Transferring dyes for thermal printing

Abstract

Dyes are transferred from a carrier by sublimation/vaporization to plastic-coated papers by a process in which the dyes used are of the general formula (I) ##STR1## where A is D--N=N-- or ##STR2## R.sup.1 and R.sup.2 are each hydrogen, alkyl, alkoxy, alkylthio or halogen and R.sup.1 and R together may furthermore form a 5-membered or 6-membered heterocyclic ring, and R and R' independently of one another are each hydrogen, phenyl which is unsubstituted or substituted by methyl or methoxy, or C.sub.5 - or C.sub.6 -cycloalkyl or C.sub.1 -C.sub.6 -alkyl which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkoxycarbonyl, C.sub.2 -C.sub.5 -alkanoyloxy, C.sub.1 -C.sub.4 -alkoxycarbonyloxy, C.sub.1 -C.sub.4 -alkoxy-C.sub.2 - or C.sub.3 -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C.sub.5 - or C.sub.6 cycloalkyl, or ##STR3## is a 5-membered or 6-membered saturated heterocyclic ring where D is a radical of a diazo component of the thiophene, thiazole, isothiazole or 1,2,4-thiadiazole series and R.sup.3 is hydrogen or CN.In the process, the dyes (I) give strong dyeings which have good light fastness and are resistant to chemical substances.

Description

In the sublimation transfer process, a transfer sheet which contains a sublimable dye with or without a binder on a carrier is heated from the rear by short heat pulses (lasting fractions of a second) using a thermal printing head, the dye being sublimed or vaporized and transferred to a receiving medium. The essential advantage of this process is that the amount of dye to be transferred (and hence the color gradation) can readily be controlled by adjusting the energy to be supplied to the thermal printing head.

In general, the color image is produced using the three subtractive primary colors, yellow, magenta and cyan (and if necessary black). In order to permit an optimum color image to be produced, the dyes must have the following properties:

i) readily sublimable or vaporizable; in general, this requirement is most difficult to meet in the case of the cyan dyes; ii) high thermal and photochemical stability and resistance to moisture and chemical substances; iii) suitable hues for subtractive color mixing; iv) a high molecular absorption coefficient; v) readily obtainable industrially.

Most of the known dyes used for thermal transfer printing do not adequately meet these requirements.

The prior art discloses dyes for this purpose.

JP-A 159091/1985 describes dyes of the formula ##STR4## where R is alkyl, aralkyl, aryl or a 5-membered or 6-membered carbocyclic ring, for this purpose.

JP-A 30392/1985 discloses dyes of the formula ##STR5## where R, R.sup.1 and R.sup.2 are each allyl, alkyl or alkoxyalkyl and X is H or methyl.

JP-A 229786/1985 describes dyes of the formula ##STR6## where R and R.sup.1 are each methyl, ethyl, propyl or butyl and X is H or methyl, for this application. In JP-A 239292/1985, dyes of the formula ##STR7## are described for the transfer process. In the formula, R.sup.1 is C.sub.1 -C.sub.8 -alkyl, R.sup.2 is H or methyl and D is ##STR8##

Quinone derivatives of the formula ##STR9## where R and R.sup.1 are each methyl, ethyl, propyl or butyl, are described for this application in JP-A 229 786/1985.

Furthermore, the use of indoaniline dyes of the general formula ##STR10## is described for this purpose in DE-A 35 24 519.

It is an object of the present invention to provide dyes which are readily sublimable or vaporizable under the conditions produced by a thermal printing head, do not undergo thermal or photochemical decomposition, can be processed to give printing inks and meet the color requirements. The dyes should also be readily obtainable industrially.

We have found that this object is achieved by a process for transferring dyes from a carrier by sublimation/vaporization with the aid of a thermal printing head to a plastic-coated paper, wherein a carrier is used on which dyes of the general formula ##STR11## where A is D--N.dbd.N-- or ##STR12## R.sup.1 and R.sup.2 independently of one another are each hydrogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkylthio or halogen and R.sup.1 together with R may form a 5-membered or 6-membered heterocyclic ring, and R and R' independently of one another are each hydrogen, phenyl which is unsubstituted or substituted by methyl or methoxy, or C.sub.5 - or C.sub.6 -cycloalkyl or C.sub.1 -C.sub.6 -alkyl which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkoxycarbonyl, C.sub.2 -C.sub.5 -alkanoyloxy, C.sub.1 -C.sub.4 -alkoxycarbonyloxy, C.sub.1 -C.sub.4 -alkoxy-C.sub.2 - or C.sub.3 -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C.sub.5 - or C.sub.6 -cycloalkyl, or ##STR13## is a 5-membered or 6-membered heterocyclic ring, D is ##STR14## R.sup.3 is hydrogen or CN, R.sup.4 is C.sub.1 -C.sub.4 -alkyl, phenyl, benzyl or CN, R.sup.5 is C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkylthio, C.sub.1 -C.sub.4 -alkoxy, C.sub.5 - or C.sub.6 -cycloalkyl, benzyl, C.sub.5 - or C.sub.6 -cycloalkylthio, C.sub.5 - or C.sub.6 -cycloalkoxy, benzyloxy or benzylthio, R.sup.6 is CN or --CHO, R.sup.7 is C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkylthio or chlorine and R.sup.8 is --CHO, CN or nitro, and R.sup.1 and R.sup.2 must not be hydrogen when A is ##STR15## and R.sup.5 is alkylthio or when A is ##STR16##

Compared with the dyes used in the conventional processes, those employed in the novel process possess better sublimability and in some cases greater lightfastness and greater resistance to chemical substances.

In the process of the invention, dyes of the general formula ##STR17## are used. In the formula, A is D--N.dbd.N-- or ##STR18##

In addition to being hydrogen, R.sup.1 and R.sup.2 are, for example, C.sub.1 -C.sub.4 -alkyl, such as CH.sub.3, C.sub.2 H.sub.5, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, C.sub.1 -C.sub.4 -alkoxy, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy, C.sub.1 -C.sub.4 -alkylthio, such as methylthio, ethylthio or butylthio or halogen, such as bromine, but preferably chlorine or fluorine. R.sup.1 together with R may furthermore form a heterocyclic ring, so that ##STR19## can correspond to the following formulae: ##STR20##

In the formulae (I) and (IIa) to (IId), R and R' independently of one another are each hydrogen or C.sub.1 -C.sub.6 -alkyl which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkoxycarbonyl, C.sub.1 -C.sub.4 -alkoxycarbonyloxy, C.sub.2 -C.sub.5 -alkanoyloxy, C.sub.1 -C.sub.4 -alkoxy-C.sub.2 - or C.sub.3 -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C.sub.5 - or C.sub.6 -cycloalkyl.

Specific examples of C.sub.1 -C.sub.6 -alkyl are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl and isohexyl.

Specific examples of C.sub.1 -C.sub.4 -alkoxy in the alkoxy-carrying substituents are methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy and isobutoxy.

Suitable halogen substituents on C.sub.1 -C.sub.6 -alkyl are bromine, chlorine and preferably fluorine.

Specific examples of C.sub.2 -C.sub.5 -alkanoyl are acetyl, propionyl, butanoyl and pentanoyl.

R' and R may furthermore be phenyl which is unsubstituted or substituted by methyl or methoxy, or may be C.sub.5 - or C.sub.6 -cycloalkyl or benzyl.

Specific examples of substituted C.sub.1 -C.sub.6 -alkyl are 2-hydroxyethyl, 2- and 3-hydroxypropyl, 3- and 4-hydroxybutyl, 2-cyanoethyl, 3-cyanopropyl and 4-cyanobutyl, benzyl, 2-phenylethyl and 2- and 3-phenylpropyl, methoxyethyl, 2- and 3-methoxypropyl, ethoxyethyl, n- and isopropoxyethyl and n- and isobutoxyethyl, 2-acetoxyethyl, 2-propanoyloxyethyl, 2-butanoyloxyethyl and 2-pentanoyloxyethyl, 2- and 3-acetoxypropyl, 2- and 3-propanoyloxypropyl, 2- and 3-butanoyloxypropyl and 2- and 3-pentanoyloxypropyl, 2-(methoxycarbonyl)-ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)-ethyl, 2-(butoxycarbonyl)ethyl and the corresponding 3-propyl derivatives, 2-(methoxycarbonyloxy)-ethyl, 2-(ethoxycarbonyloxy)-ethyl, 2-(n- and isopropoxycarbonyloxy)-ethyl, 2-(n- and isobutoxycarbonyloxy)-ethyl and the corresponding 3-(alkoxycarbonyloxy)-propyl derivatives, 2-(methoxyethoxycarbonyloxy)-ethyl, 2-(ethoxyethoxycarbonyloxy)-ethyl, 2-(n- and isopropoxyethoxycarbonyloxy)-ethyl and 2-(n- and isobutoxyethoxycarbonyloxy)-ethyl and the corresponding 3-(alkoxyalkoxycarbonyloxy)-propyl derivatives, and cyclopentylmethyl and cyclohexylmethyl.

Unsubstituted or substituted phenyl radicals R and R' are phenyl as well as 2- and 4-methylphenyl and 2- and 4-methoxyphenyl. Where R is phenyl or substituted phenyl, R' is preferably methyl and in particular hydrogen. ##STR21## may furthermore be a heterocyclic radical, such as ##STR22##

R.sup.3 is hydrogen or CN.

D is a radical of the formula ##STR23## where R.sup.4 is C.sub.1 -C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, phenyl, benzyl or CN, R.sup.5 is C.sub.1 -C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or tert-butyl, C.sub.1 -C.sub.4 -alkoxy, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy, C.sub.1 -C.sub.4 -alkylthio, benzyl, C5- or C6-cycloalkyl, C.sub.5 - or C.sub.6 -cycloalkylthio, C.sub.5 - or C.sub.6 - cycloalkoxy, benzyloxy or benzylthio, R.sup.6 is CN or --CHO, R.sup.7 is C.sub.1 -C.sub.4 -alkoxy, such as methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, or tert-butoxy, C.sub.1 -C.sub.4 -alkylthio or chlorine, and R.sup.8 is --CHO, CN or nitro.

Dyes (I) in which A is ##STR24## and R.sup.5 is alkylthio or A is ##STR25## are excluded when R.sup.1 and R.sup.2 are each hydrogen.

The following are preferred for the present process:

a) Dyes of the formula (I) where R and R' are each hydrogen or C.sub.1 -C.sub.4 -alkyl which is unsubstituted or substituted by hydroxyl, cyano or phenyl, or are each C.sub.1 -C.sub.4 -alkoxy-C2-C4-alkyl, C.sub.1 -C.sub.4 -alkoxycarbonyl-C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxycarbonyloxy-C.sub.2 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -fluoroalkyl, or phenyl which is unsubstituted or substituted by methoxy or methyl, R.sup.1 and R.sup.2 are each hydrogen, methyl, methoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy

and A is D--N.dbd.N-- or ##STR26## and where D is ##STR27## where R.sup.4 is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or cyano and R.sup.5 is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio or tert-butylthio.

b) Dyes of the formulae ##STR28## where D is ##STR29## R.sup.4 is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or CN, R.sup.5 is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio or tert-butylthio and R is hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

Particularly preferred dyes are those of the formula ##STR30## where R.sup.9 is hydrogen, C.sub.1 -C.sub.4 -alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy or tertbutoxy, R.sup.10 and R.sup.11 independently of one another are each hydrogen, C.sub.1 -C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, C.sub.1 -C.sub.4 -alkoxycarbonylethyl or C.sub.2 -C.sub.5 -alkanoyloxyethyl, and those of the formulae (IIIa), (IIIb), (IIIc) and (IIId) where D is ##STR31## and R is hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

Other particularly preferred dyes are those of the formula ##STR32## where R and R' independently of one another are each hydrogen, C.sub.1 -C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, phenyl, C.sub.2 -C5-alkanoyloxyethyl, C.sub.1 -C.sub.4 -alkoxycarbonylethyl, C.sub.1 -C.sub.4 -alkoxycarbonyloxyethyl, benzyl or cyanoethyl, R.sup.1 and R.sup.2 independently of one another are each hydrogen, C.sub.1 -C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, C.sub.1 -C.sub.4 -alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy, or C.sub.1 -C.sub.4 -thioalkyl, and R.sup.4 is C.sub.1 -C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, or phenyl.

The dyes (I) are synthesized by conventional processes or processes known per se.

Azo dyes of the general formula (V) where R, R' , R.sup.1, R.sup.2 and R.sup.4 have the stated meanings, are prepared by the process described in German Laid-Open Application DOS 3,207,290. The diazo component (R.sup.4 =CN) ##STR33## is disclosed in DE-A 34 02 024. Azo dyes (I) where D is ##STR34## and R.sup.5 is alkylthio have been synthesized by the process described in DE-C 15 44 391. Diazo components where R.sup.5 is alkyl have been prepared by the synthesis described in Chem. Ber. 87 (1954), 57.

Azo dyes (I) where D is ##STR35## have been synthesized by the process described in DE-A 31 08 077 and 35 29 831, respectively.

Dyes of the type ##STR36## have been prepared by the process described by McKusick et al., J. Am. Chem. Soc. 80 (1958), 2806, by reacting the corresponding aniline derivatives with tetracyanoethylene.

Dyes (I) in which A is ##STR37## have been obtained by known processes, by reacting appropriate p-formylanilines with malodinitrile.

To prepare the dye carriers required for the process, the dyes in a suitable solvent, eg. chlorobenzene or isobutanol, are processed with a binder to give a printing ink. The latter contains the dye in dissolved or dispersed form. The printing ink is applied to the inert carrier by means of a knife coater, and the dying is dried in the air. Examples of suitable binders are ethylcellulose, polysulfones and polyethersulfones. Examples of inert carriers are tissue paper, blotting paper and glassine, as well as plastic films possessing good heat stability, for example uncoated or metal-coated polyester, nylon or polyimide. The carrier is preferably from 3 to 30 .mu.m thick. Other carriers suitable for the novel process and binders and solvents for the preparation of the printing inks are described in DE-A 35 24 519.

Suitable dye-accepting layers are in principle all heat-stable plastic layers possessing an affinity for the dyes to be transferred, eg. polyesters.

Transfer is effected by means of a thermal printing head, which must supply sufficient heating power to transfer the dye within a few milliseconds.

The embodiments which follow are intended to illustrate the invention further.

In order to be able to test the transfer behavior of the dyes quantitatively and in a simple manner, the thermal transfer is carried out using heating jaws having a large area, instead of a thermal printing head, and the dye carriers to be tested are prepared without the use of a binder.

A) General formulations for coating the carriers with dye:

AI)

1 g of ethylene glycol, 1 g of dispersant based on a condensate of phenol, formaldehyde and Na bisulfite, 7.5 g of water and 0.5 g of dye, together with 10 g of glass spheres (2 mm diameter) are introduced into vessels and the latter are closed and shaken on a shaking apparatus (Red Devil.RTM.) until the mean particle size of the dye is .ltoreq.1 .mu.m (duration: from 8 to 12 hours, depending on the dye). The glass spheres are separated off by means of a sieve and the resulting dye dispersion, which may be diluted with water to twice its volume, is applied to paper using a 6 .mu.m knife coater and dried in the air.

AII) The dye is applied to the paper carrier once or several times in the form of a solution having a saturation of about 90% in a solvent (eg. chlorobenzene, tetrahydrofuran, methyl ethyl ketone, isobutanol or a mixture of these) by the spin-coating method. The amount of dye applied by spin coating is adjusted so that, on complete transfer to an 80 .mu.m thick polyester film (acceptor), an extinction of not less than 2 is obtained.

B) Testing the sublimation/vaporization behavior

The dyes used were tested in the following manner: The paper layer (donor) coated with the dye to be tested is placed with the dye layer on an 80 .mu.m thick polyester film (acceptor) and pressed against it. The donor and acceptor are then wrapped with aluminum foil and heated for 30 seconds between two heated plates. The amount of dye which has migrated to the polyester film is determined photometrically. If the logarithm of the extinction A of the dyed polyester films measured at various temperatures (range: 100.degree.-200.degree. C.) is plotted against the associated reciprocal absolute temperature, straight lines are obtained from whose slope the activation energy .DELTA.E.sub.T for the transfer experiment is calculated: ##EQU1##

For complete characterization, the temperature T* [.degree.C] at which the extinction A of the dyed polyester film reaches the value 1 is additionally obtained from the plots.

EXAMPLES 1 TO 27

The dyes stated in Tables 1 to 6 were processed according to AI) or AII), and the sublimation behavior of the resulting dye-coated carriers was tested according to B). The Table lists the hue on polyester and the thermal transfer parameters T* and .DELTA.E.sub.T.

TABLE 1__________________________________________________________________________ ##STR38## Example X Hue T*[.degree.C.] ##STR39##__________________________________________________________________________ 1 ##STR40## magenta 145 23 2 ##STR41## violet 156 16 3 ##STR42## magenta 153 18 4 ##STR43## violet 174 23 5 ##STR44## magenta 165 25 6 ##STR45## magenta 156 21 7 ##STR46## magenta 154 17 8 ##STR47## magenta 161 19 9 ##STR48## magenta 155 2110 ##STR49## magenta 169 1711 ##STR50## magenta 157 1712 ##STR51## magenta 173 2013 ##STR52## magenta 151 2114 ##STR53## red 170 2015 ##STR54## magenta 175 2016 ##STR55## magenta 162 1917 ##STR56## magenta 171 20__________________________________________________________________________ TABLE 1a__________________________________________________________________________ ##STR57## Example X Hue T*[.degree.C.] ##STR58##__________________________________________________________________________18 ##STR59## yellow 19019 ##STR60## greenish yellow 121 2620 ##STR61## yellow 120 2321 ##STR62## yellow 120 2522 ##STR63## yellow 130 2323 ##STR64## yellow 158 2424 ##STR65## yellow 157 2425 ##STR66## reddish yellow 130 2026 ##STR67## yellow 154 2427 ##STR68## yellow 152 21__________________________________________________________________________ TABLE 2__________________________________________________________________________ ##STR69## Example R.sup.4 X Hue T*[.degree.C.] ##STR70##__________________________________________________________________________28 CH.sub.3 ##STR71## magenta 148 1729 CH.sub.3 ##STR72## magenta 175 1830 ##STR73## ##STR74## magenta 155 1931 ##STR75## ##STR76## magenta 149 1932 CH.sub.3 ##STR77## magenta 134 2333 CH.sub.3 ##STR78## magenta 140 2534 CH.sub.3 ##STR79## magenta 141 2335 CH.sub.3 ##STR80## red 140 2536 CH.sub.3 ##STR81## red 178 1737 CH.sub.3 ##STR82## magenta 173 1638 ##STR83## ##STR84## magenta 172 2839 ##STR85## ##STR86## magenta-violet 200 1940 CH(CH.sub.3).sub.2 ##STR87## magenta 164 1641 CH.sub.3 ##STR88## magenta 167 1642 CH.sub.3 ##STR89## magenta 161 2543 CH.sub.3 ##STR90## magenta 155 2344 CH.sub.3 ##STR91## red 167 2545 CH.sub.3 ##STR92## magenta 164 2546 CH.sub.3 ##STR93## magenta 190 3247 CH.sub.3 ##STR94## magenta 199 3148 CH.sub.3 ##STR95## magenta 193 3049 CH.sub.3 ##STR96## magenta 177 2650 CH(CH.sub.3).sub.2 ##STR97## magenta 193 3151 CH(CH.sub.3).sub.2 ##STR98## magenta 199 2452 CH.sub.3 ##STR99## magenta 154 25__________________________________________________________________________ TABLE 3__________________________________________________________________________ ##STR100## Example R.sup.5 X Hue T*[.degree.C.] ##STR101##__________________________________________________________________________53 CH.sub.3 ##STR102## reddish 155 2054 SCH.sub.3 ##STR103## reddish 162 2155 CH.sub.3 ##STR104## violet 172 2356 CH.sub.3 ##STR105## violet 170 22__________________________________________________________________________ TABLE 4______________________________________ ##STR106## pleExam- X Hue [.degree.C.]T* ##STR107##______________________________________57 ##STR108## violet 180 2058 ##STR109## violet 172 1959 ##STR110## reddish blue 176 20______________________________________ TABLE 5__________________________________________________________________________ Example X Hue T*[.degree.C.] ##STR111##__________________________________________________________________________60 ##STR112## blue 170 25__________________________________________________________________________ TABLE 6__________________________________________________________________________ ##STR113## Example X Hue T*[.degree.C.] ##STR114##__________________________________________________________________________61 ##STR115## reddish blue 172 2462 ##STR116## reddish blue 180 2363 ##STR117## reddish blue 178 2364 ##STR118## cyan 165 2565 ##STR119## cyan 170 2766 ##STR120## cyan 175 2767 ##STR121## blue 169 2468 ##STR122## cyan 192 2669 ##STR123## cyan 182 2570 ##STR124## reddish blue 169 2971 ##STR125## reddish blue 173 3472 ##STR126## reddish blue 179 3273 ##STR127## neutral blue 163 2874 ##STR128## reddish blue 159 2175 ##STR129## reddish blue 165 3076 ##STR130## reddish blue 166 2577 ##STR131## violet 185 2578 ##STR132## neutral blue 178 2679 ##STR133## neutral blue 177 2780 ##STR134## cyan 174 26__________________________________________________________________________

In the case of the dye of Example 23, samples were heated as described in B) to the temperatures stated in Table 6, in each case for 30 seconds, after which the extinction of the dyeing on polyester was determined. The extinctions and temperatures for 6 measured points are stated in Table 7.

TABLE 7______________________________________Sample 20.1 20.2 20.3 20.4 20.5 20.6______________________________________t.degree. C. 137 146 154 158 168 176A 0.137 0.247 0.435 0.659 1.094 2.08______________________________________

In FIG. 1, the values are plotted in the form of log A against ##EQU2##

In the graph, .DELTA.Log A=1.14 when ##EQU3## from which .DELTA.E.sub.T can be calculated: ##EQU4##

The graph furthermore gives ##EQU5##

Claims

1. A process for transferring a dye from a carrier by sublimation/-vaporization with the aid of a thermal printing head to a plastic-coated paper, said carrier employing a dye of the formula:

where R.sup.1 is, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkylthio or halogen and R.sup.1 together with R may form a 5-membered or 6-membered heterocyclic ring, and R and R' independently of one another are each hydrogen, phenyl which is unsubstituted or substituted by methyl or methoxy, or C.sub.5-C.sub.6 -cycloalkyl or C.sub.1-C.sub.6 -alkyl, which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkoxycarbonyl, C.sub.2 -C.sub.5 -alkanoyloxy, C.sub.1 -C.sub.4 -alkoxycarbonyloxy, C.sub.1 -C.sub.4 -alkoxy-C.sub.2 - or C.sub.3 -alkoxycarbonyloxy, hydroxyl, cyano, halogen, phenyl or C.sub.5 - or C.sub.6 -cycloalkyl, or is a 5-membered or 6-membered heterocyclic ring, D is ##STR135## R.sup.7 is chlorine and R.sup.8 is --CHO, CN or nitro.

2. The process as claimed in claim 1, wherein R and R' independently of one another are each hydrogen or C.sub.1 -C.sub.4 -alkyl which is unsubstituted or substituted by hydroxyl, cyano or phenyl, or are each C.sub.1 -C.sub.4 -alkoxy-C.sub.2 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxycarbonyl-C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxycarbonyl-oxy-C.sub.2 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -fluoroalkyl, R.sup.1 is C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy or C.sub.1 -C.sub.4 -alkylthio.

3. The process as claimed in claim 1 where D is ##STR136## and R.sup.4 is C.sub.1 -C.sub.4 -alkyl, phenyl, benzyl or CN.

4. The process as claimed in claim 2 where D is R1 ? ##STR137##

5. The process as claimed in claim 1, wherein a dye of the formula: ##STR138## is used, where R.sup.9 is C.sub.1 -C.sub.4 -alkoxy and R.sup.10 and R.sup.11 independently of one another are each hydrogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxycarbonylethyl or C.sub.2 -C.sub.5 -alkanoylethyl.