GB2281710A

GB2281710A - Moulding plastics sheet material

Info

Publication number: GB2281710A
Application number: GB9416593A
Authority: GB
Inventors: John Fraser Burnett
Original assignee: POLBETH PACKAGING Ltd
Current assignee: POLBETH PACKAGING Ltd
Priority date: 1993-08-17
Filing date: 1994-08-17
Publication date: 1995-03-15
Also published as: GB9317070D0; GB9416593D0

Abstract

When moulding plastics sheet material (44) using reciprocating moulding members (18, 34), the moulding surface is partially defined by the interior surface of a cutting blade (32) having a cutting edge (40) which is arranged to contact but not cut the sheet material during the forming procedure. When the forming is complete, the cutting edge (40) cuts through the sheet (44) at the desired peripheral edge of the formed product, thus dispensing with a subsequent trimming step. The sheet may be applied to the moulding surface by blowing hot air from the other moulding member (18) which is itself heated for initial heating of the sheet, the sheet being blown against it for that purpose.

Description

MOULDING PLASTICS SHEET MATERIAL The invention is concerned with improvement in or relating to the moulding of plastic sheet material particularly, but not exclusively, for forming containers, container inserts or other shaped articles of packaging, ornamentation or the like.

It is conventional practice to provide shaped or partially contoured articles from thermoplastic sheet material using a number of techniques, vacuum forming, pressure forming, hot-drawing and the like. Such processes involve gripping edge portions of the sheet material to be shaped, carrying out the shaping operation, perhaps including both heating and cooling steps and passing the formed sheet to a further step in which the edge portions that were gripped are removed if they are not considered visually acceptable or are otherwise required to be disposed of.

It is an object of the present invention to reduce the number of stages in the production of articles to be moulded from thermoplastic sheet material.

The invention provides in one of its aspects a method of moulding articles from plastics sheet material comprising the steps of (i) procuring at least one portion of plastics sheet material, (ii) presenting the sheet portion to a plastics material forming and moulding apparatus in which marginal portions of said sheet portion are held between confronting surfaces of said apparatus, (iii) subjecting the portion of the sheet material within the marginal portions to a shaping process involving a peripheral moulding surface portion of the forming and moulding apparatus and (iv) severing the marginal portions of the sheet material in situ by means of a cutting edge provided on said peripheral moulding surface portion.

The invention further provides a method of forming thermoplastic sheet material as described in the preceding paragraph comprising placing said portion of plastics material upon a first, heated, surface of said forming and moulding apparatus, causing relative movement between said first surface and a second confronting surface of the apparatus to bring said sheet portion into touching contact with a cutting edge of a cutting blade surrounding said second surface, ensuring that the sheet material portion is uniformly heated, regulating the air pressure level in the space between said first and second surfaces to deform said sheet portion while marginal portions thereof are held by said cutting edge, said air pressure level being adjusted to cause the sheet material portion to leave said first surface and to conform to the respective contours of said second surface and of said peripheral moulding surface portion provided on said cutting blade, bringing about further relative movement between the first and second surfaces to cause the cutting edge to cut through the thickness of the sheet material portion and releasing the contoured sheet material product.

The invention provides in another of its aspects, a method of moulding articles from plastics sheet material in a forming and moulding apparatus wherein marginal portions of the sheet material are gripped against a surface by means of a cutting edge on a cutting die, in which side surfaces of said die inwardly of the cutting edge define moulding surfaces of the forming and moulding apparatus.

Advantageously, said cutting die comprises a continuous strip blade comprises a cutting edge defining a peripheral line around a portion of sheet material to be moulded, said cutting die being provided with further moulding surfaces adapted to form and shape portions of the sheet material intermediate of said peripheral line or lines. Conveniently, said further moulding surfaces may be provided upon an insert secured within the enclosure formed by the continuous strip blade.

The invention further provides, in yet another of its aspects, a cutting die comprising an at least substantially continuous strip blade having a cutting edge formed on said strip blade, an interior surface of said strip blade forming a mould surface in a forming and moulding apparatus.

There will now be described an example of apparatus and a method according to the invention. It will be understood that the description, which is to be read with reference to the drawings, is given by way of example only and not by way of limitation.

In the drawings: Figure 1 is a perspective view of a product which may be produced by the method according to the invention; Figure 2 shows a product as made according to the prior art; Figures 3 to 8 show steps in the production of the product of Figure 1 by the method according to the invention; and Figures 9 and 10 show a modification of a portion of apparatus according to the invention.

A typical product to be made according to the present invention is shown in Figure 1. The product comprises a container 2 and a lid 4. The container, which in the present example is rectangular, is formed with an internal shoulder 6 defining a peripheral flange 8 which is although substantially vertical, tapers very slightly to allow for mould release in accordance with conventional practice. Walls 10 of the container 2 exhibit a greater degree of tapering to permit nesting of the containers for ease of transport and storage prior to use.

The lid 4 comprises a cover wall 12 and a depending flange 14, the flange 14 being intended to use to be a close fit over the flange 8 of the container 2. Figure 2 shows a similar lid 4' during a stage in the production thereof according to the prior art. The lid 4' has been formed from sheet plastics material to provide a cover wall 12' and a flange 14' but in the asformed condition there is also formed integrally with the flange 14' a margin 16 which must be removed in a separate cutting operation. The cutting direction is shown on lines A. It is obvious that accuracy of registration between product and cutting device at the separate stage would be essential.

Figures 3 to 8 illustrate the steps in a method according to the present invention. A first moulding member 18 comprises a first moulding surface 20 which is heated in a conventional manner. The member 18 in the present example comprises a steel plate 22 providing the surface 20, an intermediate layer comprising a copper plate 24 and a lower, steel, plate 26. Apertures 28 are provided through which a flow of compressed air is provided as required.

A second moulding member 30 is provided by a cutting die strip blade 32 within which is received a plate 34 including apertures 36 through which compressed air may be supplied as required. Secured to the blade 32 is an insert 38, the purpose of which will be explained below. The cutting blade 32 has a cutting edge 40 and an inside surface 42 projecting beyond the insert 38.

In use, a portion of thermoplastic sheet material 44 is placed upon the surface 20 of the first mould member 18 which, in the present example, is raised until the cutting edge 40 is in contact with the sheet portion 44 but does not cut through it. The edge 40 defines the peripheral edge of the product, in this case the flange 8 of the container 2.

Air is then provided under pressure from apertures 36 to force the sheet portion 44 firmly against the surface 20 (Figure 4) to ensure uniform heating of the sheet portion 44. When the flow of air is removed from the apertures 36, a flow of heated air under pressure is directed from apertures 28 onto the sheet portion 44 to cause it to rise from the surface 20, as shown in Figure 5, to contact the second moulding surface, comprised by the under surface of member 34, the surface of insert 38 and the moulding surface 42 of the blade 32. The thermoplastic nature of the sheet material enables it to take up the exact contours of the second surface (34, 38, 42) as shown in Figure 6.

It will be observed that the pattern of apertures 28 in the member 18 is selected to conform with the area enclosed by the cutting edge 40.

In Figure 6, the member 18 is shown to be raised slightly further in order to cause the cutting edge to penetrate through the sheet portion 44 to sever the outer parts 46 of the cooling sheet material. The first moulding member 18 is then lowered as shown in Figure 7 and the parts 46 fall away, except where a small notch has been formed in the cutting edge to retain at least one narrow uncut bridge for example at a location 50 between portion 44 and part 46'. Air is then provided through the apertures 36 of the upper member (Figure 8) and the product 44 is released. It may then be removed laterally by means (not shown) which contact the part 46'. The bridge at 50 may then be broken manually to produce a container which has a clean cut periphery requiring no trimming step to be carried out.

It will be understood that the sheet material may be pre-printed or otherwise decorated to choice.

In the example above described the surface of the member 34 is shown as planar but it will be understood that the surface may be contoured for example as shown in Figure 9 to provide wall surfaces 52 utilised to produce compartments 54 in a finished container 56 as shown in Figure 10.

Various modifications may be made within the scope of the invention as defined by the following claims.

Claims

CLAIMS:

1. A method of moulding articles from plastics sheet material comprising the steps of (i) procuring at least one portion of plastics sheet material, (ii) presenting the sheet portion to a plastics material forming and moulding apparatus in which marginal portions of said sheet portion are held between confronting surfaces of said apparatus, (iii) subjecting the portion of the sheet material within the marginal portions to a shaping process involving a peripheral moulding surface portion of the forming and moulding apparatus and (iv) severing the marginal portions of the sheet material in situ by means of a cutting edge provided on said peripheral moulding surface portion.

2. A method as claimed in claim 1, comprising placing said portion of plastics material upon a first, heated, surface of said forming and moulding apparatus, causing relative movement between said first surface and a second confronting surface of the apparatus to bring said sheet portion into touching contact with a cutting edge of a cutting blade surrounding said second surface, ensuring that the sheet material portion is uniformly heated, regulating the air pressure level in the space between said first and second surfaces to deform said sheet portion while marginal portions thereof are held by said cutting edge, said air pressure level being adjusted to cause the sheet material portion to leave said first surface and to conform to the respective contours of said second surface and of said peripheral moulding surface portion provided on said cutting blade, bringing about further relative movement between the first and second surfaces to cause the cutting edge to cut through the thickness of the sheet material portion and releasing the contoured sheet material product.

3. A method of moulding articles from plastics sheet material in a forming and moulding apparatus wherein marginal portions of the sheet material are gripped against a surface by means of a cutting edge on a cutting die, in which side surfaces of said die inwardly of the cutting edge define moulding surfaces of the forming and moulding apparatus.

4. A cutting die comprising an at least substantially continuous strip blade having a cutting edge formed on said strip blade, an interior surface of said strip blade forming a mould surface in a forming and moulding apparatus.

5. A die as claimed in claim 4, wherein said strip blade comprises a cutting edge defining a peripheral line around a portion of sheet material to be moulded, said cutting die being provided with further moulding surfaces adapted to form and shape portions of the sheet material intermediate of said peripheral line or lines.

6. A die as claimed in claim 5, wherein said further moulding surfaces may be provided upon an insert secured within the enclosure formed by the continuous strip blade.

7. A method of moulding articles from plastics sheet material substantially as hereinbefore described with reference to Figures 1 and 3 to 10 of the drawings.

8. A cutting die having a moulding surface, constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures 1 and 3 to 10 of the drawings.