JP4625666B2 - Ink composition and inkjet recording method - Google Patents

Description

  The present invention relates to an ink composition and an ink jet recording method. More specifically, the present invention can fix a high-quality image at a low temperature and a high speed on a recording medium, and also has an anti-offset property and anti-blocking property (after fixing). The present invention relates to an ink composition and an ink jet recording method which are excellent in that they are not transferred to the back surface when recording media are stacked.

  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, and the system becomes complicated and expensive. The thermal transfer method is inexpensive, but uses an ink ribbon, so the running cost is high and waste material is generated. On the other hand, the ink jet method is an inexpensive apparatus and ejects ink only to a required image portion to directly form an image on a recording medium. Therefore, the ink can be used efficiently and the running cost is low. Furthermore, there is little noise and it is excellent as an image recording method.

Inkjet recording methods include, for example, a method in which ink droplets are ejected by the pressure of steam generated by the heat of a heating element, a method in which ink droplets are ejected by mechanical pressure pulses generated by a piezoelectric element, and an electrostatic field. There is a system (see Patent Documents 1 and 2) that causes ink droplets containing charged particles to fly. The method of flying ink droplets with steam or mechanical pressure cannot control the flying direction of the ink droplets, and causes the ink droplets to land precisely on the desired position on the printing medium due to distortion of the ink nozzles or air convection. Is difficult.
On the other hand, the method using an electrostatic field controls the flying direction of the ink droplets by the electrostatic field, so that the ink droplets can be landed accurately at a desired position, and a high-quality image formation (printed material) is created. It is excellent.

As an ink composition used for inkjet recording using an electrostatic field, an ink composition containing a dispersion medium and charged particles including at least a coloring material is used (see Patent Documents 3 and 4). By changing the color material, the ink composition containing the color material can create four color inks of yellow, magenta, cyan, and black, and can also create special color inks of gold and silver . Therefore, it is useful because a color image formed product (printed product) can be produced. However, in order to maintain high speed and high image quality and to stably output a color image formed product (printed product), a means for fixing to paper is required. However, in the inkjet system, it is necessary to realize fixing at low temperature and high speed and without deteriorating the image quality in a state where a solvent is present in the image portion and paper at the time of fixing. .
Japanese Patent No. 3315334 US Pat. No. 6,158,844 JP-A-8-291267 US Pat. No. 5,952,2048

  An object of the present invention is to provide an ink composition and an ink jet recording method that can fix a high-quality image at low temperature and high speed, and that are excellent in offset resistance and blocking resistance.

ここで、Ｒは水素原子または炭素数１〜３０の炭化水素基を表し、ｎは１〜５０の整数である。
Ａｒはメチル基で置換されていてもよい２価の芳香族炭化水素基を表す。
Ｙは、単結合、または以下のいずれかの構造である。

ここで、Ｒは水素原子または炭素数１〜３０の炭化水素基を表す。
Ｚは水素原子、アルキル基、アルコキシ基、メトキシカルボニル基、またはシアノ基である。
２．
前記一般式（Ｉ）におけるＸが、下記のいずれかで表される基であることを特徴とする上記１に記載のインク組成物。

３．
前記分散媒が、比誘電率が５以下で、１０ ¹⁰ Ωｃｍ以上の電気抵抗率を有する、誘電性の液体であり、インク組成物全体に対する該分散媒の含有量が２０〜９９質量％であることを特徴とする上記１又は２に記載のインク組成物。
４．
前記荷電粒子がポリエステル構造を有するコポリマーを有し、該ポリエステル構造を有するコポリマーが、下記一般式（Ａ）又は（Ｂ）で表される構造単位を有することを特徴とする上記１〜３のいずれか一項に記載のインク組成物。

一般式（Ａ）および（Ｂ）中、
Ｒ ₁ 〜Ｒ ₃ は各々独立に炭素数１から２０の２価炭化水素基を示し、炭化水素基中にエーテル結合、アミノ基、ヒドロキシ基、又はハロゲン置換基を有していてもよい。
ｎは２以上の整数である。
５．
前記ポリエステル構造を有するコポリマーが２０℃〜１２０℃の融点（Ｔｍ）を有することを特徴とする上記４に記載のインク組成物。
６．
静電界を利用したインクジェット記録方式でインク組成物をインク滴として飛翔させるインクジェット記録方法において、使用するインク組成物が、上記１〜５のいずれか一項に記載されたインク組成物であることを特徴とするインクジェット記録方法。
尚、本発明は上記１〜６に記載の構成を有するものであるが、以下、その他についても参考のため記載した。 The present invention has the following configuration.
1.
In an ink composition containing a dispersion medium and charged particles containing at least a coloring material, the charged particles contain at least one of a copolymer having a polyester structure and a polymer having a liquid crystal structure,
An ink composition, wherein the polymer having a liquid crystalline structure has a structure of the following general formula (I) in a polymer side chain.
-X-Ar-Y-Ar-Z (I)
Where
X represents a single bond or a divalent linking group with a polymer main chain skeleton, and the divalent linking group has an ester structure, an amide structure, an ether structure, a thioether structure, or a structure thereof and any of the following structures: Is a group formed by combining

Here, R represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, and n is an integer of 1 to 50.
Ar represents a divalent aromatic hydrocarbon group which may be substituted with a methyl group.
Y is a single bond or one of the following structures.

Here, R represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms.
Z is a hydrogen atom, an alkyl group, an alkoxy group, a methoxycarbonyl group, or a cyano group.
2.
2. The ink composition according to 1 above, wherein X in the general formula (I) is a group represented by any of the following:

3.
The dispersion medium is a dielectric liquid having a relative dielectric constant of 5 or less and an electric resistivity of 10 ¹⁰ Ωcm or more, and the content of the dispersion medium with respect to the entire ink composition is 20 to 99% by mass. 3. The ink composition as described in 1 or 2 above.
4).
The charged particles have a copolymer having a polyester structure, and the copolymer having the polyester structure has a structural unit represented by the following general formula (A) or (B) The ink composition according to claim 1.

In general formulas (A) and (B),
R _{1 to} R ₃ each independently represents a divalent hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group may have an ether bond, an amino group, a hydroxy group, or a halogen substituent.
n is an integer of 2 or more.
5.
5. The ink composition as described in 4 above, wherein the copolymer having a polyester structure has a melting point (Tm) of 20 ° C. to 120 ° C.
6).
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 to be used is the ink composition described in any one of 1 to 5 above. An ink jet recording method.
In addition, although this invention has the structure of said 1-6, below, it described for reference also about others.

1. An ink composition comprising a dispersion medium and charged particles containing at least a colorant, wherein the charged particles contain at least one of a copolymer having a polyester structure and a polymer having a liquid crystal structure.
2. 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 to be used contains a dispersion medium and charged particles containing at least a coloring material, and the charged particles are An inkjet recording method comprising at least one of a copolymer having a polyester structure and a polymer having a liquid crystal structure.

According to the present invention, it is possible to provide an ink composition and an ink jet recording method that can fix a high-quality image at a low temperature and a high speed, and that are excellent in offset resistance and blocking resistance.
In particular, the ink composition of the present invention exhibits a sharp temperature response and can be made into a sharp melt because the coating copolymer has a polyester structure. Furthermore, since the polyester structure is bonded to the polymer main chain, the offset resistance can be maintained even if the polyester structure melts. Furthermore, since the polyester structure can be quickly solidified by cooling after fixing, the blocking resistance can be improved.
Further, since the ink composition of the present invention contains a polymer having a liquid crystalline structure, it can be melted sharply with respect to temperature (sharp melt property), and can be rapidly crystallized by cooling after fixing. Therefore, blocking resistance can also be improved.

Hereinafter, the present invention will be described in more detail.
[Coating agent]
In the ink composition of the present invention, the coloring material such as a pigment is preferably 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 addition, it is possible to cancel the difference in dispersion stability that varies depending on the type of color material, and to impart good dispersion stability.
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.

The charged particles contained in the ink composition of the present invention are characterized by containing at least one of a copolymer having a polyester structure and a polymer having a liquid crystalline structure. In addition, you may contain the polymer which has both a liquid crystalline structure and a polyester structure.
First, a copolymer having a polyester structure will be described.
The copolymer having a polyester structure of the present invention preferably has a structural unit represented by the following general formula (A) or (B).

In general formulas (A) and (B),
R _{1 to} R ₃ each independently represents a divalent hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group may have an ether bond, an amino group, a hydroxy group, or a halogen substituent. Among these, R _{1 to} R ₃ are more preferably any of a divalent saturated hydrocarbon group having 2 to 12 carbon atoms, a cyclohexylene group which may have a substituent, and a phenylene group.
n is an integer of 2 or more, preferably an integer of 5 or more.

  The polymer containing the structural unit represented by the general formula (A) 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- 1,4-diol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, diethylene glycol and the like are preferable.

  The polymer containing the structural unit represented by formula (B) is obtained by dehydrating and condensing a carboxylic acid having a corresponding hydroxy group by a known method, or by using a cyclic ester of a carboxylic acid having a corresponding hydroxy group by a known method. Is obtained by ring-opening polymerization. Preferred 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 structure having the polyester structure may be a graft polymer type or a block polymer type. As a method for introducing a polyester structure into a polymer, as a graft polymer type; A method of copolymerizing a polyester having a polymerizable group at its terminal with another polymerizable monomer; A method in which a polymer having a functional group capable of reacting with a terminal functional group of polyester is reacted with polyester and introduced by a polymer reaction; A method in which a polyester structure is introduced by sequentially reacting a carboxylic acid having a hydroxy group or a cyclic ester compound from a polymer side chain, and the like is preferable. Further, as a block polymer type, (1) initiation capable of reacting with a terminal functional group of polyester A method of polymerizing a polymer having an agent terminal. (2) A method of introducing a polyester structure by sequentially reacting a carboxylic acid having a hydroxy group or a cyclic ester compound from the terminal of the polymer initiator is preferred, but it is not limited to these methods. In addition, the copolymer which has a polyester structure of this invention is a copolymer with the radically polymerizable monomer mentioned later other than a polyester structure.

The introduction rate of the polyester structure is preferably 1 to 99% by mass, more preferably 2 to 85% by mass, and still more preferably 5 to 70% by mass with respect to the total amount of the copolymer.
The preferred molecular weight (Mw) of the polyester structure portion is 100 to 100,000, more preferably 200 to 80,000, and still more preferably 500 to 70,000.

The polyester structure portion most preferably has a melting point (Tm), and the melting point (Tm) of the portion is preferably 20 ° C to 120 ° C.
Here, the melting point (Tm) means the peak temperature of the endothermic peak in DSC measurement. In the present invention, DSC TA3000 (manufactured by METTLER TOLEDO) was used as a measuring instrument, and the melting point (Tm) was measured in a temperature range of −90 ° C. to 150 ° C. at a heating rate of 10 ° C./min.

  The copolymer component other than the polyester structure can be obtained by radical polymerization of a radical polymerizable monomer by a known method. Although the radically polymerizable monomer is not particularly limited, preferred monomer components are; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate , T-butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, (meth) acrylic acid Hexadecyl, octadecyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 4- (meth) acrylic acid 4- Hydroxybutyl, glycidyl (meth) acrylate, (meth) acryl 2-dimethylaminoethyl acid, 2-diethylaminoethyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, o-aminosulfonylphenyl (meth) acrylate , M-aminosulfonylphenyl (meth) acrylate, p-aminosulfonylphenyl (meth) acrylate, etc. (substituted) (meth) acrylic acid ester; acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N -Ethylacrylamide, N-ethylmethacrylamide, N-hexylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethyl Acrylamide, N-hydroxyethyl acrylamide, N-phenyl acrylamide, N-phenyl methacrylamide, N-benzyl acrylamide, N-benzyl methacrylamide, N-nitrophenyl acrylamide, N-nitrophenyl methacrylamide, N-ethyl-N-phenyl Acrylamide and N-ethyl-N-phenylmethacrylamide, N- (o-aminosulfonylphenyl) (meth) acrylamide, N- (m-aminosulfonylphenyl) (meth) acrylamide, N- (p-aminosulfonylphenyl) ( Acrylamide or methacrylamide such as (meth) acrylamide; ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl Vinyl ethers such as ether, octyl 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 oxide group-containing monomers such as polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate; Ethylene monomers such as ethylene, propylene and butadiene; Styrene monomers such as styrene and 4-methylstyrene (Meth) acrylic acid, maleic acid anhydride, itaconic acid, or the like can be given monomers containing quaternary ammonium base.

  The copolymer having a polyester structure of the present invention preferably has a weight 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. More preferably, it is the range of 5000-200,000. The polydispersity (weight 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 copolymer having a polyester structure of the present invention are preferably 10 ⁶ Pa or more at a dynamic elastic modulus of 50 ° C., 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.

Next, the liquid crystalline polymer will be described.
Examples of the liquid crystalline polymer include those in which the entire polymer molecule has a liquid crystalline structure and those in which the main chain or side chain of the polymer chain has a liquid crystalline structure. Moreover, the copolymer containing the structural unit which has a liquid crystalline structure may be sufficient.
Examples of liquid crystalline polymers are described in Naoyuki Koide, “Liquid Crystal Polymer” (CMC Publishing) 1987, Takeshi Kamiya and Tetsuo Shimizu, “New Era of Liquid Crystal Polymer” (Industry Research Committee) 1991, etc. The thing that is.

  The liquid crystalline polymer of the present invention is particularly preferably one having a characteristic pattern when observed with a polarizing microscope or one having a phase transition temperature observable by DSC measurement. Particularly preferred liquid crystalline structures include those having a rigid rod-like or linear structure in which aromatic rings are connected. Moreover, it is preferable to have a liquid crystalline structure in a polymer molecule side chain.

The polymer having a liquid crystalline structure of the present invention preferably has the structure of the following general formula (I) in the polymer side chain.
-X-Ar-Y-Ar-Z (I)
In the formula, X represents a single bond or a divalent linking group to a polymer main chain skeleton, Ar represents a divalent aromatic hydrocarbon group which may have a substituent, and Y represents two adjacent groups. A divalent linking group for linking Ar is represented, and Z represents a substituent of the adjacent Ar group.
Examples of the divalent linking group represented by X include a divalent hydrocarbon group that may have a group containing one or more heteroatoms selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom. . Preferred structures include an ester structure, an amide structure, an ether structure, a thioether structure, and the like, and preferably have the following structure.

  Here, R represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may have a substituent, and n is an integer of 1 to 50.

Examples of the aromatic hydrocarbon group represented by Ar include, but are not limited to, a benzene ring which may have a substituent, and those in which 2 to 4 benzene rings form a condensed ring. In addition, a connection position is not specifically limited.
The divalent linking group represented by Y is a divalent hydrocarbon which may have a single bond or a group containing one or more heteroatoms selected from the group consisting of an oxygen atom, a nitrogen atom and a sulfur atom. Groups. More preferable structures include the following structures.

  Here, R represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may have a substituent.

  The substituent represented by Z is not particularly limited, but an alkyl group, an alkoxy group and a cyano group are particularly preferable.

  Specific examples of the structure represented by the general formula (I) are shown below, but are not limited thereto.

  The method for synthesizing the liquid crystalline polymer that can be used in the present invention is not particularly limited, but a method of polymerizing a radical polymerizable monomer having a functional group having a liquid crystalline structure or a structure having liquid crystallinity with a polymer side chain functional group. There is a method in which the functional group is bonded by a polymer reaction.

These liquid crystalline polymers may be homopolymers or copolymers with other components. The polymer structure is not particularly limited, and may be a graft polymer or a block polymer.
The monomer used as the copolymerization component is not particularly limited, and examples thereof include known polymerizable monomers. Examples thereof include the same radical polymerizable monomers that can be copolymerized with the above-described polyester structure.

The content of the monomer unit having a liquid crystalline structure in the liquid crystalline polymer is preferably 2% by mass or more, more preferably 10% by mass or more, and particularly preferably 20% by mass or more.
The weight average molecular weight Mw of the liquid crystalline polymer of the present invention is preferably in the range of 2,000 to 1,000,000 from the viewpoint of particle formability, and polydispersity (weight average molecular weight Mw / number average molecular weight Mn). Is preferably in the range of 1.0 to 5.0. More preferably, Mw is in the range of 5,000 to 200,000, and polydispersity (Mw / Mn) is in the range of 1.0 to 3.0. 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 in the range of 40 to 120 ° C. is preferable.

As the coating agent, in addition to the copolymer having the polyester structure and the liquid crystalline polymer, for example, rosins, rosin-modified phenol resin, alkyd resin, (meth) acrylic polymer, polyurethane, polyester, polyamide, polyethylene, polybutadiene, polystyrene, Examples thereof include polyvinyl acetate, a modified acetal of polyvinyl alcohol, and polycarbonate. Particularly preferred are (meth) acrylic polymers, styrene / (meth) acrylic polymers, and polyesters. Among these, from the viewpoint of ease of particle formation, a polymer having a weight average molecular weight Mw of 2,000 to 1,000,000, more preferably 5,000 to 100,000 is preferable, and polydispersity ( A polymer having Mw / Mn) in the range of 1.0 to 5.0, more preferably 1.0 to 3.0 is preferable. Further, from the viewpoint of ease of fixing, a polymer having any one of a softening point, a glass transition point, and a melting point within a range of 40 ° C. to 120 ° C. is preferable.
The content of the other polymer component is preferably in the range of 0 to 99% by mass in the coating agent, and more preferably 0 to 70% by mass.

  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.

[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: trade name of Exxon), Shellsol 70, Shellsol 71 (Shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 solvent (Amsco: Trade name of Spirits), KF-96L ( A trade name of Shin-Etsu Silicone Co., Ltd.) or the like can be used alone or in combination. The content of the dispersion medium with respect to the entire ink composition is preferably in the range of 20 to 99% by mass. In 20 mass% or more, the particle | grains containing a coloring material can be disperse | distributed to a dispersion medium favorably, and in 99 mass% or less, content of a coloring material can be satisfied.

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

  Examples of pigments for yellow ink include C.I. I. Pigment yellow 1, C.I. I. Monoazo pigments such as CI Pigment Yellow 74; I. Pigment yellow 12, C.I. I. Disazo pigments such as C.I. Pigment Yellow 17; I. Non-benzidine azo pigments such as CI Pigment Yellow 180; I. Azo lake pigments such as C.I. Pigment Yellow 100; I. Condensed azo pigments such as CI Pigment Yellow 95; I. Pigment Yellow 115 and other acid dye lake pigments, C.I. I. Pigment Yellow 18 and other basic dye lake pigments, Flavantron Yellow and other anthraquinone pigments, Isoindolinone Yellow 3RLT and other isoindolinone pigments, Quinophthalone Yellow and other quinophthalone pigments, Isoindoline Yellow and other isoindoline pigments, C.I. I. Nitroso pigments such as C.I. 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. Pigment Red 174, acidic dye lake pigments, C.I. 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 C.I. Pigment Red 122; I. Pigment Red 180 and other isoindolinone pigments, C.I. 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 and other 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, iron oxide pigments, and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black.
Furthermore, processed pigments typified by microlith pigments such as Microlith-A, -K, and -T can also be suitably used. Specific examples thereof include Microlith Yellow 4G-A, Micro Resled BP-K, Microlith Blue 4G-T, and Microlith Black CT.
Various pigments can be used as necessary, such as calcium carbonate and titanium oxide pigments for white ink, aluminum powder for silver ink, and copper alloy for gold ink.

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

[Dispersant]
In the present invention, for example, a mixture of a coloring material and a coating agent is dispersed (granulated) in a 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 weight average molecular weight is in the range of 1,000 to 1,000,000 and the polydispersity (weight average molecular weight / number average molecular weight). Is 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 is a polymer component composed of at least one of structural units represented by the following general formulas (1) and (2), and a structural unit represented by the following general formula (3). Is a graft polymer containing at least a polymer component containing at least 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 (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.

  A polymer component containing at least one of the structural units represented by the general formulas (1) and (2), and a polymerization component containing at least the structural unit represented by the general formula (3) as a graft chain. The graft polymer 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.

  The content of the dispersant with respect to the entire ink composition is preferably in the range of 0.01 to 30% by mass. Within this range, good particle formability can be obtained, and a desired particle diameter can be obtained.

[Charge control agent]
In the present invention, the mixture of the coloring material and the coating agent is preferably dispersed (particulated) in a dispersion medium using a dispersant, and a charge adjusting agent may be used in combination to control the charge amount of the particles. Further preferred.
Suitable 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. A polymer having a carboxylic acid group in the side chain, a polymer having a carboxylic acid anion group in the side chain such as a copolymer of stearyl methacrylate and tetramethylammonium methacrylate, a nitrogen atom in the side chain of a copolymer of styrene and vinylpyridine, etc. Yes That polymer, butyl and N- (2-methacryloyloxyethyl) methacrylate -N, N, polymers having an ammonium group in the side chain of the copolymer such as the N- trimethylammonium tosylate. The charge imparted to the particles may be positively charged or negatively charged. The content of the charge adjusting agent with respect to the entire ink composition is preferably in the range of 0.0001 to 10% by mass. The electrical conductivity of the ink composition of the present invention is preferably 10 nS / m to 300 nS / m, and the electrical conductivity of the charged particles is preferably 50% or more of the electrical conductivity of the ink composition. These conditions can be easily adjusted by increasing or decreasing the content of the charge control agent.

[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 Particle]
An ink composition containing the particles of the present invention can be prepared by dispersing (particulating) the coloring material and the coating agent using the above components. Examples of the method for dispersing (particulate) include the following methods.
(1) A colorant and a coating agent are mixed in advance, and then dispersed (granulated) using a dispersant and a dispersion medium, and a charge adjusting agent is added.
(2) Disperse (particulate) using a coloring material, a coating agent, a dispersant and a dispersion medium at the same time, and add a charge control agent.
(3) Disperse (particulate) using a colorant, a coating agent, a dispersant, a charge control agent and a dispersion medium 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 (the aforementioned Non-Patent Document 1).

  The volume average diameter of the particles in the present invention can be measured by centrifugal sedimentation using an apparatus such as an ultracentrifugal automatic particle size distribution analyzer CAPA-700 (manufactured by Horiba, Ltd.). The average diameter may be a volume average or a number average depending on the calculation method. In the present invention, the volume average diameter of the particles is in the range of 0.7 to 3.0 μm, more preferably 0.9 to 2.5 μm. It is. By setting the volume average diameter to 0.7 μm or more, the particles are sufficiently concentrated, and as a result, the ink is less likely to bleed when recorded on the recording medium. By setting the volume average diameter to 3.0 μm or less, clogging of the head discharge port is less likely to occur. The particle size distribution is preferably narrow and uniform.

  The viscosity (20 ° C.) of the ink composition of the present invention is preferably in the range of 0.5 to 5 mPa · s. Within this range, it is difficult to cause a problem that liquid drip from the ink discharge port of the head or ink droplets are not discharged. 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. If it is not within this range, it is difficult to cause a problem that liquid drip from the ink discharge port of the head or ink droplets are not discharged. 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 on a recording medium by an ink jet recording method. In the present invention, it is preferable to use an ink jet recording system using an electrostatic field. An ink jet recording method using an electrostatic field concentrates charged particles of an ink composition to an ejection position by an electrostatic force by applying a voltage between a control electrode and a back electrode on the back of a recording medium, and the recording medium from the ejection position It is a method to fly to. For example, when the charged particles are positive, the voltage applied between the control electrode and the back electrode is such that the control electrode is a positive electrode and the back electrode is a negative electrode. The same effect can be obtained by charging the recording medium instead of applying a voltage to the back electrode.

  As a method of flying ink, for example, there is a method of flying ink from a needle-like tip such as an injection needle, and recording can be performed using the ink composition of the present invention. However, it is difficult to replenish charged particles after the charged particles are concentrated and discharged, and it is difficult to perform stable long-term recording. When the ink is circulated in order to forcibly supply charged particles, the ink overflows from the tip of the injection needle, so the meniscus shape at the tip of the injection needle, which is the discharge position, is not stable, and stable recording is performed. It is difficult to do and is suitable for short-term recording.

  On the other hand, a method of circulating the ink composition without overflowing the ink composition from the ejection opening is preferably used. For example, ink is circulated in an ink chamber having an ejection opening, and a voltage is applied to a control electrode formed at the periphery of the ejection opening, so that it exists in the ejection opening and the leading end faces the recording medium side. In the method in which the concentrated ink droplets fly from the tip of the ink guide, the replenishment of charged particles by the circulation of the ink and the meniscus stability at the ejection position can be compatible, so that stable recording can be performed for a long time. it can. Further, in this method, since the portion where the ink is in contact with the outside air is very small with only the discharge opening, the evaporation of the solvent is suppressed and the ink physical properties are stabilized, so that it can be suitably used in the present invention.

A configuration example of an ink jet recording apparatus suitable for applying the ink composition of the present invention is shown below.
First, an outline of an apparatus that performs 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, and further the ink from the ejection head 2 A head driver 4 for driving the ejection head 2 by an output from an external device such as a computer (not shown) or a RIP, and a position control means 5. Further, the ink jet recording apparatus 1 includes a transport belt 7 stretched around three rollers 6A, 6B, and 6C, a transport belt position detection unit 8 including an optical sensor that can detect the position of the transport belt 7 in the width direction, An electrostatic 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 conveyance belt 7, the feed roller 12 and the guide 13 that supply the recording medium P from the stocker (not shown) to the conveyance belt 7, the ink is fixed to the recording medium P after peeling, and the paper discharge stocker (not shown). A fixing means 14 and a guide 15 for conveying the toner are disposed. 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 composed of 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 recording medium transported 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 is formed is neutralized by the neutralizing unit 10, peeled off by the conveying unit 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 in the vicinity of an opening and discharge is performed. 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 preferably used in 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 constitutes 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. Furthermore, 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. Accordingly, 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 side 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 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 continuous with and integrated with the ink jet recording apparatus. The temperature of the recording medium at the time of fixing is preferably in the range of 40 ° C. to 200 ° C. for ease of fixing. The fixing time is preferably in the range of 1 microsecond to 20 seconds.

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

[Recording medium]
In the present invention, various recording media can be used depending on the application. For example, if paper, plastic film, metal, and paper on which plastic or metal is laminated or vapor-deposited, plastic film on which metal is laminated or vapor-deposited, etc., printed matter can be obtained directly by ink jet recording. Moreover, an offset printing plate can be obtained if the support body etc. which roughened metals, such as aluminum, are used.
Furthermore, if a plastic support is used, a flexographic printing plate or a color filter for a liquid crystal screen can be obtained. The shape of the recording medium may be planar such as a sheet shape or three-dimensional such as a cylindrical shape. Further, if a silicon wafer or a wiring board is used as a recording medium, it can be applied to manufacture of a semiconductor or a printed wiring board.

  By combining the ink composition, the ink jet recording apparatus, and the replenishment of the ink composition described above, it is possible to stably obtain a high-quality image recorded matter with no ink bleeding and high image density over a long period of time. Can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

Synthesis Example [Synthesis of Coating Agent (AP-1)]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 55 g (0.549 mol) of methyl methacrylate, Plaxel FM5 (Mw: 700, Tm: 21 ° C.) [manufactured by Daicel Chemical Industries, Ltd.] 40 g (0.057 mol), monomer (M-1) 5 g (0.0146 mol), dimethyl 2,2′-azobis (2-methylpropionate) (manufactured by Wako Pure Chemical Industries, Ltd., V-601) 2 A mixed solvent of .858 g (12.41 mmol) and MFG 186.4 g was added dropwise at 80 ° C. over 2.5 hours under a nitrogen atmosphere, and after 2.5 hours of reaction, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 91 g of polymer (AP-1). The weight average molecular weight was 47,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 2.5.

[Coating agent (AP-2)]
(Synthesis of polyester)
Sebacic acid 141.6 g (0.7 mol), 1,10-decanediol 122.0 g (0.7 mol), p-toluenesulfonic acid monohydrate 1.33 g (7.0 mmol), xylene 322 g (45% by mass) In a three-necked flask, dehydrated and condensed at 180-190 ° C. for 4 hours, reprecipitated with methanol, and vacuum-dried to obtain 230.5 g of polyester (P-1) having a weight average molecular weight Mw of 32,000 and Tm of 80 ° C. Obtained.

(Synthesis of main chain polymer)
To a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 70 g (0.699 mol) of methyl methacrylate, 30 g (0.211 mol) of glycidyl methacrylate, dimethyl 2,2′-azobis (2-methylpro) (Pionate) (Wako Pure Chemical Industries, Ltd., V-601) 4.19 g (18.2 mmol) and MFG 186.4 g mixed solvent was added dropwise at 80 ° C. over 2.5 hours under a nitrogen atmosphere. After reacting for 2.5 hours, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 93 g of a main chain polymer (P-2). The weight average molecular weight was 33,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 1.9.
50 g of the synthesized main chain polymer (P-2), 33.3 g of polyester (P-1), and 83.3 g of THF are placed in an eggplant flask, reacted for 10 hours under reflux conditions, re-precipitated with water, and vacuum dried. A polymer (AP-2) having polyester (P-1) in the side chain was obtained. The weight average molecular weight was 97,000.

[Coating agent (AP-3)]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 70 g (0.699 mol) of methyl methacrylate, 20 g (0.154 mol) of hydroxy methacrylate, 10 g (0.0295 mol) of stearyl methacrylate, dimethyl 2, A mixed solvent of 2'-azobis (2-methylpropionate) (manufactured by Wako Pure Chemical Industries, Ltd., V-601) 4.06 g (17.65 mmol) and MFG 186.4 g was mixed at 80 ° C. under a nitrogen atmosphere at 80 ° C. The mixture was added dropwise over 5 hours, and after further reaction for 2.5 hours, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 94.3 g of a main chain polymer (P-3). The weight average molecular weight was 32,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 1.67.
The main chain polymer (P-3) /ε-caprolactone=1/1.75 (mass ratio), a total of 100 g, dimethylacetamide and dibutyltin dilaurate were mixed, heated and stirred at 160 ° C. for 8 hours, and reprecipitated with water. A coating agent (AP-3) was obtained. The weight average molecular weight was 45,000.

[Synthesis of Coating Agent (AP-4)]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 75 g (0.749 mol) of methyl methacrylate, 25 g (0.0738 mol) of stearyl methacrylate, 4,4′-azobis (4-cyanovaleric) Acid) (manufactured by Wako Pure Chemical Industries, Ltd., V-501) 9.47 g (41.14 mmol) and MFG 186.4 g in a nitrogen atmosphere were added dropwise at 80 ° C. over 2.5 hours, and 2 After reaction for 5 hours, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 91 g of a polymer (P-4) having a terminal carboxylic acid group. The weight average molecular weight was 15,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 2.4.
Polyester (P-1) (Mw: 32000, Tm: 80 ° C.) synthesized with 30 g of a terminal carboxylic acid group-containing polymer (P-4) and the above coating agent (AP-2) in THF, 1,3-dicyclohexyl Carbodiimide (0.413 g) and a catalytic amount of N, N-dimethylaminopyridine are added, and a condensation reaction is performed at 40 ° C. After filtration through Celite, water was reprecipitated to obtain a coating agent (AP-4). The weight average molecular weight was 50,000.

[Synthesis of Coating Agent (AP-5)]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 75 g (0.657 mol) of ethyl methacrylate, Plaxel FM5 (Mw: 700, Tm: 21 ° C.) [manufactured by Daicel Chemical Industries, Ltd. ] 20 g (0.0285 mol), monomer (M-1) 5 g (0.0146 mol), dimethyl-2,2′-azobis (2-methylpropionate) (manufactured by Wako Pure Chemical Industries, Ltd., V-601) ) A mixed solvent of 3.22 g (14.02 mmol), MFG184.4 g, and 2 g of water was added dropwise at 80 ° C. over 2.5 hours under a nitrogen atmosphere, and the reaction was further continued for 2.5 hours, followed by raising the temperature to 90 ° C. Reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 88 g of polymer (AP-5). The weight average molecular weight was 36,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 2.1.

Synthesis of coating polymer [Synthesis of coating AP-6]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), ethyl methacrylate 60 g (0.526 mol), 35 g (0.0916 mol) of the following liquid crystal group-containing monomer (M-1), monomer (M -2) 5 g (0.0146 mol), dimethyl 2,2′-azobis (2-methylpropionate) (V-601, manufactured by Wako Pure Chemical Industries, Ltd.) 0.985 g (4.28 mmol), MFG 186.4 g The mixed solvent was added dropwise at 80 ° C. over 2.5 hours under a nitrogen atmosphere, and after further reaction for 2.5 hours, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 91 g of a polymer (AP-6) having the following structure. The weight average molecular weight Mw was 57,000, and the polydispersity (Mw / Mn) was 3.2.

[Synthesis of Coating Agent (AP-7)]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 60 g (0.599 mol) of methyl methacrylate, 35 g (0.083 mol) of the following liquid crystalline group-containing monomer (M-3), monomer (M -2) 5 g (0.0146 mol), dimethyl 2,2′-azobis (2-methylpropionate) (V-601, manufactured by Wako Pure Chemical Industries, Ltd.) 0.802 g (3.48 mmol), MFG 186.4 g The mixed solvent was added dropwise at 80 ° C. over 2.5 hours under a nitrogen atmosphere. After further reaction for 2.5 hours, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 94 g of a polymer (AP-7) having the following structure. The weight average molecular weight Mw was 44,000, and the polydispersity (Mw / Mn) was 2.2.

[Synthesis of Coating Agent (AP-8)]
In a 500 ml three-necked flask containing 46.6 g of 1-methoxy-2-propanol (MFG), 30 g (0.300 mol) of methyl methacrylate, 10 g (0.0295 mol) of stearyl methacrylate, Plaxel FM5 (Mw700) [Daicel Chemical Industries, Ltd. Product] 20 g, monomer (M-3) 30 g (0.071 mol), dimethyl-2,2′-azobis (2-methylpropionate) (manufactured by Wako Pure Chemical Industries, Ltd., V-601) 2.04 g (14.02 mmol) and 186.4 g of MFG were added dropwise at 80 ° C. over 2.5 hours under a nitrogen atmosphere, and after further reaction for 2.5 hours, the temperature was raised to 90 ° C. and reacted for 2 hours. This reaction solution was reprecipitated with water and vacuum dried to obtain 90 g of polymer (AP-8). The weight average molecular weight was 42,000, and the polydispersity (weight average molecular weight / number average molecular weight) was 2.8.

[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 [Coating agent AP-1, see Synthesis Example 1 above]
・ Dispersant [BZ-2]
-Charge control agent [CT-1]
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

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

Dispersant [BZ-2] is a polymer of stearyl methacrylate having a methacryloyl group at its terminal (weight average molecular weight) by radical polymerization of stearyl methacrylate in the presence of 2-mercaptoethanol and further reacting with methacrylic anhydride. Was obtained by radical polymerization with styrene. The weight average molecular weight was 110,000.
The charge control agent [CT-1] was obtained by reacting 1-octadecene and maleic anhydride copolymer with 1-hexadecylamine. The weight average molecular weight was 17,000.

<Preparation of ink composition (EC-1)>
Cyan pigment (10 g) and coating agent [AP-1] (20 g) were placed in a table type kneader PBV-0.1 manufactured by Irie Shokai Co., Ltd., the heater temperature was set to 100 ° C., and the mixture was heated and mixed for 2 hours. 30 g of the obtained mixture was coarsely pulverized with a trio-brender manufactured by Trio Science Co., Ltd., and further finely pulverized with a SKM-10 sample mill manufactured by Kyoritsu Riko Co., Ltd. 30 g of the obtained finely pulverized product was predispersed in a paint shaker manufactured by Toyo Seiki Seisakusho together with 7.5 g of the dispersant [BZ-2], 75 g of Isopar G, and glass beads having a diameter of about 3.0 mm. After removing the glass beads, together with the zirconia ceramic beads having a diameter of about 0.6 mm, the type KDL dynomill manufactured by Shinmaru Enterprises Co., Ltd. was used for 5 hours while maintaining the internal temperature at 25 ° C., followed by 45 ° C. for 5 hours. Dispersion (particle formation) was performed at a rotational speed of 000 rpm. Zirconia ceramic beads were removed from the obtained dispersion, and 316 g of Isopar G and 0.6 g of charge control agent [CT-1] were added to obtain an ink composition [EC-1].

<Inkjet recording>
The ink composition [EC-1] of Example 1 was filled in the ink tank in the ink jet recording apparatus shown in FIGS. Here, a 150 dpi (three-row staggered arrangement with a channel density of 50 dpi) and 833 channel head of the type shown in FIG. 2 was used as the ejection head, and a silicon rubber heat roller incorporating a 1 kW heater was used as the fixing means. As the ink temperature control means, a throw-in heater and a stirring blade were provided in the ink tank, the ink temperature was set to 30 ° C., and the temperature was controlled with a thermostat while rotating the stirring blade at 30 rpm. Here, the stirring blade was also used as a stirring means for preventing precipitation and aggregation. In addition, the ink flow path is partially transparent, and the LED light emitting element and the light detecting element are arranged between them, and the ink dilution liquid (Isopar G) or concentrated ink (the solid content concentration of the ink composition is determined by the output signal). The concentration was controlled by charging. A fine coated paper for offset printing was used as a recording medium. After removing dust on the surface of the recording medium by air pump suction, the ejection head is brought close to the recording medium to the image forming position, image data to be recorded is transmitted to the image data calculation control unit, and the recording belt is rotated by rotation of the conveying belt. The ink composition was discharged while sequentially moving the discharge head while transporting the recording medium, and an image was formed with a drawing resolution of 2400 dpi. As the conveyor belt, a metal belt and polyimide film bonded together are used, and a line-shaped marker is placed in the vicinity of one end of the belt along the conveyor direction, and this is optically read by the conveyor belt position detection means. An image was formed by driving the control means.
At this time, the distance between the ejection head and the recording medium was kept at 0.5 mm by the output from the optical gap detector. Further, the surface potential of the recording medium was set to −1.5 kV at the time of ejection, and a pulse voltage of +500 V was applied (pulse width 50 μsec) at the time of ejection, and image formation was performed at a driving frequency of 15 kHz.
The obtained gray scale image recorded matter (printed matter) was a very clear image without streak unevenness and ink bleeding. 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.

<Fixing evaluation>
Immediately after image recording, the image is fixed using a heat roller, the temperature of the coated paper at the time of fixing is changed in increments of 5 ° C. from 60 to 100 ° C., the temperature at which the coating material flows (flow start temperature) and heat An upper limit temperature at which no offset to the roller occurs (upper limit offset temperature) was used as an evaluation criterion for fixability.
That is, it is desirable for the ink to have a flow start temperature that is achieved at a low temperature and that does not generate an offset up to a high temperature. Here, “flow” refers to a state in which the coating agent is melted and fluidized and then formed into a film.
The results are shown in Table 1.

Flow start temperature: Visual evaluation was performed by observing an SEM photograph of the image surface after fixing.
Upper limit anti-offset temperature: The occurrence of offset to the heat roller was re-transferred from the heat roller to the paper and visually evaluated on the paper.

Regarding the blocking property of the printed image, the same paper as the printing paper was layered on the fixed image at a temperature sufficiently satisfying the fixing property, a mass of about 50 g / cm ² was applied, and the sheet was left at 50 ° C. for 24 hours, and stacked. The degree of transfer of the image area onto the paper was visually evaluated.
Even when the solvent remained on the recording medium (coated paper), the flow start temperature and the upper limit offset temperature were measured in the same manner as described above, and the fixability was evaluated.

<Measurement of dynamic elastic modulus>
Set 3 g of finely pulverized sample in the sample chamber of the rheometer “Rheosol-G1000” manufactured by UBM, and melt it at 200 ° C. according to a predetermined measurement method. While the rotor was vibrated at a frequency of 1 Hz, a “temperature-dynamic elastic modulus curve” was automatically recorded, and the dynamic elastic modulus at 100 ° C. and 50 ° C. was read.
Further, it was confirmed that the “temperature-dynamic elastic modulus curve” has two inflection points in a temperature range of at least 40 to 100 ° C.

[Examples 2 to 5]
Except that the coating material [AP-1] was changed to [AP-2] to [AP-5] as the material used, the ink [EC-2] was used in the same manner as in Example 1 in the same manner. To [EC-5] were prepared, and inkjet drawing and fixing evaluation were performed.

[Example 6]
Example 1 except that instead of 20 g of the coating agent [AP-1] of Example 1, the material used was changed to 18 g of [AP-1] and 2 g of biphenyl (manufactured by Wako Pure Chemical Industries, Ltd., Tm 70 ° C.). Ink [EC-6] was prepared by the same method using the same material as above, and ink jet drawing and fixing evaluation were performed.

[Example 7]
The same material as in Example 1 except that instead of the coating polymer [AP-1] in Example 1, 18 g of [AP-5] and 2 g of Byron 220 (manufactured by Toyobo, Tm 80 ° C.) were used. Then, an ink [EC-7] was prepared in the same manner, and inkjet drawing and fixing evaluation were performed.

Example 8
<Materials used>
In Example 8, 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 [Coating polymer AP-6, see below]
・ Dispersant [BZ-2]
-Charge control agent [CT-1]
・ Dispersion medium Isopar G (manufactured by Exxon Corporation)

[Examples 8 to 10]
The ink [EC-8] is used in the same manner as in Example 1 except that the coating material [AP-1] is changed to [AP-6] to [AP-8] as the material used. [EC-10] was prepared, and inkjet drawing and fixing evaluation were performed.

[Comparative Example 1]
Ink composition [RC-1] was prepared in the same manner as in Example 1 except that the coating agent [AP-1] in Example 1 was changed to a comparative polymer polymethyl methacrylate (Mw15000) [manufactured by Aldrich] [BP-1]. Were prepared, and inkjet drawing and fixing evaluation were performed.

[Comparative Example 2]
Ink composition was the same as in Example 1 except that the coating agent [AP-1] in Example 1 was changed to the comparative copolymer benzyl methacrylate / methyl methacrylate (molar ratio 75/25, manufactured by Aldrich) [BP-2]. An object [RC-2] was prepared, ink jet drawing, and fixing evaluation were performed.

[Comparative Example 1]
Ink composition [RC-3] was prepared in the same manner as in Example 1 except that the coating agent [AP-1] in Example 1 was changed to a comparative polymer polymethyl methacrylate (Mw15000) [manufactured by Aldrich] [P-1]. Were prepared, and inkjet drawing and fixing evaluation were performed.

  Table 1 shows the evaluation results of Examples 1 to 10 and Comparative Examples 1 to 3.

(Fixability evaluation)
○: Flow start temperature 70 ° C. or lower and offset resistant upper limit temperature 80 ° C. or higher Δ: Flow start temperature 75 ° C. or higher and lower than 80 ° C., offset resistant upper limit temperature 80 ° C. or higher ×: Flow start temperature 80 ° C. or higher, or offset resistant upper limit Temperature less than 80 ° C (Evaluation of blocking resistance)
○: No transcript △: There are some transcripts ×: There are many transcripts

  As is apparent from Table 1, the present invention using a polymer having a specific structure as a coating material can be sharp-melted, and also has blocking resistance and offset resistance compared to a comparative example using a comparative polymer. It is good.

It is a whole lineblock diagram showing typically an example of an ink jet printer used for the present invention. It is a perspective view which shows the structure of the inkjet head of the inkjet recording device of this invention (In order to make it intelligible, the edge of the guard electrode in each discharge part is not drawn). FIG. 3 is a side sectional view showing a distribution state of charged particles when the number of ejection units of the inkjet head shown in FIG. 2 is large (corresponding to an arrow XX in FIG. 2).

Explanation of symbols

G Injected ink droplet P Recording medium Q Ink flow R Charged particle 1 Inkjet recording device 2, 2Y, 2M, 2C, 2K Discharge head 3 Ink circulation system 4 Head driver 5 Position control means 6A, 6B, 6C Conveying belt stretch Roller 7 Conveying belt 8 Conveying belt position detecting means 9 Electrostatic adsorption means 10 Static eliminating means 11 Mechanical means 12 Feed roller 13 Guide 14 Image fixing means 15 Guide 16 Recording medium position detecting means 17 Discharge fan 18 Solvent vapor adsorbing material 38 Ink guide 40 support rod portion 42 ink meniscus 44 insulating layer 46 first discharge electrode 48 insulating layer 50 guard electrode 52 insulating layer 56 second discharge electrode 58 insulating layer 62 floating conductive plate 64 coating film 66 insulating member 70 inkjet head 72 ink flow path 74 Substrate 75, 75A, 75B Opening 76, 76A, 76B Discharge Part 78 Discharge part

Claims (6)

In an ink composition containing a dispersion medium and charged particles containing at least a coloring material, the charged particles contain at least one of a copolymer having a polyester structure and a polymer having a liquid crystal structure ,
An ink composition, wherein the polymer having a liquid crystalline structure has a structure of the following general formula (I) in a polymer side chain .
-X-Ar-Y-Ar-Z (I)
Where
X represents a single bond or a divalent linking group with a polymer main chain skeleton, and the divalent linking group has an ester structure, an amide structure, an ether structure, a thioether structure, or a structure thereof and any of the following structures: Is a group formed by combining

Here, R represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, and n is an integer of 1 to 50.
Ar represents a divalent aromatic hydrocarbon group which may be substituted with a methyl group.
Y is a single bond or one of the following structures.

Here, R represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms.
Z is a hydrogen atom, an alkyl group, an alkoxy group, a methoxycarbonyl group, or a cyano group.   2. The ink composition according to claim 1, wherein X in the general formula (I) is a group represented by any of the following.

  The dispersion medium has a relative dielectric constant of 5 or less, 10 ^Ten 3. The ink composition according to claim 1, wherein the ink composition is a dielectric liquid having an electrical resistivity of Ωcm or more, and the content of the dispersion medium in the entire ink composition is 20 to 99% by mass. object.   The charged particle has a copolymer having a polyester structure, and the copolymer having the polyester structure has a structural unit represented by the following general formula (A) or (B). The ink composition according to any one of the above.

  In general formulas (A) and (B),
  R ₁ ~ R _Three Each independently represents a divalent hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group may have an ether bond, an amino group, a hydroxy group, or a halogen substituent.
  n is an integer of 2 or more.   The ink composition according to claim 4, wherein the copolymer having a polyester structure has a melting point (Tm) of 20 ° C. to 120 ° C. 6. 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 to be used is the ink composition according to any one of claims 1 to 5. An inkjet recording method characterized by the above.

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