A dispersant comprising a block copolymer

Abstract

A dispersant The present invention relates to a dispersant comprising a block copolymer, the block copolymer comprising: (i) a first block comprising an inert bio-based polymer, and (ii) a second block comprising an amine-based polymer, and a dispersant comprising a block copolymer, the block copolymer comprising: (i) a sterically stabilizing polymer block; and (ii) a modified poly(alk)ylene imine block, wherein the modification comprises functionality capable of crosslinking and printing ink compositions comprising said dispersants.

Description

[0001] A dispersant

[0002] FIELD

[0003]

[0001] The present invention relates to a dispersant comprising a block copolymer, the block copolymer comprising: (i) a first block comprising an inert bio-based polymer, and (ii) a second block comprising an amine-based polymer, a dispersant comprising a block copolymer, the block copolymer comprising: (i) a sterically stabilizing polymer block; and (ii) a modified poly(alk)ylene imine block wherein the modification comprises functionality capable of crosslinking and printing ink compositions comprising said dispersants.

[0004] BACKGROUND

[0005]

[0002] Pigments used in printing inks and especially inkjet inks need to be homogeneously dispersed throughout the ink. Often it is necessary to use a dispersant to stabilise pigment particles to prevent the pigment particles from agglomerating and ensure consistent ink flow and print quality. Particularly in inkjet printing, the selection of an appropriate dispersant is key to optimising print quality and preventing clogging of the nozzle. Dispersants with improved stabilisation and with improved environmental properties are desirable.

[0006] SUMMARY OF THE INVENTION

[0007]

[0003] According to a first aspect of the invention there is provided a dispersant comprising a block copolymer, the block copolymer comprising: a first block comprising an inert bio-based polymer, and a second block comprising an amine-based polymer.

[0008]

[0004] Advantageously, the second block comprising an amine-based polymer is poorly soluble and prefers to adsorb onto pigment surfaces rather than be solvated in a dispersion medium. The inert bio-based polymer, being highly soluble, preferentially remains solvated in the dispersion medium and provides steric stabilisation by physically blocking pigment particles from approaching one another.

[0009]

[0005] A “block copolymer” as referred to herein, refers to a polymer consisting of two or more distinct blocks of homopolymer. A “homopolymer” as referred to herein refers to a large molecule comprising multiple repeating units of monomers, suitably comprising at least 10 repeating units of monomers.

[0010]

[0006] The term “inert bio-based polymer” as used herein refers to a polymer which does not interact with a pigment surface and instead provides steric stabilization. The term “bio-based polymer” as used herein refers to polymers obtained from biomass, such as generated from renewable resources (for example algae, bacteria, microorganisms, plants, etc.). The bio-based polymers may be synthesized directly through biosynthesis.

[0011]

[0007] For example, the inert bio-based polymer may be a carbohydrate, such as a polysaccharide.

[0008] Preferably the inert bio-based polymer comprises cellulose and / or polylactic acid, or derivatives thereof. The cellulose may comprise a cellulose ester. Preferably, the cellulose ester is peresterified. The cellulose may be acetylated, propionylated, butyrylated, or a mixed ester of a combination of these in any ratio. Preferably the cellulose ester is a peresterified mixed ester of acetic acid and butyric acid, i.e. the cellulose ester is a cellulose acetate butyrate. Preferably, the cellulose ester comprises more butyryl groups than acetyl groups.

[0012]

[0009] The molar ratio of butyryl groups to acetyl groups on the cellulose ester may be 55:45, such as 60:40, such as 65:35, such as 70:30, such as 75:25, such as 80:20, such as 85:15, such as 90:10, or even 95:5.

[0013]

[0010] The amine-based polymer may comprise a poly(alk)ylene imine polymer. Preferably the amine-based polymer comprises a poly(alk)ylene selected from polyethylene, polypropylene, polybutylene or a combination thereof. The poly(alk)ylene imine polymer is preferably, a polyethylene imine polymer.

[0014]

[0011] The poly(alk)ylene imine polymer may be branched or linear, preferably the poly(alk)ylene imine polymer is branched.

[0015]

[0012] The amine-based polymer, such as a poly(alk)ylene imine polymer, may comprise a modified amine-based polymer, such as a modified poly(alk)ylene imine polymer. The modification may comprise functionality capable of crosslinking. The amine-based polymer may be a modified amine-based polymer comprising functionality capable of crosslinking. Typically, the modification occurs by an interaction with the primary, secondary or tertiary amine sites on the amine-based polymer, or any combination of these amine sites. The interaction may be a covalent bond, ionic bond, or mixture thereof.

[0016]

[0013] Typically, the molar ratio of compound capable of modifying the amine-based polymer to amine groups on the amine-based polymer is 1 :1 to 1 :16, wherein the amine groups are the primary, secondary and tertiary amine groups on the amine-based polymer. The molar ratio of compound capable of modifying the amine-based polymer to amine groups on the amine-based polymer may be 1 :1 to 1 :16, such as 1 :2 to 1 :12, such as 1 :3 to 1 :8, typically the molar ratio of compound capable of modifying the amine-based polymer to amine groups on the amine-based polymer is around 1 :4.

[0017]

[0014] Typically, the molar ratio of compound capable of modifying the amine-based polymer to amine groups on the amine-based polymer is 1 to at least 1 , such as 1 to at least 2, such as 1 to at least 3, such as 1 to at least 4.

[0018]

[0015] The functionality capable of crosslinking may be capable of ionic or covalent crosslinking or a mixture thereof.

[0019]

[0016] The amine-based polymer, such as a poly(alk)ylene imine polymer, may be modified with a compound which has, or its hydrolysis product has, a pKa of up to 10, preferably up to 5.

[0017] The amine-based polymer, such as a poly(alk)ylene imine polymer, is preferably modified with a compound selected from a carboxylic acid or acid anhydride. The carboxylic acid or acid anhydride is preferably selected from a di- or tri-functional carboxylic acid or a cyclic anhydride, preferably a cyclic anhydride comprising at least two anhydride groups.

[0020]

[0018] Typically, the carboxylic acid or acid anhydride may be reacted with an amine group on the amine-based polymer to form an amide bond.

[0021]

[0019] The carboxylic acid may be selected from citric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azeleic acid, sebacic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid, phthalic acid, terephthalic acid, pyromellitic acid, naphthalic acid, naphthalenetetracarboxylic acid, perylenedicarboxylic acid, perylenetetracarboxylic acid and malic acid; or a polymer or copolymer comprising carboxylic acid functional groups, such as poly(acrylic acid), poly(methacrylic acid), poly(styrene-co-acrylic acid), poly(styrene-co-methacrylic acid), poly(maleic acid), poly(fumaric acid), poly(styrene-co-maleic acid) and poly(styrene-co-fumaric acid).

[0022]

[0020] The acid anhydride may be selected from one or more of succinic anhydride, maleic anhydride, phthalic anhydride, naphthalic anhydride, perylenedicarboxylic acid anhydride, 1 ,2,3,4-cyclobutanetetracarboxylic dianhydride, 1 ,2,4,5-cyclohexanetetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone-3,3',4,4'-tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 4,4'-biphthalic anhydride, naphthalenetetracarboxylic acid dianhydride, perylenetetracarboxylic acid dianhydride, ethylenediaminetetraacetic dianhydride; or a polymer or copolymer containing anhydride functional groups, such as, poly(maleic anhydride), poly(styrene-co-maleic anhydride), poly(ethylene-co-maleic anhydride), poly(propylene-co-maleic anhydride), poly(butylene-co-maleic anhydride) and poly(isobutylene-co-maleic anhydride) or styrene maleic anhydride, preferably, wherein the acid anhydride is styrene maleic anhydride.

[0023]

[0021] The compound capable of modifying the amine-based polymer may form ionic bonds with the amine-based polymer. The compound may form covalent bonds with the amine-based polymer. An amide bond may be formed between the compound and the amine-based polymer. The compound may form ionic and covalent bonds with the amine-based polymer.

[0024]

[0022] The compound capable of modifying the amine-based polymer may form ionic bonds with at least two amine-based polymer blocks on different block copolymers. The compound may form covalent bonds with at least two amine-based polymer blocks on different block copolymers. The compound may form ionic and covalent bonds with at least two amine-based polymer blocks on different block copolymers.

[0025]

[0023] The compound capable of modifying the amine-based polymer may form ionic bonds with at least two amine groups within the same amine-based polymer block. The compound capable of modifying the amine-based polymer may form covalent bonds with at least two amine groupswithin the same amine-based polymer block. The compound capable of modifying the amine-based polymer may form ionic and covalent bonds with at least two amine groups within the same amine-based polymer block.

[0026]

[0024] The block copolymer may be an A-B block copolymer, wherein block A comprises cellulose and block B comprises an amine-based polymer.

[0027]

[0025] The block copolymer may be an AnB block copolymer, wherein n>1 . The block copolymer may be an AnB block copolymer, wherein n>1 and less than 5, preferably n=1.

[0028]

[0026] The block copolymer may be prepared by first forming block A and block B separately, then reacting block A and block B together so that block A and block B are covalently linked. Preferably, the amine-based polymer is polymerized and then reacted with the inert bio-based polymer to form the block copolymer.

[0029]

[0027] The block copolymer may be prepared by the polymerization of monomers to form a first polymer, followed by controlled polymerization with different monomers to form a second polymer in the presence of the first polymer. Suitably, the amine-based monomers may be polymerized in the presence of the inert bio-based polymer to form a block copolymer comprising an inert biobased polymer block and an amine-based polymer block.

[0030]

[0028] The inert bio-based polymer may be cellulose and / or polylactic acid. The cellulose ester may be peresterified.

[0031]

[0029] The peresterified cellulose may be selectively de-esterified. The peresterified cellulose may be selectively de-esterified at the reducing end of the cellulose, providing peresterified cellulose having a hydroxyl group at the reducing end (a hemiacetal ring form of glucose at the reducing end). The cellulose comprising a hemiacetal ring form of glucose at the reducing end may be in equilibrium with cellulose comprising an open-chain aldehyde form of glucose at the reducing end, as shown in Scheme 1 .

[0032]

[0033] Scheme 1

[0034]

[0030] The amine-based polymer, such as polyethylene imine, and the inert bio-based polymer, such as cellulose ester, may be reacted together by reductive amination. The ring opened aldehyde form of the cellulose ester may react with an amine-based polymer, such as apoly(alk)ylene imine. The resulting Schiff base is comparatively unstable and may be reduced to the corresponding secondary amine when a reducing agent is added (as shown in Scheme 1).

[0035]

[0031] The reducing agent may be any suitable reducing agent. The reducing agent may be selected from sodium borohydride, sodium triacetoxyborohydride, sodium cyanoborohydride, and 2-picoline-borane.

[0036]

[0032] In Scheme 1 , n is the number of repeating units of glucose in the cellulose chain. Preferably, n is at least 8.

[0037]

[0033] The amine-based polymer may be synthesised by ring opening polymerization, such as ring opening polymerization of aziridine.

[0038]

[0034] The amine-based polymer may be modified with with a compound selected from a carboxylic acid or acid anhydride. The carboxylic acid or acid anhydride is preferably selected from a di- or tri-functional carboxylic acid or a cyclic anhydride, preferably a cyclic anhydride comprising at least two anhydride groups.

[0039]

[0035] The amount of compound capable of modifying amine-based polymer used to modify the amine-based polymer will depend on the level of modification required.

[0040]

[0036] The modification of the amine-based polymer may comprise reacting the amine-based polymer with a compound capable of modifying the amine-based polymer in a solvent. The solvent may be any suitable solvent. The solvent may be selected from, but not limited to, methyl ethyl ketone, acetone, ethanol, isopropanol, methyl acetate, ethyl acetate, n-butyl acetate, 2-methoxy-1 -propanol, 2-methoxy-1 -propyl acetate, or any suitable blend of solvents.

[0041]

[0037] The block copolymer may comprise a further block. The further block may be an inert biobased polymer block, such as a cellulose block. The block copolymer may be an A-B-A block, wherein block A comprises an inert bio-based polymer block and block B comprises an amine-based polymer. The block copolymer may be an A-B-A block, wherein block A comprises cellulose and block B comprises a poly(alk)ylene imine polymer.

[0042]

[0038] The block copolymer may be an AnB block copolymer, wherein n>1 . The block copolymer may be an AnB block copolymer, wherein n>1 and less than 5, preferably n=1.

[0043]

[0039] The block copolymer may have a number average molecular weight (Mn) in the range of from about 2,000 to 200,000 Da, preferably about 2,000 to 150,000 Da, more preferably about 2,000 to 100,000 Da, most preferably about 2,000 to 40,000 Da.

[0044]

[0040] The block copolymer may have a number average molecular weight (Mn) of at least 2,000 Da, such as at least 3,000 Da, such as at least 4,000 Da, such as at least 5,000 Da.

[0045]

[0041] The block copolymer may have a number average molecular weight (Mn) of up to 200,000 Da, such as up to 150,000 Da, such as up to 100,000 Da, such as up to 40,000 Da.

[0042] Without being bound by theory, the block copolymer having a number average molecular weight (Mn) in the range set out above provides block A with a sufficient size for steric stabilisation, without imparting so much additional viscosity to be detrimental to printing performance.

[0046]

[0043] The inert bio-based polymer block, A, of the block copolymer may have a molecular weight (Mn) in the range of from about 2,000 to 100,000 Da, preferably about 2,000 to 70,000 Da, more preferably about 2,000 to 50,000, most preferably about 2,000 to 20,000 Da.

[0047]

[0044] The inert bio-based polymer block, A, of the block copolymer may have a molecular weight (Mn) of at least 2,000 Da, such as at least 3,000 Da, such as at least 4,000 Da, such as at least 5,000 Da.

[0048]

[0045] The inert bio-based polymer block, A, of the block copolymer may have a number average molecular weight (Mn) of up to 100,000 Da, such as up to 70,000 Da, such as up to 50,000 Da, such as up to 20,000 Da.

[0049]

[0046] The amine-based block, B, of the block copolymer may have a molecular weight (Mn) in the range of from about 200 to 25,000 Da, preferably about 200 to 15,000 Da, more preferably 200 to 10,000 Da, most preferably about 200 to 2,500 Da.

[0050]

[0047] The amine-based block, B, of the block copolymer may have a molecular weight (Mn) of at least 200 Da, such as at least 300 Da, such as at least 400 Da, such as at least 500 Da.

[0051]

[0048] The amine-based block, B, of the block copolymer may have a number average molecular weight (Mn) of up to 25,000 Da, such as up to 15,000 Da, such as up to 10,000 Da, such as up to 2,500 Da.

[0052]

[0049] The Mn of the polymers may be measured by gel permeation chromatography (GPC) using a polystyrene standard according to ASTM D6579-11 (“Standard Practice for Molecular Weight Averages and Molecular Weight Distribution of Hydrocarbon, Rosin and Terpene Resins by Size Exclusion Chromatography”). Suitable parameters include triple detection: refractive index, light scattering (right angle (RALS) and low angle (LALS)) and viscometer, solvent: unstabilised THF, retention time marker and molecular weight standard: polystyrene (Malvern PS105K, Mw = 105,529 Da and Mn = 103,389 Da), sample concentration: 10 mg / ml.

[0053]

[0050] According to a second aspect of the invention there is provided a dispersant comprising a block copolymer, the block copolymer comprising: a sterically stabilizing polymer block; and a modified poly(alk)ylene imine block wherein the modification comprises functionality capable of crosslinking.

[0054]

[0051] Any suitable features set out above in relation to the first aspect also apply to the second aspect, where appropriate.

[0052] Advantageously, the modified poly(alk)ylene imine block is poorly soluble and prefers to adsorb onto pigment surfaces rather than be solvated in a dispersion medium. The sterically stabilising polymer, being highly soluble, preferentially remains solvated in the dispersion medium and provides steric stabilisation by physically blocking pigment particles from approaching one another.

[0055]

[0053] The term “sterically stabilizing polymer block” as used herein refers to a polymer which does not interact with a pigment surface and instead provides steric stabilization.

[0056]

[0054] The sterically stabilizing polymer block may comprise any suitable sterically stabilizing polymer. The sterically stabilizing polymer may be selected from a polysaccharide, polyamide, polyester, polyacrylate, polystyrene, polyethyleneglycol, polypropyleneglycol or a polyvinyl chloride. The polysaccharide may be a carbohydrate, such as cellulose, chitin, chitosan, starches, dextrins, or derivates thereof. The polyamide may be animal or plant proteins, or derivatives thereof. The polyester may be polylactic acid, or derivatives thereof. The polyacrylate may be polymethylmethacrylate.

[0057]

[0055] Preferably, the sterically stabilizing polymer comprises cellulose and / or polylactic acid, or derivatives thereof. The cellulose may be acetylated, propionylated, butyrylated, or a mixed ester of a combination of these in any ratio. Preferably the cellulose ester is a peresterified mixed ester of acetic acid and butyric acid, i.e. the cellulose ester is a cellulose acetate butyrate. Preferably, the cellulose ester comprises more butyryl groups than acetyl groups.

[0058]

[0056] The molar ratio of butyryl groups to acetyl groups on the cellulose ester may be 55:45, such as 60:40, such as 65:35, such as 70:30, such as 75:25, such as 80:20, such as 85:15, such as 90:10, or even 95:5.

[0059]

[0057] The modified poly(alk)ylene imine polymer may be branched or linear, preferably the modified poly(alk)ylene imine polymer is branched.

[0060]

[0058] The modified poly(alk)ylene imine block may comprise a poly(alk)ylene selected from polyethylene, polypropylene, polybutylene or a combination thereof. The modified poly(alk)ylene imine block is preferably, a modified polyethylene imine block. Typically, the modification occurs by an interaction with the primary, secondary or tertiary amine sites on the polyethylene imine block, or any combination of these amine sites. The interaction may be a covalent bond, ionic bond, or mixture thereof.

[0061]

[0059] Typically, the molar ratio of compound capable of modifying the poly(alk)ylene imine block to amine groups on the poly(alk)ylene imine block is 1 :1 to 1 :16, wherein the amine groups are the primary, secondary and tertiary amine groups on the poly(alk)ylene imine block. The molar ratio of compound capable of modifying the poly(alk)ylene imine block to amine groups on the poly(alk)ylene imine block may be 1 :1 to 1 :16, such as 1 :2 to 1 :12, such as 1 :3 to 1 :8, typicallythe molar ratio of compound capable of modifying the poly(alk)ylene imine block to amine groups on the poly(alk)ylene imine block is around 1 :4.

[0062]

[0060] Typically, the molar ratio of compound capable of modifying the poly(alk)ylene imine block to amine groups on the poly(alk)ylene imine block is 1 to at least 1 , such as 1 to at least 2, such as 1 to at least 3, such as 1 to at least 4.

[0063]

[0061] The functionality capable of crosslinking may be capable of ionic or covalent crosslinking or a mixture thereof.

[0064]

[0062] The poly(alk)ylene imine block may be modified with a compound which has, or its hydrolysis product has, a pKa of up to 10, preferably up to 5.

[0065]

[0063] The poly(alk)ylene imine block is preferably modified with a compound selected from a carboxylic acid or acid anhydride. The carboxylic acid or acid anhydride is preferably selected from a di- or tri-functional carboxylic acid or a cyclic anhydride, preferably a cyclic anhydride comprising at least two anhydride groups.

[0066]

[0064] Typically, the carboxylic acid or acid anhydride may be reacted with an amine group on the polyethylene imine block to form an amide bond.

[0067]

[0065] The carboxylic acid may be selected from citric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azeleic acid, sebacic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid, phthalic acid, terephthalic acid, pyromellitic acid, naphthalic acid, naphthalenetetracarboxylic acid, perylenedicarboxylic acid, perylenetetracarboxylic acid and malic acid; or a polymer or copolymer comprising carboxylic acid functional groups, such as poly(acrylic acid), poly(methacrylic acid), poly(styrene-co-acrylic acid), poly(styrene-co-methacrylic acid), poly(maleic acid), poly(fumaric acid), poly(styrene-co-maleic acid) and poly(styrene-co-fumaric acid).

[0068]

[0066] The acid anhydride may be selected from one or more of succinic anhydride, maleic anhydride, phthalic anhydride, naphthalic anhydride, perylenedicarboxylic acid anhydride, 1 ,2,3,4-cyclobutanetetracarboxylic dianhydride, 1 ,2,4,5-cyclohexanetetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone-3,3',4,4'-tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 4,4'-biphthalic anhydride, naphthalenetetracarboxylic acid dianhydride, perylenetetracarboxylic acid dianhydride, ethylenediaminetetraacetic dianhydride; or a polymer or copolymer containing anhydride functional groups, such as, poly(maleic anhydride), poly(styrene-co-maleic anhydride), poly(ethylene-co-maleic anhydride), poly(propylene-co-maleic anhydride), poly(butylene-co-maleic anhydride) and poly(isobutylene-co-maleic anhydride) or styrene maleic anhydride, preferably, wherein the acid anhydride is styrene maleic anhydride.

[0069]

[0067] The compound capable of modifying the poly(alk)ylene imine block may form ionic bonds with the poly(alk)ylene imine polymer. The compound may form covalent bonds with thepoly(alk)ylene imine polymer. An amide bond may be formed between the compound and the poly(alk)ylene imine polymer. The compound may form ionic and covalent bonds with the poly(alk)ylene imine polymer.

[0070]

[0068] The compound capable of modifying the poly(alk)ylene imine block may form ionic bonds with at least two poly(alk)ylene imine polymer blocks on different block copolymers. The compound may form covalent bonds with at least two poly(alk)ylene imine polymer blocks on different block copolymers. The compound may form ionic and covalent bonds with at least two poly(alk)ylene imine blocks on different block copolymers.

[0071]

[0069] The compound capable of modifying the poly(alk)ylene imine block may form ionic bonds with at least two amine groups within the same poly(alk)ylene imine block. The compound capable of modifying the poly(alk)ylene imine block may form covalent bonds with at least two amine groups within the same poly(alk)ylene imine block. The compound capable of modifying the poly(alk)ylene imine block may form ionic and covalent bonds with at least two amine groups within the same poly(alk)ylene imine block.

[0072]

[0070] The block copolymer may be an A-B block, wherein block A comprises a sterically stabilizing polymer and block B comprises a poly(alk)ylene imine polymer.

[0073]

[0071] The block copolymer may be an AnB block copolymer, wherein n>1 . The block copolymer may be an AnB block copolymer, wherein n>1 and less than 5, preferably n=1.

[0074]

[0072] The block copolymer may be prepared by first forming block A and block B separately, then reacting block A and block B together so that block A and block B are covalently linked. Preferably, a poly(alk)ylene imine block is polymerized and then reacted with the sterically stabilizing polymer block to form the block copolymer. The poly(alk)ylene imine block may then be modified to form the modified poly(alk)ylene imine block copolymer.

[0075]

[0073] The block copolymer may be prepared by the polymerization of monomers to form a first polymer, followed by controlled polymerization with different monomers to form a second polymer in the presence of the first polymer. The poly(alk)ylene imine monomers may be polymerized in the presence of the sterically stabilizing polymer to form a block copolymer comprising a sterically stabilizing polymer block and a poly(alk)ylene imine block. The poly(alk)ylene imine block may then be modified to form the modified poly(alk)ylene imine block copolymer.

[0076]

[0074] The sterically stabilizing polymer may be cellulose and / or polylactic acid. The cellulose ester may be peresterified.

[0077]

[0075] The peresterified cellulose may be selectively de-esterified. The peresterified cellulose may be selectively de-esterified at the reducing end of the cellulose ester, providing peresterified cellulose having a hydroxyl group at the reducing end (a hemiacetal ring form of glucose at the reducing end). The cellulose ester comprising a hemiacetal ring form of glucose at the reducingend may be in equilibrium with cellulose comprising an open-chain aldehyde form of glucose at the reducing end (as shown in Scheme 1 above).

[0078]

[0076] The poly(alk)ylene imine block, such as polyethylene imine polymer, and the sterically stabilizing polymer block, such as cellulose ester, may be reacted together by reductive amination. The ring opened aldehyde form of the cellulose ester may react with a poly(alk)ylene imine block, such as a polyethylene imine polymer. The resulting Schiff base is comparatively unstable and may be reduced to the corresponding secondary amine when a reducing agent is added (as shown in Scheme 1 above).

[0079]

[0077] The reducing agent may be any suitable reducing agent. The reducing agent may be selected from sodium borohydride, sodium triacetoxyborohydride, sodium cyanoborohydride, and 2-picoline-borane.

[0080]

[0078] In Scheme 1 , n is the number of repeating units of glucose in the cellulose chain. Preferably, n is at least 8.

[0081]

[0079] The poly(alk)ylene imine block may be synthesised by ring opening polymerisation, such as ring opening polymerisation of aziridine.

[0082]

[0080] The poly(alk)ylene imine block may comprise a modified poly(alk)ylene imine block wherein the modification comprises functionality capable of crosslinking. The poly(alk)ylene imine block may be modified with with a compound selected from a carboxylic acid or acid anhydride. The carboxylic acid or acid anhydride is preferably selected from a di- or tri-functional carboxylic acid or a cyclic anhydride, preferably a cyclic anhydride comprising at least two anhydride groups.

[0083]

[0081] The amount of compound capable of modifying the poly(alk)ylene imine block used to modify the poly(alk)ylene imine block will depend on the level of modification required.

[0084]

[0082] The modification of the poly(alk)ylene imine block may comprise reacting the poly(alk)ylene imine block with a compound capable of modifying the poly(alk)ylene imine block in a solvent. The solvent may be any suitable solvent. The solvent may be selected from, but not limited to, methyl ethyl ketone, acetone, ethanol, isopropanol, methyl acetate, ethyl acetate, n-butyl acetate, 2-methoxy-1 -propanol, 2-methoxy-1 -propyl acetate, or any suitable blend of solvents.

[0085]

[0083] The poly(alk)ylene imine block may be modified with any suitable acid anhydride. The poly(alk)ylene imine block may be a polyethylene imine polymer and be modified with succinic anhydride, as shown in Scheme 2.

[0086]

[0087] Scheme 2

[0088]

[0084] The succinic anhydride may form covalent bonds with the polyethylene imine polymer block. Crosslinking may form between the polyethylene imine polymer blocks.

[0089]

[0085] The resulting modified polyethylene imine polymer block of the block copolymer may be capable of forming ionic crosslinks with a further polyethylene imine polymer of a block copolymer. The succinic anhydride may protonate the amine groups on a polyethylene imine block that it isnot bonded to. The ionic crosslinks may be formed between the modified groups on one polyethylene imine polymer block and the backbone of a further polyethylene imine polymer block. The ionic crosslinks may be formed between the deprotonated carboxylic acid groups on the modified polyethylene imine polymer block and the protonated amine groups on a further polyethylene imine polymer block.

[0090]

[0086] The resulting modified polyethylene imine polymer block of the block copolymer may be capable of forming ionic crosslinks with itself. The succinic anhydride may protonate the polyethylene imine block it is covalently bonded to, leading to a zwitterionic structure (Figure 1).

[0091]

[0092] Figure 1

[0093]

[0087] Ionic crosslinks may be formed between the modified groups on the polyethylene imine polymer block and the backbone of the polyethylene imine polymer block. The ionic crosslinks may be formed between the deprotonated carboxylic acid groups on the modified polyethylene imine polymer block and the protonated amine groups on the polyethylene imine polymer block.

[0094]

[0088] The poly(alk)ylene imine block may be modified with any suitable acid. The acid may be a di- or tri- functional carboxylic acid. The poly(alk)ylene imine block may be polyethylene imine and be modified with citric acid, as shown in Scheme 3.

[0095]

[0096] Scheme 3

[0097]

[0089] The citric acid may be ionically bonded to the polyethylene imine block. Suitably, the citric acid is ionically bonded at each end to a polyethylene imine block.

[0098]

[0090] Crosslinking may form between the polyethylene imine polymer blocks. The citric acid may protonate the amine groups on the polyethylene imine block. Ionic crosslinks may be formed between the citric acid compound and one or more polyethylene imine polymer blocks. The ioniccrosslinks may be formed between the deprotonated carboxylic acid groups on the citric acid and the protonated amine groups on the polyethylene imine polymer block. Ionic crosslinks may be formed between polyethylene imine polymer blocks on different block copolymers (shown in Scheme 3), and / or intramolecularly within the same polyethylene imine polymer block (as shown in Figure 2) using the citric acid compound.

[0099]

[0100] Figure 2

[0101]

[0091] The acid anhydride may be a cyclic anhydride comprising at least two anhydride groups. The poly(alk)ylene imine block may be modified with pyromellitic anhydride. The poly(alk)ylene imine block may be a polyethylene imine polymer block and modified with pyromellitic anhydride, as shown in Scheme 4.

[0102]

[0103] Scheme 4

[0104]

[0092] Crosslinking may form between the polyethylene imine polymer blocks. The pyromellitic anhydride may form covalent and ionic bonds with the polyethylene imine polymer block. The pyromellitic anhydride may form covalent and ionic bonds with more than one polyethylene imine polymer block on different block copolymers (as shown in Scheme 4), and / or intramolecularlywithin the same polyethylene imine polymer block (as shown in Figure 3). The pyromellitic anhydride may crosslink the block copolymers by covalent and ionic crosslinking.

[0105]

[0106] Figure 3

[0107]

[0093] The acid anhydride may be a polymer comprising at least two anhydride groups. The poly(alk)ylene imine block may be modified with a styrene maleic anhydride co-polymer. The poly(alk)ylene imine block may be a polyethylene imine polymer block and modified with styrene maleic anhydride co-polymer, as shown in Scheme 5.

[0108]

[0109]

[0110] Scheme 5

[0111]

[0094] Crosslinking may form between the polyethylene imine polymer blocks. The styrene maleic anhydride co-polymer may form covalent and ionic bonds with the polyethylene imine polymer block. The styrene maleic anhydride co-polymer may form covalent and ionic bonds with more than one polyethylene imine polymer block on different block copolymers (as shown in Scheme 5), and / or intramolecularly within the same polyethylene imine polymer block (as shown in Figure 4). The styrene maleic anhydride co-polymer may crosslink the block copolymers by covalent and ionic crosslinking.

[0112]

[0113] Figure 4

[0095] For the avoidance of doubt, any of the above modifications to the poly(alk)ylene imine blocks are also applicable to the poly(alk)ylene imine according to the first aspect.

[0114]

[0096] The block copolymer may comprise a further block. The further block may be a sterically stabilizing polymer block, such as a cellulose block. The block copolymer may be an A-B-A block, wherein block A comprises a sterically stabilizing polymer and block B comprises a poly(alk)ylene imine polymer. The block copolymer may be an A-B-A block, wherein block A comprises cellulose and block B comprises a poly(alk)ylene imine polymer, such as polyethylene imine polymer.

[0115]

[0097] The block copolymer may be an AnB block copolymer, wherein n>1 . The block copolymer may be an AnB block copolymer, wherein n>1 and less than 5, preferably n=1.

[0116]

[0098] The block copolymer may have a number average molecular weight (Mn) in the range of from about 2,000 to 200,000 Da, preferably about 2,000 to 150,000 Da, more preferably about 2,000 to 100,000 Da, most preferably about 2,000 to 40,000 Da.

[0117]

[0099] The block copolymer may have a number average molecular weight (Mn) of at least 2,000 Da, such as at least 3,000 Da, such as at least 4,000 Da, such as at least 5,000 Da.

[0118]

[0100] The block copolymer may have a number average molecular weight (Mn) of up to 200,000 Da, such as up to 150,000 Da, such as up to 100,000 Da, such as up to 40,000 Da.

[0119]

[0101] Without being bound by theory, the block copolymer having a number average molecular weight (Mn) in the range set out above provides block A with a sufficient size for steric stabilisation, without imparting so much additional viscosity to be detrimental to printing performance.

[0120]

[0102] The sterically stabilizing polymer block, A, of the block copolymer may have a molecular weight (Mn) in the range of from about 2,000 to 100,000 Da, preferably about 2,000 to 70,000 Da, more preferably about 2,000 to 50,000, most preferably about 2,000 to 20,000 Da.

[0121]

[0103] The sterically stabilizing polymer block, A, of the block copolymer may have a molecular weight (Mn) of at least 2,000 Da, such as at least 3,000 Da, such as at least 4,000 Da, such as at least 5,000 Da.

[0122]

[0104] The sterically stabilizing polymer block, A, of the block copolymer may have a number average molecular weight (Mn) of up to 100,000 Da, such as up to 70,000 Da, such as up to 50,000 Da, such as up to 20,000 Da.

[0123]

[0105] The poly(alk)ylene imine block, B, of the block copolymer may have a molecular weight (Mn) in the range of from about 200 to 25,000 Da, preferably about 200 to 15,000 Da, more preferably 200 to 10,000 Da, most preferably about 200 to 2,500 Da.

[0124]

[0106] The poly(alk)ylene imine block, B, of the block copolymer may have a molecular weight (Mn) of at least 200 Da, such as at least 300 Da, such as at least 400 Da, such as at least 500 Da.

[0107] The poly(alk)ylene imine block, B, of the block copolymer may have a number average molecular weight (Mn) of up to 25,000 Da, such as up to 15,000 Da, such as up to 10,000 Da, such as up to 2,500 Da.

[0125]

[0108] The Mn of the polymers may be measured by gel permeation chromatography (GPC) using a polystyrene standard according to ASTM D6579-11 (“Standard Practice for Molecular Weight Averages and Molecular Weight Distribution of Hydrocarbon, Rosin and Terpene Resins by Size Exclusion Chromatography”). Suitable parameters include triple detection: refractive index, light scattering (right angle (RALS) and low angle (LALS)) and viscometer, solvent: unstabilised THF, retention time marker and molecular weight standard: polystyrene (Malvern PS105K, Mw = 105,529 Da and Mn = 103,389 Da), sample concentration: 10 mg / ml.

[0126]

[0109] The dispersants of the present invention are typically suitable for use in printing inks. Therefore, according to a further embodiment of the invention there is provided a printing ink composition comprising the dispersant of any the earlier embodiments. Preferably the composition is an inkjet ink composition.

[0127]

[0110] DEFINITIONS

[0128]

[0111] An imine group is a group -CRNR, optionally -CHNRi wherein Ri is an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl group. Ri may be unsubstituted aliphatic, alicyclic or aryl. Optionally Ri is an alkyl group selected from methyl, ethyl or propyl, preferably ethyl.

[0129]

[0112] Unless defined otherwise herein, an ester group is optionally -OC(O)R2- or -C(O)OR2-wherein R2 can be an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl group as defined above. R2 may be unsubstituted aliphatic, alicyclic or aryl. Optionally R2 is methyl, ethyl, propyl or phenyl. The ester group may be terminated by an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl group. It will be appreciated that if R2 is hydrogen, then the group defined by -OC(O)R2- or -C(O)OR2- will be a carboxylic acid group.

[0130]

[0113] Unless defined otherwise herein, an acetyl group (or acetylated) is H3CC(O)-.

[0131]

[0114] Unless defined otherwise herein, a propionyl group (or propionylated) is H3C(CH2)C(O)-.

[0132]

[0115] Unless defined otherwise herein, a butyryl group (or butyrylated) is H3C(CH2)2C(O)-.

[0133]

[0116] EXAMPLES

[0134]

[0117] Full esterification of cellulose acetate butyrate. To a solution of cellulose acetate butyrate (25.00 g) in dimethylformamide (100 mL) was added acetic anhydride (50 mL) and pyridine (50 mL). The solution was stirred at room temperature for 24 hours. The solution was poured into water (2 L) to precipitate the product, which was then collected by filtration and washed with water (3 x 200 mL). The product was dried in vacuo at 60 °C to give peresterified cellulose acetate butyrate as a white powder (24.75 g, 99 % yield).

[0118] Selective de-esterification of fully esterified cellulose acetate butyrate. The fully esterified cellulose acetate butyrate (24.75 g) was treated with benzylamine (1 .98 mL) in THF (120 mL) for 24 h at room temperature to selectively de-esterify at the reducing end of the cellulose acetate butyrate. The reaction mixture was diluted with ethyl acetate (500 ml) and washed with 1M HCI (3 x 100 mL) and brine (3 x 100 mL), then dried over anhydrous magnesium sulfate, The magnesium sulfate was removed by filtration and the organic solvent was evaporated under reduced pressure, providing peresterified cellulose acetate butyrate having a hydroxyl group at the reducing end as a pale yellow powder (24.50 g, 99 % yield).

[0135]

[0119] Reductive amination. The peresterified cellulose acetate butyrate having a hydroxyl group at the reducing end (10.00 g) was dissolved dry dichloromethane (50 mL) and added dropwise to a flask containing dry dichloromethane (50 mL), polyethyleneimine (1.25 g), acetic acid (1.66 mL) and sodium triacetoxyborohydride (397.5 mg). The mixture was stirred at room temperature under a nitrogen atmosphere for 24 h. The reaction mixture was diluted with dichloromethane (100 mL) and washed with saturated aqueous sodium bicarbonate solution (100 mL). The phases were separated and the aqueous phase was extracted with further dichloromethane (2 x 50 mL). The combined organic extracts were washed with brine (3 x 100 mL) and dried over anhydrous magnesium sulfate. The magnesium sulfate was removed by filtration and the organic solvent was evaporated under reduced pressure, providing a cellulose ester polyethyleneimine copolymer as a pale yellow powder (10.55 g, 94 % yield).

[0136]

[0120] Modified cellulose ester polyethyleneimine co-polymer. A styrene maleic anhydride copolymer (49 mg) was added to a solution of the cellulose ester polyethyleneimine co-polymer (250 mg) in methyl ethyl ketone (4.5 mL). The mixture was shaken with an orbital shaker at room temperature (30 minutes) until the modification agent was fully dissolved, giving a solution of the modified cellulose ester polyethyleneimine co-polymer in methyl ethyl ketone. The same procedure may be carried out in any suitable solvent. Other suitable solvents include, but not limited to, acetone, ethanol, isopropanol, methyl acetate, ethyl acetate, n-butyl acetate, 2-methoxy-1 -propanol, 2-methoxy-1 -propyl acetate, or any suitable blend of solvents. Where the modifying compound has poor solubility in the chosen solvent, or is slow to dissolve, it may be added with sonication and heating. One such example is citric acid, which was added to the cellulose ester polyethyleneimine co-polymer in methyl ethyl ketone while sonicating at 50°C until the citric acid was fully dissolved.

[0137]

[0121] Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of’ or “consists essentially of’ means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than5% by weight, typically less than 3% by weight, more typically less than 1% by weight of nonspecified components.

[0138]

[0122] The optional features set out herein may be used either individually or in combination with each otherwhere appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

[0139]

[0123] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0140]

[0124] All of the features disclosed in this specification (including any accompanying claims, and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0141]

[0125] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0142]

[0126] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A dispersant comprising a block copolymer, the block copolymer comprising:(i) a first block comprising an inert bio-based polymer, and(ii) a second block comprising an amine-based polymer.

2. A dispersant according to claim 1, wherein the inert bio-based polymer comprises cellulose and / or polylactic acid, or derivatives thereof.

3. A dispersant according to claim 1 or 2, wherein the amine-based polymer comprises a poly(alk)ylene imine polymer.

4. A dispersant according to claim 2, wherein the cellulose comprises a cellulose ester.

5. A dispersant according to claim 3, wherein the poly(alk)ylene imine polymer comprises a poly(alk)ylene selected from polyethylene, polypropylene, polybutylene or combination thereof, wherein the poly(alk)ylene imine polymer is preferably, polyethylene imine.

6. A dispersant according to claim 3 or 5, wherein the poly(alk)ylene imine polymer is branched.

7. A dispersant according to any preceding claim, wherein the block copolymer is an A-B block, wherein block A comprises cellulose and block B comprises an amine-based polymer.

8. A dispersant comprising a block copolymer, the block copolymer comprising:(i) a sterically stabilizing polymer block; and(ii) a modified poly(alk)ylene imine block wherein the modification comprises functionality capable of crosslinking.

9. A dispersant according to claim 8, wherein the sterically stabilizing polymer block comprises cellulose, preferably a cellulose ester.

10. A dispersant according to claim 8 or 9, wherein the modified poly(alk)ylene imine block comprises a poly(alk)ylene selected from polyethylene, polypropylene, polybutylene, or combination thereof, wherein the modified poly(alk)ylene imine block is preferably, a modified polyethylene imine block.

11. A dispersant according to any of claims 8 to 10, wherein the crosslinking comprises ionic and covalent crosslinking.

12. A dispersant according to any of claims 8 to 11 , wherein the poly(alk)ylene imine block is modified with a compound which has, or its hydrolysis product has, a pKa of up to 10, preferably up to 5.

13. A dispersant according to any of claims 8 to 12, wherein the poly(alk)ylene imine block is modified with a compound selected from a carboxylic acid or acid anhydride.

14. A dispersant according to any of claims 8 to 13, wherein the carboxylic acid or acid anhydride is selected from a di / tri-functional carboxylic acid or a cyclic anhydride, preferably a cyclic anhydride comprising at least two anhydride groups.

15. A dispersant according to claim 13 or 14, wherein the carboxylic acid is selected from one or more of citric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azeleic acid, sebacic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid, phthalic acid, terephthalic acid, pyromellitic acid, naphthalic acid, naphthalenetetracarboxylic acid, perylenedicarboxylic acid, perylenetetracarboxylic acid and malic acid; or a polymer or copolymer comprising carboxylic acid functional groups, such as poly(acrylic acid), poly(methacrylic acid), poly(styrene-co-acrylic acid), poly(styrene-co-methacrylic acid), poly(maleic acid), poly(fumaric acid), poly(styrene-co-maleic acid) and poly(styrene-co-fumaric acid).

16. A dispersant according to any of claims 13 to 15, wherein the acid anhydride is selected from one or more of succinic anhydride, maleic anhydride, phthalic anhydride, naphthalicanhydride, perylenedicarboxylic acid anhydride, 1 ,2,3,4-cyclobutanetetracarboxylic dianhydride, 1 ,2,4,5-cyclohexanetetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone-3,3',4,4'-tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 4,4'- biphthalic anhydride, naphthalenetetracarboxylic acid dianhydride, perylenetetracarboxylic acid dianhydride, ethylenediaminetetraacetic dianhydride; or a polymer or copolymer containing anhydride functional groups, such as, poly(maleic anhydride), poly(styrene-co-maleic anhydride), poly(ethylene-co-maleic anhydride), poly(propylene-co-maleic anhydride), poly(butylene-co-maleic anhydride) and poly(isobutylene-co-maleic anhydride) or styrene maleic anhydride, preferably, wherein the acid anhydride is styrene maleic anhydride.

17. A printing ink composition comprising the dispersant of any preceding claim.

18. A printing ink composition according to claim 17, wherein the composition is an inkjet ink composition.

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