EP0344592B1 - Process for azo dye transfer - Google Patents

Description

The present invention relates to a new method for transferring azo dyes, which have a thiophene-based diazo component, from a support onto a plastic-coated paper with the aid of a thermal head.

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 is heated with a heating head with short heating pulses (duration: fractions of a second) from the back, whereby the dye migrated from the transfer sheet and diffused 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 delivered to the heating head.

• i) leichte thermische Transferierbarkeit,
• ii) geringe Migration innerhalb oder aus der Oberflächenbeschichtung des Aufnahmemediums bei Raumtemperatur,
• iii) hohe thermische und photochemische Stabilität sowie Resistenz gegen Feuchtigkeit und chemische Stoffe,
• iv) für substraktive Farbmischung die geeigneten Farbtöne aufweisen,
• v) einen hohen molaren Absorptionskoeffizienten aufweisen,
• vi) bei Lagerung des Transferblattes nicht auskristallisieren,
• vii) technisch leicht zugänglich sein.

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

• i) easy thermal transferability,
• ii) low migration within or from the surface coating of the recording medium at room temperature,
• iii) high thermal and photochemical stability and resistance to moisture and chemical substances,
• iv) have suitable shades for subtractive color mixing,
• v) have a high molar absorption coefficient,
• vi) do not crystallize out when the transfer sheet is stored,
• vii) be easily accessible technically.

Experience has shown that requirements i), iii), vii), and in particular iv) and v), are particularly difficult to meet with cyan dyes.

Therefore, most of the known cyan dyes used for thermal transfer printing do not meet the required profile.

Dyes which are used in thermal transfer printing processes are already known from the prior art. For example, EP-A-216 483 and EP-A-258 856 describe azo dyes which have thiophene-based diazo components and aniline-based coupling components.

Furthermore, disazo dyes based on thiophene and aniline are known from EP-A-218 937 for this purpose.

It was an object of the present invention to provide a process for transferring dyes, the dyes being intended to meet the above requirements i) to vii) as well as possible.

It has now been found that the transfer of azo dyes from a support to plastic-coated paper by diffusion using a thermal head is advantageously achieved when using a support on which one or more azo dyes of the formula I

befinden, in der

are in the

• R ¹ and R ^{2 are the} same or different and are each independently alkyl, alkanoyloxyalkyl, alkoxycarbonyloxyalkyl or alkoxycarbonylalkyl, the radicals each having up to 20 carbon atoms and by phenyl, C ₁ -C ₄ -alkylphenyl, C1-C4-alkoxyphenyl, benzoyloxy, C1-C4-alkylbenzyloxy or C1-C4-Alkoxybenzyloxy, halogen, hydroxy or cyano can be substituted, hydrogen, unsubstituted or C ₁ -C ₂ -alkoxy or halogen substituted phenyl, optionally substituted by C ₁ -C ₂ -alkyl, C ₁ -C ₂ o-alkoxy or halogen substituted benzyl or a radical of formula II
  
  wherein
• Y for C ₂ -C ₆ alkylene
• m for 1, 2, 3, 4, 5 or 6 and
• R ^{6 represents} C ₁ -C ₄ alkyl or phenyl optionally substituted by C ₁ -C ₄ alkyl or C ₁ -C ₄ alkoxy,
• R ^{3 is} hydrogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy or the radical -NH-CO-R ¹ , where R ^{1 has} the meaning given above,
• R ^{4 is} hydrogen, chlorine, C ₁ -C ₄ alkyl, C ₁ -C ₄ alkoxy, C ₁ -C ₄ alkylthio or optionally substituted by C ₁ -C ₄ alkyl, C ₁ -C ₄ alkoxy or halogen Phenyl and
• R ^{5 is} cyano or the radical -CO-OR ¹ , -CO-NHR ¹ or -CO-NR'R ² , where R ¹ and R ² each have the abovementioned meaning, with the exception of the following compounds:
  
  

The compounds excluded above are described in EP-A-302 628, which is state of the art for all designated contracting states in accordance with Art. 54 (3) EPC.

EP-A-133 011 and EP-A-133 012 deal with the construction of a slave sheet during dye transfer.

All alkyl radicals occurring in the above formula I can be both straight-chain and branched.

Residues Y in Formula 1 are e.g. Ethylene, 1,2- or 1,3-propylene, 1,2-, 1,3-, 1,4- or 2,3-butylene, pentamethylene, hexamethylene or 2-methylpentamethylene.

Suitable radicals R ¹ , R ² , R ³ , R ⁴ and R ⁶ in formula 1 are, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl.

R ¹ , R ² and R ³ are, for example, pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, 2-methylpentyl, heptyl, octyl, 2-ethylhexyl, isooctyl, nonyl, isononyl, decyl or isodecyl.

R ¹ and R ² are, for example, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl or eicosyl. (The designations isooctyl, isononyl, isodecyl and isotridecyl are trivial designations and come from the alcohols obtained after oxosynthesis (cf. Ullmanns Enzyklopadie der technical chemistry, 4th edition, volume 7, pages 215 to 217 and volume 11, pages 435 and 436 ).)

R ³ and R ⁴ are furthermore, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy or sec-butoxy.

R ³ radicals are furthermore, for example, pentyloxy, isopentyloxy, neopentyloxy, hexyloxy, heptyloxy, octyloxy, 2-ethylhexyloxy, nonyloxy or decyloxy.

R ⁴ radicals are also, for example, methylthio, ethylthio, propylthio, isopropylthio or butylthio.

R ¹ and R ² are furthermore, for example, benzyl, 1- or 2-phenylethyl,

A carrier on which one or more azo dyes of the formula I are located in the

• R ¹ and R ² independently of one another are alkyl, alkanoloxyalkyl or alkyloxycarbonylalkyl, where these radicals each have up to 12 carbon atoms and can be substituted by phenyl, C ₁ -C ₄ -alkylphenyl, C ₁ -C ₄ -alkoxyphenyl, hydroxy or cyano, if appropriate by C ₁ -C ₁₂ alkyl or C ₁ -C ₁₂ -alkoxy-substituted phenyl, optionally substituted by C ₁ -C ₁₂ alkyl or C ₁ -C ₁₂ -alkoxy-substituted benzyl or a radical of the formula II
  
  wherein
• Y for C ₂ -C ₄ alkylene,
• m for 1, 2, 3 or 4 and
• R ^{6 represents} C ₁ -C ₄ alkyl or phenyl optionally substituted by C ₁ -C ₄ alkyl or C ₁ -C ₄ alkoxy,
• R ^{3 is} hydrogen, C ₁ -C ₆ alkyl, C ₁ -C ₆ alkoxy or the radical -NH-CO-R ¹ , where R ^{1 has} the last-mentioned meaning given above,
• R ^{4 is} hydrogen, chlorine, C ₁ -C ₄ alkyl, C ₁ -C ₄ alkoxy or phenyl and
• R ^{5 is} cyano or the radical -CO-OR ¹ -CO-NHR ¹ or -CO-NR'R ² , where R ¹ and R ² each have the last-mentioned meaning given above.

In particular, the new process uses a carrier on which there are one or more azo dyes of the formula I in which

• R ¹ and R ² independently of one another are C ₁ -C ₁₂ alkyl which is optionally substituted by cyano, phenyl, C ₁ -C ₄ alkylphenyl or C ₁ -C ₄ alkoxyphenyl, or a radical of the formula III
  
  wherein
• n for 1, 2, 3 or 4 and
• R ^{7 represents} C1-C4-alkyl or phenyl,
• R ^{3 is} hydrogen, methyl, methoxy or acetylamino,
• _R ⁴ chlorine and
• R ^{5 is} cyano or the radical -CO-OR ', -CO-NHR' or -CO-NR'R ² , where R ¹ and R ² each have the latter meaning given above.

Particularly good results are achieved if a support is used on which there are one or more azo dyes of the formula I in which R ^{2 is} C ₁ -C ₆ -alkyl and R ^{1 has} the last-mentioned meaning mentioned above or in particular also C ₁ -C ₆ alkyl.

Particularly favorable results are also achieved if a support is used on which there are one or more azo dyes of the formula I in which R ^{5 is} cyano or the radical -CO-OR ', where R ^{1 is} alkyl, alkanoyloxyalkyl or alkyloxycarbonylalkyl, where these radicals can each have up to 12 carbon atoms, or for the radical of the abovementioned formula III, in which n and R ⁷ each have the abovementioned meaning, or R ⁷ in particular represents C ₁ -C ₆ -alkyl.

The dyes of formula 1 are known from EP-A-201 896 or can be obtained by the methods mentioned there.

Compared to the dyes used in the known processes, the dyes 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 photochemical stability, easier technical accessibility, better resistance to moisture and chemical substances, higher color strength , better solubility and especially from higher color purity.

It is also surprising that the dyes of the formula I are readily transferable, even though they have a relatively high molecular weight.

To prepare the dye carrier required for the new process, the dyes are in a suitable organic solvent, for. B. chlorobenzene, isobutanol, methyl ethyl ketone, methylene chloride, toluene, tetrahydrofuran or mixtures thereof with one or more binders, optionally with the addition of auxiliaries, processed to a printing ink. This contains the dye preferably in a molecularly disperse dissolved form. The printing ink is applied to the inert carrier using a doctor blade and the dyeing is air-dried.

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. 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. B. methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate or cellulose acetobutyrate, starch, alginates, alkyl 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 resins, polyamide resins, polyurethane resins or natural CH resins, such as gum arabic, are also suitable as binders. Further suitable binders are described in DE-A-3 524 519.

Preferred binders are ethyl cellulose or ethyl hydroxyethyl cellulose of medium to small viscosity settings.

The ratio of binder to dye preferably varies between 5: 1 and 1: 1.

Auxiliaries, such as are specified in EP-A-227 092, EP-A-192 435 or the patent applications cited therein, are also suitable as auxiliaries, in addition, in particular, organic additives which cause the transfer dyes to crystallize out during storage and when the ink ribbon is heated prevent e.g. B. cholesterol or vanillin.

Inert carriers are e.g. B. tissue, blotting paper or glassine paper or plastic films with good heat resistance, e.g. B. optionally metal-coated polyester, polyamide or polyimide. On the side facing the thermal head, the inert carrier is optionally additionally coated with a lubricating layer (slipping layer) in order to prevent the thermal head from sticking to the carrier material. Suitable lubricants are e.g. B. in EP-A-216 483 or EP-A-227 095. The thickness of the dye carrier is generally 3 to 30 µm, preferably 5 to 10 µm.

In principle, all temperature-stable plastic layers with an affinity for the dyes to be transferred can be used as the dye-receiving layer. Your glass transition temperature should be below 150 ° C. Modified polycarbonates or polyesters may be mentioned as examples. Suitable formulations for the receiver layer composition are e.g. B. 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 transfer takes place by means of a thermal head, which must 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.

Details of the production can be found in the examples, in which information on percentages, unless stated otherwise, relates to the weight.

Transfer of the dyes

• A) 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 0,25 g Farbstoff (und gegebenenfalls Hilfsmittel) in 5 ml Tetrahydrofuran eingerührt. Die so erhaltene Druckpaste wurde mit einer 80 um Rakel auf eine Polyesterfolie (Dicke: 6 bis 10 um) abgezogen und mit einem Fön getrocknet.
• B) 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 Hitachi Color Video Print Paper (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 Nehmens 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 AE_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 2 erreicht.

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

• A) General recipe for coating the support 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 0.25 g of dye (and, if appropriate, auxiliary) was stirred into 5 ml of tetrahydrofuran. The printing paste thus obtained was drawn off with a 80 μm doctor blade onto a polyester film (thickness: 6 to 10 μm) and dried with a hair dryer.
• B) Testing for thermal transferability The dyes used were tested in the following manner: The polyester film (donor) containing the dye to be tested in the coating composition (front) was placed with the front on commercially available Hitachi Color Video Print Paper (recipient) 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 shiny plastic layer of the take is proportional to the optical density (= extinction A). The latter was determined photometrically. If one plots the logarithm of the extinction A of the stained receiving paper 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 AE _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 2.

The dyes mentioned in the following tables were processed according to A) and the resulting dye-coated supports were tested for transfer behavior according to B). In the table are the Thermal transfer parameters T ^* and ΔE _T, the absorption maxima of the dyes λmax (measured in methylene chloride), the binders used and the auxiliaries are listed.

• B = Bindemittel (EC = Ethylcellulose, EHEC = Ethylhydroxyethylcellulose,
• MS = Mischung aus Polyvinylbutyrat und Ethylcellulose im Gewichtsverhältnis 2:1)
• F = Farbstoff
• HM = Hilfsmittel (Chol = Cholesterin)
  
  
  
  
  
  

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)
• F = dye
• HM = auxiliary (Chol = cholesterol)
  
  
  
  
  
  

The dyes of the formula listed in Table 5 below can be used in an analogous manner

be transmitted.

Claims (7)

1. A process for transferring azo dyes from a transfer to a plastic-coated paper by diffusion with the aid of a thermal printing head, which comprises using a transfer comprising one or more azo dyes of the formula I

where

R¹ and R² are identical or different and each is independently of the other alkyl, alkanoyloxyalkyl, alkoxycarbonyloxyalkyl or alkoxycarbonylalkyl, which each may have up to 20 carbon atoms and be substituted by phenyl, C₁-C₄-alkylphenyl, C₁-C₄-alkoxyphenyl, benzyloxy, C₁-C₄-alkylbenzyloxy, C₁-C₄-alkoxybenzyloxy, halogen, hydroxyl or cyano, or are each hydrogen, unsubstituted or C₁-C_2o-alkyl-, C₁-C₂₀-alkoxy- or halogen-substituted phenyl, unsubstituted or C₁-C₂₀-alkyl-, C₁-C₂₀-alkoxy- or halogen-substituted benzyl or a radical of the formula II

where

Y is C₂-C₆-alkylene,

m is 1, 2, 3, 4, 5 or 6 and

R⁶ is C₁-C₄-alkyl or unsubstituted or C₁-C₄-alkyl- or C₁-C₄-alkoxy-substituted phenyl,

R³ is hydrogen, C₁-C₁₀-alkyl, C₁-C₁₀-alkoxy or -NH-CO-R¹, where R¹ is as defined above,

R⁴ is hydrogen, chlorine, C₁-C₄-alkyl, C₁-C₄-alkoxy, C₁-C₄-alkylthio or unsubstituted or C₁-C₄-alkyl-, C₁-C₄-alkoxy- or halogen-substituted phenyl and

R⁵ is cyano or -CO-OR¹, -CO-NHR¹ or -CO-NR¹R², where R¹ and R² are each as defined above, excepting the following compounds:

2. A process as claimed in claim 1, wherein the transfer used comprises one or more azo dyes of the formula I where

R¹ and R² are each independently of the other alkyl, alkanoyloxyalkyl or alkyloxycarbonylalkyl, each of which may have up to 12 carbon atoms and be substituted by phenyl, C₁-C₄- alkylphenyl, C₁-C₄-alkoxyphenyl, hydroxyl or cyano, or are each independently of the other unsubstituted or C₁-C₁₂-alkyl- or C₁-C₁₂-alkoxy-substituted phenyl, unsubstituted or C₁-C₁₂-alkyl- or C₁-C₁₂-alkoxy-substituted benzyl or a radical of the formula II

where

Y is C₂-C₄-alkylene,

m is 1, 2, 3 or 4 and

R⁶ is C₁-C₄-alkyl or unsubstituted or C₁-C₄-alkyl- or C₁-C₄-alkoxy-substituted phenyl,

R³ is hydrogen, C₁-C₆ -alkyl, C₁-C₆-alkoxy or -NH-CO-R¹, where R¹ is as defined above, R⁴ is hydrogen, chlorine, C₁-C₄-alkyl, C₁-C₄-alkoxy or phenyl and

R⁵ is cyano or -CO-OR¹, -CO-NHR¹ or -CO-NR¹R², where R¹ and R² are each as defined above.

3. A process as claimed in claim 1, wherein the transfer used comprises one or more azo dyes of the formula I where

R¹ and R² are each independently of the other C₁-C₁₂-alkyl which may be substituted by cyano, phenyl, C₁-C₄-alkylphenyl or C₁-C₄-alkoxyphenyl, or a radical of the formula III

where

n is 1, 2, 3 or 4 and

_R ⁷ is C₁-C₄-alkyl or phenyl,

R³ is hydrogen, methyl, methoxy or acetylamino,

_R ⁴ is chlorine and

R⁵ is cyano or -CO-OR¹, -CO-NHR¹ or -CO-NR¹R², where R¹ and R² are each as defined above.