JP2005015770A - Ink composition for inkjet-recording and method for inkjet-recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an ink composition for inkjet-recording, always capable of ejecting ink droplets stably through a long time of the inkjet-recording and enabling the formation of a high quality image for a long time, and to provide a method for inkjet-recording. <P>SOLUTION: The ink composition for the inkjet-recording satisfies the following conditions (A) to (D) in the ink composition containing charged particles containing at least a dispersion medium and a coloring agent. (A) The electric conductivity of the ink composition at 20°C is within a range of 10-300 nS/m. (B) The electric conductivity of the charged particles is ≥50 % of the electric conductivity of the ink composition. (C) The volume average-diameter of the charged particles is within a range of 0.2-5.0 μm, and. (D) The viscosity of the ink composition at 20°C is within a range of 0.5-5 mPa s. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink composition for ink jet recording 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 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, until now, it has been difficult to stably eject ink droplets in long-time inkjet recording.

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 long-time inkjet recording, and an ink composition for inkjet recording, which enables formation of a high-quality image for a long time, and inkjet It is to provide a recording method.

As a result of intensive investigations to achieve the above object, the present inventor has found that the ejection characteristics of ink droplets must be within a specific range depending largely on the physical properties of the ink used. As a result, the present invention has been found to greatly depend on the ink supply method.
That is, the present invention is as follows.
(1) a dispersion medium, and
Charged particles containing at least a coloring material,
An ink composition for ink jet recording, wherein the ink composition satisfies all of the following conditions (A) to (D):
(A) The electric conductivity at 20 ° C. of the ink composition is in the range of 10 nS / m to 300 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm.
(D) The viscosity of the ink composition at 20 ° C. is in the range of 0.5 to 5 mPa · s.
(2) The ink composition for ink jet recording according to (1), wherein the charged particles are dispersed in a dispersion medium by a graft polymer as a dispersant.
(3) The graft polymer is composed of a main chain portion and a side chain portion which is a graft chain, the main chain portion is not dissolved in the dispersion medium, and the side chain portion is dissolved ( The ink composition for ink jet recording according to 2).
(4) An ink jet recording method in which ink droplets are ejected using an electrostatic field containing an ink composition containing charged particles including at least a dispersion medium and a coloring material and satisfying all of the following conditions (A) to (D): In this case, the ink is circulated in the ink chamber having the ejection opening, and the voltage is applied to the control electrode formed at the periphery of the ejection opening, so that the ink exists in the ejection opening and the leading end faces the recording medium side. An ink jet recording method, wherein ink droplets fly from the tip of an ink guide.
(A) The electric conductivity at 20 ° C. of the ink composition is in the range of 10 nS / m to 300 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm.
(D) The viscosity of the ink composition at 20 ° C. is in the range of 0.5 to 5 mPa · s.
(5) In an ink jet recording method in which ink droplets are ejected by an ink jet recording method using an electrostatic field, an ink composition containing charged particles including at least a dispersion medium and a colorant is used under the following conditions ( An ink jet recording method comprising replenishing a high-concentration ink composition so as to always satisfy all of A) to (D).
(A) The electric conductivity at 20 ° C. of the ink composition is in the range of 10 nS / m to 300 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm.
(D) The viscosity of the ink composition at 20 ° C. is in the range of 0.5 to 5 mPa · s.
(6) The inkjet recording method according to (5), wherein the charged particles are dispersed in a dispersion medium by a graft polymer as a dispersant.

  According to the present invention, by setting the electrical conductivity and viscosity of the ink composition, the electrical conductivity of the charged particles, and the volume average diameter to a specific range, it is possible to form a high-quality image for a long time. Ink and inkjet recording methods can be provided.

The ink composition of the present invention is recorded on a recording medium by an ink jet recording method. In the present invention, it has been found that by using an ink composition that satisfies all of the following conditions (A) to (D), ink droplets can be stably ejected constantly in long-time inkjet recording. It was.
(A) The electrical conductivity of the ink composition is in the range of 10 nS / m to 300 nS / m, preferably 30 nS / m to 200 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more, preferably 60% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm, preferably 0.3 to 3.0 μm.
(D) The viscosity of the ink composition is in the range of 0.5 to 5 mPa · s, preferably 0.8 to 4 mPa · s.

The conditions to be satisfied by the ink composition of the present invention will be described in detail below. The electrical conductivity represents a value measured at 20 ° C. unless otherwise specified.
In the present invention, the electric conductivity of the ink composition is in the range of 10 nS / m to 300 nS / m. When the electrical conductivity of the ink composition is less than 10 nS / m, ink droplets are not ejected. On the other hand, when it exceeds 300 nS / m, it conducts in the head (ejection unit) of the ink jet device and damages the head. The electric conductivity of the ink composition is more preferably 30 nS / m to 200 nS / m.

The electric conductivity of the charged particles is a value obtained by centrifuging the ink composition, measuring the electric conductivity of the supernatant liquid on which the charged particles are precipitated, and subtracting the electric conductivity of the ink composition. In the present invention, the electric conductivity of the charged particles is 50% or more of the electric conductivity of the ink composition. In the ink jet recording method using an electrostatic field, when ink droplets are ejected, the concentration of charged particles occurs. However, when the concentration is lower than 50%, the concentration is insufficient, and as a result, the ink is recorded when recorded on a recording medium. Bleeding occurs. More preferably, it is 60% or more.
The charge amount of the charged particles is preferably in the range of 5 to 200 μC / g. More preferably, it is in the range of 10 to 150 μC / g, still more preferably 15 to 100 μC / g.

  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.). The average diameter includes a volume average and a number average depending on the calculation method. In the present invention, the volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm. When it is smaller than 0.2 μm, the concentration of charged particles becomes insufficient, and as a result, ink bleeds when recorded on a recording medium. When it is larger than 5.0 μm, the head discharge port is likely to be clogged. More preferably, it is 0.3-3.0 micrometers. The particle size distribution is preferably narrow and uniform.

  In the present invention, the viscosity of the ink composition is in the range of 0.5 to 5 mPa · s. When the viscosity is smaller than this range, the ink composition drips from the ink discharge port of the head. If it is larger than this range, ink droplets are not ejected. More preferably, it is in the range of 0.8 to 4 mPa · s. The surface tension of the ink composition is preferably in the range of 10 to 70 mN / m. More preferably, it exists in the range of 15-50 mN / m.

The electrical conductivity of the ink composition and the charged particles can be adjusted by the type and amount of the dispersion medium and charge control agent used. Since the charge adjusting agent generates charge by the action of ion dissociation and adsorption to particles, it greatly contributes to the electric conductivity of the charged particles. Therefore, the conditions (A) and (B) of the present invention are achieved by using a liquid having a low electrical conductivity or a high electrical resistivity as a dispersion medium and imparting electrical conductivity to the particles with a charge control agent. Can do.
Some color materials used in the present invention have electrical conductivity, but the electrical conductivity can be concealed by coating the color material with a coating agent, and the electrical conductivity to the particles by the charge control agent. Can be easily controlled.

The volume average particle diameter of the charged particles can be adjusted by the type and amount of the dispersant used and the device used for dispersion (particulation). Since the dispersant is adsorbed to the charged particles and dispersed in the dispersion medium, the volume average diameter can be controlled by appropriately adjusting the adsorption force of the dispersant to the charged particles and the affinity to the dispersion medium. Condition (C) can be achieved.
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. By appropriately adjusting these, the condition (D) of the present invention can be achieved.

  The ink composition of the present invention contains charged particles including at least a dispersion medium and a coloring material. Each component constituting the ink composition of the present invention will be described 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 and the like, specifically, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (isopar: trade name of Exxon), 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) or the like 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, anthraquinone pigments such as flavantron yellow, isoindolinone yellow 3RLT, C.I. I. Pigment Yellow 139 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. And metal complex salt azomethine pigments such as CI Pigment Yellow 117.

  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 pigment content relative to the entire ink composition is preferably in the range of 0.1 to 50% by mass. When the amount is 0.1% by mass or more, the pigment amount is sufficient, and a sufficiently good color is obtained in the printed matter. When the amount is 50% by mass or less, the particles containing the coloring material can be favorably dispersed in the dispersion medium. More preferably, it is 1-30 mass%.

[Coating agent]
In the 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. Moreover, the difference in dispersion stability that varies depending on the type of the color material can be canceled, and similar dispersion stability can be imparted. Furthermore, 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, polyurethanes, polyesters, polyethers, polyamides, polyethylenes, polybutadienes, polystyrenes, polyvinyl acetates, and polyvinyl alcohols. Products, polycarbonate and the like. Among these, from the viewpoint of ease of 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. Polymers in the range of ~ 5.0 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.

  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 may contain an ether bond, an amino group, a hydroxy group, or a 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. 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, A polymer having Mw / Mn) in the range of 1.0 to 7.0 is preferred. Furthermore, it is most preferable to use a graft polymer or a block polymer.

  The polymer suitably used in the present invention comprises at least a polymer component composed of at least one of the 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.

  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.

  According to the present invention, it is particularly preferable to use the following graft polymer (hereinafter sometimes referred to as graft polymer A) as a dispersant in order to stably eject ink droplets in long-time inkjet recording. Such a graft polymer A is preferably a polymer having a weight average molecular weight of 1,000 or more and containing a graft chain as a side chain, which is a polymer component having a weight average molecular weight of 500 or more. The graft polymer A particularly preferable as a dispersant is one in which the main chain portion is not dissolved in the dispersion medium and the side chain portion (graft chain) is dissolved.

Here, “the main chain portion is not dissolved in the dispersion medium” means that a polymer composed only of the main chain portion having no side chain portion does not dissolve in the dispersion medium. Specifically, the solubility is preferably 3 g or less with respect to 100 g of the dispersion medium.
Further, “the side chain portion is dissolved in the dispersion medium” means that a polymer composed only of the side chain portion having no main chain portion is dissolved in the dispersion medium. Specifically, the solubility is preferably 5 g or more with respect to 100 g of the dispersion medium.
The graft polymer in which the main chain portion is not dissolved and the side chain portion is dissolved is in a state of being transparent to white turbid with respect to the dispersion medium, and is dissolved or dispersed. When such a graft polymer is used, the main chain part is not dissolved in the dispersion medium, so that the main chain part strongly adsorbs to the charged particles, while the side chain part is dissolved in the dispersion medium. The affinity of the side chain portion to the dispersion medium is improved, and as a result, the dispersibility of the charged particles in the dispersion medium is improved.

  The graft polymer A that can be suitably used in the present invention contains a structural unit represented by the following general formula (8) and a structural unit represented by the following general formula (9) at least a weight average molecular weight of 1,000 or more. The polymer.

In the general formulas (8) and (9), R ₁₅₁ , R ₁₅₂ , R ₁₆₁ and R ₁₆₂ may be the same or different and each represents a hydrogen atom or a methyl group.
R ₁₅₃ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may have a substituent. The hydrocarbon group for R ₁₅₃ may contain an ether bond, an ester bond, an amide bond, a carbamate bond, a hydroxyl group, or a halogen substituent.
X ₁₅₁ and X ₁₆₁ may be the same or different and each has a total number of atoms of 50 or less consisting of a single bond or two or more atoms selected from C, H, N, O, S and P. A divalent linking group is shown.
G represents a polymer component having a weight average molecular weight of 500 or more, or a polydimethylsiloxane group having a weight average molecular weight of 500 or more, including at least a structural unit represented by the following general formula (10).

In general formula (10),
R ₁₇₁ and R ₁₇₂ may be the same or different and each represents a hydrogen atom or a methyl group.
R ₁₇₃ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may have a substituent. The hydrocarbon group of R ₁₇₃ may contain an ether bond, an ester bond, an amide bond, a carbamate bond, an amino group, a hydroxyl group, or a halogen substituent.
X ₁₇₁ represents a single bond or a divalent linking group having a total atom number of 50 or less consisting of two or more atoms selected from C, H, N, O, S and P.
It is preferable that the total number of atoms in R ₁₇₃ is larger than the total number of atoms in R ₁₅₃ from the viewpoint of ink ejection stability.

  The graft polymer A containing at least the structural unit represented by the general formula (8) and the structural unit represented by the general formula (9) preferably used in the present invention has a radical polymerizability corresponding to the general formula (8). It can be obtained by polymerizing a monomer and a radical polymerizable macromonomer corresponding to the general formula (9) using a known radical polymerization initiator. Here, the monomer corresponding to the general formula (8) is a monomer represented by the following general formula (8M), and the macromonomer corresponding to the general formula (9) is a macro represented by the following general formula (9M). Monomer.

  Each symbol in general formulas (8M) and (9M) has the same meaning as in general formulas (8) and (9).

  Examples of the monomer represented by the general formula (8M) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, Octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate , (Meth) acrylic acid esters such as 2-methoxyethyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate, and N-methyl (meth) acrylamide, N-propyl (meth) acrylamide, N- Phenyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, etc. ) Acrylamides, styrene, methyl styrene, chlorostyrene, styrene such as methoxystyrene, hydrocarbons such as 1-butene, and vinyl acetate, vinyl ethers, and vinyl pyridine and the like.

The macromonomer represented by the general formula (9M) was obtained by polymerizing a radically polymerizable monomer of the following general formula (10M) corresponding to the general formula (10) in the presence of a chain transfer agent as necessary. It is a polymer having a radical polymerizable functional group at the terminal obtained by introducing a radical polymerizable functional group into the polymer terminal.
The weight average molecular weight of the macromonomer represented by the general formula (9M) is in the range of 500 to 500,000, and the polydispersity (weight average molecular weight / number average molecular weight) is 1.0 to 7. Macromonomers that are in the range of 0 are preferred. The macromonomer represented by the general formula (9M) may be polydimethylsiloxane having a radical polymerizable functional group at the terminal.

  Each symbol in general formula (10M) has the same meaning as in general formula (10).

  Examples of the monomer represented by the general formula (10M) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, Octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate (Meth) acrylic acid esters such as 2-hydroxyethyl (meth) acrylate, and N-methyl (meth) acrylamide, N-propyl (meth) acrylamide, N-phenyl (meth) acrylamide, N, N- (Meth) acrylamides such as dimethyl (meth) acrylamide, styrene, methyl Styrene, chlorostyrene, styrene such as methoxystyrene, hydrocarbons such as 1-butene, and vinyl acetate, vinyl ethers, and vinyl pyridine and the like.

  The graft polymer A used in the present invention may have only the structural units represented by the general formulas (8) and (9), but may contain other structural components. Specific examples of the graft polymer A suitably used in the present invention include polymers [BZ-1] to [BZ-8] represented by the following structural formula.

(In the formula, n represents a polymer and is, for example, 5 or more.)
The fact that the main chain portion is not dissolved in the dispersion medium means, for example, that the polymer not containing the structural unit represented by the general formula (9) has a solubility of 3 g or less with respect to 100 g of the dispersion medium, The side chain portion is dissolved in the dispersion medium when the polymer of G in the general formula (9) or the macromonomer of the general formula (9M) has a solubility of 5 g or more with respect to 100 g of the dispersion medium. It means that there is.

In the graft polymer A, from the viewpoint of long-term storage stability and ink ejection stability of the ink composition, the dispersant has a weight average molecular weight in the range of 1,000 to 1,000,000 and is polydispersed. The graft polymer preferably has a degree (weight average molecular weight / number average molecular weight) in the range of 1.0 to 7.0.
The weight average molecular weight of the graft polymer A is preferably 1.5 times or more with respect to the weight average molecular weight of the graft chain (preferably, the macromer component represented by the general formula (10)).
Furthermore, the mass ratio between the units constituting the main chain and the units constituting the graft chain is preferably in the range of 30:70 to 95: 5. These polymers may be used alone as a dispersant, but 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. In addition, ink particles do not aggregate on the ink discharge head and the circulation pump, so that the head and the pump can be prevented from being clogged, and the ink can be easily discharged during ink jet recording.

[Charge control agent]
In the present invention, it is preferable that a coloring material (preferably a mixture of a coloring material and a coating material) is dispersed (particulated) in a dispersion medium using a dispersing agent, and charge adjustment is performed in order to control the charge amount of the particles. More preferably, an agent is used in combination.
Suitable dispersing agents 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 positively charged particles R in the ink droplet G that has been guided by the ink guide part 78 and flew from the opening 75 to the recording medium P is the first discharge electrode 46 and the second discharge 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.

[Fixing]
In the present invention, it is preferable to fix the ink by an appropriate heating means after the ink is discharged onto the recording medium. As the heating means to be used, a contact-type heating device such as a heat roller, a heat block, or a belt heating and a non-contact type heating device such as a dryer, an infrared lamp, a visible light lamp, an ultraviolet lamp, or a hot air oven may be used. it can. These heating devices are preferably integrated with an inkjet recording apparatus.

By using the ink composition of the present invention described above, it is possible to stably discharge ink droplets for a long time. Further, by using the above-described ink jet recording apparatus, a high-quality image recorded matter having no ink bleeding and high image density can be obtained for a long time. Although the cause of this effect is not clear, for example, particles using Graft Polymer A as a dispersant do not aggregate due to shear stress or concentration on the inner wall of the head that occurs during ink ejection, and exist stably. Can be guessed. Furthermore, this factor can be presumed to be due to the fact that the graft polymer A of the present invention has a high adsorption power to the coating material or coloring material and a high ability to dissolve in the dispersion medium. In addition, blocking can be prevented when image recording materials (printed materials) that have been inkjet-recorded and fixed are overlapped. Although the cause of this effect is not clear, it can be presumed that the graft polymer A of the present invention has high affinity for particles and low affinity for the back surface before image formation.

  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.

[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] radically polymerizes styrene, 4-methylstyrene, butyl acrylate, dodecyl methacrylate and 2- (N, N-dimethylamino) ethyl methacrylate using a known polymerization initiator, Furthermore, it was obtained by reacting 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.
The dispersant [BZ-2] is a polymer of stearyl methacrylate 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 [BP-1]. ] (Weight average molecular weight was 7,600), and then obtained by radical polymerization with styrene. The weight average molecular weight was 110,000.
5 g or more of polymer [BP-1] was dissolved in 100 g of Isopar G. Moreover, although the graft polymer dispersant [BZ-2] became cloudy with respect to 100 g of Isopar G, 5 g or more was dissolved.
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 desktop 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].

The physical properties of the ink composition [EC-1] were as follows.
(A) Using the LCR meter (AG-4431 manufactured by Ando Electric Co., Ltd.) and the electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.) for the electrical conductivity of the ink composition at 20 ° C. Then, it was 100 nS / m when measured under the conditions of an applied voltage of 5 V and a frequency of 1 kHz.
(B) The ink composition was centrifuged for 30 minutes under the conditions of a rotational speed of 14500 rpm and a temperature of 20 ° C. using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd. SRX-201) to settle the charged particles. Then, the electrical conductivity of the supernatant was measured and found to be 30 nS / m. The electric conductivity of the charged particles was 70 nS / m, which was 70% with respect to the electric conductivity of the ink composition. The charged particles were positively charged.
(C) 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, and found to be 0.9 μm. The number average diameter was 0.15 μm.
(D) The viscosity of the ink composition at 20 ° C. was 1.5 mPa · s when measured at 100 rpm using a cone plate rotor with 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.

  In the preparation of the ink composition [EC-1], a magenta pigment C.I. I. Pigment Red 57: 1 (Toyo Ink Manufacturing Co., Ltd., Brilliant Carmine 6B, LR 6B FG-4213) was used in the same manner to obtain an ink composition [EM-1]. Also, yellow pigment C.I. I. Ink composition [EY-1] was obtained in the same manner except that Pigment Yellow 180 (manufactured by Clariant Co., Ltd., Toner Y HG) was used. Further, black pigment C.I. I. Ink composition [EB-1] was obtained in the same manner except that Pigment Black 7 (manufactured by Mitsubishi Chemical Corporation, carbon black MA-8) was used. Table 1 shows the physical property values of the obtained ink composition. These were all within the range of the physical property values recited in claim 1 of the present invention.

<Inkjet recording>
1-3, ink compositions [EC-1], [EM-1], [EY-1], and [EB-1] of four colors are respectively added to ink tanks connected to four heads. Filled. 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.
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. Further, 100 sheets of the obtained image recording material were stacked and stored at 40 ° C. for 3 days, but there was no adhesion between the image recording materials.

[Comparative Example 1]
An ink composition [RC-1] was prepared in the same manner as in Example 1 except that the charge adjusting agent [CT-1] was not added in the preparation of the ink composition [EC-1] of Example 1. The properties of the obtained [RC-1] are shown in Table 2. The electrical conductivity of the (A) ink composition was small.
Ink jet recording was performed using the same apparatus as in Example 1 using the ink composition [RC-1], but no ink droplets were ejected.

[Comparative Example 2]
An ink composition [RC-2] was prepared in the same manner as in Example 1 except that 1.5 g of the charge adjusting agent [CT-1] was added in the preparation of the ink composition [EC-1] of Example 1. did. The physical properties of the obtained [RC-2] are shown in Table 2. The ratio of the electrical conductivity of (B) charged particles to the ink composition was small.
When ink jet recording was performed using the same composition as in Example 1 using the ink composition [RC-2], ink droplets were ejected, but ink bleeding was observed in the obtained image.

[Comparative Example 3]
Ink composition [RC-] was prepared in the same manner as in Example 1 except that [BZ-2] was used instead of coating agent [AP-1] in the preparation of ink composition [EC-1] of Example 1. 3] was prepared ([BZ-2] was also used as a dispersant, a total of 27.5 g was used). The physical property values of the obtained [RC-3] are shown in Table 2. The volume average diameter of (C) charged particles was small.
When ink jet recording was performed using the same composition as in Example 1 using the ink composition [RC-3], ink droplets were ejected, but ink bleeding was observed in the obtained image.

[Comparative Example 4]
The ink composition [EC-1] of Example 1 was concentrated under reduced pressure to a solid content concentration of 35%, and this was designated as an ink composition [RC-4]. Table 2 shows the physical property values of the obtained [RC-4]. The viscosity (D) at 25 ° C. of the ink composition was large.
Ink jet recording was performed using the ink composition [RC-4] and the same apparatus as in Example 1, but no ink droplets were ejected.

[Comparative Example 5]
Ink jet recording was performed in the same manner as in Example 1 except that the ink composition [EC-1] of Example 1 was used and concentrated ink was not added. Up to the third day, ink droplets were ejected and a good recorded image could be produced. On the fourth day, ink bleeding was observed in the image. The ink composition was recovered and the volume average diameter of the charged particles was measured and found to be 0.18 μm. The reason why the volume average diameter is small is not clear, but it is probably because charged particles having a small diameter remain in the ink composition because charged particles having a large diameter are concentrated and discharged preferentially.

[Example 2]
<Materials used>
In Example 2, [AP-2] was used in place of [AP-1] as a coating agent. [AP-2] is synthesized by dehydration condensation from adipic acid and a small excess of p-xylylene glycol to synthesize a polyester having hydroxyl groups at both ends, and then further reacted with hexamethylene diisocyanate. Was obtained. The weight average molecular weight was 20,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 1.6. The glass transition point (midpoint) was −13 ° C., the melting point was 76 ° C., and the softening point was 74 ° C. Further, tetrabutylammonium p-toluenesulfonate obtained from tetrabutylammonium hydroxide and p-toluenesulfonic acid was also used. Other than these, the materials used in Example 1 were used.

<Preparation of ink composition [EC-2]>
Cyan pigment 10g, coating agent [AP-2] 20g, and tetrabutylammonium p-toluenesulfonate 1g are put in a flask and heated with a heater so that the internal temperature becomes 110 ° C. And mixed. 31 g of the obtained mixture was coarsely pulverized with a trio-brender manufactured by Trio Science Co., Ltd., and further pulverized with a SK-M10 type sample mill manufactured by Kyoritsu Riko Co., Ltd. 31 g of the finely pulverized product obtained 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].

The ink composition [EC-2] was measured in the same manner as in Example 1 and was as follows.
(A) The electric conductivity of the ink composition at 20 ° C. was 120 nS / m.
(B) The ratio of the electric conductivity of the charged particles to the electric conductivity of the ink composition was 85%. The charged particles were positively charged.
(C) The volume average diameter of the charged particles was 1.0 μm.
(D) The viscosity of the ink composition at 20 ° C. was 1.9 mPa · s. Further, the surface tension of the ink composition at 20 ° C. was 23 mN / m.

<Inkjet recording>
Ink jet recording was performed for 1 month using the ink composition [EC-2] in the same manner as in Example 1 while supplying concentrated ink. 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 6]
In the preparation of the ink composition [EC-1] of Example 1, [BP-1] obtained during the synthesis of [BZ-2] was used instead of the dispersant [BZ-2]. Then, an ink composition [RC-5] was prepared in the same manner as in Example 1.
The ink composition [RC-5] was measured in the same manner as in Example 1 and was as follows.
(A) The electric conductivity of the ink composition at 20 ° C. was 80 nS / m.
(B) The ratio of the electrical conductivity of the charged particles to the electrical conductivity of the ink composition was 40%. The charged particles were positively charged.
(C) The volume average diameter of the charged particles was 2.0 μm.
(D) The viscosity of the ink composition at 20 ° C. was 55 mPa · s. Further, the surface tension of the ink composition at 20 ° C. was 30 mN / m.
Ink jet recording was performed using the ink composition [RC-5] and the same apparatus as in Example 1, but no ink droplets were ejected after 2 weeks. When the head was disassembled and confirmed, ink particles adhered to the ejection port and clogged the ejection port. Moreover, when 100 sheets of the obtained image recording material were stacked and stored at 40 ° C. for 3 days, the image recording materials were adhered to each other.

[Comparative Example 7]
[BP-2] is a non-graft polymer obtained by directly polymerizing stearyl methacrylate and styrene in place of the dispersant [BZ-2] in the preparation of the ink composition [EC-1] of Example 1. An ink composition [RC-6] was prepared in the same manner as in Example 1 except that the weight average molecular weight was 130,000.
The polymer [BP-2] dissolved only 3 g or less with respect to 100 g of Isopar G.
The ink composition [RC-6] was measured in the same manner as in Example 1 and was as follows.
(A) The electric conductivity of the ink composition at 20 ° C. was 8 nS / m.
(B) The ratio of the electrical conductivity of the charged particles to the electrical conductivity of the ink composition was 30%. The charged particles were positively charged.
(C) The volume average diameter of the charged particles was 2.8 μm.
(D) The viscosity of the ink composition at 20 ° C. was 3.0 mPa · s. Further, the surface tension of the ink composition at 20 ° C. was 28 mN / m.
Ink jet recording was performed using the ink composition [RC-6] and the same apparatus as in Example 1, but no ink droplets were ejected after one week. When the head was disassembled and confirmed, ink particles adhered to the ejection port and clogged the ejection port.

[Comparative Example 8]
[BP-3] (weight average molecular weight) which is a non-graft polymer obtained by polymerizing only styrene instead of the dispersant [BZ-2] in the preparation of the ink composition [EC-1] of Example 1. Was used in the same manner as in Example 1 except that 70,000) was used, but no particles were formed.
The polymer [BP-3] is a polymer composed only of the main chain portion of the dispersant [BZ-2], but only 3 g or less was dissolved in 100 g of Isopar G.

[Example 3]
<Materials used>
In Example 2, the following materials were used.

-Magenta pigment (coloring material) Monoazo lake pigment C.I. I. Pigment Red (57: 1) (Dainippon Ink Co., Ltd., Symbol Brilliant Carmine 6B229)
-Coating agent [AP-2] used in Example 2
・ Dispersant [BZ-7]
・ Tetrabutylammonium p-toluenesulfonate ・ Charge modifier [CT-1]
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

  The structure of the dispersant [BZ-7] is shown below.

Dispersant [BZ-7] was synthesized in Example 1, stearyl methacrylate polymer [BP-1] having a methacryloyl group at its end, butyl methacrylate and methacrylic acid 2
Obtained by radical polymerization of -methoxyethyl. The weight average molecular weight was 180,000.
Dispersant [BZ-7] became cloudy with respect to 100 g of Isopar G, but dissolved 5 g or more.

<Preparation of ink composition [EM-2]>
10 g of magenta pigment, 20 g of coating agent [AP-2] and 1 g of tetrabutylammonium p-toluenesulfonate are placed in a flask and heated with a heater so that the internal temperature becomes 110 ° C. And mixed. 31 g of the obtained mixture was coarsely pulverized with a trio-brender manufactured by Trio Science Co., Ltd., and further pulverized with a SK-M10 type sample mill manufactured by Kyoritsu Riko Co., Ltd. 31 g of the finely pulverized product obtained was predispersed in a paint shaker manufactured by Toyo Seiki Seisakusho together with 9 g of the dispersant [BZ-7], Isopar G75 g, and glass beads having a diameter of about 3.0 mm. After removing the glass beads, dispersed with zirconia ceramic beads having a diameter of about 0.6 mm in a Type KDL dynomill manufactured by Shinmaru Enterprises Co., Ltd. for 8 hours at a rotational speed of 3,000 rpm while maintaining the internal temperature at 40 ° C. Particles). The zirconia ceramic beads were removed from the obtained dispersion, and 360 g of Isopar G and 0.4 g of the charge adjusting agent [CT-1] were added to obtain an ink composition [EM-2].
The ink composition [EM-2] was measured in the same manner as in Example 1 and was as follows.
(A) The electric conductivity of the ink composition at 20 ° C. was 120 nS / m.
(B) The ratio of the electrical conductivity of the charged particles to the electrical conductivity of the ink composition was 54%. The charged particles were positively charged.
(C) The volume average diameter of the charged particles was 0.7 μm.
(D) The viscosity of the ink composition at 20 ° C. was 1.7 mPa · s. Further, the surface tension of the ink composition at 20 ° C. was 26 mN / m.

<Inkjet recording>
Using the ink composition [EM-2], ink jet recording was performed for 1 month while adding concentrated ink in the same manner as in Example 1. 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 9]
In the preparation of the ink composition [EM-2] of Example 3, a non-polymer obtained by directly polymerizing stearyl methacrylate, butyl methacrylate and 2-methoxyethyl methacrylate instead of the dispersant [BZ-7]. An ink composition [RM-1] was prepared in the same manner as in Example 2 except that [BP-4] (weight average molecular weight: 18,000), which is a graft polymer, was used.
The polymer [BP-4] dissolved only 3 g or less with respect to 100 g of Isopar G.
The ink composition [RM-1] was measured in the same manner as in Example 1 and was as follows.
(A) The electric conductivity of the ink composition at 20 ° C. was 9 nS / m.
(B) The ratio of the electrical conductivity of the charged particles to the electrical conductivity of the ink composition was 36%. The charged particles were positively charged.
(C) The volume average diameter of the charged particles was 2.4 μm.
(D) The viscosity of the ink composition at 20 ° C. was 4.0 mPa · s. Further, the surface tension of the ink composition at 20 ° C. was 29 mN / m.
Ink jet recording was performed using the ink composition [RM-1] and the same apparatus as in Example 1, but no ink droplets were ejected after 2 weeks. When the head was disassembled and confirmed, ink particles adhered to the ejection port and clogged the ejection port.

[Comparative Example 10]
A non-graft polymer obtained by polymerizing butyl methacrylate and 2-methoxyethyl methacrylate in place of the graft polymer dispersant [BZ-7] in the preparation of the ink composition [EM-1] of Example 3. An ink composition was prepared in the same manner as in Example 2 except that [BP-5] (weight average molecular weight was 110,000) was used, but no particles were formed.
The polymer [BP-5] is a polymer composed only of the main chain portion of the dispersant [BZ-7], but only 3 g or less was dissolved in 100 g of Isopar G.

[Example 4]
<Materials used>
In Example 4, the following materials were used.

Yellow pigment (coloring material) Disazo pigment C.I. I. Pigment Yellow 180 (manufactured by Clariant, Toner Y HG)
・ Coating agent [AP-1]
・ Dispersant [BZ-8]
-Charge control agent [CT-1]
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

  The structure of the dispersant [BZ-8] is shown below.

Dispersant [BZ-8] is a radical polymerization of methyl methacrylate, 2-hydroxyethyl acrylate and methacryloxypropyl-terminated polydimethylsiloxane DMS-R18 (molecular weight 4,500-5,500) manufactured by Chisso Corporation. Was obtained. The weight average molecular weight was 60,000.
Both DMS-R18 and dispersant [BZ-8] were dissolved in an amount of 5 g or more with respect to 100 g of Isopar G.

<Preparation of Ink Composition [EY-1]>
8 g of yellow pigment and 22 g of the coating agent [AP-1] were placed in a table type kneader PBV-0.1 manufactured by Irie Shokai Co., Ltd., and the heater temperature was set to 100 ° C. and mixed by heating 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-8], 75 g of Isopar G, and glass beads having a diameter of about 3.0 mm. After removing the glass beads, dispersed with zirconia ceramic beads having a diameter of about 0.6 mm in a Type KDL dynomill manufactured by Shinmaru Enterprises Co., Ltd. for 8 hours at a rotational speed of 3,000 rpm while maintaining the internal temperature at 45 ° C. Particles). The zirconia ceramic beads were removed from the obtained dispersion, and Isopar G316g and a charge adjusting agent [CT-1] 0.6 g were added to obtain an ink composition [EY-1].
The ink composition [EY-1] was measured in the same manner as in Example 1 and was as follows.
(A) The electric conductivity of the ink composition at 20 ° C. was 90 nS / m.
(B) The ratio of the electric conductivity of the charged particles to the electric conductivity of the ink composition was 73%. The charged particles were positively charged.
(C) The volume average diameter of the charged particles was 1.2 μm.
(D) The viscosity of the ink composition at 20 ° C. was 1.3 mPa · s. The surface tension of the ink composition at 20 ° C. was 20 mN / m.

<Inkjet recording>
Using the ink composition [EY-1], ink jet recording was performed for 1 month while adding concentrated ink in the same manner as in Example 1. 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 11]
Example 3 except that methacryloxypropyl-terminated polydimethylsiloxane DMS-R18 manufactured by Chisso Corporation was used instead of the dispersant [BZ-8] in the preparation of the ink composition [EY-1] of Example 4. Attempts were made to prepare an ink composition in the same manner as described above, but no particles were formed.

[Comparative Example 12]
[BP] which is a non-graft polymer obtained by polymerizing methyl methacrylate and 2-hydroxyethyl acrylate instead of the dispersant [BZ-8] in the preparation of the ink composition [EY-1] of Example 4. −6] An ink composition was prepared in the same manner as in Example 4 except that the weight average molecular weight was 140,000, but no particles were formed.
The polymer [BP-6] is a polymer composed only of the main chain portion of the dispersant [BZ-8], but only 3 g or less was dissolved in 100 g of Isopar G.

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 (6)

Dispersion medium, and
Charged particles containing at least a coloring material,
An ink composition for ink jet recording, wherein the ink composition satisfies all of the following conditions (A) to (D):
(A) The electric conductivity at 20 ° C. of the ink composition is in the range of 10 nS / m to 300 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm.
(D) The viscosity of the ink composition at 20 ° C. is in the range of 0.5 to 5 mPa · s.   2. The ink composition for ink jet recording according to claim 1, wherein the charged particles are dispersed in a dispersion medium by a graft polymer as a dispersant.   3. The graft polymer according to claim 2, wherein the graft polymer includes a main chain portion and a side chain portion that is a graft chain, and the main chain portion is not dissolved in the dispersion medium, and the side chain portion is dissolved. An ink composition for inkjet recording. In an ink jet recording method in which an ink droplet is ejected using an electrostatic field, the ink composition containing charged particles including at least a dispersion medium and a coloring material and satisfying all of the following conditions (A) to (D): Ink is circulated in an ink chamber having an opening, and by applying a voltage to a control electrode formed at the periphery of the discharge opening, an ink guide that is present in the discharge opening and has a tip directed toward the recording medium side. An ink jet recording method, wherein ink droplets fly from the tip.
(A) The electric conductivity at 20 ° C. of the ink composition is in the range of 10 nS / m to 300 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm.
(D) The viscosity of the ink composition at 20 ° C. is in the range of 0.5 to 5 mPa · s. In an ink jet recording method in which ink droplets are ejected by an ink jet recording method using an electrostatic field, an ink composition containing charged particles containing at least a dispersion medium and a colorant is used under the following conditions (A) to (A) to An ink jet recording method comprising replenishing a high-concentration ink composition so as to always satisfy all of (D).
(A) The electric conductivity at 20 ° C. of the ink composition is in the range of 10 nS / m to 300 nS / m.
(B) The electric conductivity of the charged particles at 20 ° C. is 50% or more of the electric conductivity of the ink composition.
(C) The volume average diameter of the charged particles is in the range of 0.2 to 5.0 μm.
(D) The viscosity of the ink composition at 20 ° C. is in the range of 0.5 to 5 mPa · s.   6. The ink jet recording method according to claim 5, wherein the charged particles are dispersed in a dispersion medium by a graft polymer as a dispersant.

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