Stripping Of Thin Films

Abstract

Apparatus for stripping a continuous thin film from a support web on which it has been formed, comprises a pair of closely spaced driven stripping rolls disposed with their axes horizontal, an idler roll positioned on either side of the pair of stripping rolls and spaced from and parallel to the adjacent stripping roll, a take-up roll resting on each stripping roll and its adjacent idler roll and supported only by them, and means for preventing axial movement of the take-up rolls while allowing rotational and radial movement thereof.

Description

This invention is concerned with the stripping of continuous thin film from the support web on which it is formed.

It is known to make thin film of from 0.5 to 6 micron thickness of various polymers, such as cellulose esters, cellulose ethers, polystyrene, polyurethane, polysulphones, and polycarbonates, by casting a solution of the polymer on to a moving support web and drying the coating obtained to remove the solvent and leave a thin film of the polymer on the support web. The support web, carrying the thin film, is then commonly reeled with an interleaved paper web to protect the thin film. The thin films thus obtained are used for the production of capacitors after they have been metallised on one surface and for this purpose they must be stripped from the support web either before or after they have been metallised.

Whether or not the thin film is metallised, it is a delicate material in which longitudinal creases are readily formed when it is under tension. It is difficult to avoid the formation of such longitudinal creases during stripping of the thin film from the support web using conventional stripping procedures and equipment, and we have now developed an improved stripping apparatus and procedure which substantially reduces this difficulty.

The apparatus according to the invention comprises a pair of closely spaced stripping rolls disposed with their axes horizontal and which, in operation, are driven, an idler roll positioned on either side of the pair of stripping rolls and spaced from and parallel to the adjacent stripping roll, a take-up roll resting on each stripping roll and its adjacent idler roll and supported only by them, and means for preventing axial movement of the take-up rolls while allowing rotational and radial movement thereof.

The method of stripping according to the invention comprises feeding the support web and adherent thin film upwardly into the gap between the pair of stripping rolls, the gap between the rolls being just greater than the combined thickness of the support web and the thin film, taking the thin film over a part of one of the stripping rolls and on to the take-up roll supported by that stripping roll, and the support web over a part of the other stripping roll and on to the other take-up roll, the take-up rolls being rotated by their contact with the driven stripping rolls.

In order that the invention may be more fully understood, a preferred embodiment of stripping apparatus, and the operation thereof, will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic elevation of the apparatus;

FIG. 2 is an elevation, on an enlarged scale, of part of the apparatus of FIG. 1 showing the means for mounting one of the idler rolls and one of the take-up rolls, and

FIG. 3 is a section through the spindles of the stripping rolls of FIG. 1 showing the drive mechanism therefor.

The apparatus comprises a pair of horizontally disposed closely spaced stripping rolls 10, 11 which are mounted so that the gap between them is adjustable and it is adjusted to a distance just greater than the combined thickness of the support web (which is typically 25 microns thick) and the thin film (which is typically 2 microns thick). On either side of the stripping rolls 10, 11 are horizontally disposed idler rolls 12 and 13, respectively, which are spaced from and parallel to the adjacent stripping roll. The ends of the spindles 23 of the idler rolls 12 and 13 are mounted in horizontal slides, as shown for idler roll 13 in FIG. 2 (the mounting of idler roll 12 being the same). Referring to FIG. 2, a horizontal slide 24 is provided to support the spindle 23 at each end of roll 13, the spindle 23 passing freely through a horizontal slot 25 in the slide and being received in a bearing 26 mounted within a bearing housing 27. The housing 27 is slidably mounted within a recess 28 on the outer face of the slide 23 and its position along the recess is adjustable by means of a set screw 29 which passes through the end of the slide 24. By means of this arrangement, the separation between the idler rolls 12 and 13 and the adjacent stripping rolls 10 and 11, respectively, can be varied as required by adjustment of the set screws 29 while maintaining each idler roll parallel to its adjacent stripping roll.

A take-up roll 14 is supported by the stripping roll 10 and the idler roll 12 and a take-up roll 15 by the stripping roll 11 and the idler roll 13. As shown in FIG. 2, the ends of the spindle 30 of the take-up roll 13 are a loose fit between the sides of a vertically disposed channel element 31 provided at each end of the roll 13. The channel elements 31 at each end of the roll 13 serve to prevent axial movement of the roll 13, but permit rotational and vertical radial movement of the roll. The take-up roll 14 is mounted in the same way.

Referring to FIG. 3, the spindle 32 of the stripping roll 11 has secured thereto a gear 33 and a pulley 34 which receives a belt drive from a suitable variable speed motor (not shown). The gear 33 intermeshes with a gear 35 which is freely rotatable on the spindle 36 of stripping roll 10. The gear 35 forms part of a slipping clutch assembly generally designated 37, the assembly additionally comprising a back plate 38 secured to the spindle 36 by screw 39, and a felt pad 40 on one side of the gear 35, and a felt pad 41, a pressure plate 42, a clutch spring 43, and an adjusting nut 44 on the other side of the gear 35. As will be appreciated the ability of the clutch assembly 37 to transmit torque from the gear 33 through the gear 35 can be finely adjusted by adjustment of the nut 44.

The rotational speed of the stripping roll 10 can thus be finely adjusted relative to the speed of the stripping roll 11 and the tensions of the separated thin film and support web to be correctly balanced. By this arrangement, jerkiness in the stripping and non-uniform stretching or breaking of the thin film which might be caused by small differences in the peripheral speeds of the stripping rolls 10 and 11 or inequality in the drives transferred to the take-up rolls 14 and 15 due to variations in the film thickness or to slip, are substantially prevented. This arrangement also enables extensible thin films to be stripped and wound successfully.

The apparatus further comprises a supply reel 16, the spindle of which is operatively connected to a friction clutch unit (not shown) so that tension is applied to the support web taken off the reel 16. The friction clutch unit has the same construction as the slipping clutch assembly 37 shown in FIG. 3 except that the gear 35 is made fast with the mounting of the reel 16 so that the gear 35 cannot rotate. The reel 16 supports a take-up roll 17, the ends of the spindle of which are located within vertically disposed channel elements (not shown) similar to the element 31 shown in FIG. 2, which allow the roll 17 to rotate freely and also to move up and down, but do not allow it to move horizontally. Positioned below the level of the supply reel 16 and the stripping rolls 10, 11 are idler rolls 18, 19 and 20. All the rolls 10 to 20 have a length greater than the width of the support web and they are all aligned transverse to their axes.

At the commencement of the stripping operation, the supply reel 16 carrying a supply of support web with adherent thin film and an interleaved paper web is positioned as shown and connected to the friction clutch. The paper web is manually wound on to the take-up roll 17 and the carrier web 21 is passed under the idler roll 18, over the idler roll 19, under the idler roll 20 and up into the gap between the stripping rolls 10 and 11. The carrier web with the adherent thin film is passed, by hand, over the stripping roll 11 and wound on to the take-up roll 15 for a few turns. A light cut is then made across the thin film (which is on the outside of the stripping roll 11) at the point indicated by 22 so as to cut only the thin film, the thin film is peeled back, passed over the stripping roll 10 and wound for one or two turns on to the take-up roll 14. Drive to the stripping rolls 10, 11 can then be started at a slow speed and then increased to the normal working speed.

As will be seen, stripping takes place in the gap between the stripping rolls 10 and 11, the support web passing over the roll 11 to be taken up on take-up roll 15 and the thin film passing over the roll 10 to be taken up on take-up roll 14. Since the take-up rolls 14 and 15 are supported only by the rolls on which they rest, they are able to accommodate themselves to changes from true cylindricality as they are progressively built up, due to small variations in thickness across the width of the material being wound on.

The idler roll 20 is so positioned that the support web with adherent thin film 21 makes contact with the stripping roll 11 upstream of the gap between the rolls 10 and 11. This arrangement is preferred because it provides a greater length of contact between the support web and the driven roll 11, the driving force developed to pull the support web off the supply reel 16 and over the idler rolls 18, 19 and 20 being dependent on the frictional contact between the support web and the roll 11.

When the size of the take-up rolls 14 and 15 becomes too large for the initial separation between the rolls 10 and 12, and 11 and 13 respectively, this separation may be increased by moving the roll 12 or 13 horizontally outwardly as required.

Claims

What is claimed is:

1. Apparatus for stripping a continuous thin film web from a support web, comprising a pair of closely spaced stripping rolls having rotational axes in a horizontal attitude and parallel with each other, drive means operatively coupled to said stripping rolls for driving them in opposite rotational directions, a pair of freely rotatable idler rolls one positioned on one side of said pair of stripping rolls and the other positioned on the other side of said pair of stripping rolls, each idler roll being parallel with and spaced from an adjacent one of said stripping rolls, a pair of take-up rolls, each resting on a respective one of said stripping rolls and its adjacent idler roll, whereby each said take-up roll is adapted to be driven by its contact with said stripping roll to accumulate a roll of one of said webs and to rise, relative to said stripping roll and associated idler roll as said web accumulates thereon, and means preventing axial movement of said take-up rolls relative to said stripping and idler rolls.

2. Apparatus as set forth in claim 1, wherein said idler rolls comprise spindles and the ends of the spindles of said idler rolls are mounted in horizontally disposed slide means whereby the separation between each said idler roll and its adjacent stripping roll can be varied while maintaining said idler roll parallel to said stripping roll.

3. Apparatus as set forth in claim 1, wherein said drive means is directly coupled to one of said stripping rolls and the other said stripping roll is operatively coupled to the first said stripping roll through transmission means comprising gearing and finely adjustable slipping clutch means.

4. A method of stripping a continuous thin film web from a support web, which comprises the steps of feeding the support web and adherent thin film web into the gap between a pair of closely spaced, driven stripping rolls having their rotational axes in a horizontal attitude and parallel with each other, the gap between said stripping rolls being just greater than the combined thickness of the support web and the thin film web, dividing the support web and the thin film web in said gap, taking the thin film web over a part of one of said stripping rolls and on to a first take-up roll which is supported by said stripping roll, and taking the support web over a part of the other said stripping roll and on to a second take-up roll which is supported by said other stripping roll, said first and second take-up rolls being rotated by their contact with their respective supporting stripping rolls.

5. A method as set forth in claim 4, wherein the support web makes contact with said other stripping roll upstream of said gap between said stripping rolls.