August 8, 2022 Longchang Chemical

Classification of construction machinery coatings and the performance requirements of primer, medium and topcoat

Construction machinery coating is an important part of China’s coating industry. Construction machinery coating can be classified into primer, medium coating and top coating according to coating classification. The primer is the basic coating applied to the surface of the object for priming. Construction machinery, especially large construction machinery is generally open-air operation, direct contact with air, moisture, impurities, and withstand the wind and sun, part of the construction working conditions, the adhesion of the coating film and corrosion resistance mainly rely on the primer. The middle coating is the coating that plays the role of bridging between the primer and the top coating. Its main function is to fill in the bottom substrate, repair the defects of the primer layer, improve the fullness and decorative performance of the top coat, enhance the adhesion of the top coat to the coating, increase the thickness of the entire coating, and improve the water resistance and anti-corrosion performance of the entire coated object. For parts with low decorative requirements and parts with good flatness of the substrate surface, it is possible to reduce the cost of construction machinery products by not spraying the middle coating. Commonly used middle coating are epoxy middle coating and polyurethane middle coating. Top coat is the outermost layer of construction machinery products, the appearance of the product plays a pivotal role, directly affecting people’s visual senses. At present, construction machinery top coating types have been diversified.

Primer is the most basic coating in construction machinery coating, it is directly constructed on the surface of pre-treated steel. Commonly used construction machinery coating primer are epoxy ester primer, alkyd primer, epoxy primer, acrylic primer, polyurethane primer and cathodic electrophoresis primer. Construction machinery construction primer must have the following characteristics: 1, good adhesion to the substrate, in order to enhance the adhesion of the primer often add suitable adhesion promoter in the formula; 2, in the construction of the film should be formed after the excellent mechanical strength; 3, need to have a good matching of the upper layer of paint. The primer itself has good construction performance and can adapt to different kinds of coating processes.

According to the components of primer, there are two-component primer and one-component primer. One-component primer is easy to bite the bottom and reduce adhesion when constructing solvent-based topcoats, so two-component epoxy primer has become the mainstream matching program. The primer is a prerequisite for the durability and beauty of the top coat, and the good or bad primer is an important factor affecting the appearance of the top coat. We can choose different types of mechanical primers from three aspects, such as anti-corrosion performance, mechanical performance and construction performance.

The middle coating is the coating that plays a bridging role between the primer and the top coating, its main role is to fill the bottom substrate, isolate the defects of the primer layer, in order to improve the fullness of the top coating and other decorative properties, while enhancing the adhesion of the top coating to the coating, increasing the thickness of the whole matching coating, and improving the water resistance and anti-corrosion properties of the whole coated object. The requirements of engineering machinery for the middle coating are: 1, good compatibility with primer and topcoat, strong bonding with the upper and lower coatings; 2, the coating hardness is moderate, the solvent of the topcoat can not “bite up” this coating, water and moisture resistance should be good, will not cause blistering of the topcoat; sanding performance should be good, can be dried at a suitable high temperature, good dryness. Commonly used middle coating paint has epoxy middle coating and polyurethane middle coating, polyurethane middle coating has better weathering performance.

The top coat can make the construction machinery with high gloss, rich color and give a sense of beauty. The effect of the top coat directly affects the customer’s judgment of the good or bad construction machinery products, so the appearance of color and effect is increasingly important. The commonly used solvent-based topcoats are alkyd, acrylic and chlorinated rubber, polyurethane topcoats. The requirements of construction machinery topcoat are mainly reflected in the protection performance, decorative performance, construction performance, etc., respectively, are briefly described below.

Construction machinery is generally outdoor construction, outdoor storage, working conditions are harsh, facing the wind and sun, dust pollution and rain mud and water wash. Therefore, construction machinery needs to be coated with a certain thickness of coating film in order to isolate the oxygen, water, dust and other corrosive substances in the atmosphere, to protect from corrosion within a certain period of time and to ensure the service life of the equipment. Protection function is the basic function of construction machinery coating, which requires coating with good adhesion, impact resistance and flexibility and other mechanical properties.

The appearance of the coating is an important factor in the competitiveness of construction machinery products, higher gloss, higher fullness, pleasing coating color scheme, naturally easier to win the market. Also with the development of the market, construction machinery enterprises are aware of the importance of brand building and corporate image visual identity (VI), so the top coating will also play an important role in brand communication carrier. Construction machinery as a whole is huge, complex structure, it is difficult to achieve all the parts coating surface has a high appearance effect. For this reason, the construction machinery industry put forward the concept of covering parts, that is, parts covering the outside of the machine and equipment, including fuel tanks, cabs, engine covers, covers, etc. In these covering parts focus on highlighting the decorative nature of the coating, requiring the surface coating film is smooth, uniform, full, high gloss, no drawbacks, and has a certain degree of weather resistance, in a certain period of time its light loss, fading within the specified range. Therefore, UV absorbers and other photostabilizer products have important applications in construction machinery topcoats.

In the selection of construction machinery top coat, must pay attention to it and the primer, paint or putty matching, otherwise in the coating may appear the whole coating wrinkled and bite the bottom and other supporting bad phenomenon. The top coat requires good leveling, high gloss, high brightness and good fullness, but not hanging. For the case of bad leveling performance of top coat, it may lead to the disadvantages such as hanging, orange peel, poor freshness and poor fullness.

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