JP2006111799A - Ink composition for inkjet recording and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink composition for inkjet recording and an inkjet recording method, whereby ink droplets can always be discharged stably in long-time inkjet recording, high quality image formation is made possible for a long time without any stripe irregularity and ink bleeding, and stability with time is excellent. <P>SOLUTION: The inkjet composition for inkjet recording contains a dispersion medium and charged particles, wherein the charged particles contain a color material and a polymer having a polyether structure. The inkjet recording method comprises discharging the ink composition in the form of ink droplets by an inkjet recording system using electrostatic field. <P>COPYRIGHT: (C)2006,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 method (see Patent Documents 1 and 2) that causes ink droplets containing charged particles to fly. The method of flying ink droplets with steam or mechanical pressure cannot control the flying direction of ink droplets, and causes ink droplets to land accurately on the desired location on the recording medium due to distortion of the ink nozzles or air convection. Is difficult.
On the other hand, the method using an electrostatic field controls the flying direction of the ink droplets by the electrostatic field, so that the ink droplets can be landed accurately at a desired position, and a high-quality image formation (printed material) is created. It is excellent.

  As an ink composition used for ink jet recording 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.

JP-A-3-223770 (Patent Document 5) includes a dispersion medium, colorant particles, a resin component, and a charge donating agent, wherein the resin component has a polyethyleneoxy structure in the side chain. There is disclosed a wet developer for developing an electrostatic latent image characterized by being a coalescence. The copolymer is soluble in a dispersion medium, takes in a charge imparting agent (metal ion), adsorbs to the colorant particles, and generates a charge on the particle surface. However, as a demerit when the charge is generated by the adsorption of the resin soluble in the dispersion medium and the metal ion to the colorant particles, the stability of the particle charge over time is poor.
However, until now, it has been difficult to stably eject ink droplets in long-time inkjet recording. There was also room for improvement in stability over time.

US Pat. No. 6,158,844 Japanese Patent No. 3315334 US Pat. No. 5,952,2048 JP-A-8-291267 JP-A-3-223770

  An object of the present invention is to increase the charge amount of ink particles, and to stably eject ink droplets constantly in long-time inkjet recording, and to form a high-quality image without streak unevenness or ink bleeding. It is an object to provide an ink composition for ink jet recording and an ink jet recording method which can be timed and have excellent temporal stability.

  As a result of intensive investigations, the present inventors have found that, by adding a specific polymer to the charged particles, the particles are efficiently charged, and stable ink droplets can be produced under electric field conditions at low voltage and low frequency. The inventors have found that discharge is possible and completed the present invention.

The present invention is as follows.
(1) An ink composition for inkjet recording, wherein the charged particle contains a coloring material and a polymer having a polyether structure.
(2) The ink composition for ink-jet recording as described in (1) above, wherein the ink composition contains at least one of a metal salt and an onium salt.

(3) In an ink jet recording method in which an ink composition is ejected as ink droplets by an ink jet recording method using an electrostatic field, the ink composition contains a dispersion medium and charged particles, and the charged particles are a coloring material and a polyether. An ink jet recording method comprising a polymer having a structure.

  According to the present invention, since the charged particles contain a polymer having a polyether structure, this interacts with a charge adjusting agent such as a metal salt or an onium salt, and the particles are efficiently charged, resulting in low Stable ink droplet ejection is possible under conditions of electric field at voltage and low frequency. In addition, stability over time is increased. Therefore, according to the present invention, ink droplets can be ejected stably in a long period of ink jet recording, and a high-quality image can be formed for a long time without streak unevenness or ink bleeding. Ink compositions for ink jet recording and ink jet recording methods are also provided.

  That is, in the present invention, since a polymer having a polyether structure is present in the charged particles (that is, the polymer is not dissolved in the dispersion medium), for example, the metal ion is coordinated to the polyether functional group and the charged particles It is considered that the aging stability is high and stable particle ejection is possible.

Hereinafter, the present invention will be described in further detail.
The ink composition of the present invention contains charged particles containing a coloring material and a polymer having a polyether structure in a dispersion medium.

[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. Examples include 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: Spirits) Trade name), KF-96L (trade name of Shin-Etsu Silicone Co., Ltd.) and 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. When the content is 20% by mass or more, the particles containing the color material can be well dispersed in the dispersion medium, and when the content is 99% by mass or less, the content of the color material can be sufficiently secured.

[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 content of the coloring material with respect to the entire ink composition is preferably in the range of 0.1 to 50% by mass. When the amount is 0.1% by mass or more, the amount of the coloring material is satisfied, and 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 by the dispersion medium. More preferably, it is 1-30 mass%.

[Polymer having a polyether structure (coating agent)]
In the present invention, a polymer having a polyether structure functions as a so-called coating agent, and a coloring material such as a pigment is dispersed (particulated) in a state of being coated with a polymer having a polyether structure. 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, it is preferable to perform inkjet recording on a recording medium and then fix it by a heating means such as a heat roller. At this time, the coating material is melted by heat and can be fixed efficiently.

Here, the polyether structure referred to in the present invention represents a structure having a plurality of ether structures, and the ether structure means a broad ether structure including thioether, selenoether, iminoether and the like.
A preferable polyether structure includes an atomic group represented by the following general formula (1).
-(R ₁ -X _1- ) n- (R ₂ -X ₂ ) m-R ₃ (1)
In the formula, R ₁ and R ₂ represent a hydrocarbon group, preferably an alkylene group having 2 to 6 carbon atoms, or an arylene group having 6 to 12 carbon atoms, and may be the same or different. An alkylene group is preferred, and ethylene and propylene are more preferred. R ₃ represents a hydrogen atom, a monovalent group, preferably an alkyl group having 1 to 6 carbon atoms. X ₁ and X ₂ each independently represent an oxygen atom, a sulfur atom, a selenium atom, or a nitrogen atom. In the case of a nitrogen atom, it is substituted with a hydrogen atom or a monovalent group such as an alkyl group having 1 to 6 carbon atoms. Of these, an oxygen atom is preferable. R ₃ may combine with R ₁ or R ₂ to form a ring. n and m each represent an integer of 0 to 30, and are not simultaneously zero, and may be the same or different from each other. The total of n and m is preferably 3-30.

  As a method for introducing the polyether structure into the polymer, a method in which a monomer having an ethylenically unsaturated polymerizable group and a polyether structure is radically polymerized with another polymerizable monomer by a known method is preferable. The method is not limited.

  Specific examples of the monomer having an ethylenically unsaturated polymerizable group and a polyether structure are given below, but the present invention is not limited thereto.

  Other radical polymerizable monomers are not particularly limited, but preferred monomer components include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylic. Isobutyl acid, t-butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, (meth) Hexadecyl acrylate, octadecyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylic acid 4-hydroxybutyl, glycidyl (meth) acrylate, (meth) a 2-dimethylaminoethyl silylate, 2-diethylaminoethyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, o-aminosulfonylphenyl (meth) (Substituted) (meth) acrylic acid esters such as acrylate, m-aminosulfonylphenyl (meth) acrylate, p-aminosulfonylphenyl (meth) acrylate; acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-hexylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethyl Tilacrylamide,

N-hydroxyethylacrylamide, N-phenylacrylamide, N-phenylmethacrylamide, N-benzylacrylamide, N-benzylmethacrylamide, N-nitrophenylacrylamide, N-nitrophenylmethacrylamide, N-ethyl-N-phenylacrylamide, N-ethyl-N-phenylmethacrylamide, N- (o-aminosulfonylphenyl) (meth) acrylamide, N- (m-aminosulfonylphenyl) (meth) acrylamide, N- (p-aminosulfonylphenyl) (meth) Acrylamide such as acrylamide or methacrylamide; ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octi Vinyl ethers such as vinyl ether and phenyl vinyl ether; vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butyrate and vinyl benzoate; olefins such as ethylene, propylene, isobutylene, butadiene and isoprene; N-vinylpyrrolidone, N- Vinylcarbazole, 4-vinylpyridine, acrylonitrile, methacrylonitrile, etc .; ethylene glycol group-containing monomers such as polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate; ethylene, propylene , Ethylene monomers such as butadiene; styrene monomers such as styrene and 4-methylstyrene; (meth) acrylic , Maleic anhydride, itaconic acid, or the like monomers containing quaternary ammonium base.

  The content of the repeating unit having a polyether structure is preferably from 1 to 99 mol%, more preferably from 2 to 80 mol%, still more preferably from 5 to 80 mol%, based on all repeating units constituting the polymer having a polyether structure. 50 mol%.

  The polymer having a polyether structure of the present invention preferably has a mass average molecular weight in the range of 2,000 to 1,000,000, more preferably 3,000 to 500,000, from the viewpoint of ease of particle formation. 000, more preferably in the range of 5000 to 200,000. The polydispersity (mass average molecular weight / number average molecular weight, Mw / Mn) is preferably in the range of 1.0 to 7.0, more preferably 1.0 to 5.0, still more preferably 1.0. It is in the range of ~ 4.0. From the viewpoint of ease of fixing, a polymer having a glass transition point or a melting point in the range of 40 to 120 ° C. is preferable.

The physical properties of the polymer having a polyether structure of the present invention are preferably 10 ⁶ Pa or more at a dynamic elastic modulus of 50 ° C., and particularly preferably 10 ³ Pa or more and 10 ⁵ Pa or less at 100 ° C.
The dynamic elastic modulus as a physical property of the polymer indicates ease of deformation and fluidity of the polymer, and its behavior belongs to an academic system called rheology.
The dynamic elastic modulus is the thermal fluidity of ink particles, that is, the flowability, the difficulty of the image being transferred to the recording paper that is overlaid, that is, the blocking resistance, and the heat at the time of thermal fixing of the ink image. This is considered to be closely related to an offset at which a part of the image is transferred to the roller.
The measurement of the dynamic elastic modulus is well known in the art and can be measured with good reproducibility. For example, using a measuring device called a rheometer, the heat-melted polymer is sandwiched between rotors (gap 1 mm) and fixed. It is possible to obtain vibration from the frequency and to obtain the deviation from the frequency.

More specifically, for example, 3 g of a finely pulverized sample is set in a sample chamber of a rheometer “Rhesol-G1000” manufactured by UBM, and first melted at 200 ° C. in accordance with a predetermined measurement method. The rotor can be vibrated at a frequency of 1 Hz while the temperature is lowered, and a “temperature-dynamic elastic modulus curve” can be automatically recorded to measure the dynamic elastic modulus.
As a preferable behavior of this dynamic elastic modulus curve, it is preferable to have two inflection points in the range of 40 ° C to 100 ° C.

  Hereinafter, although the repeating unit of the polymer which has a polyether structure suitable for this invention is illustrated, it is not limited to these.

In the present invention, the coating agent may contain other polymers in addition to the polymer having a polyether structure. The content of the other polymer is 0 to 9 with respect to the total amount of the coating agent.
It is preferable that it is the range of 9 mass%, More preferably, it is 0-70 mass%.
Although it does not specifically limit as another polymer, It is especially preferable that they are a (meth) acrylic-type polymer, a styrene / (meth) acrylic-type polymer, polyester, etc.

  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, 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 a (meth) acrylic compound, a (meth) acrylic polymer, a copolymer of polyethylene and a (meth) acrylic compound, rosin, BYK-160, 162, 164, 182 (polyurethane polymer manufactured by Big Chemie), EFKA-401, 402 (acrylic polymer manufactured by EFKA), Solsperse 17000, 24000 (polyester polymer manufactured by Geneca), and the like. In the present invention, from the viewpoint of long-term storage stability of the ink composition, the mass average molecular weight is in the range of 1,000 to 1,000,000 and the polydispersity (mass average molecular weight / number average molecular weight). Is preferred to be in the range of 1.0 to 7.0. Furthermore, it is most preferable to use a graft polymer or a block polymer.

  The dispersant polymer particularly preferably used in the present invention has a polymer component containing at least one of the structural units represented by the following general formulas (1) and (2) as a main chain, and the following general formula (3) A graft polymer containing, as a graft chain, a polymer component containing the structural unit represented by

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 (3), 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 1) or (2).

  Examples of the radical polymerizable monomer corresponding to the general formula (1) include 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, etc., (meth) acrylate 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 (2) include styrene, 4-methylstyrene, chlorostyrene, methoxystyrene, and the like.
Examples of the radical polymerizable monomer corresponding to the general formula (2) include hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, ( (Meth) stearyl acrylate, and the like.
Specific examples of these graft polymers include polymers represented by the following structural formulas.

Contains a polymer component containing at least one of the structural units represented by general formulas (1) and (2), and a polymerization component containing at least the structural unit represented by general formula (3) as a graft chain The graft polymer to be processed may have only the structural unit represented by the general formula (1) and / or (2) and the general formula (3), 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.

[Charge control agent]
In the present invention, a coloring material (preferably a mixture of a coloring material and a coating agent) is dispersed (particulated) in a dispersion medium using a dispersing agent, but a charge adjusting agent is used in combination to control the charge amount of the particles. To do.
In the present invention, it is preferable to use at least one of a metal salt and an onium salt as a charge control agent.
Metal salts and onium salts that are preferable as charge control agents are soluble in the dispersion medium, and the solubility in the dispersion medium (25 ° C.) is preferably 0.1 g or more with respect to 100 g of the dispersion medium, 1 g or more is more preferable.

As such a metal salt or onium salt, the following are preferable.
Organics such as straight chain or branched saturated carboxylic acid having 4 to 30 carbon atoms, linear or branched unsaturated carboxylic acid having 4 to 30 carbon atoms, and aromatic carboxylic acid having an alkyl group having 1 to 20 carbon atoms Metal salt of carboxylic acid.
C4-C30 linear or branched saturated carboxylic acid, C4-C30 linear or branched unsaturated carboxylic acid, aromatic carboxylic acid having a C1-C20 alkyl group, etc. Onium salt of organic carboxylic acid.
Organics such as straight chain or branched saturated sulfonic acid having 4 to 30 carbon atoms, linear or branched unsaturated sulfonic acid having 4 to 30 carbon atoms, and aromatic sulfonic acid having an alkyl group having 1 to 20 carbon atoms Metal salt of sulfonic acid.
Organics such as linear or branched saturated sulfonic acids having 4 to 30 carbon atoms, linear or branched unsaturated sulfonic acids having 4 to 30 carbon atoms, and aromatic sulfonic acids having an alkyl group having 1 to 20 carbon atoms Onium salt of sulfonic acid.

The metal is preferably a monovalent to tetravalent metal. Examples thereof include sodium, calcium, barium, manganese, copper, lithium, titanium, zinc, lead, zirconium, cobalt, nickel, aluminum, cerium, lanthanum, chromium, strontium, vanadium, tin, magnesium, iron, and cadmium. If the metal does not have a carboxylic acid or sulfonic acid bonded to satisfy its valence, the remaining valence may be saturated with other ligands. Examples of other ligands include halogen, hydroxyl group, oxygen atom, water, ammonia, amines, phosphinic acid, and sulfides.
Examples of onium salts include ammonium salts, sulfonium salts, iodonium salts, oxonium salts, and phosphonium salts, with ammonium salts and sulfonium salts being preferred, and ammonium salts being particularly preferred. The cation of the ammonium salt is preferably substituted with an alkyl group, and more preferably substituted with an alkyl group having 4 to 12 carbon atoms.

As metal salts, zirconium naphthenate, zirconium octylate, zirconium 2-ethylhexanoate, zirconyl naphthenate, zirconyl octylate, zirconyl 2-ethylhexanoate, titanium naphthenate, titanium octylate, titanium 2-ethylhexanoate, naphthene Titanyl acid, titanyl octylate, and titanyl 2-ethylhexanoate are preferred.
As the onium salt, tetrabutylammonium bromide, tetrabutylammonium p-toluenesulfonate, tetraoctylammonium bromide, and tetraoctylammonium p-toluenesulfonate are preferable.

  The addition amount of the metal salt and the onium salt with respect to the entire ink composition is preferably in the range of 0.0001 to 10% by mass in terms of the charge amount of the ejected particles, and is preferably 0.001 to 5% by mass. Is more preferable.

  In addition, other charge control agents may be used in combination, and the amount of the other charge control agents added is preferably 50% by mass or less based on the total amount of the metal salt and the onium salt. Other charge control agents include polymers having a carboxylic acid group in the side chain, such as a polymer containing a carboxylic acid group obtained by modifying a copolymer of styrene and maleic anhydride with an amine, and tetramethylammonium salt of stearyl methacrylate and methacrylic acid. Polymers having a carboxylate anion group in the side chain such as a copolymer of styrene, polymers having a nitrogen atom in the side chain such as a copolymer of styrene and vinylpyridine, butyl methacrylate and N- (2-methacryloyloxyethyl)- Examples thereof include polymers having an ammonium group in the side chain, such as a copolymer with N, N, N-trimethylammonium tosylate salt.

[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]
As described above, the color material and the coating agent are dispersed (particulated) in a dispersion medium using a dispersant and a charge adjusting agent, thereby producing an ink composition containing charged particles including the color material. be able to. Examples of the dispersion (particulate) method include the following.
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 simultaneously.

  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.

[Physical properties of ink composition]
The ink composition produced as described above is recorded on a recording medium by an ink jet recording method. In the present invention, since the ink droplets are always stably ejected in a long time ink jet recording, the following conditions ( It is preferable to use an ink composition that satisfies 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 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.

The electrical conductivity of the ink composition at 20 ° C. is preferably in the range of 10 nS / m to 300 nS / m. When the electrical conductivity of the ink composition is 10 nS / m or more, ink droplet ejection is good. When the ink composition is 300 nS / m or less, conduction occurs in the head (ejection unit) of the inkjet apparatus, resulting in damage to the head. Absent. More preferably, it is 30 nS / m-200 nS / m.
The electric conductivity of the particles is a value obtained by centrifuging the ink composition, measuring the electric conductivity of the supernatant liquid in which the particles are precipitated, and subtracting the electric conductivity of the ink composition.
In the present invention, the electrical conductivity of the particles is preferably 50% or more of the electrical 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, in the case of 50% or more, this concentration does not occur, and as a result, when recorded on a recording medium. There is no ink bleeding. More preferably, it is 60% or more.
The charge amount of the particles is preferably in the range of 5 to 200 μC / g. When the charge amount is 5 μC / g or more, the concentration is sufficient, and when it is 200 μC / g or less, the ink is not excessively concentrated and clogging of the ink at the head discharge port can be prevented. 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 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 preferably within a range of 0.2 to 5.0 μm. When the thickness is 0.2 μm or more, the particles are sufficiently concentrated, and as a result, the ink can be prevented from bleeding when recorded on the recording medium. Further, when the thickness is 5.0 μm or less, there is no problem of clogging of the head ejection opening. 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 preferably in the range of 0.5 to 5 mPa · s. When the viscosity is 0.5 mPa · s or more, there is no problem that the ink composition leaks from the ink discharge port of the head, and when the viscosity is 5 mPa · s or less, ink droplets are ejected well. It is. 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. When the surface tension is 10 mN / m or more, there is no problem that the ink composition spills from the ink discharge port of the head, and when the surface tension is 70 mN / m or less, ink droplets are discharged well. . More preferably, it is the range of 15-50 mN / m.

[Inkjet recording apparatus]
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 method utilizing 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. By using the ink composition of the present invention, recording in a short time is possible.

  On the other hand, the ink is circulated in the ink chamber having the ejection opening, and is present in the ejection opening by applying a voltage to the control electrode formed at the periphery of the ejection opening, and the ink guide whose tip is directed to the recording medium side. In the method in which the concentrated ink droplets fly from the front end, the supply of charged particles by the circulation of ink and the meniscus stability at the ejection position can be achieved at the same time, so that recording can be performed stably for a long period of time. Further, in this method, since the portion where the ink is in contact with the outside air is very small with only the discharge opening, the evaporation of the solvent is suppressed and the ink physical properties are stabilized, so that it can be suitably used in the present invention.

A configuration example of an ink jet recording apparatus suitable for applying the ink composition of the present invention is shown below.
First, an outline of an apparatus that performs single-sided four-color printing on a recording medium shown in FIG. 1 will be described.
An ink jet recording apparatus 1 shown in FIG. 1 supplies ink to an ejection head 2 composed of ejection heads 2C, 2M, 2Y, and 2K for four colors for forming a full color image. An ink circulation system 3 for collecting
A head driver 4 for driving the ejection head 2 by an output from an external device such as a RIP, and a position control means 5 are provided. Further, the ink jet recording apparatus 1 includes a transport belt 7 stretched around three rollers 6A, 6B, and 6C, a transport belt position detection unit 8 including an optical sensor that can detect the position of the transport belt 7 in the width direction, An electrostatic attraction unit 9 for holding the recording medium P on the conveyance belt, a static elimination unit 10 and a mechanical unit 11 for peeling the recording medium P from the conveyance belt 7 after completion of image formation are provided. Upstream and downstream of the conveying belt 7, the feed roller 12 and the guide 13 that supply the recording medium P from the stocker (not shown) to the conveying belt 7, the ink is fixed to the recording medium P after peeling, and the discharge stocker (not shown). A fixing unit 14 and a guide 15 are arranged to be conveyed. In addition, the inkjet printing apparatus 1 has a recording medium position detecting means 16 at a position facing the ejection head 2 with the conveyance belt 7 interposed therebetween, and further collects the solvent vapor generated from the ink composition. A solvent recovery unit 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.

  A known roller can be used as the feed roller 12, and the feed roller 12 is arranged so as to increase the feeding ability to the recording medium. Further, since dirt, paper powder, or the like may adhere on the recording medium P, it is desirable to remove them. The recording medium P supplied by the feed roller is transported to the transport belt 7 through the guide 13. The back surface (preferably metal back surface) of the conveyor belt 7 is installed via a roller 6A. The transported recording medium P is electrostatically attracted onto the transport belt by the electrostatic attracting means 9. In FIG. 1, electrostatic adsorption is performed by a scorotron charger connected to a negative high voltage power source. The recording medium P is electrostatically adsorbed without floating on the transport belt 7 by the electrostatic adsorption means 9 and the surface of the recording medium is uniformly charged. Here, the electrostatic attraction means is also used as a charging means for the recording medium, but may be provided separately. The charged recording medium P is transported to the ejection head portion by the transport belt 7, and electrostatic ink jet image formation is performed by superimposing the recording signal voltage with the charging potential as a bias. The recording medium P on which the image has been formed is discharged by the discharging unit 10, peeled off by the transfer belt 7 by the mechanical unit 11, and transferred 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 density near the opening and discharge, and is mainly a recording medium or a recording target. Ink droplets are ejected by electrostatic attraction caused by the counter electrode disposed on the back surface of the medium. Therefore, if the recording medium or the counter electrode does not face the head, or if no voltage is applied to the recording medium or the counter electrode even at the position facing the head, the voltage is accidentally applied to the ejection electrode. Ink droplets are not ejected even when a pressure is applied or vibration is applied, and the inside of the apparatus is not soiled.

  An ejection head 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 to the recording medium P. And a plurality of discharge portions 76 that discharge toward the surface. Each of the ejection portions 76 is provided with an ink guide portion 78 that guides the ink droplet G flying from the ink flow path 72 toward the recording medium P, and the substrate 74 has an opening through which the ink guide portion 78 is inserted. 75 is formed, and the ink meniscus 42 is formed between the ink guide portion 78 and the inner wall surface of the opening 75. The gap d between the ink guide portion 78 and the recording medium P is preferably about 200 μm to 1000 μm. Further, the ink guide part 78 is fixed to the support bar part 40 on the lower end side.

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

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

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

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

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

  In this way, when a pulsed positive voltage is applied, the ink droplet G is guided by the ink guide portion 78 from the opening 75 and flies to adhere to the recording medium P, and the first ejection is applied to the floating conductive plate 62. A positive induced voltage is generated by the positive voltage applied to the electrode 46 and the second ejection electrode 56. Even if the voltage applied to the first ejection electrode 46 and the second ejection electrode 56 is pulsed, this induced voltage is a substantially steady voltage. 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 concentration of charged particles R increases near the substrate 74. As shown in FIG. 3, when the number of ejection units (that is, channels for ejecting ink droplets) to be used is large, the number of charged particles necessary for ejection increases, but the first ejection electrode 46 and the second ejection electrode to be used are used. Since the number of 56 increases, the induced voltage induced in the floating conductive plate 62 increases, and the number of charged particles R moving to the recording medium 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. Therefore, when ink is ejected for a long time, the amount of charged particles in the ink composition is 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. Therefore, by replenishing the ink composition having a higher concentration (higher solid content concentration) than the ink composition initially charged in the ink tank, the reduction of charged particles is prevented, and the electrical conductivity of the ink composition is reduced. The ratio between the electrical conductivity of the charged particles and the electrical conductivity of the ink composition can be kept within a certain range. Also, 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. The shape of the recording medium may be planar such as a sheet shape or three-dimensional such as a cylindrical shape.

[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. In addition, stability over time is increased. 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. In addition, blocking can be prevented when image recording materials (printed materials) that have been inkjet-recorded and fixed are overlapped.

  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 [P-2 above]
-Dispersant [BZ-2 mentioned above]
Charge control agent Octope 12% "Zr" (Zirconyl 2-ethylhexanoate) manufactured by Hope Pharmaceutical Co., Ltd.
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

The coating agent [P-2] is made of methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), butyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), Blemmer PME-400 (manufactured by Nippon Oil & Fats Co., Ltd.). , 50:40:10 (molar ratio) and obtained by radical polymerization using a known polymerization initiator. The weight average molecular weight was 15000.
The graft polymer dispersant [BZ-2] is a polymer of stearyl methacrylate having a methacryloyl group at its end by radical polymerization of stearyl methacrylate in the presence of 2-mercaptoethanol and further reacting with methacrylic anhydride. -1] (mass average molecular weight was 7,600) and then obtained by radical polymerization with styrene. The mass 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.

<Preparation of ink composition [EC-1]>
10 g of the cyan pigment and 20 g of the coating agent [P-2] 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-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 Octope 12% “Zr” (zirconyl 2-ethylhexanoate) and Isopar G manufactured by Hope Pharmaceutical Co., Ltd. were used. The ink composition [EC-1] was obtained by adding at 5% by mass.

The physical properties of the ink composition [EC-1] were as follows.
The electrical conductivity at 20 ° C. of the ink composition was applied using an LCR meter (AG-4431 manufactured by Ando Electric Co., Ltd.) and an electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.). It was 140 nS / m when measured under the conditions of a voltage of 5 V and a frequency of 1 kHz.
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 (SRX-201 manufactured by Tommy Seiko Co., Ltd.). The electrical conductivity of the supernatant was measured and found to be 28 nS / m. The electric conductivity of the charged particles was 112 nS / m, which was 80% with respect to the electric conductivity of the ink composition. The charged particles were positively charged.
When the volume average diameter of the charged particles was measured with a CAPA-700 manufactured by Horiba, Ltd. at a rotation speed of 5000 rpm, it was 0.95 μm. The number average diameter was 0.22 μm.
The viscosity at 20 ° C. of the ink composition was measured with an E-type viscometer manufactured by Tokyo Keiki Co., Ltd. and found to be 1.5 mPa · s. 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 24 mN / m.

<Inkjet recording>
The ink tank connected to the head was filled with the ink composition [EC-1] in the ink jet recording apparatus shown in FIGS. Here, a 150 dpi (three-row staggered arrangement with a channel density of 50 dpi), 833 channel head of the type shown in FIG. 2 was used as the ejection head, and a silicon rubber heat roller incorporating a 1 kW heater was used as the fixing means. As the ink temperature control means, a throw-in heater and a stirring blade were provided in the ink tank, the ink temperature was set to 30 ° C., and the temperature was controlled with a thermostat while rotating the stirring blade at 30 rpm. Here, the stirring blade was also used as a stirring means for preventing precipitation and aggregation. In addition, the ink flow path is partially transparent, and the LED light emitting element and the light detecting element are arranged between them, and the ink dilution liquid (Isopar G) or concentrated ink (the solid content concentration of the ink composition is determined by the output signal). The concentration was controlled by charging. A fine coated paper for offset printing was used as a recording medium. After removing dust on the surface of the recording medium by air pump suction, the ejection head is brought close to the recording medium to the image forming position, image data to be recorded is transmitted to the image data calculation control unit, and the recording belt is rotated by rotation of the conveying belt. The ink composition was discharged while sequentially moving the discharge head while transporting the recording medium, and an image was formed with a drawing resolution of 2400 dpi.

  As the conveyor belt, a metal belt and polyimide film bonded together are used, and a line-shaped marker is placed in the vicinity of one end of the belt along the conveyor direction, and this is optically read by the conveyor belt position detection means. An image was formed by driving the control means. At this time, the distance between the ejection head and the recording medium was kept at 0.5 mm by the output from the optical gap detector. Further, the surface potential of the recording medium was set to −1.5 kV at the time of ejection, and a pulse voltage of +300 V was applied (pulse width 50 μsec) at the time of ejection, and image formation was performed at a driving frequency of 15 kHz. Immediately after image recording, the image was fixed using a heat roller. The temperature of the coated paper at the time of fixing was 90 ° C., and the contact time with the heat roller was 0.3 seconds.

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

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

-Magenta pigment (coloring material) Monoazo lake pigment C.I. I. Pigment Red (57: 1) (manufactured by Dainippon Ink & Chemicals, Ltd., Symbol Brilliant Carmine 6B229)
・ Coating agent [P-7 above]
・ Dispersant [BZ-7 below]
・ Tetrabutylammonium p-toluenesulfonate ・ Charge control agent Octope 12% “Zr” (Zirconyl 2-ethylhexanoate) manufactured by Hope Pharmaceutical Co., Ltd.
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

  Coating agent [P-7] is methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), butyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), stearyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.), Blemmer PME-400 (manufactured by NOF Corporation) was obtained by radical polymerization at 45: 40: 5: 10 (molar ratio) using a known polymerization initiator. The mass average molecular weight was 13000.

<Preparation of Ink Composition [EM-1]>
10 g of magenta pigment, 20 g of coating agent [P-7], and 0.5 g of tetrabutylammonium p-toluenesulfonate are placed in a flask and heated with a heater so that the internal temperature becomes 110 ° C. for 1 hour. Stir with heat and mix. 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). Zirconia ceramic beads were removed from the obtained dispersion, and Octope 12% “Zr” (zirconyl 2-ethylhexanoate) and Isopar G manufactured by Hope Pharmaceutical Co., Ltd. were used. The ink composition [EM-1] was obtained by adding at 5% by mass.

The physical properties of the ink composition [EM-1] were as follows.
The electrical conductivity at 20 ° C. of the ink composition was applied using an LCR meter (AG-4431 manufactured by Ando Electric Co., Ltd.) and a liquid electrode (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.). When measured under the conditions of a voltage of 5 V and a frequency of 1 kHz, it was 150 nS / m.
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 (SRX-201 manufactured by Tommy Seiko Co., Ltd.). The electrical conductivity of the supernatant was measured and found to be 30 nS / m. The electric conductivity of the charged particles was 120 nS / m, which was 80% with respect to the electric conductivity of the ink composition. The charged particles were positively charged.

It was 0.98 micrometer when the volume average diameter of the charged particle was measured by Horiba Ltd. CAPA-700 with the rotation speed of 5000 rpm. The number average diameter was 0.30 μm.
The viscosity of the ink composition at 20 ° C. was measured with an E-type viscometer manufactured by Tokyo Keiki Co., Ltd. and found to be 1.4 mPa · s. 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 26 mN / m.

<Inkjet recording>
Using the ink composition [EM-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.

[Example 3]
<Materials used>
In Example 3, 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 [P-4]
・ Dispersant [BZ-8 below]
Charge control agent Octope 12% "Zr" (Zirconyl 2-ethylhexanoate) manufactured by Hope Pharmaceutical Co., Ltd.
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

  The coating agent [P-4] is vinyltoluene (manufactured by Tokyo Chemical Industry Co., Ltd.), butyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), Blemmer PME-200 (manufactured by Nippon Oil & Fats Co., Ltd.), 50: It was obtained by radical polymerization at a 40:10 (molar ratio) using a known polymerization initiator. The weight average molecular weight was 15000.

<Preparation of Ink Composition [EY-1]>
8 g of the yellow pigment and 22 g of the coating agent [P-4] 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 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 finely pulverized product obtained 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 while maintaining the internal temperature at 45 ° C. Particles). Zirconia ceramic beads were removed from the obtained dispersion, and Octope 12% “Zr” (zirconyl 2-ethylhexanoate) and Isopar G manufactured by Hope Pharmaceutical Co., Ltd. were used. The ink composition [EY-1] was obtained by adding in an amount of 5% by mass.

The physical properties of the ink composition [EY-1] were as follows.
The electrical conductivity at 20 ° C. of the ink composition was applied using an LCR meter (AG-4431 manufactured by Ando Electric Co., Ltd.) and a liquid electrode (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.). When measured under the conditions of a voltage of 5 V and a frequency of 1 kHz, it was 150 nS / m.
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 (SRX-201 manufactured by Tommy Seiko Co., Ltd.). The electrical conductivity of the supernatant was measured and found to be 30 nS / m. The electric conductivity of the charged particles was 120 nS / m, which was 80% with respect to the electric conductivity of the ink composition. The charged particles were positively charged.

It was 0.98 micrometer when the volume average diameter of the charged particle was measured by Horiba Ltd. CAPA-700 with the rotation speed of 5000 rpm. The number average diameter was 0.24 μm.
The viscosity of the ink composition at 20 ° C. was measured with an E-type viscometer manufactured by Tokyo Keiki Co., Ltd. and found to be 1.4 mPa · s. Further, the surface tension of the ink composition at 20 ° C. was measured with a FACE automatic surface tension meter manufactured by Kyowa Interface Science Co., Ltd. and found to be 25 mN / m.

<Inkjet recording>
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 1]
In the preparation of the ink composition [EC-1] of Example 1, Example 1 was repeated except that the coating agent was changed to the following AP-1. Inkjet recording was performed at a pulse voltage of +300 V using the same apparatus as in Example 1, but the obtained image recording showed noticeable image density unevenness and stripe unevenness. In order to obtain a good image, a pulse voltage of +500 V was necessary.

[Comparative Example 2]
In the preparation of the ink composition [EM-1] of Example 2, Example 2 was repeated except that the coating agent was changed to the following AP-1. Inkjet recording was performed at a pulse voltage of +300 V using the same apparatus as in Example 1, but the obtained image recording showed noticeable image density unevenness and stripe unevenness. In order to obtain a good image, a pulse voltage of +500 V was necessary.

[Comparative Example 3]
In the preparation of the ink composition [EY-1] of Example 3, Example 3 was repeated except that the coating agent was changed to the following AP-2. Inkjet recording was performed at a pulse voltage of +300 V using the same apparatus as in Example 1, but the obtained image recording showed noticeable image density unevenness and stripe unevenness. In order to obtain a good image, a pulse voltage of +500 V was necessary.

  The structures of the coating agents AP-1, AP-2, dispersants BZ-7 and BZ-8 used in the above Examples and Comparative Examples 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 mass average molecular weight was 15,000, and the polydispersity (mass 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 coating agent [AP-2] was 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 reacted with hexamethylene diisocyanate. Was obtained. The weight average molecular weight was 20,000, and the polydispersity (mass 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.

The graft polymer dispersant [BZ-7] was obtained by radical polymerization with styrene and the polymer [BP-1] of stearyl methacrylate having a methacryloyl group at the terminal, which was synthesized in Example 1. The weight average molecular weight was 180,000. Although the graft polymer dispersant [BZ-7] became cloudy with respect to 100 g of Isopar G, 5 g or more was dissolved.
The graft polymer 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 mass average molecular weight was 60,000. Both DMS-R18 and the graft polymer dispersant [BZ-8] were dissolved in 5 g or more with respect to 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 apparatus 2 Discharge head 3 Ink circulation system 4 Head driver 5 Position control means 6A to 6C Conveying belt stretching roller 7 Conveying belt 8 Conveying belt position detecting means DESCRIPTION OF SYMBOLS 9 Electrostatic adsorption means 10 Static elimination means 11 Mechanical means 12 Feed roller 13 Guide 14 Image fixing means 15 Guide 16 Recording medium position detection means 17 Exhaust fan 18 Solvent vapor adsorption material 38 Ink guide 40 Support bar part 42 Ink meniscus 44 Insulation Layer 46 First ejection electrode 48 Insulating layer 50 Guard electrode 52 Insulating layer 56 Second ejection electrode 58 Insulating layer 62 Floating conductive plate 64 Coating film 66 Insulating member 70 Ink jet head 72 Ink flow path 74 Substrate 75, 75A, 75B Opening 76 , 76A, 76B Discharge part 78 Discharge part

Claims (3)

  An ink composition for ink jet recording comprising an ink composition containing a dispersion medium and charged particles, wherein the charged particles contain a colorant and a polymer having a polyether structure.   The ink composition for ink jet recording according to claim 1, wherein the ink composition contains at least one of a metal salt and an onium salt.   In an inkjet recording method in which an ink composition is ejected as ink droplets by an inkjet recording method using an electrostatic field, the ink composition contains a dispersion medium and charged particles, and the charged particles have a colorant and a polyether structure. An ink jet recording method comprising a polymer.

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