The development process of tinplate

  Tinplate is an iron sheet coated with a layer of tin. It is not easy to rust, and its official name should be tinned steel sheet. Tinplate was first produced in Bohemia (in today's Czech Republic and Slovakia). The area has been rich in metal since ancient times, with advanced technology and know how to use water power for machine manufacturing. Tinplate has been produced since the 14th century. For a long period of time, this place has been the main producing area of ​​tinplate in the world. At that time, tinplate was mainly used to make tableware and drinking utensils.

  In the 17th century, Britain, France, and Sweden all hoped to establish their own tinplate industries, but they have not been developed due to the large capital needs. It was not until 1811 that Brian Donkin and John Hall started tinplate canned food that tinplate manufacturing developed on a large scale.

     Tinplate steel plate and steel strip product specifications: 0.13-0.80mm*380-1050mm, material: SPCC, MR, MC, L, D, executive standard: Q/HB 04-2008 "Electro-tinned steel plate and steel strip", main use: Electro-tinned steel plates and steel strips are widely used in food, beverages, sprays, chemicals, and electronics because of their substrates with suitable strength, excellent weldability and stamping properties, and surface coatings with good corrosion resistance, easy coating and printing. And paint packaging and various appliances manufacturing.

2. The main application and characteristics of tinplate!

1). Opacity:

  In addition to causing food deterioration reactions, light can also cause changes in protein and amino acids. Vitamin C is more likely to interact with other food ingredients when exposed to light, resulting in a large amount of loss. According to research and analysis, the loss of vitamin C in clear glass bottled milk is 14 times higher than that of dark bottled milk. Light can also produce oxidative odor, and the nuclides, methionine, etc. are cracked to lose nutritional value. The opacity of tinplate makes the preservation rate of vitamin C highest.

 2). Good sealing

  The barrier properties of the packaging container to air and other volatile gases are very important for the preservation of nutrients and sensory quality. Comparison of various juice packaging containers proves that the oxygen transmission rate of the container directly affects the browning of juice and the preservation of vitamin C; metal cans, glass bottles, aluminum foil laminates, and cartons with low oxygen transmission rate can preserve vitamin C It is better, and the iron can is the best.

  3) The reduction effect of tin

  The tin on the inner wall of the tinplate interacts with the oxygen remaining in the container during filling, reducing the chance of food ingredients being oxidized. The reduction effect of tin has a good preservation effect on the flavor and color of light-colored fruits and juices. Therefore, juice cans packed in unpainted iron cans have better nutrition preservation than juice cans packed with other packaging materials, and the browning change is slight. The flavour quality is better accepted, and the shelf life is thus extended.

  4). Provide a source of effective iron

  Tinplate canned foods, except for a few light-colored fruit and juice cans, mostly use internally painted empty cans to improve the corrosion resistance of the container; due to the electrochemical effect of metal, there will be a small amount of painted canned food in storage The iron dissolves out and exists in the sealed canned food in the form of divalent iron, which is easily absorbed by the human body, and the content is about 1 to 10 ppm. In terms of fruit and vegetable products, the raw material itself does not contain much iron. For iron can products, the iron content of each 350 ml beverage can is 5 ppm. Each can provides 1.75mg iron, which is about 18mg per day. One-tenth of that. If the above-mentioned fruit and vegetable juice beverage cans are rich in vitamin C, iron is more easily absorbed. Therefore, iron canned food and beverages can be a good source of iron, which is of far-reaching significance for the nutrition of iron cans. Because of these properties, tinplate cans provide a closed system that completely isolates environmental factors in addition to heat. Color-resistant foods are degraded by light, oxygen, and moisture, and will not be weakened by aroma or permeable by environmental odors. The food storage stability is better than other packaging materials, the preservation rate of vitamin C is the highest, and the preservation of nutrients is also the best.

3. The basic principle of coating the inner surface of tinplate cans and the convenience brought to us

  Coating paint on the inner surface of tinplate cans is to use a roller coater to print appropriate paint on the smooth surface of the tinplate to form a uniform and controllable coating before the tinplate is cut into can body blanks. The coating machine can independently carry out coating operations through its own feeding device, or it can be matched with the iron printing machine to form a printing coating line.

  The rotating stainless steel feeding roller is half immersed in the feeding tray, and the coating material brought up is transferred to the rubber cylinder through the leveling roller. There is an impression cylinder under the blanket cylinder with a gripper device inside. When the tinplate runs to the squeegee, the impression cylinder grips one end of the iron sheet, and the squeegee and impression cylinder cooperate to push the tinplate through to complete the printing operation. The thickness of the coating is controlled by the feed roller, screed roller, and the gap between the blanket cylinder and the impression cylinder. Because there is a gap between the tinplate sheets, a small amount of paint is taken away by the impression cylinder. Use a scraper to scrape off the impression cylinder (avoid material on the back of the iron coating), and the scraped paint flows into the receiving tray, and then flows back to the storage bucket through the conduit and is recycled. The side seam welding part of the can can not be coated with paint, otherwise the can body blank will easily penetrate the side seam during the high-frequency resistance welding process and cause waste cans. Therefore, the operator should make grooves on the blanket cylinder according to the coating area of ​​the can. The paint is printed on the tinplate by a slotted rubber roller, and the blank iron left at the slotted part is the high-frequency resistance welding part of the empty can

  We have realized in the actual operation that the size of the slot should be 1~2mm wider than the actual welding space, so that the printed space can meet the welding requirements of the empty tank. The coated tinplate is transported to the drying room by a conveyor belt, and is cured at a high temperature through the drying room driven by the circulating chain. The drying room is generally divided into three parts: the first part is to preheat the iron sheet to the baking temperature; the second part is constant temperature baking; the third part is to fully cool the iron sheet. The whole baking time needs 10-15min. After that, the iron sheet is unloaded with an automatic plate unloading machine, and the coating is transferred to the can-making process after inspection and physical and chemical tests are qualified.

4. The production process and performance characteristics of tinplate

  The tinplate of tinplate mostly adopts acidic electroplating process, and hot-dip tinning process can also be used. The surface of the steel plate is silver-white after tin electroplating. The thickness of this tin plating layer is about 0.4~4 MM, which is generally expressed by the amount of tin plating per unit area (G/M2) technically. There are many pores in the tin plating layer after tinplate electroplating, and the corrosion resistance is not good. Therefore, it is necessary to perform reflow treatment or passivation treatment after electroplating, so that a tin alloy layer and a tin oxide layer are formed on the surface respectively. Only when the coating is bright, the bonding force between the coating and the steel plate is enhanced and the pores are reduced, the corrosion resistance can be effectively improved.

  Tinplate is electroplated on the surface of tin, mainly because the electrode potential of tin is higher than that of iron, and its chemical properties are stable, so it can protect the steel plate from rust. But the tin-plated layer must be kept intact. If it is scratched, even with tiny pores that expose the steel base, the steel plate will quickly be corroded due to anodic corrosion.

  The main production process of tinplate is: pickling low-carbon thin steel plate → tin plating → softening treatment → passivation treatment → oiling → inspection → cutting → classification → packaging.

  The structure of the tinplate after metallographic analysis is: there are five layers from inside to outside. (1) Steel base plate. Generally used for can making, its thickness is 0.2~0.3MM. (2) Tin-iron alloy layer. It is a tin-iron alloy structure, the tin content of the electroplated tin plate is <1G/M2, and the hot-dip tin plate is 5G/M2. (3) Tin layer. With pure tin layer, the amount of tin plating on the electroplated tin plate is 5.6G/M2~22.4G/M2, and the hot dip tin plate is 22.4G/M2~44.8G/M2.

  (4) Oxide film layer. Mainly stannous oxide, tin oxide, etc. (5) Oil film layer. It is cottonseed oil or dioctyl sebacate.

5. Tinplate characteristics and prospects

   Tinplate is the common name for tinned cold rolled steel sheet in the packaging industry. In history, there are hot dip tinplate and electroplated tinplate. In the development process of tinplate production, reducing the cost of tinplate production is a strategic goal of manufacturers. Therefore, by the 1970s, hot-dip tinplate was eliminated due to large tin consumption. With the advancement of canning industry technology, people are

The demand for devices is increasing day by day. By the 1990s, the main types of electroplated tinplate used were: CC steel grades, large size rough iron, low tin content or chromium-plated cold-rolled thin steel sheets and secondary cold-rolled thin steel sheets with a thickness of 0.14～0.18mm. The emergence of these types of tinplate not only reduces the cost of manufacturers and can-making users, but more importantly, it satisfies various types of lids such as resistance welded cans, bonded cans, DRD cans, DI cans, and crown caps and screw caps. It provides the necessary packaging materials for the metal container packaging of food cans, various beverages, oleochemicals, daily chemicals, medicine and hygiene, cultural and educational supplies, and cosmetics.

  The above-mentioned various types of tinplates generally have to be decorated by printing iron before they can enter the market as products. In our country, printing iron refers to external printing, and printing refers to internal coating. The inner coating and the outer printing ensure that the tinplate has good canning, canning and appearance decoration. However, the thickness of the organic coating film after such printing is usually only a few microns thick, and it is difficult to completely cover the surface of the tinplate. Therefore, in order to prevent concentrated corrosion at the defects of the organic coating film, the original tinplate must be required to have high corrosion resistance, the surface oxide film to provide coating film density, and the surface oil layer to ensure coating film leveling. For this reason, in the late 1990s, tinplate manufacturers developed and invented the "laminated iron" that heats the PET plastic film to solve the above problems, and is currently in the market development stage. But whether it is tinplate, chrome-plated iron, or laminated iron, high-quality inks and coatings are inseparable for printing iron decoration.

6. Iron printing ink must have the following characteristics:

Heat resistance: The ink must have good adhesion to the tinplate after being cured into a film by heat, and the pigment does not change color after baking.

Processability: Can withstand bending, stamping, stretching and other can-making processes.

Lead-free: Lead is not contained in the ink components.

Dryness: Generally, 1% desiccant has been added to the ink in the ink factory, and 1% to 2% desiccant should be added during printing, but it should not be too much, otherwise the ink will easily crust during construction or over-baking. Wet coating, no ink loss, color fading, color mixing and other defects. High temperature sterilization resistance: the ink will not change when the food cans are sterilized.

  Light resistance and weather resistance: It is particularly important when there is only ink coating on metal containers (faceless coating). Transparency: When using metal surface gloss for printing, its ink transparency is very important. White ink: Apply primer first and then print on the metal surface.

   Iron printing decoration coatings are classified into oily, phenolic, epoxy, vinyl, polyester, acrylic, amino and other resins according to the resin system, and are classified into internal coatings, external coatings, white coatings, and glazing coatings by use. Generally, the anti-sulfur coating is zinc oxide oily resin, the anti-acid coating is epoxy phenolic resin, glazing coating, and the white coating is acrylic resin or polyester resin. The above-mentioned various types of paints and inks are coated and printed on tinplate to become metal container packaging materials. However, because the paint releases a large amount of solution gas during the high-temperature baking process, these solvent gases have obvious odor and the concentration of benzene-containing gas exceeds the standard, which brings serious pollution to the environment. Therefore, while developing tinplate coating and printing technology, the environmental protection problem of waste gas treatment cannot be ignored. In fact, foreign countries also have a long process of exploring this waste gas treatment, which consumes a lot of manpower and financial resources. From the high-altitude emissions in the 1960s (a stopgap measure), the adsorption method in the 1970s (high cost and incomplete), the catalytic combustion method in the 1980s (high cost), it was not until the 1990s that the incineration method had a complete solution. Nowadays, domestic environmental protection equipment research departments and manufacturers have devoted themselves to the research of the above-mentioned waste gas treatment. The realization of the catalytic combustion method and the incineration method has brought good news to the iron printing industry. In particular, the realization of the incineration method has not only made up the domestic gap, but also reduced the operating cost of waste gas treatment and has a broader market prospect.

  The economy of the 21st century is a knowledge economy as well as an environmental economy. This is the inevitable trend of the times. Because the rapid economic development brought about by reform and opening up has also severely damaged and polluted the ecological environment, environmental protection has become a support and growth point for sustained economic development. As far as my country's iron printing industry is concerned, according to preliminary statistics, there are nearly 1,000 printing and coating production lines. Among them, paint drying rooms with serious waste gas pollution account for about 1/2. Each paint drying room produces 214 paint tinplate with the smallest size (512×712mm), the coating film thickness is 5.5g/m2, and the production speed is 4600 sheets/hour. According to calculations, about 20kg of exhaust gas is emitted per hour, and 300kg of exhaust gas is emitted every 15 hours of production (two shifts). Therefore, the degree of environmental pollution can be imagined.

In view of this, the China Packaging Technology Association has set up a designated factory for environmental protection equipment in Shanghai, specializing in the development and production of incinerators to solve the problem of waste gas pollution that has not been resolved in the iron printing industry for many years. This has brought greater support and broad coverage to the tinplate packaging industry. Prospect

7. How to inspect the quality of finished tinplate cans

   The surface of tinplate cans must be smooth and clean, and no obvious foreign matter or debris should be attached. The tank body must not have edges, corners and burrs. There should be no serious scratches, scratches, and the appearance of the pattern and the ink color of the text should be correct, uniform and bright, the pattern should be clear, the level should be clear, the text should be clear and complete, not deformed, free of burrs, bubbles, uneven paint and other bad problems.

  The pattern and text content on the surface of the iron can should be consistent with the sample plate, and there should be no overprinting or missing printing. The pattern and text should be overprinted accurately, and the overprint accuracy should not exceed 0.5mm. The tin layer of the tank wall and the sealing edge should be complete, free of tin piles and rough tin roads, no obvious scratches and rust, and no leakage caused by blisters. The curling part of the round can shall not have quick mouths, false curls and large sags, and there shall be no incomplete curling, curling teeth, iron tongues, jumping seals, curling chipping, filling extrusion, sharp edges, vertical lips, Double lines and other defects caused by the failure of the indenter and curling roller. The cans are required to be evenly marked, and there is no phenomenon that the lid cannot be opened due to the bad marking or the easy-pull ring is welded. The easy-open ring of the can should be in the same horizontal plane as the lower edge line of the easy-open lid curling, and shall not exceed. The welding seam of the circular tank should be smooth and beautiful, the overlapping joints should be uniform, the welding points should be evenly connected, and there should be no poor welding or breakdown. The dislocation of the two sides of the welding seam should be less than 0.5mm, and the tailing of the welding seam should be less than 0.5mm. The repairing tape for circular tank joints should be smooth and uniform, completely cover the weld and the left part, solidify completely, without large bubbles and iron spots. The coating of the round tank should be free of shedding, internal flow of glue, iron sulfide, serious vulcanization spots, and oxidation circles. The shape of the round tank should be complete, and there should be no deformation such as flat tanks or sharp corners.

Conclusion: Tinplate products (tin cans) are widely present in our daily lives, and the various shapes and colors make us dazzled. Tinplate tin cans are used according to different performance parameters. Tinplate tin cans have many advantages in various industries due to their excellent printing performance and metal texture retention performance.the role of powdered milk cans, tea cans, candle aroma cans, toy tin cans, cosmetic boxes, etc.