Formula ingredients
Ratio of silicone rubber raw rubber to silicone resin: When the silicone rubber raw rubber content is high, the silicone pressure-sensitive adhesive has better viscosity at room temperature; when the silicone resin content is high, it is dry and non-sticky at room temperature and needs to be heated and pressurized to become sticky.
Selection and dosage of plasticizer: Plasticizers can increase the plasticity and flexibility of the resin, thereby affecting the viscosity. Low molecular weight polymer plasticizers, dissolved in the resin at high temperature, can adjust the viscosity of the colloid. Too much or too little of it may lead to poor viscosity.
Effect of cross-linking agent: Cross-linking agent can make the molecular structure of silicone pressure-sensitive adhesive form a network, improve cohesive strength and stability. Too high cross-linking may make the colloid hard and brittle, and reduce viscosity; insufficient cross-linking will not make the colloid cohesive strength enough and the viscosity will also be affected.
Type and dosage of catalyst: Different types of catalysts have an impact on the reaction rate, product structure and performance. For example, the activity, dosage and effective inactivation of amine catalysts will affect the stability and viscosity of silicone pressure-sensitive adhesives. If the catalyst remains, the bonding performance of the adhesive product may be unstable.
Preparation process
Reaction temperature control: If the reaction temperature is too high or too low, the molecular structure and performance of the silicone pressure-sensitive adhesive may change, thereby affecting the viscosity. If the temperature is too high, it may lead to excessive cross-linking, hardening the colloid and reducing the viscosity; if the temperature is too low, the reaction is incomplete and the viscosity cannot reach the optimal state.
Stirring speed and time: If the stirring speed is too fast or the time is too long, the macromolecular chain may be broken, the molecular weight and cohesive strength of the colloid may be reduced, and the viscosity may be affected; and if the stirring is not uniform, the components will be unevenly distributed, affecting the overall viscosity performance.
Dehydration effect: If the water generated in the polycondensation reaction is not effectively removed, the adhesive molecules will be partially hydrolyzed under the action of the residual catalyst, resulting in unstable viscosity.
Storage conditions
Temperature and humidity: High temperature will accelerate the aging of silicone pressure-sensitive adhesives and reduce viscosity; high humidity environment may cause the colloid to absorb water, affecting its performance and viscosity. Generally, it should be stored in a cool and dry place.
Storage time: Even under suitable storage conditions, the viscosity of silicone pressure-sensitive adhesive may change over time, such as increased viscosity.
Packaging sealing: If the packaging is not well sealed, the solvent in the colloid will evaporate, causing the viscosity to thicken and change.
Use environment
Temperature: The viscosity of silicone pressure-sensitive adhesive varies at different temperatures. In a low temperature environment, the colloid may become hard and brittle, and the viscosity will decrease; in a high temperature environment, the colloid may soften, the viscosity may decrease or flow, affecting the bonding effect.
Humidity: A high humidity environment will cause the surface of the adherend to absorb moisture, reduce the surface energy, affect the bonding effect of the silicone pressure-sensitive adhesive and the adherend, and cause a decrease in viscosity.
Adhesive surface properties: The surface energy, roughness, cleanliness, etc. of the adherend will affect the viscosity. Materials with low surface energy, such as polyolefins and fluoroplastics without surface treatment, are difficult to bond, but silicone pressure-sensitive adhesives have good bonding properties to them; excessive or insufficient surface roughness, as well as contaminants such as oil and dust on the surface, will reduce the contact area and bonding strength between the silicone pressure-sensitive adhesive and the adherend, thereby affecting the viscosity.