US 3168864 A
Description (OCR text may contain errors)
v proofing press.
Unite States aren't iOfiice 3,168,864 Patented Feb. 9, 1965 t a s 168 864 rrrnonuarnrc rnru rino PLATE AND Martian or raonucmo AN ilviA "E rnsnaon Robert 5. Brandi, In, St. Paul, and Edwin A. Grant, Era,
Maplewood, Minn, assignorsto Minnesota lv iiniug and Manufacturing Company, St. Paul, Minn., a corporation of Deiaware No Drawing. Filed Sept. 28, 1966, Ser. No. 58,902
15 Claims. (@l. fin-149.2)
been wet out, the background areas remain ink repellent,
whereas the image areasare water repellent and ink receptive. From such plates large number of reproductions are made by the lithographic offset process.
Lithographic. or offset plates have also been suggested which include-within the continuous hydrophilic colloid surface coating a disperse phase comprising a water repellent, ink receptive, oily or waxy material which is released to the surface of the coating under the influence it of locally applied pressure. The surface is thereby rendered water repellent and ink receptive at the treated areas. Pressure maybe applied with stylus, typewriter, or Heat is also effective. The heat image may be provided by a thermographic process involving brief intense irradiation of a thin differentially radiation.
absorptive original while the latter is held in heat-conductive pressure-contact with the plate surface. *The' plate is then wet out with water and the image areas selectively inked to provide a transferable visible image.
Unlike the direct image? plate, the lithographic master just described must be first wet out and inked before the image areas are visible. Plates'must therefore be separately provided with suitable indicia for subsequent identification and orientation, or must be transferred directly to the press and immediately inked, with no opportunity for intermediate proof-reading or inspection of image.
Polyphase system lithographic plates which are ren dered ink-receptive by pressure must be handled with unusual caution in order to avoid the formation of false images, or undesirable ink-receptivity in background:
aged under most favorable thermographic back-printing" techniques, have produced less than fully satisfactory copies, particularly with respect to sharpness of image outline and freedom from backgrounding.
The present invention overcomes these-and other de- ,fects and disadvantages of the prior art. There is provided a lithographic plate which on application of a heatimage is rendered both ink-receptive and visibly distinct pounds per 24 x36/500 ream and a superc-alender finish.
at image areas, thus permitting proof-reading and proper positioning of the lithographic master prior to inking. The lithographic master may be produced as a reproduction of a graphic original printed either on thin transparent paper or on heaw paper or cardboard. Although these visible-image plates may be employed also as direct image ofiset duplicating plates and may in some instances be rendered ink-receptive by pressure, a preferred embodiment employs a polyphase coating which is pressureresistant. i
It has now been found that polyphase system lithographic offset plates may be made visibly heat-sensitive as well as capable of becoming ink receptive on heating, by incorporating Within the plate structure chemically interreactive components capable of reacting together to form a visibly distinct reaction product on the application of heat as in thermographic copying procedures. It has also been found that superior results in terms of the formation of sharp and distinct ink-receptive images and the prevention of accidental imaging or smudging in the background areas may be obtained by the substitution, for the oily or waxy disperse phase of the prior art, of polymeric or resinous oleophilic materials, particularly in extremely fine particle size. The novel sheet materials of the invention may be imaged by thermographic back-printing from a thin printed original, to provide lithographic master plates in which the inkwreceptive image areas are fully, visible prior to wetting out and inking. A preferred procedure involves thermographic back-printing of the lithographic plate from an intermediate visibly heat-sensitive film on which a reproduction i the graphic original has been produced by thermog'raphic front-printing, thereby making possible the reproduction of originals printed on heavy paper or board, and at the same time providing for an improved inked image. y
For short-run plates, untreated paper provides anjadequate support. Various treated paper backings which provide improved strength, dimensional stability,,water. proofness and other properties are preferred, including papers treated with urea-formaldehyde, melamine-aldehyde, phenol-formaldehyde or other synthetic resins, synthetic rubbers, oils, or varnishes. Non-fibrous films. such as cellulosic or polyester films are also useful. A typical and preferred support or backing material is high Wet strength lithoplate base stock having a basis weight of on the coating surface.
Thefollowing specific examples will serve furtherto illustrate but not to limit the invention. Proportions are in part byweightunless otherwise specified. i
i I Example 1 p Mixture A j. i
Ferric stearate 19.59 Ethyl-cellulose (N-22 4.71 Acetone T 75.70
.The ferric stearate is well dispersed in the solution as ethyl cellulose by grinding in a ball mill.
I The components are mixed by ball milling. i A smooth uniform blend of Mixtures A and B in the indicated proportions is spread on,BO-poilnd,lithoplatebase with a'knife coater at an orifice of 1 to 1.5 mils and dried "a t at 50'60 C. The dry coating Weight is about 0.6 gram per square foot.
1 Mixture C:
Clay (as slurry) 100 Polyvinylalcohol .35 Polystyrene (as latex) 35 Glycerine 25 Dimethylolurea 7.5 .n-Butyl'alcohol 40 Water, to about 30% solids. Dilute hydrochloric acid to pH about 3.5. V
I The components of Mixture C are well stirred together and the, mixture is spread over the previous coating in a uniform smooth layer which after drying is found to weigh 8 to pounds per ream. Drying at up to 60 -70 C.
' is possible for short periods without causing any visible change in the visiblyheat-sensitive layer. The polyvinyl alcohol is rendered water-insoluble by reaction with the dimethylolurea during and subsequent tothe drying period. The resulting plate is white or very light butt" in appearance. The surface is hydrophilic and remainsso under localized impact from clean typewriter type faces;
A graphic original in the form of a thin 9-pound sheet of paper carrying a typewritten message on one surface is placed with its unprinted surface in contact with the coated surface of the plate and .is briefiy'intensely irradiated with radiation from an incandescent vtungsten filament, in accordance with thermographic back-printing procedures. A visible reproduction of the printed characters is' produced on the plate, permitting immediate in-' spection and proof-reading. The resulting lithographic masteris then Wet out with acidic aqueous etch solution I and employed for the production of multiple copies on-the lithographic press. j v
The gallic acid employed in Mixture B of the foregoingformula is a normally solid phenolic reactant which reacts with the ferric stearate to produce a strongly colored reaction product; Other phenols and other ferric salts are known which are equally effective, theforegoing 1 Ethyl celluloseis apreferred binder for the reactants,
since 'it provides 21 surface which while itself organo-. philicis still capable of being smoothly and uniformly wetted and covered with'the subsequently applied solution of hydrophilic colloid. Many other cellulosic or polymeric binders having similar qualities are equally useful; polyvinyl butyral is one example. Plasticizers, such as the 'triphenylphosphate, may be included where desired but are not required where the binder itself is adequately flexible.
The. presence of;a substantial proportion of clay'or other hydrophilic filler in the visibly heat-sensitive layer improves the Wettability of the surface so that the subsequently applied coating ofMixture C spreads evenly and-adheres firmlywhen dried. These properties are further enhanced by the presence'inMixture'C of the butyl alcohol; serving as a Wettingagent as well as a component of the volatile vehicle. As a result, Mixture C, forms a thin, uniform,- and firmly'anc'hored film over;
the surface of the visibly heat-sensitive sub-coat.
philic properties Without danger of chalking or loss of particles and without obscuring the visible image formed in the underlying heat-sensitive layer.
Polyvinyl alcohol as applied is Water-soluble; after curing with the dimethylolurea for a. short time at the indicated or for somewhat longer time at higher pH, it is insoluble in water but still hydrophilic. The acid is preferably added 'to reduce the pH to the indicated level shortly prior to the coating operation in order to avoid any preliminary hydrolysis of the dimethylolurea and inof the polyvinyl alcohol, due regard being given the selection of the proper tanning or insolub-ilizing agent in each instance; For example, where polyvinyl alcohol is effectively insolubilized by dimethylolurea incorporated within the coating formulation, sodium alginate or sodium polyacrylate maybe more effectively treated with a solution of zinc chloride applied over the dried coating. Again, a coating containing guar gum and polystyrene latex is insolubilized by the incorporation of cobaltous nitrate. course be selected so as to avoid undesired side reaction;
for example, calcium carbonate fillers should not be used with strongly acid binder systems. The polystyrene latex employed in Example 1, and available as"Ly tron 615 polystyrene latex,.is an extremely fine particle size dispersion in which the individual particles of polystyrene have a diameter of about 0.25 micron. Thin layers of such latex dry to an extremely fragile water-receptive.
and ink-repellent film having a contact angle for'water of about degrees. film is transparentized and becomes ink-receptive, and the contact angle increases to about 80 degrees. The "intro duction of this high molecular weight dispersephase material intothe'hydrophilic binder composition as herein Clay, or equivalent hydrophilic, filler such as calcium carbonate, silica, infu sorial earth, chalk, barium sulfate, satin white or the like, is included in Mixture C primarily to increase the wettability of the resulting surface by water and to provide a more effective smudge resistant inkrepellent background..jThe clay is added as an aqueous slurry for convenience in mixing, but fully equivalent results may be obtained by dispersing the dry-clay or other filler in -the aqueous binder solution. The amount of filler is not critical, amountsof up to ten parts for each part of binder having been 'foun'duseful, although the' approximately 3:l,rat-io employed in'Mixture C is ordescribcd yields a dried film or coating which is normally hydrophilic and remains so on localized application of pressure, but which provides a water-repellentand inkand AC-629 polyethylene latex are exemplary; Useful but somewhatlesseffective results are obtained with aqueous dispersions of Acrowax C cetylacetamide-and with Geon 351 polyvinyi chloride latex. Oils or waxes,
applied as aqueous dispersions,analogously impartja degree of heat-sensitivity butthese coatings are additionally rendered ink-receptive .Whensubjected to localized pressure, and have other deficiencies as compared'to' the product of the example.
The polystyrene polymer is present in Mixture an amountequal to that of the hydrophilic colloid, or about one-half the total of inso'lubilized 'plasticized oolloid. Ratios of about 1 to 3 parts'of the polymericparticles to three parts of the hydrophilic binder are found to be particularly applicable.
Example 2 Acetone 79 The specific system to be employed will of When heated to C. such a Similar effects are obtainedv The components are well mixed together .in the. ball? 'mill.
Mixture E 100 Polyvinyl acetate 6.83 Methyl gallate 1.45 Tetrachlorophthalic anhydride 0.15
i The solids are dissolved in the acetone.
The well-mixed blend is spread uniformly on one-half mil oriented polyester film (Mylar 50A polyester film) and dried at 50-60 C. The dry coating weight is 0.40.5 gram per square foot. The sheet is uniformly milky white and translucent, converting to intense black when briefly heated to '90l00 C.
The sheet is placed with its coated surface in contact with a graphic original, in this case a printed heavy paper such as a filing card printed in black ink, and the original is irradiated through the sheet in accordance with thermographic front-printing procedures. The printed image areas are reproduced on the copy-sheet as dense black images which are radiation-absorptive.
The sheet is then placed with its coated and imaged surface in contact with the coated surface of a lithographic plate prepared as described under Example 1, and
is again briefiy intensely irradiated. A visible reproduction of the heated image areas is produced on the plate, the corresponding surface areas being rendered inkreceptive. The resulting litho master is wet out and inked, and employed in the, lithographic printing of multiple copies of the graphic original. The reproductions are clear and sharp, with substantially no backgrounding.
When the same procedure is applied to a lithographic plate otherwise identical with the plate of Example 1 but from which the polystyrene latex has been omitted," there is obtained a lithographic master having a visible image, from which useful lithographic copies-having observable background darkening are formed.
In another modification the plate just described, in which the hydrophilic surface coating has been insolubilized, is further coated with a thin coating of a composition otherwise identical with that of Mixture C but containing no dimethylolurea or other insolubilizing component. Using the imaged heat-sensitive copy-sheet of Example 2 as there described, there is obtained a lithographic master having a visible image and producing copies with fully inked image areas, but from which the unheated portions of the surface coating are removed by p the aqueous etch and fountain solutions.
Many other visibly heat-sensitive compositions are known, which in the form of heat-sensitive copy-sheets are converted on brief heating to a radiation-absorptive modification. For the specific application here described, best results are secured with copy-sheets in which the exposed heat-sensitive layer comprises a metal salt of a higher fatty acid, of which silver stearate and silver behenate are preferred examples. When heated, the components inter-react torelease the fatty acid and form a strongly radiation-absorptive silver image.
Water 90 The'several parts are mixed together and the mixture coated on -pound lithoplate base at a coating orifice of 3 mils. The sheet dries to a light, dull buff color. Irradiation of the imaged copy-sheet of Example 2 in contact with the coated surface as hereinbefore described produces a corresponding purple-colored visible image and renders the imaged surface areas ink-receptive. The resulting sheet is used as a lithographic master in making sharp and clean. reproductions of the graphic original The components are mixed together in the proportions indicated and the mixture spread on Bil-pound lithoplate base stock at an orifice opening of 2 mils to produce a smooth coating having a dry weight of about 0.8 gram per square foot. .A'further coating of a composition and in an amount as described under Mixture C of Example 1 is then applied. The resulting plate is essentially white in appearance. It produces black ink-receptive image areas on localized heating by thermographic reproduction processes as hereinbefore described.
Somewhat greater irradiation is required in Example 1 i to produce an effective ink-receptive image than is found necessary with the procedure described in Example 2. As a result, the visible image obtained on the plate in Example 1, while adequately representing the original printed image, is not as sharply defined as is the visible image obtained on the same type of plate under the conditions of; Example 2. The plate of Example 4, on the other hand, produces a visible image of maximum sharpness and definition with somewhat greater heat input than is required for the plate of Example 1. Specific color-producing components may therefore be selected for a particular-form of plate depending on the degree of heating required to render the surface ink-receptive, to provide in each case a sharply defined visible image as well as a fully ink-receptive lithographic image.
Example 5 MixtureL 10o Z-methyl-S-N-hexadecyl hydroquinone 4 Ethyl cellulose V 4 Trichloroethylene 92 Mixture M 300 Z-methyl-S-N-hexadecyl quinone l0 Trichloroethylene 35 copy and an ink-receptive image from which a number of legible but somewhat incompletely inked copies are made. by' the lithographic olfset method. Back-printing.
from a heat-printed visibly heat-sensitive copy-sheet as described under Example 2 also produces a lithographic master having a sharp and clear visible reproduction of ateaesa 'r' the copy-sheet image, and producing a number of sharply outlined and fully inked printed images.
The two mixtures are blended together and coated on lithoplate base paper, and dried. An image is reproduced on the heat-sensitive copy-sheet of Example 2 by thermographic front-printing from a printed original as there described. The copy is placed with its imaged coated surface in contact with the plate surface and again briefly intensely irradiated as also described under Example 2. A visible reproduction is formed on the plate, and the imaged areas are found to be selectively ink-re ceptive. The plate is used in the production of further copies by lithographic offset printing.
In this example, suificient unreacted methyl gallate remains in the radiation-absorptive image areas of the visibly heat-sensitive copy-sheet to form a visible image on the plate by reaction with the ferric sulfate when transferred thereto during irradiation. Additional plates may be imaged from the same copy-sheet if desired. Other volatile reactants may be substituted for, or, used in conabsorptive graphic original, the steps comprising: subjecting said original to brief intense irradiation through a thin radiation-transmissive heat-sensitive copy-sheet in.
heat-conductive contact therewith to provide in said copysheet a visible, strongly radiation absorptive reproduction of said-image areas, and subjecting the thus treated copy- 7 sheet to further. brief intense irradiation in heat-conductive contact with a visibly heat-sensitive lithographic plate havinga hydrophilic surface which becomes hydrophobic and ink-receptive on heating, said plate including a visibly heat-sensitive coating which is chemically reactive to form a visibly distinct reaction product when heated.
2. In the method of producing an imaged lithographic master'having visibly'distinguishable ink-receptive areas corresponding to image areas of a differentially radiationabsorptive graphiooriginal, the steps comprising: subjecting said original to brief intense irradiation through a thin radiation-transmissive heat-sensitive copy-sheet hav- 7 ing in heat-conductive contact with said original a chemically reactive visibly heat-sensitive coating including at least one volatilizable reactanhthe chemical reaction occurring within said coating on heating said sheet being responsible for the visible change, to provide in said copysheet a visible,- strongly radiation-absorptive reproduction of said image areas, and subjecting the thus treated copysheet to further brief intense irradiation with said coating in heat-conductive contact with a lithographic plate having a heat-sensitive hydrophilic surface coating comprising particles of ink receptive, water repellent imaging material dispersed within a continuous phase of a hydrophilic binder and containing asecond reactant which is visibly reactive with a said volatilizable reactant of said copy-sheet when the two reactants are heated together.
3. Alithographic printing plate adapted, on subjection to a heat-image, to provide a visiblyimaged lithographic master; said plate comprising a base sheet and a visibly heat-sensitive chemically reactive layer, the chemical reaction occurring within said layer on heating said sheet being responsible for the visible change, and including a heat-sensitive layer forming the normally hydrophilic lithographic surface of said plate and comprising particles of ink receptive, water repellent imaging material dispersed within a continuous phase of a hydrophilic binder and forming an ink receptive image on the lithographic surface at areas subjected to said heat-image.
4. A lithographic printing plate comprising in order a base sheet, an intermediate chemically reactive, visibly heat-sensitive coating, the chemical reaction occurring within said coating on heating said plate being respon sible for the visible change, and a continuous non-opaque heat-sensitive surface layer forming the hydrophilic lithographic surface of the plate and consisting of a polyphase system having a hydrophilic film forming colloid as the continuous phase and a dispersed phase of an ink receptive, water repellent imaging material which forms an ink receptive image on the lithographic surface when released to the surface of the coating from the polyphase system in the imaged areas.
. 5. .-A lithographic printing plate comprising a base sheet and a smooth, continuous, visibly and physically heatsensitive layer on the surface of the basesheet, which layer forms the hydrophilic lithographic surface of the plate and consists of a heat-sensitive polyphase system having a hydrophilic, water insoluble, film forming colloid continuous phase and a dispersed phase comprising an ink receptive, water repellent imaging material which forms an ink receptive image on the lithographic surface when released to the surface of the coating from the polyphase system in the imaged areas, and said system containing chemically reactive, visibly heat-sensitive interf reactants maintained in physically distinct and chemically interactive relationship at temperatures below a conver sion temperature within the range of about C. 0t about 150 C. e
6. A lithographic printing plateadapted for providing a. visibly imaged lithographic master'by thermographic reproduction from a differentially radiation-absorptive graphic'original and comprising a base sheet and a continuous heat-sensitive polyphase layer thereon having a normally hydrophilic surface which becomes hydrophobic and ink-receptive when heated in the thermographic copying process, said layer comprising a major amount'of a hydrophilic colloidal agglutinant in continuous phase and containing a hydrophilic clay filler'in an amount by weight equal to approximately three times the weight of said agglutinant a water-insoluble soap of a higher fatty acid'in disperse phase, and a co-reactant forsaid soap, said soap and co-reactant reacting together to form a visibly distinct reaction product on heating of said layer.
7. A lithographic printing plate comprising a waterresistant paper-like base, a visibly heat-sensitive sub-coat which is chemically reactive to form a visibly distinct reaction product on heating said plateand which contains an organophilic binder and a hydrophilic inert particulate filler, and a normally hydrophilic heat-sensitive surface coating which becomes hydrophobic and ink-receptive 'on V heating in the thermographic copying process and comprising a film forming colloid and a hydrophilic inert particulate filler. I l V 8. A lithographic printing plate comprising a waterresistant paper-like base, avisibly heat-sensitive sub-coat which is chemically reactive to form a visibly distinct rehigh .rnolecular weight organophilic polymer. 5
9.'A .lithogarphic printing plate comprising a paper 9 like supporting base and a polyphase hydrophilic nonchallriug surface coating, which becomes hydrophobic and ink-receptive on heating in the therm-ographic copying process, of a water-insoluble hydrophilic film-forming colloid, containing at least about three times its weight of a hydrophilic filler powder, as a continuous phase and a discontinuous phase of high molecular weight synthetic organophilic polymer latex particles characterized as forming a fragile water-receptive and ink-repellent film when deposited as a dried thin layer of said latex, said film being rendered water-repellent and ink-receptive on being heated to 120 C.
10. A lithographic printing plate having a normally hydrophilic surface and capable of being provided with visibly distinct organophilic ink-receptive image areas by a process involving briefly subjecting to intense radiation an imaged intermediate sheet having on a transparent backing an imaged heat-sensitive coating containing silver behenate and methyl gallate while said sheet and plate are in face-to-face contact, said plate having a normally hydrophilic heat-sensitive polyphase surface layer which becomes hydrophobic and ink-receptive on being heated in the thermographic copying process and comprising a continuous film-forming hydrophilic binder, a hydrophilic mineral filler, a discontinuous phase of synthetic organophilic polymer latex particles characterized as forming a fragile Water-receptive and ink-repellent film when deposited as a dried thin layer of said latex, said film being rendered water-repellent and ink-receptive on being heated to 120 C. and a ferric salt.
11. A lithographic printing plate having a normally hydrophilic surface and capable of having imparted thereto a visibly distinct and ink-receptive image by a process involving briefly subjecting to intense radiation an inter mediate sheet having differentially radiation-absorptive image and background areas and carrying on a transparent backing a visibly heat-sensitive coating and including a volatilizable first reactant, while said intermediate sheet and said lithographic plate are in heat-conductive faceto-face contact; said plate being characterized as having a normally hydrophiiic heat-sensitive polyphase surface layer which becomes hydrophobic and ink-receptive on being heated in the therrnographic copying process and comprising a continuous phase of film-forming hydrophilic binder containing a hydrophilic filler powder, a discontinuous phase of synthetic organophilic polymer latex particles characterized as forming a fragile waterreceptive and ink-repellent film when deposited as a dried thin layer of said latex, said film being rendered waterrepellent and ink-receptive on being heated to 120 C., and a co-reactant for said first reactant, the two reactants being inter-reactive at the activation temperaure of said heat-sensitive coating with formation of a visibly distinct reaction product.
12. A lithographic printing plate having a normally hydrophilic surface and capable of having imparted thereto a visibly distinct and ink-receptive image by a process involving briefly subjecting to intense radiation an intermediate sheet having differentially radiation-absorptive image and background areas and carrying on a transparent backing a visibly heat-sensitive coating and including a volatilizable first reactant, while said intermediate sheet and said lithographic plate are in heat-conductive faceto-face contact; said plate being characterized as having a normally hydrophilic heat-sensitive polyphase surface layer which becomes hydrophobic and ink-receptive on heating in the thermographic copying process and comprising a continuous phase of three parts by weight of hydrophilic colloidal agglutinant containing a hydrophilic material filler in an amount not greater than thirty parts by weight and sufiicient to increase the wettability by water of the said layer, a discontinuous phase of synthetic organophilic polymer latex particles in an amount of from about one to about three parts by weight, and a co-reactant for said first reactant, the two reactants being inter-reactive at the activation temperature of said heat-sensitive coating with formation of a visibly distinct reaction product, the latex particles being characterized as forming a fragile water-receptive and ink-repellent film when deposited as a dried thin layer of said latex, said film being rendered water-repellent and inlereceptive on being heated to C.
13. The lithographic printing plate of claim 11 in which the hydrophilic binder is insoluble in water, and in which the organophilic polymer is polystyrene.
14. The method of producing an imaged lithographic master having visibly distinguishable ink-receptive areas corresponding to image areas of a thin differentially radiation-absorptive graphic original, comprising subjecting said original to brief intense irradiation while in heatconductive contact with a heat-sensitive lithographic plate having a hydrophilic surface which becomes hydrophobic and ink-receptive on heating, said plate including a visibly heat-sensitive coating which is chemically reactive to form a visibly distinct reaction product when heated.
15. The method of producing an imaged lithographic master having visibly distinguishable ink-receptive areas corresponding to image areas of a thin dilferentially radiation-absorptive graphic original, comprising subjecting said original to brief intense irradiation while in heatconductive contact with a heat-sensitive lithographic plate having a hydrophilic surface which becomes hydrophobic and ink-receptive on heating, said plate including one reactant component of a pair of reactant components which are chemically reactive to form a visibly distinct reaction product when heated together, and said original including the other of said pair of reactant components, said other component being a volatile reactant.
References Cited in the file of this patent UNITED STATES PATENTS 2,663,654 Miller et al. Dec. 22, 1953 2,760,432 Wood Aug. 28, 1956 2,800,077 Marron July 23, 1957 2,939,009 Tien May 31, 1960 FOREIGN PATENTS 722,023 Great Britain .Jan. 19, 1955