US3473926A - Negative material for converting from letterpress to lithography - Google Patents

Description

3,473,926 NEGATIVE MATERIAL FOR CONVERTING FROM LETTERPRESS T LITHOGRAPHY Thomas 1. Abbott and Hugo F. Huedepoh], Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed May 4, 1964, Ser. No. 364,799

Int. Cl. G03c 5/04; G03f 5/10 US. (11. 9627 17 Claims ABSTRACT OF THE DTSCLQSURE This invention concerns products for obtaining negatives which are used to convert letterpress plates to lithographic plates and methods for making these products.

Various methods have been proposed for preparing lithographic plates for use on offset presses from letterpress plates. For instance, one process utilizes a pressure collapsible opaque layer which with the pressure from small bouncing steel spheres imparts clarity in areas where the raised portions of letterpress relief characters exist. This method is disclosed in French Patent No. 1,320,351.

Another method is described by R. Maibohn in The Inland Printer, page 59, vol. 138, No. 5, 1957, Maclean Hunter Pub. Corp., Chicago, 111. This method involves proofing on normal photographic materials which are prefogged. The proofing ink vehicle acts as a resist to developing solutions and produced a density only in areas which are accessible outside of the inked areas.

Another method involves a transfer of a special solvent from the letterpress relief which causes the solution of a dyed vehicle only in areas where it strikes.

The first method involves expensive mechanical apparatus. The second method does not insure completely uniform resists to developer solutions so that undesirable spots in the negative reproduction may be obtained. The third method also does not insure uniform transfer materials and may give rise to non-uniform images.

There has been the need in the art to provide a simple method of printing onto a suitable sensitized material from a letterpress plate so that a lithographic plate could be made simply and inexpensively. The method should be inexpensive and easily carried out without requiring highly skilled personnel. In addition, this method should provide a negative so that a size change could be obtained by projection.

Attempts have been made to print a letterpress plate on a sensitized photographic emulsion. However, the ink adhering to the surface of the letterpress plate has not uniformly adhered to the surface of the sensitized material, so that it could be used for making a photographic negative. Typical silver halide emulsions containing colloids which are hydrophilic, tend to repel the oleophilic inks which are used to make the impression.

nited States Patent 0 "ice We have found a method of providing a photographic negative or lithographic plate directly from a letter press plate, which gives high quality results without fail and permits the use of existing procedures and apparatus.

One object of this invention is to provide a new light sensitive photographic product which can be used for making photographic negatives directly from a letterpress plate. Another object is to provide a method for converting a letterpress plate to a lithographic plate. An additional object is to provide a two layer photographic element having a top layer containing an ink absorbing pigment in a polymeric vehicle. A still further object is to provide a light sensitive material on a support having over the light sensitive material an ink receptive layer, which is removable in an alkaline solution. Additional objects will be apparent from the following disclosure.

In carrying out our invention, we coat a photographic light sensitive material on a support and over this light sensitive material a colloid layer containing an ink absorbent pigment.

The light sensitive material may be a hardened silver halide emulsion to form a negative. It may be a substantially unhardened colloidal silver halide emulsion which is hardened in the exposed areas by using a silver halide tanning developer which permits removal of the unhardened areas to provide a resist which can then be used for lithographic printing. 'However, it is also understood that we can use the structure described in US. 3,146,104 issued Aug. 25, 1964 in the names of Yackel and Abbott, and coat the pigment layer over this structure. In the event that a positive image is desired, a reversal type sensitive material may be used as the light sensitive layer.

The second layer comprises an alkyl acrylate-acrylic acid copolymer representing 5 0-90% of an alkyl acrylate and 1050% of acrylic acid. The alkyl group in the alkyl acrylate may contain from 1-4 carbon atoms. However, in our preferred embodiment an ethyl acrylate-acrylic acid copolymer representing ethyl acrylate and 20% acrylic acid is used. Typical copolymers are disclosed in US. Patent No. 3,062,674, issued Nov. 6 1962 to Houck et al. Cellulose ether phthalate or cellulose acetate phthalate may also be used.

The ink absorbing pigment is preferably barium sulfate, but may be, for example, silica, calcium carbonate a pigment mixture such as Lithopone (a pigment mixture of zinc oxide, zinc sulfide and barium sulfate), zinc oxide, zinc sulfide, etc. Useful pigments have an average diameter not exceeding one micron, but are preferably of smaller size.

The silver halide emulsion is preferably silver chloride and may contain desensitizers so that it is suitable for roomlight handling. However, it will be appreciated that other light sensitive silver salts including silver bromide, silver iodide, silver chlorobromide, silver bromoiodide, silver chloroiodide and silver chlorobromoiodide, can be used. The emulsions can be chemically sensitized as taught in the prior art.

Our ink receptive layer can be used over other layers which are light sensitive, including those which are known in the art for use in preparing lithographic plates.

The sensitive layer for the lithographic plate can be exposed to visible light, ultraviolet light, infrared light, or to heat patterns in order to form image areas. It is possible to use light sensitive organic compounds such as aliphatic and aromatic esters, hydrazides and amides of napthoquinone-diazide-sulfonates, cinnamalmalonic acids, their substitution products and functional derivatives, di-

azonium salts of amino-diphenyl amines and their condensation products with formaldehyde, orthoand paraquinoue diazides of benzals, anthracenes and heterocyclic systems, for example, quinoline, indazoles, benzimidazoles, diphenyloxides, also diazoketones, unsaturated ketones, orthoand paraiminoquinone diazides, derivatives of alkylnitronaphthalenesulfonates, nitroaldehydes, ecenaphthene, stilbene, azides and diazides and high molecular polymer diazo resins.

Many of these light sensitive coatings result in producing negatives which are relief images. These can be colored, e.g. by dyeing or by incorporating colorants in the Original coating.

If desired to form a lithographic plate directly, various colloids may be used which can be hardened by silver halide tanning developers. These colloids include gelatin, cellulosive derivatives, synthetic resins, polyvinyl compounds and the like which are known in the art. Other colloids known in the art, including hardened colloids may be used when a negative is desired which is then to be printed by contact or projection means.

The supports on which the silver halide may be coated are not critical and include metals, paper, glass, polymeric materials such as cellulose esters, polyesters, polyamides, polystyrene, polycarbonate, polyacetyls, polyolefins, etc.

In our preferred embodiment, the silver halide emulsion is coated by known means on a suitable support and over the emulsion is coated the polyalkyl acrylate-acrylic acid coating containing the ink absorbing pigment. The letterpress plate from which the copy is to be made, is coated uniformly with an opaque printing ink over the type face and pressed evenly on the surface of the ink absorbing coating on the sensitive material. After deposition of the opaque printing ink on the pigmented layer, the emulsion is subjected to a flash exposure through the image, then developed, fixed and washed. When a lithographic plate is to be made directly, an alkaline silver halide hardening type developer may be contained in the processing solution, in the emulsion or in the pigmented layer. The photographic solutions penetrate the pig mented layer coated over the silver halide emulsion to cause hardening of the exposed areas so that the unexposed areas are removed by washing.

The following examples are intended to illustrate our invention but not to limit it in any way.

EXAMPLE 1 Colloidal silica was dispersed in gum arabic by ball milling the following preparation for 17 hours:

Gum arabic g 10.0 Silica g 200.0 H O cc 500.0 Total volume cc 600.0

This slurry was combined with gelatin and hand coated on film base to give the following series, presented as milligrams of dried materials per ft.

1 2 3 4 5 6 7 8 9 Silica 31.0 60.0 142.0 160.0 360.0 520.0 780 940 1050 Gelatin 230.0 226.0 213.0 195.0 180.0 156.0 117 94 78 Gum Arabic 1.6 2.3 7.6 15.2 18.3 27.4 41 50 55 This series represents an increase in the ratio of pigment to hinder from 1027.5 to 1.0:0.l3 on a weight basis.

Each of the above coatings was printed on the proofing press under standard conditions and visually examined for uniformity of ink deposit formed by greasy proofing ink. (Besco Proof Black Ink, Bridgeport Engravers Supply Co., Bridgeport, Conn.) None gave a proof of the desired quality.

EXAMPLE 2 Pigments other than silica were used as in Example 1. Talcum powder, calcium carbonate and Hartwick clay were coated with gelatin and gum arabic as binders at ratios ranging from 10 parts pigment to 1.0 part binder. Satisfactory uniformity of ink deposit could not be obtained and the results were not as satisfactory as those otbained in Example 1.

EXAMPLE 3 The following were coated on ordinary photographic film:

Layer I--(Coated as an antihalation stratum on film base at a thickness of .002 inch) Carbon 3.85%

Gelatin solution (4.9%) g 50.0 Saponin (15.0%) cc H O 50.

Layer II-Emulsion (Coated at a thickness of .002 inch over Layer I) AgCl gelatin emulsion g 38.0 Bromohydroquinone solution (2%) cc 5.0 Saponin solution (15%) cc [.0 H O cc 16.0

Layer III-(Coated at .002 inch over Layer II) Gelatin solution (10%) g 50.0 Silica slurry (20 parts silica, 1 part gum arabic) g 200.0 H2O cc This coating was proofed, exposed through the inked image, activated in potassium carbonate and washed-01f in warm water. The quality of the resulting negative was still inferior due to defects in the image areas caused by non-uniformity of the ink deposit.

EXAMPLE 4 Polyethyl acrylate-acrylic acid (-20) at 8.9% solids was coated by hand at .003 inch on cellulose acetate film base. After drying, this was printed on the proofing press. The images were considerably better than those printed on a surface consisting of plain gelatin.

EXAMPLE 5 EXAMPLE 6 A ball milled slurry of polyethyl acrylate-acrylic acid (80-20) and silica was made in the following proportions:

Polyethyl acrylate-acrylic acid solution, 8.9% g 80.0 Silica g 200.0 H O cc 300.0

Total g 580.0

This was ball milled for 48 hours. A coating prepared from this slurry on film base 'gave excellent, uniform. sharp, dense, proofed images. A hardened silver chloride emulsion layer was overcoated with this slurry at various thicknesses to give the following deposits of silica and polymer in mg./ft.

Silica 1, 650. 0 825. O 618. 0 412. 5 330. 0 370. 0 Polymer 57. 5 28. 5 21. 14. 4 12. 0 l.

Each of these coatings was printed on the proofing press, exposed with an 0.15 step-tablet, developed for 1 minute in Kodak D-72 Developer, swabbed with a dry cotton pad to remove the ink carrying polymer layer, fixed, washed and dried to give usable negatives.

EXAMPLE 7 A silver chloride emulsion layer was prepared containing: Ag mg /ft. 200 Gelatin m /ft. 250 Over samples of the light sensitive layer were coated giment layers having the following proportions of the polymer of Example 6 to silica.

E l r 65 54 43 52 121 100 S510 900 760 600 450 1, 700 1, 420

All of the above coatings have good results exhibiting the known properties that as the thickness of the polymersilica layer decreased the proofed image quality decreased but exposure latitude increased. Nos. 2 and 3 represent about optimum conditions.

EXAMPLE 8 Coatings were made with colloidal silica, Super Floss by lohns-Manville, Cleveland, Ohio, which in addrtlpn to its high water absorptivity and smaller particle size has a marked afiinity for oils. Two coatings were made as follows:

Emulsion layer Silver chloride gelatin emulsion g.. 380.0 Methylene blue 033% solution cc 6.0 Saponin solution (15%) cc 4.0 Formaldehyde cc 2.0

Total g 392.0

This emulsion was coated on 0.004 inch polyester support to give the following coverage of dry materials in mg./ft.

with a coverage of dry materials in mg./ft. as follows:

Polymer 126 Silica 645 Each coating was proof printed with an excellent deposition of ink, exposed through the proofed side and processed as described previously.

EXAMPLE 9 Substitution of cellulose ether phthalate and of cellulose acetate phthalate, respectively, for the polymer in the coatings of Example 8 also results in satisfactory negatives or in directly prepared lithographic plates.

It will be appreciated that the binders which are operative in this invention are water-soluble and can be prepared in aqueous solutions for coating therefrom. However, the particular solvent is not critical provided it is compatible with the light sensitive coating over which the ink receptive layer is coated. For some purposes, it

may be desirable to add alcohol or the like to an aqueous coating solution for drying purposes, etc.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic element comprising a light sensitive layer on a support and having over said layer an ink receptive, alkali permeable layer comprising a binder selected from the group consisting of an alkyl acrylateacrylic acid copolymer, cellulose ether phthalate and cellulose acetate phthalate, and containing at least one greasy ink receptive pigment of colloidal size.

2. A photographic element of claim 1 in which said ink receptive pigment is selected from the class consisting of barium sulfate, silica, calcium carbonate, zinc oxide and zinc sulfide.

3. A photographic element of claim 1 in which said ink receptive pigment is barium sulfate.

4. A photographic element of claim 1 in which said ink receptive layer comprises a copolymer of alkyl acrylate and acrylic acid.

5. A photographic element of claim 1 in which said light sensitive layer is a light sensitive silver halide emulsion layer.

6. A photographic element of claim 1 in which the light sensitive layer comprises silver halide dispersed in an unhardened colloid subject to hardening with a tanning type silver halide developing agent.

7. A photographic element of claim 1 in which the light sensitive layer comprises a light responsive material which hardens imagewise, so that the non-image areas can be removed.

8. A photographic element of claim 1 in which the light sensitive layer comprises light responsive material which can be rendered hardened imagewise upon development, so that the non-image areas can be removed.

9. A photographic element comprising a support having thereon a light sensitive gelatino-silver halide emulsion and having coated thereon a layer comprising a copolymer of ethyl acrylate and 20% acrylic acid, having dispersed therein colloidal silica at a ratio of pigment to binder from 127.5 to 12.013.

10. A process of preparing a negative from an inked printing plate comprising contacting said inked plate with the top surface of a photographic element comprising a light sensitive layer on a support and having over said layer an ink receptive, alkali permeable layer comprising a binder selected from the class consisting of a copolymer of alkyl acrylate and acrylic acid, cellulose ether phthalate and cellulose acetate phthalate, and containing at least one greasy ink receptive pigment of colloidal size, exposing to light and processing said photographic element to remove said ink receptive layer and form an image area in said light sensitive layer.

11. A process according to claim 10 in which said ink receptive pigment is selected from the class consisting of barium sulfate, silica, calcium carbonate, zinc oxide and zinc sulfide.

12. A process according to claim 10 in which said light sensitive layer comprises silver halide dispersed in an alkali permeable colloidal material.

13. A process according to claim 10 in which said light sensitive layer comprises a direct positive silver halide emulsion.

14. A process according to claim 10 in which said light sensitive layer is an unhardened silver halide emulsion comprising developing the exposed silver halide emulsion with a tanning type silver halide developer to provide a hardened image area, and removing the non-image areas to provide a lithographic printing plate.

15. A process according to claim 10 in which the 7 8 light sensitive layer comprises a material sensitive to 1,992,965 3/1935 Rowell 9633 light, such that a hardened image area is obtained. 2,322,037 6/1943 Lindquist 96 94 16. A process according to claim 10 in which the light 2,734,298 2/ 1956 M012 et a1. 117-38 X sensitive material is a light sensitive polymer. 2,760,863 8/1956 Plambeck.

17. A process according to claim 10 in which the light 5 2,798,004 7/1957 Weigel 117--6 X sensitive material is a diazo resin. 2,810,341- 10/1957 Neugebauer et al. 101-149.: 2,903,964 9/1959 Taylor 9633 K R ferences Cited 2,927,023 3/ 1960 Martin 96 35.1 UNITED STATES PATENTS 3,284,201 11/1966 Meijs et a1. 9649 X 1,700,262 1/ 1929 Heinecke 9627 X 10 2,760,431 8/1956 Beam, 96 75 X NORMAN TORCHIN, y Exammer 3 015 23 1 19 2 Thurlow 9 33 X RICHARD E. FICHTER, ASSIStant Examiner 3,136,637 6/1964 Larson 9675 3,062,648 11/1962 Crawford 9636.3 X 1,124,594 1/1915 Cornwall 9633 15 9633, 35, 35.1, 36.3, 67, 75 1,302,919 5/1919 Hatt 9633