This invention relates to apparatus for producing a printed image and more particularly but not exclusively, a screen printed image .

Conventional screen printing processes offer a full range of possibilities for colour variations and tones, but the processes are highly labour intensive, not least because they are restricted to individual sheet feeding, rather than printing on a web. When an image is required to have an irregular shape, and the substrate on which the image is printed has to follow the shape of the image, the only practicable cutting arrangement currently is the so called "die-cutting" process which is complicated not very accurate, and expensive. Usually, there is still some weeding of waste area to be done on each individual die-cut sheet.

An alternative way of preparing images of irregular shape is to use a computer-controlled cutter. This can cut intricate shapes, logos and letter styles, to whatever standard of accuracy is built into the software and ^' plotting hardware employed. A major limitation, however, is that the colours of available materials are limited and do not match any of the recognised imaging colour schemes such as PANTONE or B.S. Tones cannot be produced easily below a dot size of 8mm diameter. If multi-coloured work is required then each individual colour must be cut and waste-weeded separately and applied manually over one of the colours used.

It is one object of the present invention to provide a screen printing method for the production of images of

irregular shape which combines the colour versatility of the screen printing process with the power of a computer to define the irregular shape of the outline of the image.

According to a first aspect of the present invention there is provided apparatus for producing on a web of substrate material a printed image of irregular periphery on a substrate sheet cut from the web and with an outline co-incident with the periphery of the image, the apparatus comprising:

a printing station controlled by logic means which accepts an input from a first index mark sensor; a cutting station controlled by logic means which accepts an input from a second index mark sensor; means to create an index mark on the web; the logic means being adapted to receive data which define a) the locus of the periphery of the image and b) the relative positions of the image and the index mark; whereby image composition data is relied upon to delineate the cut by which the substrate sheet is parted at the cutting station from the web of substrate material.

According to a second aspect of the present invention there is provided a method for producing a printed image of irregular periphery on a substrate sheet which has an outline coincident with the periphery of the image, the method comprising the steps of:

defining the periphery of the image with image composition data for inputting logic means; providing at a printing station printing apparatus controlled by the logic means; inputting the logic means with the image composition data; providing a web of substrate material carrying an index mark;

printing the image on the web at a predetermined location relative to the index mark; providing web cutting equipment at a cutting station, the equipment being controlled by the logic 5 means; inputting the cutting station logic means with the image composition data, to define the position of the image periphery relative to the index mark; advancing into the cutting station that part of 10 the web which carries the image; sensing the index mark on the web; causing the cutting equipment to part the image from the web in compliance with the inputted relative positions of the index mark and the periphery of the 15 image.

In one embodiment of the invention, a web of material on a spool is edge punched for a computer-controlled pin drive system. The drive system advances the web through the printing station. By reference to the index mark on the 20 web, the drive system positions the web for printing a line of first impressions on the web. The web is returned to the spool and then re-advanced for printing a line of second impressions in exact registry on top of the first impressions. The process is repeated, to build up a line

25 of finished images on the web. Then, the web on the spool is delivered to the cutting station at which the web is cut around the periphery of each image in the line, in succession, again under the control of a computer which relies on image periphery data drawn from the same source

30 as is used at the printing station.

For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings and the description and Example - ^• * given below. In the drawings:-

Figure 1 is a longitudinal vertical section of the printing station of one embodiment of the invention;

Figure 2 is a perspective view of the printing station; and Figure 3 is a longitudinal vertical section of the cutting station of the said embodiment.

Referring to Figures 1 and 2, a screen printing station 10 comprises a vacuum printing bed 11 beneath a screen print carriage 12, as is conventional. A product web 13 is drawn from a feed spool 14, over a dancing arm 15 and alignment roller 16 to advance over the top surface of the vacuum bed 11. A main drive roller 17 draws the web 13 off the bed 11 and the web then enters a drier 18, emerging through a cooling box 25 to pass over a dancing arm 19 and on to a take-up spool 20. As is conventional, the carriage 12 has lift gear 21 and the drier 18 has a fan 22 and associated ducting 23 but, unconventionally, the fan and drier are located beneath the vacuum bed.

The drier is the subject of a co-pending patent application of the present applicant.

Management of transport of the web 13 is by a personal computer, not shown (PC 386) . The index mark is on a sticker M applied to the leading end of the web and detected by an optical linear sensor 24 (SLS, from Allen-Bradley, Industrial Control Group, Milwaukee USA) . Sprockets on the web handling rollers engage with 3mm diameter perforations on the long edges of the web at 12.7mm spacing and with the hole centres 7mm in from the web edges. The dancing arms 15, 19 give an indication of web tension. The computer controls motors (not shown) on the feed spool 14, take up spool 20, drive roller 17 and drier 18.

The screen printing equipment is based on a KPX 2518 machine (HG Kippax & Sons Limited of Huddersfield.

Yorkshire, England) and the drier is based on an ultra-violet drier from Natgraph Limited (Nottingham, England) .

Turning now to Figure 3, the cutting station uses components from a computer-controlled knife plotter, in this case a Norris Datafont 500 (Norris-Booth Limited of Poole, Dorset, England). In other embodiments it may be a laser plotter. The plotter head 50 stands over a platen 51 over which is advanced the web 13, from a feed spool 52, over a dancing arm 53 and alignment roller 54 upstream of the platen 51 and then, downstream thereof, a main drive roller 55 dancing arm 56 and take up spool 57. In this way, the web transport system is very like the one in the print station, and should be as similar to it as possible.

A linear sensor 58, just like the one 24 in the print station 10, detects the index mark on the sticker M on the web 13, so that logic means can determine the position of the plotter head on the web 13 relative to the index mark.

The logic means is adapted to run graphic design software, for example, CORELDRAW, available from Frontline Distribution Limited of Basingstoke, England. It should be able to manage the cutting of 250m webs of vinyl material. Useful widths of such webs are 380, 466, 700, 1000, 1220mm and 1400mm.

As alternatives to screen printing there is envisaged lithographic, flexographic, bar-inkjet, spraybar and web offset printing. Jet air or infra-red curing could be used instead of u-v curing. Finishing operations could include varnishing, guillotining, waste-weeding and application taping. The digitally stored image could be utilised for computer-controlled laser exposure of the printing screens to be used on the machine.

The index mark sticker referred to above can conveniently be applied to the web a distance of from 250 to 750mm from the leading edge of the web. Conveniently, it has a hairline index mark 0.1mm in width, and perpendicular to the length direction of the web, for detection by the sensor. In other embodiments, it could be a magnetic marker but this is less preferred because it is less precise. .The index mark is perpendicular to a straight edge of the sticker which is aligned as precisely as possible on one long edge of the web. Th s, the preferred sticker is essentially of a T-shape, arranged with the top bar of the T along an edge of the web. Conveniently the sticker carries bar code information, about the web it is applied to.

The invention makes available computer-assisted process printing and cutting whereby design software is used to create an image for computer cutting of screen printing stencils each of which carries at least part of the design for printing. Material to be screen printed is then fed as a web from an edge-punched roll over drive sprockets, with the capability to be re-run to a feed roller, for successive passes through a printing station all the time being managed by the computer software.

In one embodiment there is a command, "STARTPOINT" , within the software, which determines the printing and plotting operations by identifying whereabouts the index mark is by the amount of full or partial revolutions of a given sprocket wheel on the system. An electronic device picks up the mark and trips the software to zero the web travel, whereby any movement of the web along the roll (x axis) can be measured by an electronic device measuring the movement via full or partial rotations of the given sprocket wheel on the system giving the movement along the x axis at any one time to the software and hence having the capability to rewind the roll back onto the reverse geared feed roller so that the index mark can be re-run to

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its original start position. This process of sensing the index mark and movement along the x axis is also applied to the computerized sprocket fed roller knife plotter so that pre-determined shapes can be cut from the roll after printing.

On occasions when designs entered into the design software have no facility to separate, colour layering may be introduced so that each colour can be separated by layer and adjusted for print bleed via a PRINTSET command. One layer is selected to serve as a final plot layer to give the exact whereabouts of the cutting lines required for the final computerized cutting step.

EXAMPLE

Artwork from a client is either drawn or scanned or imported into digital form.

An operator calculates the best usage of material for the job and selects the width of material required.

The operator then "cleans up" the image and separates a final plot line layer as a single entity - this becomes the only design addressed by the cutting station software for final plotting.

The operator then separates the colours by layer and using the PRINTSET command calculates and adjusts any of the colour separated designs for bleed over or bleed under for screen printing.

Having regard to the width of material and size of screen required the operator adds a number of layers to the software produced artwork. The cutting station is supplied with the relevant stencil material and cuts the separated colour layers with the lay markings for application to the photosensitive emulsion on the relevant screens. Once the printing screens have been produced in this way the material to be printed and cut is fed onto the screen printing machinery, the screen set into position and an index mark sticker placed in the relevant position.

The web is then advanced a short distance so that a sensor detects the index mark and zeros the x axis travel.

With the first colour screen ready in position, the relevant colour and finish of ink is applied to the screen and the first colour run started.

Once the first colour run is completed the web material is

run back to the index mark via the reverse geared feed roller. The first colour screen is removed and cleaned and the second colour screen is positioned according to lay markings already printed by the first colour.

After all the colours required have been printed the web is re-run onto the feed roller, removed and positioned on the cutting station. The STARTPOINT index mark is identified in exactly the same manner as with the screen printing machine and the cutting step started. This will accurately cut to the prescribed shape/s around the printed image. The result is multi-coloured shaped final products with accurate colour variations, in any required ink finish, with tones if required (that have been applied over the pre-plotted stencil material). All this is achievable at a fraction of the labour and material costs of the existing methods of production. The time required to come up with the finished result is reduced and the quality of the product is better.