Molding Methods for Plastic Closures
Plastic closures are either thermoplastic - produced via injection molding, or thermoset - produced via compression molding.
- Injection Molded Closures
Injection molded, thermoplastic closures are produced primarily from polypropylene, polyethylene or styrene. These closures offer flexibility of design and are economical in cost. Injection molded closures can be divided into two groups: unscrewing and strip molded caps.
- Compression Molded Closures
Compression molded thermoset closures are produced from phenolic (for dark colors) or urea (for light colors). These closures are extremely hard and offer excellent dimensional stability and chemical resistance.
Compression molded closures are stable at elevated temperatures and are used for autoclaving when combined with a suitable lining material. They can also be vacuum metallized in silver or gold with superior adhesion qualities.
Compression molded closures are in general heavier and significantly more expensive than injection molded closures.