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.