JP2008231224A - Aqueous ink composition and inkjet recording method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous ink composition which is excellent in color development on various recording media (e.g. plain paper, matte paper, glossy paper, actual printing paper, etc.), is capable of yielding an image excellent in glossiness particularly on glossy recording media, has a high antiseptic property and is excellent in long-term shelf stability, recovery from nozzle-clogging and discharge stability. <P>SOLUTION: The ink composition comprises at least a coloring agent coated with a water-insoluble polymer as a colorant and at least an alkylisothiazolone as an antiseptic. The ink composition particularly comprises benzisothiazolone in addition to the alkylisothiazolone, and glycol ethers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention has excellent color developability with respect to various recording media (plain paper, matte paper, glossy paper, printing paper, etc.), and obtains an image with excellent glossiness particularly with respect to glossy recording media. In addition, the present invention relates to a water-based ink composition that has high antiseptic properties and is excellent in long-term storage stability, nozzle clogging recovery properties, and ejection stability.

  The ink jet recording method is a printing method in which printing is performed by causing ink droplets to fly and adhere to a recording medium such as paper. Due to recent advances in inkjet recording technology, the inkjet recording method has been used for high-definition image recording (printing), which has been the field of photography and offset printing. High-quality recording has been demanded not only for paper and dedicated paper for ink jet recording (matte and glossy) but also for recording media such as printing paper.

  As an ink used for ink jet recording, an ink composition is generally known that includes a coloring material that is a colorant, water, a water-soluble organic solvent, a surfactant, and the like.

  As the colorant, dyes or pigments are used. In particular, water-soluble dyes are often used for color inks because of high color saturation, transparency, and high solubility in water. However, such dyes generally have insufficient light resistance and gas resistance, and because they are water-soluble, there are also problems with water resistance. The recorded matter has a drawback that the recorded image has poor storage stability.

  On the other hand, a colorant insoluble in water is advantageous in terms of water resistance. Among pigments that are insoluble in water, in particular, pigments are color materials excellent in light resistance, gas resistance, and water resistance, and therefore, pigment inks that take advantage of these color material properties have been developed. An aqueous pigment ink in which a pigment is dispersed with a surfactant or a polymer dispersant, an aqueous pigment ink using a self-dispersing pigment with a water-dispersible functional group added to the pigment surface, or a pigment coated with a water-dispersible resin An aqueous pigment ink using colored fine particles has been proposed.

  In such a pigment ink, pigment particles (including pigment-containing colored fine particles) are stably dispersed in the ink liquid. The process of drying the ink after the ink has adhered to a recording medium such as paper. As the moisture and volatile solvents evaporate, the stable dispersion system collapses and the pigments tend to aggregate. When the aggregated pigment is deposited on a recording medium such as paper, the smoothness of the surface is lost, the glossiness is deteriorated, the uniformity of the printed image is deteriorated, and there is a problem that a high-quality image cannot be obtained.

  Therefore, regarding the image quality of the pigment ink, the particle diameter of the pigment dispersed in the ink is limited for the purpose of improving glossiness and dispersibility (see Patent Document 1), and bleeding and color development are improved. Ink containing a water-insoluble vinyl polymer dispersion containing a pigment for the purpose of containing fine polymer particles (see Patent Document 2) for the purpose of improving the printing density on plain paper and glossiness on inkjet paper (See Patent Document 3) and the like.

  Further, the water-based ink composition used for inkjet recording needs to be able to eject ink stably over a long period of time. However, in the case of the ink composition proposed above, microorganisms such as bacteria and wrinkles may occur when stored for a long period of time, and this causes changes in the physical properties of the ink and nozzle clogging, and stable ejection is not possible. There is. In particular, in the case of an aqueous ink composition using a pigment as a coloring material, a polymer is used to disperse the pigment in water, which is the main solvent, or polymer fine particles are further used to improve fixability. Therefore, microorganisms such as bacteria and wrinkles are more likely to be generated than in the case of a non-aqueous ink composition. Accordingly, a relatively strong antiseptic effect is required in order to prevent the generation of microorganisms such as bacteria and sputum, not only during production but also in a long-term use environment.

  Therefore, conventional water-based inks include those using benzoisothiazolone as an ink using a dye as a colorant (for example, Patent Document 4), those using isothiazolone or benzisothiazolone (for example, Patent Document 5 and Patent Document 6). ) And those using alkylisothiazolone (for example, Patent Document 7). Further, an ink composition having a high antiseptic effect by using two types of alkylisothiazolones in combination is disclosed (for example, Patent Document 8).

  However, even when these isothiazolone preservatives are used, there are cases where sufficient antiseptic effect as ink for ink jet recording, long-term storage stability, nozzle clogging recovery property, and ejection stability cannot be obtained.

JP 2002-356737 A JP 2001-123098 A JP 2004-75988 A JP 2004-1224017 A Japanese Patent Laid-Open No. 11-228860 JP 2000-355665 A JP 2002-256193 A JP 2004-176064 A

  The present invention has been made to solve the above-described problems. That is, the object of the present invention is to have excellent color developability for various recording media (plain paper, matte paper, glossy paper, printing paper, etc.), and particularly glossy recording media. A water-based ink composition and an ink jet recording method that are capable of obtaining excellent images, have high antiseptic properties, and are excellent in long-term storage stability, nozzle clogging recovery properties, and ejection stability. There is to do.

  As a result of intensive studies, the present inventors have determined that an ink composition containing at least a colorant coated with a water-insoluble polymer as a colorant contains at least an alkylisothiazolone as a preservative. In addition, the inventors have found that the above-mentioned problems can be solved by including a glycol ether in the ink composition. The present invention is based on such knowledge, and the configuration of the present invention is as follows.

  (1) The water-based ink composition of the present invention is characterized in that, in an ink composition containing at least a colorant coated with a water-insoluble polymer as a coloring material, at least an alkylisothiazolone as a preservative.

  (2) The water-based ink composition of the invention is characterized by further containing benzisothiazolone as the preservative.

  (3) The water-based ink composition of the present invention is a polymer in which the water-insoluble polymer is obtained by copolymerizing a monomer mixture containing at least a polymerizable unsaturated monomer, a hydrophilic group monomer, and a salt-forming group monomer. It is characterized by being.

  (4) The water-based ink composition of the invention is characterized in that the water-insoluble polymer is a branched polymer.

  (5) The water-based ink composition of the invention is characterized in that the colorant is a pigment.

(6) The water-based ink composition of the invention is characterized in that the content of the alkyl isothiazolone is 3 ppm to 30 ppm with respect to the total amount of the ink.
7) The water-based ink composition of the invention is characterized in that the content of the benzisothiazolone is 2 to 10 times the content of the alkylisothiazolone.
8) The water-based ink composition of the invention is characterized in that the total content of the alkyl isothiazolone and the benzisothiazolone is 10 ppm to 120 ppm with respect to the total amount of the ink.
(9) The water-based ink composition of the present invention further comprises glycol ethers. (10) The ink jet recording method of the present invention is a liquid of the water-based ink composition as described in (1) to (9). It is characterized in that printing is performed by ejecting a target and attaching the droplets to a recording medium.

  Hereinafter, the present invention will be described in detail based on preferred embodiments thereof.

[Preservative]
The aqueous ink composition of the present invention comprises at least an alkylisothiazolone as a preservative. In the present invention, the preservative means a substance having a function of preventing the generation and growth of microorganisms, particularly bacteria and fungi (spider). Examples of alkyl isothiazolones include methyl isothiazolone and octyl isothiazolone, with methyl isothiazolone being more preferred. As a preservative containing methylisothiazolone as an active ingredient, Kathon (manufactured by Rohmman Haas) and the like are commercially available. Further, as a preservative containing octylisothiazolone as an active ingredient, Skane (manufactured by Rohmman Haas), NS-800H, NS-800G, NS-800P (manufactured by Nagase Kasei Kogyo Co., Ltd.) and the like are commercially available.
The aqueous ink composition of the present invention further contains benzisothiazolone as a preservative. By using alkylisothiazolone and benzisothiazolone together, resistant bacteria can be suppressed and a stronger antiseptic effect can be obtained. Examples of preservatives containing benzisoythiazolone as an active ingredient include Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2, Proxel TN, Proxel BD20, Proxel LV (manufactured by Arch Chemicals), Denside BIT, Denide NIPA (Nagase Kasei Kogyo Co., Ltd.) is commercially available.

  In the aqueous ink composition of the invention, the content of the alkyl isothiazolone is preferably 3 ppm to 30 ppm, more preferably 10 ppm to 30 ppm, based on the total amount of the ink. If it is 3 ppm or more, a sufficient antiseptic effect can be obtained, and if it is 30 ppm or less, good long-term storage stability, nozzle clogging recovery properties, ejection stability, and other ink jet characteristics can be satisfied.

  In the aqueous ink composition of the invention, the content of the benzisothiazolone is preferably 2 to 10 times the content of the alkylisothiazolone. If it is 2 times or more, a sufficient antiseptic effect can be obtained, and if it is 10 times or less, good long-term storage stability, nozzle clogging recovery properties, ejection stability, and other ink jet characteristics can be satisfied.

  In the aqueous ink composition of the present invention, the total content of the alkylisothiazolone and the benzisothiazolone is preferably 10 ppm to 120 ppm, more preferably 50 ppm to 120 ppm, based on the total amount of the ink composition. If it is 10 ppm or more, a sufficient antiseptic effect can be obtained, and if it is 120 ppm or less, good long-term storage stability, nozzle clogging recovery properties, and ejection stability ink jet characteristics can be satisfied.

  In addition, the water-based ink composition of the present invention can simultaneously use other types of preservatives in addition to alkylisothiazolone and benzisothiazolone. Examples include one or more selected from chloroalkylisothiazolones, bromonitroalcohols, oxazolidine compounds, and chlorxylenol.

[Colorant]
As the colorant used for the colorant coated with the water-insoluble polymer of the present invention, existing dyes and pigments described in “Dye Handbook” (publisher: Maruzen Co., Ltd.) and the like can be used.

  The colorant of the present invention is preferably a water-insoluble colorant, and a more preferred colorant is a pigment. As the pigment that can be used in the present invention, any of known inorganic pigments and organic pigments can be used, and pigments such as Pigment Yellow, Pigment Red, Pigment Violet, Pigment Blue, and Pigment Black described in the Color Index. In addition, phthalocyanine-based, azo-based, anthraquinone-based, azomethine-based, condensed ring-based pigments can be exemplified. Further, organic pigments such as yellow No. 4, 5, 205, 401; orange 228, 405; blue No. 1, 404, etc., titanium oxide, zinc oxide, zirconium oxide, iron oxide, ultramarine blue, bitumen, Examples thereof include inorganic pigments such as chrome oxide. For example, C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42, 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 150, 153, 155, 174, 180, 198, C.I. I. Pigment Red 1,3,5,8,9,16,17,19,22,38,57: 1,90,112,122,123,127,146,184,202,209, C.I. I. Pigment Bio Red 1,3,5: 1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, C.I. I. Pigment Black 1, 7, etc., and an ink composition can also be formed using a plurality of pigments.

  The pigment content in the ink composition constituting the ink set of the present invention is contained in the range of 0.5% by weight to 8% by weight from the viewpoints of color developability, glossiness, nozzle clogging recovery, and the like. Is preferred. If the content is 0.5% by weight or more, color development can be satisfied for various recording media. If the content is 8% by weight or less, in addition to the glossiness of the printed image, long-term storage stability and recovery from nozzle clogging are achieved. Ink jet characteristics such as performance and ejection stability can be satisfied.

[Colorant coated with water-insoluble polymer]
The water-insoluble polymer used in the colorant coated with the water-insoluble polymer of the present invention is a solution polymerization method using at least a polymerizable unsaturated monomer, a hydrophilic group monomer, and a salt-forming group monomer using a polymerization initiator. The water-insoluble polymer refers to a polymer having a solubility in 100 g of water at 25 ° C. of less than 1 g after neutralization. By using a hydrophilic group monomer and a salt-forming group monomer, glossiness of a printed image can be imparted.

  Examples of the polymerizable unsaturated monomer include vinyl aromatic hydrocarbons, methacrylic acid esters, methacrylamide, alkyl-substituted methacrylamide, maleic anhydride, vinyl cyanide compounds, methyl vinyl ketone, and vinyl acetate. Specifically, styrene, α-methylstyrene, vinyl toluene, 4-t-butyl styrene, chlorostyrene, vinyl anisole, vinyl naphthalene, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n- There are amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, acrylonitrile, methacrylonitrile, etc. Use alone or in combination of two or more It is also possible.

  Specific examples of the hydrophilic group monomer include polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, and ethylene glycol / propylene glycol monomethacrylate, which can be used alone or in admixture of two or more. In particular, polyethylene glycol (2-30) monomethacrylate, polyethylene glycol (1-15) / propylene glycol (1-15) monomethacrylate, polypropylene glycol (2-30) methacrylate, methoxypolyethylene glycol (2-30) methacrylate, methoxy The gloss of printed images is further improved by using monomer components that constitute branched chains such as polytetramethylene glycol (2-30) methacrylate and methoxy (ethylene glycol / propylene glycol copolymer) (1-30) methacrylate. To do.

  Specific examples of the salt-forming group monomer include acrylic acid, methacrylic acid, styrene carboxylic acid, maleic anhydride, maleic acid, maleic acid monoester, maleic acid monoamide, itaconic acid, and 2- (meth) acryloyloxyethanesulfonic acid. , 2- (meth) acryloyloxypropane sulfonic acid, 2- (meth) acrylamide-2-alkyl (1 to 4 carbon atoms) propane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, vinyl phosphate, bis ( Methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, N N-dimethylaminoethyl (meth) acrylate, N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide, vinylpyrrolidone, methacryloyloxyethyltrimethylammonium methylsulfate, methacryloyloxyethyldimethylethylammonium ethylsulfate, etc. In particular, acrylic acid, methacrylic acid, and N, N-dimethylaminoethyl (meth) acrylate are preferable. These can be used alone or in admixture of two or more.

  Furthermore, a macromer such as a styrene macromonomer or a silicone macromonomer having a polysynthetic functional group at one end, or other monomers can be used in combination.

  The colorant coated with the water-insoluble polymer of the present invention is obtained by a phase inversion emulsification method. That is, the above water-insoluble polymer is dissolved in an organic solvent such as methanol, ethanol, isopropanol, n-butanol, acetone, methyl ethyl ketone, dibutyl ether, a colorant is added to the resulting solution, and then a neutralizing agent and water are added. By adding, kneading and dispersing, an oil-in-water type dispersion is prepared, and an organic solvent is removed from the obtained dispersion to obtain an aqueous dispersion. For the kneading and dispersing treatment, for example, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring type disperser, or the like can be used.

The neutralizing agent is preferably a tertiary amine such as ethylamine or trimethylamine, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia or the like, and the pH of the resulting aqueous dispersion is preferably 6-10.
The water-insoluble polymer to be coated is preferably a polymer having a weight average molecular weight of about 10,000 to 150,000 from the viewpoint of stably dispersing a colorant, particularly a pigment. The weight average molecular weight can be measured by a molecular weight analysis method by gel permeation chromatography (GPC).

  Further, the ratio of the colorant to the water-insoluble polymer is in the ratio of colorant: water-insoluble polymer = 1: 0.2 to 1: 1, so that the dispersion stability, the storage stability of the ink, and the nozzle are clogged. From the viewpoint of prevention and the like, and from the viewpoint of glossiness on glossy media. Specifically, if the water-insoluble polymer is less than 20% of the colorant, stable dispersion cannot be achieved, and aggregation of the colorant occurs. If the water-insoluble polymer is more than 100% of the colorant, the bronzing phenomenon becomes small. This is because the color development is lowered and the gloss on the glossy media is also deteriorated.

  Further, from the viewpoint of coloring and glossiness on glossy media, the volume average particle diameter of the colorant in the ink is preferably in the range of 50 nm to 150 nm. These volume average particle diameters can be obtained by particle diameter measurement using a Microtrac UPA150 (manufactured by Microtrac) or a particle size distribution analyzer LPA3100 (manufactured by Otsuka Electronics Co., Ltd.).

  The colorant covered with the water-insoluble polymer of the present invention may have a shape in which a part of the colorant is exposed without being completely covered with the water-insoluble polymer.

[Glycol ethers]
The aqueous ink composition of the present invention further comprises glycol ethers. Glycol ethers improve the penetrability of the ink composition into the recording medium and nozzle clogging, and further improve the solubility of components in the ink composition such as a penetrant, and also have a preservative effect. Therefore, by including glycol ethers, even when only one alkyl isothiazolone is included as a preservative, a higher and sufficient antiseptic effect can be obtained. Examples of glycol ethers that can be used in the present invention include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n. -Propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monobutyl ether, 1-methyl-1-methoxybutanol, Pyrene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, Examples thereof include dipropylene glycol mono-n-propyl ether and dipropylene glycol mono-iso-propyl ether, and triethylene glycol mono-n-butyl ether is particularly preferable. These may be used alone or in combination of two or more, and are preferably contained in the ink composition in an amount of 2 to 15% by weight from the viewpoint of ensuring appropriate antiseptic properties.

[Others]
The aqueous ink composition of the present invention preferably contains water as a main solvent and a water-soluble organic solvent such as a surface tension adjusting agent, a wetting agent, and a penetration accelerator.

  As water, it is preferable to use pure or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water. In particular, water obtained by sterilizing these waters by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of mold and bacteria is prevented over a long period of time.

  The aqueous ink composition of the present invention preferably contains a surface tension adjusting agent from the viewpoint of improving the printing quality. The surface tension adjusting agent can be selected from commonly used anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants. Among these, nonionic surfactants are particularly preferable. . Specific examples of nonionic surfactants include acetylene glycol surfactants, acetylene alcohol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene phenyl ethers, and the like. An ink composition with less foaming compared to the surfactant can be obtained. Furthermore, among nonionic surfactants, acetylene glycol surfactants are particularly preferred when used in ink jet recording because an ink composition with almost no foaming can be obtained. Examples of acetylene glycol surfactants include Surfynol 420, 440, 465, 485, 104, STG (product of Air Products), Olphine PD001, PD002W, SPC, E1004, E1010 (product of Nissin Chemical Industry Co., Ltd.) ), Acetylenol E00, E40, E100, LH (product of Kawaken Fine Chemical Co., Ltd.) and the like. Examples of the polyether-modified siloxanes include BYK-346, 347, 348, and UV3530 (Bic Chemie product). One or more of these can be used in the ink composition, and the surface tension is preferably adjusted to 20 mN / m to 40 mN / m. In the ink composition, 0.1% by weight to 3% is preferable. 0.0% by weight is contained.

  It is preferable to add a wetting agent to the water-based ink composition of the present invention from the viewpoint of preventing the ink composition from drying and preventing clogging at the head of the ink jet printer. Examples of the wetting agent include glycerin, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol and dipropylene glycol. Polyhydric alcohols such as 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, glucose, mannose, fructose, ribose, xylose, arabinose , Sugars such as galactose, aldonic acid, glucitol (sorbitol), maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, sugar alcohols, hyaluronic acids, urea, 1,2 Urea derivatives such as dimethylurea, ethyleneurea, dimethylolethyleneurea, thiourea, semicarbazide, guanidine, melamine, etc., C1-C4 alkyl alcohols such as ethanol, methanol, butanol, propanol, isopropanol, 2-pyrrolidone N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane and the like. These can be used singly or in combination of two or more in the ink composition, from the viewpoint of ensuring appropriate physical properties (such as viscosity) of the ink composition, and ensuring reliability such as clogging and ejection stability. Thus, the ink composition preferably contains 5 wt% to 50 wt%.

  In the aqueous ink composition of the present invention, it is preferable to add a penetration accelerator from the viewpoint of increasing the wettability to the recording medium and increasing the permeability of the organic pigment. The penetration enhancer preferably contains 1,2-alkanediol and / or glycol ether. Specific examples of 1,2-alkanediol include 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, 4-methyl-1,2-pentanediol and the like. These solvents can be used singly or in combination of two or more, and are preferably contained in the ink composition in an amount of 2% by weight to 15% by weight from the viewpoint of ensuring appropriate permeability and drying properties.

  The aqueous ink composition of the present invention may further contain a material selected from pH adjusters, dissolution aids, antioxidants and the like as desired. These components can be used alone or in combination of two or more. Moreover, it is not necessary to add, if it is not necessary to add. Those skilled in the art can use the preferable additive selected in a preferable amount as long as the effects of the present invention are not impaired.

  As a pH adjuster, C6-C10 such as alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, ammonia, triethanolamine, ethyldiethanolamine, diethylethanolamine, tripropanolamine and the like. Although tertiary amines etc. can be used, Preferably it contains at least 1 sort (s) of pH adjusting agents selected from alkali metal hydroxide, ammonia, triethanolamine, and tripropanolamine, and it adjusts to pH 6-10. It is preferred that If the pH is out of this range, the material constituting the ink jet printer will be adversely affected, and the clogging recoverability will deteriorate.

  The dissolution aid is an additive for dissolving the insoluble matter and keeping the ink composition in a uniform solution when the insoluble matter is precipitated from the ink composition. Examples of solubilizers include pyrrolidones such as N-methyl-2-pyrrolidone and 2-pyrrolidone, ureas such as urea, thiourea and tetramethylurea, allophanates such as allophanate and methyl allophanate, biuret, dimethylbiuret, Biurets such as tetramethyl biuret can be exemplified, but not limited thereto.

  Examples of the antioxidant include, but are not limited to, L-ascorbic acid and its salts.

[Inkjet recording method]
The aqueous ink composition of the present invention can be suitably used for writing instruments such as pens, stamps and the like, but can be more suitably used as ink for inkjet recording. In the present invention, the ink jet recording method means a system in which an ink composition is ejected as droplets from a fine nozzle and the droplets adhere to a recording medium. This will be specifically described below.

  As a first method, there is an electrostatic suction method, which applies a strong electric field between the nozzle and the acceleration electrode placed in front of the nozzle, and continuously ejects ink from the nozzle in the form of droplets. This is a method in which a print information signal is applied to the deflection electrode while the ink droplet is flying between the deflection electrodes for recording, or a method in which the ink droplet is ejected in response to the print information signal without being deflected.

  The second method is a method in which ink droplets are forcibly ejected by applying pressure to the ink liquid with a small pump and mechanically vibrating the nozzle with a crystal resonator or the like. The ejected ink droplet is charged simultaneously with the ejection, and a printing information signal is given to the deflection electrode and recorded while the ink droplet flies between the deflection electrodes.

  The third method is a method using a piezoelectric element, in which a pressure and a print information signal are simultaneously applied to an ink liquid by a piezoelectric element to eject and record ink droplets.

  The fourth method is a method in which the ink liquid is rapidly expanded in volume by the action of heat energy, and the ink liquid is heated and foamed with a microelectrode in accordance with a print information signal to eject and record ink droplets.

  Any of the above methods can be used in the ink jet recording method using the aqueous ink composition of the present invention.

<Example>
Hereinafter, although the ink composition of the present invention will be described in detail with reference to examples, the present invention is not limited to these examples.

[Adjustment of colorant dispersion]
A colorant dispersion having dispersed particles of a colorant coated with a water-insoluble polymer was prepared by the following method.

[Synthesis of water-insoluble polymers 1 to 3]
In a reaction vessel sufficiently substituted with nitrogen gas using 20 parts by weight of an organic solvent (methyl ethyl ketone), 0.03 part by weight of a polymerization chain transfer agent (2-mercaptoethanol), a polymerization initiator, and each monomer shown in Table 1. The mixture was polymerized with stirring at 75 ° C., and 0.9 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) dissolved in 40 parts by weight of methyl ethyl ketone was added to 100 parts by weight of the monomer component. The polymer solution was obtained by aging for 1 hour.

(Pigment dispersion Y1)
5 parts obtained by drying the polymer solution obtained as water-insoluble polymer 1 under reduced pressure was dissolved in 15 parts of methyl ethyl ketone, and the polymer was neutralized with an aqueous sodium hydroxide solution. Furthermore, C.I. I. 15 parts of Pigment Yellow 74 was added and kneaded with a disperser while adding water. After 100 parts of ion-exchanged water was added to the kneaded mixture and stirred, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was further removed, whereby a yellow pigment having a solid content concentration of 20% by weight was removed. An aqueous dispersion was obtained (pigment: water-insoluble polymer = 1: 0.3).
(Pigment dispersion Y2)
9 parts obtained by drying the polymer solution obtained as the water-insoluble polymer 2 under reduced pressure were dissolved in 45 parts of methyl ethyl ketone, and the polymer was neutralized with an aqueous sodium hydroxide solution. Furthermore, C.I. I. 18 parts of Pigment Yellow 74 was added and kneaded with a disperser while adding water. After 120 parts of ion-exchanged water was added to the kneaded mixture and stirred, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was further removed, whereby a yellow pigment having a solid content concentration of 20% by weight was removed. An aqueous dispersion was obtained (pigment: water-insoluble polymer = 1: 0.5).
(Pigment dispersion Y3)
7 parts obtained by drying the polymer solution obtained as the water-insoluble polymer 3 under reduced pressure were dissolved in 21 parts of methyl ethyl ketone, and the polymer was neutralized with an aqueous sodium hydroxide solution. Furthermore, C.I. I. 16 parts of Pigment Yellow 74 was added and kneaded with a disperser while adding water. After 110 parts of ion-exchanged water was added to the kneaded product and stirred, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was further removed, whereby a yellow pigment having a solid content concentration of 20% by weight was removed. An aqueous dispersion was obtained (pigment: water-insoluble polymer = 1: 0.4).
(Pigment dispersion M1)
In the pigment dispersion Y1, C.I. I. Instead of CI Pigment Yellow 74, C.I. I. A dispersion M1 was obtained in the same manner as the dispersion Y1, except that CI Pigment Red 122 was used.

(Pigment dispersion M2)
In the pigment dispersion Y2, C.I. I. Instead of CI Pigment Yellow 74, C.I. I. A dispersion M2 was obtained in the same manner as the dispersion Y2, except that CI Pigment Red 122 was used.

(Pigment dispersion M3)
In the pigment dispersion Y3, C.I. I. Instead of CI Pigment Yellow 74, C.I. I. A dispersion M3 was obtained in the same manner as the dispersion Y3 except that CI Pigment Red 122 was used.

(Pigment dispersion C1)
In the pigment dispersion Y1, C.I. I. Instead of CI Pigment Yellow 74, C.I. I. A dispersion C1 was obtained in the same manner as the pigment dispersion Y1, except that CI Pigment Blue 15: 3 was used.

(Pigment dispersion C2)
In the pigment dispersion Y2, C.I. I. Instead of CI Pigment Yellow 74, C.I. I. A dispersion C2 was obtained in the same manner as the pigment dispersion Y2, except that CI Pigment Blue 15: 3 was used.

(Pigment dispersion C3)
In the pigment dispersion Y3, C.I. I. Instead of CI Pigment Yellow 74, C.I. I. A dispersion C3 was obtained in the same manner as the pigment dispersion Y3 except that CI Pigment Blue 15: 3 was used.

[Preparation of ink]
Each component was mixed in the ratios shown in Tables 2 to 4, stirred at room temperature for 2 hours, and then filtered through a membrane filter having a pore size of 8 μm to prepare each ink. However, the addition amounts shown in Tables 2 to 4 are expressed as ppm for the preservatives, and all other values are expressed as weight% concentrations, and the numbers in parentheses in the colorant dispersion are shown. Represents the solid content concentration of the colorant. The “remaining amount” of ion-exchanged water means adding ion-exchanged water so that the total amount of ink becomes 100% by weight. For the average particle size of the ink composition, each ink composition was diluted 1000 times with pure water using a particle size distribution meter (UPA-150 manufactured by Microtrack), and the particle size distribution of the diluted solution was measured. The volume average particle diameter was determined, and the results are shown in Tables 2 to 4.

[Evaluation test of ink composition]
The following evaluations 1 to 6 were performed for the prepared ink compositions of Examples 1 to 30 and Comparative Examples 1 to 9. The results are shown in Table 5.

(Evaluation 1: Antiseptic)
In order to observe the state of generation of microorganisms such as bacteria or sputum when each ink composition is filled in a cartridge of an ink jet recording apparatus EM-930C manufactured by Seiko Epson Corporation and left at 30 ° C. for half a year, 1 g of ink is taken, The culture was carried out at 25 ° C. and 30 ° C. for 4 weeks by culturing on an agar medium to observe the increase of bacteria and sputum, and the determination was made based on the following criteria.
Judgment A: When there are 100 or less bacteria or sputum Judgment B: When there are 101 or 1000 bacteria or sputum or less Judgment C; When there are 1001 or more bacteria or sputum

(Evaluation 2: Ink storage stability)
Each ink composition was left in an environment of 60 ° C. for 2 weeks with 50 g in an aluminum pack. Based on the following criteria, regarding the presence or absence of foreign matter (floating matter or sediment) after standing, and for those that do not produce foreign matter, further changes in physical properties (viscosity, surface tension, pH, particle size) Judged.
Judgment A: All ink compositions of the ink set have no foreign matter and no change in physical properties.
Judgment B: At least one of the ink compositions in the ink set produced no foreign matter, but the physical properties slightly changed.
Judgment C: At least one ink composition in the ink set causes foreign matter or physical properties to change significantly.

(Evaluation 3: Nozzle clogging recovery)
Each ink composition is filled into the head using the printer, and after confirming that the ink is normally ejected from the nozzles, the ink cartridge is not present and the printer head is not capped. It was left for 1 week in an environment of ° C. After being allowed to stand, the number of cleanings required until the ink composition was normally ejected from the nozzles again was examined, and a determination was made based on the following criteria.
Judgment A: Less than 2 cleanings Judgment B: Cleaning 3 to 5 times Judgment C: Cleaning 6 times or more

(Evaluation 4: Discharge stability)
Each ink composition was filled in the head using the printer, and a pattern including solid and ruled lines was continuously printed in a 40 ° C. environment. Evaluate whether or not ink dot missing or flying bend occurs from the start of printing to the end of the ink, and how many times the printer cleaning is required to return to normal printing when it occurs. did.
Judgment A: Does not occur or cleaning once Judgment B: Cleaning 2 to 4 times Judgment C: Cleaning 5 times or more

(Evaluation 5: Glossiness)
Each ink composition was printed on a photographic paper <gloss> (trade name: manufactured by Seiko Epson Corporation) using the printer, and after being left at 25 ° C. for 24 hours, the gloss meter GM-268 ( 20 degree specular glossiness (Gs20) was measured using Konica Minolta Co., Ltd., and judged based on the following criteria.
Determination A; 60 ≦ Gs20
Determination B; 45 ≦ Gs20 <60
Determination C; Gs20 <45

(Test 6: Color development)
For each ink composition, a solid pattern was created on Xerox-4024 using the printer, and left at 25 ° C. for 24 hours, and then the OD value of the printed matter was measured using Spectrolino (trade name: manufactured by Gretag). The color was determined based on the following criteria.
Judgment A; OD value 1.2 or more Judgment B; OD value 1.0 to less than 1.2 Judgment C; OD value less than 1.0

  As is apparent from Table 5, the aqueous ink composition of the present invention has excellent color developability with respect to various recording media (plain paper, matte paper, glossy paper, printing paper, etc.), and is particularly glossy. In addition to being able to obtain a glossy image on a recording medium, the ink composition is excellent in antiseptic properties, and has excellent long-term storage stability, nozzle clogging recovery properties, and ejection stability. It is suitable for use in.

  The present invention is not limited to the above-described embodiment, but can be applied to uses such as ink for writing instruments and ink for offset printing.

Claims (10)

  An aqueous ink composition comprising at least an alkylisothiazolone as a preservative, wherein the ink composition comprises at least a colorant coated with a water-insoluble polymer as a coloring material.   The aqueous ink composition according to claim 1, further comprising benzisothiazolone as the preservative.   The water-insoluble polymer is a polymer obtained by copolymerization of a monomer mixture containing at least a polymerizable unsaturated monomer, a hydrophilic group monomer, and a salt-forming group monomer. 3. A water-based ink composition as described in 2.   The aqueous ink composition according to claim 1, wherein the water-insoluble polymer is a branched polymer.   The water-based ink composition according to claim 1, wherein the colorant is a pigment.   6. The aqueous ink composition according to claim 1, wherein the content of the alkyl isothiazolone is 3 ppm to 30 ppm with respect to the total amount of the ink.   7. The water-based ink composition according to claim 2, wherein the content of the benzisothiazolone is 2 to 10 times the content of the alkylisothiazolone. 8.   The aqueous ink composition according to claim 1, wherein the total content of the alkyl isothiazolone and the benzisothiazolone is 10 ppm to 120 ppm with respect to the total amount of the ink.   The aqueous ink composition according to any one of claims 1 to 8, further comprising glycol ethers.   An ink jet recording method, wherein printing is performed by discharging droplets of the water-based ink composition according to claim 1 and attaching the droplets to a recording medium.