JP2008106153A - Pigment ink for ink-jet printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment ink excellent in dispersion stability, storage stability and printed image color developability, and capable of realizing high jet stability even in such an ink-jet printing method as to jet an ink by applying thermal energy, and to provide an ink set attaining high print density and ink fixation in high-speed printing. <P>SOLUTION: The ink for ink-jet printing contains a pigment and a graft copolymer. In this ink, the graft copolymer is composed of hydrophilic segments and hydrophobic segments, wherein the hydrophilic segment consists of a homopolymer or copolymer of monomer(s) having at least an anionic functional group, and the hydrophobic segment consists of a copolymer of a monomer having at least a Lewis-basic functional group and a monomer having a monocyclic or condensed polycyclic hydrocarbon. The ink set is constituted of a combination of the above ink with a reaction liquid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inkjet pigment ink that is excellent in dispersion stability and storage stability and can realize high ejection stability even when used in an inkjet recording method.

  The ink jet recording method performs recording by causing ink droplets to fly and adhere to a recording medium such as paper. Conventional inks for ink-jet recording have water as a main component, and dyes that are soluble in water as the main component have been used as colorants. Dye inks are excellent in long-term storage, are not easily clogged with nozzles, and provide printed matter with excellent saturation and transparency. However, the printed matter lacks the weather resistance and water resistance. On the other hand, for the purpose of improving the weather resistance and water resistance of printed matter, pigment ink using a pigment as a colorant has recently attracted attention. However, since pigments do not dissolve in water-based ink solvents, pigments are dispersed in ink solvents as particles to make inks, but the dispersion state of pigment particles is kept stable while suppressing aggregation and sedimentation over a long period of time. It was sometimes difficult.

  On the other hand, as one of the ink jet recording methods, there is a method in which an electrothermal converter is used as an ejection energy supply unit, and droplets are ejected by generating bubbles by applying thermal energy to ink (for example, Patent Documents 1 to 3). 3). In this method, a high-density multi-orifice of the recording head can be easily realized, and high-resolution and high-quality images can be recorded at high speed. However, when the pigment ink is ejected using this method, it is expected that an abrupt change in ink physical properties will occur particularly during foaming. For this reason, when a pigment ink with low dispersion stability is used, stable ejection characteristics may not be obtained.

  In response to the above problem, Patent Document 4 proposes that a graft copolymer in which one of the main chain or the side chain unit is a hydrophilic segment and the other is a hydrophobic segment is used as a pigment dispersant. In this case, it is said that the hydrophobic segment functions to physically adsorb to the hydrophobic pigment by hydrophobic interaction, and the hydrophilic segment spreads into the water, which is the ink solvent, to give a repulsive force to the pigment particles. Yes. In addition, pigment inks using a graft copolymer in which the hydrophobic and hydrophilic segments are clearly separated as dispersants exhibit their respective functions effectively, and the dispersion stability of pigment particles and the long-term ink Storage stability and discharge stability are improved.

  Patent Document 5 also proposes to use a graft copolymer in which one of the main chain or side chain unit is a hydrophilic segment and the other is a hydrophobic segment as a pigment dispersant. And the hydrophobic segment in this case is comprised by the monomer selected from the aryl ester of (meth) acrylic acid, N-aryl (meth) acrylamide, and vinyl aryl ester. Since many pigments have an aromatic ring in their structure, as described above, by copolymerizing a monomer having an aryl group that is an aromatic ring in the hydrophobic segment, the polymer and the pigment are mixed. The improvement of adsorption power is aimed at. Furthermore, in this proposal, in order to increase the binding force between the pigment having an acidic or basic functional group on the surface and the polymer, the basicity capable of binding to the above-described functional group as a monomer constituting the hydrophobic segment. Or the monomer which has an acidic functional group is contained.

Japanese Patent Publication No. 61-59911 Japanese Patent Publication No. 61-59912 Japanese Examined Patent Publication No. 61-59914 JP-A-6-100810 Japanese Patent Laid-Open No. 10-87768

  In recent years, in order to print high-resolution and high-quality images by inkjet at high speed, a recording method using a recording head in which nozzles are arranged at high density is required. However, when pigment ink is ejected using such a recording head, deposits such as polymers are seen in the nozzles, and ink jet recording characteristics may be insufficient. Although Examples only describe carbon black, based on the idea described in Patent Document 5, for example, an organic pigment having an acidic group is used as a basic functional group such as an amino group as a constituent monomer of the hydrophobic segment. Such a tendency was observed in the case of pigment ink dispersed by a graft copolymer containing a monomer having a group.

  This is considered as follows. When a hydrophilic monomer such as an amino group is contained in the hydrophobic segment, the hydrophobicity of the hydrophobic segment is lowered. Even with polar functional groups, pigments are generally hydrophobic, and if the hydrophobicity of the hydrophobic segment of the resin decreases, the hydrophobic interaction between the pigment and the resin decreases, and the adsorption power of the resin to the pigment Becomes weaker. For this reason, when ejected by ink jetting, the resin is easily detached from the pigment by the energy at the time of ejection, and it is considered that deposits such as polymers were seen in the nozzle. Also, most of the pigment inks are often adjusted to pH 7 to 10 for the purpose of dispersion stability and protection of the recording apparatus member, and the pigment surface characteristics in the above pH range are taken into consideration. It is necessary to determine the resin in which the resin is dispersed.

  Therefore, an object of the present invention is to provide an ink-jet pigment ink that is excellent in dispersion stability and storage stability, and further has excellent image coloration properties and can realize high ejection stability when used in an ink-jet recording method. is there.

（式中、−Ｒ¹は、−Ｈ、−ＣＨ₃、−ＣＨ₂ＯＨ及び−ＣＨ（ＣＨ₃）ＯＨの中から選ばれる。又、ｍは１又は０であって、ｍが１であるとき、−Ｘは、−Ｃ（Ｏ）ＮＨ−、−Ｏ−、−Ｃ（Ｏ）−、−ＯＣ（Ｏ）−及び−Ｃ（Ｏ）Ｏ−の中から選ばれる。ｍが０であるときｎは０乃至５のいずれかの整数であり、ｍが１であるときｎは１乃至５のいずれかの整数である。Ｒ¹が−Ｈ又は−ＣＨ₃であるとき、−Ｙは、−ＮＲ²Ｒ³、−ＳＨ及び−ＯＨの中から選ばれる。−Ｒ¹が−ＣＨ₂ＯＨ又は−ＣＨ（ＣＨ₃）ＯＨのとき、−Ｙは、−Ｈ、−ＮＲ²Ｒ³、−ＳＨ及び−ＯＨの中から選ばれる。上記Ｒ²とＲ³は、それぞれ独立に、Ｈ、ＣＨ₃及びＣ₂Ｈ₅の中から選ばれる。） The above object is achieved by the present invention described below. That is, the present invention relates to an inkjet pigment ink comprising a pigment, a graft copolymer, a water-soluble solvent, and water, wherein the graft copolymer has a hydrophilic segment and a hydrophobic segment, The segment is a copolymer comprising at least a monomer having a Lewis basic functional group represented by the following general formula (1) and a monomer having a monocyclic or condensed polycyclic hydrocarbon, and the total weight of the hydrophobic segment portion in the copolymer An ink-jet pigment ink, wherein the content of the monomer having a Lewis basic functional group is 1% by mass or more and 30% by mass or less based on

(In the formula, —R ¹ is selected from —H, —CH ₃ , —CH ₂ OH and —CH (CH ₃ ) OH. Also, m is 1 or 0, and m is 1. -X is selected from -C (O) NH-, -O-, -C (O)-, -OC (O)-and -C (O) O-, where m is 0. When n is an integer of 0 to 5, and when m is 1, n is an integer of 1 to 5. When R ¹ is —H or —CH ₃ , —Y is -NR ² R ³ , -SH and -OH, when -R ¹ is -CH ₂ OH or -CH (CH ₃ ) OH, -Y is -H, -NR ² R ³ ,- Selected from SH and -OH, wherein R ² and R ³ are each independently selected from H, CH ₃ and C ₂ H _5. )

  According to the present invention, a pigment ink having excellent dispersion stability, storage stability, and color development of an image and having high ejection stability can be obtained even when an ink jet recording method is used.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The ink of the present invention comprises a pigment, a graft copolymer, a water-soluble solvent, and water. The graft copolymer has a specific structure having a hydrophilic segment and a hydrophobic segment. It is characterized by that. That is, when the hydrophilic segment and the hydrophobic segment constituting the graft copolymer are synthesized, the following specific monomer is used. For the synthesis of the hydrophilic segment, a monomer having at least an anionic functional group is used, and for the synthesis of the hydrophobic segment, at least a monomer having a Lewis basic functional group represented by the general formula (1) and a single ring or a condensed group And a monomer having a polycyclic hydrocarbon.

  The hydrophobic segment constituting the graft copolymer used in the present invention functions to be adsorbed on the surface of the hydrophobic pigment particles by the hydrophobic interaction. And the hydrophilic segment which comprises a graft copolymer spreads in the water which is a solvent of an ink, As a result, fulfill | performs the function to provide repulsive force to a pigment particle by the steric hindrance repulsive force of hydrophilic segments. A graft copolymer in which a hydrophilic segment and a hydrophobic segment are clearly separated can be said to be the most preferred polymer as a dispersant in an aqueous ink because these functions are efficiently expressed. The graft copolymer used in the present invention is more preferably one having a structure in which the hydrophobic segment is a main chain unit of the graft copolymer and the side chain unit is a hydrophilic segment. That is, when the graft copolymer having such a structure is used, the hydrophobic segment forming the main chain unit is closely adsorbed on the pigment surface, so that the adsorption of the polymer to the pigment can be enhanced. Further, the hydrophilic segment forming the other side chain unit spreads greatly in the ink solvent, and a strong repulsive force can be imparted between the pigment particles.

  The hydrophilic segment in the present invention needs to consist of a homopolymer or copolymer of monomers having at least an anionic functional group. As described above, the hydrophilic segment of the graft copolymer spreads widely in the ink solvent and imparts repulsive force due to steric hindrance between the pigment particles to the pigment particles. When the monomer constituting the hydrophilic segment has an anionic functional group, the anionic functional group causes the pigment particles to be negatively charged. Therefore, electrostatic repulsion is further generated between the pigment particles. In particular, the side chain unit of the graft copolymer is preferably composed of a hydrophilic segment, and the hydrophilic segment is preferably a homopolymer or copolymer of a monomer having an anionic functional group. That is, when a structure having such a structure is used, a repulsive force due to steric hindrance and electrostatic repulsive force are simultaneously generated between the pigment particles, so that the pigment particles dispersed in the ink solvent have higher dispersion stability. Sex can be imparted.

  Further, since plain paper used as an ink jet recording medium has a cation as a paper component, the hydrophilic segment is at least a homopolymer or copolymer of a monomer having an anionic functional group as follows. There are also advantages. That is, by using a pigment ink containing a graft copolymer having such a hydrophilic segment, an anionic functional group in the ink reacts with a cation of the paper component, so that a printed matter having a high print density and fixability. Is obtained. Further, an ink system that forms an image using an ink set in which a reaction liquid described later and a pigment ink containing a graft copolymer as described above are used together has the following advantages. That is, when a pigment ink containing a graft copolymer having a hydrophilic segment made of a homopolymer or copolymer of a monomer having at least an anionic functional group is brought into contact with a reaction liquid containing a compound having an action of aggregating the pigment, pigment particles As a result, the printed matter having a higher print density and fixability can be obtained.

  As a monomer which has an anionic functional group which comprises a hydrophilic segment, the monomer containing carboxyl groups, such as acrylic acid, methacrylic acid, (anhydrous) maleic acid, itaconic acid, and fumaric acid, is mentioned, for example. Moreover, the monomer which has sulfo groups and phosphono groups, such as vinyl sulfonic acid, p-vinyl benzene sulfonic acid, and vinyl phosphonic acid, is mentioned. In the present invention, one or more of these monomers are appropriately selected and used as a monomer having an anionic functional group. Of these, the most preferred monomer is acrylic acid. The pigment ink containing a graft copolymer using acrylic acid as a constituent monomer of the hydrophilic segment can particularly quickly aggregate pigment particles dispersed in the ink by a reaction with a reaction liquid described later. preferable.

  The hydrophilic segment constituting the graft copolymer suitable for the present invention is synthesized using a monomer having a hydrophilic functional group as listed below, which can be copolymerized with a monomer having an anionic functional group as described above. Can do. Examples of the monomer having a copolymerizable hydrophilic functional group include monomers having a hydroxyl group such as (meth) acrylic acid hydroxyalkyl ester and mono (meth) acrylic acid ester of polyhydric alcohol such as ethylene glycol. . Moreover, the (meth) acrylic acid ester of ethylene oxide or propylene oxide is mentioned. In addition, as a monomer which comprises a hydrophilic segment, you may contain the hydrophobic monomer mentioned later in the range which does not prevent the hydrophilic property of a hydrophilic segment.

  Next, the hydrophobic segment constituting the graft copolymer characterizing the present invention will be described. In the present invention, at least a monomer having a Lewis basic functional group represented by the following general formula (1) and a monomer having a monocyclic or condensed polycyclic hydrocarbon are used as monomers constituting the hydrophobic segment. .

（式中、−Ｒ¹は、−Ｈ、−ＣＨ₃、−ＣＨ₂ＯＨ及び−ＣＨ（ＣＨ₃）ＯＨの中から選ばれる。又、ｍは１又は０であって、ｍが１であるとき、−Ｘは、−Ｃ（Ｏ）ＮＨ−、−Ｏ−、−Ｃ（Ｏ）−、−ＯＣ（Ｏ）−及び−Ｃ（Ｏ）Ｏ−の中から選ばれる。ｍが０であるときｎは０乃至５のいずれかの整数であり、ｍが１であるときｎは１乃至５のいずれかの整数である。Ｒ¹が−Ｈ又は−ＣＨ₃であるとき、−Ｙは、−ＮＲ²Ｒ³、−ＳＨ及び−ＯＨの中から選ばれる。−Ｒ¹が−ＣＨ₂ＯＨ又は−ＣＨ（ＣＨ₃）ＯＨのとき、−Ｙは、−Ｈ、−ＮＲ²Ｒ³、−ＳＨ及び−ＯＨの中から選ばれる。上記Ｒ²とＲ³は、それぞれ独立に、Ｈ、ＣＨ₃及びＣ₂Ｈ₅の中から選ばれる。）

(In the formula, —R ¹ is selected from —H, —CH ₃ , —CH ₂ OH and —CH (CH ₃ ) OH. Also, m is 1 or 0, and m is 1. -X is selected from -C (O) NH-, -O-, -C (O)-, -OC (O)-and -C (O) O-, where m is 0. When n is an integer of 0 to 5, and when m is 1, n is an integer of 1 to 5. When R ¹ is —H or —CH ₃ , —Y is -NR ² R ³ , -SH and -OH, when -R ¹ is -CH ₂ OH or -CH (CH ₃ ) OH, -Y is -H, -NR ² R ³ ,- Selected from SH and -OH, wherein R ² and R ³ are each independently selected from H, CH ₃ and C ₂ H _5. )

  In order to adsorb the graft copolymer having hydrophilic and hydrophobic segments to the pigment, the hydrophilic segments are conditioned in water, the ink solvent, while the hydrophobic segments are collected on the surface of the hydrophobic pigment and become hydrophobic. It is necessary to create an interaction. In the graft copolymer used in the present invention, since the hydrophilic segment is composed of a monomer having an anionic functional group, the ink solvent is neutral or alkaline in order to adapt the hydrophilic segment to water. In particular, it is preferably alkaline. Therefore, in order to firmly adsorb the hydrophobic segment of the graft copolymer to the pigment surface, the characteristics of the pigment surface in the alkaline region are important. Accordingly, in order to evaluate the properties of the pigment surface, the present inventors suspended various pigments in an acidic aqueous solution and performed acid-base titration with a base. As a result, many pigments were found to be Lewis acids that release protons in the alkaline region. Therefore, in the present invention, the hydrophobic segment of the graft copolymer used is constituted by a monomer having a Lewis basic functional group capable of interacting with the Lewis acidity of the pigment surface. That is, by making the hydrophobic segment of the graft copolymer into a copolymer containing a monomer having a Lewis basic functional group, the hydrophobic interaction between the pigment and the hydrophobic segment of the graft copolymer and the interaction by the acid-base are simultaneously performed. work. As a result, it is considered that the adsorptive power of the graft copolymer on the pigment surface in the alkaline region can be increased more than before.

  In the present invention, a monomer having a Lewis basic functional group represented by the general formula (1) is used as a monomer constituting the hydrophobic segment of the graft copolymer. Examples of Lewis basic functional groups include primary amines, secondary amines, tertiary amines, hydroxyl groups, and thiol groups. Examples of the monomer having a Lewis basic functional group as described above represented by the general formula (1) that can be used in the present invention include the following.

  For example, vinylethylamine, dimethylvinylamine, diethylvinylamine, dimethylaminopropene, allylamine, vinyldimethylaminomethane, vinylethylaminoethane can be mentioned. Further, vinyl (dimethylaminomethylmethane), vinyl (diethylaminomethylethane), vinylaminopropane, vinyl (ethylaminomethylpropane), vinyl (methylaminodimethylpropane), and vinyl (ethylaminoethylpropane) can be mentioned. Moreover, allyl alcohol, vinyl hydroxyl ethane, vinyl hydroxyl methyl ethane, vinyl hydroxyl propane, vinyl hydroxyl methyl propane, vinyl dimethyl hydroxyl dimethyl propane, vinyl dimethyl hydroxyl ethyl propane can be mentioned. Moreover, vinyl mercaptan, allyl mercaptan, and vinylpropyl mercaptan are mentioned.

  Moreover, (aminomethyl) vinyl ether, (diethylaminoethyl) vinyl ether, (ethylaminomethylmethyl) vinyl ether, (ethylaminomethylethyl) vinyl ether can be mentioned. Further, (dimethylaminopropyl) vinyl ether, (aminomethylpropyl) vinyl ether, (aminodimethylpropyl) vinyl ether, and (aminoethylpropyl) vinyl ether can be mentioned. Further, hydroxymethyl vinyl ether, hydroxyethyl vinyl ether, and hydroxymethyl methyl vinyl ether can be mentioned. Further, hydroxypropyl vinyl ether, hydroxymethylpropyl vinyl ether, hydroxydimethylpropyl vinyl ether, and hydroxyethylpropyl vinyl ether can be mentioned. Further, mercaptomethyl vinyl ether, mercaptoethyl vinyl ether, and mercaptomethyl methyl vinyl ether can be mentioned. Further, mercaptopropyl vinyl ether, mercaptomethylpropyl vinyl ether, mercaptodimethylpropyl vinyl ether, and mercaptoethylpropyl vinyl ether can be mentioned.

  Moreover, aminomethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, ethylaminomethylmethyl (meth) acrylate, and ethylaminomethylethyl (meth) acrylate are mentioned. Moreover, dimethylaminopropyl (meth) acrylate, aminomethylpropyl (meth) acrylate, aminodimethylpropyl (meth) acrylate, and aminoethylpropyl (meth) acrylate are mentioned. Moreover, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, and hydroxymethylmethyl (meth) acrylate are mentioned. Moreover, hydroxypropyl (meth) acrylate, hydroxymethylpropyl (meth) acrylate, hydroxydimethylpropyl (meth) acrylate, and hydroxyethylpropyl (meth) acrylate are mentioned. Further, mercaptopropyl vinyl ether, mercaptomethyl (meth) acrylate, mercaptoethyl (meth) acrylate, and mercaptomethylmethyl (meth) acrylate can be mentioned. Further, mercaptopropyl (meth) acrylate, mercaptomethylpropyl (meth) acrylate, mercaptodimethylpropyl (meth) acrylate, and mercaptoethylpropyl (meth) acrylate may be mentioned.

  Moreover, aminomethyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, ethylaminomethylmethyl (meth) acrylamide, and ethylaminomethylethyl (meth) acrylamide are mentioned. Moreover, dimethylaminopropyl (meth) acrylamide, aminomethylpropyl (meth) acrylamide, aminodimethylpropyl (meth) acrylamide, and aminoethylpropyl (meth) acrylamide are mentioned. Moreover, hydroxymethyl (meth) acrylamide, hydroxyethyl (meth) acrylamide, and hydroxymethylmethyl (meth) acrylamide are mentioned. Moreover, hydroxypropyl (meth) acrylamide, hydroxymethylpropyl (meth) acrylamide, hydroxydimethylpropyl (meth) acrylamide, and hydroxyethylpropyl (meth) acrylamide are mentioned. Further, mercaptopropyl vinyl ether, mercaptomethyl (meth) acrylamide, mercaptoethyl (meth) acrylamide, and mercaptomethylmethyl (meth) acrylamide may be mentioned. Further, mercaptopropyl (meth) acrylamide, mercaptomethylpropyl (meth) acrylamide, mercaptodimethylpropyl (meth) acrylamide, and mercaptoethylpropyl (meth) acrylamide may be mentioned.

  Further, methyl α- (hydroxymethyl) acrylate, ethyl α- (hydroxymethyl) acrylate, and t-butyl α- (hydroxymethyl) acrylate may be mentioned. Further, methyl α- (hydroxyethyl) acrylate, ethyl α- (hydroxyethyl) acrylate, t-butyl α- (hydroxyethyl) acrylate and the like can be mentioned.

  The monomer having the Lewis basic functional group represented by the general formula (1) as described above is 1% by mass or more and 30% by mass or more based on the total weight of the hydrophobic segment portion in all monomers constituting the hydrophobic segment. It is preferable to make it contain in the range of the mass% or less. When the content is more than 30% by mass, the hydrophobicity of the hydrophobic segment decreases, the hydrophobic interaction with the pigment decreases, and the adsorptive power of the graft copolymer to the pigment decreases. On the other hand, when the content is less than 1% by mass, it is too small to obtain a clear effect. A particularly preferable range of the content of the monomer having a Lewis basic functional group represented by the general formula (1) in all monomers constituting the hydrophobic segment is 5% by mass or more and 25% by mass or less.

  The graft copolymer used in the present invention includes a monomer having a monocyclic or condensed polycyclic hydrocarbon in addition to the monomer having a Lewis basic functional group represented by the general formula (1) in the hydrophobic segment. It is formed by a copolymer. This is because most of the pigments used as inks have an aromatic ring in the structure. Therefore, if the hydrophobic segment of the graft copolymer has an aromatic ring, the aromatic ring in the pigment and the graft copolymer This is because a strong interaction works with the aromatic ring.

  In the present invention, the monomer composed of a monocyclic or condensed polycyclic hydrocarbon is a benzene ring that is a monocyclic hydrocarbon, or a condensed polycyclic hydrocarbon in which a benzene ring is condensed linearly, and a vinyl group or a methyl group directly. Refers to monomers and derivatives that are bonded together. However, the monocyclic or condensed polycyclic hydrocarbon in the present invention refers to a compound in which the ring skeleton is composed of carbon atoms, and the functional group substituted on the ring is not limited to hydrocarbon, It may be a compound other than hydrogen. A monomer having such a monocyclic or condensed polycyclic hydrocarbon has high hydrophobicity. When the monomer having a Lewis basic functional group as described above is used as a constituent monomer of the hydrophobic segment, the hydrophobicity of the hydrophobic segment is lowered. On the other hand, by using a monomer having a highly hydrophobic monocyclic or condensed polycyclic hydrocarbon in combination with a hydrophobic segment and a pigment which are reduced by copolymerizing a monomer having a Lewis basic functional group. It is possible to compensate for the decrease in hydrophobic interaction and maintain the graft copolymer adsorption force to the pigment. The following are mentioned as a monomer which has especially preferable monocyclic or condensed polycyclic hydrocarbon. For example, styrene, allylbenzene, vinylnaphthalene, allylnaphthalene, propenylnaphthalene, vinylanthracene, allylanthracene, propenylanthracene, and derivatives thereof. These monomers can be used as monomers constituting the hydrophobic segment by appropriately selecting one or more kinds.

  Monomers having a monocyclic or condensed polycyclic hydrocarbon as mentioned above have a high adsorptive power with hydrophobic pigments, so that even if the amount used is small, the adsorptive power of the graft copolymer to the pigment is low. Improvement is effective. That is, the reduced hydrophobicity can be compensated by using a monomer having a Lewis basic functional group as a constituent monomer of the hydrophobic segment.

  The hydrophobic segment of the graft copolymer used in the present invention has a hydrophobic functional group copolymerizable with the monomer having the above-mentioned Lewis basic functional group or the monomer having the above monocyclic or condensed polycyclic hydrocarbon. It can synthesize | combine with the monomer which has. Examples of the monomer having a copolymerizable hydrophobic functional group used in this case include the following. Examples thereof include vinyl monomers having an aromatic functional group such as benzyl (meth) acrylate, 4-vinylbenzoic acid, vinylbenzoic acid ester, and N-vinylcarbazole. In addition, (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like can be given. Moreover, acrylamide type monomers, such as (meth) acrylamide, N-methylol (meth) acrylamide, and N, N-dimethylaminopropyl (meth) acrylamide, are mentioned. In addition, vinyl monomers such as N-vinylacetamide, N-vinylformamide, and vinyl acetate can be used. Moreover, these ethylene oxide, propylene oxide modified compounds, etc. are mentioned. The monomer constituting the hydrophobic segment of the graft copolymer used in the present invention may contain a hydrophilic monomer as long as the hydrophobicity of the hydrophobic segment is not hindered.

  The graft copolymer used in the present invention has a hydrophilic segment and a hydrophobic segment made of the monomer material as described above, and the proportion of the hydrophilic segment in the graft copolymer is within the following range. Is preferred. That is, the amount of the hydrophilic segment in the entire graft copolymer is preferably 10% by mass or more and 40% by mass or less, and the acid value of the graft copolymer is preferably 50 mgKOH / g or more and 300 mgKOH / g or less. If the content of the hydrophilic segment is less than 10% by mass or the acid value of the graft copolymer is less than 50 mgKOH / g, the solubility of the graft copolymer in the ink solvent decreases, and the dispersion of the pigment dispersion cannot be maintained stably. It is not preferable. On the other hand, when the content is higher than 40% by mass or the acid value of the graft copolymer exceeds 300 mgKOH / g, the viscosity of the ink is increased to deteriorate the discharge or the affinity of the pigment dispersion for water. May become too high, and the water resistance of the printed matter may decrease.

  The graft copolymer used in the present invention preferably has a weight average molecular weight of the side chain unit in the range of 300 to 4,000, and the weight average molecular weight of the whole polymer in the range of 1,000 to 30,000. . Furthermore, the ratio of the weight average molecular weight of the whole polymer to the weight average molecular weight of the side chain unit is preferably in the range of 1.2: 1 to 20: 1.

  The graft copolymer used in the present invention having the configuration as described above is not particularly limited except that it is obtained by copolymerizing the monomers as mentioned above, and is prepared by any known method. May be. Preferred methods for preparing the graft copolymer include the following methods. For example, a method in which a main chain unit and a side chain unit are separately prepared in advance using a monomer having a plurality of reactive functional groups, and then the main chain unit and the side chain unit are reacted and combined; A method in which a monomer synthesized in advance and constituting a main chain unit is reacted with a macromonomer synthesized in advance.

  In the ink of the present invention, the graft copolymer described above may be used as a dispersion polymer, or may be used as a water-soluble polymer to be further added to the ink described later. However, use as a dispersion polymer for the pigment contained in the ink is effective in expressing the functions of the graft copolymer. The graft copolymer is preferably contained in a range of 0.1% by mass to 15% by mass in the total mass of the ink. When the above-mentioned graft copolymer is contained in the ink, a plurality of graft copolymers may be used in combination as required, or different ones may be used depending on the pigment to be contained.

  In the ink of the present invention, if necessary, a polymer other than the graft copolymer defined in the present invention described above may be used as the dispersion polymer. The polymer that can be used in this case may be any polymer such as vinyl (co) polymer, polysaccharide, polypeptide, polyamide, polyester, polyether, and polyolefin, but is preferably a water-soluble polymer. Further, the content of these polymers in the ink is preferably in a range not exceeding the content of the above-mentioned graft copolymer in the total amount of the ink. These polymers preferably have a weight average molecular weight in the range of 1,000 to 30,000.

  In order to dissolve the dispersion polymer in the water-soluble ink solvent, the ink of the present invention may contain a base. Examples of bases used at this time include the following. Examples thereof include organic amines such as ammonia, monoethanolamine, diethanolamine, triethanolamine, aminemethylpropanol and N, N-dimethylethanolamine; and alkali metal hydroxides such as potassium hydroxide and sodium hydroxide.

  In the ink of the present invention, if necessary, a water-soluble polymer may be contained in the ink in addition to the dispersion polymer. The graft copolymer described above can also be used as the water-soluble polymer used in this case. Examples of other water-soluble polymers include those listed below. Examples thereof include water-soluble ones among (meth) acrylic polymers, polyamide polymers, polyester polymers, polypeptides, cellulose and modified products thereof, polyvinyl alcohol and polyolefins. The content of these polymers in the ink is preferably set to be equal to or less than the content of the above-described dispersion polymer. Furthermore, in order to improve the solubility of these water-soluble polymers, bases as described above may be contained in the ink.

  The pigment used in the present invention may be any pigment as long as it is an organic pigment. The content of the pigment is an amount occupied in the total mass of the ink, and is 1% by mass to 20% by mass, preferably 2% by mass to 12% by mass. More preferable organic pigments include insoluble azo pigments, condensed polycyclic pigments, phthalocyanine pigments, and the like.

Examples of insoluble azo pigments include the following. For example, C.I. I. Pigment Yellow 1, 3, 10, 13, 14, 74, 83, 98, 110, 128, 154;
C. I. Pigment Red 3, 5, 38, 112, 150, 166, 170, 185;
C. I. Pigment Blue 25;
C. I. Pigment Orange 5, 13, 13, 36;
C. I. Pigment Brown 25
Etc.

Further, other pigments that can be used in the present invention include the following condensed polycyclic pigments. For example, C.I. I. Pigment Yellow 24, 109, 110, 138, 139;
C. I. Pigment Red 122, 149, 177, 254;
C. I. Pigment Blue 60, 66;
C. I. Pigment Orange 43, 68;
C. I. Pigment Green 8;
C. I. Pigment Violet 19, 23, 38, 50, 138
Etc.

Further, other pigments that can be used in the present invention include the following phthalocyanine pigments. For example, C.I. I. Pigment Blue 15: 3, 15: 4, 15: 6, 16;
C. I. Pigment Green 7, 36
Etc. Of course, the organic pigment that can be used in the present invention is not limited to these. Of course, newly produced organic pigments can be used in addition to the above organic pigments.

  According to the study by the present inventors, among these, particularly in the case of an ink containing an insoluble azo pigment, the effect of the present invention is remarkably obtained. As a result of acid-base titration with a base, insoluble azo pigments, among various organic pigments, have a large property of accepting electron pairs in the alkaline region, that is, they have stronger properties as Lewis acids in alkalinity than other pigment types. I found out. Therefore, when a graft polymer composed of a monomer having a Lewis basic functional group having an unshared electron pair in the hydrophobic segment is used, the Lewis acid site of the pigment and the Lewis base site of the hydrophobic segment are electrons. It is considered that a high effect can be obtained because a Lewis acid-base reaction occurs due to sharing a pair.

  Hereinafter, a specific method for producing the pigment ink of the present invention having the above-described configuration will be described. The production of the pigment ink is roughly divided into two steps: a step of producing a pigment dispersion and a step of converting the pigment dispersion into an ink. It is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions. The steps for preparing the pigment dispersion are as follows. First, a dispersion medium in which at least a dispersion polymer and water are mixed is prepared, a pigment is added to the dispersion medium, mixed and stirred, and then dispersed using a dispersion means as described later. Then, if necessary, classification treatment for removing coarse particles is performed by a method such as centrifugal separation treatment to obtain a desired pigment dispersion.

  In the above dispersion medium in which the dispersion polymer and water are mixed, the dispersion polymer does not have to be completely dissolved in water, but a base may be added to increase the affinity of the dispersion polymer for water. good. As the base used in this case, for example, organic amines such as ammonia, monoethanolamine, diethanolamine, triethanolamine and aminemethylpropanol; or inorganic bases such as potassium hydroxide and sodium hydroxide are suitable. Among these, an alkaline aqueous solution containing 1 to 1.5 times the amount of potassium hydroxide as the acid value of the dispersion polymer and a dispersion medium containing the dispersion polymer are preferable.

In preparing the dispersion medium, a water-soluble solvent for dissolving the graft copolymer may be contained in the dispersion medium in order to dissolve the graft copolymer used in the present invention satisfactorily. Any water-soluble solvent may be used as long as it dissolves the graft copolymer. For example, those listed below can be used. That is, lower alcohols such as methanol, ethanol, 1-propanol, 2-propanol;
Glycols such as diethylene glycol and dipropylene glycol;
Glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether;
Glycol ethers such as propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether;
Ketones such as methyl ethyl ketone;
Cyclic ethers such as tetrahydrofuran; and the like.

  After mixing these water-soluble solvents with a solvent containing ion-exchanged water or the like in advance, the graft copolymer may be dissolved in this mixed solution, or after dissolving the graft copolymer in these water-soluble solvents in advance, You may mix with the solvent containing replacement water etc. In the ink production method, it is effective to stir the pigment dispersion and perform premixing for 30 minutes or more before the dispersion treatment. That is, such a premixing operation is preferable because it improves wettability of the pigment surface and promotes adsorption of the graft copolymer onto the pigment surface.

  Further, any dispersing machine that is generally used can be used as the dispersing machine used in the pigment dispersion treatment for obtaining the pigment dispersion described above. Examples thereof include a ball mill, a roll mill, a sand mill, a nanomizer (trade name), and an optimizer (trade name). Among these, a high speed type sand mill is preferably used. Examples of the high-speed sand mill include a super mill, a sand grinder, a bead mill, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).

  In addition, in the ink used for the ink jet recording method, it is preferable to use a pigment having an optimum particle size distribution because of demands such as clogging resistance. Methods for obtaining a pigment having a desired particle size distribution include reducing the size of the grinding media of the disperser, increasing the filling rate of the grinding media, increasing the processing time, post-grinding filters, centrifuges, etc. Classification, combinations of these techniques, and the like.

Next, the process of converting the pigment dispersion into ink will be described. To the pigment dispersion obtained above, water, a water-soluble solvent (water-soluble organic solvent), and components appropriately selected from the following additives are added and stirred to obtain the ink of the present invention. Examples of the water-soluble organic solvent used include the following. For example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol;
Amides such as dimethylformamide and dimethylacetamide;
Ketones or ketoalcohols such as acetone and diacetone alcohol;
Ethers such as tetrahydrofuran and dioxane;
Polyalkylene glycols such as polyethylene glycol and polypropylene glycol;
Alkylene glycols containing an alkylene group having 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol;
Lower alkyl ethers of polyhydric alcohols such as glycerin, ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether;
N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like.

  Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred. These water-soluble organic solvents are generally contained in the ink in a range of 3% by mass to 50% by mass, and preferably in a range of 3% by mass to 40% by mass. Water is contained in the range of 10% by mass to 90% by mass, preferably 30% by mass to 80% by mass, based on the total mass of the ink.

  The ink of the present invention is preferably adjusted to be neutral or alkaline. In this way, electrostatic repulsion acts between the pigment fine particles, the dispersion stability can be increased, and the ink can be further improved in long-term storage stability. However, since this may cause corrosion of various members used in the ink jet recording apparatus, the pH of the ink is preferably in the range of 7 to 10 in consideration of this point.

  In the present invention, in order to obtain an ink having a desired physical property value, additives such as a surfactant, an antifoaming agent and a preservative can be appropriately contained in addition to the above-described components as necessary. In particular, the surfactant functioning as a penetration accelerator is preferably contained in the ink in an appropriate amount in order to play a role of allowing the liquid component of the ink to rapidly penetrate into the recording medium. The amount of the additive that can be added (contained) in the ink is, for example, in the range of 0.05% by mass to 10% by mass, preferably 0.5% by mass to 5% by mass in the total amount of the ink. Is preferred.

  The ink of the present invention can be used in a general ink jet recording method, but is particularly preferably applied to an ink jet recording method using thermal energy as ejection energy. The recording head applied to the present invention is an apparatus that applies a recording signal to the ink of the recording head and ejects droplets by the generated thermal energy. The configuration of the recording head, which is the main part of the apparatus, is shown in FIGS.

  The head 13 is a heating head 15 having a heating resistor used for thermal recording (a thin film head is shown in the figure, but is not limited to this). Is not obtained). The heating head 15 includes a protective film 16 made of silicon oxide or the like, aluminum electrodes 17-1 and 17-2, a heating resistor layer 18 made of nichrome or the like, a heat storage layer 19, and a substrate 20 with good heat dissipation such as alumina. It has become more.

  The ink 21 reaches the discharge orifice 22 and forms a meniscus 23 by the pressure P. Here, when an electrical signal is applied to the aluminum electrodes 17-1 and 17-2, the region indicated by n of the heat generating head 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact therewith. The meniscus 23 protrudes, becomes an ink droplet 24 from the ejection orifice 22, and flies toward the recording medium 25. FIG. 3 is a schematic view of a recording head in which a large number of nozzles shown in FIG. 1 are arranged. The recording head is made by closely adhering a glass plate 27 having a large number of flow paths and a heating head 28 similar to that described in FIG. 1 is a cross-sectional view of the head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along the line AB of FIG.

An effective ink set capable of obtaining a high print density and color developing image even when printing on a recording medium such as plain paper using the ink of the present invention will be described. Using an ink set having a reaction liquid containing a compound having an action of aggregating a pigment when in contact with ink and the ink of the present invention, for example, after applying the reaction liquid to a recording medium, the ink of the present invention is applied to the reaction liquid. By applying to the recording medium so as to come into contact with the recording medium, it is possible to obtain an image with high print density and color development. The most suitable compound that causes an aggregation reaction with the pigment contained in the ink when it is brought into contact with the ink, which is used in preparing the reaction liquid, is a polyvalent metal salt. The polyvalent metal salt is composed of a divalent or higher polyvalent metal ion and an anion that binds to the polyvalent metal ion. Specific examples of polyvalent metal ions suitable for the present invention include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Fe ³⁺ , Al ^3+, etc. Of the trivalent metal ions. In addition, examples of the anion bonded to the polyvalent metal ion include Cl ⁻ , NO ₃ ⁻ and SO ₄ ²⁻ .

  A suitable solvent for such a reaction solution is a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, any of the above-mentioned water-soluble organic solvents used in ink can be used. Although there is no restriction | limiting in particular in content of the water-soluble organic solvent in a reaction liquid, It is 5 to 60 mass% of the total mass of a reaction liquid, Preferably it is the range of 5 to 40 mass%.

  In addition, the reaction solution in the present invention may further contain additives such as a viscosity adjuster, a pH adjuster, a preservative, and an antioxidant as necessary. However, the selection and content of the surfactant that functions as a penetration accelerator must be taken into account in order to suppress the penetration of the reaction liquid into the recording medium. Furthermore, the reaction liquid in the present invention is more preferably colorless, but it may be light in a range that does not change the color tone of each color ink when mixed with ink on a recording medium. Furthermore, the reaction liquid in the present invention is preferably adjusted so that the viscosity at around 25 ° C. is in the range of 1 mPa · s to 30 mPa · s.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% display in a sentence mean a mass reference | standard.

[Example 1]
(Synthesis of Macromonomer M1)
Hydrophobic macromonomer M1 for making side chain units was synthesized as follows. First, the following monomer component and chain transfer agent and azobisisobutyronitrile as a polymerization initiator were dissolved in 500 parts of propylene glycol monomethyl ether, and radical polymerization was performed at 75 ° C. under N ₂ stream. As the monomer component, 45 parts of vinyl-2-anthracene and 15 parts of ethyl methacrylate and 40 parts of thioglycolic acid as a chain transfer agent were used. To the above reaction solution, 8 parts of glycidyl methacrylate was added and further reacted at 75 ° C. under N ₂ stream. After completion of the reaction, unreacted substances were removed by precipitation purification and dried under reduced pressure to obtain side chain units. The side chain unit is a macromonomer M1 (monomer unit) having a glycidyl group at the terminal. The weight average molecular weight of this macromonomer M1 was 780.

(Synthesis of graft copolymer C1)
Using the hydrophobic macromonomer M1 for obtaining the side chain unit obtained above, a graft copolymer C1 in which the side chain unit is a hydrophobic segment and the main chain unit is a hydrophilic segment was synthesized as follows. . Using the monomer component of the following main chain unit and the macromonomer M1 obtained above, using azobisisobutyronitrile as a polymerization initiator, the material was dissolved in 500 parts of propylene glycol monomethyl ether, and an N ₂ gas stream The reaction was carried out at 75 ° C. for 2 hours. Macromonomer M1 was used in an amount of 70 parts as a solid content. Further, 60 parts of methacrylic acid, 12 parts of diethylene glycol monoacrylate and 28 parts of 2-hydroxyethyl methacrylate were used as the monomer component of the main chain unit. After the polymerization, unreacted substances were removed by precipitation purification and dried under reduced pressure to obtain graft copolymer C1. The obtained graft copolymer C1 had a weight average molecular weight of 8,500 and an acid value of 139 mgKOH / g.

(Preparation of pigment dispersion PY1)
First, the graft copolymer C1 obtained above and the following components were mixed to prepare a dispersion medium, a pigment was added to the obtained dispersion medium, and a pigment dispersion PY1 was obtained by the following method.
・ Graft copolymer C1 10 parts ・ Isopropyl alcohol 12 parts ・ Ion exchange water 77 parts ・ Potassium hydroxide 1 part

The above-mentioned components were mixed, and the graft copolymer C1 was completely dissolved to obtain a dispersion medium. Next, C.I. I. 30 parts of Pigment Yellow 74 was added, premixed for 30 minutes, and then subjected to a dispersion treatment using a disperser under the following conditions to obtain a pigment dispersion PY1.
・ Disperser: Sand grinder (Igarashi Machine)
・ Crushing media: Zirconia beads (1mm diameter)
・ Filling rate of grinding media: 75% (volume)
・ Crushing time: 3 hours

(Preparation of ink Y1)
The pigment dispersion PY1 obtained above and the following components were mixed to obtain an ink Y1.
・ Pigment dispersion PY1 40 parts ・ Glycerin 5 parts ・ Diethylene glycol 5 parts ・ Acetylenol EH (manufactured by Kawaken Fine Chemicals)
1 part 49 parts of ion exchange water

(Preparation of pigment dispersions PO1 and PV1)
C.I. used in the preparation of the pigment dispersion PY1. I. Pigment Yellow 74, C.I. I. Pigment Orange 36 or C.I. I. Pigment dispersions PO1 and PV1 were obtained in the same manner except that Pigment Violet 50 was used.

(Preparation of inks O1 and V1)
Inks O1 and V1 were obtained in the same manner as in the preparation of Y1 except that the pigment dispersion PY1 used in the preparation of the ink Y1 was replaced with the pigment dispersion PO1 or PV1, respectively.

[Example 2]
(Synthesis of Macromonomer M2)
A hydrophilic macromonomer M2 for use as a side chain unit was synthesized as follows. The following monomer component and azobisisobutyronitrile as a polymerization initiator were dissolved in 500 parts of propylene glycol monomethyl ether, and radical polymerization was performed at 75 ° C. under N ₂ stream. As the monomer component, 10 parts of α-methylstyrene dimer, 40 parts of maleic acid and 10 parts of 4-hydroxybutyl acrylate were used. After polymerization, unreacted substances were removed by precipitation purification and dried under reduced pressure to obtain macromonomer M2. The weight average molecular weight of this macromonomer M2 was 850.

(Synthesis of graft copolymer C2)
Using the hydrophilic macromonomer M2 obtained above, the side chain unit is a hydrophilic segment and the main chain unit is hydrophobic in the same manner as in Example 1 except that the monomer composition of the main chain unit shown below is used. Graft copolymer C2 composed of a hydrophobic segment and a hydrophilic segment, which is a sex segment, was synthesized. Macromonomer M2 was used in an amount of 18 parts as a solid content. Further, 29 parts of vinyl (ethylaminopropyl), 37 parts of 9-allyl anthracene and 16 parts of methyl methacrylate were used as the monomer component of the main chain unit. The obtained graft copolymer C2 had a weight average molecular weight of 9,800 and an acid value of 211 mgKOH / g.

(Preparation of pigment dispersion PY2)
A pigment dispersion PY2 was obtained in the same manner as the pigment dispersion PY1, except that the graft copolymer C2 synthesized above was used instead of the graft copolymer C1 used in the preparation of the pigment dispersion PY1 of Example 1. .

(Preparation of ink Y2)
Ink Y2 was obtained in the same manner as in Example 1 except that the pigment dispersion PY2 prepared above was used instead of the pigment dispersion PY1 used in the preparation of the ink Y1 of Example 1.

[Example 3]
(Synthesis of Macromonomer M3)
In the synthesis of the macromonomer M2 of Example 2, a hydrophilic macromonomer M3 for obtaining a side chain unit was obtained in the same manner except that the monomer component of the macromonomer was changed to the following monomer. For the monomer composition of the macromonomer M3, 10 parts of α-methylstyrene dimer, 40 parts of acrylic acid and 10 parts of 2-hydroxyethyl acrylate were used. The weight average molecular weight of this macromonomer M3 was 920.

(Synthesis of graft copolymer C3)
A graft copolymer C3 was synthesized in the same manner as in Example 2 except that the hydrophilic macromonomer M3 obtained above and the monomer composition of the following main chain unit were used. 20 parts of macromonomer M3 was used as a solid content, and 36 parts of mercaptoethylacrylamide, 36 parts of 1-propenyl-9-anthracene and 12 parts of methyl methacrylate were used as the monomer composition of the main chain unit. The obtained graft copolymer C3 had a weight average molecular weight of 10,800 and an acid value of 152 mgKOH / g.

(Preparation of pigment dispersion PY3)
A pigment dispersion PY3 was obtained in the same manner except that the graft copolymer C1 used in the preparation of the pigment dispersion PY1 in Example 1 was replaced with the graft copolymer C3 obtained above.

(Preparation of ink Y3)
An ink Y3 was obtained in the same manner except that the pigment dispersion PY1 used in the preparation of the ink Y1 of Example 1 was replaced with the pigment dispersion PY3 prepared above.

[Example 4]
(Synthesis of Macromonomer M4)
In the synthesis of the macromonomer M2 of Example 2, a hydrophilic macromonomer M4 for obtaining a side chain unit was obtained in the same manner except that the monomer component of the macromonomer was changed to the following monomer. As a monomer component of the macromonomer M4, 10 parts of α-methylstyrene dimer, 44 parts of acrylic acid and 6 parts of diethylene glycol monoacrylate were used. The resulting macromonomer M4 had a weight average molecular weight of 1,100.

(Synthesis of graft copolymer C4)
A graft copolymer C4 was synthesized in the same manner as in Example 2 except that the hydrophilic macromonomer M4 obtained above and the monomer component of the main chain unit described below were used. 25 parts of macromonomer M4 was used as a solid content, and 26 parts of 1-propenylhydroxyethane, 34 parts of allylbenzene and 15 parts of t-butyl acrylate were used as monomer components of the main chain unit. The obtained graft copolymer C4 had a weight average molecular weight of 13,200 and an acid value of 187 mgKOH / g.

(Preparation of pigment dispersion PY4)
A pigment dispersion PY4 was obtained in the same manner except that the graft copolymer C1 used in the preparation of the pigment dispersion PY1 of Example 1 was replaced with the graft copolymer C4 obtained above.

(Preparation of ink Y4)
An ink Y4 was obtained in the same manner except that the pigment dispersion PY1 used in the preparation of the ink Y1 of Example 1 was replaced with the pigment dispersion PY4 prepared above.

[Example 5]
(Synthesis of Macromonomer M5)
In the synthesis of the macromonomer M2 of Example 2, a hydrophilic macromonomer M5 for obtaining a side chain unit was obtained in the same manner except that the monomer composition of the macromonomer was changed to the following monomer. As the monomer composition of the macromonomer M5, 10 parts of α-methylstyrene dimer, 45 parts of acrylic acid and 5 parts of methyl methacrylate were used. The resulting macromonomer M5 had a weight average molecular weight of 890.

(Synthesis of graft copolymer C5)
A graft copolymer C5 was synthesized in the same manner as in Example 2 except that the hydrophilic macromonomer M5 obtained above and the monomer composition of the following main chain unit were used. 35 parts of macromonomer M5 was used as a solid content, and 13 parts of N, N-dimethylaminoethylmethacrylamide, 27 parts of 4-methoxy-1-vinylnaphthalene and 25 parts of benzyl acrylate were used as the monomer composition of the main chain unit. The obtained graft copolymer C5 had a weight average molecular weight of 10,600 and an acid value of 236 mgKOH / g.

(Preparation of pigment dispersion PY5)
A pigment dispersion PY5 was obtained in the same manner except that the graft copolymer C1 used in the preparation of the pigment dispersion PY1 of Example 1 was replaced with the graft copolymer C5 obtained above.

(Preparation of ink Y5)
An ink Y5 was obtained in the same manner except that the pigment dispersion PY1 used in the preparation of the ink Y1 of Example 1 was replaced with the pigment dispersion PY5 prepared above.

[Example 6]
(Synthesis of Macromonomer M6)
In the synthesis of the macromonomer M2 of Example 2, a hydrophilic macromonomer M6 for making a side chain unit was obtained in the same manner except that the monomer composition of the macromonomer was changed to the following monomer. As a constituent monomer of the macromonomer M6, 10 parts of α-methylstyrene dimer and 50 parts of acrylic acid were used. The resulting macromonomer M6 had a weight average molecular weight of 730.

(Synthesis of graft copolymer C6)
A graft copolymer C6 was synthesized in the same manner as in Example 2 except that the hydrophilic macromonomer M6 obtained above and the monomer composition of the following main chain unit were used. 30 parts of macromonomer M6 was used as the solid content, and 17 parts of t-butyl α- (hydroxyethyl) acrylate, 42 parts of 2-isopropenylnaphthalene and 11 parts of ethyl acrylate were used as the monomer composition of the main chain unit. The obtained graft copolymer C6 had a weight average molecular weight of 9,300 and an acid value of 214 mgKOH / g.

(Preparation of pigment dispersion PY6)
A pigment dispersion PY6 was obtained in the same manner except that the graft copolymer C1 used in the preparation of the pigment dispersion PY1 of Example 1 was replaced with the graft copolymer C6 obtained above.

(Preparation of ink Y6)
An ink Y6 was obtained in the same manner except that the pigment dispersion PY1 used in preparing the ink Y1 of Example 1 was replaced with the pigment dispersion PY6 prepared above.

[Example 7]
(Synthesis of graft copolymer C7)
A graft copolymer C6 was synthesized in the same manner as in Example 2 except that the hydrophilic macromonomer M6 obtained in Example 6 and the monomer composition of the following main chain unit were used. 26 parts of macromonomer M6 was used as a solid content, and 8 parts of 3-hydroxy-1-methylmethacrylamide, 60 parts of styrene, and 6 parts of t-butyl acrylate were used as monomer components of the main chain unit. The obtained graft copolymer C7 had a weight average molecular weight of 9,700 and an acid value of 192 mgKOH / g.

(Preparation of pigment dispersion PY7)
A pigment dispersion PY7 was obtained in the same manner except that the graft copolymer C1 used in the preparation of the pigment dispersion PY1 of Example 1 was replaced with the graft copolymer C7 obtained above.

(Preparation of pigment dispersions PO2 and PV2)
C.I. used in the preparation of the pigment dispersion PY1 of Example 1. I. Pigment Yellow 74, C.I. I. Pigment Orange 36 and C.I. I. Pigment separations PO2 and PV2 were obtained in the same manner except that Pigment Violet 50 was used.

(Preparation of inks Y7, O2, and V2)
Inks Y7, O2, and V2 were obtained in the same manner as in the preparation of Y1, except that the pigment dispersion PY1 used in the preparation of the ink Y1 of Example 1 was replaced with the pigment dispersions PY7, PO2, and PV2, respectively. .

[Comparative Example 1]
(Synthesis of graft copolymer C8)
A graft copolymer C8 used in this comparative example was synthesized in the same manner as in Example 2 except that the hydrophilic macromonomer M3 prepared in Example 3 and the monomer component of the main chain unit described below were used. 20 parts of macromonomer M3 was used as a solid content, and 32 parts of styrene and 48 parts of allyl mercaptan were used as monomer components of the main chain unit. The obtained graft copolymer C8 had a weight average molecular weight of 11,700 and an acid value of 143 mgKOH / g.

(Preparation of pigment dispersion PY8)
A pigment dispersion PY8 was obtained in the same manner except that the graft copolymer C1 used in the preparation of the pigment dispersion PY1 of Example 1 was replaced with the graft copolymer C8 obtained above.

(Preparation of pigment dispersions PO3 and PV3)
C.I. used in the preparation of the pigment dispersion PY1 of Example 1. I. Pigment Yellow 74, C.I. I. Pigment Orange 36 and C.I. I. Pigment separations PO3 and PV3 were obtained in the same manner except that Pigment Violet 50 was used.

(Preparation of inks Y8, O3 and V3)
Inks Y8, O3 and V3 were obtained in the same manner as the preparation of Y1, except that the pigment dispersion PY1 used in the preparation of the ink Y1 of Example 1 was replaced with the pigment dispersions PY8, PO3 and PV3, respectively. .

[Evaluation]
A. Evaluation of each ink (storage stability)
The pigment ink may be stored for a long time before being used after being manufactured. If the resin is detached from the pigment during that time, the repulsive force between the pigment particles due to the resin decreases and aggregates, resulting in changes such as an increase in particle size and an increase in viscosity. If the particle size increases or the viscosity increases, it is not preferable because the ejection becomes unstable. Therefore, it can be seen that, after the ink is stored at 70 ° C. for 3 months, the ink whose particle size or viscosity change rate is 10% or more is easily detached from the pigment, and the resin is not sufficiently adsorbed to the pigment. In particular, an ink having a particle size or viscosity change rate of 5% or less can be said to have high storage stability.

<Evaluation method>
The storage stability was evaluated by placing 50 ml of each of the inks Y1 to Y8, O1 to O3, and V1 to V3 in a 100 ml polyethylene container and storing them at 70 ° C. for 3 months. And evaluated. The particle diameter of the pigment particles in the ink before and after storage and the viscosity of the ink before and after storage were measured, and the rate of change during this time was determined. And it evaluated by the following reference | standard according to this change rate, respectively. The obtained evaluation results are shown in Tables 1 and 2. The average particle size (nm) of the pigment particles in the ink was measured by FPAR-1000 manufactured by Otsuka Electronics Co., Ltd. based on the dynamic light scattering method. The viscosity of the ink (mPa · s) is measured from the torque generated when the ink is rotated at a constant rotational speed (100 rpm) with a cone-disk type rotational viscometer, Toyo Sangyo Co., Ltd. RE-80L. did. In all measurements, the measurement temperature is 25 ° C.

<Evaluation criteria>
(Double-circle): Each change rate of a particle size and a viscosity is less than 5%.
◯: Each change rate of the particle diameter and the viscosity is 5% or more and less than 10%.
X: Each change rate of a particle size and a viscosity is 10% or more.

(Discharge stability)
In order to achieve excellent color development and high printing density, an ink having stable ejection characteristics is preferable. Therefore, the ejection stability of each of the inks of Examples and Comparative Examples obtained above was evaluated by the following methods and standards.
<Evaluation method>
Each ink is packed in an ink jet cartridge, set on the head mounted on an ink jet printer BJ-F890 (manufactured by Canon Inc.), and printed on a commercially available plain paper for A4 color BJ (manufactured by Canon Inc.). The subsequent discharge speed was measured.

<Evaluation criteria>
(Double-circle): The discharge rate after printing 250 sheets is less than 15% with respect to the desired rate.
A: The discharge rate after printing 250 sheets is 15% or more and less than 30% with respect to the desired rate.
X: The reduction rate of the ejection speed after printing 250 sheets is 30% or more with respect to the desired speed.

(Color development of printed matter)
The color developability of the printed matter of each ink of Examples and Comparative Examples obtained above was evaluated by the following methods and standards.
<Evaluation method>
The optical density of the printed portion of the first printed matter used for the previous evaluation of the ejection stability was measured with a reflection densitometer RD-19I (manufactured by GretagMacbeth), and the saturation C ^* was calculated from the measured value.

<Evaluation criteria: Yellow ink>
○: Saturation C ^* is 70 or more.
X: Saturation C ^* is less than 70.

<Evaluation criteria: Orange ink and violet ink>
○: Saturation C ^* is 50 or more.
X: Saturation C ^* is less than 50.

The above results are shown in Tables 1 and 2.

  As shown in Tables 1 and 2, it was found that the inks of the examples all have high storage stability. In particular, Examples 6 and 7 were confirmed to have high storage stability. Further, in the evaluation of the ejection characteristics, it was confirmed that the inks of all the examples had high ejection stability. On the other hand, the ejection speed of the ink of the comparative example was greatly reduced. In the evaluation of color developability, C.I. I. Each of the inks of Examples containing Pigment Yellow 74 had a chroma exceeding 70 and all had high color development. However, the same C.I. I. Despite containing Pigment Yellow 74, the chroma was less than 70 and color development was insufficient. Furthermore, C.I. I. Pigment Orange 36 containing ink and C.I. I. It was confirmed that all of the inks of Examples containing Pigment Violet 50 had a chroma exceeding 50 and high color developability. On the other hand, although the inks of the comparative examples were inks containing the same pigment, the saturation was less than 50 and the color development was insufficient.

  As described above, according to the present invention, an image having excellent storage stability, high ejection stability, excellent color development when used for image formation, and realizing high print density and good fixability can be obtained. An ink that can be applied is provided.

It is a longitudinal cross-sectional view which shows an example of the head of an inkjet recording device. It is a cross-sectional view showing an example of the head of the ink jet recording apparatus. FIG. 2 is an external perspective view of a head in which the head shown in FIG.

Explanation of symbols

13: head 14: ink groove 15: heating head 16: protective film 17-1, 17-2: electrode 18: heating resistor layer 19: heat storage layer 20: substrate 21: ink 22: ejection orifice (micropore)
23: meniscus 24: ink droplet 25: recording medium 26: multi-groove 27: glass plate 28: heating head

Claims (6)

In an inkjet pigment ink comprising a pigment, a graft copolymer, a water-soluble solvent, and water,
The graft copolymer has a hydrophilic segment and a hydrophobic segment,
The hydrophobic segment is a copolymer comprising at least a monomer having a Lewis basic functional group represented by the following general formula (1) and a monomer having a monocyclic or condensed polycyclic hydrocarbon,
An inkjet pigment ink, wherein the content of the monomer having a Lewis basic functional group is 1% by mass or more and 30% by mass or less based on the total weight of the hydrophobic segment portions in the copolymer.

(In the formula, —R ¹ is selected from —H, —CH ₃ , —CH ₂ OH and —CH (CH ₃ ) OH. Also, m is 1 or 0, and m is 1. -X is selected from -C (O) NH-, -O-, -C (O)-, -OC (O)-and -C (O) O-, where m is 0. When n is an integer of 0 to 5, and when m is 1, n is an integer of 1 to 5. When R ¹ is —H or —CH ₃ , —Y is -NR ² R ³ , -SH and -OH, when -R ¹ is -CH ₂ OH or -CH (CH ₃ ) OH, -Y is -H, -NR ² R ³ ,- Selected from SH and -OH, wherein R ² and R ³ are each independently selected from H, CH ₃ and C ₂ H _5. )   The inkjet pigment ink according to claim 1, wherein the Lewis basic functional group is selected from a primary amine, a secondary amine, a tertiary amine, a hydroxyl group, and a thiol group.   The monomer having a monocyclic or condensed polycyclic hydrocarbon is at least one selected from styrene, allylbenzene, vinylnaphthalene, allylnaphthalene, propenylnaphthalene, vinylanthracene, allylanthracene, propenylanthracene and derivatives thereof. The inkjet pigment ink according to claim 1 or 2.   The inkjet pigment ink according to any one of claims 1 to 3, wherein the hydrophilic segment is a homopolymer or copolymer of a monomer having an anionic functional group.   The inkjet pigment ink according to any one of claims 1 to 4, wherein the monomer having an anionic functional group is acrylic acid.   The ink-jet pigment ink according to any one of claims 1 to 5, wherein the pigment is an insoluble azo pigment.

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