Home / News & Blog / Abrasive Blog / What is the Bonding Mechanism and Bonding Agent Formula of Coated Abrasives?
In the research and understanding of the bonding mechanism of adhesives to abrasives and substrates in the manufacture of coated abrasives, many theoretical viewpoints have been proposed, but no consensus has been reached. The main bonding mechanisms are physical adsorption theory, mechanical bonding theory, diffusion theory, electrostatic theory, and chemical bond theory. Physical adsorption theory is often used to explain why abrasives are bonded to the substrate. According to the material structure theory, there are main valence forces of chemical bonds and weaker van der Waals forces (including bond forces, dipole forces, induced dipole forces, and dispersion forces) between atoms and molecules in the aggregated state of the material. The solid surface adsorbs liquids and gases due to the van der Waals force. This effect is called physical adsorption. Due to the physical adsorption effect, the adhesive completely infiltrates the surface of the adherend before curing, and the molecules are close enough to each other, so the van der Waals force between the molecules has a high adhesion strength.
Due to the rough surface of the particles, strong capillary action, and good hydrophilicity, adsorption is enhanced. The surface of paper or fabric-based substrate materials is loose, with many tiny pores and fibers. After pretreatment, the substrate exhibits good wettability and is easily adsorbed by the binder in coated abrasives. The binder structure contains polar groups, which form hydrogen bonds and dipole forces with the abrasive substrate, further increasing the bonding strength.
However, in actual production, the van der Waals forces calculated theoretically are much smaller than the actual bonding strength. Therefore, the physical adsorption theory cannot fully explain the bonding mechanism of coated abrasives. Other bonding theories reveal the true nature of the interaction between the binder and the adhered material from different perspectives.
The difference between the binder formulation for coated abrasives and that for bonded abrasives lies in the composition of substrate treatment agents, primer adhesives, and finishing adhesives: the combination and ratio between the treatment agent, primer, and finishing adhesive; and the compatibility of the binder with the abrasive material and substrate. Therefore, the binder formulation for coated abrasives is more complex.
The general principle for formulating the binder is based on the different requirements of the grinding application. The formulation can be determined according to factors such as the type of material being ground, the grinding method, the grinding conditions, the required processing quality, and the type of substrate used.
There are four bonding methods for the base glue and top glue used for coated abrasives.
1. Animal Glue Bonding: Both the primer and finishing adhesive are made from animal glue, and the substrate is paper or fabric. This type of binder can be used to produce sheet, roll, belt, or disc-shaped coated abrasives. It is suitable for applications where the grinding force is not high and utilization is low.
2. Semi-Resin Glue Bonding: In this bonding method, the primer is made from animal glue, and the finishing adhesive is made from synthetic resin. Sheet, roll, and belt products can be manufactured. This type of product offers better heat, moisture, and wear resistance than animal glue bonding, making it suitable for woodworking and surface finishing applications.
3. Full Resin Glue Bonding: In this bonding method, both the primer and finishing adhesive are made from synthetic resin. This resin is used to produce abrasive belts from paper, fabric, or steel paper, as well as disc- and roll-shaped products for grinding and processing mechanical parts.
4. Water-Resistant Bonding: This is suitable for abrasive belts with a fabric substrate grinding with water-soluble coolants. It can also be used for grinding parts made of steel, glass, ceramics, stone, and plastics. Paper-based products are mainly used to polish precision instrument parts. Water-resistant binders are typically made from water-soluble phenolic resins.
Formulating a binder involves determining the percentage content of the main ingredients and auxiliaries and the viscosity of the binder solution. The percentage content method for formulation is accurate and simple to prepare. The viscosity of the binder solution needs to be adjusted depending on the viscosity of the main ingredient (binder) and temperature. Table 2-7 lists formulations based on different surface roughness requirements and grinding conditions.
Table 2-7 Recipe Determined by Surface Roughness and Grinding Conditions
|
Workpiece |
High Roughness Value →Low Roughness Value |
High-Speed Grinding →Low-Speed Grinding |
|
Abrasive Type |
Zirconia Alumina、Alumina、Silicon Carbide、Garnet、Natural Emery |
Zirconia Alumina、Alumina、Silicon Carbide、Garnet、Natural Emery |
|
Abrasive Grain Size |
Coarse→Fine |
Fine→Coarse |
|
Sand Planting Method |
Sparse→Dense |
Dense→Sparse |
|
Binder |
Resin→Resin/Animal Glue→Animal Glue |
Resin→Resin/Animal Glue→Animal Glue |
|
Substrate |
Heavy-duty Type→Lightweight Type |
Steel Paper→Cloth→Paper |
|
Flexibility |
First Flexure→Secondary Flexure→Tertiary Flexure |
Tertiary Flexure→Secondary Flexure→First Flexure |
|
Coolant |
Dry Grinding→Water→Water-based Emulsion→Oil-based Fluid→Polishing Paste |
Water→Emulsion→Oil-based Fluid→Dry Grinding |
