Water-based paint construction process analysis and coating problems and solutions
Wen/Tan Bingsheng
Traditional coatings have a great influence on the atmospheric environment and human health. Traditional paints use organic solvents as diluents and contain a large amount of volatile organic compounds (VOCs) that can harm humans through inhalation or skin contact. According to statistics, about 2.2 million tons of VOCs are emitted into the air each year in China. In the total VOC emissions, industrial solvents accounted for about 30% of the total and became one of the major sources of emissions. The VOC emissions of coating adhesives accounted for about 70% of industrial solvents.
In addition, according to China's water-based paint production, import and export volume can be calculated in China's apparent consumption of water-based paint (= production + imports - exports), in 2015 the apparent consumption of water-based paint is approximately 1.71 million tons by 2016 Increased to 1.89 million tons, it can be seen that the water-based paint in our country's market space is relatively broad.
With the development of China's economy and technology, environmental protection has put forward higher requirements for railway painting. Waterborne coatings can not only reduce VOC emissions to a certain extent, but also reduce the level of fire risk, but the transition from solvent-based to waterborne coatings is not an overnight event. To this end, we analyze today the problems encountered in the coating process of waterborne coatings.
1st
- Waterborne paint construction process analysis -
Water-based paints have a particularly high cleanliness requirement for the coating surface. Therefore, the surface treatment before coating is particularly important. In addition to the normal steel pretreatment, the surface must be completely cleaned before painting, and the surface of the car body should be covered with white corundum. Sand blasting removes all dirt and dust on the surface of the car body. It is also possible to pre-coat a solvent-based paint before the water-based paint is applied. Generally, the pre-coated solvent-based paint is selected from a fast-drying, good-adhesion paint, such as an alcohol-soluble ethylene phosphatizing primer.
Pre-coating the primer on the car body and then painting the water-based paint, using a 65:1 airless sprayer, adjusting the air pressure at 0.3 to 0.4 MPa, the nozzle at 25P25, and performing wet-on-wet 2 coat tanker bodywork The coating thickness requirement is not less than 80μm, and the interval between two passes is 20-30min. During this period, the coating film was inspected for paint film flaws such as falling or missing paint. The brush was brushed and smoothed at the convection drop site, and the missing paint was applied. The second coating is the same as the first coating operation. If there is a small amount of flow, it should be immediately brushed with a paint brush. drying. In the temperature below 15 °C, rainy days or need to immediately leave the plant after the painting of the body should be dried, the drying temperature should be about 60 °C, drying 0.5 ~ 1.0h. After the black water-based paint is applied, the paint film is grayish green, and it appears black and dull after drying.
2nd
- Difficulties and Solutions in Waterborne Coatings -
Cracking: Mainly in the case of water-based paints and solvent-based paints. If the solvent paints are dissolved in the water-based paints that are applied later, the cracks are likely to occur.
Remedy: When spraying the solvent coating, it is necessary to protect the solvent coating from flying to the site of the water-based coating to be sprayed.
Shrinkage hole: The water-based paint uses water as the medium. When the surface to be coated is not cleaned and there is dirt, the surface tension of the water is large and the shrinkage phenomenon is likely to occur.
Solution: Thoroughly inspect the condition of the surface to be coated, and if necessary, sand the surface of the primer surface with sandpaper to make it have a certain roughness, which will facilitate the application of the topcoat.
Dropping: When thick coating, when the thickness of wet film exceeds 120μm, it is easy to crash.
Remedy: Use multiple spraying methods to meet the specified requirements. The time interval for each spraying must not be less than 5 minutes, and the thickness of each spray coating should be controlled within 30 to 40 μm (dry film).
Water-based paint market has great potential. And can be widely used in automotive hardware manufacturing outside the metal hardware coating. At present, China has become the world's largest manufacturing base. These new application areas believe that there will be a rapid growth trend in the future.
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