The bonding strength of embossed silicone is affected by many factors such as raw material characteristics, vulcanization system, process parameters, mold design, environmental control, surface treatment and additive compatibility. It is necessary to ensure the bonding performance through system optimization. The following is a specific analysis:
Raw material characteristics:
Silicone and substrates (such as cloth, metal) have differences in chemical structure, surface energy, solubility parameters, etc., which directly affect the intermolecular force. If the two are not compatible, they are directly bonded without special treatment, which is easy to debond due to external force or environmental changes.
The quality of silicone raw materials is the key. Improper selection of vulcanizers, inaccurate addition, or uneven mixing of raw materials will lead to incomplete curing or internal defects of silicone, reducing the bonding strength.
Vulcanization system and process:
Insufficient use of vulcanizers (such as platinum, peroxide) or unbalanced proportions will cause insufficient cross-linking of silicone molecules, residual uncured groups on the surface, and cause sticking or debonding.
If the vulcanization temperature is too low (such as below 150°C) or the time is too short (such as molding time <5 minutes), the silicone is not completely cross-linked, and the surface is in a semi-cured state, which affects the bonding strength.
If the post-vulcanization treatment is not thorough (such as not cleaning the vulcanization byproducts and not performing secondary vulcanization), the residue will weaken the bonding interface performance.
Process parameter control:
During injection molding or compression molding, the temperature, pressure, and time must be precisely controlled. Too high a temperature may cause the silicone to decompose and produce bubbles; too low a temperature may cause incomplete injection molding and a rough surface.
Insufficient injection pressure will lead to insufficient silicone filling and lack of glue in the product; too high a pressure may damage the mold or make the product size longer.
Mold design:
The mold structure, wall thickness, cooling system, and exhaust system design affect the fluidity and bonding effect of the silicone. Poor exhaust will cause internal bubbles or shrinkage holes, reducing the bonding strength.
If the mold contact surface is uneven or there are stress concentration points, the silicone will have uneven contact with the substrate and uneven force, affecting the bonding strength.
Environmental factors:
When the humidity of the production environment is greater than 70%, silicone is easy to absorb moisture and cause the surface to become sticky; in a high temperature environment (greater than 60°C), the molecular chains of incompletely cured silicone move actively, increasing the risk of debonding.
Insufficient cleanliness of the working environment (such as dust and oil) will contaminate the surface of the silicone or substrate, affecting the bonding effect.
Surface treatment:
The surface of the substrate needs special treatment to enhance the bonding strength with silicone. For example, metal skeletons need to remove oil and rust spots to make the surface moderately rough; fabrics need to deal with the fleece and reduce the density of fine fluff.
Coating primer can improve the bonding performance, but the appropriate type needs to be selected and applied evenly.
Additive compatibility:
Plasticizers, masterbatches and other additives have poor compatibility with the silicone matrix. After long-term storage, they may precipitate to the surface to form sticky substances, reducing the bonding strength.
The migration of additives containing silicone oil components will cause the surface to become sticky, affecting the bonding effect.