Precoated steel coil for new steel drum packaging?

Traditional steel drum production materials are cold rolled thin steel drum, hot rolled thin steel plate or galvanized thin steel plate, in the production process of steel drum is essential to the surface treatment of steel drum, painting, drying and other processes, not only the cost is high, and the quality is difficult to ensure, environmental pollution is more serious. In order to protect the environment and reduce the cost, the foreign advanced technology is to prepaint the raw materials of the steel coil plate uniformly. The barrel making factory uses the precoated steel coil plate directly to manufacture the steel drum, without the back coating, which greatly simplifies the production process of the steel drum.

Pre-coated steel coil plate is the steel plate that is directly put into production in the barrel making factory in the unit of coil or sheet after coating the thin steel plate in the coil or sheet. The base steel plate is generally made of 0.2~2.0mm thick steel coil, with the maximum width up to 2m. Mainly cold - rolled steel plate, hot - dip galvanized or electric galvanized steel plate.

1.The development and application of precoated steel coil plate

Precoated coil technology first appeared in the United States in the 1930s. The original alkyd resin paint is 0.2mm thick and 50mm wide steel strip, used to replace wood for window shutters. After World War II, there was a construction boom to recover from war wounds. Taking this as an opportunity, precoated coil as a light and cheap building material has been greatly developed. At the same time, with the economic revival after the war, the progress of science and technology has provided the material and technical basis for the development of precoated coil. At present, there are more than 300 precoated coil production lines in the world, with an annual production capacity of 15 million tons. The field of use has expanded from building materials to automobile manufacturing, ship interior decoration, household appliances, containers, drinking utensils and other aspects. At present, it has been applied to packaging field at home and abroad, especially in the metal container manufacturing industry.

The main reason for the rapid development of precoated coil is that it has good economic benefits and ADAPTS to the needs of social and economic development. First of all, it transforms the traditional finished product coating into the continuous coating of raw steel plate, which is convenient for surface treatment and quality control of coating, but not easy to produce the edge dead Angle of coating defects, and get the best coating quality. Secondly, the speed of thin steel plate in the coating line is generally 40~100m/min, the fastest has reached 240m/min, the production efficiency is far greater than the finished product coating. Third, when the film is cured, the coated plate is passed in the oven. The utilization rate of the furnace capacity is higher than that of the finished product coating. The volatile solvent can be collected and introduced into the burner for incineration during baking, and the heat energy can be reused. Finally, production emissions are convenient for centralized treatment, such as oven waste gas after incineration, organic solvent content is less than 50ppm. The relatively small size of the barrel painting oven is difficult to reach this level, it is not economic to do.

From the point of view of steel drum manufacturers, the price of pre-coated coil is about 20~30% more expensive than the same kind of original plate due to the different coating varieties and plate thickness and material, but it saves the time and raw material cost required for finished product painting. Combined, the cost of the finished product can be reduced by 5~10%.

The National Coil Coaters Association (NCCA), And the European Coil Coatings Association (ECCA, 1967). They are international associations that include producers of precoated coils and of raw materials such as coatings, steel coils and equipment. In addition to holding regular general meetings to discuss and exchange information, special technical forums and new product design competitions are also organized to promote the development of precoated coil and expand the market, and production and sales and statistics are collected and released, and relevant standards, technical manuals and publications are formulated and published, which have played a very good role in the development of precoated coil.

2. Brief introduction to the production process of precoated steel coil plate

The production process of precoated steel coil is divided into three parts, namely, the lead-in section, the pretreatment section, the coating section and the lead-out section.

The lead-in section includes uncoiling, clipping, sewing, and storage looping equipment to loosen and join the raw material coils to supply the unit with sheet steel continuously and uniformly.

The role of the pretreatment section is to clean the coated steel plate and perform surface treatment to improve corrosion resistance and adhesion of the paint film.

The coating section is the core part of the unit, usually using the positive and negative two sides at the same time coating two baking process, that is, primer - baking - coating paint - baking. Depending on the requirements of the product, it can also be only one coating one drying or only coating one side. The advantages of this method are that various thickness of the paint film can be obtained by adjusting the speed of the steel plate and the ratio of the speed of the paint roller and the gap between the paint roller and the paint roller. In order to obtain a good and fully cured film, the furnace temperature is controlled by sections. The temperature of each section is determined by the variety of paint used, the thickness of steel plate and the time it takes to go through the oven. Because it is double-sided painting, the steel plate after painting can not be supported in the furnace, so the general use of dangling or air floating oven.

Some materials require that in addition to liquid paint, laminating equipment is added after the top paint furnace, which can press plastic film on the bottom plate. At this time, the top paint roller and oven can be used to coat and activate the adhesive. With additional auxiliary devices, the coating can be printed or embossed. In order to prevent the paint film from being damaged in the process of transportation, processing and installation, a layer of strippable protective film or a layer of wax should be added to the pre-coated plate.

3. Pretreatment method of substrate in the production of precoated steel coil plate

Steel coil plate in the rolling process of the surface of the lubricant, some products before leaving the factory on a layer of anti-rust grease. In the pretreatment, the grease and other adhesion should be removed first, and then the clean surface of the steel plate through chemical treatment to generate a stable conversion film, in order to improve the corrosion resistance of the bottom plate and the bonding strength of the paint film. The speed of the bottom plate on the production line is very fast, and the pretreatment time is much shorter than that of the ordinary steel drum. In order to ensure the quality of the pretreatment, the oil removal and chemical treatment are required to be efficient, so the process index of the pretreatment liquid needs to be more strictly controlled. To form the conversion film has good toughness and adhesion, so that it can withstand the barrel processing of precoiling plate.

In general, hot lye pressure spray is used to remove oil, such as 0.5~1.5% sodium hydroxide aqueous solution containing a small amount of sodium polyphosphate at 60℃ with 3×105Pa pressure spray. There are also electrolytic methods to remove oil. Scrubbing is generally done with nylon brushes to remove surface adhesion and provide a clean surface for chemical treatment.

Chemical treatment is to form a conversion film on the surface of substrate by pressurized spray or impregnation. When spraying method is used, the slag produced by the conversion liquid in the process of use will often block the spray hole and affect the spray effect. The dipping rule avoids this problem. In order to obtain the best conversion film, different conversion liquid should be selected for different coil plates.

Iron oxide/phosphate type conversion liquid is generally used for cold rolled sheet. It is an acidic solution containing phosphoric acid, alkali metal phosphate, and oxidants (such as chlorate, nitrate, molybdate). Acid corrodes the surface of steel plate to a certain extent, forming amorphous transformation film of iron oxide/phosphate. The ratio of iron oxide to phosphoric acid in the conversion film depends on the pH of the conversion liquid and the operating temperature. The general control conversion film weight is about 0.3g/m2.

In order to improve the corrosion resistance, it is also necessary to use chromic acid solution with chromium content of 0.1~0.5% for passivation, the chromic acid in the passivation solution is reduced to trivalent chromium. After adding a small amount of phosphoric acid and fluoride, the passivated conversion film has the best performance. This partially reduced system can produce "chromium chromate" to fill the pores of the amorphous conversion film, improving its shielding property. The hexavalent chromium ions can inhibit the corrosion of the steel plate.

The pretreatment process should strictly control the indexes of the treatment liquid, and must be tested and adjusted constantly in use. After treatment, the water contains chromium or other harmful metals, and must be purified before discharge.

4. the properties and properties of pre-coated steel coil coating

Precoated coil coating must meet the characteristics of the production process and processing of precoated coil.

The production process is rapid roll coating construction, in order to ensure the thickness of the film and leveling, so it requires a certain construction viscosity. Solvent coating with 40~150s (coated -4 cups) is appropriate, waterborne coating with 28~35s is appropriate. In the process of roller coating, the traveling speed of paint roller and bottom plate is different, and the speed of each roll is also different. Taking the full reverse three-roll coating machine as an example, if the traveling speed of bottom plate is +100%, the painting roller is -120%, the paint lifting roller is -140%, and the control roller is -10%. Due to the large speed difference, the coatings between them are subjected to great shear force. This requires the paint to have little or no false plasticity. That is, the viscosity of the coating is not or rarely affected by the shear force. Otherwise, the viscosity of the coating decreases significantly with the increase of the shear force, which will make the roller adhere to the required amount of coating.

On the production line, the speed of the bottom plate is very fast. Because there is no support and the oven cannot be too long (about 50m), the baking time of the coating in the oven is very short, so the coating is required to be completely cured within 30~60 seconds below the temperature of 260℃ of the bottom plate. In addition, the drying time after painting is very short. The roller coating machine is only ten meters away from the entrance of the oven, and the drying time is only 22 seconds and a half when the speed of the bottom plate is 40m/min and the distance is 15 meters. So choose the right speed of volatilization solvent, so as not to bubble, pinhole and sea cucumber flat is not good. Commonly used is alcohol ether, ketone alcohol and high boiling point aromatic hydrocarbons and other solvents.

From the film performance requirements, coating only bottom, top paint each. The primer should have good corrosion resistance and adhesion to the substrate and topcoat, and the topcoat should have good hiding power and decoration. It also requires that the film does not crack or fall off when processing and forming, and can withstand collision and scratch when assembling, transporting and using. That is, the film should have good flexibility and hardness at the same time, but also excellent weather resistance and corrosion resistance.

5. the development direction and prospect of precoated steel coil plate

If the 1950s was a new era of precoated coil, and the 1960s was a period of great development, then the 1970s was a period of comprehensive quality improvement and development of new technologies. The arrival of the new century, is the era of comprehensive application of pre-coated coil material, the application of the packaging field is the most promising and development space, which is a task given to the packaging industry in the new century.

1, the development of high durability of the precoated coil

(1) Improve the weatherability of oil-free polyester paint (paint with excellent discoloration resistance, fading and pulverizing properties), so that it is used as steel drum external coating.

The development of polyfluoroolefin coatings. By matching with rust proof substrate, the precoated coil can be obtained which is more suitable for steel drum processing.

(3) The use of galvanized steel plate as the base material, it is not only good machinability, but also good corrosion resistance.

2. Develop pre-coated coil with good hardness, elasticity and stain resistance

The adoption of high quality rolling substrate with good processing.

(2) Based on polyester resin, through molecular weight regulation, crosslinking agent selection to sample high performance in this respect.

3. Reduce baking temperature and shorten baking time

(1) Develop new high-efficiency catalyst and high-activity curing agent.

⑵ Increase the molecular weight of the resin, make the resin multifunctional and increase the branching degree of the resin.

(3) Development of electron beam curing coatings. A lot of research work has been done on electron beam curing coatings for precoated coil, which have begun to be industrialized. But compared with the ordinary baking type, the history is not long, both varieties and yields are less, to be further developed.

4, in the packaging collar will have a greater application

1. It can replace wood and cardboard to make ordinary packing boxes, which are solid, reliable, beautiful and generous, waterproof, fire and corrosion resistant, and have the advantages of wooden cases and cartons.

(2) Replacing ordinary sheet steel to make metal containers, such as steel drums, steel cans and small drums, has the advantages of simple processing, energy saving and pollution reduction.

The replacement of tinplate manufacturing product packaging box, elegant appearance, low cost.

(4) Can replace glass bottles and other manufacturing for food, drinks, cans and other packaging, improve the safety of packaging.

⑸ Used in manufacturing large packaging products, such as containers, containers, etc., reduce cost, save energy, reduce pollution, simplify the processing process.