Decoration (Printing, Coating)
Printing Technologies for Cans
Offset printing is a major method for printing on metal cans because of its hard and non-absorbent material. The printing methods are mainly classified into two types by their can structure. Sheet printing, using lithographic plates, for metal sheet is applicable to 3-piece and DRD cans. Alternatively, curved surface printing, using plastic letterpress plates (Ref. 2-piece Can Waterless Lithographic Printing) is applicable to 2-piece DWI cans and TULC.
|Can's classification||Decorative Type||Object to be printed||Types of Can||Printing Method|
|3 Piece Can||Sheeting Printing||Coated Metal Sheet||Welded Can||Lithography Offset Printing|
|2 Piece Can||DRD|
|Curved Surface Printing||Metal Can||DWI, TULC, aTULC||Letterpress Curved Offset Printing|
|Lithography Curved Offset Printing|
|Labeling||PET Film||TULC||Gravure Printing|
- (1) Sheet Printing
- Multiple same images are coated on a pre-processed metal sheet, and then the sheet is transferred to the sheet printing machine (the rotary offset printing machine) one by one for printing. A line set up independently from a can forming line.
- The production process consists of coating and printing. Interior and exterior surface of sheets, such as tin plate, with a thickness of about 0.2 mm and large TFS (tin free steel) plates with a length and width of 1 meter are coated, and then each color is overprinted on each sheet.
- Production process includes; interior coating -> exterior coating -> printing (multiple times) -> finishing varnishing -> baking and drying
- Sizing (transparent paint utilizing the metal base for creating a metallic look) and white coating to improve whiteness are used as substrates. After printing, varnish is applied by coating to protect the surfaces and to provide gloss and smoothness.
- (2) Curved Surface Printing
- After forming the can-body, printing on the exterior surface of the 2-piece cans (DWI and TULC cans) is conducted one by one using a curved surface printing machine. Each color of ink is placed on a different (plastic letterpress) plate, and then sequentially transferred to a single rubber blanket (a rubber surface to re-transfer an inked image to a can), allowing all colors to be printed at a time. After printing and just before the ink curing process, an over varnish is applied.
- The line control system manages automatically production consistency, from can forming to finishing, including printing and coating.
- (3) Gravure Printing Lamination
- A technology that laminates pre-printed PET film onto formed cans using a gravure roll. Gravure printing is a type of intaglio printing （transcript by pouring ink on the engraved sheet）, allowing drying and overprinting by color, offering advantages in the reproduction of a wide range of color gradation（smooth color shading）and density.
- A variety of reproduced effects can be achieved such as photograph quality resolution, metallic mirror-like and pearl-like appearances. This technology is also applied to laminated TULC.