Types of Coatings-Epoxy Ester Coatings

Currently, the main types of coatings used for canned goods include epoxy phenolic coatings, epoxy amine coatings, organic solvent coatings, ethylene-based coatings, polyester coatings, acrylic coatings, and epoxy ester coatings. Below is a brief introduction to the characteristics of various resins and the performance and applications of coatings made from them.

Epoxy Ester Coatings

Epoxy ester resin is a product obtained through the esterification process of plant oil reacting with epoxy resin. This resin imparts flexibility and color to coatings.

Epoxy ester coatings are primarily used for post-printing varnish, suitable for both mixed-can products and products resistant to boiling. Therefore, it is suitable for metal can bodies, deep-drawn cans, twist-off caps, crown caps, and all types of mixed-can products.

Most epoxy ester coatings are colorless, but the addition of dyes can produce golden epoxy ester coatings used for decorating the external surfaces of twist-off caps and crown caps. The key properties and advantages include:

(1) Excellent Gloss:

Exhibits a high level of gloss.
(2) Good Color Fastness:

Maintains good color stability, crucial for external designs.
(3) Combination of Flexibility and Hardness:

Combines flexibility with good hardness.
(4) Excellent Ink Compatibility:

Exceptionally compatible with inks, especially suitable for the “wet-on-wet” production process.
Compared to other synthetic coatings, epoxy ester coatings are one of the most versatile varieties. They can achieve the same level of gloss as oil resin varnish while overcoming the drawbacks of poor color fastness and susceptibility to yellowing.

Curing for epoxy ester coatings is achieved through oxidation and thermal polymerization. For mixed-can production, a peak temperature of 160-180°C is typically used, heated for up to 10 minutes when high ink color fastness is required. The difference in dry film color is minimal within this temperature range. When used for products resistant to boiling, heating with a peak temperature of up to 190°C for a maximum of 10 minutes is needed to maximize water and steam resistance performance.

Types of Coatings-Epoxy Amine Coatings

Currently, the main types of coatings used for canned goods include epoxy phenolic coatings, epoxy amine coatings, organic solvent coatings, ethylene-based coatings, polyester coatings, acrylic coatings, and epoxy ester coatings. The characteristics of various resins, as well as the performance and applications of coatings produced from them, are briefly outlined below.

Epoxy Amine Coatings:

Epoxy amine coatings are formulated with epoxy resin and amine resin as the primary components in specific proportions. Widely used as protective coatings for the external surfaces of can lids, can bodies, twist-off caps, and sealing caps, these coatings exhibit the following key properties and advantages:

(1) Colorless Coating:

The coating is transparent, providing a colorless appearance.

(2) Excellent Chemical Resistance and Processability:

Demonstrates good resistance to chemical agents and is easily processed.

(3) High Boil Resistance:

Exhibits strong resistance to boiling conditions.

(4) Good Color Fastness Upon Re-Baking:

Maintains good color stability when subjected to additional baking.

Types of Coatings-Epoxy Amine Coatings

Epoxy amine coatings are highly sterilization-resistant, particularly in strongly alkaline water with a pH range of 9 to 10, making them the preferred choice for protecting the external surfaces of can lids. This property is also utilized in packaging latex paint. The resistance to water absorption and resistance to whitening during the cooking process are significantly better than other modified epoxy products. Their excellent heat resistance prevents mechanical abrasions during heat treatment.

The color fastness and resistance to yellowing of epoxy amine coatings during re-baking are noteworthy, making them widely applied as protective coatings for the external surfaces of three-piece beverage and food cans, including can bodies, can lids, twist-off caps, and crown caps. They are especially useful when the final baking of internal coatings may affect the performance of external coatings.

Epoxy amine coatings maintain their performance well even when exposed to contents that may spill and corrode the external coating of the can. Due to their excellent adhesion, they are also used as base coatings for printing.

Curing for epoxy amine coatings is achieved through thermal polymerization. For mixed-can products, they are typically heated to a peak temperature of 170-180°C for up to 10 minutes. When higher boil resistance and chemical resistance are required, a peak temperature of 200°C is recommended.

Epoxy amine coatings are also frequently used as internal coatings, especially in beverage cans with low corrosive contents such as dairy products and fruit juice beverages.

Epoxy Phenolic Coatings Characteristics Performance and Applications in Canned Food Packaging

Currently, the main types of coatings used for canned goods include epoxy phenolic coatings, epoxy amine coatings, organic solvent coatings, ethylene-based coatings, polyester coatings, acrylic coatings, and epoxy ester coatings. The characteristics of various resins, as well as the performance and applications of coatings produced from them, are briefly outlined below.

Epoxy Phenolic Coatings:

Epoxy phenolic coatings are formulated using epoxy resin and phenolic resin in specific proportions. This coating system finds wide application in the field of metal packaging for cans, particularly as internal coatings for beverage and food cans.

Epoxy Resin:

Epoxy resin refers to a polymer with two or more epoxy groups, with a main chain composed of aliphatic, cycloaliphatic, or aromatic segments. The epoxy group content is a crucial indicator, and in beverage and food cans, high molecular weight epoxy resins, such as Type 7 and Type 9 epoxy resins, or even higher molecular weight variants, are often required. These resins exhibit excellent impact strength and toughness due to a high concentration of oxygen-containing groups in their molecular chains, providing strong bonding capabilities.

Epoxy Phenolic Coatings Characteristics Performance and Applications in Canned Food Packaging

Phenolic Resin:

Phenolic resin is obtained through condensation reactions of phenolic and aldehyde monomers. It consists of numerous methylene (—CH2—) and rigid phenol linkages, featuring a structure with abundant polar hydroxyl groups. The molecular structure is rigid, lacking flexibility, and further curing of hydroxyl groups forms a three-dimensional structure consisting of C-C bonds. This close-knit structure imparts stability against various chemical substances, particularly notable for its corrosion resistance, especially in acidic environments. Epoxy phenolic coatings combine the advantages of both resins:

(1) Excellent adhesion to metal substrates;

(2) Superior processability;

(3) Outstanding chemical resistance (especially against sulfur and acids in food packaging);

(4) Good heat resistance and wear resistance;

(5) Low shrinkage and low porosity.

Due to its excellent corrosion resistance, epoxy phenolic coatings play a crucial role in three-piece beverage and food cans, as well as in two-piece drawn food cans. They are extensively used as internal coatings for various fruit juices, herbal teas, and cans containing highly acidic or sulfur-rich foods. Typically, epoxy phenolic coatings exhibit a golden color with vibrant and full hue, while also demonstrating outstanding physical properties (wear resistance and flexibility) and resistance to boiling. Therefore, epoxy phenolic coatings are frequently employed for interior coatings in mixed cans and external coatings for the tops and bottoms of beverage and food cans.

Epoxy phenolic coatings require baking at 200–205°C for 10 minutes for complete curing in a single application. Many epoxy phenolic coatings can achieve full curing at lower temperatures through multiple baking cycles. However, repeated baking of epoxy phenolic coatings can lead to a significant decrease in adhesion, severely impacting the quality of the coating. Additionally, the color of the coating darkens with each baking cycle. Therefore, attention must be paid to curing temperature and coating processes to minimize the number of baking cycles while ensuring complete curing.

Epoxy phenolic coatings exhibit good wetting and leveling properties on substrates such as tinplate, chrome-plated iron, and aluminum sheets, minimizing common surface defects. The surface treatment of the substrate also plays a significant role in this performance. During application, attention should be given to the viscosity; excessively high viscosity can impact the flow leveling effect and lead to surface defects, while too low viscosity can result in sagging. Dilution with specialized solvents should be considered in practical operations. Moreover, thorough stirring before use is essential to ensure the uniformity of the coating due to the presence of additives in the coating system.

Aluminum paste or zinc oxide is often added to epoxy phenolic coatings for packaging certain sulfur-rich foods, such as meats, seafood, and asparagus. The addition of mold release wax in such systems can be used for packaging canned luncheon meats. Aluminum paste primarily serves to block hydrogen sulfide generated during food sterilization from penetrating through the coating and to cover potential sulfide spots. Zinc oxide’s main function is to absorb hydrogen sulfide produced during food sterilization, preventing sulfide corrosion. However, the inclusion of aluminum paste or zinc oxide in epoxy phenolic coatings results in softer coatings, leading to decreased processability.

Global Trends in Tinplate Development: From Production Strategies to Environmental Innovations

(1) In major tinplate-producing nations worldwide, there is a general trend of no longer establishing new tinplate production units, including those for Tin-Free Steel (TFS). However, developing countries, particularly China, are still in the process of constructing new production lines, experiencing rapid growth. TFS products offer lower production costs and contribute to the conservation of scarce tin resources. Over the past 40 years, significant progress has been made, and the industry has now stabilized, with ongoing development in China.

(2) In addition to promoting TFS for tin resource conservation, another trend is the thinning of tinplate thickness. Secondary cold-rolled tinplate, including TFS, is increasingly being applied. Three-piece can bodies widely adopt tinplate with a thickness of 0.14 to 0.17mm. Two-piece steel cans, particularly in Europe, commonly use DI material with a thickness of 0.235mm (for 330mL cans, equivalent to 0.245mm for 355mL cans). Some are already using 0.205mm DI material (330mL), and 0.19mm DI material (330mL) is in the experimental phase. In Japan, TULC material has been reduced to a thickness of 0.18mm (though the can body’s thin wall thickness is 0.08mm, thicker than traditional DI cans).

Global Trends in Tinplate Development

(3) Clean Production, Reducing Environmental Pollution.

In North America and Europe, research on hexavalent chromium-free passivation is currently underway. Traditional PSA plating solutions, due to their high toxicity and substantial pollution, are gradually being replaced by MSA plating solutions. The passivation film on tinplate is composed of metal chromium, hydrated chromium oxide, tin oxide, and other components. The most commonly used passivation treatment for food and beverage cans is cathodic heavy sodium dichromate passivation. However, chromium salts cause severe environmental pollution, prompting countries to develop passivation techniques with minimal environmental impact.

In the UK, a working group consisting of tinplate producers, coating manufacturers, can makers, and chemical companies has been established to assess passivation techniques involving zirconium, titanium, cerium phosphates, silicates, and some organic coatings. Clariant, a leading electrochemical company in the UK, has developed a basic chemical substance, phenol sulfonic acid (PSA), adopted by American tinplate manufacturers. Its fundamental formula contains 2% free phenol, considered to be the most environmentally friendly. The improved Clariant formula (LPSR) reduces free phenol to 1% and diphenyl sulfone (DDS) from 1% to 0.7%. This formula is not only environmentally friendly but also has the lowest cost.

In other European countries, the focus is on evaluating chemicals such as polyacrylic salts and rosin acid siloxanes. In the United States, it is proposed that zirconium sulfate (ZOS) and fluorinated zirconium acid (F-Zr) could substitute for chromic acid.

In the Asia-Pacific region, experiments involving mixed metals such as cerium oxide, silicon oxide, and titanium salts are ongoing, with fluorinated zirconium acid proving to be the most successful.

In the field of tinplate printing, traditional solvent-based inks are being replaced by eco-friendly inks. In the iron printing sector, 70% of tinplate lines are using environmentally friendly inks, with the UK already reaching 90%. Coating applications are also actively promoting the use of healthy and safe coatings.

(4) Recycling of Metal Cans

Developed countries place significant emphasis on the recycling and reuse of post-consumer metal cans. The European Union and others have enacted legislation specifying clear targets for recycling and recycling rates. Germany, for instance, mandates recycling rates of 70% for tinplate cans and 50% for aluminum cans. In the United Kingdom, the 2008 recycling targets were set at 61.5% for steel cans and 35.5% for aluminum cans. In the United States, the recycling rates in 1998 had already reached 56% for both steel and aluminum cans. Japan achieved recycling rates of over 80% for both steel and aluminum cans in the year 2000.

(5) Co-Extruded Composite Coating

ToyoKohan, a Japanese company, has pioneered the development of co-extruded composite coating for tinplate. ToyoKohan’s strategic approach involves collaborative research with their partners in can manufacturing, leveraging their expertise in thin iron production. In 1997, ToyoKohan successfully produced the first TULC can (Toyo Ultimate Can). Between 1998 and 2001, the company achieved successful development of non-oriented pressure-sensitive film and double-sided co-extruded composite coating for tinplate. The introduction of the dry forming process in 2006 reduced the cost of TULC cans, improved production efficiency, and further minimized environmental impact.

The internal non-oriented pressure-sensitive film enhanced the tensile properties of the iron, achieving optimal can forming effects. This thin film requires lower preheating temperatures during the production process, proving effective in coating adhesion and reducing production costs.

Double-ended co-extrusion stretching (DEC) represents an advanced forming process, allowing the creation of stable films as thin as 10 micrometers or even thinner on the can wall. However, the production cycle for cans has been shortened, and the speed of production lines is limited. It is anticipated that by 2008, DEC will reach a certain speed threshold.

Cans made from polymeric-coated iron, such as those utilizing Protact technology from Corus Packaging Plus, demonstrate resilience against impacts and friction encountered throughout the entire transportation chain. The continuous growth of the recycling rate for lightweight and sturdy canned packaging is evident, with the recycling rate in the EU-15 countries reaching 63%. Iron packaging, through Protact’s polymeric-coated technology, aligns with EU regulations, contributing to reduced raw material consumption, energy usage, and environmental impact.

Protact, utilizing Corus Packaging Plus’ multi-polymer coated iron (Protact) rolling technology and its advancements, combines the characteristics of polymers and iron, offering a secure, versatile, and high-performance packaging material. Two processes are employed in Protact iron production: the film-coating process has limited production speeds, approximately 50–80m/min, while the extrusion process operates at speeds of 100m/min, reaching up to 300m/min. Protact iron can feature various interchangeable composite layers, with options for single or double-sided coating, different thicknesses of polymers (transparent or colored), and customization based on specific requirements, such as tension during production, polymer adhesion, printability, and lubrication.

According to ICI Coatings’ Global Research and Investigation Division, achieving optimal corrosion resistance and food safety for iron cans depends on an ideal coating system formulation. The coating should adapt to the entire can production chain, ensuring the quality of the empty cans. In comparison to traditional three-piece cans and draw-redraw cans (DWI), the development of draw-and-iron cans requires specialized polymer coatings to withstand strong stretching forces. As forming capabilities increase, it becomes crucial to enhance the density of polymer cross-links to improve the corrosion resistance of the can’s interior.

Different steel bases will impact the surface tension of the coating, the interaction between the coating and the steel base, and the adhesion and corrosion resistance of the coating. Temperature is a significant factor during bending, as higher temperatures may lead to coating shrinkage and loss of adhesion. The more uniform the coating surface humidity, the fewer humidifying additives are needed, reducing the solvent requirements for water-based coatings.

(6) Technistan

Technistan is a novel electrolytic process for the production of tinplate, developed by the American company Tehic. This work is currently underway in the United States. The formulation of this process consists of four components: a tin sulfate solution containing approximately 20g of tin metal per liter; 5% concentrated sulfuric acid; 5% additive Techristan TP; and an antioxidant (to prevent excessive deposits on the surface of iron due to the use of sulfuric acid). Tehic is pursuing this new process in response to the rising prices of cold-rolled coils, seeking lower production costs. However, for this process to be widely accepted in the market, an extended period of time is required, along with the validation of its environmental impact.

Epoxy Ester Coatings: Versatile and Durable Solutions for Can Protection

Epoxy Esters Coatings

Epoxy ester resin is a product obtained through the esterification process of vegetable oil and epoxy resin. This resin imparts good flexibility and color to coatings.

Epoxy ester coatings are primarily used for post-printing varnishing. They are suitable for a wide range of products, including tinplate cans, deep-drawn tins, twist-off caps, crown caps, and various other cans.

Most epoxy ester coatings are colorless, but by adding dyes, golden epoxy ester coatings can be obtained for decorative applications on the external surfaces of twist-off caps and crown caps. The main properties and advantages of these coatings are as follows:

  • Excellent gloss
  • Good color fastness, which is crucial for external designs
  • Combination of flexibility and good hardness
  • Excellent ink compatibility, especially applicable in the “wet-on-wet” production process

Compared to other synthetic coatings, epoxy ester coatings are one of the most versatile varieties. They can achieve the same level of gloss as oil-based varnishes while overcoming the drawbacks of poor color fastness and susceptibility to yellowing.

Curing of epoxy ester coatings is achieved through oxidation and thermal polymerization. For can production, when high color fastness of the ink is required, a peak temperature of 160-180°C is generally used, with a heating time of up to 10 minutes. Within this temperature range, the color difference in the dry film is minimal. When used for products resistant to boiling, a peak temperature of 190°C and a heating time of up to 10 minutes are required to maximize water and steam resistance.

Enhancing Can Protection with Epoxy Amine Coatings: A Versatile Solution

  • Epoxy Amine Coatings

Epoxy amine coatings are formulated with epoxy resin and amine resin in a certain ratio. They are widely used as protective coatings for the exterior walls of can lids, can bodies, twist-off caps, and sealing caps. The main properties and advantages of epoxy amine coatings are as follows:

 

  • Clear film appearance
  • Good chemical resistance and processability
  • Excellent boiling resistance
  • Good color fastness upon re-baking

Epoxy amine coatings exhibit high resistance to sterilization, especially in strongly alkaline water with a pH of around 9-10, making them the preferred choice for protecting the exterior walls of can lids. This property is also utilized in packaging latex paints. Epoxy amine films have significantly better water resistance and resistance to blushing during cooking compared to other modified epoxy products. They have excellent heat resistance and are less prone to mechanical abrasion during heat treatment.

Epoxy amine films maintain good color fastness and resist yellowing upon re-baking, making them widely used as protective coatings for the exterior walls of three-piece beverage cans, food cans, twist-off caps, and crown caps. They are particularly useful when the inner wall coating, applied in the last step, could potentially affect the performance of the exterior wall coating.

Epoxy amine coatings also maintain good performance when exposed to corrosive contents that may overflow and potentially attack the exterior wall coating. Due to their excellent adhesion, they can also be used as primer coatings for printing.

Curing of epoxy amine coatings is achieved through thermal polymerization. For mixed products, the recommended peak temperature is 170-180 degrees Celsius, with a maximum heating time of 10 minutes. When higher boiling resistance and chemical resistance are required, a peak temperature of 200 degrees Celsius is recommended.

Epoxy amine coatings are also commonly used as inner wall coatings, especially in beverage cans with mild corrosive contents, such as dairy products and fruit juices.

Revolutionizing Beverage Can Manufacturing: Thin Materials, Unified Alloys, and Sustainability

With the intensifying competition in the beverage packaging market, reducing the thickness of materials, minimizing wall thickness, reducing costs, improving material utilization, facilitating recycling and convenience of use have become important goals for many can manufacturing companies.

One of the key aspects of cost reduction in the production of aluminum cans is reducing the thickness of the aluminum strip used for making the cans. The thickness of can body materials has decreased from 0.42mm in the 1970s to the current 0.254mm (most are still around 0.28mm), resulting in a 39.5% reduction over the past 30 years. For every 0.01mm reduction in can body thickness, the material cost can be saved by $0.22 per thousand cans. Over the decades, the manufacturing technology of aluminum cans has been continuously improved, leading to a significant reduction in the weight of aluminum cans. In the early 1960s, the weight of a thousand aluminum cans (including can bodies and lids) was 55 pounds (approximately 25 kilograms). By the mid-1970s, it had dropped to 44.81 pounds, further reduced to 33 pounds in the late 1990s, and now it is below 30 pounds, nearly halving the weight compared to 40 years ago. Since the 1980s, canning companies in the United States have made breakthroughs in sealing machinery and other technologies, resulting in a noticeable decrease in the thickness of aluminum used in aluminum cans, from 0.343mm to around 0.259mm.

There has also been significant progress in lightweighting can lids. The thickness of the aluminum used for can lids has decreased from 0.39mm to 0.24mm. The diameter of the lids has also been reduced, leading to a continuous reduction in lid weight. At the same time, the canning speed has increased significantly. In the 1970s, the production rate was only 650-1000 cans per minute, but now it has reached over 2000 cans per minute.

Leading aluminum companies in the production of aluminum strips for beverage cans, such as Alcoa in the United States, are aiming for thin walls of around 0.18mm. This development trend is also crucial for domestic aluminum strip manufacturers for beverage cans. They must increase their research and development efforts, adjust their technological research directions, and keep up with the global industry’s development to enhance competitiveness.

Research is underway to develop a single alloy to replace the original alloys such as 3104, 5182, and 5052, making it easier for management, production, and recycling.

Beverage cans are made from three different alloys (3004 for can bodies, 5182 for can lids, and 5042 for pull tabs). This presents challenges for recycling and remelting. Therefore, with the increasing environmental awareness, a unified alloy that integrates the can body, lid, and pull tab is a new direction for the development of aluminum used in beverage cans. Some known unified canning alloys include 5017 and 5349 from Golden Aluminum in the United States. Additionally, a Japanese patent, Tokkōshō 61-9180, describes a unified canning aluminum alloy containing 0.5%-2.0% Mn, 0.4%-2.0% Mg, 0.5% Si, 1.0% Fe, 0.5% Cu, 0.5% Zn, 0.2% Cr, 0.01% Be, 0.2% Ti, with the remainder being aluminum.

The United States is currently developing a 0.3mm thick can material and changing the shape of the cup bottom from circular to polygonal. It is said that this can significantly reduce the earing rate, resulting in more material savings than just thinning the material. This new invention is worth noting.

Due to the inability to reseal the lid once opened, traditional can lids have gradually been neglected. As a result, several Japanese companies have started using twist-off caps on beverage cans. This new type of beverage can provides better sealing, effectively preventing contact between the beverage and sunlight or oxygen. Additionally, it is lighter in weight and facilitates recycling and reuse. Currently, as this new type of beverage can is gradually gaining popularity in Japan, consumers are showing an increasing preference for twist-off caps. Can manufacturers in Japan hope to regain the market share that has been occupied by plastic bottles by using this product.

In addition to developing new alloys and varieties, can material processing technologies, such as hot and cold rolling and heat treatment, are also evolving towards wider and thinner dimensions. One of the characteristics required for aluminum alloy strips used for can lids is low anisotropy. To minimize fluctuations in the mechanical properties or formability of the strips, strict control of the alloy composition, as well as precise control of hot and cold rolling conditions and plate thickness deviations, is necessary.

In terms of processing methods, it has been reported that developed countries have started using continuous casting and rolling technologies to produce aluminum alloy materials for cans, further reducing processing costs. However, further verification is needed in this regard.

Southwest Aluminum (Group) Co., Ltd., the only domestic producer of aluminum materials for beverage cans, has achieved mass production of “ultra-thin aluminum sheets.” The historical monopoly of aluminum can materials by foreign countries in China no longer exists. Since 1986, Southwest Aluminum has organized a group of experts and engineering technicians to collaborate with relevant research institutes to develop technologies for producing aluminum materials for beverage cans. Over the past ten years, two generations of technical personnel have participated in the development of this product. With the strong support and impetus from national “Ninth Five-Year Plan” scientific and technological research projects, “863” research projects, and the technology development funds of China Aluminum Corporation, Southwest Aluminum has invested a significant amount of money to address the necessary equipment for can material production. They have also devoted substantial human and material resources to the development of can material production technology. Leveraging the advantages of advanced “1+1” hot rolling production line equipment and Southwest Aluminum’s technical expertise, they have optimized and innovated the can material production process and technology based on the characteristics of “1+4” hot continuous rolling. They have developed a complete set of new technologies suitable for advanced “1+4” equipment for can material production. Southwest Aluminum was the first to develop this product domestically and has gradually reduced the product thickness from the initial 0.42mm to 0.285mm and currently to 0.275mm, which is only one step away from the international advanced level of 0.265mm. The produced can materials meet high quality standards. According to industry experts, by the latest estimate of 2008, the competitive landscape of the global aluminum can material market is expected to change, and China has the potential to become one of the world’s six major producers of can materials.

Currently, there are eight countries in the world that can produce aluminum alloy can materials, including the United States, Brazil, Australia, Japan, South Korea, Germany, France, and Russia. Additionally, some countries and regions such as Taiwan Province of China, Canada, Bahrain, and Italy can produce can lid and pull-tab materials.

However, with the development of China Southwest Aluminum Co., Ltd. in can material production and the commissioning of the hot rolling production line by Nanshan Group Aluminum Processing Co., Ltd. earlier this year, as well as the hot rolling production line of Asia Aluminum Industrial Park that started operation by the end of 2007, and the joint trial run of China’s Bohai Aluminum Industry Co., Ltd. in 2008, the can materials produced in China will participate in the global can material market competition, and China has the possibility to become one of the world’s six major can material producers.

In 2008, the can material production of China Southwest Aluminum Co., Ltd. could reach 70,000 tons, while Nanshan Group and Asia Aluminum Group may produce around 30,000 tons. The total national production could reach about 100,000 tons, accounting for approximately 55% of the domestic demand. Due to the strong technical support from Alcoa, it is estimated that after the normal operation of equipment, China’s Bohai Aluminum Industry Co., Ltd. can produce competitive can materials in China and Southeast Asia within approximately 8 months. Its trial production time will be the shortest among the four major enterprises in China.

A key constraint factor that has hindered the localization of aluminum ingots for pressure purposes in the past is the neglect of effectively improving the metallurgical quality of aluminum materials. While strengthening purification and other molten metal treatments, it is also crucial to conduct in-depth and systematic research on the mechanisms of molten metal treatment and the plastic deformation behavior of aluminum materials. This provides a reliable theoretical basis and practical guidance for the rational development of cold and hot processing technology and effective control of product structure and performance.

Since aluminum ingots for pressure purposes must have excellent plastic deformation capability and a certain strength, it is important to study the influence of factors such as material chemical composition, rolling process, and annealing process on their mechanical properties and plastic deformation behavior. However, the current research in these areas is insufficient to further explore the performance potential of materials, especially in the research of low-grade materials and thin-walled cans. The influence of intrinsic metallurgical defects in materials becomes more prominent. Therefore, it is necessary to strengthen the comprehensive treatment of aluminum melt to fundamentally eliminate the main factors affecting the plastic deformation capability of aluminum materials.

Currently, researchers at Fuzhou University have conducted in-depth and systematic research and practical work on improving the metallurgical quality and plastic deformation performance of aluminum ingots. Particularly, they have proposed the purification principle of “priority to impurity removal and gas removal as a supplement” and the melt treatment principle of “purification as the basis for transformation and refinement.” Based on this, they have obtained efficient process technology for comprehensive treatment of aluminum melt and achieved significant progress in the research of low-grade materials and thin-walled cans, turning research results into productivity.

Aluminum Packaging Industry: Global Growth and China’s Rapid Development

China’s metal container manufacturing industry has strong equipment capabilities. Since the large-scale expansion of production lines in 1995, the production of metal container products has generally exceeded demand.

Aluminum Packaging Industry

The origin of the beverage can is the United States, which is also the largest producer and consumer of beverage cans globally. In 2005, the aluminum beverage can production in the United States was around 130 billion cans (with a consumption of over 100 billion cans and exports accounting for approximately 23%). This consumed more than 2 million tons of aluminum, accounting for about 41% of its total aluminum sheet production (4.65 million tons), indicating stable development with an annual growth rate of 1% to 2%. In Japan, the aluminum can material production and sales in 2005 were approximately 440,000 tons, including 140,000 tons for can ends and pull-rings, and 300,000 tons for can bodies, also in a stable development stage with an annual growth rate of around 2%. In 2005, Europe had an aluminum can material production and sales of approximately 1.2 million tons, South Korea had 115,000 tons, Brazil had 115,000 tons, and other countries and regions had around 100,000 tons. These countries experienced annual growth rates of 5% to 10%.

Currently, the global production of aluminum can materials has reached approximately 4.3 million tons per year, including 2.89 million tons per year for can bodies and 140,000 tons per year for can ends and pull-rings. Apart from countries and regions such as the United States, Japan, and Europe that have reached a relatively stable development stage, countries like China, Brazil, and India are still in a high-growth period. Therefore, the global annual growth rate will remain above 8%.

Currently, aluminum accounts for about 25% of the total aluminum consumption in the United States in the container packaging industry, representing around 40% of rolled products. Full-aluminum two-piece beverage cans account for over three-quarters of the total beverage can market, 80% of the beer market, and 60% of the soft drink can market. In Australia, aluminum accounts for over 28% of the total consumption of aluminum semi-finished products, with aluminum cans comprising 75% to 80% of the beer market and over 72% of the beverage can market. Western Europe and Japan have relatively smaller proportions of aluminum cans, but they have been growing rapidly in recent years, especially in the production and consumption of aluminum can materials in Japan.

The consumption of full-aluminum beverage cans has stagnated in the United States and has even slightly declined. In Japan, it is in a stable period with minimal fluctuations, showing a slight overall upward trend. Europe is in a period of steady growth with an average annual growth rate of 5.5%. Developing countries like China and Brazil are in a high-growth period, with China’s average annual growth rate reaching 17.5%. By 2010, the annual average growth rate could reach 12%, and the production of beverage cans could reach 18 billion cans. Afterward, the growth rate may decrease slightly but will not exceed 10%.

China’s application history of aluminum cans is relatively short, and the foundation is relatively weak, but it has been developing rapidly in recent years. The production and sales volume was 7.5 billion cans in 2003, 8.2 billion cans in 2004, and reached 10.3 billion cans in 2005, with an average annual growth rate of 17.5%. It is estimated that it could reach 18 billion cans by 2010 and continue to grow at a rate of 10% for several years. As of the end of 2005, there were 16 aluminum can manufacturing companies in China with a total of 22 production lines and a total production capacity of 11.5 billion cans per year. In 2005, China net imported approximately 300,000 tons of aluminum sheet, of which around 65% were for can materials.

China’s per capita consumption of beverage cans (3.8 cans per person per year) is still low, only about 1/100 of the United States (380 cans per person per year). However, the development speed is fast. Based on the consumption of 70,000 cans (including 1.92% process scrap) from aluminum sheet (0.28 mm thick), China consumed a total of 10.3 billion cans in 2005, equivalent to 150,000 tons of aluminum body material and 70,000 tons of can ends and pull-rings (body to end ratio: 68:32). It is estimated that by 2010, China’s consumption of aluminum sheet for beverage cans will reach 390,000 tons per year, and by 2015 it could reach 625,000 tons per year, indicating a broad development space in China’s beverage can market. It is expected that in the near future, China will not only be a major producer of aluminum can materials but also a major consumer of aluminum cans.

In addition, the use of aluminum cans in China’s canned food industry is currently relatively small, with only a few products such as eight-treasure porridge, walnuts, and peanut milk. It is estimated that in the future, the number of aluminum cans used for canned food in China will increase at a rate of 5% annually.

Diversified Development and Market Trends of Packaging Materials

The main packaging materials include glass, paper, aluminum, steel, plastic, and paper-plastic composite containers. Due to their own characteristics and advantages, they have all undergone significant development in recent years, showing a trend of diversified development.

Beverages: In the beverage market, plastic containers are used the most in most countries. From a global perspective, PET bottles account for more than 70% of the beverage market, and the proportion of PET bottles in carbonated beverage packaging in China is about 60%. Plastic containers have begun to enter the beer industry worldwide and are competing with glass bottles for market share.

Food cans: The food can, beverage, oil and chemical industries, and other related industries continue to develop. Some varieties can be replaced by other packaging materials, but some products can only be packaged in non-metallic materials. China’s deep processing of agricultural products and the export of canned foods have continued to increase, making tinplate an important market. The total output and export volume of the can industry have maintained a double-digit growth trend for many years. Canned mushrooms, asparagus, oranges, bamboo shoots, and other products are the most exported products in the world.

Beer: China is the world’s largest beer producer and mainly uses glass bottles. Metal cans (including aluminum and steel) account for only about 3%. From a global perspective, glass bottles account for 72%, metal cans account for 28%, and PET bottles account for 0.4%. Therefore, there is great potential for the development of metal canned beer. China’s two-piece aluminum cans began the development of metal cans, and the localization of aluminum alloy thin plates is also developing. In recent years, steel cans have developed rapidly.

Foreign insiders in the metal packaging industry have felt that tinplate packaging is facing increasingly severe competition and challenges from other packaging materials such as plastic and paper, and they need to make efforts to enhance shelf visual impact and convenience functions and improve product grades.

The Manufacturing Process and Material Requirements for High-Quality Aluminum Cans

Can manufacturers have strict requirements for the quality of aluminum material. Not only must the internal quality be good with optimized chemical composition, low gas and slag content, but also the material must have good deep drawing performance, low ear-making rate (material anisotropy), and small thickness tolerances, good plate shape, and excellent surface quality.

The Manufacturing Process and Material Requirements for High-Quality Aluminum Cans

The production of aluminum cans involves over 40 processes, with the primary processes related to the performance of the aluminum strip being blanking, cup drawing, thinning and deep drawing, edge trimming, washing, external printing, internal coating, drying, necking, and flanging. The aluminum strip must have appropriate strength and good deep drawing formability to ensure smooth continuous punching, thinning and deep drawing, and to have the appropriate yield strength after baking. During the production process of the can body, the first step is to punch the 0.25-0.30mm thick strip into round blanks with a diameter of approximately 138mm, then draw two cups by deep drawing with a diameter reduction rate of more than 50%, followed by three rounds of thinning and deep drawing, reducing the wall thickness to 0.08-0.10mm with a stretching thinning rate exceeding 65%. Since the thinning and deep drawing process puts the material in an extremely low ductility state, even tiny inclusions can cause cracking or folding. Afterwards, it is required to ensure no fractures occur during edge trimming, necking, and flanging, and the material must have good plasticity. After several rounds of baking, the axial pressure resistance and bottom pressure resistance of the can body must be ensured, with the axial pressure resistance required to be 1.35kN and the bottom pressure resistance strength of 630kPa, to ensure smooth canning and storage. Therefore, the comprehensive performance of the aluminum strip used for the can body has strict requirements, including a tensile strength of 270-310MPa, a yield strength of 250-300MPa, an elongation rate greater than 3%, and an ear-making rate less than 2%. The surface of the strip must be smooth and uniform, without obvious corrugations, oxidation, or visible defects such as inclusions, pressure marks, or spots. The thickness of the strip must be uniform, with a thickness difference within 0.005mm.

Modern cover production lines use coils, with cup punching machines having 20-24 stations and material widths of 1500-1550mm. Block sheet production lines use sheet material with widths of 850-970mm. The thickness of the cover material is 0.27mm. Currently, all the pre-coated cover material used in China is imported. Cover production first involves separately producing the base and pull-tab on two production lines, then combining them to form a composite cover. The cover material has various width specifications and even more thickness specifications, including 0.22-0.315mm, such as 0.23mm, 0.25mm, 0.27mm, 0.28mm, and 0.30mm. There are many cover manufacturing companies in China, estimated to be around 50, with production capacity exceeding 40 billion per year.