IE44915B1

IE44915B1 - Composite lid

Info

Publication number: IE44915B1
Application number: IE733/77A
Authority: IE
Original assignee: Ici Ltd
Priority date: 1976-04-20
Filing date: 1977-04-06
Publication date: 1982-05-19
Also published as: DE2717298C3; DK147935C; DK147935B; NL187619C; DE2717298B2; BE853772A; GB1574145A; AU2438377A; CH614677A5; NO146275C; NO146275B; IE44915L; DK170477A; SE433070B; DE2717298A1; FR2348863B1; FR2348863A1; NL187619B; AU506977B2; NO771353L

Abstract

A connection lid with a moulded-on edge for packaging containers, in which lid distortion and the occurrence of tension in the lid, caused by shrinkage of the moulded-on or cast-on edge (2), are prevented by preformed lines of weakness (13), the lid curving out along these lines when tension occurs. The lid is manufactured by cutting out the lid plate (1), applying the predetermined lines of weakness (13) in the plate, and casting on a terminating edge (2) along the periphery of the lid plate.

Description

Ths invention relates to composite lids of the kind comprising a sheet of a first material and a rim moulded from a second material around the perimeter of the sheet.

Composite lids of this kind are suitable for closing cartons used for packaging various materials or articles offered for sale, e.g. foodstuffs such as ice eream, or articles such as nails. A composite construction enables a rim shape to be accurately moulded from a flexible thermoplastics material such as polyethylene, so as to provide a good fit around the mouth of the carton in known manner, while also providing a readily printable surface over the area of the lid enabling ready application of a decoration to provide customerappeal. The first material forming the sheet is generally cardboard, but various laminates may equally be used for this purpose. Th© second material forming ths rim, and indeed forming the carton itself, is usually polyethylene, but various other injection-mouldable thermoplastics may be applicable also.

The composite lids are manufactured by shaping the sheets to the desired outlines, and stacking them in a magazine. The sheets are normally flat even though there may be tabs around the perimeter which are bent perpendicular at some stage during the moulding operation, and the decorations are usually applied before stacking.

The shQsts are then fed to an injection moulding machine where the rim is injection moulded around the perimeter of the sheet. However, to minimise the quantities of materials required and to obtain a good sealing closure of the carton, the lids are made flexibly thin, and problems have arisen due to warping of the composite lids, in which the moulded rims become curved out of their intended plane.

According to one aspect of the invention there is provided a composite lid of the kind comprising a - 3 sheet oi a first material and a ri» moulded from a second Material around the perimeter of the sheet, wherein the sheet has at least one line of weakness extending between each two adjacent corners of the lid and following a path which on leaving one corner diverges from the portion of the moulded rira joining the two corners and converges with the rim as it approaches the other corner, to allot,? the sheet to bend along the lines of weakness and thereby relieve stresses in the lid caused by shrinkage ©£ the IS moulded rid. Relieving these stresses in this way, may reduce or even 'eliminate the warping referred to above.

Various configurations of lines of weakness may ba used, For example, the path of the line may coaprioe a plurality of straight lengths with a sharp bend between adjacent lengths, or a smooth curve from one corner to the other, cr a comb-nation of straight lengths and curved lengths. The lines extending between each pair of corners may intersect, but in general it is preferred to leave an inner area remote from all the corners, free from any of the lines of weakness. This latter provides a relatively flat area with gentle downward curvature into the corners, and moreover by suitably restricting the lines of weakness to the areas around the perimeter, an advantageous shape may bs provided wherein all areas of the sheet after bending along the lines of weakness to reduce the stresses, lie within the volume enclosed by the moulded rim. This enables the lids to ba handled on conventional machines, e.g. when destack,ing the lids ane placing them on filled cartons, whereas these machines may not always 3® accept lids wherein the sheet portion is dished upwards beyond the top of the rim, i.e. when it extends outside the volume enclosed by the rim.

According to a further aspect of the invention there is provided a method of manufacturing a composite lid comprising shaping a sheet of a first material to a desired outline and moulding a rim of a second material around the perimeter of the sheet, the improvement consisting in providing the sheet with at least one line of weakness extending between each two adjacent corners o£ the lid and following a path which'on leaving one corner diverges from the portion of the moulded rim joining the two corners and converges with the rim as it approaches the other corner.

The lines of weakness may be formed by various known 10 methods, such as by scoring or cutting-the sheet part-way through its thickness for example. Alternatively a compressible sheet may be compressed along the path where the lines are required. Where the magasine and associated mould feeding mechanism allows, the sheet may bs embossed IS to provide the lines of weakness. Where the sheet is itself preformed by a moulding operation, the lines of weakness may be provided as regions of thinner material.

A preferred method is one in which the sheet is provided with its lines of weakness before the rim is moulded around its perimeter, and it is generally convenient to provide the lines of weakness when preparing the sheet to the desired outline shape.

The -lids may be used for closing moulded containers, having a base and sides in conventional manner. However, they may similarly be used at both ends of a tube of suitable section, thereby providing both base and lid.

The invention is illustrated by four specific embodiments described herein by way of example, with reference to the drawings accompanying the provisional specification in which Figures 1 and 2 are plan views of two square lids of similar configurations Figures 3 and <5 are diagrammatical sections along the lines XIX XIX and XV XV respectively of Figures 1 and 2j - 5 Figure 5 is a plan view of a further square lid; Figure 6 is a diagrammatical section along the line VI VI of Figure 5; Figure 7 ia a plan view of a triangular lid; end 5 Figure 8 is a diagrammatical section along the line VIII VIII of Figure 7.

The composite lid shown in Figures 1 and 3 comprises a substantially square sheet 1 of a first material, e.g, cardboard, having a rim 2 moulded from a second material, e.g, polyethylene, around its periphery.

The rim has a channel section, the sides of which extend frcm the base 3 by different amounts. The outer side 4 extends the furthest, and has an integral latching ridge 5. The inner, shorter side 6 has a perpendicular flange 7 extending in the direction away from the outer side, The fcur comers 8, 9, 10* 11 are rounded. The sheet has correspondingly rounded comers, and upturned tabs 12 along each edge. Extending between adjacent comers, i.e. between 8 and 9, S and 10, 10 and 11, and 11 and 8, are lines of weakness 13, each comprising two straight portions meeting to produce a sharp bend 14. As each line leaves its corner, it diverges from the portion of the moulded rim 2 joining the two corners, and converges with the ria as it approaches the other comer. The sheet is bent along the lines 13 to give a dished profile as shown in Figure 3.

A composite lid as shown in Figures 1 and 3, is made by stacking sheets precut to tho desired outline of a square with rounded comers and edge tabs 12, and provided with a design printed on one side. Whilst cutting the outline, the printed side is cut part-way through to provide the lines 13 of weakness. The stacked sheets while still flat, are fed to the mould, and th® rims Injection moulded around the sheet with the edge tabs bent up as shown in the drawings. On removal from the mould, the sheet automatically' bends along the lines of weakness to relieve the stresses applied to the sheet by contraction οϊ the rim as it cools» The lid shorn in Figures 2 and 4 is substantially the same as that shown in Figures 1 and 3 (and like numerals have been used for like parts), except that the lines 21 of weakness form smooth curves rather than dog legs» In both lids there is an inner area 22 remote from all the corners, which is free from any of the lines of weakness, and this produces a relatively flat area with gentle downward curvature into the corners» Moreover, as will be apparent from Figures 3 and 4, this leads to all the areas of the sheets lying within the volume enclosed by the moulded rim, the upper and lower edges of the rim 'showing on either side of the sheet ia these sections» Figures 5 and 6 show a lid which is similar to the previous two, except that all the lines of weakness 51 meet at the centre» The effect cf this is to dish the sheet tc a greater displacement at the centre» Thia is acre likely to stand preud cf the moulded rim, and may then give handling greblams with some ccnvsnticnal machines» In Figures 7 and 8 is shown a triangular lid to illustrate how the invention may be applied to shapes other than the more usual square and other rectangular shapes» Like reference numerals have been used where appropriate»

Claims

1. » A composite lid of the kind comprising a sheet of a first material and a rim moulded from a second material «round the perimeter of the sheet, wherein the sheet has at least one line of weakness extending 5 between each two adjacent corners of the lid and following a path which on leaving one corner diverges from the portion of the moulded rim joining the two corners and converges with the rim as it approaches the other corner.

2. A composite lid as claimed in claim 1 wherein an 10 inner area of the cheat remote fran all the corners, is free from any lines of weakness.

3. A composite lid as claimed in claim I or claim 2 wherein all areas of the sheet after banding along the lines of weakness to reduce the stresses, lie within the 12 volume enclosed by the moulded ris.

4. Λ composite lid as claimed in any one of the preceding claims wherein the first material is cardboard.

5. A composite lid -?.ε elaimed in any ons og feha preceding claims wherwis tho second material is 20 polyethylene. δ, A composite lid substantially as hereinbefore described and as illustrated in any one of the accompanying drawings,

6. 7. A method of marsufasturirig a composite lid 25 comprising shaping a sheet cf a first material to a desired outline and moulding a rim of a second material around the perimeter of the sheet, tho improvement consisting in providing the sheet with at least one line of weakness extending between each two adjacent corners of 33 th® lid and following a path which on leaving on® corner diverges from the portion ef the moulded rim joining the two corners and converges with th® rim as it approaches the other corner. -

7. 8.8. A method according to claim 7 characterised in that the sheet is provided with its lines of weakness before th® rim is moulded around its perimeter,,

8. 9« A Esthod eeecrding to claim 7 or claim 8 5 characterised in that the lines of weakness are foraied by cutting -fee sheet part-iiay through.