Coating knowledge

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Coating knowledge: What are pigments? Pigments are any very fine solid substances that are black, white, or colored, and do not dissolve. Its main function is to impart color or special properties to a medium, with the mixing of the medium taking place through physical mixing. The difference between pigments and dyes · Pigments are insoluble in a medium, while dyes are soluble in such media as water, solvents, oils, plastics, or polymers. · Pigments are mixed into the medium through physical dispersion, while dyes dissolve in the medium. · Pigments need to be dispersed, while dyes need to be dissolved. · In a medium, pigments exist in particle form, while dyes exist in molecular form. · Definition of paint: There is no clear distinction between paint and coatings. The surfaces of many objects are prone to damage, as they are subject to erosive effects such as wind and snow, sunlight, rain, heat, friction, oxidation, chemicals, and so on. These surfaces need paint or coating for protection. If this paint or coating has color and a smooth surface, it serves a decorative purpose. The function of paint is to protect and decorate. Components of paint: The protective function of paint relies mainly on resins, which form a protective film on the surface of the substrate; resins also possess adhesiveness, allowing them to stick to the substrate. Resin can also give the substrate a smooth and shiny surface, serving as a sealer. When paint is used for decoration, pigments are the main component that provides color. Pigments require resins to adhere the pigment particles to the surface of the substrate; in decorative paints, pigments and resins are important components. If paint is not in a liquid state, it does not adhere easily to the surface of the substrate nor spread evenly; a liquid paint can penetrate the pores in the substrate’s surface and stick firmly to it, which is why a solvent is necessary for paint. The solvent for paint can be water, organic solvents, or oils, etc. In addition to resin, pigments, and solvents, various performance-enhancing additives can be added to paint to improve its properties. Paint production: Solvents dissolve resins to form varnish. If color is not needed, varnish itself is already paint. A certain amount of pigment is placed in the varnish; first, it is mixed at high speed to wet the pigment in the varnish, and then grinding equipment is used to disperse the pigment. This well-dispersed slurry is a concentrated pigment slurry (MILLBASE). Paint slurry, diluted with varnish, becomes paint. After the paint is delivered to the customer’s workshop, it is usually diluted with a solvent to achieve the appropriate viscosity for application, after which it can be used for painting. Dispersion of pigments: Pigments in their commercial form exist as aggregated particles, and it is necessary to grind them down to achieve a certain particle size in order to obtain good color, color saturation, gloss, and coloring power. There are three processes involved in the dispersion of pigments: 1. Wetting, 2. Dispersion and homogenization, 3. Stabilization – In paint production, wetting is achieved using high-speed dispersers (high-speed mixers). – The dispersion equipment mainly consists of sand mills or bead mills; three-roll mills and ball mills are also used ； Ball milling is used less frequently these days. – After the pigments are well dispersed, due to factors such as the compatibility between the resin or solvent and the pigments, or the physical properties of the pigments themselves, the pigment particles tend to become coarser; stabilization is necessary for this purpose, and dispersant additives are used for that aim. Dispersing agents can only stabilize dispersion; they cannot speed up the dispersion time. Classification of paints: Abroad, paints are classified based on their application, while in China they are classified according to the resin used. Different applications require different performance characteristics from paints, and classifying them by resin makes it difficult to meet the needs of users. It is believed that paint manufacturers in China will switch to classifying paints by application in the future.