rubber material has the greatest impact on the performance of pressure-sensitive adhesives. As the amount of silicone resin increases, the cohesive force of the pressure-sensitive adhesive increases, but the peeling force decreases. As the amount of silicone rubber increases, the initial viscosity increases. But the stickiness is reduced. This is because silicone rubber can increase the fluidity of the pressure-sensitive adhesive, thereby increasing interfacial adhesion and strong initial tack; reducing the amount of resin is not conducive to deep crosslinking, the reinforcing effect is poor, and the cohesion is reduced. The molecular weight of MQ resin has a greater impact on the adhesive properties of pressure-sensitive adhesives, because the change in molecular mass causes the viscosity and cohesive strength of the pressure-sensitive adhesive to change. When the molecular mass is high, the pressure-sensitive adhesive has high cohesive strength and good stickiness; when the molecular mass is low, its bulk viscosity is low, which can improve interfacial adhesion. When MQ resin has a wide molecular mass distribution and a number average molecular mass of about 3000, it can be used to prepare pressure-sensitive adhesives. Nicolas studied the adhesion properties of acrylic adhesives to silicone elastomers containing MQ silicone resins of different qualities to adjust the mechanical properties (mainly peel strength) of the tape. 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 method to adjust the peeling force.