At present, the primary task of the coatings industry is to develop four types of environmentally friendly coatings. Secondly, it will take time to achieve this goal. Solvent-based coatings still occupies a considerable proportion of the transitional stage. It is also important to replace toxic solvents with efficient and non-toxic solvents. An important current work. Starting from the concept of sustainable development, the development of renewable organic solvent resources is the third task facing paint workers.
Several types of environmentally friendly coatings that the coating industry will focus on in the future include:
High solids coating
High solids solvent-based coatings (HSSC) are also known as VOC solvent-based coatings. The volume (NVV) solid content of traditional solvent-based thermosetting coatings is usually about 25-35%, and some thermoplastic coatings will be lower.
There is no unified statement about the definition of high-solid coatings. There is a formulation in my country that high-solid coatings refer to coatings with a solid content greater than or equal to 70% during spraying. Some international formulations are that for automotive flash metallic paint (or topcoat base paint) its high solids refers to about 45NVV; for high-pigment primers, its high solids may be 50NVV. This requires that the molecular weight of the synthetic resin used in the coating and the average functionality of each molecule must 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 research and development of new crosslinkable resin synthesis technology and strict control of the curing conditions of the coating film have become the key to the problem. At the same time, the realization of such coatings only reduces the amount of organic solvents.
Solvent-free paint
The so-called solvent-free coating is the use of an organic solvent called a reactive solvent or reactive diluent in the coating. It can not only dissolve or disperse the film-forming substance, but also chemically 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 coating process, the pollution to the environment and the poison to the human body are reduced.
The solvent-free products currently used mainly include two-component (two-component) epoxy-based solvent-free coatings and acrylic-based light-curing coatings. The development direction of solvent-free coatings is to expand the variety, increase the adaptability to coating methods and develop thin coating products.
Water-based paint
The water is a colorless, transparent, non-toxic and odorless liquid with abundant resources. Substituting water for organic solvents as the dispersion medium of the coating resin will undoubtedly completely avoid the above three hazards caused by the use of organic solvents. Therefore, it has become an important product of the developing environment-friendly coatings.
Water-based coatings can be divided into latex coatings (Latexcoatings) and water-reducible coatings (water-reducible) two categories. At present, the mature application of latex paint products are mainly architectural latex paints, and water-reducible paints are mainly industrial water-based electrophoretic primers. The reporter learned that with the Chinese government GB18581-2001 "Interior decoration materials: Limits of hazardous substances in solvent-based wood coatings" and GB18582-2001 "Interior decoration materials: Limits of hazardous substances in interior wall coatings" and other national standards issued Began to apply, and the technology matures day by day.
However, water-based industrial coatings are affected by the need to improve the performance of water-based coatings compared with the corresponding solvent-based coatings, the relatively high cost, and the specific requirements for the coating environment. Therefore, the expansion of the product and application scope requires a certain amount of work. work.
Powder coating (powder coating)
In theory, powder coatings do not contain any volatile substances. They are absolutely zero VOC coatings and are one of the most important products for environmentally friendly coatings. However, powder coatings are subject to certain restrictions in expanding applications, and further improvements are needed. For example, its manufacturing cost is relatively high; it needs high temperature baking to form a film; it is difficult to obtain a thin film coating. It is difficult to color the paint products determined by the paint process; the uniform coating on the surface of irregular objects is poor. All these need further research and development.
Based on the above, the development of the above four types of environmentally friendly coatings is not only the unswerving work direction of Chinese paint workers, but also should be aware that it will take time to achieve this goal.
