Demand and development of domestic solvent-free polyurethane adhesives

Since 1996, domestic composite film production plants have gradually recognized the superiority of solvent-free composite processes. They have introduced more than 20 solvent-free composite film production lines, requiring nearly 1,000 tons of solvent-free adhesives per year, and solvent-free composite film adhesives in the domestic market. Demand is growing rapidly. Since there are only products available in our hospital and there are fewer varieties, we mainly rely on imports. The price of imported adhesives is higher, due to the structure of domestic composite film products. Due to differences in raw materials, etc., the same type of adhesive is used in Europe and America, but there are often problems in China. For example, solvent-free adhesives are used for films with high slip agent content, EVA films, CPA films, and the like. The migration of the isocyanate monomer is prone to occur, and the composite film is poorly heat-sealed when the bag is matured.

In order to change the status of polyurethane adhesives for solvent-free composite film mainly relying on imports, our institute has invested a lot of manpower and material resources on the basis of imported technology and developed new products for polyurethane adhesives for solvent-free composite film suitable for China.

A: Low-temperature (70 ° C) coated one-component solvent-free Polyurethane Adhesive UF7508

Although the one-component solvent-free polyurethane adhesive has some shortcomings, it is still widely used due to its convenient use, good initial adhesion, no mismatch, and low price. However, the early development of single-component solvent-free polyurethane adhesives used in composite film coating at higher temperatures (90-100 ° C), although heating can reduce viscosity, easy to apply, but the temperature is too high, the adhesive reacts quickly, The viscosity is also increased quickly, which is not conducive to coating. At the same time, the amount of coating has a great relationship with the viscosity of the adhesive. When the viscosity is high, the coating amount is large, and when the viscosity is low, the coating amount is small. To achieve a stable coating amount, it is necessary to minimize the change in viscosity of the adhesive. Moreover, the coating rubber roller of the solventless laminating machine is immersed in the adhesive of 90-100 ° C for a long time, which easily causes deformation and damage of the coating rubber roller. Therefore, in the development of one-component solvent-free polyurethane adhesives, determining the optimum coating temperature is an important factor. The single-component solvent-free polyurethane adhesive UF7508, which was successfully developed in our hospital in 2000, is a new adhesive product that can be coated at a lower temperature (70 ° C).

The one-component Pu Adhesive Glue is mostly a polyisocyanate prepolymer containing NCO groups, which is cured by reacting water in the air with the water adhered by the coated film. The one-component solventless polyurethane adhesive type is mostly the following Two kinds:

1 Polyether polyurethane polyisocyanate:

OCN-R-NCO+H-(-0R'-). -OH--→OCN-R-NH-CO-(-OR'-)nO-CO-NH-NCO

(diisocyanate) (polyether polyol) (polyether polyurethane polyisocyanate)

2 polyester polyurethane polyisocyanate

OCN-R-NCO + HO～OH--→OCN-R-NH-CO-O～O-CO-NH～NCO

(diisocyanate) (polyester polyol) (polyester polyurethane polyisocyanate)

The UF7508 developed by our institute is a mixture of these two types. It has the characteristics of high bonding strength of polyester polyurethane and improved hydrolysis resistance by polyether polyurethane.

B: New two-component solventless polyurethane adhesive with low free isocyanate monomer (UR7980/UR8160)

A quality problem in the current two-component polyurethane adhesive for solvent-free composites is that the adhesive contains more free isocyanate monomer, and the small molecule compound generated easily migrates into the film to cause contamination of the packaged product, and is small. The molecular product reduces the heat seal strength of the package. In 2000, a new two-component solvent-free polyurethane adhesive with low free isocyanate monomer developed by our institute met the needs of domestic customers and promoted the development of this technology in China.

The two-component solventless polyurethane adhesive consists of two sets of polyurethane prepolymers, the chemical structure of which is as follows.

The main component is typically a polyester polyurethane prepolymer (generally containing a reactive group - OH).

OCN-R-NCO + HO～OH--→HO～O-CO-NR-R-NH-CO-O～OH

(diisocyanate) (polyester polyol) (polyester polyurethane prepolymer)

The other component (also known as the curing agent) is a polyisocyanate prepolymer (generally containing NCO groups):

OCN-R-NCO+OH~R"-OH--→OCN-R-NH-CO-O-R"-O-CO-NH-R-NCO

(diisocyanate) (polyol) (polyisocyanate prepolymer)

Note: In the above formula, R, R\, and R" are a hydrocarbon group or a phenyl group.

When used, the two components are uniformly mixed together, and the macromolecules are formed by mutual reaction to achieve cross-linking curing. When a solvent-free two-component agent is used, the product is required to have a lower viscosity to ensure an operating temperature of between 40 and 50 °C. The viscosity of the solventless adhesive is inversely proportional to the content of the isocyanate groups in the prepolymer, and the content of the free diisocyanate group in the prepolymer is lowered, which inevitably lowers the content of the isocyanate in the product, thereby increasing the viscosity of the product. The operating temperature is increased and the operating conditions are not easily controlled. The new two-component solvent-free polyurethane adhesive of low free isocyanate monomer developed by our institute not only reduces the content of free diisocyanate in the product, but also makes the product have appropriate viscosity, and the operating temperature is moderate to meet the requirements of customers.