GB2223008A

GB2223008A - Container closures

Info

Publication number: GB2223008A
Application number: GB8919333A
Authority: GB
Inventors: Brian Edwards; Christopher Howard Sworn
Original assignee: Reed Packaging Ltd
Current assignee: Reed Packaging Ltd
Priority date: 1988-08-26
Filing date: 1989-08-25
Publication date: 1990-03-28
Anticipated expiration: 2009-08-25
Also published as: GB8820393D0; GB2223008B; GB8919333D0; FR2659599A1

Abstract

A moulded, pressfit lid 14 or cooperating lid ring 16 for a plastics container 10 is provided with a sealing layer 38 formed of a polymeric material or composition different from, and preferably softer than, that of the lid and lid ring. The container is preferably widemouthed and intended for solvent-based liquid products such as paint. A preferred method of making the container, lid and ring comprises moulding in a solvent resistant polymer a lid ring and a lid which is a press-fit therein, allowing the moulded components to cool after moulding, thereby allowing inherent shrinkage and distortion to occur, and applying to a sealing zone of the lid or lid ring a second and different polymeric material or composition, softer than the other polymeric material, and in a liquid or semi-liquid form, so as to produce an annular laminar sealing layer which adheres to the other polymeric material. <IMAGE>

Description

PLASTIC CONTAINERS This invention relates to plastic containers. More particularly, not exclusively, the invention relates to a method of making wide mouthed plastic containers for solvent-based liquid products such as gloss paints, varnishes, inks and the like. The invention also provides plastic containers made by such a method, and plastic containers per se.

Plastic containers for water based paints are now well established and provide an important alternative to the long established paint cans formed from metal.

However, difficulties have been encountered in relation to the provision of plastic containers for gloss paints, varnishes, inks and the like due, amongst other things, to the unexpected performance shortcomings of such containers in relation to provision of an airtight seal.

These problems were largely unforeseen due to the success of plastic containers for water based paints, such being moulded from polypropylene (PP) and polyethylene (HDPE). These latter materials were found not to be suitable for use with the solvents contained in gloss paints and other plastics material have been found for the purpose, such as plastic blends based on polyethylene terephthalate (PET). For example, a polyester

F last i cs C8fM), material soLd by Dupont under the name SeLar-P-Tlmay be used.

Certainly, it is reasonable to expect that a lid ring and co-operating press-fit lid moulded from these solvent resistant plastics materials would provide an adequately airtight seal for the purpose. Indeed, close tolerance plastic products are well established in many markets and accordingly it was to be expected that no serious difficulties in sealing plastic containers would arise, particularly bearing in mind the resilience of these materials and the advanced state of the art in relation to their moulding.

Nevertheless, experience has shown otherwise.- The absence from the market place at the time of filing this application of a plastic container for gloss paints, together with the publication of prior proposals for new and improved seating arrangements all indicate the existence of the problem identified above.

Of course, most problems of this sort can be solved, at a cost, by laboratory and workshop techniques including precision manufacturing methods, reduction of tolerances to a bare minimum, the strictest quality control, and so on.

However, such an approach is unacceptable in the case of a product which must necessarily compete with the well established and comparatively readily manufactured metallic product. Accordingly, the general Line of approach to the solution of the problem has been via improved seal designs incorporated into the lid ring and/or the lid itself of the container. The merit of such an approach lies in the fact that whatever the complexity of the seal design, assuming it is suitable for mass production in a mould, the unit cost on a high volume basis is relatively low, in view of the relative simplicity and rapidity of moulding the product from a uniform supply of a single plastics material.

Our research shows that this prior art approach to the problem does not and, we believe, probably cannot meet the twin requirements of high volume production at normal manufacturing tolerances together with an adequate Level of sealing so as to avoid the formation of a skin on gloss paints within a relatively short period of time.

An object of the present invention is to provide a method of making a plastic container, together with plastic containers per se offering improvements in relation to one or more of the matters discussed above, or generally.

According to the invention there is provided a method of making a plastic container, together with plastic containers per se, as defined in the accompanying claims.

In an embodiment described below we have put into practice the results of a discovery we have made in relation to the problems identified above. In the embodiment, we have provided a simple manufacturing technique which can be readily added to the existing maufacturing process for producing plastic containers, whereby the sealing problems identified above are largely eliminated, or at least substantially reduced. 8y avoiding the need for any significant improvement in manufacturing tolerances, and indeed Dy avoiding the need for any unduly complex sealing structures, we have preserved the simplicity and ease of production normally inherent in plastic moulded components. Moreover, this has been done at the same time as we have solved the sealing problem at a perfectLy acceptable minor additional cost.Indeed, there may be no extra cost if one allows for the extra cost inherent in the prior proposals for elaborate sealing structures and/or precision manufacturing techniques, grinding operations and the like.

In the embodiment, the plastic container, including the lid ring and the lid itself are conventionally moulded from a plastics material which is resistant to the solvents in gloss paints. This first or main polymer is a much harder material than PP or HDPE mentioned above.

Moreover, it is a material which is very difficult to mould consistently. Nevertheless, in the embodiment, the shrinkage and/or distortion which occurs when the lid and the lid ring are cooled after moulding, is found to be acceptable in view of the subsequent application to the sealing zones thereon of the second and different polymeric material or composition, which is softer than the PP or HDPE.

It has hitherto been considered completely unacceptable to provide a mass volume moulded product incorporating two different polymeric materials in view of the complexity of production techniques which would be inherent in such a proposal. Nevertheless, by provision of the second polymeric material or composition merely in a sealing zone, which is at a location normally out of direct contact with the contained liquid itself, this problem has been solved at an acceptable cost.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which Fig 1 shows, on a relatively large scale, a vertical section through the lid ring portion of a plastic paint container with the Lid itself assembled thereon, but not yet pushed down into its sealed and retained position, the view being a scrap view of a portion only of the assembly; and Fig 2 shows, in a view similar to Fig 1, the assembly with the lid pushed down into its sealed and retained position.

As shown in the drawings, a plastic container 10 comprises a cylindrical body 12, and a lid 14 engaging a lid ring 16 welded to body 12. All these components are moulded in PET or a like polymeric material resistant to the solvents employed in gloss paint, printing inks, varnishes and the like.

The structure of container 10 is more fully described in International Patent Application publication No.

WO88/05015, the entire disclosure of which is incorporated herein by reference.

Suffice it to say for present purposes that the container 10 has releasable lid retaining or latching means 18 which is tamper evident and child resistant, and forms part of lid 14.

Separate from the releasable latching means 18 is the sealing means 20 comprising a generally cylindrical skirt 22 forming part of lid 14 and having an annular rib 24 of generally wedge-shaped cross-sectional profile, which is engageable with an annular sealing flange 26 formed on lid ring 16. Rib 24 faces radially outwards and sealing flange 26 faces radially inwards. They are proportioned to cooperate as shown in Fig 1 prior to sealing engagement. Fig 2 shows their relationship after lid 14 has been pressed downwards into its sealed and latched condition.

It will now be apparent that when lid 14 is removed, the uppermost edge of the open-topped container 10 is the edge 28 of lid ring 16. The latching of releasable latching means 18 in its Fig 2 condition is achieved by mutual co-operation of the parallel horizontal latching faces 30, 32 formed on latching means 18 and lid ring 16 respectively.

As shown in Fig 1, lid ring 16 and lid 14 have respective seating zones 34, 36 for mutual sealing co operation on press-fitting of the lid into its Fig 2 poSition.

Manufacture of lid 14 and lid ring 16 proceeds by means of known moulding techniques. After removal from the mould, cooling of the plastic material together with such shrinkage and distortion as is inherent in such cooling occurs. Then, there is applied to the, at this stage, product uniformly comprising the PET plastics material, a second and different polymeric material or composition which is softer than the PET so as to produce an annular Laminar sealing layer 38 which adheres to the lid 14.

Layer 38 provides sealing co-operation between the sealing portions 34, 36 of the lid and ring, while permitting repeated press-fitting and de-lidding of the lid in use.

Seating Layer 38 is formed by applying the polymeric material or composition in a Liquid or semi-liquid form progessively around the annular area 36 on the lid, while the latter is rotated.

The preferred composition for the sealing layer is a water-based rubber composition in which the water acts as an inhibitor to curing. After application to the lid, the evaporatior. of the water permits curing to proceed.

Alternatively, a hot-melt polyethylene compositions may be employed. It is believed that other composition may well be developed which are suitable. Indeed, any suitable polymer, including natural and synthetic elastomers and compositions thereof with fillers and additives may be employed, including also compositions comprising the polymers conventionally used for moulding plastics containers, or other sealing compositions. The exact nature of the composition chosen for a given applicaiton will depend upon the solvent employed in the Liquid to be stored.

It can be clearly seen in Fig 1 that seaiing layer 38 is applied at the exact location where the sealing zone 34 on lid ring 16 engages the lid in the Latter's Fig 2 condition.

After application of the sealing composition in liquid or semi-liquid form, the latter is allowed to dry or cure, followed by despatch of the product. Application of the composition may be immediately after moulding, whereby the relatively high temperature of the moulded plastic components promotes rapid curing and drying of the composition.

In use, the sealing Layer 38 has a significantly lower hardness than the material of the remainder of the container 10, whereby an effective and airtight seal is formed in the Fig 2 position of the lid. All normal manufacturing tolerances due to shrinkage and distortions in the moulded plastic components are compensated-for by the natural flexibility and resilience of the sealing layer. The latter is applied in a simple and rapid single additional manufacturing step, the cost of which is relatively low.

Interestingly, in the above embodiment, the provision of a sealing layer 38 formed of a second and softer polymeric material or composision eliminates the sealing diffiSirlties inherent in the moulded PET components as discussed above. The manufacturing techniques employed are relatively so simple that the additional cost inherent in adopting two polymers instead of the conventional single polymer is acceptable, particularly since this additional step eliminates the higher manufacturing tolerances and higher reject rates which would otherwise be required.

The embodiment can be readily adapted by the use of different configurations of container lid and lid ring.

The materials for these latter may vary from those mentioned above. It is believed that substantially all suitable pLastics materials (poLymers) which are resistant to the solvents employed in gloss paints, varnishes, printing inks and the Like have a substantially higher hardness than PP or HDPE. Any such polymers may be employed and will enjoy the benefits of the invention.

Indeed, the sealing effect will equally be obtained with polypropylene and high density polyethylene, though these Latter are much easier to seal using only moulded-in sealing components.

Amongst other materials suitable for the body of the plastic container, to which the invention may be applied, are polyamides.

Of course, modification of the profile or form of the lid or lid ring to accommodate the sealing layer may be desirable. For example, a small step in the profile may be provided on the lid in the region of the sealing zone for this purpose.

Claims

1 A method of making a wide mouthed plastic container for solvent based liquid products such as paint, and having a press-fit lid, the method comprising : moulding a Lid ring for the container to define said wide mouth; moulding a lid to fit said wide mouth; said lid ring and said lid being moulded in a polymeric material which is resistant to the solvent or solvents of said solvent based liquid products, and being formed with co-operating sealing zones for mutual sealing co-operation on press-fitting said lid into said lid ring; characterised by applying to said sealing zone a second and different polymeric material or composition, said second polymeric material or composition being, in its working condition, softer than said other polymeric material;; said second polymeric material being applied to said sealing zone in a liquid or semi-liquid form so as to produce an annular laminar sealing layer which adheres to said other polymeric material and provides sealing cooperation between the sealing portions of the lid and ring in the sealing zones thereof while permitting repeated press-fitting and de-lidding of said lid in use.

2 A method of making a plastic container having apressfit lid comprising applying in liquid or semi-liquid form a second and softer ploymeric material or composition to a sealing zone of said container and/or lid to produce an annular sealing layer thereon.

3 A method according to claim 1 or claim 2 characterised in that said second polymeric material or composition is applied to a sealing zone on the lid of said container.

4 A method according to claim 3 characterised in that said sealing zone is located in an annular generally channel-section zone adapted to receive with a clipping action a co-operating annular formation provided on said lid ring.

5 A method according to any one of the preceding claims characterised in that said annular sealing layer tapers in thickness, as seen in cross-section, from its middle region to at least one of its annular edges.

6 A method according to claim 4 characterised in that said sealing layer is shaped with an annular formation to receive said annular formation on the lid ring.

7 A method according to any one of the preceding claims characterised in that said polymeric material or composition progressively cures after application to said plastic container.

8 A method of making a wide mouthed plastic container for solvent based liquid products such as paint, substantially as described herein with reference to the accompanying drawings.

9 A Lid for a plastic container made by a method according to any one of the preceding claims.

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10 A Lid ring or a plastic container incorporating same made by a method according to any one of claims 1 to 8.

11 A lid or a Lid ring for a wide mouthed Plastic container for solvent based liquid products such as paint, and in which the lid can be press-fitted into the lid ring, the lid and the lid ring being moulded in polymeric material which is resistant to the solvent or solvents of said solvent-based liquid products, and being formed with co-operatable sealing zones for mutual sealing co-operation on press fitting the lid into the lid ring, characterised by an annular laminar sealing layer comprising a second polymeric material or composition applied to said sealing zone, and adhering to said lid or lid ring, to provide sealing co-operation between the sealing portions of the lid and lid ring in the sealing zones thereof while permitting repeated press fitting and de-lidding of said Lid in use.

12 A plastic container having a press-fit lid characterised by a sealing layer on said lid or a co operating lid ring, said sealing layer being formed of a softer polymeric material or composition than the container itself.

13 A plastic container according to claim 11 or claim 12 characterised in that said second polymeric material or composition is applied to a seating zone on the lid of said container.

14 A plastic container according to claim 13 characterised in that said sealing zone is located in an annular generally channel-section zone adapted to receive with a clipping action a co-operating annular formation provided on said lid ring.

15 A plastic container according to any one of claims 11 to 14 characterised in that said annular sealing layer -t-apers-Ltn thickness, as seen in cross-section, from its at a-t at least one of its annular edges.

16 A plastic container according to- claim 14 characterised in that said sealing Layer is provided with an annular formation to receive said annular formation on the lid ring.

17 A plastic container substantially as described herein with reference to the accompanying drawings