Solvent Free Polyurethane Adhesives And Laminating Technology

Europe and the United States from the past solvent free composite processing capacity less than 10% of the total processing of composite membrane packaging materials, up to now more than 30% of solvent free composite processing technology.

Since the introduction of the first solvent-free dry compound machine in Japan since 1977, 52 years ago, it has developed to more than 60 solvent-free composite equipment.

The manufacture of composite membrane packaging materials without solvent adhesives has become a mature application technology.

At the same time, the application and development of the technology also promoted the development of solvent free polyurethane adhesives research and production.

However, before 1995, there was only one solventless compound machine in China, and the demand for solvent free polyurethane adhesives was very small.

In recent years, the price of raw materials has increased, especially the increase of solvent prices, which has reduced the economic efficiency of the composite membrane processing industry. In addition, due to the government's restrictions on the environment and people's awareness of environmental protection, and the understanding and understanding of the new technology by the composite membrane processing industry.

It has not been developed rapidly until nearly five years ago. Up to now, there are more than 20 sets of solventless dry compounding machines in China.

The demand for solvent free polyurethane adhesives is also increasing.

This paper mainly introduces the development of solvent-free polyurethane adhesive and its application technology in food packaging composite membrane processing.

This kind of adhesive has many advantages and has been widely used. It plays an important role in the processing of composite membrane.

However, a large number of solvents will be discharged into the atmosphere every year, causing serious environmental pollution and waste of resources.

The dry compound of solvent-free adhesive has the following characteristics besides keeping the solvent based adhesive dry composite.

(2) no organic solvents volatilization pollute the environment.

(3) no solvent evaporation drying section is required, and energy consumption is reduced.

(4) there is no danger of fire and explosion, no need for explosion-proof measures for solvents, and no need for storage of solvent equipment and storeroom.

(5) compound products do not contain any residual solvent damage and eliminate the impact of solvents on printing ink.

(6) without organic solvents, the composite substrate is easily affected by solvent and high temperature drying. The composite film has good dimensional stability.

(7) in the composite application, the same quality requirement, the solvent free adhesive coating quantity is less than the solvent type adhesive coating quantity, saves the cost, has the very good economy.

(8) the equipment is relatively simple, the floor space is small, and the investment is saved.

It maintains the characteristics of solvent polyurethane adhesives, and does not need any solvent (i.e. 100% solid content adhesive), and can also be applied to coating and compounding well.

Solvent free polyurethane adhesives can also be made into one component and two components.

The appearance of solvent-free polyurethane adhesives is a very viscous liquid at room temperature. It is a low viscosity mobile liquid under heating and can be applied to solventless dry machine.

It is different from the commonly seen hot melt adhesives. The hot sol is solid at room temperature, most of which are composed of thermoplastic polymer or natural products, and the solvent free polyurethane adhesive is mostly composed of reactive components.

Some people have developed the series of adhesives into three stages.

The single component polyurethane adhesive contains NCO group, which is solidified by the reaction of water in air and the water attached to the membrane.

Although single component has the advantages of convenient use, there are also shortcomings.

When the amount of coating is over 2G / m2, the curing will be bad. Because of the moisture (moisture) curing type, the coating thickness can not reach the complete reaction with the water, so the use is restricted, the coating amount can only be <2g / m2.

Thus, the requirement of cooking resistance can not be achieved, and the range of the processed composite products is affected.

This product is also called the second generation product.

This kind of adhesive is made up of two groups of polyurethane prepolymer. When used, the two components are mixed together, forming macromolecules by mutual reaction to achieve crosslinking and curing.

(for example, the production of UR7330 / UR8150 in North Chemical Institute is shown in Table 1) the viscosity of this adhesive is lower than that of one component adhesive, and some varieties can be used at room temperature.

In order to achieve high initial bonding strength, the reaction speed is very fast.

The two-component solvent-free polyurethane adhesive is used for the two component mixture when it is used, and it needs an automatic feeding system. The metering pump is usually used to achieve this purpose.

In terms of usage, both EVA and nylon films and aluminum foil can be used.

Transparent film can be used for low temperature sterilization and cooking. The main reason why it can not be used on EVA and NY is to reduce the viscosity of adhesives and use low molecular polyisocyanate. It will react with EVA and NY amide compounds to form insoluble compounds, which will make the composite products heat sealed.

The third generation solvent free adhesives have the following characteristics: strong initial adhesive force, low viscosity, operating temperature at <80 C, no restriction on composite base material and excellent performance of resistance to content.

The second generation of adhesive mentioned above solves the problem of poor heat sealing of EVA, NY film and the problem of easy to crease or peeling easily.

Because our country only has the product to supply, and the variety is few, now mainly relies on the import.

The price of imported adhesives is high, and the same type of adhesives are used in Europe and America due to the domestic composite membrane structure and raw material differences. However, problems often arise in China.

For example, solventless adhesives are used in thin films, EVA films and CPA films with high slip content.

The migration of isocyanate monomer is easy to occur, and some of the composite films are poorly sealed when cooked.

However, the early development of solvent-free polyurethane adhesives for single component solvent-free polyurethane coatings had a higher temperature (90 to 100 degrees Celsius) when applied to composite membrane coating. Although heating could reduce viscosity, it was easy to coat, but the temperature was too high, the adhesive reaction was fast, and the viscosity increased quickly, which was not conducive to coating.

At the same time, the amount of coating has a great relationship with the viscosity of adhesives. When the viscosity is high, the amount of coating is large and the amount of coating is small when the viscosity is low.

To achieve stable coating amount, viscosity changes of adhesives should be minimized.

Moreover, the coating cots of the solventless compound machine soaked in the adhesive 90 to 100 degrees for a long time, it is easy to cause the deformation and damage of the cots.

Therefore, when developing a solventless polyurethane adhesive, determining the optimum coating temperature is an important factor.

The solventless polyurethane adhesive UF7508 developed in our hospital in 2000 is a new adhesive product which can be applied at low temperature (70 degrees).