GB2240978A

GB2240978A - Improved packaging materials

Info

Publication number: GB2240978A
Application number: GB9002261A
Authority: GB
Inventors: David Lawrence Evamy
Original assignee: Psychopax Ltd
Current assignee: Psychopax Ltd
Priority date: 1990-02-01
Filing date: 1990-02-01
Publication date: 1991-08-21
Also published as: GB9002261D0

Abstract

A method of altering the resilient properties of plastics foam sheet material comprises crushing the material to a reduced thickness and releasing the crushing pressure to allow the foam to recover to a thickness smaller than the original thickness. The foam may be crushed between two platens of a press, or by passing it between two rollers. It is also possible to form shaped sheets of foam material by placing sheet between two platens, bringing the platens together to crush the foam material, and simultaneously cutting the foam material by means of blades projecting from one of the platens to form a shaped sheet. The crushed sheet material is suitable for use as cushioning material in packaging.

Description

IMPROVED PACKAGING MATERIALS The present invention relates to packaging material, and is particularly concerned with improved cushioning materials for carton linings.

Conventionally, it has been proposed to use tablets of expanded foam material to line cartons, in order to protect the contents of the carton against impact. Examples of such cartons are described in UK Patent applications numbers 88.07915 and 88.01393.

It has now been found by the applicant that the resilient properties of synthetic plastics cushioning foams may be improved by treating the foam prior to installation in a carton, and that this pre-treatment of the foam can be advantageously and easily incorporated into a process for manufacturing carton liner panels.

According to the present invention, a method of improving the resilient properties of a plastics foam sheet material comprises crushing the material to a predetermined proportion of its original thickness, and allowing the foam to recover. The sheet material may then be cut to form panels of a carton liner or may be used for internal trays, dividers or fittings within a carton.

In an advantageous development, a carton liner may be formed from a plurality of panels which are simultaneously die-cut from a sheet of expanded foam material in an operation wherein the sheet of material is placed on a fixed platen and a moving platen is brought towards the fixed platen, the moving platen being provided with an array of blades arranged so as to cut the plastics material into the shape of the required liner panels, the blades projecting from the moving platen to an extent less than the thickness of the sheet material so that as the blades pass through the sheet material, the material is simultaneously crushed to a predetermined thickness.

In such a die-cutting process, the sheet of expanded material is held compressed to a predetermined proportion of its original thickness, and is then immediately released. It may be advantageous under certain circumstances to hold the sheet material in the compressed condition for a length of time, prior to releasing it, in order to achieve a variation in the resilient properties of the material.

To demonstrate the change in resilient properties of the material, a sheet of expanded polystyrene of 18 mm thickness and a density of approximately 12.5 ounces per cubic foot (12.64 kilograms per cubic metre) was compressed to a thickness of 9 mm, i.e. 50% of its original thickness. On releasing the compression, the sheet material recovered to a thickness of 16 nmm. In order to test the resilient properties of the material, a hard sphere was dropped onto the sheet material which was supported horizontally on a hard surface. The test was repeated with untreated foam material, and the results are summarised in Table 1.

TABLE 1 Untreated Foam Treated Foam Foam Thickness 18 mm 16 mm Sphere dropped from 500 mm 500 mm Height of first rebound 160 mm 260 mm Height of second rebound 75 mm 155 mm Number of bounces to stop 4 7 It can be seen from the results obtained that the treated foam is considerably more resilient than the untreated foam.

In applying the invention to the production of packaging materials, it is proposed that a set of panels to form a liner for a carton may be cut from a sheet of expanded plastics material, expanded polystyrene being the preferred material. The sheet material may be compressed and released prior to the cutting out of the liner panels by any conventional means such as hot-wire cutting, the compression being achieved either by using a platen press, or by passing the sheet material between two fixed rolls to momentarily reduce its thickness.

Alternatively, the shaping of the sheet material into panels to line a carton may be effected simultaneously with the compression treatment, by using a die cutting technique. In such a technique, the untreated sheet will be supported on a fixed platen, and a moving platen provided with an array of blades will be brought towards the fixed platen. The extent to which the blades project above the moving platen will be arranged so that, as the blade edges touch the fixed platen, the spacing between the fixed and moving platens is a predetermined proportion of the thickness of the untreated sheet material, so that the sheet material is simultaneously compressed and cut into liner panels.

As a further alternative, the liner panels may be cut by any conventional process or by die cutting from a sheet of untreated plastics foam material, and the shaped panels may then be treated by passing them between a pair of compression rollers, or by compressing them between platens to a predetermined proportion of their original thickness.

In addition to the production of lining panels for cardboard cartons, it is envisaged that the treated foam material may be used in other applications where resilience is required.

Claims

1. A method of altering the resilient properties of a plastics foam sheet material of a first thickness, comprising crushing the material to a second thickness which is a predetermined proportion of its first thickness, and releasing the crushing pressure to allow the foam to recover to a third thickness.

2. A method according to Claim 1 in which the sheet material is crushed between two platens of a press.

3. A method according to Claim 2, wherein the sheet material is held at the second thickness for a predetermined period before releasing the crushing pressure.

4. A method according to Claim 1, wherein the sheet material is crushed to its second thickness by passing it between two rollers spaced by a distance equal to the second thickness.

5. A method according to any of Claims 2 or 3, wherein the sheet material is simultaneously formed into individual shaped sheets, the method comprising placing the sheet material between two platens, bringing the platens together until the spacing therebetween is equal to the second thickness, and thereafter moving the platens apart, one of the platens being provided with an array of blades projecting from its surface and arranged so as to cut the sheet material into the required shaped, the blades projecting from the platen to an extent equal to the second thickness.

6. A method according to Claim 4, wherein the rollers are provided with blades so that as the sheet material passes between the rollers it is simultaneously crushed and cut to shape.

7. A method of simultaneously altering the resilient properties of a sheet of foamed plastics material, and forming a packaging blank therefrom, comprising the steps of placing a sheet of plastics material of a first thickness on a fixed platen, providing a second, moving, platen with an array of blades projecting from its surface to an extent less than the said first thickness, the array of blades defining the outline of the packaging blank to be cut, bringing the moving platen towards the fixed platen so that the edges of the blades contact the fixed platen to sever the sheet material while the platens crush the sheet material to a predetermined second thickness, drawing the moving platen away from the fixed platen, and removing the cut sheet material from the platens.

8. A plastics foamed sheet material whose resilient properties have been altered by a method according to any of Claims 1 to 5.

9. A plastics foam panel for use in packaging, produced by a method according to Claims 6 or 7.