EP0273307B1 - Method of transferring cationic dyes in their de-protonated, electrically neutral form - Google Patents

Description

The present invention relates to a new process for the transfer of cationic dyes with cyanine chromophore, in their deprotonated, electrically neutral form from a support to a coated paper.

In the sublimation transfer process, a transfer sheet which contains a sublimable dye, optionally together with a binder, on a support is heated with a heating head by means of short heating impulses from the back, the dye subliming or evaporating and transferring it onto a paper serving as the recording medium becomes. The main advantage of this method is that it is easy to control the amount of dye to be transferred (and thus the color gradation) by adjusting the energy to be delivered to the heating head.

• leichte Sublimier- oder Verdampfbarkeit (im allgemeinen ist diese Anforderung bei den Cyanfarbstoffen am schwierigsten zu erfüllen);
• hohe thermische und photochemische Stabilität sowie Resistenz gegen Feuchtigkeit und chemische Stoffe;
• geeignete Farbtöne für die subtraktive Farbmischung aufweisen;
• einen hohen molekularen Absorptionskoeffizienten aufweisen
• leicht technisch zugänglich sein.

In general, the color recording is carried out using the three subtractive primary colors yellow, magenta and cyan (and possibly black). In order to enable optimal color recording, the dyes used should have the following properties:

• easy sublimability or vaporizability (in general, this requirement is most difficult to meet with cyan dyes);
• high thermal and photochemical stability as well as resistance to moisture and chemical substances;
• have suitable shades for the subtractive color mixture;
• have a high molecular absorption coefficient
• be easily technically accessible.

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

For example, DE-A-2 359 515 proposes a process for dyeing and printing polyacrylonitrile fabric, salts of cationic dyes being transferred from a support to the polyacrylonitrile material under the action of heat. The salts are said to be derived from acids, whose pK _A value is greater than 3. However, it has been shown that the thermal transfer of these salts leads to insufficient colorations, since high energy is required to convert these color salts into the gas phase by evaporation or sublimation. In addition, the dyes are partially decomposed under these conditions.

EP-A-178 832 describes the thermal transfer of salts of cationic dyes with soft anionic bases on polyester.

Finally, DE-A-2 521 988 teaches the dyeing and printing of polyacrylonitrile by thermal transfer of electroneutral, deprotonated cationic dyes in the presence of an additional indicator dye. The presence of an indicator dye is necessary to avoid the formation of faulty prints. The thermal transfer takes place at a temperature of 195 ° C. It is known, however, that many cationic dyes are not heat-stable in the form of their free color base, i.e. partial decomposition of the neutral color base often occurs during the heat.

It was an object of the present invention to provide a method for transferring dyes, the dyes being easily sublimable or vaporizable under the conditions of use of a thermal head, not suffering from thermal and photochemical decomposition, being able to be processed into printing inks and meeting the color requirements. They should also be technically easily accessible.

It has been found that the transfer of dyes from a support to an acceptor by sublimation or evaporation of the dyes with the aid of a thermal head is advantageously achieved if a support is used on which cationic dyes with cyanine chromophore, which have at least one NH group, which is part of the cyanine chromophore, is in its electrically neutral form deprotonated on the NH group, and transfers these deprotonated dyes to a coated paper.

Cationic dyes with cyanine chromophore are understood to mean those dyes which have conjugated double bonds, with a nitrogen atom at at least one end of the conjugated system, and in which the delocalization of the positive charge takes place in an alternating manner along the conjugated system (chromophore chain).

The delocalization of the positive charge is graphically represented in a manner known per se by a dotted line along the conjugate system, in which case only the single bond is drawn in the formulas.

in der

R¹ R² und R7

gleich oder verschieden sind und unabhängig voneinander jeweils Wasserstoff, C₁-C₄-Alkyl, das gegebenenfalls durch C₁-C₄-Alkoxy, C₁-C₄-Alkylthio, Halogen, Cyano, Hydroxy oder Phenyl substituiert ist oder C₅-C₇-Cycloalkyl oder R¹ und R² zusammen mit dem sie verbindenden Stickstoffatom einen 5- oder 6-gliedrigen, gesättigten heterocyclischen Rest,

R³ und R⁵

gleich oder verschieden sind und unabhängig voneinander jeweils Wasserstoff, C₁-C₄-Alkyl, C₁-C₄-Alkoxy oder Halogen,

R⁴

Wasserstoff oder zusammen mit R⁵ einen anellierten Benzoring,

R⁶

Wasserstoff, C₁-C₄-Alkyl, das gegebenenfalls durch C₁-C₄-Alkoxy, C₁-C₄-Alkylthio, Halogen, Cyano, Hydroxy oder Phenyl substituiert ist, C₅-C₇-Cycloalkyl oder den Rest

in dem R⁸, R⁹ und R¹⁰ gleich oder verschieden sind und unabhängig voneinander jeweils für Wasserstoff, C₁-C₄-Alkyl, C₁-C₄-Alkoxy oder Halogen stehen, und

   A

Sauerstoff oder Schwefel bedeuten, in ihrer deprotonierten, elektrisch neutralen Form.

Cationic dyes whose cation has the formula I are preferably transferred

in the

R1 R2 and R7

are identical or different and are each independently hydrogen, C₁-C₄-alkyl, which is optionally substituted by C₁-C₄-alkoxy, C₁-C₄-alkylthio, halogen, cyano, hydroxy or phenyl or C₅-C₇-cycloalkyl or R¹ and R² together with the nitrogen atom connecting them a 5- or 6-membered, saturated heterocyclic radical,

R³ and R⁵

are identical or different and are each independently hydrogen, C₁-C₄-alkyl, C₁-C₄-alkoxy or halogen,

R⁴

Hydrogen or a fused benzo ring together with R⁵,

R⁶

Hydrogen, C₁-C₄-alkyl, which is optionally substituted by C₁-C₄-alkoxy, C₁-C₄-alkylthio, halogen, cyano, hydroxy or phenyl, C₅-C₇-cycloalkyl or the rest

in which R⁸, R⁹ and R¹⁰ are the same or different and each independently represent hydrogen, C₁-C₄-alkyl, C₁-C₄-alkoxy or halogen, and

A

Oxygen or sulfur mean, in their deprotonated, electrically neutral form.

in der

R¹¹

die heterocyclischen Reste

oder

in denen R¹⁴ für Wasserstoff, C₁-C₄-Alkyl,
das gegebenenfalls durch Halogen, Hydroxy oder C₁-C₄-Alkoxy substituiert ist, oder C₁-C₄-Alkoxy, R¹⁵ und R¹⁶ gleich oder verschieden sind und unabhängig voneinander jeweils für Wasserstoff, C₁-C₄-Alkyl, das gegebenenfalls durch Halogen, Hydroxy, C₁-C₄-Alkoxy oder Phenyl substituiert ist, oder gegebenenfalls durch C₁-C₄-Alkyl, C₁-C₄-Alkoxy oder Halogen substituiertes Phenyl, W für Schwefel oder Di-C₁-C₄-Alkylmethylen und T für den Rest CH oder Stickstoff stehen,

R¹²

Wasserstoff, C₁-C₄-Alkyl, das gegebenenfalls durch Halogen oder C₁-C₄-Alkoxy substituiert ist, oder gegebenenfalls durch C₁-C₄-Alkyl, C₁-C₄-Alkoxy oder Halogen substituiertes Phenyl,

R¹³

Wasserstoff oder C₁-C₄-Alkyl, das gegebenenfalls durch Halogen oder C₁-C₄-Alkoxy substituiert ist,

X und Y

gleich oder verschieden sind und unabhängig voneinander jeweils den Rest CH oder Stickstoff,

Z

den Rest

und

m

0 oder 1 bedeuten, oder in der, falls m 1 ist,

die Gruppierung

auch für die Reste

steht, in denen
R¹³ und R¹⁵ jeweils die obengenannte Bedeutung besitzen, mit der Maßgabe, daß wenn m 0 ist, X und Y nicht gleichzeitig die Bedeutung von Stickstoff besitzen sollen, in ihrer deprotonierten, elektrisch neutralen Form überträgt.Another preferred procedure is to use cationic dyes whose cation has the formula II

in the

R¹¹

the heterocyclic residues

or

in which R¹⁴ represents hydrogen, C₁-C₄ alkyl,
which is optionally substituted by halogen, hydroxy or C₁-C₄-alkoxy, or C₁-C₄-alkoxy, R¹⁵ and R¹⁶ are the same or different and are each independently of the other hydrogen, C₁-C₄-alkyl, which may be substituted by halogen, hydroxy, C₁ -C₄-alkoxy or phenyl is substituted, or phenyl optionally substituted by C₁-C₄-alkyl, C₁-C₄-alkoxy or halogen, W represents sulfur or di-C₁-C₄-alkylmethylene and T represents the remainder CH or nitrogen,

R¹²

Hydrogen, C₁-C₄-alkyl, which is optionally substituted by halogen or C₁-C₄-alkoxy, or phenyl optionally substituted by C₁-C₄-alkyl, C₁-C₄-alkoxy or halogen,

R¹³

Hydrogen or C₁-C₄-alkyl, which is optionally substituted by halogen or C₁-C₄-alkoxy,

X and Y

are the same or different and each independently the radical CH or nitrogen,

Z

the rest

and

m

Represent 0 or 1, or in which, if m is 1,

the grouping

also for the leftovers

stands in which
R¹³ and R¹⁵ each have the meaning given above, with the proviso that when m is 0, X and Y should not simultaneously have the meaning of nitrogen, in their deprotonated, electrically neutral form.

The alkyl radicals occurring in the formulas I and II can be either straight-chain or branched. Fluorine, chlorine or bromine are particularly preferred as halogen.

R¹, R², R⁶ and R⁷ in formula I are, for example, hydrogen; Methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl; 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-isopropoxyethyl, 2-butoxyethyl, 2-sec-butoxyethyl, 2-methoxypropyl, 1-methoxyprop-2-yl, 2-methoxybutyl, 2-ethoxybutyl, 4-isopropoxybutyl; 2-methylthioethyl, 2-ethylthioethyl, 2-propylthioethyl, 2-isopropylthioethyl, 2-butylthioethyl, 2-isobutylthioethyl, 2-methylthiopropyl, 2-ethylthioprop-1-yl, 2-methylthiobutyl, 2-ethylthiobutyl, 4-ethylthiobutyl Propylthiobutyl; Fluoromethyl, chloromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2-chloroethyl, 2-bromoethyl, pentafluoroethyl, 2-chloro-1,1,2,2-tetrafluoroethyl, nonafluorobutyl; Cyanomethyl, 2-cyanoethyl, 2-cyanopropyl, 3-cyanopropyl, 2-cyanobutyl, 4-cyanobutyl; 2-hydroxyethyl, 2-hydroxypropyl, 1-hydroxyprop-2-yl, 3-hydroxypropyl, 2-hydroxybutyl, 4-hydroxybutyl; Benzyl, 2-phenylethyl; Cyclopentyl, cyclohexyl or cycloheptyl.

R1 and R2 in formula I together with the nitrogen atom connecting them also represent, for example, the following heterocyclic radicals: pyrrolidino, piperidino, morpholino, N-methylpiperazino, N-ethylpiperazino, N-propylpiperazino, N-isopropylpiperazino, N-butylpiperazino, N-isobutylpiperaz N-sec-butylpiperazino.

R⁶ in formula I also represents, for example, phenyl; 2-methylphenyl, 2-ethylphenyl, 2-propylphenyl, 2-isopropylphenyl, 2-butylphenyl, 2,6-dimethylphenyl, 2,6-diethylphenyl, 2,4,6-trimethylphenyl; 2-methoxyphenyl, 2-ethoxyphenyl, 2-propoxyphenyl, 2-isopropoxyphenyl, 2-butoxyphenyl, 2,4-dimethoxyphenyl, 2,6-dimethoxyphenyl; 2-methoxy-4-methylphenyl; 2-fluorophenyl, 2-chlorophenyl, 2-bromophenyl, 2,4-dichlorophenyl or 2,4,6-trichlorophenyl.

R³ and R⁵ in formula I are, for example, hydrogen; Methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl; Methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy or sec-butoxy; Fluorine, chlorine, bromine or iodine.

R¹², R¹³, R¹⁴, R¹⁵ and R¹⁶ in formula II are, for example, hydrogen; Methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl; 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-isopropoxyethyl, 2-butoxyethyl, 2-sec-butoxyethyl, 2-methoxypropyl, 1-methoxyprop-2-yl, 2-methoxybutyl, 2-ethoxybutyl, 4-isopropoxybutyl; Chloromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2-chloroethyl, 2-bromoethyl, pentafluoroethyl, 2-chloro-1,1,2,2-tetrafluoroethyl or nonafluorobutyl.

R¹² and R¹⁵ and R¹⁶ in formula II are furthermore, for example, phenyl; 2-methylphenyl, 4-methylphenyl, 2-ethylphenyl, 4-ethylphenyl, 4-isopropylphenyl, 4-butylphenyl, 2,4-dimethylphenyl, 2,4,6-trimethylphenyl; 2-methoxyphenyl, 4-methoxyphenyl, 4-ethoxyphenyl, 2,4-dimethoxyphenyl; 2-chlorophenyl, 4-fluorophenyl, 4-bromophenyl or 2,6-dichlorophenyl.

R¹⁴ in formula II can further e.g. Methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy or sec-butoxy mean.

R¹⁴, R¹⁵ and R¹⁶ also mean, for example, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 2-hydroxybutyl or 4-hydroxybutyl.

R¹⁴ and R¹⁵ can also mean, for example, benzyl or 2-phenylethyl.

W in formula II stands for example for sulfur; Prop-2-ylidene, but-2-ylidene, pent-3-ylidene, hex-2-ylidene, hept-4-ylidene or non-5-ylidene.

in dem R⁸ und R⁹ gleich oder verschieden sind und unabhängig voneinander jeweils für Wasserstoff, C₁-C₄-Alkyl oder C₁-C₄-Alkoxy und R¹⁰ für Wasserstoff stehen und A Sauerstoff bedeuten, in ihrer deprotonierten elektrisch neutralen Form überträgt.A particularly preferred procedure is that cationic dyes whose cation has the formula I in which R¹, R² and R⁷ are the same or different and are each independently hydrogen or C₁-C₄-alkyl, optionally by C₁-C₄-alkoxy , Halogen, cyano or hydroxy is substituted, or R¹ and R² together with the nitrogen atom connecting them pyrrolidino, piperidino or morpholino, R³ and R⁵ are the same or different and are each independently hydrogen, C₁-C Alkyl-alkyl or C₁-C₄-alkoxy, R⁴ hydrogen, R⁶ the rest

in which R⁸ and R⁹ are the same or different and are each independently hydrogen, C₁-C₄-alkyl or C₁-C₄-alkoxy and R¹⁰ are hydrogen and A is oxygen, in their deprotonated electrically neutral form.

Another particularly preferred procedure consists in that cationic dyes, the cation of which has the formula I, in which R¹, R² and R⁷ are the same or different and are each independently hydrogen or C₁-C₄-alkyl, which may be substituted by C₁-C₄- Alkoxy, halogen, cyano or hydroxy is substituted, or R¹ and R² together with the nitrogen atom connecting them pyrrolidino, piperidino or morpholino, R³ and R⁵ are the same or different and are each independently hydrogen, C₁-C₄-alkyl or C₁-C₄-alkoxy , R⁴ is hydrogen, R⁶ is C₁-C₄-alkyl, which is optionally substituted by C₁-C₄-alkoxy, halogen, cyano or hydroxy, and A is oxygen, in its deprotonated, electrically neutral form.

in dem R8 und R⁹ gleich oder verschieden sind und unabhängig voneinander jeweils für Wasserstoff, C₁-C₄-Alkyl oder C₁-C₄-Alkoxy und R¹⁰ für Wasserstoff stehen, und A Sauerstoff bedeuten.Particularly noteworthy is the transfer of cationic dyes whose cation has the formula I in which R¹, R² and R⁷ are the same or different and are each independently hydrogen or C₁-C₄-alkyl, R³ and R⁵ are each hydrogen, or C₁-C₄- Alkyl, R⁴ hydrogen, R⁶ hydrogen, C₁-C₄-alkyl or the rest

in which R8 and R⁹ are the same or different and are each independently hydrogen, C₁-C₄-alkyl or C₁-C₄-alkoxy and R¹⁰ is hydrogen, and A is oxygen.

in dem R¹⁴ für Wasserstoff, R¹⁵ für C₁-C₄-Alkyl und W für Di-C₁-C₄-Alkylmethylen stehen, R¹² durch C₁-C₄-Alkyl oder C₁-C₄-Alkoxy substituiertes Phenyl, R¹³ Wasserstoff, X und Y jeweils den Rest CH und m 0 bedeuten, in ihrer deprotonierten, elektrisch neutralen Form überträgt.Another particularly preferred procedure consists in that cationic dyes, the cation of which has the formula II, in the R¹¹ the heterocyclic radical

in which R¹⁴ is hydrogen, R¹⁵ is C₁-C₄-alkyl and W is di-C₁-C₄-alkylmethylene, R¹² is phenyl substituted by C₁-C₄-alkyl or C₁-C₄-alkoxy, R¹³ is hydrogen, X and Y are each the rest CH and m 0 mean, in their deprotonated, electrically neutral form.

in denen R¹⁷ jeweils C₁-C₄-Alkyl bedeutet.Other cationic dyes suitable for the process according to the invention, which are transferred in their deprotonated, electrically neutral form, are those whose cations have the formulas III and IV

in which R¹⁷ each represents C₁-C₄ alkyl.

In the previous statements, only the cations (formulas I to IV) of the cationic dyes mentioned were mentioned. However, it goes without saying that the cationic dyes in question are in salt form and each have an anion. All customary anions can be considered as anions, and fluoride, chloride, bromide, iodide, sulfate, methosulfate, ethosulfate, carbonate, perchlorate, borate, tetrafluoroborate, tetrachlorozincate, phosphate, methyl sulfonate, phenyl sulfonate, 4-methylphenyl sulfate formate or carboxylate should be mentioned in particular , Acetate, propionate, butyrate, 2-ethylhexanoate, benzoate or 4-methylbenzoate. The use of tetrachlorozincate salts to produce the deprotonated, electrically neutral dye form is preferred.

The dyes whose cations correspond to formulas I to IV are known per se or can be obtained by methods known per se.

Thus, for example, those dyes whose cation corresponds to the formula I in which A represents oxygen are obtained according to those described in DE-A-2 158 121, DE-A-3 011 154, EP-A-5451, EP- A-38736 or GB-A-1 018 797 specified manufacturing methods. The corresponding thiazine derivatives (A = sulfur) can be prepared by oxidative coupling of suitable 1,4-diaminobenzene derivatives with aniline derivatives and subsequent reaction with hydrogen sulfide or with thiosulfate.

The other cationic dyes, which are transferred in their deprotonated, electrically neutral form in the process according to the invention, can also be prepared by processes known per se, such as those e.g. in K. Venkataraman "The Chemistry of Synthetic Dyes", Volume IV, p. 161; Ullmanns Encyklopadie der Technischen Chemie, 4th edition, volume 13, p. 571; or Rev. Prog. Coloration, Vol. 5, p. 65, 1974.

To prepare the dye carriers required for the process according to the invention, it is advisable first to prepare solutions of the cationic dyes, advantageously in the form of the tetrachlorozincate salt. Suitable solvents are inert organic solvents, e.g. Isobutanol, toluene, xylene or chlorobenzene. These solutions are then treated with excess alkali alkanolate, e.g. Sodium methanolate or sodium ethanolate are added to convert the cationic dye into its deprotonated, electrically neutral form. It has proven advantageous to work with a 1.1- to 1.3-fold molar excess, based on the cationic dye, of alkali metal alkoxide.

The resulting solution containing the deprotonated, electrically neutral dye is processed with a binder to form a printing ink. This contains the deprotonated dye in dissolved or dispersed form. The printing ink is applied to the inert carrier using a doctor blade and the dyeing is air-dried.

Examples of suitable binders are ethyl cellulose, polysulfones or polyether sulfones. Inert carriers are, for example, tissue paper, blotting paper or glassine paper as well as plastic films with good heat resistance, for example metal-coated polyester, polyamide or polyimide. The thickness of the carrier is preferably 3 to 30 µm. Further carrier materials, binders and solvents suitable for the process according to the invention for the production of the printing inks are described in DE-A-3 524 519.

Acceptors in the process according to the invention are coated papers, in particular those with an acid-modified coating. Corresponding organic or inorganic materials that are sufficiently thermally stable serve as coating materials.

Suitable organic coating materials are e.g. acid-modified polyacrylonitrile, condensation products based on phenol / formaldehyde (see e.g. US-A-4 082 713), special salicylic acid derivatives (see e.g. DE-A-2 631 832) or acid-modified polyester, the latter being preferred.

Examples of inorganic coating materials are acid-activated clays, as used in carbonless papers (see e.g. Wochenblatt für Papierfabrikation, volume 21, page 767, 1982).

The deprotonated dye is transferred from the carrier to the acceptor by means of a thermal head which must deliver sufficient heating power to the carrier so that the deprotonated dye evaporates or sublimates within a few milliseconds and is thereby transferred to the plastic-coated, acid-modified paper. The transfer takes place at a temperature of 100 to 400 ° C, preferably 150 to 300 ° C.

In some cases, especially when using paper with a non-acid modified coating material, it may be advantageous to add an acidic aftertreatment, e.g. with gaseous hydrogen chloride or with dilute acetic acid.

After the thermolability of electrically neutral color bases is known, it was surprising that in the process according to the invention the deprotonated, electrically neutral form of the cationic dyes is not subject to thermal decomposition or conversion reactions under the transfer conditions mentioned, but rather is transferred to the acceptor in a quick and easy manner can be.

The invention is illustrated by the following examples:
In order to be able to test the transfer behavior of the deprotonated dyes quantitatively and in a simple manner, the thermal transfer was carried out with large-area heating jaws instead of a thermal head. A binder was not used in the production of the dye carrier to be tested.

A) General recipe for coating the carrier with deprotonated dye

First, a saturated solution of the cationic dye in the form of the tetrachlorozincate is prepared in a mixture of isobutanol and chlorobenzene (1: 1 v / v). This solution is mixed with a 1.2 molar excess, based on the cationic dye, of sodium methoxide, the deprotonated, electrically neutral form of the dye being formed. The formation of the color base can easily be recognized by the resulting change in color of the reaction mixture. The mixture is then filtered off and the filtrate is drawn off one to five times on carrier paper using a 20 μm doctor blade and air-dried. If necessary, the backing paper can also be sprayed with filtrate.

B) Testing for sublimation or evaporation behavior

The paper layer (donor) coated with the dye to be tested is placed with the side on which the dye layer is located on a coated paper (acceptor) and pressed on. The transmitter / acceptor is then wrapped with aluminum foil and heated between two heated plates for 30 seconds. (The relatively long period of 30 seconds is chosen for measurement reasons. This ensures that the acceptor can be optimally measured photometrically after the transfer has taken place). When using a paper coated with polyester as an acceptor, the paper is briefly treated with gaseous hydrogen chloride after the transfer.

The amount of dye migrated into the paper is determined photometrically. The transmission values "Tra" obtained from the remission measurements are converted into extinction values according to the relationship: A = -log Tra. If one then plots the logarithm of the absorbance A of the respective colored paper measured at different temperatures (range: 100 to 200 ° C) against the associated reciprocal absolute temperature T, straight lines are obtained, from the slope of which the activation energy ΔE _{T is} calculated for the transfer experiment becomes:

For complete characterization, the temperature T * [° C] is additionally taken from the plots, at which the extinction A of the colored paper reaches the value 1.

Only the cationic forms of the dyes are listed in the following tables. As already mentioned, tetrachlorozincate was used as the anion in all cases. Me and Et in the formulas stand for methyl and ethyl.

The cationic dyes mentioned in Tables 1 and 2 below were converted into their deprotonated, electrically neutral form by method A) and placed on a support, which was tested for sublimation or evaporation behavior by method B). Paper coated with polyester was used as the acceptor. The resulting color tone and the thermal transfer parameters T * and ΔE _T are listed in the tables.

The cationic dyes mentioned in Tables 3 and 4 below were converted into their deprotonated, electrically neutral form by method A) and placed on a support, which was tested for sublimation or evaporation behavior by method B). A paper with acid-activated clay served as an acceptor as a coating material. The transfer took place here for 30 seconds at a temperature of 130 ° C.

.

The expression "Abs" listed in Tables 3 and 4 stands for absorption. The absorption is linked to the transmission Tra by the following equation: Abs = 1-Tra

.

The cationic dyes listed in Table 5 below were transferred in their deprotonated, electrically neutral form under the conditions valid for Table 1.

Similar results were obtained with the cationic dyes mentioned in Tables 6 and 7 when their deprotonated, electrically neutral form was transferred to paper coated with acid-activated clay. The resulting color is indicated in each case.

Claims (3)

1. A process for transferring a dye from a substrate to an acceptor by sublimation or vaporization of the dye with the aid of a thermal printing head by using a substrate on which there is situated a cationic dye having a cyanine chromaphore and one or more N-H groups which are part of the cyanine chromaphore, in its electrically neutral form as the result of deprotonation at the N-H group, and transferring this deprotonated dye to a coated paper.
2. A process as claimed in claim 1, wherein the cationic dye transferred in its deprotonated, electrically neutral form has a cation of the formula I

   

   where

   R¹, R² and R⁷   are identical or different and each, independently of the others, is hydrogen, C₁-C₄-alkyl, which may be substituted by C₁-C₄-alkoxy, C₁-C₄-alkylthio, halogen, cyano, hydroxyl or phenyl, or C₅-C₇-cycloalkyl, or R¹ and R² together with the nitrogen atom joining them form a 5- or 6-membered, saturated heterocyclic radical,

   R³ and R⁵   are identical or different and each, independently of the other, is hydrogen, C₁-C₄-alkyl, C₁-C₄-alkoxy or halogen,

   R⁴   is hydrogen or together with R⁵ is a fused-on benzo ring,

   R⁶   is hydrogen, C₁-C₄-alkyl, which may be substituted by C₁-C₄-alkoxy, C₁-C₄-alkylthio, halogen, cyano, hydroxyl or phenyl, C₅-C₇-cycloalkyl or the radical

   

   where R⁸, R⁹ and R¹⁰ are identical or different and each, independently of the others, is hydrogen, C₁-C₄-alkyl, C,-C₄-alkoxy or halogen, and

   A   is oxygen or sulfur.
3. A process as claimed in claim 1, wherein the cationic dye transferred in its deprotonated, electrically neutral form has a cation of the formula II

   

   where

   R¹¹   is a heterocyclic radical

   

   or

   

   where R¹⁴ is hydrogen, C₁-C₄-alkyl which may be substituted by halogen, hydroxyl or C₁-C₄-alkoxy, or C₁-C₄-alkoxy, R¹⁵ and R¹⁶ are identical or different and each, independently of the other, is hydrogen, C₁-C₄-alkyl, which may be substituted by halogen, hydroxyl, C,-C₄-alkoxy or phenyl, or unsubstituted or C₁-C₄-alkyl-, C₁-C₄-alkoxy- or halogensubstituted phenyl, W is sulfur or di-C₁-C₄-alxyl-methylene and T is CH or nitrogen,

   R¹²   is hydrogen, C₁-C₄-alkyl, which may be substituted by halogen or C₁-C₄-alkoxy, or unsubstituted or C₁-C₄-alkyl-, C₁-C₄-alkoxy- or halogen-substituted phenyl,

   R¹³   is hydrogen or C₁-C₄-alkyl, which may be substituted by halogen or C₁-C₄-alkoxy,

   X and Y   are identical or different and each, independently of the other, is CH or nitrogen,

   Z   is the radical

   

   and

   m   is 0 or 1 or where, if m is 1,

   the group

   

   can also be

   

   or

   

   where
      R¹³ and R¹⁵ each have the abovementioned meanings, with the proviso that, if m is 0, X and Y should not simultaneously be nitrogen.