GB2469191A

GB2469191A - Polyazo dyes and their use in inkjet printing

Info

Publication number: GB2469191A
Application number: GB1005234A
Authority: GB
Inventors: Clive Edwin Foster; Toshiki Fujiwara; David Schofield
Original assignee: Fujifilm Imaging Colorants Ltd; Fujifilm Corp
Current assignee: Fujifilm Imaging Colorants Ltd; Fujifilm Corp
Priority date: 2009-04-03
Filing date: 2010-03-29
Publication date: 2010-10-06
Anticipated expiration: 2030-03-29
Also published as: GB201005234D0; GB0905732D0; GB2469191B

Abstract

A pyridobenzimidazole dye of formula (1) may be useful for ink jet printing. A and B are independently optionally substituted aryl (e.g. sulfonated naphthyl) or optionally substituted heteroaryl (e.g. thiophenyl or thiazolyl), provided that at least one of A and B is optionally substituted heteroaryl; x is 0 to 4; Y is an electron donating group (e.g. amino, hydroxy, methoxy, methyl or acetamido); Z is a substituent (e.g. C1-4alkyl, optionally substituted phenyl. CN, SO3H, CO2H, PO3H2, CONRaRband C1; Raand Rbare independently H or optionally substituted alkyl, aryl or heterocyclyl); and n is 0 to 6. A and/or B may be substituted with optionally substituted phenyl or naphthyl, SO3H and nitro. A and/or B may carry (directly or on a substituent) 1-3 water solubilising groups.

Description

POLYAZO DYES AND THEIR USE IN INK-JET PRINTING

This invention relates to dye compounds, compositions and inks, to printing processes, to printed materials and to ink-jet printer cartridges.

Ink-jet printing is a non-impact printing technique in which droplets of ink are ejected through a fine nozzle onto a substrate without bringing the nozzle into contact with the substrate. The set of inks used in this technique typically comprise yellow, magenta, cyan and black inks.

While ink-jet printers have many advantages over other forms of printing and image development there are still technical challenges to be addressed. For example, there are the contradictory requirements of providing ink colorants that are soluble in the ink medium and yet display excellent wet-fastness (i.e. prints do not run or smudge when printed). The inks also need to dry quickly to avoid sheets sticking together after they have been printed, but they should not crust over the tiny nozzles used in the printer. Storage stability is also important to avoid particle formation that could block the print-head nozzles especially since consumers can keep an ink-jet ink cartridge for several months. Furthermore, and especially important with photographic quality reproductions, the resultant images should not bronze or fade rapidly on exposure to light or atmospheric oxidising gases such as ozone.

With the advent of high-resolution digital cameras and ink-jet printers it is becoming increasingly common for consumers to print photographs using an ink-jet printer. This application is particularly demanding since a gamut of colours needs to be accurately and realistically reproduced. This is commonly achieved by applying the different inks to varying degrees. Thus, it is especially important that the shade and chroma of each applied ink is exactly right so that an image may be optimally reproduced.

Thus, the skill of an ink-jet chemist lies not only in developing new colorants but also in identifying those colorants which may be combined with existing colorants to optimise their optical properties and performance in an ink-jet printer.

The present invention provides a dye of Formula (1) and salts thereof: (z) Formula (1) wherein: A and B are independently optionally substituted aryl or optionally substituted heteroaryl provided that at least one of A and B is optionally xis 0 to 4; Y is an electron donating group; n isO to 6.

Preferably A and B, when they are optionally substituted heteroaryl, are independently an optionally substituted heteroaryl ring selected from a list consisting of; thiophenyl, furyl, pyrrolyl, pyridyl, pyrimidyl, pyrazinyl, triazinyl, imidazolyl, thiazolyl, oxazolyl, pyrazolyl, triazolyl, indolyl, benzothiophenyl, benzimidazolyl, benzothiazolyl, benzoxazolyl, thienothiazolyl, purinyl, quinolinyl, isothiazolyl and isoquinolinyl.

Preferably A and B, when they are optionally substituted aryl are independently optionally substituted phenyl or optionally substituted naphthyl.

Preferably A is an optionally substituted aryl group more preferably an Preferably B is an optionally substituted heteroaryl group especially an optionally substituted thiophenyl or an optionally substituted thiazolyl.

When x is greater than 1 each B may be the same or different.

Preferably x is 1 or 2. Y is preferably amino, hydroxy, methoxy, methyl or acetamido. More preferably Y is amino or hydroxy, especially hydroxy.

Preferably each Z is independently selected from the group consisting of optionally substituted alkyl (especially optionally substituted C14-alkyl), optionally substituted alkoxy (preferably optionally substituted C14-alkoxy), optionally substituted aryl (preferably optionally substituted phenyl), optionally substituted aryloxy (preferably optionally substituted phenoxy), optionally substituted heterocyclyl, polyalkylene oxide (preferably polyethylene oxide or polypropylene oxide), phosphonate, -P03H2, -CO2H, nitro, -ON, isonitrile, halo, ureido, quaternary amine, -SO3H, -SO2F, hydroxy, ester, NRaRb, CORa, OONRaRb, -NHOORa, sulfoxide, sulfone, and SO2NRaRb, wherein Ra and Rb are each independently H, optionally substituted alkyl (especially optionally 014-alkyl), optionally substituted aryl, or optionally substituted heteroaryl. Optional substituents for any of the substituents described above may be selected from the same list of substituents, especially -OH, -002H, -SO3H, -P03H2, nitro, -N H2, -ON, isonitrile, halo, O14alkoxy, 014a1ky1 and phenyl.

More preferably each Z is independently selected from the group consisting of optionally substituted 014-alkyl, optionally substituted phenyl, -ON, -SO3H, -CO2H, -P03H2, OONRaRb (wherein Ra and Rb are as defined above) and ch I oro.

Preferably n is 1 to 4 and more preferably n is 2 or 3.

Optional substituents which may be present on A and B are independently selected from optionally substituted alkyl (especially optionally substituted 014-alkyl), optionally substituted alkoxy (preferably optionally substituted C14-alkoxy), optionally substituted aryl (preferably optionally substituted phenyl or optionally substituted naphthyl), optionally substituted aryloxy (preferably optionally substituted phenoxy), optionally substituted heterocyclyl, polyalkylene oxide (preferably polyethylene oxide or polypropylene oxide), phosphonate, -P03H2, -CO2H, nitro, -ON, nitrile, isonitrile, halo, ureido, quaternary amine, -SO3H, -SO2F, hydroxy, ester, NRaRb, OORa, CONRaRb NHOORa, sulfoxide, sulfone, and -SO2NRaRb, wherein Ra and Rb are each independently H, optionally substituted alkyl (especially optionally substituted 014-alkyl), optionally substituted aryl or optionally substituted heterocyclyl. Optional substituents for any of the substituents described above may be selected from the same list of substituents especially -OH, -002H, -SO3H, -P03H2, nitro, -NH2, -ON, isonitrile, halo, 4alkoxy, 014a1ky1, phenyl and naphthyl.

Preferred optional substituents for A and B are selected from the group consisting of optionally substituted aryl (preferably optionally substituted phenyl or optionally substituted naphthyl), wherein the optional substituents are as listed above, -SO3H and nitro.

Preferably A and/or B carry, either directly or on a substituent, 1 to 3 water solubilising groups. Preferred water solubilising groups are -SO3H, -002H, and -P03H2 and more especially -SO3H, -002H.

The dyes of Formula (1) and salts thereof are also preferably free from fibre reactive groups. The term fibre reactive group is well known in the art and is described for example in EP 0356014 Al. Fibre reactive groups are capable, under suitable conditions, of reacting with the hydroxy groups present in cellulosic fibres or with the amino groups present in natural fibres to form a covalent linkage between the fibre and the dye. As examples of fibre reactive groups excluded from the dyes of Formula (1) and salts thereof there may be mentioned aliphatic sulfonyl groups which contain a sulfate ester group in beta-position to the sulfur atom, e.g. beta-sulfato-ethylsulfonyl groups, c3-unsaturated acyl radicals of aliphatic carboxylic acids, for example acrylic acid, alpha-chloro-acrylic acid, alpha-bromoacrylic acid, propiolic acid, maleic acid and mono-and dichloro maleic; also the acyl radicals of acids which contain a substituent which reacts with cellulose in the presence of an alkali, e.g. the radical of a halogenated aliphatic acid such as chloroacetic acid, beta-chloro and beta-bromopropionic acids and alpha, beta-dichioro-and dibromopropionic acids or radicals of vinylsulfonyl-or beta-chloroethylsulfonyl-or beta-sulfatoethyl-sulfonyl-endo-methylene cyclohexane carboxylic acids. Other examples of cellulose reactive groups are tetrafluorocyclobutyl carbonyl, trifluoro-cyclobutenyl carbonyl, tetrafluorocyclobutylethenyl carbonyl, trifluoro-cyclobutenylethenyl carbonyl; activated halogenated 1,3-dicyanobenzene radicals; and heterocyclic radicals which contain 1, 2 or 3 nitrogen atoms in the heterocyclic ring and at least one cellulose reactive substituent on a carbon atom of the ring, for example a triazinyl halide.

Acid or basic groups on the dye of Formula (1), particularly acid groups, are preferably in the form of a salt. Thus, all Formulae shown herein include the dyes in salt form.

Preferred salts are alkali metal salts, especially lithium, sodium and potassium, ammonium and substituted ammonium salts (including quaternary amines such as ((CH3)4N) and mixtures thereof. Especially preferred are salts with sodium, lithium, ammonia and volatile amines, more especially lithium and sodium salts. Dyes of Formula (1) where lithium is the major salt form are especially preferred. Dyes of Formula (1) may be converted into a salt using known techniques.

The Dyes of Formula (1) and salts thereof may exist in tautomeric forms other than those shown in this specification. These tautomers are included within the scope of the present invention.

The dyes of Formula (1) and salts thereof may be prepared by any method known in the art, and particularly by processes such as those described in W007/077931 which is incorporated herein by reference.

According to a second aspect of the present invention there is provided a composition comprising a dye of Formula (1) or a salt thereof according to the first aspect of the invention and a liquid medium.

Preferred compositions according to the second aspect of the invention comprise: (a) from 0.01 to 30 parts of a dye of Formula (1) according to the first aspect of the invention; and (b) from 70 to 99.99 parts of a liquid medium; wherein all parts are by weight.

Preferably the number of parts of (a)-'-(b)=l 00.

The number of parts of component (a) is preferably from 0.1 to 20, more preferably from 0.5 to 15, and especially from 1 to 5 parts. The number of parts of component (b) is preferably from 80 to 99.9, more preferably from 85 to 99.5 and especially from 95 to 99 parts.

Preferably component (a) is completely dissolved in component (b).

Preferably component (a) has a solubility in component (b) at 2000 of at least 10% by weight. This allows the preparation of liquid dye concentrates that may be used to prepare more dilute inks and reduces the chance of the dye precipitating if evaporation of the liquid medium occurs during storage.

Thus the present invention also provides a composition (preferably an ink) where component (a) is present in an amount of 2.5 to 7 parts, more preferably 2.5 to 5 parts (a high concentration ink) or component (a) is present in an amount of 0.5 to 2.4 parts, more preferably 0.5 to 1.5 parts (a low concentration ink).

Preferred liquid media include water, a mixture of water and organic solvent and organic solvent free from water. Preferably the liquid medium comprises a mixture of water and organic solvent or organic solvent free from water.

When the liquid medium (b) comprises a mixture of water and organic solvent, the weight ratio of water to organic solvent is preferably from 99:1 to 1:99, more preferably from 99:1 to 50:50 and especially from 95:5 to 80:20.

It is preferred that the organic solvent present in the mixture of water and organic solvent is a water-miscible organic solvent or a mixture of such solvents.

Preferred water-miscible organic solvents include 016-alkanols, preferably methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol; linear amides, preferably dimethylformamide or dimethylacetamide; ketones and ketone-alcohols, preferably acetone, methyl ether ketone, cyclohexanone and diacetone alcohol; water-miscible ethers, preferably tetrahydrofuran and dioxane; diols, preferably diols having from 2 to 12 carbon atoms, for example ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol and thiodiglycol and oligo-and poly-alkyleneglycols, preferably diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol; triols, preferably glycerol and 1,2,6-hexanetriol; mono-C14-alkyl ethers of diols, preferably mono-014-alkyl ethers of diols having 2 to 12 carbon atoms, especially 2-methoxyethanol, 2-(2- methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol, 2-[2-(2-methoxyethoxy)ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether; cyclic amides, preferably 2-pyrrolidone, N-methyl- 2-pyrrolidone, N-ethyl-2-pyrrolidone, caprolactam and 1,3-dimethylimidazolidone; cyclic esters, preferably caprolactone; sulfoxides, preferably dimethyl sulfoxide; and sulfones, preferably sulfolane. Preferably the liquid medium comprises water and 2 or more, especially from 2 to 8, water-miscible organic solvents.

Especially preferred water-miscible organic solvents are cyclic amides, especially 2-pyrrolidone, N-methyl-pyrrolidone and N-ethyl-pyrrolidone; diols, especially I,5-pentane diol, ethyleneglycol, thiodiglycol, diethyleneglycol and triethyleneglycol; and mono-C14-alkyl and C14-alkyl ethers of diols, more preferably mono-C14-alkyl ethers of diols having 2 to 12 carbon atoms.

When the liquid medium comprises organic solvent free from water, (i.e. less than 1% water by weight) the solvent preferably has a boiling point of from 30 to 200°C, more preferably of from 40 to 15000, especially from 50 to 125°C. The organic solvent may be water-immiscible, water-miscible or a mixture of such solvents. Preferred water-miscible organic solvents are any of the hereinbefore- described water-miscible organic solvents and mixtures thereof. Preferred water-immiscible solvents include, for example, aliphatic hydrocarbons; esters, preferably ethyl acetate; chlorinated hydrocarbons, preferably CH2CI2; and ethers, preferably diethyl ether; and mixtures thereof.

When the liquid medium comprises a water-immiscible organic solvent, preferably a polar solvent is included because this enhances solubility of the mixture of dyes in the liquid medium. Examples of polar solvents include C14-alcohols.

In view of the foregoing preferences it is especially preferred that where the liquid medium is organic solvent free from water it comprises a ketone (especially methyl ethyl ketone) and/or an alcohol (especially a C14-alkanol, more especially ethanol or propanol).

The organic solvent free from water may be a single organic solvent or a mixture of two or more organic solvents. It is preferred that when the liquid medium is organic solvent free from water it is a mixture of 2 to 5 different organic solvents. This allows a liquid medium to be selected that gives good control over the drying characteristics and storage stability of the ink.

Liquid media comprising organic solvent free from water are particularly useful where fast drying times are required and particularly when printing onto hydrophobic and non-absorbent substrates, for example plastics, metal and glass.

The liquid media may of course contain additional components conventionally used in ink-jet printing inks, for example viscosity and surface tension modifiers, corrosion inhibitors, biocides, kogation reducing additives and surfactants which may be ionic or non-ionic.

It is preferred that the composition according to the invention is ink suitable for use in an ink-jet printer. Ink suitable for use in an ink-jet printer is ink which is able to repeatedly fire through an ink-jet printing head without causing blockage of the fine nozzles. To do this the ink must be particle free, stable (i.e. not precipitate on storage), free from corrosive elements (e.g. chloride) and have a viscosity which allows for good droplet formation at the print head.

Ink suitable for use in an ink-jet printer preferably has a viscosity of less than 2OmPa.s (cP), more preferably less than lOmPa.s (cP), especially less than 5mPa.s (cP), at 25CC.

Ink suitable for use in an ink-jet printer preferably contains less than 500ppm, more preferably less than 25Oppm, especially less than lOOppm, more especially less than 1 Oppm in total of divalent and trivalent metal ions (other than any divalent and trivalent metal ions bound to a dye of Formula (1) or salt thereof, or any other colorant or additive incorporated in the ink).

Preferably ink suitable for use in an ink-jet printer has been filtered through a filter having a mean pore size below 10pm, more preferably below 3pm, especially below 2pm, more especially below 1pm. This filtration removes particulate matter that could otherwise block the fine nozzles found in many ink-jet printers.

Preferably ink suitable for use in an ink-jet printer contains less than SOOppm, more preferably less than 2SOppm, especially less than lOOppm, more especially less than lOppm in total of halide ions. In all cases the term ppm means parts per million by weight relative to the total ink.

The composition and inks according to the second aspect of the invention may also, in addition to the dyes of Formula (1) and salts thereof, contain further colorants. These colorants are preferably selected from those dyes listed in the Colour Index and salts thereof.

A third aspect of the invention provides a process for forming an image on a substrate comprising applying an ink suitable for use in an ink-jet printer, according to the second aspect of the invention, to the substrate by means of an ink-jet printer.

The ink-jet printer preferably applies the ink to the substrate in the form of droplets that are ejected through a small orifice onto the substrate. Preferred ink-jet printers are piezoelectric ink-jet printers and thermal ink-jet printers. In thermal ink-jet printers, programmed pulses of heat are applied to the ink in a reservoir by means of a resistor adjacent to the orifice, thereby causing the ink to be ejected from the orifice in the form of small droplets directed towards the substrate during relative movement between the substrate and the orifice. In piezoelectric ink-jet printers the oscillation of a small crystal causes ejection of the ink from the orifice.

Alternately the ink can be ejected by an electromechanical actuator connected to a moveable paddle or plunger, for example as described in International Patent Application W000/48938 and International Patent Application W000/55089.

The substrate is preferably paper, plastic, a textile, metal or glass, more preferably paper, an overhead projector slide or a textile material, especially paper.

Preferred papers are plain or treated papers which may have an acid, alkaline or neutral character. Photographic quality papers are especially preferred.

A fourth aspect of the present invention provides a material preferably paper, plastic, a textile, metal or glass, more preferably paper, an overhead projector slide or a textile material, especially paper more especially plain, coated or treated papers printed with a dye or salt thereof according to the first aspect of the invention, a composition according to the second aspect of the invention or by means of a process according to the third aspect of the invention.

It is especially preferred that the printed material of the fourth aspect of the invention is a print on a photographic quality paper printed using a process according to the third aspect of the invention.

A fifth aspect of the present invention provides an ink-jet printer cartridge comprising a chamber and a composition, preferably ink suitable for use in an ink-jet printer, wherein the composition is in the chamber and the composition is according to and as preferred in the second aspect of the present invention.

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

Example 1

SO H NH2 H3CrN

N N SOH S

HO3S N Is::myWitrite HO3S

CN

1 -hydroxy-3-methylpyrido-[1,2-a]-benzimidazole-4-carbonitrile (2.23g, 0.01 mole, prepared according to W007/077931) was suspended in water (SOmls) at 20-25°C. Calsolene oil (2 drops) was added and the pH of the mixture was raised to 7-8 by the addition of 2mol dm3 lithium hydroxide solution. The mixture was stirred for 5 minutes at 20-25°C, then the monoazo intermediate (6.2g, 0.01 mole, which was prepared according to procedures well-known in the art) was added.

The pH was then readjusted to 7-8 with 2 mol dm3 lithium hydroxide solution and stirred a further 5 minutes before reducing the pH to 1-2 by the addition of 37% hydrochloric acid. Isoamyl nitrite (3mls, 0.022 mole) was added and the mixture was stirred for 3 days at 20-25°C. The product was then precipitated by the addition of propan-2-ol (200mls) to the reaction mixture, recovered by filtration and washed with propan-2-ol. The crude product was dissolved in dilute lithium hydroxide solution and desalinated by dialysis in ViskingRTM tubing. After evaporation to dryness, the product was further purified by washing with acetone.

Weight obtained, 0.5g, yield 6%.

Example 2

H3CNS03H

SOH S

N JN HO3S

SO3H c1Ij The tetrasulfonated dye was prepared analogously to Example 1, except that the sulfonated pyridobenzimidazole derivative (prepared according to

Examples 3-15

Further examples may be prepared using analogous procedures to those described in examples 1 and 2.

Example Structure

Number ________________________________________________________

SO

CH N i3

3 jj(N

HO N N HO3S SO3H HO3S

SO

CH N i3 HO3S'

HO N N SO3H

SO

CH N i3

I H2NNN HO3S SO3H HO3S

SO

CH N i3

HO3Sq H2NNN 503H

-

(0 cc -

I I I 0 0 0

z 0) 0 0 (I) (I) (I)

-

00 I / 0 I

I I z

z\*/) J) I z zz I I Z i z z_ I 0 Z I 0 Z z z z z z z

----

0) N) -

I I I 0 0 0

I (I) o- o- o-\ \ \

-z z z

/, /, /, N) z z z // / / z\*/) / ($111 / ($111 \2 \2

I Z

o0 I 0 Z 0 Z 0 Z I I z

I I I

ZZ -z z z z z z

NO CH3 HO3S

Example 16

Preparation of Inks Inks may be prepared by dissolving 3 parts by weight of the dye of Example 1 in 97 parts by weight of a liquid medium comprising % by weight: Diethylene glycol 7% Ethylene glycol 7% 2-Pyrollidone 7% Sur{ynolTM 465 1 % Tris buffer 0.2% Water 77.8% and adjusting the pH of the ink to 8-8.5 using sodium hydroxide.

SurfynolRTM 465 is a surfactant from Air Products.

Example 17

Ink-iet Printinci Ink prepared as described above may be filtered through a 0.45 micron nylon filter and then incorporated into empty print cartridges using a syringe.

This ink may be printed on to plain paper or a specialised ink-jet media.

Further Inks The inks described in Tables A and B may be prepared using the Dye described in Example 1. Numbers quoted refer to the number of parts of the relevant ingredient and all parts are by weight. The inks may be applied to paper or specialist ink-jet media by an ink-jet printer.

The following abbreviations are used in Tables A and B: PG = propylene glycol DEG = diethylene glycol NMP = N-methyl pyrrolidone DMK = dimethylketone IPA = isopropanol MEOH = methanol 2P = 2-pyrrolidone MIBK = methylisobutyl ketone P12 = propane-i,2-diol BDL = butane-2,3-diol CET= cetyl ammonium bromide PHO = Na2HPO4 TBT = tertiary butanol TDG = thiodiglycol --bb DyeContent -c -c c c a, cii c cii cii c -a -cii c c Water N) N) N) cii 0) cii cii 0) cii

PG

N) cii 0) cii cii N) -CO cii c) c)01 DEG N) -N) N) 0) CC) 0) cii 0)

-NMP

---01 0) -cii 0) 0)

DMK NaOH

I

C) C C) S Na Stear-ate Ir-cii Im I> 0) -01 cii -0)

IPA

N) 0) -cii

MEOH

cii 0) cii -0) cii CC) -cii cii 2P 0) 0) cii cii

MIBK

bbbPbbo-iiibb Dye Content cc cc c c a cc a -cii c c cii c cii c c Water N) cii cii cii -

PG

--cii ---cii -cc 0) cii cii ci ci -c' c' c' DEG cc 0) NM P ci cii b b TBT H

-

cc ---ci ci ci 0) TDG m cii N) cii BDL ci ci ci ci -

PHO

cii N) 01 cii cii -.J 0) cii 0) 0) cii N) 2P 0) -P12 ci ci ci ci

CET cii

Claims

CLAIMS1. A dye of Formula (1) or a salt thereof: (z) Formula (1) wherein: A and B are independently optionally substituted aryl or optionally substituted heteroaryl provided that at least one of A and B is optionally xis 0 to 4; Y is an electron donating group; n isO to 6.
2. A dye of Formula (1) or a salt thereof as claimed in claim 1 wherein A is an
3. A dye of Formula (1) or a salt thereof as claimed in either claim 1 or claim 2 wherein B is an optionally substituted heteroaryl group.
4. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein B is an optionally substituted thiophenyl or an optionally
5. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein x is 1 or 2.
6. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein Y is amino, hydroxy, methoxy, methyl or acetamido.
7. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein Z is independently selected from the group consisting of optionally substituted C14-alkyl, optionally substituted phenyl, -CN, -503H, -CO2H, -P03H2, CONRaRb and chloro wherein Ra and Rb are each independently H, optionally substituted alkyl, optionally substituted aryl or optionally substituted heterocyclyl.
8. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein n is 2 or 3.
9. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein the optional substituents for A and B are selected from the group consisting of optionally substituted phenyl, optionally substituted naphthyl, -SO3H and nitro.
10. A dye of Formula (1) or a salt thereof as claimed in any one of the preceding claims wherein A and/or B carry, either directly or on a substituent, 1 to 3 water solubilising groups.
11. A composition comprising a dye of Formula (1) or a salt thereof, according to any one of claims 1 to 10, and a liquid medium.
12. A composition as claimed in claim 11 which is an ink suitable for use in an ink-jet printer.
13. A process for forming an image on a substrate comprising applying an ink according to claim 12, to the substrate by means of an ink-jet printer.
14. A material printed with a dye of Formula (1) or a salt thereof according to any one of claims 1 to 10.
15. An ink-jet printer cartridge comprising a chamber and an ink according to claim 12, wherein the ink is in the chamber.