Thermal dye transfer materials

The use of eutectic combinations of a dye and a second compound (which may also be a dye) in a binder has been found to provide benefits to thermal dye transfer materials.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to thermal dye transfer printing, and more 
particularly to dyes used in a thermal dye transfer printing construction. 
The dyes comprise a specific type of mixture known as a eutectic mixture. 
The eutectic mixture has at least two components. 
2. Background of the Art 
Various dyes are used in thermal transfer systems. Dyes are used in both 
thermal mass transfer systems, and thermal dye transfer systems. Dye 
groups described in the prior art are generally characterized as 
relatively sublimable disperse dyes or solvent dyes. Dyes are generally 
used singly or as a combination for a monochrome color. Some patents list 
dyes used in combination, but relatively little information is given to 
the composition and properties of the dye mixtures. 
Dyes are usually described as being dissolved in a solvent with the binder 
resin and coated onto a substrate to form an ink layer on the substrate. 
The dye is often described as subliming under the action of the heat 
energy of the thermal head, and transferring to an image receptive sheet. 
Dyes are also described as being suspended within the binder in the form of 
particles. To facilitate sublimation, the dyes usually have a low 
molecular weight of about 100 to 750. Criteria for selection of dyes 
include sublimation temperature, hue, weatherability, solubility of the 
dye in ink compositions or binder resins, and other factors. The dye is 
usually present in an amount which is dependent upon the degree of its 
transfer at the sublimation temperature, and the covering power in the 
transferred state. 
The broad technical area of imaging art contains a number of disclosures of 
dye- or dye former-containing eutectics, many of them used in certain 
imaging procedures. Frequently, mention is made in the literature of 
eutectic compounds or eutectic complexes. There are no such materials as 
eutectic compounds or complexes in the true technical sense normally 
understood by a chemist. Eutectics are definitely mixtures, not compounds, 
of two or more chemically distinct entities. Furthermore, a solid eutectic 
contains separate crystals of each of the mixed entities, not a mixture at 
the molecular level. 
U.S. Pat. No. 4,614,682, entitled "Thermosensitive Image Transfer Recording 
Medium" discusses a thermosensitive recording medium comprising a support 
material and a thermofusible ink layer formed thereon, which thermofusible 
ink layer comprises a dye component, a binder agent, and a pigment having 
needle-like crystal form, which is dispersed in a network form throughout 
the thermofusible ink layer. Dye components are specifically described as, 
"it is preferable that the eutectic temperatures of the dyes to be used 
with a binder agent be in the range of 50.degree. C. to 140.degree. C., 
although the eutectic temperatures vary depending upon the binder agent to 
be used in combinations." Claim 7 details "A thermosensitive image 
transfer recording medium as claimed in claim 1, wherein the eutectic 
temperature of said dye component in combination of said binder agent is 
in the range of 50.degree. C. to 140.degree. C." It appears this refers to 
a eutectic combination of a dye and a binder. 
The same mentioned patent refers to the dye as being of a smaller particle 
size than the needle-like pigments to be used, and that the dye be in a 
dissolved state. 
Japanese patent publication JP 60-056590 assigned to Mitsubishi Electric 
Corp. describes a reusable heatsensitive recording sheet which includes a 
layer containing: (a1) dye; (a2) material lowering the melting point of 
(a1); (a3) material dissolving (a1) and (a2) at elevated temperature; (a4) 
a surfactant with melting point of 40.degree. to 100.degree. C. Preferably 
the mixture of (a1) and (a2) is what is described as eutectic or 
cocrystalline material. The mixed ratio of (a1) and (a2) is 1:10 and 10:1 
Dye (a1 ) is preferably an anthraquinone or azo disperse dye. Compound 
(a2) is, e.g. p-nitrobenzaldehyde, stearamide, methyl-4-tert-butylphenol, 
etc. Material (a3) is, e.g. glycerin, diethylene glycol, triethylene 
glycol, etc. Surfactant (a4) is, e.g., an ester of a long chain fatty 
acid. The mixture (a1)-(a4) is contained in a polymeric binder. The 
advantages of this invention are good sensitivity, good gradation 
properties, and reuse. 
Matsushita Electric Corp. Japanese patent abstract JP 59-93389 speaks of a 
color sheet material for thermal transfer with particles containing at 
least two kinds of coloring material. The particles contain at least one 
of a basic subliming dye and a disperse subliming dye. Mention is made of 
microencapsulation of the dye, but it is not clear whether this refers to 
the combination or to the individual dyes. No reference to eutectics 
appears in the abstract. 
Many Ricoh patent publications (e.g. JP 62-135388, JP 62-130877, JP 
58-211493, JP 57-201693, JP 57-014094, JP 58-211493) speak of eutectics or 
eutectic compounds in connection with thermal leuco dye imaging systems. 
Work at Fuji (A. Igarashi and T. Ikeda, Proc. 1st International Congress 
on Advances in Non-Impact Printing Technologies, 1982, p. 886) definitely 
shows occurrence of true eutectics in some constructions. However, in 
contrast to the purely physical process of thermal transfer in our 
invention, the melting of the eutectic in these systems is used to trigger 
a chemical reaction which results in color formation from the colorless 
leuco dye. 
A similar situation arises in connection with thermal diazo imaging 
systems. Work at NTT (H. Sato, K. Sukegawa and Y. Ooba, J. Imaging. 
Technol., 10, 74 (1984); H. Sato, Y. Ooba and S. Sugawara, ibid., 11, 137 
(1985)) has established the importance of both binary and ternary 
eutectics in these systems, but again this is a chemistry-triggering 
situation. 
Several patents concern mixtures of dyes selected for hue adjustment. The 
abstracts make no mention of eutectics. Mitsubishi Chemical Industries (JP 
61-148096) claims a sublimation transfer recording material giving pure 
black images from a mixture of matched yellow, cyan and magenta dyes. U.S. 
Pat. No. 4,401,692 assigned to Hoechst concerns a transfer print carrier 
for printing on polymers having a mixture of blue and red to yellow, 
readily sublimable, disperse dyes giving fast black dyeings. Bayer (DE 
3537257) claims a mixture of specific azo and anthraquinone dyes for 
selectivity dyeing polyester in polyester-cotton blends by the thermosol 
or HT steam process. The azo is present at 90 to 99.5 wt %. 
Eutectic mixtures of dyes have been investigated in connection with the 
non-additivity of dye adsorption isotherms for the dyeing of fibers with 
dye mixtures (A. Johnson, R. H. Peters and A. S. Ramadan, J. Soc. Dyers 
Colour., 80, 129 (1964), but this appears to be quite unconnected with the 
present invention. Similarly, patents on eutectic dye carriers (e.g. U.S. 
Pat. No. 3,925,013 and U.S. Pat. No. 3,787,181) where the dye is not part 
of the eutectic also appear to be of no real relevance. 
Several Ricoh patents (e.g. JP 58-065441, JP 57-122040, JP 56-142536) claim 
electrophotographic elements with "eutectic crystal complexes" of a 
pyrilium dye, polymer and charge transport material, apparently analogous 
to Kodak work showing formation of a complex of thiapyrylium dye and 
polycarbonate (W. J. Dulmage et al. J. Appl. Phys., 49, 5543, (1978). 
Similarly Japanese patent publication JP 60-044553 (examined JP 87-04182) 
discusses a photoconductor sensitizing dye disclosed as a eutectic of a 
merocyanine dye and an organic electron acceptor. 
Eutectic mixtures of compounds are cited in the patent literature that 
discusses eutectic compounds related to liquid crystal compounds, 
pharmaceuticals, perfumeries, and dye carriers for textile printing. 
Japanese patent publications listing the use of anthraquinone dyes in a 
thermal transfer composition are JP 61-227093, 61-035993, 60-151097, 
60-253595, 60-131292, 60-131293, 60-131294, 60-172591, 60-031559, 
60-053563, 59-227948, 60-217266, 59-091644, 59-000221. 
Japanese patents listing the use of azo dyes in a thermal transfer 
construction are JP 51-112993, 61-227091, 61-227092, 61-224595, 61-119786, 
61-144388, 58-111176. 
SUMMARY OF THE INVENTION 
This invention provides a thermal dye transfer composition comprising a 
eutectic mixture of at least two solid organic dyes contained in a 
polymeric binder. The dyes are preferably selected from the azo, 
anthraquinone, aminostyryl, azomethine, and disulphone classes. Sets of 
two or more of the dyes are selected, mixtures of which, at atmospheric 
pressure, exhibit at least one eutectic point at a temperature at least 
5.degree. C. and preferably at least 10.degree. C. below the melting point 
of the lowest melting individual component. 
Useful constructions are obtained when at least one molar ratio of the 
eutectic components taken a pair at a time is between 0.25 and 4.0 times 
their molar ratio at a eutectic point composition. The molar ratio of 
these two dyes in this mixture at their eutectic point composition should 
be between 0.05 and 20.0, and the eutectic point temperature for the 
combinations may be in the temperature range commonly used in the art for 
thermal transfer, e.g. 70.degree. C. to 250.degree. C. It is emphasized 
that the dye mixtures should form true eutectics as defined below. 
A eutectic composition evidences particular physical properties. At a 
precise eutectic point composition, when the composition is heated to the 
melting temperature of the eutectic, the solid phase of the composition 
has the same molecular proportions of the components of the eutectic as 
does the generated liquid phase (the melt). The proportions of materials 
(either weight/weight, or mole/mole) being added to the liquid phase are 
the same as the proportions in the melt and in the solid phase. Where the 
ratio of materials which can form a eutectic differs from the ratio at the 
eutectic point composition, proportions of materials at approximately the 
eutectic point composition ratio first melt and then the residual solids 
melt. This is true no matter how many compounds make up the eutectic. 
Where two (or more) compounds are capable of forming a eutectic, the lowest 
melting point for the combination of the compounds is a eutectic point for 
the compounds. At the eutectic point composition melting usually occurs 
over a narrow temperature range. 
A eutectic mixture of at least two compounds has one or more eutectic 
points and is a thermodynamic entity with a precise and specific 
definition. Its existence is characterized by definite features displayed 
in a phase diagram. However, it is not uncommon to find references to 
eutectic mixtures in the patent and other literature where no evidence for 
conformance of the mixture to the thermodynamic criteria for a eutectic is 
presented. The term is used loosely in those situations to signify any 
mixture which exhibits a melting point depression compared to the pure 
components. Other types of non-eutectic mixtures (e.g. solid solutions) 
can show melting point depression, but they are not eutectics. We are 
concerned with mixtures which are eutectics; other mixtures are not within 
the scope of the patent. 
We use anthraquinone, azo or other dyes in specifically eutectic 
combinations with each other or with a colorless material. Our definition 
of useful mixtures is based on the amount of melting point depression at 
the eutectic point, not necessarily on component ratios of the mixture. We 
also contain this mixture in a polymer binder. We do not specifically 
require the presence of a material dissolving both the dye and the second 
eutectic component. In fact, we believe that this might sometimes reduce 
the effectiveness of the invention. 
In common with the rest of the art plasticizers, surfactants and other 
additives may be used in the donor and receptor constructions. 
Thermal dye transfer media or elements may have a variety of different 
structures and may be used in a number of different processes. The medium 
may be a single self-sustaining layer of dyes in a binder. The percentage 
of dye in the total composition of such a single layer element would tend 
to be lower than the percentage of dye in a multilayer system. This is 
because the binder in such a single layer system must provide the totality 
of structural support for the layer and cannot do so at extremely low 
percentages. The binder in such a single layer system may have to be at 
least 20% by weight of the layer and preferably is at least 40% by weight 
of a single layer transfer element. This single layer element would tend 
to provide lower optical densities than would multilayer sheets comprising 
the dye and binder coated on a carrier layer. The latter types of 
constructions use the binder to give the dye layer cohesive strength but 
do not have to provide self-sustaining independent integrity to a single 
layer. The percentage of binder in the donor layer of a supported thermal 
dye transfer element may therefore be used in a broader range than the 
binder in a single layer element. In some cases it may be possible to use 
as little as one or two percent binder or even less (99% or 98% by weight 
dye) in a supported layer. However a more typical range could be about 90% 
dye to 20% by weight dye. The preferred range for multilayer constructions 
is 70-40% by weight, and most preferred is 60-50% by weight dye to binder 
in the donor layer on the carrier sheet. 
The carrier sheet is preferably flexible, but may be rigid if the receptor 
layer is sufficiently flexible and/or conformable. The carrier layer may 
thus be glass, ceramic, metal, metal oxide, fibrous materials, paper, 
polymers, resins, coated paper or mixtures or layers of these materials. 
The carriers may be opaque, translucent or transparent and may be 
extremely thin if used with backside thermal print heads or may be thick 
if used with a front thermal exposure system. Such a front thermal 
exposure system could be a laser which would expose through a transparent 
receptor layer in contact with a donor layer having the eutectic dye 
mixture. 
This invention has utility in thermal dye transfer imaging. Constructions 
containing eutectic mixtures of dyes are found to have improved properties 
when compared with constructions containing a single dye or a simple 
mixture of dyes. Several beneficial effects are found. These may include: 
improved image density, increased dye transfer efficiency, higher image 
transparency, enhanced grey scale, better donor sheet handling 
characteristics, longer donor sheet shelf life and greater thermal and 
light stability of the image. Examples of these are given below, though 
beneficial effects are not restricted to these examples. 
It should be noted that in many cases it is particularly advantageous to 
use a eutectic mixture where both components are dyes of similar color, 
because then all material transferred to the image receptor contributes to 
image density of the required hue (e.g. compounds 3 and 32 of Example 4). 
In other cases adding a second dye to the first produces an undesirable 
hue change, and a colorless eutectic-promoting second component may be 
employed (e.g. compounds 3 and 49 of Example 4). A further option is the 
formation of a eutectic mixture of two dyes of quite different color to 
generate a hue not otherwise conveniently available (e.g. compounds 23 and 
32 of Example 4). 
The eutectic-forming mixtures of this invention may be prepared in a number 
of ways. A mixture of the components may be dissolved in a suitable 
solvent, optionally containing other additives, and a solid obtained by 
evaporation of the solvent, or by the addition of a precipitating agent. 
The components may be intimately ground together by hand or by mechanical 
means. The components may also be mixed, heated to the molten state, and 
the solid mixture obtained by cooling. It is also envisaged that the 
mixtures that are the object of this invention can be formed by 
sublimation of the components, or by extrusion of the components together 
with a suitable binder into a film or other form. Other methods may occur 
to those skilled in the art, and the method of preparation of the eutectic 
mixture is not to be construed as a limitation on the scope of the 
invention.

DETAILED DESCRIPTION OF THE INVENTION 
A univariant (i.e. pressure dependent) eutectic point occurs when two solid 
phases are in equilibrium with their liquid melt. At constant pressure the 
eutectic point becomes invariant, occurring at a unique temperature and 
composition. If a liquid of the composition of the eutectic point is 
cooled, a mixture of the solid components forms having the same 
composition as the liquid. There is no solid solution or chemical compound 
associated with the freezing of the mixture. In some cases the two 
components of the mixture can form solid compounds having congruent 
melting points at a dystectic point composition. Multiple eutectic points 
can then arise, which on freezing result in mixtures of fixed proportion 
of one of the original components and the new compound formed from the two 
components. Again there is no solid solution or new chemical compound 
associated with this eutectic point. 
At fixed pressure, the eutectic point in a binary component system 
corresponds to the lowest melting mixture of the two components. However, 
the converse is not true; when solid solutions are able to form over the 
entire composition range of the mixture, the lowest melting composition is 
not a eutectic, but either a pure component or a solid solution. Other, 
more complex, equilibria can arise, but do not change this fundamental 
picture. These are described in standard texts, e.g. "The Phase Rule and 
its Applications", A. N. Campbell and N. A. Smith, Dover Publications, 
1951, p. 133ff. 
The invention consists of a thermal dye transfer composition containing a 
mixture of at least two solid dye components selected so that this mixture 
forms at least one eutectic point at atmospheric pressure. In the 
application of this invention, the solid components of the mixture, 
present in proportions at or near the eutectic composition, are deposited 
as a film usually in a polymeric binder, optionally containing other 
additives, to form a layer as part of a donor sheet preferably on a 
suitable substrate. Preferred binders are vinyl chlorides including 
chlorinated polyvinyl chloride, polyvinyl chloride, cellulose derivatives, 
and vinyl butyrals. The donor sheet is contact with an appropriate 
receptor sheet and heat is applied in an imagewise fashion. Under the 
influence of heating the eutectic dye mixture, but substantially none of 
the binder, is transferred to the receptor sheet to form a colored image. 
Eutectic mixtures of one dye with a colorless compound have also shown 
some advantages, but there may be a loss in color quantity for a given 
addition of dye. The formation of solid solutions or chemical compounds 
between the components of the subject mixture is not excluded provided a 
eutectic point also occurs. Because of this, and the looseness with which 
the term eutectic is often applied, the identification and 
characterization of the eutectic mixture is of prime importance to this 
invention. 
Whether a mixture of components exhibits a eutectic point can be 
established most usefully by differential scanning calorimetry, and 
confirmed by other techniques such as optical microscopy or X-ray 
diffraction. Differential scanning calorimetry of a eutectic-forming 
mixture of two components at the composition of the eutectic point 
exhibits a single, sharp melting endothermic peak. At compositions of the 
mixture different from the eutectic point two endothermic peaks are seen. 
One is sharp, and occurs at the temperature of the eutectic point. The 
other peak corresponds to melting of whichever component is in excess 
relative to the eutectic composition, and is typically broader and found 
at lower temperatures than that for this component in isolation. The 
eutectic point appears as a cusp (i.e., a sharp discontinuity formed by 
the meeting of two curves) in contact with a eutectic horizontal in the 
phase diagram, which represents equilibria in the mixture as a function of 
temperature and composition at constant pressure. Solid solutions may also 
exhibit a single sharp melting endotherm at some composition corresponding 
to the lowest melting point of the mixture, but in contradistinction to 
eutectic-forming mixtures, the behavior of these as the proportion of the 
components is changed is different. A single melting endotherm is seen, 
whose temperature is dependent on composition, and which is typically 
broadened compared to that at the lowest melting point. The phase diagram 
no longer exhibits a eutectic horizontal. An instance of the eutectic 
behavior that is the subject of this invention is provided in Examples 1 
and 2. Other representative phase diagrams are given in Example 3. 
Anthraquinone dyes found useful in the practice of this invention include 
anthraquinone dyes substituted once or severally with one or more of the 
following functional groups: amino, alkylamino, arylamino, acylamino, 
aroylamino, aroylamino wherein the aryl ring is further substituted, 
alkylsulfonylamino, alkylsulfonylamino wherein the alkyl chain may be 
branched and contains from two to twenty carbons atoms, arylsulfonylamino, 
arylsulfonylamino wherein the aryl ring is further substituted, hydroxy, 
alkoxy, aryloxy, substituted aryloxy, alkylthio, arylthio, substituted 
arylthio, chloro, bromo etc. 
Azo dyes found useful for this invention include dyes consisting of an azo 
group substituted with a group A at one end and a group B at the other. 
Group A consists of an aryl group containing one or more of the following 
substitutents: hydrogen, amino, alkylamino, arylamino, substituted 
alkylamino, substituted arylamino, alicyclic amino; or group A consists of 
a pryidone, a substituted pyridone, a cyano-substituted pyridone, a 
hydroxy-substituted pyridone, an alkyl-substituted pyridone. Group B 
consists of an aryl group containing one or more of the following 
substituents: hydrogen, hydroxy, alkoxy, aryloxy, substituted aryloxy, 
alkyl, substituted alkyl, haloalkyl, aryl, substituted aryl, amino, 
alkylamino, arylamino, substituted arylamino, alicyclic amino, chloro, 
bromo, thioalkyl, thioaryl, substituted thioaryl, cyano, nitro, acylamino, 
substituted acylamino, aroylamino; or group B is: a heterocycle, a 
substituted heterocycle, a furan, a substituted furan, a thiofuran, a 
substituted thiofuran, a thiazole, a substituted thiazole, a 
benzothiazole, a substituted benzothiazole, a diazole, a substituted 
diazole, a benzodiazole, a substituted benzodiazole. 
The term "dye" as used in the practice of the present invention refers to a 
compound which absorbs at least some radiation in the visible region of 
the electromagnetic spectrum with a molar extinction coefficient in a 
suitable solvent rising at least to 500, and therefore exhibits a color. 
The material must be soluble in water or an organic solvent but does not 
have to be completely dissolved in the donor layer. In fact, because of 
the high percentage of dye used, at least some is present as solid dye 
(which is often referred to as pigment). Some of the dye is present as 
small crystals of the dye. The two or more dyes which form the eutectic 
are in an intimate physical association within the donor layer of the 
thermal transfer element so that eutectic behavior can be exhibited in the 
donor layer. The dyes are in part usually present as distinct crystals of 
individual dyes, but some dye may be present dissolved in the binder or in 
a solid solution with other dye(s). Generally at least some of each dye is 
present as distinct small particulates (usually crystals) of the 
individual dyes. 
EXAMPLE 1 
Mixtures of various molar ratios of compounds 3 and 32 were prepared by 
grinding the components with a pestle and mortar. 5 mg of such a mixture 
was placed in an aluminum boat and heated at 1.degree. C./min in a 
differential scanning calorimeter. Heat flow as a function of temperature 
was recorded from ambient temperature to 180.degree. C. FIG. 1 presents 
the results, the eutectic composition occurring at a molar ratio of dye 
3/dye 32 of 0.587. 
______________________________________ 
Figure Molar ratio 
Temperature in .degree.C. of 
number dye 3/dye 32 
first peak second peak 
______________________________________ 
1a pure 3 143.3 none 
1b 0.205 105.2 112 
1c 0.587 105.4 none 
1d 2.030 104.6 123 
1e pure 32 120.9 none 
______________________________________ 
EXAMPLE 2 
Mixtures of compounds 3 and 32 were prepared and subjected to differential 
scanning calorimetry as in Example 1. Onset of melting was determined by 
the tangent method and completion of melting was taken as the temperature 
at which 90 percent of the heat had been absorbed. The results were used 
to construct the phase diagram in FIG. 2. The temperature and composition 
at the cusp define the eutectic point and correspond to those in Example 
1. 
EXAMPLE 3 
Mixtures of compounds listed below were prepared as in Example 1 and phase 
diagrams were determined as in Example 2. The results appear in FIG. 
3(a)-(d), and the eutectic compositions (expressed as mole ratio of the 
first compound to the second) are summarized below. 
______________________________________ 
Figure Mixture Eutectic composition 
number of compounds 
as molar ratio 
______________________________________ 
3a 3 and 38 1.273 
3b 18 and 35 0.429 
3c 8 and 32 0.613 
3d 7 and 32 0.111 
______________________________________ 
EXAMPLE 4 
In view of the characteristic thermal behavior of eutectic mixtures 
described earlier and demonstrated in Example 1, a useful screening method 
for binary eutectic mixtures is differential scanning calorimetry of 
mixtures of various compositions, with the occurrence of a sharp, 
composition invariant endotherm taken to imply a eutectic-forming binary 
mixture. (A second, composition dependent, endotherm also occurs unless 
the mixture fortuitously has exactly the eutectic point composition). A 
further consideration in regard to practical utility is the eutectic 
depression, used herein to mean the difference in temperature between the 
lower of the melting points of the two pure components of the mixture and 
the melting point of their eutectic composition. Example 4A lists 
combinations of compounds found to have eutectic depressions of at least 
5.degree. C., while Example 4B lists combinations where the eutectic 
depression is less than 5.degree. C. 
EXAMPLE 4A 
Binary mixtures of the compounds tabulated below were evaluated for 
eutectic depression as defined in the text by the methods of Example 1, 
except for a 20.degree. C. per minute heating rate. 
______________________________________ 
First Second Eutectic 
component component depression (.degree.C.) 
______________________________________ 
3 32 16.5 
3 30 19.5 
3 31 22 
3 49 18 
3 47 10 
3 37 21 
3 27 12 
3 26 20 
3 33 29 
3 38 21 
46 32 9 
48 32 7 
10 32 17 
14 30 30 
14 27 7 
14 25 10 
14 33 13 
18 32 7 
18 47 10 
18 37 19 
18 35 14 
44 32 29 
44 26 36 
44 34 17 
23 32 10 
23 47 9 
1 47 8 
16 47 9 
4 30 16 
4 31 18 
4 27 16 
4 26 24 
4 25 32 
45 32 27 
45 26 52 
45 33 22 
7 47 7 
7 33 7 
9 26 7 
9 33 7 
6 47 9 
2 47 7 
24 33 9 
22 32 11 
22 47 10 
20 32 20 
20 47 25 
19 47 13 
21 32 8 
21 47 7 
13 32 9 
8 32 19 
17 32 15 
17 47 10 
29 36 19 
29 27 22 
4 41 25 
18 42 22 
3 39 17 
32 40 27 
3 43 19 
32 43 20 
______________________________________ 
EXAMPLE 4B 
Binary mixtures of the compounds tabulated below were evaluated for 
eutectic depression, as defined in the text, by the methods of Example 4A. 
______________________________________ 
First Second Eutectic 
component component depression (.degree.C.) 
______________________________________ 
44 36 1 
11 32 2 
12 32 2 
45 34 2 
15 32 3 
7 32 3 
______________________________________ 
EXAMPLE 5 
While binary eutectics are most readily studied, it should be understood 
that this invention extends to higher eutectics, such as ternary systems, 
for example. A ternary eutectic may comprise a mixture of three different 
compounds, but it is envisaged that there may also be other possibilities, 
for instance a mixture of two compounds, one of which can exist in two 
distinct crystalline phases. A ternary eutectic is exemplified by a 
mixture of compounds 4, 33 and 41, which shows a eutectic depression of 
36.degree. C. All three possible pairs of these three compounds also form 
eutectics, viz. 4 and 33 (eutectic depression 28.degree. C.) 33 and 41 
(22.degree. C.), and 4 and 41 (24.degree. C.). The ternary eutectic shows 
a eutectic depression of 8.degree. C. with respect to the lowest melting 
of the three binary eutectics. 
EXAMPLE 6 
Solid solutions or chemical compounds formed from organic component 
compounds differ from a eutectic composition of the same class of 
compounds in that the X-ray diffraction pattern of the eutectic is a sum 
or superposition of the diffraction patterns of the pure components, 
whereas that of the solid solution or compound is not. This Example 
illustrates this point. 
Compounds 3 and 32 are mixed in the ratio of the eutectic composition and 
ground with a pestle and mortar. After fusion and cooling to 
solidification, the mixture was ground again. This sample, together with 
samples of pure 3 and 32 which had been ground without melting, was used 
to obtain the X-ray powder diffraction patterns in FIG. 4. The Figures 
correspond to the following compositions: 
______________________________________ 
Figure Sample 
number number Composition 
______________________________________ 
4a 6C Pure 32 
4b 6A Eutectic composition 
of 3 and 32 
4c 6B Pure 3 
______________________________________ 
The eutectic can be seen to contain separate crystals of both 3 and 32. 
EXAMPLE 7 
The eutectics of this invention, as characterized by the methods of 
Examples 1 to 6 are preferably contained in a polymeric binder. While the 
properties of a eutectic mixture may be modified by incorporation into a 
binder, perhaps to form a higher eutectic, the major and practically 
useful depression of the melting point is related to the original eutectic 
mixture. 
A binary eutectic dye composition 7A of compounds 3 and 32 was prepared at 
the eutectic point molar ratio of dye 3/dye 32 of 0.587 as in Example 1. A 
second sample of this eutectic composition at the same molar ratio in a 
polymeric binder (7B) was prepared by incorporating 0.025 g of compound 3 
and 0.035 g of compound 32 in the formulation of donor sheet A in Example 
9. The solution was coated onto a glass plate with a number 8 wire-wound 
coating rod and allowed to air dry thoroughly to give a film which was 
then removed from the glass. Both samples were analyzed by differential 
scanning calorimetry as in Example 1 at a heating rate of 10.degree. 
C./min. The eutectic depression for 7A was 16.5.degree. C. The additional 
melting point depression on incorporating the binary mixture 7A into a 
binder (sample 7B) was 7.degree. C., demonstrating the dominant effect of 
the binary eutectic dye mixture. 
EXAMPLE 8 
While eutectic-forming mixtures at a composition corresponding to the 
eutectic point are frequency required to provide the greatest benefit to 
the thermal dye transfer imaging process, this is not always the case, and 
embodiments of the invention utilizing compositions different from the 
eutectic point can be effective. The results show that, at a molar ratio 
differing by a factor of 0.43 from that at the eutectic point composition, 
the thermal properties of the mixture as a whole substantially reproduce 
the properties observed at the eutectic point itself. 
Two mixtures of compounds 3 and 32 were prepared, one at a molar ratio of 
dye 3/dye 32 of 0.333 and the other at the eutectic composition (0.587), 
and were analyzed as in Example 1. Additionally the heat required for 
melting was obtained by integration of the endotherms. Separate 
experiments showed that the eutectic composition and compound 32 had 
essentially identical heats of fusion, so that the fraction of each 
mixture melting at the eutectic composition could be derived from the 
integration of the melting peaks, with the results below. 
______________________________________ 
Molar Ratio Fraction of mixture melting 
dye 3/dye 32 
at the eutectic composition 
______________________________________ 
0.587 100% 
0.333 75% 
______________________________________ 
EXAMPLE 9 
General information pertaining to evaluation of the eutectic mixtures of 
this invention for thermal dye transfer imaging is recorded in this 
Example. 
The following is a description of the various coating formulations referred 
to in the Examples of this patent, together with the thermal imaging 
equipment used to make images by thermal transfer of dye from donor to 
receptor sheets. All donor sheets were coated with a number 8 wire-wound 
coating rod (0.72 mil wet thickness) onto 5.7 micron Teijin F24G thermal 
film, which is representative of a thin polyester film, and dried in a 
current of air at ambient temperature unless noted otherwise. All receptor 
sheets were coated with a number 8 wire-wound coating rod onto 4 mil 
polyethylene terephthalate film and dried in a current of heated air. 
Donor sheet A 
The donor sheet formulation contained an amount of dye or eutectic mixture 
appropriate to the Example together with the following components: 
0.04 g 
Goodrich Temprite.RTM. 678.times.512 62.5% chlorinated polyvinyl chloride 
(CPVC) 
0.007 g 
60/40 blend of octadecyl acrylate and acrylic acid 
0.0025 g 
Goodyear Vitel.RTM. PE 200 polyester 
2.00 g 
tetrahydrofuran 
0.90 g 
methyl ethyl ketone 
Donor sheet B 
The donor sheet formulation contained an amount of dye or eutectic mixture 
appropriate to the Example together with the following components: 
0.04 g 
Goodrich Temprite.RTM. 678.times.512 62.5% CPVC 
0.001 g 
Emery Plastolein.RTM. 9776 polyester 
2.26 g 
tetrahydrofuran 
Donor sheet C 
The donor sheet formulation contained an amount of dye or eutectic mixture 
appropriate to the Example together with the following components: 
0.04 g 
Eastman Kodak CAB 553-0.4 cellulose acetate butyrate (CAB) 
0.015 g 
Emery Plastolein.RTM. 9776 polyester 
0.001 g 
3M Fluorad.RTM. FC 430 fluorocarbon surfactant 
1.94 g 
tetrahydrofuran 
0.90 g 
methyl ethyl ketone 
Donor sheet D 
The donor sheet formulation contained an amount of dye or eutectic mixture 
appropriate to the Example together with the following components: 
0.025 g 
Goodrich Temprite.RTM. 663.times.612 70% CPVC 
0.01 g 
60/40 blend of octadecyl acrylate and acrylic acid 
0.01 g 
Goodyear Vitel.RTM. PE 200 polyester 
1.91 g 
tetrahydrofuran 
0.28 g 
methyl ethyl ketone 
Donor sheet E 
The donor sheet formulation contained an amount of dye or eutectic mixture 
appropriate to the Example together with the following components: 
0.03 g 
Goodrich Temprite.RTM. 663.times.612 70% CPVC 
0.01 g 
60/40 blend of octadecyl acrylate and acrylic acid 
0.005 g 
Goodyear Vitel.RTM. PE 200 polyester 
2.81 g 
tetrahydrofuran (sheet E1) or 
3.71 g 
tetrahydrofuran (sheet E2) 
Donor sheet F 
The donor sheet formulation contained an amount of dye or eutectic mixture 
appropriate to the Example together with the following components: 
0.04 g 
Eastman Kodak CAB 553-0.4 CAB 
0.0015 g 
Emery Plastolein.RTM. 9776 polyester 
0.001 g 
3M Fluorad.RTM. FC 430 fluorocarbon surfactant 
2.70 g 
tetrahydrofuran 
0.15 g 
methyl ethyl ketone 
Receptor sheet A 
The receptor sheet was made from the following formulation: 
0.04 g 
Shell Epon.RTM. 1002 epoxy resin 
0.04 g 
Goodyear Vitel.RTM. PE 200 polyester 
0.05 g 
3M Fluorad.RTM. FC 430 fluorocarbon surfactant 
0.015 g 
Ciba-Geigy Tinuvin.RTM. 328 UV stabilizer 
0.04 g 
BASF Uvinul.RTM. N539 UV stabilizer 
0.05 g 
BASF Ferro.RTM. 1237 heat stabilizer 
0.08 g 
Eastman Kodak DOBP.RTM. 4-dodecyloxy-2-hydroxybenzophenone 
0.20 g 
Goodrich Temprite.RTM. 678.times.512 62.5% CPVC 
0.25 g 
ICI 382ES bisphenol A fumarate polyester 
4.56 g 
tetrahydrofuran 
1.85 g 
methyl ethyl ketone 
Receptor sheet B 
The receptor sheet was made from the following formulation: 
0.25 g 
ICI 382ES bisphenol A fumarate polyester 
0.20 g 
Goodrich Temprite.RTM. 678.times.512 62.5% CPVC 
0.04 g 
Shell Epon.RTM. 1002 epoxy resin 
0.04 g 
Goodyear Vitel.RTM. PE 200 polyester 
0.02 g 
Aldrich polyethylene glycol (MW 1000) 
0.01 g 
Cyanamid Cyasorb.RTM. 1084 UV stabilizer 
0.01 g 
BASF Uvinul.RTM. D49 UV stabilizer 
0.05 g 
BASF Uvinul.RTM. N537 UV stabilizer 
4.56 g 
tetrahydrofuran 
1.46 g 
methyl ethyl ketone 
Receptor sheet C 
The receptor sheet was made from the following formulation: 
0.25 g 
ICI 382ES bisphenol A fumarate polyester 
0.20 g 
Goodrich Temprite.RTM. 678.times.512 62.5% CPVC 
0.04 g 
Shell Epon.RTM. 1002 epoxy resin 
0.04 g 
Goodyear Vitel.RTM. PE 200 polyester 
0.02 g 
Aldrich polyethylene glycol (MW 1000) 
0.05 g 
3M Fluorad.RTM. FC 430 fluorocarbon surfactant 
0.12 g 
Ciba-Geigy Tinuvin.RTM. 292 UV stabilizer 
0.01 g 
Ciba-Geigy Tinuvin.RTM. 328 UV stabilizer 
4.50 g 
tetrahydrofuran 
1.80 g 
methyl ethyl ketone 
Printer A 
Thermal printer A used a Kyocera raised glaze thin film thermal print head 
with 8 dots/mm and 0.25 watts/dot. In normal imaging, the electrical 
energy varied from 2.64 to 6.43 joule/sq.cm, which corresponded to head 
voltages from 9 to 14 volts with a 4 msec pulse. Grey scale images were 
produced by using 32 of a maximum 64 electrical levels, produced by pulse 
width modulation. 
Printer B 
Thermal printer B used an OKI thin film, flat glazed thermal print head 
with 8 dots/mm and 0.27 watts/dot. In normal imaging, the electrical 
energy was 3 joule/sq.cm, administered with a 2.5 msec pulse. 32 
electrical grey levels were available by pulse width modulation. 
EXAMPLE 10 
In many cases transparent thermal dye transfer images are required, for 
instance for projection applications, and maximum light transmission 
through such an image is desirable. A source of reduced light transmission 
is frequently scattering by particles or crystals of dye in the image. 
This Example illustrates both this undesirable effect, and its diminution 
in a eutectic mixture. 
A thermal transfer donor sheet 10A comprising 0.03 g compound 3 and 0.03 g 
compound 32 in the donor sheet D composition of Example 9 was prepared. 
This is about 57% dye and 43% binder solids. A second donor sheet 10B was 
prepared identically except for omission of compound 3. Transferred dye 
images were formed on receptor sheet B and using printer B of Example 9. 
FIG. 5 presents absorption spectra of the transferred images from both 
donors 10A and 10B on the receptor sheet at comparable peak density. The 
transferred image from donor 10A containing compounds 3 and 32 in a molar 
ratio 0.841 (compare with the eutectic molar ratio of 0.587) showed good 
density with negligible absorbance at 700 nm. In contrast the transferred 
image from donor 10B containing only compound 32 showed significant 
absorption at 700 nm, attributable to light scattering by large dye 
crystals in the image. This was confirmed by optical microscopy, which 
showed readily resolvable crystals in the transferred image from donor 10A 
but not from donor 10B. 
EXAMPLE 11 
It is desirable to minimize the thermal energy required to produce a 
maximal image density in a dye transfer process, both from the standpoint 
of achieving the most rapid imaging, and to prolong the life of the 
thermal printing element. One approach is to employ dyes with high 
tinctorial strength so that less dye mass need be transferred to produce a 
given image density. Azo dyes have high tinctorial strength, but can 
exhibit the undesirable scattering effect described for compound 32 in 
Example 10. Combination of the azo dye in a eutectic mixture with an 
anthraquinone dye permits the use of dyes of high tinctorial strength 
which would otherwise be unsuited to the application, and facilitates 
imaging to a higher density with a given thermal energy input. This 
Example illustrates the beneficial effects of a eutectic mixture of the 
azo dye 32 and the anthraquinone dye 8 of lower tinctorial strength on the 
simultaneous optimization of efficiency of dye transfer, peak density and 
light scattering. 
Donor sheets 11A, 11B and 11C, containing respectively 0.06 g compound 8, 
0.06 g compound 32, and 0.06 g of a mixture of 8 and 32 at the eutectic 
point composition (molar ratio of dye 8/dye 32 of 0.619) were made up 
using the formulation of donor sheet A in Example 9. Transferred dye 
images were made using receptor A and printer A of Example 9 with 12 volt, 
4 msec pulses. An indicator of transfer efficiency of the dye (referred to 
herein as ITE) was computed as the ratio of the reflection optical density 
of the transferred image to the reflection optical density of the original 
donor sheet prior to imaging. The peak optical density corrected for 
scatter at 410 nm and the transmittance at 700 nm were determined from 
optical transmission spectra of the images on the receptor. The results 
are grouped in the table below. 
______________________________________ 
Donor Percent Peak optical Transmittance 
sheet ITE density (410 nm) 
at 700 nm 
______________________________________ 
11A 74 0.12 98 
11B 96 0.74 91 
11C 84 0.59 97 
______________________________________ 
Sample 11C of the mixture of the eutectic composition had an acceptable 
apparent transfer efficiency and peak optical density, while maintaining 
low light scattering. Although sample 11B had a higher apparent transfer 
efficiency and peak optical density, the transmittance of 91% at 700 nm 
indicated that the sample exhibited excessive light scattering, rendering 
it unacceptable. 
EXAMPLE 12 
This Example shows the difference between use of single dyes, and a dye 
mixture at the eutectic point, on the efficiency of dye transfer to the 
receptor as a function of thermal imaging energy. 
Donor sheets were prepared using 0.06 g of dye or dye mixture according to 
the formulation of donor sheet A in Example 9, with the components listed 
below. This is about 55% dye and 45% binder solid. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
12-1A 32 no mixture 
12-1B 8 and 32 0.250 
12-1C 8 and 32 0.619 - eutectic point 
12-1D 8 and 32 4.033 
12-2A 38 no mixture 
12-2B 3 and 38 0.255 
12-2C 3 and 38 1.275 - eutectic point 
12-2D 3 and 38 3.965 
______________________________________ 
Dye transfer images onto receptor A of Example 9 were made using printer A 
of the same Example. The ITE indicator of thermal transfer efficiency was 
determined by the method of Example 11 as a function of voltage for a 4 
msec pulse. The results are displayed graphically in FIG. 6 for images 
from donor sheets 12-1 and FIG. 7 for images from donor sheets 12-2. 
Eutectic compositions provide good transfer at all voltages without the 
undesirable light scattering observed for samples 12-1A and 12-2A. 
EXAMPLE 13 
This Example presents similar data to Example 12 but shows that the 
eutectic mixtures of this invention need not be used at the eutectic point 
composition to beneficially affect the image. 
Donor sheets were prepared using 0.06 g of dye or dye mixture according to 
the formulation of donor sheet A in Example 9 except for drying in still, 
ambient air. The resultant components are listed below. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
13A 32 no mixture 
13B 3 and 32 0.332 
13C 3 and 32 0.587 - eutectic point 
13D 3 and 32 2.042 
______________________________________ 
The ITE indicator of thermal transfer efficiency to receptor sheet A of 
Example 9 was determined as a function of thermal head voltage as in 
Example 12, and is displayed graphically in FIG. 8. The pure dye (13A) 
showed unacceptable light scattering. The results for the eutectic 
composition (13C) were good and almost identical to those for images from 
sample 13B, where the molar ratio was 0.56 times that at the eutectic 
point. 
EXAMPLE 14 
An undesirable effect sometimes observed in thermal dye transfer 
constructions of the dye sublimation kind is the transfer of polymeric 
binder from the donor sheet to the receptor, termed mass transfer. This 
can lead to excessive light scattering and a change in the perceived hue 
of the image. This Example shows the influence of eutectic mixtures on the 
occurrence of mass transfer. 
Donor sheets were prepared using 0.06 g of dye or dye mixture in the 
formulation of donor sheet B of Example 9, with the composition given 
below. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
14A 3 no mixture 
14B 3 and 32 0.332 
14C 3 and 32 0.587 - eutectic point 
14D 3 and 32 2.042 
14E 32 no mixture 
______________________________________ 
Transferred dye images on receptor sheet A of Example 9 were formed using 
printer A of the same Example, operated with a 4 msec pulse in the voltage 
range 9 to 14 volts. The lowest voltage at which the onset of mass 
transfer occurred is tabulated below. 
______________________________________ 
Donor Mass transfer 
sheet no. onset voltage 
______________________________________ 
14A 9 or less 
14B 9 or less 
14C none 
14D 12 
14E 12 
______________________________________ 
The sample with the eutectic composition (14C) was the only one to show the 
absence of mass transfer at all the voltages tested. 
EXAMPLE 15 
For good image quality the imaging system should be capable of reproducing 
a broad range of input densities. The influence of eutectic dye mixtures 
on grey scale reproduction is presented here. The results indicate that 
the compositions of this invention can be used to improve grey scale 
capability. 
The donor sheets 12-2 of Example 12 were used for imaging along with donor 
sheets 14 of Example 14. The sample compositions were as follows: 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
12-2A 38 no mixture 
12-2B 3 and 38 0.255 
12-2C 3 and 38 1.275 - eutectic point 
12-2D 3 and 38 3.965 
14A 32 no mixture 
14B 3 and 32 0.332 
14C 3 and 32 0.587 - eutectic point 
14D 3 and 32 2.042 
14E 3 no mixture 
______________________________________ 
These samples were imaged onto receptor sheet A of Example 9 with a 32 step 
grey scale obtained by pulse modulation using printer A of the same 
Example. The resultant number of resolvable steps in the thermally 
transferred images on the receptor sheet is listed below. 
______________________________________ 
Donor Number 
sheet no. of steps 
______________________________________ 
12-2A 24 
12-2B 24 
12-2C 26 
12-2D 23 
14A 24 
14B 26 
14C 28 
14D 25 
14E 23 
______________________________________ 
For both sets of mixtures, compositions at or near the eutectic point 
resulted in improved grey scale reproduction. 
EXAMPLE 16 
It has been observed that excessive crystallinity of dyes in the donor 
sheet can lead to handling problems. These can include reduced rub 
resistance, diminished shelf life, or partial transfer of the dye to the 
receptor merely under contact pressure, without any application of heat. 
This Example shows the effect of the eutectic mixtures of this invention 
on crystallinity in the donor sheet, as quantified by an index of light 
scattering. 
Donor sheets were prepared using 0.06 g of dye or dye mixture in the 
formulation of donor sheet C of Example 9, with the compositions given 
below. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
16A 18 no mixture 
16B 18 and 35 0.112 
16C 18 and 35 0.424 - eutectic point 
16D 18 and 35 3.003 
16E 35 no mixture 
______________________________________ 
An index of light scattering, termed ILS, was determined as follows. A 
transmission optical density, TOD, was determined for the donor sheet 
sample with a densitometer. The sample was then positioned over an 
aperture in a box which formed an efficient light trap and an apparent 
scattering optical denisty, SOD, normal to the sample surface was measured 
using the same densitometer with the same filters for light incident at 45 
degrees to the sample surface. ILS was computed as TOD-SOD, so that larger 
ILS values imply less scattering. The results are tabulated below. 
______________________________________ 
Donor sheet no. ILS value 
______________________________________ 
16A 1.45 
16B 1.50 
16C 2.64 
16D 1.84 
16E 1.69 
______________________________________ 
The donor sheet containing a mixture at the eutectic point composition is 
the least scattering. 
EXAMPLE 17 
It is well known in the art (e.g. M. W. Rembold and H. E. A. Kramer, Org. 
Coat. Plast. Chem., 42, 703 (1980); J. Soc. Dyers Colour., 96, 122 (1980)) 
that mixtures of dyes frequently undergo photoinduced degradation faster 
than either component dye in isolation. This phenomenon is known as 
catalytic fading, and leads to objectionable changes in hue and density of 
the image. Surprisingly, it has been found that image constructions based 
on eutectic mixtures can enhance photostability of a dye relative to the 
same dye in isolation and so result in a more durable image. This effect 
is documented here. 
Donor sheets were prepared using 0.06 g of dye or dye mixture in the 
formulation of donor sheet F of Example 9, with the compositions given 
below. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
17A 18 no mixture 
17B 18 and 36 1.66 
17C 36 no mixture 
17D 18 and 37 1.65 
17E 37 no mixture 
______________________________________ 
These donor sheets were thermally imaged onto receptor C of Example 9, 
using printer B of the same Example. The photostability of the resultant 
images was assessed by 24 hour exposure on a 360 watt 3M Model 213 
overhead projector and in an Atlas UVICON.RTM. at 350 nm and 50.degree. C. 
Results for the overhead projector are presented below as percentage loss 
in image density, while the UVICON.RTM. results are expressed as DELTA E, 
the change in (L, a, b) color coordinates. 
______________________________________ 
Sample % density loss 
DELTA E 
number O/H projector 
UVICON .TM. 
______________________________________ 
17A 12 4.0 
17B 12 8.8 
17C 12 17.2 
17D 33 6.8 
17E 45 16.7 
______________________________________ 
A stabilizing effect of the eutectic mixture with respect to one of the 
pure components is demonstrated for light exposure to either the UV or the 
visible, or both spectral regions, depending on mixture components. 
EXAMPLE 18 
This example illustrates that the beneficial photostability enhancement 
described in Example 17 can also be obtained using a eutectic mixture of a 
dye and a colorless substance. Donor sheets of dye 33 (0.0624 g) or with 
added compound 44 (0.015 g) were prepared using formulation E1 of Example 
9. Donor sheets of dye 34 (0.09 g) or with added compound 44 (0.015 g) 
were prepared using formulation E2 of Example 9. Donor sheets of dye 26 
(0.0627 g) or with added compound 44 (0.015 g) were prepared using 
formulation E1 of Example 9. The compositions of the samples are given 
below. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
18-1A 33 no mixture 
18-1B 44 and 33 0.60 
18-2A 34 no mixture 
18-2B 44 and 34 0.48 
18-3A 26 no mixture 
18-3B 44 and 26 0.50 
______________________________________ 
These donor sheets were thermally imaged on to receptor sheet C of Example 
9, using printer B of the same Example. The photostability was evaluated 
by the methods of Example 17, with the results below. 
______________________________________ 
Sample % density loss 
DELTA E 
number O/H projector 
UVICON .TM. 
______________________________________ 
18-1A 21 22.0 
18-1B 15 16.0 
18-2A 6 50.0 
18-2B 3 20.0 
18-3A 10 16.5 
18-3B 1 3.9 
______________________________________ 
A stabilizing effect of the eutectic mixture is demonstrated for light 
exposure to both the UV and the visible spectral regions in all cases. 
EXAMPLE 19 
The eutectic mixtures of this invention can also beneficially influence the 
thermal stability of the image on the receptor, as illustrated with an 
accelerated aging test at 50.degree. C. 
Donor sheets of dyes 3 and 8 either alone or in a mixture were prepared by 
combining 0.06 g of the dye or dye mixture with the formulation of donor 
sheet A of Example 9. The samples had the compositions listed below and 
were imaged onto the receptor sheet A of Example 9 using Printer A in that 
Example. 
______________________________________ 
Donor Dye or Molar 
sheet no. dye mixture ratio 
______________________________________ 
19A 3 no mixture 
19B 3 and 32 0.587 - eutectic point 
19C 3 and 38 1.275 - eutectic point 
19D 8 no mixture 
19E 8 and 32 0.619 - eutectic point 
______________________________________ 
These samples were held at 50.degree. C. for 24 hours without exposure to 
light and DELTA E, the resultant change in (L, a, b) color coordinates was 
measured. The results are tabulated below. 
______________________________________ 
Donor 
Sheet DELTA E 
______________________________________ 
19A 8.0 
19B 1.2 
19C 1.9 
19D 4.0 
19E 2.7 
______________________________________ 
Color changes caused by thermally induced aging are diminished in the 
eutectic point compositions. 
SOURCES OF MATERIALS 
Unless otherwise noted, all the components of the eutectic mixtures 
explicitly discussed herein are known compounds, in the sense that they 
have been assigned a Chemical Abstracts Registry Number, or a Color Index 
number, or have been disclosed in patents. 
Some materials are analogous to known classes of materials and can be 
prepared in the same way. For example, compounds 3, 14 and 17 can be 
prepared by the method of R. D. Desai and R. N. Desai, J. Indian Chem. 
Soc., 33, 559 (1956), while compounds 9 and 15 can be made by the method 
of P. Ruggli and E. Heinzi, Helv. Chim. Acta, 13, 409 (1930). Similarly, 
compounds 27, 28, 29, 33 and 34 can be prepared as described in European 
patent EP No. 218397. Also compound 13 can be made by the procedure of 
U.S. Pat. No. 2,848,462; compound 24 by the method of U.S. Pat. No. 
2,628,963; compound 30 as described in Federal Republic of Germany patent 
No. DE 3600349A; compound 31 according to Japanese patent No. JP 
60-079353; compound 37 as discussed in Japanese patent No. JP 62-033669; 
and compound 39 as revealed in U.S. Pat. No. 3,933,914. 
Some other materials are new, and previously unreported. Their syntheses 
are described below. 
Preparation of Compound 6 
Into a 100 ml round-bottom flask equipped with a condenser, stirrer and 
heating mantle were placed 3.32 g 1-aminoanthraquinone and 50 ml n-butyl 
acetate. 1.1 g of n-butyl isocyanate were added with stirring. A further 
0.5 g of n-butyl isocyanate were added after 48 hours of reflux. After a 
total of 100 hours reaction time the solvent was removed at reduced 
pressure and the residue was chromatographed on silica gel using 
dichloromethane as the eluent. Compound 6 was isolated by 
recrystallization from toluene. 
Preparation of Compound 8 
Into a 100 ml round-bottom flask equipped with a magnetic stirrer, 
condenser and heating mantle were added 0.4 g of copper acetate, 0.4 g of 
potassium carbonate, 1.0 g of 1-chloranthraquinone, 1.0 g of 
n-octylsulfonamide and 15 ml of o-dichlorobenzene. The mixture was 
refluxed for 3.5 hours. The product was precipitated by addition of 100 ml 
of methanol and was filtered. The precipitate was recrystallized from 
methylene chloride by addition of methanol to give compound 8. 
Preparation of Compound 20 
5.00 g of 1-bromo-4-methylamino-anthraquinone, 1.49 g of sodium 
iso-butoxide, 1.30 g of sodium acetate, 3.16 g of cupric acetate 
monohydrate and 100 ml of iso-butanol were placed in a glass bottle, which 
was then sealed. The bottle was heated in an oil bath with magnetic 
stirring at 120.degree. C. for 18 hours. The reaction mixture was cooled 
and filtered through diatomaceous earth, which was rinsed with ether. The 
combined filtrates were evaporated under reduced pressure and the residue 
was recrystallized from n-butanol to afford compound 20. 
##STR1## 
The term "thermal dye transfer" as used in the present text relates to any 
process by which dye (alone or in association with carrier materials such 
as solvents, binders, etc.) is transferred from one layer to another layer 
or sheet. Such processes are well known in the art and referred to in 
terms such as thermal dye transfer, sublimation transfer, mass transfer, 
direct transfer, strippable transfer, peel apart, and the like. Dye 
content may be as low as two percent or as high as 100 percent in such 
systems.