US3151549A

US3151549A - Electrically inscribable lithographic masters

Info

Publication number: US3151549A
Authority: US
Inventors: Raymond L Oransky; Robert L Stoddard
Original assignee: Warren SD Co
Current assignee: Warren SD Co
Priority date: 1959-02-11
Filing date: 1959-02-11
Publication date: 1964-10-06
Anticipated expiration: 1981-10-06
Also published as: NL248212A; NL120974C; GB884504A; DE1167365B; BE586149A; FR1246443A

Description

`0d- 5, 1964 R. 1 .oRANsKY ETAL l 3,151,549

ELECTRICALLY INSCRIBABLE LITHOGRAPHIC MASTERS Filed Feb. 11, 1959 la7/manif@ Wfl INVENTORS y Bym/ uwp ATTORNEYS United States Patent O 3,151,549 ELECTRICALLY INSCRIBABLE LITHOGRAPHIC MASTERS This invention relates to the production of electrically inscribable recording blanks, and more particularly to such blanks which are also adapted for use as lithographie printing masters or plates on offset duplicating machines.

Electrically inscribable recording papers are well known. They are'used, for instance, in the facsimile reception of messages or graphic intelligence such as telegrams, drawl ings, maps, pictures, and the like sent over facsimile communication systems. In such transmission an electrical signal generated as a result of the scanning of graphie message matter by a pick-up means at a recording station is transmitted to a receiving station where an electric stylus marks an electrosensitive blank of coated paper in a pattern corresponding to the original message. Such a paper may comprise a paper base made electrically conductive by reason of a filling or coating of conductive carbon black or equivalent conductive material which usually imparts a distinct coloration to the paper base. Over the conductive base there is provided a thin layer of coating of contrasting color which is slightly conductive, but much less so than the base itself. A coating containing cuprous thiocyanate powder in a resinous binder or adhesive has in the past been successfully used for such a top coat, being sufficiently conductive, opaque and white to give satisfactory results. When an energized electric stylus is moved across the surface of such paper a current passes through the coating decomposing the coating beneath the stylus and exposing the underlying base. The current converts the white cuprous thiocyanate to black cupric sulfide, so that the resulting visible mark is due in part to exposure of the black base and in part to formation of the cupric sulfide.

When such a facsimile blank is in use an electrical stylus' having a pointed tip moves across the surface of the blank in a series of closely spaced parallel paths. Whenever the stylus is energized by the transmitted signal, a spark passes between the stylus and the conductive base, burning a hole in the top coating of low conductivity, and exposing the underlying conductive base. If the matter to be recorded on the blank is a dot like the dot of an i or if it is a narrow straight line which falls completely in the path of one sweep of the stylus, it may be recorded in a single burn by a single impulse impressed on the stylus. In the case of the great .majority of characters desired to be recorded, however, several passes of the stylus across the sheet are required in order to form the character, so that the character is made up of several separate holes or burns. Asa result, the characters recorded may be somewhat discontinuous and are likely to have scalloped edges. Nevertheless, in spite of discontinuity and unevenness in outline of the inscribed characters',rthe inscriptions are usually readily legible when eight-point or larger characters are used. According to the point system for type, one point is 0.013837 inch; so eight points is about 0.11 inch.

Obviously only one copy of the message material can be inscribed at one time. Frequently, however, it is desirable to obtain several copies quickly. It has been suggested to provide the facsimile blank with a hydrophilic surface over an oleophilic base, so that the inscribed blank can be placed on a rotary offset duplicator and used as a lithographie master from which copies can be printed by the lithographie printing process.

The lithographie printing process', as is wellknown,

depends upon the immiscibility of oil and water.' The imaged areas on a lithographicfplate are oleophilic,- and attract greasy printing ink while repelling aqueous lithographic wet-out and fountain solutions. Conversely, the v unimaged or blank areas of the plate'are hydrophilic and are readily wet by acidic aqueous lithographie solutions,

and while so wet they will repel greasy ink. In the lithoi graphic offset printing process, a lithographie master bearing thereon an oleophilic image is wet by having rolled j across its surface a roller wet with aqueous lithographie solution usually made acidic by a content of phosphoric acid or acidic salt thereof. This wets thebackground areas but does not wet the oleophilic-image.` Next a roller inked with greasy lithographie printing ink isrolled across the surface. The ink adheres to the imaged areas but is repelled from the wet background areas. The inked plate is then pressed against a rubber offset blanket to which the image is transferred in reverse. -A paper sheet when pressed against the offset blanket takes off the print in its original form. The cycle is repeated as many times as there are copies desired, which may sometimes be l several hundred.

It is not difficult to produce a layer of coating of cuprous thiocyanate and hydrophilic adhesive which will possess the qualities requisite in a planographie printing surface. v There are in common use several successful coated paper greasy or resinous planographic imaging'material can readily be affixed to the surface, and good copies of' the image with clean background can be printed therefrom by the lithographie printing process.

As the term implies, planographie printing is a branch of lithography in which the printing plate has a substantially plane surface with a printing image affixed to the surface. In deep-etch lithography, on the other hand, the image is actually etched into a metal plate, so that the image is recessed below the surface of the plate.

When a coated paper is electrically inscribed by a spark from a stylus which burns away a layer of coating, the

image formed is actually that portion of the underlyingv base which is exposed by removal ofthe top coating.

The image thus lies below the surface of the top coatingy and so resembles a deep-etch lithographie image rather than a planographic image. To be usable as a lithographie printing image, obviously the exposed underlying base must be oleophilic in character.

A suitable electrically conductive base for an electrically inseribable lithographie master can be readily provided by eoating a web of paper with a conductive layer of carbon black in an oleophilic resinous binder which has relatively low electrical resistivity. When the resultp ing conductive base is given atop coating of cuprous thiocyanate and insolubilized hydrophilic adhesive sufficiently thick completely to cover the conductive coating the product is adequate in accepting aqueous lithographie solution and repelling greasy printing ink.

It is found, however, that if the above-described coated web is electrically inscribed with an image to form a lithographie printing master, then the printing results obtained therefrom are not entirely satisfactory. Instead a curious irregularity or blotchiness is frequently apparent, which greatlyreduces the legibility of the printed matter and may make eight-point type impossible to read. Such 3,151,549' Patented Oct. 6, 1596.4

blotchiness or irregularity apparently is caused in part by a tendency of the electric spark to wander on the surface of the above-described coating rather than to penetrate the coating directly beneath the stylus. Then at times the spark fails to lay completely bare the underlying oleophilic base in the image areas. The end result has been that images electrically inscribed on such hydrophilic surfaces, if not actually illegible, have displayed sufcient irregularity to be unattractive.

The present invention provides a coated paper sheet which has excellent lithographie printing qualities and yet at the same time can be inscribed electrically with an image which is a faithful copy of the original and from which substantial duplicates can be reproduced by the lithographic printing process.

According to the invention a sheet or web of paper is provided with a conductive layer of coating comprising a pigmentary component of powdered matter having good electrical conductivity, such as carbon black, bound to the paper surface by an oleophilic and water-resistant adhesive. Over this oleophilic and conductive coating is applied one or more than one layer of hydrophilic coating containing powdered cuprous thiocyanate or equivalent bound by insolubilized hydrophilic adhesive material. Such hydrophilic layer or each of such layers has relatively high electrical resistivity and hence only slight electrical conductivity. Then the tendency for the facsimile inscribing spark to wander on the surface of the hydrophilic coating can be substantially eliminated by incorporating in the surface of the hydrophilic coating a relatively small proportion of highly conductive powder such as carbon black or equivalent. Apparently when an electric stylus passes across a hydrophilic coating having conductive powder in its surface, contact between stylus and conductive powder is sufficiently good so that current passes directly into the coating at the exact point of contact with the stylus. In this case the hole, puncture, or burn is made directly beneath the tip of the stylus. Hence the resulting trace follows very closely the path of the energized stylus.

The invention is illustrated in the accompanying drawings in which FIG. 1 is a diagrammatic cross-section of. a coated paper having two layers of coating, and

FIG. 2 is a diagrammatic cross-section of a coated paper having three layers of coating.

A suitable paper base to use for the purpose of the invention is any sized paper web of reasonably level surface having strength at least as great as that of a standard printing paper of about pound basis for a ream of 500 Sheets cut 25 x 38 inches in size. In the unlikely event that where more than 500 copies may be desired to be printed from the imaged master a little wetstrength resin may be included in the paper-making furnish in the well known way. Ordinarily, however, such wet-strength is not necessary, because usually only a few copies, e.g. less than 100, are desired to be printed from such an inscribed master. A typical paper base-stock which has given satisfactory results in practicing the invention is a web of sized paper containing both long and short chemical wood fibers and a small quantity of clay filler and weighing about pounds per ream or about 75 grams per square meter.

The base paper is provided with a layer of conductive coating, suitably applied in the form of an aqueous dispcrsion by a conventional coating means, such as an airknife coater. Sufficient thickness of coating is applied to completely cover the paper base and give anadequately conductive layer. Usually about 6 pounds, dry weight, of coating per ream is adequate. A greater amount is an added safeguard, and a reasonable excess of weight is not objectionable in the conductive base coat. It has been found quite satisfactory to apply to one side of a suitable paper base by means of a conventional coating device,

eg. an air-knife coater, about 9 pounds per ream, dry weight, of an aqueous coating mixture having the following composition:

Typical Formula for Oleophilic Conductive Base Coat parts by weight of electrically conductive carbon black parts by weight of internally plasticized vinyl acetate copolymer (added in the form of a latex, No. EC 103 sold by Beechnut Packing Co.)

Water to make solids content 32% This coating is very similar to conductive coatings which have been commonly used in the past in ordinary facsimile papers, i.e. in facsimile papers not having lithographic printing surfaces. Any similar known conductive coating may be substituted therefor provided it is ymarkedly oleophilic -as well as substantially water-insoluble. The various vinyl acetate copolymers in latex form seem especially well suited for this use.

After the oleophilic conductive base-coat has been dried it preferably is smoothed by a calendering process. Thereafter a hydrophilic coating composition is applied over the base coat by means of any suitable coating device. t

The hydrophilic coating having conductive particles in its surface must be thick enough completely to cover the very oleophilic base coat. About 6 pounds dry weight of coating per ream is about as little as can safely be relied on to give complete coverage of the oleophilic base coat even if applied in two separate layers. On the other hand, it is preferable to use not more than about 12 pounds per ream, dry weight, of the hydrophilic coating, else excessive power may be required for satisfactory electrical inscription thereon.

The said hydrophilic coating may comprise one layer, or more than one layer. The top surface of the hydrophilic coating must contain particles of highly conductive powder. The major portion of the hydrophilic coating consists essentially of cuprous thiocyanate powder or equivalent, suiicient hydrophilic binder or adhesive to bind the coating to the base, and an agent to insolubilize the adhesive. Any hydrophilic adhesive commonly used in paper coating will serve satisfactorily. The insolubilizing agent should be one which does not destroy ythe hydrophilic properties of the adhesive but does render it substantially water-insoluble. Dimethylol urea and similar amino-aldehyde condensates are suitable and effective insolubilizing agents. In case the oleophilic base coat is difficult to wet with aqueous medium it is advantageous to include in the hydrophilic coating composition an e'lcient wetting agent and/ or an adhesive possessing good wetting properties, such as casein or soy protein solvated by a basic solvent.

The preferred highly conductive particles are those of conductive carbon black, because of cost, fine division, and ease of handling. Other conductive powders can be substituted therefor, but must be free from insulating coatings of grease or oxide. Since the latter requirement poses some difficulties in the use of powdered metals of low cost, carbon black remains the preferred material in spite of its undesirable discoloring effect. Because of the darkening effect of the carbon black, as well as the effect which excessive quantities of carbon black have in too greatly decreasing resistivity, the latter should make up less than 10 percent of the pigment portion of the hydrophilic coating. If the carbon black is confined strictly to the top surface of the coating as little as l percent on the weight of total pigment may suffice. In most cases not over 6 percent of carbon black would be needed.

For the white pigment in the hydrophilic coating cuprous thiocyanate is preferred, as shown in U.S. Patent No. 2,681,309. Other white pigments which decompose to darker compounds under the action of electric current may be substituted with somewhat comparable results, for example lead thiosulfate.

Following is an example in which a single layer of hydrophilic coating containing conductive particles was applied on top of the conductive oleophilic coating previously described. The coating composition was applied by means of an air-knife coating-machine in amount equivalent to about pounds, dry weight, per rearn. The coating composition was according to the following formula in which all parts are parts by weight:

Formula for Single Layer Hydrophilc Coating 88 parts of powdered cuprous thiocyanate 4 parts of conductive carbon black 8 parts of titanium dioxide 40 parts of Penford Gum, a partial hydroxyethyl starch ether 14 parts of soluble melamine-formaldehyde condensate,

Parez 611 40 Iparts anhydrous zinc acetate 1 .part Tergitol 4, a wetting agent 1/2 part tributyl phosphate, an anti-foam agent Water to make solids content 30% Tergitol 4 is the trade-name of the sodium sulfate derivative of 7-ethyl-2 methyl undecanol-4.

The coated product was dried at elevated temperature to ensure insolubilization of the coating. It was then used without any final calendering treatment. The sheet was inscribed by an electric stylus on a facsimile receiver, and the inscribed sheet was then used as a master or plate on a rotary offset duplicator. Over 200 copies were printed from the master, 4and the master at that Itime had not begun to show any evidence of deterioration. The copy was good and 8-point type was legible.

The color of the master above described was distinctly dark gray, in spite of the inclusion of some titanium dioxide in the formula to offset in part the darkening effect of Ithe carbon black.

The `formula as shown includes a quantity of zinc acetate. It is preferable, but not essential, to have zinc acetate or equivalent divalent metal salt present in the surface pores of the coating to improve the lithographie printing qualities of the master. The beneficial effects of zinc acetate or equivalent soluble divalent metal salts in the surface pores and interstices of coated paper lithographie printing masters are well known. A perfectly good and usable master can be made according to the present invention without any zinc acetate, but the use of that salt protects against accidental soiling of the master and in general permits greater latitude in operating conditions.

The structure described above is illustrated in FIG. 1 in which 1 is the paper base, 2 is the oleophilic electrically conductive coating, and 3 is the single hydrophilic coating containing both the pigment which is sensitive to electric current and the electrically conductive pigment.

Although the product of the invention made with a single layer of hydrophilic coating is a good and useful lithographie master, there are several advantages to be gained 'by using a plurality of layers of hydrophilic coating. Applying the coating in more than one layer substantially eliminate: possibility of a pin-hole or foampit extending throughout the entire thickness of the hydrophilic coating and exposing the underlying oleophilic base. Using more 'than one layer of hydrophilic coating makes possible the use of less total thickness of coating than is safe to use when a single layer is used. Three layers are in some instances even more effective than two. Improvement resul ing lfrom increasing the number of layers above three is usually too small to be worth the extra effort involved.

Improvement results from use of a plurality of layers of hydrophilic coating even if the layers are of identical composition. Additional advantages may accrue from use of hydrophilic layers of different composition. Since only at the surface are conductive particles essential, the quantity of such particles required can be considerably cut down by using such particles only in a thin top layer which is underlain by a hydrophilic layer containing no such particles. Thus any discoloration due to the conductive particles can be kept at a minimum. The interposition of a layer of substantially white hydrophilic coating between the colored oleophilic base and the very top layer containing conductive particles also substantially reduces show-through of the colored base so that hte color of t-he finished product is substantially unaffected yby the color of the olephilic base, but instead is due chiefly to ingredients of the top coating layer itself.

It is apparent that a layer of coating which contains even a small proportion of highly conductive particles, such as carbon black, will have lower electrical resistance than a similar layer free from such highly conductive matter. It is thought to be one advantage of using plural hydrophilic layers of which only the topmost layer contains highly conductive matter, that in such a case the major portion of the electrical energy used will be concentrated in the most resistant portion of the hydrophilic coating and hence near the surface of the underlying oleophilic layer. This results in clean exposure of the underlying layer in the form of the original image which will therefore pick up ink uniformly over the entire image area.

For the above and other reasons it is preferred to use at least two layers of hydrophilic coating, the topmost layer containing finely divided highly conductive particles and having a higher conductivity and lower resistivity than the lower layer or layers thereof.

When plural layers of hydrophilic coating are used the top layer can be of the same composition as that of the Formula for Single Layer Hydrophilic Coating shown above. The under portion of the hydrophilic coating can be identical except for omission of the carbon black shown in that formula.

A typical example of the application of a double layer hydrophilic coating follows:

The hydrophilic coating is applied over -a suitable paper web having thereon a conductive oleophilic coating with a calendered surface.

The base-coated web was coated on the same vside by means of an air-knife coater with about 4 pounds per ream, dry weight, of the following composition:

Formula for Intermediate Hydrophlc Coating 100 parts by weight of cuprous thiocyanate powder 18 parts by weight of casein solvated by ammonia water 1.8 parts by weight of dimethylol urea (to insolubilize the casein) 10 parts by weight of butanol (to reduce foaming) 0.5 part by weight Victawet 35B, an anionic wetting agent sold by Victor Chemical Works Water to make solids content 27% I The so-coated web was dried and smoothed by calendermg.

To the resulting smoothed coated web, there was applied on top of the previous coating, by means of an airknife coater, 4 pounds per ream, dry weight, of the following hydrophilic coating composition:

Formula for T op Hydrophlic Coating parts by Weight of cuprous thiocyanate powder l0 parts by weight of titanium dioxide 5 parts by weight of conductive carbon black 35 parts by weight of polyvinyl alcohol, medium viscosity 14 parts by weight of partially condensed urea-formaldehyde (to insolubilize the polyvinyl alcohol) 20 parts by weight of zinc acetate dihydrate 5 parts by weight of butanol (defoamer) 0.6 part by weight of Triton X100, a wetting agent sold by Rohm: Haas Company Water to make the solids content 19% This coating was dried slowly in a festoon dryer and `paper lithographie masters.

then subjected to a temperature of 700 F. for 15 seconds to cause insolubilization of the polyvinyl alcohol by the urea-formaldehyde condensate. The paper was then steamed lightly on the reverse side to offset the tendency to curl caused by the coating being on one side only, and was then wound up into a roll. After the top coating had been applied the paper was not given any further smoothing or calendering. The coated paper was not white but was definitely gray. When electrically inscribed the contrast between the gray top coat and the black base coat was adequate for good legibility. The inscribed image was of good regularity, and copies printed therefrom on an offset duplicator were excellent. More than 500 good copies were obtainable without evidence of deterioration in the master.

The above-described structure is illustrated in FIG. 2 in which 1 is the paper base, 2 is the oleophilic electrically conductive coating, 4 is the hydrophilic coating containing pigment whcih is sensitive to electric current and 5 is the hydrophilic coating containing electrically conductive pigment.

The product of the invention is a coated paper electrically inscribable lithographie master or plate which can be used on a rotary offset duplicator to produce printed copies of matter electrically inscribed thereon. It cof-nprises a paper base having thereon a groundor base-cojat of relatively low electrical resistability and comprising electrically conductive powder bound by an oleophilic and water-resistant adhesive. Over the oleophilic ground-coat is a hydrophilic coating having much higher electrical resistivity than the ground coat, but having in at least its surface a minor quantity of highly conductive particles. Said hydrophilic coating has an exposed surface which comprises pigmentary powder bound by insolubilized hydrophilic adhesive, and which has the excellent lithographic properties characteristic of high-quality coated Such a coating contains microscopic pores and interstices which preferably, but not necessarily, are lled with water-soluble zinc acetate or equivalent capable of reacting with lithographie solutions containing a phosphate ion to form a gelatinous precipitate to plug the pores and interstices and so keeping the surface wet by preventing rapid penetration of said lithographic solutions below the surface of the master.

We claim:

1. An electrically inscribable lithographie printing plate or master, comprising a paper base having on one side thereof a water-insoluble composite coating having at least three zones or layers, of which the base layer has good electrical conductivity and is strongly oleophilic; the intermediate zone contains cuprous thiocyanate and hydrophilic binder and has a lower electrical conductivity than said base layer; yand the top zone contains cuprous thiocyanate, hydrophilic binder, and .a substance which gives it a slightly higher conductivity than the intermediate zone.

2. A coated paper product adapted for use as an electrically inscribable lithographie printing master comprising a base of sized paper, a conductive base-coat of electrically conductive powder bound with water-insoluble adhesive of highly oleophilic properties, an intermediate coating of much lower electrical conductivity than said base-coat containing cuprous thiocyanate bound by an insolubilized hydrophilic adhesive, and a top coating containing cuprous thiocyanate, insolubilized hydrophilic adhesive and a small proportion of powder which possesses higher electrical conductivity than said cuprous thiocyanate, said top coating having a higher electrical conducf tivity than said intermediate coating.

3. A coated paper product adapted for use as an electrically inscribable lithographie printing master which consists of a sized paper base which has on one side an oleophilic base coating of good electrical conductivity comprising finely divided electrically conductive carbon black bound by an oleophilic and water-resistant resinous adhesive; an intermediate hydrophilic coating comprising cuprous thiocyanate bound by insolubilized protein adhesive, said intermediate coating having much lower electrical conductivity than said base coating; and a hydrophilic top coating comprising cuprous thiocyanate, a small proportion of carbon black, and polyvinyl alcohol adhesive insolubilized by an amino-aldehyde condensate, said top coating having somewhat higher electrical conductivity than said intermediate coating, said top coating possessing interstices and pores which contain water soluble zinc acetate in substantial amount.

References Cited in the file of this patent UNITED STATES PATENTS 2,534,650 Worthen Dec. 19, 1950 2,554,017 Dalton May 22, 1951 2,664,044 Dalton Dec. 29, 1953 2,693,145 Mullen Nov. 2, 1954 2,726,168 Roddin et al Dec. 6, 1955 2,766,688 Halpern et al. Oct. 16, 1956 2,951,441 Wolf et al Sept. 6, 1960 2,983,220 Dalton et al. May 9, 1961 FOREIGN PATENTS 763,528 Great Britain Dec. 12, 1956 767,074 Great Britain Jan. 30, 1957

Claims

1. AN ELECTRICALLY INSCRIBABLE LITHOGRAPHIC PRINTING PLATE OR MASTER, COMPRISING A PAPER BASE HAVING ON ONE SIDE THEREOF A WATER-SOLUBLE COMPOSITE COATING HAVING AT LEAST THREE ZONES OR LAYERS, OF WHICH THE BASE LAYER HAS GOOD ELECTRICAL CONDUCTIVITY AND IS STRONGLY OLEOPHILIC; THE INTERMEDIATE ZONE CONTAINS CUPROUS THIOCYANATE AND HYDROPHILIC BINDER AND HAS A LOWER ELECTRICAL CONDUCTIVITY THAN SAID BASE LAYER; AND THE TOP ZONE CONTAINS CUPROUS THIOCYANATE, HYDROPHILIC BINDER, AND A SUBSTANCE WHICH GIVES IT A SLIGHTLY HIGHER CONDUCTIVITY THAN THE INTERMEDIATE ZONE.