US3260612A

US3260612A - Thermographic recording process and heat-sensitive elements therefor

Info

Publication number: US3260612A
Application number: US211927A
Authority: US
Inventors: William J Dulmage; Sterling S Sweet; William A Light
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1961-07-14
Filing date: 1962-06-27
Publication date: 1966-07-12
Anticipated expiration: 1983-07-12
Also published as: US3387974A; DE1471664A1; MY6900127A; MY6600135A; NL294592A; AT290295B; GB1015926A; BE645645A; NL294591A; CH449065A; GB1015925A; CH428804A; DE1421406A1; DK115123B; MY7400257A; FR95952E

Description

THERMOQRL HEAT-SENSITIVE ELEMENTS THEREFOR Filed June 2'7, 1962 3 Sheets-Sheet 1 Fig.1

G24 Fri/ VE/Gl/VAL 1 [NI E/JEEP BAD/A T/ON JOUECE WilliamJDulma e Slerling S. S wee WilliamA.Lighf IN VEN TORS y 12, 1966 W.'-J. DULMAGE ETAL 3,260,612

THERMOGRAPHIC RECORDING PROCESS AND HEAT-SENSITIVE ELEMENTS THEREFOR 5 Sheets-Sheet 2 Filed June 27, 1962 .igzZ

m Mm n M a 2 Hz-wr swan/vs EL EMF/V T 63 A PH/C BIG/Ml- Nilliam J Dullnage ,S'terlingS. Sweet WilliamA.Light IN VEN TOR3 y 1966 w. J. DULMAGE ETAL 3,

THERMOGRAPHIC RECORDING PROCESS AND HEAT-SENSITIVE ELEMENTS THEREFOR Filed June 27, 62 6 Sheets-Sheet 3 POROUS OUTER LAYER HEAT SE'NJITI V5 LAYER JUPPORT WilliamJDulmage fi /ling 5. Sweet William A.Lighi INVENTORS ATTORNEYS United States Patent 3 260 612 THERMOGRAPHIC RlECdRDING PROCESS AND HEAT-SENSITIVE ELEMENTS THEREFOR William J. Dulmage, Sterling S. Sweet, and William A.

Light, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed June 27, 1962, Ser. No. 211,927 18 Claims. (Cl. 117-25) This is a continuation-in-part of our copending application Serial No. 124,037, filed July 14, 1961, now abandoned.

This invention relates to improved thermographic materials and processes. More particularly, the invention relates to thermographic methods and materials in which a latent image can be produced on a heat-sensitive layer, and after activation can be either transferred or developed in situ at a temperature lower than the activating temperature.

In the past, there have been two rather widely used general types of thermogr-aphic processes. The first of these comprises direct copying processes in which a visible image is produced directly on a heat-sensitive element which then becomes a final copy. This 'has the disadvantage that the final copy remains heat-sensitive in the unactivated background area and is subject to subsequent activation. Usually the copy obtained is on a thin, coated heat-sensitive sheet that does not stand up well under ordinary use.

A second type of process now in general use comprises preferentially heating only the image areas of a heatsensitive layer of a waxy material to melting temperature, and while the image areas are preferentially heated, transferring melted Wax from the image areas to a receiving sheet. Wax in the lower temperature background areas is not melted, and so does not transfer. In a typical process of this type, a 3-ply combination comprising an original document, a receiving sheet, and a heat-sensitive matrix, is exposed to infrared radiation which heats the printed areas in the document. This then melts the material in corresponding image areas of the matrix. During exposure, the receiving sheet must be in contact with the heat-sensitive material in order to effect a transfer of material from the matrix while its image areas are preferentially heated above the melting point of the heat-sensitive material. To obtain a right-reading copy in processes of this type, the receiving sheet is usually placed between the original and the heat-sensitive layer. Because the receiving sheet must be between the document in which heat is generated, and the heat-sensitive material to which the heat must be conducted, there is some thermal diffusion through the receiving sheet, and this causes considerable detriment to image definition. Because the transfer material may harden before the receiving sheet and the matrix can be separated, the receiving sheet often has to be broken away or fractured from the residual resin or wax layer of the heat-sensitive element. This breaking away results in uneven density and poor definition in the final copy due to irregular breakage characteristics.

Processes of the types mentioned above are described in a number of US. and foreign patents, for example US. 2,808,777, October 8, 1957, and 2,769,391, Novern ber 6, 1956. Normally, only one copy is made from each heat-sensitive element in these previously used processes.

An object of the present invention is to provide novel thermographic materials and methods which overcome many of the disadvantages of prior-art methods and offer advantages not heretofore available in thermographic processes and materials. Another object of the invention is to provide thermographic materials and processes employing a heat-sensitive layer in which image areas can be activated at a temperature well above room temperature .and after such activation can subsequently be either deice veloped in the image areas of the heat-sensitive layer or transferred to a receiving surface from image areas of the heat-sensitive layer, while the entire heat-sensitive element is at a uniform temperature substantially below the original activation temperature. Certain embodiments of the invention provide a dry process for reproduction of multiple copies from a single activated heat-sensitive element. The copies can be on regular white stationery or the like. The invention provides means by which a heatsensitive transfer matrix can be activated with its heatsensitive layer in direct face-to-face contact with the document being copied, thus avoiding thermal diffusion and obtaining a well resolved latent image in the layer. Copies can be made from a thermographic element after activation without the need for preferential heating of the image areas during the development or transfer step of the process. The present invention enables preparation of multiple copies from a single thermographic heat-sensitive element. It enables production of prints of excellent quality and good stability, and at materially reduced costs per copy.

These and other objects and advantages will appear from the following detailed description with reference to the accompanying drawings:

In the drawings:

FIG. 1 is a schematic elevational view showing a method of producing an image directly on a heat-sensitive element of the present invention;

FIG. 2 is a schematic elevational view of a method of exposing a heat-sensitive element of the present invention;

FIG. 2A illustrates a method of transfer of material from the image areas of the exposed heat-sensitive element of FIG. 2 to a receiving copy sheet; and

FIG. 3 is a schematic elevational view showing a tandem arrangement for exposure of a heat-sensitive element with subsequent transfer of the image areas thereof to a receiving copy sheet.

FIG. 4 is a schematic cutaway view of a heat-sensitive element embodying certain preferred embodiments of the invention.

The novel heat-sensitive element according to the invention comprises a support, usually a flexible backing such as paper, on which is coated a layer of thermoplastic material in a state of partial or complete crystallization. In this state, the thermoplastic material is substantially non-tacky, non-viscous, and dry at ambient temperatures. When heated to an original tackifying temperature well above room temperature, the material in this layer undergoes transition to an amorphous state and thereafter, for a substantial period, has a tackifying temperature substantially below the original tackifying temperature. By selectively heating only image areas in the heat-sensitive layer to a temperature above the original tackifying point, these image areas are activated, and after activation the material in these areas can subsequently be tackified at a substantially lower temperature while the unactivated background areas remain non-tacky at this lower temperature. In various embodiments of the invention the tackified image area can be developed directly on the heat-sensitive element by adhering powders having optical density to the tackified areas; or the tackified material can be transferred from the image areas to a receiving surface, and then developed on the receiving surface, and then developed on the receiving surface while still tacky; or, if the tacky material in the activated areas of the heatsensitive layer has optical density, it can be transferred from the image areas to a receiving surface to produce a printed image on the receiving surface. In all of these embodiments, the development or transfer step can be done after the activation step without the need for any preferential heating of the image areas during the development or transfer step.

Thermoplastic compositions useful in the heat-sensitive elements of the present invention have the characteristic property of remaining in a state having a reduced tackifying temperature for a substantial time after once being heated to the original tackifying temperature. The thermoplastic materials most preferred for making the heat-sensitive thermoplastic layer are polymer-containing materials having this property.

A great variety of polymers are available for making the thermoplastic material of the heat-sensitive layer. Generally, the polymer-containing thermoplastic materials useful in the invention can be divided into two general types: (a) those in which the polymer component itself is partially or completely crystallized (of course, a partially crystallized mixture of amorphous and crystalline polymers can be used) and (b) those in which the polymer component is substantially amorphous but non-tacky up to activation temperature, and non-polymeric crystalloid is the crystallized component. This crystalloid melts at the activating temperature and blends with the amorphous polymer to make a mixture having a lower tackifying temperature.

The heat-sensitive layer of the heat-sensitive element comprises a coating of one of these thermoplastic materials developed to a non-tacky state of complete, or at least partial crystallization. In this state of complete or partial crystallization, the material has a tackifying temperature substantially higher than the tackifying temperature of the same material in completely amorphous state.

The property of remaining tacky at lower temperatures after activation is accounted for by delay of recrystallization after activation. While crystallization will occur, at least to some extent, in most of the activated amorphous materials at nearly any temperature between glass transition temperature and the first-order transition temperature, it is a characteristic of these materials that the rate of recrystallization of the amorphous material at temperatures below the original tackifying temperature of the heat-sensitive layer is sufliciently slow that for a substantial period of time after activation, the activated material will be in a state having a tackifying point substantially lower than the original tackifying temperature. With most of these materials even if recrystallization should proceed to such an extent that the activated areas become non-tacky, these activated areas can usually be retackified at a temperature substantially below the original tackifying temperature. For example, a heat-sensitive layer having an original tackifying temperature of 120 C. might be activated in the image areas, and after some time material in these areas might partially recrystallize to a non-tacky state at room temperature. As with most of the thermoplastic materials of the types contemplated by this invention, these activated areas could be retackified at temperatures well below 120 C., say at 70 or 80 C, This could be done, for example, by calendering the heat-sensitive element through rolls heated to the lower tackifying temperature, or by any other means for uniformly heating the element to the lower tackifying temperature. The background areas in the heat-sensitive layer remain unactivated at such lower temperatures.

The original tackifying temperature of some partially crystallized heat-sensitive layers can be increased by annealing. By the term annealing we refer to the process of relieving intercrystalline stresses and the ripening and perfection of the crystalline phase of the orystallizable polymers. Such treatment can cause a substantial increase in the melting point of polymers. Crystallization may be promoted in many ways such as heating or stretching so as to orient, or cooling to an efficient nuclea-ting temperature by passing through cold calender rolls followed by heating, etc. or by treating with solvent or solvent v-ap-or. Any of these treatments Will affect the tackifying point.

The annealing may be done with partially crystalline polymeric films like the heat sensitive coatings of our invention, by heat-ing the coated element above the glass transition temperature of the thermoplastic composition.

The annealing is started at a temperature below the initial tackifying temperature and the heat treatment temperature may be raised fairly rapidly since the annealing process immediately begins to raise the melting point. Consequently the highest temperature during annealing may be well above the initial tackifying point but at least a few degrees below the ultimate or highest melting point characteristic of the crystalline polymers. The total annealing, or at least that much required to give the matrix the desired tackifying temperature, may be completed in less than a minute in some cases or it may require several hours in others.

It is advantageous to anneal a crystalline polymer-containing heat-sensitive layer during manufacture to a crystalline state having an original tackifying temperature higher than the tackifying temperature of the highest state of crystallization that the polymer will attain at temperatures below 50 C. upon recrystallization after being once activated by transition to the amorphous state. A matrix with such an annealed layer can be re-activated, even after material in the activated image areas has recrystallized at room temperatures, simply by uniformly heating the matrix to a temperature below the original tackifying temperature of the heat-sensitive layer, but above the tackifying temperature of the recrystallized material in the image areas.

The annealing process can be used to reclaim used, that is, exposed matrices from which the number of prior transfers made has been sufficiently small not to have re-- moved all of the heat-sensitive coating in the image areas. By .re-annealing this coating, the image areas slowly recrystallize to their initial crystalline state, and again he'- come identical to the background areas. Then the whole matrix can be put to use exactly as a new (unused) matrix.

In order to prevent unintentional activation of the heatsensitive layer by extremely high climatic temperatures, we prefer to use a heat-sensitive layer with an original tackifying temperature above 50 C. For use in most of the thermographic process machines now in use, which are designed to produce activating temperatures in a range between about 50 C. and 200 C., a heat-sensitive layer would be chosen with an original tackifying temperature in that range. In some processes, it is convenient to develop or transfer the material of the activated image areas at usual room temperature and in such cases, a heat-sensitive material would be chosen having a tackifying temperature after activation at least as low as about 15 C. Development or transfer of the activated mate-rial must be done while the heat-sensitive element is at a temperature at least as high as the tackifying temperature of the activated material in the image areas, but below the original tackifying temperature of the unactivated heat-sensitive material in the background areas.

Below glass transition temperature, amorphous thermoplastic materials become non-viscous and non-tacky. It will be obvious, since the thermoplastic mate-rial in the heat-sensitive layer must, after activation, be tackifiable at a temperature substantially below the original tackifying temperature, that the material of the heat-sensitive layer must have a glass transition temperature after activation that is substantially below the original tackifying temperature of the heat-sensitive layer.

By tackifying temperature, as the term is used in this specification, is meant the lowest temperature (or temperature range) at which the material in the state being described .will become tacky. For a completely crystal-lized thermoplastic polymer composition the tackifying temperature is the first-order transition temper-ature, and for a completely amorphous thermoplastic polymer composition, it is the second-order transition temperature, sometimes called glass transition temperature. In a composition that is partly amorphous and partly crystallized, the tackifying temperature will be a pseudo- :first-order transition temperature, more or less below the real first-order transition temperature depending upon the degree of crystallization. When a non-polymer crystalloid melts and blends with an amorphous polymer the glass transition temperature is lowered, as is the tackifying temperature. Because the same term is used herein with reference to thermoplastic compositions in all three states, amorphous, crystallized, and partly crystallized including partly crystallized compositions containing amorphous polymers and non-polymeric crystalloids, the general term tackifying temperature is most appropriate.

The thin, crystalline, heat-sensitive, polymeric films on which the utility of our heat-sensitive elements depends can be prepared using either crystalline or amorphous polymers chosen from a wide variety of linear, film-forming polymers and copolymers, such as polyvinyl derivatives, polyacrylic derivatives, polyesters, polyamides, polye-ster-amides, polycarbonates, polyethers (e.g., polyglycols), polyurethanes, polyureas, and the like.

The following are representative examples of amorphous polymers which can be used in admixture with nonpolymeric crystalloids to prepare the heat-sensitive layers of the present invention:

1) Atactic polystyrene. (2) Poly(vinyl acetate), medium-viscosity grade. (3) Butadiene, styrene copolymer of 45:55 ratio, (Goodyear Tire and Rubber Co.s Pliolite S-7.

(4) Poly(alkyl acrylates), low-and medium-viscosity grades, such as polyethyl acryl-ate, polypropyl acrylate, polybutyl acrylate etc.

(5) Poly(alkyl methacrylates), lowand mediumviscosity grade, such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, etc.

(6) Poly(terpenes), softening point range 70-ll0 C. (Schenectady Resins Co.) (Pennsylvania Chemical Co.)

(7) Poly(vinyl butyral) and other poly-acetals of lowviscosity grade.

(8) Cellulose butyrate.

(9) Cellulose acetate butyrate, low-viscosity grade.

(10) Polyethylene terephthalate, polyethylene isophthal-ate mixed copolymer of about 60:40 ratio (Goodyear Tire and Rubber Co.s Vitel PE101X).

(11) Vinyl chloride, vinyl acetate copolymer of about 87: 13 ratio (Union Carbides Vinylite VYLF).

(12) Phenol-formaldehyde resins (noncrosslinked), softening point range 70110 C. Novolacs).

The heat-sensitive layers of our invention can be coated from crystalline polymeric compositions comprising a combination of an amorphous, linear, filmforming polymer, representing for example one of the -above classes and a nonpolymeric crystalloid to yield a crystalline composition having tackifying point, glass transition temperature, and melt viscosity within the ranges specified for our heat-sensitive compositions. The useful nonpolymeric crystalloids are compounds which melt in the range of 50 to 200 C. and are compatible with the amorphous polymer at the fusion point of the composition, and on cooling into the range below the fusion point but above the glass transition temperature of the polymer-crystalloid combination, form an unstable amorphous homogeneous composition exhibiting surface tackiness as long as the temperature remains between the tackifying temperature and the glass transition temperature of the composition and until the crystalloid recrystallizes. Suitable nonpolymeric crystalloids can be chosen from the following representative examples, the specific composition and the ratio of polymer to crystalloid depending on the properties of the polymer with which it will be admixed and the temperature range, the desired tackifying point, glass transition point, melt viscosity, rate of crystallization and the like: Pentaerythritol tetraisobutyrate; 2,6 ditert-buyl-4-methylphenol; eugenol benzoate; triphenyl orthoformate; benzoin acetate; N- pentyl-1,8-naphthalimide; bis(o-methoxyphenyl) carbonate; eugenol cinnamate; 2,5,5-triphenyl-1,3-dioxalan-4- (Union Carbides one; bis(benzyloxy) diphenylmethane; 4-cyclohexylphenyl benzoate; 4-biphenylyl benzoate; pentachlorophenyl benzoate; ethyl anthraquinone-Z-carboxylate; camphor, and in fact any nonpolymeric crystalline compound melting between 50 and 200 C. which, on melting, will be miscible with the amorphous polymer and will cause a reduced tackifying temperature for mixture.

Alternatively, our heat-sensitive, crystalline, polymeric compositions can comprise crystalline polymers, chosen for example from one of the previously mentioned classes of linear, film-forming, polymers and copolymers.

Representative examples of crystalline polymeric materials useful in the present invention are given in Table I below along with the tackifying point, melt-viscosity at the tackifying point, and intrinsic viscosity for the polymers. The tackifying point shown in Table I is approximately the first order transition temperature of the pure polymer. In the heat-sensitive layerthe tackifying temperature may be modified, as by developing only partial crystallization in the layer, for instance. Melt viscosities shown are at the tackifying temperatures shown. In the table, the letter A indicates a melt-viscosity in the range from about 50 to about 500 poises, whereas the letter B indicates a melt-viscosity in the range from about 500 to about 100,000 poises. In Table I the intrinsic viscosity is given as a measure of the degree of polymerization of the polymer. Intrinsic viscosity, accordingly, also is a reflection of the molecular weight of the polymer; that is to say, as intrinsic viscosity goes up, the molecular weight of the polymer is also higher, and likewise, where the intrinsic viscosity goes down, the

molecular weight of the polymer would also be correspondingly lower. As recorded in Table I, intrinsic viscosity was measured according to the formula:

limit 1 C as C approaches zero wherein 71 is the viscosity of a dilute phenol-chlorobenzene-(lal) solution of the polymer divided by the viscosity of the phenol-chlorobenzene mixture per se measured in the same units at the same temperature, and C is the concentration in grams of the polymer per cc. of solution.

Typical polymers representative of those suitably employed in the present invention include the following:

TABLE I Melt Tacki- Viscosity Heat-Sensitive Component fying at Intrinsic Point Tacki- Viscosity C.) tying Point Poly(butene-l) 90 B 0. 24 Poly(pentene-l) 80 B 0. 26 Poly(tert-butyl acrylate) (stereo- 197 B 0. 58

symmetric). Poly (tetr amethylene carbonate). i i 60 B 0. G6 Poly(pentarnethylene carbonate)- 72 B 0. 66 78 A 0. 29 Poly (2,Z-dimethyltrirnethylene 80 B 0. 35 suecinate). 82 B 0. 45 Poly (1,4-cyclohexanedimethylene A 0. 24

suceinate Poly(1,icyelohexanedimethylene 115 A 0. 30

adipate). Poly (1 ,4-cyclohexauedimethyleue 115 B 0. 45

adipate Poly (ethylene succinate) 100-102 B 0. 40 Poly (monomethyleue succinato) 65 A 0. 39 Poly (pentamethylene 136-139 B 0. 52

terephthalate) Poly (ethylene 1 ,4-cyolohexauedicarboxylate). -171 A 0. 30 Poly(ethylene glycol) 60-63 A (6,0007,500 Incl. wt.)

Our thermographic element comprises a heat-sensitive coatable composition containing a polymeric component coated on a suitable support in a well-known manner, such as extrusion, hopper coating, dip coating, doctorblade coating, etc. Suitable supports include paper, e.g., grease-proof paper, such as Folio Transparent Copy Greaseproof Paper sold by the Rhinelander Paper Com- Oil Orange 2311, .Ultra Blue 9775 A, and A20 Oil Blue Black B. Other pany, glassine, vegetable parchment, etc.; film base, e.g., cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, etc.; polyester film base, e.g., polyethylene terephthalate; etc.

In preparing the composition for coating on a support, it is the usual practice to dissolve the components of the composition in a suitable solvent. Solvents to which we refer can include a number of hydrocarbon solvents, for example, benzene, toluene, etc.; ketones, such as acetone, Z-butanone, 4-methyl-2-pentanone, etc.; chlorinated hydrocarbons, such as methylene chloride, ethylene chloride, carbontetrachloride, and the like.

To the polymer-containing composition can also be added addenda to accomplish a variety of purposes, such as agents to modify the flexibility of the layer, to modify the surface characteristics, to impart color to the layer, to modify the adhesivity of the heat-sensitive layer to its support, and solid particle extenders to decrease the amount of polymer required. The above addenda may, without particularly affecting crystallization, have beneficial effects to both surfaces of the heat-sensitive layer, for example, increasing its adhesion to its support while on the exterior surface enabling intimate contact between it and the original document during exposure, while preventing optical contact.

Representative examples of added addenda include tricresyl phosphate, poly(alkyl acrylate), dibutyl fumarate, menthol, diethyl phthalate, eugenol, isoeugenol, dibutyl phthalate, eugenol methyl ether, isoeugenol methyl ether, clay, glass beads, ground quartz, crosslinked poly(methyl methacrylate) beads, tritanium dioxide, zinc oxide, and infrared transparent dyes. Suitable coloring addenda of this latter type include the following materials available from the Allied Chemical and Dye Corporation, for example, Azo Oil Black, Oil Black BT, Alizarin Blue G.R.L. Base, Oil Scarlet 60, Oil Red GRO, Oil Red 0, Plasto Oil MGS, Isosol Black,

coloring addenda include Nile Blue Hydroxide, Methyl Red, Prussian Blue Pigment, Iron Oxide, etc.

In preparing the heat-sensitive elements according to this invention, a single coating of the polymer-containing composition is normally made onto the support at a thickness to give a predetermined thickness when dried. Alternatively, the layer can be built up of two or more thin coats. The dry thickness of the heat-sensitive layer can vary over a wide range. For example, a suitable coating thickness can be in the range from about 0.05 to about 2.0 mils. A preferred coating thickness was found to be in the range from about 0.1 to about 1.0 mil. When extender particles are introduced for any of the priormentioned purposes, for example to modify the surface or the bulk properties of the heat-sensitive layer, the thickness measurements do not include the solid particle extenders since some of the particles normally protrude a small distance above the surface of the heat-sensitive composition.

An especially convienient method for preferentially heating image areas in the heat-sensitive element to activation temperature is to contact the heat-sensitive element with a document to be copied and, while the two are in contact, to expose the document to infrared radiation which generates heat in the printed areas of the document. This generated heat is then transmitted to the corresponding areas on the heat-sensitive element and raises the temperature of those areas to activation temperature. It is necessary that a heat-sensitive element for use in infrared exposure processes must contain no infrared-absorbing materials, or at least no materials that would generate enough heat during the period of infrared radiation to raise the temperature of the background areas in the heat-sensitive layer to activation temperature. Such elements are defined herein by the term infraredtransparent. In the exposure of heat-sensitive elements to infrared radiation, several variations may be employed in the manner in which the elements and the original document are assembled and exposed. For example, the original document can be placed on the reverse side of the heat-sensitive element with graphic portions of the document in contact with the support side of the element. In an assembly of this type, radiation would be directed onto the side of the element having the heat-sensitive coating. An exposure of this type is referred to as bi-reflex exposure. Another method, called reflex exposure, comprises placing the graphic portions of the original in contact with the heat-sensitive surface of the element. In this case, the infrared radiation is usually directed onto the support side of the heat-sensitive element. A third method called direct exposure comprises placing the heat-sensitive layer in direct contact with the reverse side of the document. Radiation is then directed onto the graphic side of the original. In exposing a two-ply combination of heat-sensitive element and original document, it is sometimes advantageous that the support for the element be heat-insulated so that heat transmitted to the element from the image area of the document during exposure will not be dissipated through the support. Heat-insulating supports are sometimes advantageous in direct exposure methods. Other heatinsulating means may be used if the support does not provide sufficient insulation. Methods of thermographic exposure are well known in the art and are described in a number of US. and foreign patents, for example, U.S. Patent No. 2,740,896, April 3, 1956, and 2,769,391, November 6, 1956.

Suitable radiant energy for exposing the heat-sensitive elements in methods of document reproduction according to the present invention can be obtained from a number of sources, for example, a carbon arc, tungsten filament lamp, overvoltaged standard infrared ray lamp, etc. Normally, it is advisable with most sources of infrared radiation to employ suitable reflectors, filters, etc., so that radiations of suitable wavelength and intensity are obtained in a manner to give sufficient radiation in an instantaneous manner. A convenient source of infrared radiation comprises a standard 500-watt infrared bulb with internal reflector, operated under overload conditions of at least about 800-watt input, and at a distance of from about one-half to about three inches from the printed graphic original. Other sources having a high output of radiant energy, particularly wavelengths of less than 25,000 A. and capable of uniformly irradiating larger areas can also be used.

Illustration of the invention is given in FIG. 1 in which the graphic original 1 is placed in contact with the heatsensitive element 2 wherein the graphic portions of said original are in contact with the support of said element. The 2-ply combination is passed behind the drag roll 3 and given a bi-reflex exposure from an infrared radiation source 4 while pressed against a hollow drum 5. The hollow drum or main roller is usually rubber covered and provided with a clamp (C) for holding the heatsensitive element and graphic original. The infrared exposure produces tackiness in the heat-sensitive layer in the areas corresponding to the image areas of the original. The element is then developed by dusting with a developing powder 8 as carried out by developing roll 6 and feed roll 7. These rolls effectively brush the tackified image areas of the heat-sensitive element 2 with the developing powder. The first clean-up brush 9 and the second clean-up brush 10 remove the powdered developer 8 from the nonimage areas of the heat-sensitive layer. Suitable developer powders can include practically any pulverizable powder having optical density, for example, lycopodium powder, talcum powder, sulfur, carbon dust, aluminum bronze powder, etc. Powdered dyes can also be used or a resin can be used which may be dyed any color desired. For example, Vinsol resin or gum copal may be melted with a small proportion of nigrosine dye,

cooled and pulverized to give a dark-colored powder suitable for use in the invention. Other dyes which can be used comprise such dyes as Rhodamine, Victoria Blue, Victoria Green, Crystal Violet, Nigrosine, Methyl Violet, etc.

It will be apparent to those skilled in the art that the heat-sensitive elements of the present invention can be used in thermographic process of the present type to produce lithographic masters, hectographic masters, etc.

In FIG. 2 a heat-sensitive element 2 is placed in contact with a graphic original 1 with the printed characters of the original in contact with the heat-sensitive surface of said element and passed into contiguous relationship with an infrared transparent carrier belt 3a with the copying element being on the exposure side of said original 1. Exposure is then given by an infrared radiation source 4 to produce tackified areas in the heatsensitive layer of element 2 corresponding to the image areas of the original 1.

Rollers

5, 6, 7 and 8 afiord carrier means past the infrared radiation source 4. In FIG. 2a the exposed heat-sensitive element 2 is placed with the heat-sensitive layer in contact with a copying sheet 9 and passed between

pressure rollers

10 and 11 past deflector means 12 to produce a right-reading copy of the graphic original 1 in the copying sheet 9. The time elapsed, after exposure and before transfer as illustrated in FIG. 2a, can vary widely, as pointed out previously, depending upon the compostion employed in the heat-sensitive layer of element 2. According to the invention, repeated transfers can be made from the exposed element 2 without requiring re-exposure. The number of copies to be obtained from a single exposure will depend largely upon composition of the heat-sensitive layer of element 2, the heat-sensitive polymer incorporated therein, total time involved in the transfer series, type of equipment used, etc.

It will be apparent that a process of the type described in the above paragraph is also suitable for preparing stencils, printing masters, for example, lithographic, hectographic, and photomechanical masters. In the latter case a transfer of a solvent, or etching resist, is made to a suitable support.

In FIG. 3 the heat-sensitive element 2 is carried on a supply roll and passed in contact with a graphic original 1 wherein the heat-sensitive layer of said element is in contact with the graphic side of said original. The 2-ply combination is then passed over roller 6 past an infrared radiation source 4 to produce a latent thermo graphic image in said heat-sensitive element 2. By a tendem arrangement, the heat-sensitive element 2 after exposure is passed between pressure transferring rollers 7 and 8 in contact with a strip of copying paper 9. Guide roller maintains continuation of movement to afford opportunities for the windup of the copying material. An adequate supply of copy or receiving paper is supplied by supply roll 11.

The invention will now be illustrated by way of the following examples, but there is no intention of being limited thereto.

Example 1.-A heat-sensitive element of the present invention was prepared as follows for use in a directdevelopment process.

A 10 percent solution of a heat-sensitive component, poly(2,2-dimethyltrimethylene succinate) having an inherent viscosity of 0.4 and a tackifying point of about 79 C., was prepared in acetone at 50 C. The solution was then doctor-blade coated at 2 mils thickness on a sheet of greaseproof paper (sold under the trade name Folio Transparent Copy Greaseproof Paper by the Rhinelander Paper Company). After coating, the element was then dried overnight at room temperature. After the solvent was removed from the coating by drying, the element was annealed for about 16 hours at 70 C.

After annealing, an original document was placed on the reverse side of the heat-sensitive element with the printed characters of the original in contact with the support of said element. The 2-ply assembly was then exposed by directing the infrared radiation onto the coated side of the element. The exposure comprised intense infrared irradiation using a standard 1000-watt tubular General Electric infrared bulb with elliptical reflector, operated under overload conditions, for example, from about 800 to 1460 watts and at a distance of about /2 inch from the exposing surface. During exposure, the radiation was absorbed by the printed characters of the original and converted into heat. The heat being generated in the graphic areas of the original was transmitted to the heat-sensitive layer of said element, causing the layer to become tackified in those areas corresponding to the printed character areas of the original.

After exposure, the heat-sensitive element was separated from the graphic original and brushed with nigrosine dye as a developer. The tacky areas in the heat-sensitive layer of said element corresponding to the printed characters, i.e., image areas of the original, picked up the black developer to produce a copy of the original having good density and definition in the image areas. No further stabilization or fixing steps were required.

Example 2.A heat-sensitive element was prepared as follows for use in a transfer process.

Seven grams of a heat-sensitive component, poly(1,4- cyclohexanedimethylene succinate) having an inherent viscosity of 0.24 and a tackifying point of about 120 C., was added to 30 grams of an ethylene chloride solution containing 1 gram of A20 Oil Blue Black B Dye (purchased from the Allied Chemical and Dye Corporation). To the above was added a solid particle extender in the form of 2 grams of glass beads having an average diameter in the range from about 18 to about 4011.. The resulting mixture was heated to 60 C. and then doctor blade coated on a glassine support at a 3-mil thickness. After removal of the solvent from the coating by drying, the element was annealed at C. for 40 minutes. The final coating thickness was about 0.3 mil and contained about 0.9 gram of solids per square foot.

The resulting thermographic material was placed in contact with an original document so that the heat-sensitive layer of said material was in contact with the graphic portions of the original. The 2-ply assembly was then exposed through the support side of said material. The infrared exposing source was the same as that used in Example 1. The exposure produced tackey areas in said material corresponding to the image areas in the original. After exposure, the original and material of this example 'were separated.

The heat-sensitive element having tackiness in the image areas was then passed between pressure rollers exerting 30 pounds per linear inch of roller length and having a roller diameter of 2 /2 inches. In the pressure transfer, the coated side of the heat-sensitive element was in contact with a copy sheet of highly absorbent wet-strength paper. The transfer produced good blue-black image reproduction of the original on the copy paper. By repeating the transfer step, several high quality copies of the original were produced from the single thermographic exposure. The time which elapsed for the production of these several copies was approximately one minute.

Example 3.-A heat-sensitive element was prepared as follows for use in preparing a lithographic printing plate.

A 10 percent solution of a heat-sensitive component, poly(2,2-dimethyltrimethylene succinate), said component having an inherent viscosity of 0.34 and a tackifying point of 79 C. was prepared in a 4:1 mixture of acetone and methylene chloride. To the solution was added Azo Oil Blue Black B Dye at a concentration to give 5 percent (by weight) dye in the dry coated composition. The composition was then coated by suitable means on to a parchment paper support. After the solvent was removed from the coating by drying, the element was annealed at 70 C. for 6 hours to give a final coating thickness of about 0.1 mil.

The heat-sensitive element was exposed as in Example 2, i.e., the heat-sensitive layer thereof was in contact with the printed characters of an original. The infrared exposure produced tackified areas in the heat-sensitive layer of said element corresponding to the printed character areas of the original. After separation from the original, the exposed element was then passed between pressure rollers, as in Example 2, with the coated side of said element in contact with a hydrophilic-type paper support. The lithographic plate was swabbed with a conventional plateconditioning solution and placed on an offset printing press. About 150 copies were run off on the press. Each of the 150 copies was of outstanding quality, exhibiting black letter outlines and good definition with substantially no background strain. There appeared to be substantially no deterioration in quality toward the end of the run of 150 copies.

Example 4.A heat-sensitive element of the present invention was prepared as follows for use in preparing a spirit duplicating master.

A heat-sensitive element of Example 1 was exposed as in Example 2. After exposure and separation from the original, the heat-sensitive element was brushed lightly with powdered methyl violet dye as a developer. The tacky areas of the exposed element corresponding to the image areas of the original document picked up the colored developer and very good density and definition was obtained in the tacky areas. The resulting product was then used as a spirit duplicating master in a conventional process wherein a spirit duplicating copy paper, dampened with methanol, was brought into contact with the duplicating master with slight pressure applied, for example, with a handroller. A methyl violet reproduction of the original document was obtained in the copy paper. Several high quality copies of the original were obtained by repeating the process.

Example 5.To prepare a heat-sensitive element of the present invention, 8.5 grams of isotactic poly(butene- 1) having an inherent viscosity of 0.24 and a tackifying point of 96 C. was dissolved in 50 grams of methylene chloride containing 0.5 gram of Oil Black ST Dye and 0.5 gram of glass beads having an average diameter of about 18 to about 40 This mixture was then coated at a wet thickness of about 3 mils on a strip of Folio Transparent Copy Greaseproof Paper. After the solvent was removed from the coating by drying, the element was annealed for 18 hours at 75 C. The resulting heatsensitive element 'was exposed in contact with an original document as in Example 2. The tacky areas produced in the heat-sensitive layer of said element resulting from the exposure were then pressed in contact with a paper copy sheet as in Example 2 to produce an excellent copy of the original. Several copies were obtained in like manner from a single exposure of the heat-sensitive element.

Example 6.To prepare a heat-sensitive element of the present invention 7.5 grams of a heat-sensitive component, poly(1,4-cyclohexanedimethyl adipate), said component having an inherent viscosity of 0.38 and a tackifying point of 92 C. were added to a solution comprising 2.5 grams of methyl violet dye in 5 grams of ethanol and 25 grams of ethylene chloride. The resulting composition was blended in a Waring Blendor for 5 minutes and then coated on a sheet of Folio Transparent Copy Greaseproof Paper with a doctor blade having a gap width of about 3 mils. After drying to remove the solvent from said coating, the element was annealed at 75 C. for 1 hour. The resulting thermographic material was given bi-reflex exposure as described in Example 1 to produce tacky areas in the heat-sensitive layer of said element corresponding to the image areas of the original. The heat-sensitive element having tackyagcas corresponding to the image areas of the original was then passed between pressure rollers with the coated side of said element in contact with a sheet of parchment copying paper. The rollers for use in the transfer process had a roller diameter of 2 /2 inches and exerted pounds pressure per linear inch of roller length. The resulting reverse-reading image was then used as a spirit duplicating master in a conventional process of this type wherein a spirit duplicating copy paper, dampened with methanol, was brought into contact with the master and subjected to slight pressure, for example, with a handroller. After pressure contacting, a methyl violet reproduction of the graphic original was obtained in the duplicating copy paper. By repeated transfer, approximately 25 copies of good quality were obtained from a single duplicating master.

Example 7.Another heat-sensitive element of the present invention for use in a transfer process was prepared by the addition of 95 grams of the condensation product of polymerized linoleic acid and a diamine (sold under the trade name Versamide 930 by General Mills), and 142 grams of benzoin acetate to 83 grams of isopropanol and 667 grams of benzene which contained 13 grams of Azo Oil Blue Black B Dye. The polymer of said composition had a tackifying point in the range from to C. and the benzoin acetate had a melting point of about 82 C.

After thoroughly mixing the above composition while holding at a temperature of about 50 C., the composition was doctor blade coated on a sheet of Folio Transparent Copy Greaseproof Paper at a thickness of about 2 mils. The coating was then dried to eliminate the tacky state. The crystallized coating was next overcoated with a 2-mil wet thickness aqueous layer of 5 weight percent of polyvinyl alcohol containing less than 0.1 weight percent of an aryl sulfonate surfactant. The overcoated element was dried at about 50 C. for 10 minutes. The purpose of a protective overcoat was to stabilize the heatsensitive element and to facilitate packaging, thermographic exposure and transfer. The resulting thermographic material was then exposed and a transfer to a paper copying sheet was made substantially as shown in Example 2 to produce a copy of the original having good quality, except that the receiver sheet was moistened with water prior to transfer and the rollers for use in the transfer process exerted 60 pounds pressure per lineal inch of roller length.

Example 8.-A heat-sensitive element of the present invention with a rapid rate of crystallization was prepared as follows for use in the integrated rapid transfer unit of FIGURE 3.

To 20.3 grams of a heat-sensitive component, poly(1,4- cyclohexanedimethyl adipate) having an inherent viscosity of 0.36 and a tackifying point of about 115 C., in 75 grams of ethylene chloride, were added 1.25 grams of Azo Blue Black B Dye, 2.5 grams of glass beads (18- 40 and 1 gram of poly(ethyl acrylate) as flexibilizer. The resulting dispersion was coated on Folio Transparent Copy Greaseproof Paper. After coating, the element was dried to yield a coating of 0.9 g./ft. After the sol vent was removed from the coating by drying, the element was annealed for about one hour at 80 C.

After annealing, the resulting thermographic material was placed in contact with an original document and the 2-ply assembly was then exposed and the tacky image areas were transferred rapidly to a third (receiving) sheet as shown in FIG. 3. The transfer operation was begun within 3 to 5 seconds after exposure and completed within the subsequent 5 to 7 seconds. A copy of excellent quality was obtained.

With this coating, .a delay of the transfer operation to 25 to 30 seconds after exposure produces an illegible copy.

Example 9.A heat-sensitive element of the present invention for use in a transfer process was prepared by coating onto Folio Transparent Copy Greaseproof Paper, a composition consisting of 9.0 grams of a heat-sensitive component, poly( 1,4 cyclohexanedimethylene adipateazelate [3:1]) having an inherent viscosity of 0.42 and a tackifying point of about 92 C., 1.0 gram of Isosol Black Dye, and 30 grams of ethylene chloride. After coating, the element was dried at 80 C. to yield a coating of 1.1 g./ft. This heat-sensitive element was overcoated with a 2 /2 weight percent solution of medium viscosity carboxymethyl cellulose to form a protective overcoat, such as the one described in Example 7. The overcoat was dried to yield a coating of 0.1 g./ft. The resulting thermographic material was then exposed and a transfer to a paper copying sheet was made substantially as shown in Example 2 to produce a copy of the original having good quality, with the exception that the watersoluble overcoat required softening before transfer either by wiping the surface of the exposed matrix with a damp sponge or by dampening each receiving sheet.

In processes of the present invention to produce copies of an original, it will be apparent that a color-forming reaction can be employed, for example, where separate color-forming components of a two-component system are incorporated in each of separate polymeric layers, on a single support, or in separate polymeric layers on separate supports. An example of a color-forming reaction of this type comprises, for example, incorporating ferric stearate in one layer and propyl gallate in a separate layer and thermographically exposing the supported layers in surface contact with a graphic original having infrared absorptive printed characters thereon. A twocomponent color system of this type is also adapted to a multiple copy system where propyl gallate is incorporated in a receiving sheet and repeated transfers of a polymeric stratum containing ferric stearate is made to the receiving sheet from a matrix sheet.

Example 10.A heat-sensitive element of the present invention was prepared by the addition of 57 grams of the condensation product of polymerized linoleic acid and a diamine (sold under the trade name Versamide 930 by General Mills), 133 grams of bis(o-methoxyphenyl carbonate, 47 grams of n-dodecylamine and 12 grams of glass beads (IS-40a), to 51 grams of isopropanol and 700 grams of benzene. The polymer of said composition had a tackifying point in the range from 105 to 115 C. and the bis(o-methoxyphenyl) carbonate had a melting point of about 87 C. The resulting dispersion was coated on Folio Transparent Copy Greaseproof Paper. After coating, the element was air-dried for 4 hours to yield a colorless matrix.

The resulting colorless heat-sensitive element was exposed in contact with an originaldocument as described in Example 2. The colorless tacky image areas produced in the heat-sensitive layer of said element resulting from the exposure were then pressed, under'60 pounds pressure per lineal inch of roller length, in contact with Diazo Paper 481 L, Blue Line ('Keuffel and Esser) as in Example 2, to produce a blue color reproduction of the original in the diazo paper receiving sheet. Several copies were obtained in like manner from a single exposure of the heat-sensitive element.

Some of the advantages of the present invention have been described in the foregoing of this specification; many others are apparent. For example, the elements produced by the present invention are permanent in storage; and during use, the heat-sensitive layers thereof are unusually resistant to wear, abrasion, cracking, etc. The processes in which the elements are employed are normally completely dry, thus not requiring chemicals, solvents, and the like. Moreover, the processes for copy reproduction normally do not require a final fixing or stabilizing step. The copies produced by processes of the invention are permanent in that they are not aifected by high temperature and/or humidity conditions, etc. The copies are ideally suited as permanent file copies for this reason.

Since high resolution and quality are obtained in the copies, they are also highly acceptable for wide use in the fields of industry and commerce.

Transfer to a receiving surface can be accomplished, even'with thermoplastic materials having melt viscosities to about 0.8-1.1 grams per square foot.

as high as 100,000 poises, by using sufficient contact pressure for the transfer. Calender rolls may be used to provide the necessary contact pressure. These rolls may be heated to a temperature in order to raise the temperature of the heat-sensitive element during transfer, thereby lowering the viscosity to a considerable extent in the activated image areas to facilitate transfer. Transfer can be effected by feeding the activated heat-sensitive element, and a receiving sheet in contact with the heatsensitive layer, through the nip of calender rolls.

In some embodiments of the present invention it is preferable to provide as a part of the heat-sensitive element some means for regulating transfer of viscous material from the activated portions of the heat-sensitive layer. With heat-sensitive layers that have melt viscosities below 200 poises such means for regulating transfer is especially advantageous for improving transfer results. It prevents excessive flow of material to the receiving surface during the transfer step, thus conserving material in the matrix for producing more additional copies from a single heatsensitive element. Because the flow is attenuated while first copies are being made, heavier coats of sensitive material can be used without causing excessive transfer while making the first copies. Thus, with heavier heatsensitive coatings, even more copies are possible from a single heat-sensitive element. Incidentally, the flow regulating means usually facilitates separation of the matrix from the transfer surface after the transfer step.

We have found that glass beads or other solid particles, preferably of an average diameter or size slightly greater than the thickness of the heat-sensitive layer, when incorporated in the heat-sensitive layer will perform this flow regulating function. These solid particles preferably extend outward slightly from the heat-sensitive layer above the surface of the layer. Examples of heatsensitive layers containing glass beads are given in the foregoing examples.

An especially preferred flow regulating means that can be incorporated in the heat-sensitive element is a thin, porous, outer layer (non-thermoplastic at the tackifying temperature of the underlayer) on the heat-sensitive element, overlying the heat-sensitive layer. This outer layer is sufficiently porous that at the contact pressures used for the transfer step, viscous material in the image area of the heat-sensitive layer can permeate the porous outer layer and be transferred to a receiving surface. FIG. 4 is a schematic cutaway view of a heat-sensitive element having such a porous outer layer coated over an inner layer of heat-sensitive material on a support.

A heat-sensitive element having no fluid transfer regulating'means can be coated for use in a transfer process with a typical thermoplastic material to a maximum coating density of about 0.05 to about 0.3 gram per square foot. Heavier coatings would cause excessive transfer to first copies and consequent loss of image definition. If a reflex exposure is to be made, the melt viscosity of the heat-sensitive material preferably should be above 200 poises at the activation temperature. At room temperature an activated material having high viscosity characteristics can be transferred to a receiving sheet by calendering the heat-sensitive element in contact with a receiving sheet through steel rolls having a nip pressure of about 50 pounds per linear inch.

By incorporating solid particles, such as glass beads having diameters from 18 to 40 microns, in the heat-sensitive layer, the maximum coating density can be increased The solid particles, preferably extending outward above the heat-sensitive layer, will inhibit the flow of viscous material from the heat-sensitive layer. Heat-sensitive materials having lower melt viscosity can be used and a contact pressure less than that required for the more viscous material can be used for the transfer step.

A preferred outer porous layer for regulating the flow of activated material from the heat-sensitive layer comprises a continuous porous Web of polyvinyl alcohol (PVA) overlying the heat-sensitive layer. Such a web can be formed on the matrix by a solution coating method. Porosity and permeability of the web can be closely predetermined by regulating the coating conditions. When properly applied, the polyvinyl alcohol coating will form a porous permeable overcoat that provides excellent means for regulating fiow of viscous materials from the underlying heat-sensitive material. The porosity of the web can be regulated to accommodate any of a wide variety of viscous transfer materials having a wide range of viscosity and flow characteristics. With such a porous outer coating as means for regulating flow, a heat-sensitive layer of low melt viscosity material can be coated to maximum density of from about 1.5 up to about 3.0 grams per square foot without causing excessive transfer to first copies, and less transfer pressure is needed than for transfer of more viscous materials.

Some advantages that can be obtained by use of the porous overcoat are summarized as follows:

(1) Control the rate of flow of viscous activated material from the heat-sensitive sheet to the receiving surface,

(2) Reduce unwanted lateral spreading of the viscous material during transfer,

(3) Provide a carrier for filter dyes, chemical reactants, patterns, such as halftone line or dot screens, opaquing grid patterns, and the like,

(4) Protect the heat-sensitive layers against abrasion and contamination, and

(5) Prevent adhesion between the heat-sensitive layer and sunfaces that come in contact with it in manufacture, packaging, storage, and use, for example, interleaving sheets, receiving sheets, the document being copied, etc.

One important factor in forming the necessary porous structure in a polyvinyl alcohol coating is the presence in the coating solution of a pore-forming agent, either a metal salt or a surfactant, or in preferred embodiments both a salt and a surfactant. Another step that sometimes improves the porous structure is the immediate heating of the matrix to a predetermined temperature as soon as the coating solution is applied over the heat-sensitive layer.

The flow regulating proper-ties of the polyvinyl alcohol can be improved for use in some embodiments by adding fine grain particles of solid material distributed throughout the porous outer layer. Coatings containing such added particles are especially advantageous for inhibiting flow of very low viscosity transfer materials.

F ollowi-ng is an example of preferred heat-sensitive element incorporating a porous polyvinyl alcohol overcoat.

Example 11.8.6 g. of a 25% solution of sodium su-lfate in water was stirred into 100 g. of a 5% solution of polyvinyl alcohol (Elvanol 5042) in water which contained 0.1 g. of a surfactant, Aerosol OT. 1.8 g. of zinc oxide was dispersed in the resulting solution using a food blendor. After the dispersion had defoamed, it was coated over a dyed heat-sensitive layer on a support of map overlay paper. The heat-sensitive layer comprised a 1.5 g./ft. coating of 85 parts of poly(1,4-cyclohexanedimethyl adipateazelate [3:1]) having a melt viscosity of 16,000 poises a-t transfer temperature (70-75 C.), 5 parts of polyethyl acrylate, and parts of A Oil Blue Black B dye. The overooating coverage was approximately 0.5 g. per ft. During application and drying of the overcoating, the coating block was maintained at C. After drying, the resulting matrix was annealed for .1 hour at 75 C.

The resulting thermographic matrix was placed in contact with a standard lithographic document and the 2-ply assembly was then exposed in a commercially available thermographic machine set for normal exposure and then separated. The tacky image areas were transferred to a receiving sheet of stationery. Ten high quality transfers ,were metered to receiving papers from the exposed matrix.

The transfers were made at a rate of 0.172 in./sec. using transfer rolls which were maintained at a temperature of 7075 C. and were loaded at 52 pounds per lineal inch.

A control process using the same heat-sensitive matrix without the overcoat was employed. The presence of the porous overcoat resulted in improved resolution, complete absence of sticking between the matrix and the receiver and an ability to make 10 transfers as compared with only two good transfers from the control material.

The polyvinyl alcohol composition used in the above example (Elvanol 5042) is a commercially available aqueous solution of 87% hydrolyzed polyvinyl alcohol. Other aqueous solutions of polyvinyl alcohol can be used, and solutions of PVA and other volatile surfactants, e.g., methanol, can be used, provided such other solvents will not attack the heat-sensitive layer during the coating process. The total solids content of the coating solution, including PVA, salt, and insoluble particles is preferably in the range from about 5%9% by weight, based on the total weight of the solution. The remainder consists essentially of solvent.

Metal salts other than sodium sulfate which are soluble in the solvent medium can be substituted as pore-forming agents in the coating solution, for instance, such salts as Na PO Na2HPO4, KA1SO4, and NaC H O and the like, can be used. Any of a wide variety of commercially available surface active agents can be used in the coating solution as web-forming agents, for example, Aerosol 22, sold by American Cyanamid Company, is especially suitable and a host of other surface active agents may be used.

The mechanism by which these salts and surfactants cause formation of the porous structure is not fully understood, but without the presence of such an agent in the coating solution, the polyvinyl alcohol coating will dry as a non-porous film. Gene-rally, as the concentration of salt, surfactant, or xthe combination of both is increased in the coating solution, the porosity of the resulting dried web is rendered more coarse and the permeability increases.

Porous webs suitable as flow regulating means for heatsensitive elements have been formed from coating solutions containing from 10 to 60 parts by weight of salt per parts PVA, using no surfactant in the solution. However, presence of a surfactant up to a maximum of about 3% of .the weight of the coating solution will improve the porous structure for most embodiments. A porous structure can be obtained by using only a surfactant without salt. However, the structure obtained using both a salt and a surfactant is preferred for most embodiments.

An excess of salt in the coating solution will cause un-' desired precipitation of polyvinyl alcohol from the coating solution.

It is necessary in order to obtain a good porous structure in the polyvinyl alcohol layer that the temperature of the coating solution be raised above a certain minimum temperature immediately upon application of the coating solution over the heat-sensitive layer, and it is necessary that the temperature be held above this minimum until the porous structure has formed and the coating has substantially dried. This minimum temperature which varies depending upon the composition of the solution will in most instances be in the range from about 35 to about 75 F. Without such immediate heating, the coating will dry as a nonporous film. Heating of the coating solution to this minimum temperature can be accomplished by applying the coating solution to the matrix while the matrix is in contact with a heated block or roll. Further heating to higher temperatures may be used to facilitate drying of the solvent from the coating, but with caution not to activate the heat-sensitive layer during high temperature drying.

Fine grain insoluble particles, such as particles of zinc oxide, can be mixed in the coating solution prior to application. Af-ter this coating has been applied and has dried as a porous layer, the fine grain particles will be evenly distributed throughout the porous web. Examples of other fine grain materials suitable for this use are colloidal silica, titanium and zirconium dioxides, clays, and the like. For use in infrared processes, this material must be substantially infrared transparent. Fine grain insoluble particles are most effective when present in concentrations from about to 8 /2 by Weight based on the weight of PVA in the solution, and concentrations from 0 to 10% may be used.

The preferred coating density for the porous overcoating layer is in the range from about 0.3 to 0.7 gram per square foot, when dried. Below 0.2 gram per square foot density, the layer usually cannot provide adequate flow control. Coating densities for the porous outer layer up to about 1.0 gram per square foot (dry) may be used.

The porous outer layer may range in thickness from about 0.0001 inch to 0.002 inch thick and the individual openings may comprise from about to about 75% of the total area. The openings are preferably evenly distributed over the matrix but some random fluctuation in distribution and size is permissible. The optimum average size of the pores, or openings, will vary depending on the viscosity of the heat-sensitive material and the conditions to be used for activation and transfer. Generally, optimum average pore size will range from about 0.1 micron .to about 500 microns and in most embodiments from about 1 to about microns.

In addition to the preferred polyvinyl-alcohol-base porous layers described above, some other porous outer layers may be used as flow regulating means. For example thin films of cellulose esters, polyesters, polyamides, polycarbonates, thin metal foils and the like, that have been perforated or preformed to obtain the desired porosity and permeability, and then applied over the heatsensitive layer will function adequately in some embodiments. Some porous papers, felted webs, and woven fabrics, having the necessary permeability and porosity requirements can be used as the porous outer layer for inhibiting flow of viscous material from the heat-sensitive layer in some embodiments.

Porous outer coatings for regulating flow of viscous material from the matrix, as described above, may be used to advantage on matrices for use in other methods of document copying that embody the general principle of transferring viscous material from image areas of a matrix to a receiving surface. With such porous outer coatings, the flow characteristics of whatever viscous fluid is being transferred can be regulated by the porous overlying layer to obtain the desired transfer characteristics. For example, in a matrix for use in the wax-transfer process mentioned above, in which wax transfer is effected while image areas in the matrix are preferentially heated to the Wax melting point, a porous outer coating could be used to prevent excessive flow of melted Wax to the transfer surface. The porous outer layer Would be designed With the necessary porosity and permeability to permit permeation by only a desired amount of wax under prescribed process conditions.

Other matrices in which a porous overlying layer could be used to advantage are those for use in photographic diffusion transfer processes, image dye diffusion transfer processes, residual developer diffusion transfer processes, and photographic and thermographic colloid transfer processes. Some processes of these types are described in US. Patent No. 2,596,756, U.S. Patent 2,769,391 and 2,808,777.

It will be understood that modifications and variations may be made within the scope of the invention as described above and as defined in the following claims.

We claim:

1. A substantially infrared transparent heat-sensitive element for use in a thermographic process comprising in combination (A) a support,

(B) a heat-sensitive layer coated on said support comprising a polymer-containing thermoplastic material in a non-tacky state of at least partial crystallization and having an original tackifying temperature from 50 to 200 C. at which original tackifying temperature said thermoplastic material will undergo transition to an essentially non-crystalline state having a substantially lower tackifying temperature, said material having the property of remaining for a substantial period of time after said transition in a state having a reduced tackifying temperature substantially below said original tackifying temperature and having the property in such a state of being transferable by pressure at said reduced tackifying temperature, and

(C) means incorporated in said element for regulating transfer of tackified material from the heat-sensitive layer to a surface in contact with the heat-sensitive side of said element, said means for regulating transfer comprising a dry, non-tacky, porous layer coated over said heat-sensitive layer, said porous outer layer being suificiently permeable by said thermoplastic material in viscous tacky state to permit some transfer of such material in such state through said outer layer.

2. The heat-sensitive element of claim 1, said porous outer layer comprising a continuous porous web of polyvinyl alcohol.

3. The heat-sensitive element of claim 2, said porous outer layer comprising a continuous porous web of polyvinyl alcohol that has been coated over said heat-sensitive layer from a solution comprising parts by Weight of polyvinyl alcohol, from 10 to 60 parts by weight of a soluble metal salt and from 0 to 3 parts by weight of a surface-active agent.

4. The heat-sensitive element of claim 2, said continuous Web containing from 5 to 10 parts by Weight per 100 parts of polyvinyl alcohol of fine grain solid insoluble particles dispersed in the polyvinyl alcohol Web.

5. The heat-sensitive element of claim 3 wherein said salt is a water soluble metal salt and said surfactant is an anionic surface active agent.

6. The heat-sensitive element of claim 4 wherein said fine grain solid particles are particles of zinc oxide.

7. A substantially infrared transparent heat-sensitive element for use in a thermographic process comprising in combination (A) a support,

(B) a heat-sensitive layer coated on said support comprising a thermoplastic material in a non-tacky state of at least partial crystallization and having an original tackifying temperature above 50 C. at which original tackifying temperature said thermoplastic material will undergo transition to an essentially non crystalline state having a substantially lower tackifying temperature, said material having the property of remaining for a substantial period of time after said transistion in a state having a reduced tackifying temperature substantially below said original tackifying temperaure and having the property in such state of being transferable by pressure at said reduced tackifying temperature, and

(C) means incorporated in said element for regulating transfer of tackified material from the heat-sensitive layer to a surface in contact with the heat-sensitive side of said element said means comprising solid inert particles having average diameter slightly greater than the thickess of said layer dispersed in said layer in a quantity sufficient to regulate said transfer.

8. A process of producing a transferred image on a receiving surface by means of a heat-sensitive matrix sheet having a heat-sensitive side on which is coated a heatsensitive layer comprising a thermoplastc material in a non-tacky state of at least partial crystallization and having an original tackifying temperature above 50 C. at which original tackifying temperature said thermoplastic 19 materal will undergo transition to an essentially noncrystalline state having a substantially reduced tackifying temperature, said material having the property of remaining for a substantial period of time after said transition in a state having a reduced tackifying temperature substantally below sad original tackifying temperature and having the property in such state of being transferable by pressure at a temperature above said reduced tackifying temperature and below said original tackifying temperature; said process comprising the steps of (l) preferentially heating only image areas on said heat-sensitive layer to at least said original tackifying temperature, and (2) after said preferential heating step and during said substantial period of time, with image areas and background areas of said heat-sensitve layer at a uniform temperature at least as high as said reduced tackifying temperature and below said original tackifying temperaure, pressing the heatsensitive side of the matrix at said areas of uniform temperature against a receivn-g surface wth pressure suificient to transfer tackified material from image areas of the heat sensitive layer to the receiving surface, said thermoplastic material containing a colorant that transfers with the tackified material giving optical density to the transfered image.

9. The process of claim 8 wherein said heat-sensitive matrix sheet further comprises a dry, non-tacky, porous outer layer coated over said heat-sensitive layer, said porous outer layer being sufficiently permeable by said thermoplastic material in a viscous tacky state to permit limited transfer of such material in such state through said outer layer when the heat-sensitive side of the matrix is pressed against a receiving surface.

10. The process of claim 9 wherein said porous outer layer comprises a continuous porous Web of polyvinyl alcohol.

11. The process of claim 8 wherein the resin component of said thermoplastic material consists essentially of a member selected from the group consisting of poly butene- 1), poly(pentene-l), poly(tert-butyl acrylate), poly(tetramethylene carbonate), poly(pentamethylene carbonate), oly(2,2-dinfethyltrirnethylene succinate), poly( 1,4-cyclohexanedimethylene succinate), poly(1,4-cyclohexanedimethylene adipate), poly(ethylene succinate), poly(.pentamethylene terephthalate), poly(ethylene 1,4-cyclohexanedicarboxylate), poly(ethylene glycol) and cyclohexanedimethylene adipate-azelate copolymers.

12. The process of claim 8 wherein said thermoplastic material consists essentially of a polymeric resin component intimately mixed with a non-polymeric crystalloid, which crystalloid will melt at an original tackifying temperature above 50 C. and upon melting will blend with said resin component to form a non-crystaline mixture that will remain for a substantial period in a state having a reduced tackifying temperature substantially below said original tackifying temperature.

13. The process of claim 8 wherein said thermoplastic material comprises a polymeric resin component which is at least partially crystallized in said layer and which at said original tackifying temperature will undergo transition to a substantially amorphous state having a second order transition temperature substantially below said original tackifying temperature.

14. A process of producing a recorded image by means of a heat-sensitive matrix sheet having a heat-sensitive side on which is coated a heat-sensitive layer comprising a polymer-contaning thermoplatic material in a non-tacky state of at least patrial crystallization and having an original tackifying temperature above 50 C., at which original tackifying temperature said thermoplastic material will undergo transition to an essentially non-crystalline state having a substantially reduced tackifying temperature, said material having the property of remaining for a substantial period of time after said transition in a state having a reduced tackifying temperature substantially below said original tackifying temperature and the thermoplastic material of said layer having a melt vis cosity below 100,000 poises at said original tackifying temperature, said process comprising the steps of (l) preferentially heating only image areas on said heat-sensitive layer to at least said original tackifying temperature, and (2) after said preferential heating step and during said substantial period of time, with image areas and background areas of said heat-sensitive layer at a uniform temperature at least as high as said reduced tackifying temperature and below said original tackifying temperature, adhering particles having optical density to tackified image areas of said heat-sensitive layer.

15. The process of claim 14 wherein said preferential heating step is accomplished by exposing to infrared radiation a graphic original having image areas that are infrared absorptive and background areas that are substantally infrared transparent while said original is in contact with the heat-sensitive matrix, for a time sufiicient to generate heat in the image areas of the original and thereby heat only the areas in the heat-sensitive matrix adjacent said image areas to at least said original tackifying temperature.

16. A process of producing a recorded image by means of a heat-sensitive matrix sheet having a heat-sensitive side on which is coated a heat-sensitive layer comprising a polymer-containing thermoplastic material in a nontacky state of at least partial crystallization and having an original tackifying temperature above 50 C. at which original tackifying temperature said thermoplastic material will undergo transition to an essentially non-crystalline state having a substantially reduced tackifying temperature, said material having the property of remaining for a substantial period of time after said transition in a state having a reduced tackifying temperature and having the property in such state of being transferable by pressure at a temperature above said reduced tackifying temperature and below said original tackifying temperature, said process comprising the steps of (1) preferentially heating only image areas on said heat-sensitive layer to at least said original tackifying temperature, and (2) after said preferential heating step and during said sub stantial period of time, with image areas and background areas of said heat-sensitive layer at a uniform temperature at least as high as said reduced tackifying temperature and below said original tackifying temperature, pressing the heat-sensitive side of the matrix at said areas of uniform temperature against a receiving surface with pressure sufiicient to transfer tackified material from image areas of the heat-sensitive layer to the receiving surface, and (3) after such transfer of tackified material to the receiving surface, adhering colored material having optical density to the transferred material on the receiving surface.

17. The process of claim 16 wherein said preferential heating step is accomplished by exposing to infrared radiation a graphic original having image areas that are infrared absorptive and background areas that are substantially infrared transparent while said original is in contact with the heat-sensitive matrix, for a time sufficient to generate heat in the image areas of the original and thereby heat only the areas in the heat-sensitve matrix adjacent said image areas to at least said original tackifying temperature.

18. A process of producing a transferred image on a receiving surface by means of a substantially infrared transparent, heat-sensitive matrix sheet having a heatsensitive side on which is coated a heat-sensitive layer comprising a thermoplastic material in a non-tacky state of at least partial crystallization and having an original tackifying temperature above 50 C. at which original tackifying temperature said thermoplastic material will undergo transition to an essentially non-crystalline state having a substantially reduced tackifying temperature, said material having the property of remaining for a substantial period of time after said transition in a state having 2.1 a reduced tackifying temperature substantially below said original tackifying temperature and having the property in such a state of being transferable by pressure at a temperature above said reduced tackifying temperature and below said original tackifying temperature, said thermoplastic material having uniformly distributed therethrough a substantially infrared transparent color material, said process comprising the steps of (1) exposing to infrared radiation a graphic original having image areas that are infrared absorbent and background areas that are substantially infrared transparent, said orignal being in heat-conductive association with said heat-sensitive matrix for a time sufficient to generate heat in the image areas of said original and thereby to heat the areas in said heat-sensitive matrix adjacent said image areas to at least said original tackifying temperature, and (2) after said exposure and during said substantial period of time, with image areas and background areas of said heat-sensitive matrix at a uniform tem- 20 a receiving surface with pressure suflicient to transfer 25 tackified material from said image areas of said heatsensitive matrix to said receiving surface.

References Cited by the Examiner UNITED STATES PATENTS Perry 117-122 Murray 250- 65.1 Walkup et a1 250-651 Groak 117--36.1

Hendricks 117122 Sandberg 117-36.1 Holt ....4 117l22 Roshkind 1'1736.1 Stolle et al 117-36.4

Roshkind 11736.7

Vander Weel 117--36.1

Marron l17-36.1

Burg 101-1495 Newman et al. 117-36.4 G-ulko 25065.1

Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

RALPH G. NILSON, Examiner.

W. G. LINDQUIST, M. KATZ, Assistant Examiners.

Claims

16. A PROCESS OF PRODUCING A RECORDING IMAGE BY MEANS OF A HEAT-SENSITIVE MATRIX SHEET HAVING A HEAT-SENSITIVE SIDE ON WHICH IS COATED A HEAT-SENSITIVE LAYER COMPRISING A POLYMER-CONTAINING THERMOPLASTIC MATERIAL IN A NONTACKY STATE OF AT LEAST PARTIAL CRYSTALLIZATION AND HAVING AN ORIGINAL TACKIFYING TEMPERATURE ABOVE 50*C. AT WHICH ORIGINAL TACKIFYING TEMPERATURE SAID THERMOPLASTIC MATERIAL WILL UNDERGO TRANSITION TO AN ESSENTIALLY NON-CRYSTALLINE STATE HAVING A SUBSTANTIALLY REDUCED TACKIFYING TEMPERATURE, SAID MATERIAL HAVING THE PROPERTY OF REMAINING FOR A SUBSTANTIAL PERIOD OF TIME AFTER SAID TRANSITION IN A STATE HAVING A REDUCED TACKIFYING TEMPERATURE AND HAVING THE PROPERTY IN SUCH STATE OF BEING TRANSFERABLE BY PRESSURE AT A TEMPERATURE ABOVE SAID REDUCED TRACKIFYING TEMPERATURE AND BELOW SAID ORIGINAL TACKIFYING TEMPERATURE, SAID PROCESS COMPRISING THE STEPS OF (1) PREFERENTIALLY HEATING ONLY IMAGE AREAS ON SAID HEAT-SENSITIVE LAYER