Application of polyurethane resin in steel drum inner and outer coating

Shanghai Xugong Coating Co., Ltd. Xu Guoxing

Polyurethane, its chemical name is called polyurethane, English name: polyurethane, so the abbreviation is called PU resin. The polyurethane resin is made of a binary or polybasic polyisocyanate and a binary or polyhydric hydroxy compound such as a polyether polyol, a polyester polyol or a small molecule polyol, a polyamine or a water chain extender or a crosslinking agent. The polymer is a polymer compound containing a -NHCOO- unit in a molecular structure, and the unit is formed by reacting an isocyanate group and a hydroxyl group, and the reaction formula is as follows:

â€“N=C=O + HOË‰ â†’ â€“NH-COOË‰

By changing the type and composition of raw materials, the shape and properties of the product can be greatly changed, and the final product, from soft to hard, can be obtained, generally in the form of polyester and polyether. Can be used in the manufacture of soft, semi-rigid and rigid foams, elastomers, paints, adhesives, sealants, synthetic leather coating resins, elastic fibers, etc., widely used in automotive manufacturing, refrigerator manufacturing, metal coatings, transportation , civil engineering, footwear, synthetic leather, fabrics, electromechanical, petrochemical, mining machinery, aviation, medical, agriculture and many other fields.

In 1937, Professor Otto Bayer of Germany first discovered that polyurethanes were obtained by polyaddition of polyisocyanates with polyol compounds. Based on this, they entered industrial applications. In the United States and the United States, the manufacturing technology of polyurethane resins was obtained from Germany in 1945 to 1947. Industrialization has begun. In 1955, Japan introduced polyurethane industrial production technology from Bayer Corporation of Germany and DuPont Company of the United States. At the end of the 1950s, China's polyurethane industry began to take off, and it has developed rapidly in the past 10 years.

After more than 60 years of development, polyurethane has become an important synthetic resin variety. In recent years, the Asia-Pacific region has become the fastest growing region in the world's polyurethane industry, and China is the country with the most potential for development. In general, due to the rapid development of the national economy in the past decade, China's polyurethane industry, from basic raw materials to products and machinery and equipment, has a considerable scale. In 2005, China's polyurethane production reached about 3 million tons, with an output value of about 60 billion yuan.

At present, many Chinese and foreign companies have been involved in the polyurethane industry, such as Yantai Wanhua, Shanghai Huayi, Shanghai Gaoqiao Petrochemical, Shanghai Chlor-Alkali Chemical, Northern Chemical, Shanghai Lianjing Group, etc., while foreign polyurethane companies include Bayer. Well-known companies such as BASF, Huntsman, Dow Chemical, GE, Kolkata, Degussa also have a certain market. The temptation of the Chinese market has attracted customers and manufacturers in Malaysia, India, Japan, South Korea and other countries.

In the future, the development of China's polyurethane industry will be mainly driven by five major aspects, namely, the total population, automobile industry, building energy conservation, paint and coating, environmental protection requirements, and leisure and entertainment. During the â€œEleventh Five-Year Planâ€ period, Chinaâ€™s PU product consumption has maintained an average annual growth rate of 15% and is the worldâ€™s largest PU product manufacturing and consumption center.

Polyurethane resins are currently widely used.

Such as foam plastics, including soft foam (mainly used in furniture and vehicles, various mats, sound insulation materials, etc.), rigid foam (mainly used for household appliances insulation, roof wall insulation waterproof spray foam, pipe insulation materials , building panels, refrigerated trucks and cold storage materials, etc.), semi-rigid foam (for car dashboards, steering wheels, etc.).

Another example is polyurethane elastomer, which has high elasticity and strength, excellent wear resistance, oil resistance, fatigue resistance and vibration resistance in a wide range of hardness, and is known as "wear rubber". Polyurethane elastomers have a small output in polyurethane products, but polyurethane elastomers have excellent comprehensive properties and have been widely used in metallurgy, petroleum, automotive, mineral processing, water conservancy, textile, printing, medical, sports, food processing, building bridges and other industries. department.

Another example is polyurethane leather, polyurethane film and the like.

Polyurethane coatings are currently a more common type of coatings, which can be divided into one-component polyurethane coatings and two-component polyurethane coatings.

One-component polyurethane coatings are moisture-curing coatings that do not require on-site blending as two-component polyurethane coatings, so construction is convenient, but usually only varnish. When the paint is manufactured, the moisture content of the pigment and the absorption and moisture during the production process will react with -nco to release the co2. In order to solve the problem of swelling, the solvent is used to remove the moisture in the color paste, and the effect is good. This moisture-cured polyurethane coating is widely used in metal, bridge, highway safety facilities, steel column splash zone on the port terminal, and tidal zone. The 890 coating used in the steel drum industry is a one-component polyurethane coating. It can be sprayed or brushed. It is easy to construct and does not need to be baked. It can be rust-proof, waterproof, grease-resistant, chemical-resistant, corrosion-resistant, etc. . It is also possible to coat a layer of 890 paint on the paint on the top of the steel drum so that the chemical liquid in the tank ensures that the paint on the top of the steel drum is unaffected.

Two-component polyurethane coatings generally consist of an isocyanate prepolymer (also known as a low molecular urethane polymer) and a hydroxyl-containing resin, commonly referred to as a curing agent component and a primary component. There are many varieties of this type of coating, and the application range is also wide. According to the different hydroxyl-containing components, it can be divided into acrylic polyurethane, alkyd polyurethane, polyester polyurethane, polyether polyurethane, epoxy polyurethane and the like. Generally have good mechanical properties, high solid content, and all aspects of performance are better. It is a kind of coating variety that has a promising future. The main application directions are wood coatings, metal coatings, automotive refinish coatings, anti-corrosion coatings, floor coatings, electronic coatings, special coatings, etc. The disadvantage is that the construction of the environment in rainy days or high humidity is likely to cause coating defects.

This is the 891 special series of coatings used in the steel drum industry for electroplating zinc steel drum coatings and open barrel coatings. Of course, there are also color steel drum coatings at room temperature and quick drying.

891 steel barrel special series coating is based on the anti-corrosion advantages of integrated epoxy coating, PVF coating, pure phenolic coating, polyurethane coating, polyester coating and amino alkyd coating. According to the characteristics of steel drum manufacturing and use, January 1989 A new type of special coating for steel drums that has been developed through dozens of improvements. The patent number is ZL 01 2 45930 . 5 , which is the only patented product currently available for domestic steel drum special coatings.

The 891 steel barrel special series coating is a two-component room temperature curing type coating. The film formation is realized by the addition and crosslinking reaction of two components in the coating. The reaction can be carried out at room temperature or under low temperature baking. get on. This reaction is a direct addition reaction in which no by-products are released and the shrinkage is small. Therefore, the coating has excellent compactness, and the dense network structure coating film has excellent corrosion resistance.

Since the 891 paint can be cured without baking, it is particularly suitable for some barrel mills that do not have baking equipment. For units that already have baking equipment, energy can also be saved and costs can be reduced.

The special series of 891 steel barrels are divided into 1 type steel barrel anti-corrosion inner coating, 2 type electro-galvanized steel barrel anti-oxidation bright coating, 3 type steel barrel outer coating anti-corrosion coating and 4 type steel barrel external high-grade imitation porcelain color coating.

891-1 steel drum anti-corrosion coating, with a wide range of adaptability. It is transparent and has various colors. Its transparent coating has excellent cost performance and high transparency and high gloss. The white paint has white tile-like vision and touch, so it has been widely used in the inner and outer coating of steel drums. In particular, the internal coating of domestic large-mouth steel drums has been widely used. When the large-mouth steel barrel made of cold-rolled sheet is coated with 891-1 transparent paint, it is like a thin layer of crystal clear crystal. The inner wall of the steel barrel is like a stainless steel mirror panel, even if it is placed in a humid and corrosive environment for several years. Bright as ever; when the ordinary steel drum is coated with 891-l white paint, the inner wall is white as snow, smooth as porcelain, and bright as a mirror, just like a layer of white ceramic tile.

The PVF green 8911 steel drum anti-corrosion coating is used by many barrel factories to replace epoxy coatings and PVF coatings because of its good anti-corrosion performance and low cost.

For example, the 200L steel drum coated with green 891 paint has been replaced by Wujiang a barrel factory for the packaging of American products. The cost of each steel drum has dropped by about 10 yuan.

The 891-1 type steel drum special inner coating is also successfully applied to the national ink printing special steel packaging steel drum and the internal coating of the anti-chemical barrel of the PLA General Equipment Department.

891-2 type electrogalvanized steel drum anti-oxidation bright paint is mainly used for the overall coating of electroplated zinc steel barrels. Since the zinc layer of the electroplated zinc steel drum is adsorbed by zinc ions under the action of current, the zinc layer structure is not as tight as the hot-dip galvanized original zinc (white iron) steel drum, and there is no dense oxidation on the surface of the original zinc steel drum. Membrane and oil film, so the appearance and anti-oxidation, anti-corrosion performance is poor, for a long time, the appearance is easy to hair, powder and rust. However, after coating a thin layer of transparent 891 paint on the exterior of the electro-galvanized steel drum, not only the overall anti-oxidation and anti-corrosion performance of the electro-galvanized steel drum is greatly enhanced, but also its appearance is crystal-clear and gorgeous. Soon. Because it only needs to be applied in a thin layer, the unit consumption is very low. Several barrel factories can apply more than twenty 200-liter electro-galvanized steel drums with one kilogram of 891 paint.

The 891-3 steel drum anti-corrosion coating is applied to the coating coated on the steel drum. When users of steel drums are filled with chemical products with corrosive properties, they will inevitably splash on the surface of the steel drum, so that the paint on the outer surface of the steel drum is often corroded and wrinkled and peeled off. However, after the outer coating of the steel drum is covered with 891-3 transparent paint, not only when the user fills the corrosive liquid, it splashes on it without damaging the coating, and the steel barrel paint is bright and beautiful. At present, not only domestic steel drum users have been required to apply this coating, but the surface of the packaging drum of German Henkel surfactant has also been coated with 891-3 steel drum anti-corrosion coating.

The 891-4 type steel drum high-grade imitation porcelain color coating is improved on the basis of the 891-3 type, so it has no baking and adhesion compared with the amino baking varnish except for all the properties of the 891-3 type coating. High, high hardness, strong anti-corrosion, its luster and vision can even be comparable to car paint. It is an ideal product for exterior coatings for steel drums.

There are many applications for 891 coatings. For example, some companies use 891 coatings as iron coatings; some companies use them as internal and external coatings for cardboard drums (the cardboard can be filled with liquid products after coating); After the weld coating for hot-dip galvanized barrels, etc.

For the 891 steel drum special coating, the two components should be mixed in a ratio of 1:1 and thoroughly mixed. After standing for 10 minutes (to make the bubbles generated by the agitation run away), it can be used. This kind of paint is applied to the inner surface of the steel drum and is fully exposed to oxygen. It is dried at normal temperature (25 Â° C) for 10 minutes, and it is dry for half an hour. The higher the temperature, the faster the curing, but when the temperature is lower than 10 Â° C The curing time is greatly extended. Therefore, many barrel factories apply 891 paint in steel drums and then cure them with a condition of baking at 100 degrees Celsius for 10 minutes. It is said that the effect is very good. Units without baking equipment If 891 coating is applied to the closed steel drum, it is best to seal the bottom cover after a few days depending on the temperature, so that it can be fully cured in full contact with oxygen.

It is hoped that the application of polyurethane resin in the inner and outer coatings of steel drums will make the coating quality of steel drums even higher.