When many Chinese people buy color-coated boards, they don't know what is the difference between the high-quality color-coated boards and the inferior color-coated boards, because our surfaces are similar, and there will be no problems without using them for a period of work. There are many elements to consider in the selection of coatings, which mainly include improving the type of coating material, coating thickness, coating color and coating gloss. In addition, sometimes we also need to consider the requirements of primers and back coatings for different coatings. At present, there are mainly polyester coatings (pe), fluorocarbon coatings (pvdf), silicon modified coatings (smp), high weather resistance coatings (hdp), acrylic coatings, polyurethane coatings (pu), plastic sol coatings (pvc) and so on.

　　01 Common coating types

　　Polyester (PE, polyester)

　　PE coating has good adhesion to materials, color-coated steel plate is easy to process and form, cheap, many products, and a wide range of colors. Polyester coatings do not need to be ideal for UV resistance and coating film chalking resistance, so the use of PE coatings still needs to be developed and is limited by some problems. Generally, they can be used in areas with less serious air pollution or products that require multiple molding technology.

　　Applicable industry

　　Ordinary industrial workshops and warehousing and logistics warehouses themselves do not corrode the color plates, and the requirements for corrosion resistance and aging resistance of the color plates are not high. More consideration should be given to the practicality and cost performance of the workshops.

　　Silicone Modified Polyester (SMP, Silicone Mobified Polyester)

　　Since the polyester contains the active group -OH/-COOH, it is easy to react with other polymer compounds. In order to improve the sun resistance and pulverability of PE, a silicone resin with good color retention and heat resistance is used for denaturation reaction. The denaturation rate of PE is between 5% and 50%.

　　High Durable Polyester (HDP, High Durable Polyester)

　　For the shortcomings of PE and SMP, the British HYDRO company (now acquired by BASF), Sweden's BECKER, etc. developed HDP polyester coatings that can achieve 60-80% weather resistance of PVDF coatings in early 2000, which is better than other ordinary silicon modified biopolyester industrial coatings., its outdoor weather resistance reaches 15 years. High weather-resistant polyester achieves a balance of improving the flexibility, weather resistance and cost of the resin through the use of cyclohexane-containing monomers in the synthesis of the resin. The design does not contain or aromatic multi-alcohol and multi-acid are used to reduce the absorption of UV light by the resin and achieve the high weather resistance of Chinese coatings. Add ultraviolet absorbers and hindered amines (HALS) to the coating formula to improve the weather resistance of the paint film. High weather-resistant polyester coil coatings have been recognized by the Chinese market countries abroad, and the cost performance of this coating is also very important.

　　Applicable industry

　　Metallurgy, electric power and other non-ferrous metal smelters (copper, zinc, aluminum, lead, etc.).

　　PVC Plastisol

　　PVC resin has good water resistance and chemical resistance. It is usually coated with a coating with high solid content. The coating thickness is between 100-300 microns. It can provide a smooth PVC coating or light embossing treatment as an embossing coating; because the PVC coating is a thermoplastic resin, the film thickness is higher, which can provide good protection for the steel plate. But PVC has weak heat resistance. In the early days, it was used more and more in European countries. Due to its relatively poor environmental protection properties, we currently use less and less requirements.

　　Fluorocarbon PVDF

　　Due to PVDF chemical bonds and bonds, there is a strong bond energy, so the coating has good corrosion resistance and color retention. In the establishment of the steel plate coating industry belt, it is an advanced product, and the key molecular weight and structure type, so in addition to chemical resistance, mechanical properties, UV resistance and heat resistance are also very prominent. In the general social environment, its anti-corrosion life can reach 20-25 years on average. In recent years, domestic enterprises have begun to develop fluorine-containing resins that are copolymerized with chlorotrifluoroethylene and vinyl ester monomers. A large amount of data is applied to the exterior walls and metal sheets of Chinese buildings. The content of fluorine is about 30% lower than that of PVDF, so its weather resistance is compared with PVDF, and there is a certain gap. The fluorocarbon coating produced by Baosteel generally has a PVDF content of the coating not less than 70% (the other is acrylic acid resin).

　　Applicable industry

　　Products in the chemical industry have volatile properties and are prone to volatile substances with strong corrosiveness such as acidic or alkaline. After encountering water, dew is easy to form and adhere to the surface of the color plate, causing corrosion to the color plate coating, and may further corrode the zinc layer or even the steel plate.

　　02 Comparison table of performance analysis of different coatings

　　For the choice of primer, there are two important factors,

　　First, consider the adhesion of primers and topcoats and substrates,

　　Second, the primer provides most of the corrosion resistance of the coating.

　　From this social point of view, epoxy resin is the best choice.

　　When considering flexibility and UV resistance, polyurethane primers can also be selected. For the back coating, the most correct choice is that if the color-coated steel plate can be used as a veneer, choose a two-layer network structure, that is, one layer of back primer and one layer of back topcoat. The primer is the same as the front variety, and the topcoat is a layer of light-colored (such as white) polyester. If the color-coated steel plate is used as a composite or sandwich board, the back is coated with an epoxy resin with excellent adhesion and corrosion resistance.

　　03 Coating surface gloss and selection

　　Gloss is not an indicator of paint performance, like color, it is just a sign. In fact, paint (coating) is relatively simple and easy to achieve high gloss on the surface.

　　However, the glare of the high-gloss surface during the day will cause light pollution (many glass curtain walls are no longer used because of light pollution). In addition, the high-gloss surface has a small friction coefficient and is easy to slip, which is easy to bring safety hazards during roof construction; the aging of the color-coated steel plate when it is used outdoors for the first time indicates the loss of light. If maintenance is required, it is easy to distinguish between old and new steel plates, resulting in poor appearance; if the gloss of the back paint is high, it is easy to produce halos when there is light indoors, resulting in visual fatigue. Therefore, under normal development, some medium and low temperature gloss (30-40 degrees) is used for color-coated steel plates for construction.

　　04 Coating thickness selection

　　Microscopically, the coating is a multi-empty structure. Water and corrosive media (chloride ions, etc.) in the air can penetrate by analyzing the weakness and parts of the coating, causing corrosion under the film, thereby increasing the coating foaming and peeling. In addition, even if we have the same coating material thickness, the secondary coating is denser than the primary coating in China. According to the research foreign literature reports and the test analysis results of related equipment corrosion, only when the front coating is more than 20μm can we effectively prevent the intrusion of corrosive media. Due to the different anti-corrosion mechanisms of primers and topcoats, it is not only necessary to specify the total film thickness, There are also students who design and require the thickness of primers ("5μm) and topcoats (" 15μm) respectively. Only in this way can the corrosion resistance of different parts of the color-coated steel plate be guaranteed to be balanced. PVDF products require thicker films. Because to provide a longer working life can be guaranteed. The requirements for the back coating depend on the use and the sandwich panel only requires one layer of adhesive primer. The formed steel plate also requires two layers due to the social and environmental problems of indoor corrosion in our country. Thickness is at least 10μm.

　　Coating for color selection (emphasis!

　　The choice of color is mainly to consider the matching with the surrounding environment and the owner's hobbies, but from a technical point of view, there are many pigment choices for light-colored coatings, and inorganic coatings (such as titanium dioxide, etc.) with superior durability can be selected. In addition, even if the coating material is discolored or powdered, the light color and the contrast with the original color after the development and change of the coating are small, and the appearance is not affected. Darker colors (especially brighter colors) are mostly organic colors, which are easy to fade under ultraviolet radiation and will change color in the shortest 3 months. According to the analysis of relevant research and test data, when the ambient temperature is the highest at noon in summer, the working temperature of the white surface is 10 degrees lower than that of the blue surface and 19 degrees lower than that of the black surface. Different colors reflect sunlight in different ways. The table below lists the reflective learning ability of different colors

　　05 Color reflectivity reflection effect

　　For color-coated steel plates, the thermal expansion coefficients of coatings and steel plates are usually different, especially the linear expansion coefficients of metal substrates and organic coatings vary greatly. When the ambient temperature changes, the interface between the substrate and the coating will generate expansion or contraction stress, and if it cannot be properly released, coating cracking will occur. Baosteel has done an 8-year sun exposure test of the same paint product variety, the same paint supplier, different and colors in Hainan Development. The results also confirmed that the light-colored paint has little discoloration. The table below shows a comparison of the exposure tests for different colors.

　　06 Gloss Color Difference Original Thickness Current Thickness

　　In addition, here are two points to explain a misunderstanding of the current choice in my country's domestic economic market:

　　First, China has a lot of white gold.

　　The main purpose of using a white primer is that we can reduce the thickness of the topcoat, because the corrosion-resistant primer used by enterprises for construction is yellow-green (so there is strontium chromate pigment), and there must be a sufficient thickness of the topcoat design to have good hiding power. In this way, it is very dangerous for corrosion resistance. First of all, the corrosion resistance of the primer is poor, and the topcoat is greatly thinned, less than 10 microns. The surface of such a color-coated steel plate looks bright, and it will take less than two years to develop the local economy in different countries. Corrosion (cuts, bending processing, underfilm, etc.).

　　The second is that the same system engineering design of color-coated steel plates used in China's building information engineering adopts various manufacturers and batches of color-coated steel plates. The color change trend analysis of different manufacturers is different.

　　There are too many examples of serious color difference. Even for products from the same supplier, it is strongly recommended to use the same system engineering for one order, because different batch numbers may increase the possibility of color difference by using products from various paint suppliers. Reasonable material selection can not only improve the service life of the building, but also reduce costs, truly environmentally friendly and resource-saving.