EP0439200B1 - Transfer process using methine dyes containing bichromophoric cyano-groups - Google Patents

Description

The present invention relates to a new method for transferring bichromophoric cyano group-containing methine dyes, which have two individual chromophores which are connected to one another via a bridge member, from a support to paper coated with plastic with the aid of 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, 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.

• 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 general, the color recording is carried out using the three subtractive primary colors yellow, magenta, cyan (and possibly black). 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 do not meet the required profile.

It was an object of the present invention to provide a new process for the transfer of dyes, bichromophoric methine dyes containing cyano groups being used as the dyes and in doing so meeting the above-mentioned requirements as well as possible.

befinden, in der

L

für ein Brückenglied, das keine Konjugation von π-Elektronen zwischen den Resten Z und Y zuläßt,

X

gleich oder verschieden ist und jeweils für Cyano, C₁-C₆-Alkoxycarbonyl oder C₁-C₆-Monoalkylcarbamoyl, wobei die Alkylgruppen jeweils durch 1 oder 2 Sauerstoffatome unterbrochen sein können, C₅-C₇-Cycloalkoxycarbonyl, C₅-C₇-Monocycloalkylcarbamoyl, Phenoxycarbonyl oder Monophenylcarbamoyl und

Z und Y

gleich oder verschieden sind und in Verbindung mit dem Brückenglied L unabhängig voneinander jeweils für einen Rest der Formel

stehen, worin

n

gleich 0 oder 1,

R¹ und R⁵

gleich oder verschieden sind und unabhängig voneinander jeweils Alkyl, Alkoxyalkyl, Alkoxycarbonylalkyl oder Alkanoyloxyalkyl, wobei diese Reste jeweils bis zu 10 Kohlenstoffatome ufweisen und gegebenenfalls durch Hydroxy oder Cyano substituiert sein können, Wasserstoff, Benzyl, Cyclohexyl, Phenyl oder Tolyl,

R² und R³

gleich oder verschieden sind und unabhängig voneinander jeweils C₁-C₈-Alkyl, C₁-C₆-Alkoxy, C₁-C₆-Alkanoylamino oder C₁-C₆-Alkylsulfonylamino,

R⁴

Wasserstoff, Halogen, C₁-C₈-Alkyl, gegebenenfalls durch C₁-C₄-Alkyl oder C₁-C₄-Alkoxy substituiertes Phenyl, gegebenenfalls durch C₁-C₄-Alkyl oder C₁-C₄-Alkoxy substituiertes Benzyl, Cyclohexyl, Thienyl oder den Rest -NHR¹, wobei R¹ die obengenannte Bedeutung besitzt, und

R⁶

Wasserstoff oder C₁-C₈-Alkyl bedeuten.

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

are in the

L

for a bridge member that does not allow conjugation of π electrons between the residues Z and Y,

X

is identical or different and in each case for cyano, C ₁ -C ₆ alkoxycarbonyl or C ₁ -C ₆ monoalkylcarbamoyl, where the alkyl groups can in each case be interrupted by 1 or 2 oxygen atoms, C ₅ -C ₇ cycloalkoxycarbonyl, C ₅ -C ₇ -monocycloalkylcarbamoyl, phenoxycarbonyl or monophenylcarbamoyl and

Z and Y

are identical or different and in connection with the bridge member L independently of one another each for a radical of the formula

stand in what

n

equal to 0 or 1,

R ¹ and R ⁵

are identical or different and are each independently alkyl, alkoxyalkyl, alkoxycarbonylalkyl or alkanoyloxyalkyl, where these radicals each have up to 10 carbon atoms and can optionally be substituted by hydroxy or cyano, hydrogen, benzyl, cyclohexyl, phenyl or tolyl,

R ² and R ³

are identical or different and are each independently of one another C ₁ -C ₈ alkyl, C ₁ -C ₆ alkoxy, C ₁ -C ₆ alkanoylamino or C ₁ -C ₆ alkylsulfonylamino,

R ⁴

Hydrogen, halogen, C ₁ -C ₈ alkyl, optionally substituted by C ₁ -C ₄ alkyl or C ₁ -C ₄ alkoxy substituted phenyl, optionally substituted by C ₁ -C ₄ alkyl or C ₁ -C ₄ -alkoxy-substituted Benzyl, cyclohexyl, thienyl or the radical -NHR ¹ , where R ^{1 has} the meaning given above, and

R ⁶

Is hydrogen or C ₁ -C ₈ alkyl.

D

eine chemische Bindung, Sauerstoff, -SO₂-, -O-CO-O-, 1,4-Cyclohexylen, Phenylen, -O-CO-(CH₂)₁-CO-O-, -O-(CH₂)_m-O-,

wobei l für 1 bis 10 und m für 2 bis 10 stehen,

E¹ und E²

gleich oder verschieden sind und unabhängig voneinander jeweils eine chemische Bindung oder C₁-C₁₅-Alkylen bedeuten.

The bridge member L, which does not allow conjugation of π electrons between the residues Z and Y, generally obeys the formula

-E ¹ -DE ² -

wherein

D

a chemical bond, oxygen, -SO ₂ -, -O-CO-O-, 1,4-cyclohexylene, phenylene, -O-CO- (CH ₂ ) ₁ -CO-O-, -O- (CH ₂ ) _m -O-,

where l is 1 to 10 and m is 2 to 10,

E ¹ and E ²

are identical or different and each independently represents a chemical bond or C ₁ -C ₁₅ alkylene.

All alkyl and alkylene radicals occurring in the above formulas can be straight-chain or branched.

Suitable radicals R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl , Hexyl, 2-methylpentyl, heptyl, octyl, 2-ethylhexyl or isooctyl.

R ¹ and R ⁵ are, for example, nonyl, isononyl, decyl, isodecyl, 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-butoxyethyl, 2-or 3-methoxypropyl, 2-or 3-ethoxypropyl, 2- or 3-propoxypropyl, 2-or 3-butoxypropyl, 4-methoxybutyl, 4-ethoxybutyl, 4-butoxybutyl, 2-cyanoethyl, 3-cyanopropyl, 4-cyanobutyl, 2-hydroxyethyl,

R ⁴ radicals are furthermore, for example, phenyl, 2-, 3- or 4-methylphenyl, 2- or 4-isopropylphenyl, 2-butylphenyl, 2-, 3- or 4-methoxyphenyl, 2-propoxyphenyl, 4-butoxyphenyl, 2- ( But-2-oxy) phenyl, benzyl, 2-, 3- or 4-methylbenzyl, 2-, 3- or 4-methoxybenzyl, fluorine, chlorine, bromine, thien-2-yl or thien-3-yl.

R ² and R ³ are furthermore methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, pentyloxy, isopentyloxy, neopentyloxy, hexyloxy, formylamino, acetylamino, propionylamino, butyrylamino, methylsulfonylamino, ethylsulfonylamino-isyl-sulfonamyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfyl-sulfonyl-sulfonyl-sulfonyl-sulfonyl-amino-sulfyl-sulfonyl-sulfonyl-amino-sulfyl-sulfonyl-sulfonyl-amino-sulfonyl-amino-

Residues X are e.g. Methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, 2-methoxyethoxycarbonyl, methylcarbamoyl, ethylcarbamoyl, 2-methoxyethylcarbamoyl, cyclopentyloxycarbonyl, cyclohexyloxycarbonyl, cycloheptyloxycarbonyl, cyclopentylcarbamoyloyl cyclohexylcarbamylloyl cyclohexylcarbamoyl cyclohexylcarbamoyl, cyclohexylcarbamoyl, cyclohexylcarbamoyl, cyclohexylcarbamoyl.

Residues E ¹ and E ² are, for example, methylene, 1,2-ethylene, ethylidene, 1,2- or 1,3-propylene or 1,4-, 1,3- or 2,3-butylene.

-O-(CH₂)₂-O-, -O-(CH₂)₃-O-, -O-(CH₂)₄-O-, -O-(CH₂)₅-O-, -O-(CH₂)₆-O-, -O-(CH₂)₇-O-, -O-(CH₂)₈-O-, -O-(CH₂)₉-O-, -O-(CH₂)₁₀-O-,

Residues D are, for example

-O- (CH ₂ ) ₂ -O-, -O- (CH ₂ ) ₃ -O-, -O- (CH ₂ ) ₄ -O-, -O- (CH ₂ ) ₅ -O-, -O - (CH ₂ ) ₆ -O-, -O- (CH ₂ ) ₇ -O-, -O- (CH ₂ ) ₈ -O-, -O- (CH ₂ ) ₉ -O-, -O- ( CH ₂ ) ₁₀ -O-,

Advantageous results are obtained when one or more methine dyes of the formula I are transferred, in which the radicals Z and Y obey the formulas IIa to IIg.

R¹ und R⁵

unabhängig voneinander Wasserstoff, C₁-C₆-Alkyl oder Cyclohexyl,

R² und R³

unabhängig voneinander Wasserstoff, Methyl, Methoxy oder Acetylamino,

R⁴

Wasserstoff oder C₁-C₆-Alkyl, gegebenenfalls durch Methyl oder Methoxy substituiertes Phenyl, Thien-2-yl oder Thien-3-yl und

R⁶

Wasserstoff oder C₁-C₆-Alkyl bedeuten.

Further good results are obtained if one or more methine dyes of the formula I are transferred, in which

R ¹ and R ⁵

independently of one another hydrogen, C ₁ -C ₆ alkyl or cyclohexyl,

R ² and R ³

independently of one another hydrogen, methyl, methoxy or acetylamino,

R ⁴

Hydrogen or C ₁ -C ₆ alkyl, phenyl optionally substituted by methyl or methoxy, thien-2-yl or thien-3-yl and

R ⁶

Is hydrogen or C ₁ -C ₆ alkyl.

E¹ und E²

unabhängig voneinander C₁-C₄-Alkylen und

D

eine chemische Bindung, Sauerstoff, -SO₂-, -O-CO-(CH₂)_l-CO-O, wobei l für 2 bis 4 steht,

bedeuten.

Particularly good results are achieved if one or more methine dyes of the formula I are transferred, in which the bridge member L has the formula

-E ¹ -DE ² -

has, wherein

E ¹ and E ²

independently of one another C ₁ -C ₄ alkylene and

D

a chemical bond, oxygen, -SO ₂ -, -O-CO- (CH ₂ ) _l -CO-O, where l is 2 to 4,

mean.

Particularly good results are also achieved if one or more methine dyes of the formula I are transferred, in which X is cyano.

The bichromophoric methine dyes used in the process according to the invention are generally known and are e.g. in GB-A-1 201 925, US-A-3 553 245, DE-A-1 569 678, DE-A-2 519 592, DE-A-3 020 473, WO-A-86/04904 or WO-A-87/01121 described 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 fixation in the recording medium at room temperature, easier thermal transferability, higher lightfastness, higher stability to moisture and chemical substances, better solubility in organic solvents, higher Ribbon stability and higher color purity.

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

Because of their high molar extinction coefficients and their high brilliance, the dyes of the formula I used in the new process are advantageously suitable for producing a trichromatic system required for the subtractive color mixture.

In addition, the good transferability allows a large variation of the plastics used as a receiver and thus a very good adaptation of the dyes to the overall system (donor / receiver).

To produce the dye carriers required for the process according to the invention, the dyes are processed to 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 disperse dissolved form. The printing ink can be applied to the inert support using a doctor blade and the dyeing can be dried in air.

Suitable organic solvents for the dyes I are, for example, those in which the solubility of the dyes I at a temperature of 20 ° C. is greater than 1% by weight, preferably greater than 5% by weight.

Examples include ethanol, propanol, isobutanol, tetrahydrofuran, methylene chloride, methyl ethyl ketone, cyclopentanone, cyclohexanone, toluene, chlorobenzene or mixtures thereof.

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 binders which, after the printing ink has dried in air, absorb the dye in the form of a clear, transparent film without the dye crystallizing out visibly.

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 ethyl cellulose, ethyl hydroxyethyl cellulose, polyvinyl butyrate or polyvinyl acetate.

The weight ratio of binder: dye is generally 1: 1 to 10: 1.

As aids, e.g. Release agents into consideration, as mentioned in EP-A-227 092, EP-A-192 435 or the patent applications cited therein. Organic additives which prevent the transfer dyes from crystallizing out during storage and when the ink ribbon is heated, e.g. Cholesterol or vanillin.

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

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 which must be able to be heated to a temperature of ≧ 300 ° C. so that the dye transfer can take place in the time range t: 0 <t <15 ms. 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.

• 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 0,25 g Farbstoff in 5 ml Tetrahydrofuran eingerührt und gegebenenfalls von unlöslichem Rückstand abfiltriert. Die so erhaltene Druckpaste wurde mit einer 80 µm Rakel auf eine Polyesterfolie (Dicke: 6 bis 10 µm) 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 (unten näher bezeichnetes) Papier (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 intervall 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: $${\text{ΔE}}_{\text{T}}\text{= 2,3 · R ·}\frac{\text{ΔlogA}}{\text{Δ}\left[\frac{\text{1}}{\text{T}}\right]}$$
  
  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.

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.

• α) 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 was stirred into 5 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 μm) using an 80 μm doctor blade and dried using a hair dryer.
• 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 side) was placed with the front side on commercially available paper (recipient specified below) 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. One carries the logarithm in the temperature interval interval between 80 and 110 ° C measured extinction A of the stained receiving paper against the associated reciprocal absolute temperature, then straight lines are obtained, from the slope of which the activation energy ΔE _{T is} calculated for the transfer experiment: $${\text{ΔE}}_{\text{T}}\text{= 2.3R}\frac{\text{ΔlogA}}{\text{Δ}\left[\frac{\text{1}}{\text{T}}\right]}$$
  
  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 of the dyes λ _max (measured in methylene chloride), the binders used and the weight ratio of dye: binder: auxiliaries.

F

= Farbstoff

B

= Bindemittel

EC

= Ethylcellulose

PVB

= Polyvinylbutyrat

Cellit

= Celluloseacetobutyrat

HCVPP

= Hitachi Color Video Print Paper (Nehmer)

SV 100

= Color Video Print Paper/Kodak AG (Nehmer)

The following abbreviations apply:

F

= Dye

B

= Binder

EC

= Ethyl cellulose

PVB

= Polyvinyl butyrate

Cellite

= Cellulose acetobutyrate

HCVPP

= Hitachi Color Video Print Paper (taker)

SV 100

= Color Video Print Paper / Kodak AG (recipient)

The following methine dyes can be transferred in an analogous manner.

Claims (2)

1. A process for transferring a bichromophoric methine dye from a transfer to a sheet of plastic-coated paper 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

   L   is a bridge member which does not permit any conjugation of π-electrons between Z and Y,

   X   is identical or different in its two appearances, denoting in each case cyano, C₁-C₆-alkoxycarbonyl or C₁-C₆-monoalkylcarbamoyl, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅-C₇-cycloalkoxycarbonyl, C₅-C₇-monocycloalkylcarbamoyl, phenoxycarbonyl or monophenylcarbamoyl, and

   Z   and Y are identical or different and, together with the bridge member L, are each independently of the other a radical of the formula

   

   

   where

   n   is 0 or 1,

   R¹ and R⁵   are identical or different and each is independently of the other alkyl, alkoxyalkyl, alkoxycarbonylalkyl or alkanoyloxyalkyl, which may each have up to 10 carbon atoms and be hydroxyl- or cyano-substituted, hydrogen, benzyl, cyclohexyl, phenyl or tolyl,

   R² and R³   are identical or different and each is independently of the other hydrogen, C₁-C₈-alkyl, C₁-C₆-alkoxy, C₁-C₆-alkanoylamino or C₁-C₆-alkylsulfonylamino,

   R⁴   is hydrogen, halogen, C₁-C₈-alkyl, unsubstituted or C₁-C₄-alkyl- or C₁-C₄-alkoxy-substituted phenyl, unsubstituted or C₁-C₄-alkyl- or C₁-C₄-alkoxy-substituted benzyl, cyclohexyl, thienyl or -NHR¹, where R¹ is as defined above, and

   R⁶   is hydrogen or C₁-C₈-alkyl.
2. A process as claimed in claim 1, wherein X is cyano.