What is Laminated Steel?

Laminated Steel is a composite material where printed plastic film is laminated onto cold-rolled thin steel sheets through melting or adhesive methods. This process replaces the traditional printing on tinplate (tin-coated steel) or chromium-coated steel.

High-Temperature Melt Laminated Steel and Low-temperature Adhesive Laminated Steel

High-Temperature Melt Laminated Steel:

Process: The steel is preheated to high temperatures, directly bonding with the film through heat. The film partially melts and adheres to the metal substrate's surface.

Applications: Primarily used in food and beverage packaging, such as food cans, two-piece cans (DRD), aerosol cans, and the tops and bottoms of chemical cans. The high-temperature melt laminated steel does not contain any glue and does not require the use of coatings on the inner walls of traditional tin cans, thus providing better food safety.

Low-Temperature Adhesive Laminated Steel:

Process: Uses glue to adhere the film to the metal substrate at low temperatures.

Performance: The adhesion is relatively poor, and corrosion resistance is weak. Products made from this type of laminated steel are only suitable for chemical cans and low-end miscellaneous cans and cannot be used for food cans, aerosol cans, or two-piece cans.

Raw Materials and Structure

Film Material: Laminated steel typically uses multi-layer polyester composite films (thickness about 20-25 microns). These films have a near-total barrier effect against corrosive media. Theoretically, the substrate for laminated steel can directly use cold-rolled thin steel, known as bare laminated steel. However, bare laminated steel tends to rust at the weld seams of cans, and the adhesion is not strong. Therefore, in practice, chromium-coated steel (TFS) is used as the substrate. TFS products have a layer of hydrated oxide film on the surface, which can form hydrogen bonds with the organic film, providing strong adhesion of the organic film.

Core Technology: The development of the film is the core technology for laminated steel. The polymer film used for laminated steel must have thermoplastic adhesion capability and be compatible with the physical and chemical properties of various canned contents to ensure good barriers to the chromium-coated substrate and the contents. Additionally, it must maintain the flavor of the packaged food during the shelf life, remain colorfast and adherent during high-temperature sterilization, and withstand high temperatures, friction, and bending during can forming.

Common Films: Potential films for TFS composite include PP, PET, PC, and PE, with PET film being the most common and having the best overall performance. PET film has excellent formability, sterilizability, hardness, abrasion resistance, and can be specially treated for printing.

Film Types: PET polyester film for laminated steel can be white, transparent, gold, or laser film. Application-wise, it can be classified into films for deep drawing, general chemical cans, and food cans.

Structure: Laminated steel for can making has distinct inner and outer walls, each with two layers of film. The outer layer of the inner wall provides a barrier effect, while the inner layer bonds with the chromium-coated steel and provides corrosion resistance. The outer layer of the outer wall protects against scratches and facilitates printing, while the inner layer bonds with the chromium-coated steel.