How to improve the adhesion of the middle layer of screen printing silicone?
Surface cleaning:
Remove dirt and impurities: Before screen printing, make sure the surface of the substrate is clean and free of dust, oil, release agent and other impurities. You can use organic solvents such as alcohol and acetone to wipe and clean, or use ultrasonic cleaning and other methods to completely remove the dirt on the surface, because these impurities will affect the contact between the silicone and the substrate and reduce the adhesion.
Polishing: For some substrates with smoother surfaces, such as plastics and metals, you can use tools such as sandpaper or grinding wheels to lightly polish and increase the roughness of the surface. Rough surfaces can provide more contact areas and mechanical anchor points, which is conducive to the adhesion of silicone. However, pay attention to the strength and uniformity when polishing to avoid excessive polishing that may damage the surface of the substrate.
Choose the right silicone material and formula:
Choose the right type of silicone: Different types of silicone have different properties and adhesion. For example, the cross-linking density of addition-type silicone is higher, and the network structure formed after curing is tighter, and the adhesion is relatively strong; while the cross-linking density of condensation-type silicone is lower, and the adhesion may be relatively weak. Choose the right type of silicone according to the specific application requirements and substrate material.
Optimize the silicone formula: In the silicone formula, some additives that can improve adhesion, such as coupling agents, tackifiers, etc., can be added. Coupling agents can form chemical bonds between silicone and substrates to enhance the bonding between the two; tackifiers can increase the viscosity of silicone and improve its adhesion on the surface of the substrate. However, when adding additives, pay attention to controlling the amount, as excessive amounts may affect other properties of silicone.
Correct screen printing process operation:
Control the screen printing thickness: The thickness of the middle layer of the screen printing silicone also affects the adhesion. If the thickness is too thin, it may not form sufficient mechanical anchoring force and chemical bonding, resulting in insufficient adhesion; if the thickness is too thick, it may generate internal stress during the drying or curing process, affecting adhesion. Therefore, it is necessary to select the appropriate screen printing thickness based on the material and shape of the substrate and the properties of the silicone.
Ensure drying and curing conditions: The drying and curing process of silicone is crucial to adhesion. Strictly follow the instructions for use of the silicone material to control the temperature, time, humidity and other conditions of drying and curing. If the temperature is too low or the time is too short, the silicone may not be completely cured, affecting the adhesion; if the temperature is too high or the time is too long, the silicone may age and become brittle, which will also reduce the adhesion.
Use surface treatment technology:
Plasma treatment: Plasma is used to treat the surface of the substrate to remove dirt and impurities on the surface, and polar groups are introduced to the surface to improve the hydrophilicity and activity of the surface, thereby enhancing the adhesion between the silicone and the substrate.
Flame treatment: For some high-temperature resistant substrates, flame treatment can be used. Flame treatment can change the molecular structure of the substrate surface, increase the surface roughness and activity, and improve the adhesion of the silicone. However, during flame treatment, it is necessary to pay attention to controlling the temperature and treatment time of the flame to avoid damage to the substrate.
Primer treatment: Before screen printing silicone, apply a layer of primer on the surface of the substrate. The primer can act as a bridge to enhance the bonding between the silicone and the substrate. Selecting a suitable primer and following the instructions can significantly improve the adhesion of the middle layer of the screen printing silicone.