US3108896A - Heat-sensitive copying-paper - Google Patents

Description

Oct. 29, 1963 R. OWEN 3,108,896

HEAT-SENSITIVE COPYING-PAPER Filed Oct. 26, 1959 I lO-SOURCE or RADIATION l4 REPRODUCED IMAGE H fi & HEAT-SENSITIVE SHEET GRAPHIC ORIGINAL l3 RADIATION- ABSORPTIVE IMAGE AREAS GRAPHIC ORIGINAL HEAT-SENSITIVE LAYER PROTECTIVE LAYER HEAT'SENSITIVE LAYER CARRIER IN VEN TOR.

RICH ARD OWE N B 5% dam 6M {#7 ATTORNEYS United States Patent "ice 3,108,896 HEAT-SENSITIVE *C OPYlNG-PAPER Richard Gwen, Brooklyn Center, Mind, assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Get. 26, 195i, Ser. No. 843,753 8 Claims. (Cl. 117-368) This application is a continuation-in-part of my copending application Serial No. 594,540, filed June 28, 1956, now Patent No. 2,910,377.

This invention is concerned with improvements in heat-sensitive copying-paper useful in preparing copies of printed matter by procedures, such as those described in Miller Patent No. 2,740,896, involving placing a printed or other graphic original in heat-conductive association with the heat-sensitive copying-paper and then briefly exposing the graphic original to intense radiant energy. The resulting elevated-temperature pattern produces in the copying-paper a visible direct copy of the graphic original. The present invention provides a stable heat-sensitive copying-paper based on a new principle of operation and capable of providing duplicate copies having improved appearance as well as other advantages.

For convenience in describing the novel copying-paper and its application to the copying of documents, the product and procedure are illustrated in the accompanying drawing, in which:

FIGURE 1 schematically illustrates in cross-section one method of copying a graphic original;

PZGURE 2 similarly illustrates an alternative method; and

FIGURE 3 illustrates in cross-section a preferred form or" heat-sensitive copying-paper.

A commercially available thermo-copying machinewidely employed for copying ofiice records on heat-sensitive copying-paper includes as the source of radiant energy a high-intensity infrared lamp such as a GE T-3" lamp having a linear coiled filament supported within a reflector which focuses the radiation in a narrow beam across the sheet as the latter is moved past the lamp assembly. Such a lamp draws 1350 watts at 280 volts to provide a color temperature of about 2800 K. Irradiation and copying of a conventional letter-size sheet requires about l-6 seconds. A non-fading copy is directly produced by such irradiation and without any subsequent processing such as developing, fixing, washing, treatment with fumes or vapors, or any other treatment.

in FIGURE 1, radiant energy from source 10 is directed through heat-sensitive copying-paper 11 to printed original 12. Energy is selectively absorbed in printed areas 13 and released in the form of heat energy, causing the occurrence of a visible change in corresponding areas 14 of the heat-sensitive layer 15 of sheet 11. The procedure is known as front-printing.

In FIUURE 2 the radiant energy from source impinges directly on the printed surface of the graphic original 22, and the resulting release of heat energy causes visible change in the heat-sensitive layer on support 26 at areas 24 corresponding to the printed and radiationabsorptive areas 2 3 of the original. The procedure has been termed back-printing.

The copying-sheet 11 of FIGURE 1 consists of a heatsensitive layer 15 on a carrier 16, which may be a thin paper. The sheet must transmit sufficient of the radiant energy to provide the required release of heat at the printed areas 13 but is preferably sufliciently visibly opaque to provide high contrast in the copy.

Still greater accuracy of copy is obtained by inverting the copying-paper 11 so that the heat-sensitive layer 15 is more closely associated with the printed surface of the graphic original 12. In this case a visibly transparent ates-nae Patented Get. 29, 1%63 carrier 16 permits viewing of the copy areas 14 through the carrier and in the same direction as the original.

The front-printing process of FIGURE 1 is applicable to a wide variety of originals and to radiation-transmissive copy-paper, whereas back-printing is most effective with originals printed on relatively thin heat-transmissive paper and the copy-paper may be fully opaque to the radiation employed.

FIGURE 3 illustrates a further variation in' heat-sensitive copyingpapers inwhich the heat-sensitive layer 35 is applied to a carrier web 36 and is covered with a protective layer 37. Either or both of web 36 and layer 37 may be visibly transparent, but in a preferred construction for front-printing operations the web 36 is transparent while the thin protective layer 37 is visibly opaque and provides high visual contrast for the visibly changed areas of the heat-sensitive layer.

The actual temperatures developed in such heat-sensitive papers by these various techniques have not been directly measured. However it has been observed that papers which change visibly when momentarily pressed against a metal test bar heated to about l20 C., or at most to about 150 C., become similarly altered under the irradiation techniques just described. On the other hand, papers which do not change on brief pressure contact with the test bar at temperatures much greater than about 150 C. are found to be ineffective as heat-sensitive copying-papers when tested in copying-machines as described hereinbefore. Since heating to such high temperatures, particularly when prolonged or frequently repeated, is likely to cause degradation or deterioration of the printed page forming the original of which a copy is desired, copy-sheets are ordinarily required to be visibly heat-sensitive at temperatures below about 150 C. and preferably at temperatures below about C.

Heat-sensitive copying papers suitable for the copying of printed and other graphic originals by methods just described have previously been developed, and such products are described in Miller et al. Patents Nos. 2,663,654- 2,663,657, in Taylor et a1. Patent No. 2,668,126, and in Clark et al. Patent No. 2,710,263. The sheet materials of the present invention operate through a different mechanism than do these prior art materials and provide a number of advantages thereover, as will be pointed out hereinafter in connection with illustrative but non-limiting examples.

Like the earlier heat-sensitive copying-papers, those of the present invention are suitable for making direct, high contrast, clear detail, permanent copies of typewritten, printed, and other graphic subject-matter. The copypaper does not adhere to nor deface the graphic original or the thermoprinting apparatus. It is stable at normal room and storage temperatures, and in particular may be stored in the light without visible change either before or after heat-copying. The present invention additionally provides for the utilization of new classes of visibly heatsensitive compositions comprising an intimate mixture of components including an organornetallic oxidizing agent and a cyclic organic reducing agent as hereinafter identified, which when sufficiently heated, as in the thermocopying process described, undergo an oxidation-reduction type reaction resulting in the formation of one or more visibly distinct reaction products. These components are normally employed in conjunction with a water-resistant film-forming binder, the combination being in the form of either a self-supporting thin film or a thin coating or coatings on a suitable paper or other carrier web. The reactants are present in amounts sufiicient to provide adequate visible change on heating, and the binder maintains the reactants in the required intimate but physically distinct association and in position on the paper backing. A similar effect may be obtained by retaining the reactants within a paper or other fibrous carrier in the substantial absence of resinous binder. Additional components, both inert and chemically reactive, may be included to improve the appearance or handling properties of the sheet, or to provide a more intense or difierently colored heat-image, or for other purposes.

As organometallic oxidizing agents I employ normally solid salts of organic acid anions and readily reducible polyvalent base metal cations having a standard reduction potential greater than one-tenth volt. Stearic, behenic, oleic, lauric, hydroxystearic, acetic, phthalic, terephthalic, butyric, m-nitrobenzoic, salicylic, phenyl-acetic, pyromellitic, p-phenylbenzoic, undecylenic, camphoric, furoic and acetamidobenzoic acids are all useful, but best results in terms of resistance to moisture and fingerprinting are attained with the water-insoluble salts of the higher molecular weight acids, and in particular the higher fatty acids such as stearic or behenic acid. The metallic ion is selected from those polyvalent base metal ions having a standard reduction potential greater than one-tenth volt, viz. the ferric, ceric, cupric, mercuric, stannic, bismuthic, thallic and palladic ions. Of these, the first four named, and more particularly the ferric and ceric cations, provide relatively easily prepared, economical, non-poisonous, light-colored and easily reducible oxidizing agents and are greatly preferred in the practice of the invention.

Reducing agents which have been found useful in conjunction with some or all of the foregoing base metal salts include the following illustrative compounds: 4,4- dimethylamino triphenylmethyl cyanide (malachite green leuco cyanide); pyrogallol; 4-azeloyl-bis-pyrogallol; 4- stearoyl pyrogallol; galloacetophenone; di-tertiary-butyl pyrogallol; gallic acid anilide; methyl gallate; ethyl gallate; normaland iso-propyl gallate; butyl gallate; dodecyl gallate; gallic acid; ammonium gallate; ethyl protocatechuate; cetyl protocatechuate; 2,5-dihydroxy benzoic acid; l-hydroxy-Z-naphthoic acid; Z-hydroxy, 3-naphthoic acid; phloroglucinol; catechol; 2,3-naphthalene diol; 4-lauroyl catechol; sodium gallate; protocatechualdehyde; 4-methyl esculetin; 3,4-dihydroxy benzoic acid; 2,3-dihydroxy benzoic acid; hydroquinone; 4,4-dihydroxy biphenyl; 3,4-dihydroxyphenylacetic acid; 4(3,4'-dihydroxyphenylazo) benzoic acid; 2,2-metl1ylene-bis-3,4,5-trihydroxybenzoic acid; orthoand para-phenylene diamine; 4,4',4"-diethylamino triphenylmethane; m-, and p-aminobenzoic acids; alpha and beta naphthols; and 4-methoxy, l-hydroxydihydronaphthalene. More broadly, there are encompassed cyclic or preferably aromatic organic reducing agents having an active hydrogen atom attached to an oxygen, nitrogen or carbon atom which is directly attached to an atom of the cyclic or aromatic ring. These reducing agents may be further characterized as being readily visibly oxidizable, a property which is conveniently determined as follows. A small amount of a dilute solution of the organic compound in a water-miscible solvent, e.g. one ml. of a 5% solution of the compound in acetone, is mixed with an equal amount, e.g. one ml. of a 5% solution, of ammonium persulfate in water, and the mixture is momentarily heated on a steam bath. A distinct color change is obtained. In general, the color change is the same as is observed on heating a copy-sheet prepared with the same reducing agent, although in some instances the color may be masked or otherwise modified by other components of the copy-sheet.

The organometallic oxidizing agent and organic reducing agent to be employed in a specific copy-sheet are further selected as capable of undergoing an oxidationreduction reaction when the sheet is heated in the thermographie copying process. In all cases the oxidation-reduction reaction causing the visible change in the copysheet will involve a change in the valence of the metallicion, which change in valence may be determined anayltically. However any visible effect produced by such valence change is ordinarily negligible, at least as compared ferred. When plasticizers for the resinous binder are found to be desirable, phosphates and phthalates, having low water absorption properties, are superior to glycols and their esters. Waxy materials may be incorporated for added moisture-resistance. Zinc sulfide, titanium dioxide, diatomaceous earth, and numerous other pigments and fillers are useful in conjunction with the protective surface coating. Dyestuffs may be added. Metal powders and carbon black may be used in substantial proportions in back-printing papers, and have been found useful in very small proportions in the surface coatings of front-printing papers, e.g. to provide somewhat higher sheet temperatures. Pigments and other particulate materials such as glass cullet or sphericles may also be added to the heatsensitive coating for special purposes where desired.

The following specific examples further illustrate the invention.

Example 1 ous solution of three moles of sodium stearate with an aqueous solution ofone mole of ferric sulfate, followed by washing and drying. Six parts by weight of the insoluble solid product is dispersed in a solution of one part of polystyrene resin in 43 parts of ethyl acetate by grinding in a ball mill for 8-l6 hours to provide a uniform and very fine dispersion. To a portion of the ferric stearate dispersion is added an equal molal quantity of 4- methoxy-1-hydroxydihydronaphthalene, with thorough mixing. The mixture is coated on map overlay tracing paper and the sheet is dried in a current of air at room temperature. The dried coating weighs approximately one-half gram per square foot of area. The sheet is light bull" in color, and is converted to a blue color at heated areas in the thermographic reproduction process and on momentary contact with a metal test bar at C.

Extraction with ethyl alcohol of the blue, completely heat-converted areas removes the blue image-forming material without removing either the residual iron salt or the polystyrene binder. The solution tests negative for iron.

A small amount of 4-methoxy-l-hydroxy-dihydronaphthalene is dissolved in acetone, and a portion is added to an aqueous solution of ammonium per-sulfate in the same amount and at the same concentration. Moderate brief warming of the mixture on a steam bath produces a distinct blue coloration in the test solution. a

The 4-methoxy-1-hydroxy-dihydronaphthalene may b separately mixed with binder solution and applied to the carrier web, the ferric stearate solution being applied subsequently over the dried first coating, to provide a copy-sheet which is somewhat less economical to manufacture but is capable of providing useful heat-copies. The two mixtures may alternatively be separately coated and dried on separate thin papers, the coated surfaces pressed firmly together, and the resulting composite employed in making a copy by the processes here described followed by separation of the two coated surfaces. Copy thus formed is not susceptible to modification by further heating.

The copy-sheet of Example 1 is preferably further provided with a thin opacifying and protective contrast coating of titanium dioxide or other suitable pigment in a film-forming binder, the heat-copy then being visible through the transparent paper carrier and against the contrasting white background.

Example 2 Ceric behenate is prepared as follows: Sodium behenate solution is first prepared by heating together for one hour at 70 C. a mixture of 25 grams of behenic acid, a solution of 3 grams of sodium hydroxide in 400 ml. of 95% ethyl alcohol, and 400 ml. of water. Separately, 6.2 grams of ceric sulfate is dissolved in water, and the two solutions are mixed together with vigorous agitation. The pH of the mixture is adjusted to 4.5 with nitric acid. The precipitated soap is recovered on a filter, washed free of sulfate ion, and dried at 55 C. It is pale yellow in color. Analysis shows a cerium content equivalent to approximately one-half of that required for complete reaction with the behenic acid.

The cerium behenate-behenic acid mixture is intimately dispersed in resinous binder solution by ball milling, a slightly larger molal amount of 4-methoxy-l-hydrox dihydronaphthalene is added, and the mixtureis applied to a transparent carrier and dried, all as described in connection with Example 1. The resulting colorless heatsensitive copy-sheet yields blue image-forming areas in the thermographic reproduction process and on momentary contact with the heated metal test bar.

Cenic stearate is equally as eifective as the eerie behenate-behenic acid mixture. The free behenic acid or other long-chain normally solid fatty acid is not essential but is found to improve the stability of the copy-sheet under high humidity storage conditions.

Example 3 Mercuric behenate is combined with methyl gallate by procedures as already described to provide an initially colorless stable coating which produces a brownish green image when the coated sheet is employed as a heat-sensitive copyapaper for thermographic reproduction. The metal ion is reduced to a lower valence state without visible change. The methyl gallate is oxidized to a visibly different compound. A similar color change occurs when methyl gallate in acetone is added to ammonium persulfate in water with gentle heating; a brownish yellow color is immediately produced.

Example 4 To a solution of 24 grams of eupric nitrate trihydrate in 500 ml. of water is added 14 grams of salicylic acid and 350 ml. of methyl alcohol, forming a clear solution. To this is next added sufficient sodiurn hydroxide solution to precipitate the cupric salicylate. The light green precipitate is recovered on a filter, washed and dried. It melts at 286 C. A 2.5 gram portion is dispersed in a solution of 2.5 grams of ethyl cellulose in 50 grams of acetone by vigorous shaking. Ten grams of the dispersion is next mixed with an equal weight of a solution in acetone of 4% methyl gallate and ethyl cellulose, and the mixture is coated on map overlay tracing paper at a coating thickness of 3 mils, and dried at room temperature. The resulting pale green colored sheet is converted to dark brown on momentary contact with a metal test bar at 150 C. and is useful as a heat-sensitive copypaper.

Example 6 Bismuth stearate is prepared by the rapid addition of hot sodium stearate solution in 1:1 ethanolzwater mixture to a 4% aqueous solution of bismuth sodium tartrate. The white precipitate is cooled, filtered, and dried under vacuum for 24 hours at 60 C. Ten grams of the soap is intimately dispersed in a solution of 3 grams of 6 polystyrene resin in grams of methylethylketone by prolonged milling in, the ball mill. To ten grams of the resulting suspension is next added 0.5 gram of malachite green leueo cyanide, and the resulting mixture is applied to paper and dried. The resulting sheet is pale green in color, rapidly converting to dark green-blue at C. on the test bar, and producing copies having good contrast when tested in the thermographic reproduction process.

Malachite green leuco'cyanide rapidly forms a dark green product on warming in solution with ammonium persulfate.

Example 7 Malachite green leuco cyanide and ferric stearate, suitably mixed and coated, provide a heat-sensitive. copysheet which converts from bull to blue-green in thermographic copying and on momentary contact with the metal test bar at 100 C.

What is claimed is as follows:

1. A heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals as herein described, comprising a thin flexible sheet material including a visibly heat-sensitive layer comprising (a) a normally solid salt of an organic acid anion and a readily reducible polyvalent non-ferrous base metal cation having a standard reduction potential greater than one-tenth volt, and (b) a cyclic organic reducing agent for said metal ions, having an active hydrogen atom attached to an atom which is selected from the class consisting of oxygen, nitrogen and carbon atoms and is directly attached to an atom of the cyclic ring, said reducing agent being further characterized as providing a distinct color change when added in dilute solution in water-miscible organic solvent to an equal concentration or" ammonium persulfate in water with momentary mild heating, said components'(a) and (b) being maintained in said layer in physically distinct relationship and being so selected and maintained as to be visibly chemically inter-reactive in an oxidation-reduction valence-change reaction on brief contact of said copy-sheet with a metal test bar at a conversion temperature within the approximate range of 90150 C.

2. A heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals as herein described, comprising a thin carrier web and a heat-sensitive coating thereon including (a) a film-forming binder, (b) a water-insoluble normally solid salt of an organic acid anion and a readily reducible polyvalent non-ferrous base metal cation having a Standard reduction potential greater than one-tenth volt, and (c) an aromatic organic reducing agent for said metallic ions, having an active hydrogen atom attached to an atom which is selected from the class consisting of oxygen, nitrogen and carbon atoms and is directly attached to an atom of the aromatic ring, said reducing agent being further characterized as providing a distinct color change when added in 5% solution in water-miscible organic solvent to an equal small volume of 5% solution of ammonium persulfate in water with momentary mild heating, said components (b) and (0) being maintained in said coating in physically distinct relationship and being so selected and maintained as to be visibly chemically inter-reactive in an oxidation-reduction valence-change reaction on brief contact of said copysheet with a metal test bar at a conversion temperature Within the approximate range of 90150 C.

3. A heat-sensitive unitary copy-sheet suitable for the preparation of right-reading high-contrast reproductions of differentially radiation-absorptive graphic originals by thermographic front-printing procedures, comprising in order a thin transparent carrier web, a heat-sensitive coating, and a ivisibly opaque protective coating, said heat-sensitive coating being capable on momentary contact of said copy-paper with a metal test bar at a conversion temperature within the approximate range of 90- 150 C. of being converted to a visibly distinct form having high contrast with said opaque coating, said heatsensitive coating comprising (a) a film-forming binder, (b) a water-insoluble normally solid salt of a higher fatty acid anion and a readily reducible polyvalent nonferrous base metal cation having a standard reduction potential greater than one-tenth volt, and (c) an aromatic organic reducing agent for said metallic ions, having an active hydrogen atom attached to an atom which is selected from the class consisting of oxygen, nitrogen and carbon atoms and is directly attached to an atom of the aromatic ring, said reducing agent being further characterized as providing a distinct color change when added in 5% solution in water-miscible organic solvent to an equal small volume of 5% solution of ammonium persul-fate in water with momentary mild heating, said components (b) and (0) being maintained in said coating in physically distinct relationship and being so selected and maintained as to be visibly chemically inter-reactive in an oxidation-reduction valence-change reaction on brief contact of said copy-sheet with a metal test bar at a conversion temperature Within the approximate range of 90-150 C.

4. A heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals as herein described, comprising a thin flexible sheet material including a visibly, heat-sensitive layer comprising (a) a normally solid water-insolubie ceric salt of a higher fatty acid, and (b) an aromatic organic reducing agent having an active hydrogen atom attached to an atom Which is selected from the class consisting of oxygen, nitrogen and carbon atoms and is directly attached to an atom of the aromatic ring, said reducing agent being further characterized as providing a distinct color change when added in dilute solution in Water-miscible organic solvent to an equal concentration of ammonium persulfate in water with momentary mild heating, said components (a) and (b) being maintained in said layer in physically distinct relationship and being so selected and maintained as to be visibly chemiically inter-reactive in an oxidation-reduction reaction on brief contact of said copy-sheet with a metal test bar at a conversion temperature within the approximate range of 90-l50 C.

5. A heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals as herein described, comprising a thin flexible sheet material including a visibly heat-sensitive layer comprising (a) a water-insoluble normally solid salt of a high molecular weight organic acid anion and a readily reducible polyvalen-t non-ferrous base metal cation having a standard reduction potential greater than onetenth volt, and (b) a solid aromatic hydroxy reducing agent capable of undergoing a distinct color change when added in dilute solution in Water-miscible organic solvent to an equal concentration of ammonium persulfate in Water with momentary mild heating, said components (a) and (11) being maintained in said layer in physically 7 ponents (a) and ([1) being maintained in said layer in physically distinct relationship and in condition for visible chemical inter-reaction in an oxidation-reduction valencech-ange reaction on brief contact of said copy-sheet with a metal :test bar at a conversion temperature Within the approximate range of 90l50 C.

7. The copy-sheet of claim 6 in which the ce-ric salt is ceric be'henate.

8. The copy-sheet of claim 6 in which the eerie salt is ceric stea-rate.

References Cited in the file of this patent UNITED STATES PATENTS 1,844,199 Bicknell et 'al. Feb. 9, 1932 2,504,593 Schoen Apr. 18, 1950 2,663,654 Miller et al Dec. 22, 1953 2,663,656 Miller et al. Dec. 22, 1953 2,663,657 Miller Dec. 22, 1953 2,910,377 Owen Oct. 27, 1959

Claims (1)

1. A HEAT-SENSITIVE COPY-SHEET SUITABLE FOR THE THERMOGRAPHIC REPRODUCTION OF DIFFERENTIALLY RADIATION-ABSORPTIVE GRAPHIC ORIGINALS AS HEREIN DESCRIBED, COMPRISING A THIN FLEXIBLE SHEET MATERIAL INCLUDING A VISIBLY HEAT-SENSITIVE LAYER COMPRISING (A) A NORMALLY SOLID SALT OF AN ORGANIC ACID ANION AND A REDILY REDUCIBLE POLYVALENT NON-FERROUS BASE METAL CATION HAVING A STANDARD REDUCTION POTENTIAL GREATER THAN ONE-TENTH VOLT, AND (B) A CYCLIC ORGANIC REDUCING AGENT FOR SAID METAL IONS, HAVING AN ACTIVE HYDROGEN ATOM ATTACHED TO AN ATOM WHICH IS SELECTED FROM THE CLASS CONSISTING OF OXYGEN, NITROGEN AND CARBON ATOMS AND IS DIRECTLY ATTACHED TO AN ATOM OF THE CYCLIC RING, SAID REDUCING AGENT BEING FURTHER CHARACTERIZED AS PROVIDING A DISTINCT COLOR CHANGE WHEN ADDED IN DILUTE SOLUTION IN WATER-MISCIBLE ORGANIC SOLVENT TO AN EQUAL CONCENTRATION OF AMMONIUM PERSULFATE IN WATER WITH MOMENTARY MILD HEATING, SAID COMPONENTS (A) AND (B) BEING MAINTAINED IN SAID LAYER IN PHYSICALLY DISTINCT RELATIONSHIP AND BEING SO SELECTED AND MAINTAINED AS TO BE VISIBLY CHEMICALLY INTER-REACTIVE IN AN OXIDATIN-REDUCTION VALENCE-CHANGE REACTION ON BRIEF CONTACT OF SAID COPY-SHEET WITH A METAL TEST BAR AT A CONVERSION TEMEPRATURE WITHIN THE APPROXIMATE RANGE OF 90-150*C.

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