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JP-7856510-B2 - Pigment dispersant, water-based ink, ink cartridge, and inkjet recording method

JP7856510B2JP 7856510 B2JP7856510 B2JP 7856510B2JP-7856510-B2

Inventors

  • 堀内 貴行

Assignees

  • キヤノン株式会社

Dates

Publication Date
20260511
Application Date
20220701
Priority Date
20210707

Claims (14)

  1. A pigment dispersant represented by the following general formula (1). (In general formula (1), each Q is independently a structure represented by general formula (2) below. Each L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.) (In general formula (2), R1 to R10 are each independently a hydrogen atom, a halogen atom, or an alkyl group. One of R11 and R12 is a bonding site with L, and the other is a hydrogen atom.)
  2. The pigment dispersant according to claim 1, wherein E has a structure represented by the following general formula (3) or general formula (4). (In general formula (3), * represents the bonding site with L. R13 are each independently a hydrogen atom or a methyl group. n is an integer of 1 or more.) (In general formula (4), * represents the bonding site with L.)
  3. The pigment dispersant according to claim 1, wherein E has a structure represented by the following general formula (5). (In general formula (5), * represents the connection site with L. q is an integer greater than or equal to 2.)
  4. An aqueous inkjet ink comprising a pigment and a pigment dispersant for dispersing the pigment, An aqueous ink characterized in that the pigment dispersant is the pigment dispersant described in claim 1.
  5. The aqueous ink according to claim 4, wherein the content (mass%) of the pigment dispersant is 0.01 times or more and 0.50 times or less in mass ratio to the content (mass%) of the pigment.
  6. The aqueous ink according to claim 4, wherein the content (by mass) of the pigment dispersant is 0.01% by mass or more and 15.0% by mass or less, based on the total mass of the ink.
  7. The aqueous ink according to claim 4, wherein the content (by mass) of the pigment dispersant is 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink.
  8. The aqueous ink according to claim 4, wherein the pigment is a pigment having a quinacridone skeleton or a diketopyrrolopyrrole skeleton.
  9. The aqueous ink according to claim 4, wherein the pigment is a pigment having a quinacridone skeleton.
  10. The aqueous ink according to claim 4, wherein the pigment content (by mass) is 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.
  11. Furthermore, the aqueous ink according to claim 4 contains a resin dispersant for dispersing the pigment.
  12. The aqueous ink according to claim 11, wherein the content (by mass) of the resin dispersant is 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink.
  13. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in any one of claims 4 to 12.
  14. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of claims 4 to 12.

Description

This invention relates to a pigment dispersant, an aqueous ink, an ink cartridge, and an inkjet recording method. In recent years, inkjet recording methods using pigment inks have been increasingly used to record images such as business documents clearly onto recording media such as plain paper, and their frequency of use has increased dramatically. For such applications, a higher level of pigment dispersion stability is required than ever before, so that images can be recorded stably even when the inkjet recording device is used for extended periods. Various technologies to improve inkjet suitability have been investigated. For example, non-aqueous inks containing specific heterocyclic compounds as pigment dispersants have been proposed (see Patent Document 1). Furthermore, aqueous inks containing surface-modified pigments with specific functional groups introduced onto the surface of the pigment particles have been proposed (see Patent Document 2). Additionally, aqueous inks containing dispersants with specific chromophores suspended from their main chains have been proposed (see Patent Document 3). Japanese Patent Publication No. 2007-023073Japanese Patent Publication No. 2020-037644Special Publication No. 2009-501253 This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention.This figure schematically shows an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The present invention will be further described in detail below, with reference to preferred embodiments. In this invention, when a compound is a salt, the salt exists in the ink dissociated as ions; however, for convenience, it will be expressed as "containing a salt." Furthermore, water-based inkjet ink may simply be referred to as "ink." A "unit" of a resin refers to the smallest repeating unit constituting the resin, meaning a structure formed by the (co)polymerization of one monomer. Unless otherwise specified, physical property values are given at room temperature (25°C). The inventors of this invention have conducted various studies on improving the dispersion stability of pigments using pigment dispersants. As a result, they found that using a pigment dispersant represented by the following general formula (1) suppresses the increase in pigment particle size and improves the dispersion stability of the pigment. The pigment dispersant represented by general formula (1) is characterized by having a structure in which multiple quinacridone skeletons are crosslinked by alkylene ethers. (In general formula (1), Q is independently a structure represented by general formula (2) below. L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.) (In general formula (2), R1 to R10 are each independently a hydrogen atom, a halogen atom, or an alkyl group. One of R11 and R12 is a bonding site with L, and the other is a hydrogen atom.) The inventors hypothesize the following mechanism by which the dispersion stability of pigments is improved by using the above-mentioned pigment dispersant. In general formula (1), Q is a quinacridone skeleton. The quinacridone skeleton has a planar structure in which aromatic rings are linked, and can be adsorbed onto the particle surface of pigments, which are inherently hydrophobic, through the action of at least one of van der Waals forces, π-π interactions, and hydrophobic interactions. E is a polyhydric alcohol residue that forms an ether bond with L. In this specification, "polyhydric alcohol residue" refers to structures other than the hydrogen atoms of the hydroxyl groups in a linear or branched polyhydric alcohol. It is not necessary for all hydroxyl groups to form ether bonds, as long as at least two of the hydroxyl groups of the polyhydric alcohol form an ether bond with L. In other words, the polyhydric alcohol residue may contain unreacted hydroxyl groups that do not form an ether bond with L. The polyhydric alcohol residue contributes to the affinity for liquid media. In liquid media such as water or organic solvents, the quinacridone skeleton is adsorbed onto the surface of the pigment particles, and the portion of the polyhydric alcohol residue with high affinity for the liquid media is oriented towards the liquid media side. Therefore, the steric hindrance of the polyhydric alcohol residue portion can increase the spacing between pigment particles and suppress pigment aggregation. L is a linking group between Q and E. In this specification, "linking group" refers to a divalent substructure between the nitrogen atom of the quinacridone skeleton and the oxygen atom of the polyhydric alcohol residue. The pigment dispersant represented by general formula (1) has m = 2 or more, meaning