Canning and Fish Packaging Technology

Unit 14 - Glass containers and Closures

14.1.11.Closures for Glass Containers
Bottle closure keeps the contents in and the contaminating substances out. At the same time it allows the used to have access to the contents at will. Closures are mainly metal or plastic, although other materials like paper, rubber glass aluminium and plastic in combination with these are used. The metals most commonly used are tinplate, aluminium or aluminium alloy. Among the plastics, thermosetting resins such as phenol formaldehyde or is used for making closures. In some cases, thermoplastics such as polyethylene, polyvinyl chloride or polystyrene also used. All these plastic and metals make rigid or semi rigid closures, compressing an interposing wad which acts as a cushion/seal against the sealing the sealing edge of the class bottle or jar. These wads are made from variety of materials such as pulp board cork, rubber and synthetic materials.