Bottle Opener Bar Tools | Screw Down Cap

Screw Down Cap 2 Screw Down Cap

cap mould for containers

As mentioned earlier it is most appropriate to injection- mould the cap mould in polyethylene material, which material unfortunately has, relatively speaking, poor gas barrier properties, and an injection- moulded polyethylene cap of the type shown in FIG. 1 causes large gas losses, especially along the thin, tearable portion 19, if the cap is not provided with any gastight cover disc 13. However, if a disc 13 of aluminium foil is fitted on the cap in the manner which has been specified, the gas leakage through the cap can be radically restricted and the contents in the container 4 are better protected against deterioration of quality, or in other words the shelf life of the package can be extended.
The use has been known for a long time of screw caps, stopperlike cap mould of the cork type, and tear-off metal caps, in connection with bottles and other containers intended for pressurized contents. In particular for non-returnable containers of plastics it has been found, however, that the available known cap constructions are not satisfactory, largely because of the elasticity of the plastic material. Thus it is difficult simply to use a stopper construction, the simplest variety of which is an ordinary bottle-cork, since contrary to a metal container or a glass container the mouth of a plastic container under the effect of pressure tends to yield elastically, so that a stopperlike cap is easily pushed out by the internal pressure prevailing in the container. The same is the case with tear-off metal caps of the known type, since the fitting of such cap mould requires a certain backing from the container mouth, and this backing as a rule is not present to a sufficient extent on thin-walled plastic containers. So-called screw caps have been used for the closing of plastic containers intended for pressurized contents, but such closures are relatively expensive, since the moulding of threads on the opening part of the plastic container is burdensome to perform and in any case diminishes the capacity in the manufacture of the containers. To solve this technical problem it has been suggested previously to use an injection moulded plastic cap of the same type in principle as that of the present application, this cap mould being adapted so as to be used in containers whose opening part has an inwardly directed, flexible, annular lip of plastic material. Such a cap in principle consists of two parts which, however, are joined before the cap is opened along a thin, readily breakable, annular portion. To allow the said portion to be easily breakable, it is necessary that the wall thickness within the portion in question should be small, and this in turn means that the gas permeablility will be great, especially if the material itself is not particularly gastight (e.g. polyethylene).
It has been found, that at least in cap mould which have been subjected to pressure from pressurized contents over a prolonged period, the disc 13 is made to burst close to where it is fixed in the stopperlike part 1 when the cap is torn up. This is in general quite desirable, since a stopper part is obtained in this manner which is free from "flash" or projecting remains of the disc 13 when the stopperlike part 1 is withdrawn from the emptying channel. If desired, however, it is possible to direct the rupture line in the disc 13 by providing one or both of the plastic layers 24 or 25 with an incision or weakening line 31.

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