Silane coupling agent is a type of organic silicon compound that contains two different chemical functional groups in its molecule. It acts at the interface between inorganic materials (such as glass, metal, or mineral) and organic materials (such as organic polymers, coatings, or adhesives), binding or coupling two completely different materials. It enhances the affinity between organic and inorganic compounds, and can strengthen and improve the physical and chemical properties of composite materials, such as strength, toughness, electrical properties, water resistance, and corrosion resistance.
Performance characteristics and advantages
When using glass fiber or mineral reinforced organic polymers, the interface or interfacial phase between the polymer and inorganic materials involves complex interactions between many physical and chemical factors. These factors are related to the resultant force, physical strength, coefficient of expansion, concentration gradient, and product performance retention. The important destructive force that affects harmony is the migration of water to the inorganic enhanced hydrophilic surface. Moisture erodes the interface and damages the adhesion.
Silane coupling agent can not only be used as elastic bridging agent between substrates, that is, to improve the adhesion between two materials with different chemical properties, so as to improve the mechanical, electrical insulation, anti-aging, hydrophobic and other comprehensive properties of products; It can also be used as a surface modifier for materials, endowing them with waterproof, anti-static, anti mold, anti odor, anti coagulation, and physiological inertness properties; It can also be used as a crosslinking curing agent for non crosslinked polymer systems to achieve room temperature and pressure curing. In composite materials, selecting appropriate silicon can increase the bending strength of the composite material by more than 40%. Silane coupling agents also enhance the bonding strength between coatings and adhesives, while increasing resistance to humidity and other harsh environmental conditions.
Other advantages that silane coupling agents can provide include:
1. Better wetting of inorganic materials
2. Compound with lower viscosity
3. Smoother surface of composite materials
4. Reduce the inhibitory effect of inorganic materials on thermosetting composite catalysts
5. Clearer and more transparent reinforced plastic
Principles for selecting silane coupling agents
Matching the organic functional groups on silicon atoms with the type of resin polymer to be bonded can guide the use of which silane coupling agent to use in specific applications. The organic groups on silane can be reactive organic groups (such as organic functional groups) or non reactive organic groups. These functional groups can be hydrophobic or hydrophilic, or possess various thermal stability properties. Due to different organic structures, the solubility parameters of functional groups vary; To some extent, this will affect the interpenetration between the polymer system and the siloxane system used for surface treatment. Table 1 lists some common characteristics of organic substituents used for silicon atoms. The selection of silane should include matching chemical reactivity, solubility, structural characteristics, and even the thermal stability of organosilane with the same parameters in the polymer structure.
Usage of Silane Coupling Agent
1. Surface treatment method
This method uses silane coupling agents to connect inorganic and polymer interfaces together to achieve optimal wetting values and dispersibility. The surface treatment method requires the silane coupling agent to be acidified into a dilute solution to facilitate sufficient contact with the treated surface. The solvents used are mostly water, alcohol, or a mixture of water and alcohol, and ion free water and inexpensive non-toxic ethanol and isopropanol are preferred. Except for aminoalkylsilane, solutions prepared from other silanes require the addition of acetic acid as a hydrolysis catalyst and the adjustment of pH to 3.5-5.5. Long chain alkyl and phenylsilane are not suitable for use as aqueous solutions due to their poor stability. During the hydrolysis process of chlorosilanes and acetoxysilanes, severe condensation reactions will occur. It is also not suitable for preparing aqueous solution or aqueous alcohol solution. For silicon coupling agent with poor water solubility, non-ionic surfactant with mass fraction of 0.1% -0.2% can be added first, and then water can be added to process it into aqueous lotion for use. In order to improve the economic benefits of hydrolysis stability of the product, a certain proportion of non carbon functional silane can also be added to the silane coupling agent. When dealing with difficult to stick materials, mixed silane coupling agents or carbon functional siloxanes can be used in combination. After the treatment solution is prepared, it can be treated by dipping, spray or brushing. Generally speaking, block materials, granular materials, and glass fibers are often treated by impregnation method; Powder materials are mostly treated by spray method: if the substrate surface needs overall coating, brush coating method is used.
The application areas of silane coupling agents include coatings and inks. The use of silicone based coatings has the following advantages:
1. Corrosion resistance
2. Improve adhesion
3. Improve rheological properties
4. Improve the dispersibility of dyes and fillers
5. UV resistant
6. Waterproof and chemical resistant
Synthetic synthetic rubber and resin coatings often encounter adhesion problems on hydrophilic silicate and metallic surfaces, especially in high tide, water, or salt environments. The protective effect of the coating relies on the adhesion promoter on the substrate surface. Whether used as a coating additive or primer, silane coupling agents can improve the performance of the coating.