Coated iron and its application prospects

Foreword

With the development of technology, consumption concepts and fashion, the competition among metal, plastic, paper and glass in packaging materials has become increasingly fierce. Metal packaging materials have always played an important role in the packaging field due to their good sealing properties, firm texture, good elasticity, good light blocking properties, and good gas barrier properties. Metal containers are still the preferred choice for meat and vegetables. . As an important component of metal packaging materials, tinplates play an important role in food, beverages, aerosol cans and chemical tanks. However, as tin is a major strategic resource, the price is relatively expensive, and resources are increasingly depleted. Therefore, chromium-plated iron, coated iron, and powder electrophoretic products are increasingly used as substitutes for tinplates and low-tin plates. attention.

2 coated iron production process and product characteristics

2.1 The production process of coated iron

The coated iron is a polyester composite film (about 20-25 μm in thickness) covered on both sides of a cold-rolled steel sheet (usually coiled steel sheet)/chrome-plated iron sheet, which is a kind of plastic film and Metal plate double-featured metal functional material. In theory, the coated iron substrate can be directly cold-rolled steel sheet, that is left blank coated iron. Color film lamination technology is unique to China, but when the empty cans are covered by an iron can, it is easy to cause corrosion at the weld seam and the adhesive strength is not strong. In Europe, America and Japan, the coated iron technology is widely used. Chrome-plated iron TFS as a substrate, that is not suitable for leaving empty coated iron. The fastness of the organic film coating is extremely high, which is mainly due to the presence of a chromium hydrated oxide film on the surface of the TFS product, which is combined with the organic film in the form of a hydrogen bond, as shown in FIG. 1 . Figure 2 is a film line directly connected to the ECCS plating section.

Fig.1 Combination of TFS substrate and organic film

Figure 2 Thin-film layer line connected to the ECCS plating section

1-Uncoiler; 2-loop; 3-ECCS section; 5-loop;6-coated wax; 7-coiler

At present, there are two kinds of film coating processes: First, the extrusion process under high temperature and high pressure. Using high-temperature film and quenching recrystallization technology, the organic film coating has a very high fastness (used in Europe and the United States and Japan more than this process); the second is the bonding process, using low-temperature bonding, the bonding fastness is lower than the high temperature High pressure method.

2.2 The characteristics of coated iron products

Compared with coating iron (ie tinplate with inner coating and outer printing (chromium plating)), coated iron has the following characteristics:

(1) It has good anti-rust, decorative, heat-insulating, shock-absorbing and other functions, and its resistance to stamping and corrosion is unmatched by coating iron. Since the covered (adhesive) film of coated iron is a multilayered polyester composite film, its ability to block the penetration of corrosive media is close to "completely repressive." For the packaging of tomato sauce cans and two-piece cans, coated iron is the ideal material. The coating iron has a conflict between corrosion resistance and adhesion.

(2) The surface pinholes are small and dense, and a variety of treatments can be performed on the film, such as marking, laser processing, etc. (compared with the coating). For secondary cold-rolled coated iron (also known as "Marnet plate"), it has excellent mechanical properties and high tensile strength. Table 1 compares the performance of secondary cold rolled coated iron with secondary cold rolled ordinary tinplate.

Table 1 Comparison of performance of secondary cold-rolled film iron and secondary cold-rolled ordinary tinplate

Product Category

hardness

Yield strength/MPa

Elongation/%

Cold rolled ordinary tinplate

DR-7.5 TH520

520

4

DR-8 TH550

550

3

DR-9 TH620

620

1

Secondary cold-rolled coated iron

(Manet board)

DR-8 ML550

550

10

DR-9 ML620

620

7

DR-9.5 ML650

650

5

DR-10 ML680

680

4

DR-10.5 ML720

720

2

It can be seen from Table 1 that the elongation of Manet plate at the hardness of DR-8 is 10%, while that of ordinary plate is 3%. According to reports in the literature, the reason why the Mannei plate is of high hardness and good extensibility is that the vacuum smelting is used in the steelmaking process to reduce the content of certain non-metallic elements (including carbon) and certain metal elements in steel materials. (10 to 5 levels).

(3) High production efficiency, low energy consumption and material cost. The surface of the coated iron is a thermoplastic resin film. Polyesters represented by polyethylene terephthalate (PET) and resins represented by polypropylene (PP) are best used. The film formation temperature is only about 70° C. The application of foreign ink on the coated surface is ideal for both production efficiency and energy consumption. In addition, coated iron substrates do not need to use tinplate as the substrate. This is the obvious cost advantage of the current situation where the price of tinplate is soaring and resources are in short supply.

(4) It is conducive to environmental protection. The inner coating of paint iron is mainly epoxy resin, and the outer paint is divided into base paint, white paint, and glazing paint, mainly acrylic acid and polyester resin. Printing ink has thermal curing and ultraviolet curing (UV), but printing ink must be matched with the coating to ensure the ink's color and adhesion properties. As the currently used paints are added with curing agents, plasticizers, toners, and other ingredients in organic polymers, they are dissolved in solvents and thinners. Therefore, there are still environmental problems in Indian Iron Works that need to be solved. In addition, for tomato sauce cans, deep-drawn two-piece cans, etc., iron coating is not stable enough. The coated iron with a thermoplastic resin film on the surface is free from exhaustion of solvent exhaust gas in the production process, which is favorable for environmental protection.

3 The development of coated iron

Since the 1990s, TFS products, one of the substitutes for tinplate, have been widely used in the United States and Japan. Its main uses are: crown caps, four-spin caps; top and bottom caps and shallow flush pots for three-piece cans; edible oil cans, canned condiments; regular containers of solid foods, tea, detergents, etc.; internal combustion engine fuel oils, paints, Paint cans and so on. However, TFS products have two disadvantages: First, the product must be coated with a protective coating film on both sides, and the printing process causes severe benzene contamination to the environment and human beings; second, some paints have unavoidable trace residues. Affect human health.

Therefore, in the late 1980s, Japan successfully produced coated iron with chromium-plated iron as the substrate. However, the product could not be deep-drawn at the initial stage of launch, and the cost difference from the DI canister was relatively large, and the market demand was limited, so it was not widely used. At present, this technical problem has been solved perfectly, and the advantages of coated iron have also been widely recognized by users. The production of coated iron rapidly increased. At present, Japan has 5 coated iron production lines, 3 Toyo Steel Corporations, 2 Nippon Steel Corporations and 1 JFE Corporation, with a total capacity of 600,000 t/a. In 2005, the actual production of coated iron in Japan was 490,000 tons, accounting for 60% of the TFS production. Since the 1990s, Germany, Britain, the United States, France and other countries have successfully developed coated irons that can completely replace tinplates and account for a large proportion of total tinplate consumption. With the scarcity of tin resources and harsh environmental protection requirements, the coated iron has been rapidly developed in recent years. Table 2 shows the production of coated iron in Asia and Europe in early 2005.

Table 2 Production of coated iron in Asia and Europe in early 2005 (unit: 10,000 tons)

Manufacturer

Yield

Total production

Japan

Nippon Steel

Nagoya

17.0

49.0

Fukuyama

12.0

Dongyang Can Making

Simomatsu

20.0

Korea

TCC

Toyo

5.5

10.5

Donbu

Tobu

5.0

Corus Group

United Kingdom

Trostre

3.0

13.5

Belgium

Duffel

4.0

Germany

Rasselstain

5.0

France

Sollac

1.5

At present, China's coated iron production is in its infancy. There are two companies: First, a private company in Wuxi, which has three production lines, uses cold-rolled sheet as the coated substrate, and uses bonding technology to produce it. The annual output is 20,000 tons. The speed of the production line is 80m/min, the fastness of adhesion between the film and the substrate is not as good as abroad; the second is the production of a coated iron line introduced by Shanghai Desheng Lianxing Co., Ltd. in 1998, although its product quality and appearance are superior to those of the same type of three drinks. Tank products, but because of the high cost of their products, they are completely incapable of competition. The production line has not been able to start construction effectively since its introduction. It can be said that the TFS substrate coated iron required by the market has no localization capability. The Cold Rolled Sheet Plant of Baosteel Co., Ltd., which has the fastest speed, the thinnest gauge, and the most advanced chrome-plated iron production line in China, has the conditions for producing coated iron with a high-temperature and high-pressure extrusion process using chromium-plated iron as a substrate. Construction plan for coated iron production line.

With the increasingly fierce competition in food packaging materials, the trend of steel-based metal materials used in the can making industry is gradually decreasing. The use of secondary cold-rolling technology can reduce the thickness of cold-rolled plates, increase the utilization rate of tons of steel, and achieve the purpose of reducing costs, thereby improving the competitiveness of steel tanks. At present, Baosteel Co., Ltd. cold-rolled sheet metal plant has a secondary cold rolling technology, product thickness specifications for the 0.15 ~ 0.36mm, the thinnest can reach 0.10mm. The use of specifications of foreign users is generally much thinner than domestic users, and now developed countries have used extremely thin steel plates with a thickness of 0.07 to 0.12 mm to make barrels and cans. The secondary market share of Baosteel's secondary cold rolled products has also reached more than 20%, and is growing continuously. For the secondary cold-rolled coated iron, Corus Group and Crown cans cooperated to study the secondary coating due to the increasing demand for two-piece cans for food use. Adaptability between cold rolled sheet and existing equipment. As represented by Lorraine sheet metal plant in France, secondary cold-rolled coated iron with excellent elongation has been produced, which is very suitable for two-piece stamping cans and easy-open covers.

4 Application Status and Prospect of Iron-Coated Iron at Home and Abroad

At present, coated iron has a good application prospect in the packaging materials market, such as stamping cans DRD, cupping DI, two-piece cans, shaped cans, Easy Opened End, and Easy Peeled End. It also provides personalized and fashionable consumer concept packaging materials for food cans, various beverages, oleochemicals, household chemicals, pharmaceuticals and health care industries.

In the overseas market for coated iron, the coated iron should not be left blank, and dry molding can be adopted when the coated iron cans do not need excessive lubricant. This can avoid the generation of large amounts of waste water and environmental pollution caused by cleaning the lubricant. Therefore, all kinds of stamping cans DRD (and cupping DI) become more and more popular. For example, coated iron coated with polyethylene terephthalate (PET) and polypropylene (PP) can be used to make lids for caps, DRD cans, sprayers, etc.; coated iron with polyester film has excellent Processing adhesion and processing corrosion resistance are suitable for the production of deep-impregnation cans and welding cans with a large amount of deformation and containing highly corrosive articles. At the same time, polyester film coating has a low absorption rate of aromas in foods and can make foods in cans. The various ingredients in the company maintain a delicate balance between them and keep them in good condition for a long period of time. The three-piece cans have been gradually reduced in developed countries due to their complicated production. Instead, they have adopted the stamping can DRD and the cupping DI. The market share of Japanese steel two-piece cans (DI and TULC) has reached 60%.

In recent years, the easy tear cover has gradually gained popularity in foreign countries. This kind of cover is actually a secondary cold-rolled steel sheet or a secondary cold-rolled aluminum sheet with a thickness of 0.07 to 0.13 mm, and it is subtly sealed on the empty can by mechanical and heating techniques. Some types of EPE can withstand high temperature sterilization. From the perspective of Europe and the United States, the technology of coated aluminum is maturer than that of coated iron. However, the cost of tearing the lid of steel is only 50% that of aluminum easy to open. Therefore, the coated iron easy tear cover is a direction for future development.

The world's largest canning group, Impress Holding, has a factory with an annual output of 1.4 billion fish cans in Germany, and 70% of them use coated aluminum cans. Crown has four production plants in France and Italy. It produces mainly canned meat (5 million cans/a) and also uses coated aluminum. It can be seen that, with the technological development of coated iron, companies aiming at pursuing profit maximization will tend to replace high-cost coated aluminum with low-cost coated iron.

At present, the application of coated iron in two-piece cans in China is still in its infancy. With the rapid expansion of the two-piece cans application in the world, the market demand for two-piece cans in China has been greatly promoted. At present, the annual consumption of two-piece cans (steel and aluminum) in China is about 10 billion yuan. Calculated at a growth rate of 10% per year, the domestic demand for two-piece cans will reach 16 billion and a net increase of 6 billion after five years. At present, the output of domestic steel two-piece cans is about 1.2 billion, and the share is only 12%. The production capacity is insufficient and the energy consumption of traditional Dl cans production process, secondary pollution problems and their inherent disadvantages (affecting the flavor can not enter the beer The market, rusted, has limited its further development. Therefore, it can be predicted that the domestic market with two-piece cans made of green and coated iron will have a very broad prospect.