Normal temperature curing steel drum inner coating
Normal temperature curing steel drum inner coating
Shanghai Xugong Coating Technology Co., Ltd. Xu Guoxing
Applying a coating to the surface of the object to dry it into a continuous film, this film is called a film, or a coating or film. The coating film protects and beautifies the object, and for the steel drum real q wall coating, it is more important to protect the steel drum from the corrosion of the contents, and at the same time ensure the purity, safety and pollution of the contents. .
It is only after the paint has dried the final film to protect and beautify. There are many methods for dry film formation of coatings, such as natural dryness at normal temperature, dry reaction at room temperature, dry reaction at ultraviolet light irradiation, dry interference at microwave interference, dry baking at high temperature, and the like.
For a long time, the inner wall coating of steel drums has been limited to coatings such as phenolic resin and epoxy resin. In recent years, there have been coatings such as polyvinyl fluoride and polyvinylidene fluoride. These coatings are all baked at high temperatures. . The use of these coatings in barrel mills with larger steel drums requires a longer drying tunnel. For the barrel factories with smaller output, in addition to the construction of drying rooms, ovens, etc., it is necessary to support the corresponding conveying equipment. Not only does it require more capital investment, but it also consumes a lot of energy. For some barrel factories that are short of funds and lack of energy, the use of these interior coatings can only be beyond reach.
Some steel drum factories turned their attention to room temperature curing coatings. However, due to many domestically produced room temperature curing coatings, some of their physicochemical properties cannot be compared with high temperature baking dry junction coatings. Therefore, the application range of these domestically produced room temperature curing inner wall coatings has been greatly reduced. In this way, some barrel factories that are eager to paint the inner paint barrel and cannot be baked at high temperature due to the conditional restrictions have to import the normal temperature solid "C paint" with good physical and chemical properties from abroad. However, the performance of this imported coating is very good, but its price is daunting, which makes the user's tolerance level greatly affected.
In fact, most of the epoxy coatings we use today are phenolic resins as curing agents. The curing cross-linking reactions are mainly as follows:
1. The methylol group in the phenolic resin reacts with the epoxy group:
2. The methylol group in the phenolic resin reacts with the epoxy resin hydroxyl group:
3. The phenolic group in the phenolic resin reacts with the epoxy group by etherification:
Among these reactions, a reaction involving an epoxy group must be carried out at a temperature of from about 180 ° C to about 210 ° C. Therefore, we must bake when we use it for the inner wall coating of steel drums.
There are many types of curing agents for epoxy coatings, and as long as the curing agent we choose can avoid the reaction of the methylol group and the phenol group with the epoxy group, it is possible to achieve room temperature curing. In fact, there are many curing agents which can react with epoxy at room temperature, such as polyamines, amine adducts, polyamides and the like. Of course, if different curing agents are used, the epoxy resin used must also be compatible.
The following are two types of room temperature curable coatings that are likely or have been used in steel drum interior coatings.
1. Two-component normal temperature reaction dry junction epoxy coating
This is an epoxy resin coating using a polyisocyanate as a curing agent. The high molecular weight epoxy resin, the curing cross-linking reaction of the secondary hydroxyl group and the polyisocyanate can be carried out at room temperature, so that a two-component normal temperature dry-junction coating can be prepared. The dried film has excellent water resistance, solvent resistance and chemical resistance, and has the flexibility required as a coating for the inner wall of the steel drum.
The curing cross-linking reaction mechanism of this coating is as follows:
The isocyanate group of the polyisocyanate reacts with the epoxy resin hydroxyl group to form a polyurethane, thereby achieving cross-linking and curing of the paint film.
Epoxy resins using polyisocyanates as curing agents should be graded E-03 (formerly known as 609 epoxy). It has an average molecular weight of 3,750, an epoxy value of 0.02 to 0.045, a hydroxyl value of about 0.39, an esterification equivalent of about 220, and a hydroxyl functionality of 17.5. As a curing agent, polyisocyanate is selected as toluene diisocyanate. And an adduct of trimethylolpropane.
The two-component normal temperature dry-junction epoxy coating has an optimum curing reaction temperature of 20 to 30 ° C, and the surface drying time is 10-20 minutes, and the steel barrel body and the bottom cover can be assembled in about 4 hours. In the summer when the temperature exceeds 30 °C, spray or apply this epoxy paint on the wall of the steel drum for about 10 minutes, and the nails will not scratch. It should be noted that in the winter, when the ambient temperature is lower than 10 ° C, the curing quality of the coating will decrease, and the curing time will be greatly extended. When the ambient temperature is lower than 10 ° C, it is best to bake in a simple baking equipment, only about 150 ° C for 2 minutes to achieve curing, it should be noted that this epoxy coating can not use alcohols and alcohols Ethers are used as solvents. Since banana water is composed of esters, ketones, alcohols, ethers, etc., it cannot be used. Its best solvent is TB.
Because the price of this coating is slightly lower than the epoxy phenolic drying paint commonly used in barrel factories, the price of TB type solvent is lower than that of banana water. 'With the energy saving, it is very beneficial to reduce the cost. This room temperature two-component dry junction epoxy coating was tested by Shanghai Chemical Co., Ltd., which proved its performance is very similar to epoxy phenolic drying lacquer. The barrel factory that used epoxy phenolic drying paint can be used.
The Shanghai Chemical Co., Ltd. uses a gas drying tunnel to quickly dry at ambient temperatures below 10 °C. Its coating cost is compared with epoxy phenolic baking varnish as follows:
Excluding electricity and temperature differences, the use of room temperature curing epoxy saves coating cost of 3.21 yuan per barrel compared to epoxy phenolic dry baking varnish, and the output can be increased by 3 times.
Second, urushiol titanium chelate high polymer anticorrosive coating
Phenol is the main ingredient of lacquer. The urushiol content in life is about 40 to 70%. Its molecular structure has not yet been determined. It is generally believed that the approximate molecular composition is that there are two hydroxyl groups at the 1,2 position of the benzene ring and an unsaturated long chain -C15H27 at the 3 position. Raw lacquer has good chemical corrosion resistance because it contains urushiol. Urushiol can chelate with titanium compounds to form a high polymer. This high polymer has a broad spectrum of excellent corrosion resistance. The coating made of the high polymer has excellent resistance to strong acid, alkali and organic solvent, salt-resistant solution, high temperature resistance, abrasion resistance and the like. It has been tested that this coating can withstand more than 5 hours in molten sodium hydroxide at 320 °C. It can withstand more than 15000 hours in 10~50% sodium hydroxide or 10-70% sulfuric acid solution at 80 °C. It has excellent corrosion resistance to various chemical media at room temperature.
The corrosion resistance at room temperature is shown in Table 1.
Table 1
The technical specifications of this coating are as follows:
Adhesion 1-2
Flexibility 0.5mm
Impact strength ≥40kg*cm
Dry for 20 minutes
Dry (25 ° C) 24 hours
Under normal circumstances, can be coated 12-14m2 per kilogram
Third, other room temperature curing coatings
There are many kinds of curing agents at room temperature, and there are also a few coatings for steel drum inner wall coatings, such as elemental organic coatings, polyurethane coatings, perchloroethylene high-chlorinated vinyl coatings, chloroacetic resin coatings, rubber coatings, styrene-polyurethane cross-linked anticorrosive coatings. Wait. Among them, styrene polyurethane cross-linking anticorrosive coating, because polystyrene and polyurethane originally have good chemical corrosion resistance, after cross-linking reaction or network structure, the coating film is dense, and the network molecule has no reactive groups. Therefore, the chemical stability is particularly good.
Below, a list of some room temperature curing coatings is described below, see Table 2.
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