The status of coating adhesives

The currently used adhesives are mainly divided into one-component adhesives and two-component adhesives. The components of one-component adhesives are mainly composed of natural rubber or synthetic rubber, and nitrocellulose and acrylic esters. Since the main agent is an elastomer and tackifiers are used as auxiliary agents, they are formulated into emulsions with organic solvents, and have the following characteristics: Hot melt, with a certain degree of adhesive strength.

With the increase in the hygienic requirements for pharmaceutical packaging materials, the application of this one-component adhesive has been gradually reduced. With the use of two-component polyurethane adhesives, it is mainly composed of a main agent and a solid agent, and the main agent generally contains many Active hydrogen, such as base, amino and other substances, and the curing agent is composed of polyisocyanate compounds. When the isocyanate stem in the curing agent comes in contact with the active hydrogen in the main agent molecule, an addition reaction is automatically performed to produce a carbamate ester structure. When the main agent and the curing agent are combined with each other, the molecular weight is doubled, and even a cross-linked product with a three-dimensional conformation with a branched chain structure is produced, which has good resistance to high and low temperature resistance to media erosion and high adhesive force, due to the fact that the polyurethane molecules Contains a large number of polar oxime groups, large dipole moment, and great affinity for the adherent material. So at the same time play a bonding role on a variety of materials.

In addition, the isocyanate stem (-NCO) in the curing agent is a very reactive group that can react with the active hydrogen in the main agent molecule and react with the active hydrogen in the surface material molecules of the adherent material. Chemical bonds are generated to bridge the adhesive molecules with the bonded materials, resulting in stronger adhesive force. Adhesive strength of these adhesives is good. They have been widely used in aluminum foil coating adhesives and various types of adhesives. Plastic film in the composite process.

In the future, the application of adhesives is developing toward a solvent-free type. It is basically a two-component type of polyhydric esters. The difference is that the main agent and curing agent have higher viscosity at room temperature, but they still have fluidity, which is a half. The solid substance, when used, the main agent and the curing agent are mixed in proportion and placed in a container with a heating and heat retention function. After the temperature is turned on, the viscosity is lowered, and then coated on the substrate by a gravure roll with a heat insulation function. The glue does not need to be dried by heating in the drying tunnel, because it does not have any solvent, and it can be directly bonded with another substrate. The use of solvent-free adhesives does not have emission problems, and does not require the use of large drying tunnels for heating, drying, and blowing devices. In foreign countries, this adhesive has been used because of its high awareness of environmental protection.