Method and apparatus of applying a design to tiles

Abstract: A method and apparatus for the printing of tiles utilises an off-set rotary gravure printing process in which the transfer roller 2 has an outer surface of silicone rubber 3. Preferably, the tiles are supported against a support roller 7, itself having a silicone rubber surface 8, during their printing by the transfer roller.

Description: The present invention relates to a method of, and apparatus for, applying a design to a ceramic tile. Decorative ceramic tiles are used, for example, in kitchens and bathrooms to enhance the appearance of the room. A number of techniques are used for providing the decorative marking on the tile during its manufacture. For example, it is known to screen print the design onto the unfired (i.e. 'biscuit') form of the tile. However the definition obtained by this method is not good and therefore only comparatively 'crude' designs may be printed. More accurate definition can be obtained by the use of transfers but this is a comparatively slow process and can only be used for applying designs to the fired tile. A rotary gravure printing process is known for applying a design to ceramic hollow-ware such as is described in British patent specification GB-1284841. In this method a flexible transfer roller is used in an apparatus for applying a design to a ceramic hollow-ware product, and having a printing station comprising a rotary gravure cylinder and a flexible transfer roller associated therewith. In French patent specification FR 2144235 a gravure cylinder is associated with a flexible transfer cylinder comprising an outer surface of silicone rubber which can be used for printing on planar surfaces. It is an object of this invention to provide a method of applying a design to a tile which obviates or mitigates the above mentioned disadvantage. According to the present invention there is provided a method of applying a design to a ceramic tile wherein the design is applied to the tile by an off-set rotary gravure printing process in which the transfer roller has an outer surface of silicone rubber, and wherein the tile to be printed passes between the transfer roller and a support roller which has an outer surface of silicone rubber against which the tile is supported during printing. The present invention also provides apparatus for applying a design to a ceramic tile the apparatus having a printing station comprising a rotary gravure cylinder, a transfer roller associated therewith and a tile support roller juxtaposed to the transfer roller, wherein the transfer roller has an outer surface of silicone rubber and said support roller has an outer surface of silicone rubber against which the tile is supported during printing. The inks used in the method of the invention preferably contain ceramic pigments. Preferably also the inks are at a higher temperature than the tile and of a type which dry quickly upon contact with the relatively cool surface of the ceramic tile. The quick drying nature of these inks allows the tile to be printed at successive rotary gravure printing stations so that a multi-colour design can be quickly and easily built up. Silicone rubber has a number of properties which render it suitable for use as the transfer surface of the transfer roller. In particular, it is heat resistant (and is thus not damaged by the application thereto of the heated inks) and also has excellent ink transfer properties. Most preferably, the silicone rubber is provided as a comparatively thin sleeve bonded onto a rigid roller. This construction ensures that the silicone rubber does not 'wobble' during rotation of the transfer roller which thus allows the accurate transfer of the ink to the tile. The tile is supported during its printing with the transfer roller by means of the support roller which has a silicone rubber surface of the same hardness as that of the transfer roller. The diameter of the transfer roller (measured across the silicone rubber surface) has to be the same as that of the support roller (also measured across its silicone rubber surface). It is necessary to use such a support roller for the printing of unfired clay tiles in order to avoid breakage. The spacing between the silicone surfaces of the transfer and support rollers will be related to the thickness of the tile to be printed and will determine the pressure which the transfer roller will apply to the tile for applying the ink thereto. It is also preferred that the silicone surface of the transfer roller be in contact with the surface of a cleaning roller for removing excess ink from the surface of the transfer roller after the latter has printed onto a tile and before it is re-inked by the gravure cylinder. The provision of a cleaning roller is also of value as is the case where tiles are being fed successively through the printing station (i.e. to be printed by the transfer roller) and there are one or more tiles missing from the feed. In this case, the transfer roller obviously does not print onto a tile and is cleaned by the cleaning roller before being re-inked. The cleaning roller preferably has a PTFE surface. Additionally, the cleaning roller should be at a lower temperature than the gravure cylinder (which will typically be at a temperature of above 100°C to ensure transfer of the ink onto the transfer roller but at a higher temperature than the transfer roller. Typically the surface of the cleaning roller will be at a temperature of 60-70°. Preferably the silicone rubber is a Room Temperature Vulcanised silicone rubber (as opposed to condensation cured) and preferably has a hardness in the range 40-50 oo Shore. Most preferably the hardness is about 45 oo Shore. As well known, gravure cylinders may be used for printing detailed designs and the invention thus allows such detailed designs to be applied successively to tiles. The gravure cylinders used should be half-tone etched cylinders which achieve a quality comparable to decals (transfers). The etched depth of the cylinder is generally of at least double that of gravure cylinders used for the printing of paper. Preferably the etched depth of the cylinder is 6.25 - 7.5 x 10⁻³cm (0.0025 to 0.003in). This compares with 2.5 to 3.8 + 10⁻³cm (0.001 to 0.0015in) in cylinders used for printing paper. The greater etched depth is required because of the different nature of the inks used in the present process, compared to those used for printing paper. The gravure cylinder will preferably have up to 50 lines/cm (120 lines/inch). The gravure cylinder will also be associated with a doctor blade arrangement for the removal of excess ink from its surface. Most preferably, reverse angle doctoring is used. Preferably the gravure cylinder is applied to the silicone rubber surface of the transfer roller so as to produce an impression therein of about .025cm (.01"). The invention will be further described by way of example only with reference to the accompanying drawing, in which: Fig. 1 is a perspective view of one embodiment of apparatus in accordance with the invention. The apparatus of Fig. 1 comprises a printing station 1 for the off-set rotary gravure printing of tiles. More particularly the printing station comprises a transfer roller 2 incorporating a silicone rubber sleeve 3 to which a design to be printed onto a tile is applied by a rotary gravure cylinder 4 (shown only schematically without details of the ink retention cells) supplied with ink from a tray 5 by a roller 6. Cylinder 4 may be internally heated by circulating hot oil therethrough and heaters (not shown) for the ink are provided in tray 5. The transfer roller 2 has a horizontal axis of rotation and is located vertically above a support roller 7 itself having a sleeve 8 of the same silicone rubber as sleeve 3. Sleeves 3 and 8 may for example be of 1.25cm (0.5") thickness and a hardness of about 45 oo Shore. A cleaning roll 9 with a PTFE surface is capable of rotating in contact with the roller 2. Doctor blades 10 and 11 are provided for cylinder 4 and roll 9 respectively. Although not specifically illustrated in the drawings, means are provided for effecting the following at the printing station. (a) varying the distance between the transfer roller 2 and support roller 7 thus allowing different thicknesses of tiles to be printed with the appropriate pressure being applied thereto by roller 2; (b) moving gravure cylinder 4 away from transfer roller 2 to facilitate setting up of the apparatus for printing; (c) moving the cleaning roll 9 away from transfer roller 2; (d) oscillating doctor blade 10 in a direction parallel to the axis of gravure cylinder 4; and (e) adjusting the angle of blade 10 relative to gravure cylinder 4. The apparatus further comprises a conveyor arrangement 12 by which tiles to be printed are supplied to and past the rollers 2 and 7. More particularly, this conveyor arrangement comprises a first pair of laterally spaced belts 13 running around and between the pulleys 14 upstream of the rollers 2 and 7, and a second pair of laterally spaced belts 15 which run around pulleys 16 from upstream of rolls 2 and 7 to downstream thereof. The spacing between belts 15 is less than that between belts 13 and at their upstream ends the belts 15 locate between the downstream ends of belts 13. Belts 13 are guided by rails 17 and are arranged such that their upper surfaces are very slightly higher than those of belts 15. Support roller 7 has two annular grooves 19 axially spaced by a distance corresponding to the lateral spacing of belts 15. As will be seen from an inset to Fig. 1 the belts 15 run in these grooves on their passage past roller 7. Provided on each of belts 15 are a plurality of upstanding projections 20 at regular spaced intervals. In the region where the belts 13 and 15 overlap are friction rollers 21 rotatable about horizontal axes locating between the adjacent belts 13 and 15. Additionally means for the lateral location of a tile are provided in the form of a line of small vertical rollers 22 at the outer side of one of the belts 13 and a pulley belt 23 at the opposite side of the other belt 13 and being adapted to be urged into contact with a tile by spring loaded rollers 24. Although not illustrated in the drawings, the illustrated apparatus incorporates a drive arrangement for the gravure cylinder 4. This arrangement has a drive shaft from which the rollers 2 and 7 and the belts 13 and 15 are also driven. The illustrated apparatus is a modular unit which may be provided as one of a line of similar apparatus (each for printing a different colour ink) for building up a multi-colour pattern on a tile. More particularly, the tiles may be fabricated in a conventional production unit by pressing from clay, drying the pressed clay, then by applying a glaze and then a sealer before the tiles are fed to the illustrated printing apparatus (or line of such apparatus) from which the printed tiles are fed to a kiln for firing. The unfired tiles T are fed to the apparatus by conveyors (not shown) and are received on the upstream ends of the belts 13 which are spanned by each tile. The tiles are thus conveyed towards the upstream end of belts 15 (which are driven at the same speed as belts 13) and engage with friction rollers 20 which slow or stop the tiles until such time as a pair of projections 20 (one on each belt 15) engage against the trailing edge of the tile and advance it towards rollers 2 and 7. During its movement towards these rollers, the tile is laterally located by the arrangement of vertical rollers 22 and belt 23 (biassed towards the tile by the rollers 24 ) described above. As mentioned above, the return pulley 14 of the belts 13 are upstream of the rollers 2 and 7 and this is by a distance such that as the leading edge of the tile becomes supported on the roller 7, the trailing edge is still supported by belts 13. The gravure cylinder 4 (rotating in the direction of arrow A) is supplied with ink by the roller 6 and applies a design to the silicone rubber sleeve 3 of roller 2 (rotating in the direction of arrow B) and this design is in turn applied to the tile which continues to be conveyed by belts 15 to the downstream end of the apparatus. The tile may then be passed to a similar apparatus (for applying a different colour ink to the tile) or to a kiln for firing. It will of course be appreciated that it is necessary to ensure that the spacing of projections 20 on the belts 13 together with the rotational speed of transfer roller 7 are so related that the printed design is applied at the correct position on successive tiles. The ink used for the printing operation comprises ceramic pigments in a pressure sensitive ink medium. The ink is held in tray 5 and maintained at an elevated temperature (by heaters not shown) for application to the printing cylinder 4 which is itself maintained at about 120°. Cylinder 4 is wiped by the doctor blade 10. This blade is oscillated in a direction parallel to the axis of the cylinder 4 to avoid uneven wear. Additionally, the angle of the blade 10 relative to cylinder 4 may be varied to suit particular printing applications. The pressure of the nip between sleeves 3 and 8 causes the ink to be readily transferred from sleeve 3 to the tile. Any residual ink on sleeve 3 is removed by cleaning roll 9 which is in turn wiped by doctor blade 11.

Claims: Method of applying a design to a ceramic tile (T) wherein the design is applied to the tile by an off-set rotary gravure printing process in which the transfer roller (2) has an outer surface (3) of silicone rubber, and wherein the tile (T) to be printed passes between the transfer roller (2) and a support roller (7) which has an outer surface (8) of silicone rubber against which the tile (T) is supported during printing. Method as claimed in Claim 1, wherein the silicone rubber of the transfer and support rollers (2, 7) is or the same hardness within the range 40-50 oo Shore, preferably about 45 oo Shore. Method as claimed in Claim 1 or Claim 2, wherein the tile (T) to be printed is of pressed clay which has not been fired. Apparatus for applying a design to a ceramic tile (T) the apparatus having a printing station (1) comprising a rotary gravure cylinder (4), a transfer roller (2) associated therewith and a tile support roller (7) juxtaposed to the transfer roller (2), wherein the transfer roller (2) has an outer surface (3) of silicone rubber and said support roller (7) has an outer surface (8) of silicone rubber against which the tile is supported during printing. Apparatus as claimed in Claim 4, wherein the silicone rubber of the transfer and support rollers is of the same hardness within the range 40-50 oo Shore, preferably about 45 oo Shore. Apparatus as claimed in Claim 4 or Claim 5, wherein a cleaning roller (9) is provided for cleaning the silicone rubber surface (3) of the transfer roller (2). Apparatus as claimed in any one of Claims 4 to 6, comprising a conveying arrangement having a first pair of laterally spaced endless belts (13) located upstream of the transfer roller (2), and a second pair of endless belts (15) extending from between the first belts (13) to downstream of the transfer roller (2), said second belts (15) having a plurality of spaced tile drive elements (20) for engaging against the trailing edge of a tile (T) transferred to the second conveyors from the first conveyors. Apparatus as claimed in Claim 7, wherein friction rollers (21) are provided in the region of the overlap of the first and second conveyors for retarding a tile being conveyed by the first conveyor until the trailing edge of the tile is engaged by tile drive elements of the second conveyor. Apparatus as claimed in Claim 7 or 8, wherein means are provided upstream of the transfer roller (2) for laterally guiding the tiles. Apparatus as claimed in Claim 9, wherein the means for laterally guiding the tiles comprises a line of guide rollers (22) rotatable about vertical axes positioned outwardly of one of the first endless belts (13), and a guide belt (23) positioned laterally outwardly of the other first endless belt (13) and having a run biassed towards the tile.

Inventors: GROSVENOR EDWARD CHARLES, KNOTT PETER, GROSVENOR,EDWARD CHARLES, KNOTT,PETER
Applicants: PRINT FLO LIMITED, PRINT-FLO LIMITED
Application year: 1988
Main classification: B41F17
IPC codes: B28B11, B41F17