How to improve the adhesion of silicone?

How to improve the adhesion of silicone?
You can start from the key aspects of silicone itself, bonded materials, surface treatment and bonding process:
Silicone selection and modification
Choose suitable silicone products: Choose suitable silicone according to the bonded materials and usage scenarios. For example, for plastic bonding, choose silicone specifically for plastic bonding; for outdoor use, choose silicone with good weather resistance.
Adding viscosity-enhancing agents: Adding viscosity-enhancing agents such as silane coupling agents to silicone can improve the chemical affinity between silicone and the surface of the bonded material and enhance the adhesion. After the silane coupling agent is hydrolyzed, one end reacts with the silanol group in the silicone and the other end reacts with the active group on the surface of the bonded material to form a chemical bond and enhance the adhesion.
Optimize the silicone formula: By adjusting the silicone formula, such as changing the polymer type, the ratio of the crosslinking agent and the type of catalyst, the structure and performance of the silicone after curing can be optimized to improve the adhesion. Appropriately increasing the amount of crosslinking agent can increase the crosslinking density of the silicone and enhance the cohesion, which is conducive to improving the adhesion, but excessive crosslinking will make the silicone brittle and need to be reasonably controlled.
Selection and treatment of bonded materials
Choose easy-to-bond materials: give priority to bonded materials with high surface energy and strong polarity, such as metal, glass and ceramic, which are easy to interact strongly with silicone and have good bonding strength.
Mechanical treatment: sandblast, polish or rub the surface of the bonded material with sandpaper to increase the surface roughness, expand the contact area with silicone, generate mechanical meshing force and improve bonding strength. For example, sandblasting the metal surface will form tiny bumps on the surface, allowing silicone to be better embedded.
Chemical treatment: treat the surface of the bonded material with chemical reagents to change its chemical properties and increase surface activity. For example, treat polyolefin plastics with chromic acid solution to introduce polar groups; aluminum alloys are degreased with alkali solution and corroded with acid to form an active oxide film to enhance the reaction ability with silicone.
Surface pretreatment
Cleaning the surface: use organic solvents such as acetone and toluene, or deionized water and neutral detergent to remove impurities such as oil, dust, mold release agent and oxide layer on the surface of the bonded material to ensure full contact between silicone and the material surface. If the metal surface is oily, wipe it clean with an organic solvent.
Primer treatment: Apply primer to the surface of the bonded material or silicone to improve the compatibility and adhesion between the two. Primer can react chemically or physically adsorb with the surface of the bonded material, and at the same time combine well with silicone. For example, when rubber and silicone are bonded, use a primer containing a silane coupling agent to improve the adhesion.
Optimize bonding process
Control the amount of glue applied: The amount of glue applied should be moderate to ensure that the silicone fully covers the bonded surface, and avoid excessive sagging and bubbles that affect the bonding effect. For different bonding areas and shapes, the appropriate amount of glue applied needs to be determined through experiments.
Ensure uniform glue application: Use appropriate glue application methods, such as brushing, spraying, and scraping, to ensure that the silicone is evenly distributed on the surface of the bonded material. Brushing is suitable for small areas and complex shapes; spraying has high efficiency and uniform glue layer, and is used for large-area bonding; scraping can accurately control the thickness of the glue layer.
Optimize curing conditions: Strictly control the curing temperature, humidity and time according to the instructions of the silicone product. Properly increasing the curing temperature can speed up the curing of silicone, increase the degree of cross-linking, and improve the bonding strength, but too high a temperature will cause silicone aging and performance degradation. Some silicones need to be cured in a specific humidity environment, so the humidity of the environment must be controlled.