CREASING OF SHEET MATERIAL

Abstract: A method of creasing plastics sheet material which comprises providing a mould having the desired shape, heating the mould, and bringing the mould into contact with the sheet material under pressure. The mould has the desired shape of the end product, for example a box blank, and may contain both cutting and creasing rules as well as other product features as desired. A single mould may be used in conjunction with a flat plate or a complementary double mould system may be used, especially for thicker materials or where a central hinge effect is required. By this means, the creasing is obtained by heat deformation (rather than simple pressure of a creasing rule) and sealing of the sheet material takes place at the same time thereby destroying elastic memory and ensuring that the dimensions of the creased area remain constant after creasing.

Description: CREASING OF SHEET MATERIAL This invention relates to the creasing and/or sealing of sheet material, in particular the creasing of relatively thick plastics sheet material. Plastics and other, e.g. board, sheet materialε are traditionally creased by means of a creasing rule. Creases are primarily used to give a hinge effect, for example in the manufacture of blanks for subsequent assembly into cartons. The creasing may be carried out in conjunction with cutting the outline shape of the blank so that the total blank can be stamped out in one operation. However, the use of traditional creasing rules with plastics material has a number of limitations. High pressure is needed and the machinery is thus relatively expensive, particularly where the sheet to be deformed is relatively thick. Moreover, in view of the elastic memory of plastic material, a constant and predictable thickness of the creased area cannot be guaranteed. In addition, only relatively thin creasing lines can be obtained. If a very thick sheet needs to be creased the risk of breakage of the material is present. Also, a double hinge effect is very difficult to obtain if required since creasing the material from both sides simultaneously often causes breakage of the sheet. The invention is primarily concerned with the creasing of thermoplastic sheet material, either homogeneous or alveolate (for example corrugated or I-beam structured) , of a thickness ranging from 1 mm to 100 mm. While the invention is equally applicable with the lesser thicknesses, it is particularly aimed at thicker materials where traditional methods are not satisfactory. The invention seeks to provide a method of sealing for such aterials improved in the above respects. According to the present invention there is provided a method of creasing plastics sheet material which comprises providing a mould having the desired shape, heating the mould, and bringing the mould into contact with the sheet material under pressure. The mould has the desired shape of the end product, for example a box blank, and may contain both cutting and creasing rules as well as other product features as desired. A single mould may be used in conjunction with a flat plate or a complementary double mould system may be used, especially for thicker materials or where a central hinge effect is required. By this means, the creasing is obtained by heat deformation (rather than simple pressure of a creasing rule) and sealing of the sheet material takes place at the same time thereby destroying elastic memory and ensuring that the dimensions of the creased area remain constant after creasing. It is preferred that the creasing rule has a rounded configuration so as gently to deform the plastic sheet material and avoid breakage, in contrast with previous creasing rules which are relatively pointed in profile. The temperature to which the mould is heated, and the pressure applied, will vary in accordance with the particular thermoplastic material used, the sheet thickness, and the sheet structure (depending on whether the sheet is homogeneous or alveolate) . However, it is usually preferred to heat the mould to a temperature just below the melting point of the plastics material of the sheet. Ideally, both parts of the mould should be heated to the same temperature, that is the parts in contact with both sides of the sheet are heated similarly. The heating of the mould may be carried out by means of an associated heating plate which is itself heated by any suitable means such as steam, oil, or electrical resistance heating. The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1(a) is a plan view of a mould of the present invention; Figure 1(b) is a section taken on line A - A of Figure 1(a); Figures 2(a) - 2(d) illustrate the mould action; Figure 3 is a view of the section of the creasing rule on an enlarged scale; Figure 4 illustrates the creasing action; and Figure 5 illustrates the traditional rule creasing action. Referring to the drawings, and in particular Figures 1 to 4, a mould generally designated (10) for producing a blank suitable for making up into a box or carton comprises a cutting rule (12) and a creasing rule (14) . As required, other desired features such as dies (16) for the formation of holes, perforations or depressions in the box botto are also provided. The mould (10) may be used on its own with a sheet material (18) resting on a flat plate or platen but as illustrated a complementary mould (10') (Figure 2) is provided. This configuration is particularly useful with thicker plastics material (18) . The mould (10) is heated by means of a heating plate (20) containing passageways (22) through which a heated medium such as steam or oil can be passed. Alternatively, electrical resistance heating or high frequency heating, or a combination of both, could be employed. Operation of the device is illustrated best in Figures 2, 3 and 4. As can be seen from Figure 2, a pair of complementary moulds (10) and (10') are brought together sandwiching a sheet (18) of plastics material. As the moulds move into full register (Figure 2(c)) the sheet material (18) is cut, creased and otherwise deformed to leave the final blank (18') - (Figure 2(d)) . The moulds (10) and (10') are heated thus ensuring that the elastic memory of the plastics sheet material (18) is destroyed and the shape (18') is therefore stable. As can be seen from Figures 3 and 4, the creasing rule (14) has a rounded edge portion so as to have a relatively gentle action on the plastic material (18) and produce a crease as illustrated at (24) . This is in marked contrast to the crease produced by the traditional creasing rule illustrated in Figure 5 from which it will be seen that a relatively pointed blade is pressed into the sheet (1) and then retracted (2) after deforming the sheet (3). The crease so formed (24') changes in dimensions (4) owing to the elastic memory of the thermoplastic material. The method of the invention provides a number of advantages over the prior process. In particular a constant and predictable thickness of the creased areas is obtained; the creased areas can be of any type, shape and width; and various constant thicknesses of different creased areas can be produced within the same blank using a single mould.

Claims: CLAIMS 1. A method of creasing plastics sheet material which comprises providing a mould having the desired shape, heating the mould, and bringing the mould into contact with the sheet material under pressure. 2. A method as claimed in claim 1 in which the mould contains both cutting and creasing rules. 3. A method as claimed in either of claims 1 or 2 in which a single mould is used in conjunction with a flat plate. 4. A method as claimed in claims 1 or 2 in which a complementary double mould system is used. 5. A method as claimed in any of claims 1 to 4 in which the creasing rule has a rounded configuration so as gently to deform the plastic sheet material and avoid breakage. 6. A method as claimed in any of claims 1 to 5 in which the temperature to which the mould is heated, and the pressure applied, varies in accordance with the particular thermoplastic material used, the sheet thickness, and the sheet structure. 7. A method as claimed in claim 6 in which the mould is heated to a temperature below the melting point of the material of the sheet. 8. A method as claimed in any of claims 1 to 7 in which the mould is heated by means of an associated heating plate which is itself heated by steam, oil, electrical resistance or high frequency heating, or a combination thereof.

Inventors: MOEDER CLAUDIO, MOEDER, CLAUDIO
Applicants: FRA MO SNC, MOEDER CLAUDIO, WHARTON PETER ROBERT, FRA.MO SNC DI FRANCA RIVA & C, MOEDER, CLAUDIO, WHARTON, PETER, ROBERT
Application year: 1996
Main classification: B29C59
IPC codes: B29C37, B29C53, B29C59