JP2005120136A - Microencapsulated pigment and method for producing the same, aqueous dispersion and ink for ink-jet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink for ink-jet recording having excellent dispersion stability and jetting stability and affording records having excellent fastness, abrasion resistance, color developing properties and high printing density of an image and scarcely bleeding the image and to provide a microencapsulated pigment producing the ink and a method for producing the pigment and an aqueous dispersion. <P>SOLUTION: The microencapsulated pigment comprises pigment particles having anionic groups on the surface and coated with a polymer having a repeating structural unit derived from a cationic polymerizable surfactant. The method for producing the microencapsulated pigment comprises adding and mixing the cationic polymerizable surfactant with an aqueous dispersion of the pigment particles having the anionic groups on the surface, then adding a polymerization initiator and carrying out emulsion polymerization. The ink for the ink-jet recording comprises at least the microencapsulated pigment and water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a microencapsulated pigment, a method for producing the same, an aqueous dispersion, and an ink for inkjet recording.

  The ink jet recording method is a method of recording characters and figures on the surface of a recording medium such as paper by discharging ink droplets from a fine nozzle head. As an ink jet recording method, an electric signal is converted into a mechanical signal using an electrostrictive element, and ink droplets stored in the nozzle head portion are intermittently ejected to record characters and symbols on the surface of the recording medium, or A part of the ink liquid is rapidly heated at a part near the ejection part of the nozzle head to generate bubbles, and ink droplets are intermittently ejected by the volume expansion caused by the bubbles, and characters and symbols are printed on the surface of the recording medium. A method for recording the image has been put into practical use.

Recently, water-based pigment inks in which pigments are dispersed in water have been provided as inks for inkjet recording. This is because the ink using the pigment has the characteristics that the water resistance and the light resistance are superior to the ink using the water-soluble dye. In such a water-based pigment ink, it is generally performed to disperse a pigment in an aqueous dispersion medium using a dispersant such as a surfactant or a polymer dispersant.
For example, in JP-A-3-157464, in a pigment ink using an acetylene glycol penetrant, a polymer dispersant is used as a dispersant for pigment particles, and water, a nonvolatile organic solvent, or a lower alcohol is used as an aqueous medium. Thus, studies are being made to ensure the dispersion stability. However, when a dispersant is used for dispersing pigment particles in this manner, the number of elements at the time of ink preparation increases, making it difficult to set desired ink physical properties such as viscosity. Further, the problem that it is difficult to secure the print density in this pigment ink is still unsolved.
Furthermore, in these water-based pigment inks, the dispersant is simply adsorbed on the surface of the pigment particles, and a strong shearing force is applied when the ink liquid is ejected through the thin nozzles of the nozzle head. There may be a tendency that the dispersant adsorbed on the particle surface is detached, the dispersibility is deteriorated, and the ejection becomes unstable. In addition, even when the water-based pigment ink is stored for a long period of time, there is a case where the dispersibility tends to become unstable.

As another technique for dispersing pigment particles in water, a technique for introducing sulfonic acid groups on the surface of the pigment particles has also been proposed. For example, a pigment ink containing a sulfonated surface-treated organic pigment obtained by treating an organic pigment dispersed in a solvent having no active protons with a sulfonating agent is known (Conventional Example 1; see Patent Document 1). ). According to Conventional Example 1, it is said that the pigment ink has excellent dispersion stability and good ejection stability from the nozzles of the recording head (characteristic that the recording head is stably ejected in a certain direction). ing.
Japanese Patent Application Laid-Open No. 11-49974 discloses that an organic pigment mass having a positively charged surface is prepared by treating an organic pigment mass into which a sulfonic acid group has been introduced with a monovalent metal ion. In addition, water-based ink compositions containing pigment fine particles prepared from the surface positively charged organic pigment mass, a dispersant, and water and having excellent storage stability (dispersion stability) are known (conventional example). 2: Refer to Patent Document 2).
However, although the ink using the surface-treated pigment particles of Conventional Example 1 and Conventional Example 2 as a colorant is superior in dispersion stability and ejection stability as compared with conventional pigment-based inkjet recording inks, The recorded material obtained by printing on a recording medium such as plain paper or an ink jet recording medium (a recording medium having an ink receiving layer for receiving ink for ink jet recording on its surface) still has insufficient abrasion resistance. It was a thing. This is presumably because the fixability of the surface-treated pigment particles on the recording medium is not good.

On the other hand, a technique using a microencapsulated pigment in which colorant particles are coated with a polymer is known for the purpose of improving the fixability of a pigment contained in a pigment-based inkjet ink to a recording medium. In JP-B-7-94634 and JP-A-8-59715, those encapsulating pigment fine particles are disclosed in JP-A-5-339516, JP-A-8-302227, JP-A-8-302228, Japanese Patent Application Laid-Open No. 8-81647 proposes a polymer obtained by graft polymerization on the surface of pigment particles. In JP-A-5-320276, a method of microencapsulating a hydrophobic powder using an amphiphilic graft polymer has been proposed, but in the microencapsulation, if a polymer polymerized in advance is used, There was a problem that the particle size became too large. In addition to the above proposals, Japanese Patent Laid-Open Nos. 08-2158015, 08-295837, 09-3376, 08-183920, 10-46075, 10 -292143, JP-A-11-80633, JP-A-11-349870, and JP-A-2000-7961 use pigments coated with a resin having film-forming properties at room temperature by a phase inversion emulsification method. Ink is disclosed in JP-A-9-31360, JP-A-9-217019, JP-A-9-316353, JP-A-9-104834, JP-A-9-151342, JP-A-10-140065. JP-A-11-152424, JP-A-11-166145, JP-A-11-166145, JP-A-11 199783 discloses an ink using a pigment coated with an anionic group-containing organic polymer compound by acid precipitation in JP-A-11-209672 has been proposed.
Furthermore, in JP-A-9-286939, JP-A-2000-44852, JP-A-2000-53897, JP-A-2000-53898, JP-A-2000-53899, and JP-A-2000-53900. Has proposed an ink using a polymer emulsion obtained by impregnating polymer fine particles with a colorant by a phase inversion emulsification method (Conventional Example 3; see Patent Documents 3 to 8).
However, even in the colorant obtained by the phase inversion emulsification method or the acid precipitation method, the polymer adsorbed on the pigment particles may be detached depending on the kind of the organic solvent such as the penetrant used in the ink. In some cases, the ink may be dissolved, and ink dispersion stability, ejection stability, image quality, and the like may not be sufficient. In the ink of Conventional Example 3, since the polymer adsorbed on the pigment particles is desorbed not a little, the pigment content in the ink is limited from the viewpoint of dispersion stability. In addition, the printed image has a low printing density. In particular, when the recording medium is plain paper, there is a problem that image bleeding tends to occur and color developability is low.

Japanese Patent Laid-Open No. 10-110129 JP-A-11-49974 JP-A-9-286939 JP 2000-44852 A JP 2000-53897 A JP 2000-53898 A JP 2000-53899 A JP 2000-53900 A

The present invention has been made in view of the above problems, and its object is to
(1) Excellent dispersion stability
(2) Excellent ejection stability from the recording head.
(3) A recorded matter having excellent image fastness can be obtained.
(4) A recorded matter having a high image printing density can be obtained.
(5) A recorded matter having excellent image abrasion resistance can be obtained.
(6) Even when plain paper is used as the recording medium, it is possible to obtain a recorded matter in which the image is less likely to bleed and the color of the image is high.
It is an object to provide a microencapsulated pigment capable of producing an ink for inkjet recording satisfying all of the above (1) to (6), a method for producing the same, and an aqueous dispersion.
Another object of the present invention is to provide an ink for ink jet recording that satisfies all of the above (1) to (6).

  As a result of intensive studies, the inventors of the present invention surprisingly produced the specific microencapsulated pigment and used the microencapsulated pigment as a colorant for the ink for inkjet recording. The present invention has been completed by finding that an ink for ink jet recording satisfying all of (1) can be obtained. That is, the technical configuration of the present invention is as follows.

(1) Pigment particles having an anionic group on the surface thereof are coated with a polymer having a repeating structural unit derived from a cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group. A microencapsulated pigment characterized by
(2) by polymerizing a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group in an aqueous dispersion in which pigment particles having an anionic group on the surface are dispersed, A microencapsulated pigment obtained by coating pigment particles with a polymer.
(3) The microencapsulated pigment according to (1) or (2), wherein the polymer further has a repeating structural unit derived from a hydrophobic monomer.
(4) The polymer (1), wherein the polymer further has a repeating structural unit derived from a crosslinkable monomer and / or a repeating structural unit derived from a monomer represented by the following general formula (1): The microencapsulated pigment according to any one of to (3).

［ただし、Ｒ^１は水素原子又はメチル基を表す。Ｒ^２はｔ−ブチル基、脂環式炭化水素基、芳香族炭化水素基、又はヘテロ環基を表す。ｍは０〜３、ｎは０又は１の整数を表す。］

[However, R ¹ represents a hydrogen atom or a methyl group. R ² represents a t-butyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group. m represents an integer of 0 to 3, and n represents an integer of 0 or 1. ]

(5) The microencapsulated pigment according to any one of (1) to (4), wherein the pigment constituting the pigment particles is carbon black or an organic pigment.
(6) The anionic group of the pigment particle is a sulfonate anion group (—SO ₃ ⁻ ) and / or a sulfinate anion group (—RSO ₂ ^— : R is a C _{1 to} C ₁₂ alkyl group or a phenyl group and its The microencapsulated pigment according to any one of (1) to (5), wherein the pigment is a modified product.
(7) The microencapsulated pigment according to any one of (1) to (5), wherein the anionic group of the pigment particle is a carboxylic acid anion group (—COO ⁻ ).
(8) The cationic group of the cationic polymerizable surfactant is selected from the group consisting of a primary amine cation, a secondary amine cation, a tertiary amine cation, and a quaternary ammonium cation. The microencapsulated pigment according to (1) or (2).
(9) The hydrophobic group of the cationic polymerization surfactant is selected from the group consisting of an alkyl group, an aryl group and a group in which these are combined, as described in (1) or (2) above Microencapsulated pigment.
(10) The polymerizable group of the cationic polymerization surfactant is an unsaturated hydrocarbon group capable of radical polymerization, and includes a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. The microencapsulated pigment according to (1) or (2), which is selected from the group consisting of:
(11) A method for producing a microencapsulated pigment in which pigment particles having an anionic group on the surface are coated with a polymer, wherein the cationic polymerizable surfactant is added to an aqueous dispersion of the pigment particles having the anionic group on the surface. A method for producing a microencapsulated pigment, comprising adding an agent and mixing, followed by emulsion polymerization by adding a polymerization initiator.
(12) A method for producing a microencapsulated pigment in which pigment particles having an anionic group on the surface are coated with a polymer, wherein the cationic polymerizable surfactant is added to an aqueous dispersion of the pigment particles having an anionic group on the surface. A method for producing a microencapsulated pigment, comprising adding an agent and mixing, emulsifying by adding a hydrophobic monomer and a cationic polymerizable surfactant, followed by emulsion polymerization by adding a polymerization initiator.
(13) A cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group is added to the aqueous dispersion of pigment particles having the anionic group on the surface, mixed, and then irradiated with ultrasonic waves. A step of treating, a step of adding and mixing a hydrophobic monomer, a step of adding a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group, mixing and irradiating with ultrasonic waves. The method for producing a microencapsulated pigment according to the above (12), which comprises a step and a step of emulsion polymerization by adding a polymerization initiator, and the steps are carried out in the order of the steps.
(14) A cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group is added to the aqueous dispersion of pigment particles having the anionic group on the surface, mixed, and then irradiated with ultrasonic waves. A cation having a cationic group, a hydrophobic group and a polymerizable group, a step of treating, a step of adding and mixing a hydrophobic monomer and a crosslinkable monomer and / or a monomer represented by the following general formula (1) (12), characterized by comprising a step of adding and mixing a polymerizable polymerizable surfactant and treating by irradiating with ultrasonic waves, and a step of emulsion polymerization by adding a polymerization initiator, the steps being carried out in the order of the steps. A process for producing a microencapsulated pigment as described in 1. above.

［ただし、Ｒ^１は水素原子又はメチル基を表す。Ｒ^２はｔ−ブチル基、脂環式炭化水素基、芳香族炭化水素基、又はヘテロ環基を表す。ｍは０〜３、ｎは０又は１の整数を表す。］

[However, R ¹ represents a hydrogen atom or a methyl group. R ² represents a t-butyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group. m represents an integer of 0 to 3, and n represents an integer of 0 or 1. ]

(15) The method for producing a microencapsulated pigment according to any one of (11) to (14), wherein the pigment constituting the pigment particles is carbon black or an organic pigment.
(16) An aqueous dispersion comprising the microencapsulated pigment according to any one of (1) to (10).
(17) An inkjet recording ink comprising the aqueous dispersion according to (16).
(18) An ink for inkjet recording, comprising at least the microencapsulated pigment according to any one of (1) to (10) and water.
(19) The ink for inkjet recording according to any one of (17) to (18), further comprising a water-soluble organic solvent.
(20) The inkjet recording ink as described in (19) above, wherein the water-soluble organic solvent is a high-boiling water-soluble organic solvent having a boiling point of 180 ° C. or higher.
(21) The ink for inkjet recording according to (19) or (20), wherein the water-soluble organic solvent is glycerin.
(22) The above-mentioned (19) to (21), wherein the water-soluble organic solvent is one or more compounds selected from the group consisting of alkyl ethers of polyhydric alcohols and / or 1,2-alkyldiols. ) Ink for inkjet recording according to any one of the above.
(23) The solid humectant is further contained in an amount of 3% by weight to 20% by weight with respect to the total weight of the ink for ink jet recording, and the ink for ink jet recording according to any one of the above (17) to (22) ink.
(24) The ink for inkjet recording according to (23), wherein the solid wetting agent is trimethylolpropane and / or 1,2,6-hexanetriol.

According to the microencapsulated pigment and the method for producing the same according to the present invention,
(1) Excellent dispersion stability
(2) Excellent ejection stability from the recording head.
(3) A recorded matter having excellent image fastness can be obtained.
(4) A recorded matter having a high image printing density can be obtained.
(5) A recorded matter having excellent image abrasion resistance can be obtained.
(6) Even when plain paper is used as the recording medium, it is possible to obtain a recorded matter in which the image is less likely to bleed and the color of the image is high.
It is possible to provide a microencapsulated pigment capable of producing an inkjet recording ink satisfying all of the above (1) to (6), a method for producing the same, and an aqueous dispersion.

Further, according to the ink for ink jet recording according to the present invention,
(1) Excellent dispersion stability
(2) Excellent ejection stability from the recording head.
(3) A recorded matter having excellent image fastness can be obtained.
(4) A recorded matter having a high image printing density can be obtained.
(5) A recorded matter having excellent image abrasion resistance can be obtained.
(6) Even when plain paper is used as the recording medium, it is possible to obtain a recorded matter in which the image is less likely to bleed and the color of the image is high.
Ink jet recording ink satisfying all of the above (1) to (6) can be provided.

The microencapsulated pigment according to the present invention comprises a repeating structural unit in which pigment particles having an anionic group on the surface thereof are derived from a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group. It is characterized by being coated with a polymer.
Such a microencapsulated pigment is a method for producing a microencapsulated pigment in which pigment particles having an anionic group on the surface thereof are coated with a polymer, and the aqueous dispersion of the pigment particles having an anionic group on the surface thereof. After the cationic polymerizable surfactant is added and mixed, it can be suitably produced by adding a polymerization initiator and emulsion polymerization.
In addition, the microencapsulated pigment according to the present invention comprises a cationic particle surfactant having a cationic group, a hydrophobic group, and a polymerizable group, and a hydrophobic monomer. It is characterized by being coated with a polymer having derived repeating structural units.
Such a microencapsulated pigment is a method for producing a microencapsulated pigment in which pigment particles having an anionic group on the surface thereof are coated with a polymer, and the aqueous dispersion of the pigment particles having an anionic group on the surface thereof. A cationic polymerizable surfactant is added and mixed, and then a hydrophobic monomer and a cationic polymerizable surfactant are added and emulsified, and then a polymerization initiator is added and emulsion polymerization is performed for suitable production.
According to such an emulsion polymerization method, the hydrophilic group on the surface of the pigment particle having an anionic group on the surface and the cationic group of the cationic polymerizable surfactant are ionically bonded in the polymerization system. Since the polymer phase is formed by the polymerization reaction by forming the micelle-like (admicelle) structure in which the cationic groups of the cationic polymerizable surfactant are oriented toward the aqueous phase on the outermost surface, the pigment before emulsion polymerization The arrangement form of the monomers present around the particles affects the polarization state of the particle surface after polymerization, and can therefore be controlled with extremely high accuracy. Therefore, the microencapsulated pigment according to the embodiment of the present invention is
(1) Excellent dispersion stability
(2) Excellent ejection stability from the recording head.
(3) A recorded matter having excellent image fastness can be obtained.
(4) A recorded matter having a high image printing density can be obtained.
(5) A recorded matter having excellent image abrasion resistance can be obtained.
(6) Even when plain paper is used as the recording medium, it is possible to obtain a recorded matter in which the image is less likely to bleed and the color of the image is high.
Ink jet recording ink satisfying all of the above (1) to (6) can be produced. In the case of a microencapsulated pigment in which a polymer prepared in advance on a pigment is coated by using a phase inversion emulsification method, an acid precipitation method, or the like, the coating on the pigment particles is performed because the polymer is prepared in advance. It is considered that the coating state of the polymer pigment particles satisfying all of the above (1) to (6) is not achieved because the state is limited.

Here, the aspect ratio (long and short) of the microencapsulated pigment is 1.0 to 1.3, and the Zingg index is 1.0 to 1.3 (more preferably 1.0 to 1.2). It is preferable that Thereby, the items (1), (2), (4) and (6) can be satisfied more reliably.
When the short diameter of a particle is b, the long diameter is l, and the thickness is t (l ≧ b ≧ t> 0), the aspect ratio (long / shortness) is 1 / b (≧ 1), and the flatness is b / t ( ≧ 1) and Zingg index = long / short / flatness = (l · t) / b ² . That is, the true sphere has an aspect ratio of 1 and a Zingg index of 1.
If the Zingg index is larger than 1.3, the microencapsulated pigment becomes flatter and becomes less isotropic. In particular, the items (1), (2), (4) and (6) above. However, sufficient results are not obtained. The method for setting the aspect ratio and Zingg index within the above ranges is not particularly limited, but microencapsulated pigments in which pigment particles having an anionic group on the surface are coated with a polymer by the above-described emulsion polymerization method can easily satisfy this condition. Can meet.
In addition, in a microencapsulated pigment produced by a method other than an emulsion polymerization method such as an acid precipitation method or a phase inversion emulsification method, the aspect ratio and the Zingg index are unlikely to fall within the above ranges.
When the microencapsulated pigment is in the range of the above aspect ratio and Zingg index, it becomes a true sphere, but this makes the ink flow characteristics easy to be Newtonian and excellent ejection stability. In addition, since the particles are spherical, when encapsulated on a recording medium such as paper, the encapsulated particles are arranged at a high density on the recording medium, and printing density and color development can be expressed with high efficiency. Further, since it is spherical, it is excellent in dispersibility and dispersion stability.

  Hereinafter, embodiments of the present invention will be described with reference to possible dispersion states of pigment particles in the above-described preferred production method. However, the dispersion state of the pigment particles listed below includes estimation.

A possible dispersion state of the pigment particles in the above-described preferred production method will be described with reference to FIG. The pigment particles 1 having an anionic group 14 as a hydrophilic group dispersed in a solvent containing water as a main component (hereinafter also referred to as an aqueous solvent) are mixed with a cationic group 11, a hydrophobic group 12, and a polymerizable group 13. The cationic group 11 of the cationic polymerizable surfactant 2 having a cation is arranged so as to face the anionic group 14 of the pigment particle 1 and adsorbs with a strong ionic bond, and further, the cationic group 11 ′ and the hydrophobic group The hydrophobic group 12 ′ and the polymerizable group 13 ′ of the cationic polymerizable surfactant 2 ′ having 12 ′ and the polymerizable group 13 ′ are the hydrophobic group 12 and the polymerizable group of the cationic polymerizable surfactant 2. 13 is adsorbed by hydrophobic interaction with 13 and the cationic group 11 ′ of the cationic polymerizable surfactant 2 ′ is directed in the direction in which the aqueous solvent exists (water phase side), that is, in the direction away from the pigment particles 1. Show.
In this state, for example, by adding a polymerization initiator, the polymerizable group 13 of the cationic polymerizable surfactant 2 and the polymerizable group 13 ′ of the cationic polymerizable surfactant 2 ′ are polymerized to obtain FIG. As shown in FIG. 2, a microencapsulated pigment 100 in which the pigment particles 1 are coated with the polymer layer 60 is produced. Here, since the surface of the polymer layer 60 has the cationic group 14 ′, the microencapsulated pigment 100 can be dispersed in an aqueous solvent. During the polymerization, if necessary, a cationic polymerizable surfactant and a hydrophobic monomer may be present in the aqueous dispersion, and in this case, the polymer layer is composed of the cationic polymerizable surfactant and A copolymer layer copolymerized with a hydrophobic monomer.
In addition to the above, the possible dispersion state of the pigment particles in the above-described preferred production method will be described with reference to FIG. The pigment particles 1 having an anionic group 14 as a hydrophilic group dispersed in a solvent containing water as a main component (hereinafter also referred to as an aqueous solvent) are mixed with a cationic group 11, a hydrophobic group 12, and a polymerizable group 13. The cationic group 11 of the cationic polymerizable surfactant 2 having the above is arranged so as to face the anionic group 14 of the pigment particle 1 and adsorbs with a strong ionic bond. In addition, the surface of the pigment particle 1 has an anionic group 14 chemically bonded at a specific density, and has a hydrophobic region 50 between the anionic groups 14, and the hydrophobic polymerizable region 50 has a cationic polymerizable interface. The hydrophobic group 12 and the polymerizable group 13 of the activator 2 face each other, and the cationic group 11 of this cationic polymerizable surfactant 2 is arranged with the cationic group of another cationic polymerizable surfactant 2 Is done. And the cationic polymerizable surfactant which has the cationic group 11 ', the hydrophobic group 12', and the polymerizable group 13 'in the hydrophobic group 12 and the polymerizable group 13 of the cationic polymerizable surfactant 2 2 ′ hydrophobic group 12 ′ and polymerizable group 13 ′ are adsorbed by hydrophobic interaction, and the cationic group 11 ′ of the cationic polymerizable surfactant 2 ′ is in the direction in which the aqueous solvent exists (water phase side). I.e., away from the pigment particles 1.
In this state, for example, by adding a polymerization initiator, the polymerizable group 13 of the cationic polymerizable surfactant 2 and the polymerizable group 13 ′ of the cationic polymerizable surfactant 2 ′ are polymerized, whereby FIG. As shown, a microencapsulated pigment 101 in which pigment particles 1 are coated with a polymer layer 60 ′ is produced. Here, since the surface of the polymer layer 60 ′ has the cationic group 14 ′, the microencapsulated pigment 101 can be dispersed in an aqueous solvent. During the polymerization, if necessary, a cationic polymerizable surfactant and a hydrophobic monomer may be present in the aqueous dispersion, and in this case, the polymer layer is composed of the cationic polymerizable surfactant and A copolymer layer copolymerized with a hydrophobic monomer.
As mentioned above, although the dispersion state was mentioned using drawing, the pigment particle 1 is in the state disperse | distributed to the aqueous solvent first by having an anionic group as a hydrophilic group on the surface. The dispersion of the pigment particles 1 in the aqueous solvent is highly dispersed as compared with the case where the pigment particles that do not have a hydrophilic group (anionic group) on the surface are dispersed with a dispersant. According to the microencapsulated pigment in which the pigment particles having the anionic group on the surface are coated with the polymer, as shown in FIGS. 2 and 4, the cationic group on the surface of the microencapsulated pigment is an aqueous solvent. Since it is regularly and densely oriented in the existing direction, the dispersion stability of the microencapsulated pigment in an aqueous solvent can be improved. Therefore, when the microencapsulated pigment according to the present invention is used as a colorant for an ink for ink jet recording and the ink solvent is an aqueous solvent, even if a larger amount of microencapsulated pigment is contained in the ink, Excellent dispersion stability equivalent to that of the microencapsulated pigment ink can be imparted. If the dispersion stability is excellent, the possibility that the microencapsulated pigment clogs the nozzles of the recording head is reduced, so that the ejection stability is also improved. That is, it is possible to produce a microencapsulated pigment ink that is excellent in dispersion stability and ejection stability and at the same time has an improved colorant weight concentration compared to conventional microencapsulated pigment inks. And by performing ink jet recording using such a microencapsulated pigment ink having a high weight concentration of the colorant, it is possible to obtain not only excellent image fastness but also a recorded matter having a high image print density. it can.

  More specifically, in the microencapsulated pigment of the present invention, as described above, it is considered that the cationic groups are regularly and densely oriented toward the aqueous solvent side. It is considered that an effective electrostatic repulsive force is generated during this period. In addition to the electrostatic repulsive force, the microencapsulated pigment of the present invention is excellent in an aqueous medium because of the effect (polymer effect) caused by steric hindrance caused by the polymer coating the pigment particles. It is considered that this is one of the reasons for having high dispersion stability.

The reason why it is possible to suppress the occurrence of image bleeding when the recording medium is plain paper, and the reason why the image printing density is high, are the pigments that are regularly and densely oriented toward the aqueous solvent side of the microencapsulated pigment. It is thought that this is largely due to the action of the hydrophilic group. When ink is ejected from the recording head and landed on plain paper, the ink solvent rapidly penetrates into the paper, but pigment particles dispersed with a conventional dispersant (the pigment particles are covered with the dispersant) were used. In the pigment ink, the pigment particles move with the solvent in the lateral direction or deep part of the paper and are not easily adsorbed on the cellulose fiber on the surface of the plain paper (this is because the hydrophilic group amount on the pigment surface is the same as that of the embodiment of the present invention). This is probably because it is less than such microencapsulated pigments and the hydrophilic groups are not regularly and densely oriented.) Therefore, the print density is low and the color developability is insufficient.
On the other hand, in the microencapsulated pigment of the present invention, hydrophilic groups (particularly cationic groups) present on the surface are easily adsorbed on the plain paper cellulose fibers by interaction with the plain paper cellulose fibers. When the ink containing the microencapsulated pigment of the present invention as the colorant is ejected from the recording head and landed on the plain paper, the colorant tends to accumulate near the landing position of the plain paper. Occurrence is considered to be suppressed.

  In addition, since the ink for inkjet recording according to the present invention is coated with a polymer, the ink has excellent fixability with respect to a recording medium as compared with an ink using conventional surface-treated pigment particles as a colorant. Further, the scratch resistance of the recorded matter can be made excellent.

Next, the components of the macroencapsulated pigment according to the present invention will be described in detail.
Pigment particles having a hydrophilic group on the surface can be suitably prepared by treating the surface of the pigment particles with a hydrophilic group-imparting agent. Therefore, the pigment constituting the pigment particles having a hydrophilic group on the surface is not particularly limited as long as it is a pigment that does not dissolve in the hydrophilic group-imparting agent. From this point of view, the following inorganic pigments and organic pigments can be mentioned as preferable pigments in the ink of the present invention.
Examples of inorganic pigments include carbon blacks such as furnace black, lamb black, acetylene black, and channel black (C.I. Pigment Black 7), iron oxide pigments, and the like. Organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments), polycyclic pigments (eg, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxanes). Pigments, thioindigo pigments, isoindolinone pigments, or quinofuranone pigments), dye chelates (eg, basic dye-type chelates or acidic dye-type chelates), nitro pigments, nitroso pigments, or aniline black. .

More specifically, as an inorganic pigment used for black, the following carbon black, for example, No. manufactured by Mitsubishi Chemical Corporation is used. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, or No2200B, etc .; Columbia-made Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc .; Cabot-made Regal 400R, Regal 330R, Regal 660L, Mull 660L 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc .; or Color from Degussa
Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black
FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, and Special Black 5S.
Moreover, as the organic pigment for black, a black organic pigment such as aniline black (C.I. Pigment Black 1) can be used.

  Examples of organic pigments for yellow ink include C.I. l. Pigment Yellow 1 (Hansa Yellow), 2, 3 (Hansa Yellow 10G), 4, 5 (Hansa Yellow 5G), 6, 7, 10, 11, 12, 13, 14, 16, 17, 24 (Flavantron Yellow) , 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108 (anthrapyrimidine yellow), 109, 110, 113, 117 ( Copper complex pigment), 120, 124, 128, 129, 133 (quinophthalone), 138, 139 (isoindolinone), 147, 151, 153 (nickel complex pigment), 154, 167, 172, 180, and the like. it can.

  Further, as organic pigments for magenta ink, C.I. l. Pigment Red 1 (Paral Red), 2, 3 (Toluidine Red), 4, 5 (lTR Red), 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21 , 22, 23, 30, 31, 32, 37, 38 (pyrazolone red), 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88 (thioindigo), 112 (Naphthol AS series), 114 (naphthol AS series), 122 (dimethylquinacridone), 123, 144, 146, 149, 150, 166, 168 (antanthrone orange), 170 (naphthol AS series), 171, 175, 176 , 177, 178, 179 (berylene maroon), 184, 185, 187, 202, 209 (dichloroquinacridone), 219, 224 (berylene), 245 (naphthol AS yarn) ) Or C.I. I. And CI pigment violet 19 (quinacridone), 23 (dioxazine violet), 32, 33, 36, 38, 43, and 50.

  Furthermore, as organic pigments for cyan ink, C.I. l. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 15: 4, 16 (metal-free phthalocyanine), 18 (alkali blue toner), 22, 25, 60 ( Slen Blue), 65 (Biolantron), 66 (Indigo), C.I. l. Vat blue 4, 60 etc. can be mentioned.

Furthermore, as an organic pigment used for color inks other than magenta, cyan or yellow ink,
C. I. Pigment green 7 (phthalocyanine green), 10 (green gold), 36, 37;
C. I. Pigment brown 3, 5, 25, 26; I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, etc. can be used.
In the macroencapsulated pigment according to the present invention, the above pigments can be used alone or in combination of two or more.

As the hydrophilic group-imparting agent for treating the surface of the pigment particles, first, a treatment agent containing sulfur can be preferably mentioned.
Examples of the treatment agent containing sulfur include sulfuric acid, fuming sulfuric acid, sulfur trioxide, chlorosulfuric acid, fluorosulfuric acid, amidosulfuric acid, sulfonated pyridine salt, and sulfamic acid. Among them, sulfur trioxide, sulfonated pyridine salt or sulfamine. Sulfonating agents such as acids are preferred. These can be used alone or in admixture of two or more. (Note that “sulfonating agent” is sulfonic acid (—SO ₃ H) and / or sulfinic acid (—RSO ₂ H: R is a C _{1 to} C ₁₂ alkyl group, or a phenyl group and a modified product thereof) Is a treatment agent for imparting
In addition, a solvent capable of forming a complex with the sulfur trioxide (a basic solvent such as N, N-dimethylformamide dioxane, pyridine, triethylamine, and trimethylamine, nitromethane, acetonitrile, etc.) and a solvent described later. It is also useful to form a complex with a mixed solvent of one or more kinds.
In particular, when sulfur trioxide itself is too reactive to decompose or alter the pigment itself, or when it is difficult to control the reaction with a strong acid, a complex of sulfur trioxide and a tertiary amine is used as described above. It is preferable to use the pigment particles for surface treatment (in this case, sulfonation).
In addition, when sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, fluorosulfuric acid, etc. are used alone, the pigment particles easily dissolve, and it is necessary to suppress the reaction for strong acids that react per molecule. It is necessary to pay attention to the type of solvent and the amount used.

  The solvent used in the reaction is selected from those which do not react with the treatment agent containing sulfur and in which the above-mentioned pigment becomes insoluble or hardly soluble, and sulfolane, N-methyl-2-pyrrolidone, dimethylacetamide, Examples include quinoline, hexamethylphosphoric triamide, chloroform, dichloroethane, tetrachloroethane, tetrachloroethylene, dichloromethane, nitromethane, nitrobenzene, liquid sulfur dioxide, carbon disulfide, and trichlorofluoromethane.

The treatment with the treatment agent containing sulfur is performed by dispersing pigment particles in a solvent, adding a treatment agent containing sulfur to this dispersion, heating to 60 to 200 ° C., and stirring for 3 to 10 hours. Specifically, a high-speed shearing dispersion using a high-speed mixer or the like, or impact-dispersing using a bead mill or a jet mill to form a slurry (dispersion liquid) is preferable. Then, after moving to gentle stirring, a treatment agent containing sulfur is added to introduce hydrophilic groups onto the surface of the pigment particles. At this time, the reaction conditions and the type of the treatment agent containing sulfur greatly depend on the determination of the introduction amount of the hydrophilic group. After this heat treatment, the treating agent containing solvent and residual sulfur is removed from the slurry of pigment particles. Removal is carried out by repeatedly washing with water, ultrafiltration, reverse osmosis, etc., centrifugation, filtration and the like.
Further, the sulfonic acid (—SO ₃ H) and / or sulfinic acid (—RSO ₂ H: R is a C _{1 to} C ₁₂ alkyl group, or a phenyl group and a modified product thereof) described above is treated with an alkali compound. As a hydrophilic group, a sulfonate anion group (—SO ₃ ⁻ ) and / or a sulfinate anion group (—RSO ₂ ^— : R is a C _{1 to} C ₁₂ alkyl group or phenyl group and a modified product thereof) are surfaced. The pigment particles can be obtained. In the present invention, it is preferably used in this state.
As the alkali compound, a cation is an alkali metal ion or a chemical formula (R ₁ R ₂ R ₃ R ₄ N) ⁺ (R ₁ , R ₂ , R ₃ and R ₄ may be the same or different, and a hydrogen atom, an alkyl group, An alkaline compound that is a monovalent ion represented by (showing a hydroxyalkyl group or an alkyl halide group) is selected. Preferably, an alkaline compound in which the cation becomes an alkanolamine cation such as lithium ion (Li ⁺ ), potassium ion (K ⁺ ), sodium ion (Na ⁺ ), ammonium ion (NH ₄ ⁺ ), and triethanolamine cation. It is.
Hydroxyl anion is preferably used as the anion of the alkali compound. Specific examples thereof include ammonia, alkanolamine (monoethanolamine, diethanolamine, N, N-butylethanolamine, triethanolamine, propanolamine, aminomethyl). Propanol, 2-aminoisopropanol, etc.) and monovalent alkali metal hydroxides (LiOH, NaOH, KOH).
The amount of the alkali compound added is preferably at least the neutralization equivalent of the sulfonic acid group and / or sulfinic acid group of the pigment particles. Furthermore, for volatile additives such as ammonia and alkanolamine, addition of 1.5 times or more of the neutralization equivalent is generally preferred.
The operation can be performed by placing pigment particles having the sulfonic acid group and / or sulfinic acid group chemically bonded to the surface in an alkali compound, and shaking with a paint shaker or the like.

Moreover, a carboxylating agent can also be mentioned suitably as a hydrophilic group provision agent for processing the surface of a pigment particle. Here, the “carboxylating agent” is a treating agent for imparting a carboxylic acid group (—COOH).
As the carboxylating agent, an oxidizing agent such as hypohalite such as sodium hypochlorite or potassium hypochlorite is used to cut off the partial bond (C = C, C-C) on the pigment particle surface. And by oxidizing. In addition to the chemical treatment described above, a carboxylic acid group may be imparted by physical oxidation such as plasma treatment, but in the present invention, if the treatment method can ensure dispersion stability in an aqueous medium, Various methods can be selected. Further, in the exemplified carboxylic acid introduction treatment, a quinone group or the like may be introduced although the amount is small. Even in such a case, if the dispersion stability of the microencapsulated pigment in the aqueous medium can be ensured, it does not contradict the gist of the present invention.
As an example of treatment with a carboxylating agent, pigment particles are preliminarily sheared and dispersed in an aqueous medium with a high-speed mixer or the like, or impact-dispersed with a bead mill or jet mill to form a slurry (dispersion). Next, a hypohalite such as sodium hypochlorite having an effective halogen concentration of 10 to 30% is mixed in an appropriate amount of water and heated to 60 to 80 ° C. for about 5 to 10 hours, preferably 10 It is performed by stirring for more than an hour. This operation involves a considerable amount of heat and requires safety precautions. Thereafter, the solvent and the remaining carboxylating agent are removed from the slurry of the surface-treated pigment particles by heat treatment. Further, if necessary, a desired aqueous dispersion can be obtained by repeatedly performing methods such as washing with water, ultrafiltration, reverse osmosis, centrifugation, filtration and the like.
Again, by treating pigment particles having a carboxylic acid group (—COOH) with an alkali compound, pigment particles having a carboxylic acid anion group (—COO ⁻ ) on the surface as a hydrophilic group can be obtained. In the present invention, it is preferably used in this state.
The kind of alkali compound and the treatment method with the alkali compound are the same as described above.

Next, a preferable introduction amount of the hydrophilic group to the pigment surface and a method for examining the introduction state will be described.
First, when hydrophilization is performed using a sulfonating agent, the amount of hydrophilic groups introduced into the pigment particle surface is preferably 0.01 mmol equivalent or more per gram of pigment particles. When the introduction amount of the hydrophilic group is less than 0.01 mmol / g, in the microencapsulation step of the pigment particles in the aqueous solvent, the aggregation of the pigment particles is likely to occur, and the average particle size of the microencapsulated pigment is increased. There is a tendency to increase. As the average particle size of the microencapsulated pigment increases, it becomes difficult to obtain an ink for ink jet recording that is excellent in dispersion stability and ejection stability and can increase the printing density of an image.
The upper limit of the introduction amount of the hydrophilic group with respect to the pigment particles is not particularly limited, but when it exceeds 0.15 mmol / g, the average particle diameter of the pigment particles may not be changed with the increase of the introduction amount of the hydrophilic group. Therefore, it is preferably 0.15 mmol / g or less from the viewpoint of cost.
Next, the amount of hydrophilic groups introduced into the pigment surface by the carboxylating agent will be described. In the surface treatment method used in the present invention, it is considered that a carboxylic acid group (—COOH) and / or a carboxylic acid anion group (—COO ⁻ ) is introduced to the pigment surface. In the present invention, the amount introduced is measured by the surface active hydrogen content. A detailed measurement method will be described later.
The active hydrogen content in the pigment obtained by such a method is preferably 1.0 mmol / g or more, and more preferably 1.5 mmol / g or more. If it is 1.0 mmol / g or less, water dispersibility becomes poor, and coalescence (particles naturally gather and increase in particle size) easily occurs during the microencapsulation process.
Although the pigment particles having a hydrophilic group on the surface have been described in detail above, the average particle diameter of the pigment particles having the hydrophilic group on the surface can be easily reduced to 150 nm or less by the above method. In particular, it is more preferable to set the average particle size to 20 nm to 80 nm by selecting the kind of pigment or hydrophilic group imparting agent, the amount of hydrophilic group introduced, and the like, and thereby excellent dispersion stability and ejection stability. In addition, it is possible to obtain a microencapsulated pigment that can more reliably produce an ink for ink jet recording that can increase the printing density of an image. (In this specification, the description of the average particle diameter is described by the measured value of the laser light scattering method.)
The pigment particles having a hydrophilic group on the surface are subsequently coated with a polymer having a repeating structural unit derived from a cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group. The microencapsulated pigment according to the embodiment of the present invention. As described above, such a microencapsulated pigment is prepared by adding a cationic polymerizable surfactant to an aqueous dispersion of pigment particles having an anionic group on the surface, mixing and emulsifying, and then adding a polymerization initiator. And can be suitably produced by emulsion polymerization.

The cationic group of the cationic polymerizable surfactant is preferably a cationic group selected from the group consisting of a primary amine cation, a secondary amine cation, a tertiary amine cation, and a quaternary ammonium cation. The primary amine cation is a monoalkylammonium cation (RNH ₃ ⁺ ) or the like, the secondary amine cation is a dialkylammonium cation (R ₂ NH ₂ ⁺ ) or the like, and the tertiary amine cation is a trialkylammonium cation (R _3). NH ⁺ ) and the like, and examples of the quaternary ammonium cation include (R ₄ N ⁺ ) and the like. Here, R is a hydrophobic group and a polymerizable group, and examples thereof include those shown below.
Examples of the counter anion of the above-described cationic group include Cl ⁻ , Br ⁻ and I ⁻ .
The hydrophobic group is preferably selected from the group consisting of an alkyl group, an aryl group, and a group in which these are combined.
The polymerizable group is preferably an unsaturated hydrocarbon group, and more specifically selected from the group consisting of a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. preferable. Among these, an acryloyl group and a methacryloyl group can be exemplified as preferable examples.
Specific examples of the cationic polymerizable surfactant include a cationic allylic acid derivative as described in JP-B-4-65824.

Examples of the cationic polymerizable surfactant used in the present invention include compounds represented by the general formula R _{[4- (l + m + n)]} R ¹ _l R ² _m R ³ nN ⁺ · X ^−. (R is a polymerizable group, R ¹ , R ² and R ³ are each an alkyl group or an aryl group, X is Cl, Br or I, and l, m and n are each 1 or 0. ). Here, as the polymerizable group, a hydrocarbon group having an unsaturated hydrocarbon group capable of radical polymerization can be preferably exemplified, and more specifically, an allyl group, an acroyl group, a methacryloyl group, a vinyl group, a propylene group, and a propylene group. Nyl group, vinylidene group, vinylene group and the like can be mentioned.
Specific examples of the cationic polymerizable surfactant include dimethylaminoethyl methyl chloride methacrylate, dimethylaminoethyl benzyl methacrylate methacrylate, methacryloyloxyethyltrimethylammonium chloride, diallyldimethylammonium chloride, 2-hydroxy-3-methacryloxypropyl. Examples thereof include trimethylammonium chloride.
A commercial item can also be used as said cationic polymerizable surfactant. Examples include Acryester DMC (Mitsubishi Rayon Co., Ltd.), Acryester DML60 (Mitsubishi Rayon Co., Ltd.), C-1615 (Daiichi Kogyo Seiyaku Co., Ltd.), and the like.
The cationic polymerizable surfactants exemplified above can be used alone or as a mixture of two or more.

More specifically, the microencapsulated pigment according to the embodiment of the present invention is preferably produced by the following procedure.
(1) A cationic polymerizable surfactant is added to a dispersion in which a pigment having an anionic group on its surface is dispersed in water. A part of the added cationic polymerizable surfactant is adsorbed to the anionic group of the “pigment having an anionic group on the surface” and is ionically bonded to the remaining cationic group. The polymerizable surfactant forms a form (admicelle) covering the cationic polymerizable surfactant in which the cationic group is immobilized with the aqueous phase side fixed.
(2) A polymerization initiator is added and emulsion polymerization is performed.
By such a procedure, a microencapsulated pigment coated with a polymer having a repeating structural unit derived from a cationic polymerizable surfactant can be preferably produced.

Furthermore, other comonomers may be added particularly for the purpose of controlling the fixability, scratch resistance and solvent resistance of the recorded matter, and controlling the storage stability of the ink.
In particular, the fixability and scratch resistance of the recorded matter can be achieved by controlling the glass transition point (Tg) of the copolymer (copolymer) covering the pigment particles of the microencapsulated pigment according to the present invention. .
When printing on a recording medium such as plain paper or a dedicated medium for inkjet recording at room temperature with an ink using the microencapsulated pigment of the present invention, an aqueous medium (water and / or water-soluble) around the microencapsulated pigment particles of the present invention is printed. Microencapsulated pigment particles come close to each other by penetrating into a recording medium such as plain paper or an inkjet recording medium and being removed from the vicinity of the microencapsulated pigment particles. When the glass transition point (Tg) of the copolymer (copolymer) covering the pigment particles of the microencapsulated pigment is not more than room temperature, the microencapsulated pigment is generated by the capillary pressure generated in the gap between the microencapsulated pigment particles. Copolymers (copolymers) covering the pigment particles are fused together to enclose the pigment inside (included) It was) for forming a state, the fixing property and scratch resistance of the image can particularly favorably.
Generally, in polymer solids, especially amorphous polymer solids, when the temperature is raised from a low temperature to a high temperature, a state where a large amount of deformation occurs with a small force from a state where a very large force is required for slight deformation (glass state). A phenomenon that suddenly changes to a temperature occurs, and the temperature at which this phenomenon occurs is called the glass transition point (or glass transition temperature). Generally, in the differential heat curve obtained by temperature rise measurement with a differential scanning calorimeter, the intersection of the base line when the tangent line is drawn from the bottom of the endothermic peak toward the end point of the endotherm. Let temperature be the glass transition point. In addition, it is known that other physical properties such as elastic modulus, specific heat, and refractive index also change abruptly at the glass transition point, and it is known that the glass transition point is also determined by measuring these physical properties. ing. In this invention, the glass transition point obtained by the temperature rising measurement with a thermal scanning calorimeter (DSC) was used.

  In order to form the microencapsulated pigment of the present invention more preferably at room temperature when printing on a recording medium such as plain paper or a dedicated medium for inkjet recording with the ink using the microencapsulated pigment of the present invention, The glass transition point (Tg) of the copolymer (copolymer) covering the pigment particles of the encapsulated pigment is preferably 30 ° C. or lower, more preferably 15 ° C. or lower, and further preferably 10 ° C. or lower. Therefore, the copolymer (copolymer) covering the pigment particles of the microencapsulated pigment is preferably designed so that the glass transition point is 30 ° C. or less, more preferably 15 ° C. or less, and still more preferably It is preferably designed to be 10 ° C. or lower. However, when the glass transition point is lower than −20 ° C., the solvent resistance tends to decrease. The glass transition point of such a copolymer (copolymer) can be within the above range by appropriately selecting the type and composition ratio of the hydrophobic monomer to be used. If the printed material can be heated at a temperature higher than the glass transition point (Tg) of the copolymer (copolymer) covering the pigment particles of the microencapsulated pigment, the glass transition point is heated. The glass transition temperature may exceed 30 ° C. because the film can be formed if the temperature is lower than the temperature, but in this case, it is necessary to attach a heating mechanism to the ink jet recording apparatus. Since problems such as cost increase occur, the glass transition point is preferably 30 ° C. or lower.

In order to satisfy the required properties such as fixability, scratch resistance, water resistance, and solvent resistance of the recorded matter, it is possible to suitably use a hydrophobic monomer. That is, the microencapsulated pigment according to the present invention has a repeating structure in which pigment particles having an anionic group on the surface thereof are derived from a cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group. It is preferred to have repeating structural units derived from units and hydrophobic monomers.
The hydrophobic monomer has at least a hydrophobic group and a polymerizable group in its structure, and the hydrophobic group is selected from the group consisting of an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. Can be illustrated. Examples of the aliphatic hydrocarbon group include a methyl group, an ethyl group, and a propyl group. Examples of the alicyclic hydrocarbon group include a cyclohexyl group, a dicyclopentenyl group, a dicyclopentanyl group, and an isobornyl group. Examples thereof include a benzyl group, a phenyl group, and a naphthyl group.
The polymerizable group is an unsaturated hydrocarbon group capable of radical polymerization, and is preferably selected from the group consisting of a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. .

Specific examples of the hydrophobic monomer include styrene and methylstyrene, dimethylstyrene, chlorostyrene, dichlorostyrene, bromostyrene, p-chloromethylstyrene, divinylbenzene, and other styrene derivatives; methyl acrylate, ethyl acrylate, acrylic acid n-butyl, butoxyethyl acrylate, benzyl acrylate, phenyl acrylate, phenoxyethyl acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, tetrahydrofurfuryl acrylate, isobol Monofunctional acrylic esters such as nyl acrylate; methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate , Butoxymethyl methacrylate, benzyl methacrylate, phenyl methacrylate, phenoxyethyl methacrylate, cyclohexyl methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, dicyclopentenyloxyethyl methacrylate, tetrahydrofurfuryl methacrylate, isobornyl methacrylate, etc. Monofunctional methacrylate esters of allyl compounds such as allylbenzene, allyl-3-cyclohexanepropionate, 1-allyl-3,4-dimethoxybenzene, allylphenoxyacetate, allylphenylacetate, allylcyclohexane, allyl polycarboxylic acid allyl, etc. ; Ester cheeks of fumaric acid, maleic acid, itaconic acid; radically polymerizable groups such as N-substituted maleimides and cyclic olefins Monomer, and the like that.
As the hydrophobic monomer, those satisfying the above-mentioned required characteristics are appropriately selected, and the addition amount thereof is arbitrarily determined.

Moreover, it is preferable that the polymer which coat | covers a pigment particle further has a repeating structural unit induced | guided | derived from the crosslinkable monomer.
By having a repeating structural unit derived from a crosslinkable monomer, a crosslinked structure is formed in the polymer, and solvent resistance (the property that the solvent contained in the ink for ink jet recording hardly penetrates into the polymer coating the pigment) ) Can be improved.
When the solvent penetrates into the polymer that coats the pigment particles, the polymer swells or deforms, and the orientation of the cationic groups of the pigment particles facing the aqueous medium is disturbed. Stability and the like may be reduced. In contrast, the formation of a crosslinked structure in the polymer that coats the pigment particles improves the solvent resistance of the microencapsulated pigment and makes the dispersion stability more stable in an ink composition in which a water-soluble organic solvent coexists. It can be excellent.

  Examples of the crosslinkable monomer that can be used in the present invention include compounds having two or more unsaturated hydrocarbon groups selected from a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. For example, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, allyl acrylate, bis (acryloxyethyl) hydroxyethyl isocyanurate, bis (acryloxy) Neopentyl glycol) adipate, 1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, Bylene glycol diacrylate, polypropylene glycol diacrylate, 2-hydroxy-1,3-diacryloxypropane, 2,2-bis [4- (acryloxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxy) Phenyl] propane, 2,2-bis [4- (acryloxyethoxy diethoxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxy polyethoxy) phenyl] propane, hydroxypentylglycol dipentyl glycoldi Acrylate, 1,4-butanediol diacrylate, dicyclopentanyl diacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, ditrimethylolpropane tetraacrylate, penta Lithritol triacrylate, tetrabromopisphenol A diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate, tris (acryloxyethyl) isocyanurate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene Glycol dimethacrylate, polyethylene glycol dimethacrylate, propylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol Dimethacrylate, 2-hydroxy-1,3-dimetac Liloxypropane, 2,2-bis [4 (methacryloxy) phenyl] propane, 2,2-bis [4- (methacryloxyethoxy) phenyl] propane, 2,2-bis [4- (methacryloxyethoxydiethoxy) ) Phenyl] propane, 2,2-bis [4- (methacryloxyethoxypolyethoxy) phenyl] propane, tetrabromobisphenol A dimethacrylate, dicyclopentanyl dimethacrylate, dipentaerythritol hexamethacrylate, glycerol dimethacrylate, hydroxybiba Neopentyl glycol dimethacrylate phosphate, dipentaerythritol monohydroxypentamethacrylate, ditrimethylolpropane tetramethacrylate, pentaerythritol trimethacrylate, pentaerythritol Tetramethacrylate, trimethylolpropane triglycidyl Se roll dimethacrylate, trimethylolpropane trimethacrylate, tris (methacryloxyethyl) isocyanurate, allyl methacrylate, divinylbenzene, diallyl phthalate, diallyl terephthalate, diallyl isophthalate, diethylene glycol bis allyl carbonate.

  Moreover, it is preferable that the polymer which coat | covers a pigment particle further has the repeating structural unit induced | guided | derived from the monomer represented by following General formula (1).

[However, R ¹ represents a hydrogen atom or a methyl group. R ² represents a t-butyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group. m represents an integer of 0 to 3, and n represents an integer of 0 or 1. ]
The R ² group, which is a “bulky” group derived from the monomer represented by the general formula (1) in the polymer, reduces the flexibility of the polymer molecule, that is, restricts the mobility of the molecule. The mechanical strength and heat resistance of the polymer are improved, and the printed matter with ink using the microencapsulated pigment of this embodiment coated with the polymer can have excellent abrasion resistance and durability. In addition, since the R ² group, which is a “bulky” group, is present in the polymer, penetration of the organic solvent into the polymer can be suppressed, so that the microencapsulated pigment of this embodiment has excellent solvent resistance. In an ink composition in which a water-soluble organic solvent coexists, more stable ejection properties, dispersibility, and long-term storage can be obtained.
In the general formula (1), examples of the alicyclic hydrocarbon group represented by R ² include a cycloalkyl group, a cycloalkenyl group, a benzyl group, a phenyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantane. Group, tetrahydrofuran group, naphthyl group, t-butyl group, and the like.

As described above, a polymer having a repeating structural unit derived from a crosslinkable monomer and a polymer having a repeating structural unit derived from the monomer represented by the general formula (1) have high Tg, mechanical strength and heat resistance. There is an advantage that it has excellent properties and solvent resistance.
However, a microencapsulated pigment coated with such a polymer is insufficient in plasticity of the polymer, and is likely to be in a state in which it is difficult to adhere to the recording medium. Rubability may be reduced.

  On the other hand, since the polymer having a repeating structural unit derived from a monomer having a long-chain alkyl group among the above-mentioned hydrophobic monomers has flexibility, the repeating structural unit derived from a crosslinkable monomer and / or a general formula By adjusting the ratio of the repeating structural unit derived from the monomer represented by (1) and the repeating structural unit derived from the monomer having a long-chain alkyl group, the mechanical strength and resistance to the extent that the plasticity is not impaired. It can be set as the polymer which has solvent property. Such a microencapsulated pigment coated with a polymer is easy to adhere to a recording medium, has excellent fixability, and has excellent solvent resistance. Therefore, the ink using the microencapsulated pigment can obtain excellent ejection stability, dispersion stability, and long-term storage stability even in an ink composition in which a water-soluble organic solvent coexists. In addition, a printed matter obtained with an ink using the microencapsulated pigment has good fixability and can be excellent in abrasion resistance, durability, and solvent resistance.

  Moreover, the following are mentioned as a specific example of the monomer represented by the said General formula (1).

The following hydrophilic monomers can be used together with the cationic polymerizable surfactant. Examples of such hydrophilic monomers include those having a hydroxyl group, an ethylene oxide group, an amide group, or an amino group as a hydrophilic group. These hydrophilic groups are considered to exist along the cationic surface along with the cationic groups in the water phase side, and since they easily form hydrogen bonds with the OH groups of the paper cellulose fibers, they have these hydrophilic groups. When ink for inkjet recording using a microencapsulated dye obtained in combination with a hydrophilic monomer as a colorant is ejected onto plain paper, the colorant is more likely to be adsorbed onto the cellulose fiber of plain paper, and landing Since it tends to stay in the vicinity of the position and in the vicinity of the paper surface, image density can be obtained and bleeding can be suppressed.
Examples of the hydrophilic monomer include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 2-hydroxybutyl methacrylate having an OH group, ethyldiethylene glycol acrylate having an ethylene oxide group, polyethylene glycol monomethacrylate, methoxypolyethylene glycol methacrylate, and the like. N-methylaminoethyl methacrylate, N-methylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl methacrylate, amino group-containing N-methylaminoethyl methacrylate, N-N-dimethylacrylamide, etc. Alkylamino esters of acrylic acid or methacrylic acid such as N- (2-dimethylaminoethyl) acrylamide, N- (2-dimethylaminoethyl) methacrylamide, N, N-dimethylaminopropylacrylamide, and other unsaturated amides having an alkylamino group, and vinylpyridine Examples thereof include vinyl ethers having an alkylamino group such as monovinyl pyridines and dimethylaminoethyl vinyl ether; vinyl imidazole and the like, N-vinyl-2-pyrrolidone, and the like.

  The polymerization reaction is preferably started by adding a polymerization initiator, and as such a polymerization initiator, a water-soluble polymerization initiator is preferable, and potassium persulfate, ammonium persulfate, sodium persulfate, 2,2- Examples thereof include azobis- (2-methylpropionamidine) dihydrochloride and 4,4-azobis- (4-cyanovaleric acid).

  The microencapsulated pigment according to the embodiment of the present invention is manufactured by adding the cationic polymerizable surfactant to an aqueous dispersion of pigment particles having an anionic group on the surface as a hydrophilic group, and if necessary. Then, water or water and an aqueous solvent are added and mixed, and after irradiation with ultrasonic waves for a predetermined time, the cationic polymerization surfactant and / or the hydrophilic monomer (in addition to these, the above-mentioned hydrophobic monomer, crosslinking agent) And a monomer represented by the general formula (1) can be added.) And water is added if necessary, and again irradiated with ultrasonic waves for a predetermined time to disperse, while performing ultrasonic irradiation and stirring, It can be suitably carried out by raising the temperature to a predetermined temperature (temperature at which the polymerization initiator is activated), adding the polymerization initiator to activate the polymerization initiator, and emulsion polymerization.

  When the hydrophobic monomer is used, more specifically, a cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group in an aqueous dispersion of pigment particles having the anionic group on the surface. A step of adding and mixing an agent and irradiating with ultrasonic waves, a step of adding and mixing a hydrophobic monomer, a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group, and It consists of a process of adding and mixing a hydrophilic monomer and irradiating with ultrasonic waves, and a process of adding a polymerization initiator and emulsion polymerization, and can be more suitably produced by carrying out in the order of the processes. .

  The addition amount of the cationic polymerizable surfactant to the pigment having the anionic group on the surface when the cationic polymerizable surfactant is added to the aqueous dispersion of pigment particles having the anionic group on the surface is as follows: The total number of moles of anionic group relative to the amount of pigment having an anionic group on the surface (= weight of the pigment used (g) × anionic group on the pigment surface (mol / g)) is 0.5. The range of ˜2 times mol is preferred, and the range of 0.8 to 1.2 times mol is more preferred. By setting the addition amount to 0.5 times mol or more, it is strongly ionically bound to pigment particles having an anionic group as a hydrophilic group, and can be easily encapsulated. By setting the addition amount to 2 times or less, the generation of the cationic polymerizable surfactant not adsorbed on the pigment particles can be reduced. The addition amount of the hydrophobic monomer is preferably in the range of about 5 to 900 parts by weight, more preferably in the range of 10 to 500 parts by weight, and particularly preferably in the range of 15 to 200 parts by weight with respect to 100 parts by weight of the pigment. . The addition amount of the cationic polymerizable surfactant that forms the outermost shell of the capsule is preferably in the range of about 0.5 to 5 times the mole of the cationic polymerizable surfactant added first, more preferably 1-2. The range is about a double mole. By setting the amount in a range of 1 mol or more, the dispersibility and dispersion stability of the encapsulated particles are excellent, and the discharge stability is also excellent. By setting the addition amount to 2 times or less, the generation of the cationic polymerizable surfactant that does not contribute to the encapsulation can be suppressed, so that the generation of polymer particles in addition to the encapsulated particles can be prevented.

When the crosslinkable monomer and / or the monomer represented by the general formula (1) are used, more specifically, a cationic group and a hydrophobic group are added to the aqueous dispersion of pigment particles having the anionic group on the surface. A step of adding a cationic polymerizable surfactant having a polymerizable group and a polymerizable group, mixing and irradiating with ultrasonic waves, a crosslinkable monomer and / or a monomer represented by the general formula (1) And a step of mixing, a step of adding a cationic polymerizable surfactant and / or the hydrophilic monomer, mixing and irradiating with ultrasonic waves, and a step of emulsion polymerization by adding a polymerization initiator. It can manufacture more suitably by implementing in the said process order.
Further, when the crosslinkable monomer and / or the monomer represented by the general formula (1) is used, more specifically, a cationic group is added to the aqueous dispersion of pigment particles having the anionic group on the surface. And a step of adding and mixing a cationic polymerizable surfactant having a hydrophobic group and a polymerizable group and irradiating with ultrasonic waves, and a crosslinkable monomer and / or the general formula (1). A step of adding and mixing a monomer and a monomer having a long-chain alkyl group, a step of adding a cationic polymerizable surfactant and / or the hydrophilic monomer, mixing and irradiating with ultrasonic waves, and a polymerization initiator It can be more suitably manufactured by carrying out the emulsion polymerization step and adding the step.

  According to the emulsion polymerization method of the present invention, first, a cationic polymerizable surfactant is adsorbed to the hydrophilic group on the surface of the pigment particle having an anionic group on the surface, and then a hydrophobic monomer is added, and then the cationic polymerization is performed. By adding ultrasonic surfactants and / or hydrophilic monomers and irradiating them with ultrasonic waves, the arrangement of the polymerizable surfactants and monomers existing around the pigment particles is extremely highly controlled. A state in which the cationic groups are oriented toward the aqueous phase is formed. Then, the monomer is converted into a polymer by the emulsion polymerization while maintaining this highly controlled form, and the microencapsulated pigment according to the embodiment of the present invention is obtained. According to said method, the production | generation of the water-soluble oligomer and polymer which are a by-product can be reduced. As a result, the viscosity of the resulting microencapsulated pigment dispersion can be reduced, and the purification process such as ultrafiltration can be facilitated, and the ink using the microencapsulated pigment has improved dispersion stability. It is excellent in ejection stability from the recording head, and it is difficult to bleed even on plain paper, and a high color and high density printed image can be obtained.

  The reaction is preferably carried out using a reaction vessel equipped with an ultrasonic generator, a stirrer, a reflux condenser, a dropping funnel and a temperature controller.

  The addition of the polymerization initiator can be suitably carried out by dropping an aqueous solution in which a water-soluble polymerization initiator is dissolved in pure water.

  The activation of the polymerization initiator can be preferably carried out by raising the temperature of the aqueous dispersion to a predetermined polymerization temperature. After completion of the polymerization, it is preferable to adjust the pH within the range of 7.0 to 9.0 and perform filtration. Here, as described above, the aqueous solvent is a solvent containing water as a main component. In addition to water, the aqueous solvent includes, as an optional component, for example, a water-soluble solvent such as glycerin or glycol. May be. The polymerization temperature is preferably in the range of 60 ° C to 90 ° C. In addition, when the pigment particles having an anionic group on the surface as a hydrophilic group are not in the state of an aqueous dispersion, as a pretreatment, a dispersion treatment is performed using a general disperser such as a ball mill, a roll mill, an Eiger mill, or a jet mill. It is preferable to carry out.

  In the microencapsulated pigment according to the embodiment of the present invention obtained as described above, the pigment particles having a small average particle diameter are completely covered with the polymer layer (no defect portion), and the hydrophilic group of the polymer layer Is considered to be regularly oriented toward the aqueous solvent (see FIG. 2 and FIG. 4), it has high dispersion stability with respect to the aqueous solvent.

Although the microencapsulated pigment according to the embodiment of the present invention has been described above, the particle size of the microencapsulated pigment is preferably 400 nm or less, more preferably 300 nm or less, and particularly preferably 50 to 200 nm.
[Aqueous dispersion]
The aqueous dispersion according to the embodiment of the present invention contains the microencapsulated pigment according to the embodiment of the present invention. As such an aqueous dispersion, the liquid after emulsion polymerization in the embodiment of the present invention is used. Can be suitably exemplified. The ink jet recording ink according to the embodiment of the present invention can be manufactured by adding other blending components for making the ink for ink jet recording to this aqueous dispersion by a conventional method.
[Ink for inkjet recording]
As described above, the ink for inkjet recording according to the embodiment of the present invention includes an aqueous dispersion.

  An ink for inkjet recording according to another embodiment of the present invention includes at least the microencapsulated pigment and water according to the embodiment of the present invention. The content of the microencapsulated pigment is preferably 1% by weight to 20% by weight and more preferably 3% by weight to 15% by weight with respect to the total weight of the ink for ink jet recording. In particular, 5% by weight to 15% by weight is preferable for obtaining a high printing density and high color developability.

  In addition, the solvent of the ink for inkjet recording according to the embodiment of the present invention preferably contains water and a water-soluble organic solvent as a basic solvent, and may contain any other component as necessary.

  Examples of water-soluble organic solvents include C1-C4 alkyl alcohols such as ethanol, methanol, butanol, propanol, and isopropanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and ethylene glycol monomethyl ether acetate. Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, Triethylene glycol mono-n-butyl ether, Tylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl Ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, propylene glycol mono-n- Glycol ethers such as butyl ether or dipropylene glycol mono-n-butyl ether; There may be mentioned formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, acetin, diacetin, triacetin, or sulfolane and the like.

  In addition, the ink for inkjet recording according to the embodiment of the present invention contains a wetting agent composed of a high-boiling water-soluble organic solvent as a water-soluble organic solvent for the purpose of providing water retention and wettability of the ink for inkjet recording. Is preferred. As such a high boiling water-soluble organic solvent, a high boiling water-soluble organic solvent having a boiling point of 180 ° C. or higher can be exemplified.

Specific examples of the water-soluble organic solvent having a boiling point of 180 ° C. or higher include ethylene glycol, propylene glycol, diethylene glycol, pentamethylene glycol, trimethylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3- Hexanediol, 2-methyl-2,4-pentanediol, tripropylene glycol monomethyl ether, dipropylene glycol monoethyl glycol, dipropylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol, triethylene glycol monomethyl ether, Tetraethylene glycol, triethylene glycol, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl Ether, tripropylene glycol, polyethylene glycol having a molecular weight of 2000 or less, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1, Examples include 6-hexanediol, glycerin, mesoerythritol, and pentaerythritol. An organic solvent having a boiling point of 200 ° C. or higher is preferred. These can be used alone or as a mixture of two or more. Accordingly, it is possible to provide an ink for ink jet recording that maintains fluidity and redispersibility for a long time even when left in an open state (in a state where it is exposed to air at room temperature). Furthermore, nozzle clogging is less likely to occur during printing or when restarting after printing interruption, and high ejection stability is obtained.
The content of these water-soluble organic solvents is preferably about 10 to 50% by weight and more preferably 10 to 30% by weight with respect to the total weight of the ink for ink jet recording.

Further, as the water-soluble organic solvent, polar solvents such as 2-pyrrolidone, N-methylpyrrolidone, ε-caprolactam, dimethyl sulfoxide, sulfolane, morpholine, N-ethylmorpholine, 1,3-dimethyl-2-imidazolidinone and the like are used. One or more of these may be selected and used. The addition of these polar solvents has an effect on dispersibility and can improve the ejection stability of ink.
The content of these polar solvents is preferably 0.1% by weight to 20% by weight and more preferably 1% by weight to 10% by weight with respect to the total weight of the ink for inkjet recording.

  The ink for ink jet recording according to the embodiment of the present invention preferably contains a penetrant for the purpose of promoting the penetration of the aqueous solvent into the recording medium. By rapidly penetrating the aqueous solvent into the recording medium, it is possible to reliably obtain a recorded matter with less image bleeding. As such a penetrant, polyhydric alcohol alkyl ethers (also referred to as glycol ethers) and 1,2-alkyldiols are preferably used. Specifically, as the alkyl ether of polyhydric alcohol, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol mono- n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono- t-butyl ether, diethylene glycol mono-t-butyl Ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene Glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, etc. It is done. Specific examples of the 1,2-alkyldiol include 1,2-pentanediol and 1,2-hexanediol. In addition to these, linear carbonization such as 1,3-propanediol, 1,4-butanediol 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, etc. It may be appropriately selected from hydrogen diols.

  In particular, in the embodiment of the present invention, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, 1,2-pentanediol, and 1,2-hexanediol are preferable. The content of these penetrants is preferably 1 to 20% by weight, more preferably 1 to 10% by weight, based on the total weight of the ink for inkjet recording. If the content of the penetrant is less than 1% by weight, the penetrability is not effective, and if it exceeds 20% by weight, problems such as a decrease in print quality due to image bleeding and an increase in viscosity occur. In particular, by using 1,2-alkyldiols such as 1,2-pentanediol and 1,2-hexanediol, the drying property and bleeding after printing are remarkably improved.

  In particular, in the embodiment of the present invention, by including glycerin, ink clogging reliability and storage stability can be sufficiently ensured.

  Furthermore, since one or more compounds selected from the group consisting of alkyl ethers of polyhydric alcohols and 1,2-alkyl diols can be included, the permeability of the ink solvent component to the recording medium can be increased. Combined with the effect of the microencapsulated pigment which is an embodiment of the invention, even when printing on plain paper, recycled paper, etc., the bleeding of the image is drastically reduced and the printing quality can be remarkably improved.

  Moreover, when using the above-mentioned glycol ethers, it is particularly preferable to use glycol ethers in combination with an acetylene glycol compound as a surfactant described later.

  The ink for inkjet recording according to the embodiment of the present invention preferably contains a surfactant, particularly a cationic surfactant and / or a nonionic surfactant.

In particular, the ink for inkjet recording according to the embodiment of the present invention desirably contains an acetylene glycol surfactant and / or an acetylene alcohol surfactant as the surfactant. Thereby, the permeability of the aqueous solvent constituting the ink to the recording medium can be increased, and printing with less bleeding can be expected on various recording media.
Preferable specific examples of the acetylene glycol compound used in the present invention include compounds represented by the following formula (6).

In the above formula (6), m and n are numbers satisfying 0 ≦ m + n ≦ 50, respectively. R ¹ , R ² , R ³ and R ⁴ are each independently an alkyl group (preferably an alkyl group having 6 or less carbon atoms).
Among the compounds represented by the above formula (6), 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3, 6-diol, 3,5-dimethyl-1-hexyn-3-ol and the like. As the compound represented by the above formula (6), it is also possible to use a commercially available product that is commercially available as an acetylene glycol-based surfactant. TG (all available from Air Products and Chemicals. Inc.), Orphine STG, Orphine E1010 (above, Nissin Chemical Co., Ltd. trade name).
Examples of the acetylene alcohol surfactant include Surfynol 61 (available from Air Products and Chemicals. Inc.).
The content of these surfactants is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total weight of the ink for ink jet recording.
Moreover, the ink for inkjet recording which concerns on embodiment of this invention can also contain a pH adjuster, Preferably, pH is set to the range of 4-7, More preferably, it is set to the range of 6-7.

  Specific examples of the pH adjuster include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, lithium carbonate, sodium phosphate, potassium phosphate, lithium phosphate, diphosphate. Potassium metal such as potassium hydrogen, dipotassium hydrogen phosphate, sodium oxalate, potassium oxalate, lithium oxalate, sodium borate, sodium tetraborate, potassium hydrogen phthalate, potassium hydrogen tartrate, ammonia, methylamine, ethylamine , Diethylamine, trimethylamine, triethylamine, tris (hydroxymethyl) aminomethane hydrochloride, triethanolamine, diethanolamine, diethylethanolamine, triisopropenolamine, butyldiethanolamine, morpholine, And amines such as Ropanoruamin are preferred.

  Moreover, the ink for inkjet recording which concerns on embodiment of this invention is benzoic acid, dichlorophen, hexachlorophene, sorbic acid, p-hydroxybenzoic acid ester, ethylenediaminetetraacetic acid (for the purpose of antifungal agent, antiseptic | rusting, and rust prevention). EDTA), sodium dehydroacetate, 1,2-benchazolin-3-one [product name: Proxel XL (manufactured by Avicia)], 3,4-isothiazoline-3-one, 4,4-dimethyloxazolidine, etc. it can.

The ink for ink jet recording according to the embodiment of the present invention can contain urea, thiourea, and / or ethylene urea for the purpose of preventing the nozzles of the recording head from drying.
The ink for inkjet recording according to the embodiment of the present invention is
(1) A microencapsulated pigment according to an embodiment of the present invention,
(2) one or more compounds (penetrant) selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and / or 1,2-alkyldiol having 4 to 10 carbon atoms,
(4) glycerin,
(5) water,
At least.
Such an ink for ink jet recording is particularly excellent in dispersion stability and ejection stability, and further, stable printing can be performed without clogging of the nozzles over a long period of time. In addition, in recording media such as plain paper, recycled paper, and coated paper, it is possible to obtain a high-quality image having good drying properties after printing, no bleeding, high printing density, and excellent color development. .
Another aspect of the inkjet recording ink according to the particularly preferred embodiment of the present invention is as follows:
(1) A microencapsulated pigment according to an embodiment of the present invention,
(2) one or more compounds (penetrant) selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and / or 1,2-alkyldiol having 4 to 10 carbon atoms,
(3) Acetylene glycol surfactant and / or acetylene alcohol surfactant,
(4) glycerin,
(5) water,
At least.
Such an ink for ink jet recording is particularly excellent in dispersion stability and ejection stability, and further, stable printing can be performed without clogging of the nozzles over a long period of time. In addition, in recording media such as plain paper, recycled paper, and coated paper, it is possible to obtain a high-quality image with particularly good dryness after printing, almost no bleeding, and high color density with high printing density. it can.

  Generally, when dispersing a pigment, a dispersant such as a surfactant or a polymer dispersant is used. However, since these dispersants are merely adsorbed on the surface of the pigment particles, Due to environmental factors, the dispersant tends to be detached from the pigment particle surface. On the other hand, in the embodiment of the present invention, as described above, the surface of the pigment particle having the hydrophilic group on the surface is completely included in the polymer film or the crosslinked polymer film, and the surface of the pigment particle is surrounded. It is considered that the polymer film or the cross-linked polymer film is very firmly fixed to the surface of the pigment particle and thus is difficult to be detached from the surface of the pigment particle.

  More specifically, the above acetylene glycol surfactant and / or acetylene alcohol surfactant and diethylene glycol using a pigment dispersion obtained by dispersing a pigment using a dispersant such as a surfactant or a polymer dispersant. When ink is improved in permeability with penetrants such as monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, or 1,2-alkyldiol, when ejected through a thin nozzle Due to the strong shearing force applied, the dispersant easily desorbs from the pigment surface, resulting in deterioration of dispersibility, and discharge tends to be unstable.

  On the other hand, in the ink for inkjet recording using the microencapsulated pigment according to the embodiment of the present invention, such a phenomenon is not recognized at all and is stably ejected. In addition, since the polymer film includes the pigment particles, good solvent resistance can be obtained, so that the penetration of the penetrant from the pigment particles and the swelling of the polymer are less likely to occur. Excellent dispersion stability can be maintained.

  In addition, an ink composition using a pigment dispersion in which a pigment is dispersed using a dispersant such as a surfactant or a polymer dispersant and having improved permeability is generally adsorbed on the pigment surface from the beginning of dispersion. The viscosity of the ink composition is high due to the dispersant dissolved in the liquid, or the dispersant is desorbed from the pigment as time passes after dispersion, and the viscosity of the ink composition is high due to the desorbed dispersant. Tend to be. For this reason, the pigment content is often limited. Therefore, particularly for plain paper and recycled paper, sufficient color density cannot be obtained, so that good color developability cannot often be obtained. On the other hand, in the ink composition using the microencapsulated pigment according to the embodiment of the present invention, since the polymer film includes the pigment particles as described above, it is difficult to remove the polymer from the pigment particles. There is no increase in viscosity of the composition. Accordingly, it is easy to lower the viscosity of the ink composition, and there are advantages that more pigment particles can be contained, and a sufficient printing density can be obtained on plain paper or recycled paper.

  In the above-described particularly preferred embodiment of the present invention, the addition amount of diethylene glycol monobutyl ether and triethylene glycol monobutyl ether as the penetrant of (2) is preferably 10% by weight or less based on the total weight of the ink composition. More preferably, it is 0.5 to 5% by weight. Addition of diethylene glycol monobutyl ether or triethylene glycol monobutyl ether has a remarkable effect on improving the permeability and helps to improve the printing quality. Further, diethylene glycol monobutyl ether and / or triethylene glycol monobutyl ether improves the solubility of the acetylene glycol surfactant.

  In the particularly preferred embodiment of the present invention described above, the addition amount of the 1,2-alkyldiol having 4 to 10 carbon atoms as the penetrant of (2) is preferably 15 weights with respect to the total weight of the ink composition. % Or less. A 1,2-alkyldiol having 3 or less carbon atoms is not preferable because sufficient permeability cannot be obtained. If the carbon number exceeds 15, it is difficult to dissolve in water. If the added amount exceeds 15% by weight, a tendency to increase the viscosity appears, which is not suitable. Specifically, 1,2-pentanediol or 1,2-hexanediol is preferably used as the 1,2-alkyldiol, and these can be used alone or in combination. 1,2-pentanediol is preferably added in the range of 3 to 15% by weight. If it is less than 3% by weight, good permeability cannot be obtained. 1,2-hexanediol is preferably added in the range of 0.5 to 10% by weight. If it is less than 0.5% by weight, good permeability cannot be obtained.

In particular, in the ink for ink jet recording according to the embodiment of the present invention, the solid wetting agent is added in an amount of 3% by weight with respect to the total weight of the ink in order to improve the characteristic that clogging hardly occurs (clogging reliability). It is preferably contained at -20% by weight.
In this specification, the solid wetting agent refers to a water-soluble substance that is solid at room temperature (25 ° C.) and has a water retention function. Preferred solid wetting agents are sugars, sugar alcohols, hyaluronate, trimethylolpropane, 1,2,6-hexanetriol. Examples of sugars include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides) and polysaccharides, preferably glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol. (Sorbit), maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, and the like. Here, the polysaccharide means a saccharide in a broad sense, and is used to include a substance that exists widely in nature, such as alginic acid, α-cyclodextrin, and cellulose. The derivatives of these saccharides are represented by the reducing sugars of the saccharides described above (for example, sugar alcohol (general formula HOCH ₂ (CHOH) _n CH ₂ OH (where n represents an integer of 2 to 5)). ), Oxidized sugars (eg, aldonic acid, uronic acid, etc.), amino acids, thiosaccharides, etc.). Sugar alcohol is particularly preferable, and specific examples include maltitol, sorbitol, xylitol and the like. As the hyaluronate, a commercially available sodium hyaluronate 1% aqueous solution (molecular weight 350,000) can be used. These solid wetting agents are used alone or in admixture of two or more. A particularly preferred solid wetting agent is trimethylolpropane, 1,2,6-hexatriol.
By using a solid wetting agent, evaporation of moisture can be suppressed by its water retention function, so the ink does not increase in viscosity around the flow path and the nozzle, and a film is difficult to form, so clogging is less likely to occur. . In addition, since the above-described solid wetting agent is chemically stable, the performance can be maintained for a long time without being decomposed in the ink. Further, even when the above-described solid wetting agent is added, the ink does not wet the nozzle plate, and stable ejection can be obtained. In particular, it is excellent when trimethylolpropane and 1,2,6-hexanetriol are used.
In the present invention, when used alone, the content of the solid wetting agent is preferably 3 to 20% by weight, more preferably 3 to 10% by weight based on the total weight of the ink composition for ink jet recording. When two or more types are used in combination, the total amount of the two or more types is preferably 3 to 20% by weight, more preferably 3 to 10%, based on the total weight of the ink for inkjet recording. % By weight. A preferred combination in the case of using a mixture of two or more is a combination of a group of saccharides, sugar alcohols and hyaluronate with a group of trimethylolpropane and 1,2,6-hexanetriol. This combination is preferable because an increase in the viscosity of the ink due to the addition can be suppressed. If the content of the solid wetting agent is less than 3% by weight, a sufficient effect for improving the clogging property cannot be obtained, and if it exceeds 20% by weight, the viscosity increases and it is difficult to obtain a stable discharge. .

  In the above-described particularly preferred embodiment of the present invention, the amount of the acetylene glycol surfactant and / or acetylene alcohol surfactant (3) is preferably 0.01 to 10 with respect to the total weight of the ink. % By weight, more preferably 0.1 to 5% by weight.

  As described above, the ink for inkjet recording according to the embodiment of the present invention has been described. However, as described above, the microencapsulated pigment according to the embodiment of the present invention contained as a colorant has a spherical shape, and the ink It is thought that the fluidity of the water is likely to be Newtonian, and that the cationic groups on the surface are regularly and densely oriented toward the aqueous solvent side, and it is considered that an effective electrostatic repulsive force is generated. . As a result, the ink for ink jet recording has excellent ejection stability compared to conventional microencapsulated pigments, more dispersibility (high dispersibility) and dispersion stability, and further improved colorant content. Can be produced.

  Ink jet recording is preferably performed by mounting the ink for ink jet recording according to the embodiment of the present invention on a known ink jet printer and printing on a recording medium such as plain paper or an ink jet recording medium. In addition to improving the ejection stability of the ink from the head, it is possible to obtain a recorded matter that is excellent in image fastness, abrasion resistance and color developability, has a high image printing density, and is difficult to bleed. Further, even when plain paper is used as a recording medium, a recorded matter is obtained in which the image is less likely to bleed and the color of the image is high.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.
Here, the “introduced amount of hydrophilic group on the surface of the pigment particle” shown below was determined by the following method.

<Example>
"Quantification of introduced amount of anionic group"
(When an anionic group is introduced by a sulfonating agent)
Pigment particles whose surface has been treated with a sulfonating agent are treated by an oxygen flask combustion method and absorbed in a 0.3% aqueous hydrogen peroxide solution, and then sulfate ions (divalent) are obtained by an ion chromatography method (Dionex Corp .; 2000i). ) Was quantified, and this value was converted to a sulfonic acid group and expressed as a molar amount (mmol / g) per 1 g of pigment.

(When an anionic group is introduced by a carboxylating agent)
As a method, the Twizel method is used. Diazomethane is dissolved in a suitable solvent and added dropwise to exchange all active hydrogen on the surface of the pigment particles with methyl groups. To the pigment thus treated, hydroiodic acid having a specific gravity of 1.7 is added and heated to vaporize methyl groups as methyl iodide. The methyl iodide gas is trapped with a silver nitrate solution and precipitated as methyl iodide. The amount of the original methyl group, that is, the amount of active hydrogen was measured from the weight of the silver iodide, and indicated as the molar amount (mmol / g) per gram of the pigment. That is, the amount of active hydrogen on the surface of the pigment particles corresponds to the amount of carboxylic acid groups.

“Preparation of black pigment particle“ P1 ”having an anionic group on its surface”
Carbon black ("MA-7" manufactured by Mitsubishi Chemical Co., Ltd.) 15 parts is mixed in 200 parts of sulfolane, and Eiger Motor Mill M250 type (Eiger Japan Co., Ltd.) is used under the conditions of 70% bead filling and 5000 rpm. Dispersed for 1 hour, the dispersed pigment paste and solvent mixture was transferred to an evaporator, heated to 120 ° C. while reducing the pressure to 30 mmHg or less, and the water contained in the system was distilled off as much as possible. Controlled. Next, 25 parts of sulfur trioxide was added and reacted for 6 hours. After completion of the reaction, after washing several times with excess sulfolane, the mixture was poured into water and filtered to obtain black pigment particles “P1”.
The amount of introduced anionic groups (sulfonic acid anion groups) in the obtained black pigment particles “P1” was 0.12 mmol / g.

“Preparation of black pigment particle“ P2 ”having an anionic group on its surface”
After mixing 300 g of commercially available acidic carbon black “MA-100 (Mitsubishi Chemical Corporation)” with 1000 ml of water, 450 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise thereto, and then at 80 ° C. for 15 hours. Stir. The obtained slurry was Toyo Filter Paper No. While being filtered through 2, it was repeatedly washed with ion exchange water. As a standard at the completion of washing with water, the test was performed until the cloudiness disappeared when a 0.1 N aqueous solution of silver nitrate was added to the ion-exchanged water that passed through the filter paper. This pigment slurry was redispersed in 2500 ml of water, desalted with a reverse osmosis membrane until the electric conductivity became 0.2 microsiemens or less, and further concentrated to a pigment concentration of about 15% by weight.
The obtained surface-treated pigment dispersion was acid-treated (acidified with aqueous hydrochloric acid), concentrated, dried and pulverized to obtain a powder. The amount of introduced anionic groups (carboxylic acid anion groups) in the obtained black pigment particles “P2” was 2.8 mmol / g.

“Preparation of cyan pigment particle“ P3 ”having an anionic group on its surface”
20 parts of phthalocyanine pigment (CI Pigment Blue 15: 3) is mixed with 500 parts of quinoline, and Eiger Motor Mill M250 type (manufactured by Eiger Japan Co., Ltd.) is used for 2 hours under conditions of 70% bead filling and a rotation speed of 5000 rpm. The mixture of the dispersed pigment paste and solvent was transferred to an evaporator, heated to 120 ° C. while reducing the pressure to 30 mmHg or less, and water contained in the system was distilled off as much as possible, and the temperature was controlled to 160 ° C. Next, 20 parts of a sulfonated pyridine complex is added and allowed to react for 8 hours. After completion of the reaction, the mixture is washed several times with excess quinoline, poured into water, and filtered to give cyanide having a hydrophilic group (anionic group) on the surface. Pigment particles “P3” were obtained.
The amount of introduced anionic groups in the obtained cyan pigment particles “P3” was 0.04 mmol / g.

“Preparation of yellow pigment particle“ P4 ”having an anionic group on its surface”
In “Preparation of cyan pigment particles“ P3 ”having a hydrophilic group on the surface”, “20 parts of phthalocyanine pigment (CI Pigment Blue 15: 3)” is replaced with “isoindolinone pigment (CI Pigment Yellow). 110) 20 parts ”, except that the yellow pigment particles“ P4 ”having an anionic group on the surface were obtained by the same treatment method.
The amount of introduced anionic groups in the obtained yellow pigment particles “P4” was 0.045 mmol / g).

“Preparation of magenta pigment particle“ P5 ”having hydrophilic group (anionic group) on its surface”
In “Preparation of Cyan Pigment Particles“ P3 ”Having Hydrophilic Groups on the Surface”, “20 parts of phthalocyanine pigment (CI Pigment Blue 15: 3)” is replaced with “isoindolinone pigment (CI Pigment Red). 122) Magenta pigment particles “P5” having an anionic group on the surface were obtained by the same treatment method except that the content was changed to “20 parts”.
The amount of introduced anionic groups in the obtained yellow pigment particles “P5” was 0.06 mmol / g.

Production of microencapsulated pigments “MCP1” to “MCP6” (Example 1)
“Manufacture of microencapsulated pigment“ MCP1 ””
1.25 g of dimethylaminoethyl methyl chloride methacrylate as a cationic polymerizable surfactant is added to and mixed with an aqueous dispersion in which 100 g of magenta pigment particles “P5” having an anionic group are dispersed in 500 g of ion-exchanged water. After that, ultrasonic waves were irradiated for 15 minutes. Next, 12 g of benzyl methacrylate and 8 g of dodecyl methacrylate were mixed and mixed with stirring. Further, 1.50 g of dimethylaminoethyl methyl chloride methacrylate was added, and ultrasonic waves were irradiated again for 30 minutes. This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After raising the internal temperature of the reaction vessel to 80 ° C., 2,2′- in which 0.6 g of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as a polymerization initiator was dissolved in 20 g of ion-exchanged water. Azobis (2-methylpropionamidine) dihydrochloride aqueous solution was dropped, and polymerization was carried out at 80 ° C. for 6 hours while introducing nitrogen. After completion of the polymerization, the pH was adjusted to around 6 with disodium citrate, and ultrafiltration was performed to obtain a dispersion of the desired microencapsulated pigment “MCP1”. The volume average particle size of the obtained dispersion was measured using a laser Doppler type particle size distribution analyzer Microtrac UPA150 manufactured by Leeds & Northrop Co. As a result, it was 100 nm. The obtained dispersion was dried at room temperature, and the glass transition point of the coated polymer was measured using a thermal scanning calorimeter (differential scanning calorimeter: DSC) DSC200 (manufactured by Seiko Electronics Co., Ltd.). 7 ° C.

(Example 2)
"Manufacture of microencapsulated pigment" MCP2 ""
1.25 g of dimethylaminoethyl methyl chloride methacrylate as a cationic polymerizable surfactant is added to and mixed with an aqueous dispersion in which 100 g of magenta pigment particles “P5” having an anionic group are dispersed in 500 g of ion-exchanged water. After that, it was processed by irradiating with ultrasonic waves for 15 minutes. Next, 12 g of benzyl methacrylate and 8 g of dodecyl methacrylate were mixed and mixed with stirring. Further, 0.5 g of 2-hydroxyethyl methacrylate and 1.5 g of dimethylaminoethyl methyl methacrylate were added, and ultrasonic waves were irradiated again for 30 minutes. And processed. This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After raising the internal temperature of the reaction vessel to 80 ° C., 2,2′- in which 0.6 g of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as a polymerization initiator was dissolved in 20 g of ion-exchanged water. Azobis (2-methylpropionamidine) dihydrochloride aqueous solution was dropped, and polymerization was carried out at 80 ° C. for 6 hours while introducing nitrogen. After completion of the polymerization, the pH was adjusted to around 6 with disodium citrate, and ultrafiltration was performed to obtain a target microencapsulated pigment “MCP2” dispersion. The volume average particle size of the obtained dispersion was measured using a laser Doppler type particle size distribution analyzer Microtrac UPA150 manufactured by Leeds & Northrop Co. As a result, it was 100 nm. The obtained dispersion was dried at room temperature, and the glass transition point of the coated polymer was measured using a thermal scanning calorimeter (differential scanning calorimeter: DSC) DSC200 (manufactured by Seiko Electronics Co., Ltd.). 7 ° C.

(Example 3)
“Manufacture of microencapsulated pigment“ MCP3 ””
0.81 g of dimethylaminoethyl methyl chloride methacrylate as a cationic polymerizable surfactant is added to and mixed with an aqueous dispersion in which 20 g of black pigment particles “P1” having an anionic group are dispersed in 80 g of ion-exchanged water. After that, it was processed by irradiating with ultrasonic waves for 15 minutes. Next, 2.45 g of isobornyl methacrylate and 2.55 g of lauryl methacrylate were mixed and stirred and mixed, then 1.0 g of dimethylaminoethylmethyl chloride methacrylate was added and mixed, and then ultrasonic waves were irradiated again for 30 minutes. And processed. This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After raising the internal temperature of the reaction vessel to 80 ° C., 2,2′- in which 0.3 g of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as a polymerization initiator was dissolved in 20 g of ion-exchanged water. Azobis (2-methylpropionamidine) dihydrochloride aqueous solution was dropped, and polymerization was carried out at 80 ° C. for 6 hours while introducing nitrogen. After completion of the polymerization, the pH was adjusted to around 6 with disodium citrate, and ultrafiltration was performed to obtain a target microencapsulated pigment “MCP3” dispersion. The volume average particle size of the obtained dispersion was measured using a laser Doppler type particle size distribution analyzer Microtrac UPA150 manufactured by Leeds & Northrop Co. As a result, it was 100 nm. The obtained dispersion was dried at room temperature, and the glass transition point of the coated polymer was measured using a thermal scanning calorimeter (differential scanning calorimeter: DSC) DSC200 (manufactured by Seiko Electronics Co., Ltd.). ° C.

Example 4
"Manufacture of microencapsulated pigment" MCP4 ""
1.0 g of dimethylaminoethyl methyl chloride methacrylate as a cationic polymerizable surfactant is added to and mixed with an aqueous dispersion in which 100 g of cyan pigment particles “P3” having an anionic group are dispersed in 500 g of ion-exchanged water. After that, it was processed by irradiating with ultrasonic waves for 15 minutes. Next, 17.3 g of benzyl methacrylate, 7.7 g of dodecyl methacrylate and 0.05 g of diethylene glycol dimethacrylate were mixed and mixed with stirring, 1.5 g of dimethylaminoethylmethyl chloride methacrylate was further added, and ultrasonic waves were again applied for 30 minutes. Irradiated and processed. This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After raising the internal temperature of the reaction vessel to 80 ° C., 2,2′- in which 0.6 g of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as a polymerization initiator was dissolved in 20 g of ion-exchanged water. Azobis (2-methylpropionamidine) dihydrochloride aqueous solution was dropped, and polymerization was carried out at 80 ° C. for 6 hours while introducing nitrogen. After completion of the polymerization, the pH was adjusted to about 6 with disodium citrate, and ultrafiltration was performed to obtain a target microencapsulated pigment “MCP4” dispersion. The volume average particle size of the obtained dispersion was measured using a laser Doppler type particle size distribution analyzer Microtrac UPA150 manufactured by Leeds & Northrop Co. As a result, it was 100 nm. The obtained dispersion was dried at room temperature, and the glass transition point of the coated polymer was measured using a thermal scanning calorimeter (differential scanning calorimeter: DSC) DSC200 (manufactured by Seiko Electronics Co., Ltd.). ° C.

(Example 5)
"Manufacture of microencapsulated pigment" MCP5 ""
2.8 g of methacryloyloxyethyltrimethylammonium chloride as a cationic polymerizable surfactant was added to and mixed with an aqueous dispersion in which 150 g of yellow pigment particles “P4” having an anionic group were dispersed in 800 g of ion-exchanged water. Then, ultrasonic waves were irradiated for 15 minutes. Next, 12 g of isobornyl methacrylate, 0.05 g of 1,6-hexanediol dimethacrylate and 8 g of dodecyl methacrylate were mixed and mixed with stirring. Further, 2.9 g of methacryloyloxyethyltrimethylammonium chloride was added and ultrasonic waves were applied again. Treated by irradiation for 30 minutes. This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After raising the internal temperature of the reaction vessel to 80 ° C., 2,2′- in which 0.6 g of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as a polymerization initiator was dissolved in 20 g of ion-exchanged water. Azobis (2-methylpropionamidine) dihydrochloride aqueous solution was dropped, and polymerization was carried out at 80 ° C. for 6 hours while introducing nitrogen. After completion of the polymerization, the pH was adjusted to around 6 with disodium citrate, and ultrafiltration was performed to obtain a target microencapsulated pigment “MCP5” dispersion. The volume average particle size of the obtained dispersion was measured using a laser Doppler type particle size distribution analyzer Microtrac UPA150 manufactured by Leeds & Northrop Co. As a result, it was 100 nm. The obtained dispersion was dried at room temperature, and the glass transition point of the coated polymer was measured using a thermal scanning calorimeter (differential scanning calorimeter: DSC) DSC200 (manufactured by Seiko Electronics Co., Ltd.). ° C.

<Comparative example>
“Production of microencapsulated pigments“ MCP6 ”to“ MCP9 ””
MCP6 (microencapsulated cyan pigment) and MCP7 (microencapsulated magenta pigment) were produced.
(Comparative Example 1)
“Production of“ MCP6 ””
The flask was charged with 250 g of methyl ethyl ketone, heated to 75 ° C. with stirring under a nitrogen seal, n-butyl methacrylate 155 g, n-butyl acrylate 20 g, 2-hydroxyethyl methacrylate 35 g, methacryloyloxyethyltrimethylammonium chloride 40 g and A mixed solution composed of 5 g of a polymerization initiator perbutyl O was dropped over 2 hours, and further reacted for 15 hours to obtain a vinyl polymer solution.
10 g of the above polymer solution, 7 g of cyan pigment (CI Pigment Blue 15: 3), 40 g of methyl ethyl ketone, and 150 g of ceramic beads having an average particle diameter of 0.5 mm are placed in a stainless steel container, and a bead mill disperser is used. Then, the ceramic beads were separated by filtration to prepare a microencapsulated pigment paste.
Next, 20 g of the above microencapsulated pigment paste is used as an organic solvent phase, and this organic solvent phase is stirred while being irradiated with ultrasonic waves. Disodium citrate is added to 25 g of ion-exchanged water to adjust the pH. The aqueous phase adjusted to 6 was added dropwise over 20 minutes to phase-emulsify to obtain a microencapsulated pigment-containing aqueous dispersion.
Furthermore, the solvent was distilled off by distilling this microencapsulated pigment-containing aqueous dispersion at 85 ° C. In this way, C.I. I. A dispersion of Pigment Blue 15: 3 microencapsulated pigment MCP6 was obtained.

(Comparative Example 2)
“Production of“ MCP7 ””
C. I. 100 g of Pigment Red 122 and 60 g of a polymerizable surfactant dimethylaminoethylmethyl chloride methacrylate are added to 800 g of water, irradiated with ultrasonic waves, and further dispersed with a sand mill (manufactured by Yaskawa Seisakusho) for about 2 hours. This dispersion is put into a reaction vessel equipped with an ultrasonic generator, a stirrer, a temperature controller, a reflux condenser, and a dropping funnel. Next, 10 g of benzyl methacrylate, 20 g of butyl metallate, 2 g of dicyclopentanyl dimethacrylate, 10 g of N, N′-dimethylaminoethyl methacrylate, 1 g of the above polymerizable surfactant and 2,2′-azobis (2-methyl) Propionamidine) dihydrochloride (0.5 g) and water (100 g) are mixed to prepare an emulsion, which is gradually dropped into the above reaction vessel with a dropping funnel. After completion of the dropping, a polymerization reaction is carried out at 60 ° C. for 48 hours. The obtained colorant dispersion was adjusted to about pH 6 with disodium citrate, filtered through a 0.4 μm filter to remove coarse particles, and a dispersion of microencapsulated pigment MCP7 was obtained. The average particle size measured with a laser Doppler type particle size distribution analyzer Microtrac UPA 150 (Leeds & Northrop) was 130 nm.

"Preparation of ink for inkjet recording"
(Example 6) to (Example 10)
Based on the composition shown in Table 1, inks for inkjet recording of Examples 6 to 10 were prepared.

(Comparative Example 3) to (Comparative Example 4)
Based on the composition shown in Table 2, ink jet recording inks of Comparative Examples 3 to 4 were prepared.

The inkjet recording inks of Examples 6 to 10 and Comparative Examples 3 to 4 and the recorded matter printed using these inks were evaluated by the following methods.
(Evaluation)
Evaluation 1: Dispersibility Ink jet recording inks of Examples and Comparative Examples were used at 20 ° C. with a rolling ball viscometer AMVn using a capillary with an inner diameter of 0.9 mm and a steel ball with a diameter of 0.794 mm and a density of 7.850 g / cm ^3. The gradient in the sin θ-viscosity curve obtained by measuring the viscosity when the inclination angle is 70 °, 60 °, 50 °, 40 °, 30 °, plotting the horizontal axis as sin θ and the vertical axis as the viscosity, Asked. The dispersibility of the ink was evaluated according to the following criteria.
A: The slope in the sin θ-viscosity curve is 0 to −0.05, exhibits Newtonian properties, and particularly good dispersibility.
B: The slope in the sin θ-viscosity curve is −0.05 to −0.1, close to Newtonian property, and exhibits good dispersibility after A.
C: The gradient in the sin θ-viscosity curve is −0.1 to −0.15, indicating non-Newtonian properties, but dispersibility is slightly good.
D: The slope in the sin θ-viscosity curve is smaller than −0.15, exhibits non-Newtonian property, tends to cause sedimentation, and has poor dispersibility.

Evaluation 2: Dispersion stability The ink jet recording inks of Examples and Comparative Examples were placed in glass sample bottles and sealed, and then left at 60 ° C. for 2 weeks, and the viscosity of the ink before and after being left was examined. The measurement was performed at 20 ° C. using a rheometer PHYSICA MCR300 manufactured by Paar Physica with a cone radius of 37.50 mm, a cone angle of 1 °, and a measurement gap of 0.05 mm (CP75-1 manufactured by Paar Physica) at a shear rate. Measured the viscosity at 150 / S. The obtained results were evaluated according to the following criteria.
A: The amount of change is less than ± 0.1 mPa · s.
B: The amount of change is ± 0.1 or more and less than 0.3 mPa · s.
C: Change amount is ± 0.3 mPa · s or more.

Evaluation 3: Precipitation property With respect to the inks for ink jet recording of Examples and Comparative Examples, the sedimentation property of the colorant in the ink can be evaluated from the intensity distribution of the backscattered light and transmitted light in the height direction of the sample. It measured at 20 degreeC using TURBISCAN 2000 made from FORMUL ACTION. The measurement principle of TURBISCAN 2000 manufactured by FORMUL ACTION is shown below. In this device, when a glass tube filled with ink is set at a predetermined position of the device and measurement is started, a stage installed around the glass tube (in the radial direction) moves up and down along the glass tube. The light source installed on the stage and the detector of scattered light and transmitted light are scattered and transmitted light in the vertical direction of the glass tube in accordance with the vertical movement of the stage. Is a measuring device that can measure the intensity of light over time when there is a particle movement or particle diameter change by repeating this operation at an arbitrary time interval. is there.
Evaluation was performed according to the following criteria.
A: No sedimentation phenomenon was observed even after 2 weeks.
B: A sedimentation phenomenon was observed after 2 weeks.

Evaluation 4: Printing density The ink for ink jet recording of Examples and Comparative Examples was filled in an ink cartridge, and this was loaded into an ink jet printer PM-720C (manufactured by Seiko Epson Corporation), and plain paper Xerox P paper (Xerox Corporation) Made with 100% duty, and the density of this solid printed part was measured with a spectrophotometer (GRETAG SPM-50, manufactured by Gretag Macbeth Co.), and the obtained results were evaluated according to the following criteria: .
A: OD value of black ink: 1.4 or more OD value of color ink: 1.2 or more B: OD value of black ink: 1.3 or more and less than 1.4 OD value of color ink: 1.15 or more Less than 2 C: OD value of black ink: less than 1.3 OD value of color ink: less than 1.15

Evaluation 5: Print quality The ink for ink jet recording of Examples and Comparative Examples is filled in an ink cartridge, and this is loaded into an ink jet printer PM-720C (manufactured by Seiko Epson Corporation). 24 letters each of uppercase and lowercase letters of the alphabet were printed, and visually observed, and evaluated according to the following criteria.
AA: No bleeding occurs on all papers.
A: Almost no bleeding occurs on all papers.
B: Slight bleeding is only observed on 2-3 sheets.
C: Slight bleeding is observed on all papers.
D: There is much bleeding on the entire paper.
The printing paper used for the evaluation is Conqueror paper, Favorit paper, Modo paper, Rapid Copy paper, EPSON EPP paper, Xerox P paper, Xerox 4024 paper, Neneha Bond paper, Rcopyy 6200 paper, Yamayuri (recycled paper), Xerox R (recycled paper). 12 recycled paper).

Evaluation 6: Color development property Ink-jet recording inks of Examples and Comparative Examples were filled in an ink cartridge, which was loaded into an ink-jet printer PM-720C (manufactured by Seiko Epson Corporation), and MC photo paper semi-gloss (Seiko Epson Corporation) (Corporation) and Xerox P paper (Xerox) were each printed with 100% duty, the C ^* value of the solid printed part was measured, and C on MC photo paper semi-gloss (Seiko Epson Corporation) ^* determine the ratio of the C ^* value on Xerox P paper (manufactured by Xerox Corp.) with respect to the value, and the color developing property on plain paper was evaluated by the following criteria.
A: 0.9 or more B: 0.8 or more and less than 0.9 C: Less than 0.8

Evaluation 7: Clogging reliability After printing in the evaluation 5, the printer was turned off and allowed to stand, and a similar printing test was conducted one week later. The “ink discharge status” at that time was visually observed. And it evaluated by the criteria shown below.
A: At the same time as sending a print signal to the printer, normal printing is started without a cleaning operation.
B: Normal printing is performed within 3 cleaning operations.
C: Normal printing is performed within 6 cleaning operations.
D: Even if the cleaning operation is repeated seven times or more, normal printing cannot be performed.

As shown in Table 3, the ink jet recording inks of the examples were excellent in all evaluation items.
An ink for inkjet recording (Comparative Example 3) using a conventional microencapsulated pigment in which a pigment not treated with an anionic group-imparting agent is coated with a polymer is used as a colorant (Comparative Example 1). And clogging reliability was particularly inferior.

  The present invention is not limited to the above-described embodiment, and a part of the ink liquid is rapidly heated at a part near the discharge part of the nozzle head to generate bubbles, and the ink liquid is generated by volume expansion due to the bubbles. The present invention can also be applied to applications such as inkjet recording methods, printing inks, writing instruments, and the like that intermittently eject droplets to record characters and symbols on the surface of a recording medium.

It is confirmed that the cationic group of the cationic polymerizable surfactant is ionically adsorbed on the anionic group of the pigment particle having an anionic group on the surface, and that the cationic polymerizable surfactant forms a micelle state. It is a schematic diagram shown. FIG. 2 is a schematic diagram showing that a cationic polymerizable surfactant is polymerized in FIG. 1 to form a polymer layer. The cationic group of the cationic polymerizable surfactant is ionically adsorbed on the anionic group of the pigment particle having an anionic group on the surface, and the hydrophobic surface of the pigment particle having the anionic group on the surface is cationic. It is a schematic diagram showing that a hydrophobic group of a polymerizable surfactant is adsorbed and further a micelle state is formed by a cationic polymerizable surfactant. FIG. 4 is a schematic diagram showing that a cationic polymerizable surfactant is polymerized in FIG. 3 to form a polymer layer.

Explanation of symbols

1 Pigment Particles 2, 2 ′ Cationic Polymerizable Surfactant 11, 11 ′ Cationic Group 12, 12 ′ Hydrophobic Group 13, 13 ′ Polymerizable Group 14 Anionic Group 60, 60 ′ Polymer Layer (Polymer)
100,101 Microencapsulated pigment

Claims (21)

  The pigment particle having an anionic group on its surface is coated with a polymer having a repeating structural unit derived from a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group. Microencapsulated pigment.   By polymerizing a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group in an aqueous dispersion in which pigment particles having an anionic group on the surface are dispersed, the pigment particles are obtained. A microencapsulated pigment coated with a polymer.   The microencapsulated pigment according to claim 1 or 2, wherein the polymer further has a repeating structural unit derived from a hydrophobic monomer. The polymer according to any one of claims 1 to 3, further comprising a repeating structural unit derived from a crosslinkable monomer and / or a repeating structural unit derived from a monomer represented by the following general formula (1): A microencapsulated pigment according to claim 1.

[However, R ¹ represents a hydrogen atom or a methyl group. R ² represents a t-butyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group. m represents an integer of 0 to 3, and n represents an integer of 0 or 1. ]   The microencapsulated pigment according to any one of claims 1 to 4, wherein the pigment constituting the pigment particles is carbon black or an organic pigment. The anionic group of the pigment particle is a sulfonate anion group (—SO ₃ ⁻ ) and / or a sulfinate anion group (—RSO ₂ ^— : R is a C _{1 to} C ₁₂ alkyl group or phenyl group and a modified product thereof). The microencapsulated pigment according to claim 1, wherein the pigment is a microencapsulated pigment. 6. The microencapsulated pigment according to claim 1, wherein the anionic group of the pigment particle is a carboxylate anion group (—COO ⁻ ).   The cationic group of the cationic polymerizable surfactant is selected from the group consisting of a primary amine cation, a secondary amine cation, a tertiary amine cation, and a quaternary ammonium cation. 3. The microencapsulated pigment according to 1 or 2.   The microencapsulated pigment according to claim 1 or 2, wherein the hydrophobic group of the cationic polymerization surfactant is selected from the group consisting of an alkyl group, an aryl group, and a group in which these are combined.   The polymerizable group of the cationic polymerization surfactant is an unsaturated hydrocarbon group capable of radical polymerization, and includes a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. The microencapsulated pigment according to claim 1, which is selected from the group consisting of:   A method for producing a microencapsulated pigment in which pigment particles having an anionic group on the surface are coated with a polymer, wherein the cationic polymerizable surfactant is added to an aqueous dispersion of the pigment particles having an anionic group on the surface A method for producing a microencapsulated pigment, comprising adding a polymerization initiator and emulsion polymerization after mixing.   A method for producing a microencapsulated pigment in which pigment particles having an anionic group on the surface are coated with a polymer, wherein the cationic polymerizable surfactant is added to an aqueous dispersion of the pigment particles having an anionic group on the surface A method for producing a microencapsulated pigment, which comprises emulsifying by adding a hydrophobic monomer and a cationic polymerizable surfactant after mixing, followed by emulsion polymerization by adding a polymerization initiator.   A step of adding a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group to the aqueous dispersion of pigment particles having the anionic group on the surface, mixing the mixture, and irradiating with ultrasonic waves for treatment. And a step of adding and mixing a hydrophobic monomer, a step of adding and mixing a cationic polymerizable surfactant having a cationic group, a hydrophobic group and a polymerizable group and irradiating with ultrasonic waves, The method for producing a microencapsulated pigment according to claim 12, comprising a step of emulsion polymerization by adding a polymerization initiator, and the steps are carried out in the order of the steps. A step of adding a cationic polymerizable surfactant having a cationic group, a hydrophobic group, and a polymerizable group to the aqueous dispersion of pigment particles having an anionic group on the surface, mixing the mixture, and irradiating with ultrasonic waves for treatment. And a step of adding and mixing a hydrophobic monomer, a crosslinkable monomer and / or a monomer represented by the following general formula (1), and cationic polymerization having a cationic group, a hydrophobic group and a polymerizable group The method according to claim 12, comprising a step of adding and mixing a surfactant and irradiating with ultrasonic waves, and a step of emulsion polymerization by adding a polymerization initiator and performing the steps in the order of the steps. Method for producing encapsulated pigment.

[However, R ¹ represents a hydrogen atom or a methyl group. R ² represents a t-butyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group. m represents an integer of 0 to 3, and n represents an integer of 0 or 1. ]   The method for producing a microencapsulated pigment according to any one of claims 11 to 14, wherein the pigment constituting the pigment particles is carbon black or an organic pigment.   An aqueous dispersion comprising the microencapsulated pigment according to claim 1.   An ink for inkjet recording comprising the aqueous dispersion according to claim 16.   An ink for ink-jet recording, comprising at least the microencapsulated pigment according to claim 1 and water.   The ink for inkjet recording according to any one of claims 17 to 18, further comprising a water-soluble wetting agent.   The ink for inkjet recording according to claim 19, wherein the water-soluble wetting agent is one or more compounds selected from the group consisting of glycerin, trimethylolpropane, 1,2,6-hexanetriol, and saccharides. . 21. The ink for inkjet recording according to claim 17, further comprising one or more compounds selected from the group consisting of alkyl ethers of polyhydric alcohols and 1,2-alkyldiols.

Images