What is powder coating?
The powder coating is present in the form of a solid powder. Powder generally refers to solid particles having a diameter of less than 1 mm. The production of powder coatings is the process of pre-mixing, melting, extruding, tableting, sieving and other raw materials of synthetic resin, pigment filler, auxiliary agent, etc., and the coating is mainly based on electrostatic spraying. Due to the excellent energy saving and environmental protection performance of powder coatings, it is the fastest growing coating variety in recent years. According to the data, if the pure solids are compared, the amount of powder coating will be discharged to the top three in 2010. At the same time, raw materials and milling equipment related to powder coatings have made great progress. Below we mainly discuss the additives in the raw materials of powder coatings.
First, the classification of powder coating additives
According to the production and application of additives, the additives are divided into the following three categories.
1. Conventional additives
Conventional auxiliaries are essential additives for the production of ordinary flat powder coatings, including leveling agents, brighteners, benzoin, matting agents, dry powder flow agents, etc. Some of these additives can change the leveling of the coating film, some can change the gloss of the coating film, some can change the flow properties of the powder during construction, and some can improve the storage stability of the powder. Commonly used leveling agents are mostly polyacrylates, and also use Tsinghua castor oil, polyvinyl butyral, acetobutyl cellulose as an auxiliary leveling agent. The brightening agent is a coupling agent, a dispersing agent, and the like for improving the dispersion of the pigment filler. There are many types of powder matting agents, such as chemical types that participate in the reaction, such as the commonly used models B68 and 208; physical types that do not participate in the reaction, such as matting waxes 823 and 3329. The dry powder flow agent uses more fine powder and is added to the finished finished powder, such as fumed silica M-5, alumina C.
2. Texture additives
The texture additive is a powder additive developed to cover the surface roughness of the workpiece or to obtain an aesthetically pleasing coating effect. It optimizes the cumbersome formulas of the previous ones, so that the powder achieves a relatively stable art decoration effect. The main varieties are wrinkle agent, hammering agent, sanding agent, cotton agent, foaming agent, moirÃ© agent, point flower diffusing agent, and three-dimensional pattern agent. The amount of texture auxiliaries is small, both in a few thousandths, and is generally extruded and redispersed. Moreover, these additives have strict requirements on the properties of the resin, such as viscosity, reactivity, glass transition temperature, and impurity content. Ordinary wrinkle powder, if the content of the catalyst in the resin is high, the grain is fine or not. To make a powder, it is required that the organic chlorine content of the epoxy resin does not exceed 0.1%.
3. Functional additives
Functional additives are additives to improve and expand the function of coating film. These additives are among the most developed and most widely used types of additives, such as anti-yellowing agents, UV absorbers, energizing agents, and elimination. Foaming agent, light stabilizer, anti-blocking agent, hardening agent, coupling agent, adhesion promoter, antistatic agent, conductive agent, dispersant, mold inhibitor, catalyst, heat stabilizer, flame retardant, wear resistance Agents, etc. These additives used in powder coatings can be borrowed from coatings or plastics as long as they do not affect the properties of the powder.
Second, the application of powder additives
1. Application of UV absorbers
This product is a preventive stabilizer. It can strongly absorb ultraviolet light from 270 to 380nm. It is characterized by good thermal and light stability and low volatility. It has synergistic effect with phenolic antioxidants and hindered amine light stabilizers. It can absorb the ultraviolet rays before they endanger the polymer molecules, and protect the polymer from ultraviolet rays, thereby improving the weather resistance of the coating film to varying degrees.
2. Application of powder defoamer
The problem of powder defoaming is getting more and more attention. When the powder coating is cured, the air entrained by the workpiece or the coating itself reaches the surface for a longer period of time, and the coating film is formed for a relatively short period of time, thus forming bubbles or pinholes. The most used defoamer is fine wax powder, the typical representative is BYK961; the best domestic application is 4430; the ethylene glycol treated carbonate can be used in various powders. Defoamer 4430 can eliminate the pores formed by the water itself due to water, eliminate the pores caused by the plate of cast iron and aluminum parts, improve the fluidity of the powder particles and the leveling of the powder coating, and replace the benzoin. Yellowing caused by benzoin. However, if the powder coating is sprayed to a thickness of more than 200 Î¼m, the pinhole cannot be eliminated.
3. Application of dry powder flow agent
To achieve thin coating of the powder, the particle size of the powder must be small. The powder particle size is fine, the powder particles are easy to agglomerate, the gun is easy to be blocked when sprayed, and there is scar after curing. The main function of the dry powder flow agent is to reduce the friction between the powder particles, thereby reducing the angle of repose, improving the fluidity of the powder during the spraying process, and prolonging the storage period of the powder. This variety we have produced has been recognized by manufacturers in Taiwan, Singapore and other places.
4. Application of anti-adhesive hardening series additives
The surface hardness of the coating film is also subject to the attention of the powder manufacturer. The products with excellent coating film are often scratched by friction during the packaging and transportation process, which makes the product quality greatly reduced. Our anti-blocking agent and hardening agent are one. An inert polyamide-based material that perfectly solves the above problems and has good anti-pollution properties. There are also manufacturers who add less than 0.5% anti-blocking agent when making thermal transfer powder.
Third, the development prospects of powder additives
At present, powder coatings still have some limitations. For example, powder coating must be electrostatically sprayed, powder can only be used for metal workpieces; powder coatings must be baked at high temperature to form a film, wood or plastic that is not resistant to temperature, and bulky cannot enter the oven. No artifacts can be applied. The leveling and gloss of the powder does not reach the level of certain solvent-based coatings, such as automotive topcoats, and there are no practically applicable powder coatings. All of this limits the application and development of powder coatings. Large foreign companies are studying these issues. For example, in recent years, domestic sales of BYK, Sanye, Dexinli, and Troy have set up sales offices in key cities in China. The localization of these materials is the focus of our work. The 21st century is the century of functional coatings. The development of functional coatings is inseparable from the development of additives. The current additives are also developing towards functionalization and compounding with multiple characteristics.
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