Definition of coating
Coating is a kind of liquid or powder substance, which can be uniformly covered and attached to object surface to form a continuous and dense coating layer. After dried and cured by natural or thermal condition then a solid coating film will be formed. Coating layer has protection, decoration or other special functions to object. Although the definitions of coating are slightly different in different documents, they all emphasize two characteristics of coating – it contain film-forming properties and has important impact on the substrate.
Classification of film-forming substances
Generally, the composition of paint is divided into three types: main film-forming substances, secondary film-forming substances, and auxiliary film-forming substances.
1. Main film-forming substances
Main film-forming substance refers to the polymer material which is the basic substance in the coating. It can be filmed stand alone or together with other ingredients in the coating. The main film-forming material used in early age was vegetable oil or natural resin paint, it was often called paint. Although the current main film-forming materials have been changed to synthetic resins, it is customary to call coatings as paints. The word “lacquer” is sometimes used in specific paint names, such as varnishes and enamels.
2. Secondary film-forming substances
Secondary film-forming substances include pigments, extender pigments and functional material additives. They do not have the ability to form a complete coating film alone, but they can help the main film-forming substance for better coating film, give the coating film color or a certain function, can also change the coating physical and mechanical properties.
3. Auxiliary film-forming substances
Auxiliary film-forming substances include various additives and thinners. Additives can improve a certain characteristic of the coating in production, processing, storage, and construction. The thinner can dissolve and dilute the main film-forming materials, which is convenient for coating construction and forming a perfect coating film. The auxiliary film-forming materials have the characteristics of small dosage and significant effect.
The role of coating
1. Protection
All kinds of production and living utensils and equipment used in daily life are mostly made of metal, wood, plastic and other materials. These materials, especially metal materials, are easily corroded by corrosive substances in the environment, moisture, and oxygen in the air. Corrosion and corrosion are more serious in harsh environments such as high salt, high humidity, and oceans. The annual economic losses caused by corrosion are extremely considerable worldwide. Among various metal anti-corrosion measures, the use of coating protection is the most convenient and effective method.
The paint film barrier formed by the paint on the surface of the object, on the one hand, can keep the surface of the object intact; on the other hand, it can isolate the object from the environment, protect it from sunlight, air, rain, corrosive gas and chemicals, and become more durable . In addition to the “shielding” effect of the coating film, the components contained in the coating that can inhibit or pre-corrode the metal can also extend the service life of metal products. For metal workpieces used in harsh environments, the protective effect of the coating film is even more significant.
The coating film can provide good protection not only to metal but also to the surface of wood products and plastic products. It can prevent wood products from rot due to moisture and microorganism damage. It can slow down the photo-aging and oxidation process of plastics that are easily degraded by light and heat, avoid solvents and chemicals to corrode plastics; reduce the volatilization rate of plasticizers contained in plastics, thereby extending the service life of plastic products.
2. Decoration
Using various colors to beautify objects, beautify life and work environment is the emotional need of human beings. Because the paint is easy to be mixed into various colors, the formed coating is not only smooth and bright, but also can obtain the effect of three-dimensional texture, plus the convenience of paint construction, so paint coating has become an important decorative method in production and life. The appearance of the products after coating decoration is more beautiful, pleasing to the eye, and gives people a beautiful enjoyment.
3. Functional purpose
In addition to protective and decorative effects, some coatings also have special functions. Such coatings are called functional coatings. Functional coatings are new materials with strong specificity and special functions developed based on the composition and structure of coatings and combined with special optical, acoustic, mechanical, electromagnetic and biological properties. For example, the enameled wire formed by coating the insulating paint with insulating function on the copper wire is a conductive material that can conduct electricity in the wire and insulate between the wires.
Such as the use of its biological function to use anti-fouling coatings and anti-mold coatings on the underwater parts of ships; high-temperature coatings, high-temperature resistant coatings, fire-retardant coatings that use its thermal function; such as ablative coatings, coatings on the surface of rocket shells, Temperature control coatings inside satellites; anti-static coatings, electromagnetic wave absorbing coatings and conductive coatings used in the electronics industry using its electromagnetic function; luminous coatings, fluorescent coatings, and reflective coatings using its optical functions; acid-resistant coatings using its chemical functions Alkali and other chemical-resistant paints. These special functions of coatings increase the use of products, broaden their scope of use, and put forward higher requirements for coating technology.
In addition, the coating film also serves as a sign. It is often used as color signs and traffic signs. Paint with high brightness and strong contrast on traffic management, chemical pipelines and containers, large-scale or special machinery and equipment as a sign. In order to cause people to be alert and avoid dangerous accidents, it also makes the operators easy to identify, and plays a role in ensuring operational safety or traffic safety.
