THIS INVENTION relates to a printing apparatus and method and more particularly to a printing apparatus and a method for making single or multi-colour prints.

Known hand proof processes for printing one off prints or a small quantity of prints require the use of photoresists. The processes involve the following steps: placing a substrate in a fixed position on a print bed; applying a first colour pigment to the substrate; applying an opaque photoresist over the colour pigment; exposing the photoresist to light through a mask, so that exposed portions of the photoresist harden; removing the unhardened portions of the photoresist using water; removing the colour pigment which is no longer covered by the photoresist with a hydrocarbon solvent; removing the remaining photoresist with a further solvent which does not affect the colour pigment; and applying an isolation layer over the remaining colour pigment.

Such known hand proof processes require extensive use of hydrocarbon solvents. Further, these processes require the photo mask to be a negative image of the required print.

The present invention seeks to provide a printing apparatus and method which is simple to use, employs low cost equipment and, through the combination of these two features, permits designers, creative technicians or other persons who are not trained or unqualified in graphic reproduction to reproduce for presentation purposes a

colour print of design concepts. The resulting colour print simulates a pre-press proof.

Accordingly, in one aspect, the present invention provides a method of producing a coloured print, comprising the steps of: providing a substrate upon which a print image is to be applied; applying to the substrate a layer of a light sensitive composition including a photo¬ sensitive vehicle and colour pigment; positioning a photo mask to cover selected portions of the layer of light sensitive composition and to leave selected portions of the layer of light sensitive composition uncovered; exposing the uncovered portions of the layer of light sensitive composition to a light source, which exposure chemically alters the uncovered portions of the layer of light sensitive composition; and removing uncovered portions of the layer of light sensitive composition with a developer solution which dissolves those portions of the layer of light sensitive composition which have been chemically altered.

In another aspect, the invention provides an apparatus for producing a colour print comprising: a substantially flat bed for receiving a substrate upon which a print is to be applied; a means for applying a layer of a light sensitive composition onto the substrate; a photo¬ mask to cover selected portions of the layer of light sensitive composition; and a light source to expose uncovered portions of the layer of light sensitive composition to light, which exposure chemically alters the uncovered portion of the light sensitive composition.

A further aspect of the invention provides a light sensitive composition comprising a positive working

lithographic coating component which is chemically altered upon exposure to light and a colour pigment component.

The apparatus and method embodying the invention allow modification of such a proof without the experience and cost of expensive equipment normally associated with such graphic reproduction.

Further, the present invention reduces the number of operating stages required to produce a colour print, thus saving time and reducing skill requirements.

A preferred method embodying the invention also reduces or eliminates the use of hydrocarbons or other organic solvents thereby reducing and/or eliminating health and safety risks in line with increasingly strict legislative controls.

A method embodying the invention allows a print to be made from a positive photo mask as opposed to a negative photo mask which is required for use with known processes thereby simplifying evaluation and positioning of the photo mask.

A method embodying the invention also enables the optical definition and resolution of the resultant print to be increased to accommodate refined designer techniques and colour separation output of computer graphics technology.

In order that the present invention be more readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawing, the single figure of which is a perspective view of an apparatus embodying the present invention.

Referring to the drawing, an apparatus embodying the present invention comprises a flat base platform 1 of substantially rectangular configuration. The base platform 1 is geometrically flat and is manufactured from, for example, a metal or other material which does not suffer from surface distortion.

A bed 2 comprising a layer of rubber or synthetic foam is adhered on top of the base platform 1 to act as a pressure absorption bed. A feed roll 3 provides a supply of absorbent paper 4 which is laid over the pressure bed 2 to cover the bed 2. The paper 4 extends from one end of the bed 2 and is rolled around a waste roll 5 at the other end of the bed 2. The absorbent paper 4 is wound from the feed roll 3, across the bed 2, and on to the waste roll 5 by winding the waste roll 5 which is provided with a winding handle 6. The absorbent paper 4 collects any waste or overspill from compositions applied to the bed 2. As the paper 4 becomes saturated, a fresh length is wound into position.

A sprung clip 7 is hingedly mounted on and with respect to the base platform 1. The absorbent paper 4 is fed under the clip 7. A substrate 8, upon which a print image or proof is to be printed, is held in place between the clip 7 and the bed 2, the absorbent paper 4 lying underneath the substrate 8. The absorbent paper 4 is slidable under the substrate 8 whilst the substrate 8 is being held by the clip 7.

Preferably, the substrate is manufactured from a transparent cell material such as "Melinex" (supplied by ICI) or an opaque white plastic paper such as "Polyart" (supplied by Robert Home & Co.).

A coating rod 9 formed from a mild steel core 10 wound with a stainless steel wire 11 is laid across the base platform 1 adjacent the clip 7. The coating rod 9 is moveable along the bed 2 to coat the substrate 8 with a respective composition.

A process pad 13 is also provided and comprises a handle portion 14 and an underlay portion 15 which is releasably attachable to the handle portion 14. The underlay portion 15 is manufactured from a felt or mohair material of the kind used in standard painting pads. The process pad 13 is used to spread a developer solution over the substrate 8 and to remove solutions from the substrate 8. The precise function of the process pad 13 and the developer solution will be discussed in detail later.

Conveniently, a plurality of coating rods 9 are provided, each coating rod 9 being used to apply to the substrate a particular one of a number of coating compositions used in methods embodying the present invention. The plurality of coating rods 9 are kept separately in respective storage tubes 17 containing solutions for cleaning and storing the coating rods 9 when not in use. Preferably, the wire 11 wound around the core 10 has a diameter of 0.011" (0.28mm).

A conventional electric fan drier 16 is provided to dry respective solutions during the process.

The apparatus further comprises a separate ultraviolet (UV) exposure unit, not shown. The exposure unit is a standard unit such as those used by photo litho printers or screen printers.

A method embodying the present invention involves the following steps. Firstly, the substrate 8 is placed in a fixed position on the base platform 1, the substrate being held in place by the sprung clip 7. A light sensitive colour composition is then laid down as a bead 12 on the substrate 8. The light sensitive colour composition has two components, the first being photo-sensitive vehicle in the form of a positive working lithographic coating such as one of those disclosed in GB-A-0 706 028, GB-A-0 711 726, EP-A-0 021 716 and US-A-3 635 709. The second component of the colour composition is a first colour pigment.

The photo-sensitive vehicle of the colour composition is selected from the group of napthoquinone diazode sulphonic acid esters of phenol/formaldehyde resins. Most preferably, the photo-sensitive vehicle is a combination of phenol/formaldehyde novolak resins and the 1, 2, napthoquinone diazide sulphuric acid esters of phenol/formaldehyde novolak resins. An example of such a photo-sensitive vehicle is Positive Diazo P22 (supplied by PJS Chemicals) in combination with, for example, Alnovol 430 (supplied by Hoechst Chemicals Limited) or Rutaphen K790 (supplied by Bakelite Polymers Limited) .

The bead 12 is spread evenly over the substrate 8 by drawing the coating rod 9 over the substrate 8. The coating is drawn by hand across the substrate 8 using minimal pressure. This provides an optically clear coating of the respective composition.

The colour composition is then dried on the substrate 8 using the fan drier 16.

The substrate 8 is then removed from the bed 2 and placed in the UV exposure unit and the substrate is illuminated with UV light through a photo mask (not shown) which is a positive image of the image to be formed on the substrate. The areas of the colour composition which have been exposed to the UV light through the photo mask become soluble in a developer solution comprising an alkaline water solution. The unexposed areas remain insoluble in such a water solution.

The exposed areas are then dissolved away with the developer solution using the process pad 13. Preferably, the developer solution comprises a 5% to 15% solution in water of alkaline crystals and, most preferably, the alkaline crystals are crystals of trisodium phosphate. The developing process can be monitored visually and, once completed, the surface is washed with water and dried with the fan drier 16. Thus, the substrate 8 now carries a positive colour print corresponding to the positive photo mask.

The next stage is to protect the colour print using an isolation layer of a transparent lacquer. The lacquer is provided as second coating over the substrate 8. The lacquer needs to be resistant to the developer solution and any second coating of colour composition which is to be applied.

To produce a multi-colour print, the above¬ described process can be repeated using further colour compositions containing respective colour pigments and subsequent applications of isolation layers to build up the print using as many colours as required.

The above described method allows the production of a permanent colour-proof print. Using the above described method and variations thereof it is possible to produce a transferable (decal) colour proof and a transferable (decal) proof of a foil image.

To produce a transferable (decal) colour proof, a similar technique to the above described method is used except that a release lacquer is first applied to the substrate 8 prior to the first coating of a colour composition. As the final stage, an adhesive coating is applied.

The finish of the decal surface can be either glazed or matt and this is determined by the substrate 8. When, for example, Melinex is used as the substrate 8, a gloss finish is produced. A matt finish will be produced from any generally available sheets of polythene or butadiene.

The method of producing a transferable colour proof comprises the following steps. A chosen transparent substrate 8 is located on the pressure bed 2. A transparent water soluble lacquer containing a release agent is applied and dried using the fan drier 16. The preferred release agent is a water soluble silicone (supplied by Basildon Chemical Co.). As described above in relation to the method of producing a print, a chosen colour composition is then coated onto the release coating. Once the colour composition has been dried and exposed to ultraviolet light through the photo mask, the exposed colour composition is dissolved away using the aforementioned developer solution. Since the developer solution comprises a substantial amount of water, the water soluble silicone release agent coating is also dissolved

away in any unmasked exposed areas. Thus, the unexposed area of colour composition protected by the photo mask remains insoluble, those areas of colour composition also acting as a mask to protect, in precise registration, the underlying areas of the release agent. Therefore, only the image formed using the colour composition is supplied with a release agent layer. Areas where no colour composition remains are not provided with a release agent. The resultant substrate is then dried using the fan drier 16.

To effect a transfer of the resultant image it is necessary to apply an overall adhesive coating which has a tack level exceeding the holding power of the release mechanism and has a brittle-shear quality which permits only the adhesive on the image to become effective. The dried substrate is coated with a liquid adhesive, preferably water-based, which is beaded onto the substrate and evenly coated over the complete substrate using a coating rod. The substrate is then dried using the fan drier 16. The adhesive applied to areas where no colour composition remains has no underlying release mechanism and, therefore, remains on the substrate.

A preferred feature of the adhesive solution is that, in addition to the adhesive compounds, there is also a white pigment dispersion therein. The purpose of the white pigment dispersion is to provide opacity to an otherwise transparent image. The balance of opacity is controlled to retain adequate transparency of the substrate to allow positioning of the image prior to being transferred. Transfer application employs a standard technique of positioning the unreleased image on a receiver surface and rubbing the reverse side of the transfer substrate with a stylus or ballpoint. The adhered image

attaches to the receiver surface and releases from the original substrate.

To produce a transferable (decal) proof of a foil image, the technique is the same as that described above in relation to transferable proofs but with the additional step of providing a metallic layer. A release layer is applied to the substrate and this is then followed by the application of the metallic layer. The provision of the colour composition and the following steps are then carried out as normal.

The finish of the foil decal can be either a mirror metallic finish or a satin (non-mirror) finish. As with the above described colour decals, the optically flat surface of polyester (such as Melinex) will generate a mirror surface, whereas the grained surface texture of polythene or butadiene will produce a satin finish.

In the production of a transferable (decal) proof of a foil image, the release lacquer may include dyes which act as a colour filter. The metallic layer is generally silver and thus the filter changes the effective colour of the silver. Thus, a gold finish can be achieved by using, for example, a yellow filter. Many metallic colours are achievable using this filter technique.

The colour composition may contain a white dispersion pigment. As previously described, a chosen substrate is located on the flat base platform 1. A bead of dyed release lacquer is poured on to the substrate and evenly coated with a respective coating rod 9. The release lacquer coating is dried using the fan drier 16. Preferably, the release lacquer is water-based and contains silicone as previously described. Further, the release

lacquer includes dyes (as available from Sandoz & Co.). The metallic layer is then applied and dried.

Preferably, the metallic layer comprises ultra fine particles of aluminium suspended in ISO - propylalcohol. The preferred blend is Metalure L-5494 (supplied by Eckart UK) . Subsequently, the colour composition including the white dispersion pigment, is applied using the coating technique and then dried. The coated substrate is then overlayed with a photo mask and exposed to UV light. Exposed areas of the colour composition are then dissolved away using the developer solution previously mentioned. The developer solution also dissolves through the underlying metallic layer and the release layer. Unexposed areas of colour composition act as a photoresist to underlying layers such that underlying metallic layers are not dissolved. Once the image has been completed, the substrate is washed in water and dried. As previously described in relation to the colour decals, the whole area of the substrate is coated with a water-based adhesive, dried and ready for use as described in relation to the colour decal process.

In another method of producing a transferable (decal) colour proof in accordance with the invention, a similar technique to the previously described method is used except that a water soluble polyvinyl acetate (PVA) solution is first applied to the substrate 8 prior to the coating of a light-sensitive composition. As a final stage, an adhesive coating is applied.

A feature of the PVA solution, in addition to being water soluble, is that it has a natural release mechanism from substrates. Added to this solution are colour pigments to provide a range of pre-designated colours.

A single light-sensitive composition including a white pigment dispersion is used in this alternative method. The purpose of the white pigment dispersion is to provide opacity to the otherwise transparent image provided by the coloured PVA solution in addition to the prime function of the light-sensitive composition as the photo¬ active image former.

The balance of opacity in the white light-sensitive composition is controlled to provide adequate opacity to the transparent colour in the finished proof, whilst providing sufficient transparency to ultraviolet light penetration during exposure.

The finish of the decal surface can be either glazed or matt and thiε is determined by the substrate 8 employed. When, for example, Melinex is used as the substrate a gloss finish is produced. A matt finish will be produced from most generally available substrates of the polythene or butadiene type materials.

The method of producing a transferable colour proof comprises the following steps. A chosen transparent substrate 8 is located on the pressure bed 2. A chosen PVA colour composition is applied and dried using the fan drier. The white light-sensitive composition is then coated on top. Once the white composition has been dried and exposed to ultraviolet light through the photo mask, the exposed white composition is dissolved away using the aforementioned developer solution. Since the developer solution comprises a substantial amount of water, the water soluble PVA colour coating is also dissolved away in any unmasked exposed areas. Thus, the unexposed areas of white composition protected by the photo mask remains insoluble, those areas of white composition also acting as a mask to

protect, in precise registration, the underlying areas of the PVA colour composition. Areas where no white composition remains do not retain any colour composition or release mechanism. The resultant substrate is then dried usng the fan drier.

To effect a transfer of the resultant image, it is necessary to apply an overall adhesive coating which has a tack level just exceeding the holding power of the release mechanism and has a shear quality which permits only the adhesive on the images to become effective. The dried substrate is thuε coated finally with a liquid adhesive which is beaded onto the substrate and evenly coated over the complete substrate using a coating rod. The substrate is then dried using the fan drier 16. The adhesive applied to areas where no white composition remains has no underlying release mechanism and, therefore, remains on the substrate.

The colour composition may also include additives such as resin, plasticisers and wetting agents to improve the properties of the coating, its adhesion to various substrates and the speed of development and retained image strength.

For example, a useful improvement in image development speed and retained image strength can be achieved through the addition of cellulose acetate phalate, cellulose acetate butyrate or hydroxypropylcellulose.

A preferred additive is Klucel (supplied by Hercules BV of Holland) which can be used in amounts from 1% to 5% by weight) . This additive controls the development time and image strength of the basic photo¬ sensitive vehicle of the light sensitive colour composition. This additive acts as a stabiliser to ensure that the resultant print enjoys a constant colour or mix of colours.

Preferably, respective layers of colour composition when in contact with another, are inert with respect to one another and subsequent layers.