US3076707A - Heat developable copy sheet and compositions useful therefor - Google Patents

Description

United States atent 1" 3,076,707 HEAT DEVELOPABLE COPY SHEET AND COMPOSITIONS USEFUL THEREFOR WilliamR. Lawton and Eugene -F. Lopez, Nashua, NH, .assignors to NashuaCorporation, Nashua, N .H., a corporation ofDelawai-e "NDrawing. Filed Apr. -22, 1959, Ser. No. 808,012 8 Claims. (C13 96--75) This invention relates to the duplicating arts 'an'd pro- :vides a heat-developable cor'n'posit-iom-an'd more particularlya photosensitive compositionthatmay be developed -to. producea colored image simply by the application of heat. The composition is accordingly ideally suited asthe sensitive component of thermographic and photographic "copy-sheets of the direct exposure type, and sheets embodying theinventionareinexpensive, stable and of utanosttconvenience in use. A copy may be formed by exposing thetsheet to ultraviolet rays through a masterand .then heating it to .produce a visible duplicate of the master. Copysheets embodying this invention may be stored without deterioration for considerable periods of time, upto several months at ordinary temperatures, and under conditions of relatively high humidity, and when used for copying :purposes they combine the versatility, cleanliness andLpermanence'of copy of the diazotype sheet :With the speed and convenience of the thermofacsimile type sheet.

Of the numerous systems available for making copies of graphic works, the most useful for general office use, Where only one or a fewcopies are desired, are those that provide copy directly by contact exposure of the copy sheet to the master. Three types of system in common use are the silver emulsion type, the diazo type and the thermofacsimile type. Of these only the last two provide a direct copy (positive); the silver emulsion type produces a negative by direct exposure which is then by chemical means transferred in reverse to a positive sheet. The thermofacsimile type is the most convenient to use, for it simply requires a single exposure of the copy sheet to the master under infrared radiation, and the copy is produced directly in a single exposure. The copy, however, suffers from the disadvantage of not being sharp and distinct, and subsequent heating will cause a darkening in the manner of an original exposure and obliterate the copy. The sheets currently available for thermofacsimile copies are moreover formed of materials transparent to thermal radiation, and lack the texture, finish, stiffness and body of paper.

Diazotype copy sheets, on the other hand, produce a copy which is generally superior to thermo'facsimile in clearness, distinctness, sharpness, contrast and permanence, and the sheets may be formed on any kind of paper or other backing material, which permits any desired texture or other character. Diazotype sheets presently available commercially, however, require a treatment subsequent to the exposure to develop the copy. Generally the sheet is either brought into contact with ammonia vapors, as in the Ozalid type, or is treated with a basic solution reactive with the photosensitive material in the sheet, as in the Bruning type sheet. In either case, additional equipment and processing is necessary following the exposure of the sheet.

Diazotype copy sheets are conventionally dependent on the fact that certain diazonium compounds are light sensitive and decompose when exposed to actinic rays. The same compositions are dyestutf components and react under basic conditions with a class of compounds, certain phenols, known as azo couplers, to form dyes. Upon exposure of the diazotype copy sheet to actinic rays, the diazo compound in the exposed area is destroyed, remain- ,Fice

The formulation of the photosensitive coatingon'couve'ntional *diazoshe'ets may'include'only thediazoniurn compound, in which case development is'brou'g'ht about -by treatin'gthe sheetwith a developersolution containing the az'o'coupler compound and a base. Alternatively, the coating may include both components of 'the diazo system, the diazo'nium compound and the azo coupler, "t'

' geth'e'r "with-stabilizers (such as urea and thioii'rfeaf) and acid material which prevents prema ur reaction between the diazonium compound andthe'azocouplercompound.

Such a paper' may b'e developed-'simply by applyinga base,

'itnost conveniently by exposure to ammonia vapors, 'and is-"generally referred to'as an ammonia'developing diazotype paper. a I V The present inventionis directed primarily to improving the versatility" and convenience of diazotypecopylcompositions by incorporating in the"diazo system a'latentjdei- -velo'per"whi'ch is activatibl'e by heat aloneto brihgabout the color forming reaction of this type jot system.v The invention -in this sense does not contemplate any fiinda} mental change in 'the chemical reactions that normally 'take 'pl'a'c'e, but rather makes use of a class of composi} tions by which a-developerfo'r the diazo system is made physically present, but in a lateut, stable and unreactive manner. Latentdevelopers'cmployedinfthe compositions of invention constitute ing'ene'ral a class ofcoinpoiindswhich exist as stable, solid materials at normal conditioiis of temperature and humidity and dissociate "at an elevated temperature to yield a base. Compounds of this known to the art constitute abase and; sane-r e pound with which the base will crystallize and fauna stable crystal complex containing the base within a crystal lattice in the form of a distinct 'plfysical chen iical entity. The latentdevejlop'ers, although'coiita'ining ab'asic component, do not exhibit substantial basic prepares and may accordingly be incorporated in the 'di'azo system without causing a dye forming reactionft o take place; They are, however, dissociable at relatively lc'u'ii' elevated temperatures and the base is released in fully active condition and ma'deavailable for the reaction. I

Latent developers most suitable for this inv n ibn" ai'e those stable under conditions normally encountered in the manufacture, storage and shipment of'frnate'rials or this type. These conditions are referred to in this sped,- fica'tion and in the appended claims by the term normal? and may be typified by conditions of temperature below about 100 F. and a relative humidity less than 96 percent. The term is not used, h ov'vefve'r, in an ass-ante sense, but rather with reference to the general ian'ge of conditions one might expect to prevail undr actual conditions of use, and to the fact that dissociation -Will occur at some higher temperature which is practically developers include in general the class of compounds" formed when a base, generally an amine, and a ma terial which will crystallize with the base are "combined to form a solid stable material, which may desig netted a crystal complex, characterized bystab1 1ty at normal conditions of temperature and humidity, ness with reference to its basic characteristics; and disc" 3 sociability at a convenient elevated temperature to yield the base.

These latent developers include such crystal complexes as the co-crystal adducts of a bisphenol, and the in clusion compounds. Although these various types of complexes are sometimes referred to as different classes of materials, they are for the purposes of the present invention essentially the same with regard to the physical characteristics required of a latent developer. In each case a base and carrier compound, i.e. a bisphenol or urea, are combined in a manner such that the resultant complex conceals the characteristics of the base and exists in stable, inert form, while dissociating at an elevated, but relatively low, temperature to provide basic conditions. They are designated as complexes because the base and carrier compound are combined or associated by a low energy bond.

Although certain specific compositions are herein designated as examples of latent developers, it should be noted that one skilled in the art and familiar with this disclosure will not in any way be limited in a selection of suitable latent developers to the materials specifically set forth. He may rather employ any composition comprising a basic component combined with a carrier compound component to form a crystal complex, and having the requisite properties of inertness, stability and dissociability. The selection of such compositions may readily be made on the basis of known, or readily determined, properties, as in any case of selecting a material that possesses the characteristics required for its intended use. The chemical nature of the latent developer is significant primarily in-that it must include a base effective to effectuate a dye forming reaction in the diazo system, but such bases are well known to those skilled in this field of chemistry, and this invention is not otherwise concerned with the chemical aspects of diazo systems. When the base is released by the dissociation of the latent developer the reaction that occurs is not essentially different from that occurring in the development of diazo systems by already known techniques. In this respect the invention relates to a physical combination of ingredients long known to be reactive, and is essentially characterized by the way that the ingredients are combined in an unreactive manner.

The selection of a suitable latent developer can readily be made to provide for a variety of characteristics in the copy sheet. Assuming that a given base or class of bases, such as primary hydroxyl amines, is selected as the desired basic component on the basis of the known chemistry of the reaction, and that numerous solid association products, or crystal complexes, of such an amine or amines with a bisphenol or urea will be available, the one having the desired characteristics of stability, inertness, and activation temperature may then readily be selected on the basis of those characteristics which are known or easily determined with the aid of simple experiments within the skill of anyone versed in laboratory technology. If for instance an activation temperature of between 90 and 100 C. is desired, the various complexes may be heated to within this range in the presence of a color indicator to determine whether a basic condition is brought about. Another suitable procedure is to apply a sample of the various complexes to a sheet of commercial ammonia developing type diazo paper, and then heat the sheet to the desired range to see whether development occurs.

If stability is a factor, the various crystal complexes may be applied to a diazotype sheet which may then be stored under test conditions, such as relatively high temperature and humidity, to determine whether any development occurs.

These test procedures, it will be noted, involve purely manipulative steps which determine the presence of properties on the basis of which a selection may readily be made without in the least involving any inventive effort.

The latent developer may be incorporated in the diazotype sheet in any of numerous ways, the only requirement being that it be present throughout the diazo system in potentially reactive association with that composition. Heating of the sheet to cause dissociation of the crystal complex and a release of the basic component will thus cause uniform development over the heated area. The latent developer may be combined with ordinary commercial diazotype copy sheets which contain both the diazo compound and the azo coupler, as a coating over the sensitive coating. In one preferred embodiment, the latent developer is dispersed in a solution of a binder and coated onto the sensitized surface of the diazotype sheet by conventional means. In some cases a solution of the latent developer may be formed and applied to the diazotype sheet. An alternative procedure is to form a coating composition containing the diazo compound, azo coupler, and latent developer in suspension, and applying this composition to paper or other suitable backing material as a single coat.

Crystal complexes suitable as latent developers and currently known to the art include in general organic bases co-crystallized with bisphenol carrier compounds to form co-crystai adducts of the general type described in US. Patent 2,829,175; and inclusion compounds of organic bases with urea as described in US. Patents 2,569,984 and 2,520,716.

Any amine otherwise suit-able as a basic developer for a diazotype sheet may be employed including primary, secondary and tertiary aliphatic amines, alicyclic amines, aromatic amines, heterocyclic amines, hydroxyl amines, but preferably an amine having highly basic characteristics is preferred, e.g. hydroxyl amines, polyfunctional amines and primary aliphatic and alicyclic amines.

Latent developers of the co-crystal adduct and inclusion compound type are formed by dissolving the amine and the carrier compound in a sutiable solvent and crystallizing out the co-crystal complex, which may then be recovered and incorporated into a sutiable coating medium for use as described herein.

Representative examples of this invention setting forth the best mode presently contemplated of carrying out the invention and representative types of latent developers which may be used are given below. In each example it will be seen that a latent developer is prepared ancl is then incorporated in a diazotype copy sheet. The components of the diazotype sheet are themselves well known in the art and are not considered as constituting per se any part of this invention. Such systems are described in US. Patents 1,444,469 and 1,628,- 279.

In each of the following Examples 128 the carrier compound was first dissolved in the solvent at a temperature of about F., and the base was then added and agitated for 30 minutes with a motor-driven stirrer. The mixture was then chilled for about 14 hours (overnight is sufiicient) at about 30 F., during which a precipitate formed. The precipitate was filtered, washed thoroughly three times with n-hexane at room temperature (70 F.), filtered, and dried. In each case the resulting product constituted a latent developer. The examples set forth the proportions and identities of the several ingredients. All ingredients were technical grade unless otherwise noted, and all operations were carried out in glass vessels.

EXAMPLE 1 G. Carrier: Bisphenol A 113 Base: Isopropylamine 30 Solvent: Toluol 550 Product: Co-crystal adduct of isopropylamine and bisphenol A, M.P. 154-157" C.

EXAMPLE 2 v G. Carrier: Bisphenol A... 113 Base: Ethylene diamine 3O Solvent: Toluol A 1. 550 Product: Co-crystal edduct of bisphenol A and ethylene diamine, M.P. 91-96" C.

EXAMPLE 3 Carrier; Blsfihenol A 113 Base: Cyclohexylamine 5-1 Solvent: Toluol 550 Product: (Jo-crystal adduct of bisphenol A and cyclohexylamine, M.P. 108-1l0 C.

EXAMPLE 4 Carrier: Eisphenol A 1 13 Base: Diethylamine Solvent: Toluol 550 Product: Co-cr'ysta'l adduct of bisphenol A and cli- 'ethylamine, M.P. 117-153 C.

EXAMPLE 5 Carrier: Bisphenol A 113 Base: Di-n-pr.o1:yla1nine S1 "Solvent: Toluol 55,0 Product: Co-crystal adduct of bisphenol A and "di- 'n-propylamine, M.P. 154-156" vC.

EXAMPLE 6 Carrier: Bisphenol A 113 Base: Tributylamine L. '93 ;Solvent: Toluol "550 Product: (Io-crystal adduct of bisphenol A and t-ributylamine, M.P. 117-155 C.

EXAMPLE 7 Carrier: Tetrachlorobisphenol A 183 Base: Diethanolamine 5 3 Solvent: Toluol 364 Product: Co-crystal adduct of tetrachlorobisphenol A and diethanolamine, M.P. '144-149 C.

EXAMPLE -8 "Carrier: Tetrachlorobisphenol A 182 Base: Diethy'lamine 37 Solvent: Toluol 364 Product: Co-crystal adduct of tetrachlorobispl'renol A and 'diethylanrine, M.P. -142--175 C.

EXAMPLE '9 Carrier: Tetrachlorobisphenol A 182 Base: H-ydroxyethyldiethylenetriamine 75 .Solvent: To'luol 364 Product: Co-crystal adduct of tetrachlorobisphenol A and hydroxyethyldiethylenetriamine, M.P. 93-

EXAMPLE '10 Carrier: Tetrachlorobisphenol A; 182 Base: Isooctylamine -65 .Solvent: Toluol 364 Product: Co-crystal adduct of isooctylarnine and tetrachlorobisphenol A, M.P. 172-185 C.

EXAMPLE 1 1 G. "Carrier: Tetrachlorobisphenol A 182 Base: N-decylamine 75 Solvent: Toluol 364 Product: Co-crystal adduct of n-decylamine and tetrachlOrobisphenol A, M.P. l92-198 C.

6 EXAMPLE 12 a G. Carrier: Tetrachlorohiephenol A 182 Base: Tributylamine 93 Solvent: Toluol v 364 Product: Co-crystal adduct of tributylamine and and tetrachlorobisphenol A, M.P. -1 12 C.

EXAMPLE 13 Carrier: Tetrachlorobisphenol A 182 Base: Triethanolamine v 75 Solvent: Toluol 364 Product: Co-crystal adduct of triethanolarnine and tetrachlorobisphenol A, M.P. 134l40 C.

EXAMPLE 14 Carrier: 'Tetrachloroblsphenol A 182 Base: Ethanolamine 31 Solvent: Tolunl 364 Product: Co-crystal adduct of ethanolamine and tetrachlorobisphenol A, M.P. 96-104 C.

EXAMPLE 15 Carrier 4,4-thio-bis-(6-tert. b1ity1-m-cresol) 144 Base: Ethylene diarnine 310 Solvent: Stoddard solvent 200 Solvent: Toluol 800 Product: Co-crystal adduct of ethylene diamine and 4,4-thio-bis (6-tert. butyl m-cresol), M.P. 112- 115 C.

EXAMPLE 16 Carrier: 4,4'-thio-bis-(-6-tert. butyl-n1-creso1 144 Base: Cyclohexylamine 51 Solvent: Stoddard solvent 200 Solvent: Toluol- I V V 800 Product: Co-crystal adduct of cyclohexylamine and 4,4"-thio -'bis-'(6-tert. butyl-m c're'sol), M.P. 79- 96'C.

EXAMPLE '17 Carrier: 4,4 butylidene bis (6 tert. butyl m eresol) 161 Base: Ethylene diamine 37 Solvent: Stoddard solvent 200 Solvent: T0lu01 800 Product: Co-crystal adduct of ethylene diamine and 4,4'-butylidene-bis-Q6 tert. butyl-m-cresol), 212 246 C.

EXAMPLE 18 Carrier: 4,4-butylidene-bls-(6-tert. butyl-m-cre 01,) iBase: .N- methy-lethanolamine."A 38 Solvent: Stoddard solvent; H A v Solvent: T011101. E 800 Product: Co-crystal adduct of N-met ylethanol amine and 4,4 -butylidene bis-,(6-tert. .butyl-mcreso1),'M.P. 2-13-216 .C.

' EXAMPLE 19 carrier; 4,4 -'butylidene-bis-(6-tert. butyl-m-cresol) e 6 Base Tetrarnethylg'uanidine A 5 8 Solvent: Stoddard solvent 200 Solvent: Toluol .800

Product: (Do-crystal adduct of ,te'tramethylguanidine and 4,4'-blutylidene-bis-(6-tert. butyl-m-creso l), M.P. .183--C.

EXAMPLE 20 "Carrier: 2,2T-methylene-bis-j(44methyl 6-tert. butyl p 141) Base: Diethanolamine 53 'Solvent: Stoddard s0lvent 560 2,2 methylene -'b is-(4-rnethy1-6-tert. butyl .phe- 'nol), M.P. 110-117" C.

7 EXAMPLE 21 G. Carrier: Tetrachlorobisphenol A 182 Base: Z-amino-l-butanol 44.5 Solvent: T011101 364 Product: Co-crystal adduct of 2-amino-1-butanol and tetrachlorobisphenol A.

EXAMPLE 22 Carrier: Tetrachlorobisphenol A 182 Base: Monoisopropanolamine 37.5 Solvent: Toluol 364 Product: Co-crystal adduct of monoisopropanolamine and tetrachlorobisphenol A.

EXAMPLE 23 Carrier: Tetrachlorobisphenol A 182 Base: Methyldiethanolamine 59.5 Solvent: Toluol 364 Product: Co-crystal adduct of methyldiethanolamine and tetrachlorobisnhenol A.

EXAMPLE 24 Carrier: Tetrachlorobisphenol A 182 Base: Propylenediamine (70%) 53 Solvent: Tolnol 364 Product: Co-crystal adduct of propylenediamine and tetrachlorobisphenol A.

EXAMPLE 25 Carrier: Tetrachlorobisphenol A 182 Base: 2-amino-2-ethyl-l,3-propanediol 59 Solvent: Toluol 364 Product: Co-crystal adduct of 2-amino-2-ethyl-1,3-

propanediol and tetrachlorobisphenol A.

EXAMPLE 26 Carrier: Bisphenol A 113 Base: Isobutylamine 36 Solvent: Tolunl 550 Product: Co-crystal adduct of isobutylamine and bisphenol A.

EXAMPLE 27 Carrier: Bisphenol A 113 Base: Dimethylaminopropylamine 51 Solvent: Toluol 550 Product: Co-crystal adduct of dimethylaminopropylamine and bisphenol A.

EXAMPLE 28 Carrier: Tetrachlorobisphenol A 182 Base: Aminobispropylamine 66 Solvent: Toluol 364 Product: C-crystal adduct of aminobispropylamine and tetrachlorobisphenol A.

In the foregoing examples the bisphenol A and the tetrachlorobisphenol A were commercial products. The 2,2-methylene-bis-(4-methyl-6-tert. butyl phenol) is sold as Antioxidene 2246. The 4,4'-thio-bis-(6-tert. butyl-mcresol) is sold as Santowhite crystals, and 4,4-butylidenebis-(6-tert. butyl-m-cresol) is sold as Santowhite powder.

The co-crystal adduct formed in each of the preceding Examples 1-28 was incorporated into a standard ammonia developing diazotype paper, e.g. Ozalid paper, by the following technique: Ten grams of the co-crystal adduct were dispersed in 50 g. of a 1.5 percent solution of polyvinylethylether dissolved in hexane, by milling the co-crystal adduct with the solution for four hours in a ball mill operating in a chilled room at 40 F. The dispersion was coated by means of a Mayer rod onto the diazotype paper to a dry weight of 3-5 pounds/ 3000 square feet, and the paper was then dried. Samples of the dry treated sheet were exposed to a master under ultraviolet light in accordance with standard practice, and the sheet was then heated for five seconds on a hot plate heated to 300 F. In each case a clear and legible copy of the master was formed.

In each of the foregoing examples the polyvinylethylether solution serves as a mechanical binder by which the latent developer is retained in potentially reactive association with the underlying diazo composition. Other film forming materials such as methylmethacrylate polymer, vinyl chloride polymers, polyvinylalcohol, natural resins and gums and similar materials may also be used when dissolved in suitable solvents which are not solvents for the crystal complex. Where the solvent will also dissolve the crystal complex, the base may become released in reactive form and cause premature dye formation within the diazotype system. It has been found, however, that certain crystal complexes do not result in base release when dissolved. For instance, the co-crystal adduct of diethanolamine and 2,2'-methylene-bis-(4-methyl-6-tert. butyl phenol) described in Example 20 may be dissolved in trichloroethylene or in octane and coated upon a standard ammonia developing diazotype paper without premature development.

In the following examples the use of crystal complexes other than the adducts of an amine and a bisphenol are described. In Examples 29-31, the carrier compound was first dissolved in the solvent at a temperature of about 150 F. and the solution was then left to stand overnight (14 hours) at room temperature (70 F.). The base was then added with mechanical stirring, and the solution was then again left to stand overnght (14 hours) at room temperature (70 F.) during which a precipitate formed. The precipitate was filtered out, washed thoroughly three times with n-hexane at room temperature (70 F filtered and dried. In each case the resulting product constituted a latent developer. The examples set forth the proportions and identities of the several ingredients, all of which were technical grade unless otherwise indicated. All mixing operations were carried out in glass vessels.

EXAMPLE 29 Carrier: Urea Base: Di-n-hexylamine 45 Solvent: Methanol 396 Product: Inclusion compound of di-n-hexylamine in urea.

EXAMPLE 30 Carrier: Urea 90 Base: Di-n-butylamine 45 Solvent: Methanol 396 Product: Inclusion compound of di-n-butylamine in urea.

EXAMPLE 31 Carrier: Urea 98.8 Base: N-decylamine 49.4 Solvent: Methanol 434.2

Product: Inclusion compound of n-decylamine in urea.

The inclusion compounds formed in each of the preceding Examples 29-31 was incorporated into a standard ammonia developing diazotype paper, e.g. Ozalid paper, by the following technique:

Nine and one-half grams of the inclusion compound were dispersed in g. of a 5 percent solution of methylmethacrylate polymer (Acryloid 8-82) dissolved in toluol, by milling the inclusion compound with the solution for 4 hours in a ball mill operating in a chilled room at 40 F. The dispersion was coated by means of a Mayer rod onto an ammonia developing diazotype sheet to a dry weight of about 3 pounds/3000 square feet, and dried. The dry sheet was exposed through a master to ultraviolet light according to standard practice, and was then heated for 5 seconds on a hot plate heated to 350 F. In each case a clear and legible copy of the master was formed.

In the following examples the latent developer is combined with the components of the diazotype system, and

ammo? 9 then coated upon a suitable support. A single coating is thus formed which is itself light-sensitive and heat-developable.

EXAMPLE 32 The following ingredients in the following amounts were charged into a ball mill:

P-olyvinylthylether, 25% solution in heptane 480 The'components were milled 'to'getherfor 4 hours in a roomchilled to 40 F. Twenty-five grams of the diazo system composition p'repared'in the ball mill and 'g. of the co=crystal addu ct prepared in Example 11 and 25 g. of hexane were combined in a ball mill and milled for 4*hours 'in a room chilled to 40 F. to disperse the cocrystal adduct in the diazo system composition. The mixture was then coated by a Mayer "rod to a-dry weight of approximately 3 pounds/ 3000 square feet'on a 60 pound chromekote paper, and dried. The dried sheet was ex- "posed to ultraviolet lightthrough a master and then heated for 5 seconds at 350 F. to produce a legible copy of the -master.

EXAMPLE 33 Twenty-five grams of the diazo system composition ,prepared in Example 32, 5 got the co-crystal adduct prepared in Example 10, and 25 g. of a 2 percent solution .of .Acryloid B32 dissolved in trichloroethylene were anixedtogether in aball mill for 4 hours ina roomchilled -to40 F. The mixture wasapplied by means'ofa Mayer .rod to a dry weight of approximately 3 pounds/3000 square feet to a 60 pound chromekote paper, and dried. The dried. sheet was :exposed to ultraviolet light through a master and then heated at 350 F. for 5 seconds toprowide a legible copy of the master.

In selecting "a particular latent developer, the lowest temperature at which development will occur within a -reasonablevheating time will "be of dbviousinte'rest. This may be considered as the temperature at Which dissociation of the latent developer occurs with the release of its 'basic component. That temperature is referred to herein -'as the base release temperature. Anexper'imental prorcedure to determine the base release temperature of a latent developer -'is "as follows:

BaseRelease Test 1A'coating dispersion is formed 'by charging a ball 'mill with '100 grams df latent developer, and 500 grains of a 2 /2 percent solution of polyvinylethylether (Bakelite FEDBM) in hexane, and milling for 15 hours. The comiposition is then coated onto gl-as's'ine to-give a coating hav- -irig a dry weight of 2-3 pounds/3000 square feet, and dried. The coated glassine is then cut into a strip tinequarter inch wide, andiplaced coated side down against ran indicator paper (e. g. pH ydrion, -"6&08;0 pH range, in which the essential ingredient is a Sulfonphthaleininditcator) on a *hot plate. A cork stopper hau ing its me :cut"-toione-quart'er inch in Width is placed crosswise over the "coated rglas'sine strip to i give a contact area of one- -qnarterinch by one-quarter inch and is weighted with a 500 gram Weight. The temperature of 'the plate is raised by increments of 5 F., each step being maintained for t1 minute, and the lowest temperature at which a col-or fehang'etakes place is'noted. I

The same "procedure may he employed using a 'commercial ammonia developing 'dia'z'otype paper, preferably one designated as slow speed (which has a low acid content) such as Tecnifax 25-8. When the latent developer "does :not contain an ionizing medium, the use of standard indicator papers cannot be relied upon since the the color change may not occur in the absence of such medium. The use of a standard ammonia developing -diazotype sheet is therefore better suited for determining the base release temperature of "such "latent develo'pers. I

The base release temperature, determined as outlined above, for several of the latent developers described in the examples are given in Table I.

TABLE -1 Base release temperature, 'F., as determined with- Example I Tecnifa'x A pHydrion a (60-810 25-8 Generally, suitable latent developers will have a base release temperature, determined 'asdescribed above, above about 110 F. and preferably above about 140 F. The time and temperature of development are frequentlyinterrelated in that development may occur within shorter periods at higher temperatures while requiring longer periods at lower temperatures. The base release temperature will necessarily reflect this interrelationship and its value in a given case :will depend on the conditions under which:it5is measured. The !procedure set forth is useful for purposes of comparison as a standardized 'reference, and-in view-of the long durationat which the'sarnpies are maintained at each temperature step, the results will approximate the absolute minimum at which release of the base from the latent developer will-occur. It is conceivable, however, that release of the base will occur atlower temperatures within longer periods of time, or that the temperature may momentarily be raised to above the rep orted base release temperature for "shorter periods of time.

In addition to the base release temperature, a factor "relating to the selection of particiilar latent developments is the stability ofthedeveloper and its reactivity or inertness toward the particular diazo system. This may be most readily determined by coating a dispersion of the developer onto an ammonia developing diazo sheet, and then subjecting the sheet to actual, or simulated exaggerated, conditions of storage. A latent developer having the desired characteristics inaythen be selected and a comparison of various developers may be readily made.

The reaction of the base in causing development or diazo systems is not fully understood, but it is known that a stable composition requires that the diazonium compound be in the form of itsacid salt and additional acidic compounds are frequently included in diazo systems to improve their stability. The base apparently serves to neutralize the acids present in thesystem and also to convert the diazonium salt to its more reactive base form. Since the acidity or acid content of different diazo systems will' be different, different amounts of base are required for development, but in any'event the amount required for any given system may easily be determined experimentally if it is not already known.

The amount of latent developer required in any given application will depend on the amount of base required for development, which will in turn depend upon the nature, including the acidity, of the diazo system. No precise amount can be set forth as a proportion of the composition except according to the general rule that sufficient base must be present to effect development, and the determination of that amount is well Within the abilities of one skilled in the chemistry of diazotype processes.

The nature of the image formed in any particular system will be determined by the precise nature of the diazo components, and it should here be noted that any of the diazo systems known to the art will be suitable. The compositions of Examples 32 and 33 employ conventional diazo compounds and azo couplers, but others may also be employed with comparable results. For example, the following diazo compounds may be used:

ZnCI -P-diazo-N-dimethylphenylenediamine ZnCl -diazo compound of 4-(N-methyl-N-hydroxyethylamino) -aniline 2,l-diazohydroxynaphthalene-S-sulfonic acid ZnCl -diazo compound of N-ethanol-ethylarninol-aminobenzene Zncl -P-diazodimethylaniline ZnCl -tetrazodiphenylpiperazine ZnCl -N,N-diethylaniline-P-diazoniumchloride ZnCl -N,N-dimethylaniline-P-diazoniumchloride ZnCl -4-N,N-diethylaminobenzenediazoniumchloride ZnCl -4-N,N-benzyl-N-ethylbenzenediazoniumchloride ZnCl -P-diazo-N-rnethyl-N-hydroxyethylaniline ZnCl -P-diazo-N-ethylarnino-o-toluidine CdCl -N-ethylaniline-P-diazoniumchloride CdCl -N-methylaniline-P-diazoniumchloride ZnCl -N-hydroxyethylaniline-P-diazoniumchloride ZnCl -N-propylaniline-P-diazoniumchloride 2,5,4-triethoxydiphenyl-1-diazonium acid sulfate Naphthalene-Z-diazo-l-oxide-S-sulfonic acid P-diethylaminobenzenediazoniumborofiuoride ZnCl -4-benzoylamin0-2,S-diethoxybenzenediazoniumchloride P-phenylamine benzenediazonium sulfate ZnCl -N-hydroxyethyl-N-methylamino-P-benzenediazoniumchloride ZnCl -1-(N-hydroxyethyl-N-ethyl) amino-3-methyl-4- benzenediazoniumchloride 2,5,4'-triethoxydipheuyl-4-diazouiumacid sulfate ZnCl -l-benzoylamino-2,5-diethoxy-4-benzenediazoniumchloride ZuCI -l-ethylamino-3-methyl-4-benzenediazoniumchlo.

ride ZnCl -4-( N-methyl-N-hydroxymethyl) aminobenzenediazoniumchloride The diazonium components of the compounds above which are metal dichloride complexes may also be used.

Azo couplers which may be used include:

2,3-dihydroxynaphthalene-6-sulfonic acid resorcinol N-fi-hydroxyethyl-a-resorcylamide a-Resorcylamide N-phenyl-a-resorcylamide Mono-a-resorcylamide of ethylene diamine Phloroglucinol dihydrovynaphthalene Na-naphthalene 1,3,6-trisulfonic acid Phenylmethylpyrazolone diresorcinolsulfoxide 7-hydroxy-l,Z-naphthimidazole resorcinolmonoacetate resorcinolmonocarbazate resorcinol-mono-N- (B-aminoethyl) carbamate resorcinol-mono-N,N-diethylcarbamate resorcinol-mono-ethylcarbonate Z-diethylaminoethylresorcinolmonobenzenesulfonate Z-hydroxyphenylthiourea Z-hydroxyphenylthiourea 4-hydroxyphenylthiourea 6-methyl-4-hydroxy-2 1)-pyridone 6-ethyl-4-hydroxy-l-methyl-2(1)-pyridone Typical diazo systems will generally include, in addition to a diazonium compound and an azo coupler, other materials such as stabilizing acids and other stabilizers. Typical stabilizing acids are: citric acid, maleic acid, formic acid, phosphoric acid, tartaric acid, boric acid, hydrochloric acid, ascorbic acid and isoascorbic acid; and other stabilizers include: thiourea, zinc chloride, aluminum sulfate. Other types of diazo systems utilize a single diazonium compound, which upon exposure to actinic radiation decomposes to form an azo coupler compound. A brief exposure of such a compound will result in partial decomposition and form a coating containing undecomposed diazonium compound and the decomposition product, an azo coupler. Such are described in US. Patent No. 2,313,288.

As shown in the examples described above, photocopy sheets provided by this invention may be exposed to the master in the same way as conventional diazotype paper, but development of the latent image is much more easily accomplished simply by heating the paper. Another convenient method of making use of the photocopy paper of this invention is to use a light source rich in both ultraviolet and infrared radiation by which the paper may be simultaneously exposed and developed. Standard duplieating equipment of the type used for exposing thermofacsimile may also be used. It should be noted in this connection that the thermofacsimile process is also suitable since infrared radiation of the dark areas will cause selective heating and develepoment of the diazotypc paper there, without affecting the light areas. Subsequent exposure of the sheet to ultraviolet light will then destroy the diazonium compound in the light areas and obviate the possibility of further darkening therein.

In this connection it will be noted that the systems of this invention may employ, in place of the diazo components, the color indicator material utilized in the procedures reported in Table 1 which also changes color in the presence of a basic organic amine.

The foregoing description sets forth in detail the technical aspects of this invention and describes representative examples of compositions and procedures that may be employed in its practice. These are given to familiarize those skilled in the art with its advantages and features and to set forth not only various specific compositions that may be used, but also procedures by which suitable materials other than those herein described may be selected and the full scope of applicants contribution may be made use of.

A commercially useful heat developable photosensitive composition has long been sought but without practical success. Suggestions that have been advanced have included the incorporation of heat activatable material which is potentially reactive with the constituents of the diazo system, but none of the systems heretofore proposed has provided a commercial commodity. Potentially reactive developers suggested in the past have for the most part been in the nature of solid materials which themselves are reactive, as when heated or dissolved, but which remain relatively dormant in the system until heated, whereupon their reactivity is increased. As an example, urea and dimethylurea may be included in the diazonium composition, as shown by Morrison in US. Patent No. 2,732,- 299, to provide a relatively stable composition which is described as requiring a rather long development (1 minute) at a high developing temperature of C.

Both urea and dimethylurea have been tried as latent developers in connection with the present development, but they have been found to produce a result quite difapropos ferentfrom that attained byraean's i 'the latent developers employed in compositions of this invention. Both of these compounds caused an irregular, gradual darkening when the paper was heated; -first the area just outside the heated portion turned blue (when employing a bluedeveloping diazotype sheet) and then the heated area reddened. Apparently, as the urea was heated to activation temperature, there was initially a decomposition which formed ammonia vapors causing development just outside the heated area. Continued heating caused melting of the urea, and some kind of color-forming reaction resulted. This type of reaction, marked by bringing the urea, or dimethylurea, to reactive conditions, was in marked contrast to the mechanism of applicants system wherein the dissociation of the crystal complex releases the base in a fully reactive state. The practical significance of this is instantaneous and complete color formation upon reaching the developing temperature.

By way of example, it will be noted from Table I that the latent developers of Examples 30 and 31 both employ urea, not as a developer but as the carrier compound. These show base release temperatures of 225 F. and 115 F. respectively. The same test, using urea alone as though it were a latent developer, coated from its aqueous solution onto glassine paper, shows with Tecnifax 25-S paper a blue color formation in the area surrounding the test area at 170280 F., and a reddening in the contact area at 245280 F. With dimethylurea, the initial blue color formation outside the contact area occurred at 260- 290 F. with reddening in the contact area at 260290 F.

Ammonium carbonate may also be employed as a kind of potential developer as shown by Dieterle in US. Patent No. 2,228,562. It is activatable at a much lower temperature than urea and its derivatives but may not be preliminarily combined with the diazonium system since development will occur even at room temperature after a relatively short period of time. This material is neither inert nor stable. Neither of these systems which have heretofore been suggested has made use of a latent developer which is both stable and inert at normal conditions of temperature and humidity while being dissociable at an elevated temperature to yield a base in fully reactive state effective to cause instantaneous and complete development.

Photothermographic papers embodying this invention stand in marked contrast to the diazo systems proposed in the past. They possess the general advantageous characteristics of conventional diazotype papers, but are easily developed completely by heating to temperatures ranging upwards from the base release temperatures reported by an amount depending on the time of heating. Development occurs by release of the base from the latent developer in already reactive condition, and the reaction occurs quickly and completely upon heating within periods of time as short as a few seconds. Processing of the paper other than by heating is entirely unnecessary; the image originally formed is stable and since exposureto ultraviolet light has destroyed the diazonium compound in the exposed, undarkened areas, there is no danger of subsequent development in these areas.

We claim and desire to secure by Letters Patent:

1. A heat developable photo copy composition comprising a potentially reactive photosensitive azo dyeforming material in stable unreactive condition but reactive with a basic organic amine to form a dye and a stable, unreactive latent developer in potentially reactive association with said material, said latent developer being an organic amine in combination with a bisphenol forming a solid crystalline complex which is stable undernormal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine.

2. A heat developable photo copy composition comprising a potentially reactive photosensitive azo dye-forming material in stable, unreactive condition but reactive with a basic organic amine to form a dye and a stable untemperature to yield said amine.

1-4 reactive 'lafent developer in potentially reactive association with said material, said latent developer being an organic amine in combination with urea forming a solid "inclusion compound which is stable under normal conditions of temperature and humidity and dissociable at said'activation 3. A photosensitive heat developable copy sheet com prising a support carrying a potentially reactive photosensitive azo dye-forming material in stable, unreactive condition but reactive with a basic organic amine to form a dye, and a latent developer in potentially reactive association with said material, said latent developer being an organic amine in combination with a bisphenol forming a solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine.

4. A photosensitive heat developable copy sheet comprising a support carrying a potentially reactive photosentitive azo dye-forming material in stable, unreactive condition but reactive with a basic organic amine to form a dye, and a latent developer in potentially reactive association with said material, said latent developer being an organic amine in combination with urea forming a solid inclusion compound which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine.

5. A photosensitive heat developable copy sheet comprising a support carrying a potentially reactive photosensitive azo dye-forming material in stable, unreactive condition but reactive with a basic organic amine to form a dye, and a coating containing a latent developer uniformly distributed over said material and in potentially reactive association therewith, said latent developer being an organic amine in combination with a bisphenol forming a solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine.

6. A photosensitive heat developable copy sheet comprising a support carrying a potentially reactive photosensitive azo dye-forming material in stable, unreactive condition but reactive with a basic organic amine to form a dye, and a coating containing a latent developer uniformly distributed over said material and in potentially reactive association therewith, said patent developer being an organic amine in combination with urea forming a solid inclusion compound which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine.

7. A heat marking copy sheet responsive to heating to an elevated activation temperature by changing visibly to a contrasting color comprising, in combination, a support carrying indicator material which changes color in the presence of a basic organic amine, and a stable unreactive latent heat sensitive developer in intimate association with said material for causing a color change upon heating said sheet to an activation temperature greater than F., said developer being an organic amine in combination with a bisphenol forming a solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine to cause said color change.

8. A heat marking copy sheet responsive to heating to an elevated activation temperature by changing visibly to a contrasting color comprising, in combination, a support carrying indicator material which changes color in the presence of a basic organic amine, and a stable unreactive latent heat sensitive developer in intimate association with said material for causing a color change upon heating said sheet to an activation temperature greater than 110 F., said developer being an organic amine in combination with urea forming a solid inclusion compound which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine to cause said color change.

(References on following page) References Citeai in the file of this patent UNITED STATES PATENTS Dieterle Jan. 14, 1941 Barde Mar. 9, 1943 Greig Sept. 22, 1953 Morrison I an. 24, 1956 16 Van Dam July 28, 1959 OTHER REFERENCES Saunders: The Aromatic Diazo Compounds, Edward 366 and 368.

5 Arnold & Co., London, 1949, page 365, lines 19-23, pages

Claims (2)

1. 3. A PHOTOSENSITIVE HEAT DEVELOPABLE COPY SHEET COMPRISING A SUPPORT CARRYING A POTENTIALLY REACTIVE PHOTOSENSITIVE AZO DYE-FORMING MATERIAL IN STABLE, UNREACTIVE CONDITION BUT REACTIVE WITH A BASIC ORGANIC AMINE TO FORM A DYE, AND A LATENT DEVELOPER IN POTENTIALLY REACTIVE ASSOCIATION WITH SAID MATERIAL, SAID LATENT DEVELOPER BEING AN ORGANIC AMINE IN COMBINATON WITH A BISPHENOL FORMING A SOLID CRYSTALINE COMPLEX WHICH IS STABLE UNDER NORMAL CONDITIONS OF TEMPERATURE AND HUMIDITY AND DISSOCIABLE AT SAID ACTIVATION TEMPERATURE TO YIELD SAID AMINE.
2. 4. A PHOTOSENSITIVE HEAT DEVELOPABLE COPY SHEET COMPRISING A SUPPORT CARRYING A POTENTIALLY REACTIVE PHOTOSENSITIVE AZO DYE-FORMING MATERIAL IN STABLE, UNREACTIVE CONDITION BUT REACTIVE WITH A BASIC ORGANIC AMINE TO FORM A DYE, AND A LATENT DEVELOPER IN POTENTIALLY REACTIVE ASSOCIATION WITH SAID MATERIAL, SAID LATENT DEVELOPER BEING AN ORGANIC AMINE IN COMBINATION WITH UREA FORMING A SOLID INCLUSION COMPOUND WHICH IS STABLE UNDER NORMAL CONDITIONS OF TEMPERATURE AND HUMIDITY AND DISSOCIABLE AT SAID ACTIVATION TEMPERATURE TO YIELD SAID AMINE.