Composition of adhesive

At present, the adhesives used are multi-component synthetic resin adhesive, and the single component adhesive can not meet the requirements in use. Synthetic adhesive is composed of main agent and auxiliary agent, the main agent is also called main material, base material or adhesive material; auxiliary agent includes curing agent, diluent, plasticizer, filler, coupling agent, initiator, thickener, antioxidant, polymerization inhibitor, stabilizer, complexing agent, emulsifier, etc. according to the requirements and Application, it can also include flame retardant, foaming agent, defoamer, colorant and mildew inhibitor.

1. The main agent is the main component of the adhesive, which dominates the adhesion performance of the adhesive, and is also an important symbol to distinguish the adhesive types. The main agent is usually composed of one or two or even three kinds of polymers, which requires good adhesion and wettability. The commonly used adhesives are:

Natural polymer compounds such as protein, skin gum, fish gum, rosin, peach gum, bone glue, etc. 2) Synthesis of polymer compounds ① thermosetting resins, such as epoxy resin, phenolic resin, polyurethane resin, urea formaldehyde resin, silicone resin, etc. ② Thermoplastic resin, such as polyvinyl acetate, polyvinyl alcohol and acetal resin, polystyrene, etc. ③ Elastic materials, such as nitrile rubber, chloroprene rubber, polysulfide rubber, etc. ④ A variety of synthetic resin, synthetic rubber mixture or graft, inlay and copolymer.

2. Additives in order to meet the specific physical and chemical characteristics, the various auxiliary components are called additives. For example, in order to form a network or body structure of the main adhesive and increase the cohesive strength of the adhesive layer, curing agents are added (they react with the main binder and produce cross-linking effect); curing accelerators or catalysts are added to accelerate the curing and reduce the reaction temperature; in order to improve the atmospheric aging resistance In order to give the adhesive some specific properties and reduce the cost, the fillers are added to reduce the cost; the toughening agent is added to reduce the rigidity and toughness of the adhesive layer; the diluent is added to improve the processability, reduce the viscosity and prolong the service life. include:

1) Curing agent curing agent, also known as hardener, is a component that can accelerate the curing of bonding materials through chemical reaction. It is the main matching material in adhesives. Its function is to react with the main polymer directly or through catalyst. After curing, the curing agent molecules are introduced into the resin, making the original thermoplastic linear main polymer into a tough and hard network structure.

There are many kinds of curing agents. Different resins and different requirements need different curing agents. The bonding process and its performance are determined by the performance and quantity of curing agent added.

2) Toughening agent
The active group of the toughening agent directly participates in the curing reaction of the adhesive and enters into a macromolecular chain structure of the cured product. After adding the toughening agent, it is easy to crack. The adhesive with toughening agent has better impact strength and peel resistance. Different toughening agents can also reduce the internal stress, curing shrinkage and improve the low temperature performance.

The commonly used toughening agents are polyamide resin, synthetic rubber, acetal resin, polysulfone resin, etc.

3) Diluent diluent, also known as solvent, is mainly used to reduce the viscosity of adhesive, increase the wettability of adhesive and improve the process performance. Some of them can reduce the activity of adhesive and prolong the service life. However, if the content is too much, the adhesive strength, heat resistance and medium resistance will be reduced. The commonly used diluents are acetone, paint and other solvents compatible with adhesive.

4) Generally, the filler does not react in the adhesive. The use of filler can improve the strength, impact toughness, wear resistance, aging resistance, hardness, maximum service temperature and heat resistance of the adhesive joint, and reduce the linear expansion coefficient, curing shrinkage and cost. Commonly used fillers are copper oxide, magnesium oxide, silver powder, porcelain powder, mica powder, asbestos powder, talcum powder, etc.

5) Modifier modifier is to improve the performance of a certain aspect of the adhesive to meet the special requirements of some components. For example, in order to increase the bonding strength, coupling agent, preservative, mildew inhibitor, flame retardant and stabilizer can be added.