1. Field of the invention.
[0001] The present invention relates to ecologically acceptable light-stabilizers for use
in thermal dye sublimation transfer and to a method of forming a light-fast dye image
by thermal dye sublimation transfer.
2. Background of the invention.
[0002] Thermal dye transfer methods include thermal dye sublimation transfer also called
thermal dye diffusion transfer. This is a recording method in which a dye-donor element
provided with a dye layer containing sublimating dyes having heat transferability
is brought into contact with a receiver sheet and selectively, in accordance with
a pattern information signal, heated with a thermal printing head provided with a
plurality of juxtaposed heat-generating resistors, whereby dye is transferred from
the selectively heated regions of the dye-donor element to the receiver sheet and
forms a pattern thereon, the shape and density of which are in accordance with the
pattern and intensity of heat applied to the dye-donor element.
[0003] A dye-donor element for use according to thermal dye sublimation transfer usually
comprises a very thin support e.g. a polyester support, one side of which is covered
with a dye layer comprising the printing dyes. Usually, an adhesive or subbing layer
is provided between the support and the dye layer. Normally, the opposite side of
the support is covered with a slipping layer that provides a lubricated surface against
which the thermal printing head can pass without suffering abrasion. An adhesive layer
may be provided between the support and the slipping layer.
[0004] The dye layer can be a monochromic dye layer or it may comprise sequential repeating
areas of differently coloured dyes e.g. dyes having a cyan, magenta, yellow, and optionally
black hue. When a dye-donor element containing three or more primary colour dyes is
used, a multicolour image can be obtained by sequentially performing the dye transfer
process steps for each colour.
[0005] A primary coloured dye layer e.g. a magenta or cyan or yellow dye layer may comprise
only one primary coloured dye (a magenta, cyan, or yellow dye respectively) or may
comprise a mixture of two or more primary coloured dyes of the same hue (two magenta,
two cyan, or two yellow dyes respectively).
[0006] All imaging dyes are unstable to light to some extent. Dyes are indeed known to degrade
through a number of pathways, which often involve dye triplet states, radicals and/or
singlet oxygen. Any improvement in the light stability of dyes is highly desirable
therefore.
[0007] In photographic silver halide systems various light-stabilizers for dyes are known.
For instance UV-absorbers are used frequently in a top layer to shield dyes from the
harmful influence of ultraviolet radiation.
[0008] Unfortunately, such technique cannot be used in thermal transfer systems, because
the dyes, after having been thermally transferred to a receiver sheet, are located
in the very top layer of said receiver sheet. If in that case UV-absorbers would be
present as well in said top layer, they would intimately mix with the transferred
dyes and thus give rise to a so-called catalytic fading effect, which would degrade
the dyes even faster.
[0009] For use in thermal transfer other types of light-stabilizers such as singlet oxygen
quenchers and metal chelates have been described e.g. in EP 312,812. Although these
compounds are known to constitute a class of effective stabilizers to light, their
performance is not equally adequate for all types of dyes. But above all, the use
of such light-stabilizers is undesirable because most of them comprise heavy metal
ions, which nowadays raises increasing resistance for ecological reasons.
[0010] Furthermore, certain known light-stabilizers cause an undesirable stain in the receiver
sheet.
3. Summary of the invention.
[0011] It is therefore an object of the present invention to provide ecologically acceptable
light-stabilizers for dyes.
[0012] It is another object of the present invention to provide a dye-donor element for
use according to thermal dye sublimation transfer comprising ecologically acceptable
light-stabilizers for dyes.
[0013] It is another object of the present invention to provide a method of forming a light-fast
dye image by thermal dye sublimation.
[0014] It is a further object of the present invention to provide a dyed receiver sheet
comprising at least one dye and at least one ecologically acceptable light-stabilizer
that does not cause undesirable stain in said receiver sheet.
[0015] It is a further object of the present invention to provide a receiver sheet comprising
an ecologically acceptable light-stabilizer for dyes.
[0016] These and other objects are achieved according to the present invention by means
of a dye-donor element for use according to thermal dye sublimation transfer, said
dye-donor element comprising a support having thereon a dye layer comprising at least
one dye and a binder, wherein said dye layer or a top layer thereon also comprises
a light-stabilizer for said at least one dye, said light-stabilizer being a leuco-indoaniline
dye preferably corresponding to the following general formula :

wherein :
R¹ represents hydrogen or any substituent,
n is zero or a positive integer chosen from 1 to 4, and when n is 2, 3, or 4, R¹ has
same or different significances,
each of R² and R³ (same or different) represents hydrogen, -COCOR¹⁰, or an acyl group
chosen from -COR¹⁰, -SO₂R¹⁰, and -OPR¹⁰R¹¹,
X is zero or represents the atoms needed to complete an aromatic, alicyclic, or heterocyclic
ring or ring system, or a such ring or ring system in substituted form,
each of R⁴, R⁵, R⁶, and R⁷ (same or different) represents hydrogen, an alkyl group,
a substituted alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an
aryl group, a substituted aryl group, an alkyloxy group, a substituted alkyloxy group,
an aryloxy group, a substituted aryloxy group, a carbamoyl group, a substituted carbamoyl
group, a sulphamoyl group, a substituted sulphamoyl group, hydroxy, a halogen atom,
-NH-SO₂R¹², -NH-COR¹², -O-SO₂R¹², or -O-COR¹², or R⁴ and R⁷ together and R⁵ and R⁶
together represent the atoms necessary to complete an aliphatic ring, a substituted
aliphatic ring, a heterocyclic nucleus, a substituted heterocyclic nucleus, a heterocyclic
nucleus carrying a fused-on cycloaliphatic, aromatic, or heterocyclic ring or ring
system, or a substituted heterocyclic nucleus carrying a fused-on cycloaliphatic,
aromatic, or heterocyclic ring or ring system, or R⁴ and R⁸ and/or R⁵ and R⁹ together
and R⁵ and R⁶ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R⁸ and R⁹ (same or different) represents hydrogen, an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an aryl group, a
substituted aryl group, a heterocyclic nucleus, a substituted heterocyclic nucleus,
or R⁸ and R⁹ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R¹⁰, R¹¹, and R¹² (same or different) represents an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an alkenyl group,
a substituted alkenyl group, an aryl group, a substituted aryl group, an alkyloxy
group, a substituted alkyloxy group, an aryloxy group, a substituted aryloxy group,
an alkylthio group, a substituted alkylthio group, an arylthio, a substituted arylthio
group, an amino group, a substituted amino group, a heterocyclic nucleus, or a substituted
heterocyclic nucleus.
[0017] The present invention also provides a method of forming a light-fast dye image by
image-wise heating a dye-donor element comprising a dye layer comprising a binder
and at least one dye, and in said dye layer or in a layer on top of said dye layer
a light-stabilizer for said dye, said light-stabilizer being a leuco-indoaniline dye
preferably corresponding to the above general formula, and causing transfer of the
image-wise heated dye and light-stabilizer to a receiver sheet.
[0018] According to an alternative embodiment of the method of forming a light-fast dye
image according to the present invention, the method comprises forming a light-fast
dye image by image-wise heating a dye-donor element comprising a dye layer comprising
a binder and at least one dye, and causing transfer of the image-wise heated dye to
a receiver sheet, wherein said receiver sheet comprises as a light-stabilizer for
the transferred dye, a leuco-indoaniline dye preferably corresponding to the above
general formula.
[0019] The present invention further provides a dyed receiver sheet comprising at least
one dye and at least one light-stabilizer for said dye, wherein said dye and said
light-stabilizer are present in an image-wise distribution produced by thermal dye
sublimation transfer from a dye-donor element and said light-stabilizer dye is a leuco-indoaniline
dye preferably according to the above general formula.
[0020] The present invention also provides a receiver sheet for receiving an image-wise
distribution of dye by thermal dye sublimation transfer from a dye-donor element,
wherein said receiver sheet comprises as a light-stabilizer for said dye a leuco-indoaniline
dye.
4. Detailed description of the invention
[0022] The compounds corresponding to the above general formula can be prepared by reducing
the corresponding dye and, if necessary, derivatizing the leuco dye with acyl chlorides.
This will become apparent from the preparation examples given hereinafter.
Preparation Example 1 : synthesis of compound S.05
[0023] Compound S.05 is prepared according to the following reaction scheme :

10 g (0.025 mol) of Compound A prepared as described in US 4,987,119 is added under
nitrogen atmosphere to a solution of 1.5 g of sodium cyanide and 0.5 ml of water in
50 ml of 1,1,1-trichloroethane. The solution is refluxed for 1 h. 4.2 ml of triethylamine
and 2.1 ml of acetyl chloride are added and the hot solution is stirred for 1 h. The
solution is washed twice with 0.1 N hydrochloric acid, once with a saturated sodium
hydrogen carbonate solution, and once with a saturated sodium chloride solution. The
solution is dried over sodium sulfate, filtered, concentrated under reduced pressure,
and purified by column chromatography.
Yield : 4.7 g of pure Compound S.05
Preparation Example 2 : synthesis of compound S.11
[0024] 30 g of Compound A is dissolved in 500 ml of ethyl acetate. 500 ml of water and 37:6
g of sodium hydrosulfite are added thereto with vigorous stirring until discolouration.
The water layer is removed and the organic phase is washed with a saturated sodium
chloride solution. The product is dried over magnesium sulphate, concentrated under
reduced pressure, and purified by column chromatography.
Yield : 5 g of pure Compound S.11
[0025] Compound S.09 can be prepared as described in JP 02-238059.
[0026] The other compounds listed in Table 1 as well as other compounds not listed in Table
1 but corresponding to the above general formula can be prepared in an analogous way
as described in the above preparation examples.
[0027] Any dye can be used in the dye layer of the dye-donor element of the present invention
provided it is transferable by the action of heat to the receiver sheet and provided
it is not altered chemically by the light-stabilizer by said action of heat.
[0028] As mentioned before the dye layer can be a monochromic dye layer or it may comprise
sequential repeating areas of differently coloured dyes. In case the dye layer is
a monochromic dye layer the light-stabilizer may be incorporated therein. In case
the dye layer consists of repeating areas of different dyes the light-stabilizer may
be incorporated together with the different dyes in said repeating areas. In that
case the light-stabilizer is transferred together with dye during the same heating
cycle. This brings the advantage that at areas of minimum density (Dmin), i.e. areas
to which little or no dye is transferred, also little or no light-stabilizer is transferred
and that at areas of maximum density (Dmax), i.e. areas to which high amounts of dye
are transferred, also high amounts of light-stabilizer are transferred; in other words
there is a direct quantitative relation between transferred dye and transferred light-stabilizer
so that an optimal light-stabilization of the transferred dye is guaranteed.
[0029] It is, of course, also possible to incorporate the light-stabilizer in separate repeating
areas that do not comprise dye. In that case it is transferred during a heating cycle
that is different from that causing transfer of dye.
[0030] The light-stabilizer can be used in amounts of 10 to 200 % by weight, preferably
20 to 150 % by weight, calculated on the weight of dye.
[0031] The dye layer of the dye-donor element is formed preferably by adding the dyes, the
light-stabilizer, a polymeric binder medium, and other optional components to a suitable
solvent or solvent mixture, dissolving or dispersing these ingredients to form a coating
composition that is applied to a support, which may have been provided first with
an adhesive or subbing layer, and dried.
[0032] The dye layer thus formed generally has a thickness of about 0.2 to 5.0 µm, preferably
0.4 to 2.0 µm, and the amount ratio of dye to binder generally ranges from 9:1 to
1:3 weight, preferably from 3:1 to 1:2 by weight.
[0033] The light-stabilizer can also be present in the dye-donor element in separate repeating
areas that do not comprise dye or even in a separate layer on top of the dye layer.
Such separate repeating areas or such separate layer may then comprise a polymeric
binder and other optional components in addition to the light-stabilizer.
[0034] The following polymers can be used as polymeric binder : cellulose derivatives, such
as ethyl cellulose, hydroxyethyl cellulose, ethylhydroxy cellulose, ethylhydroxyethyl
cellulose, hydroxypropyl cellulose, methyl cellulose, cellulose nitrate, cellulose
acetate formate, cellulose acetate hydrogen phthalate, cellulose acetate, cellulose
acetate propionate, cellulose acetate butyrate, cellulose acetate pentanoate, cellulose
acetate benzoate, cellulose triacetate; vinyl-type resins and derivatives, such as
polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, copolyvinyl butyral-vinyl
acetal-vinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetoacetal, polyacrylamide;
polymers and copolymers derived from acrylates and acrylate derivatives, such as polyacrylic
acid, polymethyl methacrylate and styrene-acrylate copolymers; polyester resins; polycarbonates;
copolystyrene-acrylonitrile; polysulfones; polyphenylene oxide; organosilicones, such
as polysiloxanes; epoxy resins and natural resins, such as gum arabic. Preferably,
the binder for the dye layer of the present invention comprises cellulose acetate
butyrate or copolystyrene-acrylonitrile.
[0035] The dye-donor element of the present invention can be used for the recording of a
coloured image together with primary colour dye-donor elements comprising a magenta
dye or a mixture of magenta dyes, a cyan dye or a mixture of cyan dyes, and a yellow
dye or a mixture of yellow dyes respectively.
[0036] The light-stabilizers can be used alone or mixed with one another, or even mixed
with other primary colour dyes.
[0037] Typical and specific examples of other primary colour dyes for use in thermal dye
sublimation transfer have been described in e.g. EP 400,706, EP 209,990, EP 216,483,
EP 218,397, EP 227,095, EP 227,096, EP 229,374, EP 235,939, EP 247,737, EP 257,577,
EP 257,580, EP 258,856, EP 279,330, EP 279,467, EP 285,665, US 4,743,582, US 4,753,922,
US 4,753,923, US 4,757,046, US 4,769,360, US 4,771,035, JP 84/78,894, JP 84/78,895,
JP 84/78,896, JP 84/227,490, JP 84/227,948, JP 85/27,594, JP 85/30,391, JP 85/229,787,
JP 85/229,789, JP 85/229,790, JP 85/229,791, JP 85/229,792, JP 85/229,793, JP 85/229,795,
JP 86/268,493, JP 86/268,494, JP 85/268,495, and JP 86/284,489.
[0038] The dye layer and/or the layer comprising the light-stabilizer may also contain other
additives, such as curing agents, preservatives, organic or inorganic fine particles,
dispersing agents, antistatic agents, defoaming agents, viscosity-controlling agents,
these and other ingredients having been described more fully in EP 133,011, EP 133,012,
EP 111,004, and EP 279,467.
[0039] Any material can be used as the support for the dye-donor element provided it is
dimensionally stable and capable of withstanding the temperatures involved, up to
400°C over a period of up to 20 msec, and is yet thin enough to transmit heat applied
on one side through to the dye on the other side to effect transfer to the receiver
sheet within such short periods, typically from 1 to 10 msec. Such materials include
polyesters such as polyethylene terephthalate, polyamides, polyacrylates, polycarbonates,
cellulose esters, fluorinated polymers, polyethers, polyacetals, polyolefins, polyimides,
glassine paper and condenser paper. Preference is given to a support comprising polyethylene
terephthalate. In general, the support has a thickness of 2 to 30 µm. The support
may also be coated with an adhesive of subbing layer, if desired.
[0040] The dye layer and/or the layer comprising the light-stabilizer can be coated or printed
by a printing technique such as a gravure process.
[0041] A dye-barrier layer comprising a hydrophilic polymer may be provided between the
support and the dye layer of the dye-donor element to enhance the dye transfer densities
by preventing wrong-way transfer of dye backwards to the support. The dye barrier
layer may contain any hydrophilic material that is useful for the intended purpose.
In general, good results have been obtained with gelatin, polyacrylamide, polyisopropyl
acrylamide, butyl methacrylate-grafted gelatin, ethyl methacrylate-grafted gelatin,
ethyl acrylate-grafted gelatin, cellulose monoacetate, methylcellulose, polyvinyl
alcohol, polyethyleneimine, polyacrylic acid, a mixture of polyvinyl alcohol and polyvinyl
acetate, a mixture of polyvinyl alcohol and polyacrylic acid, or a mixture of cellulose
monoacetate and polyacrylic acid. Suitable dye barrier layers have been described
in e.g. EP 227,091 and EP 228,065. Certain hydrophilic polymers e.g. those described
in EP 227,091 also have an adequate adhesion to the support and the dye layer, so
that the need for a separate adhesive or subbing layer is avoided. These particular
hydrophilic polymers used in a single layer in the dye-donor element thus perform
a dual function, hence are referred to as dye-barrier/subbing layers.
[0042] Preferably the reverse side of the dye-donor element has been coated with a slipping
layer to prevent the printing head from sticking to the dye-donor element. Such a
slipping layer would comprise a lubricating material such as a surface-active agent,
a liquid lubricant, a solid lubricant or mixtures thereof, with or without a polymeric
binder. The surface-active agents may be any agents known in the art such as carboxylates,
sulfonates, phosphates, aliphatic amine salts, aliphatic quaternary ammonium salts,
polyoxyethylene alkyl ethers, polyethylene glycol fatty acid esters, fluoroalkyl C₂-C₂₀
aliphatic acids. Examples of liquid lubricants include silicone oils, synthetic oils,
saturated hydrocarbons, and glycols. Examples of solid lubricants include various
higher alcohols such as stearyl alcohol, fatty acids and fatty acid exters. Suitable
slipping layers have been described in e.g. EP 138,483, EP 227,090, US 4,567,113,
US 4,572,860, US 4,717,711. Preferably the slipping layer comprises copolystyrene-acrylonitrile
or a styrene-acrylonitrile-butadiene copolymer or a mixture thereof or a polycarbonate
as described in European patent application no. 91202071.6, as binder and a polysiloxane-polyether
copolymer or polytetrafluoroethylene or a mixture thereof as lubicrant in an amount
of 0.1 to 10% by weight of the binder or binder mixture.
[0043] The receiver sheet for receiving an image-wise distribution of dye by thermal dye
sublimation transfer from a dye-donor element may also comprise a said light-stabilizer
corresponding to the general formula in claim 1.
[0044] The support for the receiver sheet that is used with the dye-donor element may be
a transparent film of e.g. polyethylene terephthalate, a polyether sulfone, a polyimide,
a cellulose ester or a polyvinyl alcohol-co-acetal. The support may also be a reflective
one such as a baryta-coated paper, polyethylene-coated paper or white polyester i.e.
white-pigmented polyester. Blue-coloured polyethylene terephthalate film can also
be used as support.
[0045] To avoid poor adsorption of the transferred dye to the support of the receiver sheet
this support can be coated with a special layer called dye-image-receiving layer,
into which the dye can diffuse more readily. The dye-image-receiving layer may comprise
e.g. a polycarbonate, a polyurethane, a polyester, a polyamide, polyvinyl chloride,
copolystyrene-acrylonitrile, polycaprolactone, or mixtures thereof as binder. The
dye-image receiving layer may also comprise a heat-cured product of poly(vinyl chloride/co-vinyl
acetate/co-vinyl alcohol) and polyisocyanate. Suitable dye-image-receiving layers
have been described in e.g. EP 133,011, EP 133,012, EP 144,247, EP 227,094, and EP
228,066.
[0046] The light-stabilizer corresponding to the above general formula may be present in
a dye-image-receiving layer comprising a binder. In that case the dye-donor element
need not comprise the light-stabilizer.
[0047] The light-stabilizer corresponding to the above general formula can be present in
the dye-image-receiving layer in an amount of 10 to 100% by weight calculated on the
weight of binder present in said dye-image-receiving layer.
[0048] In order to further improve the light-fastness and other stabilities of recorded
images singlet oxygen quenchers such as HALS-compounds (Hindered Amine Light-stabilizers)
and/or antioxidants can be incorporated into the dye-image-receiving layer.
[0049] The dye layer of the dye-donor element or the dye-image-receiving layer of the receiver
sheet may also contain a releasing agent that aids in separating the dye-donor element
from the receiver sheet after transfer. The releasing agents can also be incorporated
in a separate layer on at least part of the dye layer and/or of the dye-image-receiving
layer. Suitable releasing agents are solid waxes, fluorine- or phosphate-containing
surface-active agents and silicone oils. Suitable releasing agents have been described
in e.g. EP 133,012, JP 85/19,138, and EP 227,092.
[0050] The dye-donor elements according to the invention are used to form a dye transfer
image, which process comprises placing the dye layer of the dye-donor element in face-to-face
relation with the dye-image-receiving layer of the receiver sheet and image-wise heating
from the back of the dye-donor element. The transfer of the dye is accomplished by
heating for about several milliseconds at a temperature of 400°C.
[0051] When the process is performed for but one single colour, a monochromic dye transfer
image is obtained. A multicolour image can be obtained by using a dye-donor element
containing three or more primary colour dyes and sequentially performing the process
steps described above for each colour. The above sandwich of dye-donor element and
receiver sheet is formed on three occasions during the time when heat is applied by
the thermal printing head. After the first dye has been transferred, the elements
are peeled apart. A second dye-donor element (or another area of the dye-donor element
with a different dye area) is then brought in register with the dye-receiving element
and the process is repeated. The third colour and optionally further colours are obtained
in the same manner.
[0052] In addition to thermal heads, laser light, infrared flash, or heated pens can be
used as the heat source for supplying heat energy. Thermal printing heads that can
be used to transfer dye from the dye-donor elements of the present invention to a
receiver sheet are commercially available. In case laser light is used, the dye layer
or another layer of the dye element has to contain a compound that absorbs the light
emitted by the laser and converts it into heat e.g. carbon black.
[0053] Alternatively, the support of the dye-donor element may be an electrically resistive
ribbon consisting of e.g. a multilayer structure of a carbon-loaded polycarbonate
coated with a thin aluminium film. Current is injected into the resistive ribbon by
electrically addressing a printing head electrode resulting in highly localized heating
of the ribbon beneath the relevant electrode. The fact that in this case the heat
is generated directly in the resistive ribbon and that it is thus the ribbon that
gets hot leads to an inherent advantage in printing speed using the resistive ribbon/electrode
head technology as compared to the thermal head technology, according to which the
various elements of the thermal head get hot and must cool down before the head can
move to the next printing position.
[0054] The following examples illustrate the invention in more detail without, however,
limiting the scope thereof.
EXAMPLE 1
[0055] Receiver sheets were prepared by coating a polyethylene terephthalate film support
having a thickness of 175 µm with a dye-image-receiving layer from a solution in ethyl
methyl ketone of 3,6 g/m² of poly(vinyl chloride/co-vinyl acetate/co-vinyl alcohol)
(Vinylite VAGD supplied by Union Carbide), 0,336 g/m² of diisocyanate (Desmodur VL
supplied by Bayer AG), and 0,2 g/m² of hydroxy-modified polydimethylsiloxane (Tegomer
H SI 2111 supplied by Goldschmidt).
[0056] Dye-donor elements for use according to thermal dye sublimation transfer were prepared
as follows:
[0057] A solution comprising an amount of light-stabilizer as indicated in the following
Table 2, 0.5 % by weight of dye as indicated in Table 2, and 0.5 % by weight of copolystyrene-acrylonitrile
(Luran 388S, supplied by BASF, Germany) as binder in ethyl methyl ketone was prepared.
[0058] From this solution a dye layer having a wet thickness of 100 µm was coated on a polyethylene
terephthalate film support having a thickness of 6 µm and carrying a conventional
subbing layer. The resulting dye layer was dried by evaporation of the solvent.
[0059] The opposite side of the film support was coated with a subbing layer of a copolyester
comprising ethylene glycol, adipic acid, neopentyl glycol, terephthalic acid, isophthalic
acid, and glycerol.
[0060] The resulting subbing layer was covered with a solution in methyl ethyl ketone of
0.5 g/m² of a polycarbonate having the following structural formula to form a heat-resistant
layer :

wherein x = 55 mol% and y = 45 mol%.
[0061] Finally, a top layer of polyether-modified polydimethylsiloxane (Tegoglide 410, Goldschmidt)
was coated from a solution in isopropanol on the resulting heat-resistant polycarbonate
layer.
[0062] The dye-donor element was printed in combination with a receiver sheet in a Mitsubishi
colour video printer CP100E.
[0063] The receiver sheet was separated from the dye-donor element and the colour density
value of the recorded image was measured by means of a Macbeth TR 924 densitometer
in the red, green, and blue region in Status A mode.
[0064] The above described experiment was repeated for the dyes and light-stabilizers indicated
in Table 2 hereinafter.
[0065] Finally, each receiver sheet was subjected to irradiation by means of a xenon lamp
of 150 klux for a time indicated in hours in Table 2 and the colour density values
were measured again. The density change was calculated and is listed in percent in
Table 2.
[0067] The results listed in Table 2 show that the light-stabilizers used according to the
present invention are capable of making a wide range of dyes belonging to various
structural classes more stable to light.
EXAMPLE 2
[0068] Dye-donor elements were prepared as described in Example 1, with the proviso that
dyes, light-stabilizers according to the present invention, a prior art light-stabilizer
described in EP 312,812 (taken for comparison purposes), and amounts, all as indicated
in Table 4 hereinafter, were used.
[0069] The prior art light-stabilizer COMP. corresponds to the following structural formula
:

Commercially available elements supplied by Mitsubishi, Type CK 100 S were used
as receiver sheets for tests 1 to 14. Receiver sheets as described in Example 1 hereinbefore
were used for tests 15 to 17.
[0070] All tests and measurements were carried out as described in the above Example 1.
[0071] The results of the tests are listed in Table 4 hereinafter.
Table 4
Test N° |
Dye N° |
Light-stabilizer |
Density change in % after xenon exposure for |
|
|
N° |
% by wt. used |
4 h |
12 h |
1 |
D01 |
|
none |
- 2 |
-47 |
2 |
D01 |
S.08 |
0.2 |
- 3 |
-21 |
3 |
D01 |
COMP. |
0.2 |
- 1 |
-17 |
4 |
D01 |
S.08 |
0.5 |
0 |
- 8 |
5 |
D01 |
COMP. |
0.5 |
0 |
- 9 |
6 |
D02 |
|
none |
- 9 |
-69 |
7 |
D02 |
S.08 |
0.2 |
- 2 |
-40 |
8 |
D02 |
COMP. |
0.2 |
- 3 |
-31 |
9 |
D02 |
S.08 |
0.5 |
+ 3 |
-18 |
10 |
D02 |
COMP. |
0.5 |
- 5 |
-19 |
11 |
D08 |
|
none |
- 3 |
- 5 |
12 |
D08 |
COMP. |
0.1 |
- 6 |
-15 |
13 |
D08 |
COMP. |
0.25 |
-11 |
-27 |
14 |
D08 |
COMP. |
0.5 |
-19 |
-36 |
15 |
D08 |
|
none |
- 5 |
-23 |
16 |
D08 |
S.07 |
0.2 |
-33 |
-52 |
17 |
D08 |
S.07 |
0.5 |
-47 |
-66 |
[0072] The results of tests 1 to 10 show that the light-stabilizers according to the present
invention perform as good as prior art light-stabilizers. However, the light-stabilizers
of the present invention have the supplemental advantage of being free of heavy metal
ions, which means that they are far more acceptable from an ecological standpoint
than most prior art light-stabilizers. Moreover, thanks to the fact that both the
dye and the light-stabilizer had been incorporated in the dye layer as described in
Examples 1 and 2, a direct quantitative relation is created between transferred dye
and transferred light-stabilizer so that an optimal light-stabilization of the transferred
dye is guaranteed.
1. Dye-donor element for use according to thermal dye sublimation transfer, said dye-donor
element comprising a support having thereon a dye layer comprising at least one dye
and a binder, wherein said dye layer or a top layer thereon also comprises a light-stabilizer
for said at least one dye, said light-stabilizer being a leuco-indoaniline dye.
2. Dye-donor element according to claim 1 wherein said leuco-indoaniline dye corresponds
to the following general formula :

wherein :
R¹ represents hydrogen or any substituent,
n is zero or a positive integer chosen from 1 to 4, and when n is 2, 3, or 4, R¹ has
same or different significances,
each of R² and R³ (same or different) represents hydrogen or an acyl group chosen
from the group of -COR¹⁰, -SO₂R¹⁰, and -OPR¹⁰R¹¹,
X is zero or represents the atoms needed to complete an aromatic, alicyclic, or heterocyclic
ring or ring system, or a such ring or ring system in substituted form,
each of R⁴, R⁵, R⁶ and R⁷ (same or different) represents hydrogen, an alkyl group,
a substituted alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an
aryl group, a substituted aryl group, an alkyloxy group, a substituted alkyloxy group,
an aryloxy group, a substituted aryloxy group, a carbamoyl group, a substituted carbamoyl
group, a sulphamoyl group, a substituted sulphamoyl group, hydroxy, a halogen atom,
-NH-SO₂R¹², -NH-COR¹², -O-SO₂R¹², or -O-COR¹², or R⁴ and R⁷ together and R⁵ and R⁶
together represent the atoms necessary to complete an aliphatic ring, a substituted
aliphatic ring, a heterocyclic nucleus, a substituted heterocyclic nucleus, a heterocyclic
nucleus carrying a fused-on cycloaliphatic, aromatic, or heterocyclic ring or ring
system, or a substituted heterocyclic nucleus carrying a fused-on cycloaliphatic,
aromatic, or heterocyclic ring or ring system, or R⁴ and R⁸ and/or R⁵ and R⁹ together
and R⁵ and R⁶ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R⁸ and R⁹ (same or different) represents hydrogen, an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an aryl group, a
substituted aryl group, a heterocyclic nucleus, a substituted heterocyclic nucleus,
or R⁸ and R⁹ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R¹⁰, R¹¹, and R¹² (same or different) represents an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an alkenyl group,
a substituted alkenyl group, an aryl group, a substituted aryl group, an alkyloxy
group, a substituted alkyloxy group, an aryloxy group, a substituted aryloxy group,
an alkylthio group, a substituted alkylthio group, an arylthio, a substituted arylthio
group, an amino group, a substituted amino group, a heterocyclic nucleus, or a substituted
heterocyclic nucleus.
3. A dye-donor element according to claim 1 or 2, wherein said light-stabilizer is used
in amounts of 20 to 150 % by weight calculated on the weight of said dye.
4. Dyed receiver sheet comprising at least one dye and at least one light-stabilizer
for said dye, wherein said dye and said light-stabilizer are present in an image-wise
distribution produced by thermal dye sublimation transfer from a dye-donor element
and said light-stabilizer is a leuco-indoaniline dye.
5. Dyed receiver sheet according to claim 4, wherein said leuco-indoaniline dye corresponds
to the following general formula :

wherein :
R¹ represents hydrogen or any substituent,
n is zero or a positive integer chosen from 1 to 4, and when n is 2, 3, or 4, R¹ has
same or different significances,
each of R² and R³ (same or different) represents hydrogen or an acyl group chosen
from the group of -COR¹⁰, -SO₂R¹⁰, and -OPR¹⁰R¹¹,
X is zero or represents the atoms needed to complete an aromatic, alicyclic, or heterocyclic
ring or ring system, or a such ring or ring system in substituted form,
each of R⁴, R⁵, R⁶, and R⁷ (same or different) represents hydrogen, an alkyl group,
a substituted alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an
aryl group, a substituted aryl group, an alkyloxy group, a substituted alkyloxy group,
an aryloxy group, a substituted aryloxy group, a carbamoyl group, a substituted carbamoyl
group, a sulphamoyl group, a substituted sulphamoyl group, hydroxy, a halogen atom,
-NH-SO₂R¹², -NH-COR¹², -O-SO₂R¹², or -O-COR¹², or R⁴ and R⁷ together and R⁵ and R⁶
together represent the atoms necessary to complete an aliphatic ring, a substituted
aliphatic ring, a heterocyclic nucleus, a substituted heterocyclic nucleus, a heterocyclic
nucleus carrying a fused-on cycloaliphatic, aromatic, or heterocyclic ring or ring
system, or a substituted heterocyclic nucleus carrying a fused-on cycloaliphatic,
aromatic, or heterocyclic ring or ring system, or R⁴ and R⁸ and/or R⁵ and R⁹ together
and R⁵ and R⁶ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R⁸ and R⁹ (same or different) represents hydrogen, an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an aryl group, a
substituted aryl group, a heterocyclic nucleus, a substituted heterocyclic nucleus,
or R⁸ and R⁹ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R¹⁰, R¹¹, and R¹² (same or different) represents an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an alkenyl group,
a substituted alkenyl group, an aryl group, a substituted aryl group, an alkyloxy
group, a substituted alkyloxy group, an aryloxy group, a substituted aryloxy group,
an alkylthio group, a substituted alkylthio group, an arylthio, a substituted arylthio
group, an amino group, a substituted amino group, a heterocyclic nucleus, or a substituted
heterocyclic nucleus.
6. Receiver sheet for receiving an image-wise distribution of dye by thermal dye sublimation
transfer from a dye-donor element, wherein said receiver sheet comprises a light-stabilizer
for said dye, said light-stabilizer being a leuco-indoaniline dye.
7. Receiver sheet according to claim 6, wherein said leuco indoaniline dye corresponds
to the following general formula :

wherein :
R¹ represents hydrogen or any substituent,
n is zero or a positive integer chosen from 1 to 4, and when n is 2, 3, or 4, R¹ has
same or different significances,
each of R² and R³ (same or different) represents hydrogen or an acyl group chosen
from the group of -COR¹⁰, -SO₂R¹⁰, and -OPR¹⁰R¹¹,
X is zero or represents the atoms needed to complete an aromatic, alicyclic, or heterocyclic
ring or ring system, or a such ring or ring system in substituted form,
each of R⁴, R⁵, R⁶, and R⁷ (same or different) represents hydrogen, an alkyl group,
a substituted alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an
aryl group, a substituted aryl group, an alkyloxy group, a substituted alkyloxy group,
an aryloxy group, a substituted aryloxy group, a carbamoyl group, a substituted carbamoyl
group, a sulphamoyl group, a substituted sulphamoyl group, hydroxy, a halogen atom,
-NH-SO₂R¹², -NH-COR¹², -O-SO₂R¹², or -O-COR¹², or R⁴ and or R⁷ together and R⁵ and
R⁶ together represent the atoms necessary to complete an aliphatic ring, a substituted
aliphatic ring, a heterocyclic nucleus, a substituted heterocyclic nucleus, a heterocyclic
nucleus carrying a fused-on cycloaliphatic, aromatic, or heterocyclic ring or ring
system, or a substituted heterocyclic nucleus carrying a fused-on cycloaliphatic,
aromatic, or heterocyclic ring or ring system, or R⁴ and R⁸ and/or R⁵ and R⁹ together
and R5 and R⁶ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R⁸ and R⁹ (same or different) represents hydrogen, an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an aryl group, a
substituted aryl group, a heterocyclic nucleus, a substituted heterocyclic nucleus,
or R⁸ and R⁹ together represent the atoms necessary to complete to complete a heterocyclic
nucleus or a substituted heterocyclic nucleus,
each of R¹⁰, R¹¹, and R¹² (same or different) represents an alkyl group, a substituted
alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an alkenyl group,
a substituted alkenyl group, an aryl group, a substituted aryl group, an alkyloxy
group, a substituted alkyloxy group, an aryloxy group, a substituted aryloxy group,
an alkylthio group, a substituted alkylthio group, an arylthio, a substituted arylthio
group, an amino group, a substituted amino group, a heterocyclic nucleus, or a substituted
heterocyclic nucleus.
8. Receiver sheet according to claim 6, wherein said light-stabilizer is present in a
dye-image-receiving layer comprising a binder.
9. Receiver sheet according to claim 8, wherein said light-stabilizer is present in an
amount of 10 to 100% by weight calculated on the weight of said binder.
10. Method of forming a light-fast dye image by image-wise heating a dye-donor element
comprising a dye layer comprising a binder and at least one dye, and in said dye layer
or in a layer on top of said dye layer a light-stabilizer for said dye, said light-stabilizer
being a leuco-indoaniline dye, and causing transfer off the image-wise heated dye
and light-stabilizer to a receiver sheet.
11. Method of forming a light-fast dye image by image-wise heating a dye-donor element
comprising a dye layer comprising a binder and at least one dye, and causing transfer
of the image-wise heated dye to a receiver sheet, wherein said receiver sheet comprises
a light-stabilizer for the transferred dye, said light-stabilizer being a leuco-indoaniline
dye.