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What is coil steel paint?
May 25, 2018

Used in coil coating in addition to conventional performance requirements for coating, the width, must also be made to stand from processing to finished goods not paint film and to adapt to the rapid operation of coating line coating requirements, including primers and paint and paint on the back, because is different to the requirement of the coating, now on the to the bottom, paint a shallow on learning evaluation for readers. 1 coil primer coil with the most varieties in the primer is epoxy primer and polyester primer (polyester - amino primer and polyester polyurethane primer), in addition to water soluble acrylic primer, the characteristics of the primer is as follows: (1) : epoxy primer with good adhesion, water resistance, good alkali resistance, chemical corrosion resistance, but its flexibility than other primer. (2) polyester-amino primer: it has good adhesion to the substrate, good flexibility, but is sensitive to wet environment, and less resistant to chemical corrosion than epoxy primer. (3) water-soluble acrylic primer: good adhesion to the substrate, good flexibility, less organic solvents, low temperature curing, but not suitable for storage in moist environment, high pretreatment requirements. (4) polyurethane (polyester - polyurethane) primer: chemical corrosion resistance, friction resistance, durability and flexibility. Adopted by the epoxy primer based on bisphenol A type epoxy resin E - 06 or E - 03, the current coil with epoxy primer formula with earlier formula the titanium dioxide content of the main difference is that it is low, and adopt A safer solvents, and its restricting factors is the price. As technology advances, the speed of the coil assembly line increases while the storage time (in the oven) decreases, so the time in the oven is determined by the wire speed. For a given linear velocity, there are only two possible ways to increase heat input. The second way is to keep the oven longer, which increases the time spent in the oven. However, in most cases do not apply in economy, so we must improve on the reaction rate of the primer, but for coil 2 face, paint applicator roll soon arrive at primer paint sprayers into contact with the coil, it is a very common practice, so a problem is encountered by the exit chamber after the paint film is tender. When the primer is passed through the subsequent guide roller and storage device, the uncured coating is pulled off and deposited on the roller. To overcome this problem, additional urea-formaldehyde resin is needed. This is not a significant reduction in its flexibility, and it would not be beneficial to combine epoxy resin with more expensive melamine - formaldehyde resin instead of urea-formaldehyde resin. In order to reduce the cost of raw materials, the content of titanium dioxide in the primer is much lower than before. In order to improve the construction performance of primer in higher pipeline speed, the viscosity should be reduced, but this increases the problem of pigmentation, especially strontium chromate. Reducing the distribution of pigment in the upper layer of opaque primer will produce a dark color primer, making it more difficult to mix bright colors. In order to overcome this problem, the need to prevent the settlement agent added to the formula, this includes hydrophobic pyrolysis silica, it not only helps to prevent subsidence, but also helpful to rust resistance of the primer. So far, no satisfactory economic solution has been found for the above problems caused by chromic acid salinized epoxy primer. When epoxy primer is used with polyurethane finish, it must be painted with paint. Be especially careful, because if fluoropolymer is 70% in the substrate, it will pass through ultraviolet rays. Therefore, this kind of paint must be carefully matched with pigment to block the transmission of ultraviolet rays, otherwise it will reach the primer and cause powdering, resulting in subsequent inter-layer adhesion problems. A special primer based on epoxy and phenolic resins has been prepared for coating polyvinylidene polyvinylidene topcoat to resist acid rain. For coil in addition to the hot dip galvanized steel sheet, there are some alternative substrate, such as a sacrifice on the steel plating such as zinc alloy, such as the requirements in the primer formula to increase the dosage of chromic acid strontium in order to maintain good anticorrosive, especially in the nude on the cutting edge all around. However, strontium chromate is now considered to be potentially harmful to health. Although coil coating roller coating method eliminates the spray mist, but must carry on the processing of the metal coating manufacturing still have potential dangers, and coil coating substrate at the expiration of its use of disposal are also worth considering. As a substitute for chromate, a great deal of work has been done to develop ion-exchange silica, which needs field test to verify its practical effect. A sol-gel coating has also entered people's attention. This product, developed in the 1970s, has been used in many fields, including aviation coatings primer. It is mainly used as an alternative to chromate pigments in aviation coatings, and this technology will also be used in coil coatings. Such as wide range of the coating and metal substrate has very good adhesion, can form a very dense and strong air tightness coating, have higher microhardness, impact resistance, flexibility, corrosion resistance and wear resistance, etc. It usually consists of alkoxy silicone or periodic table Ⅲ, Ⅳ, V some elements of the alkoxy compounds or other subgroup elements. , inorganic salts containing this part of the film-forming substances dissolved in some aliphatic alcohols solvent, under the action of acid catalyst can be hydrolytic polymerization into transparent colloidal dispersion, match with fillers and additives can solidify into the oxide film, and can use various methods, including roller coating construction. Back to epoxy primer, although it with corrosion resistance and adhesion see wins, but the lack of flexibility, the spell is commonly used in coil coating mix way to improve, because polyester and polyurethane primers with flexibility, so modification use it more. , of course, this is not to say that in addition to the epoxy primer other primer should not be taken into consideration, for example, because of the usage as high demand for household appliances and colored steel slabs flexibility, is adopted, such as polyester primer is more likely. Now there is a trend and has been put into practice, that is, in the world many coil coating lines in the use of so-called "universal primer." Economic and effective, it has good adhesion to the substrate, and of various types of coating has good adhesion between the layers, and can adapt to the requirement of processing molding, and the primer is belong to the kind of polyurethane. The polyester resin coating is the kind with the largest dosage, and its curing agent is melamine resin. In recent years, the technology of nonuniformity of this kind of resin in paint film has been used to improve its performance. For example, for low hydroxyl polyester resin, low relative molecular weight methionated melamine resin with high etherification degree is adopted to volatilize through the amine and be neutralized by the acid catalyst and baked into the coating. In baking process, melamine resin on the coating surface near produce selective since the condensation reaction, the results after baking the concentration of melamine resin coating from the inside to the surface of a sharp rise, lead to its excellent sense of etherification melamine resin coating concentration distribution of the poor, in high concentration, coating surface and the internal is low, the surface hardness of the coating or polluting high resistance, good processability, internal the volume made of steel plate can be widely used in refrigerators, washing machines, air conditioning separate-bodied air-conditioners, etc. For polyester resin mixed with butyl etherification melamine resin system, may be due to the low surface energy of butyl etherification melamine resin in coatings high concentration zone is formed on the surface, which reduces the pollution increases bonding resistance. If the composition of molecules with rigid and flexible component of special resin blended with polyester resin, at the same time can increase the elongation and tensile strength, which can be developed coating good workability and high hardness of coil coatings. The morphological control technology of the film, such as controlling the shape of the film surface, can be used to obtain a low gloss and subgloss appearance. As a technology with patterned patterns, resin balls or inorganic mixtures are often added to the coating to form a physical concave and convex structure. But the addition of hard materials in the paint will reduce its machinability, and its surface small concave and convex shape is easy to be dirty, reducing the pollution resistance. To this end, on the coating surface crosslinking film contraction caused by too much, on the premise of not reduce machining or polluting resistance produce inferior smooth move or soft tactility, don't mix kind of additives can make the paint film formation of concave and convex and won't reduce the processability. Recently developed coating can form mm - grade bump shape by controlling the flow of coating during baking. In response to the primer coating baking with molten mix, is because most of the resin in the primer coating surface free energy difference and produce mm level of concave and convex, coating on the paint can get orange peel shape appearance, when the bump height and peak can free control, can simulate the same appearance as the powder coating or electrophoretic painting. And in the process of baking paint coating with special crystalline molten resin ball, due to the effect of surface tension will form the concave and convex, this resin ball directly after coating due to its low surface tension was floating on the surface coating, the ball is formed around the uplift 0. The convex part of 1mm grade, which lost its crystallinity due to the melting of the ball in the baking process, was immersed in the coating due to the increase of surface tension, while 0. The 1mm convex part is fused into the mm convex part. Adopting this technology made of steel plate can be widely used in refrigerators, washing machines, air-conditioning unit of separate-bodied air-conditioners, etc., made with the technology of coating color or concave and convex degree, the change of the peak and its appearance changes can have a protean myriad. Of polyester resin itself also has a newer technology, generally USES different Tg of mixed type, and weatherability of the composition of polyester resin selection of components, the more amazing is the import in the polyester resin resistance amine light stabilizers, in order to improve the weatherability of the coating, with this kind of structure of polyester resin combined with ultraviolet absorption agent and crosslinking agent, corresponds to the coating made of weather resistance is very close to the fluorine resin coating, more on organic silicone modified polyester, this paint can be used for outdoor use building materials. In the modern polyester roll coating formulation, the curing agent used in addition to amino resin, but also some sealing isocyanate. The reason for this is that these isocyanates contain hydrogen and are easy to be formed by hydrogen bonds in the system, which is very suitable for the coil coatings to have considerable processability. Because once the coil coating is subjected to the processing force, these microcolloidal structures can act as a buffer, thus offsetting part of the force and keeping the system in good condition. Polyester paint, coil coating paint system with the most is PVC plastisol, poly (vinylidene fluoride in time, whereas/polyester polyurethane system in progressing, is the fastest-growing varieties in these systems, it is based on: (1) when the pu/polyester system combined with granular polyamide can generate a three-dimensional pattern, high abrasion resistance coatings (the single-channel coating and 2 way coating system has 20 ~ 25 microns thickness). (2) as a thick coating or multi-channel coating system, a tough and flexible system can be generated, which can replace PVC and poly-vinylidene multi-channel system (50-100 total thickness). (3) high durability finish (generally 20 ~ 30 cm in thickness) for rolling materials used for covering metal and roof. (4) in view of its toughness and abrasion resistance, it can replace light-colored poly-vinylidene fluoride at a thickness of 20. (5) excellent balance between machinability, hardness and hydrolysis stability can be provided in household electrical products. (6) when used in the automotive field, its advantages are deep impact adaptability and high film thickness. (7) for commercial vehicles and trailers covered with metal and household appliances, its excellent printing adaptability and ink absorbance are helpful for marking paint. However, closed polyurethane coil coatings also have some shortcomings. When the temperature of desealing is reached during the roasting process, the cracking sealant volatilizes and condenses and remains on the line. With assembly line speed, not clean, day month long, contamination on the assembly line of blocking agent, such as material would fall on the coating line caused by the product quality and appearance is damaged, now haven't come up with good solutions to this. Another problem with polyurethane coatings is that if the temperature is not strictly controlled in the oven, it will change color (or even black smoke) and decompose quite rapidly at excessive baking temperatures. The types of polyisocyanate used in polyurethane topcoat include H12MDI prepolymer, IPDI isocyanurate, HDI diurea condensation and HDI isocyanurate. The sealants used are as follows: PI - caprolactam, butanone oxime, dimethylpyrazole, diethyl malonate, etc. Objects to the reaction of isocyanate, binary or polyols used most frequently, this includes the saturated polyester, acrylic acid, phenolic type, such as polyols class structure to determine the final coating properties play an important role. Its linear low - Tg system presents high flexibility but poor durability and chemical resistance. High Tg polyols, which contain more aromatic dicarboxylic acids, and have branched chain structures, contribute to increased hardness and toughness, but are more durable despite their lack of flexibility. Hydroxyl functional groups also have an impact on the performance of the paint film: the low hydroxyl value has good adhesion, and the high hydroxyl value has good stain resistance. The durability can be improved by using lipid ring family and hydrogenated diacids. The ratio of polyol to polyisocyanate is about l: 1, and above or below this ratio are unfavorable to the performance of the paint film. The combination of thermoplastic polyamide and polyurethane can improve the flexibility and abrasion resistance of the coating. At present, melamine resin is used as crosslinking agent in most polyester resin coil coatings, but it is easy to be attacked by acids because of its basic properties in the crosslinking reaction. New cross-linking methods have been adopted to replace melamine cross-linking, known as HCT. The system contains heat-latent catalytic materials of sealed hydroxylic acid/epoxy group and acrylic resin system, and the resulting coating has excellent pollution resistance, weather resistance and acid rain resistance. It is the hydroxy acid esterification using vinyl ether and closed, one-component, storage stability, once under the heat generated by dissociation, catalytic to happen 2 - hydroxy ester/vinyl ether addition reaction, in accordance with the formation of coating.