WO2001025350A1

WO2001025350A1 - Ink composition

Info

Publication number: WO2001025350A1
Application number: PCT/GB2000/003553
Authority: WO
Inventors: Philip Macfaul
Original assignee: Avecia Limited
Priority date: 1999-10-05
Filing date: 2000-09-15
Publication date: 2001-04-12
Also published as: GB9923353D0; AU7432300A

Abstract

Aqueous inks for non-contact ink jet printing comprising an optionally substituted hydroquinone such as hydroquinone itself, 2,5-dihydroxy benzene sulphonic acid and 2,5-dihydroxy benzoic acid and a dye containing at least one group of formula (1), wherein R1 is hydrogen or optionally substituted alkyl.

Description

INK COMPOSITION

This invention relates to inks, particularly inks suitable for use in ink jet printing (UP), to cartridges containing the inks and to ink jet printing methods UP 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 There are many demanding performance requirements for dyes and inks used in UP For example they desirably provide sharp, non-feathered images having good water-fastness, light-fastness and optical density A high light-fastness is particularly important for photo- realistic prints prepared by means of an ink jet printer to minimise fading of the print over

Furthermore, the inks are often required to dry quickly when applied to a substrate to prevent smudging, but they should not form a crust over the tip of an ink jet nozzle because this will stop the printer from working The inks should also be stable to storage over time without decomposing or forming a precipitate which could block the fine nozzle It has proved difficult to obtain an ink which is acceptable in all of the above properties, because optimisation of one ink property often has a detrimental effect on another

JP 03 243 671A discloses certain inks containing radical inhibitors including a quinone and a hydroquinone The inks are stated to be storage stable over long periods of time

EP 373 574 A discloses inks containing hydroquinone diethers and diesters to prevent fading

JP 59 053 567 discloses inks containing a water-soluble anti-oxidant and a quencher The presence of these two components are described as increasing the hght- fastness of printed images

We have now found that inks containing certain dyes and an optionally substituted hydroquinone provide prints with a surprisingly high light-fastness This is of particular value in photo-realistic ink jet printing where there is a requirement for very high light- fastness According to the present invention there is provided an ink comprising

(a) an optionally substituted hydroquinone,

(b) a dye containing at least one group of the Formula (1 ) or a salt thereof,

Formula (1 ) wherein:

R¹ is H or optionally substituted alkyl; and (c) a liquid medium.

Preferably the ink contains: from 0.01 to 20, more preferably from 0.1 to 10 and especially from 0.5 to 5 parts of component (a); from 0.01 to 30, more preferably 0.1 to 20 and especially from 0.5 to 5 parts of component (b); and from 50 to 99.98, more preferably from 70 to 99.8 and especially from 90 to 99 parts of component (c); wherein the parts are by weight based and the sum of the parts (a)+(b)+(c) =100.

Optionally Substituted Hydroquinone (Component (a))

When the hydroquinone is substituted, the substituents are present on the aromatic ring of the hydroquinone. Preferred optional substituents include -COOH; -SO₃H; -OH; -PO₃H; alkyl optionally substituted by -COOH, -SO₃H or -OH; substituted amino; amino; -OR², -OC(O)R² or -C(O)OR² wherein R² is alkyl optionally substituted by -COOH, -SO₃H -OH, amino or substituted amino. More preferably the optional substituents are selected from -COOH; -SO₃H; -OH; -PO₃H; C_1-6-alkyl optionally substituted by -COOH, -SO₃H or -OH; -NH₂; or amino substituted by C_1-4-alkyl, hydroxy-C^-alkyl, carboxy-C_1-4- alkyl, sulpho-C_1-4-alkyl, or -COR³; -OR³, -OC(O)R³ or -C(O)OR³ wherein R³ is C_1-4-alkyl optionally substituted by -COOH, -SO₃H, -OH or amino. It is especially preferred that the optional substituents on the hydroquinone are selected from -COOH and -SO₃H.

When the hydroquinone carries an ionisable substituent, for example a -COOH group or a -SO₃H group, the ionisable substituent may be in the free acid or salt form. Preferred salts are those with alkali metals, especially sodium, lithium, potassium and mixed salts thereof. Examples of preferred optionally substituted hydroquinones include 1 ,4- dihydroxybenzene (hydroquinone) and 2,5-dihydroxy benzene sulphonic acid. It is especially preferred that component (a) is 2,5-dihydroxybenzoic acid. Dve (Component (b))

R¹ in Formula (1 ) is preferably H or optionally substituted C_1-6-alkyl, more preferably H or C^-alkyl optionally substituted by -OH, -SO₃H or -COOH. It is especially preferred that R¹ is H. The floating sulpho group in Formula (1 ) is preferably attached meta to the -NR¹- group.

The dye of component (b) may contain a single group of the Formula (1 ) or two or more such groups, more preferably one or two groups of the Formula (1). The dye is preferably a mono-azo or bis-azo dye, more preferably a water-soluble mono or bis azo dye.

Preferred mono azo dyes are of the Formula (2) and salts thereof:

Formula (2) wherein:

Ar is optionally substituted aryl;

Q is optionally substituted benzoyl, optionally substituted naphthoyl, a substituted triazinyl group or an arylsulphonyl group; and R¹ is as hereinbefore defined. Ar is preferably optionally substituted phenyl or optionally substituted naphthyl.

When Ar carries a substituent, the substituent is preferably C_1-9-alkyl,

halogen, hydroxy, optionally substituted carbamoyl, optionally substituted sulphamoyl, optionally substituted amino, nitro, sulphonic acid ester,

sulphonyl, C_6-15- arylsulphonyl, COOH, carboxylic acid ester or SO₃H. When the substituent is alkyl, it is preferably C_1-6-alkyl and especially C_1-4-alkyl.

Preferred substituents in carbamoyl, sulphamoyl and amino are C^-alky! groups. Preferred sulphonic acid ester groups contain a C_1-9-alkyl group. Halogen is preferably iodine, bromine and especially chlorine. Preferred carboxylic acid ester groups contain a C_1-9-alkyi group and may contain either a -OCO- group or a -COO- group.

Particularly useful dyes for use in the inks according to the invention contain a residue Ar which is substituted by sulphonic acid or C_1-4-alkyl, such as methyl. When Q is optionally substituted benzoyl or naphthoyl it is preferably CI Reactive Red 180 or one of the dyes described in JP 60-81250, EP 588 316 A2 or GB application number 2340839, especially one of the dyes of the following formulae and salts thereof:

When Q is a substituted triazinyl group it is preferably a group of the Formula (3):

Formula (3) wherein:

T¹ and T² each independently is a labile or non-labile atom or group.

When or T² represents a labile atom or group, it is preferably an atom or group which is bound by a covalent bond to the triazine nucleus, which atom or group is displaceable by a hydroxyl group of cellulose under mildly alkaline aqueous conditions to form a covalent bond between the triazine nucleus and cellulose. Preferred labile atoms or groups include halo, for example F and CI; sulphonic acid groups; thiocyano groups; quaternary ammonium groups, for example trialkylammonium groups and optionally substituted pyridinium groups, for example 3- and 4-carboxy pyridinium groups. More preferably when T¹ or T² is a labile atom or group it is a quaternary ammonium group or halo, especially 3- or 4-carboxypyridinium, F or CI, and more especially CI.

When T¹ or T² is a non-labile group it is preferably -OR⁴, -SR⁴ or -NR⁵R⁶ wherein

R⁴, R⁵ and R⁶ are each independently H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted aralkyl, optionally substituted aryl or R⁵ and R⁶ together with the nitrogen atom to which they are attached form a 5 or 6 membered ring.

Preferably R⁴, R⁵ and R⁶ are each independently selected from H; optionally substituted C.,.₁₀-alkyl, more preferably optionally substituted C_1-4-alkyl; optionally substituted phenyl; and optionally substituted -(CH₂)_1-4-phenyl, especially optionally substituted benzyl. The preferred optional substituents on R\ R⁵ or R⁶ are selected from C -alkyl, C^-alkoxy, C_1-4-alkylamino, C_2-4-hydroxyalkyl, di-(C₁^-alkyl)amino, C_2-4-hydroxyalkylamino di-(C₂^-hydroxyalkyl)amino, -OH, -CN, -COOH, PO₃H₂ and NH₂. More preferably the substituents are selected from -OH, -CH₃, -OCH₃, -SO₃H and -CO₂H. When R³ and R⁴ together with the nitrogen atom to which they are attached form a

5- or 6-membered ring it is preferably morpholine, piperidine or piperazine optionally substituted by C_1-4-alkyl or hydroxy-C_M-alkyl, more preferably it is piperazine optionally substituted at the 4-position by C_1-4-alkyl or hydroxy-C_2-4-alkyl.

Preferred groups of the formula -OR⁴, -SR⁴ or -NR⁵R⁶ include OH; SH; C_1-4-alkoxy, for example methoxy or ethoxy; mono- or di-(C_2-4-hydroxyalkyl)amino, for example mono or di-(2-hydroxyethyl)amino; morpholinyl; piperidinyl; piperazinyl; 4-(hydroxy-C_2-4-alkyl)-piperazin-1-yl, for example 4-hydroxyethylpiperazin-1-yl; 4-(C_1-4-alkyl)piperazin-1-yl, for example 4-methylpiperazin-1-yl; C_Lβ-alkylamino, for example dimethylamino, n-butylamino or n-hexylamino; carboxy-C-_1-4-alkylamino, for example 2-carboxymethylamino; arylamino, for example phenylamino, mono-3- or di-3, 5-carboxyanilino; or aralkylamino, for example benzylamino, mono-3- or di-3,5-carboxyphenylmethylamino.

Preferred dyes of the Formula (2) wherein Q is a group of the Formula (3) include OI. Reactive Red 3.1 , the dyes described in WO99/01510, especially the dyes in Examples 1 to 7, the dyes described in GB 2,330,841 A, the dyes described in EP 692 003, especially the dye described in Example 19 thereof, the dyes described in EP 194 885A1 , the dyes described in EP 682 088 A1 , especially Dye (1 ) therein, and the dyes of the formulae and salts thereof:

or

When Q is an arylsulphonyl group it is preferably an optionally substituted phenylsulphonyl group. A preferred dye of the Formula (2) wherein Q is an arylsulphonyl group is C.I. Acid Red 249.

Preferred bis azo dyes are the dyes described in EP 468 648 A1 , especially the dyes of the formula (1 ) described therein, more especially the dye of Example 3, the dyes described in EP 717 089 A1 , the dyes described in EP 559 310 A1 , especially the dye of Example 1 , the dyes described in EP 866 105 A2, especially dyes of the 1 to 52 described therein and OI. Direct Red 227.

It is especially preferred that the dye is one of the dyes of the Formula (1 ) described in WO99/01510, more especially a dye of the following formula and salts thereof:

The ink may contain a single dye or mixture of two or more dyes.

The dyes may be, and preferably are, purified to remove undesirable impurities before they are incorporated into inks for ink jet printing. Conventional techniques may be employed for purifying the dyes, for example ultrafiltration, reverse osmosis and/or dialysis.

As disclosed hereinbefore, the dyestuff may be present in the ink in the form of its free acid or in the form of a salt. Preferred salts are those of the alkali metals such as sodium, potassium and lithium including mixtures thereof and especially mixtures of sodium and lithium salts. Other preferred salts are ammonium or substituted ammonium salts, and mixtures thereof including their mixture with alkali metal salts. Examples of substituted ammonium salts are those formed with methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, isopropylamine, n- butylamine, sec-butylamino, iso-butylamine, tert-butylamine, piperidine, morpholine and pyridine. Liquid Medium (Component (c))

The liquid medium comprises water, a mixture of water and an organic solvent, or an organic solvent free from water. Preferably the dye has a solubility in the liquid medium at 20°C of at least 10%. This allows concentrates to be prepared which can be diluted to form inks. A high dye solubility also reduces the probability of the dye forming precipitates in the ink if the liquid medium evaporates during storage.

When the liquid medium comprises a mixture of water and an 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. Preferably the organic solvent is a water-miscible organic solvent or a mixture of such solvents. Preferred water-miscible organic solvents include C_1-6-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 pentane-1 ,5-diol, 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-C^-alkyl ethers of diols, preferably mono-C_lJ(-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; sulphoxides, preferably dimethyl sulphoxide and sulpholane. Preferably the aqueous 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 1 ,5-pentane diol, ethyleneglycol, thiodiglycol, diethyleneglycol and triethyleneglycol; and mono- C_M-alkyl and C^-alkyl ethers of diols, more preferably mono- C_1j(-alkyl ethers of diols having 2 to 12 carbon atoms, especially 2-methoxy-2-ethoxy-2-ethoxyethanol.

Examples of further suitable ink media comprising a mixture of water and one or more organic solvents are described in US 4,963,189, US 4,703,113, US 4,626,284, EP 425.150A and US 5,207,824.

When the liquid medium comprises an 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 150°C, 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 dye in the liquid medium. Examples of polar solvents include C_1-4-alcohols. In view of the foregoing preferences it is especially preferred that where the liquid medium is an organic solvent free from water it comprises a ketone (especially methyl ethyl ketone) &/or an alcohol (especially a C_1-4-alkanol, such as 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 medium is an organic solvent free from water it is a mixture of 2 to 5 different organic solvents. This allows a medium to be selected which gives good control over the drying characteristics and storage stability of the composition according to the first aspect of the invention.

Liquid media comprising an 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 ink may also contain additional components conventionally used in ink jet printing inks, for example viscosity and surface tension modifiers, corrosion inhibitors, biocides, kogation reducing additives, anti-cockle agents to reduce paper curling and surfactants which may be ionic or non-ionic.

The optionally substituted hydroquinones exhibit a high solubility in aqueous media over a wide pH range. This enables the optionally substituted hydroquinone to be used in a wide range of ink formulations, thus allowing an ink formulator to tailor the ink formulation, and particularly the ink pH, to optimise printing performance whilst still providing stable inks with a high light-fastness. The pH of the ink is preferably from 2 to 12, more preferably from 4 to 10.

The ink preferably has a viscosity at 25°C of less than 20cP, more preferably less than 10cP and especially less than 2cP.

When the inks according to the first aspect of the invention are used as ink jet printing inks, the ink preferably has a concentration of less than 500 parts per million, more preferably less than 100 parts per million of halide ions. It is especially preferred that the ink has less than 100, more preferably less than 50 parts per million of divalent and trivalent metals, wherein parts refer to parts by weight relative to the total weight of the ink. We have found that purifying the inks to reduce the concentration of these undesirable ions reduces nozzle blockage in ink jet printing heads, particularly in thermal ink jet printers. In view of the foregoing preferences the ink preferably comprises:

(a) from 0.01 to 20, more preferably 0.1 to 10 parts in total of a hydroquinone optionally substituted by -COOH or -SO₃H, or a salt thereof;

(b) from 0.01 to 30, more preferably 1 to 20 parts in total of water-soluble mono-azo or bis-azo dye(s) which contain at least one group of the Formula (1 ) hereinbefore defined; and

(c) from 50 to 99.98, more preferably 70 to 98.9 parts of a liquid medium comprising water or a mixture of water and one or more water-miscible organic solvent; wherein all parts are by weight and the number of parts of (a)+(b)+(c)=100. The inks according to the first aspect of the present invention which combine the use of dyes containing a group of the Formula (1 ) with the presence of an optionally substituted hydroquinone (or a salt thereof), provide prints which have high light fastness. Surprisingly these improvements can usually be achieved without adversely affecting the other, highly demanding performance requirements for ink jet printing inks such as wet- fastness, brightness, durability, storage stability and reliability.

According to a second aspect of the present invention there is provided a process for printing an image on a substrate comprising applying thereto an ink comprising a dye containing at least one group of the Formula (1 ) as hereinbefore defined by means of an ink jet printer such that the dye, when situated on the substrate, is in contact with an optionally substituted hydroquinone.

There are many ways for ensuring that the dye, when situated on the substrate, is in contact with the optionally substituted hydroquinone. For example, the process of this second aspect of the invention may use an ink as defined in the first aspect of the present invention. This ensures that the dye and the optionally substituted hydroquinone are both present in the ink and remain together when they have been printed on the substrate. In an ink jet printer containing several different inks, for example a full colour printer having yellow, magenta, cyan and black inks, one may include the optionally substituted hydroquinone in one or more than one of the inks. Any inks which do not contain the optionally substituted hydroquinone may still come into contact with it by virtue of the overlap between inks on the substrate which usually occurs to give full colour prints.

A second way is to apply a composition, preferably a colourless or weakly coloured composition, comprising an optionally substituted hydroquinone and a liquid medium to the area of the substrate which carries the image or will carry the image, by means of an ink jet printer, before, during or after printing the image on the substrate. The liquid medium is preferably as described above in relation to the ink, except that it contains no colorant. The particular liquid medium used in the ink and in the colourless or weakly coloured composition comprising the optionally substituted hydroquinone may be different or the same.

A third way is to apply an ink comprising a dye containing at least one group of the Formula (1 ) as hereinbefore defined by means of an ink jet printer to a substrate which is coated or impregnated with an optionally substituted hydroquinone. In this way the dye is in contact with the optionally substituted hydroquinone present in the coated or impregnated substrate. Furthermore, there is no need to re-formulate current stocks of inks or risk blockage problems in temperamental ink jet printer heads.

Preferably the substrate is impregnated or coated with a composition comprising an optionally substituted hydroquinone, a liquid medium and optionally a binder.

The liquid medium preferably comprises water or a mixture comprising water and an organic solvent.

The substrate is preferably a paper, plastics material, textile, metal or glass, more preferably a paper, an overhead projector slide or a textile material, especially paper A preferred composition suitable for coating or impregnating the substrate comprises:

(a) from 0.01 to 30, more preferably 1 to 10, parts of an optionally substituted hydroquinone;

(b) from 0.01 to 30, more preferably 1 to 10, parts of a binder;

(c) from 0.01 to 99.97, more preferably 0.1 to 50, parts of a water-miscible organic solvent; and

(d) from 0.01 to 99.97, more preferably 0.1 to 50 parts water; wherein all parts are by weight and the total number of parts (a) + (b) + (c) + (d) = 100.

The composition suitable for coating or impregnating the substrate is preferably colourless, weakly coloured or white.

The binder is preferably a polymeric or polymerisable binder, more preferably a water-soluble or water-dissipatable polymeric or polymerisable binder. The substrate preferably carries porous inorganic particles, e.g. alumina (especially boehemite) or siliceous particles, especially particulate amorphous precipitated silica having a calculated multimodal particle size distribution wherein the particle sizes at the modes are less than 10 micrometers, as described in US 5,804,293, and the siliceous particles referred to in PCT/US96/19361 , page 9, lines 21 to 29 which are incorporated herein by reference thereto. These particles improve absorbency of the substrate for inks, resulting in better wet and rub fastness properties for the substrate. Optionally the porous inorganic particles are incorporated into the substrate as a component of the binder. Preferred water-soluble binders include starches, preferably hydroxy alkyl starches, for example hydroxyethylstarch; celluloses, for example cellulose, methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethyl methyl cellulose and carboxymethlycellulose (and salts thereof) and cellulose acetate butyrate; gelatin; gums, for example guar, xanthan gum and gum arabic; polyvinylalcohol; polyvinylphosphate; polyvinylpyrrolidone; polyvinylpyrrolidine; polyethylene glycol; hydrolysed polyvinylacetate; polyethylene imine; polyacrylamides, for example polyacrylamide and poly(N,N-dimethyl acrylamide); acrylamide-acrylic acid copolymers; polyvinylpyridine; polyvinylphosphate; vinylpyrrolidone-vinyl acetate copolymers; vinyl pyrrolidone-styrene copolymers; polyvinylamine; poly(vinyl pyrrolidonedialkylaminoalkyl alkylacrylates), for example poly vinylpyrrolidone-diethylaminomethylmethacrylate; acid- functional acrylic polymers and copolymers, for example poly(meth)acrylic acid and copolymers of (meth)acrylic acid and other (meth)acrylate monomers; amine-functional acrylic polymers and copolymers, for example polydimethylaminoethylmethacrylate; acid or amine functional urethane polymers, preferably those containing dimethylolpropanoic acid and/or pendant or terminal polyethylene glycols; ionic polymers, especially cationic polymers, for example poly (N,N-dimethyl-3,5-dimethylene piperidinium chloride); polyesters, preferably those which carry water-solubilising groups, especially acid groups, for example polyesters obtainable by polymerising a polyol with sodiosulphoisophthalic acid.

Preferred water-dissipatable binders are water-dissipatable polymers, more preferably latex polymers, for example cationic, non-ionic and anionic styrene-butadiene latexes; vinyl acetate-acrylic copolymer latexes; acrylic copolymer latexes which carry quaternary ammonium groups, for example a polymethylacrylate trimethylammonium chloride latex; and dispersions of poly(acrylate), poly(methacrylate), polyester, polyurethane or vinyl polymers and copolymers thereof. The polymer dispersions are preferably prepared by emulsion, suspension, bulk or solution polymerisation followed by dispersion into water.

The binder may comprise a single binder or comprise a mixture of two or more binders, especially the preferred binders described above. The binder may also be a Quikote™ coating material available from PPG Industries Inc. Colour bleed in the resultant substrate can be reduced or even eliminated if the binder contains (1 ) water-soluble film- forming organic polymer which is substantially free of onium groups, and (2) a water- soluble or water-dispersible onium addition polymer consisting essentially of onium- containing mer units. Preferably the weight ratio of the binder to the optionally substituted hydroquinone is from 99:1 to 1 :99, more preferably from 80:20 to 20:80. The preferred water-miscible organic solvents are as described above in relation to the inks of the first aspect of the present invention.

The optionally substituted hydroquinone and binder are preferably dispersed or more preferably dissolved in the liquid medium. Preferred methods for coating or impregnating the substrate with the optionally substituted hydroquinone include, for example, dip coating, reverse roller coating, K-bar coating, spraying and ink jet printing.

When the substrate is coated or impregnated with the optionally substituted hydroquinone in the form of a mixture with a liquid medium prior to ink jet printing with an ink it is preferred that the coated or impregnated substrate is dried before the ink is applied. Any suitable drying method may be used, for example hot air drying.

The above ways for ensuring that the dye, when situated on the substrate, is in contact with the optionally substituted hydroquinone, may be used alone, in a combination of any two ways, or in fact all three together. In this second aspect of the invention, the ink jet printer preferably applies the ink or the colourless composition to the substrate in the form of droplets which 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 or colourless composition in a reservoir by means of a resistor adjacent to the orifice, thereby causing the ink or the colourless composition to be ejected 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 or the colourless composition from the orifice.

The substrate is preferably a paper, plastic, textile, metal or glass, more preferably a 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. Examples of commercially available treated papers include HP Premium Coated Paper (available from Hewlett Packard Inc), HP Photopaper (available from Hewlett Packard Inc.), Stylus Pro 720 dpi Coated Paper, Epson Photo Quality Glossy Film (available from Seiko Epson Corp.), Epson Photo Quality Glossy Paper (available from Seiko Epson Corp.), Canon HR 101 High Resolution Paper (available from Canon), Canon GP 201 Glossy Paper (available from Canon), and Canon HG 101 High Gloss Film (available from Canon). These papers may easily be modified to include a compound of Formula (1 ) during their manufacture. For example, one may perform the process described in PPG's US Patent No. 5,880,196, Example 1 , or US 5,804,293, Examples 1 to 110, or in the Examples of US 4,892,779, modified such that an optionally substituted hydroquinone is included as an ingredient in the coating compositions described in these Examples.

When the substrate is a textile material the ink or the solution is preferably applied to the textile material by an ink jet printer followed by heating the printed textile material at a temperature of from 50°C to 250°C.

Preferred textile materials are natural, synthetic and semi-synthetic materials.

Examples of preferred natural textile materials include wool, silk, hair and cellulosic materials, particularly cotton, jute, hemp, flax and linen. Examples of preferred synthetic and semi-synthetic materials include polyamides, polyesters, polyacrylonitriles and polyurethanes.

The composition referred to in the second aspect of the present invention is preferably colourless. In this case, the ink and the colourless solution are preferably applied to the substrate through different nozzles. For example, in the case of a full colour ink jet printer, the coloured inks, which may or may not contain an optionally substituted hydroquinone, are applied to the substrate by means of an ink jet printer through different nozzles than the weakly coloured or colourless composition containing the optionally substituted hydroquinone. A suitable ink jet printer and a method for its control is described in EP 657 849.

According to a third aspect of the present invention there is provided a substrate, preferably a paper, an overhead projector slide or a textile material, printed with an ink according to the first aspect of the present invention or by means of the process according to the second aspect of the present invention.

According to a fourth aspect of the present invention there is provided an ink jet printer cartridge comprising a chamber and liquid, wherein the liquid is present in the chamber and the liquid is an ink according to the first aspect of the invention or a composition, preferably a colourless or weakly coloured composition, comprising a liquid medium and an optionally substituted hydroquinone (preferably as defined above in relation to the composition for coating or impregnating a substrate).

.According to a fifth aspect of the present invention there is provided an ink jet printer containing an ink jet printer cartridge, wherein the ink jet printer cartridge is as defined in the fourth 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

Dve d⁾

Dye (1 ) wherein X is a mixture of sodium and lithium cations, in which 40% of the total cations are lithium cations.

Dye (1 ) was prepared using a method analogous to that described in EP 692 003 A1 , Example 19.

Inks

A series of inks were prepared with the formulation:

4 parts of Dye (1 ); the optionally substituted hydroquinone at the loading shown in Table 1 , col. 2;

5 parts of 2-pyrolidone; 5 parts of thiodiglycol;

2 parts of Surfynol 465 (a non-ionic surfactant); balance to 100 parts with water

Control Ink The Control Ink was identical to the inks described above except that water was used in place of the optionally substituted hydroquinone.

Light Fastness Measurements

The inks were printed onto the substrates shown in Table 1 , column 3 using a Hewlett Packard DeskJet 690c ink jet printer.

After drying, the prints were mounted, half covered, in an Atlas Ci35a weatherometer and irradiated for 50 hours. The prints were removed and the reflected optical density of the exposed and covered portions were measured using an X-Rite™938 densitometer. These readings were used to calculate the percentage optical density loss following the irradiation. Each print was then irradiated for a further 50 hours (ie 100 hours in total) and the light-fastness was re-measured as described above.

The light-fastness results for each substrate (ΔE) are shown in Table 1 , cols 4 and 5. A low figure for ΔE indicates low fading, i.e. high light-fastness. Table 1

The results in Table 1 clearly show that inks containing Dye (1 ) and an optionally substituted hydroquinone generally provide prints with a higher light-fastness (i.e. lower ΔE) than prints prepared using the Control Ink which does not contain a hydroquinone.

Comparative Example 1 Comparative Inks

Comparative Inks were prepared of the same formulations as those in Example 1 except in place of Dye (1 ) there was used the Comparative Dye of the formula:

Comparative Dye

The Comparative Inks shown in Table 2 were prepared. Each Comparative Ink was of the formula:

4 parts of Dye (1 ); the optionally substituted hydroquinone at the loading shown in col. 2 of Table 2

5 parts of 2-pyrolidone; 5 parts of thiodiglycol; 2 parts of Surfynol 465 (a non-ionic surfactant); balance to 100 parts with water Each ink was printed onto the substrate shown in Table 2 and the light-fastness of each was measured as described in Example 1.

Table 2

The results in Table 2 show that although the presence of the optionally substituted hydroquinone improves light-fastness, the improvement is not as marked as that obtained when the hydroquinone is used with Dye (1 ).

By way of illustration Ink 2, containing 4% hydroquinone sulphonic acid when printed on HP Glossy paper gave a ΔE of 16.49, compared to 44.89 for the Control Ink with no hydroquinone gave a ΔE of 44.89, ie a 63% improvement in light-fastness. On the other hand the same ink formulations with the Comparative Dye only improved the light- fastness from 53.95 to 32.25, ie just 40%.

Comparative Example 3

Comparative Ink 7 of the formula below was prepared: 4 parts of Dye (1 ); 4 parts 2,3-dimethoxybenzoic acid;

5 parts of 2-pyrolidone; 5 parts of thiodiglycol;

2 parts of Surfynol 465 (a non-ionic surfactant); balance to 100 parts with water. Comparative Ink 7 was printed onto the substrates shown in Table 3 and the light-fastness of the resulting prints was measured as described in Example 1. Table 3

The results in Table 3 show that the 2,3-dimethoxybezoic acid does not show the marked improvement in light-fastness compared to the inks of the present invention. Compare the results in Table 3 with Ink 4 in Table 1 (an ink according to the present invention). On HP Glossy Paper Ink 4 gave a ΔE (100 hrs) of 16.49 compared to 65.11 for Comparative Ink 7, i.e. Ink 4 according to the invention gives prints with a far higher light- fastness than those obtained using Comparative Ink 7. In Tables 1 to 3 the following abbreviations have been used:

HP Gloss Hewlett Packard Glossy Paper

HG201 HG201 Glossy Paper available for Canon

SEC GF Seiko Epson Glossy Film.

Claims

1. An ink comprising:

(a) an optionally substituted hydroquinone;

(b) a dye containing at least one group of the Formula (1 ) or a salt thereof:

Formula (1 )

wherein:

R¹ is H or optionally substituted alkyl; and (c) a liquid medium.

2. An ink according to claim 1 wherein component (a) is a hydroquinone optionally substituted by -COOH or -SO₃H or a salt thereof.

3. An ink according to claim 1 or claim 2 wherein the floating sulpho group in Formula (1) is attached meta to the -NR - group.

4. An ink according to any one of the preceding claims wherein the dye is a mono- azo or bis-azo dye.

5. An ink according to any one of the preceding claims wherein the dye is of the Formula (2) or a salt thereof:

wherein:

Ar is optionally substituted aryl;

Q is optionally substituted benzoyl, optionally substituted naphthoyl, a substituted triazinyl group or an arylsulphonyl group; and R¹ is as defined in claim 1.

. An ink according to any one of the preceding claims comprising:

(a) from 0.01 to 20 parts in total of a hydroquinone optionally substituted by -COOH or -SO₃H, or a salt thereof; and (b) from 0.01 to 30 parts in total of water-soluble mono-azo or bis-azo dye(s) which contain at least one group of the Formula (1 ) as defined in claim 1 ; and (c) from 50 to 99.98 parts of a liquid medium comprising water or a mixture of water and one or more water-miscible organic solvent; wherein all parts are by weight and the number of parts of (a)+(b)+(c)=100.

7. A process for printing an image on a substrate comprising applying thereto an ink containing a dye containing at least one group of the Formula (1 ) as defined in claim 1 by means of an ink jet printer such that the dye, when situated on the substrate, is in contact with an optionally substituted hydroquinone.

8. A process according to claim 7 wherein the ink is as defined in any one of claims 1 to 6.

9. A process according to claim 7 or claim 8 wherein the substrate is coated or impregnated with an optionally substituted hydroquinone.

10. A process according to any one of claims 7 to 9 wherein a composition comprising an optionally substituted hydroquinone and a liquid medium is applied to the area of the substrate which carries the image or will carry the image, by means of an ink jet printer, before, during or after printing the image on the substrate.

11. A composition comprising:

(a) from 0.01 to 30 parts of an optionally substituted hydroquinone; (b) from 0.01 to 30 parts of a binder;

(c) from 0.01 to 99.97 parts of a water-miscible organic solvent; and

(d) from 0.01 to 99.97 parts water; wherein all parts are by weight and the total number of parts (a) + (b) + (c) + (d) = 100.

12. A substrate printed with an ink according to any one of claims 1 to 6 or by means of the process according to any one of claims 7 to 10.

13. An ink jet printer cartridge comprising a chamber and liquid, wherein the liquid is present in the chamber and the liquid is an ink according to any one of claims 1 to 6 or a composition comprising a liquid medium and an optionally substituted hydroquinone.

14. An ink jet printer containing an ink jet printer cartridge, wherein the ink jet printer cartridge is as defined in claim 13.