CLOSURES

The closure is the most critical component of the package, as far as stability of the product is concerned. An effective closure system must prevent the contents from escaping and should not allow any substance to enter the container.

Closures are available in five basic designs.
1. Screw-on type (threaded or lug, type),
2. Crimp-on type (crown),
3. Press-on type,
4. Roll-on type, and
5. Friction type closures.

Screw-on type:

(a) Threaded screw cap: When the screw cap is placed on the container, its threads match with the
corresponding threads on the neck of the bottle. There is usually a linear present in the cap, pressed against the opening of the container. This seals the product in the container by overcoming irregularities in the sealing surface. Screw caps are usually made of metal such as tin or aluminium, or of plastic. Metal caps are coated with lacquer, to prevent corrosion.
(b) Lug cap: The lug cap is similar to a threaded screw cap. It is simply an interrupted thread on the glass finish, instead of a continuous thread. It is used to engage a lug on the cap sidewall and draw the cap down to the sealing surface of the container. Unlike the threaded closure, it requires only a quarter turn. Lug caps can be used for normal atmospheric pressure and vacuum pressure closing. It offers a hermatic seal and can be used in sterile products. It is also suitable on production lines.

Crimp-on type closures or crowns:

This is very commonly used for beverage bottles. Crowns are made up of metals such as tin or tin coated metal.

Roll-on type closures:

It gives secured seals. It can be opened easily and then resealed effectively. Usually, they are made up of aluminium. These type of closures are used in foods, beverages, chemicals and
pharmaceuticals. The types available in the roll-on type of closures are resealable, non-resealable and pilfer proof (pp). Roll-on type of closures are extremely suitable for glass containers, since these closures allow for dimensional changes in the glass container. Each roll-on closure precisely fits a specific container.
(a) Pilfer proof closures: It is similar to a normal roll-on closure, but it has greater skirt length. This additional skirt length extends below the threaded portion, to form a bank. This bank or ring is attached to the basic cap by narrow metal “bridges”. When the container is opened by removing pilfer proof closure, these narrow bridges break and the ring remains in place over the neck of the container. The consumer can reseal the container, but the separated or detached ring indicates that the package has been opened. Therefore, it is called pilfer proof. Sometimes, in the industry the term “R.O.P.P” caps is used. This implies “Roll-On Pilfer proof” caps.
(b) Non-resealable or non-resealable Roll-On closures: Sometimes a reusable cap is not desirable. Nonresealable caps require unthreaded glass finishes. The skirts of these closures are rolled under retaining rings on the glass container. Closures of this kind are of tear-off type, and they are tamper-proof and pilfer proof.