Comparison of the price of domestic and foreign coatings for domestic 20-200 liter steel drums
Shanghai Xugong Coating Technology Co., Ltd. Xu Guoxing
At present, the benefits of the domestic steel drum industry are generally not very good, and the steel drum market is highly competitive. Therefore, how to improve the cost performance of steel drum raw materials is an important issue worthy of our attention. This paper introduces the performance, construction method, curing conditions, price and unit consumption of domestic and foreign coatings that are commonly used in domestic 20-200 liter steel drums.
First, the steel barrel coating
The function of the paint in the steel drum is to isolate the inner wall of the steel drum from the contents, and to protect the steel drum from the corrosion of the contents, and to ensure that the contents are not contaminated by the corrosion of the inner wall of the steel drum. The most basic performance also requires the adhesion strength to the steel drum substrate, and the manufacturing process of the steel drum should be taken into consideration, because the construction of the paint in the steel drum is generally carried out before the bottom and the cover are not applied, so as a steel drum The inner coating should be able to withstand the curling of the barrel of the steel barrel when it is cured and formed into a film.
At present, the most commonly used steel drum coatings in the country are epoxy phenolic drying anticorrosive paint, polyvinyl fluoride coating, phenolic resin coating, polyurethane white dry coating.
1. Epoxy phenolic drying anticorrosive paint
Epoxy phenolic drying anticorrosive paint is the earliest and most common internal coating used in the domestic steel drum industry. The epoxy molecular chain in this coating contains hydroxyl groups, ether groups and very reactive epoxy groups. Among them, the hydroxyl group and the ether group have a strong polarity, so that it generates a strong force with an adjacent interface. Therefore, there is a strong adhesion to the surface of the object to be coated, and a reactive epoxy group imparts a high strength bonding force to the surface of the coating and the object to be coated.
The epoxy molecular chain in the epoxy phenolic drying anticorrosive paint is composed of carbon-carbon bonds and ether bonds, and is chemically stable. Therefore, its chemical resistance and acid and alkali resistance are very good. In addition, since the epoxy group of the epoxy resin is at both ends of the molecule, the internal rotation resistance of the molecular chain is young, so its flexibility is good. This is very suitable for the inner coating process of the steel drum industry (coating of the barrel and the bottom of the bucket, top coating, baking and curing, and then re-winding).
The epoxy phenolic drying anticorrosive paint is formed by crosslinking and curing the epoxy resin and the butanol-depleted phenolic resin at a high temperature. The cross-linking curing reaction at this high temperature only releases three parts of water, and no other process. The by-product is released and the shrinkage is small, so the coating has a strong and firm dense network structure film after cross-linking and curing, thereby further enhancing the adhesion, mechanical properties, corrosion resistance and chemical resistance of the coating. .
The coating quality of the epoxy phenolic drying anticorrosive paint is better by spraying. Generally, it should be coated with two layers and baked twice. Its standard curing conditions are: the first layer is baked at 180 ° C for 10 minutes, and the second layer is baked at 80 ° C for 40 minutes. The baking conditions of each barrel factory are different now, so the baking time and temperature can be determined according to the specific conditions, but the consistent approach is to increase the baking temperature and shorten the baking time. It is proposed here that the coated steel drum should be gradually heated to a high temperature from a relatively low temperature during baking, and cannot enter the high temperature zone at once.
The prices of epoxy phenolic drying anticorrosive paints vary from 16,000 yuan per ton to 26,000 yuan per ton. Generally, about 3 barrels of 200 liter steel drum can be coated per kilogram of anti-corrosion paint.
2, polyvinyl fluoride coating
In addition to its particularly good weatherability, polyvinyl fluoride coatings are used by our steel drum industry for their excellent chemical resistance. Its main film-forming material, polyvinyl fluoride resin, has excellent weather resistance, oil resistance, chemical resistance, heat resistance, voltage resistance, water resistance, solvent resistance and corrosion resistance. It is not attacked by most boiling acids and bases, and at temperatures below 10 ° C, almost no solvent can lacquer it.
The coating film of polyvinyl fluoride coating is flexible, folding resistant, wear-resistant, wear-resistant, cold-resistant and impact-resistant; and has good non-stick properties, which is suitable for steel drum contents with polyvinyl fluoride coating as inner coating. Unloading and cleaning up is very beneficial. In addition, it has excellent moisture resistance, mold resistance, salt spray resistance and hygienic non-toxicity, so it can also be used for food-like items.
Polyvinyl fluoride resin has only one fluorine atom in the carbon-carbon molecular chain, and the other three nitrogen atoms, its symmetry is not good, so the polyvinyl fluoride resin is used as a film forming material for the steel barrel with polyvinyl fluoride coating The defects are chemical substances that are not resistant to polarity, such as acrylonitrile, acrylic acid, etc., and are not resistant to concentrated hydrochloric acid, concentrated sulfuric acid, nitric acid and nitrogen water, which are highly oxidizing.
Polyvinyl fluoride coatings should be applied by spraying. Since the solid content is very low (about 24070 or so), the coating obtained after baking the film is thin, and the coating film is liable to cause pinholes. Therefore, it should be sprayed. Since the solid content is very low (about 24070 or so), the coating obtained after baking the film is thin, and the coating film is liable to cause pinholes. Therefore two layers should be sprayed to misalign the pinholes and increase the thickness of the coating. It is best not to dilute when spraying normally. If it is too thick and inconvenient to spray, it can be reduced by heating. If there is no heating condition, consider diluting with propylene carbonate because propylene carbonate has better dilution effect on polyvinyl fluoride coating. It is possible to lower the viscosity with less diluent so as not to lower the solids content of the coating.
Polyfluoroethylene coatings are formed by high-temperature plasticization, and plasticization can only be carried out at a plasticizing temperature. Therefore, the baking should be carried out at a high temperature so that the plasticizer can quickly gain energy into the polyvinyl fluoride molecules. Plasticized film formation is achieved between the chains. Its plasticizing conditions are about 260 degrees and 15 minutes.
The price of polyvinyl fluoride coating is basically about 2-2-25,000 yuan per ton, and about 200 barrels of steel barrels per kilogram of polyvinyl fluoride coating can be applied (two layers).
3, phenolic resin coating
The phenolic resin coating used in our steel drum is thermosetting. At high temperature, the active methylol on the phenolic benzene ring in the coating can crosslink with the excess formaldehyde in the resin to form a dense network structure. Stable coating. Therefore, it is mildewproof, anticorrosive, moisture resistant, oil resistant, solvent resistant, salt spray resistant, chemical resistant, and resistant to any concentration of hydrochloric acid and various organic acids. Moreover, after high-temperature crosslinking, the methylene bond in the phenolic resin of the coating has considerable stability, so its heat resistance is superior to that of epoxy resin and unsaturated polyester resin, and can be used for a long time even at 120 °C.
The excellent anticorrosive properties of phenolic resin coatings are in addition to the inherent properties of their phenolic molecules, especially the dense, three-dimensional multi-ring network formed by cross-linking at high temperatures. However, this multi-ring network structure enhances the anticorrosive properties of the phenolic resin while making it more brittle, which is the biggest weakness of the phenolic resin.
The other weakness is that it is resistant to strong oxidizing acids such as concentrated sulfuric acid and nitric acid because of the benzene ring present in its molecular structure, which can undergo nitrification and sulfonation reactions. In addition, due to the presence of a phenol group in the structure, the hydroxyl group on the benzene ring is weakly acidic, and its hydrogen can be substituted by sodium to form a water-soluble sodium phenolate product, so that the alkali resistance is also poor. Also, it is not resistant to molten phenolic products.
The phenolic resin coating can be applied by spraying and brushing, and the second coating and baking process should also be adopted. Its optimum curing conditions are 170 ° C for 30 minutes. The price of phenolic resin coatings is about 14,000 yuan per ton, and each kilogram of paint can be coated with 5 steel bottles (two coatings).
4, polyurethane white dry coating
The polyurethane white dry paint is applied to the inner surface of the steel drum at a normal temperature for 15 minutes, and the surface is dried. The coating is two-component, one of which is an epoxy resin. Its properties have been discussed in the first inner coating, epoxy phenolic drying anticorrosive paint described herein. Another component is an adduct of polyoxolipid. The film formation of the polyurethane white dry paint is achieved by crosslinking the high molecular weight epoxy resin with the adduct of the polyoxoacid fat. This reaction is carried out at normal temperature. Moreover, this reaction is a direct addition reaction in which no by-product is released and the shrinkage is small. Therefore, the coating is more excellent in adhesion and compactness. This high-adhesion dense network structure coating film has excellent corrosion resistance and is stable to general acid, alkali chemicals, salts, solvents, greases, pesticides, surfactants, etc. Sex. Therefore, polyurethane white dry paint is used as the steel drum for the inner coating, which has wide adaptability. The scope of application is basically the same as that of epoxy phenolic drying anticorrosive paint used in steel drum factories. For general chemicals such as 5070 tartaric acid; 10070 or less hydrochloric acid, nitric acid, lactic acid, formic acid, citric acid; 20% or less potassium hydroxide; 30070 or less sulfuric acid; 40070 or less sodium hydroxide, formaldehyde; 50% or less Phosphoric acid, carbon tetrachloride, butyl acetate, salts, solvents, greases, pesticides, surfactants, etc. all have good stability. Moreover, since the polyurethane white dry paint is a room temperature curing type, it does not need to be dried, and it is particularly suitable for the inner barrel steel drum for some barrel factories without baking equipment. For units with existing baking equipment, energy can also be saved and costs can be reduced.
When using polyurethane white dry paint, mix the two components in a ratio of 4:3 and mix well. Then add the active diluent and mix again. Leave it for 15 minutes before use. The paint thus configured works best in four hours, and the performance of the paint is greatly reduced over six hours. The construction method is similar to ordinary paint, and can be applied by brush or spray. If you apply two layers, the middle part can be separated by half an hour.
The price of polyurethane white dry paint is 1.6-1.8 million yuan per ton, and about 8 barrels of 200 liter steel drum can be coated per kilogram of paint, and no baking is required. Polyurethane white dry paint also has clear paint without pigment. This clear paint is used for large-mouth barrel instead of novolac lacquer. The cost is similar to that of novolac, but the coating performance is greatly improved, and it is quick-drying, bright, beautiful, and rust-proof. , mold, moisture, salt spray, acid and alkali, chemical corrosion resistance.
Second, steel drum coating
The main function of the outer coating of steel drum is to protect the steel drum and beautify the appearance. The domestic steel drum industry currently uses phenolic blending paint, alkyd enamel, amino alkyd baking paint and powder coating.
1, phenolic blending paint
The phenolic blending paint widely used in our steel drum factory is a coating made of rosin modified phenolic resin.
Phenolic blending varnish has the characteristics of high hardness, good gloss, weather resistance, good adhesion, water resistance, acid and alkali resistance and insulation properties. Its disadvantage is that the color is deep, and the paint film is easy to yellow during the aging process, so it is not suitable to manufacture white and Light paint. Such coatings are cheap and have good corrosion resistance. Therefore, steel coatings can be used for such occasions.
However, due to the recent decline in the price of petroleum resins and the lower processing cost of paints than phenolic blending paints, many paint manufacturers have incorporated petroleum resins in phenolic blending varnishes to reduce costs, or simply use petroleum resins to make paints. Pretending to be phenolic vertical and lacquer.
The phenolic blending paint can be applied by spraying or brushing. It has a dry time of about 4 hours at room temperature and a dry time of 24 hours. The price is between 7 and 11,000 yuan per ton. Each kilogram of phenolic blending paint can be coated with about 200 litres of steel drums.
2, alkyd enamel
Alkyd enamel is a paint with an alkyd resin as the main film former.
The alkyd resin itself is a separate paint. The paint made with it is not easy to age, has good weather resistance, long-lasting gloss, flexible and wear-resistant paint film, and is resistant to mineral oil and alcohol solvents. The disadvantage is that the paint film is soft, easy to wrinkle, relatively dry for a relatively long time, and is not scratch resistant. At the same time, since the molecular structure contains an ester group, it is poor in water resistance, moisture resistance, alkali resistance, and poor in ester and ketone resistance.
Its construction method, price and unit consumption are similar to phenolic blending paint.
3, amino alkyd drying enamel
The amino alkyd baking enamel used in our steel drum industry is a cross-linked product of amino resin and alkyd resin as the main film-forming material. It is one of the main varieties of baking varnish. Its curing is achieved by heating an etherification reaction between a methylol group in an amino resin and a hydroxyl group in an alkyd resin, and a polycondensation reaction of an amino resin. The paint is characterized by fullness, toughness, good adhesion, high mechanical strength, good weather resistance, anti-powdering, anti-cracking and good wet and dry performance. It is not sticky after drying; it has certain water and acid resistance. Alkali resistance, oil resistance and good electrical insulation properties; and good construction performance, the paint film is not easy to wrinkle, easy to level.
Amino alkyd drying enamel should be applied by spraying method. The standard curing condition is 105-120 ° C for 1.5 to 2 hours (although there are also low-temperature fast-setting amino baking varnishes, the cost performance is relatively poor for steel drums. ). Temperature and time need to be strictly controlled. The temperature is low, the film is easy to stick when the time is short; the paint film is brittle. However, due to the fact that China's current steel drum production line cannot have such a long baking time, it has been tested by the steel drum coating research department and baked for IO minutes at 175-1800C. Its various indexes can also be close to the standard curing conditions. Performance.
The price of aminoalkyd drying enamel is between 1.4 and 18,000 yuan per ton, and about 5 liters of steel can be coated per kilogram of enamel.
4, powder coating
Powder coating is a coating that is completely free of organic solvents, coated in powder form and baked to form a coating. It saves energy and resources, eliminates environmental pollution, can be recycled with excess powder, and has high mechanical strength. Features.
At present, the powder coatings used in the exterior coating of steel drum industry in China are mainly thermosetting epoxy polyesters. Its curing consists of two parts, one of which is the crosslinking of epoxy resin and dicyandiamide. The network structure formed by this crosslinking reaction provides high adhesion of the coating film and excellent corrosion resistance and mechanical properties. A part of the curing reaction is the crosslinking of the epoxy wax and the polyester resin, and the network of the three-two structure formed by the crosslinking reaction provides excellent weather resistance, decorative properties and mechanical properties of the coating film.
At present, the domestic coating method of powder coating is mainly electrostatic spraying, and its curing condition is 180 ° C for 20 minutes. Its price is between 1.8 and 25,000 yuan per ton, and can be coated with about 200 liters of steel drum per kilogram of powder coating.
5, it is very likely to become a new type of steel drum outer coating
Everyone can find that the exterior paints of some local buildings in the country are becoming more and more colorful, and their life expectancy is getting longer. The main film-forming material of this exterior wall coating is acrylic resin. The most remarkable properties of this resin are aging resistance, weather resistance, light resistance and bright color.
Now the resin begins to enter the outer coating of the steel drum, but the coating made of acrylic resin alone has poor chemical and solvent resistance. The outer coating of the steel drum is modified by two components. The purpose of the modification is to improve its chemical resistance and solvent resistance, and to increase its hardness and drying speed.
At present, this kind of coating has been applied to steel drums, and its paint film performance and appearance are superior to aminoalkyd drying enamel. The construction method, curing time, price and unit consumption are similar to the polyurethane white dry coating in the steel drum coating.
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