1. Silane coupling agents are selective

It is not a coupling agent that can be applied to any system, but needs to be matched. In addition to the selection according to the reactivity between the organic active functional groups of the coupling agent and the polymer, the acidity and alkalinity of the system should also be considered.

Amino silane coupling agent is suitable for epoxy, phenolic, melamine, polyurethane, urea formaldehyde, neoprene and other adhesives; Epoxy silane coupling agent is suitable for epoxy, polyurethane, polysulfide rubber, etc; KH-570 is applicable to acrylic resin (instant drying adhesive SGA, anaerobic adhesive, etc.), unsaturated polyester resin, etc.; KH-580 and kh-590 are applicable to epoxy, polysulfide, silicone rubber, etc.; A-1160 is applicable to phenolic, polyurea, urea formaldehyde and other adhesives. The coupling agent has a certain acid or alkali, and the polymer and filler in the adhesive also have a certain acidity and alkalinity. If the acid and alkali are compatible, it will have a better coupling effect.

According to the test, KH-550 is highly alkaline, ND-42 is nearly neutral, KH-560 is weakly acidic, epoxy resin, phenolic resin, polyurethane, unsaturated polyester, butadiene rubber, chloroprene rubber, PVB and CPVC are weakly acidic, nylon, urea formaldehyde resin and melamine resin are alkaline, inorganic filler silica is acidic, light calcium carbonate is alkaline, and alumina is weakly acidic.

2. The real role of silane coupling agents

It is a molecular layer of 1 to 3 coupling agents tightly adsorbed on the surface of the adherend or filler, and the thickness of the monomolecular layer is the best. The appropriate amount of silane coupling agents directly added to the adhesive is 1% to 3% of the mass fraction of the resin or rubber.

For bonding with higher performance requirements, an ethanol solution with a mass fraction of 0.5 to 1% silane coupling agent can be used to treat the adherend, wash it, dry it, and then glue it. The effect is the most ideal.

If the amount of silane coupling agent is too large, the hydrolyzed silanol can not completely react with the adhered surface. It will accumulate on the surface and become an isolation zone, which will affect the coupling agent combined with the surface and then coupled with the adhesive. Therefore, too much dosage is harmful and useless.

3. Hydrolysis of silane coupling agents

It is the basic condition to realize the coupling effect. The composition, pH value and stirring time of the solution must be controlled to ensure the complete stability of the hydrolysis reaction. Hydrolysis is usually carried out in acidic solution.

When preparing the silane coupling agent aqueous solution, there is no need to use deionized water, let alone fluoride-containing ion water.

The silane coupling agent, which is easy to polycondensate of the hydrolyzed product, can easily precipitate out of the solution. It should be prepared for immediate use. Once white precipitate appears, it cannot be used.

The combination of several silane coupling agents can be suitable for a variety of functional groups required by different bonding systems. The hydrolysis rate and reaction activity can be adjusted and controlled to obtain the best bonding strength and durability.