It often takes a period of time for the paint to be used, and it is required that the quality does not change during storage. Therefore, there are certain requirements for the storage stability of the coating, including the absence of settlement, caking, skinning, and viscosity changes. For the spraying process, the most concerned is whether the coating has precipitation during the storage period and the effective service life of the coating.
1. Precipitation
It is not uncommon for pigments and other solid particles suspended in paint to settle during storage. The most direct adverse effect of the precipitation of the color paint on the spraying process is the color difference in the coating film due to the uneven distribution of the pigment. In view of the specific occurrence of precipitation, corresponding measures should be taken during the spraying process. Most paints need to be stirred frequently during use to maintain the uniformity of the paint. Some paints that are prone to precipitation, such as metallic paint, also need to be continuously circulated between the mixing station and the spraying station, and stirred in the storage tank to prevent Settling of these paints occurs. In view of the situation where precipitation is easy to occur, sometimes a small-diameter nozzle and a small-diameter delivery pipeline are used in the spraying system to achieve better results, because this speeds up the flow of the fluid and is conducive to reducing the amount of sedimentation. .
For the stored paint, the principle of "first in, first out" should be followed, so that the paint stored first can be used as soon as possible to prevent precipitation due to extended storage period.
In order to reduce precipitation, various stirring equipment can be used, but when using these equipment, attention should be paid to using the lowest stirring speed as far as possible under the premise of achieving the required uniform effect. Because most of the paints are pseudoplastic non-Newtonian fluids, their viscosity will change under the action of stirring and shearing. In order to prevent the adverse effects of the viscosity change on the spray paint, the stirring speed should not be too high.
2. Shelf life
In order to ensure the spraying effect, be sure to use the paint within the shelf life. Therefore, you must carefully read the instructions on the paint packaging before use, and actually observe whether the paint has deteriorated. Particular attention should be paid here to the use of two-component coatings. The resin and curing agent of thermosetting two-component coatings are usually stored separately and mixed in a certain proportion before use. Since the two components react chemically once they are mixed and start to cure, its service life is very short. . The pot life refers to the time when the mixed paint can be placed. For different two-component paints, the pot life can range from a few seconds to a few hours, so be sure to read the instructions carefully before use. Many two-component paints will generate a lot of heat after mixing, and the temperature of the paint will rise. The pot life of the paint is different at different temperatures. If the mixed paint is stored at a lower temperature, the pot life will last longer. Extend it, otherwise it will be shorter than the applicable period specified in the instructions.
Ordinary spraying equipment cannot be used to spray two-component coatings, but special equipment should be used for precise metering and coating, and special equipment should be used to clean the spraying equipment after use. Great care should be taken when using two-component coatings, and the system should be as simple as possible to reduce the possibility of problems. After the spraying process is completed. The two-component paint remaining in the equipment must be cleaned before the end of the pot life of the paint, and it must not be cleaned until after the pot life has passed, otherwise it will be difficult to clean after it solidifies in the equipment. It is also not possible to use the method of mixing the two-component paint in the storage tank and then spraying it, because the mixed paint is not used up, and it cannot be reused due to curing, which will cause a lot of waste, so only this paint can be used. The special equipment for two-component spraying introduced at the back of the book. Although the one-time investment of this equipment is relatively large, in the long run, the cost will be recovered quickly.
