JP2006249246A - Electrostatic ink-jet ink composition and ink-jet printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic ink-jet ink composition capable of setting high-quality printed images at low temperatures and in high speed on a printing media, and to provide an ink-jet printing method using the ink composition. <P>SOLUTION: The electrostatic ink-jet ink composition comprises a dispersion medium, charged particles essentially containing a coloring material, and an electric charge adjuster, wherein the electric charge adjuster consists of an electric charge generator composition obtained by mixing an electric charge generator, a solvent and a polar monomer species together followed by conducting a polymerization reaction. The ink-jet printing method comprises jetting the ink composition as ink droplets by an ink-jet printing system utilizing the electrostatic field. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic ink jet ink composition and an ink jet recording method.

  As an image recording method for forming an image on a recording medium such as paper based on an image data signal, an electrophotographic method, a sublimation type and melt type thermal transfer method, an ink jet method and the like have been known so far. Among these, the electrophotographic system requires a process of forming an electrostatic latent image on a photosensitive drum by charging and exposure, and therefore the system is complicated and the apparatus is expensive. The thermal transfer method is less expensive than the electrophotographic method, but has problems such as high running costs and waste materials due to the use of an ink ribbon. On the other hand, the ink jet method is an inexpensive apparatus and ejects ink only to a required image portion to form an image directly on a recording medium. Therefore, the ink can be used efficiently and the running cost is low. Furthermore, there is little noise and it is excellent as an image recording method.

Inkjet recording methods include, for example, a method in which ink droplets are ejected by the pressure of steam generated by the heat of a heating element, a method in which ink droplets are ejected by mechanical pressure pulses generated by a piezoelectric element, and an electrostatic field. There is a method (see Patent Documents 1 and 2) that causes ink droplets containing charged particles to fly. Here, the method of flying ink droplets with steam or mechanical pressure cannot control the flying direction of the ink droplets, and the ink droplets are accurately delivered to the desired position on the printing medium due to distortion of the ink nozzles or air convection. May be difficult to land on.
On the other hand, the method using an electrostatic field controls the flying direction of the ink droplets by the electrostatic field, so that the ink droplets can be landed accurately at a desired position, and a high-quality image formation (printed material) is created. Can be better.

  As an ink composition used for inkjet recording using an electrostatic field, an ink composition containing a dispersion medium and charged particles including at least a coloring material is used (see Patent Documents 3 and 4). By changing the color material, the ink composition containing the color material can create four color inks of yellow, magenta, cyan, and black, and can also create special color inks of gold and silver . Therefore, it is useful because a color image formed product (printed product) can be produced. However, in order to maintain high speed and high image quality and to stably output a color image formed product (printed product), a means for fixing to paper is required. Furthermore, in an inkjet recording system, it is necessary to realize low-temperature and high-speed fixing without deteriorating image quality in a state where a solvent is present in the image area and paper at the time of fixing. It was difficult at present.

Patent Document 5 also discloses a method for stabilizing a charge director solution comprising a step of mixing a charge director, a solvent, and a polar monomer species, and a step of starting a polymerization reaction to proceed to completion. However, this technique relates to the components of the liquid developer used in the electrophotographic system, and is completely different from the electrostatic ink jet recording system. Further, Patent Document 5 describes that a small drawing dot required for an electrostatic ink jet recording method, for example, a dot diameter of about 10 μm is formed with high positional accuracy, and a high particle charge necessary for concentrated discharge is obtained. Not seen at all.
Japanese Patent No. 3315334 US Pat. No. 6,158,844 JP-A-8-291267 US Pat. No. 5,952,2048 JP-T-4-503262

  The present invention has been made in view of the above-described problems in the prior art, and provides an ink composition for electrostatic ink jet and an ink jet recording method capable of fixing a high quality image at low temperature and high speed on a recording medium. It is intended to provide.

  As a result of diligent studies to achieve the above object, the present inventor has found that small drawing dots required for electrostatic ink jet recording systems can be obtained by using a specific charge generator composition as a charge control agent in an ink composition. For example, a dot diameter of about 10 μm can be formed with high positional accuracy, ink particle charge generation efficiency is excellent, the electrophoretic speed of the ink particles at the ejection part is sufficiently high, and the ink particles are sufficiently concentrated. As a result, the inventors have found that an image with good quality without bleeding can be obtained and completed the present invention.

The present invention is as follows.
(1) An electrostatic ink jet ink composition containing a dispersion medium, charged particles containing at least a coloring material, and a charge adjusting agent, wherein the charge adjusting agent comprises a charge generating agent, a solvent, and a polar monomer species. An ink composition for electrostatic ink jet, comprising a charge generator composition obtained by mixing and polymerizing the mixture.

  (2) An ink jet recording method, wherein ink droplets are ejected by an ink jet recording method using an electrostatic field, using the ink composition according to (1).

  In the present invention, by using a specific charge generating agent composition as a charge adjusting agent in the ink composition, a small drawing dot required for an electrostatic ink jet recording method, for example, a dot diameter of about 10 μm is formed with high positional accuracy. The ink particle charge generation efficiency can be improved, and in the drawn image by the ink jet recording method, the electrophoretic speed of the ink particles at the ejection part is sufficiently high, and the ink particles are sufficiently concentrated, so there is no bleeding and good Image of high quality can be obtained. Therefore, according to the present invention, there are provided an ink composition for electrostatic ink jet and an ink jet recording method capable of fixing a high quality image at low temperature and high speed on a recording medium.

Hereinafter, each component of the ink composition of the present invention will be described.
[Dispersion medium]
The dispersion medium used in the ink composition of the present invention is preferably a dielectric liquid having a high electrical resistivity, specifically, 10 ¹⁰ Ωcm or more. If a dispersion medium having a low electrical resistivity is used, electrical continuity is generated between adjacent recording electrodes, which is not suitable for this embodiment. Further, the dielectric constant of the dielectric liquid is preferably 5 or less, more preferably 4 or less, and still more preferably 3.5 or less. By setting the relative dielectric constant in such a range, an electric field is effectively applied to charged particles in the dielectric liquid, which is preferable.

  Examples of the dispersion medium used in the present invention include linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, or aromatic hydrocarbons, halogen substitution products of these hydrocarbons, and silicone oil. For example, hexane, heptane, octane. Isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (Isopar: from Exxon) Trade name), Shellsol 70, Shellsol 71 (Shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 solvent (Amsco: trade name of Spirits), KF-96L (trade name of Shin-Etsu Silicone) Etc. can be used alone or in combination. The content of the dispersion medium with respect to the entire ink composition is preferably in the range of 20 to 99% by mass. In 20 mass% or more, the particle | grains containing a coloring material can be disperse | distributed to a dispersion medium favorably, and in 99 mass% or less, content of a coloring material can be satisfied.

[Color material]
As the coloring material used in the ink composition of the present invention, known dyes and pigments can be used, and can be selected according to applications and purposes. For example, it is preferable to use a pigment from the viewpoint of the color tone of the recorded image recorded matter (printed matter) (for example, “Distribution Stabilization and Surface Treatment Technology / Evaluation” issued by the Technical Information Association, December 25, 2001 1) (hereinafter also referred to as “Non-Patent Document 1”). By changing the color material, four color inks of yellow, magenta, cyan, and black can be created. In particular, the use of offset printing inks or pigments used for proofing is preferable because the same color tone as that of offset printed matter can be obtained.

  Examples of pigments for yellow ink include C.I. I. Pigment yellow 1, C.I. I. Monoazo pigments such as CI Pigment Yellow 74; I. Pigment yellow 12, C.I. I. Disazo pigments such as CI Pigment Yellow 17; I. Non-benzidine azo pigments such as CI Pigment Yellow 180; I. Azo lake pigments such as CI Pigment Yellow 100; I. Condensed azo pigments such as CI Pigment Yellow 95; I. Pigment Yellow 115, etc., acidic dye lake pigments, C.I. I. Pigment Yellow 18 and other basic dye lake pigments, anthraquinone pigments such as Flavantrone Yellow, isoindolinone pigments such as isoindolinone yellow 3RLT, quinophthalone pigments such as quinophthalone yellow, isoindoline pigments such as isoindoline yellow, C.I. I. Nitroso pigments such as CI Pigment Yellow 153, C.I. I. Metal complex azomethine pigments such as CI Pigment Yellow 117; I. And isoindolinone pigments such as CI Pigment Yellow 139.

  Examples of pigments for magenta ink include C.I. I. Monoazo pigments such as CI Pigment Red 3; I. Disazo pigments such as CI Pigment Red 38; I. Pigment red 53: 1 etc. and C.I. I. Azo lake pigments such as CI Pigment Red 57: 1; I. Condensed azo pigments such as CI Pigment Red 144; I. Acidic dye lake pigments such as C.I. Pigment Red 174; I. Basic dye lake pigments such as CI Pigment Red 81; I. Anthraquinone pigments such as CI Pigment Red 177; I. Thioindigo pigments such as CI Pigment Red 88; I. Perinone pigments such as CI Pigment Red 194; I. Perylene pigments such as CI Pigment Red 149; I. Quinacridone pigments such as CI Pigment Red 122; I. Isoindolinone pigments such as CI Pigment Red 180; I. And alizarin lake pigments such as CI Pigment Red 83.

  Examples of the pigment for cyan ink include C.I. Disazo pigments such as CI Pigment Blue 25, C.I. I. Phthalocyanine pigments such as CI Pigment Blue 15; I. Pigment Blue 24, etc., acidic dye lake pigments, C.I. I. Basic dye lake pigments such as CI Pigment Blue 1; I. Anthraquinone pigments such as CI Pigment Blue 60; I. And alkaline blue pigments such as CI Pigment Blue 18.

Examples of the pigment for black ink include organic pigments such as aniline black pigments and iron oxide pigments, and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black.
Furthermore, processed pigments typified by microlith pigments such as Microlith-A, -K, and -T can also be suitably used. Specific examples thereof include Microlith Yellow 4G-A, Micro Resled BP-K, Microlith Blue 4G-T, and Microlith Black CT.
Various pigments can be used as necessary, such as calcium carbonate and titanium oxide pigments for white ink, aluminum powder for silver ink, and copper alloy for gold ink.

Basically, it is preferable to use one kind of pigment for each color, from the viewpoint of simplicity of ink production. However, as a hue adjustment, for example, for black ink, phthalocyanine is mixed with carbon black. Are preferably used in combination of two or more. Alternatively, the pigment may be surface-treated by a known method such as rosin treatment (Non-Patent Document 1).
The content of the color material (pigment) with respect to the entire ink composition is preferably in the range of 0.1 to 50% by mass. When the amount is 0.1% by mass or more, the pigment amount is sufficient, and a sufficiently good color is obtained in the printed matter. When the amount is 50% by mass or less, the particles containing the coloring material can be favorably dispersed in the dispersion medium. More preferably, it is 1-30 mass%.

[Coating agent]
In the ink composition of the present invention, the coloring material such as a pigment is preferably dispersed (particulated) in a state of being coated with a coating agent, rather than directly dispersed (particulated) in a dispersion medium. By covering with a coating agent, it is possible to shield the charge of the color material and to impart desirable charge characteristics. In the present invention, after ink jet recording on a recording medium, the image is fixed by a heating means such as a heat roller. At this time, the coating material is melted by heat and can be fixed efficiently.

  Examples of the coating agent include rosins, rosin-modified phenolic resins, alkyd resins, (meth) acrylic polymers, polyurethane, polyester, polyamide, polyethylene, polybutadiene, polystyrene, polyvinyl acetate, polyvinyl alcohol, acetal-modified products of polyvinyl alcohol, polycarbonate, and the like. Can be mentioned. Among these, from the viewpoint of easy particle formation, the weight average molecular weight is in the range of 2,000 to 1,000,000, and the polydispersity (weight average molecular weight / number average molecular weight) is 1.0 to 5 Polymers in the range of 0.0 are preferred. Furthermore, from the viewpoint of easiness of fixing, a polymer in which any one of the softening point or the glass transition point is in the range of 40 ° C to 120 ° C is preferable.

  In the present invention, the polymer suitably used as the coating agent is a polymer containing at least one of the structural units represented by the following general formulas (1) to (4).

In the formula, X ₁₁ represents an oxygen atom or —N (R ₁₃ ) —. R ₁₁ represents a hydrogen atom or a methyl group, R ₁₂ represents a hydrocarbon group having 1 to 30 carbon atoms, and R ₁₃ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms. R ₂₁ represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. R ₃₁ , R ₃₂ and R ₄₁ each represent a divalent hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon group of R ₁₂ , R ₂₁ , R ₃₁ , R ₃₂ , and R ₄₁ may contain an ether bond, an amino group, a hydroxy group, or a halogen atom.

  The polymer containing the structural unit represented by the general formula (1) can be obtained by radical polymerization of a corresponding radical polymerizable monomer by a known method. Examples of the radical polymerizable monomer used include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and (meth) acrylic. Octyl acid, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, (meth) (Meth) acrylic acid esters such as 2-hydroxyethyl acrylate, N-methyl (meth) acrylamide, N-propyl (meth) acrylamide, N-phenyl (meth) acrylamide, N, N-dimethyl (meth) Examples include (meth) acrylamides such as acrylamide.

  The polymer containing the structural unit represented by the general formula (2) can be obtained by radical polymerization of a corresponding radical polymerizable monomer by a known method. Examples of the radical polymerizable monomer used include ethylene, propylene, butadiene, styrene, and 4-methylstyrene.

  The polymer containing the structural unit represented by the general formula (3) can be obtained by dehydrating condensation of a corresponding dicarboxylic acid or acid anhydride and a diol by a known method. Examples of the dicarboxylic acid used include succinic anhydride, adipic acid, sebacic acid, isophthalic acid, terephthalic acid, 1,4-phenylenediacetic acid, diglycolic acid and the like. Examples of the diol used include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, and 2-butene- Examples include 1,4-diol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, and diethylene glycol.

  The polymer containing the structural unit represented by the general formula (4) is prepared by dehydrating condensation of a carboxylic acid having a corresponding hydroxy group by a known method or a known cyclic ester of a carboxylic acid having a corresponding hydroxy group. It is obtained by ring-opening polymerization by a method. Examples of the carboxylic acid having a hydroxy group or a cyclic ester thereof include 6-hydroxyhexanoic acid, 11-hydroxyundecanoic acid, hydroxybenzoic acid, and ε-caprolactone.

  The polymer containing at least one of the structural units represented by the general formulas (1) to (4) may be a homopolymer of the structural units represented by the general formulas (1) to (4). It may be a copolymer (copolymer) with these constituent components. In addition, these polymers may be used alone as a coating agent, or two or more kinds may be used in combination.

  Particularly preferred coating agents include polyester, acrylic, styrene-acrylic, polyethylene, polyurethane, and the like, and optimally, polyester, acrylic, styrene-acrylic, polyethylene, and the like.

  The content of the coating agent with respect to the entire ink composition is preferably in the range of 0.1 to 40% by mass. When the amount is 0.1% by mass or more, the amount of the coating agent is sufficient, and sufficient fixability is obtained. When the amount is 40% by mass or less, particles containing the coloring material and the coating agent can be favorably formed.

[Dispersant]
In the present invention, for example, a mixture of a coloring material and a coating agent is dispersed (granulated) in a dispersion medium, but it is more preferable to use a dispersant in order to control the particle diameter and suppress the sedimentation of the particles.
Suitable dispersants include surfactants typified by sorbitan fatty acid esters such as sorbitan monooleate and polyethylene glycol fatty acid esters such as polyoxyethylene distearate. Further, for example, a copolymer of styrene and maleic acid, and an amine-modified product thereof, a copolymer of styrene and a (meth) acrylic compound, a (meth) acrylic polymer, a copolymer of polyethylene and a (meth) acrylic compound, rosin, BYK-160, 162, 164, 182 (polyurethane polymer manufactured by Big Chemie), EFKA-401, 402 (acrylic polymer manufactured by EFKA), Solsperse 17000, 24000 (polyester polymer manufactured by Geneca), and the like. In the present invention, from the viewpoint of long-term storage stability of the ink composition, the mass average molecular weight is in the range of 1,000 to 1,000,000 and the polydispersity (mass average molecular weight / number average molecular weight). Is preferred to be in the range of 1.0 to 7.0. Furthermore, it is most preferable to use a graft polymer or a block polymer.

  The polymer that is particularly preferably used as a dispersant in the present invention is represented by a polymer component composed of at least one of the structural units represented by the following general formulas (5) and (6), and the following general formula (7). It is a graft polymer containing at least a polymer component containing at least a structural unit as a graft chain.

In the formula, X ₅₁ represents an oxygen atom or —N (R ₅₃ ) —. R ₅₁ represents a hydrogen atom or a methyl group, R ₅₂ represents a hydrocarbon group having 1 to 10 carbon atoms, and R ₅₃ represents a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms. R ₆₁ represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, a halogen atom, a hydroxyl group, or an alkoxy group having 1 to 20 carbon atoms. X ₇₁ represents an oxygen atom or —N (R ₇₃ ) —. R ₇₁ represents a hydrogen atom or a methyl group, R ₇₂ represents a hydrocarbon group having 4 to 30 carbon atoms, and R ₇₃ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms. The hydrocarbon group of R ₅₂ and R ₇₂ may contain an ether bond, an amino group, a hydroxy group, or a halogen atom.

  The graft polymer is obtained by polymerizing a radical polymerizable monomer corresponding to the general formula (7), preferably in the presence of a chain transfer agent, introducing a polymerizable functional group at the terminal of the obtained polymer, It can be obtained by copolymerizing with a radically polymerizable monomer corresponding to 5) or (6).

  Examples of the radical polymerizable monomer corresponding to the general formula (5) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylic acid. (Meth) acrylic esters such as cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and N-methyl (meth) acrylamide And (meth) acrylamides such as N-propyl (meth) acrylamide, N-phenyl (meth) acrylamide, and N, N-dimethyl (meth) acrylamide.

Examples of the radical polymerizable monomer corresponding to the general formula (6) include styrene, 4-methylstyrene, chlorostyrene, methoxystyrene, and the like.
Examples of the radical polymerizable monomer corresponding to the general formula (7) include hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, ( (Meth) stearyl acrylate, and the like.
Specific examples of these graft polymers include polymers represented by the following structural formulas.

  Contains a polymer component containing at least one of the structural units represented by general formulas (5) and (6) and a polymerization component containing at least the structural unit represented by general formula (7) as a graft chain. The graft polymer to be processed may have only the structural unit represented by the general formula (5) and / or (6) and the general formula (7), or may contain other components. The preferable composition mass ratio of the polymer component containing the graft chain and the other polymer components is 10:90 to 90:10. Within this range, good particle formability is obtained, and a desired particle diameter is easily obtained, which is preferable. These polymers may be used alone as a dispersant, or may be used in combination of two or more.

  The content of the dispersant with respect to the entire ink composition is preferably in the range of 0.01 to 30% by mass. Within this range, good particle formability can be obtained, and a desired particle diameter can be obtained.

[Charge control agent]
The ink composition of the present invention contains a charge adjusting agent in order to control the charge amount of the charged particles.
In the present invention, the specific charge generating agent composition described below is used as the charge control agent.

The charge generating composition in the present invention is obtained by mixing a charge generating agent, a solvent, and a polar monomer species and causing a polymerization reaction.
The charge generating agent is a compound that controls the charge amount of charged particles. In the present invention, lecithin, nitrohumic acid, chromanindene resin, alkylbenzene sulfonate, dioctyl sulfonate, naphthenate, 2-ethylhexanoate, Octylate, stearate, ethylenediaminetetraacetate, β-alkylalanine and the like are preferable.
The polar monomer species is not particularly limited as long as it is soluble in a solvent and can be polymerized in the dispersion medium in the presence of an appropriate initiator, and the polymer after polymerization becomes insoluble in the solvent. For example, 1-vinyl-2-pyrrolidone, 2-vinylpyridine, vinylfurans, methyl (meth) acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide, methacrylamide, styrene, p-methoxystyrene, vinylimidazole Vinyl acetate and the like are preferable.
The solvent is preferably the same as the dispersion medium used in the ink composition.
The initiator used in the polymerization reaction may be appropriately selected from known ones, and examples thereof include azobisisobutyronitrile, benzoyl peroxide, triphenylazobenzene, hydroperoxide, and t-butyl peracetate.

In the polymerization reaction, for example, a solvent is placed in a reaction vessel, heated to about 50 ° C. in a nitrogen atmosphere, a charge generating agent is slowly added and mixed therein, and the solution is heated to about 80 to 90 ° C. The charge generator composition in the present invention can be obtained by adding a polar monomer species and an initiator, keeping the temperature constant, and conducting a polymerization reaction for about 24 hours.
The addition amount of the polar monomer species is 5% by mass or more, preferably 10 to 17% by mass with respect to the charge generating agent.

  In the charge generator composition in the present invention, it is considered that a polymer of a polar monomer species is taken into the nucleus of the micelle of the charge generator, and the charge generator and the polymer are associated and stabilized. The micelles of the charge generating agent are formed such that the charge generating agent molecules aggregate, the polar portion of the charge generating agent molecule faces inward and the nonpolar portion faces outward. Due to this action, a small drawing dot required for the ink jet recording method, for example, a dot diameter of about 10 μm can be formed with high positional accuracy, and the charge generation efficiency of ink particles is improved. It is considered that the electrophoretic speed of the ink particles is sufficiently high and the effect of sufficiently concentrating the ink particles is excellent.

  If necessary, other charge control agents can be used in combination. For example, metal salts of organic carboxylic acids such as zirconium naphthenate and zirconium octenoate, ammonium salts of organic carboxylic acids such as tetramethylammonium stearate, sodium dodecylbenzenesulfonate, magnesium dioctylsulfosuccinate, etc. Carboxylic acid groups in the side chains of organic sulfonic acid metal salts, organic sulfonic acid ammonium salts such as toluene sulfonic acid tetrabutylammonium salt, polymers containing carboxylic acid groups in which a copolymer of styrene and maleic anhydride is modified with an amine A polymer having a carboxylic acid anion group in the side chain, such as a copolymer of stearyl methacrylate and a tetramethylammonium salt of methacrylic acid, a polymer having a nitrogen atom in the side chain, such as a copolymer of styrene and vinylpyridine , Butyl and N- (2-methacryloyloxyethyl) -N, N, polymers having an ammonium group in the side chain of the copolymer of N- trimethylammonium tosylate salt. The charge imparted to the particles may be positively charged or negatively charged.

  The content of the charge adjusting agent with respect to the entire ink composition is preferably in the range of 0.0001 to 10% by mass. More preferably, it is 0.0003-5 mass%. In the charge generating agent composition of the present invention, the amount of charge generating agent is calculated as the amount of charge adjusting agent. Moreover, as for the ratio of the said charge generating agent composition in a charge control agent, 1-100 mass% is preferable. The electrical conductivity of the ink composition of the present invention is preferably 10 nS / m to 300 nS / m, and the electrical conductivity of the charged particles is preferably 50% or more of the electrical conductivity of the ink composition. These conditions can be easily adjusted by increasing or decreasing the content of the charge control agent.

[Other ingredients]
In the present invention, a preservative for preventing corruption, a surfactant for controlling surface tension, and the like can be further contained depending on the purpose.

[Create charged particles]
The ink composition containing the charged particles of the present invention can be prepared by dispersing (particulating) the coloring material and the coating agent using the above components. Examples of the method for dispersing (particulate) include the following methods.
(1) A colorant and a coating agent are mixed in advance, and then dispersed (granulated) using a dispersant and a dispersion medium, and a charge adjusting agent is added.
(2) Disperse (particulate) using a coloring material, a coating agent, a dispersant and a dispersion medium at the same time, and add a charge control agent.
(3) Disperse (particulate) using a coloring material, a coating agent, a dispersant, a charge control agent, and a dispersion medium at the same time.

  Examples of the apparatus used for mixing and dispersing include a kneader, a dissolver, a mixer, a high-speed disperser, a sand mill, a roll mill, a ball mill, an attritor, and a bead mill (the aforementioned Non-Patent Document 1).

  The ink particles (charged particles) in the present invention should have a diameter of 0.5 to 4 μm, preferably 0.7 to 3.5 μm, more preferably 0.8 to 3 μm. This size is larger than normal electrophotographic liquid developer toner (0.1 to 0.4 μm) and smaller than normal electrophotographic dry developer toner (5 to 15 μm).

  The viscosity (20 ° C.) of the ink composition of the present invention is preferably in the range of 0.5 to 5 mPa · s. Preferably, it exists in the range of 0.8-4 mPa * s. The surface tension of the ink composition is preferably in the range of 10 to 70 mN / m. More preferably, it exists in the range of 15-50 mN / m.

[Inkjet recording apparatus]
In the present invention, the ink composition described above is recorded on a recording medium by an ink jet recording method. In the present invention, it is preferable to use an ink jet recording system using an electrostatic field. Ink jet recording methods that use an electrostatic field concentrate the charged particles of the ink composition at the discharge position by electrostatic force by applying a voltage between the control electrode and the back electrode on the back of the recording medium, and record from the discharge position. This is a method of flying to a medium. For example, when the charged particles are positive, the voltage applied between the control electrode and the back electrode is such that the control electrode is a positive electrode and the back electrode is a negative electrode. The same effect can be obtained by charging the recording medium instead of applying a voltage to the back electrode.

  As a method of flying ink, for example, there is a method of flying ink from a needle-like tip such as an injection needle, and recording can be performed using the ink composition of the present invention. However, it is difficult to replenish charged particles after the charged particles are concentrated and discharged, and it is difficult to perform stable long-term recording. When the ink is circulated in order to forcibly supply charged particles, the ink overflows from the tip of the injection needle, so the meniscus shape at the tip of the injection needle, which is the discharge position, is not stable, and stable recording is performed. It is difficult to do and is suitable for short-term recording.

  On the other hand, a method of circulating the ink composition without overflowing the ink composition from the ejection opening is preferably used. For example, ink is circulated in an ink chamber having a discharge opening, and a voltage is applied to a control electrode formed at the periphery of the discharge opening, whereby the tip exists in the discharge opening and the leading end faces the recording medium side. In the method in which the concentrated ink droplets fly from the tip of the ink guide, the replenishment of charged particles by the circulation of the ink and the meniscus stability at the ejection position can be compatible, so that stable recording can be performed for a long time. it can. Further, in this method, since the portion where the ink is in contact with the outside air is very small with only the discharge opening, the evaporation of the solvent is suppressed and the ink physical properties are stabilized, so that it can be suitably used in the present invention.

A configuration example of an ink jet recording apparatus suitable for applying the ink composition of the present invention is shown below.
First, an outline of an apparatus that performs single-sided four-color printing on a recording medium shown in FIG. 1 will be described.
An ink jet recording apparatus 1 shown in FIG. 1 supplies ink to an ejection head 2 composed of ejection heads 2C, 2M, 2Y and 2K for four colors for forming a full-color image, and further the ink from the ejection head 2 A head driver 4 for driving the ejection head 2 by an output from an external device such as a computer (not shown), a RIP (raster image processor), and a position control means 5. Further, the ink jet recording apparatus 1 includes a transport belt 7 stretched around three rollers 6A, 6B, and 6C, a transport belt position detection unit 8 including an optical sensor that can detect the position of the transport belt 7 in the width direction, An electrostatic attraction unit 9 for holding the recording medium P on the conveyance belt, a static elimination unit 10 and a mechanical unit 11 for peeling the recording medium P from the conveyance belt 7 after completion of image formation are provided. The feed roller 12 and the guide 13 that supply the recording medium P from a stocker (not shown) to the conveyance belt 7 are fixed upstream and downstream of the conveyance belt 7, and ink is fixed to the recording medium P after separation, and a paper discharge stocker (not shown). A fixing means 14 and a guide 15 for conveying the toner are disposed. In addition, the inkjet printing apparatus 1 has a recording medium position detection means 16 at a position facing the ejection head 2 with the conveyance belt 7 interposed therebetween, and further collects the solvent vapor generated from the ink composition. A solvent recovery unit composed of the exhaust fan 17 and the solvent vapor adsorbent 18 is disposed, and the vapor inside the apparatus is discharged outside the apparatus through the recovery unit.

A known roller can be used as the feed roller 12, and the feed roller 12 is arranged so as to increase the feeding ability to the recording medium. Further, since dirt, paper powder, or the like may adhere on the recording medium P, it is desirable to remove them. The recording medium P supplied by the feed roller is transported to the transport belt 7 through the guide 13. The back surface (preferably metal back surface) of the conveyor belt 7 is installed via a roller 6A. The recording medium transported is electrostatically attracted onto the transport belt by the electrostatic attracting means 9. In FIG. 1, electrostatic adsorption is performed by a scorotron charger connected to a negative high voltage power source. The recording medium P is electrostatically adsorbed without floating on the transport belt 7 by the electrostatic adsorption means 9 and the surface of the recording medium is uniformly charged. Here, the electrostatic attraction means is also used as a charging means for the recording medium, but may be provided separately. The charged recording medium P is transported to the ejection head portion by the transport belt 7, and electrostatic ink jet image formation is performed by superimposing the recording signal voltage with the charging potential as a bias. The recording medium P on which the image is formed is neutralized by the neutralizing unit 10, peeled off by the conveying unit 7 by the mechanical unit 11, and conveyed to the fixing unit. The peeled recording medium P is sent to the image fixing means 14 and fixed. The fixed recording medium P is discharged through a guide 15 to a discharge stocker (not shown). The apparatus also has a means for recovering the solvent vapor generated from the ink composition. The recovery means is composed of the solvent vapor absorbing material 18, and a gas containing solvent vapor in the apparatus is introduced into the adsorbent by the exhaust fan 17, and after the vapor is adsorbed and recovered, it is exhausted outside the apparatus. The apparatus is not limited to the above example, and the number, shape, relative arrangement, charging polarity, and the like of constituent devices such as rollers and chargers can be arbitrarily selected. In the above system, four-color drawing is described. However, a multicolor system may be combined with light color ink or special color ink.

  The ink jet recording apparatus used in the above ink jet printing method includes an ejection head 2 and an ink circulation system 3. The ink circulation system 3 further includes an ink tank, an ink circulation device, an ink concentration control device, an ink temperature management device, and the like. In addition, the ink tank may include a stirring device.

As the ejection head 2, a single channel head, a multi-channel head, or a full line head can be used, and main scanning is performed by the rotation of the transport belt 7.
An ink jet head suitably used in the present invention is an ink jet method in which charged particles in an ink flow path are electrophoresed to increase the ink concentration in the vicinity of the opening and discharge is performed. Ink droplets are ejected by electrostatic attraction caused by the counter electrode disposed on the back surface of the medium. Therefore, if the recording medium or the counter electrode does not face the head, or if no voltage is applied to the recording medium or the counter electrode even at the position facing the head, the voltage is accidentally applied to the ejection electrode. Ink droplets are not ejected even when a pressure is applied or vibration is applied, and the inside of the apparatus is not soiled.

  An ejection head preferably used in the ink jet apparatus is shown in FIGS. As shown in FIGS. 2 and 3, the inkjet head 70 includes an electrically insulating substrate 74 that constitutes the upper wall of the ink flow path 72 where the ink flow Q in one direction is formed, and the ink to the recording medium P. And a plurality of discharge portions 76 that discharge toward the surface. Each of the ejection portions 76 is provided with an ink guide portion 78 that guides the ink droplet G flying from the ink flow path 72 toward the recording medium P, and the substrate 74 has an opening through which the ink guide portion 78 is inserted. 75 is formed, and the ink meniscus 42 is formed between the ink guide portion 78 and the inner wall surface of the opening 75. The gap d between the ink guide portion 78 and the recording medium P is preferably about 200 μm to 1000 μm. Further, the ink guide part 78 is fixed to the support bar part 40 on the lower end side.

The substrate 74 includes an insulating layer 44 that electrically isolates two discharge electrodes at a predetermined interval, a first discharge electrode 46 formed above the insulating layer 44, and an insulation that covers the first discharge electrode 46. It has a layer 48, a guard electrode 50 formed on the insulating layer 48, and an insulating layer 52 that covers the guard electrode 50. The substrate 74 includes a second ejection electrode 56 formed below the insulating layer 44 and an insulating layer 58 that covers the second ejection electrode 56. The guard electrode 50 is provided in order to prevent an electric field from being affected by the voltage applied to the first ejection electrode 46 and the second ejection electrode 56 in the adjacent ejection section.

Further, the ink jet head 70 constitutes the bottom surface of the ink flow path 72, and the ink flow is generated by the induced voltage that is constantly generated by the pulsed discharge voltage applied to the first discharge electrode 46 and the second discharge electrode 56. A floating conductive plate 62 that moves positively charged ink particles (charged particles) R in the path 72 upward (that is, toward the recording medium side) is provided in an electrically floating state. In addition, a coating film 64 that is electrically insulating is formed on the surface of the floating conductive plate 62 to prevent the physical properties and components of the ink from becoming unstable due to charge injection into the ink. The electric resistance of the insulating coating film is preferably 10 ¹² Ω · cm or more, and more preferably 10 ¹³ Ω · cm or more. In addition, the insulating coating film is desirably resistant to corrosion with respect to ink, and this prevents the floating conductive plate 62 from being corroded by ink. Further, the floating conductive plate 62 is covered with the insulating member 66 from below, and the floating conductive plate 62 is completely electrically insulated by such a configuration.

  There are one or more floating conductive plates 62 per head unit (for example, when there are four heads C, M, Y, and K, the number of floating conductive plates is at least one each, and C and M The floating conductive plate is not shared between the head units.

  As shown in FIG. 3, in order to cause ink to fly from the inkjet head 70 and record on the recording medium P, the ink in the ink flow path 72 is circulated to generate an ink flow Q, and the guard electrode A predetermined voltage (for example, +100 V) is applied to 50. Furthermore, a flying electric field that attracts the positive charged particles R in the ink droplet G that has been guided by the ink guide portion 78 and flew from the opening 75 to the recording medium P is generated by the first ejection electrode 46 and the second ejection electrode. A positive voltage is applied to the first ejection electrode 46, the second ejection electrode 56, and the recording medium P so as to be formed between the recording medium P and the recording medium P (1 kV when the gap d is 500 μm). A potential difference of about ~ 3.0 kV is taken as a guide).

In this state, when a pulse voltage is applied to the first ejection electrode 46 and the second ejection electrode 56 in accordance with the image signal, the ink droplet G having an increased charged particle concentration is ejected from the opening 75 (for example, initial charged particles). When the concentration is 3 to 15%, the charged particle concentration of the ink droplet G is 30% or more).
At that time, the ink droplet G is applied to the first ejection electrode 46 and the second ejection electrode 56 so that the ink droplet G is ejected only when the pulse voltage is applied to both the first ejection electrode 46 and the second ejection electrode 56. Adjust the voltage value.

  In this way, when a pulsed positive voltage is applied, the ink droplet G is guided by the ink guide portion 78 from the opening 75 and flies to adhere to the recording medium P, and the first ejection is applied to the floating conductive plate 62. A positive induced voltage is generated by the positive voltage applied to the electrode 46 and the second ejection electrode 56. Even if the voltage applied to the first ejection electrode 46 and the second ejection electrode 56 is pulsed, this induced voltage is a substantially steady voltage. Accordingly, the charged particles R that are positively charged in the ink flow path 72 are subjected to the upward movement force by the electric field formed between the floating conductive plate 62 and the guard electrode 50 and the recording medium P, and The concentration of charged particles R increases near the substrate 74. As shown in FIG. 3, when the number of ejection units (that is, channels for ejecting ink droplets) to be used is large, the number of charged particles necessary for ejection increases, but the first ejection electrode 46 and the second ejection electrode to be used are used. Since the number of 56 increases, the induced voltage induced in the floating conductive plate 62 increases, and the number of charged particles R moving to the recording medium side also increases.

  In the above, an example in which the colored particles are positively charged has been described. However, the colored particles may be negatively charged. In that case, all the above-mentioned charging polarities are reversed.

  In the present invention, it is preferable to fix the ink by an appropriate heating means after discharging the ink onto the recording medium. As the heating means to be used, a contact-type heating device such as a heat roller, a heat block, or a belt heating, and a non-contact type heating device such as a dryer, an infrared lamp, a visible light lamp, an ultraviolet lamp, or a hot air oven may be used. it can. These heating devices are preferably continuous with and integrated with the ink jet recording apparatus. The temperature of the recording medium at the time of fixing is preferably in the range of 40 ° C. to 200 ° C. for ease of fixing. The fixing time is preferably in the range of 1 microsecond to 20 seconds.

[Replenishment of ink composition]
In the ink jet recording method using an electrostatic field, charged particles in the ink composition are concentrated and discharged. Accordingly, when the ink composition is discharged for a long time, the charged particles in the ink composition are reduced, and the electrical conductivity of the ink composition is lowered. Further, the ratio between the electric conductivity of the charged particles and the electric conductivity of the ink composition changes. Further, when discharging, charged particles having a larger diameter tend to be discharged preferentially than charged particles having a smaller diameter, so that the average diameter of the charged particles is reduced. Further, since the solid content in the ink composition changes, the viscosity also changes.
Due to these changes in physical property values, as a result, ejection failure occurs, the optical density of recorded images decreases, and ink bleeding occurs. For this reason, by reducing the amount of charged particles by replenishing the ink composition having a higher concentration (higher solid content concentration) than the ink composition initially charged in the ink tank, the electrical conductivity of the ink composition The ratio between the electric conductivity of the charged particles and the electric conductivity of the ink composition can be kept within a certain range. Further, the average particle diameter and viscosity can be maintained. Further, by maintaining the physical property value of the ink composition within a certain range, the ink discharge is stably and uniformly performed for a long time. The replenishment at this time is preferably performed mechanically or manually, for example, by detecting a physical property value such as the electrical conductivity or optical density of the ink liquid used and calculating the shortage. Further, the amount of the ink composition to be used may be calculated based on the image data, and may be formed mechanically or manually.

[Recording medium]
In the present invention, various recording media can be used depending on the application. For example, if paper, plastic film, metal, and paper on which plastic or metal is laminated or vapor-deposited, plastic film on which metal is laminated or vapor-deposited, etc., printed matter can be obtained directly by ink jet recording. Moreover, an offset printing plate can be obtained if the support body etc. which roughened metals, such as aluminum, are used. Furthermore, if a plastic support is used, a flexographic printing plate or a color filter for a liquid crystal screen can be obtained. The shape of the recording medium may be planar such as a sheet shape or three-dimensional such as a cylindrical shape. Further, if a silicon wafer or a wiring board is used as a recording medium, it can be applied to manufacture of a semiconductor or a printed wiring board.

  By using the ink composition of the present invention described above, it is possible to stably obtain a high-quality image recorded matter with no ink bleeding and high image density over a long period of time.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

Example 1
<Materials used>
In Example 1, the following materials were used.

Cyan pigment (coloring material) phthalocyanine pigment C.I. I. Pigment Blue (15:
3) (Toyo Ink Manufacturing Co., Ltd., LIONOL BLUE FG-7350)
・ Coating agent [Butyl acrylate / Methyl methacrylate: 75/25% by mass copolymer (Aldrich Co., Ltd.)
・ Dispersant [BZ-2]
・ Charge control agent [See below]
・ Dispersion medium Isopar G (manufactured by Exxon)

  The structure of the dispersant [BZ-2] is shown below.

  The dispersant [BZ-2] is a polymer of stearyl methacrylate (mass average molecular weight) having a methacryloyl group at its terminal by radical polymerization of stearyl methacrylate in the presence of 2-mercaptoethanol and further reacting with methacrylic anhydride. Was obtained by radical polymerization with styrene. The weight average molecular weight was 110,000.

<Creation of charge control agent>
Under a nitrogen atmosphere, 1400 g of Isopar G was placed in a glass reaction vessel equipped with a reflux condenser and a stirrer, and heated to 50 ° C. Next, 600 g of lecithin was gradually added and stirred. The solution was heated to 80 ° C., an initiator composition in which 102 g of 1-vinyl-2-pyrrolidone and 3 g of azobisisobutyronitrile were suspended in 10-20 ml of Isopar G was added, and the heating temperature at 80 ° C. was increased. While maintaining, a polymerization reaction was performed for 24 hours to obtain a charge generator composition.

<Preparation of ink composition [EC-1]>
10 g of a cyan pigment and 18 g of a coating agent [butyl acrylate / methyl methacrylate: 75/25% by mass copolymer (manufactured by Aldrich Co.)] are put into a table type kneader PBV-0.1 manufactured by Irie Shokai Co., Ltd. The heater temperature was set to 100 ° C. and heated and mixed for 2 hours. 30 g of the obtained mixture was coarsely pulverized with a trio-blender manufactured by Trio Science Co., Ltd., and further finely pulverized with a SK-M10 type sample mill manufactured by Kyoritsu Riko Co., Ltd. 30 g of the obtained finely pulverized product was predispersed in a paint shaker manufactured by Toyo Seiki Seisakusho, together with 7.5 g of the dispersant [BZ-2], 75 g of Isopar G, and glass beads having a diameter of about 3.0 mm. After removing the glass beads, together with zirconia ceramic beads having a diameter of about 0.6 mm, Shinmaru Enterprises Co., Ltd., Type KDL Dino Mill, while maintaining the internal temperature at 25 ° C. for 5 hours, followed by 45 ° C. for 5 hours, Dispersion (particle formation) was performed at a rotational speed of 2,000 rpm. Zirconia ceramic beads were removed from the obtained dispersion, and 316 g of Isopar G and 0.1 g of a charge adjusting agent were added to obtain an ink composition [EC-1]. The particle size of the particle component in the obtained ink composition was 0.93 μm, and the particle content of 0.2 μm or less was 0.6% or less.

<Inkjet recording / image evaluation>
The ink composition [EC-1] of Example 1 was filled in the ink tank in the ink jet recording apparatus shown in FIGS. Here, a 150 dpi (three-row staggered arrangement with a channel density of 50 dpi) and 833 channel head of the type shown in FIG. 2 was used as the ejection head, and a silicon rubber heat roller incorporating a 1 kW heater was used as the fixing means. As the ink temperature control means, a throw-in heater and a stirring blade were provided in the ink tank, the ink temperature was set to 30 ° C., and the temperature was controlled with a thermostat while rotating the stirring blade at 30 rpm. Here, the stirring blade was also used as a stirring means for preventing precipitation and aggregation. In addition, the ink flow path is partially transparent, and the LED light emitting element and the light detecting element are arranged between them, and the ink dilution liquid (Isopar G) or concentrated ink (the solid content concentration of the ink composition is determined by the output signal). The concentration was controlled by charging. A fine coated paper for offset printing was used as a recording medium. After removing dust on the surface of the recording medium by air pump suction, the ejection head is brought close to the recording medium to the image forming position, image data to be recorded is transmitted to the image data calculation control unit, and the recording medium is rotated by the rotation of the conveyor belt. The ink composition was discharged while sequentially moving the discharge head while transporting the recording medium, and an image was formed with a drawing resolution of 2400 dpi. As the conveyor belt, a metal belt and polyimide film bonded together are used, and a line-shaped marker is placed along the conveying direction near one end of this belt, and this is optically read by the conveyor belt position detection means. An image was formed by driving the control means. At this time, the distance between the ejection head and the recording medium was kept at 0.5 mm by the output from the optical gap detector. Further, the surface potential of the recording medium was set to −1.5 kV at the time of ejection, and a pulse voltage of +500 V was applied (pulse width 50 μsec) at the time of ejection, and image formation was performed at a driving frequency of 15 kHz.

<Evaluation of dot diameter and position accuracy>
With respect to the gray scale image recorded matter (printed matter) obtained by the inkjet recording, the dot diameter and the positional accuracy were evaluated. The dot diameter was calculated by analyzing the recorded image with a dot analyzer (manufactured by Oji Scientific Instruments). Further, the positional accuracy was obtained by analyzing an image recorded matter recorded in a lattice shape with a dot analyzer (manufactured by Oji Scientific Instruments) and calculating a standard deviation (1σ) of a deviation width between dots.

<Charge evaluation>
The charge amount of the ink composition is obtained from the specific conductivity measured using the LCR meter and the liquid electrode (manufactured by Kawaguchi Electric Manufacturing Co., Ltd., LP-05 type) under the conditions of an applied voltage of 5 V and a frequency of 1 kHz. The conductivity of the ink particles was determined by subtracting the specific conductivity of the supernatant obtained by applying the ink composition to the centrifuge from the specific conductivity of the entire ink composition. Centrifugation was carried out for 30 minutes using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd., SRX-201) under conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C.

The charge generation efficiency of the ink particles was obtained from the following equation.
Ink particle charge generation efficiency (%) = (ink particle charge amount Q1 / ink composition charge amount Q2) × 100

<Evaluation of inkjet drawing image quality>
The gray scale image recorded matter (printed matter) obtained by the inkjet recording was visually evaluated as follows for the degree of stripe unevenness and ink bleeding.

Evaluation of ink-jet drawing image quality Visual evaluation of the degree of bleeding in the drawn image ○: No bleeding Δ: Slight bleeding ×: Bleeding

Example 2
The ink composition was prepared in the same manner as in Example 1 except that lecithin in <Creation of charge control agent> in Example 1 was changed to zircon 2-ethylhexanoate (manufactured by Wako Pure Chemical Industries, Ltd.). EC-2] was created. The particle size of the particle component in the obtained ink composition was 0.99 μm, and the particle content of 0.2 μm or less was 0.5% or less. Using this ink composition, dots were formed as in Example 1. Evaluation of diameter and position accuracy, charge evaluation, and inkjet drawing image quality were performed.

Example 3
Ink was produced in the same manner as in Example 1 except that 1-vinyl-2-pyrrolidone in <Creation of charge control agent> in Example 1 was changed to methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.). A composition [EC-3] was prepared. The particle size of the particle component in the obtained ink composition was 1.03 μm, and the particle content of 0.2 μm or less was 0.5% or less. Using this ink composition, dots were formed in the same manner as in Example 1. Evaluation of diameter and position accuracy, charge evaluation, and inkjet drawing image quality were performed.

Comparative Example 1
An ink composition [RC-1] was prepared in the same manner as in Example 1 except that the charge control agent used in Example 1 was changed to zircon naphthenate. The particle size of the particle component in the obtained ink composition was 0.99 μm, and the particle content of 0.2 μm or less was 0.6% or less. Using this ink composition, dots were formed as in Example 1. Evaluation of diameter and position accuracy, charge evaluation, and inkjet drawing image quality were performed.
These results are shown in Table 1 below.

  As shown in Examples 1 to 3, by using a specific charge generating agent composition as the charge adjusting agent, it is possible to provide excellent dot diameter and positional accuracy. In addition, the ink particle charge generation efficiency is improved, and in the ink jet drawing image by this method, the electrophoretic velocity of the ink particles at the ejection part is sufficiently fast and the ink particles are sufficiently concentrated, so there is no bleeding and good quality Images can be obtained.

  In Comparative Example 1, since conventional zircon naphthenate (metal soap) is used as a charge control agent, the results of the evaluation of dot diameter and positional accuracy are insufficient. In addition, the ink particle charge generation efficiency is insufficient, and in the ink jet drawing image by this method, the electrophoretic speed of the ink particles at the discharge part is slow, and the ink particles do not concentrate sufficiently, so that bleeding occurs. A good quality image cannot be obtained.

It is a whole lineblock diagram showing typically an example of an ink jet printer used for the present invention. It is a perspective view which shows the structure of the inkjet head of the inkjet recording device of this invention (In order to make it intelligible, the edge of the guard electrode in each discharge part is not drawn). FIG. 3 is a side sectional view showing a distribution state of charged particles when the number of ejection units of the inkjet head shown in FIG. 2 is large (corresponding to an arrow XX in FIG. 2).

Explanation of symbols

G Ink Drop P Recording Medium Q Ink Flow R Charged Particle 1 Inkjet Recording Device 2, 2Y, 2M, 2C, 2K Discharge Head 3 Ink Circulation System 4 Head Driver 5 Position Control Means 6A, 6B, 6C Roller 7 Conveyor Belt 8 Conveyance Belt position detection means 9 Electrostatic adsorption means 10 Static elimination means 11 Mechanical means 12 Feed roller 13 Guide 14 Image fixing means 15 Guide 16 Recording medium position detection means 17 Discharge fan 18 Solvent vapor adsorbent 38 Ink guide 40 Support bar 42 Ink meniscus 44 Insulating layer 46 First ejection electrode 48 Insulating layer 50 Guard electrode 52 Insulating layer 56 Second ejection electrode 58 Insulating layer 62 Floating conductive plate 64 Coating film 66 Insulating member 70 Ink jet head 72 Ink flow path 74 Substrate 75, 75A , 75B Opening 76, 76A, 76B Discharge section 78 Ink guide

Claims (2)

  An electrostatic ink-jet ink composition comprising a dispersion medium, charged particles containing at least a coloring material, and a charge adjusting agent, wherein the charge adjusting agent is a mixture of a charge generating agent, a solvent, and a polar monomer species. An electrostatic ink-jet ink composition comprising a charge generator composition obtained by polymerization reaction.   An ink jet recording method, wherein an ink droplet is ejected by an ink jet recording method using an electrostatic field, using the ink composition according to claim 1.

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