JP2005325328A - Composition for inkjet recording and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition for inkjet recording that can form an image approximately equal to a printed matter required for a color proof, an on-demand color printing or the like by an inkjet method and to provide an inkjet recording method. <P>SOLUTION: The ink composition for inkjet recording comprises a dispersion medium and charged particles containing at least a coloring material and a coating agent for the coloring material wherein the ink composition includes a polymer soluble in the dispersion medium which has (a) a mass average molecular weight of 1,000-50,000 and (b) a dynamic modulus of elasticity at 50°C of 5×10<SP>5</SP>Pa or more and at 100°C of 1×10<SP>3</SP>Pa or more. The inkjet recording method comprises causing the ink composition as ink droplets to fly toward a recording medium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording composition and an ink jet recording method, and more specifically, an ink jet having blocking resistance and friction resistance, which can relax image fixing conditions and impart and enhance glossiness to an image. The present invention relates to a recording composition and an ink jet recording method.

  As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic method, a sublimation type and a melt type thermal transfer method, an ink jet method and the like. The electrophotographic system requires a process of forming an electrostatic latent image on a photosensitive drum by charging and exposure, which complicates the system and becomes an expensive apparatus. The thermal transfer method is inexpensive, but uses an ink ribbon, so the running cost is high and waste material is generated. On the other hand, the ink jet system is an inexpensive apparatus and ejects ink only to a required image portion to form an image directly on a recording medium. Therefore, the ink can be used efficiently and the running cost is low. Furthermore, there is little noise and it is excellent as an image recording method.

Inkjet recording methods include, for example, a method in which ink droplets are ejected by the pressure of steam generated by the heat of a heating element, a method in which ink droplets are ejected by mechanical pressure pulses generated by a piezoelectric element, and an electrostatic field. There is a system (see Patent Documents 1 and 2) that causes ink droplets containing charged particles to fly. The method of flying ink droplets with steam or mechanical pressure cannot control the flying direction of 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 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. In order to maintain the high speed and high image quality of the formed image and to stabilize the color image formed product (printed product), the ink image is fixed on the paper. This fixing mainly involves the resin contained in the ink under heat and pressure. A heat roller system that is softened and pressed onto paper is used. This fixing is usually effective in most cases. However, when the recording medium is used under severe usage conditions or repeated use, the ink image may show off when the printed material is stacked, or the image may be scratched or worn. May cause image quality degradation. In particular, such a phenomenon tends to occur when the fixability of the image is poor. In order to prevent this, means for setting the heating temperature or the pressure to be applied high can be considered, but in that case, problems such as curling, twisting, wrinkling, distortion, and meandering of the printed matter tend to appear. Further, when an image is formed on coated paper, the glossiness of the image is also an important image quality factor, and the glossiness is increased by fixing at a high temperature and high pressure.

  In addition, it is preferable to protect the formed image in order to maintain the image quality of the image, or to prevent fading and fading due to ultraviolet light. Until now, it has been known that the surface of printed matter is covered with an overcoat film generally called a laminate. However, in this method, a laminate film is separately required, and there is no air bubble, and a device capable of rapid lamination. Is also required. On the other hand, means for directly applying or spraying the protective agent in the form of a solution to the surface of the printed material and then drying it has been proposed, but it is not practical. In an inkjet recording system, fixing must be realized at a low temperature and at a high speed and without deteriorating the image quality in the state where a solvent is present in the image area and paper at the time of fixing. It is difficult.

  In recent years, the progress of inkjet technology has been remarkable, and it has become possible to record high-quality images at high speed. Various images (hard copies) such as silver halide photographs have been developed, and color proofs for printed materials such as offset printing have been developed. Applications such as creation and color on-demand printing have come to be considered.

  For example, Patent Document 5 includes an ink head portion that performs image recording by ink jet and a fixing portion that fixes an image after image recording, and preferably includes an accumulating portion before and after the fixing portion, There has been disclosed an ink jet printer which is intended to form an image having a glossiness similar to that of a photographic image by performing a fixing process quickly and at a predetermined timing.

  Further, Patent Document 6 discloses that a pigment image is formed by jetting and ejecting a pigment ink onto a recording medium, and the C value of the pigment image is set to 60 or more so that a gloss like a silver salt photograph is obtained. An ink jet recording method has been disclosed which has a feeling and suppresses a metallic luster called bronzing.

  Further, Patent Document 7 discloses a surface which is formed by dip-coating curable silicone as a means for fixing an image by ink jet and then heat-curing the curable silicone, and has a peeling force of 30 g / 5 cm or more. An inkjet recording method is disclosed in which a fixing belt having a layer has good gloss after fixing, there is no peeling of the fixing member film, and offset of the image can be prevented.

Japanese Patent No. 3315334 US Pat. No. 6,158,844 JP-A-8-291267 US Pat. No. 5,952,2048 JP 2003-80692 A JP 2003-103898 A JP 2003-1118090 A

  However, according to the ink jet recording disclosed in each of the above-mentioned patent documents, it is possible to form an image having gloss equivalent to that of a silver salt photograph. However, it was not sufficient for forming a color proof of the printed material and forming an image similar to the printed material, such as an image required for color on-demand printing by inkjet.

In order to put color proofing and color on-demand printing by inkjet into practical use, images such as high-quality paper, coated paper, cast coated paper, etc. are used to form images such as printed matter. It is preferable to do this.
However, the glossiness of images according to each of the above-mentioned patent documents often depends on the recording medium having a thermoplastic resin on the surface, and in this respect as well, it is sufficient for the creation of color proofs by ink jet and on-demand printing. I was not satisfied.

  Accordingly, an object of the present invention is to provide an ink jet recording composition and an ink jet recording method which can form an image similar to a printed matter, which is required for color proofing or color on-demand printing by ink jet. In particular, image fixing and protection can be achieved at high speed and low temperature, the target image can be maintained with high image quality, curling, twisting, wrinkling, distortion, etc. of the printed matter is small, and the material of the recording medium Provided are an ink jet recording composition and an ink jet recording method having blocking resistance and friction resistance capable of imparting and enhancing glossiness to an image while maintaining the original suppleness regardless of the configuration and properties. That is.

The present invention is as follows.
(1) In an ink composition for ink jet recording containing a dispersion medium and charged particles containing at least a colorant and a colorant coating agent, a polymer soluble in the dispersion medium that satisfies the following conditions a) and b) An ink composition for ink-jet recording, comprising at least one of the above.
a) The mass average molecular weight of the polymer soluble in the dispersion medium is 1000 to 50000.
b) The dynamic elastic modulus of the dispersion medium-soluble polymer is 5 × 10 ⁵ Pa or more at 50 ° C. and 10
It is 1 × 10 ³ Pa or more at 0 ° C.
(2) The ink composition for ink jet recording according to the above (1), further satisfying the following conditions c), d) and e):
c) The addition amount of the polymer soluble in the dispersion medium is 1 to 70% by mass with respect to the whole ink composition.
d) The glass transition point of the polymer soluble in the dispersion medium is in the range of 40 ° C to 120 ° C.
e) The rate of increase in the viscosity of the ink composition obtained by adding a soluble polymer to the dispersion medium is 20 to 300% as compared to before addition.
(3) An ink jet recording method in which the ink composition for ink jet recording described in (1) or (2) is ejected as ink droplets by an ink jet recording method using an electrostatic field.

  According to the present invention, image fixing and protection are achieved at high speed and low temperature, and recording is used as main paper in printing on high-quality paper, finely coated paper, coated paper, art paper, cast coated paper, printing film, and the like. Using media, it is possible to maintain high-quality images that are close to printed matter required for inkjet color proofing or color on-demand printing, with little curling, twisting, wrinkling, distortion, etc. An ink composition for ink jet recording and an ink jet recording method having blocking resistance and friction resistance capable of imparting and enhancing gloss to an image while maintaining flexibility are provided.

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

Examples of the dispersion medium used in the present invention include linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, or aromatic hydrocarbons, halogen substitution products of these hydrocarbons, and silicone oil. For example, hexane, heptane, octane. Isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (Isopar: Exxon Corporation) Trade name), Shellsol 70, Shellsol 71 (Shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 solvent (Amsco: trade name of Spirits), KF-96L (trade name of Shin-Etsu Silicone) Etc. can be used alone or in combination. The content of the dispersion medium with respect to the entire ink composition is preferably in the range of 20 to 99% by mass. In 20 mass% or more, the particle | grains containing a coloring material can be disperse | distributed favorably in a dispersion medium, and content of a coloring material can be satisfied in 99 mass% or less. More preferably, it exists in the range of 40-95 mass%.

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

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

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

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

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

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

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

  Examples of coating agents include rosins, rosin-modified phenolic resins, alkyd resins, (meth) acrylic polymers, polyurethanes, polyesters, polyamides, polyethylene, polybutadiene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol acetal modified products, polycarbonate And the like. Among these, from the viewpoint of ease of particle formation, the mass average molecular weight is in the range of 2,000 to 1,000,000 and the polydispersity (mass average molecular weight / number average molecular weight) is 1.0. Polymers in the range of ~ 5.0 are preferred. Furthermore, from the viewpoint of ease of fixing, a polymer having any one of a softening point, a glass transition point, and a melting point within the range of 40 ° C to 120 ° C is preferable.

  In the present invention, the polymer 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, amino group, hydroxy group, or halogen substituent.

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

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

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

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

  The polymer containing at least one of the structural units represented by the general formulas (1) to (4) may be a homopolymer of the structural units represented by the general formulas (1) to (4). It may be a copolymer (copolymer) with these constituent components. These polymers may be used alone as a coating polymer, 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 formed satisfactorily. More preferably, it exists in the range of 0.5-35 mass%.

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

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

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

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

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

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

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

  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. More preferably, it exists in the range of 0.4-25 mass%.

[Polymer soluble in dispersion medium]
The polymer soluble in the dispersion medium used in the present invention (hereinafter sometimes referred to as dispersion medium-soluble polymer) is an alkyl group, an alkoxyl group, a dialkylamino group, a halogen group, an amino group, a sulfone group, and / or Examples thereof include homopolymers or copolymers such as (meth) acrylates having a nitro group, diene compounds, acetylene, and rosin.
In addition, the dispersion medium-soluble polymer needs to satisfy the following conditions a) and b).
a) The mass average molecular weight is 1000 to 50000, preferably 2000 to 20000, and more preferably 2000 to 15000.
b) The dynamic elastic modulus is 5 × 10 ⁵ Pa or higher at 50 ° C. and 1 × 10 ³ Pa or higher at 100 ° C., preferably the dynamic elastic modulus is 1 × 10 ⁶ Pa or higher at 50 ° C., and 1x1 at 100 ° C
0 ⁴ Pa or more, and more preferably, the dynamic elastic modulus is 1 × 10 ⁶ to 1 × 10 ⁸ Pa at 50 ° C.
And 1 × 10 ⁴ to 1 × 10 ⁵ Pa at 100 ° C.

In addition, the ink composition of the present invention preferably further satisfies the following conditions c), d) and e) in addition to the dispersion medium-soluble polymer satisfying the conditions a) and b).
c) The addition amount of the dispersion medium-soluble polymer is 1 to 70% by mass, preferably 3 to 50% by mass, and more preferably 5 to 40% by mass with respect to the entire ink composition.
d) The glass transition point of the polymer soluble in the dispersion medium is -40 ° C to 120 ° C, preferably -20 ° C to 100 ° C.
e) The increase rate of the viscosity of the ink composition in which the soluble polymer is added to the dispersion medium is 5 to 300%, preferably 10 to 250%, compared to before the addition.
The viscosity of the ink composition is the viscosity of the ink composition at 20 ° C., and the viscosity can be easily measured using, for example, a product name TV-22 viscometer manufactured by Toki Sangyo Co., Ltd. it can.

  The dispersion medium-soluble polymer particularly preferably used in the present invention is a polymer containing a polymer component of a structural unit represented by the following general formula (8).

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. The hydrocarbon group for R ₅₂ may contain an ether bond, an amino group, a hydroxy group, or a halogen substituent.

  Specific examples of the dispersion medium-soluble polymer include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, stearyl acrylate, stearyl methacrylate, cetyl acrylate. Cetyl methacrylate, decyl acrylate, decyl methacrylate, dodecyl acrylate, dodecyl methacrylate, nonyl acrylate, nonyl methacrylate, vinyl 2-ethylhexyl ether, vinyl isoamyl ether, vinyl stearate, vinyl laurate, butyl acrylate, butyl methacrylate, hexyl acrylate, hex Methacrylate, benzyl acrylate, benzyl methacrylate, lauryl acrylate, monomers or copolymers and lauryl methacrylate, derivatives thereof, and halogen-substituted products and the like.

  Preferred structural units are shown below.

The action of the dispersion medium-soluble polymer in the present invention is as follows.
The polymer firmly adheres the charged particles composed of the color material and the coating agent and forms a film on the surface.
Conventionally, at the time of fixing, heat and pressure are simultaneously applied to soften and crush the coating material to ensure adhesion between the particles and the recording medium. For this reason, it is necessary to increase the heating and pressurizing conditions to some extent.
When an ink composition containing a dispersion medium-soluble polymer is used, the solvent causes the polymer to bind charged particles or embed the charged particles in a continuous film, thereby relaxing the fixing conditions. Furthermore, the fixing time can be shortened, and the fixing device can be reduced in weight and simplified.
The dispersion medium-soluble polymer in the present invention is different from the dispersant polymer that disperses and particles the mixture of the coloring material and the coating agent contained in the ink composition. For example, the dispersant polymer has a higher molecular weight than the dispersion medium-soluble polymer, and the solubility is 95% to 60%, preferably 90% to 70% at room temperature with respect to 100 g of the dispersion medium.

  By using the dispersion medium-soluble polymer in the present invention, without using a dedicated recording medium, printing on high-quality paper, fine coated paper, coated paper, art paper, cast coated paper, printing film, etc. By using the recording medium to be used, it is possible to form an image that approximates a printed matter by offset printing by inkjet, and it is possible to suitably create a color proof of the offset printed matter and full color on-demand printing by inkjet.

[Charge control agent]
In the present invention, it is preferable that a mixture of a colorant and a coating agent (coating polymer) is dispersed (particulated) in a dispersion medium using a dispersing agent, and a charge adjusting agent is used to control the charge amount of the particles. More preferably, it is used in combination.
Suitable charge control 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, dioctyl Metal salts of organic sulfonic acids such as magnesium sulfosuccinate, ammonium salts of organic sulfonic acids such as toluenebutyl tetrabutylammonium salt, polymers containing carboxylic acid groups modified with amines of copolymers of styrene and maleic anhydride, etc. Polymers having a carboxylic acid group in the side chain, polymers having a carboxylic acid anion group in the side chain such as a copolymer of stearyl methacrylate and tetramethylammonium methacrylate, side chains such as a copolymer of styrene and vinylpyridine Has a nitrogen atom Rimmer, 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 imparted 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]
The ink composition in the present invention can be prepared by dispersing (particulating) a colorant and preferably a coating agent (coating polymer) using the above components. Examples of the method for dispersing (particulate) include the following methods.
(1) A colorant and a coating agent are mixed in advance, and then dispersed (granulated) using a dispersant and a dispersion medium, and a charge adjusting agent is added.
(2) Disperse (particulate) using a coloring material, a coating agent, a dispersant and a dispersion medium at the same time, and add a charge control agent.
(3) Disperse (particulate) using a colorant, a coating agent, a dispersant, a charge control agent and a dispersion medium at the same time.

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

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

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

[Inkjet recording apparatus]
In the present invention, the ink composition described above is recorded by flying as ink droplets toward a recording medium by, for example, an ink jet recording method to form an image. 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 single-sided four-color printing on 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.
Furthermore, an ink circulation system 3 that collects ink from the ejection head 2, a head driver 4 that drives the ejection head 2 by output from an external device such as a computer (not shown), a RIP (raster image processor), and a position control unit 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 adsorption unit 9 for holding the recording medium P on the conveyance belt, a static elimination unit 10 and a mechanical unit 11 for separating the recording medium P from the conveyance belt 7 after completion of image formation are provided. Upstream and downstream of the conveyance belt 7, the recording medium P is fed from a stocker (not shown) to the conveyance belt 7, the ink is fixed to the feed roller 12 and the guide 13, and the peeled recording medium P and conveyed to a paper discharge stocker (not shown). A fixing means 14 and a guide 15 are arranged. The ink jet printing apparatus 1 has a recording medium position detecting means 16 at a position facing the ejection head 2 with the conveying belt 7 interposed therebetween, and further collects solvent vapor generated from the ink composition. A solvent recovery unit comprising the exhaust fan 17 and the solvent vapor adsorbent 18 is disposed, and the vapor inside the apparatus is discharged outside the apparatus through the recovery unit.

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

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

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

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

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

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

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

  As shown in FIG. 3, in order to fly ink from the inkjet head 70 and record on the recording medium P, the ink flow Q is generated by circulating the ink in the ink flow path 72, and the guard electrode 50. A predetermined voltage (for example, +100 V) is applied to. Further, a flying electric field that attracts the positive charged particles R in the ink droplet G that has been guided by the ink guide portion 78 and flew from the opening 75 to the recording medium P is generated by the first ejection electrode 46 and the second ejection electrode 56. A positive voltage is applied to the first ejection electrode 46, the second ejection electrode 56, and the recording medium P so as to be formed between the recording medium P and the recording medium P (when the gap d is 500 μm, 1 kV to 3. (The standard is to form a potential difference of about 0 kV).

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

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

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

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

In particular, it is preferable to fix an image by a heating and fixing means comprising a heating member having at least one rotating body and being in pressure contact with each other and a pressure member. Further, it is preferable that at least one of the heating member and the pressure member is a roller or a shape of an endless belt. The heating roller can be composed of a heat conductive substrate, for example, a cylindrical core made of aluminum, an elastic layer thereon, and a release layer. An intermediate layer may be provided between the elastic layer and the release layer. Examples of the material of the elastic layer include silicone rubber and fluorine rubber. The release layer provided on the outer side of the elastic layer can improve the durability of the elastic layer while improving the releasability with the ink particles. Examples of the material of the release layer include silicone rubber, fluororesin, and fluororubber. The intermediate layer provided between the elastic layer and the release layer is provided for enhancing the adhesion between the two and suppressing the swelling of the elastic layer. Examples of the material for the intermediate layer include fluororubber and a mixture of fluororesin and fluororubber. An example of the pressure roller is the same as that of the heating roller described above, and it is particularly preferable to use a soft roller made of foamed rubber as the elastic layer. Examples of the endless belt include a heat-resistant resin layer such as a nickel electroformed layer or polyimide, and a coating layer having the same layer structure as the heating roller, and is elastically deformable.
The 60 ° gloss value of the fixed image recorded on the recording medium measured with a PG-1 apparatus manufactured by Nippon Denshoku Industries Co., Ltd. is 20% to 300% of the glossiness of the recording medium alone. % Is preferred.

[Dynamic elastic modulus]
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.
According to the study by the present inventors, it has been found that the dynamic elastic modulus is an index of the fixability of the ink image and is deeply related to the blocking resistance and the friction resistance. That is, the dynamic elastic modulus is the thermal fluidity of the ink image, that is, the flow property, the difficulty of the image to be transferred to the recording paper that is overlaid, that is, the blocking resistance, and the thermal fixing of the ink image. This is closely related to an offset at which a part of the image is transferred to the heat 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. While the temperature is lowered, the rotor is vibrated at a frequency of 1 Hz, and a “temperature-dynamic elastic modulus curve” is automatically recorded, and the dynamic elastic modulus at 50 ° C. can be measured.

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

[Recording medium]
In the present invention, various recording media can be used depending on the application. For example, if paper, plastic film, metal, and paper on which plastic or metal is laminated or vapor-deposited, plastic film on which metal is laminated or vapor-deposited, etc., printed matter can be directly obtained by ink jet recording. Further, an offset printing plate can be obtained by using a roughened support such as aluminum. Furthermore, if a plastic support is used, a flexographic printing plate or a color filter for a liquid crystal screen can be obtained. The shape of the recording medium may be planar such as a sheet shape or three-dimensional such as a cylindrical shape. Further, if a silicon wafer or a wiring board is used as a recording medium, it can be applied to manufacture of a semiconductor or a printed wiring board.
In particular, if a recording medium used as the main paper for printing, such as fine paper, fine coated paper, coated paper, art paper, cast coated paper, and printing film, an image that approximates printed matter by offset printing is formed. Therefore, it is possible to suitably perform color proofing of offset prints and full-color on-demand printing by inkjet.

  By combining the ink composition, the ink jet recording apparatus, and the replenishment of the ink composition described above, there is no ink bleeding, the image is glossy, has blocking resistance and friction resistance, and has high image density and high image quality. An image recording can be obtained stably over a long period of time.

  Hereinafter, although an example and a comparative example explain the present invention in detail, the present invention is not limited to these. Unless otherwise specified, the composition ratio and% represent mass ratio and mass%.

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

Cyan pigment (coloring material) phthalocyanine pigment C.I. I. Pigment Blue (1
5: 3) (Toyo Ink Manufacturing Co., Ltd., LIONOL BLUE FG-7350)
・ Coating polymer [AP-1]
・ Dispersant [BZ-2]
-Dispersion medium soluble polymer [KP-1]
-Charge control agent [CT-1]
・ Dispersion medium Isopar G (isoparaffin type, manufactured by Exxon)

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

The coating polymer [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 dispersant [BZ-2] is a polymer of stearyl methacrylate (mass average molecular weight) having a methacryloyl group at its terminal by radical polymerization of stearyl methacrylate in the presence of 2-mercaptoethanol and further reacting with methacrylic anhydride. Was obtained by radical polymerization with styrene. The mass average molecular weight was 110,000.
The dispersion medium-soluble polymer [KP-1] was obtained by polymerizing lauryl methacrylate in toluene using an initiator V65 (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain a polymer of lauryl methacrylate. At this time, the polylauryl methacrylate had a mass average molecular weight of 6,000, a dynamic viscoelasticity of 1 × 10 ⁶ Pa at 50 ° C., 3 × 10 ³ Pa at 100 ° C., and a glass transition point (Tg) of 10 ° C. It was.
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 cyan pigment and 20 g of the coating polymer “AP-1” were put into a table type kneader PBV-0.1 manufactured by Irie Shokai Co., Ltd., the heater temperature was set to 100 ° C., and the mixture was heated and mixed for 2 hours. 30 g of the obtained mixture was coarsely pulverized with a trio-brender manufactured by Trio Science Co., Ltd., and further finely pulverized with a SK-M10 type sample mill manufactured by Kyoritsu Riko Co., Ltd. 30 g of the obtained finely pulverized product was predispersed in a paint shaker manufactured by Toyo Seiki Seisakusho together with 7.5 g of the dispersant [BZ-2], 75 g of Isopar G, and glass beads having a diameter of about 3.0 mm. After removing the glass beads, together with 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. The zirconia ceramic beads are removed from the obtained dispersion, and 316 g of ISOPAR G and 0.6 g of the charge control agent [CT-1] are added thereto. Further, 25 g of a dispersion medium-soluble polymer [KP-1] is obtained as polylauryl methacrylate. Was added to obtain an ink composition [EC-1]. The obtained composition had an electric resistivity of 5 × 10 ¹⁰ Ω · cm and a dielectric constant of 2.68.
Further, the increase rate of the viscosity of the ink composition to which the dispersion medium-soluble polymer [KP-1] was added was 25% as compared with that before the addition.

<Inkjet recording>
The ink composition [EC-1] of Example 1 was filled in the ink tank in the ink jet recording apparatus shown in FIGS. Here, a 150 dpi (three-row staggered arrangement with a channel density of 50 dpi) and 833 channel head of the type shown in FIG. 2 was used as the ejection head, and a silicon rubber heat roller incorporating a 1 kW heater was used as the fixing means. As the ink temperature control means, a throw-in heater and a stirring blade were provided in the ink tank, the ink temperature was set to 30 ° C., and the temperature was controlled with a thermostat while rotating the stirring blade at 30 rpm. Here, the stirring blade was also used as a stirring means for preventing precipitation and aggregation. In addition, the ink flow path is partially transparent, and the LED light emitting element and the light detecting element are arranged between them, and the ink dilution liquid (Isopar G) or concentrated ink (the solid content concentration of the ink composition is determined by the output signal). The concentration was controlled by charging. Coated paper for offset printing (made by Hokuetsu Paper Co., Ltd., trade name Perfect W) was used as the 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. After image formation, heating and pressure fixing were performed with a pair of heat rollers.
The image fixing unit 14 is a heating and fixing unit including a heating roller having a heating source and a pressure roller in pressure contact with the heating roller. The heating roller has an aluminum cylindrical core member with a diameter of 65 mm and a halogen lamp heater built therein as a heat source, an elastic layer made of silicon rubber with a thickness of 2 mm on the core member, and a thickness of 20 μm on the elastic layer. An intermediate layer made of fluororubber and a release layer made of silicon rubber having a thickness of 80 μm on the intermediate layer was used. The surface temperature of the heating roller was set to 80 ° C., the nip pressure was set to 0.3 MPa, and the speed was set to 18 mm / sec. The heating roller has a (center line average) roughness Ra of 0.15 μm. On the other hand, a pressure roller having the same configuration as the heating roller was used except that the elastic layer had a thickness of 1 mm.

Using a coated paper (Perfect W, manufactured by Hokuetsu Paper Co., Ltd.) as the recording medium, a solid image having a reflection density of 1.55 was formed.
When the glossiness of the obtained image surface was measured, it was 31.
In addition, using the same coated paper, a solid image of the same color and the same density was printed by an offset printer, and the glossiness of the image was measured in the same manner. As a result, the glossiness of the printed image was 32, and it was confirmed that the image formed in this example was an image having a texture very close to a printed matter using coated paper. The gloss of the coated paper itself measured in the same manner was 21.

Example 2
The dispersion medium-soluble polymer in Example 1 was used except that 20 g of polylauryl acrylate having a weight average molecular weight of 12,000, a dynamic viscoelasticity of 4 × 10 ⁶ Pa at 50 ° C., and 5 × 10 ³ Pa at 100 ° C. was used. Produced a similar ink composition [EC-2]. The polylauryl acrylate of Example 2 had Tg = −10 ° C., and the increase rate of the viscosity of the ink composition to which polylauryl acrylate was added was 18% compared with that before the addition.

Example 3
The dispersion medium-soluble polymer in Example 1 was a poly (diethylaminoethyl methacrylate) having a weight average molecular weight of 10,000, a dynamic viscoelasticity of 3 × 10 ⁶ Pa at 50 ° C., and 4 × 10 ³ Pa at 100 ° C. A similar ink composition [EC-3] was prepared except that 28 g was used. The polydiethylaminoethyl methacrylate of Example 3 had Tg = 35 ° C., and the rate of increase in the viscosity of the ink composition to which polydiethylaminoethyl methacrylate was added was 20% as compared to before addition.

Comparative Example 1
A similar ink composition was prepared except that the dispersion medium-soluble polymer was not added in Example 1.

<Fixing evaluation>
After image formation, heat is applied using a heat roller, and the temperature of the coated paper, which is the printing paper, is changed from 60 to 100 ° C. in increments of 5 ° C., and fixing is performed. Then, the same paper as the printing paper is overlaid on the image, and about 50 g / cm ²
The film was left at 50 ° C. for 24 hours, and the degree of transfer of the image portion onto the back surface of the stacked paper was visually evaluated.
Table 1 shows the results obtained in the above Examples and Comparative Examples.

[Fixability]
○: Flow start temperature 70 ° C. or less and offset resistant upper limit temperature 80 ° C. or more × Flow start temperature 80 ° C. or more or offset resistant upper limit temperature 80 ° C. or less [blocking resistance]
○: No transfer x: Transfer exists [Glossiness]
Actual value by gloss meter. It is 60 degree glossiness measured with Nippon Denshoku Industries Co., Ltd. PG-1 apparatus.

As described above, the glossiness of the coated paper itself is 21, but the glossiness of the image printed by the offset printing machine is 32, and generally the difference from the glossiness of the offset print image is ± 5 or less. It can be said that the texture of the image is close. Therefore, it was confirmed that the images formed in Examples 1 to 3 have a texture very close to a printed matter using coated paper.
On the other hand, in Comparative Example 1 in which the dispersion medium-soluble polymer was not used, the image fixing property, the blocking resistance, and the glossiness were inferior to each of the Examples.

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. 1 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 (3)

In an ink composition for ink jet recording containing a dispersion medium and charged particles including at least a color material and a color material coating agent, at least one polymer soluble in the dispersion medium satisfying the following conditions a) and b): An ink composition for inkjet recording, comprising at least one type.
a) The mass average molecular weight of the polymer soluble in the dispersion medium is 1000 to 50000.
b) The dynamic elastic modulus of the dispersion medium-soluble polymer is 5 × 10 ⁵ Pa or more at 50 ° C. and 10
It is 1 × 10 ³ Pa or more at 0 ° C. 2. The ink composition for ink jet recording according to claim 1, further satisfying the following conditions c), d) and e).
c) The addition amount of the polymer soluble in the dispersion medium is 1 to 70% by mass with respect to the whole ink composition.
d) The glass transition point of the polymer soluble in the dispersion medium is in the range of 40 ° C to 120 ° C.
e) The rate of increase in the viscosity of the ink composition obtained by adding a soluble polymer to the dispersion medium is 20 to 300% as compared to before addition.   An ink jet recording method in which the ink composition for ink jet recording according to claim 1 or 2 is ejected as ink droplets by an ink jet recording method using an electrostatic field.

Images