Coatings are generally made up of four parts: film-forming materials, pigments, fillers, solvents and auxiliaries. According to the performance requirements, sometimes the ingredients will change slightly, for example, there are no pigments and fillers in varnish, and no solvent can be found in the final coating.
1. the film forming material, also known as the base material and resin, is the main material that makes the coating firmly attached to the coating surface and forms the continuous film. In general, some resins and oils containing special functional groups are formed by physical or chemical change, which is a dense, continuous solid film firmly adhered to the surface of the coated material. It should be quite stable during the storage period of the paint without obvious physical and chemical changes. There are mainly two kinds of materials for coating materials:
Natural oil film forming substances: including vegetable oil and animal fat, which mainly use vegetable oil, including dry oil such as tung oil, catalpa oil, linseed oil; semi dry oil such as sub oil, sunflower oil; non drying oil such as castor oil, coconut oil and so on.
Synthetic resin film forming material: resin is a mixture of many polymer organic compounds, which is a transparent or opaque amorphous viscous liquid or solid state. Soluble in organic solvents. Some of them are also soluble in water. Resins for coatings can be divided into the following categories according to their sources.
A, natural resins: plants and animals derived from nature. Such as rosin, shellac and so on.
B, synthetic resin: nitrocellulose, such as modified rosin, lime rosin, glycerin rosin, etc., obtained from the processing of natural polymer compounds such as nitrification of cotton by nitric acid.
C, synthetic resin: synthesized from various chemical materials by condensation, polymerization and other chemical reactions. Such as phenolic resin, alkyd resin, acrylic resin and so on. With the development of petrochemical industry, the excellent synthetic resin has basically replaced the newly used animal and vegetable oils as the main coating material.
2, pigment is the color and hiding power of the paint film, and it can also enhance the mechanical properties, durability and special functions of the paint film (anti-corrosion, antifouling, etc.). Pigments can be divided into inorganic pigments, organic pigments, and body pigments.
Inorganic pigments, namely mineral pigments, are mostly of stable chemical properties, light resistance, high temperature resistance, no color change, fixed color and color penetration, strong covering power and good filling ability, but their color is small and their colors are not bright.
Organic pigments: compared with inorganic pigments, most varieties are light resistant, high temperature resistant, discolourful, chromaticity and covering power are poor, but they are brightly colored, contain no heavy metal and have high price.
Physical pigment: also called filler, refers to those white or colorless pigments that do not have coloring and covering power, such as talcum powder and white powder. The main purpose is to increase the thickness of the paint film, play a filling role, enhance the abrasion resistance, light resistance and filling of the paint film, and reduce the cost of painting.
3, the solvent refers to the material that can dissolve other substances and form a homogeneous liquid, so that the coating can be constructed. Solvents play an important role in liquid coatings, and have a great influence on the viscosity, gloss, leveling, wettability and adhesion of coatings. After construction, all will be evaporated into the atmosphere and will not remain in the paint film.
Solvents have different dissolving power to different resins, strong dissolvability to some resins, but little or even insolubility to the other resins. This is the relativity and selectivity of solvents for resin dissolution. Therefore, proper solvent selection must be made to understand the corresponding solvent varieties of each film forming material, otherwise the wrong solvents will cause turbidity, precipitation and precipitation of coatings. Losing light or even scrapping.
(2) evaporation rate: the rate of volatilization refers to the rate of solvent volatilization from the coating to the air. The evaporation rate is influenced by many factors, such as solvent boiling point, ambient temperature, effective evaporation area, surface tension of the solvent itself, vapor pressure and the properties of the specific paint system. The relationship between solvent evaporation rate and solvent boiling point is in fact a discriminant relationship: Generally speaking, the solvent with low boiling point is faster than the solvent with high boiling point. Therefore, the boiling point usually used to roughly distinguish the evaporation speed. Solvents are classified into three categories according to boiling point.
A, low boiling point solvents such as propanol, ethanol, acetic acid, ethyl ester, etc. This kind of solvent volatiles quickly and helps prevent the wet coating from flowing.
B, medium boiling point solvent: toluene, butyl acetate, etc. The solvent evaporation rate is moderate and volatilized after coating low boiling point solvent, which is conducive to the flat and dense coating of wet coating.
C, high boiling point solvents: turpentine and so on. This type of solvent volatiles slowly, and finally volatiles in the coating, which is conducive to film leveling and prevents the paint from whitening in high temperature and high humidity.
According to the construction characteristics of the coating and its drying and curing properties, solvents are required to match the "time volatilization" rule, otherwise the quality of the coating and the construction performance of the coating will be seriously affected. For example, volatile paint, all volatile coating of solvent, namely dry conjunctiva, when the solvent evaporates quickly, the coating quickly coagulates, which is not conducive to leveling and operation, and is easy to whiten in damp and low temperature weather. Generally, a single solvent is difficult to meet the requirement of solvent speed in film forming process, and it is often a mixture of solvents with different volatilization speed and various properties. When the temperature is high, slow down the dry solvent and speed up the dry solvent when the temperature is low.
In general, strong solvents can enhance the levelling and feel of paints, but will increase the cost.
4. auxiliaries: coating auxiliaries, also known as additives, are not film-forming substances. The amount used in coatings is the least (usually a few thousandths). However, they can significantly improve the storage and constructability of paints, and also have obvious effects on the physical properties of the paint film. The functions of coating auxiliaries can be summarized in the following aspects:
1, improve the coating process: initiator, emulsifier, catalyst, dispersant and polymerization agent.
2 improve the storage properties of coatings, such as anti skinning agents, anti settling agents and antifreeze agents.
3 improve the performance of coatings: leveling agent, defoamer, thickening agent, anti flow agent and tide agent.
4 improve the performance of coatings: UV absorbers and antioxidants can improve light resistance and weatherability of coatings. In addition, there are heat stabilizers, wear-resistant agents, flame retardants, anti scratch agents, etc.