Neck Finish Specifications
The effectiveness of a plastic bottle as a container depends on the creation of a seal between the bottle and its closure to keep the contents from escaping, while permitting easy opening and resealing of the closure. To achieve a proper seal requires compatibility between the mating bottle and closure threads and other points of engagement; that is, compatibility requires standardization. When plastic blow molding began, standard neck finish specifications developed by the glass industry were used, but subsequently the plastics industry adopted specifications developed by The Plastic Bottle Institute, a division of The Society of the Plastics Industry, Inc. See Fig. 1. for bottle-finish terminology; the three most commonly used finish specifications: SP-400, SP-410, and SP-415. Other standard finish specifications are available from The Plastic Bottle Institute. Having a copy of their technical bulletin PB1-2 on hand will be very helpful.
Although standard specifications are widely used, container manufacturers produce many nonstandard neck finishes to mate with specialized closures and dispensing fitments. Such nonstandard finishes have proliferated during recent years to meet packaging requirements for
- cost reduction by using snap on and linerless closures;
- improved assembly of fitments which lock in place to dispense products by drop, stream, or spray;
- consumer convenience by dispensing through the closure; and
- child and pilfer resistance in accordance with government safety regulations.
Specifications for such nonstandard finishes tend to be proprietary to each container manufacturer and are not generally available for publication.
It should be noted that the ability of certain plastic blow molding processes (such as injection-blow) to mold neck-finish configurations and close tolerances (not possible in glass), and the unique properties of plastics used in containers and mating fitments, have provided package designers with great freedom and latitude to develop new package forms.
Many of the terms referring to various sections of blown plastic containers have been adopted from glass terminology. The following are definitions of the terminology used in Fig. 1
Neck: The section of the container above the shoulder, where the cross-sectional area is smaller than the body of the container.
Base of Neck: The point where the neck meets the shoulder of the container. The base of neck (B.O.N.) often is a reference point for measuring container fill level.
Finish: Shaping of the neck section with a thread form or other configuration suitable for attaching a closure.
Bead: An enlarged diameter of the neck finish used for various purposes: aesthetics；’ stabilization of the closure, and as a location point for secondary machining of the neck.
Shoulder: The section of the container where the body decreases in size to meet the neck. The shoulder surface generally is a radius shape.
Base: The bottom surface, on which the container stands upright.
Push-up: A section depressed upward within the base surface. The depression assures that the container will stand upright without rocking on projections caused by parison pinch lines, gate marks, engraving, coding, or other interruptions in the base surface.