What is Tinplate?
Tinplate is a highly sustainable and environmentally conscious packaging material. tinplate is a thin steel sheet coated on both sides with a thin layer of tin for added corrosion resistance and easy soldering. Its primary use today is in the production of tin cans and tin boxes. It is a prime example of utilizing natural resources in an efficient and eco-friendly manner.
Tinplate is steel sheets made from a combination of steel and tin. The steel used is of the highest quality, with a low carbon content of well below 0.1 % to ensure a smooth finish. The tin coating is applied with precision, either through the hot dipping process or the electrolytic coating process, to create a shiny, smooth surface. The result is a material that is not only strong and durable but also has a sleek, polished appearance. It’s a pleasure to work with tinplate as it offers great metallurgical bonding to base steel and uniform controlled thickness.
Tinplate as a food packaging material since the early 19th century. Its popularity can be attributed to its outstanding properties, including its strength, flexibility, and durability. Being lightweight, airtight, and gas impermeable, it makes the perfect container for preserving food. Its opacity and thermal conductivity also make it ideal for packaging carbonated beverages and juices. The fact that it is relatively chemically inert, easy to print on, and recyclable makes it an even more attractive option. With constant advancements in technology, tinplate has become even more versatile and can now be used to package all types of food products. It’s truly a marvel of modern packaging.
Tin is a remarkable metal that is widely used as a coating on steel due to its exceptional properties. Its resistance to corrosion in a variety of environments, especially indoors, makes it an ideal choice for protecting steel. Tin is also easily soldered and maintains its solderability well, making it a great option for a wide range of applications. Its safety in contact with food is a major advantage as it poses no health risks and does not affect the taste of the food. The softness of tin is also a beneficial characteristic as it allows for easy cold working, creates smooth threads on fasteners, and helps to seal joints. Overall, tin is a reliable and versatile metal that is perfect for protecting steel and prolonging its lifespan.
The History Of Tinplate As a Food Packaging Material
Tinplate has stood the test of time as a reliable and durable food packaging medium for over 200 years. The idea of preserving food in tin cans was first patented by Peter Durand in 1810 and quickly gained acceptance and popularity. Tinplate cans were used to transport the food across continents, with countries such as Russia, Germany, and the United States being among the first to commercialize production and export food to places like South America and the Far East. Throughout the 19th century, advancements in technology improved production efficiency, can sealing, and the variety of can shapes available. By the time of the World Wars, tinplate cans had become an integral part of food packaging. The longevity of tinplate as a food packaging medium is a testament to its effectiveness and practicality in preserving and transporting food.
The preservation of food in tin cans has been a reliable and valuable method for over a century. The discovery of a 100-year-old canned product in perfect condition in 1938 solidified the effectiveness of this method. Over the years, advancements in packaging design and technology have made cans more user-friendly and durable. The use of high-quality steel and the integration of recycling infrastructure have contributed to the evolution of the tinplate can to meet the changing needs of consumers. While the tin can has proven to be an essential tool for preservation, there is still room for innovation with lighter designs. The current developments in food can making suggest that a further reduction in weight of up to 23% is possible.”
The electrolytic tinning process has played a significant role in reducing the amount of tin used in tinplate. This precise method allows for the precise and minimal application of tin onto steel sheets. The tinplate is then flash melted, which not only gives it a shiny appearance and reduced porosity but also forms an Inter-metallic alloy. As the amount of tin used has decreased, the proportion of tin in the alloy layer has also decreased, making the recycling process more challenging. However, this process has allowed for more efficient and sustainable use of resources.
Tinplate Production Process
1. Production of Steel Sheets
The steel employed in the production of tinplate is a high-quality, low-carbon material that is specially selected for its light gauge properties. The manufacturing process of tinplate is a delicate and intricate one, involving a series of crucial steps that play a significant role in determining the final properties of the tinplate produced. Each step is carefully monitored and adjusted to ensure that the highest standards are met and that the end product is of the utmost quality.
Hot Rolling: The hot rolling process employed in the production of tinplate is a precise and efficient method that utilizes continuously cast steel slabs. These slabs are carefully selected for their exceptional cleanliness and are scarfed or cleaned to eliminate any surface imperfections. The slabs are then heated to precise temperatures between 1200 to 1300°C and expertly rolled to produce the finest quality thin gauge sheets. This method of hot rolling ensures a consistent and high-quality product that meets the highest standards.
Pickling: The pickling process of tinplate production is a vital step that ensures the sheets are thoroughly cleaned of any oxide that may have formed during the production process. With the advancements in technology, new methods have been introduced that make this process more environmentally friendly. The sheets are cooled and cleaned using acid-free and oil-free solutions, resulting in a cleaner and more sustainable production process. This attention to detail and constant strive for improvement ensures that the final product is of the highest quality, meeting the rigorous standards of the industry.
Cold Reduction: The cold reduction process in the production of tinplate is an essential step that refines and improves the final product. The hot steel sheets are cooled with precision and care using a combination of water and lubricating oil, before undergoing further rolling. This method of cold reduction ensures that the steel sheets maintain their integrity and strength, while also achieving the desired thickness and smoothness. This meticulous approach guarantees that the final product meets the highest standards of quality, and is ready for use in a wide range of applications.
Cleaning: The cleaning process in the production of tinplate is an important step that ensures the final product is of the highest caliber. The cooling liquids are removed using a combination of alkaline phosphates, silicates, and sodium hydroxide, and finally with hot air. This method of cleaning is specifically chosen for its ability to effectively remove all impurities and debris while leaving the steel perfectly clean and ready for the next stage of production. This process ensures that the final product is of the highest quality, free of any contaminants, and ready to be utilized in various applications.
Annealing: The annealing process in the production of tinplate is a delicate and crucial step that ensures the final product is of the highest standard. This step makes the steel soft and achieves the desired grain structure, which is essential for the final product. Batch annealing produces a deep-draw, hard, and stiff steel that can withstand vacuum and pressures, making it perfect for the manufacture of cans and bottles. Continuous annealing, on the other hand, is a shorter process that results in smaller-grained steel. Both methods are carefully chosen to suit the intended application, guaranteeing that the final product is of the highest quality, with the perfect balance of strength and malleability.
Temper Rolling: The temper rolling process in the production of tinplate is a delicate and crucial step that ensures the final product is of the highest standard. The soft steel after annealing is expertly rolled to produce sheets of the final desired thickness. This process allows the steel to be shaped and formed to the desired dimensions while maintaining its structural integrity and ensuring that the final product is of the highest quality and consistency. The temper rolling process is a vital step that guarantees the final product meets and exceeds all industry standards and is ready for final use.
Double Reduction: The double reduction process in the production of tinplate is an advanced and innovative method that ensures the final product is of the highest standard. This method of reduction is used as an alternative to temper rolling, and it involves a second round of rolling the steel. This process produces sheets that are thinner, stronger, and more versatile, making them ideal for packing materials. The sheets produced can be as thin as 0.14 – 0.24 mm, which not only improves the strength-to-weight ratio but also makes them more attractive as packing material as it saves transport costs and reduces carbon emissions. This double-reduction process is a vital step that guarantees the final product meets and exceeds all industry standards, and is both strong and lightweight, making it ideal for packaging.
2. Electrolytic Tinning Process
The method of applying tin to steel sheets has evolved over time, with electrolysis becoming the standard method since the 1940s. This method has replaced the previous technique of hot dipping. Tinplate production is the primary use of tin and accounts for 30% of all tin produced. In recent years, there has been a growing emphasis on sustainability, and by 2018, 30% of all tin production was from recycled sources.
The electrolytic process offers several advantages, including the ability to achieve thin tin coatings and precise control over coating thickness. This is essential in producing a ‘differential coated tinplate’ which has different coating thicknesses on each side of the steel sheet. Modern tinplate has coatings that are only 0.1 to 1.5 microns thick, reflecting the ongoing efforts toward efficiency and sustainability in production.
Plating: The steel sheets are carefully passed through plating tanks filled with electrolytes, where 99.9% pure tin anodes are immersed, and the steel is coated with a layer of tin through electrolysis. This process ensures that the tinplate is of the highest quality, with a consistent and even coating of tin. At the end of the process, any excess tin on the sheet is removed and recycled, not only ensuring the highest quality of the final product but also promoting sustainability by minimizing waste. This plating process is a vital step that guarantees the final product meets and exceeds all industry standards, and is ready for use in various applications.
Flow-melting: In this process, the tin coating is heated to a high temperature so that it melts and forms an iron-tin alloy layer. This process enhances the anti-corrosive properties of tin and provides an additional layer of protection to the steel surface. This method not only improves the quality of the final product but also increases the durability of the tinplate making it more resistant to corrosion and wear, which is particularly important in the packaging industry. The flow-melting process is a vital step that guarantees the final product meets and exceeds all industry standards, and is ready for use in various applications where the steel is exposed to harsh conditions.
Passivation: The tin coating can become oxidized, forming a thin film that can compromise the quality of the final product. To prevent this layer from growing, a layer of chromium is expertly added, followed by a layer of food-grade oil during the passivation process. This method not only improves the quality of the final product but also stabilizes the coating and extends the life of the tinplate. This process ensures that the final product is of the highest quality, free of any contaminants, and ready to be utilized in various applications. The passivation process is a vital step that guarantees the final product meets and exceeds all industry standards and is ready for use in the food packaging industry.
Features Of Tinplate
The tinplate has several features which are described below:
- Appearance – Tinplate boasts a shiny, polished metallic finish that adds a touch of elegance and sophistication to any product. With a variety of surface finishes available, the possibilities are endless for creating unique and beautiful designs.
- Paintability and printability – Tinplates offer an exceptional canvas for creativity, with their smooth surface allowing for flawless application of paint and ink. The ability to skillfully print using a variety of lacquers and inks makes tinplate the perfect choice for creating visually striking designs.
- Formability and strength – Tinplates possess a remarkable combination of malleability and durability, making them the ideal choice for a wide range of applications. By carefully selecting the appropriate temper grade, tinplates can be expertly crafted to achieve both the desired level of formability and the necessary strength for any project.
- Corrosion resistance – Tinplate boasts exceptional corrosion resistance, making it an ideal choice for containers. By carefully selecting the coating weight, it can effectively resist the corrosive effects of its contents. Additionally, coated items made from tinplate can withstand 24-hour exposure to a 5% salt spray without showing signs of corrosion.
- Solderability and weldability – Tinplate is highly versatile in terms of its ability to be joined and connected. Both soldering and welding techniques can be used, making it a valuable material for creating a wide variety of cans.
- Hygienic – Tinplate is an excellent choice for food packaging due to its hygienic properties. The tin coating provides a safe and non-toxic barrier that effectively protects food products from impurities, bacteria, moisture, light, and odors, ensuring that the contents stay fresh and safe for consumption.
- Safety aspects – Tinplate is an ideal choice for food packaging due to its unique combination of lightweight and high strength. This makes it easy to ship and transport, ensuring that the contents arrive at their destination in the best possible condition, providing a high level of safety for consumers.
- Eco-friendly – Tinplate offers 100 % recyclability and is eco-friendly.
- Low-temperature application – Tin is not suitable for extremely low-temperature applications as it may undergo structural changes and lose its adhesive properties when exposed to temperatures below -40 degrees Celsius.
Specifications of Tinplate
Tinplates are typically characterized by a variety of factors such as the steel substrate used, the level of tempering applied, the coating weight, the annealing method, and the surface finish. For tin cans or tin boxes, the quality and suitability of tinplate is determined by certain properties, which are often outlined in technical specifications, such as the tin coating weight, steel substrate, temper, passivation, and surface finish. The tin coating weight is particularly significant. Currently, the tin coating weights of commercial tinplates are standardized. To differentiate between different tinplates, it is common to draw two parallel lines on the surface with a higher coating weight. The distance between these lines is determined by the coating and defined in industry standards. Recently, low tin coating tinplates (LTS) have been introduced for specific uses, as they offer a more cost-effective alternative to standard tinplates.
The base steel is of the following three types:
- Type MR – The steel used in this base type has low residual elements and offers good corrosion resistance properties. It is widely used in a variety of general applications.
- Type L – This type of steel has extremely low residual elements such as copper, nickel, cobalt, and molybdenum, and offers exceptional corrosion resistance to certain types of food products.
- Type D – This type utilizes aluminum-killed base steel, making it suitable for applications that involve deep drawing or other forms of severe forming which can cause Lueders lines to appear.
Single-reduced Tinplates
Single-reduced tinplates are produced with a variety of surface finishes. The industry recognizes five basic surface finishes. The surface finish is indicated by ‘Ra,’ which is the arithmetic average of the absolute values of the profile height deviations from the mean line, recorded within the evaluation length. Simply put, Ra is the average of a set of individual measurements of a surface’s peaks and valleys.
- Bright finish – This type of finish is characterized by a smooth surface provided by a flow-brightened tin coating on a smooth finish steel base (steel roughness is lower than 0.35 micrometers Ra). Bright finishes are typically used for general-purpose applications.
- Light stone finish – This type of finish is characterized by a surface provided by a flow-brightened tin coating on a steel base finish with a light directional pattern (steel roughness is between 0.25 micrometers Ra and 0.45 micrometers Ra).
- Stone finish – This type of finish is characterized by a surface provided by a flow-brightened tin coating on a steel base finish with a directional pattern (steel roughness is between 0.35 micrometers Ra and 0.60 micrometers Ra). This type of finish makes the scratches of printing and can-making less conspicuous.
- Matt finish – This type of finish is characterized by a surface provided by an un-melted coating, typically on a shot-blast finish steel base (steel roughness is over 0.90 micrometers Ra). This is a dull type of finish and is mainly used for making crowns.
- Silver finish – This type of finish is characterized by a matt finish product that has been flow-melted. This type of finish is also known as a satin finish. This is a rough dull finish mainly used for making artistic cans.
Two Grades of Tinplates
Tinplates are often classified into two grades, the standard grade, and the second grade.
The standard grade represents the typical production that goes through regular inspection and classification procedures, and it is suitable for lacquering and printing across the entire surface.
The second grade, which is available in some countries, is made up of the best sheets that were rejected from the standard grade, these sheets may have minor surface imperfections, tinning defects, shape, and other minor imperfections but do not contain off-gauge material or sheets with pinholes.
While there isn’t an official third grade, some off-gauge, and pin-holed materials may be suitable for certain non-critical purposes and may be referred to as the ‘waste category’. National and international specifications prescribe a sampling scheme for assessing tinplate grades.
Uses Of Tinplate
When utilizing tinplate, it is important to be mindful of the following considerations to ensure its proper handling and use:
- The tinplate is covered by a soft metallic coating, so it’s essential to handle it with care to avoid scratches during transportation and storage.
- Over time, the properties of tinplate such as paintability, printability, solderability, and mechanical properties may deteriorate, so it’s best to use it as soon as possible after receipt and not to store it for long periods.
- Even though tinplate has good corrosion resistance, it may rust in a humid atmosphere. Therefore, it’s important to use it immediately after unpacking.
- Tinplate is not suitable for use with strongly alkaline solutions as it can dissolve in them. When using tinplate for making cans for alkaline contents, it’s important to paint the internal surface.
- Contents that have sulfur content can cause discoloration of the tinplate. In such cases, painting of the internal surface is necessary to maintain its appearance.
Tinplate is widely used in the packaging industry due to its many benefits. Being non-toxic, lightweight, strong, and corrosion-resistant, it is well-suited for packaging. Additionally, it can be easily formed, soldered, and welded, and it provides an excellent surface for printing. The tin coating has a low melting point, which provides lubrication and imparts a pleasing appearance. Tin boxes made from tinplate are convenient to handle, store, and recycle.
Tinplate is a Versatile Material
Tinplate is a versatile and durable material that is widely used in the packaging industry for its ability to preserve and protect food and beverages. It is also used in the production of containers for a wide range of products, including confectionery tins, tea tins, candle tins, cosmetic packaging, wine packaging, promotional gift tins, oils, paints, powders, and chemicals. Its versatility extends to the manufacturing of aerosol containers and caps, making it an essential component in many industries.
Environmental Consideration
Tinplate is a highly sustainable and environmentally friendly material that is widely used in Europe, particularly in the packaging industry. The production process has undergone significant innovation in recent years to make it even more convenient and eco-friendly.
These include reducing the use of chemicals during processing, improving the preservation of canned food, using sustainable lacquers,
making tin cans or tin boxes lighter, and using recycled tinplate which requires 60% less energy and results in 30% less air pollution, as well as weight reduction of 46% in many cases over the last 30 years.
These efforts demonstrate the industry’s commitment to protecting the health of consumers and the environment.
