WO1999050361A1

WO1999050361A1 - Coloured polyurethanes

Info

Publication number: WO1999050361A1
Application number: PCT/GB1999/000783
Authority: WO
Inventors: Peter Gregory; Mark Robert James; David Alan Pears; John Christopher Padget
Original assignee: Avecia Limited
Priority date: 1998-03-31
Filing date: 1999-03-25
Publication date: 1999-10-07
Also published as: GB9806791D0; AU3154899A

Abstract

The invention relates to polyurethanes, inks comprising polyurethanes and their use in ink-jet printing where the polyurethane comprises a coloured water-dissipatable polyurethane obtainable by chain-extension of a polyurethane prepolymer with a colorant.

Description

1

COLOURED POLYURETHANES

This invention relates to polyurethanes, to inks comprising polyurethanes and to their use in ink jet printing.

Ink jet printing methods involve printing an image onto a substrate by ejecting ink droplets through a fine nozzle onto the substrate without bringing the fine nozzle into contact with the substrate.

There are many demanding performance requirements for colorants and inks used in ink jet printing. For example they desirably provide sharp, non-feathered images having good water-fastness, light-fastness and optical density. The inks are often required to dry quickly when applied to a substrate to prevent smudging, but they should not form a crust which would block the tip of the nozzle. The inks should also be stable to storage over time without decomposing or forming a precipitate which could also block the fine nozzle. Thermal and piezoelectric ink jet printers are widely used, thus there is a need for inks, suitable for use in both types of printers, having high colour strength and giving images having a high light fastness and water-fastness when printed on a typical substrate, especially plain paper.

EP 0769 509 describes a high molecular weight chain extended polyurethane, formed from a coloured isocyanate-terminated polyurethane, prepolymer for use in ink jet printers with piezo heads. However this composition is not ideal for use in ink jet printers with thermal heads because the use of heat can result in nozzle blockage and other operability problems.

According to a first aspect of the present invention there is provided a coloured, water-dissipatable polyurethane obtainable from a process comprising the steps: i) reacting a mixture comprising components (a) and (b) wherein component (a) is at least one organic polyisocyanate and component (b) is at least one isocyanate-reactive compound providing water dispersing groups; and ii) chain extending the product of step i) with component (c) wherein component (c) comprises a colorant having at least two functional groups capable of reacting with component (a) or (b). Preferably the coloured water-dissipatable polyurethane has a weight average molecular weight (Mw) less than 50,000 because this molecular weight leads to an improved performance of inks containing the polyurethane, especially for use in thermal ink jet printers. The Mw of the polyurethane is preferably less than 40,000, more preferably less than 30,000. The Mw of the polyurethane is preferably greater than 700. The Mw may be measured by gel permeation chromatography. The gel permeation chromatography method used for determining Mw preferably comprises applying the polyurethane to a chromatography column packed with cross- inked polystyrene/divinyl benzene, eluting the column with tetrahydrofuran at a temperature of 40°C and assessing the Mw of the polyurethane compared to a number of a polystyrene standards of a known Mw Suitable chromatography columns packed with cross-linked poiystyrene/divinyl benzene are commercially available from Polymer Laboratories

As an alternative to the gpc method for determining Mw one may use other methods, for example multi-angle light scattering

Component (a) may be any organic polyisocyanate known in the art, preferably having two isocyanate groups, and include aliphatic, cycloaliphatic, aromatic or araliphatic isocyanate Examples of suitable organic polyisocyanates include ethylene dnsocyanate, 1 ,6-hexamethyiene dnsocyanate, isophorone dnsocyanate, tetramethylxylene dnsocyanate, 1 ,4-phenylene dnsocyanate, 2,4-toluene dnsocyanate, 2,6-toluene dnsocyanate, 4,4'-dιphenyl-methane dnsocyanate and its hydrogenated derivative, 2,4'-dιphenylmethane dnsocyanate and its hydrogenated derivative, and 1,5- naphthyiene dnsocyanate Mixtures of the polyisocyanates can be used, particularly isomenc mixtures of the toluene dnsocyanates or isomeπc mixtures of the diphenylmethane dnsocyanates (or their hydrogenated derivatives), and also organic polyisocyanates which have been modified by the introduction of urethane, allophanate, urea, biuret, carbodnmide, uretonimme or isocyanurate residues .

Preferred organic polyisocyanates include cycloaliphatic polyisocyanates, especially isophorone dnsocyanate, and aliphatic isocyanates, especially 1 ,6-hexamethylene dnsocyanate or hydrogenated 4,4-dιphenyl methyl dnsocyanate A small quantity of trnsocyanates may be included as part of component (a) but this amount preferably does not exceed 5% by weight relative to the total weight of component (a) In a preferred embodiment component (a) consists of a mixture of dnsocyanate and from 0 to 5% of trnsocyanate by weight relative to the dnsocyanate Component (b) providing water-dispersing groups preferably has at least one, and preferably has two, isocyanate-reactive groups Preferred isocyanate-reactive groups are selected from -OH, -NH₂, -NH- and -SH Isocyanate-reactive compounds having three isocyanate-reactive groups may be present as part of component (b), preferably in low levels not exceeding 5% by weight relative to the total weight of component (b) These isocyanate-reactive groups are capable of reacting with an isocyanate (-NCO) group in component (a) or any component (c)

The water-dispersing groups are preferably present in the polyurethane as in- chain, pendant or terminal groups Further water-dispersing groups may be introduced into the polyurethane by means of a capping reagent having one isocyanate or isocyanate-reactive group and a water-dispersing group

The nature and level of water-dispersing groups in the polyurethane influences whether a solution, dispersion, emulsion or suspension is formed on dissipation of the polyurethane

The water-dispersing group content of the polyurethane may vary within wide limits but is usually selected to be sufficient to ensure the polyurethane forms stable ink-jet printing inks in water and aqueous media The polyurethane is preferably soluble in water, although a minor amount of the polyurethane may be insoluble in water and exist as dispersed particles when mixed with aqueous media or water Preferably the proportion of water- insoluble polyurethane is less than 50 %, more preferably less than 40% and especially less than 30% by weight relative to the total weight of the polyurethane

The water-dispersing groups may be ionic, non-ionic or a mixture of ionic and non-ionic water-dispersing groups Preferred ionic water-dispersing groups include cationic quaternary ammonium groups and anionic sulphonic acid groups, phosphonic acid groups and carboxy c acid groups The ionic water-dispersing groups may be incorporated into the polyurethane in the form of a low molecular weight polyol or polyamine bearing the appropriate ionic water-dispersing groups Preferred isocyanate-reactive compounds providing water- dispersing groups are diols having one or more carboxyhc acid groups, or sulphonic acid groups, where examples include bιs(2-hydroxyethyl)-5-sodιosulphoιsophthalate , and dihydroxy alkanoic acids, especially 2,2-dιmethylol propionic acid and/or mixtures thereof

The carboxyhc and sulphonic acid groups may be subsequently fully or partially neutralised with a base containing a cationic charge to give a salt If the carboxyhc or sulphonic acid groups are used in combination with a non-ionic water-dispersing group, neutralisation may not be required The conversion of any free acid groups into the corresponding salt may be effected during the preparation of the polyurethane and/or during the preparation of an ink from the polyurethane

Preferably the base used to neutralise any acid dispersing groups is ammonia, an amine or an inorganic base Suitable amines are tertiary amines, for example tπethylamine or tπethanolamine Suitable inorganic bases include alkaline hydroxides and carbonates, for example lithium hydroxide, sodium hydroxide, or potassium hydroxide A quaternary ammonium hydroxide, for example N⁺(CH₃)₄OH^", can also be used Generally a base is used which gives the required counter ion desired for the ink which is prepared from the polyurethane For example, suitable counter ions include Lι⁺, Na⁺, K⁺, NH₄ ⁺, Cs⁺ and substituted ammonium salts, including tπbutylammonium, imidazohum, tetraethyl ammonium, tetrabutyl ammonium, tetrabutyl phosphonium and trimethyl sulphonium salts NH₄ ⁺ is especially preferred

Prefered non-ionic water-dispersing groups are in-chain, terminal and pendant polyoxyalkylene groups, more preferably polyoxypropylene and polyoxyethylene groups Examples include groups of the formula RO(CH₂CH₂0)_nH, RO(CH₂CH₂0)_n(CH₂CH(CH₃) 0)_yCH₂CH(CH₃)NH₂, or

H₂NCH(CH₃)CH₂(CH(CH₃)CH₂0)_y(CH₂CH₂0)_n(CH₂CH(CH₃)0)_yCH₂CH(CH₃)NR¹R¹ , wherein n = 1 to 100, R is H or CH₃, each R¹ independently is H or a substituted or unsubstituted C, ₁₀ alkyl group (especially -CH₂CH₂-OH) and y = 2 to 15 Optionally the mixture comprising components in step i) further comprises an isocyanate-reactive compound which is free from water-dispersing groups Preferably such compounds are organic polyols or polyamines having a molecular weight up to 3000, more preferably up to 2000, especially from 400 to 2000. Preferred organic polyols include diols which are free from water-dispersing groups and mixtures thereof. Such diols may be members of any of the chemical classes of polymeric diols used or proposed to be used in polyurethane formulations. In particular, the diols may be polyesters, polyesteramides, polyethers (other than ones providing polyethyleneoxide and/or polypropyleneoxide groups), polythioethers, polycarbonates, polyacetals, polyolefins or polysiloxanes.

Further examples of optional diols which are free from water-dispersing groups include organic diols and polyols having a molecular weight below 400. Examples of such diols and polyols include ethylene glycol, diethylene giycol, tetraethylene glycol, bis(hydroxyethyl) terephthalate, cyclohexane dimethanol, furan dimethanol, polyethylene glycol and polypropylene glycol.

The function of component (c) is to colour and to chain extend the product of step i). Component (c) preferably comprises a chromophoric group and at least two functional groups capable of reacting with the terminal groups on the polyurethane resulting from step i). Preferably the colorant has two of said functional groups. Colorants having three of said functional groups may be present in low levels, preferably not exceeding 5% by weight relative to the weight of colorant having two of said functional groups.

The functional groups may be attached directly to the chromophoric group or may be attached through a linker group. An example of a suitable linker group is an alkylenediamine attached to a chromophoric group via a triazine ring.

For example, if the product of step i) has terminal isocyanate groups then component (c) may be selected to have at least two isocyanate-reactive groups, if the product of step i) has terminal isocyanate-reactive groups then component (c) may be selected to have at least two isocyanate groups, and if the product of step i) has terminal isocyanate groups and terminal isocyanate-reactive groups then component (c) may be selected to be a mixture of colorants each of which has either isocyanate- reactive groups or isocyanate groups or component (c) will be selected to have at least one isocyanate group and at least one isocyanate-reactive group.

The chromophoric group preferably comprises an azo, anthraquinone, pyrroline, phthalocyanine, polymethine, aryl-carbonium, triphenodioxazine, diarylmethane, t arylmethane, anthraquinone, phthalocyanine, methine, polymethine, indoaniiine, indophenol, stilbene, squarilium, aminoketone, xanthene, fluorone, acridene, quinolene, thiazole, azine, induline, nigrosine, oxazine, thiazine, indigoid quinonioid, quinac done, lactone, pyrroline, benzodifuranone, or indolene group or a combination of such groups. More preferred chromophoric groups are azo groups (especially monoazo, disazo and trisazo), and phthalocyanine groups. Especially preferred monoazo groups comprise two aryl groups linked by an azo group where optionally one or both aryl groups are heteroaryl groups. 5

Preferably the colorant is a dye comprising a chromophoric group and functional group(s) capable of reacting with component (a) and/or (b). The colorant preferably comprises or consists from 1 to 10, more preferably 1 to 5, especially 1 , 2 or 3 of said dyes. Preferably the dye is soluble in organic solvents and/or in water. The dye is preferably soluble in water. Water solubility of the dye may be achieved by the presence of acidic groups in the dye. Preferred acidic groups are phosphonic, carboxyhc or sulphonic acids, and combinations and salts thereof.

The amount of component (c) used in step ii) normally depends on the ratios of components (a) and (b) and the amount of chain extension and coloration desired. Component (c) preferably comprises at least 3% by weight, more preferably at least 5% by weight and preferably less than 40% by weight of total amount the components (a),

(b) and (c).

Component (c) in addition to the colorant may include colourless compounds having one or more functional groups capable of reacting with component (a) or (b). Examples include low molecular weight polyols, polyamines, diols, dihydrazines, dihydrazides, disemicarbazides, dialkoxyamines, and linear or cyclic and diamines.

Preferably 10 to 100%, more preferably 30 to 100% and most preferably 50 to 100% by weight of component (c) comprises a colorant having at least two functional groups capable of reacting with component (a) or (b). Terminating compounds may be used to cap off any excess isocyanate or isocyanate-reactive end groups in the polyurethane resulting from step ii), by the addition of compounds having one isocyanate or isocyanate-reactive group. The terminating compounds may also bear dispersing groups as hereinbefore described.

Terminating compounds having one isocyanate-reactive group include for example monoalcohols, monohydrazides, mono hydrazines, monoamines and monothiols, hydroxy functional amines, especially isopropanol. Compounds having one isocyanate group include for example alkyl monoiscocyanates.

The coloured water-dissipatable polyurethane is preferably obtained by chain extending the product of step i) with component (c) at a temperature of from 10°C to 130°C, more preferably 15°C to 100°C.

The reaction in step i) is usually continued until the reaction between components (a) and (b) is substantially complete.

Preferably step i) is performed in an organic solvent or as a melt of components (a) and (b). Preferably step i) is performed under anhydrous conditions. The relative amounts of components (a) and (b) are preferably selected such that the mole ratio of isocyanate groups to isocyanate-reactive groups is greater than 1:1 . The relative amounts of components (a) and (b) is preferably selected such that the mole ratio of isocyanate groups to isocyanate-reactive groups from 1.1 to 3:1 , preferably from 1.2:1 to 2:1. Optionally an organic solvent is included in step i) to lower its viscosity.

Preferably water-miscible solvents are used, for example N-methylpyrrolidone, dimethyl sulphoxide, dialkyl ether of a glycol acetate methyl ethyl ketone or a combination thereof.

Step ii) is preferably performed by reacting the product of step i) with component (c). Step ii) is preferably performed in a solvent, for example in water, in water-miscible organic solvent or in a water-immiscible organic solvent or a mixture thereof. The product of step ii) may then be dissipated in water.

For example the product of step i) may be added to a solution of component (c) or a solution of component (c) may be added to the product of step i).

If desired a catalyst may be used in step i) and/or step ii) to assist polyurethane formation. Suitable catalysts include butyl tin dilaurate, stannous octoate and tertiary amines as known in the art .

The polyurethane may contain further linkages in addition to urethane linkages, for example urea, amide, thiourea or thiourethane linkages.

Preferably the polyurethane (and any resultant inks) is yellow, magenta, cyan or black.

Preferably the polyurethane according to the first aspect of the present vention has been obtained by the stated process.

The polyurethane may be purified if desired in the usual way for colorants used in ink jet printing inks. For example a mixture of the polyurethane and water may be purified by ion-exchange, filtration, reverse osmosis, dialysis, ultra-filtration or a combination thereof. In this way one may remove co-solvents used for the polymerisation, low molecular weight salts, impurities and free monomers.

In a second aspect of the present invention there is provided an ink comprising a polyurethane according to the first aspect of the present invention and a liquid medium. A preferred ink comprises:

(a) from 0.25 to 30 parts of a coloured water-dissipatable polyurethane according to the first aspect of the present invention; and

(b) up to 99.75 parts of a liquid medium; wherein all parts are by weight and the number of parts of (a)+(b)=100. The number of parts of component (a) is preferably from 0.5 to 28, more preferably from 2 to 25, and especially from 2.5 to 20 parts.

The inks according to the second aspect of the invention may be prepared by mixing the coloured water-dissipatable polyurethane with a liquid medium. Suitable techniques are well known in the art, for example agitation, ultrasonication or stirring of the mixture. The mixture of coloured water-dissipatable polyurethane and liquid medium may be in the form of a dispersion, emulsification, suspension, solution or mixture thereof.

Preferably the coloured water-dissipatable polyurethane is mixed with a first liquid medium, followed by mixing the resultant mixture with a second liquid medium. The liquid medium preferably comprises water, a mixture of water and an organic solvent and an organic solvent free from water. For example the coloured water- 7

dissipatable polyurethane may be added to water followed by the addition of one or more organic solvents. Preferably the first liquid medium is an organic solvent and the second liquid medium is water or a mixture comprising water and one or more organic solvents. 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 60:40.

It is preferred that the organic solvent present in the mixture of water and organic solvent is a water-miscible organic solvent or a mixture of such solvents. Preferred water- miscible organic solvents include C^-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-C₁.₄-alkyl ethers of diols, preferably mono-C^-alkyl ethers of diols having 2 to 12 carbon atoms, especially 2-methoxyethanol, 2-(2-methoxyethoxy)ethanoi, 2-(2-ethoxyethoxy)-ethanol, 2-[2-(2-methoxyethoxy)ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)- ethoxyj-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 liquid medium comprises water and 2 or more, especially from 2 to 8, water-soluble organic solvents.

Especially preferred water-soluble organic solvents are cyclic amides, especially 2- pyrrolidone, N-methyl-pyrrolidone and N-ethyl-pyrroiidone; diols, especially 1 ,5-pentane diol, ethyleneglycol, thiodiglycol, diethyleneglycol and triethyleneglycol; and mono- C_1-4- alkyl and C^-alkyl ethers of diols, more preferably mono- C_1-4-alkyl ethers of diols having 2 to 12 carbon atoms, especially 2-methoxy-2-ethoxy-2-ethoxyethanol.

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. 8

When the liquid medium comprises a water-immiscible organic solvent, preferably a polar solvent is included because this enhances solubility of the polyurethane in the liquid medium. Examples of polar solvents include C^-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) and or an alcohol (especially a C_1-4-alkanol, more especially ethanol or propanol).

The organic solvent free from water may be a single organic solvent or a mixture of two or more organic solvents. It is preferred that when the 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 ink.

Ink 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.

A preferred liquid medium comprises:

(a) from 75 to 95 parts water; and

(b) from 25 to 5 parts in total of one or more solvents selected from diethylene glycol, 2-pyrrolidone, thiodiglycol, N-methylpyrrolidone, cyclohexanol, caprolactone, caprolactam and pentane-1 ,5-diol; wherein the parts are by weight and the sum of the parts (a) and (b) = 100.

The ink may also contain a surfactant. This helps to dissipate the polyurethane in addition to the dissipation caused by water-dispersing groups provided by component ii) of the polyurethane. Optionally the ink may also contain further ingredients conventionally used in ink jet printing inks, for example conductivity agents, defoamers, anti-oxidants, corrosion inhibitors, bacteriocides and viscosity modifiers.

The ink preferably has a pH of from 3 to 11 , more preferably of from 4 to 10. Such a pH may be obtained by the addition of a acid base, or a pH buffer. Where a base is used this is preferably the same base as was used to neutralise the anionic dispersing group during the preparation of the coloured water-dissipatable polyurethane.

The viscosity of the ink is preferably less than 20cp, more preferably less than 10cp, at 20°C.

Preferably the ink has been filtered through a filter having a mean pore size below 10 μm, preferably below 5μm more preferably below 2μm especially below 0.45 μm. In this way particulate matter is removed which could otherwise block the fine nozzles in an ink jet printer.

The inks of the second aspect of the present invention have the advantage that they are suitable not only for the use of piezoelectric ink jet printers but also for the use of thermal and continuous ink jet printers. Inks of the second aspect of the present invention form discrete droplets on the substrate with little tendency for diffusing. Consequently sharp images with excellent print quality and little if any bleed between colours printed side by side can be obtained. Furthermore the inks show good storage stability, wet and light fastness and fastness to both acidic and alkaline highlighter pens.

A further aspect of the invention provides a process for printing an image on a substrate comprising applying thereto an ink containing a polyurethane of the present invention by means of an ink jet printer.

The ink used in this process is preferably as defined in the second aspect of the present invention.

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

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

Preferred papers are plain, coated or treated papers which may have an acid, alkaline or neutral character. Most preferably the substrate is a plain or coated paper.

According to a further feature of the invention there is provided an ink jet printer cartridge containing an ink as hereinbefore defined.

The invention will now be described by example only. All parts and percentages are by weight unless specified otherwise. In the examples, compounds referred to by reference to Cl numbers are the dyestuffs identified by these numbers in the Colour Index International, 3^rd Edition, 3^rd Revision.

Dyes

A). Dye 1 was prepared from Cl Reactive Red 11 as follows:

.NH,

Dye 1

Ethylene diamine (60 parts) was dissolved in distilled water (500 parts) and the pH was adjusted to 8.0 by the addition of concentrated hydrochloric acid. A prefiltered solution of

Cl Reactive Red 11 (120 parts) in distilled water (1500 parts) was then added dropwise over 1 hour while maintaining the temperature at 25°C and the pH at 8.0. The mixture was 10

heated at 50°C for 2 hours and at 70°C for 1.5 hours while maintaining the pH at 8.0. The Dye 1 was precipitated from the cooled reaction mixture by the addition of 20%w/w salt and filtered off. The crude product was redissolved in distilled water (3000 parts), filtered through a cascade of filters (glass microfibre GF/A, GF/F and membrane) to 0.45 micron and then desalinated by reverse osmosis using a 500 MW cut off membrane and evaporated to dryness.

B). Dye 2 was prepared as described in European patent application EP 0579123,

Example 1 , stages a, b and c, incorporated herein by reference.

H,N

Dye 2

Examples 1 , 2, 3 and 4: Coloured, water-dissipatable polyurethanes were prepared using the method described in steps i) and ii) below and the components described below in Table 1.

Step i): Preparation of a polyurethane prepolymer

Components 1, 2, 3, and 4 were charged to a stirred reaction vessel under a nitrogen atmosphere, heated to 90°C and then component 5 was added. The reaction exothermed by about 3°C and was then maintained at 90-95°C for 3 hours. After 3 hours the isocyanate (-NCO) content of the resultant polyurethane prepolymer was measured. Step ii): Chain extension with a colorant The product from step i) (15g) at 90°C was mixed with component 6, 7 and 8 at

30°C. During the mixing of the product of step i) with the components 6, 7 and 8 the temperature of the water rose to about 35°C. At approximately 10 minutes after complete addition of the prepolymer solution component 9 (a terminating compound) either ethanolamine or JEFFAMINE M1000 (a colourless terminating compound polyoxyethylene mono amine with a Mw of approximately 1000 available from Huntsman Corporation, Houston, Texas) was added dropwise to the aqueous mixture. The resultant mixture was stirred for a further one hour and cooled to room temperature before being filtered through a 50μm cloth filter.

The resultant coloured polyurethanes were found to have a solids content, pH, Mn and Mw as shown in Table 1. 11

Table 1

Number Component Example (Weight (g))

Ex 1 Ex 2 Ex 3 Ex 4

1 Isophorone diisocyanate 49.2 49.2 36.9 49.2 2 polypropylene glycol of molecular 35.8 35.8 26.8 35.8 weight 1000

3 dimethylol propionic acid 15.0 15.0 11.25 15.0 4 N-methylpyrrolidone (solvent) 25.0 25.0 18.75 25.0 5 dibutyl tin dilaurate (catalyst) 0.1 0.1 0.08 0.1

6 Dye 1 5.0 5.0 10.1 or Dye 2 10 isocyanate content 4.8% 4.9% 4.8% 4.9%

7 Distilled water 50.3 50.3 101.9 185 pH adjusted to 8.7 with 25% aqueous ammonia (weight (g) 1.2 1.2 3.2 3.9

8 Distilled water 70.1 52.0 - -

9 Jeffamine M1000 15.9g 13.8g 26.3 or Ethanolamine 1.46

solids content 25.5% 25.1 % 26.5% 27.9% pH 7.0 6.8 7.0 6.75

Mw (weight average molecular N/M N/M 8464 7750 weight)

Mn (number average molecular N/M N/M 2695 2152

weight)

N/M = not measured Preparation of inks

Inks containing the number of parts of colorant (i.e. the coloured polyurethanes from Examples 1 , 2, 3 and 4) and control inks containing the number of parts of colorant (Dye 1 or Dye 2) as specified in Table 2 below were prepared in a stock solution of water (90 parts) and N-methylpyrrolidone (10 parts) with the addition of concentrated ammonia to give a pH of 9-10. The inks were then filtered through a 0.45 micron membrane filter and a series of vertical and horizontal bars were printed onto Conqueror High White Wove plain paper 100g/m² from Arjo Wiggins Limited using a Hewlett Packard 560 thermal ink jet printer to give test prints. The properties of the resultant prints are shown in Table 2 below. 12

Table 2

Colorant Amount of a = colour b = colour Optical Wet fastness colorant parts co-ordinates co-ordinates density (Run down (OD) / 1 hour)

Control: 2.5 +51.3 -2.1 1.29 3 Dye 1^* control: 2.5 +16.8 -41.3 1.42 3 Dye 2*

Example 1 15 +52.6 -13.7 0.76 7

Example 2 2.5 +55.1 -17.5 0.74 7

Example 2 5 +60.0 -15.8 0.92 5-6

Example 2 10 +56.3 -14.6 1.01 4

Example 3 10 +48.7 -13.1 1.05 6

Example 3 15 +47.2 -13.3 1.05 5

Example 4 15 +0.5 -23.3 0.60 7-8

* = as free dye (i.e. not incorporated into a polyurethane as a chain extender).

Highlighter test: The test prints prepared above were tested for smear resistance to highlighter pens. Yellow highlighter pens (acid and alkaline) were used to draw a horizontal line across the series of printed vertical bars. The amount of ink smear on the white paper between the vertical bars was assessed visually. Prints prepared from the inks containing the water-dissipatable coloured polyurethane prepared in Examples 1 to 4 were fast to both acid and alkaline highlighter pens. Prints prepared from the inks containing the Dye 1 or Dye 2 (i.e. as free dye) showed some smearing.

Wet Fastness

Wet fastness is determined as follows; 0.5 cm³ of water is run down the test prints prepared above one hour after printing. The scale is from 1 to 10 with 1 not being fixed at all and 10 being completely fixed i.e. producing no stain on the white paper.

Colour coordinates, lightness and optical denisty

Colour coordinates, lighness and the optical density were measured on the test prints prepared above using an X-rite 938 spectrophotometer.

The optical density is a measure of colour strength on a logarithmic scale. The colour coordinates define the brightness and colour on a colour scale, where

'a' is a measure of redness (+a) or greenness (-a) and 'b' is a measure of yellowness

(+b) or blueness (-b). The coordinates 'a' and 'b' approach zero for neutral colours

(white, greys and blacks). The higher the values 'a' and 'b' are, the more saturated a colour is. Inks:

Further inks may be prepared having the formulations described in Table 3 and

Table 4 below wherein the following abbreviations are used. Water is included in each 13

formulation to make the total number of parts up to 100. These inks may be applied to plain or coated papers using an ink jet printer.

FRU fructose

PU* Identifies which of the coloured polyurethanes as prepared in examples 3, 4, 5 or 6 may be used. The number of parts by weight of PU is shown in brackets.

BZ Benzyl alcohol

DEG Diethylene glycol

DMB Diethyleneglycol monobutyl ether

ACE Acetone

IPA Isopropyl alcohol

MEOH Methanol

2P 2-Pyrollidone

MIBK Methylisobutyl ketone

SUR Surfynol 465 (a surfactant)

PHO K₂PO₄

TEN triethanolamine

NMP N-methylpyrollidone

TDG Thiodiglycol

CAP Caprolactam

BUT Butylcellosolve

GLY Glycerol

Table 3

PU^* BZ DEG ACE NaOH (NH₄)₂SO₄ IPA MEOH 2P MIBK GLY NMP BUT o

(parts)

1(10) 5 6 4 1 2 10

1(10) 3 0.2 2 15 9 15

2(6) 2 0.5 3 2

2(12) 8 9 0.4 9 1 1

3(5) 3 3 5 4 3 2 2

4(15) 15 0.3 10 4 4

4(5) 19 2 15 10 2

4(18) 4 4 4

3(4) 5 2 10 0.1 0.1 5 5 6

3(10) 5 5 4

2(14) 7 4 2 10 3 5 5

2(12) 5 0.2 2 2

2(5) 2 8 3 10 6 1 3

1(4) 10 2 7 0.3 13 10

1(7) 5 1 0.1 6 14 2 1

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Claims

16CLAIMS

1. A coloured, water-dissipatable polyurethane obtainable from a process comprising the steps: i) reacting a mixture comprising components (a) and (b) wherein component (a) is at least one organic polyisocyanate; and component (b) is at least one isocyanate-reactive compound providing water-dispersing groups; and ii) chain extending the product of step i) with component (c) wherein component (c) is a colorant having at least two functional groups capable of reacting with components (a) and/or (b).

2. A polyurethane according to claim 1 wherein step ii) is performed in water.

3. A polyurethane according to claim 1 or 2 wherein step ii) is performed at a temperature of 10┬░C to 130┬░C.

4. A polyurethane according to claim 1 or 3 wherein step ii) is performed in organic solvent.

5. A polyurethane according to any one of the preceding claims which is soluble in water.

6. A polyurethane according to any one of the preceding claims having a Mw less than 50,000.

7. An ink comprising a polyurethane according to any one of claims 1 to 6 and a liquid medium.

8. An ink according to claim 7 having a viscosity less than 20cp at 20┬░C.

9. An ink according to claim 7 or 8 which has been filtered through a filter having a mean pore size below 10╬╝M.

10. An ink according to any one of claims 7 to 9 which is yellow, magenta, cyan or black.

11. A process for printing an image on a substrate comprising applying thereto an ink containing a polyurethane according to any one of claims 1 to 6, by means of an ink jet printer. 17

12. An ink jet printer cartridge containing an ink according to any one of claims 7 to 10.

13. A coloured, water-dissipatable polyurethane substantially as hereinbefore described and as exemplified in examples 1 to 4.

14. An ink substantially as hereinbefore described and as exemplified in Table 2, 3 or 4.