NO774516L - WATER-PRODUCABLE LITHOGRAPHIC PRINTING PLATE - Google Patents

Description

Water-developable lithographic printing plate.

This invention relates to a new method for the production of presensitized lithographic printing plates,

and they thereby produced new lithographic printing plates. More specifically, this invention relates to a new method for the production of aluminum-based photosensitive lithographic printing plates, which comprises coating at least one surface of an aluminum base sheet with a non-light-sensitive, water-soluble, polymer resin and finally applying to said .surface a water-insoluble and ink-receptive lithographically suitable photosensitive composition to obtain the desired photosensitive lithographic printing plate.

To date, on the contrary, there has been a problem in the industry to produce a more ecologically acceptable lithographic printing plate and a method for developing it. It is known to produce such plates for which it is necessary to use various chemical developing agents which must be disposed of after use, typically by the public waste disposal service. Such developers are expensive to buy, and it is undesirable to dispose of them through sanitary systems. With the present invention, a lithographic printing plate is produced which can be developed with. ordinary tap water, which is both cheap and ecologically acceptable.

In the prior art, it is known to use certain water-soluble diazo-type mixtures in the production of lithographic printing plates which become water-insoluble upon pictorial exposure to . ultra violet radiation by standard techniques. This method does not allow for the removal of non-.1 exposed areas by developing with water. However, the images produced in this way are extremely weak and cannot withstand the stress of long-term printing. The plates formed by this method therefore need a printing ink-receptive varnish or other similar coating to be applied to the image area. after development, and it is this coating which really prints the desired image and not the diazo compound. It is important to note that these varnishes also contaminate their rinse water. An example of such a water-soluble diazo system is described in U.S. Patent No. 3,179,518, issued to Sus et al.

Other attempts include using a mixture of a water-soluble diazo compound and. a water-soluble resin which is rendered water-insoluble by exposure by standard methods. However, images produced by this method are not ink-receptive and are therefore not useful in the production of lithographic printing plates. The present invention relates only to water-insoluble mixtures of ink-susceptible lithographic photosensitizer and resin, which mixtures use

des in the top coating.

Until now, in the production of commercially acceptable presensitized lithographic printing plates for which a subsequent varnish application is not required on the plate areas where an image has been formed, it has been necessary to use photosensitive. mixtures which could not be developed with ordinary tap water;

Plates produced according to these methods could only be developed using expensive, special and environmentally-contaminated . chemical agents.

The present invention provides an improved lithographic printing plate which can be developed satisfactorily using ordinary tap water, which is both cheap and environmentally acceptable. ■ In the present invention, it has been found that a satisfactory plate satisfying these criteria can be produced by first applying a non-photosensitive water-soluble polymer to the surface of a metal sheet substrate, and then coating the thus treated substrate with a photosensitive composition comprising.a water-insoluble lithographic photosensitizer and a water-insoluble resin. This coating mixture for the upper part is characterized as water-insoluble, ink-receptive and alternatively either water-permeable or water-impermeable. By water-permeable is meant that the mixture is insoluble in water, and yet water can be filtered through the mixture. In a negative-acting system, the upper coating is initially water-permeable and by pictorial exposure through a suitable mask by methods known to those skilled in the art, the exposed areas are made water-impermeable and remain ink-receptive. When washing an image-exposed plate with water, the water therefore penetrates through the negatively acting photosensitive mixture in the unexposed•non-image area, and reaches and dissolves the water-soluble polymer below the non-image area., and under- thus digging and devouring the substrate for the non-image area. These areas that lack sufficient support can be quickly and easily swept away by a combination of water and a light scrubbing. Since the areas where the image is formed were made ■ water-impermeable by the exposure, water could not reach it. fixed support under the image areas. These areas are therefore not undermined or lifted away. The areas where an image has been formed are thus ink-receptive and the pure metal substrate that coincided with the removed non-image areas is by nature ink-repellent. The result is a commercially satisfactory lithographic printing plate.

In a positive acting system, the photosensitive upper layer is initially water-impermeable and upon exposure is made water-permeable in the exposed areas and remains water-impermeable in the unexposed areas. The development is carried out in the same way as previously described.

It is therefore an object of the present invention to provide a commercially acceptable lithographic printing plate. which can be induced by using ordinary tap water.

It is a further object of the present invention to provide a commercially acceptable lithographic printing plate which can be developed using ordinary tap water, and which does not require the subsequent application of varnish or similar substance to develop the image. '

Another object of the present invention is to provide a commercially acceptable lithographic printing plate for which there is no need to use expensive and ecologically questionable chemicals for development.

These and other purposes of the present invention

will be partly discussed and partly apparent when considering the detailed description of the preferred embodiments later in the description.

As mentioned above, the present invention provides a commercially acceptable, water-developable, lithographic printing plate.

As a first step in the production of the lithographic printing plate according to the invention, a metal sheet substrate, preferably aluminum and its alloys, especially such aluminum compositions which are suitable for the production of lithographic printing plates such as "Alcoa" 3003 and "Alcoa " 1100, which has possibly been pre-treated by giving it a grained surface and/or by etching and/or by anodizing techniques that are well known in the industry, and

optionally treated with a mixture suitable for use as an intermediate layer in lithographic plates, coated with a non-photosensitive, water-soluble resin. This coated substrate is then treated with a layer of a substance which.' comprises a water-insoluble lithographic photosensitizer and a water-insoluble resin. This substance is characterized as water-insoluble, ink-susceptible and alternately water-permeable or water-impermeable before exposure to ultraviolet or actinic radiation. The photosensitizer-resin substance is preferably not a film-former which will prevent water permeability.

In a negatively acting system.becomes by pictorial exposure

through a mask by methods such as. is known to professionals,, the front

said top layer substance which was initially water-permeable is rendered water-impermeable in the exposed areas while remaining water-permeable in the unexposed areas. This is true only for negatively acting systems.

In a positive acting system the upper coating is initially water impermeable and upon exposure the unexposed areas will remain water impermeable and the exposed areas will be made water permeable.

In a negative-acting system, a water-insoluble, negative-acting, lithographic photosensitizer is mixed with

a water-permeable, oleophilic, water-insoluble resin. The resulting mixture is also photosensitive, water-permeable,

oleophilic and water-insoluble. After exposure to ultraviolet or actinic radiation, the photosensitizer binds more closely to the resin and the mixture is rendered water-impermeable.

In a negative-acting system, a water-insoluble, water-impermeable, positive-acting, lithographic photosensitizer is mixed with a water-permeable, oleophilic, water-insoluble resin. The resulting mixture is also oleophilic and water-insoluble, but the photosensitizer binds more closely to the resin and the resulting mixture is therefore water-impermeable. After exposure, as above, the photosensitizer becomes water-permeable, and this makes the total mixture water-permeable in the exposed areas.

The plate will be. then rinsed with water, with or without scrubbing. As a result, the water-permeable areas allow water to filter through to the water-soluble resin in the lower part of the plate, causing dissolution of the resin and undermining of the water-permeable areas.

of the upper coating which now loosens and is washed away. In the water-permeable • areas, a printing ink-receptive image remains, which can be used as a lithographic printing plate.

Common metal substrate pretreatments include electrolytic anodizing in sulfuric acid, chromic acid, hydrochloric acid, and/or phosphoric acid, or electrolytic etching in hydrochloric or sulfuric acid, and/or chemical or mechanical treatment to produce a grainy appearance, by methods that are all well known to professionals. Interlayer compositions useful in the practice of this invention include aqueous solutions of

alkali metal silicate, such as sodium silicate, silicic acid, fluorides

of metals, in group IV-B, the alkali metal salts or their acids,

.polyacrylic acids, the alkali zirconium fluorides, such as potassium zirconium hexafluoride, or hydrofluorozirconic acid in concentrations of

0.5 to 20% by volume.

Water-soluble resins in the bottom layer as previously described may include polyvinylpyrrolidone, polyvinyl alcohols, polyacrylamides and copolymers, synthetic gums such as starch, dextrins, natural gums such as gum arabic and hydroxyethylcellulose gum.

These resins are applied to the substrate with a coating weight of from approx. 0.0054 to approx. 0.210 mg/cm, preferably from approx. 0.11 to approx. 0.105 mg/cm<2>, and most preferably from approx. 0.02 7 to approx. 0.064 ■ mg/cm 2 .

Water-permeable oleophiles. resins useful in the topcoat include, epoxy resins (such as "Epon" 1031, 1001-1009-Shell Oil Company); ... poly-urethanes (such as Goodrich's "Estan" series 5714 , 5715 );. polyesters (eg, DV 521 available from Polychrom Corp.); formvar (such as 12/85 from Monsanto)'; low molecular weight urethanes (such as DV 53, DV 532 from Polychrom Corp.); butryl resins (commercially available product from Monsanto); polyox (polyethylene oxide series from Union Carbide); and polyvinyl hydrogen phthalate (commercially available from Eastman Kodak).

The photosensitive compositions which can be satisfactorily used in carrying out this invention are those which are lithographically suitable and which are reactive towards actinic and/or ultraviolet light. The photosensitive mixtures that can be used as part of this invention are those that are negatively or positively acting and include such negatively acting photosensitive agents as the aromatic diazo compounds such as the reaction product between para-diazo-diphenyl-amine-para-condensate and 2 -hydroxy-4-methoxy-benzophenone-sulfonic acid; and the azido-pyrenes, e.g. 1-azido-pyrene, 6-nitrb-l-azidopyrene, 1,6-diazidopyrene, 1., 8-diazidopyrene , l-propionyl-6-azidopyrene , l-acetyl-6-azidopyrene ,'• l-n-butyryl-6 -azidopyrene, 1-n-propionyl-8-bromo-6-azidopyrene and 8-n-propibnyl-1,6-diazidopyrene; and such positively acting photo-sensitive agents as aromatic diazo-oxide compounds, e.g. .benzoquinone, diazides, na phtoquinone diazides, and. polyacetals which depolymerize under ultra violet ■ radiation, polymonochloroacetaldehyde, polypropionaldehyde, poly-n-butyra lde.hyde, poly-cyano-^acetaldehyde, poly-B-cyanopropionaldehyde, poly-cyanopentaldehyde, poly-cyano-valeraidehyde,'poly-isbbutyraldehyde , poly-valeraldehyde, poly-heptaldehyde. The most satisfactory photosensitizers can be selected by the person skilled in the art depending on the results sought to be achieved.

The optimum amount of each ingredient and the choice of special mixtures naturally depend on the particular characteristics of

..creates as desired for the final lithographic plate. Self

if in reality there is an unlimited range for the ratio between the amounts of photosensitizer and resin, then a practically applicable ratio between sensitizer and resin in the tppp coating is from approx. 1 to 10 parts by weight sensitizer to from approx. 50 to 1 part by weight of resin. A preferred ratio is from. about. 1 to 5 parts by weight sensitizer to from approx. 10 to 1 part by weight resin. The most preferred ratio is from approx. 1 to 3 parts by weight sensitizer to from approx. 4 to 1 part by weight resin. •

The coating weight for the mixture of photosensitizer and resin on the plate is from approx. 0.005 in 4 6il ■ approx. 0.32 0 mg/cm 2,. with a preferred range of from approx. 0.038 to approx. 0.210 mg/cm, and a most preferred range of from approx. 0.054 to approx. 0.105

,2

mg/cm .

Such a produced plate, by pictorial exposure by methods well known to those skilled in the art, can be developed using water rinsing, with or without physical rubbing. Usable development times vary from 5 seconds up to approx. 4 minutes depending on the size of the plate. Preferred development times vary from approx. 5 seconds to approx. 1 minute..Development for significantly longer times can result in a certain unwanted undermining of the water- and iron-permeable surface areas.

The following examples are provided to illustrate the practice of the present invention, and are in no way limiting its scope...

EXAMPLE 1

An aluminum substrate for lithographic use was prepared by making the surface grainy with wet pumice and then anodizing in sulfuric acid until an oxide weight of o 0.210 mg/cm 2. The sample was further treated in a 5% solution of sodium silicate for 1 minute at 82°C 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 o 0.021 mg/cm 2 . One drop per 100 ml with the wetting agent "Triton". X-100 was incorporated into this solution to improve its wetting and film-forming properties.

creates. Immediately after the solution had dried, it became

the treated substrate coated with a water-permeable, lithographically suitable, light-sensitive composition with a coating weight of

0.066 mg/cm 2 . This mixture was composed of 1 weight dough. sensitizer (para-diazo-diphenylamine sulfate resin reacted with 2-hydroxy-4-methoxy-benzophenone-sulfonic acid), 2 parts by weight epoxy resin ("Epon" 1031 Shell Chemical), 0.1 part by weight basic blue dye and 0.025 parts by weight methyl orange in a solvent system of 28% methyl alcohol, 28% methylcellosolve and 44% methylene chloride. As soon as the applied mixture was dried, the coated aluminum sheet was exposed by a negative transpa-

clean with a conventional.NuArc ultraviolet exposure unit for 2 minutes . Immediately after exposure, the plate was developed using ordinary tap water at 15.5°C to remove the unexposed non-image areas of the plate. The plate was placed in a conventional offset press and 10,000 acceptable impressions were made.

EXAMPLE 2

An unanodized aluminum substrate was chemically etched

in a 10% solution of potassium hydroxide for 1 minute at 82°C. The surface was then treated with a 5% solution of sodium silicate as an intermediate layer. Then the treated substrate was first coated with polyvinyl alcohol to a coating weight of

0.032 mg/cm 2 and was then applied a top layer comprising 1 part by weight of sensitizer, as in example 1, 1 part by weight of epoxy resin

(1031 Shell), 1 part by weight epoxy resin•(1007 Shell), 0.14. parts by weight basic blue dye and 0.05 parts by weight methyl orange dye in a solvent system of 44% methylene chloride,

28% methyl cellosolve and 28% methyl alcohol, with a coating weight of 0.086 mg/cm 2 . This plate was then exposed, developed

with ordinary tap water and it was used in a conventional printing press at 5,000 impressions.

EXAMPLE 3

The procedure from Example 1 was followed, except that the bottom layer comprised polyvinylpyrrolidone with a coating weight of 0.32 mg/cm 2 , and the top layer comprised 1 part by weight of sensitizer as in Example 1, 1 part by weight of "Epon" epoxy 1031 ( Shell) in a solvent system as in Example 1, at a coating weight of 0.08.1 mg/cm 2 . Similar results were obtained.

EXAMPLE 4

The procedure of Example 2 was followed, except that the bottom layer comprised a mixture of polyvinyl alcohol and starabin rubber (Staley Co.) and had a coating weight of 0.032 mg/cm 2 , and the top coating comprised 1 part by weight of sensitizer as in example 1, 1 part by weight of epoxy 1.031. ("Epon" Shell) and 1 part by weight of polyurethane ("Estane" 5714 Goodrich) in the solvent system of Example 2, and it had a coating weight of 0.086 mg/cm 2 . After exposure and development in ordinary tap water, the plate was placed in a conventional printing press and used for 25,000 acceptable printings.

EXAMPLE 5

The procedure from example 1 was followed, except that the substrate was not anodized, that the bottom layer comprised hydroxyethyl cellulose rubber with a weight of 0.04.3. mg/cm 2 and at. the top layer comprised 1 part by weight of sensitizer as in example 1, 1 part by weight of epoxy resin ("Epon" 1031 Shell), 1 part by weight of polyurethane ("Estane" 5715 Goodrich) in the solvent system from example 1, and had a coating weight of 0.105 mg/cm 2 . After exposure and development with ordinary tap water, 30,000 acceptable impressions were printed on the plate in an offset press.

It should of course be understood that the preceding disclosure is intended to illustrate the invention, and that numerous changes can be made in the operating conditions and quantities indicated without deviating from the scope of the invention as disclosed and defined in the subsequent claims.

Claims (14)

1. A water-developable lithographic printing plate comprising a metal sheet substrate on which there is a coating of a water-soluble, non-photosensitive resin and wherein <:> this be layered substrate is coated with a water-insoluble, ink-receptive, photosensitive composition comprising a water-permeable, water-insoluble, oleophilic resin and a lithographically suitable photo sensitizer selected from the group consisting of positively acting and negatively acting lithographic^ photosensitizers. 2. Lithographic printing plate according to claim 1, wherein said metal sheet substrate comprises aluminium. 3. Printing plate according to claim 2, where said aluminum sheet substrate has been anodized. '4. Printing plate according to claim 2, where said aluminum sheet substrate is given a grainy surface. 5." .\. t Printing plate according to claim 1, where on said metal sheet substrate is applied, between the upper surface of this substrate and the water-soluble, non-light-sensitive resin, an intermediate layer mixture comprising a substance selected from the group consisting of alkali metal silicate, silicic acid, fluorides of metals from group IV-B, the alkali metal salts or acids thereof, polyacrylic acid, the alkali zirconium fluorides and hydrofluorozirconic acid. • 6. Printing plate according to claim 1, wherein said water-soluble, non-photosensitive resin comprises a compound selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohols, polyacrylamides and copolymers, synthetic rubbers and natural rubbers. ■ 7. Printing plate according to claim 1, wherein said positively acting, lithographically suitable photosensitizer contains a photosensitizer selected from the group consisting of aromatic diazo-oxide compounds, polyacetals which depolymerize under ultraviolet radiation, polymonochloroacetaldehyde, polypropionaldehyde, poly-n-butyraldehyde , polyisobutyraldehyde, polyvaleraldehyde and polyheptaldehyde, said photosensitive mixture being characterized as water-impermeable <g> or <g> before exposure to ultraviolet or actinic radiation and water-permeable after such exposure. 8. Printing plate according to claim 1, where said negatively acting, lithographically suitable photosensitizer contains a photosensitizer selected from the group consisting of the aromatic diazo compounds and the azido-pyrenes, said photosensitive mixture being characterized as water-permeable: before, exposure to ultraviolet or actinic radiation, and water-impervious after such exposure. 9. Printing plate according to claim 1, where said oleophilic resin comprises a compound selected from the group consisting of epoxy resins, polyurethane. polyester, foam, urethane, butyryl resins, polyethylene oxides due to polyvinyl hydrogen phthalate. 10.. Printing plate according to claim 1, where the coating weight of the water-soluble resin is from approx. 0.054 to approx. 0.210 mg/cm 2 , and the coating weight of the mixture of the lithographically suitable photosensitizer and the oleophilic resin is from approx. 0.0054 to approx. 0.32 0 mg/cm <2> .. 11. Printing plate according to claim 1, where the ratio between lithographically suitable photosensitizer and oleophilic resin is from approx. 1 to approx. 10 parts photosensitizer to from approx. 50 to approx. 1' shares oleophilic resin. 12. Method for making a water-developable lithographic printing plate, which comprises applying a non-photosensitive water-soluble resin to at least one surface of a number sheet substrate and then coating the thus treated substrate with a photosensitive composition comprising a. water-permeable, water-insoluble, oleophilic resin and a lithographically suitable photosensitizer. 13. Method for making a water-developed 11-*bar lithographic printing plate, which comprises applying a hydrophilic interlayer mixture to at least one surface of an aluminum substrate, then treating this substrate with a water-soluble, non-photosensitive resin and then coating the thus treated substrate with a photosensitive composition comprising a water-permeable, water-insoluble, oleophilic resin and a lithographic photosensitizer. 14. Process for producing a water-developable lithographic printing plate, which comprises applying one hydrophilic interlayer mixture selected from the group consisting of alkali metal silicate, silicic acid, the fluorides of metals from group IV-B, the alkali metal salts or acids thereof, polyacrylic acid, alkali the zirconium fluorides and hydrofluorozirconic acid on at least one surface of an aluminum sheet substrate, then applying to said substrate exi a non-photosensitive, water-soluble substance selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohols, polyacrylamides and copolymers, synthetic gums and natural gums, and then apply to the thus treated substrate a photo-sensitive mixture comprising a water-permeable, water-insoluble, oleophilic resin selected from the group consisting of epoxy- . resins, polyurethane, polyester,, formware, urethane, butyryl resins,, polyethylene oxides and polyvinyl hydrogen phthalate and a lithographically suitable photosensitizer containing a photosensitizer selected from the group consisting of aromatic diazo oxide compounds, polyacetals which depolymerize under ultraviolet radiation, polymonochloroacetaldehyde, polypropionaldehyde, poly-n-butyraldehyde, poly-cyano-pentaldehyde, polycyanovaler-aldehyde, poly-n-butyraldehyde, polyisobutyraldehyde, polyvaler-, aldehyde, polyheptaldehyde, the aromatic diazo compounds and the azidopyrenes.