Application areas of silane coupling agents

1. Composite materials: Composite materials refer to materials processed by specific equipment such as matrix resin, reinforcing materials (fillers, glass fibers), functional additives (coupling agents, release agents, toughening agents), etc. There are unsaturated polyester composite materials, phenolic molding compound, epoxy molding compound, epoxy potting compound, epoxy casting compound, epoxy glass fiber cloth, etc. Its characteristics are: high strength, high electrical performance, good formability and so on.

The silane coupling agent contains siloxane groups that can react with inorganic fillers, and epoxy groups, amino groups, vinyl groups, etc. that can react with organic resins. As a commonly used additive in composite materials, its function is to improve the wettability of the matrix resin to fillers and glass fibers, so that the matrix resin is connected with fillers or glass fibers through chemical bonds, thereby improving the flexural strength, impact strength, Water resistance, electrical properties, etc.

Toughening silane coupling agent refers to a flexible long chain with a certain molecular weight between the siloxane group and the organic active group. Due to the existence of flexible long chains, the chemical bonding density of the filler surface layer in the composite material is appropriately reduced. When the composite material is subjected to external impact, the flexible chain wrapped on the surface of the filler can absorb the impact energy well. This improves the impact strength of the composite and reduces stress cracking. At the same time, because most of the long-chain silane coupling agent is dispersed in the surface layer of the filler, and the content in the resin layer is small, the thermal deformation temperature and glass transition temperature of the composite material have little effect under the appropriate dosage.

The composites added with toughening silane coupling agent have high toughness and low internal stress, but the heat resistance is not decreased. Compared with general silane coupling agents, long-chain silane coupling agents also have unique advantages in improving the wettability of glue to fillers, especially for those fillers with high surface energy such as glass fiber, nano- Silica, etc. The long-chain silane coupling agent greatly reduces the surface energy of the filler due to its hydrophobic and flexible long-chain, so that the solvent, resin, and auxiliary in the glue can evenly penetrate into the glass fiber or It is uniformly dispersed on the surface of the nano-filler, which improves the impact strength, heat resistance, etc. of the composite material. When the glass fiber cloth treated with general silane coupling agent is coated with glue (such as epoxy-glass fiber prepreg for copper clad laminate production), due to the capillary phenomenon, acetone and dimethyl in the glue on the surface of the fiber cloth are always present. Low-molecular-weight polar solvents such as methylformamide diffuse preferentially in the glass fiber, which makes the viscosity of the glue on the surface of the fiber cloth increase sharply, and it is difficult for the resin and curing agent in the glue to quickly penetrate into the glass fiber. The composite material has poor impact strength and heat resistance. In addition, glass fiber composites treated with long-chain silane coupling agents have also been shown to have better resistance to ion migration.

Due to the influence of the long chain, the reaction speed of the toughened silane coupling agent and the filler or the silanol bond on the surface of the glass fiber is slightly slower, so it is necessary to appropriately prolong the processing time of the filler.

2. Organic adhesive: Silane coupling agent is a compound that can produce a certain binding force with polar substances and non-polar substances at the same time. It is characterized by having both polar and non-polar parts in the molecule, which can be expressed as Y ( CH2)nSiX3, where Y represents alkyl, phenyl and vinyl, epoxy, amino, mercapto and other organic functional groups, often chemically combined with organic functional groups in the adhesive matrix resin; X represents chlorine, methoxy, ethyl These groups are easily hydrolyzed into silanols and react with oxides or hydroxyl groups on the surface of inorganic substances (glass, silica, metal, clay, etc.) to form stable silicon-oxygen bonds. Therefore, by using a silane coupling agent, a "molecular bridge" can be set up between the interfaces of inorganic substances and organic substances to connect two materials with completely different properties together, thus effectively improving the bonding strength of the interface layer. . Adding a silane coupling agent to the adhesive can not only improve the adhesive strength, but also improve the durability and moisture-heat aging resistance of the adhesive. For example, although polyurethane has high adhesion to many materials, its durability is not ideal, and its durability can be significantly improved after adding a silane coupling agent. When Chen Ruizhu et al. studied the wet heat durability of titanium alloy adhesives, by adding a silane coupling agent to the epoxy adhesive used, the shear strength retention rate of the adhesive after wet heat aging was increased from about 80% to 100%. Around 97%. Silane coupling agents can even be directly used as adhesives for bonding silicone rubber, fluororubber, nitrile rubber, etc. with metals, such as adhesives CK-1 and Chemlock 607 (US) are silanes. In order to improve some properties of organic adhesives (such as heat resistance, self-extinguishing property, dimensional stability, etc.), or to reduce the cost of organic adhesives, some inorganic fillers are often added to adhesives. If the filler is treated with a silane coupling agent in advance, because the polar groups on the surface of the filler react with the silane coupling agent, the structuring effect of the filler and the resin is greatly reduced, not only the filler's effect on the adhesive matrix resin is reduced. Compatibility and dispersibility are greatly improved, and the viscosity of the system is significantly reduced, thus increasing the amount of filler. However, it is not effective for all fillers to be treated with coupling agents. Different types of fillers have different effects, and some even have no effect. For fillers with a large number of hydroxyl groups on the surface, such as silica, glass, and aluminum powder, the effect is the best, but for calcium carbonate, graphite, boron, and other fillers without hydroxyl groups on the surface, it has no effect.

3. Plastics: Filling modification is one of the important means of plastic modification. Rigidity and toughness are two important performance indicators of plastic products. How to ensure that plastic products have good rigidity and toughness at the same time has been an important subject of material science research for a long time. one.

One of the technical keys to improve the effect of filling and modification is the surface treatment technology of inorganic powder. At present, the most widely used is the coupling agent activation technology. There are many industrial varieties of coupling agents, mainly including silanes, titanates, aluminates, aluminum-titanium complex esters, phosphates, borate and other coupling agents. Coupling agents are usually amphiphilic substances, some of which are adsorbed on the surface of the filler or react with the bound water or OH on the surface; other groups (or long chains) are entangled with the polymer matrix to improve the interaction between the inorganic filler and the surface. The compatibility of the substrate resin improves its dispersion in the matrix and interfacial adhesion. However, due to the short organic segment of the organic coupling agent and the small interaction with the matrix, the improvement of the mechanical properties of the material is limited.

It is hoped that a coupling agent with a new structure can not only maintain the amphiphilic structure of the traditional coupling agent, but also bond, associate or form other forms of physical interaction with the filler and the base resin with stronger binding force. The structural characteristics of rare earth elements just meet this demand. Guangdong Weilinna Co., Ltd. uses rare earth elements and organic ligands to synthesize a new type of modifier with toughening coupling and multi-functional properties for PVC application systems. Developed a new surface treatment agent. This product can be used as a toughening agent for inorganic rigid particles for PVC. It is multifunctional and has a unique cost-effective and synergistic modification effect on PVC or PVC/CaC03 filling systems. It has been applied in industry.