Coupling Agents in Abrasives: What You Need to Know

In recent years, the application of coupling agents in abrasives has become increasingly widespread. Especially now that the market is seriously involuntary, colleagues who make grinding wheels hope to make their products well and make their own characteristics. Many grinding wheel friends have consulted about the coupling agent. This article will briefly introduce it, hoping to provide a reference for everyone.

1. Common types of coupling agents

In the manufacture of abrasive tools, especially resin grinding wheels, a high-performance modified material is needed to improve the interface performance between phenolic resin and inorganic filler or reinforcing material, and the coupling agent is one of them. . It can reduce the viscosity of synthetic resin melt during the manufacturing process of resin grinding wheel, improve the dispersion of fillers to improve processing performance, and then make the product obtain good surface quality and mechanical, thermal and electrical properties.

Its dosage is generally 0.5-2% of the filler dosage. The coupling agent generally consists of two parts: one part is an inorganic group, which can interact with inorganic fillers or reinforcing materials; the other part is an organophilic group, which can interact with phenolic resins.

According to the chemical structure and composition of the coupling agent, it can be divided into four categories: organic chromium complexes, silanes, titanates and aluminate compounds:

Chromium complex coupling

Chromium complex coupling agent was developed in the early 1950s. The metal chromium complex formed by unsaturated organic acid and trivalent chromium ions has relatively mature synthesis and application technology and low cost, but the variety is relatively single.

A silane coupling agent
The general formula of the silane coupling agent is RSiX3, where R represents groups such as amino, mercapto, vinyl, epoxy, cyano and methacryloxy groups. These groups and different base resins have strong Reactivity, X represents an alkoxy group capable of hydrolysis (such as methoxy, ethoxy, etc.). There are several types of silane coupling agents in China: KH550, KH560, KH570, KH792, DL602, and DL171.

Titanate coupling agent
According to their unique molecular structure, titanate coupling agents include four basic types: ① Monoalkoxy type coupling agents are suitable for a variety of resin-based composite material systems, especially suitable for free water, only containing Filling system of chemically bonded water or physical water; ②Monoalkoxy pyrophosphate type This type of coupling agent is suitable for a variety of resin-based composite material systems, especially suitable for filler systems with high moisture content ; ③Chelating type The coupling agent This kind of coupling agent is suitable for a variety of resin-based composite material systems. Because of their very good hydrolytic stability, this type of coupling agent is especially suitable for aqueous polymer systems; ④ Ligand type This type of coupling agent is used in a variety of It has good coupling effect in resin-based or rubber-based composite material systems, and it overcomes the shortcomings of general titanate coupling agents used in resin-based composite material systems.

Other coupling agents

Zirconium coupling agent is a low molecular weight inorganic polymer containing zirconium aluminate . It can not only promote the adhesion between different substances, but also improve the performance of composite material systems, especially the rheological properties. This type of coupling agent is suitable for both thermosetting resins and thermoplastic resins . In addition, there are magnesium coupling agents and tin coupling agents.

In reinforced plastics , chemical substances that can improve the interfacial bonding force between the resin and the reinforced material.

A substance that promotes or establishes a stronger bond at the interface between the resin matrix and the reinforcing material.

2. Introduction of main commonly used coupling agents

(1) Silane coupling agent series

1.  γ-Aminopropyltriethoxysilane

Domestic brand: KH-550; Dow Corning: Z-6011; Japan Shin-Etsu: KBM-903.

The main purpose:

1) Coatings, adhesives and sealants

This aminosilane is an excellent adhesion promoter for acrylic coatings, adhesives and sealants. For sulfide, urethane, RTV, epoxy, nitrile, and phenolic binders and sealants, aminosilanes improve pigment dispersion and enhance adhesion to glass, aluminum, and steel.

2) Reinforcement of glass fiber

Used in glass fiber reinforced thermosets and thermoplastics, this product can greatly improve the flexural strength, tensile strength and interlaminar shear strength in wet and dry conditions and significantly improve wet electrical performance. When this silane is used in wet and dry conditions, the flexural and tensile strengths of glass fiber reinforced thermoplastics, polyamides, polyesters and polycarbonates are increased before and after water immersion.

3) Fiberglass and mineral wool insulation

Adding it to the phenolic resin binder can improve moisture resistance and resilience after compression.

4) Mineral filler and resin system

This product can greatly improve the physical and mechanical properties and electrical properties of phenolic resin, polyester resin, epoxy, polyamide, polyurethane, polycarbonate and other thermoplastic and thermosetting resins filled with inorganic fillers, and improve the wetting of fillers in polymers. Moisture and dispersibility.

5) Foundry application

This product can improve the cohesion of phenolic binder and foundry sand.

6) Grinding wheel manufacturing

This product helps to improve the adhesion and water resistance of wear-resistant no-bake sand and phenolic binders.

7) Engineering plastics

This product greatly improves the compatibility of inorganic fillers and resins, increases their fluidity; and can improve the strength and toughness of engineering plastics.

Applicable resins: phenolic, epoxy, PA, PU, ​​PC, PET, melamine, acrylic, etc.

2. γ-(2,3-Glycidoxy)propyltrimethoxysilane

Domestic brand: KH-560; Dow Corning: Z-6011, Z-6040; Japan Shin-Etsu: KBM-403.

The main purpose:

1) Epoxy resin electronic potting glue

This product can improve the compatibility of inorganic fillers and epoxy resins, improve the adhesion between products and substrates, thereby improving the electrical properties of epoxy resin electronic materials and packaging.

2) Glass fiber and FRP

This product can improve the wet physical and mechanical strength and wet electrical performance of composite materials; it can also improve the aggregation, protection and processing technology of glass fibers. Improve antistatic performance, increase strength and improve toughness.

3) paint

This product can improve the compatibility between fillers and resins, prevent sedimentation, reduce viscosity, increase the coating surface area; increase the adhesion with the substrate surface, improve strength and weather resistance.

4) Filler modification

As a surface treatment agent for inorganic fillers, this product is widely used in the surface treatment of inorganic fillers such as clay, talcum powder, wollastonite, white carbon black, quartz, aluminum powder, and iron powder.

Applicable resins: epoxy resin, PA66, saturated polyester (PBT), acrylic, etc.

3. γ-Methacryloxypropyltrimethoxysilane _ _

Domestic brand: KH-570; Dow Corning: Z-603; Japan Shin-Etsu: KBM-503.

The main purpose:

1) Composite materials

KH-570 is mainly used for unsaturated polyester composite materials, which can improve the mechanical properties, electrical properties and light transmission properties of composite materials, especially the wet performance of composite materials can be greatly improved.

2) Fiberglass and FRP

Treating glass fiber with sizing agent containing KH-570 silane coupling agent can improve the strength of glass fiber products and improve the mechanical strength and electrical properties of products in wet state.

3) Wire and cable

Using silane coupling agent KH-570 to treat filler-filled oxide cross-linked EPM and EPDM systems improves the consumption factor and specific capacitance reactance. At the same time improve the anti-aging and weather resistance of wire and cable.

4) Coatings, adhesives and sealants

KH-570 is copolymerized with vinyl acetate and acrylic or methacrylic monomers to provide excellent adhesion and durability.

Applicable resin: unsaturated resin, EPDM rubber, ABS, PVC, PE, PP, PS, acrylic acid, etc.

4.  N-(β-aminoethyl)-γ-aminopropyltrimethyl(ethyl)oxysilane

Domestic brand: KH-792; Dow Corning: Z-6020; Japan Shin-Etsu: KBM-603.

The main purpose:

1) Improve the adhesion, improve the dry and wet tensile strength and modulus, flexural strength and compressive strength of the composite material. Especially the wet electrical performance of the product.

2) It is mainly used to improve the performance of epoxy, phenolic, melamine, furan and other resin laminated materials, and it is also effective for polypropylene, polyethylene, polyacrylate, silicone, polyamide, polycarbonate and polyvinyl cyanide.

3) It is mainly used as glass fiber finishing agent, and is also widely used in silicon-containing substances such as glass beads, white carbon black, talc, mica, clay, and fly ash.

5.  Isopropyl dioleate (dioctyl phosphate acyloxy) titanate

Domestic brands: GR-102; Kenrich KR-12.

The main purpose:

1) Thermosetting resins and coatings

This product can be used to reduce the baking temperature and shorten the baking time in alkyd paint, and has good dispersion and anti-sedimentation effects on pigments. It is especially effective for anti-settling and caking of acrylic baking paints.

2) Aluminum silver paste

This product is used in aluminum silver paste, which can improve the dispersion and adhesion of aluminum powder in the paste.

3) Composite materials

This product is used to treat calcium carbonate, barium sulfate, talcum powder and other inorganic filler filled polar resins, such as ABS, PBT, soft PVC, LDPE, can improve the dispersion and adhesion of fillers in the resin, and improve the processing fluidity. Improve the mechanical strength of composite materials.

Applicable resins: PVC, ABS, PBT, alkyd resin, acrylic, etc.

6. Isopropoxy tris(dioctyl pyrophosphate acyloxy) titanate

Domestic brands: GR-201; Kenrich KR-38S.

The main purpose:

1) plastic

This product is a pyrophosphate titanate coupling agent, which can be used to treat calcium carbonate, talcum powder, kaolin, magnesium hydroxide, aluminum hydroxide, titanium dioxide, lithopone, calcium oxide, starch, wood flour and inorganic pigments . The filler treated with this product is added to polar or weak polar thermoplastics, which can improve the impact strength and elongation of plastic products, and at the same time improve the processing performance of products. The filler treated with this product can add 30%-50% more parts without affecting the mechanical properties of the product.

2) paint

Using this product to treat fillers or pigments used in coatings can reduce the viscosity of the system, increase the hiding power and tinting power of the pigments, and improve the anti-corrosion, water resistance and fire resistance of the coating.

3) Rubber, plastic, cable

This product is used in cable materials, which can improve the tensile strength, tear strength, elongation at break and anti-aging performance of the product.

Applicable resins: PP, PVC, PS, PC, AS, ABS, PBT, SBS natural rubber, butadiene, butyl, neoprene, etc.

7. Tetraisopropyl bis(dioctyl phosphite) titanate

Domestic brands: GR-401; Kenrich KR-46B.

The main purpose:

1) FRP

GR-401 is used in unsaturated polyester FRP to improve the mechanical properties and anti-aging performance of FRP.

2) paint

This product is used in high solid content titanium dioxide, clay and epoxy coatings to reduce the amount of titanium dioxide and solvents, increase the filling amount of clay, and at the same time not change the viscosity of the system; increase the adhesion of coatings to glass and metal.

3) Inorganic materials

Surface treatment is used to treat inorganic fillers such as metal powder to improve the dispersibility and anti-sedimentation of fillers.

Applicable resins: alkyd resin, acrylic, epoxy, polyurethane, etc.

8. Aluminate coupling agent series

Isopropyl Distearic Acid Aluminate GR-AL18, DL411

1) In addition to stable quality, the inorganic powder activated by this product also has light color, non-toxicity, low odor, synergistic thermal stability and lubricity to PVC, wide application range, convenient use and low price.

2) Various powders that have been activated and modified by this product will form a layer of organic molecules due to the chemical action on the surface, changing from hydrophilic to organic. Experiments have proved that the surface of inorganic powder is modified by this product and used in composite products. The coupling agent’s pro-inorganic fracture and pro-organic fracture can chemically react or entangle with the surface of inorganic filler and organic resin respectively, which strengthens the inorganic powder. Interfacial compatibility with organic resin, so modifying with aluminum coupling agent can not only improve the processing performance of plastic products filled with inorganic powder, but also significantly improve the physical and mechanical properties of the product, so that the product’s water absorption rate decreases and oil absorption The value decreases and the filler is dispersed evenly. For some low-filling plastic products, generally, the amount of filler can be greatly increased (more than 50% more than the original filling amount), the processing performance can be improved (melt viscosity is reduced, and the wear on the mold is reduced), the product quality can be improved, and the production cost can be reduced. Has obvious economic benefits.

3. How to use coupling agent (mainly silane type)

Before choosing a coupling agent, the moisture content of the filler used should be measured first, and the specific species should be determined according to the moisture content state and the characteristics of the aforementioned titanate esters. The dry filler should be monoalkoxy type, and the wet filler is optional. Chelate type or monoalkoxy pyrophosphate type.

When selecting a coupling agent, the melting point, crystallinity, molecular weight, polarity, aromaticity, fat feet, copolymerization structure, etc. of the polymer should also be considered. For thermosetting polymers, the curing temperature and curing mechanism should also be considered.

The shape, specific surface, moisture content, acidity and alkalinity, and chemical composition of fillers can all affect the coupling effect. Generally, the coupling effect of coarse particle fillers is not as good as that of fine particles, but the effect of superfine fillers (such as CaCO 3 ≥ 2000 mesh) has the opposite phenomenon.

The amount of coupling agent is generally 0.5-3% of the weight of the treated product, and the recommended amount is 0.8-1.5%. The amount and the effect are not directly proportional. If the amount is too much, the coupling agent will be excessive and the performance will be reduced instead. If it is too little, the effect will not be significant due to incomplete encapsulation. Therefore, it is necessary to test out the optimal dosage during application, so as to be economical and effective.

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