JP2006232928A - Oily ink composition and method of inkjet-recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink composition used for an inkjet-recording, enabling the ejection of ink drops always stably in the inkjet-recording for a long time and the formation of an image having a high image quality, and a method of the inkjet-recording. <P>SOLUTION: This oily ink composition comprises charged particles containing at least a coloring material, and dispersion medium, wherein the electrophoretic mobility of the charged particles at 25°C is ≥0.02 μmcm/Vs. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oil-based 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 system is an inexpensive apparatus and ejects ink only to a required image portion to form an image directly on a recording medium, so that ink can be used efficiently and 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. 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 ink jet recording utilizing an electrostatic field, an oil-based ink composition containing charged particles including at least a dispersion medium and a coloring material is used (see Patent Documents 3 and 4). An oil-based ink composition containing a color material can create four colors of inks of yellow, magenta, cyan, and black by changing the color material, and also create special inks of white, gold, and silver Therefore, a color image formed product (printed product) can be produced, which is useful.

In oil-based inks used in such electrostatic ink jet recording systems, as a charge control agent, a metal soap, ionic compound, or surfactant that is soluble in a dispersion medium is added to sufficiently charge the color material in the ink. It is necessary to let In Patent Document 5, by using a specific polymer and metal soap, a sufficiently high zeta potential can be imparted to the coloring material, thereby enabling high-density and low-bleed dots to be stably printed at high speed. It is described that can be.
Japanese Patent No. 3315334 US Pat. No. 6,158,844 JP-A-8-291267 US Pat. No. 5,952,2048 Japanese Patent Application Laid-Open No. 2001-139856

However, it is difficult to achieve both the formation of an image without causing the ink to sufficiently concentrate and bleed, and the discharge at a low voltage of, for example, 300 V, and the technique described in Patent Document 5 is still stable. It was insufficient for ink ejection.
Accordingly, it is an object of the present invention to provide an oil-based ink composition and an ink jet recording method capable of forming images without blurring and forming images at a low voltage.

  As a result of diligent studies, the present inventor has found that the ejection characteristics of ink droplets greatly depend on the charging characteristics of the ink used and must be within a specific range. Invented. That is, it has been found that the reason why it is difficult to achieve both the image formation without bleeding and the low voltage discharge in the conventional oil-based ink for inkjet is that the charge density on the surface of the charged particles is insufficient. In conventional inkjet oil-based inks, a sufficient charge density is not obtained, and even in the charge application technique described in Patent Document 5, the electrophoretic mobility of charged particles converted from zeta potential is 0.15 μmcm / It is about Vs, and it has been found that further charge density improvement is necessary for stable ink ejection.

That is, this invention consists of the following structures.
(1) An oil-based ink composition comprising charged particles containing at least a coloring material and a dispersion medium, wherein the charged particles have an electrophoretic mobility at 25 ° C. of 0.20 μmcm / Vs or more. Composition.
(2) The oil-based ink composition as described in (1) above, wherein the standard deviation of the volume diameter of the charged particles is 0.45 μm or less.
(3) The oil-based ink composition as described in (1) or (2) above, wherein the charged particles contain a polymer containing a basic group.
(4) The oil-based ink composition as described in any one of (1) to (3) above, further comprising at least one compound selected from a basic compound and an onium salt.
(5) An ink jet recording method in which an ink droplet is ejected using an electrostatic field by using the oil-based ink composition according to any one of (1) to (4) above, wherein the ink is placed in an ink chamber having a discharge opening. By applying a voltage to the control electrode that is circulated and formed at the periphery of the ejection opening, concentrated ink droplets are present from the front end of the ink guide that exists in the ejection opening and the front end faces the recording medium. An ink jet recording method, wherein:

The oil-based ink composition of the present invention contains at least charged particles including at least a coloring material and a dispersion medium.
The charged particles used in the present invention may be those in which the color material has electrical conductivity. However, the electrical conductivity can be concealed by coating the color material with a coating agent, and the particles can be formed by the charge control agent. It is possible to easily control the charge application.
In the ink composition of the present invention, in order to control the particle diameter of the charged particles and to suppress the sedimentation of the particles, it is preferable to disperse (particle) in the dispersion medium using a dispersant. In order to control this, it is more preferable to use a charge control agent in combination.

  In the present invention, the electrophoretic mobility at 25 ° C. of the charged particles in the ink composition is in the range of 0.20 μmcm / Vs or more. A preferable electrophoretic mobility of the charged particles in the ink composition is 0.25 μmcm / Vs or more and 0.50 μmcm / Vs or less. More preferably, it is 0.30 μmcm / Vs or more and 0.50 μmcm / Vs or less. According to the present invention, by setting the electrophoretic mobility of charged particles in the ink composition to 0.20 μmcm / Vs or more, the concentration by electric field is improved, the concentration of ejected matter is increased (the solvent is decreased), and As a result, an image with less bleeding can be obtained. Further, even when the head voltage is as low as 300V, ink droplets can be sufficiently discharged. On the other hand, if the electrophoretic mobility is too large, the electrophoretic mobility of the charged particles is 0.50 μmcm / Vs or less because the electroconductivity may be conducted in the head (ejection unit) of the ink jet device and damage the head. Is preferred.

  In order to increase the electrophoretic mobility of charged particles according to the present invention, the particle size distribution of charged particles is narrowed (the standard deviation of the volume average diameter of charged particles is reduced), and basic groups are used as coating agents for charged particles. Using a polymer to be contained, appropriately selecting and using a technique such as adding a basic compound or onium salt as an additive of the ink composition, and if necessary, the type of dispersion medium and charge control agent to be used, dispersant This can be achieved by appropriately adjusting the amount and the like. This will be specifically described below.

  Depending on the calculation method, the average diameter of the charged particles may be volume average, number average, etc. In the present invention, the volume average diameter of the charged particles is preferably in the range of 0.2 to 5.0 μm, more preferably 0.3 to 2.0 μm. The volume average diameter of the charged particles is preferably 0.2 μm or more in order to achieve an electrophoretic mobility of 0.20 μm cm / Vs or more, whereby sufficient concentration of the charged particles can be obtained, and the recording medium This is preferable because ink bleeding does not occur when the recording is performed. On the other hand, it is preferable that the volume average diameter of the charged particles is 5.0 μm or less because there is no inconvenience such as clogging of the head ejection opening. The volume average 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 order to achieve an electrophoretic mobility of 0.20 μmcm / Vs or more, the standard deviation of the volume average diameter of the charged particles is preferably within a range of 0.45 μm or less, more preferably 0.40 μm or less. 0.35 μm or less is more preferable. Within this range, the concentration of charged particles becomes insufficient due to the influence of fine particles. As a result, ink bleeds when recorded on the recording medium, and clogging of the head discharge port occurs due to coarse particles. Inconveniences such as being easy to occur are less likely to occur, which is preferable. The particle size distribution 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.).

  The volume average particle diameter and distribution of the charged particles can be adjusted by the amount of the dispersant used and the apparatus used for dispersion (particulation). Since the dispersant is adsorbed on the charged particles and dispersed in the dispersion medium, the concentration of the dispersant is appropriately adjusted within the range of 0.1% to 5% by weight. By doing this, the volume average diameter and distribution can be controlled, and the electrophoretic mobility at 25 ° C. of the present invention can be 0.20 μmcm / Vs or more.

  Moreover, by using a polymer containing a basic group as a coating agent for charged particles, the surface charge density of the coating agent can be increased, and the electrophoretic mobility of the charged particles can be increased. Further, by adding a basic compound or onium salt to the ink composition, cations are generated from these compounds and adsorbed to the particles, whereby the surface charge density and electrophoretic mobility of the particles can be increased.

  Furthermore, the electrophoretic mobility of the charged particles in the ink composition can be appropriately adjusted according to the type and amount of the charge adjusting agent as required. Since the charge adjusting agent generates charge by the action of ion dissociation and adsorption to particles, it greatly contributes to the electrophoretic mobility of charged particles. Therefore, even when a non-aqueous non-polar liquid having a low electrical conductivity or a high electrical resistivity is used as a dispersion medium, by applying a charge to the particles with an optimal charge control agent amount of a dissociative charge control agent, The electrophoretic mobility at 25 ° C. can be 0.20 μmcm / Vs or more.

  According to the present invention, recording is performed on a recording medium by an electrostatic ink jet recording method using the oil-based ink composition of the present invention that satisfies the electrophoretic mobility at 25 ° C. of 0.20 μmcm / Vs or more. As a result, it is possible to stably eject ink droplets constantly in long-time inkjet recording, and it is possible to form a high-quality image without streak unevenness or ink bleeding for a long time.

First, each component that can be used in the oil-based ink composition of the present invention will be described in detail.
[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: 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. Within this range, the colorant-containing particles can be favorably dispersed in the dispersion medium while satisfying the colorant content, which is preferable.

[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, 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 (see Non-Patent Document 1 above).
The content of the pigment with respect to the whole ink composition is preferably in the range of 0.1 to 50% by mass, and more preferably 1 to 30% by mass. When the amount is 0.1% by mass or more, the amount of pigment is satisfied, and sufficiently good color development is obtained in the printed matter. Also, when the amount is 50% by mass or less, the particles containing the coloring material can be dispersed in the dispersion medium. preferable.

[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.

  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, polyvinyl alcohol, acetal-modified products of polycarbonate, polycarbonate Etc. 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. Further, 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 a range of 40 ° C to 120 ° C is preferable. Further, from the viewpoint of increasing the surface charge density of the coating agent, a polymer containing a basic group is preferred, and a polymer containing an amino group is particularly preferred. For example, as described later, a copolymer with an amino group-containing monomer such as N, N-dimethylaminoethyl acrylate can be preferably used.

  In the present invention, the polymer particularly preferably 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 contains an ether bond, or a substituent such as an amino group, a hydroxy group, a heterocyclic ring, a phosphino group, a sulfido group, or a halogen. May be. More preferably, the hydrocarbon group of R ₁₂ , R ₂₁ , R ₃₁ , R ₃₂ and R ₄₁ has a basic group such as an amino group, a heterocyclic ring, a phosphino group, or a sulfide group.

  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, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, and N-methyl (meth) acrylamide, N -Propyl (meth) acrylamide, N-phenyl (meth) Acrylamide, N, N-dimethyl (meth) acrylamide, (meth) 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, 4-methylstyrene, vinyl pyridine, vinyl imidazole, vinyl piperidine and derivatives thereof.

  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 may be used in combination of two or more.

  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, 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 weight average molecular weight is in the range of 1,000 to 1,000,000 and the polydispersity (weight 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, And stearyl (meth) acrylate.
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.

  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.

[Basic compound additive]
The basic compound used in the present invention is not particularly limited, but an organic amine is preferable. The organic amine is preferably a tertiary amine. Further preferred are amines containing two or more amino groups in the molecule. The organic amine is preferably tertiary piperidine and its derivatives. Furthermore, it is more preferable that the amine has a boiling point of 150 ° C. or higher because of less odor.

Specific examples of basic compounds suitable for the present invention include decylamine, dodecylamine, N, N-dimethyldodecylamine, stearylamine, cetylamine, benzylpiperidine, N, N-dimethylcyclohexylamine, mono, di, or tri Ethanolamine, aminopropanol, aminobutanol, aminohexanol, dimethylaminohexanol, morpholine, aminoethylmorpholine, aminopropylmorpholine, aminoethylpiperazine, aminoethylpyrrolidine, bis (hydroxyethyl) piperazine, aminopropylpyrrolidinone, aminoethoxyethanol, dimethyl Aminoethyl morpholine, phenyl morpholine, 1,3-bis [1- (2-hydroxyethyl) -4-piperidyl] propane, gramine, 1- (2-Fe Til) -4-piperidone, ethylenediamine, trimethylenediamine, tetramethylene, hexamethylenediamine, aniline, N, N-diethylaniline, dodecylaniline, aminobiphenyl, aminophenol, 4-aminoacetanilide, aminoacetophenone, aminobenzamide, amino Benzanilide, aminobenzophenone, aminopyridine, dimethylaminomethylthiophene, dimethylaminophenethyl alcohol, polyethyleneimine, polyarylamine, polyvinylpyridine, piperidine and its derivatives (eg 4-hydroxy-1-methylpiperidine), N, N-dimethyl Copolymers of aminoethyl methacrylate and methacrylates (for example, butyl methacrylate), N, N-diethylaminoethyl methacrylate And copolymers of acrylic esters (eg ethyl acrylate), copolymers of dimethylaminomethylstyrene and styrene, 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and 1,4-butanedioic acid And the like. These can also be used in combination.
Content of a basic compound is 0.0001-10 mass% with respect to an ink composition, Preferably it exists in the range of 0.0005-5 mass%.

[Onium salt additive]
Examples of the onium salt used in the present invention include ammonium salts, sulfonium salts, phosphonium salts, and the like. Among them, ammonium salts are preferable.
Specific examples of onium salts suitable for the present invention include tetramethylammonium bromide, tetraethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrabutylammonium toluenesulfonate, tetrabutylammonium trifluoromethane. Sulfonate, tetrabutylammonium tetrafluoroborate, decyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, cetyltrimethylammonium chloride, benzyltrimethylammonium bromide, triphenylsulfonium toluenesulfonate, tri (methylphenyl) sulfonium toluene Sulfonate, g (Chlorophenyl) sulfonium toluenesulfonate, tetraphenylphosphonium bromide, a copolymer of toluenesulfonate of N, N, N-trimethylammonioethyl methacrylate and methacrylate esters (eg butyl methacrylate), trimethylammoniomethylstyrene and styrene A copolymer etc. are mentioned. These can also be used in combination.
The content of the onium salt is, for example, in the range of 0.0001 to 10% by mass, preferably 0.0005 to 5% by mass with respect to 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]
The ink composition containing the charged particles of the present invention can be prepared by dispersing (particulating) the colorant and preferably 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 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).

  The viscosity of the ink composition of the present invention is preferably in the range of 0.5 to 5 mPa · s, more preferably in the range of 0.8 to 4 mPa · s. Within this range, it is preferable that the ink droplets are discharged satisfactorily without the ink composition dripping from the ink discharge port of the head. The viscosity of the ink composition can be adjusted by the type and amount of the polymer component such as the dispersion medium used and the dispersant dissolved in the dispersion medium. Further, the viscosity can be adjusted by further using a surfactant.

  The surface tension of the ink composition is preferably in the range of 10 to 70 mN / m, and more preferably in the range of 15 to 50 mN / m. When the surface tension of the ink composition is within this range, the ink composition is preferably ejected from the ink ejection port of the head, and the ink droplets are favorably ejected.

[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 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 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 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 an 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, this 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, 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.

[Electrophoretic mobility]
Electrophoretic mobility of charged particles was measured using a laser Doppler method. For example, using Malvern Nano-ZS, the migration speed of charged particles when a voltage of 40 V is applied to the ink is measured and divided by the electric field E. At the time of measurement, it was diluted with Isopar G so that the particle concentration was 0.007 wt%, and the measurement was performed after 3 hours or more. A Malvern universal dip cell and glass cell (PCS1115) were used for the measurement.

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

  The structures of the coating agent [AP-1], the dispersant [BZ-2], and the charge control agent [CT-1] are shown below.

The coating agent [AP-1] was prepared by using styrene, 4-methylstyrene, butyl acrylate, dodecyl methacrylate and 2- (N, N-dimethylamino) ethyl methacrylate as a polymerization initiator (2,2-azobisbutyro Nitrile) was used for radical polymerization and further reacted with methyl tosylate. The weight average molecular weight was 15,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 2.7. The glass transition point (mid point) was 51 ° C., and the softening point by the strain gauge method was 46 ° C.
Dispersant [BZ-2] is a polymer of stearyl methacrylate having a methacryloyl group at its terminal (weight average molecular weight) 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.
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 the cyan pigment and 20 g of the coating agent [AP-1] were put into 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 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 10 ° C., and subsequently at 45 ° C. for 5 hours. Dispersion (particle formation) was performed at a rotational speed of 000 rpm. The zirconia ceramic beads are removed from the obtained dispersion, Isopar G is added so that the particle concentration is 7 wt%, and 0.6 g of the charge control agent [CT-1] is further added, and the ink composition [EC- 1] was obtained.

The physical properties of the ink composition [EC-1] were as follows.
(A) The obtained ink was diluted 1000 times with Isopar G, and electrophoretic mobility was measured using Nano-ZS manufactured by Malvern. As a result, 0.22 μmcm / VS was obtained.
(B) When the volume average diameter of the charged particles was measured with a CAPA-700 manufactured by Horiba, Ltd. at a rotation speed of 5000 rpm, it was 0.90 μm and the standard deviation was 0.39 μm.
(C) The viscosity of the ink composition at 20 ° C. was 1.5 mPa · s as measured by an E-type viscometer manufactured by Tokyo Keiki Co., Ltd. Further, the surface tension of the ink composition at 20 ° C. was measured with a FACE automatic surface tension meter manufactured by Kyowa Interface Science Co., Ltd. and found to be 25 mN / m.

<Inkjet recording>
The ink composition [EC-1] was filled in the ink tank connected to the ejection head 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 +300 V was applied (pulse width 50 μsec) at the time of ejection, and image formation was performed at a driving frequency of 15 kHz.
Immediately after image recording, the image was fixed using a heat roller. The temperature of the coated paper at the time of fixing was 90 ° C., and the contact time with the heat roller was 0.3 seconds.

The obtained image recorded matter (printed matter) was a very clear image with no stripe unevenness and ink blur. No image formation failure or the like was observed, and no image deterioration due to dot diameter change or the like was observed even when the outside air temperature changed or the recording time increased, and good image formation was possible. After the end of recording, the ink jet recording apparatus was retracted 50 mm from a position close to the conveying belt in order to protect the ink jet head.
Also, maintenance is required for one month by storing the head in a cover filled with vapor of Isopar G after supplying the head with Isopar G for 10 minutes after cleaning and cleaning it. A good image recorded product could be produced without any problem.

[Example 2]
<Materials used>
In Example 2, [AP-2] was used in place of [AP-1] as a coating agent. Coating agent [AP-2] uses methyl methacrylate, butyl methacrylate, stearyl methacrylate and 2- (N, N-diethylamino) ethyl methacrylate as a polymerization initiator (2,2-azobisbutyronitrile). And obtained by radical polymerization. The weight average molecular weight was 20,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 2.7. The glass transition point (midpoint) was 45 ° C.

<Preparation of ink composition [EC-2]>
Cyan pigment (10 g) and coating agent [AP-2] (20 g) were heated and stirred for 1 hour while mixing with a heater so that the internal temperature was 110 ° C., and mixed. 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 9 g of the dispersant [BZ-2], Isopar G75 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, the type KDL dynomill manufactured by Shinmaru Enterprises Co., Ltd. was used for 5 hours while maintaining the internal temperature at 25 ° C., and subsequently at 50 ° 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 360 g of Isopar G and 0.4 g of the charge control agent [CT-1] were added to obtain an ink composition [EC-2].

[Example 3]
Disperse with Sympel Enterprises Co., Ltd. Type KDL Dynomill in the same manner as the ink composition [EC-1], remove zirconia ceramic beads, add Isopar G to a particle concentration of 7 wt%, An ink composition [EC-3] was obtained by adding 0.6 g of a charge control agent [CT-1] and further adding 0.001 wt% of methylpiperidine as an amine additive.

[Example 4]
Disperse with Type KDL Dynomill manufactured by Shinmaru Enterprises Co., Ltd. in the same manner as the ink composition [EC-2], remove zirconia ceramic beads, add Isopar G to a particle concentration of 7 wt%, An ink composition [EC-4] was obtained by adding 0.6 g of a charge control agent [CT-1] and further adding 0.001 wt% of methylpiperidine as an amine additive.

  The ink compositions [EC-2], [EC-3], and [EC-4] were measured in the same manner as in Example 1. As shown in Table 1, all had an electrophoretic mobility of 0.20 μmcm · Vs. As described above, the volume average particle size was 0.5 μm or more, and the standard deviation of the volume average particle size was 0.45 μm or less.

<Inkjet recording>
Using ink compositions [EC-2], [EC-3], and [EC-4], ink jet recording was performed at a discharge voltage of +300 V for one month while supplying concentrated ink in the same manner as in Example 1. went. During this time, a very clear image without streak unevenness and ink bleeding was obtained, and a good image recorded product could be produced without the need for maintenance work.

[Comparative Example 1]
With the same composition as the ink composition [EC-1], pre-dispersion with a paint shaker is performed for 6 hours, glass beads are removed from the obtained dispersion, and Isopar G is added so that the particle concentration is 7 wt%. In addition, 0.6 g of a charge control agent [CT-1] was further added to obtain an ink composition [RC-1].
The physical properties of the ink composition [RC-1] were as follows.
(A) The obtained ink was diluted 1000 times with Isopar G, and electrophoretic mobility was measured using Nano-ZS manufactured by Malvern. As a result, 0.17 μmcm / VS was obtained.
(B) When the volume average diameter of the charged particles was measured with a CAPA-700 manufactured by Horiba, Ltd. at a rotation speed of 5000 rpm, it was 0.92 μm and the standard deviation was 0.51 μm.
(C) The viscosity of the ink composition at 20 ° C. was 1.5 mPa · s as measured by an E-type viscometer manufactured by Tokyo Keiki Co., Ltd. Further, the surface tension of the ink composition at 20 ° C. was measured with a FACE automatic surface tension meter manufactured by Kyowa Interface Science Co., Ltd. and found to be 25 mN / m.
When drawing was performed in the same manner as [EC-1] using [RC-1], the responsiveness was poor at a pulse voltage of +300 V, and blurring and ejection delay occurred during image formation.

The image formability indicates the presence or absence of ejection and bleeding at a pulse voltage of 300 V.
X means no ejection, Δ means ejection, but blurring occurs, ○ means that bleeding sometimes occurs, and ◎ means that there is no bleeding.
From the results in Table 1, it can be seen that the image formability is improved by changing the electrophoretic mobility.

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 apparatus 2 Discharge head 3 Ink circulation system 4 Head driver 5 Position control means 6A to 6C Conveying belt stretching roller 7 Conveying belt 8 Conveying belt position detecting 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 portion 42 Ink meniscus 44 Insulating layer 46 First discharge electrode 48 Insulating layer 50 Guard electrode 52 Insulating layer 56 Second discharge electrode 62 Floating conductive plate 64 Coating film 66 Insulating member 70 Inkjet head 74 Substrate 76 Discharge unit 78 Discharge unit

Claims (5)

  An oil-based ink composition comprising a charged particle containing at least a coloring material and a dispersion medium, wherein the charged particle has an electrophoretic mobility at 25 ° C. of 0.20 μmcm / Vs or more.   2. The oil-based ink composition according to claim 1, wherein a standard deviation of a volume diameter of the charged particles is 0.45 μm or less.   The oil-based ink composition according to claim 1, wherein the charged particle contains a polymer containing a basic group.   The oil-based ink composition according to claim 1, further comprising at least one compound selected from a basic compound and an onium salt.   An ink-jet recording method in which the oil-based ink composition according to any one of claims 1 to 4 is ejected using an electrostatic field, wherein the ink is circulated in an ink chamber having a discharge opening. By applying a voltage to the control electrode formed at the periphery of the opening, concentrated ink droplets fly from the tip of the ink guide that exists in the discharge opening and the tip is directed to the recording medium. An inkjet recording method.

Images