EP0479076B1 - Process for transfer of indoaniline dyestuffs - Google Patents

Description

The present invention relates to a new method for transferring indoaniline dyes from a support to a plastic-coated paper using an energy source.

In the thermal transfer printing process, a transfer sheet, which contains a thermally transferable dye in one or more binders, optionally together with suitable auxiliaries, on a support, with an energy source, e.g. with a heating head or a laser, heated by short heating impulses (duration: fractions of a second) from the back, whereby the dye migrates from the transfer sheet and diffuses into the surface coating of a recording medium. 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 released from the energy source.

In general, the color recording is carried out using the three subtractive primary colors yellow, magenta, cyan (and possibly black).

• leichte thermische Transferierbarkeit,
• geringe Migration innerhalb oder aus der Oberflächenbeschichtung des Aufnahmemediums bei Raumtemperatur,
• hohe thermische und photochemische Stabilität sowie Resistenz gegen Feuchtigkeit und chemische Stoffe,
• für subtraktive Farbmischung die geeigneten Farbtöne aufweisen,
• einen hohen molaren Absorptionskoeffizienten aufweisen,
• bei Lagerung des Transferblattes nicht auskristallisieren.

In order to enable optimal color recording, the dyes must have the following properties:

• easy thermal transferability,
• low migration within or from the surface coating of the recording medium at room temperature,
• high thermal and photochemical stability as well as resistance to moisture and chemical substances,
• have the appropriate shades for subtractive color mixing,
• have a high molar absorption coefficient,
• do not crystallize out when storing the transfer sheet.

Experience has shown that these requirements are very difficult to meet at the same time.

Therefore, most of the known dyes used for thermal transfer printing, in particular those which have the basic color cyan, do not meet the required profile.

From JP-A-268 493/1986 and JP-A-249 860/1989 it is now known to transfer those indoaniline dyes whose coupling component is derived from aniline derivatives and which, in addition to chlorine, also contains methyl and ethoxycarbonylamino or methylamino and butylcarbonylamino on the indoaniline residue have as further substituents.

However, it has been shown that these dyes do not give adequate results.

JP-A-219 693/1990, JP-A-84 388/1990 and EP-A-366 963 also describe the use of indoaniline dyes with an aniline residue in thermal transfer processes.

Furthermore, EP-A-415 203, which applies to the designated contracting states as state of the art according to Art. 54 (3), EPC, includes Indoaniline dyes with a thiazole residue and a method for their thermal transfer are known.

It was therefore an object of the present invention to provide a new process for the transfer of indoaniline dyes, the dyes used having the properties mentioned at the outset.

befinden, in der

R¹, R² und R³

gleich oder verschieden sind und unabhängig voneinander jeweils Wasserstoff, Methyl, Fluor oder Chlor,

X

Fluor oder Chlor und

K

einen Rest der Formel II

bedeuten, worin

R⁴

für Wasserstoff, Methyl, Methoxy, C₁-C₄-Mono- oder -Dialkylaminosulfonylamino, C₁-C₄-Alkylsulfonylamino oder den Rest -NHCOR⁷ oder -NHCO₂R⁷ wobei R⁷ die Bedeutung von Phenyl, Benzyl, Tolyl oder C₁-C₈-Alkyl, das gegebenenfalls durch ein oder zwei Sauerstoffatome in Etherfunktion unterbrochen ist, besitzt,

R⁵

für Wasserstoff, C₁-C₈-Alkyl, das gegebenenfalls substituiert ist und durch ein oder zwei Sauerstoffatome in Etherfunktion unterbrochen sein kann, oder C₅-C₇-Cycloalkyl und

R⁶

für Wasserstoff, Methyl oder Methoxy stehen.

It has now been found that the transfer of indoaniline dyes from a support to a plastic-coated paper by diffusion or sublimation with the aid of an energy source is advantageously achieved when using a support on which one or more methine dyes of the formula I

are in the

R¹, R² and R³

are identical or different and are each independently hydrogen, methyl, fluorine or chlorine,

X

Fluorine or chlorine and

K

a radical of formula II

mean what

R⁴

for hydrogen, methyl, methoxy, C₁-C₄-mono- or -dialkylaminosulfonylamino, C₁-C₄-alkylsulfonylamino or the radical -NHCOR⁷ or -NHCO₂R⁷ where R⁷ is phenyl, benzyl, tolyl or C₁-C₈-alkyl, optionally by has one or two oxygen atoms interrupted in ether function,

R⁵

for hydrogen, C₁-C₈-alkyl, which is optionally substituted and can be interrupted by one or two oxygen atoms in ether function, or C₅-C₇-cycloalkyl and

R⁶

represent hydrogen, methyl or methoxy.

All of the alkyl groups occurring in the abovementioned formula II can be either straight-chain or branched.

When substituted alkyl groups appear in the above formula II, e.g. Cyano, phenyl, tolyl, hydroxy, C₁-C₆-alkanoyloxy, C₁-C₄-alkoxycarbonyl or C₁-C₄-alkoxycarbonyloxy, in which case the alkoxy group may be substituted by phenyl or C₁-C₄-alkoxy.

Suitable radicals R², R⁵ and R⁷ are, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl or sec-butyl.

R⁵ and R⁷ are still e.g. Pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, 2-methylpentyl, heptyl, octyl, 2-ethylhexyl, 2-methoxyethyl, 2- or 3-methoxypropyl, 2-ethoxyethyl, 2- or 3-ethoxypropyl, 2-propoxyethyl, 2- or 3-propoxypropyl, 2-butoxyethyl, 2- or 3-butoxypropyl, 3,6-dioxaheptyl or 3,6-dioxaoctyl.

Residues R⁵ are still e.g. 2-cyanoethyl, 2- or 3-cyanopropyl, 2-acetyloxyethyl, 2- or 3-acetyloxypropyl, 2-isobutyryloxyethyl, 2- or 3-isobutyryloxypropyl, 2-methoxycarbonylethyl, 2- or 3-methoxycarbonylpropyl, 2-ethoxycarbonylethyl, 2- or 3-ethoxycarbonylpropyl 2-methoxycarbonyloxyethyl, 2- or 3-methoxycarbonyloxypropyl, 2-ethoxycarbonyloxyethyl, 2- or 3-ethoxycarbonyloxypropyl, 2-butoxycarbonyloxyethyl, 2- or 3-butoxycarbonyloxypropyl, 2- (2-phenylethoxycarbonyloxy) ethyl, 2- or 3 - (2-Phenylethoxycarbonyloxy) propyl, 2- (2-ethoxyethoxycarbonyloxy) ethyl, 2- or 3- (2-ethoxyethoxycarbonyloxy) propyl, benzyl, 2-methylbenzyl, 1- or 2-phenylethyl, cyclopentyl, cyclohexyl or cycloheptyl.

R⁴ are e.g. Mono- or dimethylaminosulfonylamino, mono- or diethylaminosulfonylamino, mono- or dipropylaminosulfonylamino, mono- or diisopropylaminosulfonylamino, mono- or dibutylaminosulfonylamino, (N-methyl-N-ethylaminosulfonyl) amino, methylsulfonylamylamylamylamylamylamylylylamino, ethylsulfonylamino, ethylsulfonylamino, ethylsulfonylamino,

befinden, in der

R⁴

Wasserstoff, Methyl oder Acetylamino,

R⁵

Wasserstoff, C₁-C₆-Alkyl, das gegebenenfalls substituiert ist und durch ein oder zwei Sauerstoffatome in Etherfunktion unterbrochen sein kann, oder C₅-C₇-Cycloalkyl und

R⁶

Wasserstoff bedeuten und

R¹, R², R³ und X

jeweils die obengenannte Bedeutung besitzen.

Particularly worth mentioning is a procedure in which a carrier is used on which one or more dyes of the formula III

are in the

R⁴

Hydrogen, methyl or acetylamino,

R⁵

Hydrogen, C₁-C₆-alkyl, which is optionally substituted and can be interrupted by one or two oxygen atoms in ether function, or C₅-C₇-cycloalkyl and

R⁶

Mean hydrogen and

R¹, R², R³ and X

each have the meaning given above.

A procedure is particularly preferred in which a support is used on which there are one or more dyes of the formula I in which R 1 and R 2 are each hydrogen or methyl and R 3 and X are each chlorine.

The indoaniline dyes of the formula I can be prepared by methods known per se, as described, for example, in the earlier patent applications EP-A-416 434 and EP-A-0 449 109, which belong to the prior art according to Art. 54 (3) EPC , getting produced.

In comparison to the dyes used in the known processes, the dyes of the formula I which are transferred in the process according to the invention are generally distinguished by improved migration properties in the recording medium at room temperature, easier thermal transferability, higher thermal and photochemical stability, easier technical accessibility, better resistance to moisture and chemical substances, higher color strength, better solubility or better suitability for subtractive color mixing (higher color purity, more favorable form of the absorption band, eg narrow half-width or greater flank steepness on the short-wave side). They are also particularly advantageous for dye mixtures with triazolopyridine dyes, as described in the earlier patent application EP-A-416 434. This applies mainly with regard to better transferability, higher ribbon stability (better compatibility with the binder), higher lightfastness, better distribution of the transfer dyes in the recording medium and in particular for the production of better black mixtures.

To produce the dye carriers required for the process according to the invention, the dyes are processed into a printing ink in a suitable organic solvent or in mixtures of solvents with one or more binders, if appropriate with the addition of auxiliaries. This contains the dye preferably in a molecularly dispersed form. The printing ink can be applied to the inert support using a doctor blade and the dyeing can be dried in air.

All resins or polymer materials which are soluble in organic solvents and are capable of binding the dye to the inert support in an abrasion-resistant manner are suitable as binders. Preference is given to those binders which, after the printing ink has dried in air, absorb the dye in the form of a clear, transparent film, without any visible crystallization of the dye occurring.

Examples of such binders are cellulose derivatives, e.g. Methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate or cellulose acetobutyrate, starch, alginates, alkyd resin, vinyl resin, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyrate or polyvinyl pyrrolidone. Polymers and copolymers of acrylates or their derivatives, such as polyacrylic acid, polymethyl methacrylate or styrene-acrylate copolymers, polyester resin, polyamide resin, polyurethane resin or natural CH resin, such as gum arabic, are also suitable as binders. Other suitable binders are e.g. in DE-A-3 524 519.

Preferred binders are cellulose derivatives or polyvinyl butyrate.

The weight ratio of binder: dye is generally 1: 1 to 5: 1.

Examples of suitable auxiliaries are release agents such as those mentioned in EP-A-227 092, EP-A-192 435 or the patent applications cited therein. In addition, particular mention should be made of organic additives which prevent the transfer dyes from crystallizing out during storage or when the ribbon is heated, for example cholesterol or vanillin.

Inert carriers are e.g. Silk, blotting or glassine paper or plastic films with good heat resistance, e.g. optionally metal-coated polyester, polyamide or polyimide. The inert carrier is optionally additionally coated with a slip layer on the side facing the energy source in order to prevent the energy source, in particular the thermal head, from sticking to the carrier material. Suitable lubricants are e.g. in EP-A-216 483 or EP-A-227 095. The thickness of the dye carrier is generally 3 to 30 »m, preferably 5 to 10» m.

In principle, all temperature-stable plastic layers with affinity for the dyes to be transferred can be used as the dye-receiving layer, e.g. modified polycarbonate or polyester. Suitable formulations for the receiver layer composition are e.g. in EP-A-227 094, EP-A-133 012, EP-A-133 011, EP-A-111 004, JP-A-199 997/1986, JP-A-283 595/1986, JP- A-237 694/1986 or JP-A-127 392/1986 described in detail.

The transmission takes place by means of an energy source, e.g. by means of a laser or by means of a thermal head, the latter having to be heatable to a temperature of ≧ 300 ° C. so that the dye transfer can take place in the time range t: 0 <t <15 msec. The dye migrates from the transfer sheet and diffuses into the surface coating of the recording medium.

The following examples are intended to explain the invention in more detail. Unless otherwise stated, percentages relate to weight.

Transfer of the dyes

• α) Allgemeines Rezept für die Beschichtung der Träger mit Farbstoff:
  1 g Bindemittel wurde in 8 ml Toluol/Ethanol (8:2 v/v) bei 40 bis 50°C gelöst. Dazu wurde eine Lösung aus 0,5 g Farbstoff in 30 ml Tetrahydrofuran eingerührt und gegebenenfalls von unlöslichem Rückstand abfiltriert. Die so erhaltene Druckpaste wurde mit einer 80 »m Rakel auf eine Polyesterfolie (Dicke: 6 bis 10 »m) abgezogen und mit einem Fön getrocknet.
• β) Prüfung auf thermische Transferierbarkeit
  Die verwendeten Farbstoffe wurden in der folgenden Weise geprüft:
  Die den zu prüfenden Farbstoff in der Beschichtungsmasse (Vorderseite) enthaltende Polyesterfolie (Geber) wurde mit der Vorderseite auf kommerziell erhältliches Color Video Frint Paper der Fa. Hitachi (Nehmer) gelegt und aufgedrückt. Geber/Nehmer wurden dann mit Aluminiumfolie umwickelt und zwischen zwei beheizten Platten bei verschiedener Temperatur T (im Temperaturintervall 70°C < T < 120°C) erhitzt. Die in die glänzende Kunststoffschicht des Nehmers diffundierte Farbstoffmenge ist proportional der optischen Dichte (= Extinktion A). Letztere wurde photometrisch bestimmt. Trägt man den Logarithmus der im Temperaturintervall zwischen 80 und 110°C gemessenen Extinktion A der angefärbten Nehmerpapiere gegen die zugehörige reziproke absolute Temperatur auf, so erhält man Geraden, aus deren Steigung die Aktivierungsenergie ΔE_T für das Transferexperiment berechnet wird:
  
  Zur vollständigen Charakterisierung wurde aus den Auftragungen zusätzlich die Temperatur T* [°C] entnommen, bei der die Extinktion A der angefärbten Nehmerpapiere den Wert 1 erreicht.
  Die in den folgenden Tabellen aufgeführten Farbstoffe wurden nach α) verarbeitet und die erhaltenen, mit Farbstoff beschichteten Träger nach β) auf das Transferverhalten geprüft. In den Tabellen sind jeweils die Thermotransferparameter T* und ΔE_T, die Absorptionsmaxima λ_max und die verwendeten Bindemittel aufgeführt.
  Dabei gelten folgende Abkürzungen:

  B =

  Bindemittel

  EC =

  Ethylcellulose

  EHEC =

  Ethylhydroxyethylcellulose,

  MS =

  Mischung aus Polyvinylbutyrat und Ethylcellulose im Gewichtsverhältnis 2:1

In order to be able to check the transfer behavior of the dyes quantitatively and in a simple manner, the thermal transfer was carried out with large-area heating jaws, the transfer temperature varying in the range from 70 ° C <T <120 ° C and the transfer time being set at 2 minutes.

• α) General recipe for coating the carrier with dye:
  1 g of binder was dissolved in 8 ml of toluene / ethanol (8: 2 v / v) at 40 to 50 ° C. For this purpose, a solution of 0.5 g of dye was stirred into 30 ml of tetrahydrofuran and any insoluble residue was filtered off. The printing paste thus obtained was drawn off onto a polyester film (thickness: 6 to 10 »m) using an 80» m doctor blade and dried with a hairdryer.
• β) Testing for thermal transferability
  The dyes used were tested in the following way:
  The polyester film (donor) containing the dye to be tested in the coating composition (front) was placed with the front on commercially available color video frint paper from Hitachi (Nehmer) and pressed on. The encoder / receiver was then wrapped with aluminum foil and heated between two heated plates at different temperatures T (in the temperature interval 70 ° C <T <120 ° C). The amount of dye diffused into the glossy plastic layer of the receiver is proportional to the optical density (= extinction A). The latter was determined photometrically. If one plots the logarithm of the extinction A of the colored receiving papers measured in the temperature interval between 80 and 110 ° C against the associated reciprocal absolute temperature, straight lines are obtained, from the slope of which the activation energy ΔE _T for the transfer experiment is calculated:
  
  For complete characterization, the temperature T * [° C] was additionally taken from the plots, at which the extinction A of the colored receiving papers reached the value 1.
  The dyes listed in the following tables were processed according to α) and the resulting dye-coated supports were tested for transfer behavior according to β). The tables show the thermal transfer parameters T * and ΔE _T , the absorption maxima λ _max and the binders used.
  The following abbreviations apply:

  B =

  binder

  EC =

  Ethyl cellulose

  EHEC =

  Ethyl hydroxyethyl cellulose,

  MS =

  Mixture of polyvinyl butyrate and ethyl cellulose in a weight ratio of 2: 1

Claims (3)

1. A process for transferring indoaniline dyes from a transfer to a plastic-coated paper by diffusion or sublimation with the aid of an energy source, which comprises using a transfer on which there is or are one or more dyes of the formula I

   

   where

   R¹, R² and R³   are identical or different and each is independently of the others hydrogen, methyl, fluorine or chlorine,

   X   is fluorine or chlorine, and

   K   is a radical of the formula II

   

   where

   R⁴   is hydrogen, methyl, methoxy, C₁-C₄-mono- or - dialkylaminosulfonylamino, C₁-C₄-alkylsulfonylamino or the radical -NHCOR⁷ or -NHCO₂R⁷, where R⁷ is phenyl, benzyl, tolyl or C₁-C₈-alkyl which may be interrupted by one or two oxygen atoms in ether function,

   R⁵   is hydrogen, C₁-C₈-alkyl, which may be substituted and which may be interrupted by one or two oxygen atoms in ether function, or C₅-C₇-cycloalkyl, and

   R⁶   is hydrogen, methyl or methoxy.
2. A process as claimed in claim 1, wherein there is or are on the transfer one or more dyes of the formula III

   

   where

   R⁴   is hydrogen, methyl or acetylamino,

   R⁵   is hydrogen, C₁-C₆-alkyl, which may be substituted and which may be interrupted by one or two oxygen atoms in ether function, or C₅-C₇-cycloalkyl,

   R⁶   is hydrogen, and

   R¹, R², R³ and X   are each as defined in claim 1.
3. A process as claimed in claim 1, wherein there is or are on the transfer one or more dyes of the formula I where R¹ and R² are each hydrogen or methyl and R³ and X are each chlorine.