JP2010150314A - Oil-based pigment ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oil-based pigment ink composition with excellent storage stability. <P>SOLUTION: When ions in the oil-based pigment ink composition, which at least includes a quinacridone pigment, a polymer compound, and an organic solvent, are subjected to phase inversion to pure water, total concentration of monovalent cations in the aqueous phase is maintained at 100 ppm or lower. The oil-based pigment ink composition produces only slight quantity of precipitates even after long time of storage, and has excellent storage stability. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oil-based pigment ink composition containing at least a quinacridone pigment, a polymer compound, and an organic solvent, and particularly to an oil-based pigment ink composition suitably used for an ink jet recording system.

  The ink jet recording method is a recording method in which printing is performed by ejecting liquid ink from a nozzle toward a recording medium by using pressure, heat, electric field or the like as a driving source. Such a recording method has recently been expanding the market because of its low running cost, high image quality, and the ability to print various inks according to the application.

  As the ink used in the ink jet recording system as described above, a water-based dye ink using a dye as a coloring material and water as a dispersion solvent has been mainly used, but the dye ink is inferior in fastness. For this reason, an aqueous pigment ink using a pigment as a coloring material and an ink jet printer using the same have been developed and used for posters for indoor use. However, since water-based inks are inferior in water resistance, they are not suitable for outdoor use, and water-based inks have a problem that it is difficult to print on plastic substrates such as polyvinyl chloride. For this reason, development of oil-based pigment ink using a pigment as a color material and an organic solvent as a dispersion solvent has been performed.

For example, a pigment, a polymer compound having a solubility in water and ethanol of less than 3% by mass at 25 ° C., and 30 to 90% by mass of a (poly) alkylene glycol derivative and 1 to 1 of a nitrogen-containing heterocyclic compound as an organic solvent. An oil pigment ink having improved weather resistance and fixability by using an oil pigment ink composition containing 30% by mass has been proposed (for example, Patent Document 1). Further, unlike the water-based dye ink, the oil-based pigment ink as described above is liable to cause ejection failure because the pigment is not dissolved in the ink. Therefore, for the purpose of improving the dispersion stability of the pigment in the organic solvent, it is selected from the group consisting of a pigment, a binder resin, a pigment dispersant, at least one glycol ether acetate, and cyclohexanone and isophorone. An oil-based pigment ink containing at least one organic solvent has been proposed (for example, Patent Document 2).
Japanese Patent Laid-Open No. 2005-60716 JP 2006-56991 A

  By the way, the pigments used in the oil-based pigment inks as described above are roughly classified into inorganic pigments such as titanium oxide and organic pigments such as carbon black, azo, azomethine, and quinacridone. When using an oil-based pigment ink as an ink-jet ink, a pigment exhibiting each hue of cyan, magenta, yellow, white, and black is selected from these pigments according to desired characteristics, and prepared using each pigment. Ink-jet printing is used in the form of an ink set combined with an ink tank filled with the oil-based pigment ink.

  However, when a quinacridone pigment is used as the pigment of the oil-based pigment ink as described above, there has been a problem that nozzle clogging frequently occurs when ink is stored for a long period of time, and ejection by an ink jet printer becomes difficult.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an oil-based pigment ink composition having a quinacridone pigment as a coloring material, which causes less nozzle clogging in an inkjet printer even after long-term storage. Another object of the present invention is to provide an oil-based pigment ink composition capable of performing stable ink jet printing.

  The present invention is an oil-based pigment ink composition containing at least a quinacridone pigment, a polymer compound, and an organic solvent, and when the ions in the oil-based pigment ink composition are phase-inverted to pure water, The total cation concentration is 100 ppm or less.

  According to the oil pigment ink composition, when the ions in the ink composition are phase-inverted into pure water, the total concentration of monovalent cations in the aqueous phase is 100 ppm or less, and thus quinacridone even after long-term storage. Generation | occurrence | production of the precipitate originating in a pigment can be suppressed. In particular, among monovalent cations, sodium ions and potassium ions are likely to form precipitates, and therefore the total concentration of these ions is preferably 100 ppm or less.

  The specific conductivity of the aqueous phase is preferably 150 μS / cm or less. A low specific conductivity means that when the ions in the ink composition are phase-inverted to pure water, the amount of ions phase-inverted is small. Therefore, if the specific conductivity is 150 μS / cm or less, the content of not only monovalent cations but also other ionic impurities such as anions is small. For this reason, generation | occurrence | production of a precipitate can be suppressed further.

  As described above, according to the present invention, it is possible to provide an oil-based pigment ink composition that generates less precipitates derived from quinacridone pigments. Thereby, even when the ink is stored for a long period of time, it is possible to obtain an ink-jet ink that can be stably ejected with less nozzle clogging.

  First, the development history of the oil-based pigment ink composition according to the present embodiment will be described. When oil-based pigment inks containing quinacridone pigments are stored for a long period of time, nozzle clogging is greater than oil-based pigment inks containing other pigments. As a result of investigating the frequent cause, solid precipitates different from the quinacridone pigment itself were adhered to the filter provided in the supply pipe connecting the ink tank and nozzle of the ink jet printer, which caused clogging. It was confirmed that Since no precipitate was generated in the ink at the time of ink preparation, it was considered that this precipitate was generated by long-term storage of the ink.

  For this reason, as a result of examining components that can form precipitates in the ink composition, the ionic impurities contained in the quinacridone pigment are eluted in the ink by long-term storage, and the salt is generated due to the cause of the precipitates. It was estimated that. That is, in the production process of a quinacridone pigment, first, a crude quinacridone pigment is synthesized. During this synthesis, anions such as chloride ions and nitrate ions derived from raw materials or by-products are unavoidable in the crude quinacridone pigment. Mixed in. In addition, the synthesized crude quinacridone pigment is generally a lump and is produced as crystals that are not suitable for use as a pigment. For this reason, the pigmentation which adjusts a particle diameter, a crystal structure, a hue, etc. by further processing a crude quinacridone pigment is performed. As an industrial method for pigmentation, a salt milling method is generally performed in which a crude quinacridone pigment is pulverized with an inorganic salt and then the resulting quinacridone pigment is acid extracted. Accordingly, quinacridone pigments produced by the salt milling method contain ionic impurities such as alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium and barium.

  When an ink in which such a quinacridone pigment containing ionic impurities is dispersed in an organic solvent is stored for a long period of time, the ionic impurities are dissolved in the ink by a small amount of water contained in the organic solvent. Thus, it is considered that a salt is formed, and thereby a precipitate is generated.

  Furthermore, as a result of detailed analysis of the metal component in the precipitate, the precipitate contained a monovalent alkali metal such as sodium or potassium as the main metal component rather than a divalent alkaline earth metal such as calcium. Therefore, it was considered that the monovalent cation in the inorganic salt mixed in the above-mentioned pigmentation was mainly produced during the long-term storage. Therefore, it can be expected that the generation of precipitates can be suppressed with an ink composition in which at least one of monovalent cations and anions, which are the main factors for generating such precipitates, is reduced.

  Based on the above knowledge, the present inventors paid attention to the amount of monovalent cations in the ink composition and studied to reduce the amount of ions, but the oil-based pigment ink composition was used as a dispersion solvent. Since an organic solvent is used, it is difficult to directly detect the amount of cations in the ink composition. For this reason, as a result of further investigation, if the ions in the ink composition are phase-inverted to pure water containing no ionic component and the total concentration of monovalent cations in the aqueous phase is below a certain value, It was found that depending on the cation concentration, an ink with little generation of precipitates can be obtained even after long-term storage. That is, when the ions in the oil-based pigment ink composition are phase-inverted to pure water, the total concentration of monovalent cations in the aqueous phase is 100 ppm or less, preferably 50 ppm or less. However, the generation of precipitates is suppressed, and an ink having excellent storage stability can be obtained. If the organic solvent contains a water-soluble organic solvent and the water-soluble organic solvent is also phase-inverted into the aqueous phase when the oil-based pigment ink composition is brought into contact with pure water, the water-soluble By measuring the total concentration of monovalent cations in the aqueous phase containing the organic solvent, the amount of monovalent cations in the ink composition can be determined.

  In addition, when the present inventors phase-converted ions in the oil-based pigment ink composition to pure water as described above, if the specific conductivity of the aqueous phase is a certain value or less, the generation of precipitates is further reduced. I also found out. That is, since the precipitate is considered to be a salt containing a monovalent cation, the amount of precipitation is also influenced by the amount of anions. Moreover, although there are few precipitates containing bivalent cations, such as calcium, as mentioned above, alkaline earth metal salts, such as calcium, are also contained in the precipitate to some extent. Therefore, in order to suppress the generation of precipitates, it is preferable to reduce divalent cations such as anions and calcium. For this reason, if the content of ionic impurities in the entire ink composition is reduced, the generation of precipitates can be expected to be further suppressed. However, the amount of ions of these ionic substances in the ink affects the specific conductivity. To do. As a result of examination from the above viewpoint, it has been found that the generation of precipitates is extremely small when the specific conductivity of the aqueous phase is preferably 150 μS / m or less, more preferably 100 μS / m or less.

  In the oil-based pigment ink composition of the present embodiment, the total concentration of monovalent cations in the aqueous phase when the ions in the ink composition are phase-inverted to pure water, and the specific conductivity of the aqueous phase are in the above range. When adjusting to the above, it is preferable to use a quinacridone pigment which is considered to be the main cause of the generation of precipitates and has a small amount of ionic impurities. In particular, in the range of the content of the quinacridone pigment when used as an inkjet ink, the generation of precipitates by using a quinacridone pigment having a specific conductivity of 65 μS / m or less, more preferably 50 μS / m or less. Is suppressed. Examples of a method for obtaining such a low specific conductivity quinacridone pigment include a method of washing a commercially available quinacridone pigment with distilled water or ion-exchanged water. If the content of quinacridone pigment is high, the total concentration of monovalent cations in the aqueous phase and the specific conductivity of the aqueous phase will increase, so use a quinacridone pigment with the lowest specific conductivity possible. It is preferable to do.

  Next, each component used in the oil-based pigment ink composition of the present embodiment will be specifically described.

  Specific examples of the quinacridone pigment used in the present embodiment include C.I. I. Pigment red 5, C.I. I. Pigment red 7, C.I. I. Pigment red 12, C.I. I. Pigment red 48 (Ca), C.I. I. Pigment red 48 (Mn), C.I. I. Pigment red 57 (Ca), C.I. I. Pigment red 57: 1, C.I. I. Pigment red 112, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 168, C.I. I. Pigment red 184, C.I. I. Pigment red 202, C.I. I. Pigment red 209, C.I. I. Pigment red 254, C.I. I. Pigment violet 19 and the like. These may be used alone or in combination.

  The content of the quinacridone pigment in the ink composition is not particularly limited, but when used as an ink for an ink jet printer, it is preferably 0.1 to 10 parts by mass with respect to the entire ink composition. 1.5-7 parts by mass is more preferable.

  The oil-based pigment ink composition of the present embodiment contains a polymer compound. Such a polymer compound is used as a pigment dispersant or / and a fixing resin. A pigment dispersant made of a polymer compound has excellent affinity with a quinacridone pigment, and can improve dispersion stability. In addition, the fixing resin made of a polymer compound has excellent adhesion to the substrate, and can improve the durability of the printed matter. In addition, depending on the type of the polymer compound, one type may have both of the above functions.

  The polymer compound as described above preferably has a solubility in water and ethanol of less than 3% by weight, particularly less than 1% by weight. The pigment dispersant and the fixing resin remain on the surface or the surface layer of the substrate after printing by the ink jet recording method, and are dried and fixed. For this reason, if the resin component is readily soluble in water, the printed matter lacks water resistance, and the printed matter may flow due to rain or the like when used outdoors. Further, when a printed material is used as a poster or the like, a coating agent or the like may be sprayed onto the surface, and many of these coating agents contain an alcohol component as a main solvent. For this reason, if the polymer compound is easily soluble in alcohol, the printed matter may be dripped by the coating agent. Therefore, water resistance and alcohol resistance can be improved by using a polymer compound having low solubility in water and ethanol.

  As the pigment dispersant, an ionic or nonionic surfactant or an anionic, cationic or nonionic polymer compound is preferably used. Among these, a polymer compound having a cationic group or an anionic group is more preferable from the viewpoint of dispersion stability, water resistance, squeezing resistance, and the like. Specific examples of the pigment dispersant as described above include SOLPERSE manufactured by Lubrizol, DISPERBYK manufactured by Big Chemie, and EFKA manufactured by Fuka Additives.

  Examples of the fixing resin include at least one selected from the group consisting of acrylic resins, polyester resins, polyurethane resins, vinyl chloride resins, and nitrocellulose. Among these, at least one selected from the group consisting of polyurethane resin, polyester resin, vinyl chloride resin, and nitrocellulose resin is preferable, and vinyl chloride resin is more preferable. These resins are excellent in fixability to a plastic substrate, and water resistance, dispersion stability, printability, and the like can be controlled by changing functional groups and structures in the resin. Specific examples of the acrylic resin include John Crill manufactured by Johnson Polymer Co., Ltd., and ESREC P manufactured by Sekisui Chemical Co., Ltd. Specific examples of the polyester resin include Elitel manufactured by Unitika and Byron manufactured by Toyobo. Specific examples of the polyurethane resin include Byron UR manufactured by Toyobo Co., Ltd., NT-Hilamic manufactured by Dainichi Seika Co., Ltd., Crisbon manufactured by Dainippon Ink and Chemicals, Nipponran manufactured by Nippon Polyurethane Co., Ltd., and the like. . Specific examples of the vinyl chloride resin include SOLBIN manufactured by Nissin Chemical Industry Co., Ltd., Sekisui PVC-TG, Sekisui PVC-HA manufactured by Sekisui Chemical Co., Ltd., and the UCAR series manufactured by Dow Chemical Co., Ltd. . Specific examples of nitrocellulose include HIG, LIG, SL, VX manufactured by Asahi Kasei Corporation, and industrial nitrocellulose RS and SS manufactured by Daicel Chemical Industries. The weight average molecular weight of the fixing resin is preferably 2,000 to 100,000, more preferably 5,000 to 80,000, and most preferably 10,000 to 50,000. When the weight average molecular weight is less than 2,000, the effect of steric repulsion is hardly obtained when the anionic resin is adsorbed to the pigment particles in the ink composition, and the effect of improving the storage stability is small. Moreover, it is difficult to obtain the effect of improving the fixability between the medium and the pigment particles, and there is a possibility that the coating film strength cannot be sufficiently obtained. On the other hand, when the weight average molecular weight exceeds 100,000, the effect is saturated and the viscosity of the ink is increased, and the fluidity may not be sufficiently exhibited.

  In the present embodiment, when a pigment dispersant made of a polymer compound is used, the content of the pigment dispersant varies depending on the types and dispersion conditions of the quinacridone pigment, the pigment dispersant and the organic solvent, but usually quinacridone 5-150 mass parts is preferable with respect to 100 mass parts of a pigment. When a fixing resin made of a polymer compound is used, the content of the fixing resin varies depending on the type and dispersion conditions of the quinacridone pigment, the fixing resin and the organic solvent, but usually 100 mass of the quinacridone pigment. 5-300 mass parts is preferable with respect to a part.

  The oil-based pigment ink composition of the present embodiment contains an organic solvent. Various known solvents can be used as such an organic solvent. Among these, (poly) alkylene glycol derivatives are particularly preferable.

  Although content of an organic solvent is not specifically limited, 30-99 mass parts is preferable with respect to the whole ink composition, and 50-98 mass parts is more preferable. In particular, the content of the (poly) alkylene glycol derivative is preferably 1 to 95 parts by mass, more preferably 20 to 90 parts by mass, and still more preferably 50 to 90 parts by mass with respect to the entire ink composition.

  Examples of the (poly) alkylene glycol derivative include (poly) alkylene glycol, that is, a compound having two or more free hydroxyl groups such as alkylene glycol; (poly) alkylene glycol monoalkyl ether compound or monoalkyl ester compound, etc. Compounds having one free hydroxyl group; (poly) alkylene glycol monoalkyl ether monoalkyl ester compounds, dialkyl ether compounds, dialkyl ester compounds and the like compounds having no free hydroxyl group. Among these, one compound selected from the group consisting of a monoalkyl ether monoalkyl ester compound, a dialkyl ether compound, and a dialkyl ester compound, which is a compound having no free hydroxyl group, is preferable. One type selected from the group consisting of alkyl ether monoalkyl ester compounds and dialkyl ester compounds is more preferred.

  Specific examples of such (poly) alkylene glycol monoalkyl ether monoalkyl ester compounds, dialkyl ether compounds and dialkyl ester compounds include, for example, ethylene glycol monoalkyl ether monoalkyl esters and diethylene glycol monoalkyl ether monoalkyl esters. , Triethylene glycol monoalkyl ether monoalkyl ester, tetraethylene glycol monoalkyl ether monoalkyl ester, propylene glycol monoalkyl ether monoalkyl ester, dipropylene glycol monoalkyl ether monoalkyl ester, tripropylene glycol monoalkyl ether monoalkyl ester, Tetrapropylene glycol monoalkyl ether monoa Kill ester, ethylene glycol dialkyl ester, diethylene glycol dialkyl ester, triethylene glycol dialkyl ester, propylene glycol dialkyl ester, dipropylene glycol dialkyl ester, tripropylene glycol dialkyl ester, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, Examples include propylene glycol dialkyl ether, dipropylene glycol dialkyl ether, and tripropylene glycol dialkyl ether. These may be used alone or in combination.

  In addition to the quinacridone pigment, the polymer compound, and the organic solvent, the oil-based pigment ink composition of the present embodiment includes, as necessary, a surfactant, a surface conditioner, a leveling agent, an antifoaming agent, an oxidation agent. Including known additives such as inhibitors, pH adjusters, charge imparting agents, bactericides, antiseptics, deodorants, charge control agents, wetting agents, anti-skinning agents, UV absorbers, fragrances, pigment derivatives, etc. Also good.

  As a method for preparing the oil-based pigment ink composition of the present embodiment, a conventionally known method can be used. The following preparation methods are mentioned as a preferable preparation method. First, a pigment dispersion is prepared by dispersing a quinacridone pigment, a polymer compound (pigment dispersant), a part of an organic solvent, and optionally other optional components. Examples of the disperser include a container drive medium mill such as a ball mill, a centrifugal mill, and a planetary ball mill; a high-speed rotating mill such as a sand mill; a medium agitation mill such as a stirring tank mill; and a disper.

  Next, a polymer compound (fixing resin) and the remaining organic solvent are further added to the obtained pigment dispersion and mixed uniformly using a stirrer. Specific examples of the stirrer include a three-one motor, a magnetic stirrer, a disper, and a homogenizer. Moreover, you may use mixers, such as a line mixer. Furthermore, a dispersing machine such as a bead mill or a high-pressure jet mill may be used for the purpose of further reducing the particles in the ink composition.

  The oil-based pigment ink composition thus prepared preferably has a surface tension of 20 to 40 mN / m (25 ° C.), and preferably has a viscosity of 2 to 15 mPa · s (25 ° C.). When the surface tension and viscosity are set within the above ranges, when used as an ink-jet ink, excellent jetting with little jet bending is obtained, and bleeding when printed on a substrate such as plain paper or matte paper is obtained. Can be suppressed. The dispersion average particle size of the quinacridone pigment in the oil-based pigment ink composition is preferably 20 to 200 nm, more preferably 50 to 160 nm. When the dispersion average particle diameter is less than 20 nm, the light resistance of the printed matter may be deteriorated because the particles are fine. On the other hand, if the dispersion average particle diameter exceeds 200 nm, the fineness of the printed matter may be lowered. Furthermore, in order to prevent clogging, the maximum dispersed particle diameter is preferably 1,000 nm or less. The surface tension, viscosity, dispersion average particle diameter, and maximum dispersion particle diameter described above can be easily adjusted by changing the type and content of each component.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Hereinafter, “parts” means “parts by mass”. In addition, the apparatus used in the following Example used what was previously wash | cleaned with the pure water in order to exclude the influence of an ionic substance.

<Preparation of quinacridone pigment>
A commercially available quinacridone pigment (a) (manufactured by Sun Chemical Co., Ltd., quinacridone magenta pigment, Quindo Magenta 202RV6843) was prepared. 100 parts of this quinacridone pigment (a) and 500 parts of pure water (ion concentration: 0 ppm, specific conductivity: 0 μS / m) were put into a 1,000 cc plastic disposable cup, and this was added to a room temperature (25 The mixture was stirred at 10 ° C. for 10 minutes, and the washing step of sucking and filtering the mixed solution using filter paper (pore size: 1 μm) was repeated to prepare quinacridone pigments (b) to (e) having different washing times.

  The specific conductivity of each quinacridone pigment obtained as described above was measured as follows. Table 1 shows the results.

[Specific conductivity of quinacridone pigments]
3 parts of quinacridone pigment and 60 parts of pure water (ion concentration: 0 ppm, specific conductivity: 0 μS / m) are put into a 200 cc beaker, and this is put into an oil bath (manufactured by Riko Kagaku Sangyo Co., Ltd., MH-5H) Heated and boiled for 5 minutes. After natural cooling, the solution was filtered using a syringe filter (manufactured by Millipore Corporation, a syringe filter provided with filters of 5 μm, 0.45 μm, and 0.2 μm in order). The filtrate was measured with a compact conductivity meter (HORIBA, B-173 type), and the obtained specific conductivity was defined as the specific conductivity of the quinacridone pigment.

<Preparation of ink>
Example 1
Each component is weighed in a 250 cc plastic bottle at the blending amount shown in Table 2 below, and 100 parts of zirconia beads (diameter: 0.3 mmφ) are added to the bottle and dispersed for 1 hour with a paint conditioner (manufactured by Toyo Seiki Co., Ltd.). Thus, a pigment dispersion (I) was prepared.

  Next, each component was weighed in a 100 cc plastic bottle at the blending amounts shown in Table 3 below, and the solution was stirred with a magnetic stirrer for 30 minutes, followed by suction filtration using a glass filter (manufactured by Kiriyama Seisakusho). An ink was prepared (content of quinacridone pigment: 4 parts).

(Example 2)
A pigment dispersion (II) was prepared in the same manner as in Example 1 except that the quinacridone pigment (d) was used as the pigment in Example 1. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (II) was used (content of quinacridone pigment: 4 parts).

(Example 3)
A pigment dispersion (III) was prepared in the same manner as in Example 1 except that the quinacridone pigment (c) was used as the pigment in Example 1. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (III) was used (content of quinacridone pigment: 4 parts).

Example 4
A pigment dispersion (IV) was prepared in the same manner as in Example 1, except that 4 parts of the quinacridone pigment (c) was used as the pigment. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (IV) was used (content of quinacridone pigment: 1.5 parts).

(Example 5)
A pigment dispersion (V) was prepared in the same manner as in Example 1 except that 24 parts of the quinacridone pigment (e) was used in Example 1. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (V) was used (content of quinacridone pigment: 6.7 parts).

(Comparative Example 1)
A pigment dispersion (VI) was prepared in the same manner as in Example 1 except that the quinacridone pigment (a) was used as the pigment in Example 1. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (VI) was used (content of quinacridone pigment: 4 parts).

(Comparative Example 2)
A pigment dispersion (VII) was prepared in the same manner as in Example 1 except that the quinacridone pigment (b) was used as the pigment in Example 1. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (VII) was used (content of quinacridone pigment: 4 parts).

(Comparative Example 3)
A pigment dispersion (VIII) was prepared in the same manner as in Example 1 except that 10 parts of the quinacridone pigment (a) was used as a pigment in Example 1. An ink was prepared in the same manner as in Example 1 except that this pigment dispersion (VIII) was used (content of quinacridone pigment: 3.4 parts).

(Comparative Example 4)
An ink was prepared according to Example 1 of JP-A No. 2006-56991. First, in a 250 cc plastic bottle, each component was weighed in the blending amounts shown in Table 4 below, and 100 parts of zirconia beads (diameter: 0.3 mmφ) were added thereto, and a paint conditioner (manufactured by Toyo Seiki Co., Ltd.) The pigment dispersion (IX) was obtained by dispersing for 1 hour.

  Next, each component was weighed in a 100 cc plastic bottle with the blending amount shown in Table 5 below, stirred for 30 minutes with a magnetic stirrer, and then suction filtered using a glass filter (manufactured by Kiriyama Seisakusho). An ink was prepared (content of quinacridone pigment: 4 parts).

  The following evaluation was performed for each ink of the examples and comparative examples prepared as described above.

[Monovalent cation concentration and specific conductivity]
While stirring 34 parts of pure water (ion concentration: 0 ppm, specific conductivity: 0 μS / m) with a magnetic stirrer, 6 parts of ink was slowly dropped into pure water and further stirred at room temperature (25 ° C.) for 30 minutes. . After the solution was filtered using a membrane filter (pore size: 0.65 μm), the concentration of sodium ions in the obtained filtrate (aqueous phase) was measured with a compact sodium ion meter (HORIBA, model C-122). The concentration of each ion was measured with a compact potassium ion meter (HORIBA, model C-131), and each measured value was divided by the ink concentration (0.15) in the solution and converted to 100 parts of ink. The cation concentration was determined.
Further, the specific conductivity of the filtrate (aqueous phase) was measured with a compact conductivity meter (HORIBA, model B-173), and the measured value was divided by the ink concentration (0.15) in the solution to obtain ink 100. Specific conductivity when converted to parts was determined.

[Storage stability]
A storage acceleration test was conducted in which the ink was filled in a 30 cc glass bottle and stored in a thermostat at 70 ° C. for one week. After the storage, the presence or absence of precipitates in the ink was visually observed, and the case where no precipitation of precipitates occurred was evaluated as ◯, and the case where precipitates were generated was evaluated as ×.

(Filter permeability)
The ink after storage evaluated based on the storage stability was passed through a filter (pore diameter: 10 μm), and the filter permeability was evaluated according to the following criteria.
○: No filter clogging ×: Filter is clogged and ink does not pass through

  Table 6 shows the types of quinacridone pigments used in Examples and Comparative Examples and the evaluation results.

  As shown in the above table, when the ions in the ink are phase-shifted to pure water, the total concentration of sodium ions and potassium ions in the aqueous phase is 100 ppm or less, and the specific conductivity of the aqueous phase is 150 μS / m or less. It can be seen that the ink does not generate precipitates and can be ejected stably even after storage. This is presumably because sodium ions and potassium ions, which are monovalent cations that generate precipitates in the ink, are small, and the amount of ionic substances in the entire ink is small. Further, it can be seen that the generation of precipitates is suppressed when the total concentration of sodium ions and potassium ions is 100 ppm or less, regardless of whether the content of the quinacridone pigment is large or small.

  On the other hand, it can be seen that the ink of the comparative example containing sodium ions and potassium ions at high concentrations produces precipitates and is inferior in storage stability. For this reason, it can be seen that these inks are clogged even with a large pore size filter after storage. Further, even when the quinacridone pigment is washed to reduce the concentration of sodium ions and potassium ions in the ink, it can be seen that if these total concentrations exceed 100 ppm, precipitates are generated. Furthermore, it can be seen that even when the same quinacridone pigment is used and the content is reduced, precipitates are generated when the total concentration of sodium ions and potassium ions is more than 100 ppm. In addition, even in the conventional ink having improved storage stability, when the total concentration of sodium ions and potassium ions is high, precipitates are similarly generated, indicating that the storage stability is poor.

Claims (3)

  An oil-based pigment ink composition comprising at least a quinacridone pigment, a polymer compound, and an organic solvent, wherein when ions in the oil-based pigment ink composition are phase-inverted to pure water, monovalent cations in the water phase An oil-based pigment ink composition having a total concentration of 100 ppm or less.   The oil-based pigment ink composition according to claim 1, wherein the aqueous phase contains one or both of sodium ions and potassium ions as the monovalent cation.   The oil-based pigment ink composition according to claim 1 or 2, wherein the specific conductivity of the aqueous phase is 150 µS / cm or less.