Crown Caps
Known for its appearance, the crown cap is used for sealing bottles of beer, carbonated beverages, sparkling mineral water, and fermenting wine. The dimensions adopted by large-sized punch presses are 907¡Á1018mm (width ¡Á length), with 702 closures produced from each sheet, while the dimensions adopted by small-sized punch presses are 508¡Á712mm (width ¡Á length), with 270 closures produced from each sheet. The common steel sheet thickness is 0.23mm.
At present, most crown caps are produced from TFS products. With transparent printing, the surface of the closure is light grey. A small minority of crown caps are produced from ETP products because of the aesthetic need for a beautiful appearance or upon special requirements. Normally, transparent printing is adopted to make the surface of the closure look light grey. As a bottle cap, the crown cap is normally to be printed on the outside with the inside surface sealed to be corrosion resistance. Therefore, the crown cap manufacturing process is composed of the following steps:
Tinplate (steel strip) ¡ú Rust resistance treatment on the back side (epoxy phenolic resin) ¡ú Application of adhesion agent on the back side (PVC organosol) ¡ú Priming on the front side (PET) ¡ú Printing on the front side (printing ink) ¡ú Varnishing on the front side (PET varnish) ¡ú Defect inspection ¡ú Punch forming ¡ú Molding (PVC/PE) ¡ú Quality inspection ¡ú Packaging/p>
Note: The back side refers to the inner surface of crown caps for injection molding while the front side refers to the outer surface for printing.
Purposes and Control Points of Major Processes
| No. | Major Process | Purpose | Control Points |
|---|---|---|---|
| 1 | Painting and coating |
To ensure good application
performance of closures and ends |
Uniform coating; specific coating weight;
baking temperature and time |
| 2 | Printing |
To indicate the trademark,
product features or advertising or promotion information |
Text and graphics are correctly printed;
the trademark is in conformity with applicable requirements; overprint is accurate and bright-colored |
| 3 | Punch forming |
To make the appearance look
beautiful and the bottom end unobstructed |
Consistent dimensions; no scratches,
cracks and wears; no burrs resulting from cutting of the shell; |
| 4 | Gasket forming |
To make the closure clean,
complete, and well-sealed |
Complete forming with no breach,
deformation, or eccentricity; clean, free of impurities and pollution; gaskets weight |
