WO2001096124A1

WO2001096124A1 - Ink receptive substrate and printing process

Info

Publication number: WO2001096124A1
Application number: PCT/GB2001/002351
Authority: WO
Inventors: Mark Kenworthy; Philip Macfaul; Tom Annable; Stephen George Yeates
Original assignee: Avecia Limited
Priority date: 2000-06-13
Filing date: 2001-05-25
Publication date: 2001-12-20
Also published as: GB0014397D0; AU2001260454A1

Abstract

The invention relates to an ink jet printing process and substrates, comprising applying to a substrate an ink containing a colorant by means of an ink jet printer such that the colorant, when situated on the substrate, is in contact with a water-dissipatable polyester which has been applied to the substrate other than as a component of the ink with the result that the light-fasteness of the resultant print is surprisingly improved. An ink receptive substrate comprising a sheet material coated or impregnated with water-dissipatable polyester is also described.

Description

INK RECEPTIVE SUBSTRATE AND PRINTING PROCESS

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates to an ink jet printing process using a composition containing a water-dissipatable polyester and ink in combination and to ink jet printers, cartridges and substrates.

2. RELATED BACKGROUND ART

Ink jet printing is a process for forming an image by ejecting minute droplets of ink onto a substrate such as paper.

Inks used in conventional inkjet printing commonly comprise a colorant, water and organic solvents. WO98/14524 describes ink jet printing inks containing a water, solvents, dye and a water-dissipatable polyester.

With the increasing usage of ink jet printers to print photorealistic images a need has arisen for the resultant images to have good light-fastness. Conventional silver halide photography yields prints with excellent light-fastness, but development of images resulting from conventional photography is slower and much less convenient than printing images using an ink jet printer.

We have now found that if a water-dissipatable polyester is applied to a print separately from the coloured ink, either before, after or during application of the coloured ink, the light-fastness of the resultant print is surprisingly improved.

3. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a process for printing an image on a substrate comprising applying thereto an ink containing a colorant by means of an ink jet printer such that the colorant, when situated on the substrate, is in contact with a water-dissipatable polyester which has been applied to the substrate other than as a component of the ink.

There are many ways for ensuring that the colorant, when situated on the substrate, is in contact with the water-dissipatable polyester which has been applied to the substrate other than as a component of the ink. For example the ink may be applied to a substrate which has been coated or impregnated with a water-dissipatable polyester. In this way the colorant is in contact with the water-dissipatable polyester present in the coated or impregnated substrate. This process has the advantage of avoiding the need to re- formulate current stocks of inks and avoids the potential risk of nozzle blockage problems in temperamental inkjet printers. Preferably when the ink is applied to a substrate which has been coated or impregnated with a water-dissipatable polyester the substrate is dry immediately before the ink is applied thereto.

An alternative way for ensuring that the colorant, when situated on the substrate, is 5 in contact with the water-dissipatable polyester which has been applied to the substrate other than as a component of the ink is to apply by means of an ink jet printer a colourless or weakly coloured composition comprising the water-dissipatable polyester and a liquid medium to the area of the substrate which carries the image or will carry the image before, during or after application of the ink to the substrate. The liquid medium is preferably as l o described above in relation to the ink, except that it contains no colorant.

In this alternative way, the ink jet printer preferably applies the ink and 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

15 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.

20 In one embodiment, the ink and the composition are preferably applied to the substrate through different nozzles of the same ink jet printer. For example, in the case of a full colour ink jet printer, the coloured inks are applied to the substrate by means of the ink jet printer through different nozzles than the weakly coloured or colourless composition. A suitable ink jet printer and a method for its control is described in EP 657 849.

25 The above ways for ensuring that the colorant when situated on the substrate is in contact with the water-dissipatable polyester, may be used alone or in a combination.

The particular liquid medium used in the ink and in the colourless or weakly coloured composition comprising the water-dissipatable polyester may be different or the same.

30 4. THE COMPOSITION

Preferably the colourless or weakly coloured composition comprises:

(a) from 0.2 to 20, more preferably 0.5 to 10 parts of water-dissipatable polyester; and

(b) from 80 to 99.8, more preferably 90 to 99.5 parts of liquid medium; 35 wherein all parts are by weight and the number of parts of (a) + (b) add up to 100.

Components other than (a) and (b) may of course be present in the composition, for example preservatives, biocides, viscosity modifiers, etc. The composition used in the present invention preferably has a pH of 3 to 11 , more preferably 6 to 9. A pH adjuster may be used to provide such a pH, e.g., an acid such as acetic acid, hydrochloric acid, p- toluenesulfonic acid, lactic acid and propionic acid or a base such as sodium hydroxide, sodium carbonate and ammonium hydroxide. The composition preferably has a surface tension in the range of from 25 to 50 dyn/cm, and more preferably from 30 to 40 dyn/cm. The composition preferably has a viscosity in the range of from 1.1 to 20 cP (centi poise), more preferably from .3 to 15 cP, especially 1.4 to 3 cP.

4.1 THE POLYESTER

The water-dissipatable polyester preferably has a number average molecular weight ("Mn") of up to 30,000. The Mn is preferably in the range from 500 to 30,000, more preferably 1000 to 25,000, especially 2000 to 20,000. These Mn lead to particularly good storage stability for the resultant compositions. The measurement of Mn is well known to those skilled in the art, and may for example be effected using gel permeation chromatography in conjunction with a standard polymer such as polystyrene or polymethylmethacrylate of known molecular weight. The water-dissipatable polyester preferably has a hydroxyl number of from 0 to

225mg KOH/g, more preferably 0 to 125mg KOH/g, especially from 0 to 50mgKOH/g.

The Tg of the water-dissipatable polyester (i.e. the temperature at which the polymer changes from a glassy, brittle state to a plastic, rubbery state) is preferably in the range -38°C to 105°C, more preferably -20 to 70°C, especially -10°C to 60°C. The water-dissipatable polyester can be prepared using conventional polymerisation procedures known to be effective for polyester synthesis. Thus, it is well known that polyesters contain carbonyloxy (i.e. -C(=O)-O-) linking groups and may be prepared by a condensation polymerisation process in which an acid component (including ester-forming derivatives thereof) is reacted with a hydroxyl component. The acid component may be selected from one or more polybasic ca^'rboxylic acids, e.g. di- and tri-carboxylic acids or ester-forming derivatives thereof, for example acid halides, anhydrides or esters. The hydroxyl component may be one or more polyhydric alcohols or phenols (polyols), for example, diols, triols, etc. (It is to be understood, however, that the polyester may contain, if desired, a proportion of carbonylamino linking groups -C(=O)-NH- (i.e. amide linking groups) by including an appropriate amino functional reactant as part of the "hydroxyl component"; such as amide linkages). The reaction to form a polyester may be conducted in one or more stages. It is also possible to introduce in-chain unsaturation into the polyester by, for example, employing as part of the acid component an olefinically unsaturated dicarboxylic acid or anhydride. Preferably the water-dissipatable polyester carries ionic water-dispersing groups and/or non-ionic water-dispersing groups.

Polyesters of this type are commercially available from Eastman Kodak Company and Avecia Limited. Examples include Eastman AQ29D and AQ55W. The water-dissipatable polyester preferably bears ionised carboxy and/or sulphonate groups, especially ionised sulphonate groups, because these assist water dissipatability of the polymer. Such groups can be chain pendant and/or terminal.

Polyesters bearing ionised sulphonate groups may be prepared by using at least one monomer having two or more functional groups which will readily undergo an ester condensation reaction (e.g. carboxyl groups, hydroxyl groups or esterifiable derivatives thereof) and one or more sulphonic acid groups (for subsequent neutralisation after polyester formation) or ionised sulphonate groups (i.e. neutralisation of the sulphonic acid groups already having been effected in the monomer) in the synthesis of the polyester. In some cases it is not necessary to neutralise sulphonic acid groups since they may be sufficiently strong acid groups as to be considerably ionised in water even without the addition of base. Often, the sulphonic acid or ionised sulphonate containing monomer is a dicarboxylic acid monomer having at least one ionised sulphonate substituent (thereby avoiding any need to effect neutralisation subsequent to polyester formation). (Alternatively, alkyl carboxylic acid ester groups may be used in place of the carboxylic acid groups as ester-forming groups). Such a monomer will therefore be part of the acid component used in the polyester synthesis.

Preferred polybasic carboxylic acids which can be used to form the polyester have two or three carboxylic acid groups. For example, one can use C₄ to C₂₀ aliphatic, alicyclic and aromatic compounds having two or more carboxy groups and their ester forming derivatives (e.g. esters, anhydrides and acid chlorides), and dimer acids such as C36 dimer acids. Specific examples include adipic acid, fumaric acid, maleic acid, succinic acid, itaconic acid, sebacic acid, nonanedioic acid, decanedioic acid, 1,4- cyclohexanedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid, 1 ,2- cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid and tetrahydrophthalic acid and their acid chlorides. Anhydrides include succinic, maleic, phthalic and hexahydrophthalic anhydrides.

Preferred polyols which can be used to form the polyester include those having from 2 to 6, more preferably 2 to 4 and especially 2 hydroxyl groups per molecule. Suitable polyols having two hydroxy groups per molecule include diols such as 1 ,2- ethanediol, 1 ,3-propanediol, 1 ,4-butanediol, 1 ,6-hexanediol, 2,2-dimethyl-1 ,3- propanediol (neopentyl glycol), the 1,2-, 1,3- and 1 ,4-cyclohexanediols and the corresponding cyclohexane dimethanols, diethylene glycol, dipropylene glycol, and diols such as alkoxylated bisphenol A products, e.g. ethoxylated or propoxylated bisphenol A. Suitable polyols having three hydroxy groups per molecule include triols such as trimethylolpropane (1,1 ,1-tris (hydroxymethyl)ethane). Suitable polyols having four or more hydroxy groups per molecule include pentaerythritol (2,2-bis(hydroxymethyl)-1 ,3- propanediol) and sorbitol (1 ,2,3,4,5,6-hexahydroxyhexane). Compounds having two or more groups which readily undergo an ester condensation reaction and have one or more sulphonate groups are dicarboxylic acid monomers having at least one ionised sulphonate group. Examples of such compounds are aromatic dicarboxylic acids having an ionised sulphonate group, for example those of

the formula: wherein M is a cation (preferably sodium, lithium, potassium or ammonium); and each R^c independently is H, a cation or C,-.₄-alkyl (preferably methyl or ethyl). Preferred compounds of the above formula are of formula:

wherein M and R^c are as defined above. Particularly preferred is the mono sodium salt, this material being known as sodio-5-sulphoisophthalic acid (SSIPA).

Other useful compounds which have two or more groups which readily undergo an ester condensation reaction and have one or more sulphonate groups are dihydroxy monomers having at least one sulphonate group, especially those of the formula:

wherein M is as hereinbefore defined above and each R^d independently is alkylene, preferably C^- alkylene. Preferred compounds of the above formula are:

wherein M is as hereinbefore defined. Polyesters bearing ionised carboxy groups can be prepared by various means. For example, if the hydroxyl component of the reactants is stoichiometrically in excess of the acid component, a hydroxyl-terminated polyester can be formed, which may be subsequently converted to a carboxy terminated polyester by wholly or partially reacting the hydroxyl groups with an appropriate reagent (e.g. an acid anhydride or a dicarboxylic acid). Alternatively, terminal carboxy functionality may be directly introduced by employing an appropriate stoichiometric excess of the acid component reactants. In another alternative, chain-pendant carboxy groups may be introduced by using reagents such as dimethylol propionic acid (DMPA) since if appropriate reaction conditions are employed (e.g. polymerisation temperature below 150°C) the hindered carboxy group thereof does not take part to any significant extent in the ester-forming reactions during the polyester synthesis and the DMPA effectively behaves as a simple diol. Chain- pendant and/or terminal carboxy groups could also be introduced by employing a tri- or higher functionality carboxylic acid or anhydride in the polyester synthesis, for example, trimellitic acid or anhydride. Combinations of the above procedures could also be used. It is thus seen that terminal or side-chain carboxy groups or both can be introduced as desired. These can be fully or partially neutralised with an appropriate base to yield ionised carboxy groups. The counter ions used may be as for the ionised sulphonate groups described above (apart from H⁺ since the carboxylic acid groups themselves are normally insufficiently ionised to provide a significant amount of ionised carboxy groups - although F substituents would increase acid strength), with alkali metal ions such as Na⁺, Li⁺ and K⁺ again being particularly preferred, and ammonium and organic amine derived cations less preferred because some have an undesirable odour.

The water-dissipatable polyester may optionally have hydrophilic non-ionic segments, for example within the polyester backbone (i.e. in-chain incorporation) or as chain-pendant or terminal groups. Such groups may act to contribute to the dispersion stability or even water-solubility of the polyester. For example, polyethylene oxide chains may be introduced into the polyester during its synthesis by using as part of the hydroxyl component, ethylene oxide-containing mono, di or higher functional hydroxy compounds, especially polyethlene glycols and alkyl ethers of polyethylene glycols, examples of which include :

R^e-O-(CH₂CH₂O)_n-H, HO-(CH₂CH₂O)_n-H,

_/ CH₂-O-(CH₂CH₂O)_p-H

R^e-C-CH₂-O-(CH₂CH₂O)_p-H ^X CH₂-O-(CH₂CH₂O)_p-H wherein R^e is C.,.₂₀-alkyl, preferably C^-alkyl, more preferably methyl; n is 1 to 500; and p is 1 to 100.

A small segment of a polyethylene oxide chain could be replaced by a propylene oxide or butylene oxide chain in such non-ionic groups, but should still contain ethylene oxide as a major part of the chain.

The amount of ionised sulphonate and/or carboxy groups present in the polyester should be sufficient to provide or contribute to water-dissipatability of the polyester, although it should not be so high as to render the resulting polyester unacceptably water- sensitive. This amount will depend, inter alia, on factors such as the hydrophilicity/hydrophobicity of units provided by other monomers in the polyester synthesis or any surfactants (if used), and also the relative proportions of ionised sulphonate/carboxy groups. With regard to the last mentioned point, ionised sulphonate groups are more effective at providing or contributing to water-dissipatability than ionised carboxy groups and so can be used at considerably lower levels in comparison to ionised carboxy groups.

If the polyester is wholly or predominantly sulphonate stabilised (by which is meant the water dissipatability-providing groups are provided wholly or predominately by ionised sulphonate groups). The ionised sulphonate group content is preferably within the range from 7.5 to 100 milliequivalents (more preferably 10 to 75 milliequivalents and particularly 11 to 56 milliequivalents) per 100 g of polyester. When using SSIPA as the monomer for providing the ionised sulphonate groups, the amount of this monomer used in the polyester synthesis, based on the weight of all the monomers used in the polyester synthesis, will usually be within the range from 2 to 20% by weight (more usually 3 to 15% by weight). The carboxylic acid value (AV) of the polyester which is predominantly sulphonate stabilised, i.e. an AV based on the carboxylic acid groups only (i.e. excluding sulphonate groups) will generally be within the range of from 0 to 100 mgKOH/g, more preferably 0 to 50 mgKOH/g, especially 0 to 25 mgKOH/g, more especially 0 to 10mgKOH/g.

If the polyester is predominantly stabilised by ionised carboxy groups, the carboxylic acid value AV of the polyester is preferably within the range of from 20 to 140 mgKOH/g (more preferably 30 to 100 mgKOH/g).

Usually, the polyester is either predominantly sulphonate-stabilised or predominantly carboxylate stabilised (preferably the former).

If the polyester contains polyethylene oxide chains, the polyethylene oxide chain content should preferably not exceed 25% by weight (and more preferably should not exceed 15% by weight), based on the total weight of the polyester, in order to avoid unacceptable water-sensitivity. Therefore the amount is preferably 0 to 25% by weight (more preferably 0 to 15% by weight) based on the total weight of polyester. Further information about suitable polyesters and their preparation are described in International Patent Publication Number WO98/59007A1 , page 6, line 7 to page 10, line 5, which is included herein by reference thereto.

4.2 THE LIQUID MEDIUM Preferably the liquid medium comprises water, a mixture of water and organic solvent or an organic solvent free from water. Preferred organic solvents are water- miscible organic solvents.

In a preferred embodiment the liquid medium comprises: (a) from 50 to 99 parts, more preferably 70 to 98 parts of water; and (b) from 1 to 40 parts, more preferably 2 to 30 parts of organic solvent, wherein the number of parts of (a) and (b) add up to 100.

Suitable water-miscible organic solvents include C^-alkanoIs, e.g. methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol and isobutanol; amides, e.g. dimethylformamide and dimethylacetamide; ketones and ketone alcohols, e.g. acetone and diacetone alcohol; C₂.₄-ether, e.g. tetrahydrofuran and dioxane; alkylene glycols or thioglycols containing a C₂-C₆ alkylene group, e.g. ethylene glycol, propylene glycol, butylene glycol, pentylene glycol and hexylene glycol; poly(alkylene-glycol)s and thioglycol)s, e.g. diethylene glycol, thiodiglycol, polyethylene glycol and polypropylene glycol; polyols, e.g. glycerol and 1 ,2,6-hexanetriol; and lower alkyl glycol and polyglycol ethers, e.g. 2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy) ethanol,

2-(2-butoxyethoxy)ethanol, 3-butoxypropan-1 -ol, 2-[2-(2-methoxyethoxy)-ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]-ethanol; cyclic esters and cyclic amides, e.g. optionally substituted pyrrolidones; sulpholane; and mixtures containing two or more of the aforementioned water-miscible organic solvents. Preferred water-miscible organic solvents are C.,.₆-alkyl mono ethers of C₂.₆-alkylene glycols and C.,.₆-alkyl mono ethers of poly(C₂.₆-alkylene glycols).

Water-immiscible organic solvents which may also be included in the liquid medium include aromatic hydrocarbons, e.g. toluene, xylene, naphthalene, tetrahydronaphthalene and methyl naphthalene; halogenated aromatic hydrocarbons, e.g. chlorobenzene, fluorobenzene, chloronaphthalene and bromonaphthalene; esters, e.g. butyl acetate, ethyl acetate, methyl benzoate, ethyl benzoate, benzyl benzoate, butyl benzoate, phenylethyl acetate, butyl lactate, benzyl lactate, diethyleneglycol dipropionate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di (2-ethylhexyl) phthalate; alcohols having six or more carbon atoms, e.g. hexanol, octanol, benzyl alcohol, phenyl ethanol, phenoxy ethanol, phenoxy propanol and phenoxy butanol; C₅.₁₄ ethers, e.g. anisole and phenetole; nitrocellulose, cellulose ether, cellulose acetate; low odour petroleum distillates; turpentine; white spirits; naphtha; isopropylbiphenyl; terpene; vegetable oil; mineral oil; essential oil; and natural oil; and mixtures of any two or more thereof. Benzyl alcohol is especially preferred. The number of parts of the water-dissipatable polyester is calculated on a 100% solids basis. For example 50g of a 20% solids polyester is taken as 10g of polyester.

5. THE INK Preferably the ink is yellow, magenta, cyan or black. The ink preferably comprises:

(a) 50 to 99.8, more preferably 60 to 99 parts of liquid medium; and

(b) from 0.01 to 30, more preferably 0.1 to 10, especially 1 to 6 parts in total of colorant; wherein all parts are by weight and the number of parts of (a)+(b) =100.

The ink may of course contain further components in addition to (a) and (b), for example biocides, anti-fungal agents, anti-oxidants, anti-kogation agents, viscosity modifiers, surfactants etc.

The liquid medium is preferably as defined above in relation to the liquid medium of the composition. The liquid medium used in the ink may be the same as the liquid medium used in the composition or it may be different. The ratio of water-miscible organic solvent to water-immiscible organic solvent is preferably 19:1 to 1 :1 , more preferably 8:1 to 1 :1 , especially 5:1 to 1 :1.

5.1 THE COLORANT

The colorant is preferably a dye, a pigment or a mixture thereof. Preferred dyes are disperse dyes and water-soluble dyes containing an anionic or cationic group. When a pigment is used as the colorant it may be free from charge or it may carry an ionic charge. Preferred water-soluble dyes having an anionic group are any of water-soluble acid dyes, direct dyes and reactive dyes listed in the COLOUR INDEX, without any particular limitations, having an anionic group. Dyes not listed in the COLOUR INDEX may also be used. The water-soluble dyes herein referred to also includes of course those having a dependence of solubility on pH. The pigments which may be used in the present invention include ionically modified carbon black pigments, for example carbon black carrying a cationic or anionic group (e.g. as obtainable from Cabot Corporation). Other carbon black pigments may be used, as exemplified by carbon black produced by the furnace process or the channel process. Those having one or more properties selected from a primary particle diameter of from 15 to 40 μm., a specific surface area of from 50 to 300m² /g as measured by the BET method, a DBP oil absorption of from 40 to 150 ml/100 g, a volatile content of from 0.5 to 10% and a pH value of from 2 to 9 are preferred. Commercially available products having such properties are exemplified by No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, and No. 2200B (trade names; all available from Mitsubishi Chemical Industries Limited); RAVEN 1255 (trade name; available from Columbian Carbon Japan Limited); REGAL 400R, REGAL 330R, REGAL 660R, and MOGUL L (trade names; all available from Cabot Corp.); COLOR BLACK FW1 , COLOR BLACK FW18, COLOR BLACK S170, COLOR BLACK S150, PRINTEX 35, and PRINTEX U (trade names; all available from Degussa Japan Co., Ltd.), any of which may preferably be used.

Preferred yellow pigments include C.I. Pigment Yellow 1 , C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 13, C.I. Pigment Yellow 16 and C.l. Pigment Yellow 83. Preferred magenta pigments include C.l. Pigment Red 5, C.l. Pigment Red 7, C.l. Pigment Red 12, C.l. Pigment Red 48 (Ca), C.l. Pigment Red 48 (Mn), C.l. Pigment Red 57 (Ca), C.l. Pigment Red 112 and C.l. Pigment Red 122. Preferred cyan pigments include C.l. Pigment Blue 1 , C.l. Pigment Blue 2, C.l. Pigment Blue 3, C.l. Pigment Blue 15:3, C.l. Pigment Blue 16, C.l. Pigment Blue 22, C.l. Vat Blue 4 and C.l. Vat Blue 6. Examples are by no means limited to these. In addition to the foregoing, it is of course possible to use pigments newly produced for the present invention.

When the colorant comprises a pigment the ink preferably contains a dispersant.

5.2 THE DISPERSANT

The dispersant which may be incorporated in the ink when the pigment is used, preferably has a weight average molecular weight in the range of from 1 ,000 to 30,000, more preferably from 3,000 to 15,000. Such dispersants include block copolymers, random copolymers or graft copolymers comprised of at least two monomers (at least one of which is a hydrophilic monomer) selected from styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of ethylenically unsaturated α, β -carboxylic acids, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, vinyl acetate, vinyl pyrrolidone, acrylamide, and derivatives thereof; or salts of these. Natural resins such as rosin, shellac and starch may also preferably be used. These resins are alkali-soluble resins which are soluble in an aqueous solution in which a base has been dissolved. The amount of dispersant for the pigment is preferably in an amount ranging from 0.1 to 5% by weight based on the total weight of the ink.

In the case of the ink containing the pigment, it is preferable for the whole ink to be adjusted to neutrality or the alkaline side. By doing so, the solubility of the dispersant can be improved to obtain inks having a much better long-term storage stability. Preferably the pH of pigment inks is 7 to 10.

To ensure the pH is in the desired, range a pH adjuster may be used e.g., various organic amines such as diethanolamine and triethanolamine, inorganic alkali agents including alkali metal hydroxides such as sodium hydroxide, lithium hydroxide and potassium hydroxide, and various organic acids and mineral acids. 6. THE SUBSTRATE

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. 5 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 0 (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 composition 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 5 to 110, or in the Examples of US 4,892,779, modified such that a composition is included as an ingredient in the coating compositions described in these Examples.

7. MEDIA

According to a further feature the present invention provides an ink receptive 0 substrate comprising a sheet material coated or impregnated with a water-dissipatable polyester.

The ink receptive substrate may be coated or impregnated with a water-dissipatable polyester by, for example, applying a composition comprising water, the water-dissipatable polyester and optionally a binder to the substrate. Preferably this composition is colourless, 5 weakly coloured or white. For example, the composition may be applied to the substrate by means of an ink jet printer during or, more preferably after the ink is applied to the substrate. The liquid medium used in the composition may be different or the same as the liquid medium in the ink.

The substrate is preferably a paper, plastics material, textile, metal or glass, more o 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 40, more preferably 1 to 30, parts of water-dissipatable polyester;

(b) from 0.01 to 30, more preferably 1 to 10, parts of binder; 5 (c) from 0.01 to 99.97, more preferably 0.1 to 50, parts of 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 binder is preferably a polymeric or polyrηerisable binder, more preferably a water-soluble or water-dissipatable polymeric or polymerisable binder. The substrate preferably carries porous inorganic particles, e.g. alumina (especially boehmite) 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).

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 compound of water- dissipatable polyester is from 99:1 to 1 :99, more preferably from 80:20 to 20:80.

Preferred methods for coating or impregnating the substrate with the composition 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 composition and dried before the ink is applied any suitable drying method may be used, for example hot air or microwave drying.

A still further feature of the invention provides a printed substrate obtained by a process according to a first aspect of the present invention.

The invention will now be illustrated by the following Examples in which all parts and percentages are by weight unless specified otherwise.

Example 1 - Underprint with Polyester

Stage A - Preparation of Water-Dissipatable Polyester ("Polyester 1")

To a glass reactor fitted with distillation column and condenser were charged ingredients A, B, D, E, F, G and 50% of C and 50% of H. The contents were heated with stirring to a reaction temperature of 210°C until the mixture was clear and the acid value was <10 mgKOH/g. At this point the remainder of C and H were charged and the temperature raised to 230°C. The reaction was continued under reduced pressure until an acid value of 9.4 mgKOH/g was obtained. The resin was further characterised by a hydroxyl value = 12.8 mgKOHg, ICI Cone and Plate Viscosity @ 125°C = >500 poises and a Tg (onset) = 18°C. The number average molecular weight as determined by gel permeation chromatography (PS Equivalent) was 1800. The resin was readily dispersed in warm distilled water to give a clear solution having a solids content of 20 % w/w.

Stage B - Preparation of Ink 1

Ink 1 was prepared by dissolving the dye of Formula (1) (0.1 parts) in tetrahydro furan (99.9 parts). The dye of Formula (1) was prepared as described in International Patent Application No. PCT/GB97/02547 (WO98/14523), Example 1.

Formula (1)

Stage C - Preparation and Printing of the Substrate

Polyester 1 (solids content of 20% w/w) was coated onto Champion Datacopy paper using a K-bar (#2) and left to dry for 24 hours. Ink 1 was then coated onto the polyester coated paper also by use of the K-bar.

After drying for 24 hours, the samples were half covered and placed in an HPUV accelerated indoor fadeometer. The samples were exposed for the equivalent of three years based on the standard indoor conditions of 450 lux for 12 hours per day. After fading, the prints were removed and the reflected optical density of the unfaded and faded portions of the sample were measured using an X-Rite™938 spectrodensitometer. The percentage of reflected optical density lost was then calculated using the equation:

%ROD loss = (reflected optical density before exposure - reflected optical density after exposure) x 100 reflected optical density before exposure

A lower value for %ROD loss indicates higher lightfastness. The result is shown in

Table 1.

Comparative Example 1

In comparative Example 1 ink 1 was directly coated onto Champion Datacopy paper using the K-bar without the resin being present. The sample was then dried and faded under the same conditions as above and the %ROD loss measured. The result is also shown in Table 1.

Comparative Example 2

Ink 2 was prepared by dissolving the dye of formula (1) (0.1 parts) and Polyester 1 (20 parts, 20% solids) in 2-pyrrolidone (79.9 parts). Ink 2 was then coated onto Champion Datacopy using the K-bar. The sample was then dried and faded under the same conditions as above and the %ROD loss . The result is also shown in Table 1.

Table 1

As can be seen from Table 1 , the undercoat with polyester 1 resulted in lower fade (and therefore higher light-fastness) than when the polyester was included in the ink or omitted.

Example 2 - Overprint with Polyester

Ink 1 , as used in example 1 , was coated onto Champion Datacopy using the K- bar. After leaving the sample to dry for 24 hours, Polyester 1 ( 20% solids content w/w) of the resin in water was coated onto the sample using the K-bar and left to dry for 24 hours. The lightfastness of this sample was measured as in the way as example 1 , and is shown in Table 2. For comparison the control experiment from example 1 with no resin present is also included in Table 2.

Table 2

Example 3 - Underprint with Polyester Stage A - Preparation of Ink 3

Ink 3 was prepared by dissolving a dye of Formula (2) (0.15 parts) in 2-pyrollidone (99.85 parts).

Formula (2) Stage B

Ink 4 was prepared by dissolving the dye of formula (2) (0.15 parts) and Polyester 1 the resin (20 parts) in 2-pyrrolidone (79.85 parts). The method of Example 1 , stages A and C were then repeated except that in place of Ink 1 there was used Ink 3, and in place of ink 2 there was used ink 4.

The results are shown in Table 3.

Table 3

Example 4 - Overprint with Polyester

The method of Example 2 was repeated except that in place of Ink 1 there was used Ink 5. The results are shown in Table 4. For comparison purposes the comparative examples from Table 3 are also included in Table.

Table 4

Example 5 - Undercoat with Polyester 1 Stage A - Preparation of Ink 5

Ink 5 was prepared comprising a dye of Formula (3) (0.35 parts) and 2-pyrollidone (99.65 parts).

Formula (3)

Stage B - Underprint with Polyester Comparative ink 6 was prepared by dissolving the dye of formula (2) (0.35 parts) and the resin (20 parts) in 2-pyrrolidone (79.65 parts). The method of Example 1 , stages A and C was repeated except that in place of Ink 1 there was used Ink 5, and in place of ink 2 there was used ink 6. The results are shown in Table 5.

Table 5

Example 6

Ink 5 as used in example 5 was coated onto Champion Datacopy using the K-bar. After leaving the sample to dry for 24 hours, Polyester 1 (20% solids w/w in water) was coated onto the sample using the K-bar and left to dry for 24 hours. The lightfastness of this sample was measured as in the way as Example 1 , and is shown in Table 6. For comparison, the control experiment from example 5 with no resin present is also included in Table 6, together with the comparative examples from Table 5.

The method of Example 2 was repeated except that in place of Ink 1 there was used Ink 5. The results are shown in Table 6. Table 6

Claims

1. A process for printing an image on a substrate comprising applying thereto an ink containing a colorant by means of an ink jet printer such that the colorant, when situated on the substrate, is in contact with a water-dissipatable polyester which has been applied to the substrate other than as a component of the ink.

2. A process according to claim 1 wherein the substrate is a substrate which has been coated or impregnated with the water-dissipatable polyester.

3. A process according to any one of the preceding claims which further comprises applying by means of an ink jet printer a colourless or weakly coloured composition comprising the water-dissipatable polyester and a liquid medium to the area of the substrate which carries the image or will carry the image before, during or after application of the ink to the substrate.

4. A process according to claim 3 wherein the ink and the composition are applied to the substrate through different nozzles of the same inkjet printer.

5. A process according to claim 3 or 4 wherein the colourless or weakly coloured composition comprises:

(a) from 0.2 to 20 parts of water-dissipatable polyester; and

(b) from 80 to 99.8 parts of liquid medium; wherein all parts are by weight and the number of parts of (a) + (b) add up to 100.

6. A process according to any one of the preceding claims wherein the ink jet printer applies the ink to the substrate in the form of droplets which are ejected through a small orifice onto the substrate.

7. An ink receptive substrate comprising a sheet material coated or impregnated with a water-dissipatable polyester.

8. An ink receptive substrate according to claim 7 obtained by applying a composition comprising water-dissipatable polyester and a binder to the .sheet material.

9. An ink receptive substrate according to claim 7 obtained by applying a composition comprising water, the water-dissipatable polyester and optionally a binder to the sheet material.

- 10. An ink receptive substrate according to claim 8 or 9 wherein said composition is colourless, weakly-coloured or white.

11. An ink receptive substrate according to claim 8 or 9 wherein the composition comprises:

(a) from 0.01 to 40 parts of water-dissipatable polyester;

(b) from 0.01 to 30 parts of binder;

(c) from 0.01 to 99.97 parts of 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.

12. A printed substrate obtained by a process according to any one of claims 1 to 6.