Search

US-12617963-B2 - Inkjet ink, inkjet printing process and ink set for forming an image on a substrate and aqueous pigment dispersion for forming the inkjet ink

US12617963B2US 12617963 B2US12617963 B2US 12617963B2US-12617963-B2

Abstract

Inkjet ink for forming an image on a substrate includes a pigment P, a first block copolymer dispersant D1 for dispersing the pigment P and a second block copolymer dispersant D2 for dispersing the pigment P, and an aqueous carrier. The first block copolymer dispersant D1 is different from the second block copolymer dispersant D2. Each block copolymer dispersant D1, D2 includes an anchoring segment A1, A2 for anchoring to the pigment P. Each of the block copolymer dispersants D1, D2 additionally includes a matrix stabilization segment M for aqueous phase stabilization of the pigment P. The anchoring segment A1 of the first block copolymer dispersant D1 includes a repeating unit R1 and the anchoring segment A2 of the second block copolymer dispersant D2 includes a repeating unit R2, where the repeating unit R1 is less hydrophobic than the repeating unit R2.

Inventors

  • Werner Jozef Johan Op de Beeck
  • Lode Erik Dries Deprez
  • Wouter Jeroom Maria Van Gaens
  • Nils Margaretha Robert DE VOS
  • Lore WYNS

Assignees

  • XEIKON MANUFACTURING N.V.

Dates

Publication Date
20260505
Application Date
20211004
Priority Date
20201005

Claims (20)

  1. 1 . An inkjet ink for forming an image on a substrate, the inkjet ink comprising: a pigment P, a first block copolymer dispersant D1 for dispersing the pigment P, a second block copolymer dispersant D2 for dispersing the pigment P, and an aqueous carrier; wherein said first block copolymer dispersant D1 is different from said second block copolymer dispersant D2, wherein each block copolymer dispersant D1, D2 comprises an anchoring segment A1, A2 for anchoring to the pigment P, wherein each of the block copolymer dispersant D1, D2 additionally comprises a matrix stabilization segment M for aqueous phase stabilization of the pigment P, wherein the anchoring segment A1 of the first block copolymer dispersant D1 comprises a repeating unit R1 and the anchoring segment A2 of the second block copolymer dispersant D2 comprises a repeating unit R2, and wherein the repeating unit R1 is less hydrophobic than the repeating unit R2.
  2. 2 . The ink according to claim 1 , wherein the repeating unit R1 has a Hansen Solubility Parameter value δ(polar+hydrogen) R1 , wherein δ(polar+hydrogen) R1 >7.2 cal 1/2 cm −3/2 , wherein the Hansen Solubility Parameter value δ(polar+hydrogen) is defined as √[δ(polar) 2 +δ(hydrogen) 2 ].
  3. 3 . The ink according to claim 1 , wherein the repeating unit R1 is a non-ionic repeating unit.
  4. 4 . The ink according to claim 1 , wherein the repeating unit R2 has a Hansen Solubility Parameter value δ(polar+hydrogen) R2 , wherein δ(polar+hydrogen) R2 <7.2 cal 1/2 cm −3/2 , wherein the Hansen Solubility Parameter value δ(polar+hydrogen) is defined as √[δ(polar) 2 +δ(hydrogen) 2 ].
  5. 5 . The ink according to claim 1 , wherein the anchoring segment A1 of the first block copolymer dispersant D1 has another repeating unit R1′ different from R1, and wherein the other repeating unit R1′ has a Hansen Solubility Parameter value δ(polar+hydrogen) R1 >7.2 cal 1/2 cm −3/2 ; and/or wherein the anchoring segment A2 of the second block copolymer dispersant D2 has another repeating unit R2′ different from R2, and wherein the other repeating unit R2′ has a Hansen Solubility Parameter value δ(polar+hydrogen) R2 <7.2 cal 1/2 cm −3/2 .
  6. 6 . The ink according to claim 1 , wherein the anchoring segment A1 is formed using at least one monomer Mn 1 , and the anchoring segment A2 is formed using at least one monomer Mn 2 , wherein the monomer M 1 , M 2 is selected from the group consisting of a methacrylate, an acrylate, and vinyl monomers, and wherein the monomer Mn 2 of the anchoring segment A2 comprises an alkyl, alkenyl or aryl group.
  7. 7 . The ink according to claim 6 , wherein the monomer Mn 2 of the anchoring segment A2 is at least one of benzyl methacrylate, butyl methacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, lauryl methacrylate, stearyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate, cyclohexyl methacrylate, benzyl acrylate, butyl acrylate, methyl acrylate, ethyl acrylate, propyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, p-tolyl acrylate, sorbyl acrylate, cyclohexyl acrylate, and any mixture thereof and/or wherein the monomer Mn 1 of the anchoring segment A1 is at least one of tri (ethylene glycol) methyl ether acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, dimethylaminoethyl acrylate (DMAA), N,N-dimethylacrylamide, acryloyl morpholine (ACMO), N-vinylpyrrolidone (NVP), vinyl methyl oxazolidinone (VMOX),) and 2-(2ethoxyethoxy)ethyl acrylate (EOEOEA), phenoxyethyl methacrylate, methacrylonitrile, ethylene glycol methyl ether methacrylate, 2-ethoxyethyl methacrylate, di(ethylene glycol) methyl ether methacrylate, tri (ethylene glycol) methyl ether methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, di(propylene glycol) methyl ether methacrylate, phenoxyethyl acrylate, ethylene glycol methyl ether acrylate, 2-ethoxyethyl acrylate, di(ethylene glycol) methyl ether acrylate, 2-[[(butylamino) carbonyl]oxy]ethyl acrylate, and any mixture thereof.
  8. 8 . The ink according to claim 7 , wherein the monomer Mn 1 of the anchoring segment A1 is an acrylate or methacrylate and comprises an monoethyleneglycol group or polyethyleneglycol group.
  9. 9 . The ink according to claim 1 , wherein the matrix stabilization segment M is formed using at least one monomer Mn 3 for obtaining an ionic hydrophilic repeating unit for aqueous phase stabilization of the pigment, the ionic hydrophilic repeating unit optionally containing a neutralized acid group, neutralized basic group or other ionic functionalities such as a quaternary ammonium group.
  10. 10 . The ink according to claim 1 , wherein the matrix stabilization segment M is formed using at least one monomer Mn 3 which is selected from the group consisting of methacrylic acid, acrylic acid, maleic acid, maleic acid monoester, itaconic acid, itaconic acid monoester, crotonic acid, crotonic acid monoester, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, t-butylaminoethyl methacrylate, t-butylaminoethyl acrylate, and mixtures thereof.
  11. 11 . The ink according to claim 1 , wherein the matrix stabilization segment M comprises at least one repeating unit R3, which comprises an ionic moiety.
  12. 12 . The ink according to claim 1 , wherein the repeating units R1, R2 of the anchoring segment A1, A2 do not have an ionic group.
  13. 13 . The ink according to claim 1 , wherein the anchoring segment A1 has a number of repeating units n and wherein the repeating units R1 are at least 50 number-% of the total number of repeating units n1; and/or wherein the anchoring segment A2 has a number of repeating units n and wherein the repeating units R2 are at least 50 number-% of the total number of repeating units n2.
  14. 14 . The ink according to claim 1 , wherein the weight ratio between the block copolymer dispersant D1 and the block copolymer dispersant D2 is between 0.1 and 10.
  15. 15 . The ink according to claim 1 , wherein the weight ratio between the pigment P and the sum of the block copolymer dispersant D1 and the block copolymer dispersant D2 is between 0.2 and 10.0.
  16. 16 . The ink according to claim 1 , wherein the weight ratio between the pigment P and the block copolymer dispersant D1 is between 0.05 and 10.0.
  17. 17 . The ink according to claim 1 , wherein the weight ratio between the pigment P and the block copolymer dispersant D2 is between 0.05 and 10.0.
  18. 18 . The ink according to claim 1 , wherein the block copolymer dispersant D1 and/or the block copolymer dispersant D2 is a diblock copolymer.
  19. 19 . Pigment dispersion for forming an inkjet ink, the pigment dispersion comprising a pigment P, a first block copolymer dispersant D1 for dispersing the pigment P and a second block copolymer dispersant D2 for dispersing the pigment P, and an aqueous carrier; wherein said first block copolymer dispersant D1 is different from said second block copolymer dispersant D2, wherein each block copolymer dispersant D1, D2 comprises an anchoring segment A1, A2 for anchoring to the pigment P, wherein each of the block copolymer dispersant D1, D2 additionally comprises a matrix stabilization segment M for aqueous phase stabilization of the pigment P, wherein the anchoring segment A1 of the first block copolymer dispersant D1 comprises a repeating unit R1 and the anchoring segment A2 of the second block copolymer dispersant D2 comprises a repeating unit R2, wherein the repeating unit R1 is less hydrophobic than the repeating unit R2; wherein the aqueous carrier contains water, and optionally a total amount of water soluble organic solvent, which is less than 20 wt % of the total weight of the aqueous carrier, and wherein the repeating unit R1 has a Hansen Solubility Parameter value δ(polar+hydrogen) R1 (=√[δ(polar) 2 +δ(hydrogen) 2 ]), wherein δ(polar+hydrogen) R1 >7.2 cal 1/2 cm −3/2 .
  20. 20 . Pigment dispersion according to claim 19 , wherein the amount of pigment P in the pigment dispersion is in the range of 10-80 wt-% based on weight of the pigment dispersion.

Description

This application is a national stage filing under 35 U.S.C. 371 of pending International Application No. PCT/EP2021/077306, filed Oct. 4, 2021, which claims priority to Netherlands Patent Application No. 2026619, filed Oct. 5, 2020, the entirety of which applications are incorporated by reference herein. FIELD OF INVENTION The field of the invention relates to an inkjet ink, inkjet printing process and ink set of inkjet inks for forming an image on a substrate and aqueous pigment dispersion for forming the inkjet ink. The inkjet printing process for forming an image on a substrate uses an inkjet ink according to the present invention. The ink set of inkjet inks for forming an image on a substrate comprises an inkjet ink according to the present invention. The field of the invention further relates to an aqueous pigment dispersion for forming the inkjet ink according to the invention. BACKGROUND An inkjet printing process for forming an image on a substrate by applying a plurality of inkjet inks on the substrate is generally known. Inkjet inks for industrial printing applications primarily use pigments as colorants, except in the textile industry which often still uses reactive dye based inkjet inks. Pigments are solid materials that also remain as a solid in the inkjet ink carrier, in contrast to dyes which actually dissolve in the carrier medium. The pigment particles are finely dispersed in an ink and are of nanometer scale size. A typical inkjet printing process uses 3 or 4 colors of inkjet inks to create multicolor images. Typical colors are cyan (C), magenta (M), yellow (Y) and black (K). The CMY color inkjet inks are typically made up of organic pigments, wherein some contain a metal atom in a complex, whereas the K inks use organic pigments typically made of carbon black. The pigment powders are commercially not available as nanometer particles, but come as agglomerates and aggregates of pigment particles formed during the synthesis process. The agglomerates and aggregates of pigments need to be made smaller and will typically be brought to the nanometer scale size by grinding, milling, or other techniques to break up the agglomerates and aggregates. The particle size reduction of the pigment powder particles is often carried out in a carrier medium that will be used in a later stage in the ink. Such a process step of making pigment particles smaller is often done at higher pigment concentration than in the final ink and is then referred to as the pigment dispersion. As discussed above, the pigments are mechanically broken down to sizes of 30-300 nm which are needed to be stabilized by adding dispersing agents (or surfactants) to physically and/or electrostatically prevent the pigments to re-agglomerate. Typically this is a physico-chemical phenomenon as there is no chemical bond between the pigment surface and the dispersing agent, which can be polymeric dispersing agents (e.g. random copolymer, block-copolymers, grafted copolymers) or surfactants. Sometimes also covalently bound chemicals can be used for pigment particle stabilization in water based inks, but requires mostly an expensive production process. A known approach for making pigment dispersions is based on random polymerized dispersing agents: they are used in analog inks e.g. for flexographic printing, but also in inkjet inks. Typically, the random polymers are built up of two kinds of monomers, one which is more pigmentophilic and another which is more compatible with the carrier liquid or matrixophilic so to speak. These monomers are randomly spread out in the polymer, so no polymer structure (i.e. monomer sequence) and no number of monomeric repeating units is pre-defined. Hence a number of polymers will have a favorable structure, capable of stabilizing pigment particles in the liquid, but there is a non-active population as well having a “bad” structure for stabilization (e.g. not enough pigment anchors, not close enough to each other pigment anchors, too few matrixophilic groups). These fractions often are not adsorbed or readily desorbed yielding in a non-stable dispersion. Other side effects may occur that are undesired when manufacturing dispersions for inkjet inks. Two of the main problems are that the not-absorbed high molecular weight dispersant molecules are present in the matrix and therefore contribute to a higher dispersion viscosity. Additionally visco-elastic properties of the final ink may be affected negatively. Both effects of increased viscosity and affected visco-elastic properties of the final ink may disturb the drop forming process, such as by increased mist forming. Another known approach is block copolymer dispersants. Block copolymer dispersants containing hydrophobic and hydrophilic block segments have been disclosed in numerous inkjet ink patents. U.S. Pat. No. 5,859,113 (DU PONT) discloses an AB block copolymer dispersant with a polymeric A segment and a polymeric B segment. A wide variety of polymeric dis