Injection Moulding: Definition and Cosmetic Packaging Applications

What Is Injection Moulding?

Injection moulding is a manufacturing process used to produce highly accurate plastic components. In cosmetic packaging, it is commonly used for closures, overcaps and reducing plugs.

Plastic resin is fed into a heated barrel and screw, where it is melted and then injected at high pressure into a water-cooled mould. The mould may contain several moving parts and is held closed by a clamping unit to withstand the injection pressure.

Once the plastic has filled the mould cavity, it cools and solidifies into the required shape. After sufficient cooling, the mould opens and the finished component is ejected. The process can then be repeated.

Materials Used in Injection Moulding

Polypropylene (PP) is one of the most commonly used materials for injection moulding. It can be divided into several types with different properties.

PP Homopolymer

PP homopolymer is commonly used for general-purpose moulding of closures.

PP Random Copolymer

Random copolymer can provide excellent clarity and is suitable for applications such as overcaps and closures with active hinges, including flip-top closures.

PP Block Copolymer

Block copolymer generally provides lower clarity but offers greater impact resistance. It is therefore commonly used for coloured components where clarity is less important.

Injection Moulding in Cosmetic Packaging

Polypropylene can also be advantageous when used together with bottles made from different materials, such as HDPE, PVC or PETG, as it can help improve compatibility and reduce binding issues between the two components.