US 3559578 A
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United States Patent- I l l 1 Inventors Appl. No.
Theodore A. Haas Maplewood:
Collin 11. Alexander, Falcon Heights, Minn. 773,358
Sept. 19, 1968 A Feb. 2, 1971 Minnesota Mining and Manufacturing Company St. Paul, Minn.
a corporation of Delaware LlTHOGRAPl-IIC DUPLICATING METHOD AND LITHOPLATE MASTER THEREFOR 12 Claims, No Drawings US. Cl 101/467; 7 101/462, 101/450; 250/65 Int. Cl 841m 5/00, B41n 3/00  Field of Search 101/450,
[ 56] References Cited UNITED STATES PATENTS 3,094,417 6/1963 Workman l01/467UX 3,094,619 6/1963 Grant 250/65( 1) 3,168,864 2/1965 Brandl et al. 101/467 3,299,807 1/1967 Evensen 101/467 Primary ExaminerDavid Klein Attorney-Kinney, Alexander, Sell, Steldt & Delahunt coreactant, and heating the plate.
LITHOGRAPHIC DUPLICATING METHOD AND LITHOPLATE MASTER THEREFOR This invention relates to the art of duplicating and more particularly to materials and methods useful in the planographic or lithographic printing art.
The duplicating of graphic matter by lithography normally involves the ereationon a preferentially hydrophilic surface of preferentially oleophilic ink receptive image areas corresponding to the image-defining areas of the original. An oily ink is selectively taken up by the image areas while the nonimage areas are maintained in a water wet and ink repellent state. The ink is then transferred under pressure, either directly or by way of an intermediate transfer surface, to the surface of the paper or other print sheet.
Various methods have been devised for forming the ink receptive image. A waxy image may be imparted to a water receptive surface, e.g. with wax crayons, or by heat-, impact-, or pressure-induced transfer from a wax-coated carbon paper or other transfer sheet. Water-soluble or hydrophilic light-sensitive coatings, e.g. of dichromated colloid or of diazo resin, may be rendered ink receptive on exposure to a light image. Oily or waxy or polymeric ink receptive inclusions within a hydrophilic coating may be made available at the surface by localized application of pressure or heat.
Transfer of reactant materials from an exposed light sensitive intermediate sheet to a receptor sheet containing an image forming coreactant has previously been suggested, e.g. in U.S. Pat. Nos. 3,094,417 and 3,094,619. Under reflex exposure the first reactant is made nonreactive above the reflective background areas but a small portion of the reactant lying above the light absorptive image areas of the original remains unchanged. Heating the exposed intermediate against a receptor sheet then causes reaction with the coreactant and formation of a corresponding image on the receptor. This procedure, along with others, is suggested in German'Pat. No. 1,263,032, as a method of forming oleophilic image areas on a lithographic plate containing a reducible metal salt such as cupric nitrate or ferric sulfate as coreactant, the metal salt being reduced to an oleophilic imaging material.
The present invention likewise involves the imaging with a first reactant of a sheet material containing a coreactant, but differs from the prior art in a number of significant respects, most particularly in the material employed as coreactant. The first reactant is an alpha-naphthol as defined in U.S. Pat. No. 3,094,619, having directly attached to the'hydroxy-substituted aromatic ring a preponderance of electron donor groups, as represented particularly by 4-methoxy-lnaphthol. These normally reactive compounds are desensitized by exposure to ultraviolet radiation or, in the presence of a sensitizer such as erythrosin, by exposure to visible light, and are therefore particularly useful in the reproduction of printed or other graphic originals.
The lithographic plates employed in making these lithomasters may include silicated aluminum or other preferentially hydrophilic treated metal plates, but preferably comprise a dimensionally stable support coated with a preferentially hydrophilic composition, e.g. containing clay or other hydrophilic mineral powder filler in a cross-linked or otherwise insolubilized polyvinyl alcohol or other water-insoluble hydrophilic binder. Plasticizers, humectants, coloring materials, and other adjuvants or modifiers may be included as desired. Additionally there is present an ionic iodide coreactant for the alpha-naphthol. The inorganic iodides such as sodium or potassium iodide are effective, but the organic ionic iodides generally, and in particular the quaternary ammonium iodides, are particularly advantageous. Compounds of the latter type are found in particular to be highly resistant to migration within the hydrophilic coating under storage at high humidities. Typical ionic organic iodide coreactants exhibiting high resistance to migration include methyl triethyl ammonium iodide, propyl tributyl ammonium iodide, ethyl triethanol ammonium iodide, phenyl trimethyl ammonium iodide, methyl tris-(2-nitriloethanol) ammonium iodide, l-ethyl-quinaldinium iodide. l-methyl-quinolinium iodide. l-cthylpyridinium iodide. trimethyl sulfonium iodide. trimethyl sulfoxonium iodide.
Nonionic iodides or iodine compounds. such for example iodoform. carbon tctraiodide. phenyl iodide. or butyl iodide. are ineffective as eoreactants for the a-naphthols in the practice of this invention. as may be determined by means of the following simple test procedure.
A stock solution of 4-methoxy-l-naphthol in equal parts of acetone and water is first prepared. For this purpose the pure compound is ineffective; but material which has undergone moderate exposure to light or contact with the air. is fully ef fective. Accordingly. unless extreme precautions have been taken to assure the use of the pure compound, a solution prepared under normal laboratory conditions and procedures will be found to meet all requirements of the test. To a small portion of the solution thus prepared is then added a small amount of an aqueous solution of the compound under test. The rapid formation of a deep blue coloration indicates that the compound will be useful as a coreactant. Reactant concentrations and amounts are so selected as to permit recognition of the color change. The nonionic compounds fail to cause the indicated color formation, whereas the blue color is quickly obtained with the ionic iodides.
The coreactant must be present at or near the surface of the hydrophilic coating to insure prompt and efficient reaction with reactants transferred thereto. Thus the material may be incorporated within the composition prior to coating, but is more efficiently supplied as a subsequent top-coating applied over the previously coated, dried and insolubilized hydrophilic material. Simple swabbing of the plate surface with a dilute aqueous solution of the coreactant. using a saturated cotton pledget. is fully effective although usually productive of uneven or incomplete coatings. Use of a coating roller, air knife, or other mechanical device permits more accurate application. The coreactant may alternatively be added to the hydrophilic coating composition prior to applying the same to the supporting backing. As little as .025 gm./sq.m. of coreactant has been found adequate when carefully applied as a sur face coating, although commercial coating practice usually requires somewhat larger amounts. for example of .4 gm./sq.m. to insure complete coverage. On the other hand, good results have been obtained with as much as 2.5 gm./sq.m. of coreactant when introduced into the hydrophilic coating composition. Much larger amounts of these water-soluble materials tend to reduce the anchorage of the oleophilic image and thus to shorten the press life of the plate.
The combination of photoreducible dye and 4-methoxy-lnaphthol or equivalent substituted a-naphthol as described in U.S. Pat. No. 3,094,417 provides an intermediate sheet which under reflex exposure to visible light is easily desensitized at background areas. Heating the thus exposed intermediate in face-to-face contact with a lithographic master prepared as above-described results in the formation at the plate surface of a faint blue image which is preferentially oleophilic and ink receptive, and which is surprisingly resistant to removal. Lithoplates imaged in the manner described have delivered many thousands of excellent copies without any discernible reduction in image quality or density.
In the following illustrative Examples all proportions are given in parts by weight unless otherwise indicated.
EXAMPLE 1 A commercial light sensitive intermediate sheet as described in U.S. Pat. No. 3,094,417 and containing erythrosin and 4-methoxy-l-naphthol in a polymeric binder on a thin transparent backing is placed against a printed original which is then exposed through the intermediate to uniform illumination from an incandescent tungsten filament source. Exposure is just suffieient to cause complete desen sitization at the areas contacting the reflective unprinted background areas.
The intermediate is then placed in face-to-face contact with a lithoplate master having a preferentially hydrophilic surface coating on a heavy paper backing. The coated surface has been swabbed lightly with a dilute aqueous solution of potassium iodide. and dried. The composite is heated for a few seconds on a smooth heating platen maintained at about l20 C. On removal of the intermediate. the plate is found to contain a faint blue image corresponding to the printed image of the original.
The plate is wet out with acidic aqueous etch solution, placed on a press. and used in printing several thousand excellent copies.
EXAMPLE 2 A coating composition is prepared to the following formula:
Parts Polyvinyl alcohol 5 Kaolin 50 Glycerine 0. 5 Dirnethylolurea 1 Potassium iodides 1. 5
. Butanol (anti-foam agent) 4 Water ea 150-200 The amount of water is just sufficient to provide a smoothly coatable mixture. The composition is coated on high wet strength 73 lb. lithobase paper at a coating weight, after drying, of lbs/ream of 3000 sq.ft. The coating weight is not critical but should be sufficient to provide complete coverage and a smooth surface while avoiding excessive curling of the sheet or cracking of the coating. The sheet is dried and the coating is insolubilized by heating for 1 hour at 60 C., to provide a lithoplate master.
An intermediate sheet is prepared by coating thin transparent map overlay tracing paper with a composition containmg:
Parts 4-methoxy-1-naphthol 10 Cellulose acetate butyrate 3 Diphenyl phthalate 0. 3
in sufficient acetone to provide a coatable solution, and drying. The dry coating weight is approximately 4.5 gm./sq.m.
The intermediate sheet is placed in face-to-face contact with the lithoplate master and a document having printed image areas on a thin onionskin paper is laid over the intermediate with the printed surface exposed. The three-sheet composite is passed through a Thermofax infrared-copying machine in the back print" position. A blue image is fon'ned on the lithoplate master. The plate is etched and run on the press, with production of a large number of lithographic copies.
The same intermediate is useful in imaging one or more additional plates by the same procedure.
EXAMPLE 3 A lithoplate master is prepared by coating lithobase paper with a composition containing:
Watersufficient for spreading.
The coated sheet is dried and heated as in Example 2. The dry coating weight is 10 lbs. per ream of 3000 sq.ft.
The coated surface is further coated with an aqueous 3 percent solution of tetraethylammonium iodide, at a coating weight after drying of0.4 gm./sq.m.
An intermediate prepared as in Example 2 is imprinted on the uncoated surface with suitable indicia, applied with a typewriter and by hand lettering, to provide differentially radiation absorptive image and background areas. The intermediate is placed against the Iithoplate master and the composite is passed through the Thermofax" infrared-copying machine in back-print position, formingblue image areas on the plate surface. The plate is etched and run on the press, producing a large number ofcopies.
The master plates prepared under this Example remain fully effective after storage in a humidity cabinet.
EXAMPLE 4 Carbon black is dispersed in a volatile liquid alcohol-ketone mixture to form a writing ink. To portions of such ink are added small amounts of various naphthols. the concentration being in the range of one-half to 4 percent. Using a felt tip pen, markings are made with the several inks on a lithoplate master prepared as described under Example 3, and the plate is held for a few seconds against a platen heated to F. The plate is etched and run on the press. Each of the marks made with the ink containing a naphthol produces good copy; the control mark, made with ink containing no naphthol, does not reproduce. The specific naphthols tested are:
4-methoxyl -naphthol 2-methyl-4-methoxyl -naphthol 4-ethoxyl -naphthol l ,4-dihydroxynaphthalene l ,3-dihydroxynaphthalene 4-aminol -naphthol We claim:
1. Method of printing comprising: applying a ring-substituted a-naphthol first reactant at image-defining areas to a lithoplate master having a preferentially hydrophilic-printing layer containing at the surface thereof a water-soluble ionic iodide coreactant, and heating at least said areas, to provide on said master a preferentially oleophilic image-defining pattern; and then printing from said master by the lithographicprinting process; said a-naphthol being further characterized as having directly attached to the hydroxy-substituted aromatic ring a preponderance of electron donor groups selected from the class consisting of alkyl, aryl, alkoxy, aryloxy, hydroxy and amino groups.
2. Method of claim 1 wherein said a-naphthol is applied by transfer from a uniformly coated source sheet held in face-toface contact with said master.
3. Method of claim 2 wherein said source sheet is heated at least at image-defining areas during transfer of said anaphthol.
4. Method of claim 3 wherein said source sheet is locally heated at image-defining areas by exposure of a differentially radiation absorptive imaged original to intense radiation.
5. Method of claim 3 wherein said source sheet is uniformly heated during transfer of said a-naphthol and wherein said anaphthol is present on said source sheet only at image-defining areas.
6. Method of claim 5 including the step of preparing the source sheet by reflex exposure of a graphic original to actinic radiation applied through said source sheet, said source sheet initially having a uniform coating of a said a-naphthol which is desensitizable by said radiation.
11. A paper lithoplate master including a paper base and a preferentially hydrophilic coating comprising a hydrophilic water-insoluble binder and a hydrophilic particulate filler and containing a water-soluble ionic iodide.
12. The lithoplate master of claim 11 wherein said iodide is at maximum concentration adjacent the exposed surface of said coating.