The status quo of organic coated steel plate and its application prospect in packaging industry

Generally, steel plates are not used without a protective layer. According to the composition of the protective layer, they can be divided into inorganic layers and organic layers. The surface is an inorganic protective layer, which is customarily referred to as a plate, because the protective layer is usually Formed by hot dip or electroplating, such as galvanized or tin plated. The organic protective layer on the surface is collectively referred to as an organic coated steel plate. Because organic paint has a wide variety of colors and is rich in colors and colors, it can meet different needs. Therefore, the organic coated steel plate is widely used. In order to increase the need for protection or aesthetics of the substrate, organic coating is still applied outside the inorganic protective layer. When the galvanized sheet is used as an exposed part, it is generally coated with a layer of anti-corrosion performance, and can also give the surface of the steel plate Rich color organic coating. Coatings used for organic coated boards have different properties depending on the type, color, or coating thickness. According to the different coating thickness and main purpose, the organic coated steel plate can be divided into two categories: thin coating plate and thick coating plate. The former coating thickness is less than 5μm, generally l ~ 2μm; the latter coating thickness Generally above 15μm, thick-coated products are often referred to as color-coated panels. According to current production and consumption conditions, organic coating products are mainly thick-coated products.

First, the development of organic coated steel plate

The organic coated steel plate was first created in the United States in the 1930s. With the development of the coating industry and coating technology, the use of building materials as a breakthrough was rapidly developed in the 1950s. In the 1950s, the United States formed a complete organic coated steel plate industrial system; after the 1990s, the number of organic coated steel plate production lines in the United States accounted for 50% to 55% of the world's production lines. The American organic coated steel plate technology is exported to a large number of countries, which promotes the development of organic coated steel plates in Europe and Japan. Especially in Japan, after the 1980s, a series of organic coating products with unique properties were developed. By the end of the 1990s, it had nearly 50 production lines and its annual output reached 2.7 million tons, making it the largest producer of organic coated steel plates in the United States. The production of organic coated steel plates in China started later but developed rapidly. After the 1980s, China began to introduce the production technology and equipment of organic coated steel plates. In recent years, the rapid development of the national economy has led to a rapid development of China's construction industry, strong demand for the building materials market, and the scale of home appliance production in the world. This has greatly promoted the consumption and development of organic coated steel plates, and production and consumption have increased year after year. In 1997, the apparent consumption of organic coated plates nationwide was only about 600,000 tons, and most of them were imported. According to the data analysis released by the relevant state departments, in 2007 China's coated plate (belt) output reached 3.1721 million tons, an increase of 36.1% over 2006, China began to become a net exporter from a net importer. According to the current incomplete statistics, from January to September 2008, the output of coated plates (belts) in China reached 2.6481 million tons, an increase of 11.4% over the same period of 2007. Due to the rapid increase in market demand, not only domestic major steel group companies (such as Baosteel, Wuhan Iron and Steel, Anshan Iron and Steel, Panzhihua Iron and Steel, Maanshan Iron and Steel, etc.) have completed and put into production a number of continuous color coating production lines, but also led joint ventures and private enterprises to build a large number of color coating. Board production line. According to statistics from the China Iron and Steel Association, currently the domestic organic coating unit has a production capacity of nearly 10 million tons, of which more than 80% are non-member units outside the China Iron and Steel Association, which are mainly concentrated in coating production companies that need to source substrates from the market. The large number of construction of these coating units on the one hand satisfies the need for rapid increase in the domestic consumption of coated steel plates, but on the other hand there are many low-level redundant constructions. Most of the production lines are subject to low level of equipment, weak technical power, and raw materials. Affected by factors such as supply instability, the unit operating rate is low. In particular, the soaring prices of domestic steel products in 2006 and 2007 have caused some confusion in the rapid growth of color-coating panels in consumption and production. Some units that have invested tens of millions have just stopped production since they started production.

Second, the production process of organic coated steel plate

The production process of organic coated steel plates has undergone the development of single-sheet coating → semi-continuous coating → continuous coating. Coatings used in the production process of coated plates are mainly liquids. The usual production method is to apply liquid coating on the substrate and then dry it to solidify. A uniform and uniform coating film is formed on the surface of the substrate, commonly known as roller coating. In the production of organic coated plates, the roll coating method is the most widely used, accounting for about 85% to 90%. The process section is coated with a liquid coating from a roll of a roll coater, and the coating is applied to the pretreatment by a coating roll. The upper and lower surfaces of the strip are then heated and baked into a curing oven to completely volatilize the solvent in the coating, and the exhaust gas containing the solvent is discharged to the incinerator for treatment. The coating is baked and then cooled to be a finished product; One method is to preliminarily make the organic paint into a plastic film and then apply the film to the adhesive-coated substrate. This method is called lamination (or roll pressing). In the early 1980s, about 90% of organic coated plates were produced by roll coating, and the remaining 10% were produced by laminating; in addition, powder coating methods that have been formed by electrostatic coating in recent years have also been used. Applied, the powder coating method is a new process. After pretreatment, the surface of the substrate is coated with a powder adhesive, which is cured by induction heating. After the substrate is cooled by an internal water cooling roller, it enters a powder coating device. In a powerful electrostatic field, the powdered rotating brush generates a paint powder cloud. The solid particles of the powder cloud carry a very high charge. They fly to a high-speed substrate and generate a large enough boundary penetration force. The powder particles are uniform. Deposited on the strip surface.

At the beginning of the continuous coating production line, the roller coating process used a one-coat, one-bake process, producing a single organic coating plate. However, due to the limitations of the thickness of the primary coating film of the roll coater and the ability of the baking curing oven, if the product requires a large coating thickness, multiple coating and baking curing are required. Therefore, in order to meet the requirements of different coating thicknesses, a two-coat two-bake or even three-coat, three-bake-type production process was developed. Japan took the lead in establishing a two-coat, two-baking, double-layer color coating production line in the 1960s. To date, this type of process still occupies a dominant position in color coating production lines all over the world. In the late 1970s, a three-coat, three-baked, color-coated board production line was established in the United States and Japan. However, due to its complicated process and high product cost, only a few plants have been used so far, and its products are mainly used in special requirements. Therefore, at present, the commonly used technologies for color coating production lines at home and abroad are still two-coat and two-dry.

Third, the application of organic coated steel

According to the different application fields, organic coated steel sheets can be divided into several major categories for construction, home appliances, metal containers, and special properties. Different application fields have unique requirements for organic coated steel sheets.

1, the application of organic coated steel plate in the construction industry

When organic coated steel plate was introduced in the United States in 1936, it was preferred for applications in the construction industry. With the large-scale construction of steel structures, organic coated steel plates have become more widely used in the construction industry, such as the construction of the “Bird's Nest”, the main stadium of the Beijing Olympics, and the first Antarctic inland science survey constructed in China just before the Spring Festival. Station - China Antarctic Kunlun Station has used organic coated steel plates. The main part of the project, which is mainly steel construction, can be prefabricated in different places and then installed on site. This will ensure the high quality of construction and ensure the high speed of construction. According to the data from the 2003 annual meeting of ECCA, in North America, the proportion of color-coated steel plates as building panels is 66%, which is still the largest application market for organic coated plates in the construction industry in China. It is estimated that the amount of color coated sheets for construction purposes accounts for about 70% of the total output. It is also reported that the amount of color coated sheets for construction purposes in China accounts for more than 90% of the total output. The coated steel plates used in construction are divided into three categories for internal use, external use and other uses. Among them, 60% to 70% are external boards, mainly used for roof covering (more than 30% of total volume) and external wall plates (total The amount of nearly 30%). Organic coated panels for external use in buildings need to be subjected to wind, solarization, and rain for a long period of time. After many years of cold and heat changes, the main performance requirements are impact resistance, pressure resistance, fire resistance, water leakage prevention, and heat insulation. Sound insulation, durable weather resistance, stain resistance, process repairability, etc. In addition, beautiful colors, novel samples, rich textures, and coordination with the entire building and its surrounding environment are also required. The characteristics of several typical resin coating materials are shown in Table 1.

Table 1 Characteristics of Typical Resin Coatings

Resin category

Coating hardness

Processing performance

Glossy color

Pollution resistance

Corrosion resistance

Weather resistance

Film thickness μm

Polyester

excellent

good

excellent

good

good

good

20

Propyl tree

good

good

excellent

good

good

good

20

Silicon Polyester

good

good

excellent

good

good

excellent

20

Polyvinyl chloride

can

excellent

inferior

can

excellent

good

200

PVC film

good

excellent

can

can

excellent

can

200

Polyvinyl fluoride

good

excellent

inferior

excellent

excellent

excellent

25

Polyvinyl fluoride film

good

excellent

can

excellent

excellent

excellent

40

Polymer Polyester

good

excellent

excellent

good

good

good

20

Although the construction industry is the main consumption area of ​​organic coated steel, due to the relatively low requirements of the coating industry for the application of the construction industry, the existing domestic color coating production lines are basically positioned for construction purposes, so intense among various manufacturers. Competition is unavoidable. In addition, due to the cost of switching, some users who are supposed to use organic coated boards are still using substitutes. Taking the production of plastic steel doors and windows as an example, in order to improve the corrosion resistance of doors and windows and prolong their service life, the Ministry of Construction stipulates that steel bases are not allowed to use bare boards. Production plants can use both color-coated and galvanized steel plates as substrates. The market price is higher than that of galvanized sheet. Therefore, despite the better corrosion resistance of the color-coated sheet, in order to reduce costs, galvanized sheet is not used as much as possible for the door and window manufacturers, and the use of other materials is also used. similar. Many aspects of China's construction industry are still at a relatively low level compared with developed countries. They only focus on short-term benefits and practicality, and they are rarely considered from a long-term and aesthetic point of view. Despite the superior corrosion resistance and attractive appearance of the color-coated panels, due to the relatively high prices, the rapid increase in domestic production and sales in recent years has not solved the problems in the organic coated panel production industry. With the financial crisis, The impact of global economic development has expanded and perhaps more production units will be forced to stop production. At present, the color coating substrates for construction are developing with a thin gauge, large width, and high strength, and the proposed unit must fully consider this.

2. Application of organic coated steel plate in home appliance industry

Organic coated steel plates have a wide range of uses in the manufacture of household appliances such as refrigerators, washing machines, dishwashers, and microwave ovens. The user's requirements for organic coated plates are quite different and more stringent than the construction industry, such as good plate shape, precise thickness control, complete elimination of surface defects, and no surface contamination.

In addition, the substrate is required to have enough processing and forming properties to meet the processing and deformation requirements in the production process of household electrical appliances; home appliances must inevitably undergo close selection by the user and require that the surface reach a “zero” defect level. The organic coating plate coating can not cover the surface defects of the substrate, and because the bright color has a certain amplification effect on the substrate defects, so the substrate surface must also meet the "zero" defect level, and the plate shape is good to ensure the substrate and Good combination of coating. In addition to the strict requirements on the substrate, the coated board for home appliances also has different requirements for the coating. Organic coated plates are generally used as housings for home appliances. The coating must be uniform in color, and there must be sufficient bonding strength between the coating and the substrate during the manufacturing process to ensure that the coating does not fall off; the coating should also have good processing properties. To ensure that the coating at the bending deformation is crack-free.

The application of organic coated plates in the home appliance industry can reduce process operations, shorten process time, and eliminate various costs, which will bring about significant economic benefits. Although the total demand for organic coated boards in the home appliance industry is much smaller than that in the construction industry, it will increase steadily for a certain period of time, mainly due to the continuous improvement of various requirements for daily necessities such as furniture and home appliances after the development of the household appliances industry and the improvement of people’s living standards. At the same time, the existing home appliance production line equipped with the spray equipment gradually aging, eliminated, and according to the development trend of the world today, will be sprayed into the professional manufacturer to stabilize and improve the quality of coated plates, simplifying the user process will be an inevitable trend. It is no longer necessary for home appliance manufacturers to renew or build new spray equipment. It is convenient and economical to directly purchase coated plates from professional manufacturers. Therefore, the vigorous development of the domestic appliance industry will inevitably lead to a large number of applications of organic coated steel plate in the industry, and there will be higher requirements for the product specifications and color quality of organic coated steel plates.

As the coated board for home appliance use has a very high appearance, the production requirements for the organic coated board unit are also very strict: To prevent the occurrence of pitting, it is necessary to strictly control the dust in the environment and float in the air. Fiber and other harmful substances. For this purpose, the production workshop shall be sealed against dust, and if necessary, the production line shall be fully enclosed. The furnace shall be cleaned regularly, the pressure of the furnace shall be controlled, the entrance of the furnace inlet and outlet air shall be prevented, the indirect heating of the hot air, the cleanliness of the staff shall be used, etc. Measures. In order to control the product quality, various inspection instruments are also installed on the coating production line, such as on-line color meter, on-line film thickness meter, micro-hole detector, board temperature meter, and pre-treatment solution concentration meter.

Due to the stringent requirements of the above-mentioned home appliance industry for organic coated boards, only a few production lines in China can achieve. Therefore, high-quality organic coated boards that can meet the requirements of the home appliance industry still have a broad market prospect.

3, organic coated steel plate for the manufacture of metal packaging containers

Metal drums are ideal packaging containers for various chemical, petroleum, and food packaging applications. Tinplates, galvanized sheets, or cold-rolled sheets are often used directly outside the barrels and cans. Common metal cans are pre-printed organically. Layers, metal barrels are mostly painted after manufacture. In recent years, foreign developed countries have gradually adopted organic coated steel plates for the manufacture of metal drums. According to the different types of items contained in the tank, the corresponding organic coating is selected to meet the requirements of hygiene, corrosion resistance and chemical reaction. Because the inside of the barrel tank is in direct contact with the product, the hygienic and corrosive properties of the leaching material in the organic coating must be taken into account. It is neither harmful to the human body nor smelly, nor can it be degraded. There are many kinds of coatings and coating films used in the coating of metal drums. The usual coating is to add hardeners, plasticizers, toners and other ingredients to the organic polymer, dissolved in solvents and thinners. The main coatings are: epoxy-based coatings such as epoxy phenols, epoxy ureas, epoxy esters, epoxy acrylates, etc.; vinyl coatings such as pure ethylene, modified ethylene, and ethylene organosols; propylene, propylene, propylene, epoxy, etc. Coatings and polyester coatings. Among them, epoxy, vinyl, and polyester paints are mainly used in barrels and cans. Outside the barrel tank, mainly acrylic and polyester paints are used. In addition, a thermoplastic resin film having a thickness of several tens of micrometers can also be used on the clad sheet. From the aspects of processability and adaptability to tank contents, polyester represented by polyethylene terephthalate (PET) and polyolefin resin represented by polypropylene (PP) are preferably used.

Environmental issues have received more and more attention and attention from people. The development of organic coating production processes for metal containers must adapt to this trend. First, consider reducing the volatile components in the paint. Use new paints such as water-based paints, quick-drying paints, and powder coatings. Second, use paints that do not need to discharge solvents, or use organic paints that have been previously applied to metal plates. Laminate board. The total amount of organic coated steel plates consumed as food packaging barrels and tanks is small, but the quality requirements are relatively high. As people's health awareness continues to increase, canned foods are almost faded out of the table, and metal cans are mainly used for beverages and beer packaging. In addition, metal barrels and cans, as packaging containers, also face competition from plastics and other packaging materials, as well as competition between steel tanks and aluminum cans. Therefore, in recent years, the production and consumption of organic coated steel plates for food packaging containers have been in a relatively stable state and have not increased as rapidly as the production and consumption of buildings and household appliances industries. There are only a few production lines in China. To meet the demand.

IV. Conclusion