Developing the trend of environmentally friendly coatings

The strategy of sustainable development has become one of the hotspots in the world today. To achieve long-term development in the paint industry, the current priority is to develop environmentally friendly coatings. Of course, it will take time to achieve this goal. Solvent-based coatings also occupy a considerable proportion of the transitional period. The replacement of toxic solvents with highly efficient and non-toxic solvents is also an important task at present.

The four types of environmentally friendly coatings that the coatings industry will focus on in the future include:

High-solids coatings High-solids solvent-borne coatings (HSSCs) are also known as solvent-borne coatings for VOCs. The volume fraction (NVV) of conventional solvent-based thermosetting coatings is usually about 25-35%, and some thermoplastic coatings will be lower.

There is no uniform definition for the definition of high solids coatings. In China, there is a reference that high solids coatings refer to coatings with solids greater than or equal to 70% when sprayed. Some international references are that high solids for automotive flash metallic paints (or basecoat paints) are around 45NVV; and for high pigmented basecoats, high solids may be 50NVV. This requires that the molecular weight of the synthetic resin used for the coating and the average functionality per molecule have to be reduced and the molecular weight distribution must be narrowed. In this case, it is difficult to maintain the function of the coating film at the same time. Therefore, the development of a new crosslinkable resin synthesis technology and strict control of the curing conditions of the coating film has become the key issue. At the same time, the realization of this type of paint is only to reduce the amount of organic solvents.

Solvent-Free Coatings So-called solvent-free coatings use an organic solvent known as a reactive solvent or reactive diluent in coatings. It can not only dissolve or disperse the film-forming substance, but also can react with the film-forming substance during the film-forming process to form a non-volatile component and remain in the coating film. Since the organic solvent does not overflow during the filming process, the environmental pollution and the toxicity to the human body are reduced.

The currently used solvent-free products mainly include two-component (two-component) epoxy-type solvent-free coatings and acrylic-type photo-curable coatings. The development direction of solvent-free coatings is to expand the variety, increase the adaptability to coating methods and develop thin-coated products.

Water-based paints are colorless, transparent, non-toxic and tasteless liquids, and they are rich in resources. The use of water instead of organic solvents as the dispersion medium for the coating resin will undoubtedly completely eliminate the above-mentioned three hazards associated with the use of organic solvents. As a result, it has become an important category of environmentally friendly coatings for development.

Water-based paints can be classified into Latex coatings and water-reducible coatings. At present, the latex coating products that are maturely applied are mainly architectural latex paints, and the water dilution coatings are mainly industrial aqueous electrophoretic primers. Along with the Chinese government GB 18581-2001 "interior decoration materials: wood-based coatings solvent hazardous substances limit" and GB 18582-2001 "interior decoration materials: interior wall paint harmful substances limit" and other national standards issued waterborne wood coating also began Application, and technology is maturing.

However, due to the need to improve the performance of waterborne coatings compared with the corresponding solvent-based coatings, the relatively high cost, and the specific requirements for the coating environment, it is necessary to extend the range of products and applications to work. work.

Powder coating (powder coating)

Powder coating theoretically does not contain any volatile substances. It is an absolute zero-VOC coating and is one of the key development products of environmentally friendly coating products. However, powder coatings have been limited in their application and need further improvement. For example, its manufacturing cost is high; high temperature baking is required to form a film; it is difficult to obtain a thin film coating. It is difficult to adjust the color of the coating product as determined by the lacquer process; even coating on the irregular surface is poor. These need further research and development.