JP4802674B2 - Encapsulated pigment and method for producing the same - Google Patents

Description

  The present invention relates to an encapsulated pigment and a method for producing the same.

  In an ink jet recording method in which ink droplets are ejected from a fine nozzle head and characters and figures are recorded on the surface of a recording medium such as paper, a pigment is recently dispersed in water because of its excellent water resistance and light resistance. Water-based pigment inks that have been used have been used. In general, such a water-based pigment ink is often used in which a pigment is dispersed in an aqueous dispersion medium using a dispersant such as a surfactant or a polymer dispersant. When the pigment is dispersed with the dispersant as described above, since the dispersant is simply adsorbed on the surface of the pigment particle, in the ink jet recording method in which a strong shearing force is applied to the pigment particle, the surface of the pigment particle The dispersant adsorbed on the surface may be detached. As a result, the dispersibility of the pigment ink is deteriorated, and the discharge stability (characteristic that the ink is stably discharged in a certain direction) may be deteriorated. Also, pigment inks using pigments dispersed with dispersants such as surfactants and polymer dispersants tend to absorb and desorb these dispersants, and the dispersion is unstable when stored for a long period of time. It is easy to become.

On the other hand, a technique using an encapsulated 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.
There have been proposed ones in which pigment particles are encapsulated (for example, see Patent Documents 1, 2, and 3) and those obtained by graft polymerization of a polymer on the surface of pigment particles (for example, see Patent Documents 4 to 7). In addition, a method for encapsulating hydrophobic powder using an amphiphilic graft polymer has been proposed (see, for example, Patent Document 8). There was a problem that the particle size became too large.

In addition to the above proposal, an ink using a pigment coated with a resin capable of forming a film at room temperature by a phase inversion emulsification method (see, for example, Patent Documents 9 to 17), or an anionic group-containing organic polymer by an acid precipitation method An ink using a pigment coated with a compound (for example, see Patent Documents 18 to 27) has been proposed.
Furthermore, an ink using a polymer emulsion in which polymer fine particles and a color material are impregnated by a phase inversion emulsification method has been proposed (see, for example, Patent Documents 28 to 33). However, even in the colorant obtained by the phase inversion emulsification method or the acid precipitation method, depending on the type of the organic solvent such as the penetrant used in the ink, the polymer adsorbed on the pigment particles may be desorbed 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 order to solve the above problems, in the field of ink for ink jet recording, by microencapsulating pigment particles, (1) excellent dispersion stability and (2) excellent discharge 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) When using plain paper as a recording medium, an ink for ink jet recording having an effect such that an image is difficult to bleed and a recorded matter with high color developability of the image can be obtained. (Patent document 34). However, in the conventional microencapsulation methods, the amount of monomer that can be incorporated into the micelle as a polymerization site is determined by the number of ionic groups present on the surface of the core material, and there is an upper limit on the film thickness. That is, even if the monomer compounding ratio is increased to increase the film thickness, there is a limit to the amount of monomer that can enter the micelle, and also the number of ionic groups that can be present (adsorbed) on the particle surface. There is an upper limit due to the area occupied by the molecules. On the other hand, increasing the layer thickness of the microencapsulated product is a very important issue from the viewpoint of enhancing the functionality of the microencapsulated product.

Japanese Patent Publication No. 7-94634 JP-A-8-59715 JP 2003-306661 A JP-A-5-339516 JP-A-8-302227 JP-A-8-302228 JP-A-8-81647 JP-A-5-320276 Japanese Patent Laid-Open No. 8-21815 JP-A-8-295837 JP-A-9-3376 JP-A-8-183920 Japanese Patent Laid-Open No. 10-46075 JP-A-10-292143 Japanese Patent Laid-Open No. 11-80633 JP-A-11-349870 JP 2000-7961 A JP-A-9-31360 JP-A-9-217019 JP 9-316353 A Japanese Patent Laid-Open No. 9-104834 Japanese Patent Laid-Open No. 9-151342 Japanese Patent Laid-Open No. 10-140065 JP-A-11-152424 JP-A-11-166145 Japanese Patent Application Laid-Open No. 11-199783 JP-A-11-209672 JP-A-9-286939 JP 2000-44852 A JP 2000-53897 A JP 2000-53898 A JP 2000-53899 A JP 2000-53900 A JP 2005-97476 A

 The present invention has been made in view of the above-mentioned problems, and its object is to increase the thickness of the encapsulated pigment, particularly in the field of ink jet recording, thereby providing a highly functional encapsulated pigment. Is to provide. Moreover, it is providing the manufacturing method of this encapsulated pigment.

In addition, the present invention was made in view of the above problems in the pigment ink for inkjet recording, and the object thereof is as follows:
(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 a recording medium, all of the above (1) to (6), which can obtain a recorded matter with which an image hardly bleeds and a high color developability of the image, is satisfied. In addition, an object of the present invention is to provide an encapsulated pigment capable of producing an ink for inkjet recording, which can exhibit various other functions highly, and a method for producing the same.

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 (2) and exhibiting various other functions can be obtained. That is, the technical configuration of the present invention is as follows.
(1) An encapsulated pigment having a charge on the surface of the pigment, wherein (I) the pigment particles are coated with a coating layer mainly composed of a polymer, and the polymer is at least (i) a charge on the surface of the pigment A repeating structural unit derived from the ionic polymerizable surfactant A and / or ionic monomer having an opposite charge to (ii), and (ii) an ionic polymerizable having the same or opposite charge as the charge on the pigment surface An encapsulated pigment comprising repeating structural units derived from Surfactant B, wherein (II) an electrolyte is used in producing the polymer.
(2) The encapsulated pigment according to (1), wherein the electrolyte is an inorganic salt.
(3) The encapsulated pigment according to (2), wherein the inorganic salt is sodium sulfate or sodium chloride.
(4) An inkjet recording ink containing the encapsulated pigment according to (3).
(5) A method for producing an encapsulated pigment in which pigment particles having a charge on the surface thereof are coated with a coating layer comprising a polymer as a main component, wherein at least (I) an aqueous dispersion of pigment particles having a charge on the surface Adding an ionic polymerizable surfactant A and / or ionic monomer having a charge opposite to the charge on the pigment particle surface, and (II) having the same or opposite charge as the charge on the pigment particle surface A method for producing an encapsulated pigment, comprising: adding an ionic polymerizable surfactant B; (III) adding an electrolyte; and (IV) adding a polymerization initiator to form a polymer.
(6) The method for producing an encapsulated pigment according to (5), wherein the step of adding an electrolyte is after micelle formation.

  According to the encapsulated pigment and the method for producing the same according to the present invention, the surface of the micelle serving as the encapsulated pigment coating layer is added by adding an electrolyte to the liquid in which the micelle that is the encapsulated pigment is dispersed. Rebound decreases. As a result, the ability of the monomer to solubilize in the micelle is increased, and the monomer, which is the main material of the coating layer, is taken into the micelle as a polymerization site and polymerized, thereby increasing the thickness of the coating layer. be able to. Furthermore, by increasing the film thickness of the coating layer, it is possible to give the coating layer various functions, thereby realizing high functionality of the coating layer.

Hereinafter, the encapsulated pigment of the present invention and the production method thereof will be described in detail.
The encapsulated pigment according to the present invention is an encapsulated pigment in which (1) a pigment particle having a charge on its surface is coated with a coating layer containing a polymer as a main component, and the polymer is (i) the surface of the pigment particle. A repeating structural unit derived from the ionic polymerizable surfactant A and / or ionic monomer having a charge opposite to the charge, and (ii) an ionic polymerizable interface having the same or opposite charge as the surface charge of the pigment particles It has at least a repeating structural unit derived from the activator B, and (2) is characterized in that an electrolyte is used in producing the polymer.

 Such an encapsulated pigment is obtained by adding (1) an ionic polymerizable surfactant A and / or an ionic monomer having a charge opposite to the surface charge of pigment particles to an aqueous dispersion of pigment particles having a charge on the surface. After mixing, (2) ionic polymerizable surfactant B having the same or opposite charge as the surface charge of the pigment particles is added, mixed and emulsified, then added with a polymerization initiator and polymerized in water to form a coating layer It can manufacture suitably by doing.

  The time for adding the electrolyte is not particularly limited as long as the production of the encapsulated product is not hindered, but it is preferably after the emulsification and before the polymerization. Moreover, various monomers can be added to the encapsulated pigment of the present invention, and the coating layer can be thickened by the addition of the monomer.

 According to such a polymerization method, (1) the ion of the ionic polymerizable surfactant A and / or the ionic monomer having a charge opposite to the ionic group on the surface of the pigment particle and the ionic group on the surface of the pigment particle. (2) an ionic polymerizable surfactant having a charge that is the same as or opposite to the surface charge of the pigment particles and the hydrophobic group of the ionic polymerizable surfactant A and / or ionic monomer The hydrophobic groups of the agent B face each other, and a coating layer is formed between the hydrophobic groups.

  That is, the arrangement form of the ionic polymerizable surfactant and / or ionic monomer existing around the pigment particles before the polymerization reaction is extremely highly controlled, and the ionic group is formed toward the aqueous phase in the outermost shell. An oriented state is formed. Then, the ionic polymerizable surfactant and / or ionic hydrophilic monomer is converted into a polymer by the polymerization reaction in the highly controlled form. Therefore, the microencapsulated pigment of the present invention is an admicelle whose structure is controlled with extremely high accuracy.

Thus, 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) An ink jet satisfying all of the above (1) to (6), in which even when plain paper is used as the recording medium, it is possible to obtain a recorded matter in which an image is less likely to bleed and a high color developability of the image. Recording ink 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.

  Then, by adding an electrolyte after emulsification and before polymerization, electrostatic repulsion on the surface of the admicelle is reduced, and the monomer component existing outside the admicelle can be taken into the admicelle. By this incorporation, the coating layer can be thickened.

  In the encapsulated pigment of the present invention, the coating layer can be formed into multiple layers. In the case where the coating layer is formed into a multi-layer, taking an example of a two-layer encapsulated pigment, (1) an ionicity having a charge opposite to the surface charge of the pigment particle in the aqueous dispersion of the pigment particle having a charge on the surface Polymeric surfactant A and / or ionic monomer are added and mixed, and then (2) ionic polymerizable surfactant B having the same or opposite charge as the surface charge of the pigment particles is added, mixed and emulsified, and then polymerized. An initiator is added to polymerize in water to form a first coating layer, and then (3) the surface dispersion of the first coating layer is opposite to the aqueous dispersion of the coating having the first coating layer. After adding and mixing ionic polymerizable surfactant C and / or ionic monomer having a charge, (4) ionic polymerizable surfactant D having the same or opposite charge as the surface charge of the first coating layer In addition, after mixing and emulsification, a polymerization initiator is added and polymerized in water. By forming the second coating layer can be suitably produced. The method for producing an encapsulated pigment having three or more layers is the same.

  In the method for producing a multi-layer encapsulated pigment, the timing of addition of the electrolyte is not particularly limited, but it is preferably after emulsification and before polymerization in each coating layer forming step. Depending on which coating layer the electrolyte is added to, the thickness of each coating layer can be adjusted. That is, an arbitrary coating layer can be made thick by adding an electrolyte when forming the coating layer to be thickened.

The aspect ratio (long and short) of the encapsulated pigment of the present invention is 1.0 to 1.3, and the Zingg index is 1.0 to 1.3 (more preferably 1.0 to 1.2). Preferably there is.
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.
When the Zingg index is greater than 1.3, the encapsulated pigment becomes flatter and isotropic. The method of setting the aspect ratio and Zingg index within the above ranges is not particularly limited, but an encapsulated pigment in which pigment particles having an ionic group on the surface are coated with a polymer by the above-described emulsion polymerization method can easily satisfy this condition. Can satisfy.

In addition, in an encapsulated pigment prepared 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.
The encapsulated pigment of the present invention, in which the core substance is a pigment, has an aspect ratio and a Zingg index within the above ranges and becomes a spherical shape. This makes the ink flow characteristics easily Newtonian and has excellent ejection stability. It becomes. Moreover, since it is a spherical shape, when it lands on a recording medium such as paper, the encapsulated pigment is arranged at a high density on the recording medium, and the printing density and color development can be expressed with high efficiency. Further, since it is spherical, it is excellent in dispersibility and dispersion stability.

  FIG. 1 shows an example of the encapsulated pigment of the present invention. Pigment particles 1 having an anionic group 14 on the surface as a hydrophilic group are dispersed in a solvent containing water as a main component (hereinafter also referred to as an aqueous solvent), and a cationic group 11, a hydrophobic group 12, and a polymerizable group. A cationic hydrophilic monomer or a cationic polymerizable surfactant 2 having 13 and an anionic polymerizable surfactant 3 having an anionic group 14 ', a hydrophobic group 12' and a polymerizable group 13 '. On the other hand, FIG. The cationic hydrophilic monomer or the cationic polymerizable surfactant 2 is arranged so that the cationic group 11 faces the anionic group 14 of the pigment particle 1, and adsorbs with a strong ionic bond. And, for the hydrophobic group 12 and the polymerizable group 13 of this cationic hydrophilic monomer or cationic polymerizable surfactant 2, the hydrophobic group of the anionic polymerizable surfactant 3 is obtained by hydrophobic interaction. 12 ′ and the polymerizable group 13 ′ face, and the anionic group 14 ′ of the other anionic polymerizable surfactant 3 faces the direction in which the aqueous solvent exists, that is, the direction away from the pigment particles 1.

  For example, by adding a polymerization initiator to such an aqueous dispersion, the polymerizable group 13 of the cationic hydrophilic monomer or the cationic polymerizable surfactant 2 and the polymerizable group 13 of the anionic polymerizable surfactant 3 are used. By polymerizing ', a microencapsulated pigment 100' in which pigment particles 1 are coated with a polymer layer 60 'is produced as shown in FIG. Here, since the surface of the polymer layer 60 ′ has the anionic group 14 ′, the microencapsulated pigment 100 ′ can be dispersed in an aqueous solvent. In the case where a hydrophilic monomer having an anionic group as a hydrophilic group is used instead of the anionic polymerizable surfactant 3, a microencapsulated pigment can be prepared in the same manner. During polymerization, a hydrophilic monomer having a cationic hydrophilic monomer and / or a cationic polymerizable surfactant and an anionic polymerizable surfactant and / or an anionic group in an aqueous dispersion, if necessary. In which case the polymer layer comprises a cationic hydrophilic monomer and / or a cationic polymerizable surfactant and an anionic polymerizable surfactant and / or Alternatively, it can be a copolymer layer copolymerized from a hydrophilic monomer having an anionic group and a comonomer.

  Hereinafter, various raw materials used for producing the encapsulated pigment of the present invention will be described first, and then a method for producing the encapsulated pigment using these raw materials will be described.

Next, the components of the microencapsulated pigment according to the present invention will be described in detail.
[Pigment particles]
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 such a 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 (CI pigment black 7) such as furnace black, lamb black, acetylene black, and channel black, and iron oxide pigments. 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 .; 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc .; or Color Black FW1, Fla2 ck, Color Black FW2, Clk, FW2V, C, Degussa Lor Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Speck 4 or Speck.
Moreover, as the organic pigment for black, a black organic pigment such as aniline black (CI Pigment Black 1) can be used.

  Examples of organic pigments for yellow ink include C.I. I. 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. I. 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. I. 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. I. Vat blue 4, 60 etc. can be mentioned.

Furthermore, as organic pigments used in color inks other than magenta, cyan or yellow inks, C.I. I. Pigment green 7 (phthalocyanine green), 10 (green gold), 36, 37; C.I. 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 cited.
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” refers to 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 with one or more kinds.
In particular, when sulfur trioxide itself is too reactive to decompose or alter the pigment itself, or 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).

Further, when sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, fluorosulfuric acid or the like is used alone, the pigment particles are easily dissolved, and it is necessary to suppress the reaction for a strong acid that reacts for each 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 sulfonic acid 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, the 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 alkali 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 treatment 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 a 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 carried out by stirring for more than an hour. This operation involves a considerable amount of heat and requires safety attention. Thereafter, the solvent and the remaining carboxylating agent are removed from the surface-treated pigment particle slurry by heat treatment. Further, if necessary, it is possible to obtain a desired aqueous dispersion by repeatedly performing washing, ultrafiltration, reverse osmosis and the like, 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 as the introduction amount of the hydrophilic group is increased. 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. Since this is not possible, 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. When the concentration is 1.0 mmol / g or less, water dispersibility is deteriorated, and coalescence (particles naturally gather and increase in particle size) easily occurs in 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 inkjet 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.)

[Ionic polymerizable surfactant]
The ionic polymerizable surfactant used in the present invention is an ionic surfactant having an ionic group, a hydrophobic group, and a polymerizable group.
Examples of the ionic group include an anionic group and a cationic group, and are appropriately determined according to the use of the encapsulated product. The ionic polymerizable surfactant is referred to as an anionic polymerizable surfactant and a cationic polymerizable surfactant, respectively, depending on whether the ionic group has an anionic group or a cationic group.

As the anionic group, a sulfonic acid group, a sulfinic acid group, a carboxyl group, a phosphoric acid group, a sulfonic acid ester group, a sulfinic acid ester group, a phosphoric acid ester group, and those selected from the group of these salts are suitable. Can be illustrated. Examples of the salt include Na salt, K salt, Ca salt, and organic amine salt.
As the cationic group, a cationic group selected from the group consisting of a primary ammonium cation, a secondary ammonium cation, a tertiary ammonium cation, and a quaternary ammonium cation is preferable. The primary ammonium cation is a monoalkyl ammonium cation (RNH ₃ ⁺ ) or the like, the secondary ammonium cation is a dialkyl ammonium cation (R ₂ NH ₂ ⁺ ) or the like, and the tertiary ammonium cation is a trialkyl ammonium cation (R ₃ NH). ⁺ ) And the like, and examples of the quaternary ammonium cation include (R ₄ N ⁺ ). Here, R is a hydrophobic group, and examples thereof include the following. Examples of the counter anion of the cationic group include Cl ⁻ , Br ⁻ , I ⁻ , CH ₃ OSO ₃ ⁻ , C ₂ H ₅ OSO ₃ ^{—, and the} like.

  The hydrophobic group is preferably one or more selected from the group consisting of an alkyl group having 8 to 16 carbon atoms and an aryl group such as a phenyl group and a phenylene group, and the alkyl group and the aryl group in the molecule. It is also possible to have both.

  The polymerizable group is preferably an unsaturated hydrocarbon group capable of radical polymerization, and 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. It is preferred that Among these, an allyl group, a methacryloyl group, and an acryloyl group are particularly preferable.

[Anionic polymerizable surfactant]
The anionic polymerizable surfactant used in the present invention is an anionic surfactant having an anionic group, a hydrophobic group, and a polymerizable group.
As the anionic group, a sulfonic acid group, a sulfinic acid group, a carboxyl group, a phosphoric acid group, a sulfonic acid ester group, a sulfinic acid ester group, a phosphoric acid ester group, and those selected from the group of these salts are suitable. Can be illustrated. Examples of the salt include Na salt, K salt, Ca salt, and organic amine salt.
The hydrophobic group is preferably one or more selected from the group consisting of an alkyl group having 8 to 16 carbon atoms and an aryl group such as a phenyl group and a phenylene group, and the alkyl group and the aryl group in the molecule. It is also possible to have both.
The polymerizable group is preferably an unsaturated hydrocarbon group capable of radical polymerization, and 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. It is preferred that Among these, an allyl group, a methacryloyl group, and an acryloyl group are particularly preferable.
Specific examples of the anionic polymerizable surfactant include an anionic allyl derivative as described in JP-B-49-46291, JP-B-1-24142, or JP-A-62-104802. Anionic propenyl derivatives as described in JP-A-62-221431, anionic acrylics as described in JP-A-62-34947 or JP-A-55-11525 Examples thereof include acid derivatives and anionic itaconic acid derivatives described in JP-B-46-34898 or JP-A-51-30284.

  Examples of the anionic polymerizable surfactant used in the present invention include the following general formula (31):

[Wherein R ²¹ and R ³¹ are each independently a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms,
Z ¹ is a carbon-carbon single bond or a formula:
—CH ₂ —O—CH ₂ —
M is an integer of 2 to 20, X is a group represented by the formula —SO ₃ M ¹ , and M ¹ is an alkali metal, an ammonium salt, or an alkanolamine. ]
Or a compound represented by the following general formula (32):

[Wherein, R ²² and R ³² each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, and D represents a carbon-carbon single bond or a formula:
—CH ₂ —O—CH ₂ —
N is an integer of 2 to 20, Y is a group represented by the formula —SO ₃ M ² , and M ² is an alkali metal, an ammonium salt, or an alkanolamine. ]
The compound represented by these is preferable.

  Examples of the anionic polymerizable surfactant represented by the formula (31) include compounds described in JP-A-5-320276 or JP-A-10-316909. By appropriately adjusting the value of m in the formula (31), it is possible to adjust the hydrophilicity of the surface of the encapsulated color material particles obtained by encapsulating the color material particles. Preferable polymerizable surfactants represented by the formula (31) include compounds represented by the following formula (310), and more specifically, the following formulas (31a) to (31d) The compound represented by these can be mentioned.

[Wherein, R ³¹ , m and M ¹ are the same as the compound represented by the formula (31). ]

A commercial item can also be used as said anionic polymerizable surfactant. Adeka Soap SE-10N manufactured by Asahi Denka Kogyo Co., Ltd. is a compound represented by formula (310) in which M ¹ is NH ₄ , R ³¹ is C ₉ H ₁₉ , and m = 10. Adeka Soap SE-20N manufactured by Asahi Denka Kogyo Co., Ltd. is a compound represented by formula (310) in which M ¹ is NH ₄ , R ³¹ is C ₉ H ₁₉ , and m = 20.

  In addition, examples of the anionic polymerizable surfactant used in the present invention include a general formula (33):

[In the formula, p is 9 or 11, q is an integer of 2 to 20, A is a group represented by —SO ₃ M ³ , and M ³ is an alkali metal, an ammonium salt or an alkanolamine. ]
The compound represented by these is preferable. Preferred examples of the anionic polymerizable surfactant represented by the formula (33) include the following compounds.

[Wherein, r is 9 or 11, and s is 5 or 10. ]
A commercial item can also be used as said anionic polymerizable surfactant. Examples of commercially available products include Aqualon KH series (Aqualon KH-5 and Aqualon KH-10) (above, trade names) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and the like. Aqualon KH-5 is a mixture of a compound represented by the above formula (33) wherein r is 9 and s is 5, and a compound where r is 11 and s is 5. Aqualon KH-10 is a mixture of a compound represented by the above formula wherein r is 9 and s is 10, and a compound where r is 11 and s is 10.

  Moreover, as an anionic polymerizable surfactant used for this invention, the compound represented by following formula (34) is preferable.

[Wherein, R is an alkyl group having 8 to 15 carbon atoms, n is an integer of 2 to 20, X is a group represented by —SO ₃ B, and B is an alkali metal, an ammonium salt or an alkanolamine] It is. ]
A commercial item can also be used as said anionic polymerizable surfactant. As a commercial item, Asahi Denka Kogyo Co., Ltd. Adeka rear soap SR series (Adeka rear soap SR-10, SR-20, SR-1025) (above, a brand name) etc. can be mentioned, for example. The ADEKA rear soap SR series is a compound in which B is NH ₄ in the general formula (34), SR-10 is n = 10, and SR-20 is n = 20.

  Moreover, as an anionic polymerizable surfactant used for this invention, the compound represented by a following formula (A) can also be used.

[In the above formula (A), R ⁴ represents a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, 1 represents a number of 2 to 20, and M ⁴ represents an alkali metal, an ammonium salt, or an alkanolamine. . ]
A commercial item can also be used as said anionic polymerizable surfactant. As a commercial item, the Dai-Ichi Kogyo Seiyaku Co., Ltd. product Aqualon HS series (Aquaron HS-10, HS-20, and HS-1025) (above, a brand name) is mentioned, for example.

  Examples of the anionic polymerizable surfactant used in the present invention include sodium alkylallylsulfosuccinate represented by the general formula (35).

A commercial item can also be used as said anionic polymerizable surfactant. As a commercial item, Elyoinol JS-2 of Sanyo Chemical Industries Ltd. can be mentioned, for example, In the said General formula (35), it is a compound represented by m = 12.

  Examples of the anionic polymerizable surfactant used in the present invention include methacryloyloxypolyoxyalkylene sulfate sodium salt represented by the general formula (36). In the following formula, n is 1-20.

A commercial item can also be used as said anionic polymerizable surfactant. As a commercial item, the Eleminol RS-30 of Sanyo Chemical Industries Ltd. can be mentioned, for example, In the said General formula (36), it is a compound represented by n = 9.

  Moreover, as an anionic polymerizable surfactant used in this invention, the compound represented by General formula (37) can be used, for example.

A commercial item can also be used as said anionic polymerizable surfactant, and Antox MS-60 of Nippon Emulsifier Co., Ltd. corresponds to this.

  The anionic polymerizable surfactants exemplified above can be used alone or as a mixture of two or more.

[Cationically polymerizable surfactant]
The cationic polymerizable surfactant used in the present invention is a cationic surfactant having a cationic group, a hydrophobic group, and a polymerizable group.
As the cationic group, a cationic group selected from the group consisting of a primary ammonium cation, a secondary ammonium cation, a tertiary ammonium cation, and a quaternary ammonium cation is preferable. The primary ammonium cation is a monoalkyl ammonium cation (RNH ₃ ⁺ ) or the like, the secondary ammonium cation is a dialkyl ammonium cation (R ₂ NH ₂ ⁺ ) or the like, and the tertiary ammonium cation is a trialkyl ammonium cation (R ₃ NH). ⁺ ) And the like, and examples of the quaternary ammonium cation include (R ₄ N ⁺ ). Here, R is a hydrophobic group, and examples thereof include the following.
The hydrophobic group is preferably one or more selected from the group consisting of an alkyl group having 8 to 16 carbon atoms and an aryl group such as a phenyl group and a phenylene group, and the alkyl group and the aryl group in the molecule. It is also possible to have both.
Examples of the counter anion of the cationic group include Cl ⁻ , Br ⁻ , I ⁻ , CH ₃ OSO ₃ ⁻ , C ₂ H ₅ OSO ₃ ^{—, and the} like.
The polymerizable group is preferably an unsaturated hydrocarbon group capable of radical polymerization, and 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. It is preferred that Among these, an allyl group, a methacryloyl group, and an acryloyl group are particularly preferable.
Examples of the cationic polymerizable surfactant include compounds represented by the general formula R _{[4- (l + m + n)]} R ¹ _l R ² _m R ³ _n N ⁺ · X ⁻ (the above general formula R is a polymerizable group, R ¹ , R ² and R ³ are each an alkyl group having 8 to 16 carbon atoms and an aryl group such as a phenyl group and a phenylene group, and X ⁻ is Cl ⁻ , Br ^−. , I ⁻ , CH ₃ OSO ₃ ⁻ , C ₂ H ₅ OSO ₃ ^— , and each of l, m and n is 1 or 0). Here, examples of the polymerizable group include those described above.

  Specific examples of the cationic polymerizable surfactant include dimethylaminoethyl methacrylate methacrylate, dimethylaminoethyl octyl chloride methacrylate, dimethylaminoethyl cetyl chloride methacrylate, dimethylaminoethyl decyl chloride methacrylate, dimethyl methacrylate Examples thereof include aminoethyl dodecyl chloride salt, dimethylaminoethyl tetradecyl chloride salt methacrylate, and the like. The cationic polymerizable surfactants exemplified above can be used alone or as a mixture of two or more.

[Ionic monomer]
The ionic monomer used in the present invention is a compound having an ionic group and a polymerizable group and is water-soluble.
The ionic group may be either an anionic group or a cationic group, and is appropriately selected according to the use of the encapsulated product. Depending on whether an ionic group has an anionic group or a cationic group, it is recognized as an anionic water-soluble monomer or a cationic water-soluble monomer, respectively.

  The polymerizable group is preferably an unsaturated hydrocarbon group capable of radical polymerization, and 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. It is preferred that Among these, an allyl group, a methacryloyl group, and an acryloyl group are particularly preferable.

As the anionic group, a sulfonic acid group, a sulfinic acid group, a carboxyl group, a phosphoric acid group, a sulfonic acid ester group, a sulfinic acid ester group, a phosphoric acid ester group, and those selected from the group of these salts are suitable. Can be illustrated. Examples of the salt include Na salt, K salt, Ca salt, and organic amine salt.
As the cationic group, a cationic group selected from the group consisting of a primary ammonium cation, a secondary ammonium cation, a tertiary ammonium cation, and a quaternary ammonium cation is preferable. The primary ammonium cation is a monoalkyl ammonium cation (RNH ₃ ⁺ ) or the like, the secondary ammonium cation is a dialkyl ammonium cation (R ₂ NH ₂ ⁺ ) or the like, and the tertiary ammonium cation is a trialkyl ammonium cation (R ₃ NH). ⁺ ) And the like, and examples of the quaternary ammonium cation include (R ₄ N ⁺ ). Here, R is a hydrophobic group, and examples thereof include the following. Examples of the counter anion of the cationic group include Cl ⁻ , Br ⁻ , I ⁻ , CH ₃ OSO ₃ ⁻ , C ₂ H ₅ OSO ₃ ^{—, and the} like.

  Preferred specific examples of the cationic water-soluble monomer that can be used in the present invention include dimethylaminoethylmethyl chloride methacrylate, dimethylaminoethylbenzyl chloride methacrylate, methacryloyloxyethyltrimethylammonium chloride, diallyldimethylammonium chloride, and 2-hydroxy-3-methacryloxypropyltrimethylammonium chloride salt and the like. A commercial item can also be used as said cationic water-soluble monomer, For example, Acryester DMC (Mitsubishi Rayon Co., Ltd.), Acryester DML60 (Mitsubishi Rayon Co., Ltd.), and C-1615 (Daiichi Kogyo Seiyaku) (Co., Ltd.)). The cationic water-soluble monomers exemplified above can be used alone or as a mixture of two or more.

  Preferable specific examples of the anionic water-soluble monomer that can be used in the present invention include, as a monomer having a carboxyl group, for example, acrylic acid, methacrylic acid, crotonic acid, propylacrylic acid, isopropylacrylic acid, 2-acryloyloxyethylsuccinic acid. 2-acryloyloxyethyl phthalic acid, 2-methacryloyloxyethyl succinic acid, 2-methacryloyloxyethyl phthalic acid, itaconic acid, fumaric acid, maleic acid and the like. Among these, acrylic acid and methacrylic acid are preferable. Examples of the monomer having a sulfonic acid group include 4-styrene sulfonic acid and its salt, vinyl sulfonic acid and its salt, sulfoethyl acrylate and its salt, sulfoethyl methacrylate and its salt, sulfoalkyl acrylate and its salt, sulfoalkyl Methacrylate and its salt, sulfopropyl acrylate and its salt, sulfopropyl methacrylate and its salt, sulfoaryl acrylate and its salt, sulfoaryl methacrylate and its salt, butylacrylamide sulfonic acid and its salt, 2-acrylamido-2-methylpropanesulfone Examples include acids and salts thereof. Examples of the monomer having a phosphone group include phosphoric acid group-containing (meth) acrylates such as phosphoethyl methacrylate. The anionic water-soluble monomers exemplified above can be used alone or as a mixture of two or more.

[Ionic polymerizable surfactant A]
The ionic polymerizable surfactant A used in the present invention has an ionic group having a charge opposite to the charge on the surface of the pigment particle, a hydrophobic group, and a polymerizable group.
The ionic group, hydrophobic group and polymerizable group are the same as those described in the item of the ionic polymerizable surfactant.
The anionic polymerizable surfactant and the cationic polymerizable surfactant used as the ionic polymerizable surfactant A used in the present invention are the same as those described in the item of the aforementioned ionic polymerizable surfactant. It is.

[Ionic polymerizable surfactant B]
The ionic polymerizable surfactant B used in the present invention has an ionic group, a hydrophobic group, and a polymerizable group having the same kind or opposite charge to the charge on the surface of the pigment particle.
The ionic group, hydrophobic group and polymerizable group are the same as those described in the item of the ionic polymerizable surfactant.
The anionic polymerizable surfactant and the cationic polymerizable surfactant used as the ionic polymerizable surfactant B used in the present invention are the same as those described in the item of the ionic polymerizable surfactant described above. It is.

(Hydrophobic monomer)
In the present invention, it is also possible to use a hydrophobic monomer as a constituent component of the polymer. The hydrophobic monomer means a polymerizable monomer having at least a hydrophobic group and a polymerizable group in the structure, and the hydrophobic group is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group. The thing selected from the group can be illustrated.
Examples of the aliphatic hydrocarbon group include a methyl group, an ethyl group, and a propyl group, and examples of the alicyclic hydrocarbon group include a cyclohexyl group, a dicyclopentenyl group, a dicyclopentanyl group, and an isobornyl group. Examples of the group hydrocarbon group include a benzyl group, a phenyl group, and a naphthyl group.
As the polymerizable group of the hydrophobic monomer, the same group as described in the item of the ionic polymerizable surfactant can be used.

  Specific examples of the hydrophobic monomer include styrene derivatives such as styrene, methylstyrene, vinyltoluene, dimethylstyrene, chlorostyrene, dichlorostyrene, t-butylstyrene, bromostyrene, and p-chloromethylstyrene; methyl acrylate, acrylic Ethyl isopropyl acrylate, n-butyl acrylate, butoxyethyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate, octadecyl acrylate, benzyl acrylate, acrylic acid Phenyl, phenoxyethyl acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, Cyclopentenyloxyethyl acrylate, tetrahydrofurfuryl acrylate, and isobornyl acrylate, isoamyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, ethoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate, methoxydipropylene glycol acrylate, phenoxy polyethylene glycol acrylate Monofunctional acrylic acid esters such as nonylphenol EO adduct acrylate, isooctyl acrylate, isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl diglycol acrylate, octoxypolyethylene glycol polypropylene glycol monoacrylate, methyl methacrylate, Ethyl tacrylate, isopropyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, tridecyl methacrylate , Stearyl methacrylate, isodecyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, methoxydiethylene glycol methacrylate, polypropylene glycol monomethacrylate, benzyl methacrylate, phenyl methacrylate, phenoxyethyl methacrylate, cyclohexyl methacrylate, tetrahydromethacrylate Furfuryl, t-butylcyclo Monofunctional methacrylates such as hexyl methacrylate, behenyl methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, dicyclopentenyloxyethyl methacrylate, butoxymethyl methacrylate, and isobornyl methacrylate, octoxy polyethylene glycol polypropylene glycol monomethacrylate, etc. Allyl compounds such as allylbenzene, allyl-3-cyclohexanepropionate, 1-allyl-3,4-dimethoxybenzene, allylphenoxyacetate, allylphenylacetate, allylcyclohexane, and polyvalent allyl carboxylate; fumaric acid, Unsaturated esters such as maleic acid and itaconic acid; radical polymerizable groups such as N-substituted maleimide and cyclic olefin Such as monomers and the like.

  In addition to the film forming properties, coating film strength, chemical resistance, water resistance, light resistance, weather resistance, and optical properties of the encapsulated pigment of the present invention, the physical properties and chemical properties are the structure of the hydrophobic monomer and the hydrophobic properties It is determined by the structure of the copolymer consisting of monomers. Therefore, it is possible to select a hydrophobic monomer according to the performance required for the encapsulated pigment. For example, the fixability and abrasion resistance of the recorded matter required when the encapsulated pigment of the present invention is used as a recording material are the glass transition point (Tg) of the copolymer (copolymer) covering the colorant particles. It is possible by controlling 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. Temperature is taken as 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. Furthermore, the glass transition point can be calculated by the Fox formula from the weight fraction of the monomer used in synthesizing the copolymer and the glass transition point of the homopolymer obtained by homopolymerizing the monomer. (In the present invention, the glass transition point obtained by the Fox equation is used.) That is, the temperature environment where the encapsulated pigment of the present invention is placed covers the pigment particles of the encapsulated pigment of the present invention. When the temperature is higher than the glass transition point of the polymer, the copolymer is in a state where a large deformation occurs with a small force, and further melts when the melting point is reached. At this time, if another encapsulated pigment is present in the vicinity, the encapsulated pigments are fused to form a film. In addition, even when the environmental temperature does not reach the melting point, when the encapsulated pigments come into contact with each other with a strong force, the copolymer molecules covering each encapsulated pigment can be entangled with each other. Under such conditions, the copolymers (copolymers) covering the encapsulated pigment may be fused together.

  When the encapsulated pigment of the present invention is used for an inkjet ink, when printing is performed on a recording medium such as plain paper or a dedicated recording medium for inkjet recording with this ink, water around the encapsulated pigment of the present invention and / or When the aqueous medium composed of the water-soluble organic solvent penetrates into the plain paper or the exclusive recording medium for ink jet recording, it disappears from the vicinity of the encapsulated pigment particles, and the encapsulated pigment particles come close to each other. At that time, when the glass transition point (Tg) of the copolymer covering the encapsulated pigment is not more than room temperature, the pigment particles are coated by the capillary pressure generated in the gap between the encapsulated pigments. The film is formed in a state where the copolymer (copolymer) is fused and the pigment particles are encapsulated (included) inside. Thereby, fixability and abrasion resistance of the pigment to the recording medium can be obtained. In this case, when the glass transition point of the copolymer covering the encapsulated pigment of the present invention is preferably 30 ° C. or lower, more preferably 15 ° C. or lower, and further preferably 10 ° C. or lower, More preferably, the film is formed at room temperature. Therefore, when the encapsulated pigment of the present invention is used as an inkjet ink, it is preferable to design the glass transition point of the copolymer (copolymer) covering the encapsulated pigment to be 30 ° C. or less, More preferably, it is designed to be 15 ° C. or lower, more preferably 10 ° C. or lower. However, when the glass transition point is lower than −20 ° C., the solvent resistance tends to decrease, so care must be taken. As the hydrophobic monomer, those satisfying the respective required characteristics described above are appropriately selected, and the addition amount thereof is arbitrarily determined.

[Other polymerization components]
The encapsulated pigment of the present invention is obtained by coating pigment particles with a material containing a polymer as a main component, and as a raw material, in addition to the polymerizable surfactant and the ionic monomer, and in some cases, a hydrophobic monomer, Other polymerizable monomer components can be used as long as the effects of the present invention are not impaired. Examples of other polymerizable monomers used in the present invention include crosslinkable monomers. By adding a crosslinkable monomer to the polymerization component and copolymerizing with the hydrophobic monomer, the mechanical strength and heat resistance of the polymer can be increased, and the shape maintenance of the capsule wall material is improved. In addition, swelling of the polymer by the organic solvent and penetration of the organic solvent into the polymer can be suppressed, and the solvent resistance of the capsule wall material can be improved. As a result, for example, in an ink composition for ink jet recording coexisting with a water-soluble organic solvent, the dispersibility of the colorant particles, the storage stability of the ink composition, and the discharge property of the ink composition from the ink jet head are also achieved. Can be increased.

  The crosslinkable monomer used in the present invention includes a compound having two or more unsaturated hydrocarbon groups of at least one selected from vinyl group, allyl group, acryloyl group, methacryloyl group, propenyl group, vinylidene group, and vinylene group The thing which has is mentioned. Specific examples of the crosslinkable monomer include, for example, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, allyl acrylate, and bis (acryloxyethyl) hydroxyethyl isocyanurate. Bis (acryloxy neopentyl glycol) adipate, 1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, propylene glycol diacrylate, polypropylene glycol diacrylate, 2-hydroxy-1 , 3-Diacryloxypropane, 2,2-bis [4- (acryloxy) phenyl] propane, 2,2- [4- (acryloxyethoxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxydiethoxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxy polyethoxy) phenyl] propane , Hydroxybivalic acid neopentyl glycol diacrylate, 1,4-butanediol diacrylate, dicyclopentanyl diacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tri Acrylate, tetrabromobisphenol A diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate, tris (acryloxyethyl) isocyania Rate, 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-dimethacryloxypropane, 2,2-bis [4- (methacryloxy) phenyl] propane, 2 , 2-bis [4- (methacryloxyethoxy) phenyl] propane, 2,2-bis [4- (methacryloxyethoxydie) Toxi) phenyl] propane, 2,2-bis [4- (methacryloxyethoxypolyethoxy) phenyl] propane, tetrabromobisphenol A dimethacrylate, dicyclopentanyl dimethacrylate, dipentaerythritol hexamethacrylate, glycerol dimethacrylate, hydroxy Neopentyl glycol dimethacrylate, dipentaerythritol monohydroxypentamethacrylate, ditrimethylolpropane tetramethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, triglycerol dimethacrylate, trimethylolpropane trimethacrylate, tris (methacryloxyethyl) ) Isocyanurate, allyl methacrylate, divinylben Emissions, diallyl phthalate, diallyl terephthalate, diallyl isophthalate, and diethylene glycol bis allyl carbonate.

  As a monomer used for synthesizing the polymer which is the main component of the capsule wall material of the present invention, a monomer represented by the following general formula (2) can be used as long as the effects of the present invention are not impaired.

[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. ]
In the general formula (2), examples of the alicyclic hydrocarbon group represented by R ² include a cycloalkyl group, a cycloalkenyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantane group. Examples of the heterocyclic group include a tetrahydrofuran group.
Specific examples of the monomer represented by the general formula (2) include the following.

By introducing the R ² group, which is a “bulky” group derived from the monomer represented by the general formula (2), into the polymer of the capsule wall material, the flexibility of the molecule of the polymer is reduced, that is, the molecular The mobility can be lowered to increase the mechanical strength and heat resistance of the polymer. For this reason, the ink composition containing the encapsulated pigment of the present invention can provide a printed matter having excellent abrasion resistance and durability. Further, since the R ² group which is a “bulky” group is present in the polymer constituting the capsule wall material, the penetration of the organic solvent in the ink composition into the polymer can be suppressed. The solvent resistance of the material can be made excellent. As a result, in the ink composition for ink jet recording coexisting with a water-soluble organic solvent, the dispersibility of the colorant particles, the storage stability of the ink composition, and the discharge property of the ink composition from the ink jet head can be improved. it can.

  A polymer having a repeating structural unit derived from the above crosslinkable monomer or a polymer having a repeating structural unit derived from the monomer represented by the general formula (2) has a high glass transition temperature (Tg) and is mechanical. It has the advantage of excellent strength, heat resistance and solvent resistance.

On the other hand, among the above-mentioned hydrophobic monomers, a polymer having a repeating structural unit derived from a monomer having a long-chain alkyl group has flexibility. Therefore, the ratio of the repeating structural unit derived from the crosslinkable monomer and / or the repeating structural unit derived from the monomer represented by the general formula (2) and the repeating structural unit derived from the monomer having a long chain alkyl group By appropriately adjusting the ratio, it is possible to synthesize a capsule wall material polymer having excellent mechanical strength and excellent solvent resistance in combination with preferable plasticity. An ink composition containing encapsulated pigment particles coated with such a polymer has excellent dispersion stability and long-term storage stability even when it contains a water-soluble organic solvent, and stable ejection properties from an inkjet head. Also excellent in properties. Furthermore, an image of a printed matter printed using the ink composition containing the encapsulated pigment particles has good fixability to a recording medium such as paper or an inkjet-dedicated medium. Furthermore, this ink composition can obtain an image excellent in abrasion resistance, durability, and solvent resistance.
Furthermore, in this invention, in addition to the various polymerizable monomers mentioned above, other well-known polymerizable monomers can be used in the range which does not impair the effect of this invention.

(Polymerization initiator)
As described above, the polymer constituting the capsule wall material of the encapsulated pigment of the present invention is obtained by polymerizing a monomer containing a surfactant and a hydrophobic monomer. This polymerization reaction can be performed using a known polymerization initiator, and it is particularly preferable to use a radical polymerization initiator. As the polymerization initiator, a water-soluble polymerization initiator is preferable, and potassium persulfate, ammonium persulfate, sodium persulfate, 2,2-azobis- (2-methylpropionamidine) dihydrochloride, and 4,4-azobis- ( 4-cyanovaleric acid) and the like. In addition, a redox initiator in which potassium persulfate, ammonium persulfate, sodium persulfate, and the like are combined with sodium sulfite, sodium hyposulfite, ferrous sulfate, or the like can also be used.

〔Electrolytes〕
The electrolyte used in the present invention is not particularly limited as long as it reduces the electrostatic repulsion by acting on the charge on the surface of the pigment particles or the ionic group of the ionic polymerizable surfactant, but preferably sodium chloride, sulfuric acid Sodium, potassium sulfate, potassium chloride and the like are used, and sodium chloride and sodium sulfate are particularly preferably used.
[Other ingredients]
The encapsulated pigment of the present invention is obtained by coating a core material with a material containing a polymer as a main component, and in addition to the above-described raw materials, an ultraviolet absorber as long as the effects of the present invention are not impaired. Other components such as a light stabilizer, an antioxidant, a flame retardant, a plasticizer, and a wax can be contained in the polymer.

[Polymerization method of encapsulated pigment]
A method for producing the encapsulated pigment of the present invention will be described below.
The encapsulated pigment capsule wall material is synthesized by a polymerization reaction, and this polymerization reaction can be carried out using a reaction vessel equipped with an ultrasonic generator, a stirrer, a reflux condenser, a dropping funnel, and a temperature controller. preferable.
A method for producing the encapsulated pigment of the present invention will be described. First, the ionic polymerizable surfactant A and / or ionic monomer having a charge opposite to the charge on the surface of the pigment particle is added to and mixed with the dispersion of pigment particles having a charge on the surface. At this time, it is preferable to irradiate the mixture with ultrasonic waves so that the ionic group of the ionic polymerizable surfactant A and / or the ionic monomer is easily ionically bonded to the ionic group on the pigment particle surface.

  The amount of the ionic polymerizable surfactant A having a charge opposite to the charge on the pigment particle surface and / or the ionic monomer having the charge opposite to the charge on the surface of the pigment particle to the pigment particle dispersion is as follows: The total number of moles of ionic groups on the surface (that is, the amount of ionic groups present on the surface of the pigment particles of 1 g of the pigment particles used [mol / g]) is in the range of 0.5 to 2 times the mole. Is preferable, and the range of 0.8 to 1.2 times mol is more preferable. The ionic polymerizable surfactant A having an ionic group opposite to the ionic group on the pigment particle surface and / or the ionic group on the pigment particle surface with respect to the total molar amount of the ionic group on the pigment particle surface. On the other hand, an encapsulated pigment having good dispersibility can be obtained by a subsequent polymerization reaction by adding 0.5 times mole or more of an ionic monomer having an opposite charge. This is presumably because the pigment particles can be sufficiently covered with the ionic polymerizable surfactant A and / or an ionic monomer having an opposite charge to the ionic groups on the surface of the pigment particles. On the other hand, polymer particles having no pigment particles are obtained by setting the addition amount of the ionic polymerizable surfactant A and / or the ionic monomer having the opposite charge to the ionic group on the surface of the pigment particles to 2 times mole or less. Generation | occurrence | production of (the particle | grains which consist only of a polymer) can be suppressed. This is considered to be because the amount of the ionic monomer having an opposite charge to the ionic group on the surface of the ionic polymerizable surfactant A and / or the pigment particle that is not adsorbed to the pigment particle can be reduced.

  Next, in some cases, a hydrophobic monomer is added and mixed. In this case, the polymerizable monomer is selected from the group consisting of a hydrophobic monomer, a crosslinkable monomer, a compound represented by the above general formula (2), and other known polymerizable monomers, as long as the effects of the invention are not impaired. A selected monomer can be used in combination. Also when adding and mixing the said polymerizable monomer, it is preferable to irradiate an ultrasonic wave.

  Further, an ionic polymerizable surfactant B having the same or opposite charge as that of the ionic group on the pigment particle surface is added and mixed. Here, the addition amount of the ionic polymerizable surfactant B is 1 time with respect to the ionic monomer having an opposite charge to the ionic group on the surface of the ionic polymerizable surfactant A and / or pigment particles. It is preferably in the range of 10 moles to 10 moles, more preferably in the range of 1 moles to 5 moles. By setting the addition amount to 1 mol or more, an encapsulated pigment dispersion with excellent dispersion stability can be obtained because aggregation of the encapsulated pigment can be suppressed. Furthermore, the ink composition using the encapsulated pigment dispersion of the present invention has excellent ejection stability from an inkjet recording head, improved adsorptivity to paper fibers, and excellent printing density and color development. Become. Moreover, by making the addition amount 10 times mole or less, the amount of the ionic polymerizable surfactant B that does not contribute to the encapsulation reaction of the pigment particles is reduced, and the generation of polymer particles having no pigment particles is suppressed. it can.

Through the above steps, the surface of the pigment particle having a charge on the surface is charged with the ionic polymerizable surfactant A having the opposite charge to the ionic group and / or the charge opposite to the ionic group on the surface of the pigment particle. The ionic monomer having the ionic monomer is electrostatically attached, the hydrophobic monomer may be localized on the outside of the ionic monomer, and the outer surface of the ionic monomer may have the same or opposite charge as the charge of the ionic group on the pigment particle surface. It is presumed that the functional surfactant B orients its ionic group toward the aqueous phase to form an admicell.
It should be noted that ultrasonic irradiation is not always necessary when the formation of admicelle is obtained without performing ultrasonic irradiation in the above process, but in order to control the particle size of the encapsulated particles, It is particularly preferable to irradiate sound waves.

  After the formation of the admicelle, an electrolyte is added to the mixed solution and further irradiated with ultrasonic waves. The electrolyte may be added before admicelle formation, but preferably after admicelle formation. By adding the electrolyte to the liquid mixture, the electrostatic repulsion between the ionic groups on the surface of the ionic surfactant B is reduced, and the ionic monomer and the hydrophobic monomer are taken into the admicelle and the particle size of the admicelle is increased. .

  Next, a polymerization initiator is added to the mixed solution prepared as described above to perform a polymerization reaction. The polymerization initiator may be added to the liquid mixture heated to a temperature at which the polymerization initiator is activated, or the polymerization initiator may be added at once or dividedly or continuously. Moreover, after adding a polymerization initiator, you may heat the said liquid mixture to the temperature in which a polymerization initiator is activated. In the present invention, a water-soluble polymerization initiator is preferably used as a polymerization initiator, and an aqueous solution obtained by dissolving it in pure water is preferably added dropwise to the aqueous dispersion in the reaction vessel. The added polymerization initiator is cleaved to generate an initiator radical, which causes a polymerization reaction by attacking the polymerizable group of the ionic polymerizable surfactant or the polymerizable group of the polymerizable monomer. The polymerization temperature and the polymerization reaction time vary depending on the type of polymerization initiator used and the type of polymerizable monomer, but those skilled in the art can easily set preferable polymerization conditions as appropriate. In general, the polymerization temperature is preferably in the range of 60 ° C to 90 ° C, and the polymerization time is preferably 3 hours to 10 hours.

In the polymerization reaction, the ionic polymerizable surfactants A and B, the hydrophobic monomer, the crosslinkable monomer, the compound represented by the general formula (2), and other known polymerizable monomers are each 1 Species or two or more can be used. Moreover, since the said emulsion polymerization reaction is performed using ionic polymerizable surfactant, the emulsification state of a liquid mixture is often favorable even if it does not use an emulsifier. Therefore, it is not always necessary to use an emulsifier, but at least one selected from the group consisting of known anionic, nonionic, and cationic emulsifiers may be used as necessary.
After completion of the polymerization, it is preferable to adjust the pH of the obtained aqueous dispersion of the encapsulated pigment of the present invention to a range of 7.0 to 9.0 and further perform filtration. Filtration is preferably ultrafiltration.

  According to the polymerization method described above, the ionic polymerizable surfactant A having an opposite charge to the ionic group on the pigment particle surface and / or the ionic monomer having the opposite charge to the ionic group on the pigment particle surface are adsorbed. It is thought that it is done. Then, in some cases, a polymerizable monomer containing a hydrophobic monomer is added, and further an ionic polymerizable surfactant B having the same or opposite charge as that of the ionic group on the surface of the pigment particle is added, and ultrasonic waves are irradiated. To process. By this treatment, the arrangement form of the ionic polymerizable surfactant and polymerizable monomer molecules existing around the pigment particles is extremely highly controlled, and in the outermost layer, an ionic group (anionic group or cation) is directed toward the aqueous phase. It is considered that a state in which the functional group) is oriented is formed. By adding an electrolyte to the admicelle in this state, the monomer is taken into the admicelle and an admicelle having a large particle size is formed. Further, by polymerizing in this state, a polymer having repeating structural units derived from the polymerizable groups of the ionic polymerizable surfactant A and the ionic polymerizable surfactant B around the pigment particles is obtained. It is considered that an encapsulated pigment is obtained. When a hydrophobic monomer is added, not only the polymerizable group of the ionic polymerizable surfactant A and the ionic polymerizable surfactant B but also a polymer having a repeating structural unit composed of a hydrophobic monomer is contained in the pigment particles. Although it is formed around, the addition of an electrolyte makes it possible to increase the number of repeating structural units composed of monomers around the pigment particles as compared with the case where no electrolyte is added. By using the polymerization method of the present invention, the production of water-soluble oligomers and polymers as by-products can be suppressed. Thereby, a low-viscosity encapsulated pigment dispersion can be obtained, and a purification process such as ultrafiltration can be easily performed.

  The encapsulated pigment of the present invention obtained as described above has high dispersion stability with respect to an aqueous solvent, but this is because the pigment particles are completely covered with the polymer layer (there is no uncoated part). At the same time, it is considered that the hydrophilic groups of the polymer layer of the capsule wall material are regularly oriented toward the aqueous solvent.

  The encapsulated pigment obtained in the present invention has a form in which the surface of the pigment particle is coated with a polymer which is a capsule wall material. If desired, before the polymerization or during the polymerization reaction, an antioxidant or a plasticizer is contained in the mixed solution. These additives can also be contained in the polymer by adding, for example. Known materials can be used as such antioxidants and plasticizers.

  The particle diameter of the encapsulated pigment of the present invention thus obtained is preferably 400 nm or less, more preferably 300 nm or less, and particularly preferably 20 to 200 nm. The particle size of the encapsulated pigment obtained according to the present invention is such that the ultrasonic wave is reacted and mixed under a predetermined irradiation condition (mainly the difference in irradiation energy, which can be controlled by, for example, the frequency and irradiation time) before the polymerization reaction starts. Desired particle size by irradiating the liquid, difference in whether or not the reaction mixture is irradiated with ultrasonic waves during the polymerization reaction, and controlling the irradiation conditions when irradiating the reaction mixture with ultrasonic waves during the polymerization reaction Can be controlled.

  Furthermore, in the encapsulated pigment of the present invention, the glass transition temperature (Tg) of the polymer that is the main component of the capsule wall material is preferably 50 ° C. or lower. Especially preferably, it is 30 degrees C or less. A desired glass transition temperature can be obtained by appropriately selecting the monomers used for polymerizing the polymer. In order to predict the glass transition temperature of the polymer obtained after the polymerization from the glass transition temperature of the homopolymer and the composition of the monomer used for the polymerization, for example, the following calculation formula:

(In the above formula, Tg _[p] is the glass transition temperature of the resulting polymer, i is the number assigned to each of the different types of monomers, Tg _{[hp] i} is the glass transition temperature of the homopolymer of monomer i used for polymerization, x _i represents the weight fraction of monomer i with respect to the total weight of monomers to be polymerized.).
By setting the glass transition temperature of the polymer, which is the main component of the capsule wall material, to 50 ° C. or less, an image having excellent gloss, high saturation, and excellent sharpness can be obtained, and the encapsulated pigment is recorded. It becomes easy to adhere to the medium. Furthermore, when the Tg of the polymer, which is the main component of the capsule wall material, is 30 ° C. or less, the encapsulated color materials are easily bonded to each other on the recording medium, thereby further improving the abrasion resistance of the image, Since adhesion is also improved, it is more preferably 10 ° C. or lower.

  The dispersion of the encapsulated pigment of the present invention obtained as described above is an aqueous dispersion, and a desired material is further mixed with this to prepare an ink composition. However, the dispersion is not contained in the aqueous dispersion. It is preferable to remove and purify the reactive monomer (such as a polymerizable compound such as an ionic polymerizable surfactant or a hydrophobic monomer) in advance. An image prepared by using an inkjet recording ink using the encapsulated color material obtained by the present invention on plain paper by purifying an aqueous dispersion containing the encapsulated pigment to reduce the concentration of unreacted monomer. Has excellent saturation, can increase the printing density (printing density), and can suppress the occurrence of blurring of the image. Further, an image obtained when this ink is used with a dedicated medium for ink-jet recording, particularly an ink-jet glossy medium, further has good glossiness.

The amount of the unreacted monomer contained in all components other than the solid content of the aqueous dispersion containing the encapsulated pigment obtained in the present invention is preferably 50,000 ppm or less, and more preferably 10,000 ppm or less. preferable.
As a method for purifying the aqueous dispersion containing the encapsulated pigment, a centrifugal separation method, an ultrafiltration method, or the like can be used. In addition, the amount of the unreacted monomer can be easily measured by using gas chromatography or liquid chromatography of a measurement sample for a sample containing an unreacted monomer having a known concentration.

[Resin particles added to ink composition]
Polymer fine particles can be further added to the ink composition of the present invention. The fine polymer particles are preferably in the following forms.
Polymer fine particles having an ionic group of the same kind as that of the encapsulated pigment surface of the present invention on the surface, a glass transition temperature of 30 ° C. or lower, and a volume average particle diameter of 10 to 100 nm.
As described above, a capsule wall material mainly composed of a polymer having a repeating structural unit derived from a crosslinkable monomer and / or a polymer having a repeating structural unit derived from a monomer represented by formula (2) The coated encapsulated pigment has high mechanical strength, heat resistance, and solvent resistance, but the plasticity of the polymer is insufficient, and the fixability to a recording medium and the abrasion resistance tend to be reduced. . However, even if the capsule wall material of the encapsulated pigment is insufficient in plasticity, the encapsulated pigment is used in an image formed on a recording medium using the obtained ink composition by using in combination with the polymer fine particles. The fine polymer particles can be covered, and the fixability of the image to the recording medium and the abrasion resistance of the image can be increased.

  As the polymer fine particles, those having film-forming properties are particularly preferable. “Having film formability” means that a polymer film can be formed when polymer fine particles are dispersed in water to form an aqueous emulsion and the water in the aqueous emulsion is evaporated. The ink composition of the present invention containing polymer fine particles having film-forming properties has a property of forming a polymer film when the solvent component is evaporated. With this polymer film, the encapsulated pigment in the ink can be more firmly fixed to the surface of the recording medium. As a result, an image having better abrasion resistance and water resistance can be formed.

  In order for the polymer fine particles to have good film formability, the glass transition temperature of the polymer is preferably 30 ° C. or lower, more preferably 15 ° C. or lower, and particularly preferably 10 ° C. or lower. . The glass transition temperature of the polymer can be set within a preferable temperature range by appropriately selecting the type and composition ratio of the monomer to be used, and is a method well known to those skilled in the art. In the present invention, as the glass transition temperature of the polymer, the glass transition temperature obtained by temperature rise measurement using a thermal scanning calorimeter (DSC) was used. That is, in the differential heat curve obtained by measuring the temperature rise of the polymer with a thermal scanning calorimeter, when a tangent line is drawn from the bottom of the endothermic peak toward the end point of the endotherm, the intersection of the tangent line and the baseline Was the glass transition temperature (Tg) of the polymer.

  When an ink composition containing such polymer fine particles and the encapsulated pigment of the present invention is used for printing on a recording medium such as plain paper or a dedicated medium for inkjet recording, the aqueous medium in the ink composition is the recording medium. The polymer particles and the encapsulated pigment particles are in close proximity to each other, and the polymer particles and / or the coating polymers of the encapsulated pigment particles are bonded to each other and / or the polymer particles of the encapsulated pigment particles are fused to the pigment particles A polymer film is formed on the recording medium in a state of being wrapped inside. Thereby, the fixing property of the image to the recording medium and the abrasion resistance of the image can be made particularly good.

Further, when the polymer fine particles have the same kind of ionic group as the encapsulated pigment on the surface thereof, the polymer fine particles and the encapsulated pigment of the present invention do not aggregate even if they coexist in the ink composition. It is preferable because it can be stably dispersed.
Furthermore, it is preferable that the polymer fine particles have a volume average particle size in the range of 10 to 100 nm. A volume average particle size of 100 nm or less is preferable because glossiness and image clarity of an image are improved.

In the ink composition of the present invention, the contact angle on the Teflon (registered trademark) plate of an aqueous emulsion in which polymer fine particles are dispersed in an aqueous medium at a concentration of 10% by weight is preferably 70 ° or more. Furthermore, the surface tension of an aqueous emulsion in which polymer fine particles are dispersed in an aqueous medium at a concentration of 35% by weight is preferably 40 × 10 ⁻³ N / m (40 dyne / cm, 20 ° C.) or more. By using the polymer fine particles having the characteristics as described above, it is possible to more effectively prevent the flying bend of the ink droplets in the ink jet recording method, and it is possible to print an image with good image quality.

  Further, by incorporating polymer fine particles having a relatively large number of ionic groups on the surface as described above into the ink composition, better image abrasion resistance can be realized. The reason is not clear, but it can be considered as follows. That is, when the ink composition according to the present invention is attached to the surface of a recording medium such as paper, first, water and a water-soluble organic solvent in the ink composition penetrate into the recording medium. Then, the encapsulated pigment particles and polymer fine particles of the present invention remain in the vicinity of the surface of the recording medium. At this time, the ionic groups on the surface of the polymer fine particles act on the hydroxyl groups and carboxyl groups of cellulose constituting the paper fiber, and the polymer fine particles are firmly adsorbed on the paper fiber. The water and water-soluble organic solvent in the vicinity of the polymer fine particles adsorbed on the paper fibers further penetrate into the paper and decrease. Furthermore, as described above, since the polymer fine particles have film-forming properties, when water and the water-soluble organic solvent disappear from the vicinity of the encapsulated pigment and the polymer fine particles on the recording medium, the particles are coalesced (capsule). A polymer layer is formed by encapsulating the pigment, and a state in which the pigment particles are coated with the polymer is formed. This polymer can be more firmly bonded to the surface of the recording medium by an ionic group. However, these are hypotheses for explaining the effects of the present invention.

Specifically, the polymer fine particles are preferably made of a polymer containing at least 1 to 10% by weight of a repeating unit derived from an unsaturated vinyl monomer having an ionic group.
Furthermore, it has a structure in which a repeating unit derived from an unsaturated vinyl monomer having an ionic group is contained by 1 to 10% by weight and is cross-linked by a cross-linkable monomer having two or more polymerizable double bonds. It is more preferable that it is made of a polymer containing 0.2 to 4% by weight of a structure derived from this crosslinkable monomer. Crosslinkable monomers having two or more, and more preferably three or more, double bonds capable of polymerization during polymerization are copolymerized with other polymerizable monomers to crosslink the polymer chain, and such crosslinked polymers By using the polymer fine particles made of the above in the ink composition, the nozzle plate surface of the ink jet recording apparatus is further difficult to wet with the ink composition, so that it is possible to prevent the ink droplets from flying and to improve the ejection stability.

  The polymer fine particles used in the present invention can be produced by a known emulsion polymerization method. For example, polymer fine particles can be obtained by emulsion polymerization of an unsaturated vinyl monomer (unsaturated vinyl monomer) in water containing a polymerization initiator and an emulsifier.

  Examples of the unsaturated vinyl monomer include acrylic acid ester monomers, methacrylic acid ester monomers, aromatic vinyl monomers, vinyl ester monomers, vinyl generally used in emulsion polymerization. Examples include cyanide monomers, halogenated monomers, olefin monomers, and diene monomers. Further, specific examples include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate. Acrylic acid esters such as octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, and glycidyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n- Hexyl methacrylate, 2- Methacrylic acid esters such as tilhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, and glycidyl methacrylate; vinyl esters such as vinyl acetate; vinyl such as acrylonitrile and methacrylonitrile Cyanogen compounds; halogenated monomers such as vinylidene chloride and vinyl chloride; aromatic vinyl monomers such as styrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylanisole, and vinylnaphthalene Olefins such as ethylene, propylene, and isopropylene; dienes such as butadiene and chloroprene; and vinyl Ethers, vinyl ketones, and vinyl monomers such as vinyl pyrrolidone.

  Examples of the unsaturated vinyl monomer having an ionic group include unsaturated vinyl monomers having an anionic group selected from a sulfonic acid group, a sulfinic acid group, a carboxyl group, a carbonyl group, and salts thereof. Specifically, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, sodium vinyl sulfonate, 2-sulfoethyl methacrylate, and 2-acrylamido-2-methylpropane sulfonic acid Etc. can be illustrated. Further, dimethylaminoethyl methyl chloride salt, dimethylaminoethyl benzyl methacrylate salt, methacryloyloxyethyltrimethylammonium chloride salt, diallyldimethylammonium chloride salt, 2-hydroxy-3-methacryloxypropyltrimethylammonium chloride salt, etc. An unsaturated vinyl monomer having a cationic group can also be exemplified.

  Furthermore, in addition to the above monomers, polymer fine particles produced using acrylamides or hydroxyl group-containing vinyl monomers are used in the ink composition, so that when this ink composition is used in an ink jet recording method, ink jet recording is performed. The ejection stability of the ink composition from the head can be improved. Examples of the acrylamides include acrylamide and N, N′-dimethylacrylamide. Examples of the hydroxyl group-containing vinyl monomer include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate. Use one or more of these. Can do.

  As described above, the polymer constituting the polymer fine particle is preferably a polymer having a structure in which the structural unit derived from the monomer is cross-linked by a cross-linkable monomer having two or more polymerizable double bonds. . Examples of the crosslinkable monomer having two or more polymerizable double bonds include polyethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, polypropylene glycol diacrylate, 2,2′-bis (4-acryloxypropyroxyphenyl) propane, and 2,2 Diacrylate compounds such as' -bis (4-acryloxydiethoxyphenyl) propane; Triacrelanes such as trimethylolpropane triacrylate, trimethylolethane triacrylate, and tetramethylolmethane triacrylate Compounds; tetraacrylate compounds such as ditrimethylol tetraacrylate, tetramethylolmethane tetraacrylate, and pentaerythritol tetraacrylate; hexaacrylate compounds such as dipentaerythritol hexaacrylate; ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, Polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, poly Butylene glycol dimethacryl And dimethacrylate compounds such as 2,2′-bis (4-methacryloxydiethoxyphenyl) propane; trimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate; methylenebisacrylamide; and divinyl Benzene is mentioned.

In addition, a polymerization initiator, an emulsifier, a surfactant, a molecular weight adjusting agent, a neutralizing agent, and the like used for emulsion polymerization of polymer fine particles can also be used in accordance with the above-described known methods. In particular, when the anionic polymerizable surfactant described above is used as an emulsifier, the anionic polymerizable surfactant is copolymerized with the monomer, so that there is no or little emulsifier in the liquid. Accordingly, since the foaming of the liquid is suppressed, the ejection stability of the ink composition used in combination with the encapsulated pigment of the present invention can be enhanced. In addition, when the same kind of anionic polymerizable surfactant used in the encapsulated pigment of the present invention is used as an emulsifier, the ink composition used in combination with the encapsulated pigment of the present invention has a dispersion stability and a storage stability. Is particularly excellent.
When the polymer fine particle is used in the ink composition of the present invention, the polymer fine particle can be used as a fine particle powder, but is preferably contained in the ink composition in the form of a polymer emulsion in which the polymer fine particle is dispersed in an aqueous medium. It is preferable to mix with other components. The amount of polymer fine particles contained in the ink composition is preferably about 0.01 to 10% by weight, more preferably about 0.01 to 5% by weight, based on the total weight of the ink composition.

[Other ink composition additives, etc.]
The ink composition of the present invention can contain a pH adjuster. When the pigment particle or polymer particle surface has an anionic group, the pH of the ink composition is preferably adjusted to 7 to 11, more preferably 8 to 9, and a basic compound is used as the pH adjuster. Is preferred. When the pigment particle or polymer particle surface has a cationic group, it is preferable to adjust the pH of the ink composition to 5 to 7, more preferably 6 to 7, and an acidic compound is used as the pH adjuster. It is preferable.

Specific preferred basic compounds as pH adjusters are sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, lithium carbonate, sodium phosphate, potassium phosphate, lithium phosphate. Alkali metal salts such as potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium oxalate, potassium oxalate, lithium oxalate, sodium borate, sodium tetraborate, potassium hydrogen phthalate, and potassium hydrogen tartrate; ammonia As well as methylamine, ethylamine, diethylamine, trimethylamine, triethylamine, tris (hydroxymethyl) aminomethane hydrochloride, triethanolamine, diethanolamine, diethylethanolamine, triisopropenolamine, butyrate Diethanolamine, morpholine, and the like amines such as propanolamine.
Among these, when an alkali hydroxide compound or an amine alcohol is added to the ink composition, the dispersion stability of the pigment particles having an anionic group in the ink can be improved.

In addition, for the purpose of mold prevention, antiseptic or rust prevention, benzoic acid, dichlorophen, hexachlorophene, sorbic acid, p-hydroxybenzoic acid ester, ethylenediaminetetraacetic acid (EDTA), sodium dehydroacetate, 1,2-benchazoline One or more compounds selected from -3-one [product name: Proxel XL (manufactured by Avicia)], 3,4-isothiazolin-3-one, 4,4-dimethyloxazolidine and the like in the ink composition of the present invention. Can be added.
In addition, at least one selected from the group consisting of urea, thiourea, and ethylene urea can be added to the ink composition of the present invention for the purpose of preventing the nozzles of the inkjet recording head from drying.

An example of a particularly preferred embodiment of the ink composition of the present invention is as follows:
(1) the encapsulated pigment,
(2) one or more compounds (penetrant) selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and 1,2-alkyldiol having 4 to 10 carbon atoms,
(4) glycerin, and (5) water,
Is an ink composition containing at least

Another example of a particularly preferred embodiment of the ink composition of the present invention is:
(1) the encapsulated pigment,
(2) one or more compounds (penetrant) selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and 1,2-alkyldiol having 4 to 10 carbon atoms,
(3) Acetylene glycol surfactant and / or acetylene alcohol surfactant,
(4) glycerin, and (5) water,
Is an ink composition containing at least

  In each of the above embodiments, when diethylene glycol monobutyl ether and / or triethylene glycol monobutyl ether of (2) is used as a penetrant, the amount added is 10% by weight or less based on the total weight of the ink composition. Is preferable, and it is more preferable that it is 0.5 to 5 weight%. By adding diethylene glycol monobutyl ether and / or triethylene glycol monobutyl ether to the ink composition, the penetrability of the ink composition into the recording medium can be improved, which helps to improve the print quality. Further, diethylene glycol monobutyl ether and / or triethylene glycol monobutyl ether also has an effect of improving the solubility of the acetylene glycol surfactant.

  In each of the above embodiments, the addition amount in the case of using the C2-C10 1,2-alkyldiol of (2) above as a penetrant is 15% by weight or less with respect to the total weight of the ink composition. Preferably there is. When a 1,2-alkyldiol having 3 or less carbon atoms is used, sufficient permeability of the ink composition to the recording medium cannot be obtained, and 1,2-alkyldiol having more than 15 carbon atoms dissolves in water. Since it becomes difficult, it is not preferable. If the amount of 1,2-alkyldiol in the ink composition exceeds 15% by weight, the viscosity of the ink composition tends to increase, such being undesirable. Specifically, 1,2-pentanediol or 1,2-hexanediol is preferably used as the 1,2-alkyldiol, and either one can be used alone or both can be used in combination. 1,2-pentanediol is preferably added in an amount of 3 to 15% by weight based on the total weight of the ink composition. By adding 3% by weight or more of 1,2-pentanediol to the ink composition, an ink composition having good permeability can be obtained. 1,2-Hexanediol is preferably added in a range of 0.5 to 10% by weight with respect to the total weight of the ink composition, and an ink composition having good permeability can be obtained in the above range.

  In addition, when the ink composition of each of the above embodiment examples is used in an ink jet recording method, the solid wetting agent is added to the total weight of the ink composition so that clogging of the ink jet nozzle is less likely to occur (improvement of clogging reliability). It is preferable to make it contain in 3 to 20 weight% with respect to. The addition of the solid humectant is not limited to the above embodiments, and can be added to the ink composition using the encapsulated pigment of the present invention.

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 saccharides, sugar alcohols, hyaluronate, trimethylolpropane, and 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. Sorbitol, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose and the like. Here, saccharide means saccharide in a broad sense, and is used to include substances that exist widely in nature, such as alginic acid, α-cyclodextrin, and cellulose. The derivatives of these saccharides are represented by reducing sugars of the saccharides (for example, sugar alcohol (general formula HOCH ₂ (CHOH) _n CH ₂ OH (where n represents an integer of 2 to 5)). ), Oxidized sugar (eg, aldonic acid, uronic acid, etc.), amino acid, thio sugar, etc.). Sugar alcohols are particularly preferred, 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. Particularly preferred solid wetting agents are trimethylolpropane, 1,2,6-hexatriol, sugars, and sugar alcohols. One or more solid wetting agents can be added to the ink composition of the present invention.

  By using a solid wetting agent in the ink composition, it is possible to suppress water evaporation of the ink by its water retention function, so that the viscosity of the ink composition does not increase around the ink flow path and the inkjet nozzle of the inkjet printer, Further, since the formation of a film due to water evaporation of the ink composition is less likely to occur, nozzle clogging is less likely to occur. In addition, since the solid wetting agent is chemically stable, the quality of the ink composition can be maintained over a long period of time without being decomposed in the ink composition. Even when the above-described solid wetting agent is added to the ink composition, the ink composition does not wet the nozzle plate, and the ink composition can be stably ejected from the inkjet nozzles. When the compound selected from trimethylolpropane, 1,2,6-hexanetriol, saccharides, and sugar alcohols is used as the solid moisturizing agent, the above-described effect is particularly excellent.

  The total amount of the solid wetting agent added to the ink composition of the present invention is preferably 3 to 20% by weight, and preferably 3 to 10% by weight, based on the total weight of the ink composition. More preferably. A preferred combination when two or more solid wetting agents are used in combination is selected from one or more selected from saccharides, sugar alcohols, and hyaluronates, trimethylolpropane, and 1,2,6-hexanetriol. A combination with one or more. When a solid wetting agent is added to the ink composition in this combination, an increase in the viscosity of the ink composition can be suppressed. By making the amount of the solid wetting agent contained in the ink composition 3% by weight or more, an effect of preventing clogging of the ink jet nozzle is obtained, and the amount of the solid wetting agent contained in the ink composition is 20% by weight. % Or less, the ink composition can be stably ejected from the ink jet nozzle, so that an ink composition having a sufficiently low viscosity can be obtained.

  In the latter embodiment, the acetylene glycol surfactant and / or acetylene alcohol surfactant (3) is added to the ink composition. The total amount of these surfactants is the same as that of the ink composition. It is preferable that it is 0.01 to 10 weight% with respect to the total weight, and it is especially preferable that it is 0.1 to 5 weight%.

  The ink compositions shown in the above embodiment examples are particularly excellent in pigment dispersion stability and ejection stability from an inkjet head nozzle when used in an inkjet recording method, and also clogged nozzles over a long period of time. And stable printing is possible. In addition, when the ink composition is printed on a recording medium such as plain paper, recycled paper, and coated paper, the drying property of the ink after printing is good, and there is no bleeding by using this ink composition. A high-quality image having a high printing density and excellent color developability can be obtained.

Although the present invention has been described above, there are the following differences between an ink composition prepared using the encapsulated pigment of the present invention and an ink composition prepared using a conventionally known pigment.
A pigment dispersion in which a pigment is dispersed using a dispersant such as a surfactant or a polymer dispersant, and penetration of the acetylene glycol surfactant and / or acetylene alcohol surfactant and diethylene glycol monobutyl ether The ink composition using the agent is easily ejected from the pigment surface due to the strong shearing force applied when ejected through a thin inkjet nozzle, resulting in deterioration of dispersibility, and unstable ejection. Tend to be. On the other hand, the ink composition obtained by the present invention does not show such a phenomenon at all, and can discharge the ink composition stably through an inkjet nozzle for a long period of time. Further, since the encapsulated pigment particles obtained by the present invention have good solvent resistance, it is difficult for the penetrating agent to detach the polymer of the capsule wall material from the surface of the pigment particles or to swell the polymer. The pigment particles can be stably dispersed in the ink composition over a long period of time.

  In addition, in a known ink composition that uses a pigment dispersion obtained by dispersing a pigment using a dispersant such as a surfactant or a polymer dispersant and has improved penetrability, the pigment is generally dispersed in the dispersion. Since not all of the dispersant is initially adsorbed on the pigment surface when dispersed in the medium, the viscosity of the ink composition tends to increase due to the dispersant dissolved in the pigment dispersion, As the time elapses, the dispersant is desorbed from the pigment, and the viscosity of the ink composition tends to increase due to the desorbed dispersant. For this reason, there are many cases where the content of the pigment contained in the pigment dispersion cannot be increased. When a pigment dispersion with a low pigment content is used, when the ink composition is used, especially when printing on plain paper or recycled paper, a sufficient print density cannot be obtained, and a good color development of the image can be obtained. In many cases, sex cannot be obtained. On the other hand, in the ink composition using the encapsulated pigment obtained according to the present invention, the viscosity of the ink composition is hardly increased over time. Therefore, the ink composition using the encapsulated pigment obtained according to the present invention has the advantages that it is easy to lower the viscosity and can contain more pigment particles, and uses plain paper or recycled paper as a printing medium. Even in such a case, a sufficiently high printing density can be obtained.

  Furthermore, since the encapsulated pigment obtained by the present invention has a true spherical shape, the fluidity of the ink composition using this pigment tends to be Newtonian. This is thought to be because the ionic groups on the surface of the encapsulated pigment are regularly and densely oriented toward the aqueous solvent side, and an effective electrostatic repulsive force is generated between the encapsulated pigments. Conceivable. For this reason, the ink composition using the encapsulated pigment obtained by the present invention is superior in ejection stability of the ink composition from the inkjet head in the inkjet recording method as compared with the conventional encapsulated pigment. Further, even if the amount of encapsulated pigment contained in the ink composition is increased, the dispersibility and dispersion stability of the pigment are excellent (high dispersibility). An image having a high printing density can be obtained by using the ink composition. The ink composition obtained by the present invention is particularly preferable as an ink composition for use in an ink jet recording method, but its application is not limited.

  Moreover, it is preferable that the ink composition prepared using the microencapsulated pigment of the present invention further comprises a compound represented by the following formula (1).

(In the formula, R ₁ and R ₂ each independently represent an alkyl group having 1 to 10 carbon atoms, m and n are respectively the number of repeating units, and m + n is 0 to 10 on average.)

In the compound of the above formula (1), R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms, m and n are respectively the number of repeating units, and m + n is 0 to 10 on average. However, there is less bleeding on plain paper and high color development, and on special paper it is possible to create ink that has fixability in addition to sufficient color development. In order to obtain a water-based ink composition capable of securing a sufficient line width, the carbon number of R ₁ + R ₂ is preferably 5 or more and 15 or less, and m + n is preferably in the range of 0 to 7.

  Further, the content of the compound in the ink composition comprising the compound of the formula (1) is preferably 0.1 to 20% by weight, more preferably 0.3% with respect to the total weight of the ink composition. -10% by weight. In order to obtain particularly good glossiness and image clarity, 0.5 to 10% by weight is preferable.

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.
[Example]

“Preparation of magenta pigment particle“ P1 ”having an anionic group on its surface”
20 g of isoindolinone pigment (CI Pigment Red 122) was mixed with 500 g of quinoline, and dispersed for 2 hours with Eiger Motor Mill M250 (Eiger Japan) under the conditions of a bead filling rate of 70% and a rotational speed of 5000 rpm. The dispersed mixture of the pigment paste and the 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 at 160 ° C. Next, 20 g of a sulfonated pyridine complex is added and reacted for 8 hours. After completion of the reaction, the mixture is washed several times with excess quinoline, poured into water, and filtered to obtain magenta pigment particles having hydrophilic groups (anionic groups) on the surface. “P1” was obtained.

“Preparation of magenta pigment particle“ P2 ”with anionic polymerizable surfactant adsorbed on the surface”
20 g of isoindolinone pigment (CI Pigment Red 122) was mixed with 2 g of anionic polymerizable surfactant Aqualon KH-10 and ion-exchanged water, and a bead filling rate of 70 with an Eiger Motor Mill M250 (manufactured by Eiger Japan). % And a rotational speed of 5000 rpm for 2 hours to obtain a dispersion of magenta pigment particles “P2” in which the target anionic polymerizable surfactant was adsorbed on the surface.

Production of microencapsulated pigment dispersions “M1” to “M3” “Production of microencapsulated pigment dispersion“ M1 ””
To an aqueous dispersion in which 100 g of magenta pigment particles “P1” having an anionic group on the surface are dispersed in 500 g of ion-exchanged water, 1.25 g of dimethylaminoethyl methacrylate methacrylate as a cationic polymerizable surfactant was added and mixed. Then, ultrasonic waves were irradiated for 15 minutes. Next, 4 g of lauryl methacrylate, 4 g of benzyl methacrylate, and 12 g of isobornyl methacrylate were added and mixed with stirring. 9.1 g of anionic polymerizable surfactant Aqualon KH-10 previously dissolved in 50 g of ion-exchanged water was then added. Then, 0.5 g of 2-acrylamido-2-methylpropanesulfonic acid was added as a hydrophilic monomer, and the mixture was again irradiated with ultrasonic waves for 30 minutes. To this, 60 g of 0.2 mol / l sodium sulfate aqueous solution was added, and ultrasonic waves were irradiated 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 the internal temperature of the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.4 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 1 mol / l aqueous potassium hydroxide solution. Subsequently, this was subjected to ultrafiltration by a cross flow method using an ultrafiltration device, and the target macroencapsulated pigment dispersion “M1” was obtained.

"Production of microencapsulated pigment dispersion" M2 ""
In the “production of microencapsulated pigment dispersion“ M1 ””, the same treatment method was used except that “0.2 mol / l sodium sulfate aqueous solution 60 g” was replaced with “0.4 mol / l sodium sulfate aqueous solution 60 g”. As a result, a microencapsulated pigment dispersion “M2” was obtained.

"Production of microencapsulated pigment dispersion" M3 ""
After adding 1.25 g of dimethylaminoethyl chloride methacrylate as a cationic polymerizable surfactant and mixing with 600 g of a dispersion of magenta pigment particles “P2” having an anionic polymerizable surfactant adsorbed on the surface, Ultrasound was irradiated for 15 minutes. Next, 4 g of lauryl methacrylate, 4 g of benzyl methacrylate, and 12 g of isobornyl methacrylate were added and mixed with stirring. 9.1 g of anionic polymerizable surfactant Aqualon KH-10 previously dissolved in 50 g of ion-exchanged water was then added. Then, 0.5 g of 2-acrylamido-2-methylpropanesulfonic acid was added as a hydrophilic monomer, and the mixture was again irradiated with ultrasonic waves for 30 minutes. To this, 60 g of 0.2 mol / l sodium sulfate aqueous solution was added, and ultrasonic waves were irradiated 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 the internal temperature of the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.4 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 1 mol / l aqueous potassium hydroxide solution. Next, this was subjected to ultrafiltration by a cross flow method using an ultrafiltration device, to obtain a target macroencapsulated pigment dispersion “M3”.
[Comparative example]

"Production of microencapsulated pigment dispersion" H1 ""
To an aqueous dispersion in which 100 g of magenta pigment particles “P1” having an anionic group on the surface are dispersed in 500 g of ion-exchanged water, 1.25 g of dimethylaminoethyl methacrylate methacrylate as a cationic polymerizable surfactant was added and mixed. Then, ultrasonic waves were irradiated for 15 minutes. Next, 4 g of lauryl methacrylate, 4 g of benzyl methacrylate, and 12 g of isobornyl methacrylate were added and mixed with stirring. 9.1 g of anionic polymerizable surfactant Aqualon KH-10 previously dissolved in 50 g of ion-exchanged water was then added. Then, 0.5 g of 2-acrylamido-2-methylpropanesulfonic acid was added as a hydrophilic monomer, and the mixture was again irradiated with ultrasonic waves 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 the internal temperature of the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.4 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 1 mol / l aqueous potassium hydroxide solution. Next, this was subjected to ultrafiltration by a cross flow method using an ultrafiltration device, and the intended single-layer macroencapsulated pigment dispersion “H1” was obtained.

"Production of microencapsulated pigment dispersion" H2 ""
After adding 1.25 g of dimethylaminoethyl chloride methacrylate as a cationic polymerizable surfactant and mixing with 600 g of a dispersion of magenta pigment particles “P2” having an anionic polymerizable surfactant adsorbed on the surface, Ultrasound was irradiated for 15 minutes. Next, 4 g of lauryl methacrylate, 4 g of benzyl methacrylate, and 12 g of isobornyl methacrylate were added and mixed with stirring. Then, 0.5 g of 2-acrylamido-2-methylpropanesulfonic acid was added as a hydrophilic monomer, and the mixture was again irradiated with ultrasonic waves 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 the internal temperature of the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.4 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 1 mol / l aqueous potassium hydroxide solution. Next, this was subjected to ultrafiltration by a cross flow method using an ultrafiltration device, and the target macroencapsulated pigment dispersion “H2” was obtained.

"Evaluation"
The volume average particle size (diameter) of the obtained dispersion was measured using a laser Doppler type particle size distribution analyzer Microtrac UPA150 manufactured by Leeds & Northrop.
As shown in Table 1, the film thickness growth amount from the particle base of the microencapsulated pigment particles of Examples 1 to 3 to which salt was added exceeded the results of Comparative Examples 1 and 2 to which no salt was added. It became.
In particular, Examples 1 and 2 to which a salt was added using magenta pigment particles having an anionic group on the surface showed a large film thickness growth amount.

The encapsulated pigment having an anionic group on the surface is dispersed in an aqueous solvent and coexists with the cationic hydrophilic monomer and / or the cationic polymerizable surfactant and the anionic polymerizable surfactant. It is a schematic diagram which shows the state which exists. FIG. 2 is a schematic diagram showing a state in which a cationic hydrophilic monomer and / or a cationic polymerizable surfactant and an anionic polymerizable surfactant are polymerized in the dispersed state shown in FIG. 1.

Explanation of symbols

  1 pigment particle, 2 cationic hydrophilic monomer and / or cationic polymerizable surfactant, 3 anionic polymerizable surfactant, 11 cationic group, 12, 12 ′ hydrophobic group, 13, 13 ′ polymerizable group , 14, 14 'anionic group, 60' polymer layer (polymer), 100 'encapsulated pigment

Claims (6)

  An encapsulated pigment having a charge on the surface of the pigment, wherein (1) the pigment particles are coated with a coating layer mainly composed of a polymer, and the polymer is at least (i) with respect to the charge on the pigment surface Repeating structural unit derived from ionic polymerizable surfactant A and / or ionic monomer having opposite charge, and (ii) ionic polymerizable surfactant having the same or opposite charge as the charge on the pigment surface An encapsulated pigment comprising repeating structural units derived from B, wherein (2) an electrolyte is used in producing the polymer.   The encapsulated pigment according to claim 1, wherein the electrolyte is an inorganic salt.   The encapsulated pigment according to claim 2, wherein the inorganic salt is sodium sulfate or sodium chloride.   An ink for inkjet recording, comprising the encapsulated pigment according to claim 3.   A method for producing an encapsulated pigment in which pigment particles having a charge on a surface thereof are coated with a coating layer mainly composed of a polymer, wherein at least (1) the pigment is charged into an aqueous dispersion of the pigment particles having a charge on the surface. Adding an ionic polymerizable surfactant A and / or an ionic monomer having a charge opposite to the charge on the particle surface; and (2) ionic polymerization having the same or opposite charge as the charge on the pigment particle surface. A method for producing an encapsulated pigment, comprising: a step of adding a surfactant B, (3) a step of adding an electrolyte, and (4) a step of adding a polymerization initiator to form a polymer. After micelles formed by adding a ionic polymerizable surfactant B having a charge the same as or opposite charge of the pigment particles the surface of the (2), to perform the step of adding an electrolyte of the (3) The method for producing an encapsulated pigment according to claim 5.