GB2275479A - Ink - Google Patents

Abstract

An ink suitable for use in ink jet printing comprising a solution of a colorant in an aqueous medium, the colorant comprising at least 80% by weight of a water-soluble black dye of Formula (1> <IMAGE> wherein W is COOH X is H, COOH, SO<3>H, halo, hydroxy, nitro, cyano, C1-6-alkyl, C1-6-alkoxy, or C1-6-acylamino; Y is H, COOH or SO<3>H; Z is H, COOH or SO<3>H; and R is H or C1-4-alkyl; provided that there are at least two COOH groups and that the number of COOH groups is equal to or greater than the number of SO3H groups and up to 20% of one or both of two other water-soluble dyes, one of which is a defined yellow dye and the other is a defined cyan dye.

Description

INK This specification describes an invention relating to an ink suitable for use in ink jet printing and, in particular, a neutral black ink with good wet-fastness.

According to the present invention there is provided an ink comprising a solution of a colorant in an aqueous medium, the colorant comprising at least 80% by weight of a water-soluble black dye of Formula (1) as hereinafter defined and up to 20% of one or both of two other water-soluble dyes, one of which is a yellow dye of the Formula (2) as hereinafter defined and the other is a cyan dye of Formula (9) as hereinafter defined.

The colorant preferably comprises at least 85%, more preferably at least 90% and preferably up to 98% by weight of the black dye and up to 15% by weight of the yellow and/or the cyan dye, more preferably up to 10% and preferably at least 2%. One specifically preferred colorant comprises from 90% to 95% of the black dye and from 10t to 5% of the cyan dye, another specifically preferred colorant comprises from 90% to 98% of the black dye and from 10% to 2% of the yellow dye and another specifically preferred colorant comprises from 90% to 98% of the black dye and from 10% to 2% of a mixture of the yellow dye and the cyan dye.

The mixture of yellow and cyan dyes preferably comprises from 90:10 to 10:90, more preferably from 80:20 to 20:80 and especially from 60:40 to 40:60 by weight of yellow dye to cyan dye.

The amount of the colorant in the ink is preferably from 0.5t to 20%, more preferably from 0.5t to 15% and especially from 1% to 5%, by weight with respect to the total weight of the ink. The aqueous medium is preferably substantially water but preferably comprises up to 20%, more preferably up to 15% and especially up to 10%, by weight of one or more water-soluble organic liquids. The ink may also comprise other conventional additives, especially those used in ink jet printing inks.

The water-soluble organic liquid(s) is conveniently selected from C14-alkanols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol and isobutanol; amides such as dimethylformamide and dimethylacetamide; ketones and ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; alkylene glycols or thioglycols containing a C2-C6 alkylene group such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol and hexylene glycol,; poly(alkylene-glycol)s and thioglycol)s such as diethylene glycol, thiodiglycol, polyethylene glycol and polypropylene glycol; polyols such as glycerol and 1,2,6hexanetriol; and lower alkyl glycol and polyglycol ethers, such as 2methoxyethanol, 2- (2-methoxyethoxy) ethanol 2- (2-ethoxyethoxy) ethanol, 2-(2-butoxyethoxy)ethanol, 2-[2-(2-methoxyethoxy)-ethoxy] ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]-ethanol, or a mixture containing two or more of the aforementioned water-soluble organic liquids.

However it is preferred that the organic liquid(s) is selected from heterocyclic ketones or sulphones, such as 2-pyrrolidone, N-methyl2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone and sulpholane, especially 2-pyrrolidone and sulpholane. Other preferred organic liquids are 2- (2-butoxyethoxy) ethanol and n-pentan-1,4-diol.

We have found that the present inks, wherein the medium contains up to 20% by weight of one or more of these preferred organic liquids, especially 2-pyrrolidone, are more stable than equivalent inks wherein the medium contains one or more of the other aforementioned organic liquids.

Examples of other ingredients which may be present in the inks are a penetrant, to assist permeation of the dye into a paper substrate, a kogation-reducing agent, to prevent or reduce the build-up of residue (koga) on the resistor surface in thermal ink jet printers, and a buffer, such as sodium borate, to stabilise the pH of the ink.

The kogation-reducing agent is preferably an oxo anion, such as described in EP 425150A. The oxo-anion may be C2O42-, S42-, so42-, molybdate, As043- or more preferably a phosphate ester, a diorganophosphate or more especially a phosphate salt which is particularly effective in reducing kogation. Examples of phosphate salts are dibasic phosphate (HPo42-), monobasic phosphates (H2PO4-) and polyphosphates (P2Q4). The selection of the counterion is not believed to be critical and examples include alkali metals, ammonium and alkylammonium cations.

The amount of kogation-reducing agent in the ink is preferably from 0.001% to 15%, based on oxo-anion, and more preferably from 0.01% to 1%, by weight with respect to the total ink.

A further aspect of the present invention provides a process for printing a substrate with an ink as hereinbefore defined by ink jet printing.

In ink jet printing an ink is formed into small droplets by ejection from a reservoir through a small orifice so that the droplets of ink are directed at a substrate. Suitable ink jet printing processes for the present ink are piezoelectric ink jet printing, and more especially thermal ink jet printing. In thermal ink jet printing, programmed pulses of heat are applied to the ink by means of a resistor, adjacent to the orifice during relative movement between the substrate and the reservoir.

Preferred substrates include cellulosic sheet materials, such as clear cellulosic sheets suitable for projector slides and more preferably paper, especially plain paper, which may be acidic, alkaline or neutral.

According to a further aspect of the present invention there is provided a cellulosic substrate, especially paper or a projector slide printed with an ink according to the invention.

Although the ink may contain other dyes than those hereinbefore defined, it preferably free from such other dyes as the ink containing only the hereinbefore defined dyes in the preferred proportions has a particularly attractive neutral black shade and especially high wetfastness on cellulosic substrates.

Black Dve The black dye, in the free acid form, has the Formula (1):

wherein W is COOH X is H, COOH, So3H, halo, hydroxy, nitro, cyano, C1.6-alkyl, C16-alkoxy, or C1 6-acylamino; Y is H, COOH or SQH; Z is H, COOH or SQH; and R is H or Cl4-alkyl; provided that there are at least two COOH groups and that the number of COOH groups is equal to or greater than the number of SQH groups.

The group X is preferably selected from H; COOH; SQH; halo especially chloro or bromo; hydroxy; nitro; cyano; C, 4-alkyl especially methyl; CL 4-alkoxy especially methoxy; and Cl 4-alkylcarbonylamino; especially acetamido. However X is more preferably H or COOH, and especially COOH.

Where X is H, the COOH group on Ring A represented by W may be in the ortho, meta or para position with respect to the azo group but is preferably in the meta or para position. However, it is preferred that X is COOH and that the two COOH groups are in the 3,4-, 2,5- and especially the 3,5- positions on Ring A.

The black dye preferably contains from 2 to 4 COOH groups and preferably not more than two SO3H groups, i.e. not more than one of X, Y and Z is SQH, i.e. there are preferably the same number of COOH and SQH groups or an excess of 1 or 2 COOH groups.

The group R is preferably H or methyl, and more especially H.

Preferred diazo components from which Ring A is derivable are, 2-aminobenzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, 2-aminophthalic acid, 3-aminophthalic acid, 4-aminoisophthalic acid, 2aminoisophthalic acid, 2-aminoterephthalic acid and especially 5-aminoisophthalic acid, Preferred couplers from which the central group B is derivable are, 1,6-Cleves acid, 1,7-Cleves acid, mixed Cleves acids, 8-amino-2naphthoic acid, 5-amino-2-naphthoic acid and 5-amino-2,3-dicarboxynaphthalene and especially l-naphthylamine.

Preferred couplers from which the third group C is derivable are, N-methyl-Gamma acid, N-butyl-Gamma acid and especially Gamma acid.

Suitable black dyes of Formula (1), in the ammonium (+NH4) salt form, in which R is H are set out in the following table: Dve X W Y Z; Dve X W Y Z B1 3-COOH 5-COOH H H; B8 3-COOH 5-COOH COOH H; B2 3-COOH 5-COOH H SO3H; B9 3-COOH 5-COOH H COOH; B3 3-COOH 5-COOH SO3H H; B10 3-COOH 5-COOH COOH COOH; B4 H 4-COOH H COOH; B11 H 3-COOH COOH H; B5 H 3-COOH H COOH; B6 2-COOH 5-COOH H H; B12 2-COOH 3-COOH H H; B7 2-COOH 4-COOH H SO3H; B13 3-COOH 4-COOH H H; Preferred black dyes are Dye B2 and, more especially, Dye B1.

The black dye is described in greater detail in EP 356,080 the contents of which are incorporated herein by reference.

Yellow Dve The yellow dye, in the free acid form, has the structure shown in Formula (2):

wherein: Ar and Arl are each independently aryl or substituted aryl providing at least one of Ar and Arl has at least one substituent selected from COOH and COSH; R1, R2, R3, and R4 are each independently H, alkyl or substituted alkyl; L is a divalent organic linking group; n is 0 or 1; J and J1 are each independently of formula (3), (4) or (5)::

wherein each R5 is independently selected from H, alkyl, substituted alkyl, alkoxy, halogen, CN, ureido and NHCOR6; R6 is H, alkyl, substituted alkyl, aryl, substituted aryl, aralkyl or substituted aralkyl; each T is independently alkyl; each W is independently selected from H, CN, CONR10Rll, pyridinium and COOH; each M is an alkylene chain having 2 to 8 carbon atoms; B is H, alkyl or COOH; and R10 and R11 are each independently H, alkyl or substituted alkyl; each X is independently carbonyl or a group of the Formula (6), (7) or (8):

wherein Z is oR7, SR7 or NR8RS; Y is H, Cl, CN or Z; E is Cl or CN; and R7, R8 and R9 are each independently H, alkenyl, substituted alkenyl, alkyl, substituted alkyl, aryl, substituted aryl, aralkyl or substituted aralkyl, or R8 and R9 together with the nitrogen atom to which they are attached form a 5 or 6 membered ring; provided that (a) if the compound of Formula (2) has no -SQH groups then it has at least two groups selected from -COOH and -COSH; (b) the compound of Formula (2) has at least as many groups selected from -COOH and -COSH as -SQH groups; and (c) that the structures of the groups Ar-N=N-J and Ar-N=N-J1 are such that the compound of Formula (2) is yellow.

It is preferred that the yellow dye of Formula (2) has at least as many -COOH as -SO3H groups and, if it has no -SO3H groups that it has at least two and, more preferably at least three, -COOH groups. It is especially preferred that the yellow dye has up to 2 -SO3H groups and from 2 to 5 -COOH. It is also preferred that the yellow dye is free from cellulose reactive groups.

The groups Ar and Ar1 are preferably independently selected from phenyl and substituted phenyl. Each optional substituent on Ar and Ar is preferably selected from optionally substituted alkyl, especially C1 4-alkyl; alkoxy, especially C1 4-alkoxy; -SO3H; -PO3H2; -COSH; -OH; -CO2H; and halogen, especially Cl or Br. It is especially preferred that when Ar or Ar1 is substituted phenyl, each substituent is independently selected from CO2H, COSH and SO2H, and more especially each substitutent is CO2H. In especially preferred structures, at least one of Ar and Ar1 has at least one -COOH and it is further preferred that each of Ar and Ar1 has at least one -COOH and more preferably at least two -COOH groups, for example, dicarboxyphenyl.It is preferred that both Ar and Ar1 are the same, and more especially that each is 3,5-dicarboxyphenyl.

It is preferred that each of J & J1 is of Formula (3) and that each R5 is independently selected from H, optionally susbtituted C1 4-alkyl, C1 4-alkoxy, Cl, CN, Br, ureido and NHCOR6, more preferably H, O14-alkyl, C14-alkoxy, ureido and NHCO(C1 4-alkyl), and especially H, methyl, methoxy or ureido. When R5 is not H it is preferably ortho with respect to the azo group (-N=N-).

When J and J1 are of Formula (4) or (5), each T is preferably independently C1 6-alkyl, especially Cl 4-alkyl; the group M may be branched chain alkylene but is preferably straight chain alkylene; W is preferably H, CN, CONR10R11 or COOH; R6 is preferably H, C1 4-alkyl, phenyl or (CH2)1 4-phenyl, each of which may be unsubstituted or substituted, and more especially C1-4-alkyl and B is preferably H.

It is preferred that n is 0 so that the two amino groups, NR1 and NR4, are linked by a single group, X, and it is further preferred that X is of Formula (6).

Z is preferably NR8R9, especially NHC2H4OH, N(C2H4OH)2, morpholino, NH(C1 6-alkyl), NH- (CH2)2-CO2H, NHCH2CSH4CO2H, mono- or di-carboxyanilino, NHC6H4SO3H or NHCH2SO3H.

R1, R2, R3 and R4 are preferably each independently H, C1-4-alkyl or Cl 4-hydroxyalkyl, and more especially H.

R7, R8 and R9 are preferably independently selected from H, optionally substituted C1-alkyl, C3-4-alkenyl, optionally substituted phenyl and optionally substituted (CH2)1 4-phenyl, more preferably from H, allyl, C1 4-alkyl, benzyl, C1 4-hydroxyalkyl and especially from H, methyl, ethyl and 2-hydroxyethyl. The optional substituents on R7, R8 and R9 are preferably independently selected from -OH, -SQH and -COOH, especially -OH. When R8 and R9 together with the nitrogen atom to which they are attached form a 5 or 6 membered ring this is preferably a morpholine or piperidine ring.

The yellow dye is described in greater detail in EP 468,647 the contents of which are incorporated herein by reference.

An especially preferred yellow dye, hereinafter called Dye Y1, is a dye of Formula (2) in which Ar and Ar1 are both 3,5-dicarboxy-phenyl; J and J1 are both phen-1,4-ylene; R1 and R4 are both H; n is 0; X is of Formula (6) and Z is morpholino, in the ammonium (+NH4) salt form.

Cvan Dve The cyan dye, in the free acid form, has the structure shown in Formula (9) or the structure shown in Formula (10).

(a) Cvan dve of Formula (9)

Formula a ( 9) wherein: Pc is a metal-free or metal-containing phthalocyanine radical having a valency from 3 to 4; R1 is H, optionally alkyl, alkenyl or aralkyl; R2 is H, alkyl, alkoxy, halo or optionally substituted amino; and (t+q) is from 3 to 4 inclusive.

In the dye of Formula (9), the COOH group is preferably at the 2-, 3-, 5- or 6-position, especially the 3-position, on the phenyl group.

The metal present in the metal-containing phthalocyanine radical may be any of the metals known to complex with phthalocyanine nuclei, but is preferably scandium, titanium, vanadium, chromium, manganese, iron, cobalt or zinc, more preferably nickel and especially copper.

When the metal is tri- or tetra-valent, it may coordinate with chlorine or oxygen, e.g. VO, AlCl, PbCl2.

The group R'1 is preferably H; C4-alkenyl, such as allyl; optionally substituted C7.11-aralkyl, especially benzyl; optionally substituted C1.4-alkyl, especially methyl, ethyl or hydroxyethyl.

The group R2 is preferably H; C1 4-alkyl, especially methyl; C1 4-alkoxy, especially methoxy; chloro; or an amino group, -NX1X2, wherein X1 and X2 are each independently H, or optionally substituted alkyl or aryl. When X1 or X2 is alkyl it is preferably Cl 1ç,-alkyl, more preferably C1 6-alkyl. When X1 or X2 is optionally substituted aryl it is preferably optionally substituted phenyl, especially phenyl or phenyl having 1 or 2 substituents selected from C1 l2-alkyl, C1 l2-alkoxy, halo and carboxy.Examples of amino groups, NX1X2, are n-hexylamino, N,N-din-butylamino, phenylamino, methyl amino, dimethylamino, diethylamino, dipropylamino, ethylamino, n-propylamino, n-butylamino, n-octylamino and 3 - carboxyphenylamino.

It is especially preferred that R1 and R2 are both H.

The value of t is preferably at least 0.5, more preferably from 0.5 to 2, and especially about 1; the value of q is preferably greater than or equal to t, and especially about 3; and (t+q) is preferably 4.

Where the value, of (t+q) is not integral, the dye of Formula (9) will actually comprise a mixture of dyes with different values of (t+q).

The cyan dye of Formula (9) is described in greater detail in EP 559309A the contents of which are incorporated herein by reference.

An especially preferred cyan dye, hereinafter called Dye C1, is of Formula (9) wherein Pc is copper phthalocyanine; R1 and R2 are both H, t is 1 and q is 3, and the COOH group is in the 3-position, in the ammonium (+NH4) salt form.

(b) Ovan dve of Formula (10) Pe (S4H),(SO, -NRI-L-NR2-X-NR3-G) 4 (10) wherein: Pc is a metal-containing phthalocyanine nucleus; R9, R2 and R3 are each independently H, alkyl, substituted alkyl, alkenyl, substituted alkenyl, aralkyl or substituted aralkyl; L is a divalent organic linking group; G is a colourless organic radical substituted by one or two groups selected from COSH and COOH; (t+q) is from 3 to 4 inclusive; and each X independently is carbonyl or a group of formula (11), (12) or (13):

wherein: each Z independently is NR4R5, SR6 or oR6; each Y independently is H, C1, Z, SR7 or oR7; each E independently is Cl or CN; R4, RS, R6 and R7 are each independently H, alkyl, substituted alkyl, aryl, substituted aryl, aralkyl or substituted aralkyl or R4 and R5 together with the nitrogen atom to which they are attached form a 5 or 6 membered ring.

The cyan dye of Formula (10) is preferably free from COSH groups and also preferably contains at least as many -COOH groups as -SO3H groups.

The metal present in the metal-containing phthalocyanine nucleus may be any of the metals known to be found in complex association with phthalocyanine nuclei, but is preferably selected from Sc, Ti, V, Cr, Mn, Fe, Co and Zn, and more especially from Ni and Cu. When the metal is tri- or tetra-valent, it may carry one or two chlorine atoms.

R1, R3, R6 and R7 are preferably each independently selected from H, C1.4-alkyl and hydroxy-C1 4-alkyl, more preferably H, and C1.4-alkyl.

It is particularly preferred that R1 and R3 are H.

The group R2 is preferably H, C1 4-alkyl, such as methyl or hydroxy-C1 4-alkyl, such as hydroxyethyl.

The groups R4 and R5 are preferably each independently H, or optionally substituted C1 4-alkyl, preferred substituents being -COOH, SO3H or, more especially, -OH. Where R4 and R5 together with the N atom to which they are attached form a 5- or 6-membered ring, this is preferably morpholinyl or piperidinyl.

When X is of Formula (12), Z is preferably attached to the C atom between the two ring N atoms and Y is preferably tara with respect to Z.

However, X is preferably of Formula (11).

Z is preferably N545S, especially C1 4-hydroxyalkylamino such as hydroxyethylamino, or OH.

The value of q is preferably greater than or equal to the value of t and (t+q) is preferably 4.

The identity of the divalent organic linking group L is not critical but is preferably C2 6-alkylene, such as eth-1,2-ylene, or optionally substituted phenylene.

G is preferably substituted alkyl, especially C1 4-substituted alkyl; substituted aralkyl, especially substituted phenyl-(C13-alkyl); substituted phenyl; or substituted naphthyl wherein at least one of the substituents is selected from -COOH, -(CH2)n-COOH, -O-(CH2)n-COOH, -S-(CH2)n-COOH and -NR8(CH2)n-COOH in which n is an integer from 1 to 6 and RB is H or C1 4-alkyl. The group G is preferably carboxyphenyl or dicarboxyphenyl.

The cyan dye of Formula (10) is described in greater detail in EP 468,649 the contents of which are incorporated herein by reference.

The present invention relates not only to an ink containing a colorant comprising a black and a yellow and/or a cyan dye as hereinbefore defined in the free acid form, but also in the form of salts, preferably alkali metal, ammonium or substituted ammonium salts, and especially salts derived from ammonia or a volatile amine.

Furthermore, although any amino groups in the formulae for the dyes are shown in neutral form, these groups may exist as substituted ammonium cations, especially if the dye is capable of existing in zwitterionic form.

In the salt form, especially as alkali metal, ammonium or substituted ammonium salts or mixtures thereof, at pH 7.5 and above, especially from pH 7.5 to 9.0, the dyes have good solubility in water, often up to 10% or more, by weight. However, the water-solubility drops sharply below pH 7.5 and below pH 6 they are generally insoluble in water and aqueous media.

The cation in the ammonium or substituted ammonium salts is preferably a quaternary ammonium group of the formula +NQq in which p and q are each independently integers from 0 to 4 provided that (p+q) = 4, and each Q independently is an organic radical; or 2 or 3 Qs, together with the N atom to which they are attached, form a heterocyclic ring and any remaining Qs are C1 4-alkyl.

Organic radicals represented by Q are preferably C1.4-alkyl, especially methyl; aryl, especially phenyl; or aralkyl, especially benzyl. Heterocyclic rings formed by NO4 are preferably 5- or 6membered heterocycles, such as morpholinyl, piperidinyl or pyridyl.

Examples of quaternary ammonium groups of formula +WHpQq are +NH2(CH3), +NH2(CH3)2, +NH(CH,),, W(CH3)4, +N(CH2CH3)4, N-methyl pyridinium, N,N-dimethyl piperidinium and N,N-dimethylmorpholinium.

The dyes can be converted into their ammonium or substituted ammonium salts by dissolving in water, as a salt with an alkali metal, acidifying the solution with a mineral acid, adjusting the pH to 9-9.5 with ammonia or an amine or a quaternary ammonium hydroxide and removing alkali metal salt by dialysis.

The inks may be prepared by dissolving the dyes, individually or mixed together to form the colorant, in water alone and optionally adding a water-soluble organic liquid or in an ink medium comprising water and a water-soluble organic liquid. Other ingredients can be added to the ink either before or after the dyes. The ink is preferably filtered prior to use in ink jet printing in order to remove any undissolved matter which can cause blockages in the nozzles of an ink jet printer.

The invention is further illustrated by the following Examples in which all parts and percentages are by weight unless otherwise indicated.

Examples Appropriate amounts of the dyes identified in Table 1 were dissolved in the identified ink media in order to prepare the Inks 1 to 11 identified in Table 1 each ink containing 2.5 colorant. The inks were then assessed for printing quality by printing onto an acid paper (Ac, Xerox 4024 DP) and an alkaline paper (Alk, Hammermill Fore DP3V-2) using a Hewlett-Packard Deskjet printer. The parameters measured were print density (PD), luminance (L), colour space coordinates (A & B), wet-fastness (WF (%)), light-fastness (LF (Blue scale rating)) and visual appearance (VA), the latter to detect the presence or absence and extent of bronzing. The components of the ink media (Med) were water (W), 2-pyrrolidone (P) and sulpholane (S) and the proportions (prop) were by weight.

Table 1 Ink Dve k Med & Prop Payer PD L A B WF LF 2 B1 95 W:P 90:10 Ac 25.5 27.1 2.4 -5.6 97 3 C1 5 Alk 14.5 34.5 3.8 -7.7 94 3 3 B1 90 W:P 90:10 Ac 23.2 28.4 2.8 -4.9 97 3 C1 10 Alk 16.5 32.7 3.2 -7.8 94 3 4 B1 95 W:P 90:10 Ac 26.5 26.8 1.7 -3.8 98 3 Y1 5 Alk 14.7 34.5 2.9 -6.1 92 3 5 B1 90 W:P 90:10 Ac 27.5 26.5 1.1 -3.5 98 3 Y1 10 Alk 17.8 32.2 2.2 -4.4 91 3 6 B1 95 W:S 95:5 Ac 28.7 25.6 3.5 -4.5 96 3 C1 5 Alk 18.2 31.3 4.2 -7.3 90 3 7 B1 90 W:S 95:5 Ac 28.9 25.5 3.2 -4.7 96 3 C1 10 Alk 16.8 32.3 3.9 -8.3 91 3 8 B1 95 W:S 95:5 Ac 27.9 26.1 2.7 -4.0 99 3 Y1 5 Alk 22.0 29.1 4.0 -4.8 84 3 9 B1 90 W:S 95: :5 Ac 28.6 26.0 2.5 -3.0 98 3 Y1 10 Alk 20.0 30.5 3.1 -4.5 84 3 10 B1 90 Y1 5 W:P 90:10 Ac 27.3 26.4 1.5 -4.3 97.5 3 C1 5 11 B1 85 W:P 90:10 Ac 26.7 27.0 0.6 -2.8 97.5 3 Y1 15 Notes: Med & Prop is ink medium and proportions by weight W is water S is sulpholane Tr Br is trace bronzing No Br is no bronzing

Claims (6)

1. Claims 1. An ink comprising a solution of a colorant in an aqueous medium, the colorant comprising at least 80% by weight of a water-soluble black dye of Formula (1) as herebefore defined and up to 20% of one or both of two other water-soluble dyes, one of which is a yellow dye of the Formula (2) as hereinbefore defined and the other is a cyan dye of Formula (9) as hereinbefore defined.
2. 2. An ink according to Claim 1 wherein the colorant comprises from 90% to 98% of the black dye and from 10% to 2% of the yellow dye.
3. 3. An ink according to Claim 1 wherein the colorant comprises from 90% to 95% of the black dye and from 10% to 5% of the cyan dye.
4. 4. An ink according to any one of Claims 1 to 3 wherein the black dye is the dye of Formula (1) wherein W is 3-COOH, X is 5-COOH and Y, Z and R are H, in the ammonium salt form.
5. 5. An ink according to Claim 1 or Claim 2 wherein the yellow dye of Formula (2) in which Ar and Arl are both 3,5-dicarboxyphenyl; J and J1 are both phen-1,4-ylene; R1 and R4 are both H; and n is 0, in the ammonium salt form.
6. 6. An ink according to Claim 1 or Claim 3 wherein the cyan dye is of Formula (9) wherein Pc is copper phthalocyanine; R1 and R2 are both H, t is 1 and q is 3, and the COOH group is in the 3-position, in the ammonium salt form.