EP0097134B1

EP0097134B1 - Photo-electrostatic method for glaze-decorating ceramic tiles, machine therefor, and end product obtained therefrom

Info

Publication number: EP0097134B1
Application number: EP19830830121
Authority: EP
Inventors: Eugenio Morandi
Original assignee: OFFICINA MECCANICA MORANDI LEO
Current assignee: OFFICINA MECCANICA MORANDI LEO
Priority date: 1982-06-15
Filing date: 1983-06-14
Publication date: 1986-10-08
Also published as: DE3366755D1; ES523297A0; ES8504557A1; EP0097134A1

Description

The invention relates to a photo-electrostatic method and machinery for applying decorative glaze to ceramic tiles, and to the end-product turned out by adoption of such a method that is, a new method, partly inspired by the Xerox photocopy principle, which will enable printing of a decorative glaze onto ceramic tiles by utilising the appropriate machinery. Thus, the method itself, the machine, and the end-product obtained, constitute the collective subject which the application seeks to protect with letters patent.
The prior art in this field consists of a variety of tile glaze-decorating methods and relative devices which provide for projection of the glaze- medium in liquid state through stencils onto the surface requiring decoration; said projection being brought about either centrifugally by disc, or by free-fall, or by spray-gunning, or with a system of revolving delivery-receptacles, or by silkscreen process - this with either a flat screen, or a set of screens fitted to a revolving drum. All such techniques are characterised by the use of glaze in liquid state. Systems whereby glaze is applied to tiles by projection in the liquid state require - amongst other things - a long production line per colour, which signifies capacious factory premises and a great deal of ancillary equipment to cover each single type of tile, not to mention all the necessary dust-vacuuming, cleaning and wash-down plant. In the case of silkscreening, a screen assembly per single colour is necessary, as well as one operative for each such assembly, and time in which to set up the screens themselves and keep a constant check on the glaze compound for correct consistency. Whatever the individual system employed, the liquid glaze medium requires preparation, and cannot always be utilised to the last drop. Finally, production methods involving the application of glaze in liquid state give rise to a large reject percentage.
The prior art thus outlined stands in need of improvement - considerable improvement - especially with regard to the undesirability of applying glaze in liquid state, and by the same token, of overlarge plant used therefor, of vacuum and other cleaning installations, and wash-down facilities, and of uneconomical man-power requirements; such improvement bringing with it an end-product characterised by better finishing and enhanced definition. Transferring normal toner images to ceramic bodies was known from GB-A-658699.
From the foregoing, one may discern the need for a solution to the technical problem of discovering a glaze-decoration method capable of applying the medium in its dry state, and a machine for carrying said method into effect - a machine such as will rationalise the production of glazed ceramic tiles by reducing space-requirements, man-power, wasted material, operating- time and costs, and rejects.
The invention described herein solves said problem through the adoption of a decorating- method which is to some extent inspired by xero- printing, the application of xerography to photocopy reproduction developed by the Xerox company. The Xerox method makes provision for build-up of a positive charge in a selenium-coated conductor to some 6000 volts (this by inducing a 'corona' phenomenon) in order to render it light- sensitive. Light reflected by the white areas of the image to be reproduced will then hit the selenium correspondingly, so as to allow selective earthing-out of the positive charge, leaving behind a positively-charged area which will correspond to the image's dark parts. Being thus positively charged, the conductor-image is then capable of attracting a special black powder which is negatively charged and consists of a carrier-medium (graphite, usually) and a thermoplastic resin pigment, this being strewn onto the blank copy-paper and fixed by heat-treatment, so as to obtain a permanent reproduction.
The method to which the invention relates is featured in claim 1. In accordance with the Xerox principle, a cylindrical conductor having a selenium covering is charged to 6000V by the corona phenomenon, replaces the special black powder aforesaid with a normal glaze compound in dry state and having a negative charge; the image to be transferred onto the tile being provided by a transparency caused to reciprocate horizontally through a longitudinal path above said cylindrical conductor, whilst projection of the image onto the cylinder top-side is brought about by lamp and optic fibres; movement of the transparency being synchronised with that of the tile which travels horizontally beneath the cylinder and opposed thereto, reproduction of the image onto the cylinder during the transparency's return travel being precluded by application of light from an auxiliary source; the cylinder being caused to rotate and transfer said image downwards towards a first convergence produced by a feed-cylinder from which the negatively-charged dry glaze medium is imparted to the image-transfer cylinder and caused to adhere to the positively-charged dark areas of the latter; there being a second restriction located in opposition to the optic fibres and at the bottom side of said image-transfer cylinder where the tile itself, positively-charged by conductors position beneath, passes beneath in order to receive the glaze therefrom; said glaze adhering to the tile-surface by virtue both of the agency of a lamp which causes earthing-out of the positive charge, and of prior dampening of the tile-surface followed by application of a neutral base coat incorporating a bonding-agent. Multi-colour decoration involving three or four shades can be carried through by a set of machine-assemblies thus embodied, linked in series, with a final fix of the decoration being provided by a protective frit applied to the finished surface.
An improved embodiment of the machine set forth as per the invention described herein envisages positioning of the transparency within a revolving glass cylinder which is caused to turn synchronously both with the image-tranfer cylinder, and with the ongoing movement of the tile beneath, whilst the tile's position with respect to the image-transfer cylinder is adjustable, such synchronous movement provided for a drive-and-transmission associating all the machine's rotating parts one with the other.
Advantages offered by the invention are these: a simplified glazing-procedure; elimination of glaze in the liquid state, and attendant problems; a more compact glaze-decoration plant; less maintenance; little or no waste/rejects; quick setup for the single product scheduled; no large vacuum and cleaning installations; no glaze-encrusted equipment to clean and wash down; reduction in manpower and running-costs; a more faithful reproduction of the projected image; and finally, a cleaner and more clear-cut reproduction, perfectly centred on the decorated surface of the tile.
There are two possible embodiments of the invention illustrated-purely by way of example - in the ten sheets of drawings depicting the machine which accompany this specification, wherein:

Figure 1 is a side view of one possible embodiment, seen in cutaway;
Figure 2 is a vertical cross-section of fig. 1 taken through II-II, whose main purpose is that of illustrating the travel of both transparency and tile at that part of the machine;
Figure 3 is a horizontal section taken along those parallel planes passing through the axes of the machine's rotary components;
Figure 4 is a schematic view from one side of the machine whiuch shows its transmission arrangement;
Figure 5 is a large-scale section through fig. 3, or fig. 9, illustrating the fed-cylinder;
Figure 6 illustrates the electrostatic contact- zone between tile and cylinder;
Figure 7 is the same view as that in fig. 1, though of a machnine in which the transparency is fitted up inside a revolving glass cylinder;
Figure 8 is a vertical cross-section through VIII-VIII in fig. 7;
Figure 9 is horizontal section as per fig. 3, taken through the second embodiment as described herein;
Figure 10 is a side view of the machine in its second described embodiment, which illustrates the transmission arrangement;
Figure 11 is the same drawing as in fig. 6, though referred to the second said embodiment.

With reference to the drawings, 1 denotes a pair of belts carrying the single tiles 2 forward onto a cog-belt denoted 3 which propels them further forward onto guides 4 at the bottom side of the cylinders, these lying above said cogbelt 3, and between further lateral guides 5; 6 denoting the teeth fixed to belt 3 which drag each single tile along through the machine, as well as carrying a synchroniser block 7 for timing purposes. 8 denotes a pair of guides made fast to the upper part 9 of the machine framework, this in turn associated with the base 10 by way of uprights 11, said guides 8 accommodating the slide of a carriage 12 which reciprocates the transparency 13 providing one of the colours to be printed on tile 2. 14 is the vertically-disposed reflector of a lamp 15 mounted to upper-framework 9 which projects a beam of light through transparency 13 by way of the slot 16 located in a baffle denoted 17; ventilation is afforded by a tube 18. 19 denotes a transparent plate fitted to the frame 20 forming part of carriage 12, and providing the mount for said transparency 13, which is held in position by the weight of a further top transparent plate 21 hinged to said frame. 22 denotes a spring anchored at one end to the end of frame 20, and at the other to framework 9. 23 denotes the extremity of a cable fixed to the carriage 12 carrying transparency 13, and sliding within a flexible sheath 24 attached to the entry end of upper framework 9 and bent round and away so as to turn back in toward the machine and connect up with a longitudinal member 25 disposed at centre and fixed to two cross-members 26. The pair of guides 4, together with lateral guides 5, their respective pairs of longitudinal supports 27 and 28-both associated with flexibly-mounted exit cross-member 29-the entry-end cross-member 30 hinged to base 10, and the two cross-members 26 affording support to longitudinal member 25, all combine in making up the chassis denoted T which oscillates vertically and within the section of machine being described, whilst bearing ceramic tile 2 and timing-block 7 along with it. 31 denotes a horizontal slot in said longitudinal member 25 extending the entire length of the latter and accommodating the slide of two bottom cross-pieces 32, 32' associated with the cycle timing-block 7. 33 is an adjustable sleeve fitted to the entry-end of said longitudinal and provided with a raked face 34 designed to draw the first cross-piece 32' offered by block 7 down into a recess 35 located below the level of slot 31 at that end thereof, such that the timing-block 7 itself dips forward and down so as to disengage its own trailing top-end 36 from the tooth 6 which would hitherto have been drawing it along together with tile 2. 37 denotes a transverse slot at the underside of said longitudinal member 25 wich underlies the first cross-piece 32' when in its drawn-back position, whilst 38 is a stop associating with said slot by virtue of its being fixed to the end of a flexible lath 39 fitted likewise to the underside of longitudinal member 25.
40 represents an electromagnet which frees slot 37 whenever it is wished to avoid timing-block 7 being carried forward by tooth 6 - in short, when there is no tile 2 to be decorated.
41 denotes the opposite end of the cable aforesaid made fast in like manner to end 23, in this case to the trailing end of the timing-block 7. 42 denotes a transversely-disposed screen of optic fibres located beneath the slot 16 in baffle 17 and arranged in two staggered sets, borne up thus at either side by the two side-walls 43 of a box structure 44 mounted on base 10. A pair of opaque side-members 45 fixed to the upper part of box 44 converge downward toward the optic fibres, and have the function of gathering in those outer rays emanating from lamp 15 whose beam is intended exclusively for the fibres 42 themselves. 46 denotes the basic structure of a cylindrical conductor designed to transfer the decorative image, whose transversely-set shaft 47 lies in a vertical plane passing through the centre-line of lamp 15 and fibres 42 alike, said shaft journalled at either end to side-walls 42 and thus free to rotate; the outer cylindrical surface 48 of said conductor coated with selenium glass, and the entire component thus embodied - being a conductor - connected to earth. 49 is a tungsten filament, taut and transversely disposed upward and way from cylinder 46―48, and boxed within an enclosure 50 fixed at either end to side-walls 43, this being the means by which a positive charge is imparted to cylindrical surface 48 by the corona effect aforementioned (see fig. 6), which raises some 6000 volts between the filament itself and earth. 51 denotes a lamp having a reflector 52 with its throw-aperture 53 directed toward that bend of cylindrical surface 48 exposed to the beam emanating from optic fibres 42, provision being made for a shutter 54 attached to one end of a flexible strip 55 mounted to a support 56 suspended between side-walls 43. 57 is a further electromagnet designed to attract strip 55 aforesaid in order to open up aperture 53 during the return travel of transparency 13-this in order that the beam from lamp 51 may cancel out the positive charge induced into surface 48 by filament 49 - said electromagnet being operated by the action of a cam during said return travel. 58 denotes a hopper-likewise a conductor- mounted between side-walls 43 and insulated therefrom, and containing the glaze compound in dry state (denoted 59, and of whatever colour happens to be selected for this machine stage) into which a nagative electrostatic charge of a few hundred volts is induced. The hopper incorporates transversely-disposed rods 60 of prismatic shape, designed to agitate the dry glaze. 61 denotes a further agitator-rod, embodied cylindrically and located at the bottom end of the hopper alongside a further cylinder - the feed cylinder aforementioned - having an insulated body section 62 and a shaft 63 journalled to the sides 64 of the hopper 58 itself. The surface-speed of cylinder 62 is greater than that of cylinder 46―48 by an amount sufficient to compensate for non-conductive interspaces. 65 denotes strips of conductive material (figs. 3, 5) disposed about the cylindrical surface area of feeder 62, which makes contact with image-transfer cylinder 46―48 at the bottom entry-side thereof. 66 and 67 denote sectors-to-a-circle of differing length, both conductive, annular in shape, and making-up one common circumference; said sectors fixed to the inside of one of said hopper-walls 64 and disposed thus coaxial with feed-cylinder 62, and furnished with radial conductors 68 directed toward the outer surface of said feed-cylinder. Sector 66 is wired to a source of electrical energy supplying some few hundred volts positive charge - preferably of a lower potential than that of hopper 58-whilst sector 67 is wired to a negative source, and positioned nearest the image-transfer cylinder 46―48. 69 denotes the bottom-most point of topper 58, which is radiused parallel with the cylindrical surface of feeder 62, and has its farthest extremity located within that area where the two cylinders 62 and 46-48 turn away from one another following contact. 70 denotes a vertical baffle (likewise conductive) fitted to hopper 58 and disposed within a transverse plane dividing feed-cylinder 62, whose lower edge exhibits a bevel, and rides alongside the outer cylindrical surface of feeder 62 at distance such as will allow passage therebetween of a 'dusting' of glaze some few tenths-of-a-millimetre thick. 71 denotes further conductors ranged in alignment below the lower generatrix offered by cylinder 46-48-that is, at the point of actual image - transfer onto the tile; said conductors fashioned from metal, directed toward the cylinder-generatrix, insulated from composite- chassis T aforedescribed, and wired so as to receive a positive electrical charge. These conductors ride all-but-in-contact with the reverse face of the single tile 2. A further lamp 72 having a reflector 73 and positioned at the opposite side of the image-transfer cylinder to that of cylinder 62, has its rays directed at the image-transfer line so as to cancel out the positive charge retained by that part of the cylindrical outer surface 48 already beyond the transfer-line and approaching the lamp itself.
74 represents a roller-brush turning around shaft 75 and suspended in rotation between side- walls 43 so as to lie parallel with cylinder 46, 48 and act thereon at a point between filament 49 and lamp 72; the bristles of said brush performing a purely mechanical function: that of cleaning off residual glaze 59 from the surface of the image-transfer cylinder. 76 denotes a casing within which brush 74 is enclosed, together with a filter 77 and a fan 78 which provide for the removal of residual glaze. In fig. 1, 79 denotes the hinge-pin about which chassis T is caused to pivot, the remaining end of the chassis itself resting upon springs 80, these providing suspension for same. In fig. 4, 81 is a gearmotor which drives a shaft 82 journalled to base 10, whilst 83 and 84 are pulleys keyed onto said shaft 82 and further shaft 85, respectively, creating the loop for cogbelt 3 aforementioned. A further pulley 86 likewise keyed to shaft 82 transmits drive by way of a belt 87 to shafts 47 and 75, which drive the image-transfer cylinder 46―48 and roller-brush 74, respectively. A pulley 88 mounted into return shaft 85 transmits to further shaft 89, this in turn driving a belt 90 whose function is that of turning feed-cylinder shaft 63, cylindrical agitator rod 61 and prismatic rods 60. It will be observed that the gearmotor 81, being the only source of drive, guarantees synchronous movement of the machine's moving parts. S denotes the gaps between feed-cylinder 62 and image-transfer cylinder 46-48, whilst S' represents a similar gaps between the latter and the tile 2 to be decorated. In fig. 7, 91 denotes a pair of cogbelts, these carrying tiles forward into the machine; 92 denotes a pair of uprights issuing from base 10 to which lateral guides 5 are made fast. Bracket-type fixtures 93 associated with uprights 92 and facing inwards afford support, by way of springs 94, to a pair of guides 95 directing the top branches of said belts 91, these being driven by a pair of drive pulleys 96 and returned by further idle pulleys 97, the drive pulleys being keyed to a shaft 98 journalled at either end to base 10. 99 represents a speed variator imparting motion to shaft 98 by way of a drive-belt 100. 101 denotes a chain located centrally in the machine at a point between said pair of belts 91, and provided with a detent 102 designed to slow up and position the single tile 2, said chain 101 turning at a lesser speed than that of belts 91. 103 denotes the drive-sprocket for chain 101, and 104 the idle return- sprocket. An electromagnetically operated stop 105 halts the passage of the tiles upon triggering of a microswitch not shown. 106 denotes uprights issuing from the base 10 of the machine, whose function is that of supporting the box structure 44 within which all the glazing-equipment carried by the machine is housed.
107 denotes a transversely-disposed, hollow glass cylinder having solid ends 108 supported in rotation by trunnions 109, these fitted to respective appendages 110 extending upwards from the side-walls 43 of box 44. A transparency 111 bearing the image for one of the glaze colours to be applied to tile 2 is mounted onto a sector of the inside surface of glasscylinder 107, whilst-likewise inside the cylinder- a vertically disposed reflector 112 and associated tube lamp 113 are associated with said trunnions 109 at either end. 114 is the baffle defining a slot 115, beneath which one has the two staggered sets of optic fibres 42 aforementioned, suspended between the two side-walls 43 of box-structure 44, as in the first embodiment described. In fig. 8, 116 denotes appendages from guides 95 which carry conductors 71 aforedescribed. A pulley 117 keyed onto drive-shaft 98 (see fig. 10) turns a cog-belt 11"8 passing around the following rotary components: the shaft 75 of roller-brush 74, shaft 47 of the image-tranfer cylinder 46―48, pulley 119 turning one end 108 of glass-cylinder 107, the uppermost of the two prismatic agitator-rods 60, and further pulley 120 keyed to the sprocket 103 driving chain 101. Pulley 120 and drive-sprocket 103 are of size such that the speed of said chain 101 will be less than that of the pair of cog-belts 91 - this in order to enable positioning of the single tiles 2 beneath cylinder 46―48 by means of the detent 102. Pulleys 117 and 119 are of relative diameter such that the surface speed of said glass-cylinder 107 will be equal to the travel- speed of belts 91. Provision is made for a screw- adjusted stretcher 122 acting on belt 118 at a point between pulleys 119 and 120, whilst a further stretcher 123 tensioned by means of a spring is located between pulleys 120 and 117: by working stretcher 122 back or forth at the turn of its screw, pulley 120 can be made to advance or retard with respect to pulley 119 so as to synchronise movement of the transparency 113 with that of the detent 102 offered by chain 101, this bringing about the correct timing between tile 2 and transparency 113. 124 denotes a pulley keyed to the shaft of the uppermost agitator-rod of the two denoted 60 (prismatic) so as to transmit drive to the lower agitator rod 60, the cylindrical agitator-rod 61, and the shaft 63 of feed-cylinder 62 - this by way of a belt 125 looped around same.
Function of the machine, in the case of the embodiment as illustrated in figs. 1-6, is as follows: having started the gearmotor 81 and supplied electrical power to those parts of the machine requiring same in all stages of the line-e.g. three such units as described herein, in the case of a glaze-decoration involving three distinct colours - and mounted the three transparencies into their respective sliding carriages 12, tiles may be fed onto the belt 3 appropriately spaced apart, already moinstened and given their neutral glaze base-coat. The leader-tile now triggers electromagnet 40, whichy engages the trailing top-end 36 of the timing-block 7 with the tooth 6 offered by belt 3 already propelling tile forward into the machine; thus tooth 6 carries block 7 forward, and occasions movement of the carriage 12 and transparency 13 in the opposite direction by way of cable 41-23. As the transparency passes little-by-little beneath the beam emitted by lamp 15, the optic fibres 42 below project the image line by line onto the top side of transfer-cylinder 46, whose outer surface 48 is already invested with a uniform positive electric charge produced by the 'corona' phenomenon generated by filament 49. The clear areas of the transparency allow passage to the light which, as a result, cancel out the corresponding positively-charged areas on 48 of the cylinder passing beneath. Thus, the positively-charged area, or pattern remaining on surface 48 will correspond to the transparency's dark parts, whilst the boundary of the transparency either matches, or is proportioned to, that of the tile 2 itself. Cross-piece 32' forming part of the timing-block 7 now comes up against the recess 35 offered by longitudinal member 25 and, thanks to the incline incorporated thereinto, top-end 36 is freed from tooth 6 of the carrier belt 3, and the carriage 12 and timing-block 7 make their respective returns- to-original-position, at the same time triggering electromagnet 57 whose excitation permit light- emission from lamp 51 so as to render the transparency 13 without influence during its return. With the formed image now round at the meeting-point of the two cylinders 62 and 46―48- clearance at point S narrowing to some few tenths-of-a-millimetre- a dusting of negatively-charged glaze is carried into the narrowed area by the feed-cylinder 62 itself - this by virtue of the fact that strips 65 aforementioned are positively - charged by sectorial conductor denoted 66, and thus attract the negatively-charged dry glaze particles. Passing from thence into the negatively-charged sector denoted 67, strips 65 reverse polarity so as to throw the powdered glaze toward area S and onto the facing surface offered by image-transfer cylinder 46―48, still retaining the pattern received from the transparency 13.
The dry glaze adheres to the 'dark' parts of surface 48, being positively-charged, though not to those areas already discharged. A remnant will return toward the hopper held by the positively-charged areas of feed-cylinder 62, whilst the particles 59 held by positive charge on surface 48 continue toward the second narrowed area, S', where a tile will be moving forward, in receipt of a positive charge from the conductors 71 beneath. At this point, glaze 59 adhering to the dark areas of cylinder-surface 48 are attracted by the positively-charged tile, to whose surface they immediately 'take', according to the image imparted, since the light emitted by lamp 72 earths-out the positive charge carried by surface 48, and in addition, the base-coat already applied to the tile itself incorporates a bonding agent, as mentioned at the outset. Once the final colour has been thus copied onto the tile, a fix provided by frits or a transparent glaze-compound will provide the protective final coat. Referring now to figs. 7-11, function comes about thus: - having started up the motorvariator 99 and supplied electrical power to all parts of the machines making up the line - e.g. three such units as described herein, in the case of a glaze-decoration involving three distinct colours - and mounted the transparencies 111 into their three respective glass-cylinders 107, the tiles 2, already moistened and given their neutral glaze base-coat, can be fed onto the pair of carrier cog-belts 91. The tiles will in fact be appropriately spaced apart by stop 105 via triggering of a microswitch timed with the detent 102 offered by chain 101, such that the detent - travelling at a lesser speed than that of the belts 91 themselves - is enabled to position the single tiles correctly with respect to said glass-cylinder 107; transparency 111 mounted within the latter being synchronised with said stop 105 so as to pass over the slot 115 in baffle 114, the result of which is that the beam emitted from lamp 113 passes through the optic fibres 42 so as to project the image line by line onto surface 48 of the transfer-cylinder 46, this retaining a formed image which will correspond to the transparency's dark area. Once the border of the transparency passes over slot 115, any further image therefrom will be cancelled out automatically from cylinder 46―48 by light emitted from lamp 51 which projects through the aperture 53 at that point opened up by excitation of electromagnet 57, this operated by a cam timed by glass-cylinder 107 itself. The actual image-transfer stages are similar in all respects to that described in the case of the embodiment in figs. 1-6. Synchronous movement of cylinders 107 and 46―48 with tile 2 is obtained by the transmission system which associates chain 101, glass-cylinder 107 and image-transfer cylinder 46-48 by way of a single drive-belt 118 looped around the self-same motor- variator output shaft 99 turning belts 91. Pulley- diameters are such that the speed travelled by belts 91 matches the surface-speeds of both cylinders 107 and 46―48; also, the speed travelled by chain 101 - hence of detent 102 - is less than that of belts 91, thus permitting correct alignment of the single tile 2 with respect to the image revolving on cylinder 48. Fine adjustment of the tile-position thus obtained, giving perfect alignment both with the image on surface 48 and with the transparency 111 itself, is then had by working the screw-operated stretcher 122, so as to advance or retard pulley 120 (that driving chain 101) with respect to the two cylinders which bring about image-transfer: glass-cylinder 107, and transfer-cylinder 46-48.
When carrying the invention into effect, materials, dimensions, constructional and design details such as the shape of hopper 58, the method of synchronising carriage 12 by means of timing-block 7 (substituting pulley-drive for sheath 24, for instance), may all differ from those disclosed, whilst not departing from the scope of the invention as claimed. With this in mind, the microswitch which operates stop 105 might well be cam-controlled from the end 108 of glass- cylinder 107, or from the shaft 47 of image-transfer cylinder 46―48, or from the chain's 101 drive-sprocket 103, or even from the detent 102 offered by said chain, or, indeed, from any other moving part of the machine whose operation is sychronised with said cylinders 107 and 46―48.

Claims

1. A photo-electrostatic method for applying glaze decoration to ceramic tiles wherein an image is projected optically by means of a lamp and a transparency (13 or 111) onto a revolving conductive image-transfer cylinder (46) having an outer surface of selenium glass (48) to which a positive charge of some 6000V is imparted, characterised in that glaze in dry state invested with some few hundred volts is transferred, by means of a feed-cylinder (62) electrostatically charged onto the dark areas of said image onto said image tranfer cylinder (46), the surface of said feed cylinder (62) being divided in two portions having opposite electric charges; that said glaze is further transferred according to the pattern of said image from said transfer cylinder (46) onto a single tile (2) passing, beneath said cylinder at a distance not less than a gap S', said tile having been previously moistened and given a base-coat of neutral glaze-and-bonding agent on its top side, and in receipt of a positive charge of some few hundred volts imparted by conductors, whilst residual positive charge carried by said image transfer cylinder is earthed out optically at the point of transfer; provision being made to cause said transparency (13, 111) either to reciprocate or rotate and to make movement of the tile to come about synchronously with and in the opposite direction to that of said transparency during said image-transfer, and for further transfer of said image to said cylinder during return travel of the transparency to be inhibited by optic means; multi-colour decoration being brought about by utiulising one machine per colour envisaged, with relative amounts of coloured glazes calculated on the basis of the degree of darkness betweeen one transparency and the next.

2. Machine to carry out the method of claim 1, characterised in that a carriage (12) and associated frame (20) carrying said transparency (13) between two transparent plates (19 & 21) -the topmost of which hinged to said frame-is caused to slide back and forth through a longitudinal path along horizontal guides (8) fixed to the upper part (9) of the machine framework and directly above said image-transfer cylinder (46―48); such alternating movement being regulated by the action of a spring (22) and synchronised with the movement of a timing-block (7) drawn together with said tile (2) by teeth offered by a cog-belt (3) carrying said tiles through a longitudinal and horizontal path and looped therefor around pulleys (83 & 84), with drive imparted by a gear-motor (81); the top branch of said belt travelling marginally below said image-transfer cylinder (46, 48) and disposed at a level slightly below a pair of lower guides (4) along which the tile slides forward whilst bounded at either side by further, lateral guides (5).

3. Machine as in claim 2 characterised in that said pairs of guides (4 lower & 5 lateral) are fixed to a rear cross-member (30) associated with the machine base (10) by way of a hinge (79), and to an exit cross-member (29) floating on a pair of suspension springs (80), thus constituting an oscillating chassis (T) operating in conjunction with belt (3) aforementioned which carries the tiles (2) forward over a longitudinal member (25) fixed to further cross-members (26) of the chassis itself; said longitudinal member (25) provided with a transverse and horizontal slot (31) in which timing-block (7) aforesaid is caused to slide.

4. Machine as in claims 2 and 3 characterised in that said timing-block (7) is furnished with a trailing top-end (36) and a pair of bottom cross-pieces (32 & 32') designed to slide in said slot (31), the leading one of which comes up at the end of its forward travel against the raked surface (34) of an adjustable end-sleeve (33) associated with said longitudinal (25) so as to engage in a recess (35) incorporated into the latter at one end of, and slightly below, said slot (31); said longitudinal further comprising a second, transverse slot (37) underlying cross-piece (32) of the timing-block in its fully-drawn-back position, said slot (37) closed by a stop (38) fixed to one end of a flexible lath (39) associated with the underside of said longitudinal; provision being made for an electromagnet (40) located beneath said stop and connected to the underside of said longitudinal member (25).

5. Machine as in claims 2, 3 and 4 characterised in that one end of the carriage (12) carrying said transparency (13) is connected by way of a cable with forward-upper and rear-lower ends (23 and 41 respectively) to the trailing end of said timing-block (7), said cable bent through an arc and passing within a sheath (24) between carriage and timing-block, one end of said sheath made fast to the upper part (9) of the machine framework at its entry end, and the remaining end made fast at bottom to the rear end of said longitudinal member (25) in the cenre of the machine.

6. Machine as in claims 2, 3 and 4 characterised in that it comprises a longitudinally-disposed box structure (44) mounted to base (10) between the carriage (12) carrying said transparency (13) and the cog-belt (3) carrying single tiles (2) and operating in conjunction with the oscillating chassis (T) carrying timing-block (7), said box structure accommodating said image-transfer cylinder (46) with its outer selenium surface (48) and shaft (47), the latter disposed transversely and journalled to said box structure; it being envisaged that the vertical plane concurrent with said shaft (47) further coincide with a lamp (15) and surrounding reflector (14) provided with a baffle (17) at bottom having a slot (16) through which a beam may pass, gathered in by converging members (45), to optic fibres (42) beneath, the lower end of the latter lying marginally above the topmost generatrix of said cylinder (46―48)-these components located above the latter; whilst in the same plane, and below said cylinder: metallic conductors (71) imparting a positive charge to, and riding all but on the reverse side of said tiles (2) during their passage along the guides (4) offered by chassis (T); at which point the bottom-most generatrix of cylinder (46-48) and the tile itself meet, thus defining the gaps or area of convergence S'.

7. Machine as in claim 6 characterised in that said box=structure (44) which houses the image-transfer cylinder (46―48) also accommodates, at the machine-entry side of said cylinder and following rotation of same: a lamp (51) whose reflector (52) is directed toward the top of said cylinder through an aperture (53) during return travel aforementioned of the transparency (13), said aperture closed by a shutter (54) attached to a flexible strip (55) and operated by electromagnetic (57) when triggered by a cam, said strip anchored to a support (56) suspended between side-walls (43) of the box structure itself; also, a conductive hopper (58) made fast to and insulated from said side-walls, containing dry state glaze particles (58) negatively-charged with some few hundred volts, and furnished with agitator-rods, two of which prismatic (60) and one cylindrical (61); also, a feed-cylinder (62), likewise insulated and having a shaft (63) journalled to the sides (64) of said hopper, which revolves in the opposite direction to that of said image-transfer cylinder (46―48) and combining with the latter at its bottom adjacent quadrant to form a first gap or area of convergences allowing a clearance of some few tenths-of-a-millimetre; said feed-cylinder located at the bottom end of said hopper at the outlet thereof, and positioned beneath a vertical baffle (70) such that a few tenths-of-a-millimetre's clearance remains between the two, the cylinder in turn located some few tenths-of-a-millimetre above the similarly radiused and parallel curved hopper bottom- section, and below and to one side of said cylindrical agitator rod-this located at the opposite side of feed-cylinder (62) to that area of convergence S aforesaid.

8. Machine as in claim 7 characterised in that said feed cylinder (62) is furnished with peripheral longitudinal strips (65) ranged one next to the other, and has one of its ends located within an appendage of one of the hopper (58) sides (64) where two annular conductive sectors (66 & 67) are accommodated, these insulated one from the other and tying concurrent to a common cylindrical surface placed outwardly of and coaxial with said feed-cylinder, said sectors furnished with radially-disposed conductors (68) directed inward towards the latter; said sector (67) nearest the image-transfer cylinder being negatively charged, and of lesser angular length than its counterpart (66) in order to induce an electrostatic charge only into those strips (68) on the feed-cylinder moving through said area of convergence.

9. Machine as in claim 56, characterised in that said box structure (44) which houses the image-transfer cylinder (46―48) also accommodates, at the machine-exit side of said cylinder and following rotation of same:-a lamp (72) whose reflector (73) projects light toward the image-transfer area immediately following the transfer-cylinder's bottom generatrix as the latter revolves upward thence; also, a roller-brush (74) suspended in rotation between side-walls (43) of the box-structure itself (44), within a casing (76) also housing a filter (77) and extractor-fan (78), whose function is that of cleaning-off said image-transfer cylinder (46―48); and a filament (49) disposed transversely within an enclosure (50) fixed to said sidewalls (43) and charged with some 6000V, whose location is alongside said cylinder, and between the roller-brush and the topmost cylinder-generatrix.

10. Machine as in claim 2, and 7, characterised in that it comprises a transversely-disposed revolving glass cylinder (107) located directly above said image-transfer cylinder, supported in rotation via trunnions (109) at its two ends (108) in a pair of respective appendages (110) extending upwards from the side-walls (43) of said box-structure (44); it being envisaged that a transparency (111) be mounted to the internal surface of said cylinder, and that a tubular lamp (113) and relative reflector (112) be suspended between said trunnions (109) within the cylinder itself (107); the bottom-most generatrix of said cylinder disposed directly over a transverse slot (115) let into the top face of said box structure (44) above optic fibres (42) aforesaid.

11. Machine as in claim 10, characterised in that it comprises a pair of longitudinally-disposed cog-belts (91) carrying the tiles (2) forward, the top branches of which travel marginally below said image-transfer cylinder (46―48), and a chain (101) provided with a detent (102) designed to slow up the single tile (2) and position it with respect to said cylinder (46-48); said chain being located immediately prior to said cylinder along the line of travel of the tiles, and caused to move at a slower speed than that of said belts (91); the top branches of said belts (91) sitting upon a pair of guides (95) positioned via springs (94) so as to rest on bracket fixtures (93) extending from respective uprights (92) issuing from the machine base (10).

12. Machine as in claims 10 and 11, characterised in that said cog-belts (91) are driven from a motor-variator (99) which transmits drive by way of a cog-belt (118) to glass-cylinder (107), image-transfer cylinder (46―48) and chain (101); pulley- diameters and associated drive-components being such that surface-speed of the glass- cylinder (107) and of the image-transfer cylinder (46―48) will match drive-speed of said pair of belts (91), and that the speed travelled by said chain (101) will be less than that of said belts (91

13. Machine as in claims 10, 11 and 12, characterised in that it comprises a screw-operated belt- stretcher (122) located between the pulley (119) turning said glass-cylinder (107) and the pulley (121) driving said chain (101), whose adjustment back or forth produces advance or retard of said pulley (121) with respect to said pulley (119) in order to sychronise movement of detent (102) aforementioned offered by said chain (101) with that of transparency (111) mounted within said glass-cylinder (107); provision being made for a spring-tensioned stretcher (123) which operates in conjunction with said screw-operated stretcher (122).

14. Machine as in claims 10, 11, 12 and 13, characterised in that the agitator-rods (60 & 61) and glaze feed-cylinder (62) aforesaid are turned by a drive-belt (125) from a pulley (124) keyed to the upper of the two prismatic agitator rods (60), this in receipt of initial rotation from said cog-belt (118).

15. Machine as in claims 10 to 11, characterised in that its entry-point is provided with a stop (105) bringing tiles (2) to a halt on arrival-in from off the infeed belts (1); said stop (105) actuated by electromagnet and triggered by a microswitch cam-operated from one of the ends (108) of said glass cylinder (107), or from the shaft (47) of said image-transfer cylinder (46-48), or from the shaft (121) turning the sprocket (103) driving chain (101) aforesaid; it being envisaged that such a microswitch might equally well be operated by the detent (102) offered by said chain (101).