US3440050A - Lithographic plate - Google Patents

Description

United States Patent Office 3,440,050 Patented Apr. 22, 1969 3,440,050 LITHOGRAPHIC PLATE Simon Chu, New York, N.Y., assignor to Polychrome Corporation, Yonkers, N.Y. No Drawing. Filed Feb. 5, 1965, Ser. No. 430,153 Int. Cl. G03c 1/94; B41n 1/04 US. CI. 90-75 13 Claims ABSTRACT- OF THE. DISCLOSURE There are disclosed herein lithographic light-sensitive plates, and a method for making such plates, having an anodized aluminum base sheet, a reaction product on the surface of the aluminum base sheet formed by a reaction between the anodized aluminum surface and a Group IV-B metal fluoride, and a light-sensitive coating thereover.

This invention relates to sheet materials useful for photochemical processes such as the preparation of lithographic plates, and relates particularly to sheet materials which comprise an aluminum base having overcoats of a light-sensitive material such as the various diazo compounds known to the art.

The art of lithographic printing depends upon a printing surface having both hydrophilic and hydrophobic areas and the consequent preferential retention of greasy image-forming substances by the hydrophobic areas with a similar retention of an oleophobic dampening fluid by the hydrophilic areas.

When a greasy image is printed upon a suitable surface, and the entire surface has been moistened with an aqueous solution, the greasy image areas will repel the water, and the non-greasy areas will retain the water. Upon subsequent application of greasy printers ink, the image portion will retain the ink whereas moist, nonimage areas will repel it. The image is then transferred to a paper or cloth etc. via an intermediate cylinder, i.e., a so-called offset or blanket cylinder, which is necessary to prevent mirror-image printing.

It has been a problem in the art to provide treatment for metallic plates which would cause the metallic plate to be so strongly bonded to subsequently applied lightsensitive compounds that very large numbers of prints, e.g., in excess of 100,000 prints, can be consistently obtained from relatively inexpensive lithographic plates. Some of the treatments known to the art by which an aluminum base sheet has been made more receptive and adherent to light-sensitive overcoats include sand blasting, brush-graining, and marbling the plate surface.

Anodizing the aluminum by use of alternating current has also been proposed in the prior art. Plates having aluminum bases so anodized were useful for direct imaging, for example, receiving the oleophilic image area from a typewriter ribbon. However, as a base for a lightsensitive coating such as an albumin dichromate or lithographic diazo, these anodized sheets were useful for only very short press runs or for line work but were not acceptable for use in the printing industry to provide good quality prints over long press runs. To remedy the deficiencies of these anodized aluminum plates, light-sensitive cinnamyl derivatives were used in conjunction with the anodized aluminum. These were very expensive and extraordinary care had to be taken in preparing and processing the plates.

Therefore, up to the present time, in order to insure runs of over 100,000 lithographic copies, the printer had to use deep-etch type plates or the equivalent. In runs up to about 250,000 copies, standard deep-etch type plates of either zinc or aluminum have been used. These plates are all far more expensive to produce than the novel plates described in the instant application. Furthermore, the processing steps required for the preparation of these known plates in the print shop require time and the skill of a trained experienced worker. Applicants have now found that sheets which comprise an aluminum surface which has been subjected to anodizing by alternating current in hydrochloric acid and has a zirconium fluoridetype overcoat and a lithographic diazo topcoat thereover provide excellent quality copies to be obtained on press runs of up to 250,000 copies. The plate of the invention is the first low-cost, easy to process, lithograph plate, capable of giving such long printing runs.

It is an object of the present invention to provide a sheet useful for receiving a light-sensitive coating to form an exceptionally durable lithographic plate. It is the further object of the invention to provide a lithographic plate which is useful for exceptionally long press runs. It is a further object of the invention to provide a means for adherently coating resinous materials on aluminum surfaces.

Other light-sensitive compounds may be used rather than the diazo compound. However, advantageously, the light-sensitive compound is the condensation product of paradiazodiphenylamine with formaldehyde, such as paraformaldehyde zinc chloride. This condensation is carried out in concentrated sulfuric acid and the process and product formed thereby are well known in the lithographic printing art. The diazo product is in fact a zinc chloride double salt. However, in this application the term diazo shall be meant to include not only lightsensitive diazo compounds which are known to the art such as the aforementioned double salt but is also in tended to include the reaction products of certain coupling agents and diazos as disclosed in the copending application U.S. Ser. No. 307,025, filed by Simon Chu on Sept. 6, 1963, now Patent No. 3,300,309, and other light-sensitive diazo reaction products, for example, the reaction product of a diazo and potassium ferrocyanide disclosed in US. Patent 3,113,023.

The term nitrogen containing compound is used to define, not only diazo compounds discussed above, but also azides and other such light-sensitive compounds known to the art.

The aluminum used as the base sheet is preferably 99% or more pure. For example, aluminum alloys such as the 1100 or 1145 alloys are suitable. Purer alloys than these two types would not appear to have any advantage because they would have less mechanical strength and would be higher in cost.

It is usually necessary to degrease the aluminum prior to the anodizing process. The anodizing processing is carried out as is substantially known to the art. The electrolyte is advantageously a 0.5 to 2.0% solution of hydrochloric acid. The temperature of the anodizing bath is usually maintained between 15 C. and C. The time of anodization is desirably between about 5 to 20 minutes at 6 to 14 volts. The spacing of the plates being anodized is conveniently from 1.5 to 4.0 inches. It will be understood by those skilled in the art that the time required for the anodization process will be reduced as the acid temperature is increased or as the voltage is increased.

After the anodization process, plates are immersed in a dilute basic solution, such as a 1% aqueous solution of ammonia. This step is taken in order to neutralize the surface of the plate on which residual hydrochloric acid may be present after the anodization process. The treatment with the base is followed by reacting the plates in a hot aqueous bath of a compound such as zirconium fluoride from about 30 seconds to 5 minutes at a temperature of from about to C. to form a hydrophilic layer of the aluminum plate. The potassium zirconium fiuoride solution is suitably of from about 0.5 to 1% concentration.

Compounds useful for forming a hydrophilic layer include not only zirconium compounds but also compounds of the other Group IV-B compounds, i.e.,'

hafnium and titanium. Furthermore, salts of the formula MlMzF in which M is hydrogen, in alkali metal, an alkaline earth metal or an ammonium cation, M is selected from Ti, Zr or Hf, and n is 5 or 6, may also be advantageously used in the process of the present invention. In reading this general formula, of course, it is to be understood that the number of fluorine and M atoms will differ depending on the valence state of the Group IV-B atom. U.S. Patent 3,160,506 contains further information relating to the use of these compounds on aluminum sheets preparatory to coating a lightsensitive layer thereover. Among such compounds are Na ZrF KZIFS, KZZI'FS, KzTlFg, K HfF NZlHfF5, and H ZrF Plates prepared as described above can be used for lithographic printing. However, a longer shelf life can be obtained and scumming can be prevented by subjecting the plates to an additional mild alkali treatment. This treatment neutralizes any of the fluoride coating which may remain on the surface of the aluminum, and which would tend to oxidize and then react to form hydrophobic areas with the subsequently applied light-sensitive coating. This additional alkali treatment can be advantageously carried out by submerging the plate in a 0.5 to aqueous solution of potassium tetrapyrophosphate at a temperature from 55 C. to 65 C. from about seconds to 5 minutes. Other mild alkalis or inhibited alkalis such as those known to the art may also be used. Care should be taken, however, that no etching action takes place. Such action may be detected by a bubbling of the alkaline solution.

The plate, prepared as described above, is in condition for shipment to the printer who would wipe on a light sensitive compound and proceed with the processing and use of the plate as is known in the art.

However, where it is desirable to add a light-sensitive coating, that is to presensitize the plate at the place of its manufacture, an additional acidifying step is highly desirable wherein an aqueous solution of about 0.005% of a compound such as K ZrF (or a dilute acetic acid solution) is used to acidify the plate surface at room temperature. The plate is subsequently dried and coated with a light sensitive diazo compound.

Other coatings over the aluminum plate such as those described in U.S. Patent 2,714,066 by Jewett and Case, are not desirable inasmuch as they are, on account of their alkaline nature, more reactive with the light-sensitive compounds.

In this application and accompanying drawings, I have shown and described a preferred embodiment of my invention and have suggested various alternatives and modifications thereof, it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions herein are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof, and will be able to modify it and embody it in a variety of forms, each as may be best suited to the condition of a particular case.

I claim:

1. A sheet adapted to receive a light-sensitive coating to form a lithographic printing plate which comprises an aluminum base sheet, said aluminum base sheet having an anodized surface thereon, and a hydrophilic coating on said anodized surface, said coating being essentially the reaction product of said anodized aluminum surface and a Group IV-B metal fluoride compound of the formula M 1 or of the formula M M F in which M is a 4 hydrogen, an alkali metal, an alkaline earth metal or an ammonium cation, M is a Ti, Zr or Hf cation, and n is the integer 5 or 6.

2. A lithographic plate comprising an aluminum base sheet, said aluminum base sheet having an anodized surface thereon, a hydrophilic coating on said anodized surface, said coating being essentially the reaction product of said anodized aluminum surface and a metal fluoride compound of the formula M 1 or of the formula M M F in which M is a hydrogen, an alkali metal, an alkaline earth metal or an ammonium cation, M is a Ti, Zr or Hf cation, and n is the integer 5 or 6, and a light-sensitive nitrogen compound coated over said hydrophilic coating.

3. A lithographic plate according to claim 2 wherein said metal fluoride compound is a zirconium fluoride salt.

4. A lithographic plate according to claim 2 wherein said light-sensitive nitrogen compound is a light-sensitive diazo compound.

5. A lithographic plate according to claim 2 wherein said light-sensitive nitrogen compound is a condensation product of paradiazodiphenylamine and formaldehyde.

6. A lithographic plate according to claim 2 wherein said light-sensitive nitrogen compound is a reaction product of (1) a condensation product of paradiazodiphenylamine and formaldehyde and (2) a coupling agent therefor.

7. A process for making a lithographic plate which comprises anodizing a surface of an aluminum base sheet, reacting the anodized surface of said aluminum base sheet with essentially a metal fluoride compound of the formula M 1 or of the formula M M F in which M is a hydrogen, an alkali metal, an alkaline earth metal or an ammonium cation, M is a Ti, Zr or Hf cation, and n is the integer 5 or 6, to form a hydrophilic reaction product layer on said base sheet, and coating a light-sensitive nitrogen compound over said hydrophilic reaction product layer.

8. A process according to claim 6 wherein said anodizing is carried out in an aqueous hydrochloric acid solution of about 0.5 to 2.0% by weight concentration of HCl for 5 to 20 minutes at 15 to 35 C.

9. A process according to claim 6 wherein said anodizing is carried out in a dilute acid solution under an AC voltage of 6 to 14 volts with the aluminum base sheets to be anodized spaced 1.5 to 4.0 inches apart.

10. A process according to claim 6 wherein said metal fluoride compound is a zirconium fluoride salt.

11. A process according to claim 6 wherein said metal fluoride compound is potassium zirconium fluoride.

12. A process according to claim 7 wherein said lightsensitive nitrogen compound is a condensation product of paradiazodiphenylamine and formaldehyde.

13. A process according to claim 7 wherein said lightsensitive nitrogen compound is a reaction product of (l) a condensation product of paradiazodiphenylamine and formaldehyde and (2) a coupling agent therefor.

References Cited UNITED STATES PATENTS 2,008,733 7/1939 Tosterud 204-35 3,066,055 11/1962 Pimbley 148-627 3,181,461 5/1965 Fromson 96-33 X 3,030,210 4/1962 Chebiniak 96-33 X 3,160,506 12/1964 OConnor et al. 96-33 3,169,065 2/1965 Sorkin et al. 96-33 NORMAN G. TORCHIN, Primary Examiner.

R. E. MARTIN, Assistant Examiner.

U.S. Cl. X.R.