METHOD AND APPARATUS FOR PRINTING ON SHEET MATERIAL

Abstract: A method of printing paper or textile material comprises directing light through an array of electronically operated light shutter units (5 or 6 or 7 or 8) arranged in a two-dimensional area formed on the surface of a hollow control drum (1 or 2 or 3 or 4) towards a parallel light sensitive printing drum (9 or 10 or 11 or 12) rotatable in contact with material (13) to be printed, printing medium capable of adhering to the portions of the drum on which light has fallen being applied to the printing drum before said portions of the drum come into contact with the material to be printed. Selected light shutter units are set open and shut according to the pattern to be printed so that light passing through the open shutter units will affect the light sensitive printing drum whereby printing medium applied to the printing drum will adhere to the drum in the pattern to be printed for transfer during rotation of the drum to the material to be printed.

Description: METHOD AND APPARATUS FOR PRINTING The subject of this invention is a method and apparatus for printing on sheet material such as webs of textile material and sheets of paper. Various methods for the high speed printing of sheet material both in black and white and in colour have been proposed. one form of apparatus employing a Laser device includes a rotating mirror structure so arranged that the beam from a Laser directed on to the rotating mirror is caused to scan 0 across a Light sensitive printing drum while the output of the laser is controlled by a computer to produce sensitized points on the printing drum in the form of a Line of dots. The laser is so switched that the spacing of the dots in each scanning line 5Ϊ is determined to form a Line of the desired pattern, the pattern being built up by the addit on of subsequent scanning lines of dots on the printing drum so that the lines of dots come together on the prin ng dru to delineate the pattern to appear on the web- 3 Toner, i.e. printing pigment, is then applied to the printing drum and adheres to the poirts where the laser light has fallen on the drum so that as the drum is rotated in contact with the web the pattern is printed on the web. this device which so far > has been mainly or only used for printing on sheets of paper suffers from the disadvantage that because pf parallax and angularity effects at the ends of each scanning line distortion is introduced. To overcome this difficulty another proposal has been 1 to provide a continuous light source having its Light • directed as a Line across a series of Liquid crystal (LCS) units, each shutter unit being controlled by a control computer to be open or shut according to whether or not a beam of Light is to be allowed to pass through at that point so as to provide a dot or a blank space at that point. In this device the Light beams passing through the shutter units are not subjected to parallax or angularity effects so there is no distortion anywhere along each line of dots . A disadvantage of the known apparatus using liquid crystal shutters is that the pattern is created by a continuous operation of successive Line formation. Since every line has a different spacing of dots from the dot spacing in the preceding Line in the formation of most patterns the Line of shutters has to be reset to a new . confi guration for each succeeding Line of the pattern and even in forming repeat patterns each repeat is a completely fresh pattern-forming operation. As it is necessary in forming patterns of high quality to provide at least 120 dots per cm t w ll be understood the rate of emission of shutter control impulses by the controlling computer must be very high, at Least 120 times the width of the web of material being printed in cm times the depth of the design in cm times the number of patterns to be reproduced per second. The rate at which the control impulses have to be applied by the control computer to the shutters for operation at commercial sp*eeds of printing may thus be as high as 100 mHz for each printing colour. For colour print ng at Least found separate colour printing units are required, For high quality work even more colours are often required. Thus the control computer must be able to operate at a speed of at least 400 mHz and often considerably faster. A computer able to operate at th s speed is extremely expensive, po.ssibly so expensive as to render the whole operation uneconomic. It is an object of the present invention to provide a method and apparatus capable of printing on sheet material at commercially acceptable speeds yet us ng a low cost computer capable only of operating at Low rates of impulse generation. According to the invention a method of printing paper or texti le material by directing light on to a light sensitive printing surface through electronically operated light shutter units and applying printing medium to the Light sensitive printing surface whereby the printing medium adheres to the portions of the printing surface on which the Light has fallen and then bringing the printing surface into contact with the material to be printed is characterized by arranging the shutters in an array forming a two -di ensional area disposed in pro im ty to the light sensitive surface and setting the shutters in a pre- arranged pattern for passage or non-passage of light through the shutters of the array then applying Light to whatever portion of the array is at any particular time adjacent to the light sensitive printing surface. The light sensitive printing surface may be a rotatable printing drum and the two-dimensional area constituting the array of shutters may be constituted by at least a portion of the surface of a second and hollow control drum the axis of which is parallel to the a is of the printing drum the light being applied to that portion of the inner surface of said control drum which is for the time being adjacent to the printing drum, said printing drum and said control drum being arranged to rotate in opposite directions at the same peripheral speed. A machine for printing sheet material according to the invention incorporating a rotatable light sensitive printing drum arranged to be sensitized to retain printing medium applied thereto at any point on the surface where a beam of Light falls on that point on the surface, eLectroni ca L ly operated shutter units operable to permit or block the passage of Light therethrough to the printing drum, a Light source arranged to apply light to the shutters and 0 means for applying printing medium to the printing drum at a position where it can be retained at sensitized points is characterized in that the shutter units are arranged to form at Least a portion of the wall of a second and hollow control drum disposed parallel 5 to the printing drum and arranged to rotate in a direction opposite to that of the printing drum and ' at the same peripheral speed, the Light projecting means be ng Located ithin said control drum and being arranged to project L ght against the Light 0 shutter units forming that portion of the wall of .the control drum which is at that instant closest to the printing drum. A practical embodiment of the invention is illustrated diagrammaticalLy in the accompanying 5 drawing in which 1, 2, 3 and 4 denote hollow drums the wall of at least a portion of each of which is constituted by an array of electrically operated Light shutters 5, 6, 7 and 8 respectively. The hollow drums 1, 2, 3 and 4 contain within them Light sources ( not illustrated). 9, 10, 11 and 12 denote Light sensitive printing drums each arranged with its axis parallel to the axis of the associated control drums 1, 2, 3 and 4, the light source inside the drums -5- 1 , 2, 3 and 4 being located to direct the light against the portion of the wall of the associated drum 1, 2, 3 or 4 closest to the associated drum 9, 10, 11 and 12. Means (not shown) is provided for directing printing medium (toner) of the appropriate colour against each drum. The printing drums 9, 10, 11 and 12 are in contact with the sheet 13 of material to be printed. A controL computer (not shown) is operativeLy connected to the individual Light shutters of the arrays 5, 6, 7 and 8 to set open o r closed each individual shutter according to the pattern to be printed. In practice, the l ght sources ithin the control drums 1, 2, 3 and 4 direct Light continually towards the shutter devices adjacent to the printing drums 9, 10, 11 and 12. Each shutter device if open allows a dot of light to pass through to the associated Light sensitive printing drum or prevents Light from passing through at the point of that part cular shutter device. A pattern is thus built up on each printing drum as it rotates along ith the associated control drum so that each printing drum carries on its surface an electrical pattern of the entire presentation of the design in a particular colour. Toner of that particular colour applied to each printing drum adheres to the printing drum at the electrified points and as the printing drum rotates the toner is transferred to the sheet of materiat—to be printed 13. The controL computer sets up the entire pattern on each controL drum 1, 2, 3, 4 by arranging for the shutters to be open or shut over the entire surface of the drum, the shutters being left in that position until that pattern is no longer required. Each controL drum is then illuminated by the associated Light source and as each portion of the array of Light shutters s brought successi ely across the associated light sensitive printing drum that portion of .the pattern appears on the light sensitive printing drum in the form of sensitized spots to which printing medium applied to the drum adheres for transfer to the sheet 13 as the drum rotates. There is thus no question of a pattern having to be built up of individual dots applied fast enough to allow the printing to take place at normal commercial speeds and since the pattern setting operation requires to be done just once it can be set in advance before any printing is done at all by a comparatively slow and cheap control computer. Also by the method and apparatus of the invent on the speed of printing is limited only by the normal mechanical limitations of the apparatus.

Claims: C LA I MS 1. A method of printing paper or textile material by directing light on to a l ght sensitive printing surface through electronically operated light shutter units and applying printing medium to the Light sensitive printing surface whereby the printing medium adheres to the portions of the printing surface on which the Light has fallen and then bringing the printing surface into contact with the material to be printed is characterized by arranged the shutters (5 or 6 or 7 or 8) in an array forming a two-dimensional area disposed in pro imity to the light sensitive surface (9 or 10 or 11 or 12) and setting the shutters in a pre-arranged pattern for passage o r non-passage of light through the shutters of the array then applying light to whatever portion of the array is at any part cular. time adjacent to the light sensitive printing ,. surface. 2. A method of printing paper or textile material according to claim 1, characterized in that the light sensitive printing surface is a rotatable printing drum (9 or 10 or 11 or 12) and the two dimensional area constituting the array of shutters is constituted by at Least a portion of the surface of a second and hollow control drum (1 or 2 or 3 or 4) the axis of which is parallel to the axis of the printing drum (9 or 10 or 11 or 12) constituting the light sensitive printing surface, the Light being applied to that portion of the inner surface of said control drum (1 or 2 or 3 or 4) " w ich is for the time being adjacent to the printing drum (9 or 10 or 11 or 12), said printing drum and said control drum being arranged to rotate in opposite directions at the same peripheral speed.. 3. A machine for printing sheet material incorporating a rotatable light sensitive printing drum (9 or 10 or 11 or 12) arranged to be sensitized to retain printing medium applied thereto at any point on the surface where a beam of light falls on that point on the surface, electronically operated shutter units (5 or 6 or 7 or 8) operable to permit or bLock the passage of light therethrough to the printing drum, a Light source arranged to apply light to the shutters and means for applying printing medium to the printing drum at a position where it can be retained at sensitized points is characterized in that the shutter units (5 or 6 or 7 or 8) are arranged to form at Least a portion of the wall of a second and hollow controL drum (1 or 2 or 3 or 4) disposed paraLlel to the printing drum C9 or 10 or 11 or 12) and arranged to rotate in a direction opposite to that of the printing drum and at the same peripheral ~ speed, the light projecting means being Located within said control drum (1 or 2 or 3 or 4) and being arranged to project light against the Light shutter units (5 or 6 or 7 or 8) forming that portion of the wall o.f the control drum (1 or 2 or 3 or 4) which is at that instant closest to the printing drum (9 or 10 5 or 11 or 12).

Inventors: FERGUSON WILLARD, FERGUSON, WILLARD
Applicants: COATS VIYELLA TECHNOLOGIES LIM, COATS VIYELLA TECHNOLOGIES LIMITED
Application year: 1988
Main classification: B41J3
IPC codes: G06K15