JP2008081705A - Aqueous pigment dispersion and ink composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion that has excellent dispersion stability and heat resistance, and further provide an ink composition that can achieve stable ink jetting over a long time not only in the piezo-system but also in the thermal system, and, in addition, has high optical density and high gloss. <P>SOLUTION: The aqueous pigment dispersion comprises (A) dioxazine pigment, (B) a pigment derivative prepared by introducing a sulfonic acid group into an dioxazine pigments, (C) water and (D) water-soluble organic solvent. The ink composition including the aqueous pigment dispersion is diluted with water to set the concentration to 10 ppm in the total of (A) and (B). In this case, among the peaks of the absorption spectra, the ratio of the absorbance of the maximum peak between 550 to 600 nm wave length to the absorbance of the maximum peak between 500 to 550 nm wave length is more than 0.99. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aqueous pigment dispersion excellent in dispersion stability and heat resistance, and an ink composition using the same. In particular, the present invention relates to an 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 inkjet inks, but pigments are insoluble in water, unlike dyes, so it is important for inkjet inks that use pigments to be stably dispersed in water in the form of fine particles. It is. 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 is known (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.

  In addition, a method of stably dispersing an organic pigment in water by using an organic pigment sulfonated derivative has been proposed (see Patent Documents 2 to 6). 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. However, in both piezo and thermal ejection methods, ultrafiltration membranes, semipermeable membranes, reverse osmosis membranes are required to obtain good ejection stability from inkjet nozzles, clogging resistance, and ink storage stability. A complicated purification process using a membrane or the like is required.

    In addition, a method has been proposed in which copper phthalocyanine pigment is stably dispersed in water in the form of fine particles by optimizing the synthesis conditions of the pigment sulfonated derivative (see Patent Document 7). In this method, the absorption spectrum of the aqueous pigment dispersion is changed by changing the number of introduced sulfonic acid groups of the pigment sulfonated derivative, and the piezo is set by changing the absorbance ratio of the peak of the absorption spectrum to a certain value or more. An ink composition having good ejection stability in the system and the thermal system is provided. Usually, an ink composition comprising a copper phthalocyanine pigment is used as a cyan ink. The three-color ink set with cyan, magenta, and yellow color pigment inks, which are the three subtractive primary colors, has a limit in expanding the color reproduction range, and prints with high image quality comparable to silver salt photography and plate-making printing. The level that can be provided is not reached.

On the other hand, as a piezo ink-jet ink, there is a technique in which dioxazine pigments are used for ink-jet ink in order to make a six-color ink set by adding red and blue to yellow, magenta, cyan, black (see Patent Document 8). . Here, the dioxazine pigment PV23 is used as the colorant of the blue ink, and the styrene-acrylic acid copolymer is used as the dispersant, whereby the pigment particles are dispersed and stabilized in water. Further, by reducing the pigment concentration in the ink to 2% by weight, the color reproduction range of the printed matter is expanded and the glossiness of the printed matter is improved. However, when this ink is used, it is difficult to increase the optical density of the printed matter because the pigment concentration is low.
Japanese Patent Laid-Open No. 5-179183 (page 4) JP 2002-121419 A (2nd page) JP 2002-121460 A (page 3) JP 2002-285067 A (second page) JP 2002-309122 A (2nd page) JP 2002-241638 A (first page) JP 2006-176759 A (2nd page) International Publication No. 02/100959 Pamphlet (Page 3, Pages 17-19)

  The present invention aims to provide an aqueous pigment dispersion in which dispersion stability and heat resistance of a finely divided organic pigment are compatible, and further a thermal method that requires not only a piezo method but also ink stability at a high temperature In addition, an object of the present invention is to provide an ink composition which can realize stable ink ejection over a long period of time and can obtain a glossy printed matter having a high optical density.

  That is, the present invention is an aqueous pigment dispersion containing (A) a dioxazine pigment, (B) a pigment derivative having a sulfonic acid group introduced into a dioxazine pigment, (C) water, and (D) a water-soluble organic solvent. Of the absorption spectrum peaks when the ink composition containing the aqueous pigment dispersion is diluted with water and the concentration of the combined (A) dioxazine pigment and (B) pigment derivative is 10 ppm, the wavelength is 550. It is an aqueous pigment dispersion in which the ratio of the absorbance at the maximum peak at ˜600 nm and the absorbance at the maximum peak at a wavelength of 500 to 550 nm is 0.99 or more, and an ink composition containing the aqueous pigment dispersion .

  ADVANTAGE OF THE INVENTION According to this invention, the aqueous pigment dispersion liquid which is excellent in the dispersion stability in the fine particle state of a dioxazine type pigment, and is excellent in the heat resistance in high temperature can be supplied. In addition, since the ink composition produced using the aqueous pigment dispersion of the present invention has excellent heat resistance, stable ejection is realized not only in the piezo method but also in the thermal method that requires stability of the ink at high temperatures. it can. Furthermore, even if the concentration of the pigment contained in the ink is increased, the optical density is high in the printed state, and the pigment particles are present in a finer state, resulting in gloss.

  The present invention is an aqueous pigment dispersion containing (A) a dioxazine pigment, (B) a pigment derivative having a sulfonic acid group introduced into a dioxazine pigment, (C) water, and (D) a water-soluble organic solvent, The ink composition containing the aqueous pigment dispersion is diluted with water and the concentration of (A) the dioxazine pigment and (B) the pigment derivative is 10 ppm. The ratio of the absorbance at the maximum peak at 600 nm to the absorbance at the maximum peak at wavelengths of 500 to 550 nm needs to be 0.99 or more.

  In the present invention, the ratio between the absorbance at the maximum peak at a wavelength of 550 to 600 nm and the absorbance at the maximum peak at a wavelength of 500 to 550 nm is determined as follows. The maximum peak at a wavelength of 550 to 600 nm is determined, and the peak value (absorbance) is read. This is the absorbance [1]. Next, the maximum peak at a wavelength of 500 to 550 nm is determined, and the peak value (absorbance) is read. This is designated as absorbance [2]. The absorbance ratio is calculated from absorbance [1] / absorbance [2]. In the present invention, the ratio of the maximum peak absorbance at a wavelength of 550 to 600 nm and the maximum peak absorbance at a wavelength of 500 to 550 nm (hereinafter, absorbance ratio) is 0.99 or more, preferably 1.00 or more. is there. If the absorbance ratio is less than 0.99, the dispersion stability of the pigment dispersion may decrease, and if the absorbance ratio is less than 1.00, the heat resistance of the pigment dispersion may decrease.

  The absorbance ratio described above changes depending on the degree of sulfonation of the dioxazine pigment derivative, and thus the dispersion stability of the aqueous pigment dispersion greatly changes. In order to improve the dispersion stability of the aqueous pigment dispersion, the degree of sulfonation of the dioxazine pigment derivative to be added is optimized, the maximum peak absorbance at a wavelength of 550 to 600 nm, and the maximum peak at a wavelength of 500 to 550 nm. It is necessary to make the ratio with the absorbance of 0.99 or more.

  The absorbance ratio can be controlled by the reaction conditions (reaction temperature, reaction solution concentration, reaction time, etc.) when synthesizing the pigment derivative (B) contained in the pigment dispersion. For example, by appropriately adjusting the concentration and mixing ratio of concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or a mixture thereof, the reaction conditions are appropriately set within the reaction temperature range of 0 to 150 ° C. and the reaction time range of 1 to 24 hours. By changing, the absorbance ratio can be made 0.99 or more.

  The ratio of the peak absorbance of the absorption spectrum in the present invention is measured, for example, by preparing the following sample. The pigment dispersion is diluted with ion-exchanged water so that the total concentration of the (A) dioxazine pigment and the (B) pigment derivative is 10 ppm with respect to the total amount of the pigment dispersion. Subsequently, the absorption spectrum of the obtained solution is measured using an ultraviolet-visible spectrophotometer (for example, MultiSpec-1500 manufactured by Shimadzu Corporation). Using the absorption spectrum obtained by the measurement, the absorbance ratio is calculated based on the calculation method shown above.

  The (A) dioxazine pigment used in the present invention is a compound having a dioxazine skeleton in which the main component of the pigment is represented by the general formula (1).

R ¹ and R ^{2 in} the general formula (1) may be the same or different and are selected from a hydrogen atom, halogen, amino group, amide group, alkyl group, aryl group or heterocyclic group, The group may further have a substituent. R ³ , R ⁴ , R ⁵ and R ⁶ may be the same or different and are selected from an alkyl group, an alkoxy group, an amide group, a carbazole group or a benzimidazole group, and further, a carbazole group and The benzimidazol group may have an alkyl group, an alkoxy group, an aryl group, a halogen, an alkyl, an alkoxy, or an alkoxycarbonyl substituent. R ³ and R ⁴ may be condensed to form a ring, and R ⁵ and R ⁶ may be condensed to form a ring.

  Specific examples of the (A) dioxazine pigment used in the present invention include blue pigment PB80, purple pigment PV23, PV37 and the like. Since the coloring power of the pigment is high and the color tone is excellent, the use of PV23 is particularly preferable.

  In the present invention, (B) a pigment derivative in which a sulfonic acid group is introduced into a dioxazine pigment is (b-1) a pigment derivative in which a sulfonic acid group is introduced into the same pigment as the (A) dioxazine pigment to be used, (b -2) Refers to two types of pigment derivatives in which a sulfonic acid group is introduced into a pigment having the same chemical structure as part of the chemical structure of the (A) dioxazine pigment used, (b-1) and (b -2) may be used alone or in combination. For example, when a dioxazine pigment PV23 is used as the organic pigment (A), a pigment derivative in which a sulfonic acid group is introduced into PV23 as (b-1), or PV23 and a part of the chemical structure as (b-2) The pigment derivatives in which the sulfonic acid group is introduced into the pigment PV37 having the same singularity are used alone or in combination of (b-1) and (b-2). These pigments and pigment derivatives are strongly bonded by intermolecular force, and negatively charge the surface of the fine particles. In order to further increase the bonding strength between the pigment and the pigment derivative, it is more preferable to combine the pigment and a pigment derivative having a sulfonic acid group introduced into the pigment itself. In the following description, (B) is collectively referred to as “pigment derivative having a sulfonic acid group introduced”.

  The pigment derivative having a sulfonic acid group introduced therein (B) used in the present invention is a mixture of compounds having 1 to 4 sulfonic acid groups introduced in one molecule. The average number of introduced sulfonic acid groups per molecule of the pigment derivative into which the sulfonic acid group has been introduced is preferably 1.1 or more, more preferably 1.4 or more. When the average number of introduced sulfonic acid groups is less than 1.1, the electrostatic repulsive force between the pigment particles becomes weak and the dispersion state may become unstable. On the other hand, if the average number of introduced sulfonic acid groups is less than 1.4, the heat resistance of the aqueous pigment dispersion may decrease. On the other hand, when the average number of introduced sulfonic acid groups is more than 4, the solubility of the pigment derivative into which the sulfonic acid group has been introduced in water may be too high and the dispersion may become unstable.

  The absorption spectrum of the pigment derivative having a sulfonic acid group introduced in the present invention (B) is obtained by mixing the pigment derivative having a sulfonic acid group introduced therein with ion-exchanged water, and having a maximum absorbance of 3 (normal UV-visible spectrophotometry). Prepare a liquid mixture with a concentration not exceeding the detection limit of the meter, and measure in the state of this liquid mixture. The pigment derivative having a sulfonic acid group introduced in the present invention preferably has a maximum absorption wavelength of 575 nm or more in the absorption spectrum at a wavelength of 400 to 800 nm of the mixed solution. When the maximum absorption wavelength of the absorption spectrum is on the shorter wavelength side than 575 nm, the aggregation of the pigment tends to occur.

  In addition, the maximum absorption wavelength of the absorption spectrum of a pigment derivative having a sulfonic acid group introduced can be controlled by the reaction conditions (reaction temperature, reaction solution concentration, reaction time, etc.) when (B) the pigment derivative is synthesized. It is. For example, by appropriately adjusting the concentration and mixing ratio of concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or a mixture thereof, the reaction conditions are appropriately set within the reaction temperature range of 0 to 150 ° C. and the reaction time range of 1 to 24 hours. By changing, the maximum absorption wavelength of the absorption spectrum can be set to 575 nm or more.

  The method for measuring the maximum absorption wavelength of the absorption spectrum of the pigment derivative in the present invention is performed, for example, by the following method. The pigment derivative is charged into ion-exchanged water, and then a mixed solution of the pigment derivative and ion-exchanged water is prepared by a method such as applying a ball mill, a bead mill, or ultrasonic waves. As the most preferable method, a mixed liquid of a pigment derivative and ion-exchanged water is prepared by applying ultrasonic waves for an appropriate time. Next, the absorption spectrum of the mixed solution is measured using an ultraviolet-visible spectrophotometer (for example, MultiSpec-1500 manufactured by Shimadzu Corporation). In the wavelength range of 400 to 800 nm, the peak wavelength of the absorption spectrum showing the maximum absorbance is defined as the maximum absorption wavelength.

  The pigment derivative introduced with the sulfonic acid group (B) used in the present invention is synthesized, for example, by the following method. The organic pigment 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.

  Examples of the neutralizing agent at this time include ammonia, ethylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, triethanolamine, N-methyldiethanolamine, N-phenyldiethanolamine, monoethanolamine, dimethylethanolamine, and diethylethanol. Examples thereof include organic amines such as amine, morpholine, N-methylmorpholine, and 2-amino-2-ethyl-1-propanol, and inorganic alkalis such as sodium hydroxide and potassium hydroxide.

  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, 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 greater than 130, 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 polyurethane 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. When the weight average molecular weight of the polyurethane is less than 10,000, the fixability of the print obtained from the polyurethane-containing ink composition to paper may be lowered. On the other hand, if the weight average molecular weight of the polyurethane is larger than 180,000, the viscosity of the polyurethane-containing ink composition may be undesirably increased, resulting in poor thermal discharge characteristics. The molecular weight of the polyurethane can be controlled by, for example, the synthesis conditions (reaction temperature, reaction time, etc.) of the polyurethane. In the present invention, the molecular weight of the polyurethane can be determined in terms of polystyrene using, for example, gel permeation chromatography.

  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 absorbance ratio of the aqueous pigment dispersion of the present invention is also affected by the dispersion conditions when the coarse particles of the pigment are refined. If shearing stress of an appropriate size is not applied to the coarse pigment particles, the dispersion stability of the pigment dispersion is lowered, and the absorbance ratio may be smaller than 0.99. That is, a normal dioxazine pigment has a characteristic that it has a very large specific surface area 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). more than). For this reason, if the shear stress when the coarse particles of the pigment are refined and dispersed is too large, the specific surface area of the pigment increases rapidly, and pigment particles may not be sufficiently adsorbed by the pigment derivative. Pigment particles that are not sufficiently adsorbed by the pigment derivative have a weak electrostatic repulsive force, and aggregation may occur between the pigment particles starting from the particles.

  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 a dioxazine pigment 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 higher than 13 m / s, the shearing stress applied to the pigment is too large, so that the dispersion stability of the dioxazine pigment dispersion may be lowered. On the other hand, the peripheral speed of the disperser is 6 m / s. If it is smaller than s, the shear stress applied to the pigment is too small, so that coarse particles may remain in the dioxazine pigment dispersion.

  The absorbance ratio of the aqueous pigment dispersion of the present invention is also affected by the surface tension of the aqueous pigment dispersion. For this reason, it is desired to apply a shear stress of an appropriate size to the coarse pigment particles and appropriately control the surface tension of the pigment dispersion by the method as described above.

  In the present invention, the surface tension of the aqueous pigment dispersion at 25 ° C. is preferably 60 mN / m or less, more 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 may be difficult to uniformly transmit the shear stress of the zirconia beads to the coarse pigment particles, and it may be difficult to obtain a pigment dispersion having a uniform pigment particle size. is there. On the other hand, the surface tension at 25 ° C. of the aqueous pigment dispersion 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 a 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, and a polymer dispersant, but the storage stability of the pigment in the pigment dispersion. In consideration of the 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, propylene carbonate Etc. can be used.

  In the aqueous pigment dispersion of the present invention, the content of the coloring component combining (A) the dioxazine pigment and (B) the pigment derivative having a sulfonic acid group introduced is 7 to 20% by weight based on the total amount of the aqueous pigment dispersion. It is preferably 8 to 16% by weight. If the content of the coloring component is too small, the production efficiency of the dispersion is low and the cost is increased. On the other hand, if the content is too large, it becomes very difficult to stabilize the dispersion state.

  In the present invention, the mixing ratio of (A) the dioxazine pigment and (B) the pigment derivative having a sulfonic acid group introduced is, as a weight ratio, dioxazine pigment: pigment derivative having a sulfonic acid group introduced = 50 to 99: 50 to 1, preferably 60 to 97:40 to 3, more preferably 70 to 95:30 to 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 pigment derivative is too large, the color tone may change unfavorably.

  In the case of using polyurethane in the present invention, the color component and polyurethane, which are a combination of (A) a dioxazine pigment and (B) a pigment derivative having a sulfonic acid group introduced, are colored component: polyurethane = 30 to 30 by weight ratio. 90: 70-10, preferably 40-80: 60-20. If the amount of polyurethane is too small, it cannot be expected to improve the adhesion. On the other hand, if the amount of polyurethane is too large, the coloring power of the print obtained from the ink composition is lowered. The timing of mixing the pigment and the polyurethane may be any of before the coarse particles of the pigment are refined and dispersed, during the dispersion, and after the dispersion.

  In the aqueous pigment dispersion of the present invention, the sulfate ion concentration when the concentration of the coloring component combining (A) the dioxazine pigment and (B) the pigment derivative into which the sulfonic acid group is introduced is 4% by weight is 50 ppm or less, Preferably it is 20 ppm or less, More preferably, it is 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 greatly increases and the possibility of clogging of the dialysis membrane increases.

  In the aqueous pigment dispersion of the present invention, the sulfate ion concentration increases in proportion to the color component concentration. Therefore, when the coloring component 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 color component 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 by 4 times. When the coloring component of the aqueous pigment dispersion is more than 4% by weight, the concentration of the coloring component is adjusted to 4% by dilution of the aqueous pigment dispersion with ion-exchanged water, and the sulfate ion concentration is measured.

  In order to reduce the sulfate ion concentration in the aqueous pigment dispersion, the raw material (A) dioxazine pigment, (B) a pigment derivative having a sulfonic acid group introduced, (C) water, (D) water solution It is preferable that the sulfate ion concentration contained in each of the basic organic solvents 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) dioxazine-based pigment used in the present invention, it is preferable to use one obtained by sufficiently washing sulfate ions by washing with, for example, ion exchange water or distilled water. Since organic pigments usually have a low affinity with water, sulfate ions can be easily removed by a known method such as water filtration.

  In the pigment derivative introduced with the sulfonic acid group (B) used in the present invention, a large amount of sulfate ions usually remain from the reaction solution 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.

  The pH of the aqueous pigment dispersion of the present invention is preferably in the range of 1.5 to 7.5. The more sulfonic acid groups introduced into the pigment molecule, the more easily the pigment derivative dissolves in water. If the pH of the aqueous pigment dispersion is greater than 7.5, a derivative having two or more sulfonic acid groups introduced may elute from the pigment particle surface into water, and the dispersion state of the pigment dispersion may become unstable. . On the other hand, if the pH is less than 1.5, it is difficult to bring the ink composition produced by diluting the aqueous pigment dispersion into an appropriate pH range. The pH of the aqueous pigment dispersion of the present invention is, for example, ammonia, ethylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, triethanolamine, N-methyldiethanolamine, N-phenyldiethanolamine, monoethanolamine, dimethylethanolamine, It can be adjusted to an appropriate range by organic amines such as diethylethanolamine, morpholine, N-methylmorpholine, 2-amino-2-ethyl-1-propanol, and inorganic alkalis such as sodium hydroxide and potassium hydroxide.

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 ⁻² Pa or less, more preferably 1 × 10 ⁻³ Pa. Within this range, it can be said that the dispersibility of the pigment is stable. The dispersibility of the pigment can be controlled by controlling the number of introduced (B) pigment derivative sulfonic acid groups into which sulfonic acid groups are introduced within an appropriate range.

The viscosity of the aqueous pigment dispersion of the present invention is desired to be in the range of 1 to 50 mPa · s, preferably 3 to 10 mPa · s. Within this range, it becomes easy to produce an ink composition having a viscosity suitable for ink ejection. In order to keep the viscosity of the aqueous pigment dispersion within the above range, it is required to stabilize the dispersion state of the pigment by appropriately controlling the number of introduced sulfonic acid groups of the organic pigment as described above. The pigment in the aqueous pigment dispersion is desired to have an arithmetic average diameter of preferably 1 to 150 nm, more preferably 5 to 100 nm. When the arithmetic average diameter of the pigment is larger than 150 nm, there is a high possibility of causing clogging in the ink jet nozzle. Moreover, when the arithmetic average diameter of a pigment is larger than 100 nm, the glossiness of a printed matter may fall. On the other hand, if the arithmetic average diameter is too small, the specific surface area of the particles becomes too large and the pigment in the ink composition tends to aggregate. An aqueous pigment dispersion having a Casson yield value of 1 × 10 ⁻² Pa or less is stored for a long period of time even when subjected to treatments such as dilution and heating because the dispersion state of the finely dispersed pigment is stable. Even in this case, the dispersed particle diameter of the pigment is maintained without being changed due to aggregation.

  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. In the present invention, the coloring component combined with (A) a dioxazine pigment and (B) a pigment derivative having a sulfonic acid group introduced is 1 to 16% by weight, preferably 2 to 8% by weight, based on the total amount of the ink composition. It is preferably contained. When there are too few coloring components in an ink composition, the coloring power of printed matter will become small and favorable drawing cannot be performed. On the other hand, when there are too many coloring components, although the coloring power of printed matter increases, the gloss decreases.

  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 polyhydric alcohols, γ-butyrolactone, N-methyl-2-pyrrolidone, dimethyl sulfoxide and the like, 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 preferably in the range of 6-9. If it is in this range, there are few safety problems even if it touches the human body. The pH of the ink composition can be appropriately adjusted using an inorganic alkali such as ammonia, organic amine, potassium hydroxide or sodium hydroxide, or a buffer solution such as phosphoric acid.

  In the ink composition of the present invention, an anionic, cationic, nonionic or amphoteric surfactant can be added to adjust the surface tension or improve the permeability to the substrate, thereby preventing the generation of bubbles. An antifoaming agent can be added to prevent this.

  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. The optical density of the printed material is 2 or more, preferably 2.2 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 fixability of the printed matter obtained from the ink composition of the present invention to paper can be evaluated, for example, by the following method. The printed matter obtained from the ink composition is subjected to a cellophane tape peeling test, the peeled cellophane tape is attached to glossy paper, and the optical density is measured with an optical densitometer. The optical density of the cellophane tape after the printed material peel test is preferably 0.3 or less, more preferably 0.2 or less. Since the optical density when the cellophane tape that has not been peeled off is pasted on glossy paper is usually about 0.1, the lower limit of the optical density of the cellophane tape after the peel test is 0.1. Presumed.

  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 at a measurement angle of 45 ° is desired to be 50 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.

  The aqueous pigment dispersion of the present invention can be applied to pigment inks for inkjet printers, and can also be applied to the formation of pixel films for color filters for liquid crystal displays.

  Hereinafter, although this invention is demonstrated in detail using 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. Absorbance ratio of the pigment dispersion The pigment dispersion was diluted with ion-exchanged water so that the concentration of the coloring component consisting of (A) a dioxazine pigment and (B) a pigment derivative was 10 ppm, and an ultraviolet-visible spectrophotometer (Shimadzu Corporation) The absorption spectrum of the resulting solution was measured at room temperature using MultiSpec-1500 manufactured by Seisakusho. Among the peaks of the absorption spectrum expressed in the wavelength range of 400 to 800 nm, the peak having the maximum peak at the wavelength of 550 to 600 nm was determined, the absorbance was read, and this was designated as absorbance [1]. Next, among the peaks of the absorption spectrum expressed in the wavelength range of 400 to 800 nm, the peak having the maximum peak at the wavelength of 500 to 550 nm was determined, the absorbance was read, and this was designated as absorbance [2]. From the obtained value, absorbance [1] / absorbance [2] (absorbance ratio) was calculated.

B. Absorption spectrum of pigment derivative A mixture liquid is prepared by putting a pigment derivative into ion-exchanged water and applying ultrasonic waves, and using an ultraviolet-visible spectrophotometer (MultiSpec-1500, manufactured by Shimadzu Corporation) Measurements were made. As a result of the measurement, the wavelength at which the peak with the highest absorbance value is located at 400 to 800 nm was defined as the maximum absorption wavelength.

C. The average number of introduced sulfonic acid groups in the pigment derivative Using m-nitrobenzyl alcohol as a matrix, the negative ion measurement of the pigment derivative was performed using a fast atom bombardment ionization mass spectrometer (JMS-SX102A manufactured by JEOL Ltd.). It was. The 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 the number of introduced sulfonic acid groups of the pigment derivative from the obtained m / z strength. Asked. Further, the average number of introduced sulfonic acid groups per molecule was calculated from the intensity ratio of the spectrum.

D. Surface tension of pigment dispersion Surface tension of pigment dispersion at 25 ° C. using surface tension measuring instrument (A-06, manufactured by Yamamoto Kakin Tester Co., Ltd.) and A-06-P01 as platinum ring Was measured by the 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.

E. Viscosity of Pigment Dispersion The viscosity of the pigment dispersion at 25 ° C. was measured using a conical plate viscometer (RE100L manufactured by Toki Sangyo Co., Ltd.).

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

G. 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.

H. Particle size measurement in the pigment dispersion state in the pigment dispersion The pigment dispersion was diluted with ion-exchanged water so that the concentration of the coloring component (A) dioxazine pigment and (B) pigment derivative was 0.1% by weight. Using a dynamic light scattering type particle size distribution measuring device (LB-500, manufactured by Horiba, Ltd.), the arithmetic average diameter of the volume-based pigment particles at 25 ° C. was determined.

I. Evaluation of ink fading at the time of 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 continuously from the ink jet nozzle. Printing was performed on 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.

J. et al. 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.

K. 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. .

L. 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 PV23 (“Hostaperm” (trade name) RL-NF, manufactured by Clariant) was added to 780 g of fuming sulfuric acid (28 wt% SO ₃ ) with stirring under ice cooling. The temperature of the solution during the reaction was 0 to 5 ° C. After stirring for 3 hours, the reaction solution was added onto 1500 g of ice. 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 put into 2000 ml of pure water, neutralized with an aqueous ammonia solution (added with an aqueous ammonia solution until the pH reached 7 or more), and filtered. The obtained wet crystals were washed with pure water and then dried at 80 ° C. The operations obtained by drying, washing with pure water, filtering, and drying were repeated 10 times to obtain 65 g of PV23 sulfonic acid group-containing derivative VS-A. When the absorption spectrum of VS-A was measured by the method shown above, the maximum absorption wavelength was 576 nm.

  Next, VS-A and ion-exchanged water were mixed to prepare a slurry containing sulfate ions. The prepared slurry was dialyzed using a PMMA dialysis module ("Fill Riser" (trade name) B3-20A manufactured by Toray Industries, Inc.) to obtain a PV23 derivative dialyzate VS-Ad.

  80 g of PV23, 20 g of VS-Ad, 150 g of triethylene glycol monobutyl ether, and 750 g of ion exchange water were mixed and stirred with a homodisper to prepare a slurry. The slurry was connected to a circulating bead mill dispersing machine (“Ultra Apex Mill” (trade name) UAM-015, manufactured by Kotobuki Kogyo Co., Ltd.) filled with zirconia beads with a tube and subjected to a dispersion treatment, whereby an aqueous pigment dispersion 1 ( Color component concentration of PV23 and VS-Ad: 10% by weight) was obtained. 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.

  The absorption spectrum of the aqueous pigment dispersion 1 was measured by the method described above, and the resulting chart is shown in FIG. The ratio of peak absorbance in the absorption spectrum was 1.009.

Example 2
The sulfonation reaction was performed in the same manner as in Example 1 except that the reaction temperature was 40 ° C., to obtain 66 g of PV23 sulfonated derivative VS-B. When the absorption spectrum of VS-B was measured by the method shown above, the maximum absorption wavelength was 586 nm. Next, dialysis was performed in the same manner as in Example 1 to obtain a derivative dialysate VS-Bd. Dispersion treatment was performed in the same manner as in Example 1 using PV23 and VS-Bd to obtain an aqueous pigment dispersion 2 (colored component concentration of PV23 and VS-Ad: 10% by weight). When the absorption spectrum of the aqueous pigment dispersion 2 was measured by the method described above, the peak absorbance ratio of the absorption spectrum was 1.004.

Example 3
Sulfone was prepared in the same manner as in Example 1 except that 60 g of PV23 was added to a solution obtained by mixing 390 g of fuming sulfuric acid (28 wt% SO ₃ ) and 390 g of concentrated sulfuric acid (98 wt% H ₂ SO ₄ ). A 68 g PV23 sulfonated derivative VS-C was obtained. When the absorption spectrum of VS-C was measured, the maximum absorption wavelength was 585 nm. Next, dialysis was performed in the same manner as in Example 1 to obtain a derivative dialysate VS-Cd. Dispersion treatment was performed using PV23 and VS-Cd in the same manner as in Example 1 to obtain an aqueous pigment dispersion 3 (colored component concentration of PV23 and VS-Cd: 10% by weight). When the absorption spectrum of the aqueous pigment dispersion 3 was measured by the method described above, the peak absorbance ratio of the absorption spectrum was 0.994.

Comparative Example 1
Sulfone was prepared in the same manner as in Example 1 except that 60 g of PV23 was added to a solution obtained by mixing 260 g of fuming sulfuric acid (28 wt% SO ₃ ) and 520 g of concentrated sulfuric acid (98 wt% H ₂ SO ₄ ). A 68 g PV23 sulfonated derivative VS-D was obtained. When the absorption spectrum of VS-D was measured, the maximum absorption wavelength was 574 nm. Next, dialysis was performed in the same manner as in Example 1 to obtain a derivative dialysate VS-Dd. Dispersion treatment was performed using PV23 and VS-Dd in the same manner as in Example 1 to obtain an aqueous pigment dispersion 4 (colored component concentration of PV23 and VS-Dd: 10% by weight). The absorption spectrum of the aqueous pigment dispersion 4 is measured by the method described above, and the resulting chart is shown in FIG. The ratio of peak absorbance in the absorption spectrum was 0.978.

Example 4
Example 1 except that 80 g of PV23, 20 g of VS-Ad, 150 g of triethylene glycol monobutyl ether, and 750 g of ion-exchanged water were mixed, and the peripheral speed of the circulating bead mill disperser was changed to 5 m / s. Thus, an aqueous pigment dispersion 5 (color component concentration of PV23 and VS-Ad: 10% by weight) was prepared. When the absorption spectrum of the aqueous pigment dispersion 5 was measured by the method described above, the peak absorbance ratio of the absorption spectrum was 1.003.

Example 5
80 g of PV23, 20 g of VS-Ad, 150 g of triethylene glycol monobutyl ether and 750 g of ion-exchanged water were mixed, and the peripheral speed of the circulating bead mill disperser was changed to 5 m / s and the zirconia bead diameter was changed to 0.3 mmφ. Except for the above, an aqueous pigment dispersion 6 (colored component concentration of PV23 and VS-Ad: 10% by weight) was prepared in the same manner as in Example 1. When the absorption spectrum of the aqueous pigment dispersion 6 was measured by the method described above, the peak absorbance ratio of the absorption spectrum was 0.992.

  Tables 1 and 2 show various evaluation results of the aqueous pigment dispersions obtained in Examples 1 to 5 and Comparative Example 1.

Reference example 1
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. Plaxel 205BA is a carboxylic acid-modified polycaprolactone diol obtained by lactone-modifying dimethylolbutanoic acid. After stirring PLACCEL 205BA and methyl ethyl ketone for 30 minutes, 64 g of isophorone diisocyanate was 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. 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 aqueous hydrochloric acid 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: Amount of 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.

Example 6
85 g of the aqueous pigment dispersion 1 obtained in Example 1 (concentration of colored components combining PV23 and VS-Ad: 10% by weight) and 12% of the polyurethane dispersion (polyurethane concentration: 35% by weight) obtained in Reference Example 1 0.1 g is mixed with 2.9 g of ion-exchanged water, and an aqueous pigment dispersion 7 containing polyurethane (colored component concentration of PV23 and VS-Ad: 8.5% by weight, polyurethane concentration: 4.25% by weight) Got. When the absorption spectrum of the aqueous pigment dispersion 7 was measured by the method described above, the peak absorbance ratio of the absorption spectrum was 1.013. Various evaluation results of the aqueous pigment dispersion 7 are shown in Tables 1 and 2.

Example 7
To 40 g of the aqueous pigment dispersion 1 obtained in Example 1, 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. A composition (concentration of colored components combining PV23 and VS-Ad: 4% by weight) was prepared, and ejection stability, optical density, paper fixing property, and glossiness were evaluated. The results are shown in Table 3.

Examples 8-11, Comparative Example 2
Using each aqueous pigment dispersion obtained in Examples 2 to 5 and Comparative Example 1, ink compositions were prepared in the same manner as in Example 7, and various evaluations were performed. The results are shown in Table 3.

Example 12
In 47.1 g of the aqueous pigment dispersion 7 obtained in Example 6, 40.9 g of ion-exchanged water, 9.6 g of glycerin, 1.44 g of 1,2-hexanediol, 0.8 g of ethylene glycol, 0.8 g of triethanolamine. 16 g was added to prepare an ink composition (colored component concentration of PV23 and VS-Ad: 4% by weight, polyurethane concentration: 2% by weight), and various evaluations were performed. The results are shown in Table 3.

Comparative Example 3
The blue ink composition was extracted from the ink cartridge (manufactured by Seiko Epson Corporation, (trade name) ICBL33) and diluted 1000 times with ion-exchanged water. When the absorption spectrum of the diluted blue ink composition was measured by the method described above, the peak absorbance ratio of the absorption spectrum was 0.978. ICBL33 was installed in a piezo inkjet printer (“Calario” (trade name) PX-G920 manufactured by Seiko Epson Corporation), and various evaluations of the blue ink composition were performed by the methods described above. The results are shown in Table 2. Next, the ink composition extracted from the ICBL 33 is placed in an ink cartridge (Canon, Inc., (trade name) BCI-3eC) of a thermal ink jet printer (Canon, Inc. “Pixus” (trade name) 550i). Attempts were made to eject ink by the method described above, but no ink was ejected. After repeating the cleaning of 550i Nozno five times, ink ejection was attempted again, but no ink was ejected.

Comparative Example 4
The blue ink composition was extracted from an ink cartridge (manufactured by Canon Inc., (trade name) PFI-101B) and diluted 1000 times with ion-exchanged water. When the absorption spectrum of the blue ink composition diluted by the method described above was measured, the peak absorbance ratio of the absorption spectrum was 0.947. The ink composition extracted from PFI-101B is an ink cartridge (Seiko Epson Corporation, (trade name) ICBL33) of a piezo-type inkjet printer ("Calario" (trade name) PX-G920, manufactured by Seiko Epson Corporation). The blue ink composition was evaluated by the method described above. Next, the ink composition extracted from the PFI-101B is used as an ink cartridge of a thermal ink jet printer ("Pixus" (trade name) 550i manufactured by Canon Inc., manufactured by Canon Inc., (trade name) BCI-3eC). The ink composition was evaluated by the method described above. The results are shown in Table 3.

The chart which showed the absorption spectrum in the wavelength range of 400-800 nm of the aqueous pigment dispersion liquid 1 obtained in Example 1 The chart which showed the absorption spectrum in the wavelength range of 400-800 nm of the aqueous pigment dispersion 4 obtained by the comparative example 1

Explanation of symbols

1 Absorbance of the maximum peak at a wavelength of 550 to 600 nm 2 Absorbance of the maximum peak at a wavelength of 500 to 550 nm

Claims (4)

An aqueous pigment dispersion containing (A) a dioxazine pigment, (B) a pigment derivative in which a sulfonic acid group is introduced into the dioxazine pigment, (C) water, and (D) a water-soluble organic solvent, Of the absorption spectrum peaks when the concentration of the ink composition containing the dispersion is diluted with water and the combined concentration of the (A) dioxazine pigment and the (B) pigment derivative is 10 ppm, the maximum at a wavelength of 550 to 600 nm. An aqueous pigment dispersion in which the ratio of the peak absorbance to the maximum peak absorbance at a wavelength of 500 to 550 nm is 0.99 or more. The aqueous pigment dispersion according to claim 1, wherein (B) the pigment derivative has a maximum absorption wavelength of 575 nm or more in the absorption spectrum at 400 to 800 nm of the mixture of the pigment derivative in which a sulfonic acid group is introduced into the dioxazine pigment and water. . The aqueous pigment dispersion according to claim 1, which contains polyurethane. An ink composition comprising the aqueous pigment dispersion according to any one of claims 1 to 3.

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