Because traditional coatings have an impact on the environment and human health, people are now thinking of ways to develop green coatings. The so-called "green coatings" refer to energy-saving, low-pollution water-based coatings, powder coatings, and high-solids coatings (or solvent-free coatings). ) and radiation curing coatings, etc. Before the 1970s, almost all coatings were solvent-based. Since the 1970s, due to the increasing price of solvents and the increasingly stringent requirements for reducing VOC emissions, more and more low organic solvent content and organic solvent-free coatings have been greatly developed. Green paints are increasingly used now, and the following new paints are currently well developed.
1. Solid content solvent-based coatings. The high solids solvent type is developed from the general solvent-based coatings to meet the increasingly stringent environmental protection requirements. Its main feature is to reduce the amount of organic solvent and improve the solid content under the premise of utilizing the original production method and coating process. This type of coating was developed in the United States since the early 1980s. Typical low solids solventborne coatings have a solids content of 30% to 50%, while high solids solvent based (HSSC) requires solids of 65% to 85% to meet increasingly stringent VOC limits. In the formulation process, the use of some solvents that are not in the VOC as a diluent is a modification to strict VOC restrictions, such as acetone. A very small amount of acetone can significantly reduce the viscosity, but because acetone evaporates too quickly, it poses a potential fire and explosion hazard and needs to be strictly controlled.
2. Water-based paint. Water is different from most organic solvents in that it is non-toxic, odorless and non-combustible. Introducing water into coatings not only reduces the cost of coatings, but also causes fires caused by the presence of organic solvents during construction, and greatly reduces VOC. Therefore, water-based paints have made great progress and development since their inception. The China Environmental Labeling Certification Committee promulgated the "Technical Requirements for Environmental Labeling Products for Waterborne Coatings", which stipulates that the content of volatile organic compounds in products should be less than 250g/L; during the production process, compounds containing heavy metals should not be artificially added, and the total content of heavy metals should be Less than 500mg/kg (in terms of lead); formaldehyde and polymer should not be artificially added during the production process. The content should be less than 500mg/kg. In fact, water-based paints now account for about half of all coatings. Water-based coatings are mainly available in three types: water solubility, water dispersibility and latex properties.
3. Dust paint. Dust paint is a relatively advanced paint in China. Dust paint is theoretically an absolute zero VOC coating with its unique advantages. Perhaps it is one of the most important directions for the development of coatings after VOC is completely abandoned in the future. However, its application limitations require more extensive and in-depth research. For example, the manufacturing process is relatively complicated, the coating manufacturing cost is high, and the baking temperature of the dust coating is much higher than that of the general coating, and it is difficult to obtain a thin coating. The color matching property of the paint is poor, and the uniform coating property of the irregular object is poor. These need further improvement, but it is one of the future directions.
4. Liquid solvent-free coating. Liquid solvent-free coatings without organic solvents are two-liquid type, energy beam curing type, and the like. The latest development trend of liquid solvent-free coatings is to develop a single-liquid type, liquid-solvent coating that can be applied by ordinary painting and painting processes.
The research and development direction of coatings is becoming more and more clear. It is to seek coatings with continuous reduction of VOC to zero, and its use range should be as wide as possible, superior performance, and appropriate equipment investment. Therefore, water-based coatings, powder coatings, solvent-free coatings, etc. may become the main direction of future coating development.
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