GB1590058A - Process for producing a printing plate from a presensitized plate - Google Patents

Description

(54) PROCESS FOR PRODUCING A PRINTING PLATE FROM A PRESENITIZED PLATE (71) We, FUJI PHOTO FILM CO., LTD., a Japanese Company, of No. 210, Nakanuma, Minami Ashigara-Shi, Kanagawa, Japan, 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: The present invention is directed to a photomechanical system, and more particularly to a process of preparing a printing plate using a presensitized plate having high press-life and high photosensitivity.

A process for preparing a printing plate including exposing a presensitized (PS) printing material to light from a reflection original through an optical system using a lens is known.

However, conventional presensitized printing plates have not been widely used in commercial printing because they have poor photosensitivity, or even if they have sufficiently high sensitivity, poor press-life or poor resolving power is obtained. Further, an alternative process for directly preparing a printing plate has been utilized, which comprises photographing an original on a film of small size followed by development processing to obtain an original of reduced size, printing the original onto a PS plate and then subjecting the PS plate to development processing, through an optical system using a lens. However, this approach has not been fully utilized yet because the photosensitivity of the conventional presensitized printing plate is too low and the plate is sensitive to only light of short wavelengths such as ultraviolet light. Further, this approach is not advantageous because only poorly reproduced images can be obtained since the amount of light is decreased due to the absorption by the camera lens.

An object of the present invention is to improve these defects.

According to the present invention we provide a process of producing a lithographic printing plate, which comprises (i) exposing to imagewise light from a reflection original, or enlargingly exposing to imagewise light from a reduced size transmission original through an optical system including a lens, a presensitized plate comprising: a) an aluminium support having an anodized oxide layer on the surface thereof, and b) a photosensitive layer comprising a photosensitive silver halide, a tannable hydrophilic colloid and a tanning developing agent, (ii) subjecting said exposed plate to development processing to initiate tanning development, and then (iii) washing out untanned areas of said photosensitive layer thereby to reveal main imagewise pattern said anodized oxide layer which is hydrophilic and forms areas of the lithographic printing plate which are repellent of oily ink.

The aluminum support for the PS plate employed in accordance with the present invention can be an aluminum foil, an aluminum sheet or a sheet of paper, film of a synthetic resin or sheet of another metal laminated with a layer of aluminum, the aluminum surface being in each case covered with an aluminum oxide layer formed by an anodic oxidation treatment.

More specifically, suitable aluminum plates which can be used in the present invention include plates of pure aluminum and of aluminum alloys. A variety of alloys can be used including these containing silicon, copper, manganese, magnesium, chromium, zinc, lead bismuth, nickel, etc. Some representative examples of suitable alloy compositions are shown in the following table. The values given in the table are percent by weight, with the remainder being aluminum.

Compositions of Typical Aluminum Alloys Alloy No. Si Cu Mn Mg Cr Zn 1S 0.25 2S 0.4 - - 0.6 - 3S - - 1.2 - 24S - 4.5 0.6 1.5 52S - - - 2.5 0.25 61S 0.6 0.25 - 1.0 0.25 75S - 1.60 - 2.50 0.30 5.60 rhese compositions generally include, in addition, small amounts of Fe and Ti and negligible amounts of impurities not shown in the table.

The surface of the aluminum plate is usually subjected to chemical cleaning such as a degreasing with solvents or alkaline agents, as described in detail in Kinzoku Hyomen Gijutsu Binran (A Handbook on Metallic Surfaces), pp. 86-210, Nikkan Kogyo Shinbunsha, Tokyo (1969), for the purpose of exposing a clean surface free of grease, rust or dust which is usually present on the aluminum surface. Depending on the requirement, the surface is grained.

Suitable graining methods which can be used include glass bead'graining, ball graining, sand blasting, brush graining as described in Japanese Patent Application (OPI) No. 33411/73, electrolytic graining as described in Japanese Patent Application (OPI) No. 28123/73 and British Patent 896,563. Any of these methods can be employed, however, graining is not always necessary and a polished surface of aluminum can be used as the printing surface of an offset printing support, although a grained support for offset printing exhibits a better water retention, thus giving preferred printed materials. Further, following the graining operation, according to the requirements, a treatment of the aluminum with an aluminum etching agent can be used in order to reduce background staining, as is set forth in Japanese Patent Application (OPI) No.49501/73.

An anodized oxide layer is then formed on the thus conditioned aluminum support immersed as anode in a solution containing one or more acids selected from sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, etc., an anodized oxide coating is formed on the surface of the aluminum support.

Typical anodizing conditions, of course, depend on the composition of the electrolytic solution used and thus cannot be defined unequivocally. In general, suitable anodizing conditions are as follows: acid concentration: about 1 to 80 % by weight; temperature of solution: about 5 to 70"C; current density: about 0.5 to 60 amp/dm2; voltage: about 1 to 100 volts; period of electrolysis: about 30 sec. to 50 min. Suitable anodizing procedures are disclosed in, for example, U.S. Patent Nos. 3,808,000, 3,181,461, 3,280,734 and 3,511,661.

The following table summarizes suitable anodic oxidation processing conditions in greater detail.

Solution Electrolytic Concent- Tempera- Current Time Solution ration ture Density Voltage Period (Ro) ( C) (A/dm2) (V) (min) Sulfuric Acid 1-70 5-65 0.5-30 1-50 1-30 Oxalic Acid 1-20 20-60 0.5-20 10-70 5-40 Phosphoric Acid 2-60 20-60 0.5-20 10-60 1-30 Chromic Acid 2-30 30-60 0.5-10 10-60 1-56) The photosensitive layer is formed by coating a photosensitive silver halide emulsion containing a tanning developing agent, and further, if necessary, finely divided particles of an olephilic resin as disclosed in Japanese Patent Application (OPI) No. 154627/77 which are substantially water-insoluble, can be dispersed and incorporated therein. A suitable coating amount of silver halide ranges from 1 to 200 mmols/m2 with the photosensitive layer having a thickness of 0.2 to 20 ,. As necessary, a coating aid, a dye or a pigment can also be incorporated therein. Suitable binders for the silver halide emulsion layer include gelatin, gelatin derivatives, polyvinyl alcohol or polyvinyl alcohol derivatives.

Typical examples of tanning developing agents which are incorporated in the photosensi tive silver halide emulsion include hydroquinones, catechols and pyrogallols. Specific exam ples of tanning developing agents which can be used are disclosed in British Patent Specifica tion No. 1,547,040. More specifically, the tanning developing agents used in the present invention are preferably those described in C.E.K. Mees, The Theory of the Photographic Process (Revised Ed.), pp. 580-584, and, from a chemical standpoint, are benzenes having at least one hydroxyl group or derivatives thereof, more preferably, polyhydroxybenzenes substituted with a halogen atom such as a chlorine atom, a bromine atom, an iodine atom or a fluorine atom, an aryl group, an amino group, an unsubstituted or substituted alkyl group having 1 to 6 carbon atoms or an alkoxy group.

Examples of suitable tanning development agents are hydroquinone; toluhydroquinone, chlorohydroquinone, pyrogallol, resorcinol, hexylresorcinol, phloroglucinol, 4-benzylcatechol and 4-phenylcatechol.

These tanning developing agents can be added directly to the silver halide emulsion, or added in the form of a solution after dissolving the tanning developing agents in an organic solvent if necessary. A suitable amount of the tanning developing agents which can be used is a molar ratio of 1/1000 to 1/100 per mol of the photosensitive silver halide. It is particularly preferred for the tanning developing agents to be dissolved in ethyl acetate or in a solvent mixture of ethyl acetate and a high boiling point organic solvent which is slightly soluble in water, such as tricresyl phosphate or dibutyl phthalate and then emulsion-dispersed in the silver halide emulsion.

A subbing layer can be provided between the support and the photosensitive layer, if desired. Binders which can be suitably employed in the subbing layer include gelatin, gelatin derivatives, polyvinyl alcohol or derivatives thereof and, depending upon necessity, the layer can further contain polymer particles, developing agents, developing aids, dyes and pigments and further can also contain silver halide grains if necessary.

Suitable tanning developing agents for silver halide which can be employed in the subbing layer include hydroquinones, catechols and pyrogallols. Examples of developing aids, which can be employed, include 3-pyrazolidones, 2-methylimidazoles, aminophenols, mercapto compounds and benzotriazoles. The tanning developing agents can be incorporated into not only the photosensitive layer but also into the subbing layer.

A typical example of a subbing layer is a hydrophilic colloid layer containing finely divided particles of an olephilic synthetic resin which are substantially water-insoluble, as disclosed in Japanese Patent Application (OPI) No. 15462/77.

In addition, a resinous layer having an olephilic surface as described in Japanese Patent Application (OPI) No. 154626/77, i.e., an ink-receptive protective layer can be provided on the photosensitive layer, if desired.

Such a resinous layer is characterized as providing a high oleophilicity while being permeable to water and as not hardening the silver halide emulsion layer thereunder.

Examples of compounds which can be used for this optional protective resinous layer can be selected from polymers and oligomers such as polyesters, polyamides, phenol-aldehyde resins, polyurethanes, epoxy resins, silicone resins, polyamides, polystyrenes, polyacrylates, polyvinyl acetate, hydroxypropyl methyl cellulose or hexahydrophthalate. A suitable molecular weight for the above-described polymers can range from 5,000 to 100,000 and a suitable molecular weight for the above-described oligomers is 500 to 5,000. Polymers and oligomers such as polystyrenes, polyacrylates, polyvinyl acetate, polyurethanes or hydroxypropyl methyl cellulose or hexahydrophthalate are particularly preferred. These synthetic resins can be used individually or as a combination of two or more thereof.

The optional protective resinous layer has the following characteristics.

Firstly, the resinous layer is not completely dissolved out and remains in the image portions on development of the silver halide emulsion layer. In particular, the solubility of the synthetic resin is less than 10 wt. % in water at 25 "C; thus, it is considered to be substantially insoluble in water.

Second, the resinous layer must be sufficiently permeable to water and an alkaline solution so that development and other processings of the silver halide emulsion layer can be performed.

Thirdly, the surface of the resinous layer is oleophilic. The degree of olephilicity can be evaluated by means of the difference between the contact angle of water in kerosine 0 w/o and the contact angle of kerosine in water 0 o/w at ordinary temperature (about 24"C). As for the resinous layer, it is particularly preferred for the value of -O o/w - 0 w/o] to be positive. Contact angles and their measurement are described in general in Jikken Kagaku Koza (Lecture on Experimental Chemistry), Maruzen Co., Vol. 7, pp. 74-85 (1971) and the contact angles 0 o/w and 0 w/o in particular can be measured using the "Captive Bubble Method" described in Mitsuo Obana, "Wetting Phenomenon of Lithographic Plates", Japan Printer, 25 (Oct. 1968). A 0 o/w of 0 to less than 90" is considered to be oleophilic and a 0 w/o of 90" or higher is considered to be hydrophilic and thus the expression H = - [0 w/o] is a measure of the ink receptivity and such is preferably greater than about 300.

The permeability to water of the resinous layer can be evaluated by means of the rate of increase in film thickness due to swelling by water which is measured using samples comprising a support having thereon a gelatin layer of a dry thickness of about 4,u having thereon a resin layer of a dry thickness of about 1 ,. With a permeability of 1, no permeation of water into the synthetic resin layer occurs and with this as a basis, a preferred permeability of water into the resinous layer is about 1.3 or higher.

In addition, the photosensitive silver halide emulsion layer can also optionally have thereon, in the place of the above described resinous layer, a hydrophilic colloid layer containing finely divided particles of a synthetic oleophilic resin, which particles are substantially insoluble in water, described in the aforesaid Japanese Patent Application (OPI) No.

15462/77.

The aluminum oxide layer provided on the surface of the aluminum support minimizes harmful interactions between aluminum and silver halide or substances contained in the subbing layer and can strengthen the adhesion with the photosensitive layer.

Specific examples of photosensitive silver halides which can be employed in the photosensitive layer of the material used in the present invention are silver chloride, silver bromide, silver iodide or mixtures of at least two kinds of silver halides, which can be an external latent image type silver halide or an internal latent image type silver halide. If desired, these photosensitive silver halides can be subjected to chemical sensitization or spectral sensitization to thereby extend their spectral sensitivity from the ultraviolet region to the visible region.

Methods for preparing the printing plate of the present invention include, for example, the methods as described in Insatsu-Zasshi, pages 25-31, December (1975), published by Insatu-Gakkai, Shuppan bu, Tokyo, and TAGA Proceedings (Technical Association of the Graphic Arts Proceedings), pages 1-22 (1975). For example, a printing plate can be produced by enlarging and exposing using an image from a reduced-size transparent or reflex original image onto a plate or automatically or semi-automatically exposing images of a plurality of pages onto a plate and then subjecting the plate to a series of development treatments. Exposure can be achieved using light from a tungsten lamp or a xenon lamp, a laser beam and an electron beam for a period of from a flash exposure of the order of 10- 5 sec.

to a relatively long exposure time. Suitable wavelengths for exposure can range from the near ultraviolet region to the near infrared region.

One of the characteristic features of the present invention is that, when a usual type of plate-making camera is used in a plate-making process including an enlargement step, the ratio of enlargement which is acceptable would be at most 1.5 times, whereas in the process of the present invention, the ratio of enlargement can be 2 to 20, preferably 2 to 8, times.

The present invention is explained in greater detail by reference to an example below.

However, the present invention is not to be construed as being limited thereto. Unless otherwise indicated herein, all percentages are by weight.

Example Preparation ofPS Plate: A 2S aluminum sheet having a thickness of 0.24 mm was degreased. After an alternating current of about 10 volts was applied at room temperature (about 24"C) for about 20 mins. in a hydrochloric acid aqueous solution of a concentration of about 1 %, and then an anodic oxidation treatment was carried out in a 20 wt. % aqueous sulfuric acid solution at an electric current density of 1 A/dm2 for 5 mins. to produce an aluminum oxide layer on the surface of the aluminum sheet. The sheet was washed with water and then dried.

A mixture was prepared having the following composition: Coating Solution for Subbing layer: Silver Halide Gelatin Emulsion (silver iodobromide; iodidie content: 1 mol%; average grain size: 0.06cm) 60 g Dispersion of a solution of 2.5 g of 4-Phenylcatechol and 2.5 g of Tricresyl Phosphate in 10 ml of Ethyl Acetate in 60 g of a 2 wt. % Aqueous Solution of Gelatin whole amount of prepared dispersion Water 60 g The mixture was warmed at 35"C to form a homogenous composition, which was coated onto the anodized support in a dry thickness of about 0.6 g/m2, using a coating machine.

Then, a photosensitive coating solution having the following composition was prepared: Coating Solution for Photosensitive layer: Dispersion of a Solution of (a) 6 g of a Copolymer, which is a reaction product of 86 % of vinyl chloride, 13 % of vinyl acetate and 1 %ofvinylchloride, 13 %ofvinyl acetate and 1 % of maleic anhydride, and (b) 6 g of Tricresyl Phosphate and (c) 6 g of 4-Phenylcatechol in 24 ml of Ethyl Acetate, in a Solution Mixture of 185 gofa 10 wt. % Aqueous Gelatin Solution and 5 g of a 10 wt. % Aqueous whole amount Nonylphenyl Phosphate Solution of prepared dispersion Silver Halide Gelatin Emulsion (silver chlorobromide; bromide content: 30 mol%; average grain size: 0.28 it) 108g 0.1 % Methanol Solution of 1,3-Diethyl 5- t2- f 3-(3-sulfopropyl) benzoxazolyl- 2 idene]ethylideneS 3 thiohydantoin Sodium Salt 10 ml 0.5 %Aqueous Solution of 4-Hydroxy-6methyl-1,3-3,3a-7-tetraazaindene 10ml 10 wt%Aqueous Solution of sodium Benzenesulfinate 6ml The mixture was warmed at 35"C to dissolve the components and the solution was coated in a dry thickness of about 2.0 g/ m2 using a coating machine, followed by drying.

Then, a coating solution which was prepared by dissolving a mixture of 1 part of the reaction product of 2 mols of hydroxyethyl acrylate and 1 mol of 4,4'methylenephenyldiisocyanate and 1 part of the reaction product of 86 %ofvinylchloride, 13 % of vinyl acetate and 1 % of maleic anhydride in a solvent mixture of ethyl acetate and ethylene chloride in a 1:1 volume ratio was coated on the photosensitive layer in a dry weight of about 1 Plate Making Method An original (containing line images) was photographed 1/4 reduced size on Mini Copy Film HR-II (tradename for roll film, made by Fuji Photo Film Co., Ltd.) using a camera and then subjected to automatic development at 300C using an automatic developing machine AP-4 filled with Developer MD-285 (time for development; 20 secs.). Using an enlargement printer with a xenon light source (4 kw), printing-out was performed for 5 secs. at a lens F stop of 11 in an enlargement of 4 times.

The imagewise exposed PS plate was passed through an automatic developing machine to obtain a plate for printing. The automatic developing machine has the following function.

That is, it comprises a development zone adjacent a washing out zone, a rinsing zone or an after-treatment zone, and further an adjacent drying zone. In the development zone, development was performed with a developer having the following composition at 35"C for 60 secs. and then followed by washing-out with warm water at 400C for 30 secs. to thereby produce a relief positive image. Water washing was performed for about 10 secs. in the rinsing zone and subsequently drying was carried out for 30 secs. in the drying zone. The plate for printing was thus obtained about 130 secs. after insertion into the automatic developing machine.

Composition ofDeveloper: Sodium Carbonate (anhydrous) 112.5 g Potassium Bromide 1.5 g Sodium Hexametaphosphate 1.0 g Water to make 1000 ml The thus obtained printing plate was employed for printing using a printing machine Heidelberg KOR "Heidelberg" is a registered Trade Mark made by Heidelberg Druckmaschinen Aktienegesellschaft) and oily printing ink. Chinese characters could be reproduced in Ming dynastic type and Gothic type of 10th Class as well as agate printing types alongside thereof, and 100,000 impressions could be obtained. For comparison, a PS plate LN-L made by Eastman Kodak Co., Ltd. was printed out in place of the PS plate used in accordance with the present invention followed by development for 3 mins. and 30 secs. with a developer for the PS plate LN-L. However, no images were obtained at all. It was found that the PS plate of the present invention had a high sensitivity of about 2500 times that of the Printing Plate LN-L described above.

Claims (10)

WHAT WE CLAIM IS:

1. A process of producing a lithographic printing plate, which comprises (i) exposing to imagewise light from a reflection original, or enlargingly exposing to imagewise light from a reduced sized transmission original through an optical system including a lens, a presensitized plate comprising: (a) an aluminium support having an anodized oxide layer on the surface thereof, and (b) a photosensitive layer comprising a photosensitive silver halide, a tannable hydrophilic colloid and a tanning developing agent, (ii) subjecting said exposed plate to development processing to initiate tanning development, and then (iii) washing out untanned areas of said photosensitive layer thereby to reveal in an imagewise pattern said anodized oxide layer, which is hydrophilic and forms areas of the lithographic printing plate which are repellent of oily ink.

2. A process as claimed in Claim 1, wherein said presensitized plate further contains a hydrophilic subbing layer between the aluminium support and the photosensitive layer.

3. A process as claimed in Claim 1 or 2, wherein the exposing is an enlargement of the original image and the degree of enlargement is 2 to 20 times.

4. A process as claimed in Claim 3, wherein the degree of enlargement is 2 to 8 times.

5. A process as claimed in any preceding claim, wherein the tanning developing agent is a hydroquinone, catechol or pyrogallol.

6. A process as claimed in any preceding claim, wherein said presensitized plate additionally includes an ink-receptive protective layer on said photosensitive layer.

7. A process as claimed in any preceding claim, wherein said presensitized plate additionally includes a hydrophilic colloid layer on the photosensitive layer.

8. A process as claimed in any preceding claim, wherein said photosensitive layer and/or subbing layer additionally contains finely divided particles of an oleophilic resin which are substantially water-insoluble.

9. A process of producing a printing plate, substantially as hereinbefore described with reference to the Example, excluding the comparative sample.

10. Printing plates made by the process of Claim 9.