WO2002055617A1

WO2002055617A1 - Ink-jet ink and recording material

Info

Publication number: WO2002055617A1
Application number: PCT/EP2002/000090
Authority: WO
Inventors: Stéphane BIRY; Christian Zumwald
Original assignee: Ciba Specialty Chemicals Holding Inc.
Priority date: 2001-01-15
Filing date: 2002-01-08
Publication date: 2002-07-18

Abstract

The invention relates to an ink-jet ink, an ink-jet recording material and an ink-jet system containing at least one hydroquinone of general formula (I) wherein Q is selected from the residues: -COO-M+, wherein M?+, is H+¿, a monovalent, divalent and trivalent metal cation or a group N+(R21)(R22)(R23)(R24), wherein R21, R22, R23 and R24 independently of one another are H, unsubstituted C1-C4alkyl or C1-C4alkyl substituted by 1 to 3 OH or C1-C4alkyl interrupted by O; allyl, cyclopentyl, cyclohexyl, phenyl or tolyl, or R21 and R22 together with the nitrogen atom to which they are each bonded, mya form an unsubstituted 5- or 6-membered heterocyclic ring or a 5- or 6-membered heterocyclic ring substituted by one or two C1-C4alkyl groups; -SO3-M+, wherein M+ is as defined above; -P(O)(O-M+)2, wherein M+ is as defined above; -N+(R21)(R22)(R23)X-, wherein R¿21?, R22 and R23 are as defined above and X?-¿ is an inorganic or organic anion; -CO-N+(R21)(R22)(R23)X-, wherein X-, R21 and R23 are as defined above; -SO2N+(R21)(R22)(R23)X-, wherein X-, R21 and R23 are as defined above; K is 1 or 2; and n is an integer from 1 to 10.

Description

Ink-jet ink and recording material

The present invention relates to an ink-jet ink, an ink-jet recording material and an ink-jet system with improved properties.

In the ink-jet process, an image is produced by ejecting ink droplets onto a recording material through a nozzle. The ink is in most cases an aqueous solution of a dye. The recording material should rapidly and permanently fix the said dye. Specially prepared papers or plastic films provided with a dye-binding layer are mostly used for this purpose. Owing to the fineness of the nozzles, dyes which are completely dissolved in the ink vehicle are preferred to pigments. Besides, dyes offer a higher chroma and a better colour gamut when compared to pigments. However, dyes usually have a poorer fastness to light than, for example, the coloured pigments customary in conventional printing inks. As a result, images produced by printing usually have a limited lifetime when subjected to light and thus rapidly begin to fade or discolour.

Some hydroquinone derivatives are already known as an additive for inks or recording materials for ink-jet printing. Thus, GB-A-2 088 777 and EP-A-956 970, for example, describes dihydroxybenzenes which are substituted by -COOH, -S0₃H, alkyl or dialkyl. Dihydroxy-substituted benzoate and benzene sulfonate salts are mentioned in EP-A-897 808. Furthermore, dihydroxybenzenes and trihydroxybenzenes are described, for example, in jP-A-58 08 684. The use of dialkoxybenzenes as ink-jet ink or media additives is disclosed in US 5,098,477 and US 5,073,448. The use of a water-insoluble hydroquinone together with UV absorbers and radical inhibitors is described in US 5,948,150.

There is, however, still a need for effective light stabilisers for ink-jet inks or recording materials. This object is achieved by the use of defined hydroquinones.

It has now been found that certain hydroquinone derivatives are particularly suited for stabilising ink-jet prints against light fading. The present invention therefore relates to an ink-jet ink containing at least one hydroquinone of the general formula (I):

wherein

Q is selected from the residues:

-COO^"M⁺, wherein M⁺ is H⁺, a monovalent, divalent or trivalent metal cation or a group

N⁺(R₂₁)(R₂₂)(R₂₃)(R₂₄), wherein R₂₁, R₂₂, R₂₃ and R₂₄ independently of one another are H, unsubstituted C,- .alkyl or C,-Q.alkyl substituted by 1 to 3 OH or C,-C₄alkyl interrupted by O; allyl, cyclopentyl, cyclohexyl, phenyl, benzyl or tolyl, or R₂₁ and R₂₂ together with the nitrogen atom to which they are each bonded, may form an unsubstituted 5- or 6-membered heterocyclic ring or a 5- or 6-membered heterocyclic ring substituted by one or two C,-C₄alkyl groups;

-S0₃ ^'M⁺, wherein M⁺ is as defined above;

-P(0)(0^'M⁺)₂, wherein tvf is as defined above;

-N⁺(R₂₁)(R-₂)(R₂₃)X^", wherein R₂₁, R₂₂ and R₂₃ are as defined above and X^" is an inorganic or organic anion;

-CO-N⁺(R₂₁)(R₂₂)(R₂₃)X^", wherein X^", R₂„ R^ and R₂₃ are as defined above;

-S0₂N⁺(R₂.)(R₂₂)(R₂₃)X^", wherein X^", R₂₁, R₂₂ and R₂₃ are as defined above; k is 1 or 2; and n is an integer from 1 to 10.

The invention also relates to an ink-jet recording material containing at least one compound of the formula (I) as defined above. Furthermore, the invention relates to an ink-jet system, containing a recording material and at least one coloured ink to be applied to the recording material by means of an ink-jet nozzle, characterised in that at least either the recording mateπal or at least one coloured ink contains at least one hydroquinone of general formula (I) as defined above.

Furthermore, the invention relates to a process for stabilising ink-jet prints.

Concerning formula (I), k is preferably 1 and n is an integer from 1 to 6. Preferably n is an integer from 1 to 3, more preferably n is 3.

The chain C_nH_{2n+l k}may be a straight alkylene chain like for example -CH₂-CH₂-CH₂- or a branched alkylene chain like for example a -CH₂-CH₂-CH₂-CH(CH₃)- chain.

Possible monovalent, divalent or trivalent metal cations can, for example, be Na⁺, K⁺, Li⁺, Mg²⁺, Ca²⁺, Zn²⁺, Cu²⁺, Mn²⁺, Ni²⁺, Al³⁺, Fe³⁺ and Cr³⁺.

Preferably M⁺ is Li⁺ or NH/.

When the group R₂„ R₂₂, R₂₃ or R₂₄ is unsubstituted C.-C₄alkyl, C,-C₄alkyl substituted by 1 to 3 OH or C,-C₄alkyl interrupted by O it may be, for example, a methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, t-butyl, 1 -hydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl, 3- hydroxybutyl, 4-hydroxybutyl, 2,3-dihydroxypropyl, 2-methoxyethyl, 2-ethoxyethyl, 2-n- propoxyethyl or a 2-n-butoxyethyl group.

When the groups R₂₁ and R₂₂ together with the nitrogen atom to which they are bonded form an unsubstituted 5- or 6-membered heterocyclic ring, or a 5- or 6-membered heterocyclic ring substituted by one or two C,-C₄alkyl groups, this ring may be a pyrrolidine, piperidine, morpholine or a 2,5-dimethyl morpholine ring.

The term inorganic or organic anion refers, for example, to an anion of phosphate, carbonate, bicarbonate, nitrate, chloride, bromide, fluoride, iodide, bisulfite, sulfite, bisulfate, sulfate, borate, carboxylate, alkylsulfonate, arylsulfonate or a phosphonate anion like, for example, diethylenetriaminepentamethylenephosphonate anion. X^' as carboxylate anion especially is a carboxylate anion of a mono-, di-, tri- or tetracarboxylic acid, mainly of 1 -18 carbon atoms, such as a formate, acetate, benzoate, citrate, oxalate, tartrate, acrylate, polyacrylate, fumarate, maleate, itaconate, glycolate, gluconate, malate, mandelate, tiglate, ascorbate, polymethacrylate or of nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid.

The solubility of particularly advantageous compounds of formula (I) in water at 20°C and standard pressure is at least 0.1 g/l, preferably at least 1 g/l.

Some of the compounds of formula (I) are new. Therefore, this invention also pertains to compounds of the formula (I), wherein Q is -COO^'fvf, wherein M⁺ is as defined above, with the proviso that when n is 3, then M⁺ is neither H⁺ nor Na⁺.

Acid salts of formula (I) can be prepared by neutralisation of the corresponding acid or by hydrolysis of the corresponding ester with an organic or inorganic base. The ester group may be converted into an amide by treatment with an amine. The ammonium salts of formula (I) are usually synthesised by neutralisation of the corresponding amine with an acid. They may also be synthesised by quaternisation using alkyl halides.

The above mentioned acid, ester and amine compounds from which the salts of formula (I) can be obtained, can be prepared, for example, as described in US 4,484,000 or US 4,430,425, wherein it is said that such compounds can be prepared by reacting a hydroquinone with a functional alkylating agent in the presence of a catalyst. Suitable alkylating agents are for example those listed in US 4,484,000. The alkylation step is conveniently carried out at a temperature ranging from 20°C to 150°C, but preferably in the range 80°C to 130°C. The acid catalyst may be a Bronsted or Lewis acid or active earth. Bronsted acids suitable for the purpose may be organic or inorganic or a partial salt thereof and may be an inorganic mineral acid such as hydrochloric, sulphuric, perchloric, and orthophosphoric acid; an alkyl, aryl or alkaryl substituted inorganic acid such as methane and ethane sulphonic acids, benzene sulphonic acid p-toluene sulphonic acid and methane phosphonic acid; an organic acid such as dichloro acetic acid, trichloroacetic acid, and trifluoroacetic acids. Lewis acids suitable for alkylation include boron trifluoride, ferric chloride, aluminum chloride, and stannic chloride. Active earth suitable for alkylation include Fulmont 237 (trademark) and Fulcat 22 (trademark). The preferred catalyst for the alkylation is p-toluene sulphonic acid.

Preferred ink-jet inks, ink-jet recording materials or ink-jet systems are those which contain at least one hydroquinone of the formula (I), wherein k is 1, n is an integer from 1 to 3, and

Q is selected from the residues:

-COO^'fvf , wherein M⁺ is H⁺, a monovalent metal cation or a group N⁺(R₂,)(R₂₂)(R₂₃)(R_2i)), wherein R₂₁, R₂₂, R₂₃ and R₂₄ independently of one another are H, unsubstituted C,-C₄alkyl, C C₄alkyl substituted by 1 to 3 OH or C.-C₄alkyl interrupted by O;

-S0₃ ^"M⁺, wherein M⁺ is as defined above;

-P(0)(0^"M wherein M⁺ is as defined above;

-N⁺(R₂₁)(R₂₂)(R₂₃)X^', wherein R₂„ R₂₂ and R₂₃ are as defined above and X^' is a phosphate, carbonate, bicarbonate, nitrate, chloride, bromide, fluoride, iodide, bisulfite, sulfite, bisulfate, sulfate, borate, carboxylate, an alkylsulfonate, an arylsulfonate or a phosphonate anion.

Especially preferred ink-jet inks, ink-jet recording materials or ink-jet systems are those which contain at least one hydroquinone of the formula (I), wherein k is and n is 3, Q is-COO ^*, wherein M⁺ is H\ Li⁺, Na⁺, K⁺, NH₄ ⁺ or N⁺(CH₃)H, preferably Li⁺ or NH₄ ⁺, more preferably Li⁺.

The compounds of formula (I) are used either in the ink-jet recording material or in the ink- jet ink or in both.

Examples of especially suited compounds of formula (I) include those wherein k is 1 and n is 3 and Q is -COOir or -COO NH/; or n is 2 and Q is -P(0)(0^'Li⁺)₂; or n is 1 and Q is -COO^'Li⁺ or -S0₃ Li⁺.

Concerning the new compounds of formula (I), preferred are those compounds wherein Q is -COO NT and M^* is H⁺, a monovalent metal cation or a group N⁺(R₂₁)(R₂₂)(R₂₃)(R₂₄) wherein R₂₁, R₂₂, R₂₃ and R₂₄ independently of one another are H, unsubstituted^' C,-C₄alkyl, C,-C₄alkyl substituted by 1 to 3 OH or C,-C₄alkyl interrupted by O, k is 1 and n is an integer from 1 to 3; with the proviso that when n is 3, then M^* is neither H⁺ nor Na\ Preferably n is 3 and M⁺ is Li⁺, K⁺, NH₄ ⁺ or N⁺(CH₃)H, most preferably Li⁺ or NH₄ ⁺.

Compounds of formula (I) are preferably added to casting or coating dispersions which are applied by customary techniques to the support of the ink-jet recording material, or they can be absorbed onto the material from an aqueous or organic solution. If the recording material contains more than one layer, the compounds according to this invention can be added to one layer or can be distributed over a plurality of layers, wherein they can be applied to a plurality of layers in the same or different concentrations.

The ink-jet ink according to this invention preferably contains 0.01 to 30% by weight, in particular 0.1 to 20% by weight, of at least one compound of formula (I).

The ink-jet recording material according to this invention preferably contains 1 to 10000 mg/m², most preferably 50 to 2000 mg/m², of at least one compound of the formula (I).

The invention also relates to a process for stabilising ink-jet prints, which comprises applying to a recording material for ink-jet printing an ink composition containing a water soluble dye or a solution of a dye in an organic solvent and at least one compound of the formula (I) as defined above and drying said recording material.

In another embodiment the process comprises applying to a recording material for ink-jet printing a casting or coating dispersion or an aqueous or organic solution containing at least one compound of the formula (I) as defined in claim 1 and further applying either an ink composition containing a water soluble dye or a solution of a dye in an organic solvent; or an ink composition containing a water soluble dye or a solution of a dye in an organic solvent and at least one compound of the formula (I) as defined in claim 1 and drying said recording material.

Compounds of formula (I) are preferably used to stabilise ink-jet inks or recording materials, but may also be incorporated in ink compositions for felt-tipped pens, ink pads, fountain pens, and pen plotters, as well as for offset, book, flexographic and intaglio printing, and also for typewriter ribbons for dot matrix and calligraphic printing. Compounds of formula (I) can further be used in silver halide photographic materials as well as in recording materials for pressure-sensitive copying systems, icrocapsule photocopier systems, heat- sensitive copier systems, dye diffusion transfer printing, thermal wax transfer printing and dot matrix printing, and for use with electrostatic, electrographic, electrophoretic, magnetographic and laser-electrophotographic printers, recorders or plotters.

Amongst the printers used for ink-jet printing, a distinction is usually made between continuous and drop-on-demand printers. The ink-jet system according to this invention is suited for use with both type of printers.

The ink compositions according to this invention are preferably water-borne inks and may contain water-soluble solvents such as ethylene glycol, diethylene glycol, triethylene glycol or higher ethylene glycols, propylene glycol, 1 ,4-butanediol, or ethers of such glycols, thiodiglycol, glycerol and the ethers and esters thereof, polyglycerol, mono-, di- and triethanolamine, propanolamine, dimethyl formamide, dimethyl sulfoxide, dimethyl acetamide, N-methylpyrrolidone, 1 ,3-dimethylimidazoϋdone, methanol, ethanol, isopropanol, n-propanol, diacetone alcohol, acetone, methyl ethyl ketone or propylene carbonate.

The ink compositions according to this invention preferably contain water soluble dyes, such as those known for dyeing natural fibres. These can, for example, be acid dyes, direct dyes, reactive dyes, mono-, di- or polyazo dyes, triphenylmethane dyes, xanthene dyes or phtalocyanine dyes. Specific examples of such dyes are Food Black 2, Direct Black 19, Direct Black 38, Direct Black 168, Sulphur Black 1, Acid Red 14, Acid Red 35, Acid Red 52, Acid Red 249, Direct Red 227, Reactive Red 24, Reactive Red 40, Reactive Red 120, Reactive Red 159, Reactive Red 180, Acid Yellow 17, Acid Yellow 23, Direct Yellow 86, Direct Yellow 132, Acid blue 9, Acid Blue 185, Direct Blue 86, Direct Blue 199, copper phtalocyanines and the azo dyes listed in EP-A-366 121 .

The ink compositions according to this invention may be nonaqueous and consist of a solution of dyes in an organic solvent or a mixture of organic solvents. Examples of solvents used for this purpose are alkyl carbitols, alkylcellosolves, dialkylformamides, dialkylacetamides, alcohols, acetone, methylethylketone, diethylketone, diethyl ketone, methyl isobutyl ketone, diisopropyl ketone, dibutyl ketone, dioxane, ethyl butyrate, ethyl isovalerate, diethyl malonate, diethyl succinate, butyl acetate, triethyl phosphate, ethylglycol acetate, toluene, xylene, tetralin or petroleum fractions. Example of solid waxes as solvents, which, as an ink carrier, must first be heated, are stearic or palmiric acid. Solvent based inks contain dyes soluble therein, for example Solvent Red, Solvent Yellow, Solvent Orange, Solvent Blue, Solvent Green, Solvent Violet, Solvent Brown or Solvent Black.

The ink compositions according to this invention may also contain minor amounts of conventional modifiers such as binders, surfactants, biocides, corrosion inhibitors, sequestrants, pH buffers or conductivity additives. They may also contain further light stabilisers or UV absorbers, including the compounds disclosed in US 5,073,448, US 5,089,050, US 5,096,489, US 5,124,723, US 5,098,477 and US 5,509,957.

The ink compositions according to this invention may also consist of more than one phase. Ink compositions that consist of an aqueous phase in which the dye is dissolved and a dispersed oil phase that contains an UV absorber and/or an antioxidant are for example disclosed in jP-A-0 1 1 70 675, JP-A-0 1 182 379. |P-A-0 1182 380, JP-A-0 1 182 381 , jP-A-0 1 193 376. Oil soluble dyes can be dissolved in an oil together with UV absorbers and/or antioxidants. The oil is either emulsified or dispersed in an aqueous phase as described, inter alia, in JP-A-0 1170 674 and jP-A-0 1170 672. Further suited ink-jet ink compositions are described in EP-A-672 538.

The recording materials according to this invention consist of a substrate having a surface which is printable by means of an ink-jet. The substrate is usually plain paper or polyolefine- laminated paper or a plastic sheet and is usually coated with at least one layer which is able to absorb ink. The substrate preferably has a thickness of 80 to 250 μm.

Uncoated paper might also be used. In this case, the paper acts simultaneously as substrate and ink absorbing layer. Materials made of cellulosic fibres and textile fibres materials such as cotton fabrics or blends of cotton and polyacrylamide or polyester, which might contain compounds of formula (I), can also be used as printing materials.

The recording materials may also be transparent, as in the case of overhead projection transparencies.

The compounds of formula (I) can be incorporated in the substrate during production thereof, conveniently by addition to the pulp during paper manufacture. Another method of application consists in spraying the substrate with a solution of the compound of formula (I) in water or in a readily volatile organic solvent. The use of emulsions or dispersions is also possible.

Usually, however, at least one coating composition with high dye affinity is coated onto the substrate and, in this case, the compounds of formula (I) are added to at least one of the said coating compositions. Typical coating compositions comprise, for example, a solid filler, a binder and conventional additives.

Example of suitable fillers are Si0₂, kaolin, talc, clay, calcium silicate, magnesium silicate, aluminium silicate, gypsum, zeolites, bentonite, diatomaceous earth, vermiculite, starch or the surface modified Si0₂ described in JP-A-60 260 377. Small amounts of white pigments, for example titanium dioxide, barytes, magnesium oxide, lime, chalk or magnesium carbonate, can be used with the filler in the coating composition, provided they do not significantly lower the print density of the ink-jet prints. Coating compositions which are intended for transparent, projectable recording materials must not contain any light-scattering particles, such as pigments and fillers.

The binder binds the fillers to one another and to the substrate. Typical conventional binders are water-soluble polymers such as polyvinyl alcohol, partially hydrolysed polyvinyl acetate, cellulose and cellulose derivatives such as hydroxyethyl cellulose, polyvinyl pyrrolidone and copolymers thereof, polyethylene oxide, salts of polyacrylic acid, sodium alginate, starch and starch derivatives, Na alginate, polyethylene imine, polyvinylpyridinium halide, gelatines and gelatine derivatives such as phthaloyl gelatines, casein, vegetable gum, dextrin, albumin, dispersions and polyacrylates or acrylate/methacrylate copolymers, lattices of natural or synthetic rubber, poly(meth)acrylamide, polyvinyl ethers, polyvinyl esters, copolymers of maleic acid, melamine resins, urea resins, water soluble polyurethanes and polyesters, or the chemically modified polyvinyl alcohols disclosed in jP-A-61 134 290 or jP- A-61 134 291.

An additional dye receptor or a mordant which enhances the fixation of the dye to the coating may be added to the binder. Dye receptors for acid dyes are cationic or amphoteric. The cationic mordants can be soluble or dispersible in water. Exemplary cationic mordants are polymeric ammonium compounds such as polyvinylbenzyldi- or trialkylammonium compounds, optionally quaternised poly(di)ailylammonium compounds, polymeth- acryloxyethyldimethylhydroxyethylammonium chloride, polyvinylbenzylmethylimidazolium chloride, polyvinylbenzylpicolinium chloride or polyvinylbenzyltributylammonium chloride. Further examples are basic polymers such as poly(dimethylaminoethyl)methacrylate, polyalkylenepolyamines and their condensation products with dicyanodiamide, amine/epichlorohydrin polycondensates or the compounds disclosed in jP-A-57-36692, 57- 64591, 57-187289, 57-191084, 58-177390, 58-208357, 59-20696, 59-33176, 59-96987, 59-198188, 60-49990, 60-71796, 60-72785, 60-161188, 60-187 582, 60-189481 , 60- 189482, 61 -14979, 61 -43593, 61 -57379, 61 -57380, 61 -58788, 61 -61887, 61 -63477, 61 - 72581, 61 -95977, 61 -134291 or in US-4,547,405 and 4,554,181 as well as in DE-A- 341 582 and EP-B-609 930. The mordants used can also be compounds containing phosphonium groups (EP-B-609 930) as well as ground cationic ion exchange resins which are introduced in the mordant layer in a finely divided form. Further suitable cationic mordants are described in US 6,102,997. The cationic mordants can be soluble or dispersible in water and have an average molecular weight (weight average) of preferably at least 2,000 and, in particular, at least 20,000.

Besides the dye acceptor layer(s), the ink-jet recording material might comprise other layers on the ink receiving side, which are intended, for example, for providing scratch resistance, absorbing water or controlling whiteness and/or glossiness. The backside of the substrate might also be coated with at least one binder layer, in order to prevent buckling of the recording material.

The ink-jet recording material according to this invention might also contain a number of other additives such as antioxidants, further light stabilisers (also including UV absorbers), viscosity improvers, fluorescent whitening agents, biocides, wetting agents, emulsifiers and spacers. Suitable spacers are in particular spherical, have an average diameter of 1 to 50 μm, and in particular 5 to 20 μm, and have a narrow particle size distribution. Suitable spacers consist, for example, of polymethylmethacrylate, polystyrene, polyvinyl toluene, silicon dioxide and insoluble starch.

Illustrative examples of particularly suitable antioxidants are sterically hindered phenols, hydroquinones and hydroquinone ethers, for example the antioxidants disclosed in GB-A-2 088 777 or JP-A-60-72785, JP-A-60-72786 and jP-A-60-71796.

Illustrative examples of particularly suitable light stabilisers are organic nickel compounds and sterically hindered amines, for example the light stabilisers disclosed in jP-A-58-152072, jP-A-61 -146591 , JP-A-61 -163886, jP-A-60-72785 and 1P-A-61 146591 or in EP-A-373 573, EP-A-685 345 and EP-A-704 316, GB-A-2 088 777, JP-A-59-169883 and JP-A-61 -177279.

Suitable UV absorbers are disclosed, inter alia, in Research Disclosure No. 24239 (1984) page 284, 37254 part VIII (1995) page 292, 37038 part X (1995) page 85 and 38957 part VI (1996), GB-A-2 088 777, EP-A-280 650, EP-A-306 083 and EP-A-711 804. These compounds are preferably introduced into the layer(s) farthest from the support. In a particular embodiment, the UV absorbers are contained in a layer above the layer(s) containing the compounds of the formula (I). Suitable UV absorbers for concurrent use with a compound of formula (I) in recording materials for ink-jet printing are in particular those of the 2'-hydroxyphenylbenzotriazole and 2'-hydroxyphenyltriazine class and, most particularly, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole and 2-(2'-hydroxy-3'-tert- butyl-5'-polyglycolpropionate-phenyl)benzotriazole. Further examples of particularly suited UV absorbers are listed in US-6,102,997. The UVabsorbers can be soluble or insoluble in water and added to the coating composition as dispersion or emulsion, optionally together with high-boiling solvents, using suitable dispersing agents or emulsifiers. Suitable high boiling solvents are described in Research Disclosure No. 37254 part VIII (1995) page 292.

The binders in the individual layers, and in particular gelatines, can also be crosslinked by suitable compounds, so-called hardening agents, in order to improve the water and scratch resistance of the layers. Suitable hardening agents are described in Research Disclosure No. 37254 part IX (1995) page 294, 37038 part XII (1995) page 86 and 38957 part IIB (1996) page 599 et seq. The hardening agents are normally used in quantities of 0.005 to 10% by weight, and preferably 0.01 to 1% by weight, based on the binder to be hardened.

The ink-jet recording material according to this invention can be produced in one pass from the support material and a casting solution for each layer to be applied, by means of a cascade or curtain casting device of the kind known from the production of photographic silver halide materials. After the casting solution(s) has/have been cast on the support, the material is dried and is then ready for use. The individual layers have a dry layer thickness of 0.1 to 20 μm, and preferably 0.5 to 5 μm.

If the compound of general formula (I) is a salt, it can be dissolved either directly in the ink or coating composition or added thereto in the form of an emulsion or suspension. If the compound of formula (I) is an acid, it can be dissolved in the ink or coating composition by addition of an alkali metal hydroxide. As already mentioned, the compounds of formula (I) can be also applied to the recording material in a separate operation, alone or together with other already described components, as a solution in water or in a suitable organic solvent. Application can be made by spraying, by sizing in a sizing press, by a separate coating operation or by immersion in a vat. After subjecting the recording mateπal to such an aftertreatment, an additional drying step is necessary.

The invention is illustrated by the following non-limitative Example.

An ink-jet ink is prepared by dissolving 2 g of dye in 20 g of diethylene glycol and 78 g of deionized water. The dye used is Acid red 52. The stabiliser is weighed in an amount of 0.15 g into a test tube and dissolved in 2.85 g of ink. The obtained ink is filtered through a filter having a pore size of 0.45 μm and transferred into an emptied and carefully cleaned cartridge of a Deskjet 510 printer (Hewlett-Packard). A stepped image is then printed onto plain paper (sihl+eika). The produced print is left to dry at 50°C under vacuum for two hours and thereafter irradiated behind a 5 mm thick window glass in an Atlas Ci-35 light fading device equipped with a Xenon lamp. The Atlas device is operated at 43°C, 50%RH without dark cycles and the light intensity is 461 W/m² (300-800 nm). The colour density of each step is measured before and after exposure using a MacBeth TR 924 densitometer. The results are summarised in the table below, for an initial density of 1. Lower density loss values indicate higher light fastness.

As above table shows, Compound A according to this invention is able to improve substantially the light fastness of the ink-jet print.

Claims

Claims:

1. An ink-jet ink containing at least one hydroquinone of the general formula (I):

wherein

Q is selected from the residues:

-COO^'M^*, wherein M⁺ is H⁺, a monovalent, divalent or trivalent metal cation or a group

N⁺(R₂.)(R₂₂)(R₂₃)(R₂₄), wherein R₂₁, R₂₂, R₂₃ and R₂₄ independently of one another are H, unsubstituted C,-C₄alkyl or C.-C₄alkyl substituted by 1 to 3 OH or C,-C„alkyl interrupted by O; allyl, cyclopentyl, cyclohexyl, phenyl, benzyl or tolyl, or R₂₁ and R₂₂ together with the nitrogen atom to which they are each bonded, may form an unsubstituted 5- or 6-membered heterocyclic ring or a 5- or 6-membered heterocyclic ring substituted by one or two C.-C₄alkyl groups;

-S0₃ ^'M⁺, wherein M⁺ is as defined above;

-P(0)(0^'M⁺)₂, wherein M⁺ is as defined above;

-N⁺(R₂.)(R₂₂)(R₂₃)X^", wherein R₂₁, R₂₂ and R₂₃ are as defined above and X^" is an inorganic or organic anion;

-CO-N⁺(R₂₁)(R₂₂)(R₂₃)X^', wherein X^", R₂„ R_a and R₂₃ are as defined above;

-S0₂N^*(R₂,)(R₂₂)(R₂₃)X^', wherein X^", R₂₁, R₂₂ and R₂₃ are as defined above; k is 1 or 2; and n is an integer from 1 to 10.

2. An ink-jet recording material containing at least one compound of the formula (I) as defined in claim 1.

3. An ink-jet system, comprising a recording material and at least one coloured ink to be applied to the recording material by means of an ink-jet nozzle, characterised in that at least either the recording material or at least one coloured ink contains at least one hydroquinone of general formula (I) as defined in claim 1.

4. An ink-jet ink, an ink-jet recording material or an ink-jet system according to any one of claims 1 to 3, wherein k is 1 , n is an integer from 1 to 3, and

Q is selected from the residues:

-COO^'M⁺, wherein M⁺ is H⁺, a monovalent metal cation or a group N⁺(R₂₁)(R₂₂)(R₂₃)(R₂₄), wherein R_2I/ R_22/ R₂₃ and R₂ independently of one another are H, unsubstituted C.-C₄alkyl, C.-C₄alkyl substituted by 1 to 3 OH or C.-C₄alkyl interrupted by O;

-S0₃ ^'M⁺, wherein M⁺ is as defined above;

-P(0)(0^"M⁺)₂, wherein M⁺ is as defined above;

-N⁺(R₂,)(R₂₂)(R₂₃)X^', wherein R₂₁, R₂₂ and R₂₃ are as defined above and X^' is a phosphate, carbonate, bicarbonate, nitrate, chloride, bromide, fluoride, iodide, bisulfite, sulfite, bisulfate, sulfate, borate, carboxylate, an alkylsulfonate, an arylsulfonate or a phosphonate anion.

5. An ink-jet ink, an ink-jet recording material or an ink-jet system according to claim 4, wherein n is 3 and Q is-COO M⁺, wherein M⁺ is H⁺, Li⁺, Na⁺, K⁺, NH₄ ⁺ or N⁺(CH₃)₃H; or n is 2 and Q is -P(0)(0^'L.⁺)₂; or n is 1 and Q is -COO^'LP or -SO.^'LT.

6. An ink-jet ink according to claim 1, containing 0.01 to 30% by weight of at least one compound of formula (I).

7. An ink-jet recording material according to claim 2, containing 1 to 10000 mg/m² of at least one compound of formula (I).

8. A process for stabilising ink-jet prints, which comprises applying to a recording material for ink-jet printing an ink composition containing a water soluble dye or a solution of a dye in an organic solvent and at least one compound of the formula (I) as defined in claim 1 and drying said recording material.

9. A process for stabilising ink-jet prints, which comprises applying to a recording material for ink-jet printing a casting or coating dispersion or an aqueous or organic solution containing at least one compound of the formula (I) as defined in claim 1 and further applying either an ink composition containing a water soluble dye or a solution of a dye in an organic solvent; or an ink composition containing a water soluble dye or a solution of a dye in an organic solvent and at least one compound of the formula (I) as defined in claim 1 and drying said recording material.

10. A compound of the formula (I), wherein k is 1 or 2 and n is an integer from 1 to 10, and Q is -COO M⁺, wherein M⁺ is H⁺, a monovalent, divalent or trivalent metal cation or a group N⁺(R₂.)(R₂₂)(R₂₃)(R₂₄), wherein R₂„ R₂₂, R₂₃ and R₂₄ independently of one another are H, unsubstituted C.-C₄alkyl or C,-C₄alkyl substituted by 1 to 3 OH or C,-C₄alkyl interrupted by O; allyl, cyclopentyl, cyclohexyl, phenyl, benzyl or tolyl, or R₂, and R₂₂ together with the nitrogen atom to which they are each bonded, may form an unsubstituted 5- or 6- membered heterocyclic ring or a 5- or 6-membered heterocyclic ring substituted by one or two C--C alkyl groups; with the proviso that when n is 3, then M⁺ is neither H⁺ nor Na⁺.

11. A compound according to claim 10, wherein k is 1 , n is 3 M⁺ is Li⁺, K⁺, NH₄ ^* or N⁺(CH₃)₃H, preferably Li⁺ or NH₄ ⁺.

12. Use of a hydroquinone of the general formula (I) as defined in claim 1 as light stabiliser for ink-jet inks or recording material.