WO2000014601A1

WO2000014601A1 - Method of production of a negative photomechanical film, substrate and ink composition for carrying out such a method

Info

Publication number: WO2000014601A1
Application number: PCT/IB1998/001386
Authority: WO
Inventors: Giuseppe Paccagnella
Original assignee: Giuseppe Paccagnella
Priority date: 1998-09-07
Filing date: 1998-09-07
Publication date: 2000-03-16
Also published as: AU8819198A

Abstract

The present invention relates to a method of production of a negative photomechanical film suitable as master for graphic arts and other similar printing processes, using a conventional inkjet printer. The film is made of a transparent substrate, coated with a hydrophobic and water-insoluble resin, opaque to the light (and specifically to the visible and UV light). The ink composition, when printed on the coated film, renders the coating water soluble, so that it can be washed off with washing agents such as plain water, leaving on the film 'negative' images. The invention encompasses the transparent substrate film, the material used to render the film opaque to the visible and UV light and the inkjet ink composition, which does not contain colorants or colouring agents nor pigments, is transparent and colorless and adapted to render water-soluble the opaque resin of the coating. The colouring agents used in the coating of the transparent film of this invention ar actual colouring agents, organic and inorganic pigments and polymeric hollow microspheres. The components of both the coating and the inkjet ink may include pH adjusting agents, humectants, biocides, defoamers surfactants. The properties of the resulting photomechanical negative film are very high opacity against UV and visible light, dimensional stability, water-proof, high resistance against scratch, stability over time, absence of chemicals for exposure and fixing, therefore it is environmental friendly.

Description

METHOD OF PRODUCTION OF A NEGATIVE PHOTOMECHANICAL FILM, SUBSTRATE AND INK COMPOSITION FOR CARRYING OUT SUCH A METHOD

Field of the Invention

The present invention generally relates to printing technique and more particularly to a method of producing a negative photomechanical film suitable for use as master for graphic arts, publishing, offset, screen, flexo and other printing processes.

Further aspects of the invention relate to a negative photomechanical film obtained with the method, substrate and ink composition for the carrying out of the process.

Background Art

A large number of photomechanical films are known which pertain to a group of coated films sensitive to the light, be it UV, visible or infrared. The impact of light on the sensitive coating of these films yields an image which, to be visible, needs chemical processes of development and fixing, and the washing off with water of the residuals.

The use of new digital systems adopting a variety of light beams, also of the laser type, to generate those images does not change the basic concepts of this method, since light-sensitive coatings must always undergo a chemical process in a developing machine.

Such process is relatively expensive, because of the cost of the equipment needed and of maintenance thereof, the materials used (silver on films, and chemicals for their development and fixing) and is still nowadays far from an easy and automatic job, because the parameters for the correct exposure and development have an interrelated influence on the final outcome. Inkjet printing is a well known printing technique wherein a stream of ink droplets is projected onto the surface of a substrate, while the direction and the amount of the stream is controlled electronically so that the droplets are caused to form the desired printed message on that surface.

A main aspect of inkjet printing is that it requires no physical contact between the printing head and the substrate which will receive the ink, so that the image may be printed also on uneven, irregular surfaces.

Another important aspect is that images may be yielded directly on the substrate (transparent film, paper and others) without necessitating intermediate processes, means or ancillary operations.

Further aspects and uses of the inkjet printing technique are exemplary known from the following publications: Kuhn: Scientific American, April 1979, 162 -178; Keeling, Phys. Technol. 12(5), 196-303 (1981); a variety of inkjet printing mechanisms have been described in the following US patents: US-A-3 060429, US-A-3 298 030, US-A- 3 373 437, US-A-341 153, US-A-3 673 601.

As to the inkjet ink, its composition must meet certain rigid requirements to be used in inkjet printing operations, especially in the field of the printing industry. This relates particularly to viscosity, resistivity, solubility, compatibility of components and wettability of the substrate. Furthermore, the ink must be quick drying, smear and rubbing resistant, capable of passing through the inkjet nozzles without clogging them, and allow a rapid cleanup of the printer's components with minimum effort.

All these requirements have resulted in an important R&D effort in the area of the composition of inkjet inks and of their substrates. There is a significant number of patents and publications the most relevant of which are reported below: GB-A-2 105 735, US-A-4 155 768, US-A-4 197 135, US-A-4 680 332, US-A-4 692 188, US-A-4 849 286, US-A-5 080 716, US-A-5 098 475,

US-A-5 100 470, US-A-5 120 361 , US-A-5 131 949, US-A-5 178 671 ,

US-A-5 207 825, US-A-5 213 613, US-A-5 215 577, US-A-5 254 158,

US-A-5 254 159, US-A-5 256 193, US-A-5 266 106, EP-A-0 631 880, US-A-5 316 575, US-A-5 393 331 , US-A- 5 596 027.

In general, however, this printing technique is particularly advantageous when the total area to be covered with an opaque ink is not very large when compared to the total area of the substrate, for instance when text covers between 10 and 30% of a film, as it happens when a positive image is produced.

If, on the other hand, a negative film must be produced, with the same percentage of text-covered surface (for instance 10%), then the film should be 90% covered with the opaque ink, a rather expensive and time-consuming procedure (in this case: 9 times as much).

Moreover, printing so much ink on such a large area also involves some problems to the uniformity of the ink layer, its drying, and its overall stability.

Disclosure of the Invention

A principal aim of the present invention is to create directly photomechanical films which can be used as master for graphic arts, publishing, screen and offset processes, taking advantage of the well known inkjet printing technique.

A particular object of the present invention is to provide a method of producing a photomechanical film, that is to yield opaque images on a transparent substrate suitable for printing industries, which is extremely simple, environment friendly and inexpensive. Another particular object of the present invention is to provide a method of producing a photomechanical film which allows to completely eliminate the need of light- sensitive materials thereby avoiding the application of highly expensive and time consuming developing and fixing process.

Another object is to conceive a method of production of a negative photomechanical film and the use of materials which significantly reduce the costs, toxicity and complexity of the conventional printing methods.

Still another object is to provide a method of production of a photomechanical film which makes use of conventional and well known inkjet printers thereby avoiding complicate and expensive apparatuses for developing and fixing the images on a substrate.

A further object is to provide a substrate and an ink composition allowing the use of a conventional inkjet printer.

In accordance with a preferred aspect of the invention, there is provided a method of producing photomechanical film comprising the steps of a) providing a substrate transparent to light and with minimum light absorption, b) coating the substrate with a hydrophobic material, opaque to UV and visible light, c) providing an ink for inkjet printer having a predetermined composition suitable to react with the material forming the coating to render it hydrophilic and water-soluble, d) providing an image, e) printing said image on said coated substrate by means of a digitally driven inkjet printer using said ink of predetermined composition to thereby render the printed area hydrophilic and water-soluble, f) washing off the substrate with a washing agent to remove the hydrophilic coating material from the area reproducing the image rendering it perfectly transparent, so that the remaining area of the coated substrate which is opaque reproduces said image in negative. Preferably, the substrate is a transparent film of plastic materials such as polyesters, polymethacrylates, polyamides, polyolefines, polystyrene and polycarbonates.

The opaque coating may consist of a hydrophobic acidic resin which contains colorants, solvents, humectants and anti-blocking agents.

The ink composition has an oxydril functionality and comprises a mixture of water, solvents, surfactants, humectants and pH adjusting agents.

The said pH adjusting agent may be chosen among the category of the base products such as ammonium hydroxide, methylamine, ethylamine, dimethylamine, diethylamine, triethylamine, morpholine, ethanolamine, diethanolamine, triethanolamine, methylethanolamine, dimethylethanolamine, sodium hydroxide, potassium hydroxide.

The washing agent for washing off the hydrophilic coating material is preferably plain, deionised or distilled water.

Preferred embodiment of the invention

The method of production of negative photomechanical film according to the invention comprises the steps of providing a transparent substrate, such as a polyester film, specially made to minimize light absorption and maximize transparency; and coating it with a water-repellent acidic resin and its solvent, which resin contains colorants and/or pigments opaque to the UV and to the visible light.

An image is electronically generated and is printed on the coated substrate with a conventional, digitally driven inkjet printer using a special inkjet ink which may include pH adjusting agents and other components, so that, when it is printed on the film coating, this latter is rendered water soluble. The water-soluble residuals are finally washed off with water or other washing agents. In this way it becomes possible to produce directly a negative film with an inkjet printer, where the negative image comes out to be perfectly transparent against a surrounding area opaque to UV and visible light.

The commercial importance of such a negative photomechanical film is due to the fact that this type of film may be used in flexo printing (and, generally speaking, in the production of all photopolymeric cliches) as well as in newspaper printing and in negative offset printing.

The resulting negative photomechanical film is suitable as master film (i.e. a film for copying images on light-sensitive materials used in the printing industry) for the preparation of offset plates, screens and flexo cliches, digitally produced using a standard inkjet printer.

The method relies on two essential and complementary materials:

- the hydrophobe, water-proof coating material, opaque to the UV and to the visible light, to be applied onto the transparent substrate;

- A special inkjet ink which, when printed on the film coating, renders it water soluble, so that it can be washed off with water or any washing agent.

When compared with the traditional silver-based photomechanical films, the film obtained with the present method exhibits a higher density of the opaque areas, high dimensional stability (thanks to the water-proof coating) insensitivity to humidity and static, scratch-resistance, no ageing problems. It is evident that, to produce an image using the inkjet process, two coherent elements are needed: the ink and the substrate's coating. The composition of the coating applied onto the transparent film may include, in addition to the pH adjusting agents, solvents, humectants, biocides, defoamers, surfactants, distenders, all of which fulfils all the requirements for being used as a substrate for inkjet printing.

The ink used for the printing method fulfils all the requirements for being used in an inkjet printer. Moreover, it is odourless, non toxic and is completely eliminated by the subsequent wash-off with water, preferably deionized or distilled.

The compositions and properties of the above mentioned materials are set forth below.

The transparent substrate is made of the same material used in the production of traditional, silver-based films: polymeric films derived from polyesters, polymetacrylates, polyamides, polyolefines, polystyrenes, polycarbonates, polymeric films derived from ethylenglycoltereftalic acids and semi-transparent papers.

Most of these materials need a surface treatment, to facilitate the adherence of the coating to their surface. Polyolefines (such as polypropylene) have low surface tension and need a suitable surface treatment or a primer, such as, among others, primers based on vinyldenchloride, or gels and polymers containing quaternary ammonium moieties. Commonly used surface treatments are chemical oxidation, with radiation and corona

The most widely used transparent substrate is a film made of polyethylentereftalate, commonly called polyester film. To guarantee the stability and planarity required by the printing industry Its thickness is normally between 80μ and 200μ (μ= micron = one millionth of a meter). The coating of the film must be opaque to the visible and to the UV light, create a slightly matte surface and have a very limited shrinking when drying up, to ensure dimensional stability and planarity.

It should also be insensitive to modifications of the environment in terms of relative humidity, must adhere to the substrate and have a very uniform distribution of colouring agents and pigments, basically without grain.

This opaque coating can be made of colouring agents, acidic resins, solvents, co- solvents, surfactants, anti-blocking agents. The coating includes colouring agents whose purpose is to be a shield against UV and visible light.

The colouring agents which may be utilized in the present invention are organic and inorganic pigments, colorants, solvent-based colorants, carbon black, graphite, polymeric hollow microspheres which increase the opacity of the coating, and various combinations of the above-mentioned components.

Colorants and components must be chosen primarily with regard to their capacity of acting as a shield against light, particularly UV light. Carbon black is the preferred colouring agent for the coating of the film. Carbon black may include Channel black, Furnace black and Lamp black. Other types of pigments which may be used are covering pigments such as titanium bioxide, zinc oxide, zinc sulphide, lithopone.

In the coating of the film of this invention, also polymeric hollow microspheres may be used, since they contribute to the opacity of the coating, because they disperse the light rays (reflection and refraction phenomena). The polymeric microspheres for this purpose are commercially available also under the commercial name Ropaque of Rohm and Haas.

The quantity of colouring agents utilized depends on the type and nature of the colorants; as a guideline, a coating with a thickness between 3μ and 6μ should offer a UV density of at least 4 (DMax = 4) when measured with a UV densitometer (geared to UV light -360/380 nm) and of 5 (DMax=5) when measured with a visible light densitometer.

The coating of the film of the present invention should also be comprehensive of an acidic resin which reacts with the polyamine components of the ink in such a way as to render soluble in water the otherwise water-proof coating, so that it can easily be washed out with water where it has been hit by the ink. After the wash out the image will be visible as a transparent image within a coloured or black, opaque surrounding.

A variety of polymeric resins with an acidic carboxylic moiety (sulfonic or phosphoric), suitable for this purpose, is available on the market, but for this specific application the best choice is polymeric resins with anacidic carboxylic group. The above- mentioned acrylic or alkylacrylic polymer may include a variety of carboxylic groups and are therefore soluble in a basic solution, such as water and ammonia. Moreover, the above-mentioned alkylacrylic polymers may include a variety of carboxylic moieties, and may therefore be soluble in a basic solution such as water and ammonia.

The most suitable carboxyl-containing acidic resins are those having an acid number in the range of from 20 to 400 and an average molecular weight in the range of from 500 to 20,000, with a softening point of from 80°C to 120°C. Even more suitable are the acidic resins having an acid number in the range of from 100 to 300, a molecular weight from 1 ,000 to 5,000, and a softening point of from 100°C to 110°C

The acidic resins which may be employed in the present invention include resins water soluble or water dispersible, such as the acrylic resins or the styren-anhydride- maleic ones. The acrylic resins which may be applied in the present invention are obtained by copolymerizing an unsaturated monomer acid with another monomer, such as metacrylate, ethylacrylate, propylacrylate, butylacrylate, methylmetacrylate, propylmetacrylate, butylmetacrylate, hydroxypropylmetacrylate, hydroxybutylmetacrylate and combinations thereof.

Examples of unsaturated monomer acids which may be used in the present invention include acrylic acids, metacrylic acids, maleic acids, fumaric acids, itaconic acids, citraconics acids, cynnamic acids, crotonic acids, styrene-sulfonic acids and all their combinations

The acrylic resins may include one or more co-monomers such as styrene. alpha- methyl-styrene and 1-chloromethylstyrene

Various acidic resins suitable for use for this invention are available on the market. These materials are commercially known as Rhoplex ® of Rohm and Haas Co., Bright Plate and Joncryl of Johnson & Johnson and Carboset of Goodrich Chemical.

The acidic carboxylic moiety is an active group which may be solubilized by amines such as ammonia.

Other resins which can be used in the present invention are styrene-acrylic resin copolymers such as Lucidene of Morton Norwich Products, Rhoplex ® of Rohm and Haas and other different compositions such as PVP K 15 polyvinylpyrrolidinone of GAF Chemical; Pentalyn, Dresinol, Natrosol and Klucel all commercial names of Hercules Inc.; Scrypset ®, modified polystyrene of Monsanto Co. and Neoprene Latex, synthetic rubber of Dupont. All these resins are easily dissolved in organic solvents by simple stirring.

Different percentages of acidic resins may be used in the present invention, thanks to the large variety of available products. It is anyhow recommended to use an amount of resin ranging 2% to 20% of the finished product weight, to be used to create the opaque coating of the present invention or, preferably, a 4% to 17% by weight of the composition, or even better 4.5% to 16% of the above-mentioned weight.

The final composition of the resin to be coated on the film must have a pH value ranging 4 to 7, preferably a pH value ranging 4,5 to 6,6 or, even better, ranging 5 to 6.

Solvents used in the present invention must be compatible with the used colouring agents and with resins employed in the coating of the transparent polyester film. Normally, most solvents have these properties, but some of them have a boiling point perfectly suitable to the mechanical coating. Among these, methylpenthylchetone, alcohols such as ethylic, methylic, isopropylic, benzylic and ethers such as methoxypropanole, ethoxypropanole; acetates such as ethylic, methylic, isopropylic, butylic acetates and their combinations. These solvents, depending on the resin or colouring agent used, may be included in the composition of the coating of the transparent polyester film.

The percentages may vary 40% to 80% by the weight of the coating, preferably 40% to 70% of the total weight, or even better 40% to 65% of the weight.

Co-solvents are also used in this invention, to slow down the drying up of the ink on the coated film, so as to allow a deeper penetration. Such co-solvents must have a rather high boiling point, preferably at least 120° C, or even better a boiling point between 150X and 250°C

The co-solvents normally used in all the coating operations are glycols such as ethylene glycol, propylene glycol, glycerin, diethylenglycol and the glycol ethers such as ethylene-glycol-methylether, diethylenglycoldiethylen and other solvents such as Solfolane and N-methylpyrrolidinone. Propylenglycol and N-methylpyrrolidinone are particularly preferred solvents. Such solvents can be used in various percentages, e.g. 0,5% to 8% by the weight of the composition, preferably 1 % to 5%.

The coating of this invention requires another additive, a surfactant, and even better a fluorate surfactant such as Fluorad ® of 3M, to obtain a perfect spreading of the coating on the film, so that it will create a planar, smooth, homogeneous surface, without pinholes, lumps and irregularities (orange-peel surface). A percentage 0,01% to 0,1% by the weight of the coating is recommended.

The use of anti-blocking agents in the composition of the coating of this invention is also recommended, in order to avoid the sticking of the film onto the reels during the production process. To this end, components based on colloidal silica have been used, with granules 5 to 10 μ in diameter, and percentages 0.2% to 0.5% by the total weight of the coating.

As to the coating, one of the many traditional coating processes may be adopted, such as with reverse rolls, knife overroll, Mayer rod-coating. The thickness of the coating may vary 5μ to 15μ or preferably 6μ to 12μ or even better 7μ to 8μ. Anyhow, the thickness of the coating must be such as to provide an opacity to UV and to visible light, measured on a photomechanical densitometer, of at least DMax „ 4. The coating will be dried up at a temperature 80°C to 90°C for a time span of at least 2 to 3 minutes.

The following examples further illustrate the present invention but, of course, should not be construed as in any way limiting its scope:

Example n. 1

The transparent polyester film, 100m thick, is coated according to this formulation: Carbon Black Special 6 9,0 %

Rhoplex acrylic-styrenic resin 20,0 %

N-methylpyrrolidinone 5,0 %

Methylpropylenglycol 19,0 % MEK 46,4 %

Fluorad 170 0,6 %

100,0 %

The coating has been obtained using a Mayer bar n. 24, resulting in a dry coating 6μ thick, with a DMax = 4.20 when measured with a Macbeth TR 524 densitometer with a yellow filter for visible light.

Example 2

This product is a modification of Example 1 , having added the anti-blocking agent OK-412. Carbon Black 25 9,0 % Rhoplex acrylic-styrenic resin 18,0 % N-methylpyrrolidinone 5,0 % Methylpropylenglycol 19,0 % MEK 46,4 %

Fluorad 170 0,6 % OK-412 2,0 %

100,0 %

The product obtained according to the formulation of Example 2 has yielded excellent coating results, with good UV density, rapid drying, high quality of the coated, opaque surface As explained before, the ink composition used in the method according to the invention must meet certain rigid requirements that relate particularly to viscosity, resistivity, solubility, compatibility with the printer's cartridges and printing heads; it must obviously be a complement to the coating and be easily absorbed, quick drying, smear resistant, and provide high-definition images after wiping.

In addition, the inkjet ink must be capable of passing through the capillary tubes and the nozzles of the printing heads without clogging. Moreover it must be characterized by such a fluidity to solve dried out residuals. The ink must neither be corrosive, nor produce toxic vapours; it must be odourless.

The composition of the ink of the present invention comprises a suitable ink carrier and pH-adjusting agents that can topically modify the film's coating from hydrophobic to hydrophilic so that it can be easily washed out with plain water, thus yielding a photomechanical digital negative film. It comprises also polyamines, co-solvents, humectants.

Many suitable ink carriers may be used in the preparation of a jet ink with the same characteristics as the present invention's. Water can be used in an amount of from 30%o to 80% by weight, preferably in an amount of from 40% to 70% by weight of the composition. When water is used as the carrier, in order to prevent the clogging of the nozzles by the salts dissolved in the water, deionized water, or better distilled water, is preferably used.

The inkjet ink composition of the present invention comprises also pH-adjusting agents. The pH necessary to dissolve the acidic coating's resins is dependent upon the particular acidic resin used and upon the other components employed.

Many suitable pH-adjusting agents may be used so as to maintain the pH of the inkjet ink composition in the range of from 8 to 12, preferably in the range from 8.5 to 11.5. To this purpose, base agents can be used, including: ammonium hydroxide, methylamine, ethylamine, dimethylamine, diethylamine, triethylamine, morpholine, ethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, sodium hydroxide, potassium hydroxide. Among the mentioned bases the most suitable should be chosen considering that a faster evaporating base will affect the coating for a limited amount of time, contrary to less readily evaporating bases.

Since the printed coating is washed out with water after a short while, ammonium hydroxide, methylamine, ethylamine, dimethylamine, diethylamine, triethylamine and combinations thereof are preferably used for controlling the desired pH.

The amount of the pH-adjusting agent varies according to the other components of the inkjet ink and to the coating to be printed on. The preferred amount of pH adjusting agent ranges from 15% to 20% by total weight of ink.

Co-solvents are agents promoting a fast interaction between the acidic resin within the coating and the basic agent used in the inkjet ink composition. The co-solvent include alcohols and ethers, which are easily mixed with water in any desired proportion and are at the same time suitable solvents for the acidic resins of the coating. Preferred co-solvents are ethyl- and butyl-alcohol and propylglycolether or combinations thereof.

The ink composition of the present invention preferably comprises humectants to prevent drying of the ink during the printing process as well as during storage. Humectants are hydrophilic solvents with high boiling point, preferably above 100°C and more preferably in the range from 150°C to 250°C. Examples of suitable humectants include ethylene glycol, propylene glycol, glycerine, diglycerin, diethyleneglycol, glycol ethers and other solvents such as sulfolane and N-methyl pyrrolidinone. Propylene glycol and N-methyl pyrrolidinone are preferred humectants for the purpose of this invention.

The suitable amount of humectants to be used ranges from 0.5% to 5% by weight of the ink composition, preferably from 1 % to 3% by weight of the ink composition.

The following examples further illustrate the present invention but must not be construed to limit in any way its scope.

Example 3

This example illustrates the preparation of an inkjet ink composition comprising water as the carrier, a pH adjusting agent, co-solvents and humectants.

The following components were combined and mixed by a high-speed mixer, until a clear and homogeneous ink composition was obtained; it was then vacuum-filtered through a 0.4μ filter.

Deionized or distilled water 66%

Propylene glycol 12% Ethyl alcohol 10%

Diethylamine 12%

100%

The above formulation was tested using an Epson Stylus Pro XL ® with excellent results as far as the water solubility of the opaque coating was concerned, thus allowing an easy removal of the printed image resulting in high definition, transparency and precision. Example 4

Deionized or distilled water 49%

Propylene glycol 9% Ethyl alcohol 95% 21%

Propylglycoether 11 %

Ammonium hydroxide (39/30% water solution) 10%

100%

While the invention has been described and disclosed with reference to certain preferred embodiments and procedures, this is not intended to limit the invention to those specific embodiments. Rather it is intended to cover all such alternative embodiments and modifications as fall within the scope of the invention, as outlined in the following claims.

Claims

1. A method of producing a photomechanical negative film suitable as master for graphic arts, publishing, offset, screen flexo and other printing processes, comprising the steps of: a) providing a substrate transparent to light and with minimum light absorption; b) coating the substrate with a hydrophobic material, opaque to UV and visible light; c) providing an ink for inkjet printer having a predetermined composition suitable to react with the material forming the coating to render it hydrophilic and water-soluble; d) providing an image; e) printing said image on said coated substrate by means of a digitally driven inkjet printer using said ink of predetermined composition to thereby render the printed area hydrophilic and water-soluble; f) washing off the substrate with a washing agent to remove the hydrophilic coating material from the area reproducing the image rendering it perfectly transparent, so that the remaining area of the coated substrate which is opaque reproduces in negative said image.

2. A method according to claim 1 , wherein said substrate is a transparent film of plastic materials such as polyesters, polymethacrylates, polyamides, polyolefines, polystyrene and polycarbonates.

3. A method according to claim 1 , wherein said coating, opaque to the UV and to the visible light consists of a hydrophobic acidic resin.

4. A method according to claim 3, wherein said acidic resins comprises colorants, solvents, humectants and anti-blocking agents.

5. A method according to claim 1 , wherein said predetermined ink composition consists of a mixture of water, solvents, surfactants, humectants and pH adjusting agents.

6. A method according to claim 1 , wherein said washing agent consists of plain water.

7. A method according to claim 1 , wherein said washing agent consists of deionised or distilled water.

8. A substrate for producing a photomechanical negative film using a method according to any preceding claims, comprising a film of transparent materials coated with a hydrophobic and water-insoluble material opaque to

UV and visible light, said coating material being suitable to become hydrophilic and water-soluble when printed with an inkjet ink of predeterminated composition using a conventional inkjet printer.

9. A substrate according to claim 8, wherein said materials forming said transparent film are choosen among plastic materials such as polyesters, polymethacrylates, polyamides, polyolefines, polystyrene and polycarbonates.

10. A substrate according to claim 8, wherein said coating material comprises acidic resins, colorants, solvents, humectants and anti-blocking agents.

11. An inkjet ink for producing a photomechanical negative film using the method according to any claims 1 to 7, wherein said ink has a composition suitable to render hydrophilic and water-soluble an hydrophobic and water-insoluble material, opaque to UV and visible light, coated on a transparent substrate.

12. An inkjet ink according to claim 11, wherein said inkjet ink composition has an oxydril functionality.

13. An inkjet ink according to claim 10, wherein said inkjet ink composition consists of a mixture of water, solvents, surfactants, humectants and pH adjusting agents.

14. An inkjet ink according to claim 13, wherein said pH adjusting agents are chosen among the category of the base products such as ammonium hydroxide, methylamine, ethylamine, dimethylamine, diethylamine, triethylamine, morpholine, ethanolamine, diethanolamine, triethanolamine, methylethanolamine, dimethylethanolamine, sodium hydroxide, potassium hydroxide.