SUPPORTING OR GUIDING ROLLER

Abstract: Described is a roller comprising a thin seamless metal sleeve (52) at its surface which is provided with a surface structure (3, 5, 6, 9) for preventing the formation of an air cushion when such (52) roller is used for guiding or supporting a moving web-type substrate. Such surface structure (3, 5, 6, 9) is further pro­ tected with a wear-resistant top layer of ceramic, glass, quartz or polytetrafluoroethylene. Also is described an apparatus comprising one or more of such rollers (52).

Description: The present invention relates to a roller for use in the guiding and/or supporting of a moving web-type substrate, in an apparatus for treatment thereof wherein the surface of said roller which comes into contact with the substrate is provided with a surface structure as a result of which a predetermined volume of gas is enclosed between the substrate which is in contact with the surface structure and the roller and the structure is given a form such that said volume of gas remains essentially the same at the substrate conveying speeds used. Such rollers are generally used as supporting or guiding rollers in apparatuses for treating web-type media, in which connection treatment may be understood to mean a large number of operations such as coating, printing, subjecting to corona discharge, exposure etc. A roller of the indicated type is described in GB-A-1 056 372 which discloses a guide roller assembly for a paper web handling machine. A limited number of surface structures is described which all serve to prevent the build up of an air cushion between the moving paper web and the guiding roller in the handling machine concerned. Said known guide roller has as a disadvantage that a large number of different rollers is needed when the handling machine is intended for various purposes and/or various substrates. SUMMARY OF THE INVENTION. The present invention has as an object to provide a roller of the type concerned which does not show said disadvantage and which allows for fast and easy changing of the surface structure thereof. Said roller is thereto characterized in that the roller comprises a seamless metal sleeve at its surface which comes into contact with the substrate and the surface structure is provided at.the surface of the sleeve. said sleeve being mounted such that exchange thereof is allowed. By providing a roller of which the surface is formed by a separate seamless metal sleeve a rapid change of surface structure is possible as will be explained later in detail. With respect to the present invention reference is made to the following references. EP-A-0 253 981, which describes a guiding roller, comprising a cylindrical sleeve which is elastically deformable in a certain pressure region, and which is closed with end caps. Said sleeve can be pressurized by a pressure fluid to generate and to maintain an overpressure inside. No surface structure is present. DE-A-3 023 246 concerns a single or multi-layer covering for a guiding roller. The covering may have properties for preventing gas build up and wear resistance. DE-A-3 302 843 relates to a guiding roller for foils, especially plastic foils, said roller comprising an exterior rubber surface which is provided with a structure comprising numerous closely spaced bulges. During operation of the roller at high speeds air can escape between the bulges. GB-A-1 195 592 describes a guide roller assembly for a paper web handling machine, comprising an imperforate freely rotatable idler roller, in the surface of which a plurality of alternating ridges and grooves is present. These ridges and grooves are present to prevent gas build up. None of these references discloses the use of a seamless metal sleeve being exchangeable. Expediently such a seamless metal sleeve is a nickel sleeve having a thickness between 150 and 500 micrometer and in particular between 150 and 250 micrometer. Such nickel sleeves are manufactured by the applicant and may be provided with any desired circumference length and in any axial length. The surface of such sleeves may be given any desired surface structure which may be applied in a plurality of ways as will be explained in the drawings. With a roller of the type described a rapid wear of the surface structure may be observed, for example when guiding or supporting paper materials having great roughness or high filler percentages. This problem is solved according to the present invention by providing the surface structure with a top layer of high wear resistance. In particular such a top layer comprises a wear resistant material chosen from: nitrides such as of titanium or boron, carbides such as of silicon, boron, tungsten and titanium, glass and quartz. Of course many other materials may be mentioned in this respect; in above series titanium-nitride is of particular importance. It is a very hard, wear-resistant material having a very attractive light yellow colour; it may very effectively apply to a surface by sputtering techniques such as sputtering of TiN or reactive sputtering of Ti in a nitrogen containing atmosphere. In order to prevent damage to the substrate as much as possible, it is attractive to round off the parts of the surface structure of the roller which come into contact with the substrate. With very great advantage, the surface structure of the roller according to the invention is provided with a top layer having high wear resistance, such as a nickel-phosphorus layer or chromium layer; the surface structure may also, for example, be provided with a polytetrafluoroethylene coating layer in order to prevent wear of the roller and damage to the substrate as much as possible. In one attractive embodiment, the sleeve incorporated in the roller is mounted under axial stress between two end rings or flanges mounted on a shaft. Such a roller has the advantage that the weight thereof can be extremely low, as a result of which the roller will readily start to rotate concomitantly with the substrate to be supported or guided. In the embodiment described above, instead of a continuous sleeve, use may also be made of a sleeve provided with perforations such as, for example, a metal rotary screen-printing stencil. Such a stencil may be composed, for example, of nickel and have a fineness of 250-500 mesh (= holes per linear inch), although lower or higher finenesses are possible. The thickness may vary between 100 and 250 micrometers or thicker. If such a perforated sleeve is used, the surface structure may comprise a separately provided structure which is superimposed on the structure of the perforation pattern of the sleeve. In certain cases, the structure of the perforation pattern itself will also be sufficient to guarantee that the sheet-type substrate always remains in contact with the surface of the sleeve. In an attractive embodiment, means such as, for example, a labyrinth of partitions are present inside the sleeve in order to make it possible to adjust an axially extending pressure profile inside the perforated sleeve in a predetermined manner. Such a labyrinth structure may optionally rotate concomitantly with the perforated sleeve; the pressure profile may be in the overpressure range and (possibly partly), in the underpressure range. Regulation of the pressure inside the perforated sleeve makes possible a further perfecting of the substrate contact behaviour, as a result of which even locally occurring imperfections in the substrate contact can be remedied. When the seamless metal sleeve is used measures may be taken to provide sufficient rigidity to the sleeve used. One general approach is to mount the sleeve, either unperforated or perforated between two end rings or flanges under axial stress. This will provide a basic rigidity to such sleeve or screen which is sufficient for low contact pressure of the guided web. If higher pressures are to be taken a sleeve, in this case having no perforations, may have rigidity by a filling in the interior thereof of a material of low density such as a cured foam plastic material or a pressurized gas such as air. As an example of a suitable foam plastic a polyurethane may be mentioned such as polyurethane HHR® of Voss Chemie. This material is a semi-hard foam having a density of approx. 26 kg/m³. Also a foam H 450® of Voss Chemie may be used; this is a polyurethane foam which exhibits high pressure (5-6 kg/cm² overpressure) during hardening and has a density of 450 kg/m³. When air is used to provide rigidity to a sleeve up to 1.3 kg/cm² overpressure may be used. In another attractive embodiment, a sleeve can be carried in a clamping manner by a supporting cylinder which is provided with axle means. In connection with the lastmentioned embodiment of the roller, reference is made to European Patent Specification 0,160,341 of Stork Screens. Said patent specification describes a method for manufacturing a screen roller in which a thin-walled seamless cylindrical screen is pushed around the surface of a hollow thick-walled or solid roller. To mount the screen around the circumference of the supporting cylinder, the perforations of the screen are sealed, after which the diameter of the screen is temporarily increased with the aid of, for example, air pressure, with the result that the screen can be pushed around the roller. To manufacture the roller according to the present invention, in which process the roller is formed by a supporting cylinder around which a seamless metal sleeve is pushed in a clamping manner, the technique described in said patent specification may also be used. Another form of a supporting roller is a so-called compressible stretching roller such as is described in the non-prepublished Dutch Patent Application Publication No. 88 00 781 (published 16.10.1989) of Stork Screens. In said document, a supporting roller is described with, at the surface, a continuous coating which can be pressed in. By pushing a sleeve over a short distance around the coating and feeding a medium under pressure, for example gas, between the sleeve and the coating, this latter can be pressed in and the possibility of pushing the entire sleeve around the coating. Especially in the case of a sleeve having large wall thickness, this compressible roller will readily be sufficient for forming the roller according to the invention. The invention also relates to a roller for use in the guiding and/or supporting of a moving web-type substrate, in an apparatus for treatment thereof wherein the surface of the roller which comes into contact with the substrate is provided with a surface structure as a result of which a predetermined volume of gas is enclosed between the substrate which is in contact with the surface structure and the roller and the structure is given a form such that said volume of gas remains essentially the same at the substrate conveying speeds used, which is characterized in that the roller is a massive or thick-walled metal roller and the surface structure is provided with a top layer of high wear resistance. In order to protect the surface structure of the inventive roller against influences of abrasive materials it has proved very advantageous to provide the surface structure of such roller with a top layer of high wear resistance. Such top layer may thereto comprise various materials of which may be mentioned: nitrides such as titanium and boron nitride, carbides such as silicon, boron, tungsten and titanium nitride, glass and quartz. In particular titanium nitride is found to offer valuable properties in terms of hardness, wear resistance and appearance. Also the top layer may comprise a metal layer such as a nickel-phosphorus or chromium layer. Attractive is also a polytetrafluoroethylene layer having a very low coefficient of friction; in this respect also mixed ceramic-polytetrafluoroethylene layers may be mentioned. The latter layers may expediently be applied by a plasma spraying process. The invention finally relates to an apparatus for treating a moving web-type substrate which comprises one or more substrate treatment units, substrate moving units and one or more substrate supporting rollers, such an apparatus being characterized in that the substrate supporting rollers have the form as described above for a roller according to the invention. Such an apparatus for treating a moving web-type substrate may, for example, be an apparatus for applying a coating to a web-type substrate. As an example, mention may be made of the application of an emulsion to a web-type substrate such as a polyester substrate. The uniformity of such a coating is of the greatest importance; constructing the substrate supporting or guiding rollers according to the invention in the coating apparatus guarantees, as regards the conveying section of the apparatus, that a disadvantageous effect is not exerted on the substrate or the coating applied to the substrate. Expediently, such an apparatus is, for example, a rotary screen-printing apparatus in which a uniform coating is applied to, for example, a polyester web with the aid of a seamless nickel screen-printing stencil. Apart from the abovementioned components of such an apparatus, it may also comprise, for example, drying units in order to be able to subject the layer or layers applied to a drying operation. BRIEF DESCRIPTION OF THE DRAWINGS: The invention will now be described with reference to the drawings, wherein: Figures 1 to 4 show diagrammatically in partial section and plan view a number of possible forms of a surface structure of the roller; Figure 5 shows a special form of a component of the surface structure of a roller; Figures 6 and 7 show a special form of a surface structure which serves to make possible gas removal to the ends of the roller; Figures 8 and 9 show surface structures of divergent efficiency; Figures 10 and 11 show a surface structure which is obtained by electrolytically depositing metal; Figure 12 shows the principle of fitting a metallic seamless cylindrical sleeve around the surface of a supporting cylinder; and Figures 13 and 14 show the embodiment in which a non-supported sleeve is used. In Figure 1a, 1 indicates in partial section the body of a roller or a metallic seamless sleeve, while 2 and 3 indicate the surface structure situated on the surface of the roller or sleeve. From Figure 1b it can be seen in partial plan view that the surface structure comprises spherules 2 with gaps 3, while the spherules are arranged in equilateral triangle structure. It is pointed out that the regular structure shown here is not a necessity; a rough nature may also be given to the surface of a roller or sleeve by, for example, abrasion, sandblasting, beadblasting or shot peening, in which case the peak-to-valley height will expediently have a value Ra of up to 12.5 micrometer. A normal smooth roller or a metal sleeve obtained by electrodeposition such as a nickel sleeve will have a peak-to-valley height Ra ≦ 0.2 micrometer. Figure 2a indicates that cavities 5 have been formed in the roller body or sleeve body 4 by etching. It will be possible for the width and depth and also the pattern configuration of the grooves 5 to be chosen as a function of the application. Figure 3 indicates that the roller body or sleeve body 7 is provided with a structure of arbitrarily arranged spherules 6, such spherules being joined to the surface of the roller or sleeve by cementing. It is pointed out that, with such an embodiment, a calibration operation should additionally be carried out subsequent to forming the surface structure layer in order to provide, in this way, the roller with true running; the calibration also serves to guarantee that all the spherular components have one and the same height above the surface of the roller or sleeve. Figure 3b indicates the situation in Figure 3a in plan view, as was also the case in Figure 2b in relation to Figure 2a. In Figure 4a, 9 indicates a groove in the surface of a roller or sleeve, the elevations between the grooves being indicated by 8. From Figure 4b it is evident that the grooves extend helically in the longitudinal direction of the roller, assuming that the axial direction of the roller extends in the direction of the arrow which is indicated in Figure 4b. Incidentally, it is pointed out that in all the figures given above, an axial direction of the roller or sleeve is assumed which is identical to the direction of the arrow in Figure 4b. Figure 4c indicates that the tips of the material 8 between the grooves 9 are rounded off by additional operational steps such as bright pickling, latching, etching or the like. Figure 5 indicates that a surface structure can be obtained by machining, with a milling wheel, the surface of the roller or a sleeve to be used, as a result of which recesses 10 are obtained which are connected to one another by means of channels 10', with the result that a possibility of mutually displacing gas between the recesses is nevertheless ensured. Apart from the abovementioned mechanical forming of the recesses, the forming of recesses can, of course, also be conceived by means of electron beam engraving or laser beam engraving in metal. Figures 6 and 7 indicate two very attractive embodiments of a surface structure of a roller or sleeve in which the structures are formed as mirror images with respect to each other around the centre of a roller. In Figure 6, a groove pattern 13 is shown in part 11 on the right-hand side of the centre, the pattern 13 being helically arranged in such a manner that, on rotating a roller in the correct direction, a gas transport takes place to the right in the drawing. At the left-hand side of the centre of the roller in part 12, the groove pattern is oppositely directed, as a result of which, with the same rotation, a gas transport can occur to the left. In Figure 7 the same situation is indicated in which a pattern of overlapping opposite thread is present in each of the two parts on either side of the centre of the roller. In such a situation, a groove width gradient can be used, as a result of which, for example, the resistance to displacement in the grooves decreases from left to right for one of the threads and from right to left for the other thread. Such embodiments arranged in mirror form appear to be very advantageous if, apart from a controlled pressure build-up of the gas, there has to be a requirement for effects which have to promote positional accuracy of the substrate during movement thereof. As a result of a symmetrical air displacement starting from the centre of the roller, an improved positional accuracy of the substrate with respect to the roller is obtained, in which case a certain flattening side effect on the substrate sheet is also observed, and this is extremely desirable for specific materials and low sheet thicknesses. To form such patterns, use may advantageously be made of etching techniques using photoresist patterns, it also being possible for a groove depth variation to be achieved by using special techniques. Of course, in that case, recourse may also be made to the abovementioned beam machining techniques using electron or laser beams for forming the groove patterns. Figure 8 shows a surface structure of a roller 19 in which circumferential grooves 20 are present. In this case no displacement of air takes place towards the ends of the roller; nevertheless, suitable dimensioning of the grooves can guarantee continuous contact of the substrate with the material between the grooves 20. Figure 9 shows a situation in which the surface 21 is provided with axially extending grooves 22. In practice this situation proves less adequate and, for certain groove dimensions, may result in vibration of the substrate sheet. Figures 10 and 11 indicate that a surface structure can be obtained on a roller or sleeve with the aid of electroplating techniques. Figure 10 indicates a roller body or sleeve body 23, while 25 indicates an electroplated metal deposit which has grown between photoresist regions which were previously situated at the positions which are now indicated by 24. In Figure 11 an electroplated deposit 27 is formed on a roller body or sleeve body 26 with an overhang 28, the overhang having taken place over photoresist areas which were situated at the positions indicated by 29. Regulation of the airflow over the surface of the roller or sleeve can suitably be taken into account by choice of the upward growth/overhang ratio. Figure 12 indicates diagrammatically how a sleeve 30 can be fitted around the surface of a roller 32 in a manner such as is indicated in the abovementioned European Patent Specification 0,160,341. In this case the roller is a thick-walled hollow roller which is provided with supporting axles 35 and 36 which have disc-type sections 37 which are pushed in a clamping manner into the ends of the cylinder. The disc-type sections 37 rest against a collar at the inside of the cylinder. One of the ends of the cylinder 32 is provided with a number of radial openings 38 which debouch at the outside circumference of the cylinder and which are in communication with axially directed channels 40 which are provided in the left-hand disc-type section 37. Each of the channels 40 has a blind end or a sealing plug 39; the other end of the channels 40 is in communication with the internal space 33 of the supporting cylinder 32. The disc-type section 37 at the right-hand side of the cylinder has at least one axially directed channel 34 which is, on the one hand, in communication with the space 33 and, on the other hand, with a connecting nipple 41. The nipple 41 can be connected via a hose, which is not shown, with a source, which is equally not depicted, of the medium, usually compressed air. In order to fit the sleeve 30 on the roller 32, the outermost section of the cylinder 32 is chamfered, with the result that the sleeve 30 can be pushed over the chamfered part up to the openings 38. A pressurized medium is then fed into the space 33 via the connection 41 and the channel 34 in a manner such that the sleeve 30 is expanded elastically and, as a result, can be pushed further over the supporting cylinder 32. In this connection, the pressurized medium has the double function of expanding the sleeve 30 somewhat and at the same time acting as a lubricant in pushing the sleeve over the supporting cylinder. After completing the pushing-on operation, a connection to the source of pressurized medium can be broken and this medium leaks away, after which the sleeve 30 is situated on the supporting cylinder 32 in a clamping manner. In Figure 12, a broken line on the surface of the supporting cylinder 32 indicates that the outside of the cylinder is chromium-plated or covered with a thin chromium-plated cuff which serves to provide the surface of such a cylinder with adequate wear resistance, with the result that it can be used many times. As regards the rollers or sleeves to be used according to the invention, it may be pointed out that, in general, a high degree of wear resistance will be aimed at which, on the one hand, can be achieved by using a wear-resistant material with low coefficient of friction such as polytetrafuoroethylene; on the other hand a wear-resistant material may also be used with a high hardness. Ion implantation technique, CVD (chemical vapour deposition) and PVD (physical vapour deposition) may also be used to provide wear-resistant properties at the surface of a roller or sleeve. The materials which may be applied with use of above techniques can be various. Mention can be made of: nitrides such as of titanium and boron, carbides such as of silicon, boron, tungsten and titanium, quartz and glass. Of above materials in particular titanium nitride is useful. Said material may be applied to the surface of a sleeve having a surface structure by sputtering techniques. Titanium nitride may be sputtered directly from a titanium nitride target or formed by reactive sputtering of titanium from a titanium target in a nitrogen-gas comprising atmosphere. Other layers of high hardness can furthermore be deposited, for example, by electroplating or by electro-lessplating such as, for example, a chromium layer or a nickel-phosphorus layer. As regards the hardness, a hardness which exceeds 500° Vickers will give good results. Figure 13 shows the situation where a roller according to the invention comprises a sleeve 52 received between end rings, which sleeve may be a closed sleeve or a sleeve having perforations which is provided with an additional surface structure. The end rings are in this case stencil end rings 50 such as are used, for example, in rotary screen-printing machines. The ends 53, 54 of the rings are constructed so that they can be received in the stencil heads of the apparatus in, for example, a bayonet connection. The rings can exert an axial stress in a machine on the sleeve 52; that is not, however, necessary. The end rings 50 and 51 may also be replaced by end rings mounted on a common axle; axial stress can be obtained if necessary by pushing the rings apart on the axle. As indicated before inside the sleeve 52 a filling of a low density material may be provided such as a plastic material, in particular a cured foam plastic or a pressurized gas to impart rigidity to the roller. Figure 14 shows the situation where the sleeve 52 is a perforated sleeve such as a rotary screen-printing stencil. The axle 56 in this case carries a labyrinth 57 in order to achieve a predetermined pneumatic pressure profile over the length of the sleeve. By varying the labyrinth partition spacings and suitably arranging gas supply and/or removal openings, a suitable axial profile comprising underpressure and/of overpressure locations can be established. An underpressure may be desirable in cases of high web transportation speeds at low web tension; a slight degree of overpressure may be expedient when working at low web speeds at high web tension.

Claims: Roller for use in the guiding and/or supporting of a moving web-type substrate, in an apparatus for treatment thereof wherein the surface of said roller which comes into contact with the substrate is provided with a surface structure (3, 5, 6, 9) as a result of which a predetermined volume of gas is enclosed between the substrate which is in contact with the surface structure (3, 5, 6, 9) and the roller and the surface structure is given a form such that said volume of gas remains essentially the same at the substrate conveying speeds used, characterized in that in that the roller comprises a seamless metal sleeve (52) at its surface which comes into contact with the substrate and the surface structure (3, 5, 6, 9) is provided at the surface of the sleeve (52) said sleeve being mounted such that exchange thereof is allowed. Roller according to claim 1, characterized in that the sleeve (52) is a seamless nickel sleeve having a thickness between 150 and 500 micrometer, in particular between 150 and 250 micrometer. Roller according to one or more of the preceding Claims, characterized in that the surface structure (3, 5, 6, 9) is provided with a top layer of high wear resistance. Roller according to Claim 3, characterized in that the top layer comprises a wear-resistant material chosen from: nitrides such as of titanium or boron, carbides such as of silicon, boron, tungsten and titanium, glass and quartz. Roller according to Claim 3, characterized in that the top layer comprises a layer of a metal of high wear resistance and hardness such as a nickel-phosphorus layer or a chromium layer. Roller according to Claim 3, characterized in that the top layer comprises a layer of polytetrafluoroethylene. Roller according to one or more of the Claims 1-6, characterized in tha t the sleeve (52) is mounted between two fixed end rings or flanges (50; 51). Roller according to Claim 7, characterized in that the sleeve (52) is a sleeve provided with perforations. Roller according to Claims 7 or 8, characterized in that means (57) are provided inside the sleeve (52) for establishing a predetermined pneumatic pressure pattern in the axial direction. Roller according to Claim 7, characterized in that the roller has been given rigidity by filling the interior of the sleeve (52) with a material of low density. Roller according to Claim 10, characterized in that the sleeve (52) has been filled with a material chosen from a cured foam plastic and a pressurized gas. Roller according to one or more of the Claims 1-6, characterized in that the sleeve (30) is carried in a clamping manner by a supporting cylinder (32) provided with axle means (35, 36, 37).

Inventors: DIEBELS, BERNARD PIERRE, EKKEL, RONALD
Applicants: STORK SCREENS B.V.
Application year: 1990
Main classification: B65H27
IPC codes: B65H27, B65H20