GB1588620A

GB1588620A - Water developable lithographic printing plate

Info

Publication number: GB1588620A
Application number: GB19117/78A
Authority: GB
Original assignee: Polychrome Corp
Current assignee: Polychrome Corp
Priority date: 1977-05-19
Filing date: 1978-05-12
Publication date: 1981-04-29
Also published as: SE7805736L; JPS53145707A; DE2821776A1; FR2391488A1; NL7801624A; DK565077A; NO774516L; AU3602578A

Description

(54) WATER DEVELOPABLE LITHOGRAPHIC PRINTING PLATE (71) We, POLYCHROME CORPORATION, a corporation organized and existing under the laws of the State of New York, United States of America, of 137 Alexander Street, Yonkers, State of New York 10702, United States of America. (Assignees of Eugene Golda, Alan Leonard Wilkes and Simon Long Chu), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to a novel method for the production of presensitized lithographic printing plates and to the novel lithographic printing plates produced thereby.

Heretofore it has been a problem in the art to produce a more ecologically acceptable lithographic printing plate and a method for its development. It is known to produce such plates which require the use of various chemical developing agents which must be discarded after use, typically through community waste removal facilities. Such developers are costly to purchase and disposal through sanitary systems is undesirable. By the instant invention a lithographic printing plate is produced which is developable by ordinary tap water which is both inexpensive and ecologically acceptable.

The prior art teaches the use of certain water soluble, diazo type compositions in the manufacture of lithographic printing plates.

which become water insoluble upon imagewise exposure to ultraviolet radiation by standard techniques. This method' does allow- remvai- of non-exposed'areas by development with water. However, the images thus formed are exceedingly frail and cannot withstand thestrain of prolonged printing. Hence, plates made according to this procedure require that an ink. receptive lacquer or other similar coating be applied'to the image area after development and it is this coating which. actually prints the desired image and not the diazo composition.

It is important to note that these lacquers also pollute their rinse water. One example of such a water soluble diazo system is described in U.S. Patent 3 179 518 issued to Sus, et al.

Other attempts include use of a water soluble diazo and a water soluble resin composition which. is rendered water insoluble upon exposure by standard methods. However, images produced by this procedure are not ink receptive and therefore not useful for the manufacture of lithographic printing plates.

The instant invention relates solely to water insoluble, ink receptive lithographic photosensitizer-resin compositions which are employedin the top coating.

Heretofore in the production of commercially acceptable presensitized lithographic printing plates which did not require a subsequent lacquer application. to the imaged plate areas, it had been necessary to employ photosensitive compositions which could not be developed by ordinary tap water. Plates manufactured according to these methods could only be developed by means of costly, specialized, and environment polluting chemical agents.

The present invention provides an improved lithographic printing plate which may be satisfactorily developed by use of ordinary tap water which is both inexpensive and environmentally acceptable. By the instant invention it has been found that a satisfactory plate which meets these criteria may be produced by first applying a non-light sensitive, water soluble- polymer to the surface of a metal sheet substrate and subsequently coating.the thus treated substrate with a photosensitive com position- which comprises- a water insoluble lithographic photosensitizer and a water insoluble resin. This upper level coating composition is characterized as water insoluble, ink receptive, and alternatively either water permeable or water impermeable.Water permeability means the composition is insoluble in water, yet water may filter through the composition. In a negative working system, the upper coating is initially water permeable and.upon imagewise exposure through a suitable mask by methods known to the skilled worker the exposed areas are rendered water impermeable and remain ink receptive. Therefore, upon washing an imagewise exposed plate with water, the. water permeates the negative working photosensitive composition at the unexposed non image area, reaches- and dissolves the water soluble polymer under the non image area, thus undermining and eroding the foundation of the non image area. These areas which lack adequate foundation.may be quickly and easily swept away by a combination of water and a slight rubbing action.Since the imaged areas were rendered non-water permeable upon exposure, water could not reach the water soluble polymer foundation beneath the image areas. These areas are therefore not undermined nor lifted away. The imaged areas are thus ink receptive and the bare metal substrate which coincided with the removed non-image areas is by its nature ink repelling. The result is a commercially satisfactory lithographic printing plate.

In a positive working system the photosensitive upper layer is initially water impermeable and upon exposure is rendered water permeable at the exposed areas and remains water impermeable at the unexposed areas.

Development is accomplished in the same way as hereinbefore mentioned.

The present invention seeks to provide a commercially acceptable lithographic printing plate which may be developed by using ordinary tap water, which does not require the subsequent application of a lacquer or similar substance to the developed image, and which does not require the use of expensive and ecologically objectionable chemicals for development.

As hereinbefore mentioned, the present invention provides for a commerically acceptable, water developable, lithographic printing plate.

As the first step in the production of the lithographic printing plate of this invention, a sheet metal substrate, preferably aluminium and the alloys thereof, especially those aluminum compositions suitable for the manufacture of lithographic printing plates such as Alcoa 3003 and Alcoa 1100, which may or may not have been pre-treated by standard graining and/or etching and/or anodizing techniques as are well known in the art and also may or may not have been treated with a composition suitable for use as and interlayer for lithographic plates, is coated with a non-light sensitive, water soluble resin. Said coated substrate is then treated with a stratum of a substance which comprises a water insoluble lithographic photosensitizer and a water insoluble resin.Said substance is characterized as water insoluble, ink receptive and alternatively water permeable or water impermeable prior to exposure to ultraviolet or actinic radiation. The photosensitizer resin substance is preferably not a film former which would impede water permeability. In a negative working system, upon imagewise exposure through a mask by methods known to the skilled worker, the aforementioned top layer substance which is initially water permeable is rendered water impermeable at the exposed areas while remaining water permeable at the unexposed areas. This is true only for negative working systems. In a positive working system the upper coating is initially water impermeable and upon exposure the unexposed areas remain water impermeable and the exposed areas are rendered water permeable.

In a negative working system a water insoluble negative acting lithographic photosensitizer is mixed with a water permeable, oleophilic, water insoluble resin. The resulting composition is also photosensitive, water permeable, oleophilic and water insoluble. After -exposure to ultraviolet or actinic radiation the photo sensitizer binds more closely with the resin and the composition is rendered water impermeable.

In a positive working system a water insoluble, water impermeable positive acting lithographic photo sensitizer is mixed with a water permeable, oleophilic, water insoluble resin.

The resulting composition is also oleophilic and water insoluble but the photo sensitizer closely binds to the resin and the resulting composition is therefore water impermeable. After exposure, as above, the photosensitizer becomes water permeable rendering the overall composition water permeable at the exposed areas.

The plate is then rinsed with water, with or without scouring. As a result, the water permeable areas allow water to filter through to the water soluble resin in the lower level of the plate, thus causing dissolution of the resin and undermining the water permeable areas of the upper coating which is now loosened and washed away. At the water impermeable areas an ink receptive image remains which can be employed as a lithographic printing plate.

Standard metal substrate pretreatments include electrolytically anodizing in sulfuric, chromic, hydrochloric and/or phosphoric acids, or electrolytically etching in hydrochloric or phosphoric acid, and/or chemical or mechanical graining by methods which are well known to the skilled worker. Interlayer compositions employable in the practice of this invention include aqueous solutions of alkali metal silicate, such as sodium silicate, silicic acid, the Group IV-B metal flourides, polyacrylic acid, the alkali metal zirconium fluorides, such as potassium zirconium hexafluoride, or hydrofluozirconic acid in concentration of 0.5% of 20% by volume.

Water soluble resins which comprise the bottom layer as previously described may in dude, polyvinyl pyrollidone, polyvinyl alcohols, polyacrylamides and copolymers, synthetic gums such as, starabic, dextrines, natural gums such as, gum arabic and hydroxyethyl cellulose gum.

These resins are applied to the substrate at a coating weight of from 5 to 200 mg/sq.ft., preferably from about 10 to about 100 mg/ sq.ft., and most preferably from about 25 to about 60 mg/sq.fi.

Water permeable oleophilic resins usable in the upper coating substance include, epoxy resins (such as Epon 1031, 1001-1009-Shell oil Company); polyurethane (such as Goodrich's Estane Series 5714, 5715); polyester (for example DV 521 available from Polychrome Corp.); Formvar Reg. Trade Mark (polyvinyl formal resin such as 12/85 from Monsanto); urethanes of low molecular weight (such as DV 53, DV 532 available from Polychrome Corp.); polyvinyl butyral resins (commercially available product of Monsanto) polyox (polyethylene oxide homopolymers having a molecular weight of from 100,000 to 5 million, commercially available from Union Carbide); and polyvinyl hydrogen phthalate (commercailly available from Eastman Kodak).

The photosensitive compositions which may be satisfactorily employed in the practice of this invention are those which are lithographically suitable and are actinic and/or ultraviolet light reactive. The photosensitive compositions which may be used as part of this invention are those which are negative or positive acting and include such negative acting photosensitive agents as the aromatic diazo compounds such as the reaction product of paradiazo diphenyl amine-para-formaldehyde condensate and 2-hydroxy4-methoxy benzophenone sulfonic acid; and the azidopyrenes, for example, l-azido-pyrene, 6-nitro-l-azidopy- rene, 1, 6 diazidopyrene, 1,8-diazido-pyrene, l-propionyl-6-azidopyrene, 1-acetyl-6-azido- pyrene, 1 -n-butyryl-6azidopyrene, l-n-pro pionyl-8 -bromo -i-azido-pyrene; and 8-n-propionyl-l, 6-diazidopyrene; and such positive acting photosensitive agents as aromatic diazoaxide compounds, for example, benzoquinone diazides, naphthoquinone diazides, and polyacetals which depolymerize under ultraviolet radiation, polymonochioroacetaldehyde, polypropionaldehyde, poly-n-butyraldehyde, polycyanoacetaldehyde, poly-B-cyanopropionaldehyde, poly-cyano-pentaldehyde, polycyano-valeraldehyde, polyisobutyraldehyde, poly-valeraldehyde, poly-heptaldehyde. The most satisfactory photosenstive agent may be selected by the skilled worker, depending upon the results sought to be achieved.

The optimum proportion of each ingredient and selection of a particular composition naturally depends on the specific properties desired in the final lithographic plate. Although there is virtually an infinite range to the ratio of the amount of photosensitizer to resin, a practical, operable ratio of sensitizer to resin in the top coating is from about 1 to 10 parts by weight sensitizer to from about 50 to 1 part by weight resin. A preferred ratio is from about 1 to 5 parts by weight sensitizer to from about 10 to 1 part by weight resin. A most preferred ratio is from about 1 to 3 parts by weight sensitizer to from about 4 to 1 part by weight resin.

The coating weight of the photosensitizerresin composition on the plate is from 5 to 300 mg/sq.ft., with a preferred range of from about 35 to about 200 mg/sq.ft., and a most preferred range of from about 50 to about 100 mg/sq.ft.

The thus produced plate, upon imagewise exposure by methods well known to the skilled worker may be developed by use of a water rinse, with or without physical rubbing. Operable development times range from 5 seconds up to about 4 minutes depending on the size of the plate. Preferably development time ranges from about 5 seconds to about 1 minute.

Development for substantially longer times may result in some undesirable undermining of the non-water permeable surface areas.

The present invention will now be further described by means of the following Examples.

EXAMPLE 1.

An aluminum substrate was prepared for lithographic use by wet pumice graining the surface followed by an anodizing step in sulfuric acid to an oxide weight of 200 mg/sq.ft. The sample was further treated in a 5% solution of sodium silicate for 1 minute at 180 degrees F to improve the hydrophilic properties of the substrate surface. The substrate was first coated with a 1% aqueous solution of polyvinyl chloride to a coating weight of 20 mg/sq.ft. One drop/100 ml of Triton X-100 wetting agent was incorporated in this solution to improve its wetting and film forming propensities. Once dried, a water permeable lithographically suitable, light sensitive composition was applied to the treated substrate at a coating weight of 61 mg/sq.ft.This composition was comprised of, 1 part by weight sensitizer (para-diazodiphenylamine sulfate resin reaction product with 2-hydroxy4-methoxy benzophenone sulfonic acid); 2 parts by weight epoxy resin (Epon 1031 Shell Chemical); 0.1 part by weight basic blue dye; 0.025 parts by weight methyl orange; in a solvent system of 28% methyl alcohol, 28% methyl Cellosolve Reg. Trade Mark (etheylene glycol monomethyl ether); 44% methylene chloride. Once dried, the coated aluminum plate was exposed with a negative transparency by a conventional NuArc ultraviolet exposing unit for 2 minutes. Once exposed the plate was developed by means of ordinary tap water at 60 degrees F. to remove the unexposed, non-image areas of the plate.

The plate was mounted on a conventional offset press and run for 10,000 acceptable impressions.

EXAMPLE 2 An unanodized aluminum substrate was chemically etched in a 10% solution of potassium hydroxide for 1 minute at 180 degrees F.

The surface was then treated with a 5% solution of sodium silicate as an interlayer. Subsequently, the treated substrate was first coated with polyvinyl alcohol to a 30 mg/sq.ft., coating weight and then applied with a top layer which comprised, 1 part by weight sensitizer, as Example 1; 1 part by weight epoxy resin (1031 Shell); 1 part by weight epoxy resin (1007 Shell); 0.14 parts by weight basic blue dye; 0.05 parts by weight methyl orange dye in a solvent system of 44% methylene chloride; 28% methyl Cellosolve Reg. Trade Mark; 28% methyl alcohol at a coating weight of 80 mg/ sq.ft. Said plate was subsequently exposed, developed with ordinary tap water and run on a conventional printing press for 5000 impressions.

EXAMPLE 3 The procedure of Example 1 was followed except the bottom layer was comprised of polyvinylpyrrolidone at a coating weight of 30 mg/sq.ft., and the top layer was comprised of, 1 part by weight sensitizer of Example 1 1 part by weight Epon epoxy 1031 (Shell); 1 part by weight Epon epoxy 1007 (Shell) in the solvent system of Example 1, at a coating weight of 75 mg/sq.ft. Similar results were obtained.

EXAMPLE 4 The procedure of Example 2 was followed except the bottom coating was comprised of a mixture of polyvinyl alcohol and starabic gum (Staley Co.) at a coating weight of 30 mg/sq.ft.

and the top coating was comprised of, 1 part by weight sensitizer of Example 1; 1 part by weight epoxy 1031 (Epon Shell); 1 part by weight polyurethane (Estane 5714 Goodrich) in the solvent system of Example 2 and at a coating weight of 80 mg/sq.ft. After exposure and development in ordinary tap water, the plate was mounted on a conventional printing press and run for 25,000 acceptable printing impressions.

EXAMPLE 5 The procedure of Example 1 was followed except the substrate was not anodized, the bottom layer was comprised by hydroxy ethyl cellulose gum at a weight of 40 mg/sq.ft. and the top layer was comprised of, 1 part by weight sensitizer of Example 1; 1 part by weight epoxy resin (Epon 1031 Shell); 1 part by weight polyurethane (Estane 5715 Goodrich) in the solvent system of Example 1 and at a coating weight of 100 mg/sq.ft. After exposure and development with ordinary tap water, the plate printed 30,000 acceptable impressions on an offset press.

WHAT WE CLAIM IS: 1. A water developable lithographic printing plate which comprises a metal sheet substrate having coated thereon a water soluble, nonlight sensitive resin and having applied over said resin coating a water insoluble, ink receptive, photosensitive composition which comprises a water permeable, water insoluble, oleophilic resin and a photosensitizer selected from positive working and negative working lithographic photosensitizers.

2. A lithographic printing plate as claimed in Claim 1 wherein said metal sheet substrate is comprised of aluminum.

3. A printing plate as claimed in Claim 2 wherein said aluminum sheet substrate has been anodized.

4. A printing plate as claimed in Claim 2 wherein said aluminum sheet substrate has been grained.

5. A printing plate as claimed in any pne of Claims 1 to 4 wherein said metal sheet substrate has applied thereto between the upper surface of said substrate and the water soluble, nonlight sensitive resin an interlayer composition which comprises a substance selected from alkali metal silicates, silicic acid, the GroupIV B metal fluorides, polyacrylic acid, the alkali metal zirconium fluorides and hydrofluozirconic acid.

6. A printing plate as claimed in any one of Claims 1 to 5 wherein said water soluble nonlight senstive resin is selected from polyvinyl pyrollidone; polyvinyl alcohols; polyacrylamides; synthetic gums and natural gums.

7. A printing plate as claimed in any one of Claims 1 to 6 wherein said positive working lithographic photosensitizer contains a photosensitizing agent selected from aromatic diazo oxide compounds, polyacetals which depolymerize under ultraviolet radiation, polymonochloroacetaldehyde, polypropionaldehyde, poly-n-butyraldehyde, poly-cyano-pentaldehyde, polycyanovaleraldehyde, poly-n-butyraldehyde, polyisobutyraldehyde, polyvaleraldehyde and polyheptaldehyde, said photosensitive composition being characterized as water impermeable prior to exposure to ultraviolet or actinic radiation and water permeable after such exposure.

8. A printing plate as claimed in any one of Claims 1 to 6 wherein said negative working lithographic photosensitizer contains a photosensitizing agent selected from the aromatic diazo compounds and the azidopyrenes said photosensitive composition being characterized as water permeable prior to exposure to ultraviolet or actinic radiation and water impermeable after such exposure.

9. A printing plate as claimed in any one of Claims 1 to 8 wherein said oleophilic resin is selected from epoxy resins; polyurethane; polyester; polyvinyl formal resin; urethane, polyvinyl butyral resins; polyethylene oxides and polyvinyl hydrogen phthalate.

10. A printing plate as claimed in any one of Claims 1 to 9 wherein the coating weight of water soluble resins is from 5 to 200 mg/sq.

ft., and the coating weight of the lithographic photosensitive-oleophilic resin composition is from 5 to 300 mg/sq.ft.

11. A printing plate as claimed in any one of Claims 1 to 10 wherein the ratio of lithographic photo sensitizer to oleophilic resin is from 1 to 10 parts photosensitizer to from 50 to 1 part oleophilic resin.

12. A process for producing a water developable lithographic printing plate which comprises applying a non-light sensitive water suluble resin to at least one surface of a metal sheet substrate and subsequently applying over said resin coating, a coating of a photosensitive composition which comprises a water permeable, water insoluble, oleophilic resin and a lithographic photo sensitizer.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. methyl alcohol at a coating weight of 80 mg/ sq.ft. Said plate was subsequently exposed, developed with ordinary tap water and run on a conventional printing press for 5000 impressions. EXAMPLE 3 The procedure of Example 1 was followed except the bottom layer was comprised of polyvinylpyrrolidone at a coating weight of 30 mg/sq.ft., and the top layer was comprised of, 1 part by weight sensitizer of Example 1 1 part by weight Epon epoxy 1031 (Shell); 1 part by weight Epon epoxy 1007 (Shell) in the solvent system of Example 1, at a coating weight of 75 mg/sq.ft. Similar results were obtained. EXAMPLE 4 The procedure of Example 2 was followed except the bottom coating was comprised of a mixture of polyvinyl alcohol and starabic gum (Staley Co.) at a coating weight of 30 mg/sq.ft. and the top coating was comprised of, 1 part by weight sensitizer of Example 1; 1 part by weight epoxy 1031 (Epon Shell); 1 part by weight polyurethane (Estane 5714 Goodrich) in the solvent system of Example 2 and at a coating weight of 80 mg/sq.ft. After exposure and development in ordinary tap water, the plate was mounted on a conventional printing press and run for 25,000 acceptable printing impressions. EXAMPLE 5 The procedure of Example 1 was followed except the substrate was not anodized, the bottom layer was comprised by hydroxy ethyl cellulose gum at a weight of 40 mg/sq.ft. and the top layer was comprised of, 1 part by weight sensitizer of Example 1; 1 part by weight epoxy resin (Epon 1031 Shell); 1 part by weight polyurethane (Estane 5715 Goodrich) in the solvent system of Example 1 and at a coating weight of 100 mg/sq.ft. After exposure and development with ordinary tap water, the plate printed 30,000 acceptable impressions on an offset press. WHAT WE CLAIM IS:

1. A water developable lithographic printing plate which comprises a metal sheet substrate having coated thereon a water soluble, nonlight sensitive resin and having applied over said resin coating a water insoluble, ink receptive, photosensitive composition which comprises a water permeable, water insoluble, oleophilic resin and a photosensitizer selected from positive working and negative working lithographic photosensitizers.

13. A process for producing a water develop

able lithographic printing plate which comprises applying a hydrophilic interlayer composition to at least one surface of an aluminum substrate, then treating said substrate with a water soluble, non-light sensitive resin and subsequently coating the thus treated substrate with a photosensitive composition which comprises a water permeable, water insoluble, oleophilic resin and a lithographic photosensitizer.

14. A process for producing a water developable lithographic printing plate which comprises applying a hydrophilic interlayer selected from alkali metal silicates, silicic acid, the Group IV-B metal fluorides, polyacrylic acid, alkali metal zirconium fluorides and hydrofluozirconic acid to at least one surface of an aluminum sheet substrate, then applying to said substrate a non-light sensitive, water soluble substance selected from polyvinyl pyrollidone, polyvinyl alcohols, polyacrylamides synthetic gums and natural gums and subsequently applying to the thus treated substrate a photosensitive composition which comprises a water permeable, water insoluble, oleophilic resin selected from epoxy resins, polyurethane, polyester, polyvinyl formal resin, urethane, polyvinyl butyral resins, polyethylene oxides and polyvinyl hydrogen phthalate and a lithographic photo sensitizer containing a photosensitizing agent selected from aromatic diazo oxide compounds, polyacetals which depolymerize underultraviolet radiation, polymonochloroacetaldehyde, polypropionaldehyde, poly-n-butyraldehyde, polycyano-pentaldehyde, polycyanovaleraldehyde, poly-n-butyraldehyde, polyisobutyraldehyde, polyvaleraldehyde, polyheptaldehyde, the aromatic diazo compounds and the azidropyrenes.

15. A printing plate as claimed in Claim 1 and substantially as hereinbefore described with reference to any one of the Examples.

16. A process as claimed in Claim 12 for producing a water developable lithographic printing plate substantially as hereinbefore described with reference to any one of the Examples.