GB2069935A - Film Embossing - Google Patents

Abstract

According to this invention a method of producing roll embossed film comprises passing a film (10) consecutively through a nip between a grooved roll (22) and a first plain roll (20), passing the film around the grooved roll (22) and passing the film through a nip between the grooved roll and a second plain roll (24), said grooved roll (22) being heated. Preferably the first plain roll (20) may also be heated and the three rolls may be disposed with their axes in a common plane. The film material may be polyethylene or polypropylene. <IMAGE>

Description

SPECIFICATION Film embossing This invention concerns film embossing.

Processes have been known for some time which involve passing a sheet of film of plastics material, such as, and especially, polypropylene and polyethylene, between two rolls whilst the film is hot, usually at a temperature lower than its crystalline melting point. For example the manufacture of various products by processes involving such a step, one or both rolls being heated and one or both rolls being "textured" with a succession of fine annular grooves, is described in UK Patent Specification No. 1260837. Such a step is known in the art as the roll embossing of film and the film after passage between the rollers is known as roll embossed film (REF).

In order to produce satisfactory REF substantial pressure must be exerted by the rolls. Because bending of the rolls causes inaccuracies in the grooves embossed on the film, large diameter rolls are used, since these allow the use of high pressure without excessive bending. However, the problem of bending leads to progressively greater difficulties when designing machines to process increasing widths of film. The reason for this is that increase in roll length to cope with wider film requires even greater roll diameters if bending is to be kept within acceptable bounds, and this leads to serious problems in forming the grooves in the rolls, as well as heavy expense since the rolls are made from expensive tool steel or similar material. The grooves are very fine (e.g. 1 0-30 per cm) and must be ground in using a very accurately profiled grinding wheel.Because of the considerable increase of wear on the grinding wheel which occurs when grinding fine annular grooves in a roll it is both difficult and timeconsuming to produce such large-diameter rolls with grooves of the required accuracy.

It is plain that, if the roll pressures required could be reduced, then rolls of smaller diameter could be used, and the problems and difficulties referred to above considerably eased. That is the object of the present invention, and according to it REF is produced by passing it first through the nip between a grooved roll and a plain roll, then around the grooved roll, and then through the nip between the grooved roll and another plain roll, at least the grooved roll being heated. We have found that by proceeding in this way the roll pressures needed are relatively modest so that, even with long rolls, the roll diameter is kept down and the expense and difficulty of making large diameter rolls is entirely avoided.

In preferred embodiments the grooved roll is of substantially smaller diameter than the plain rolls, and indeed can be of smaller diameter than the grooved rolls conventionally used for processing film of half the width of those which can be processed by using the present invention. The plain rolls are preferably heated as well as the grooved rolls. Conveniently the film passes halfway around the grooved roll in moving from the first nip to the second.

The invention extends to apparatus for putting this process into effect and to REF so produced.

The invention will now be described further, by way of example only, with reference to the accompanying drawings, in which:~ Fig. 1 is a diagram illustrating a typical prior art process for making REF; and Fig. 2 is a diagram illustrating a process for making REF in accordance with the present invention.

In the diagrams the thickness of the film and the depth of the roll grooves are very greatly exaggerated to assist in an understanding of the present invention.

In the typical prior art process illustrated in Fig. 1 the film 10 passes successively around a guide roller 12, a heated plain roll 14, and a heated grooved roll 16, at a speed of 30 metres per minute. This enables REF for subsequent conversion into tape for carpet backing to be produced. The rolls 12, 14 are 25 cm in diameter, are of sufficient width to process film 80 cm wide.

In order to produce proper profiling the roll temperatures must be in the range 800C-1 100C and the pressure on the film must be between 45-90 kg per cm length of the nip through which it passes. It will be noted that the opposite surface of the film to that which passes in contact with the grooved roll 16 is heated during its passage in contact with the plain roll 14 before the film reaches the nip, which is obviously not the best surface to heat. It would be pointless to reverse the direction of the film and to pass it over a substantial part of the circumference of the grooved roll 16, because the lands between the grooves are usually about .025-.05 mm wide so that heat transfer to the film would be extremely poor.The pressures required would be reduced if the film could be more effectively pre-heated, but this would require additional film pre-heat rolls in order to obtain limited benefits, and this would be costly.

Turning now to Fig. 2 the film 10 passes around a guide roller 18, around a heated plain roll 20, through the nip between the roll 20 and a heated grooved roll 22, around the roll 20, and through the nip between the roll 22 and a heated plain roll 24. The rolls are heated by circulating hot oil to between 800C and 1 00C and are wide enough to process film 2 metres in width. The plain rolls are 32 cm in diameter and the grooved roll 15 cm in diameter. We anticipate that wider, but otherwise substantially the same, REF as described in connection with Fig. 1 can be produced at a speed substantially higher and with roll pressures substantially lower than when using the apparatus of Fig. 1, and without any unacceptable bending of the rolls. It will be seen from the diagram that the grooves start to be formed in the nip between rolls 20, 22, and that the film is further heated as it passes around the grooved roll 22. This further heating is very effective, since there is good and extensive surface contact with the hot roll 22, and the heat is applied exactly where it is needed.

Consequently when the film passes through the nip between rolls 22, 24 it is further embossed to its finished profile very readily with the reduced roll pressure employed. As will be seen the diameter of the grooved roll 22 is actually less than that of the grooved roli 1 6, and no additional pre-heat rolls are needed.

Claims (17)

1. A method of producing roll embossed film comprising passing a film through a nip between a grooved roll and a first plain roll, passing the film around the grooved roll and passing the film through a nip between the grooved roll and a second plain roll, said grooved roll being heated.

2. A method according to Claim 1 , wherein said first plain roll is heated.

3. A method according to Claim 1 or 2, wherein said rolls are disposed with their axes of rotation substantially in a common plane.

4. A method according to any one of the preceding claims wherein the diameter of said grooved roll is less than the diameter of either of said plain rolls.

5. A method according to any one of Claims 2 to 4, wherein said film is caused to pass around more than one half of the circumference of said first plain roll.

6. A method according to any one of Claims 2 to 5, wherein said second plain roll is heated.

7. A method according to any one of the preceding claims for forming a roll embossed film composed of either polyethylene or polypropylene.

8. A method according to Claim 7, wherein said heated rolls are maintained between 800C and 1100C.

9. A method of producing roll embossed film substantially as hereinbefore described with reference to and as illustrated in Fig. 2 of the accompanying drawings.

10. A roll embossed film producing apparatus comprising a rotatably mounted grooved roll, rotatably mounted first and second plain rolls, disposed adjacent said grooved roll the axes of rotation of said rolls being substantially parallel, and means for heating said grooved roll.

11. An apparatus according to Claim 10 incorporating means for heating said first roll.

12. An apparatus according to Claim 10 or 1 1, wherein the rolls which are heated are provided with internal passages for circulation of heated fluid.

13. An apparatus according to any one of Claims 10 to 12 wherein said axes of rotation lie substantially in a common plane.

14. An apparatus according to any one of Claims 10 to 13, incorporating a guide roller arranged to maintain the film in contact with at least one half of the circumference of said first plain roll.

15. An apparatus according to any one of Claims 10 to 14, wherein the diameter of said grooved roll is less than the diameter of either of said plain rolls.

16. An apparatus for producing roll embossed film substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

17. A roll embossed film produced in accordance with the method claimed in any one of Claims 1 to 9 or by apparatus as claimed in any one of Claims 10 to 16.