How to evaluate the state of the paint by visual inspection? Observe whether the paint is crusted, gelled, delaminated, precipitated and fine. If conditions permit, it is better to measure the storage stability of the paint according to the national standard GB 6753.3.
(1) Crust.
After the paint is unpacked, it is often found that there is a layer of crust on the top layer, which is formed by the oxidation and curing of the alkyd paint . Observe the degree of crusting, if there is crusting, separate and remove it along the inner wall of the container. The crust layer can no longer be used, and the lower layer of paint can continue to be used, and it should be stirred evenly during use. The paint for removing the crust should be used up as soon as possible, otherwise the crust will appear again after a period of time , or even be scrapped.
(2) Gelling.
When the paint gels, it can be stirred or added with a solvent, and filtered before use. If it cannot be dispersed into a normal state, the paint is scrapped.
(3) Layering.
After the paint is stored for a period of time, the paint will appear delamination phenomenon, the paint particles will sink, and a layer of water quality solution will be formed on the upper quarter , and we can see that this layer of liquid is colorless or slightly yellow when selecting , relatively clear and clean, no or little floating matter, which indicates that the paint quality is very good. If the water quality solution is turbid, showing the color of the paint or a large number of floating objects inside, or even covering the surface of the solution, it means that the quality of the paint is poor or the storage shelf life has expired, so it is not suitable for use .
(4) Fineness of paint particles.
We can use a cup of clear water to test, take a small amount of paint into the water, after gently stirring, if the water in the cup is still clear, the paint particles are relatively independent in the clear water, there is no adhesion phenomenon, and the particle size is relatively uniform, indicating that the quality of the paint is very good good. If the water in the cup becomes turbid immediately after stirring, and the particle size is differentiated, it means that the quality of the paint is not up to standard, it is better not to use it. In addition, you can insert a wooden stick into the slip to mix the paint evenly, and then pick it up with a wooden stick. When the good paint flows down, it will form a fan shape. Touch it with your fingers. The genuine paint should feel smooth and delicate.
(5) Appearance color.
The paint used in the color coating production line is a colloidal body containing color. The normal appearance requirement is that the color is consistent, no floating color is produced, and the color is not allowed to be dark or light. Check the paint color, usually with the naked eye, or compare it with the standard color plate provided by the manufacturer, and it should meet the specified color difference range.
