Polymeric Dispersant, Dispersion Therewith and Printing Method

Abstract

The polymeric dispersant is a copolymer obtainable by copolymerizing at least a first monomer chosen from a maleimide compound and maleic anhydride, and a second monomer being an ethylenically unsaturated monomer and in case of maleic anhydride, conversion of resulting maleic anhydride units to N-substituted maleimide units, wherein the first monomer comprises a first substituent having a substantially non-polar chain and wherein the second monomer comprises a second, more polar substituent. In one embodiment of the copolymerisation method, first and second monomers are used with copolymerisation parameters r1, r2, such that r1 and r20.5. This results in an at least moderately alternating copolymer. The conversion of maleic anhydride units to maleimide may be partial, for instance at least 10%. The polymeric dispersant can be used in an ink dispersion further comprising colorant particles and an aqueous and/or alcoholic carrier liquid.

Claims

1. A polymeric dispersant, which is a copolymer comprising first and second repealing units each carrying a substituent, which the second repeating units are N-substituted and optionally further substituted maleimide units, which copolymer is obtainable by: copolymerizing at least a first monomer being an ethylenically unsaturated monomer and a second monomer chosen from an N-substituted maleimide compound and a maleic anhydride compound, which compounds are optionally substituted at a 2- and/or 3-position, and converting of at least part of resulting maleic anhydride units to N-substituted maleimide units, in a case that the second monomer is maleic anhydride, wherein the second repeating unit comprises a first substituent having a substantially non-polar chain and wherein the first repeating unit comprises a second, more polar substituent that comprises at least one heteroatom chosen from sulphur (S) and oxygen (O).

2. The polymeric dispersant as claimed in claim 1, wherein the heteroatom is present as at least one of a thiol, a sulfonyl, sulfinyl, ether and oligo-(alkyleneoxide), wherein the alkylene is chosen from ethylene, propylene and butylenes.

3. The polymeric dispersant as claimed in claim 2, wherein the second substituent comprises an oligo-(alkyleneoxide), wherein the alkylene is chosen from ethylene, propylene and butylenes.

4. The polymeric dispersant as claimed in claim 3, wherein the oligo-(alkyleneoxide) is a copolymer of ethylene oxide and propylene oxide.

5. (canceled)

6. The polymeric dispersant as claimed in claim 26, wherein the first monomer has formula (I)
YHCCH.sub.2(I), wherein YOR.sub.1, OC(O)R.sub.1, NR.sub.2C(O)R.sub.1, Y being the second, more polar substituent R.sub.1=substituted C.sub.1-C.sub.24 alkyl, C.sub.2-C.sub.24-cycloalkyl, C.sub.2-C.sub.24 alkene, C.sub.2-C.sub.24 cycloalkene, arylalkyl, alkoxyalkyl; R.sub.2C.sub.1-C.sub.5 alkyl.

7. The polymeric dispersant as claimed in claim 6, wherein Y is chosen from OR.sub.1, OC(O)R.sub.1, NR.sub.2C(O)R.sub.1, wherein R.sub.1 is chosen from substituted C.sub.1-C.sub.10 alkyl.

8. (canceled)

9. (canceled)

10. The polymeric dispersant as claimed in claim 1, wherein the first substituent Z to the maleimide is chosen from C.sub.8-C.sub.24 alkyl, alkyl- or aryl-substituted alkyl.

11. The polymeric dispersant as claimed in claim 1, wherein the second monomer is maleic anhydride and wherein the maleic anhydride is converted at least partially into N-substituted maleimide after the copolymerization.

12. The polymeric dispersant as claimed in claim 11, wherein the conversion of the maleic anhydride to N-substituted maleimide is partial, and wherein at least 10% of the maleic anhydride groups in the copolymer are converted into maleimide.

13. The polymeric dispersant as claimed in claim 1, wherein the molar ratio between the second monomer and the first monomer is in the range of 0.3 to 7.

14. (canceled)

15. (canceled)

16. The polymeric dispersant as claimed in claim 1, wherein the copolymer has a weight-average molecular weight of 2.000-500.000 g/mol.

17.-21. (canceled)

22. An inkjet dispersion comprising colorant, an aqueous and/or alcoholic carrier liquid and a polymeric dispersant, which is a copolymer comprising first and second repeating units each carrying a substituent, which second units are N-substituted maleimide units, which copolymer is obtainable by copolymerizing at least a first monomer being an ethylenically unsaturated monomer and a second monomer chosen from a maleimide compound and a maleic anhydride compound, which compounds are optionally substituted at a 2- and/or 3-position, and, in case that the second monomer is a maleic anhydride compound, converting at least part of the resulting maleic anhydride units to the second, N-substituted maleimide units, wherein the second repeating unit comprises a first substituent having a substantially non-polar chain and wherein the first repeating unit comprises a second, more polar substituent, which comprises at least one heteroatom chosen from sulphur (S) and oxygen (O).

23. The inkjet dispersion as claimed in claim 22, wherein the polymeric dispersant is at least partially adsorbed to a surface of the colorant.

24. (canceled)

25. (canceled)

26. The polymeric dispersant as claimed in claim 1, wherein the first monomer is chosen from the group of vinyl ethers, vinyl esters, and vinyl amides.

27. The polymeric dispersant as claimed in claim 7, wherein the substituent of the substituted alkyl is chosen from the group of XR.sub.3R.sub.4 and oligo(C.sub.2-C.sub.4-alkyleneoxide), wherein X is chosen from amino, sulfonyl, sulfinyl, thiol, thioether, ether and R.sub.3, R.sub.4 is H or C.sub.1-C.sub.4 alkyl, and/or wherein XR.sub.3R.sub.4 together forms a cyclic group chosen from heteroalkyl and heteroaryl.

28. The polymeric dispersant as claimed in claim 11, wherein at least 50% of the maleic anhydride groups in the copolymer are converted into maleimide.

29. The polymeric dispersant as claimed in claim 1, wherein part of the second repeating units is substituted with the first substituent and another part of the second repeating units is substituted with a second substituent.

30. The polymeric dispersant as claimed in claim 13, wherein said molar ratio is in the range of 0.9 to 5.

31. The inkjet dispersion as claimed in claim 23, wherein the polymeric dispersant is at least partially adsorbed to a surface prior and during printing until carrying out a fusing step.

32. A method of printing an inkjet dispersion onto a substrate, comprising using the inkjet dispersion of claim 22.

Description

BRIEF INTRODUCTION OF FIGURES

[0038] These and other aspects of the invention will be further elucidated with reference to the Figures and on the basis of several examples, wherein:

[0039] FIG. 1 shows the reaction equations for the synthesis of the polymeric dispersant of the invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0040] The Figures are not drawn to scale and purely diagrammatical in nature. Equal reference numerals in different FIGURES refer to equal or corresponding features.

[0041] FIG. 1 diagrammatically shows a reaction equation for the preparation of the polymeric dispersant of the invention. FIG. 1 shows two different reaction protocols to arrive at the polymer dispersant. In the first step, the ethylenically unsaturated compound (first monomer), herein more specifically identified as a vinyl ether is reacted with maleic anhydride (second monomer). Preferably, the molar ratio of the second monomer to the first monomer is larger than 1, at least in the resulting polymer, as a consequence of synthetic conditions.

[0042] After the polymerisation, the said polymer of maleic anhydride and vinyl ether or other second monomer is brought in contact with an amine ZNH.sub.2, to form maleimide groups. The extent of conversion of the maleic anhydride groups may be chosen so as to obtain suitable molar ratios of first substituents OR.sub.1 and second substituents Z.

[0043] According to a second protocol shown in FIG. 1, a process is used, wherein conversion occurs before polymerisation; i.e. the polymerisation involves a copolymerisation of maleimide and a first monomer, herein illustrated as a vinyl ether compound. The maleimide is suitably obtained from maleic anhydride. It is feasible, but not necessary that maleic anhydride is present as a further monomer according to this second protocol. The optional presence of maleic anhydride and/or repeating units based on maleic anhydride is indicated by means of brackets in FIG. 1. Alternatively, the second step of the two-step reaction may be carried out by using more than one amine Z.sub.1NH.sub.2 and Z.sub.2NH.sub.2. This leads to the presence of two different substituted maleimide groups within the polymer and optionally any maleic anhydride groups.

[0044] Furthermore, R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are all and independently chosen from hydrogen, halogen, alkyl and substituted alkyl. The choice of hydrogen and/or lower alkyl, such as methyl, ethyl, propyl is preferred, as larger substituents tends to reduce the rate of the polymerisation step. Particularly preferred are methyl and hydrogen, most preferably wherein any of R.sub.5 and R.sub.6 are hydrogen or wherein R.sub.5 is hydrogen and R.sub.6 is methyl, or alternatively wherein R.sub.5 and R.sub.6 are both methyl. In again an alternative embodiment, the groups R.sub.5 and R.sub.6 may form with the adjacent part of the maleimide or maleic anhydride a ring structure, that optionally contains a heteroatom such as oxygen. When both maleimide and maleic anhydride are present as monomers, the respective substituents R.sub.7, R.sub.8 and R.sub.5, R.sub.6 may differ from each other.

[0045] Moreover, while not preferred, it is not excluded that any further monomer is used in the synthesis. Such further monomer may be configured for dilution of the number of first and/or second substituents, for integration of specific functionality into the copolymer, such as cross linking groups, for instance based on acrylamide or acrylic acid, groups that allow chemical binding to an inorganic surface, such as silanol-groups or to a binder resin, and furthermore also for tuning any desired degree of alternating behaviour.

[0046] Furthermore, the *-symbol indicates a bond with a further monomer within the polymer. In a strictly alternating copolymer, the maleic anhydride/maleimide unit and the vinylether unit alternate. In less completely alternating copolymers, the structure of the chain may vary more. According to a preferred embodiment of the invention, the copolymer is a moderately alternating copolymer. Typically, the extent to which a copolymer is an alternating copolymer is specified by so-called copolymerisation parameters.

[0047] Theoretically, copolymerization is as a type of chain polymerization in which two (or more monomers) are simultaneously polymerized. The two monomers enter into the copolymer in overall amounts determined by their relative concentrations and reactivities. Different types of copolymers exist: statistical, alternating, block and graft copolymers. The following section is described in Polymer Handbook, 4.sup.th Edition, Brandrup J., Immergut E. H., Grulke, E. A. (2003). In a statistical copolymer, the monomer distribution along the copolymer chain follows some statistical law, for example, Bernoullian (zero-order Markov) or first- or second-order Markov. A subclass of the statistical copolymers are the random copolymers. These are more particularly copolymers formed via Bernoullian processes, wherein the two monomer units are distributed randomly. In a strictly alternating copolymer the monomer units (M.sub.1 and M.sub.2) are present in equimolar amounts in a regular alternating distribution: -M.sub.1-M.sub.2-M.sub.1-M.sub.2-M.sub.1-M.sub.2-.

[0048] In practical terms, it is hard to avoid that strictly alternating copolymers also include randomness to a certain degree. These could be random fragments of the chain, or alternatively, fragments wherein the alternating order is less perfect. For instance, there may be alternation between a unit consisting of a single first monomer and a unit consisting of a plurality of second monomers. The number of second monomers could vary between 1 and 10 for instance, typically from 1 to 5. Rather than a unit of a single first monomer, there could be units with two, three or four first monomers. This degree of randomness will depend on the type of monomers, and may further depend on the reaction conditions, such as concentration of monomers, and temperature. The extent of alternating copolymerisation has been studied and described by means of copolymerisation parameters. For a given combination of two monomers, copolymerization parameters can be experimentally derived. When one considers the propagation step of a copolymerization reaction, the propagating species (i.e. the monomer on the reactive end of the propagating polymer) can be M.sub.1* or M.sub.2*. These propagating species can then react with another monomer, being M.sub.1 or M.sub.2, thereby leading to four possible different propagation steps:

##STR00001##

[0049] where k.sub.11 is the rate constant for a propagating chain ending in M.sub.1 adding to monomer M.sub.1, k.sub.12 that for a propagating chain ending in M.sub.1 adding to monomer M.sub.2, k.sub.21 that for a propagating chain ending in M.sub.2 adding to monomer M.sub.1 and k.sub.22 that for a propagating chain ending in M.sub.2 adding to monomer M.sub.2. The aforementioned copolymerization parameters (r.sub.1 and r.sub.2)or monomer reactivity ratios aredefined as the ratio of the rate constants of a propagating species reacting with the same monomer versus the reaction with the other monomer. Thus r.sub.1=k.sub.11/k.sub.12 and r.sub.2=k.sub.22/k.sub.21.

[0050] Copolymerizations can be classified into three types based on whether the product of the two copolymerisation parameters r.sub.1r.sub.2 is unity, less than unity, or greater than unity. When the monomer reactivity product r.sub.1 r.sub.2=1, the copolymerization is termed ideal and a statistical (random) copolymer is formed. Herein, the two types of propagating species M.sub.1* and M.sub.2* show the same preference for adding one or the other of the two monomers. When the two copolymerisation parameters are different, that is, r.sub.1>1 and r.sub.2<1 or r.sub.1<1 and r.sub.2>1, the copolymer will contain a larger proportion of the more reactive monomer in random placement. When the two copolymerisation parameters are smaller than 1 down to 0, the resulting copolymer is alternating to an increasing extent. A strictly alternating copolymer is obtained if the product r.sub.1r.sub.2=0, wherein both r.sub.1 and r.sub.2=0-0.1. Moderate alternating behavior occurs when either (1) both r.sub.1 and r.sub.2 are small, preferably r.sub.1, r.sub.20.4, more preferably r.sub.1, r.sub.20.3, most preferably r.sub.1, r.sub.20.2 for instance r.sub.1r.sub.20.1 or (2) one r value is small (for instance r.sub.10.5, preferably r.sub.10.4, more preferably r.sub.10.3, most preferably r.sub.10.2 and the other r is zero (r.sub.1r.sub.2=0). The copolymer composition tends toward alternation but is not the perfectly alternating structure. According to the invention, the copolymer is suitably and substantially in the form of an alternating or moderate alternating copolymer of the structure A-B-A-B-A-B-, wherein A refers to the group obtained from the first monomer and B refers to the group obtained from the second monomer, and more particularly based on maleimide. Each of these groups A, B may contain more than one monomers. Suitably, the number of second monomers in the polymer dispersant is higher than the number of first monomers. Then, typically, the groups B may contain one or more second monomers, whereas the groups A typically contain one monomer. For sake of clarity, it is observed that the term monomer herein refers to the structural entity, i.e. wherein the double bond has been converted to bonds to neighbouring monomers. The second monomer based on maleimide can be synthetically obtained in a two step method wherein the maleimide is only formed from maleic anhydride after polymerisation. Similarly in the context of the present application, the terms second repeating unit based on maleimide, maleimide repeating unit refer to units in the polymer that are based on the specified monomer, but need not be synthetically prepared from the maleimide monomer.

[0051] More particularly, the copolymerisation parameter r.sub.1 for maleic anhydride and maleates is in the range of 0-0.1 for a plurality of different second comonomers. Vinylic comonomers have a copolymerisation parameter r.sub.2 of typically less than 0.2, and typically less than 0.1, when used in combination with maleic anhydride. Examples of such vinylic compounds are styrene, vinyl acetate, vinyl chloride, n-butyl vinyl ether, stilbene. On the other hand, acrylic compounds and acrylates with small side chains (such as methyl acrylates) typically have a copolymerisation parameter above 1.

EXAMPLES

Test Methods

[0052] Stability Test of Ink The viscosity of the dispersion is measured with a Haake Rheostress RS6000 operated in shear rate sweep from 0.1 to 3000 1/s at 25 C. and expressed in mPas. The instrument is equipped with a cone/plate geometry type C60/1 and the gap is set to 0.052 mm. The viscosity at 3000 1/s is The particle size is measured with a Mastersizer 3000 from Malvern.

Dispersing Agents

Example 1

[0053] Dispersing agent based on 2-ethylhexyl vinyl ether (2EHVE), maleic anhydride (MA) and amine (A1) with the formula MeO(PO).sub.29-(EO).sub.6NH2, wherein Me is methyl, PO is propylene oxide and EO is ethylene oxide. The amine has 29 propylenoxide units and 6 ethyleneoxide units. This amine is commercially available from Huntsman under the tradename Jeffamine M2070.

(Method of Polymerization A)

[0054] In a 1 liter flask, 2-ethylhexyl vinyl ether (40 g, 0.257 mol), commercially available from BASF, is heated to 110 C. and degassed under vacuum/nitrogen 3 times. In a separate flask, of maleic anhydride (25.2 g, 0.257 mol, 1 eq.) is dissolved in toluene (250 g). After dissolution, WAKO V-601 (1.00 g, 1 wt %), commercially available from Wako Chemicals and being dimethyl 2,2-azobis(2-methylpropionate), is added to the maleic anhydride solution which is subsequently degassed under vacuum/nitrogen. This solution is then added to the heated 2-ethylhexyl vinyl ether (under a nitrogen atmosphere) over a period of 30 minutes. After full addition of the maleic anhydride solution, the mixture is allowed to react further at 110 C. for an additional 15 minutes. When the polymerization is complete, a solution of the amine A1 (103 g, 0.05 mol, 1 eq.) in toluene (60 g) is added dropwise to the polymer solution at 110 C. over 15 minutes under a nitrogen atmosphere. Afterwards the temperature is raised to 175 C. and the reaction is continued for 60 minutes. Finally all volatiles are evaporated to yield the desired dispersing agent.

Ink Preparation and Composition

[0055] An pigment dispersion with a composition as mentioned in table 1 is prepared in a bead mill type PML from Buhler AG. The ink is milled with 0.3 mm YTZ beads for 4 hours at a speed of 10 m/s

TABLE-US-00001 TABLE 1 Pigment dispersion 1C Weight % Pigment type Heliogen Blue 15 D7079 (*) Dispersing agent example 1 15 Water 70 (*) pigment commercially available from BASF

[0056] Afterwards this pigment dispersion is diluted to an ink composition with the following composition

TABLE-US-00002 TABLE 2 Inkjet 1C Weight % Pigment dispersion 1C 20 Surfactant: Byk 333 (*) 0.75 Humectant: 2-pyrrolidone 15 Polyethyleenglycol 600 5 Water 59.25 (*) commercially available from Byk. It is a polyether modified polydimethylsiloxane

[0057] The physical properties of the ink inkjet 1C are:

Viscosity (at 3000 1/s): 10.2 mPas
Particle size dv50: 125 nm

Test Results

[0058] This ink composition inkjet 1C is filtered over of 1 m filter and charged into a DMP-2831 printer available from Fuji. No problems were observed during the print test.