Composition and application of two-component polyurethane adhesive

Two-component polyurethane adhesives are usually composed of an isocyanate component containing NCO (curing agent) and a hydroxyl component containing a hydroxyl group (main agent). When in use, the two liquid components are mixed according to a certain proportion, the reaction of NCO and OH is used to produce solid polyurethane, and then the polar groups of polyurethane are used to form hydrogen bonds and other bonds on the surface of the substrate, so as to play the role of bonding.

Two-component polyurethane adhesive came out earlier, the development began in the 1950s, Bayer company first developed Desmoders series of diisocyanate and Desmophens series of low molecular weight hydroxyl polyester polyols, the two in accordance with a certain proportion of configuration, can obtain Polystal series of two-component solvent-based polyurethane adhesive. It laid the foundation for the future industrial development of two-component polyurethane adhesives.

Two-component polyurethane adhesives are reactive adhesives, and the two components are cross-linked and solidified and bonded when mixed. Usually can be cured at room temperature, can also be heated to cure, the final bond strength is generally larger than the single-component polyurethane adhesive, can meet the requirements of structural adhesives. In addition, the amount of two components of the two-component polyurethane can be adjusted within a certain range, the formula is flexible, by adjusting the raw materials and molecular weight of the two components, products with different properties can be obtained, which can be used for the bonding of plastics, films, metals, wood, glass and other materials, and the bonding range is wide.

Two-component polyurethane adhesives can be divided into solvent-based and solvent-free types according to the presence or absence of solvents.

Although solvent-based two-component adhesives have good infiltration, strong bond strength and strong permeability to the substrate, they are not conducive to environmental protection and health.

Solvent-free two-component adhesives do not contain solvents, will not cause pollution due to solvent volatilization, safe operation. It has a relatively good development prospect. The main agent and curing agent of solvent-free two-component polyurethane have high viscosity at room temperature, but still have fluidity, and the two are mixed proportionally when used, and the temperature is raised to 50-60 ° C, so that the viscosity is reduced, because it does not contain solvent itself, so it can be directly coated on the substrate without heating and drying this process.

The two-component polyurethane adhesive is mainly composed of two components, and it is customary to call the polyisocyanate component A or A component, and the hydroxyl component B or B component. In fact, group A (component A) can also be a hydroxyl component, and Group B (component B) can be a polyisocyanate component. Component A (polyisocyanate component) is mainly composed of polyisocyanates, small molecule chain extender crosslinking agents, auxiliaries and fillers, while component B (hydroxyl component) is mainly composed of polyols or hydroxyl end polymers generated by the reaction of polyols and isocyanates, small molecule chain extender crosslinking agents, catalysts, auxiliaries and fillers.

Two-component polyurethane adhesive has good mechanical properties, adhesion, chemical resistance, adjustable performance, large bonding strength, wide bonding range and other advantages, widely used in metal, plastic, packaging materials, insulating materials and other substrates bonding. From the application classification, it can be divided into general two-component polyurethane adhesive, two-component adhesive for composite film, two-component adhesive for shoes, two-component polyurethane sealant, two-component polyurethane structural adhesive.

Universal two-component polyurethane adhesive

A class of solvent-based two-component polyurethane adhesives developed and applied in the early stage is usually called "two-component polyurethane adhesives". The main characteristics of this kind of adhesive are: the organic solution of hydroxy-terminated polyurethane prepared by polyethylene glycol adipate and toluene diisocyanate as the main raw materials is the main agent, and the organic solution of trimethylol propane-toluene diisocyanate admixture is used as the curing agent. This kind of adhesive film is strong, impact resistance, water resistance, oil resistance, low temperature resistance. Widely used in bonding metal and non-metallic materials, can also be used for general packaging materials, decorative materials composite.

Two-component polyurethane adhesive for composite films

The main ingredient of two-component polyurethane adhesive for composite film is adipate polyester polyurethane polyol, copolyester polyurethane polyol (copolyester polyol modified by isocyanate) or aromatic polyester polyol. Curing agents are generally TMP-TDI adducts. The solvent of this type of adhesive is generally ethyl acetate, and the solid content is low. Mainly used for packaging dry food. The formulation of adhesives for high performance composite films may contain primary agents that enhance bond strength. When used, the two components are mixed in a certain proportion, and then diluted with solvent to a certain concentration for coating.

Two-component polyurethane adhesive for shoes

Polyurethane adhesive for shoes is based on solvent-based two-component polyurethane adhesive, the main agent of this adhesive is the solution of thermoplastic polyurethane, characterized by high viscosity, low solid content, rapid crystallization after solvent volatilization, high initial adhesion, suitable for cold bonding process of shoe materials. The preparation of the two-component polyurethane adhesive for shoes is focused on the synthesis of the main agent, the main component of which is the adhesive TPU prepared by crystalline polyester diol and MDI. The curing agent component is usually a polyisocyanate crosslinking agent. The commonly used solvents of the main agent components are generally ethyl acetate, toluene, methyl ethyl ketone, etc., and mixed solvents are usually used.

Two-component polyurethane sealant

The main agent of two-component polyurethane is usually the terminal NCO prepolymer obtained by the reaction of polyether polyols and polyisocyanates. The curing agent is composed of polyether polyols, polyamines and other active hydrogen compounds, fillers, thixotropic agents, antioxidants, catalysts, etc. A small amount of two-component polyurethane sealant is based on hydroxyl component (or polyether filler mixture or hydroxy-terminated prepolymer) as the main agent, and polyisocyanate as the curing agent. With the advantages of fast curing rate, good chemical resistance and low cost, it has a wide market in the field of construction and road engineering.

Two component polyurethane structural adhesive

Structural adhesive refers to a high-performance adhesive that can replace bolts, rivets or welding forms to bond metal, plastic, glass, wood and other structural components and can withstand large loads for a long time. Two-component polyurethane structural adhesives are usually solvent-free two-component polyurethane adhesives. The general curing agent component is composed of terminal NCO polyurethane prepolymer obtained by reaction of polyol and excess polyisocyanate. The main agent part is composed of binary amine and its blend. After curing, polyurethane-urea is formed. Mainly used in automobiles, water vehicles, elevators, baths, residential (bonding between external decorative materials) and other fields.