Plastic Closures
Plastic closures are plugs, caps and grips that are protective devices for the ends of products and also keep containers closed and their contents inside. They enclose the ends of tubes, pipes, fittings, connectors, screws and bars, as well as provide a lid for containers like bottles and jars. The chemical, photography, agrochemical, printing, bottle production, cosmetic, food processing, pharmaceutical, automotive and packaging industries all use plastic closures for a number of applications. Products like bottle caps, camera lense caps, car plugs and pill bottle caps are considered plastic closures. They are manufactured a couple of different ways, including injection molding. However, the most common manufacturing process is dip molding, which uses a mandrel, or mold, which is dipped into molten plastic material.
During plastic closure manufacturing, a mandrel is produced with the exact same dimensions as the container, part or product that is being sealed, closed or plugged. The closures can be literally any shape, but are commonly round, square or rectangular. Many mandrels feature threading, which creates a twist-on and water tight seal between the cap and the container or part. Once the mandrel has been formed and cleaned, it is partially dipped into molten plastisol, polycarbonate, PVC or polyurethane and left in for a certain amount of time, called the dwell time. The longer the mold is left in, the thicker the closure's walls will be. When the dwell time has finished, the mold is slowly removed from the plastic at a constant speed. Virtually no secondary processing is needed, and the plastic closure is easily slipped off the mandrel because of plastic's elastic properties.