Solvent free adhesives can be classified according to a variety of different methods. The most common classification method is to classify the adhesives according to their chemical structures, components or uses.
1. Classification by chemical structure
Polyurethane adhesive is prepared by the reaction of isocyanate and hydroxyl containing compounds (polyester or polyether). According to the different hydroxyl compounds used, there are polyether type solvent-free adhesive, polyester type solvent-free adhesive and polyester polyether mixed type solvent-free adhesive; according to the different isocyanate used, there are aromatic solvent-free adhesive and fat type solvent-free adhesive There are three parts.
2. Classification by component
According to the different components of solvent-free adhesives, there are two-component solvent-free adhesives and one-component solvent-free adhesives.
The two-component solvent-free adhesive can be widely used in the production of all plastic flexible packaging materials due to the chemical reaction between the two components in the process of use; the one-component solvent-free adhesive needs to rely on the reaction between water molecules in the air and the isocyanate of the adhesive, and carbon dioxide is generated during the curing process, which needs to be emitted to the air through the substrate Therefore, it can only be applied to the composite of base materials containing loose materials such as paper. In the field of solvent-free composite, two-component solvent-free adhesive has an overwhelming advantage over single-component solvent-free adhesive in terms of application area or amount, but it does not mean that one-component solvent-free adhesive is a useless and dispensable variety. In the paper plastic and paper aluminum composite, the single component solvent-free adhesive has outstanding advantages over the two-component polyurethane solvent-free adhesive: due to the high molecular weight, high viscosity and low fluidity of the single-component solvent-free adhesive, the adhesive is not easy to penetrate into the interior of the paper in the composite process, so it can ensure the composite product's performance under the condition of less glue amount So as to reduce the production cost of composite flexible packaging materials.
3. Classification by use
① According to the different uses, solventless adhesives are divided into: ordinary room temperature solvent-free adhesives, low temperature (80 ℃) water cooking solvent-free adhesives, boiling solvent-free adhesives, high-temperature cooking (121 ℃, 135 ℃) cooking solvent-free adhesives, aluminum film composite solvent-free adhesives and various functional solventless adhesives (dielectric resistant solvent-free adhesives) Fast curing solvent-free adhesive, smooth resistant solvent-free adhesive, etc.
② Some people also divide solvent-free adhesives into room temperature coating type solvent-free adhesive, medium temperature (40-60 ℃:) coating type solvent-free adhesive and high-temperature coating type (70-100 ℃) solvent-free adhesive.