GB2111965A - Moulded closure caps - Google Patents

Abstract

A moulded plastic closure cap (1) having sealing fins (7) to engage the rim of a container (6) has its seal improved by a coating (10) of a material softer than the material of the closure cap. Preferred materials for the coating include plastisol resins such as polyvinyl chloride homopolymers and copolymers of vinyl chloride, particularly vinyl acetate- vinyl chloride copolymers. <IMAGE>

Description

SPECIFICATION Moulded closure caps This invention relates to closure caps for sealing containers formed of glass or plastic or other materials and more particularly but not exclusively to a moulded plastic closure cap where the sealing means includes integral sealing ribs or fins moulded as an integral portion of the closure cap.

Plastic closures with sealing ribs or fins are presently used to seal containers in various packaging applications. A closure of this type is applied to the container's threaded neck and creates a seal when its ribs or fins press against the container finish. Such closures are commonly called linerless closures.

Certain packages require a seal which retains a vacuum within the sealed container for preserving the packaged product. Although the general type of plastic closure described above does maintain vacuum in a certain percentage of sealed packages, the percentage of packages in which the seal fails to maintain vacuum is unacceptably high in many cases.

Plastic caps with sealing ribs or fins are usually moulded in one piece from polyolefin materials, often a polypropylene type. The sealing fins are relatively rigid in comparison to other materials such as plastisol gaskets normally used to seal containers. The polyolefin sealing fins thus lack the softness to attain intimate contact with container finishes such as is necessary to maintain a vacuum especially during the handling of the packages. Although containers are manufactured to specified tolerances, they do not always have perfect finishes due to problems inherent in their manufacturing process.

Another problem with the materials used to make linerless plastic closures is that adhering other materials to the polyolefin surfaces is very difficult.

According to the present invention, a moulded closure cap has integrally moulded sealing means for sealing a container and a relatively thin coating of a material softer than the material of the moulded closure covering the surfaces of the sealing means of the closure. Thus improved sealing capability is achieved by placing a softer sealing material which may for example be a wax, hot melt, epoxy, or plastisol over the surfaces of the sealing means such as sealing ribs or fins of the closure cap. For example, paraffin wax and plastisol have been tested and both have improved the ability of the closure to hold vacuum. When plastisol is used, it may be applied as a liquid over the sealing fins and then heated to cause the liquid plastisol to fuse or gel into a solid. The liquid plastisol may be applied to the fins by a stationary nozzle while the closure is rotated.A thickness of the plastisol of 0.025 to 0.05 mm over the ribs or fins has proved useful as described below.

By means of the invention, it is possible to achieve an acceptable percentage of properly sealed vacuum packages where the sealing is done on automatic sealing machinery at extremely high sealing rates.

The invention may be carried into practice in various ways but four closure caps embodying the invention and a method of applying a coating to a closure cap will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation, partially in section, of a first closure cap; Figure 2 is an enlarged fragmentary detailed sectional view of the closure cap of Fig. 1 sealing a container; Figure 3 is a view similar to Fig. 2 of a second closure cap; Figures 4 and 5 are enlarged fragmentary detailed sectional views of two further closure caps; and Figure 6 is a side elevation illustrating a preferred method of applying the soft sealing coating to the sealing members of the closure.

The closure cap 1 shown in Figs. 1 and 2 has a cover 2 and a depending skirt 3 including container engaging threads 4. The outer surface of the skirt 3 may include knurls or other gripping means 5 for applying and removing the closure cap 1 from the container 6. The cover 2, skirt 3 and threads 4, together with a container sealing means comprise a unitary or onepiece moulded closure cap formed on conventional cap moulding machinery.

There are a number of suitable integral container sealing means which usually take the form of fins or ribs or rings which extend downwardly from the underside of the closure cap. Sealing means of this general type have been described in prior patents such as U.S. patent No.

3,815,771 (S.N. 86,316), dated June 11, 1974. This prior U.S. patent and other issued patents describe projecting ribs or fins which are moulded as an integral part of the closure cap and which are positioned for engaging the container rim. The fins or ribs engage the container rim and provide the seal for the contents of the sealed container.

As illustrated, the sealing fins 7 have an angular alignment with both the closure cap cover 2 and the container rim 8 so that they yield and accommodate themselves against the adjacent container rim 8 in a sealing relationship.

A thin film 9 of a softer sealing material is applied over the fins 7. Suitable sealing films 9 include easily applied films such as waxes, hot melts, epoxies, plastisols and other soft plastic materials applied as a thin film over the fins 7.

Films of these materials have been tested and have proved to significantly increase the sealing capabilities of moulded closures and in particular have increased the ability of the closures to hold a vacuum within the sealed containers.

When a plastisol is employed, it is sprayed or otherwise distributed over the sealing fins 7 and is then heated and fused or gelled into a continuous resilient sealing film over the fins. Plastisol films having a thickness of 0.025 to 0.5 mm have been tested and found to be effective in providing the improved sealing action.

The fused or gelled plastisol conforms generally to the shape of the plastic sealing fins and is held in the closure not only by its own adhesive qualities but also be the physical interlock resulting between the film 9 and the sealing fins 7. Even though packages sealed with fins coated in the above manner were subjected to elevated temperatures, such as those resulting from the use of steam by the vacuum forming sealing apparatus, no significant loss of the sealing action of the films has been found to result.

The preferred plastisols are formed of a properly dispersed mixture of ingredients such as; dispersion resins, blending resins, plasticizers, stabilizers, lubricants, wetting agents, viscosityreducing agents, pigments, and fillers. The resin can be polyvinyl chloride homopolymer or copolymers of vinyl chloride such as vinyl acetate-vinyl chloride copolymer.

When a moulded polyolefin closure is subjected to enough heat, is can shrink or melt. To avoid these effects, the heat used to cause the liquid plastisol to fuse or gel into a solid must be relatively mild. Experimental work has shown that certain copolymer dispersion resins which are designed to fuse at relatively low temperatures are particularly well suited for this application.

Temperatures of 150"C to 165"C and times of 3 to 4 minutes have been used successfully.

Butyl benzyl phthalate (BBP) plasticizer was found to lower the required heating cycle significantly.

One preferred plastisol composition comprising vinyl chloride copolymers and other plastisol ingredients which fuses or gels at low temperatures is the following: Formulation (Phr) 1 2 3 RESIN 100 100 100 PLASTICIZER (D.O.P. or B.B.P.) 60 100 100 STABILIZER (Ferro (707X) 2 1 2 PIGMENT (Horsehead A-410) - 2 2 LUBRICANT (Crodamide OR) 5 5 5 LUBRICANT (Crodamide ER) - - 7 Resin Description Supplier Designation Vinyl Chloride Homopolymer Hooker FPC-605 Tenneco 1759 Vinyl Chloride-Vinyl Acetate Hooker FPC-6338 Copolymer Stauffer SCC-40 Stauffer Scc-52 Diamond Shamrock PVC-7401 Tenneco 0565 Cinyl Chloride-Proprietary Vinyl Ester Copolymer B.F. Goodrich Geon 138 As a group, the six copolymer resins listed above were found to be superior to the homopolymer resins because they require less heat for fusion or gellation. In particular, SCC-40, PVC-7401, Geon 1 38 and FPC 6338 copolymer resins develop physical properties with much less heat than required for FPC-605 or Tenneco 1 759 homopolymer resins.Furthermore, the copolymer resins attain higher maximum tensile strength than do the homopolymer resin, as listed below: Maximum Tensile Resin Strength hPa PVC-7401 7145 Geon 138 6860 FPC-6338 6690 SCC-40 6620 SCC-52 6483 0565 5862 1759 5415 FPC-605 5207 These data indicate that not only do copolymer resins such as SCC-40, Geon 138, PVC-7401, and FPC-6338 develop physical properties at milder conditions of heat than do the homopolymer resins, but also that they are inherently stronger than homopolymer resins similar to FPC-605 and Tenneco 1 759.

Therefore, copolymer resins such as SCC-40, Geon 138, and PVC-7401 have been found to be eminently well suited for this application.

The ability of this formulation to fuse at relatively low temperatures protects the moulded plastic cap shell from damage during the coating, fusing or gelling step.

Figs. 1 and 2 illustrate a coating in accordance with the invention with a middle range of thickness and where the coating material 9 fills the space between the two sealing fins 7. In this case, the coating is seen to provide the sealing contact between the closure 2 and the container 6.

Fig. 3 illustrates a similar closure but with a coating 10 which is of lesser thickness and conforms more closely to the shape of the sealing fins 7. Nevertheless, such coatings with a thickness near the lower side of the thickness range provide improved vacuum sealing capability.

Fig. 4 illustrates a closure cap 11 having a differing sealing means comprising three sealing fins 1 2 having differing lengths and having a lesser angle with the cover 1 3 of the closure 11.

The coating applied to the fins functions in a similar manner to the coatings previously described to provide the improved sealing capability.

Fig. 5 illustrates another embodiment where the closure 1 4 is in sealing engagement with a container 1 9 and where a coating 1 6 forms a seal between the slanted fins 1 5 and the container finish edges 1 8.

Fig. 6 shows a preferred method of applying these coatings in controlled thicknesses. The caps are mounted in rotating nests of a typical gasket applying machine. A spray nozzle positioned to direct a coating spray onto the sealing members operates for a sufficient period to apply the desired coating thickness. After the application of the coating, in the case where a plastisol or other material requiring curing has been used, the cap is transferred to a suitable heating means for the curing or gelling step.

It will be seen that an improved linerless closure cap is provided with the addition of a soft coating giving the vacuum sealing capabilities. The caps can be manufactured in the same manner as presently known caps with the addition of the coating steps.

Claims (11)

1. A moulded closure cap having integrally moulded sealing means for sealing a container and a relatively thin coating of a material softer than the material of the moulded enclosure covering the surfaces of the sealing means of the closure.

2. A closure cap as claimed in Claim 1 which has at least one fin-like sealing member comprising the means for engaging the container, the said coating being applied to surfaces of the or each member.

3. A closure cap as claimed in Claim 1 or Claim 2 in which the said coating has a thickness of from 0.025 to 0.5 mm.

4. A closure cap as claimed in Claim 1 or Claim 2 or Claim 3 in which the said coating comprises a wax, hdt melt, epoxy or plastisol.

5. A closure cap as claimed in Claim 1 or Claim 2 or Claim 3 in which the said coating comprises a plastisol resin.

6. A closure cap as claimed in Claim 5 in which the plastisol resin is a polyvinyl chloride homopolymer.

7. A closure cap as claimed in Claim 5 in which the plastisol resin is a copolymer of vinyl chloride.

8. A closure cap as claimed in Claim 7 in which the plastisol resin is a polyvinyl chloride homopolymer.

9. A closure cap as claimed in Claim 7 in which the plastisol resin is a copolymer of vinyl chloride.

10. A closure cap as claimed in Claim 9 in which the resin is a vinyl acetate-vinyl chloride copolymer.

11. A closure cap as claimed in Claim 9 in which the copolymer resin is SCC-40, Geon 138, PVC-7401, or FPC-6338.

1 2. A closure cap as claimed in Claim 9 in which the said coating comprises one of the following compositions consisting of the ingredients in the parts indicated: Formulation (Phr) 1 2 3 RESIN (Copolymer of vinyl chloride) 100 parts 100 parts 100 parts PLASTICIZER (D.O.P. or B.B.P.) 60 100 100 STABILIZER (Ferro 707X) 2 1 2 PIGMENT (Horsehead A-410) - 2 2 LUBRICANT (Crodamide OR) 5 5 5 LUBRICANT (Crodamide ER) - - 7 1 3. A closure cap substantially as described herein with reference to Figs. 1 and 2 or Fig. 3 or Fig. 4 or Fig. 5 of the accompanying drawings.