JP2005255869A - Inkjet composition and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an ink composition which can stably discharge ink droplets all the time in long-time inkjet recording and enables long-time formation of high-quality images, and to provide an inkjet recording method. <P>SOLUTION: The ink composition contains a dispersion medium and charged particles containing at least a colorant. The charged particles contain an epoxy resin which has (a) a dynamic modulus (G') at 50°C of ≥10<SP>4</SP>Pa, (b) a molecular weight (GPC (gel permeation chromatography) mass average) of ≤50,000, and (c) a glass transition temperature (Tg) of 30-100°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an 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, there are an electrophotographic method, a sublimation type and a melt type thermal transfer method, an ink jet method and the like. The electrophotographic system requires a process of forming an electrostatic latent image on a photosensitive drum by charging and exposure, which complicates the system and becomes an expensive apparatus. The thermal transfer method is inexpensive, but uses an ink ribbon, so the running cost is high and waste material is generated. On the other hand, the ink jet method is an inexpensive apparatus and ejects ink only to a required image portion to directly form an image 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 system (see Patent Documents 1 and 2) that causes ink droplets containing charged particles to fly. The method of flying ink droplets with steam or mechanical pressure cannot control the flying direction of the ink droplets, and causes the ink droplets to land precisely on the desired position on the printing medium due to distortion of the ink nozzles or air convection. Is difficult.
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. It is excellent.

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), it is necessary that ink particles (charged particles) are concentrated at the tip of the ejection unit at a high electrophoresis speed. For this purpose, it has been confirmed that it is necessary to apply sufficient charge to the ink particles. For this reason, it is difficult to apply the inkjet system to a liquid developer or the like composed of toner particles of 0.5 μm or less that is generally used in an electrophotographic system, and the particle diameter does not deteriorate the image quality (0.8 It is necessary to increase the amount of charge per ink particle by increasing the size to .about.2.0 .mu.m and eliminating fine particles of 0.2 .mu.m or less. Furthermore, it is necessary to narrow the particle size distribution in order to prevent the increase in the ink particles having a small particle size accumulated during the running, but the current particle formation technology is not yet satisfactory.
Japanese Patent No. 3315334 US Pat. No. 6,158,844 JP-A-8-291267 US Pat. No. 5,952,2048

  The present invention has been made for the purpose of always ejecting ink droplets stably in a long-time inkjet recording, and an ink composition capable of forming a high-quality image without bleeding for a long time, and An inkjet recording method is provided.

  As a result of intensive investigations to achieve the above-mentioned object, the present inventor has made it possible to form a high-quality image without bleeding for a long time by using an epoxy resin satisfying specific physical property value conditions as charged particles. The inventors have found that an ink composition can be obtained and have completed the present invention.

That is, the present invention is as follows.
(1) An ink composition containing a dispersion medium and charged particles containing at least a coloring material, wherein the charged particles contain an epoxy resin that satisfies the physical property value conditions a) to c) below. Ink composition.
a) Dynamic elastic modulus at 50 ° C. (G ′): 10 ⁴ Pa or more b) Molecular weight (GPC mass average): 50,000 or less c) Glass transition point (Tg): 30 to 100 ° C.

  (2) The ink composition as described in (1) above, wherein the epoxy resin is a linear polymer.

  (3) The ink composition as described in (1) above, wherein the epoxy resin is represented by the following general formula (I).

  (In the formula, X represents an optionally substituted alkylene group, cycloalkylene group, alkenylene group, alkynylene group, arylene group, aralkylene group or bridged cyclic hydrocarbon linking group. N represents the degree of polymerization.)

  (4) The charged particles are prepared by a mechanical media dispersion method, and particles having a particle diameter corresponding to 1/5 or less of a volume average particle diameter in a centrifugal sedimentation method are 1% or less ( The ink composition as described in 1).

  (5) An ink jet recording method in which the ink composition according to any one of (1) to (4) is ejected as ink droplets by an ink jet recording method using an electrostatic field.

  According to the present invention, by using an epoxy resin that satisfies a specific property value condition, the particle size and distribution of the ink particles can be made a preferable region. The electrophoretic speed is fast, the ink particles are sufficiently concentrated, and an image of good quality without blur is obtained. Even if running is performed, stable drawing can be performed over a long period of time.

The ink composition of the present invention is characterized in that the charged particles contain an epoxy resin that satisfies the physical property value conditions a) to c) below.
a) Dynamic elastic modulus (G ′) at 50 ° C .: 10 ⁴ Pa or more, preferably 10 ⁴ to 10 ⁹ Pa, more preferably 10 ⁵ to 10 ⁸ Pa.
b) Molecular weight (GPC mass average): 50,000 or less, preferably 2,000 to 40,000, more preferably 3,000 to 30,000. In addition, the GPC mass average as used in the field of this invention means the mass average molecular weight measured by gel permeation chromatography.
c) Glass transition point (Tg): 30 to 100 ° C, preferably 30 to 90 ° C, more preferably 40 to 80 ° C.

As in the system of the present invention, in order to apply a shearing force to the pigment-polymer mixture to pulverize and disperse, when the cohesive force of the polymer is high, much energy is required to pulverize and disperse, -There are many cases that cannot be distributed. That is, in the system of the present invention, physical properties related to the brittleness and cohesive force of the polymer are important. If it is too soft, the shearing force is not easily transmitted to the pigment-polymer mixture, and if it is too hard, the shearing force is well transmitted. Since there is a problem of becoming too fine, it is necessary that the dynamic elastic modulus (G ′), mass average molecular weight (Mw), and glass transition point (Tg) are within the ranges defined above.
When the dynamic elastic modulus G ′ is less than 10 ⁴ Pa, the physical properties of the rubber elastic region are exhibited in the temperature range in the pulverization-dispersion process. Dispersion makes particle formation difficult.
If the molecular weight of the polymer is higher than the above range, the cohesive force of the polymer becomes high, and the cohesive force tends to be non-uniform in the pigment-polymer mixture, so that uniform particle formation is difficult and particles with a wide particle size distribution are generated. End up.
When Tg is lower than 30 ° C., brittleness due to polymer crushing is insufficient, force from the media is not easily applied, and particle formation is difficult by mechanical dispersion with media. Moreover, when Tg exceeds 100 degreeC, the cohesion force between polymer molecules will become high, and it will become difficult to disperse | distribute a polymer finely.

  In the present invention, the epoxy resin used as a coating agent (coating polymer) is not particularly limited as long as it satisfies the above specific physical property value conditions, but is preferably a linear polymer epoxy resin, and more preferably It is an epoxy resin represented by general formula (I).

  (In the formula, X represents an optionally substituted alkylene group, cycloalkylene group, alkenylene group, alkynylene group, arylene group, aralkylene group or bridged cyclic hydrocarbon linking group. N represents the degree of polymerization.)

In the general formula (I), the linking group X preferably represents an alkylene group, cycloalkylene group, alkenylene group, alkynylene group, arylene group, aralkylene group or bridged cyclic hydrocarbon linking group having 1 to 22 carbon atoms. These may be substituted.
Specifically, X is an alkylene group having 1 to 22 carbon atoms which may be substituted (for example, methylene, ethylene, propylene, butylene, hexylene, heptylene, octylene, nonylene, decylene, dodecylene, tridecylene, tetradecylene, hexadecylene, octadecylene. , Eicosylene, docosylene, 2-chloroethylene, 2-bromoethylene, 2-cyanoethylene, 2-methoxycarbonylethylene, 2-methoxyethylene, 3-bromopropylene, etc.), optionally substituted alkenylene having 4 to 18 carbon atoms Groups such as 2-methyl-1-propenylene, 2-butenylene, 2-pentenylene, 3-methyl-2-pentenylene, 1-pentenylene, 1-hexenylene, 2-hexenylene, 4-methyl-2-hexenylene, desenylene, Dodeseni , Tridecenylene, hexadecenylene, octadecenylene, linolenylene, etc.), an aralkylene group having 7 to 12 carbon atoms which may be substituted (for example, benzylene, phenethylene, 3-phenylpropylene, naphthylmethylene, 2-naphthylethylene, chlorobenzylene, bromo) Benzylene, methyl benzylene, ethyl benzylene, methoxy benzylene, dimethyl benzylene group, dimethoxy benzylene group, etc.), cycloalkylene group having 5 to 8 carbon atoms which may be substituted (for example, cyclohexylene, 2-cyclohexyl ethylene) , 2-cyclopentylethylene, etc.), an arylene group having 6 to 12 carbon atoms which may be substituted (for example, phenylene, naphthylene, tolylene, xylylene, propylphenylene, butylphenylene, octylphenylene, dodecylph) Nylene, methoxyphenylene, ethoxyphenylene, butoxyphenylene, decyloxyphenylene, chlorophenylene, dichlorophenylene, bromophenylene, cyanophenylene, acetylphenylene, methoxycarbonylphenylene, ethoxycarbonylphenylene, butoxycarbonylphenylene, acetamidophenylene, propionamidophenylene, Decyloylamidophenylene, etc.) and a bridged cyclic hydrocarbon group (eg, norbornyl group, adamantyl group, etc.).

  Moreover, X may represent the organic residue which couple | bonds and forms a ring with a nitrogen atom, respectively. The organic residue may further contain a hetero atom (for example, an oxygen atom, a nitrogen atom, a sulfur atom, etc.). Examples of the cyclic ammonium group to be formed include those obtained by quaternizing a morpholino group, piperidino group, pyridyl group, imidazolyl group, quinolyl group, oxazoline group and the like. Examples of the cyclic sulfonium group include those obtained by quaternizing a thiophene group, a tetrahydrothiophene group, a benzothiophene group, a thiazole group, or the like.

  Examples of commercially available products include Epicoat 1001, Epicoat 1002, Epicoat 1004, Epicoat 1005F, Epicoat 4004P, and Epicoat 4110 manufactured by Japan Epoxy Resin Co., Ltd.

  In the ink composition of the present invention, an epoxy resin satisfying the above specific property value conditions may be used alone as a coating agent, or may be used in combination of two or more kinds.

The volume average particle diameter of the charged particles can be measured by a centrifugal sedimentation method using an apparatus such as an ultracentrifugal automatic particle size distribution analyzer CAPA-700 (manufactured by Horiba, Ltd.). In the present invention, the volume average particle diameter of the charged particles is preferably in the range of 0.8 to 2.0 μm. Within the above-mentioned range, it is possible to obtain a stable ink that can sufficiently charge the surface of each ink particle and that does not change in charge over time.
In the present invention, the charged particles are preferably prepared by a mechanical media dispersion method, and the particle diameter corresponding to 1/5 or less of the volume average particle diameter in the centrifugal sedimentation method is preferably 1% or less. More preferably, it is 0.5% or less. Here, the mechanical media dispersion method is a method of obtaining the desired dispersion while finely crushing the dispersion by changing the kinetic energy of beads such as glass and zirconia into shear / impact force due to the collision of the beads. Generally, a paint shaker, a dynomill, or the like is used as a device for moving the beads.

  The ink composition of the present invention contains charged particles containing a dispersion medium and at least a coloring material. The above components will be described in detail below.

[Dispersion medium]
The dispersion medium 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: Exxon Corporation) 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 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, Flavantron Yellow and other anthraquinone pigments, Isoindolinone Yellow 3RLT and other isoindolinone pigments, Quinophthalone Yellow and other quinophthalone pigments, Isoindoline Yellow and other isoindoline pigments, 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 coloring material 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 amount of the coloring material is satisfied, and sufficiently good color development is obtained in the printed matter. Further, 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 present invention, it is preferable that the coloring material such as a pigment is 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 printing medium, fixing is performed by a heating means such as a heat roller. At this time, the coating material is melted by heat and can be fixed efficiently.

  As the coating agent, in addition to the epoxy resin satisfying the above specific physical property value conditions, for example, rosins, rosin-modified phenol resin, alkyd resin, (meth) acrylic polymer, polyurethane, polyester, polyamide, polyethylene, polybutadiene, Polystyrene, polyvinyl acetate, a modified acetal of polyvinyl alcohol, polycarbonate, or the like may be used in combination. Among these, from the viewpoint of ease of particle formation, the mass average molecular weight is in the range of 2,000 to 1,000,000 and the polydispersity (mass 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 ease of fixing, a polymer having any one of a softening point, a glass transition point, and a melting point within the range of 40 ° C to 120 ° C is preferable.

In the present invention, the polymer that can be used together with the epoxy resin having specific physical properties as a 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, amino group, hydroxy group, or halogen substituent.

  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. Moreover, you may use these polymers in combination of 2 or more types.

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.
In addition, when using together the epoxy resin and other coating agent which satisfy | fill the said specific physical-property value condition, the compounding ratio of other coating agents shall not exceed 40 mass% with respect to the coating material whole quantity. Preferably it is 30 mass% or less.

[Dispersant]
In the present invention, preferably, the mixture of the colorant and the coating agent is dispersed (particulated) in the 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 (meth) acrylic compound, a (meth) acrylic polymer, a copolymer of polyethylene and (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 Polymers that are in the range of 1.0 to 7.0 are preferred. Furthermore, it is most preferable to use a graft polymer or a block polymer.

  The polymer used particularly preferably in the present invention comprises a polymer component composed of at least one of structural units represented by the following general formulas (5) and (6), and a structural unit represented by the following general formula (7). A graft polymer containing at least a polymer component contained 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 substituent.

  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. Hexyl (meth) acrylate cyclohexyl, phenyl (meth) acrylate, benzyl (meth) acrylate, (meth) acrylic acid esters of 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 (6) 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. A preferred composition ratio between 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 kinds.

  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]
In the present invention, the mixture of the colorant and the coating agent is preferably dispersed (particulated) in a dispersion medium using a dispersant, and a charge adjusting agent may be used in combination to control the charge amount of the particles. Further preferred.
Suitable dispersants include 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, dioctylsulfosuccinate. Organic sulfonic acid metal salt such as magnesium acid salt, organic sulfonic acid ammonium salt such as toluenesulfonic acid tetrabutylammonium salt, polymer containing carboxylic acid group-modified styrene and maleic anhydride copolymer with amine A polymer having a carboxylic acid group in the side chain, a polymer having a carboxylic acid anion group in a side chain such as a copolymer of stearyl methacrylate and a tetramethylammonium salt of methacrylic acid, and a side chain such as a copolymer of styrene and vinylpyridine. Poly with nitrogen atoms Chromatography, butyl methacrylate and N- (2-methacryloyloxyethyl) -N, N, polymers having an ammonium group in the side chain of the copolymer of N- trimethylammonium tosylate. The charge applied to the particles may be positively charged or negatively charged. The content of the dispersant with respect to the entire ink composition is preferably in the range of 0.0001 to 10% by mass. Within this range, the electrical conductivity of the ink composition can be easily adjusted within the range of 10 nS / m to 300 nS / m. Furthermore, the electric conductivity of the charged particles can be easily adjusted to 50% or more of the electric conductivity of the ink composition.

[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]
An ink composition containing the charged particles of the present invention can be prepared by dispersing (particulating) a colorant and preferably a 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 colorant, 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).

[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. An ink jet recording method using an electrostatic field concentrates charged particles of an ink composition to an ejection position by an electrostatic force by applying a voltage between a control electrode and a back electrode on the back of a recording medium, and the recording medium from the ejection position It is a method to fly to. 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 an ejection opening, and a voltage is applied to a control electrode formed at the periphery of the ejection opening, so that it exists in the ejection 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 four-color printing on one side of the 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. A head driver 4 for driving the ejection head 2 by an output from an external device such as a computer (not shown) or a RIP, 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 adsorption unit 9 for holding the recording medium P on the conveyance belt, a static elimination unit 10 and a mechanical unit 11 for separating the recording medium P from the conveyance belt 7 after completion of image formation are provided. Upstream and downstream of the conveyance belt 7, the recording medium P is fed from a stocker (not shown) to the conveyance belt 7, the ink is fixed to the feed roller 12 and the guide 13, and the peeled recording medium P and conveyed to a paper discharge stocker (not shown). A fixing means 14 and a guide 15 are arranged. The ink jet printing apparatus 1 has a recording medium position detecting means 16 at a position facing the ejection head 2 with the conveying belt 7 interposed therebetween, and further collects solvent vapor generated from the ink composition. A solvent recovery unit comprising 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.

  As the feed roller 12, a known roller can be used, 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 to the recording medium P, it is desirable to remove them. The recording medium P supplied by the feed roller is conveyed to the conveying 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 transported recording medium 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 electrostatic adsorbing means 9 electrostatically adsorbs the recording medium 9 on the conveying belt 7 without floating, and uniformly charges the surface of the recording medium. 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 image-formed recording medium P is neutralized by the neutralizing unit 10, peeled off by the conveying belt 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 near the opening and discharge, and mainly a recording medium or a recording medium rear surface. Ink droplets are ejected by electrostatic attraction caused by the counter electrode disposed on the surface. Therefore, if the recording medium or the counter electrode is not facing the head, or if no voltage is applied to the recording medium or the counter electrode even at a position facing the head, the voltage is improperly applied to the ejection electrode. Ink droplets are not ejected even when applied or when vibration is applied, and the inside of the apparatus is not soiled.

  An ejection head suitably used for 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 forms the upper wall of the ink flow path 72 where the ink flow Q in one direction is formed, and the ink is directed toward the recording medium P. And a plurality of discharge portions 76 for discharging. 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 75 through which the ink guide portion 78 is inserted. 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 fly ink from the inkjet head 70 and record on the recording medium P, the ink flow Q is generated by circulating the ink in the ink flow path 72, and the guard electrode 50. A predetermined voltage (for example, +100 V) is applied to. Further, 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 56. 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 (when the gap d is 500 μm, 1 kV to 3. (The standard is to form a potential difference of about 0 kV).

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.

  As described above, when a pulsed positive voltage is applied, the ink droplet G is guided by the ink guide 78 from the opening 75 and flies to adhere to the recording medium P, and the floating conductive plate 62 has the first ejection electrode. A positive induced voltage is generated by the positive voltage applied to 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, the induced voltage is a substantially steady voltage. Therefore, 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 substrate In the vicinity of 74, the concentration of charged particles R increases. 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 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 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, a plastic film on which metal is laminated or vapor-deposited, etc., printed matter can be directly obtained by ink jet recording. Further, an offset printing plate can be obtained by using a roughened support such as aluminum. 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 combining the ink composition, the ink jet recording apparatus, and the replenishment of the ink composition 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. Can do.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.
The various epoxy resins used in the examples are commercially available products and synthetic products, and the present invention is not limited to the epoxy resins used in these examples.
Table 2 shows a list of epoxy resins used in the examples.

Creation of epoxy resin
[Epoxy resin 1]
In a 1 L three-necked separable flask equipped with a stirrer, reflux condenser and thermometer, 41.36 g (0.35 mol) of p-xylylene diol (manufactured by Tokyo Chemical Industry) and 26 g of NaOH were dissolved in 300 ml of water. And put it in. The mixture was heated in an oil bath at 50 ° C. for 10 minutes with vigorous stirring. Next, 46.26 g (0.5 mol) of epichlorohydrin (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the temperature was gradually raised to 95 ° C. over 30 minutes. After reacting for 40 minutes, the stirring was stopped and the supernatant was cooled. Water separated as a liquid was removed by a gradient method. Subsequently, 300 ml of water was added, the mixture was heated and stirred at 80 to 95 ° C., the supernatant was removed in the same manner as described above, and this washing operation was repeated until the aqueous phase showed no alkalinity. Finally, after sufficiently removing water, while the polymer obtained by heat dehydration at 150 ° C. for about 30 minutes was hot, it was quickly taken out and vacuum-dried to obtain about 75 g of an epoxy resin.

[Epoxy resin 2-9]
Using various diol components (see Table 1), various epoxy resins shown in Table 2 were synthesized in the same manner as in the epoxy resin 1.

[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 [Epicoat 1001]
・ Dispersant [BZ-2]
-Charge control agent [CT-1]
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

  The structures of the dispersant [BZ-2] and the charge control agent [CT-1] are 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 mass average molecular weight was 110,000.
The charge control agent [CT-1] was obtained by reacting 1-octadecene and maleic anhydride copolymer with 1-hexadecylamine. The weight average molecular weight was 17,000.

<Preparation of ink composition [EC-1]>
10 g of a cyan pigment and 20 g of a coating agent [Epicoat 1001] were placed in a table type kneader PBV-0.1 manufactured by Irie Shokai Co., Ltd., the heater temperature was set to 100 ° C., and the mixture was heated and mixed for 2 hours. 30 g of the obtained mixture was coarsely pulverized with a trio-brender 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 the zirconia ceramic beads having a diameter of about 0.6 mm, the type KDL dynomill manufactured by Shinmaru Enterprises Co., Ltd. was used for 5 hours while maintaining the internal temperature at 25 ° C., followed by 45 ° C. for 5 hours. Dispersion (particle formation) was performed at a rotational speed of 000 rpm. Zirconia ceramic beads were removed from the obtained dispersion, and 316 g of Isopar G and 0.6 g of charge control agent [CT-1] were added to obtain an ink composition [EC-1].

<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 belt is rotated by rotation of the conveying 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 in the vicinity of one end of the belt along the conveyor direction, 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.
The resulting gray scale image recorded matter (printed matter) was evaluated for the degree of stripe unevenness and ink bleeding. In addition, the ink drawing image quality was similarly evaluated after continuous use for one month.

[Comparative Example 1]
Ink [RC-1] was prepared in the same manner as in Example 1 except that the coating material [Epicoat 1001] was changed to [Epoxy resin a] as the material used. Using this ink, particle diameter and distribution evaluation and ink jet drawing were performed.

[Comparative Example 2]
Ink [RC-2] was prepared in the same manner as in Example 1 except that the coating material [Epicoat 1001] was changed to [Epoxy resin b] as the material used. Using this ink, particle diameter and distribution evaluation and ink jet drawing were performed.

[Comparative Example 3]
Ink [RC-3] was prepared in the same manner as in Example 1 except that the coating material [Epicoat 1001] was changed to [Epoxy resin c] as the material used. Using this ink, particle diameter and distribution evaluation and ink jet drawing were performed.

  Table 3 shows the results of Example 1 and Comparative Examples 1 to 3.

1) Inkjet drawing image quality The degree of bleeding of a drawing image was visually evaluated.
○ No bleeding △ Slight bleeding × Bleeding ×× Severe bleeding

As shown in Example 1, when the charged particles include an epoxy resin [Epicoat 1001] that satisfies the specific physical property value of the present invention, the particle diameter and distribution of the ink particles can be made a preferable region. In the ink jet drawing image by the method, the electrophoretic speed of the ink particles at the discharge portion is sufficiently high and the ink particles are sufficiently concentrated, so that an image of good quality with no bleeding can be obtained. Moreover, even if running is performed, stable drawing can be performed over a long period of time.
On the other hand, in Comparative Example 1, since [high molecular weight epoxy resin a] is used as the coating agent, the cohesive force of the polymer is high, and in the pigment-coating agent composite, the cohesive force tends to be nonuniform and uniform particles Formation is difficult and particles with a wide particle size distribution are produced.
In Comparative Example 2, since soft [low Tg epoxy resin b] is used as a coating agent, the polymer is not brittle enough to be crushed, and further, it is difficult to apply force from the media, and particles cannot be formed by mechanical dispersion with media. .
Furthermore, in Comparative Example 3, the dynamic elastic modulus G ′ of the coating material is low, and the physical properties of the rubber elastic region are exhibited in the temperature range in the pulverization-dispersion process. Particles cannot be formed by mechanical dispersion.
As described above, other than the epoxy resin that satisfies the specific property value conditions in the present invention, the target ink particles cannot be obtained, and the electrophoretic speed of the ink particles in the ejection portion is slow in the ink jet drawing image by this method. Ink particles are not sufficiently concentrated, so that bleeding occurs and a good quality image cannot be obtained.

[Examples 2-31]
Ink compositions [EC-2 to EC-31] were prepared in the same manner as in Example 1 except that the coating agent was changed to that shown in Table 4 below in the preparation of the ink composition [EC-1] of Example 1. Created.

The ink composition obtained above was evaluated in the same manner as in Example 1. As a result, by using the coating agents of Examples 2 to 31, the particle size and distribution of the ink particles can be made a preferable region, and the electrophoretic velocity of the ink particles at the discharge portion in the ink jet drawing image according to this method. Is sufficiently fast and the ink particles are sufficiently concentrated, so that it was confirmed that an image of good quality without blur was obtained. It was also confirmed that stable drawing was possible for a long time even when running.

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 Injected ink droplet 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 Conveying belt stretch Roller 7 Conveying belt 8 Conveying belt position detecting means 9 Electrostatic adsorption means 10 Static eliminating means 11 Mechanical means 12 Feed roller 13 Guide 14 Image fixing means 15 Guide 16 Recording medium position detecting means 17 Discharge fan 18 Solvent vapor adsorbing material 38 Ink guide 40 support rod portion 42 ink meniscus 44 insulating layer 46 first discharge electrode 48 insulating layer 50 guard electrode 52 insulating layer 56 second discharge electrode 58 insulating layer 62 floating conductive plate 64 coating film 66 insulating member 70 inkjet head 72 ink flow path 74 Substrate 75, 75A, 75B Opening 76, 76A, 76B Discharge Part 78 Discharge part

Claims (5)

An ink composition comprising a dispersion medium and charged particles containing at least a colorant, wherein the charged particles contain an epoxy resin that satisfies the following physical property value conditions a) to c): .
a) Dynamic elastic modulus at 50 ° C. (G ′): 10 ⁴ Pa or more b) Molecular weight (GPC mass average): 50,000 or less c) Glass transition point (Tg): 30 to 100 ° C.   The ink composition according to claim 1, wherein the epoxy resin is a linear polymer. The ink composition according to claim 1, wherein the epoxy resin is represented by the following general formula (I).

(In the formula, X represents an optionally substituted alkylene group, cycloalkylene group, alkenylene group, alkynylene group, arylene group, aralkylene group or bridged cyclic hydrocarbon linking group. N represents the degree of polymerization.)   The charged particles are prepared by a mechanical media dispersion method, and particles having a particle diameter corresponding to 1/5 or less of a volume average particle diameter in a centrifugal sedimentation method are 1% or less. Ink composition.   An ink jet recording method in which the ink composition according to any one of claims 1 to 4 is ejected as ink droplets by an ink jet recording method using an electrostatic field.

Images