Silane Coupling agents contain at least two different reactive groups within their molecules. One of these functional groups forms chemical bonds with inorganic materials, and the other forms chemical bonds with organic materials. This property enables silane coupling agents to function as intermediaries in bonding organic materials to inorganic materials, which normally tend not to bond with each other.
Higher-quality composite materials
Silane coupling agents improve dispersion during mixing of resins and fillers, and improve the mechanical strength, water and heat resistance, transparency, adhesion and other properties of the composite materials. Silane coupling agents are also highly effective in improving the chemical bonding of heat-cure resins and their compatibility with polymers.
Resin modification / Surface treatment
Reacting a resin with a silane coupling agent can improve its anchorage to inorganic materials, its low temperature humidity curing properties, and improve its weatherability and resistance to heat, acids and solvents. Silane coupling agents can also be used to treat the surface of inorganic materials to improve the materials' surface characteristics.
The alkoxysilyl group reacts with water to yield a silanol group that is not stable and will condense rapidly to form a siloxane structure. A silanol is usually not stable in the presence of water, but it is more stable in weakly acidic solutions. Aminosilanes are an exception since the amino group helps the silane to become more stable in water solutions. The following table gives information concerning water solutions of several products and their most stable pH values.
Silanes are usually diluted with water to a concentration of approximately 0.1 - 2.0 %. If using silanes that are not soluble in water, a combination of 0.1 - 2.0 % of acetic acid in water or water-alcohol (acetic acid, water, and alcohol together) is recommended. Acetic acid is used to control hydrolysis rates. Adjustment of the pH greatly influences the stability of silanols.
We understand that the solutions of silane coupling agent ares diluted when silane coupling agents are applied. Howare the solutions made?
Basic Structure
Functions
How to Use
Applications
Key Products
Silane coupling agents have two different types of reactive functional groups.
Inorganic Reactive Silanes
In the presence of water, coupling agents produce highly reactive silanols. Subsequently, these silanols begin to condense, forming oligomeric structures while also forming weak hydrogen bonds to the surface of inorganic materials. Finally, drying the inorganic materials leads to further condensation and dehydration between the coupling agent and the surface. This process yields multiple strong, stable, covalent bonds to the surface.
Organic Reactive Silanes
The improved adhesion between the surfaces of inorganic materials treated with silane coupling agents and organic resins is caused by:
Many different factors affect the above four items, such as the type of thermoplastic or thermosetting resins, whether or not functional groups remain, the abundance and reactivity of the remaining functional groups, and the overall polarity or non-polarity of the resins.
Thermoplastic resins
For thermoplastics, the chemical bonds introduced by reactive silanes are often relatively weak. A limited number of highly polar thermoplastics will develop weak interactions with some silane coupling agents. In these specific situations, both the thermoplastic resin and the silane are capable of forming hydrogen bonds. Therefore, the effectiveness of resin modification is highly dependent on the compatibility of each organic resin and its ability to form hydrogen bonds.
Thermosetting resins
Unlike thermoplastics where considerations such as the critical surface tension, the dissolution parameters, and other similar factors may be used to evaluate resin compatibility, these factors are not meaningful for predicting the strength of composite materials prepared from thermosetting resins. To maximize the strength and other physical properties of a thermosetting composite, it is generally recommended to first react the organic functional group of the silane with the thermosetting resin before curing the composite. It is important to use a reactive silane coupling agent bearing an appropriate functional group that matches the functional reactivity of the thermosetting resins.
There are two basic approaches for using silane coupling agents. The silane can either be used to treat the surface of the inorganic materials before mixing with the organic resin or it can be added directly to the organic resin.
The Surface Treatment of Inorganic Materials
By mixing a slurry of the inorganic materials in a dilute solution of the silane coupling agent, a highly uniform and precise surface treatment of the inorganic material can be obtained.
A high shear, high speed, mixer is used to disperse the silane coupling agent into the inorganic materials. The silane is generally applied either neat or as a concentrated solution. When compared to the Wet Method, the Dry Method is most often preferred for large-scale production, treating a large amount of filler in a relatively short time and generating relatively little mixed waste; however, it is more difficult to obtain uniform treatment with this method.
Addition To Organic Materials
Compared to the methods for the surface treatment of inorganic materials, adding the silane to the organic resin is more widely used in industries because of its excellent process efficiency, although curing may be more difficult. There are two general methods.
This method involves simple blending of the silane coupling agent into the composite formula as the inorganic and organic materials are mixed together.
In this method, the silane coupling agent is first added to a small amount of the organic resin material to form what is referred to as a "master batch". Usually in the form of pellets or large granules, the master batch can be easily added along with the pellets of the organic resin when producing the composite materials.
(1) Glass fiber reinforced epoxy resins
In order to meet the electrical properties and heat resistance requirements of epoxy resin laminated plates used with molten solder alloys, silane coupling agents are recommended as a resin modifier for the thermosetting composites. In this case, silane coupling agents are generally used to treat glass fibers that have been pre-treated with a water solution and then dipped in a resin vanish.
The most common use for coupling agents in epoxy molding compounds is as a semiconductor sealing agent that improves the moisture resistance and electrical characteristics of the resultant composite materials. The coupling agents form an interfacial bond between the resins and the filler that is stronger and more hydrolytically stable, yielding a better moisture resistant interface. In this case, volume resistivity and bending strength are also greatly improved.
The casting parts are comprised of fire resistant aggregates (sand) and adhesives. The quality of the resultant casting is reflects the strength of the adhesives coated on the surface of the sand particles. The coupling agents play an important role by improving the strength of the cast as well as preventing moisture. In most cases, the coupling agents are pre-added directly to the resins.
Thermoplastics
The results obtained from using coupling agents in thermoplastic resins are generally lower than when compared with that of thermosetting resins. However, in a limited number of systems such as nylon and plastic magnets, good results are achieved due to the high polarity of the thermoplastic resins that are used.
Resin modification
The uses of silane coupling agents are not limited to the interfaces of composite materials. Resin modification can create high performance resins with unique and superior characteristics. Typically, resins modified with silanes display improved adhesion to inorganic materials and moisture curable properties at low temperature, as well as superior resistance to weathering, acid, heat, and solvents. Product development continues, including the applications of polyolefins for electrical wires and acrylic resins for modified sealants.
For resin modifications with the silicon-based compounds, the following reactions are possible:
Grafting is widely used to produce polyolefin based materials for sealing electrical wires. Polyolefins that incorporate an unsaturated silane couplant (e.g., vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, etc.) have a silyltrimethoxy group grafted to the polyolefin backbone that enables moisture crosslinkable resins. Moisture crosslinkable polyolefins are highly preferred for electrical wire applications because of their reasonable cost and excellent electrical insulation, as well as their dielectric and mechanical stability. In these applications, common silanol condensation catalysts such as dibutyltindilaurate, dibutyltindioleate, dibutyltindiacetate, tetrabutyltitanate, and stannous octanoic acid are used in conjunction with the a peroxide for the grafting reaction.
Given the variety of silane coupling agents that are available bearing different organic functional groups as well as the many different types of organic resins produced, a large number of chemical reactions can be developed between using these compounds as reactants. Examples of applications for this type of silane modified resins include modified sealants, where polyoxyalkylene resins bearing a terminal aryl group react with a hydrosilane in the presence of platinum catalyst, and moisture curable urethane resins, where thermoplastic urethane resins have been modified by an amino functional alkoxysilane. These types of methods for resin modification are expected to continue to produce new resins in the future.
Copolymerization of an unsaturated silane monomer along with one or more organic monomers is widely used to modify acrylic resins for paints. This method often uses a silane couplant with a methacrylic functional group with compatible co-monomers.
KBE-9007
KBE-9007 is recommended to improve the adhesion of composite materials.
KBM-5103
KBM-5103, a new product with a reactive acryloxy functional group, is designed to significantly improve the adhesion and reinforcement of materials.
KBE-9103
KBE-9103 is used as an additive to epoxy or phenolic systems that would not otherwise allow a one-component system due to reactivity or incompatibility with aminosilanes.