US 3578451 A
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May 11, l1971 '1'l DQGGETT 3,578,451
INTEGRAIJ NEGATIVE TIPEl POSITIVE PHOTOLITHOGRAPHIC PLATE Filed March 29, 1967 RESINOUS BARRIER COATING PHOTOGRAPHIC EMULSION COATING LITHOGRAPHIC PLATE DIAZO COATING OVER HYPROPHILIC SURFACE 0F PLATE United States Patent O 3,578,451 INTEGRAL NEGATIVE TYPE POSITIVE PHOTOLITHOGRAPHIC PLATE Towers Doggett, Westbrook, Maine, assignor to Scott Paper Company, Delaware County, Pa. Filed Mar. 29, 1967, Ser. No. 626,874 Int. Cl. G03f 7/02 U.S. Cl. 96-33 2 Claims ABSTRACT OF THE DISCLOSURE A normally negative-working lithographie plate is coated with a conventional silver halide emulsion, an intermediate water-'barrier coating being used to prevent co-mingling of the sensitized layers. The resulting plate is image-wise exposed to a positive original and developed to form as in-situ mask or integral negative for a subsequent exposure of the diazo layer. Following the second exposure the emulsion layer is removed and the resulting plate used to reproduce the original positive pattern.
SUMMARY OF THE INVENTION A negative-working diazo-sensitized plate is an excellent photolithographic plate that produces strong images and gives a Wide press latitude. However, it is insufliciently light sensitive to permit exposure by a camera and it does, of course, produce a negative instead of a positive.
The present invention resides in the realization that these disadvantages of a conventional diazo-sensitized photolitograhpic plate can be overcome by applying a conventional photographic emulsion coating over the diazo coating. In use, the photographic emulsion coating is exposed to a positive original either directly or with a reflex camera and developed in a conventional manner. The exposed emulsion thereafter serves as an in situ negative, permitting exposure of the diazo coating in the image areas of the original positive pattern to strong actinic light, usually ultra-violet light, and development of the required organophilic-hydrophobic properties of the diazo coating in these areas. The emulsion layer is removed after exposure of the diazo layer to prepare the plate for the press.
A thin intermediate lacquer or resinous water-barrier coating is applied over the diazo coating prior to the application of the emulsion coating to prevent co-mingling of the emulsion when applied with the diazo coating, which is usually hydrophilic and water-soluble until exposed. This layer can be pigmented, but not so much so as to bar the passage of light. Preferably, this lacquer layer is removed only in the non-image areas of the plate, after the plate has been exposed, and left in the image areas to reinforce the image.
DRAWING The drawing is a self-explanatory schematic illustration in greatly enlarged cross-section of the improved photolithographic plate of this invention.
PREFERRED EMBODIMENT A commercially available negative working presensitized foil-laminate plate (Fotoramic 12, S. D. Warren Company), described in U.S. lPat. No. 3,161,517 to the present inventor, is first coated with a resinous coating consisting of:
Part by Weight Polyvinyl butyral (Butvar B-76; Shawinigan Resins Corp.) 8 Virginia Red Toner (RE 6570; Holland-Suco Color Co.) 2 70 TiO2 (R-510; E. I. du Pont de Nemours Co.) 10
Methyl isobutyl ketone 180 The coating is applied with a Mayer bar in the amount of 2 pounds per ream (dry basis) and dried 1 minute at 200 F.
A photographic emulsion is prepared as follows.
(l) Two solutions are prepared- Solution l:
AgNO3-50 g. H2O-500 cc.
KBr-40 g. Gelatin- 15 g. H2O-400 cc.
Solution 1 is then added to solution 2 thru a nozzle with stirring in 3 minutes at 70 C. The resulting emulsion is held at C. for 10 minutes and then is rapidly cooled to 45 C.
(2) 60 g. of gelatin is added to the emulsion at 45 C. with stirring for about 30 minutes to dissolve the gelatin. The emulsion is cooled until gelled then noodled (3) The noodles are washed with Water for three hours then remelted at 40 C. The total weight is thereafter made up to 1500 g. with the stirred addition of 25 g. of gelatin and water. After dissolving the gelatin, the temperature is raised to 60 C. and held there for 60 minutes.
(4) The emulsion is cooled to 40 C., and 5 g. of saponin are added.
The emulsion is coated on the lacquered lithographic plate at 10 lbs/ream (3300 sq. ft.) dry basis, chilled for 5 minutes at 5 C. then dried at 50 C. With forced air.
The plate is exposed 20 seconds to a positive with a Kenro 18 (Kenro Company) camera, and then is immersed in a standard negative type developer such as Eastman Kodak Companys Kodalith Developer for about 10 seconds until the non-image areas are dense black. This is followed by immersion in Kodaks Indicator Stop Bath.
The plate without drying is then exposed to a twin 35 amperes arc lamp at 35 inches for 60 seconds. Thereafter the plate is swabbed with cotton wetted with a 25% n-propanol solution which removes the emulsion from all areas of the plate and the lacquer coating from the non-image areas to expose the original hydrophilic planographic printing surface of the plate in those areas.
The thus prepared plate is placed on an Addressograph- Multigraph 1250 press using that companys ML-36 ink along with its Repelex diluted with water, one part to seven, to produce ten thousand satisfactory copies with excellent fidelity.
Any conventional high contrast photographic emulsion, containing no hardening agent can be used in place of the above. A developing agent can be incorporated in the emulsion also.
It will be appreciated that since this invention embodies the interaction in more or less of a mechanical way of two conventional photosensitive coatings to achieve the desired result, the invention is not to be restricted to any particular chemical types or natures of the diazo-sensitized and emulsion coatings.
Also, any known planographie plate having the proper lithographic surface can be used as a base for the coatings. Metal or paper based plates are equally satisfactory such as those described in U.S. Pats. Nos. 2,714,066, 2,778,735 and 3,280,734. Any of the numerous negative working diazo coatings can be used such as those described in U.S. Pats. Nos. 2,063,631, 2,649,373 and 3,235,382.
The water barrier coating will normally be applied from a solvent solution. Any solvent-soluble hlm-forming material can be used such as the vinyl resins, the cellulose derivatives, or the acrylic resins.
Having described this invention, what is sought to be formly to actinic radiation sufficient to insolubilize protected by Letters Patent is succinctly set forth in the the diazo coating in the light-struck areas, and following claims. (d) treating with a solvent which removes from all I claim: areas of the plate the photographic emulsion coating 1. A photolithographic printing plate photosensitized and from the non-image areas. the water-barrier with a negative-working diazo coating having adjacent coating. the surface of said coating a water-barrier coating of References Cited polyvinyl 'butyral and a layer of silver halide photographic UNITED STATES PATENTS emulsion overlying said Water-barrier coating.
2. The method of imaging the plate according to claim 10 3,143,414 8/ 1964 Yackel et al 96--35 1 comprising the steps of 2,725,296 11/ 1955 Kendall 96--69 (a) exposing the plate to light through an original for a time sucient to image the photographic emul- NORMAN G- TORCHIN, Pllmafy EXa-mlllel SOH J. WINKELMAN, Assistant Examiner (b) developlng sa1d emulsion, whereby the areas of 15 the photographic emulsion exposed to light are rend- U,S C1. X R
ered opaque 96--68 (c) exposing the surface of the developed plate uni-