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Specific Application of Silane Coupling Agent

Feb 25, 2021

The silane coupling agent  is mainly used for glass fiber reinforced plastics. The molecular structure of the silane coupling agent is generally: Y-R-Si(OR)3 (where Y is an organic functional group and SiOR is a siloxy group). Siloxy groups are reactive to inorganic substances, and organic functional groups are reactive or compatible to organic substances. Therefore, when the silane coupling agent is between the inorganic and organic interface, a bonding layer of organic matrix-silane coupling agent-inorganic matrix can be formed. Typical silane coupling agents include A151 (vinyl triethoxy silane), A171 (vinyl trimethoxy silane), A172 (vinyl tris (β-methoxyethoxy) silane) and the like.

Here, n=0~3; X-hydrolyzable group; Y-organic functional group, which can react with resin. X is usually a chlorine group, methoxy group, ethoxy group, methoxyethoxy group, acetoxy group, etc. When these groups are hydrolyzed, silanol (Si(OH)3) is formed, which combines with inorganic substances to form Siloxane. Y is a vinyl group, an amino group, an epoxy group, a methacryloxy group, a mercapto group or a ureido group. These reactive groups can react with organic substances to bond. Therefore, through the use of silane coupling agents, a "molecular bridge" can be built between the interface of inorganic and organic substances to connect two materials with very different properties to improve the performance of composite materials and increase the bonding strength. This characteristic of silane coupling agent was first applied to glass fiber reinforced plastics (glass fiber reinforced plastic) as a surface treatment agent for glass fiber, which greatly improved the mechanical properties, electrical properties and anti-aging properties of glass fiber reinforced plastic. The importance of has long been recognized.

The use of silane coupling agents has expanded from glass fiber reinforced plastics (FRP) to glass fiber surface treatment agents for glass fiber reinforced thermoplastics (FRTP), surface treatment agents for inorganic fillers and sealants, resin concrete, and water crosslinking Polyethylene, resin packaging materials, shell molding, tires, belts, coatings, adhesives, abrasive materials (grindstones) and other surface treatment agents. Among the two groups of silane coupling agents with different properties, the Y group is the most important, which has a great influence on the performance of the product, and plays a role in determining the performance of the coupling agent. Only when the Y group can react with the corresponding resin can the strength of the composite material be improved. Generally, the Y group is required to be compatible with the resin and capable of coupling reaction.

Application field
The application of silane coupling agent can be roughly summarized into three aspects:
Surface treatment
It can improve the bonding performance of glass fiber and resin, greatly improve the strength, electrical, water resistance, weather resistance and other properties of glass fiber reinforced composite materials. Even in the wet state, it can improve the mechanical properties of composite materials and the effect is very significant. . The use of silane coupling agents in glass fibers is quite common. The silane coupling agents used in this area account for about 50% of the total consumption. Among them, the most used varieties are vinyl silane, amino silane, and methyl. Acryloyloxysilane, etc.

Filled plastic
The filler can be surface treated in advance, or directly added to the resin. It can improve the dispersion and adhesion of the filler in the resin, improve the compatibility between the inorganic filler and the resin, improve the process performance and improve the mechanical, electrical and weather resistance properties of the filled plastic (including rubber).
Used as a sealant, adhesive and paint thickener

It can improve their bonding strength, water resistance, weather resistance and other properties. Silane coupling agents can often solve the problem that certain materials cannot be bonded for a long time. The principle of action of silane coupling agent as a tackifier is that it has two groups; one group can be combined with the frame material to be adhered; and the other group can be combined with polymer materials or adhesives , Thus forming a stronger chemical bond at the bonding interface, greatly improving the bonding strength. There are generally three methods for the application of silane coupling agents: one is as a surface treatment agent for framework materials; the other is to add to the adhesive, and the third is to directly add to the polymer material. From the perspective of giving full play to its effectiveness and reducing costs, the first two methods are better.

The specific applications of silane coupling agents in the adhesive industry are as follows:①In the structural adhesive, the metal and non-metal bonding, if a silane type tackifier is used, it can condense with the metal oxide or with another silanol, so that the silicon atoms are in close contact with the surface of the object. For example, adding silane as a tackifier in the nitrile phenolic structural adhesive can significantly improve the bonding strength.② Silane has been widely used as a treatment agent in bonding glass fibers at home and abroad. It can chemically react with the interface to improve the bonding strength. For example, if chloroprene glue is not used as a treating agent, the peel strength of the glue is 1.07 kg/cm2, and if aminosilane is used as a treating agent, the peel strength of the glue is 8.7 kg/cm2.③In the bonding of rubber and other materials, silane tackifier has a special function. It obviously improves the bonding strength of various rubbers and other materials. For example, when glass and polyurethane rubber are glued, if silane is not used as a treatment agent, the peel strength of the glue is 0.224 kg/cm2, and if silane is added, the peel strength is 7.26 kg/cm2.④ Bonding problems that cannot be solved with general adhesives can sometimes be solved with silane coupling agents. For example, aluminum and polyethylene, silicon rubber and metal, silicon rubber and organic glass, can be based on the chemical bond theory, select the corresponding silane coupling agent, and get a satisfactory solution. For example, vinyl triperoxide tert-butyl silane (Y-4310) can be used to bond polyethylene to aluminum foil; butadienyl triethoxy silane can make the pull-off strength of silicone rubber and metal reach 21.6~ 22.4 kg/cm2. General adhesives or resins combined with coupling agents can not only increase the adhesive strength, but also increase the water resistance and durability of the adhesive force. For example, polyurethane and epoxy resin have high adhesion to many materials, but the durability and water resistance of adhesion are not ideal; after adding silane coupling agent, the performance in this area can be significantly improved .⑤ It can be used for organic treatment in the production process of electrolytic copper foil. That is, the silane coupling agent is uniformly sprayed on the surface of the copper foil to form an organic film, which further improves the oxidation resistance and solder resistance, and also helps to improve the bonding force between the copper foil and the substrate.

Other applications
Other applications of silane coupling agents include:
①Attach the immobilized enzyme to the surface of the glass substrate,
②Sand control during oil well drilling,
③Make the masonry surface hydrophobic,
④The fluorescent lamp coating has a higher surface resistance by preventing moisture absorption;
⑤Improve the moisture absorption performance of the organic relative to the glass surface in the liquid chromatography column.

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