JP2008144098A - Aqueous pigment dispersion and ink composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion excellent in dispersion stability and heat resistance and having a small arithmetic-average particle size, and to provide an ink composition achieving stable ink discharge over a long period not only in a piezo-system but also in a thermal system for which ink storage stability at high temperatures is required, and imparting a printed matter with high optical density and high gloss. <P>SOLUTION: The aqueous pigment dispersion comprises (A) an azo-based yellow pigment PY74, (B) a pigment derivative obtained by introducing a sulfonic acid group into an azo-based yellow pigment which has a higher molecular weight than the azo-based yellow pigment PY74, (C) water, and (D) a water-soluble organic solvent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aqueous yellow pigment dispersion excellent in dispersion stability and heat resistance and an ink composition using the same. In particular, the present invention relates to a yellow ink composition used for a piezo ink jet printer or a thermal ink jet printer.

  In recent years, the use of pigments having excellent fastness instead of dyes as colorants used in inks for ink jet printers and inks for writing instruments has been studied. Ink jet ink ejection methods include a piezo method in which a piezoelectric element is deformed by applying a voltage to push out the ink, and a thermal method in which the ink is blown off by pressure generated during foaming by heating. In general, water is used as a solvent in ink jet inks, but pigments are insoluble in water unlike dyes. Therefore, it is important for ink jet inks using pigments to be stably dispersed in water in the form of fine particles. . In particular, in the thermal method, the ink is instantaneously exposed to a high temperature of 400 to 500 ° C. at the time of ejection, so that heat resistance at high temperature and dispersion stability of the pigment are required.

  As a method for stably dispersing pigment fine particles in water, a method using a polymer dispersant has been reported (see Patent Document 1). However, in this method, it is necessary to adsorb the polymer dispersant on the pigment particle surface. Therefore, it is effective for stabilizing the dispersion of inorganic pigments such as carbon black having a relatively large polarity, but is not so effective for stabilizing the dispersion of organic pigments having a small polarity on the particle surface.

  Moreover, the method of disperse | distributing an organic pigment stably in water by using an organic pigment sulfonic acid derivative is proposed (refer patent documents 2-4). In these methods, the organic pigment sulfonic acid derivative is strongly adsorbed on the surface of the organic pigment, and aggregation of the pigment is suppressed by the electrostatic repulsive force of the sulfonic acid derivative. In addition, by combining an organic pigment sulfonic acid derivative and a polymer dispersant having an amino group in the side chain, the organic pigment is submerged in water by firmly bonding the polymer dispersant to the organic pigment via the organic pigment sulfonic acid derivative. A method of stably dispersing has been proposed (see Patent Document 5).

  In the methods disclosed in Patent Documents 2 to 5, the organic pigment is used in combination with an organic pigment derivative in which a sulfonic acid group is introduced into the pigment and / or a pigment derivative in which a sulfonic acid group is introduced into the same type of pigment. used. For example, the quinacridone red pigment PR122 is used together with a pigment derivative in which a sulfonic acid group is introduced into PR122 and / or a pigment derivative in which a sulfonic acid group is introduced into another quinacridone pigment, such as a purple pigment PV19 or a red pigment PR209.

  However, in the methods shown in Patent Documents 2 to 4 using an organic pigment sulfonic acid derivative, good ejection stability from an inkjet nozzle, clogging resistance, storage stability, etc., in any of the piezo and thermal ejection methods. It has been pointed out that a complicated purification process using an ultrafiltration membrane, a semipermeable membrane, a reverse osmosis membrane or the like is necessary to obtain the above. Further, in the method disclosed in Patent Document 5 in which an organic pigment sulfonic acid derivative and a polymer dispersant having an amino group in the side chain are combined, a complicated purification process using an ultrafiltration membrane, a semipermeable membrane, a reverse osmosis membrane, or the like. However, there is a problem that the polymer dispersant tends to separate from the organic pigment sulfonic acid derivative at a high temperature, which makes it difficult to discharge by a thermal method.

In a color ink jet printer, normally, four colors of ink, cyan, magenta, and yellow, which are three primary colors of black ink and subtractive color mixture, are used. As a yellow pigment for yellow ink, an azo yellow pigment PY74 is generally used because of good color development. As a method for improving the jetting stability and storage stability of a yellow recording liquid using an azo yellow pigment, a method of introducing a sulfonic acid group to the surface of the azo yellow pigment to make it hydrophilic has been proposed (Patent Literature). 6). When this method is applied to PY74, there is a problem that sulfonic acid groups are peeled off from the pigment surface at a high temperature and the dispersion state becomes unstable, making it difficult to discharge by the thermal method.
Japanese Patent Laid-Open No. 5-179183 (page 4) JP 2002-121419 A (pages 2 and 8) JP 2002-285067 A (2nd page, 8th page) JP 2002-309122 A (2nd page, 5th page) JP 2005-2186 A (pages 4 and 10) JP 2000-265094 A (3rd page, 15th page)

  An object of the present invention is to provide an aqueous yellow pigment dispersion in which the dispersion stability and heat resistance of a finely divided organic pigment are compatible. Further, not only the piezo method but also the storage stability of ink at high temperatures is required. An object of the present invention is to provide an ink composition that can realize stable ink ejection over a long period of time even in the thermal method.

  That is, the present invention includes (A) an azo yellow pigment PY74, (B) a pigment derivative in which a sulfonic acid group is introduced into an azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74, (C) water, (D ) An aqueous yellow pigment dispersion containing a water-soluble organic solvent.

  According to the present invention, it is possible to supply an aqueous yellow pigment dispersion that is excellent in dispersion stability of a finely divided yellow organic pigment and that is excellent in heat resistance at high temperatures. In addition, the ink composition produced using the aqueous yellow pigment dispersion of the present invention is excellent in heat resistance, so that it is stable not only in the piezo method but also in the thermal method requiring storage stability of the ink at a high temperature. In addition, the ink composition of the present invention has a high optical density in a printed state and is glossy because pigment particles are present in a finer state.

  In the present invention, an azo yellow pigment PY74 is used as the yellow pigment. Inkjet color drawing is generally performed by subtractive color mixing, and therefore, three color inks of cyan, magenta, and yellow are essential as color inks. The azo-based yellow pigment PY74 is preferred as a pigment for yellow ink because it is commercially available in large quantities and can be obtained at a relatively low cost, and has an excellent color tone and a wide color reproduction range.

  In order to stabilize the dispersion of the azo yellow pigment PY74, a method of introducing a sulfonic acid group into the surface and making it hydrophilic as described in Patent Document 6 is effective. However, since the sulfonated derivative of PY74 has high solubility in water at high temperature, the sulfonic acid group is peeled off from the pigment surface at high temperature, and the dispersion state of PY74 becomes unstable. For this reason, although thermal ejection is difficult, the present invention allows adsorption to the surface of PY74 by using a sulfonated derivative of an azo yellow pigment having a chemical structure similar to PY74 and having a molecular weight larger than that of PY74. In addition, the dispersion state of the pigment can be kept good even at high temperatures, and the thermal injection can be stabilized. It is presumed that when the molecular weight is larger than that of PY74, the hydrophobicity is increased and the water resistance is improved.

  Examples of the azo yellow pigment having a molecular weight larger than that of PY74 used in the present invention include PY12, PY13, PY14, PY17, PY55, PY81, PY83, PY97, PY101, PY120 and the like. PY97 is particularly preferred because of its high properties and good water resistance at high temperatures.

  The pigment derivative in which a sulfonic acid group is introduced into an azo yellow pigment having a molecular weight larger than that of (B) the azo yellow pigment PY74 used in the present invention is synthesized, for example, by the following method. An azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74 is added to concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or a mixture thereof to perform a sulfonation reaction. The resulting reaction solution is diluted with water and optionally neutralized with a metal alkali aqueous solution or an amine or an aqueous solution thereof. The suspension thus obtained is filtered, washed with an aqueous washing solution, and dried.

  When neutralization is performed in the above synthesis process, a metal alkali aqueous solution or an amine or an aqueous solution thereof is used, but an amine or an aqueous solution thereof is preferably used. If the ink composition contains a metal alkali, the metal alkali component remains on the substrate even after the ink droplets are attached to the substrate and the solvent is volatilized. In this case, when the substrate is again wetted with water, the hydrophilicity of the portion where the remaining metal alkali component is colored may be increased and bleeding may easily occur. On the other hand, since amine is easily volatilized, there is little risk of such bleeding.

  As the aqueous amine solution used for neutralization, an aqueous solution of ammonia, monoethanolamine, triethanolamine, tetramethylammonium hydroxide, or the like can be used. In the present invention, various amine aqueous solutions can be used without being particularly limited to these, but the use of ammonia is preferred because of its ease of volatilization.

  In the present invention, the mixing ratio of (A) the azo yellow pigment PY74, (B) the azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74, and the pigment derivative having a sulfonic acid group introduced is PY74 in weight ratio. : A pigment derivative in which a sulfonic acid group is introduced into an azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74 = 50 to 99:50 to 1, preferably 60 to 97:40 to 3, more preferably 70 to 95. : Mixed at 30-5. If the amount of the pigment derivative is too small, the pigment dispersion stabilizing effect cannot be exhibited. Conversely, if the amount of the pigmented derivative is too large, the color tone may change unfavorably.

  In the present invention, (A) the azo yellow pigment PY74 and (B) the azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74, the solid content of the pigment derivative in which the sulfonic acid group is introduced to the entire pigment dispersion. Is 4 to 20% by weight, preferably 8 to 16% by weight. If the concentration is too low, the production efficiency of the dispersion is low and the production cost is increased. On the other hand, if the concentration is too high, it becomes difficult to stabilize the dispersion state.

  In the present invention, the surface tension of the aqueous pigment dispersion at 25 ° C. is 60 mN / m or less, preferably 50 mN / m or less. When the surface tension is greater than 60 mN / m, the wetness of the pigment and the pigment derivative to water is poor, so that coarse particles tend to remain. On the other hand, if the surface tension is greater than 50 mN / m, it is difficult to uniformly transmit the dispersion energy of the disperser to the pigment particles. This makes it difficult to obtain a pigment dispersion having a uniform pigment particle size, resulting in poor ink ejection characteristics. The surface tension of the aqueous pigment dispersion at 25 ° C. is preferably 25 mN / m or more. If the surface tension of the aqueous pigment dispersion is too small, the surface tension of the ink composition is also reduced, so that the penetrability of the ink into the paper is increased, which may cause bleeding.

  Examples of the method for adjusting the surface tension of the aqueous pigment dispersion of the present invention include a method of adding a water-soluble organic solvent, a surfactant, a polymer dispersant, etc., and the storage stability of the pigment in the pigment dispersion. In view of the properties and heat resistance of the pigment dispersion, it is preferable to add a water-soluble organic solvent.

  The water-soluble organic solvent (D) used in the present invention is desired to have a relative dielectric constant of 5 or more, preferably 10 or more, more preferably 15 or more. If the non-dielectric constant of the water-soluble organic solvent to be used is too small, the relative dielectric constant of the aqueous pigment dispersion is also small, so that the electrostatic repulsion between the pigment particles becomes weak and the dispersion stability is lowered.

  Examples of water-soluble organic solvents that satisfy the above ranges include ethers, alcohols, ether alcohols, esters, ketones, acids, amines, acid amides, and the like. For example, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, glycerin, γ-butyrolactone, N-methyl-2-pyrrolidone, dimethyl sulfoxide, ethylene carbonate, carbonic acid Propylene or the like can be used.

  In the present invention, the mixing ratio of water and the water-soluble organic solvent is a weight ratio of water: water-soluble organic solvent = 95-50: 5-50, preferably 90-60: 10-40. If the mixing ratio of the water-soluble organic solvent is too small, it is difficult to adjust the surface tension to 60 mN / m or less. Conversely, if the mixing ratio is too large, the dispersion stability may be lowered.

  In the aqueous pigment dispersion of the present invention, (A) the azo yellow pigment PY74 and (B) the solid content concentration of the pigment derivative in which the sulfonic acid group is introduced into the azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74 The sulfate ion concentration when is 4% by weight is 50 ppm or less, preferably 20 ppm or less, more preferably 10 ppm or less. If the sulfate ion concentration is higher than 50 ppm, the dispersion state of the pigment dispersion may become unstable, and if the sulfate ion concentration is higher than 20 ppm, the heat resistance of the pigment dispersion may deteriorate. The lower limit of the sulfate ion concentration is preferably 0.1 ppm. For example, if the sulfate ion concentration is to be made smaller than 0.1 ppm by dialysis, the number of times dialysis is repeated increases so much that the dialysis membrane is clogged.

  In the aqueous pigment dispersion of the present invention, the sulfate ion concentration increases in proportion to the solid content concentration. Therefore, when the solid content of the aqueous pigment dispersion is less than 4% by weight, the sulfate ion concentration can be calculated in terms of conversion. For example, when the solid content concentration of the aqueous pigment dispersion is 1% by weight, the sulfate ion concentration at 4% by weight can be calculated by multiplying the value obtained by measurement four times.

  When the solid content of the aqueous pigment dispersion is more than 4% by weight, the aqueous pigment dispersion is diluted with ion-exchanged water so that the solid content becomes 4% by weight and the sulfate ion concentration is measured.

  In order to reduce the sulfate ion concentration in the aqueous pigment dispersion, the raw material (A) azo yellow pigment PY74 and (B) azo yellow pigment yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74 are used. It is preferable that the sulfate ion concentration contained in each of the pigment derivative into which the sulfonic acid group is introduced, (C) water, and (D) the water-soluble organic solvent is low.

  As (C) water used by this invention, what does not contain sulfate ions, such as ion-exchange water and distilled water, can be used, for example.

  As the (A) azo yellow pigment PY74 used in the present invention, it is preferable to use a material in which sulfate ions are sufficiently washed by washing with ion-exchanged water or distilled water, for example. Since organic pigments usually have a low affinity with water, sulfate ions can be easily removed by a known method such as water filtration. Moreover, organic impurities can be simultaneously removed together with sulfate ions by washing with methanol.

  In the pigment derivative in which a sulfonic acid group is introduced into an azo yellow pigment having a molecular weight larger than that of the (B) azo yellow pigment PY74 used in the present invention, a large amount of sulfate ions as a raw material is usually mixed after the sulfonation reaction. . In order to remove sulfate ions from the pigment derivative, a technique of dialysis or ion exchange can be mentioned. In particular, dialysis is effective without increasing the viscosity of the slurry by removing water and sulfate ions through a dialysis membrane from the slurry of pigment derivative, water and sulfate ions, and adding the same amount of ion-exchanged water as the amount removed. It is possible to remove sulfate ions. In order to efficiently remove sulfate ions, it is preferable to use a hollow fiber membrane having a large dialysis effective area. As a material of the hollow fiber membrane, polysulfone, polymethyl methacrylate, polyacrylonitrile, or the like can be used.

  In the present invention, the pH of the aqueous pigment dispersion is desirably in the range of 2 to 8, preferably 3 to 7. When the pH of water is too high, the pigment derivative having a sulfonic acid group introduced into the pigment molecule has a high affinity for water and the possibility of peeling off from the pigment surface increases. On the other hand, if the pH is too low, it is difficult to bring the ink composition produced by diluting the aqueous pigment dispersion into an appropriate pH range.

  The aqueous pigment dispersion of the present invention applies shear stress to coarse pigment particles (usually 1 to 50 μm) that are aggregates of a large number of primary particles in water, and the coarse pigment particles are converted into primary particles or a small number of primary particles. It can be produced by making fine particles dispersed in the aggregate. As a disperser for applying a shear stress to coarse particles in water, a method using a sand mill, a ball mill, a bead mill, a three roll mill, an attritor or the like is preferably employed. In order to refine the coarse particles to primary particles or an aggregate of a small number of primary particles, it is preferable to apply a shear stress by a dispersion medium. Examples of the dispersion medium include zirconia beads, alumina beads, glass beads, and the like, and it is particularly preferable to use zirconia beads for efficient miniaturization.

The degree of dispersion stabilization of the yellow pigment dispersion of the present invention is also affected by the dispersion conditions when the coarse particles of the pigment are refined. The dispersion stability of the pigment dispersion may be lowered unless an appropriate size of shear stress is applied to the coarse pigment particles. That is, the azo yellow pigment PY74 is characterized by having a very large specific surface area as compared with a copper phthalocyanine pigment, a quinacridone pigment, etc. (when the average primary particle size is 50 nm, the specific surface area is 100 m ² / g or more). For this reason, if the shear stress when finely dispersing and dispersing coarse particles of the pigment is too large, the specific surface area of the pigment increases rapidly, and the azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74 has sulfonic acid groups. In some cases, pigment PY74 particles may be formed in which the introduced pigment derivative is not sufficiently adsorbed. Pigment PY74 particles in which the pigment derivative is not sufficiently adsorbed have a weak electrostatic repulsive force, and aggregation may occur between the pigment particles starting from this particle.

  As the dispersion conditions, the shear stress can be adjusted to an appropriate size by appropriately controlling the bead diameter of the zirconia beads, the peripheral speed of the disperser, and the coarse particles of the pigment can be efficiently refined. . The bead diameter of the zirconia beads used for dispersion is preferably in the range of 0.3 to 0.01 mmφ, more preferably 0.2 to 0.02 mmφ. If the bead diameter is larger than 0.3 mmφ, the shear stress applied to the pigment may be too large, which may reduce the dispersion stability of the pigment dispersion. If the zirconia bead diameter is larger than 0.2 mmφ, the pigment dispersion The heat resistance of the liquid may decrease. On the other hand, if the diameter of the zirconia beads is smaller than 0.01 mmφ, it is difficult to remove the zirconia beads from the pigment dispersion. If the diameter of the zirconia beads is smaller than 0.02 mmφ, the shear stress applied to the pigment is too small. In addition, coarse particles may remain in the pigment dispersion.

  In the pigment dispersion when the azo yellow pigment PY74 is used as in the present invention, the peripheral speed of the disperser is preferably in the range of 6 to 13 m / s. If the peripheral speed of the disperser is greater than 13 m / s, the shearing stress applied to the pigment may be too large, and the dispersion stability of the azo yellow pigment PY74 dispersion may be reduced. If it is less than 6 m / s, the shear stress applied to the pigment is too small, so that coarse particles may remain in the yellow pigment PY74 dispersion.

  The aqueous pigment dispersion of the present invention may contain a polymer in order to improve the fixability of the pigment ink to paper. The polymer can contain a water-soluble polymer that dissolves in water and / or a water-dispersible polymer that does not dissolve in water. Specific examples of the polymer include polyester, polyurethane, and polyphenol. It is done. Polyurethane is preferably used because of its excellent fixability to paper, and it is particularly preferable to use polyurethane modified with carboxylic acid among the polyurethanes because the thermal discharge characteristics of the pigment ink are good.

  Normally, polyurethane is produced by an addition reaction between a compound containing an isocyanate group and a compound containing an active hydrogen such as a hydroxyl group. In order to obtain a polyurethane modified with a carboxylic acid, for example, a diol containing a carboxyl group is preferably used as the compound containing active hydrogen.

  The acid value of the polyurethane used in the present invention is preferably 50 to 130 KOH · mg / g. If the acid value of the polyurethane is less than 50 KOH · mg / g, the heat resistance of the aqueous pigment dispersion containing polyurethane may be poor. On the other hand, if the acid value of the polyurethane is larger than 130 KOH · mg / g, the water resistance of the print obtained from the ink composition containing polyurethane may be poor. The acid value of the polyurethane can be controlled, for example, by changing the content in the polyurethane of a compound containing a carboxyl group and a hydroxyl group used as a component of the polyurethane.

  The acid value of polyurethane means the number of milligrams of potassium hydroxide required to neutralize 1 g of polyurethane. In the present invention, the acid value of the polyurethane is measured as follows. An aqueous hydrochloric acid solution or the like is dropped onto the polyurethane to precipitate the polyurethane, and then the supernatant is filtered and the polyurethane is sufficiently washed with ion-exchanged water. Thereafter, the neutralizing agent, hydrochloric acid, water and the like are completely removed from the polyurethane by drying at a temperature of 100 ° C. or higher for several hours, and then the polyurethane is dissolved in ethanol at a concentration of 10% by weight or less. When polyurethane does not completely dissolve in ethanol, a water-soluble organic solvent such as methyl ethyl ketone is added and dissolved. In this way, a sample for measuring the acid value of polyurethane is prepared. Based on JIS standard K0070 (1992), after adding several drops of phenolphthalein solution to this polyurethane solution, titration is performed using a 0.1 mol / l potassium hydroxide solution to calculate the acid value of the polyurethane. .

  The water-soluble polymer that is soluble in water and / or the water-dispersible polymer that is not soluble in water used in the present invention preferably has a weight average molecular weight in the range of 10,000 to 180,000, more preferably 13,000 to 150,000. A water-soluble polymer that is soluble in water and / or a water-dispersible polymer that is not soluble in water and has a weight average molecular weight of less than 10,000. In some cases, the fixability of a print obtained from an ink composition containing a toner to paper is lowered. On the other hand, when the weight average molecular weight of the water-soluble polymer that dissolves in water and / or the water-dispersible polymer that does not dissolve in water is greater than 180,000, the water-soluble polymer that dissolves in water and / or the water dispersibility that does not dissolve in water. In some cases, the viscosity of the ink composition containing the polymer increases undesirably, resulting in poor thermal discharge characteristics. The molecular weight of the water-soluble polymer that is soluble in water and / or the water-dispersible polymer that is not soluble in water is, for example, the synthesis conditions of the water-soluble polymer that is soluble in water and / or the water-dispersible polymer that is not soluble in water ( The reaction temperature, reaction time, etc. can be controlled. In the present invention, the molecular weight of a water-soluble polymer that dissolves in water and / or a water-dispersible polymer that does not dissolve in water can be determined, for example, in terms of polystyrene using gel permeation chromatography.

  In the present invention, when a water-soluble polymer that is soluble in water and / or a water-dispersible polymer that is not soluble in water is used, (A) yellow pigment PY74 and (B) azo-based yellow pigment PY74 have a larger molecular weight. A colored component obtained by combining a pigment derivative in which a sulfonic acid group is introduced into an azo yellow pigment and a water-soluble polymer that is soluble in water and / or a water-dispersible polymer that is not soluble in water are colored components: water by weight ratio. The water-soluble polymer that dissolves in water and / or the water-dispersible polymer that does not dissolve in water = 30 to 90:70 to 10, preferably 40 to 80:60 to 20. If the amount of the water-soluble polymer that dissolves in water and / or the water-dispersible polymer that does not dissolve in water is too small, the effect of improving the adhesive force cannot be expected. Conversely, if the amount of the water-soluble polymer that dissolves in water and / or the water-dispersible polymer that does not dissolve in water is too large, the coloring power of the print obtained from the ink composition is lowered. The timing of mixing the pigment with the water-soluble polymer that dissolves in water and / or the water-dispersible polymer that does not dissolve in water can be any of before the coarse particles of the pigment are finely dispersed, during dispersion, and after dispersion. Good.

The dispersion stability of the aqueous pigment dispersion of the present invention can be evaluated by measuring the Casson yield value of the pigment dispersion. The smaller the Casson yield value, the less agglomeration of particles in the particle dispersion. In the present invention, the Casson yield value of the pigment dispersion is preferably 1 × 10 ⁻³ Pa or less.

  The heat resistance of the aqueous pigment dispersion of the present invention can be evaluated by the following method, for example. Treat at 65 ° C. for 30 days and measure the rate of change in viscosity before and after treatment. The smaller the rate of change in viscosity before and after the treatment, the better the heat resistance, and the rate of change in viscosity is preferably 50% or less, more preferably 10% or less.

  The pigment in the aqueous pigment dispersion of the present invention has a volume-based arithmetic average diameter of 5 to 150 nm, preferably 10 to 100 nm. When the volume-based arithmetic average diameter of the pigment is larger than 150 nm, there is a high possibility of causing clogging in the inkjet nozzle. On the other hand, when the volume-based arithmetic average diameter of the pigment is larger than 100 nm, the glossiness of the printed matter is lowered. If the volume-based arithmetic average diameter is small, it is preferable because a glossy printed matter having a high optical density is obtained, but if the volume-based arithmetic average diameter is too small, the specific surface area of the particles becomes too large, and the pigment in the ink composition There is a tendency to easily aggregate.

  Next, an ink composition using the aqueous pigment dispersion of the present invention will be described. As described above, an ink composition is obtained by diluting the obtained aqueous pigment dispersion with water and adding the following additives.

  The ink composition of the present invention may contain a water-soluble organic solvent for the purpose of preventing drying of the ink composition at the ink jet nozzle portion and improving the paintability and penetrability of the ink composition. Examples of organic solvents used for such purposes include glycol ethers such as diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, glycerin and the like. In addition to aprotic polar solvents such as polyhydric alcohols, γ-butyrolactone, N-methyl-2-pyrrolidone, dimethyl sulfoxide, acetylene glycols, acetylene alcohols, alkylene glycols and the like can be mentioned. The amount of these water-soluble organic solvents is usually suppressed to 50% by weight or less with respect to the total solvent of the ink. When the water-soluble organic solvent is contained in an amount exceeding 50% by weight, the dispersion state of the pigment may be destabilized.

  A preservative can be added to the ink composition of the present invention for the purpose of preventing the entry of mold and bacteria. Zinc pyridinethion-1-oxide, 1,2-benzisothiazolin-3-one, amine salt of 1-benzisothiazolin-3-one, and the like can be suitably used. These are usually contained in the ink composition in an amount of 0.05 to 1% by weight. If these addition amounts are small, the effect of preventing the mixing of molds and bacteria cannot be exhibited, and if the addition amount is too large, the dispersion state of the pigment may be destabilized.

  The pH of the ink composition of the present invention is desirably in the range of 5 to 10, preferably 6 to 9. If it is in this range, it can be used safely even if it comes into contact with the human body. The pH of the ink composition can be appropriately adjusted using a pH adjusting agent such as ammonia or organic amine or a buffer solution such as phosphoric acid.

  When the ink composition of the present invention is used as an ink for a piezo-type ink jet printer, anionic, cationic, nonionic, and amphoteric surfactants are used to adjust the surface tension and improve the permeability to the substrate. An antifoaming agent can be added to prevent the generation of bubbles.

  When the ink composition of the present invention is used for an ink jet printer, the viscosity of the ink composition is 10 mPa · s or less, preferably 5 mPa · s or less. If the viscosity is high, it will be difficult to generate ink droplets of an appropriate size and skip them.

  The optical density of the printed matter obtained from the ink composition of the present invention can be measured, for example, with an optical densitometer. It is desired that the optical density of the printed material is 1.8 or more, preferably 1.9 or more. If the optical density is too small, the coloring power of the printed matter is reduced, making it difficult to obtain a good printed matter.

  The glossiness of the printed matter obtained from the ink composition of the present invention can be measured by, for example, a gloss meter. The glossiness is desired to be 45 or more, preferably 60 or more. If the gloss is too small, it is difficult to obtain a printed material with a smooth surface and gloss.

  Since the ink composition of the present invention is excellent in heat resistance, stable ink ejection can be realized over a long period of time not only in a piezo ink jet printer but also in a thermal ink jet printer. An image drawn on a substrate using this ink composition is excellent in ozone resistance and hardly discolored. In addition, since the pigment particles are present in a miniaturized state, it is possible to obtain a printed material with a smooth surface and gloss. The ink composition of the present invention can be used as an inkjet ink composition in the field of color printing such as an inkjet printer.

  Hereinafter, although this invention is demonstrated in more detail using a preferable embodiment, the efficacy of this invention is not restrict | limited at all by the embodiment used. The pigment derivatives, pigment dispersions and ink compositions in the examples were evaluated by the following methods.

<Measurement method>
A. Mass analysis of pigment derivatives with sulfonic acid group introduction Using m-nitrobenzyl alcohol as a matrix, negative ion measurement of pigment derivatives was performed using a fast atom bombardment ionization mass spectrometer (JMS-SX102A manufactured by JEOL Ltd.). It was. Measurement is performed in the range of 10 to 2000 in terms of the ratio (m / z) of the mass (m) and charge (z) of ions generated by ionization, and introduction of sulfonic acid groups into the pigment derivative from the obtained m / z strength. It was confirmed.

B. Measurement of surface tension of pigment dispersion Using surface tension measuring instrument (A-06, manufactured by Yamamoto Kakin Tester Co., Ltd.), using A-06-P01 as a platinum ring, The surface tension was measured by a ring method. The pigment dispersion whose temperature was adjusted to 25 ° C. was immersed in a petri dish, and the petri dish was placed on the stage of a surface tension measuring device. Next, the surface of the pigment dispersion was brought into contact with the platinum ring by slowly lifting the stage. The surface tension was determined by slowly pulling the platinum ring vertically and measuring the force required to pull the platinum ring away from the surface of the pigment dispersion.

C. Viscosity measurement of pigment dispersion The viscosity of the pigment dispersion and the ink composition at 25 ° C. was measured using a cone-plate viscometer (RE100L manufactured by Toki Sangyo Co., Ltd.).

D. Measurement of Yield Value of Pigment Dispersion Using a cone-and-plate viscometer (RE100L manufactured by Toki Sangyo Co., Ltd.), the viscosity at three different shear rates was measured and determined by using the Casson equation. The storage stability of the pigment dispersion was evaluated from the obtained yield value.

E. Heat resistance of pigment dispersion The pigment dispersion was subjected to a heat treatment at 65 ° C. for 30 days, and the viscosity before and after the heat treatment was compared to obtain an index of the heat resistance of the pigment dispersion.

F. Measurement of the particle size of pigment particles in the pigment dispersion The pigment dispersion is treated with ion-exchanged water so that the concentration of colored solids composed of the pigment and the pigment derivative in which the sulfonic acid group is introduced into the pigment is 0.1 wt% in total. After dilution, the volume-based arithmetic average diameter of the pigment particles was determined using a dynamic light scattering particle size distribution analyzer (LB-500 manufactured by Horiba, Ltd.).

G. Evaluation of ejection stability during printing using the ink composition The ink composition is packed in an ink cartridge of a thermal ink jet printer ("Pixus" (trade name) 550i manufactured by Canon Inc.) and arranged three times for 5 hours from the ink jet nozzle. Printing was performed on continuous plain paper ("White Recycled Paper" (trade name) EW-500 manufactured by Canon Inc.), and the following evaluation was performed. If all three units are not smeared after 5 hours ◎ If one or more inks are smeared after 5 hours, but if the smearing is improved by cleaning the inkjet nozzles ○ If one or more units are inks after 5 hours The case where there was faintness and the fainting did not improve even after cleaning was marked as x.

  The ink composition was packed in an ink cartridge of a piezo-type inkjet printer (“Calario” (trade name) PX-G920, manufactured by Seiko Epson Corporation), and three units were arranged side by side on a regular paper (made by Canon Inc.) Printing was performed on “white recycled paper” (trade name) EW-500, and the following evaluation was performed. If all three units are not smeared after 5 hours ◎ If one or more inks are smeared after 5 hours, but if the smearing is improved by cleaning the inkjet nozzles ○ If one or more units are inks after 5 hours The case where there was faintness and the fainting did not improve even after cleaning was marked as x.

H. Evaluation of optical density of a print obtained from an ink composition when applied to a printed material and printing The ink composition is recorded in an ink cartridge of a thermal inkjet printer ("Pixus" (trade name) 550i manufactured by Canon Inc.) and recorded. Printing was performed on a medium ("Super Photo Paper" (trade name) SP-101 manufactured by Canon Inc.) to obtain a solid image of 5 cm x 5 cm. The ink composition is packed in an ink cartridge of a piezo-type inkjet printer (“Calario” (trade name) PX-G920 manufactured by Seiko Epson Corporation), and a recording medium (trade name: photo glossy paper manufactured by Seiko Epson Corporation). A 5 cm × 5 cm solid image was obtained. The optical density of the obtained solid image portion was measured using an optical densitometer (SPECTROEYE, manufactured by GRETAG) at a light source D50 and a viewing angle of 2 degrees.

I. Evaluation of fixability to paper of print obtained from ink composition when applied and printed on printed matter After leaving solid image obtained on glossy paper at room temperature for 24 hours, cellophane tape with a width of 15 mm (LP manufactured by Nichiban Co., Ltd.) -15 (trade name)) was pasted on the image over a length of 30 mm. After 1 minute, one corner of the cellophane tape was held with a finger, and the cellophane tape was peeled off for 1 second perpendicular to the solid image. The cellophane tape after the peel test of the printed material was attached to glossy paper, and the optical density was measured with an optical densitometer (SPECTROEYE, manufactured by GRETAG) at a light source D50 and a viewing angle of 2 degrees. In addition, when the cellophane tape with a width of 15 mm was pasted on glossy paper and measured using a light densitometer (SPECTROEYE, manufactured by GRETAG) with a light source D50 and a viewing angle of 2 degrees, the optical density was 0.1. .

J. et al. Evaluation of Glossiness of Prints Obtained from Ink Composition when Applied to Printed Material and Printing Using a gloss meter (GM-3D, manufactured by Murakami Color Research Laboratory Co., Ltd.), the glossiness of the obtained solid image portion , Measured at a measurement angle of 45 degrees.

Example 1
60 g of PY97 (“Novoperm” (trade name) Yellow FGL, manufactured by Clariant) was added to 780 g of concentrated sulfuric acid having a concentration of 90 wt% while stirring at 10 ° C. After stirring for 3 hours, the mixture was poured into 1500 g of ice water. After standing for 30 minutes, the resulting suspension was filtered, and the resulting product was washed with 300 ml of pure water. The product was charged into 2000 ml of pure water, neutralized by adding an aqueous ammonia solution until the pH reached 7 or higher, and then filtered. The obtained wet crystals were washed with pure water and then dried at 80 ° C. Operations obtained by drying, washing with pure water, filtering, and drying were repeated 10 times to obtain 61 g of a PY97 sulfonic acid group-containing derivative. As a result of mass spectrometry, a peak of m / z = 669 was observed, and it was confirmed that 1 mol of a sulfonic acid group was added to PY97.

  A PY97 sulfonic acid group-containing derivative and ion-exchanged water were mixed to prepare a slurry containing sulfate ions. The prepared slurry was dialyzed using a PMMA dialysis module ("Filtizer" (trade name) B3-20A manufactured by Toray Industries, Inc.) to obtain a PY97 sulfonic acid group-containing derivative dialyzate.

  200 g of PY74 (Yellow Seika Chemical Co., Ltd. Yellow No. 46) was put into 5000 ml of methanol, stirred at room temperature for 4 hours, filtered, and dried at 60 ° C. to obtain 160 g of methanol-washed PY74. 80 g of methanol-washed PY74 and 20 g of PY97 sulfonic acid group-containing derivative dialyzate were mixed with 750 g of ion-exchanged water together with 150 g of triethylene glycol monobutyl ether, and stirred with a homodisper to prepare a slurry. An aqueous pigment dispersion (PY74) is obtained by connecting the slurry with a circulating bead mill dispersing machine (“Ultra Apex Mill” (trade name) UAM-015, manufactured by Kotobuki Industries Co., Ltd.) filled with zirconia beads and a tube, and carrying out a dispersion treatment. And PY97 sulfonic acid group-containing derivative were combined to obtain a coloring component concentration: 10% by weight). Dispersion treatment conditions were as follows: zirconia bead diameter: 0.03 mmφ, zirconia bead input amount: 400 g, peripheral speed of circulating bead mill disperser was 10 m / s, and pre-dispersed slurry was sheared using a circulating bead mill disperser The time for applying the stress was 2 hours.

  To 40 g of the obtained aqueous pigment dispersion, 48 g of ion-exchanged water, 9.6 g of glycerin, 1.44 g of 1,2-hexanediol, 0.8 g of ethylene glycol, and 0.16 g of triethanolamine were added, and an ink composition (PY74 and A coloring component concentration combining the PY74 sulfonic acid group-containing derivative: 4% by weight) was prepared, and ejection stability, optical density, paper fixing property, and glossiness were evaluated. The evaluation results are shown in Table 2.

Comparative Example 1
A PY74 sulfonic acid group-containing derivative was obtained in the same manner as in Example 1 except that PY74 was used instead of PY97. As a result of mass spectrometry, a peak of m / z = 465 was observed, and it was confirmed that 1 mol of a sulfonic acid group was added to PY74.

  Dialysis treatment was performed in the same manner as in Example 1 to obtain a PY74 sulfonic acid group-containing derivative dialyzate. Aqueous pigment dispersion (color component concentration combining PY74 and PY74 sulfonic acid group-containing derivative: 10) in the same manner as in Example 1 except that the dialyzed PY74 sulfonic acid group-containing derivative was used instead of the PY97 acid group-containing derivative dialyzed material. % By weight). An ink composition was prepared in the same manner as in Example 1 using the obtained aqueous pigment dispersion, and various evaluations were performed. The evaluation results are shown in Table 2.

Example 2
Polyurethane was synthesized as follows. In a four-necked flask equipped with a thermometer, stirrer, nitrogen inlet tube, and condenser tube, 116 g of carboxylic acid-modified polycaprolactone diol (“Placcel” 205BA (trade name) manufactured by Daicel Chemical Industries, Ltd.) and 120 g of methyl ethyl ketone I put it in. “Placcel” 205BA is a carboxylic acid-modified polycaprolactone diol obtained by lactone modification of dimethylolbutanoic acid. “Placcel” 205BA and methyl ethyl ketone are stirred for 30 minutes, then 64 g of isophorone diisocyanate is charged into a four-necked flask, stirred at room temperature for 1 hour in a nitrogen atmosphere, heated to 70 ° C., and reacted at 70 ° C. for 4 hours. It was. After the reaction, the mixture was cooled to room temperature to obtain a urethane prepolymer solution having a concentration of 60% by weight. 19.3 g of triethanolamine and 350 g of ion-exchanged water were put into a four-necked flask and stirred with 250 g of a urethane prepolymer solution at room temperature for 30 minutes. After raising the temperature to 80 ° C. in a nitrogen atmosphere, chain extension reaction was performed at 80 ° C. for 2 hours. After the reaction, methyl ethyl ketone and a part of water were removed using a rotary evaporator and an aspirator, and then ion-exchanged water was added so that the recovered amount was 548 g to obtain a polyurethane dispersion having a polyurethane concentration of 35% by weight. The resulting polyurethane had an acid value of 81 KOH · mg / g and a weight average molecular weight of 28,000.

The acid value of the polyurethane was measured at room temperature by the neutralization titration method based on JIS K0070 (1992). Ion exchange water was added to the aqueous polyurethane dispersion to prepare a polyurethane concentration of 5% by weight. While stirring an aqueous dispersion having a polyurethane concentration of 5% by weight in a beaker, a 0.1 mol / l hydrochloric acid aqueous solution was added until the polyurethane was completely precipitated. After the supernatant was filtered, the polyurethane was washed with ion-exchanged water. After the polyurethane was washed with water 10 times and dried at 100 ° C. for 2 hours, the neutralizing agent, hydrochloric acid and water were completely removed from the polyurethane. Polyurethane was added to a triangular flask together with ethanol to adjust the polyurethane concentration to 4% by weight, and then a few drops of phenolphthalein solution were added and shaken well until the sample was completely dissolved. If the polyurethane was not completely dissolved in ethanol, methyl ethyl ketone was added until the polyurethane was completely dissolved. Next, 0.1 mol / l ethanolic potassium hydroxide solution was added to the burette, and the polyurethane solution was titrated at room temperature. The end point was when the light red color of the indicator lasted for 30 seconds. The acid value was calculated from the following formula.
A = B × 5.661 / S
A: Acid value B: 0.1 mol / l potassium hydroxide ethanol solution used for titration (ml)
S: Weight of polyurethane (g).

  The average molecular weight of polyurethane was gel permeation chromatography (water 410 manufactured by Water). First, polystyrene having a weight average molecular weight / number average molecular weight of 1.1 or less and a weight average molecular weight of 1300, 9700, 21000, 66000, 370000 as a standard sample was dissolved in tetrahydrofuran so as to be 0.2% by weight. . The molecular weight of polystyrene was measured using a packed column for organic solvent GPC (KF-804L, manufactured by Showa Denko KK) at a column temperature of 40 ° C. and a flow rate of 0.8 ml / min. A calibration curve of retention time and molecular weight was prepared from the retention time and peak intensity of the obtained polystyrene. Next, the polyurethane is dissolved in tetrahydrofuran so that the polyurethane concentration becomes 0.2% by weight, and the retention time and peak intensity of the polyurethane are measured under the same measurement conditions as described above, and the weight of the polyurethane is measured using a calibration curve made of polystyrene. The average molecular weight was calculated.

  85 g of the aqueous pigment dispersion (PY74 and PY97 sulfonic acid group-containing derivative combined color component concentration: 10% by weight) obtained in Example 1 and the polyurethane dispersion (polyurethane concentration: 35% by weight) obtained by the above method. ) 12.1 g was mixed with 2.9 g of ion-exchanged water, and an aqueous pigment dispersion 7 containing polyurethane (colored component concentration combining PY74 and PY97 sulfonic acid group-containing derivative: 8.5% by weight, polyurethane concentration: 4) .25% by weight). An ink composition was prepared in the same manner as in Example 1 using the obtained aqueous pigment dispersion, and various evaluations were performed. The evaluation results are shown in Table 2.

Comparative Example 2
An aqueous pigment dispersion (PY74 and PY74 sulfone) containing polyurethane in the same manner as in Example 2 except that the aqueous pigment dispersion obtained in Comparative Example 1 was used instead of the aqueous pigment dispersion obtained in Example 1. Coloring component concentration combined with acid group-containing derivative: 8.5% by weight, polyurethane concentration: 4.25% by weight). An ink composition was prepared in the same manner as in Example 1 using the obtained aqueous pigment dispersion, and various evaluations were performed. The evaluation results are shown in Table 2.

Claims (3)

(A) Azo-based yellow pigment PY74, (B) A pigment derivative in which a sulfonic acid group is introduced into an azo-based yellow pigment having a molecular weight larger than that of the azo-based yellow pigment PY74, (C) water, and (D) a water-soluble organic solvent. An aqueous pigment dispersion containing. (B) The aqueous pigment dispersion according to claim 1, wherein the azo yellow pigment having a molecular weight larger than that of the azo yellow pigment PY74 is PY97. An ink composition comprising the aqueous pigment dispersion according to claim 1.