GB2323057A

GB2323057A - Finishing machine for foil and plate manufacture

Info

Publication number: GB2323057A
Application number: GB9705310A
Authority: GB
Inventors: Adolf Seide
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-17
Filing date: 1997-03-14
Publication date: 1998-09-16
Anticipated expiration: 2017-03-14
Also published as: GB9705310D0; DE19605951C2; DE19605951A1; GB2323057B

Abstract

Finishing machine for the manufacture of thermoplastic plastics plates and foils, which may be finished on both sides, is described which is applicable both to the manufacture of plates with thicknesses of, for example, 50 mm and more and to surface finished flat foils with very small thicknesses despite the very different respective prerequisites for such manufacturing objective. The new finishing machine has its inlet gap facing the slit nozzle (2) of an extruder, the gap being formed between a finishing and cooling roller (3) and an endless metal belt (6) rotating around two guide rollers (4 and 5) adjacent to the finishing roller (3). The metal belt (6) partially winds round the finishing roller (3) in the circumferential direction and with it forms a gap for the passage of the plastics melt film (1) issuing from the slit nozzle (2). There may be a second finishing roller 9 onto which the foil winds from the roller 3. Roller 9 may have a clearance from roller 3 and include its own metal belt 6. There may be a cooling device 13. Roller 3 may be a cooling roller. Belt 6 may cover more than one half the circumference of the finishing roller. Other arrangements are disclosed.

Description

Finishing Machine For Foil And Plate Manufacture The invention relates to a finishing machine for use in the manufacture of foils and plates finished on both sides.

In the manufacture of foils and plates from thermoplastic plastics, depending on the desired end use there is frequently the desire, or even the necessity, to provide at least one of the two sides, or even both sides, with a structured, or even with a matt or bright smooth surface. Various procedures are known for achieving this, these procedures depending substantially on the thickness of the finished foil sheet or plate which it is intended to attain.

In the manufacture of thin foils with a thickness of about 0.5 mm or less, it is known, for example, to press the melt issuing from an extruder nozzle by means of an air nozzle, also called air brush or air knife, against a finishing roller and to cool it by means of this finishing roller and then to guide the formed foil sheet around one or more additional finishing rollers, before the finished foil sheet is then supplied onwards to its end use. In this method, the foil sheet can only be made to reflect light on one side and the thickness of the foil sheet attained results indirectly from the throughput of the extruder and from the draw off speed used.

Foil sheets which are smooth on one side can also be manufactured in thicknesses down to less than about 0.2 mm in known manner with the use of electrostatic measures. The melt issuing from the slit die of the extruder is here pressed with electrostatic means against a finishing roller arranged after the slit nozzle and is then guided by this finishing roller by way of one or more additional finishing rollers.

In the manufacture of plates and foils which are finished on both sides and have a thickness range of about 50 to 0.5 mm, it is conventional to introduce the plastics melt, which is plasticized in the extruder and is discharged by way of a slit nozzle in the form of a film, a sheet or suchlike, into the gap of predetermined width formed by two finishing rollers arranged in the region of the slit nozzle and to guide the plastics melt through this gap. The differences in thickness of the melt film are levelled out and the surface shine or the surface pattern of the two finishing rollers is applied to the plastics sheet (plate or foil) which has in the process been formed on cooling, whereupon the plastics sheet is if necessary guided around one or more additional finishing rollers and is finally supplied to its intended end use.

Because the surface temperature of the finishing rollers is substantially lower than the temperature of the plastics melt, the temperature of the plastics material, decreases at a relatively great speed, with corresponding viscosity increases to below the softening or crystallization point, thereby affecting the hardness for use. In this respect, not only are the material properties of the thermoplastic plastics used dependent on the thickness of the melt film, i.e.

the supply of thermal energy inherent therein, but so is the cooling speed.

With very small melt film thicknesses the cooling of the melt can already take place in the first roller gap so much so that the increase in hardness is so great that the plastics can no longer roll out below a certain thickness. In the process, the forces occurring between the rollers can become so great that the finishing rollers deform elastically and in this way impermissible deviations in thickness occur in the plastics sheet.

Apart from the thermomechanical properties of the plastics used, the minimum finished thickness of a foil sheet is limited by the elastic deformation of the finishing rollers with respect to their bending and flattening, i.e. bulging, namely because of the danger of mutual contact of the finishing rollers, the increasingly worsening thickness tolerance of the foil sheet and finally because of the inadmissibly growing roller gap forces.

To be able to manufacture flat foils in thicknesses below the limit applicable to finishing on both sides, contacting of the plastics melt with the second finishing roller is dispensed with and the minimum required pressure of the plastics melt against the one finishing roller is generated, the lack of an applied surface shine on the second side of the arising foil sheet and of the lack of levelling of the differences in foil thickness by the air nozzle mentioned above or by electrostatic means then having to be accepted. With these procedural methods, because the cooling speed is lower than when two finishing rollers are used, when semi-crystalline thermoplastics are cooled, properties appropriate to end use other than those obtainable by finishing between two finishing rollers also result.

In order to compensate for the mechanical roller deformation it is also possible to use as second finishing roller a roller with elastomer surface coating, with the elastomer roller surface allowing passage of the plastics melt or plastics foil, as the case may be, through the roller gap with differences in thickness, being accommodated without inadmissibly high forces occurring or acting between the rollers.

However, here too, the disadvantages of finishing on only one side and of the lack of levelling of the foil thickness also occur.

According to the present invention, there is provided a finishing machine for the manufacture of foils and plates made of thermoplastic plastics material finished on both sides and produced from melt discharged by an extruder by way of a slit nozzle, which machine includes a slit nozzle for extrusion of the plastics melt and comprises a finishing roller and, opposed thereto and defining therebetween an inlet gap facing the slit nozzle, a support-free region of an endless metal belt rotating around a pair of guide rollers, which metal belt is arranged tangentially to the finishing roller, winding partially round it in the circumferential direction in the region between the guide rollers.

With such a device, it is possible to achieve both the manufacture of plates of thermoplastic plastics, finished on both sides, up to a thickness of, for example, 50 mm and more, and the manufacture of flat foils of thermoplastic plastics, finished on both sides, up to very small thicknesses which lie below the hitherto usual limit for foils finished on both sides.

With the use of a finishing roller known in itself on the one hand and a thin elastic rotating endless metal strip on the other hand, it is possible to achieve advantageously the result that a plastics melt sheet issuing from the slit nozzle of an extruder, during its passage through the gap formed between the glazing roller and the rotating endless metal strip, is made to have a finish which may be a shine or a pattern applied to both surfaces without a melt bead being formed due to unavoidable small differences in thickness of the melt sheet in the inlet region of the gap. Indeed, one surface may be given one type of finish and the other another type of finish. The formation of a melt bead is prevented by the elastic deformability of the thin metal belt.

It is also an advantage that the rate of cooling with a thin plastics melt sheet can be kept lower by the limited heat absorption capacity of the metal belt in contrast to the greater heat absorption capacity of a pair of finishing rollers. Furthermore, in particular with relatively thick plastics melt sheets, it is an advantage that, as a consequence of the relatively large angle of contact of the metal belt with the finishing roller, a correspondingly large-area mechanical support of the plastics melt sheet is ensured, quite in contrast to a mere linear contact between the finishing rollers and the plastics melt sheet with the use of two finishing rollers which oppose each other.

It is particularly advantageous to use a seamless endless metal belt. On the one hand this has the advantage that an undesirable marking of the plastics sheet by a seam region of the metal belt is avoided, and on the other hand the seamless belt meets demands with respect to the constantly occurring alternating bending stresses to a greater extent than a metal belt which is joined to form an endless belt by means of the formation of a seam. Finally, a seamless endless metal belt also allows, in a favourable manner, the use of smaller guide radii and therefore guide rollers which are dimensioned to be smaller in diameter. This in turn makes it possible on the one hand to position the guide roller which is adjacent to the slit nozzle of the extruder relatively closely to the outlet gap of the slit nozzle and on the other hand to use very thin metal belts.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made, by way of example only to the accompanying drawings only, wherein.

Figure 1 shows in schematic representation a side view of a finishing machine embodying this invention having an inlet gap formed by a finishing roller and an endless metal belt; Figures 2a and 2b show in the same manner a finishing roller and an endless metal belt with adjusting and tensioning device in operative and nonoperative states respectively; Figure 3 shows a variant of Figure 1; Figure 4 shows another variant of Figure 1 with a second rotating metal belt at the second finishing roller; Figure 5 shows a finishing roller with an endless belt winding around about half of it; Figure 6 shows an embodiment with a finishing roller and two endless metal belts arranged behind each other and cooperating with the finishing roller; Figure 7 shows an embodiment where the melt film is pressed by means of low pressure against the finishing roller, and Figure 8 shows an embodiment for the use of the metal belt as supporting belt when the melt layer is thick.

Throughout the drawings, like reference symbols are always used for the same parts.

In Figure 1, a plastics melt strip 1 moves downwards out of the slit nozzle 2 of the extruder, which is otherwise not shown, into a gap 7 formed between a finishing and cooling roller 3 and the endless metal belt 6 rotating around the guide rollers 4 and 5, whereby plastics film 8 being formed is made shining on both sides by the finishing roller 1 and the metal belt 6 as a result of the roller 3 and belt 6.

After leaving the region of the metal belt 6 the plastics foil is guided further around the finishing roller 1 and through a roller gap 10 of specified width formed with a second finishing roller 9 and is finally guided further over the second finishing roller 9.

Instead of there being mere linear contact between the plastics foil 8 and the finishing rollers 3 and 9 in the roller gap 10, the metal belt 6 winds around the finishing roller 3 over a considerable part of its circumference. In particular the plastics melt film 1 makes contact with the metal belt 6 in a region which runs substantially tangentially off from the guide roller 4 and runs substantially likewise tangentially on to the finishing roller 3. In this way a contact is attained which is not only linear but rather areal and differs from that attained with the conventional use of two finishing rollers which cooperate with each other.

In this way it is not only possible to influence the plastics mass located between the finishing roller 3 and the metal belt 6 over a large distance insofar as applied pressure and temperature are concerned but, as a result of the use of the substantially rigid finishing roller 3 with the elastic metal belt 6, a shine or pattern from the metal belt is applied without gaps onto the surface of the solidifying plastics melt despite potential small differences in thickness of the plastics melt film. This is all because the metal belt compensates for these differences elastically.

Apart from a cooling of the plastics melt 1, entering between the finishing roller 3 and the metal belt 6, resulting from use of the finishing roller 3 which also acts as cooling roller, a cooling is also effected by the metal belt 6 when the guide roller 4 and/or the guide roller 5 are constructed as cooling rollers, one or the other of which is additionally also constructed as drive roller.

As a result of the arrangement and construction of the guide rollers 4 and 5 and the metal belt 6, a gap or spacing of predetermined width, filled with the plastics melt 1, inevitably results between the finishing roller 3 and the metal belt 6, with the thickness of the manufactured foils thereby being defined. As can be appreciated from the drawings, it will be easily possible also to effect a greater winding around the finishing roller 3 than that shown by the use of a longer metal belt 6. Likewise it can be easily recognized that with the use of a guide roller 4 of smaller diameter it is possible to move the roller gap 7 closer to the slit nozzle 2, whereby the plastics melt 1 can be influenced very soon after the plastics melt 1 has left the slit nozzle 2.

The slit nozzle 2 indicated with broken lines shows that it is possible to modify the extrusion of plastics suitably to different arrangements and constructions of the guide rollers 4 and 5 and the metal belt 6 through appropriate arrangement of the slit nozzle 2, so that the best possible entry of the plastics melt 1 into the inlet gap 7 formed is attained in any one case according to the given conditions.

According to Figures 2a and 2b the guide rollers 4 and 5 are mounted in lateral links 11 and can be adjusted by them - as indicated by the arrows - in the direction of the finishing roller 3 into the operating position (Figure 2a) or away from the finishing roller into the non-operative state (Figure 2b). Apart from being influenced by the adjusting movement in the direction of the finishing roller 3, the application force and the tension of the metal belt 6 can additionally be influenced by a spring tensioning device 12 in the desired or required manner.

In the embodiment of Figure 3 a cooling device 13 indicated with broken lines is arranged within the endless metal belt 6. This cooling device can be provided to supplement the effect of the construction of the guide rollers 4 and/or 5 as cooling rollers or can be provided in place of this function.

Furthermore, within the endless metal belt 6 is arranged a tensioning roller 14 indicated with broken lines and by means of which the tension of the metal belt 6 can be appropriately influenced. In addition, in this respect, it can also be provided that the spacing between the guide rollers 4 and 5 can be varied so that in this way it is possible additionally to influence the tension of the metal belt 6 and therefore its application force in the direction of the finishing roller 3, and therefore also the adjustment of the gap width between the finishing roller 3 and the metal belt 6.

According to Figure 4, an endless metal belt 6 rotating around guide rollers 4 and 5 is not only associated with the first finishing roller 3, but in the same way, a second such belt is associated with the second finishing roller 9. In this way, the result is achieved that the melt strip is cooled on both sides over a longer distance than with mere line contact and the curvature imparted to the solidifying melt strip is minimised.

The supply of the plastics melt strip 1 from the slit nozzle 2 takes place here substantially horizontally, in contrast to what has been shown hitherto herein. However, it could of course also take place in a more or less vertical or inclined direction because, in a finishing machine in accordance with the invention, basically any supply direction is possible.

The construction of roller gaps with linear contact between two adjacent rollers and with the plastics film guided between them is also avoided in the embodiment of Figure 5, where the single finishing roller 3 is areally covered by the endless metal belt 6 travelling over approximately one half the circumference of the finishing roller 3. Here the metal belt 6 runs over the three guide rollers 4 and 5 and the roller 14 which is advantageously constructed as tension roller. If required, the individual guide rollers may be provided and constructed as cooling roller and drive roller. Two cooling devices 13 are additionally provided within the metal belt 6.

However, if they are provided, then the construction of the guide rollers as cooling rollers may be dispensed with.

According to Figure 6 the plastics melt 1 is brought from the slit nozzle 2 at the upper side of a single finishing roller 3 of relatively large diameter diagonally downwards into the gap 7 between the finishing roller 3 and a first rotating metal belt 6 and the foil produced is then guided through the gap between the finishing roller 3 and a second metal belt 6 arranged with clearance therefrom and is finally guided over the guide roller 15 away from the finishing roller 3. With regard to the construction of the metal belts 6 and the guide rollers 4 and 5 as cooling and/or drive roller and the additional cooling devices and finally also the possibility of tensioning the metal belts by changing the clearance between the guide rollers 4 and 5 and/or adjustment in the direction towards or in the direction away from the finishing roller 3, the same criteria apply as have already been described previously in connection with the other Figures. Instead of introducing the plastics melt into the upper region of the finishing roller 3 it could of course also be provided at another position, for example approximately at the level of the axis of the finishing roller 3.

The arrangement and construction of Figure 7 corresponds substantially to that of Figure 6, apart from the fact that only one pair of guide rollers 4 and 5 and correspondingly also only one endless metal belt 6 is provided and that a pressing of the plastics melt 1 against the finishing roller 3 during entry into the gap 7 is achieved by under a low generated pressure.

Finally, Figure 8 shows the use of the endless metal belt 6 rotating around the guide rollers 4 and 5 as support belt and finishing device with a thick melt layer on a finishing roller 3 which has a relatively large diameter. The plastics melt 1 issuing from the slit nozzle 2 is initially guided through the gap formed between the finishing roller 3 and the supporting roller 16 and thereafter through the gap formed between the finishing roller 3 and the metal belt 6 in order to be finally guided through gap 10 formed between the finishing roller 3 and an additional finishing roller 9 before being guided away. With regard to the construction of the guide rollers 4 and 5 as cooling and/or drive roller, the possibility of tensioning the metal belt 6 and adjustment in the direction towards the finishing roller 3 or also away from it, additional cooling devices etc, the requirements set out earlier herein apply equally well here.

The different exemplifying embodiments shown, indicate how numerous variants of the inventive concept are conceivable without departing from the basic idea of the invention.

Claims

1. Finishing machine for the manufacture of foils and plates made of thermoplastic plastics material finished on both sides and produced from melt discharged by an extruder by way of a slit nozzle, which machine includes a slit nozzle for extrusion of the plastics melt and comprises a finishing roller and, opposed thereto and defining therebetween an inlet gap facing the slit nozzle, a support-free region of an endless metal belt rotating around a pair of guide rollers, which metal belt is arranged tangentially to the finishing roller, winding partially round it in the circumferential direction in the region between the guide rollers.

2. Finishing machine according to claim 1, wherein the endless metal belt is constructed as a seamless belt.

3. Finishing machine according to claim 1 or 2, wherein the guide roller of said pair which is nearer to the slit nozzle is constructed as a drive roller.

4. Finishing machine according to any one of claims 1 to 3, wherein at least one of the pair of guide rollers is constructed as cooling roller.

5. Finishing machine according to any one of claims 1 to 3, additionally comprising, a cooling device arranged in the region of the section of the endless metal belt facing the finishing roller.

6. Finishing machine according to claim 5, which comprises cooling provision for the plastics material constituted by said cooling device and at least one of the guide rollers constructed as a cooling roller.

7. Finishing machine according to any one of claims 1 to 6, wherein the guide roller adjacent to the slit nozzle is arranged in such a way that the plastics melt issuing from the slit nozzle in use makes contact with the endless metal belt in a region of the metal belt which faces the finishing roller, the region being located behind this guide roller and extending from it tangentially to the finishing roller.

8. Finishing machine according to any one of claims 1 to 7, wherein in that a tensioning roller is arranged between the guide rollers and within the endless metal belt and the spacing between the guide rollers is variable.

9. Finishing machine according to any one of claims 1 to 8, wherein the guide rollers are rotatably mounted in lateral connection links or clamps.

10. Finishing machine according to claim 9, wherein one of the guide rollers mounted in the lateral mountings includes a tensioning device.

11. Finishing machine according to claim 10, wherein the tensioning device is a tension or compression spring.

12. Finishing machine according to one of claims 9, 10 or 11, wherein the lateral links are adjustably arranged together at right angles to the direction of the axis of the finishing roller.

13. Finishing machine according to any one of claims 9 to 12, wherein the lateral links are adjustably arranged in the circumferential direction of the finishing roller.

14. Finishing machine according to any one of claims 1 to 13, comprising two said endless metal belts with guide rollers, one belt being arranged adjacent to the slit nozzle and the other being arranged downstream thereof.

15. Finishing machine according to claim 14, wherein said other endless metal belt is arranged in the region of a finishing roller which is arranged with clearance after the finishing roller which is adjacent to the slit nozzle.

16. Finishing machine according to any one of claims 1 to 15, wherein the g de rollers are formed from an elastomer material or Are formed as rollers coated with an elastomer.

17. Finishing machine according to any one of claims 1 to 16, wherein the or each rotating metal belt is adapted to be pressed with defined force against its associated finishing roller and the plastics melt film located between the finishing roller and the metal belt.

18. Finishing machine according to any one of claims 1 to 17, wherein the metal belt surface facing its associated finishing roller and the plastics melt film is polished to give a mirror finish.

19. Finishing machine according to any one of claims 1 to 18, wherein the metal belt surface facing its associated finishing finishing roller and the plastics melt film is provided with a relief pattern.

20. Finishing machine for the manufacture of foils and plates, substantially as hereinbefore described with reference to, and as shown in, any one of Figures 1 to 8 of the accompanying drawings.