JP2005060567A - Method for producing inkjet ink composition and inkjet ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an inkjet ink composition especially enabling a high-density dot hardly causing bleeding to be printed stably at a high speed. <P>SOLUTION: The method for producing the ink composition for an inkjet recording device, at least containing a nonaqueous solvent, a coloring matter covered with a resin insoluble in the nonaqueous solvent, and a dispersant comprises using 5-50 pts. mass of the dispersant based on 100 pts. mass of the coloring matter covered with the resin insoluble in the nonaqueous solvent, and subjecting the coloring matter covered with the resin insoluble in the nonaqueous solvent to a dispersion treatment in the nonaqueous solvent together with the dispersant within a temperature range of 10-50°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an ink-jet ink composition that ejects ink and forms characters and images on a transfer medium such as recording paper, and an ink-jet ink composition. The present invention relates to a method for producing an ink-jet ink composition capable of stably printing at high speed, and an ink-jet ink composition.

  The ink jet recording method that performs printing by flying ink onto a recording medium to form recording dots is attracting interest as a non-impact recording method that can be easily colored and recorded directly on plain paper. Printers using this method Have been put to practical use. Inkjet recording methods include, for example, Takeshi Aoiin “Real Color Hard Copy” Sangyo Tosho Co., Ltd. (1993), Shin Ohno “Non-impact Printing—Technology and Materials”, CMC (1986), Takeshi Amari. It is described in a book such as “inkjet printer technology and material” CMC Co., Ltd. (1998), and there are on-demand (optional injection) and continuous (continuous injection) systems. Further, a recording method called an electrostatic method (Sweet type, Hertz type) is known for the continuous type, and a piezo piezoelectric method, a shear mode piezo piezoelectric method, or a thermal ink jet method is known for the on-demand type. As one of the on-demand inkjet recording methods, Susumu Ichinose, Yuji Ohba, IEICE Transactions Vol.J66-C (No.1), p.47 (1983), Tadayoshi Ohno, Mamoru Mizuguchi, The Institute of Image Electronics Engineers of Japan There is known a system called electrostatic acceleration type ink jet or slit jet described in magazines Vol. 10, (No. 3), p. 157 (1981). In this method, a voltage is applied to a plurality of recording electrodes arranged opposite to the recording medium and a counter electrode arranged on the back surface of the recording medium, and is supplied onto the recording electrodes due to a potential difference generated between both electrodes. A specific mode is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 56-170, 56-4467, and 57-151374. Has been. In this method, instead of the nozzles in the conventional inkjet head, an elongated slit-like ink discharge port having a large number of recording electrodes on the inner wall is used, and ink is supplied to the slit-like ink chamber, and these electrodes are selected. In particular, by applying a high voltage, recording is performed by ejecting ink in the vicinity of the electrode onto a recording sheet that is in close proximity to the slit.

  For this reason, there is less concern about ink clogging, and a simple construction of the head can be expected to reduce the manufacturing cost, and a so-called long line head having a length that can cover a wide range in the width direction of the recording medium. This is also an effective way to achieve this.

  An example of a drop-on-demand type full-color recording head constituted by the electrostatic acceleration type ink jet method is disclosed in, for example, Japanese Patent Publication No. 60-59569, Journal of the Institute of Electrical Communication, Vol. J68-C, 2 (1985), pages 93 to 100.

In this electrostatic acceleration type inkjet head, an oil-based ink in which a dye is dissolved in an organic solvent is preferably used, and the constituent material of the ink is not disclosed in detail, but in the example shown in Non-Patent Document 6 below, An ink having a physical property value of 10 ⁷ to 10 ⁸ Ω · cm, a surface tension of 22 mN / m, and a viscosity of 3.1 to 6.9 cP is used.

  However, such oil-based ink has a surface tension lower than that of water-based ink generally used in other in-jet methods, and therefore has a very high permeability to recording paper. In particular, printing is performed on plain paper. In some cases, the print density tends to decrease, blur, or show through.

  A coloring material concentration discharge type electrostatic system that does not use a slit-shaped recording head is disclosed in Japanese Patent Application Laid-Open No. 9-193389 and Japanese Patent Application Laid-Open No. 10-138493. This is a control comprising a plurality of individual electrodes for applying an electrostatic force to a colorant component in ink, and an insulating substrate having a through hole and a control electrode formed corresponding to the through hole. It consists of an electrode substrate and a convex ink guide arranged almost at the center of this through hole. The surface of this convex ink guide is transported to the ink droplet flying position by surface tension, and a predetermined voltage is applied to the control electrode. Is applied to cause ink droplets to fly on the recording medium for recording.

  In this color material concentration discharge type electrostatic ink jet system, color material particles are concentrated on the discharge port portion by electrophoresis, and ink droplets are ejected in a form in which the color material particles are concentrated to a high concentration. For this reason, unlike the above-described method, the ink components are not discharged while containing a large amount of liquid components in a uniform state, but are discharged in a state where the color material particles are aggregated and the liquid components are small. This solves the above-mentioned problems. Further, by using a pigment as a coloring material, advantageous results can be obtained in terms of water resistance and light resistance of a printed image as compared with an ink jet head using a conventional dye.

  In such a color material concentration discharge type electrostatic inkjet ink, first, in order to obtain good print characteristics with high print density and no blurring or show-through, the volume resistivity of the ink is sufficiently high. It is necessary. As a result, the electric field formed by the recording electrode and the counter electrode and applied to the ink can reach the colorant particles. Also, if the volume resistivity of the ink is low, the ink is charged and charged by the voltage applied by the recording electrode, and the ink is discharged while containing a large amount of liquid component due to electrostatic repulsion. The tendency becomes stronger. Next, since it is necessary to concentrate the color material particles at the discharge port portion by electrophoresis at a sufficient speed, the color material particles have a sufficient charge amount, that is, the color material particles are positive or negative. It is necessary to have a high particle conductivity.

  In recent years, as the demand for higher speed printers and higher image quality has increased, even in the above-described ink jet heads with concentrated color material discharge, a small amount of ink droplets with high color material concentration can be stably maintained for a long time. There is a need for a technique for printing a higher-definition image at a high speed by discharging the ink at a high speed.

It has been confirmed that such printing performance largely depends on the physical property value of the ink. In order to obtain sufficient printing performance, as described above, when preparing the ink, preferably 10 ⁸ Ω · cm. While maintaining a high volume resistivity as described above, it is necessary to impart a high particle conductivity of 100 pS / cm or more to the colorant particles. If the particle conductivity of the color material particles is less than 100 pS / cm, the color material particles cannot be moved at high speed to the discharge port, that is, the discharge electrode tip by electrophoresis, and the supply of the color material particles becomes insufficient. The cohesiveness of the color material particles is deteriorated and the discharge response frequency is lowered.

  Furthermore, since the electric repulsive force between the surface of the discharge electrode and the color material particles is weak, there may be a case where the color material particles adhere to and accumulate on the discharge electrode and stable discharge cannot be performed. For these reasons, there arise problems that a sufficient print density cannot be obtained and stable and high-speed printing cannot be performed.

The above-mentioned color material particles are preferably composed of a color material such as a pigment and a resin, and as a resin for coating the color material, in general, (1) a color material mixture is formed by sufficiently covering the pigment surface. It has adequate fluidity due to heat, etc., (2) it is well dispersed in the dispersion medium by coating the color material, (3) it is as transparent as possible, and (4) it is fixed to the recording medium by fixing. In addition to having characteristics such as giving sufficient scratch resistance, the electrostatic inkjet ink described above can impart (5) particle conductivity with high positive or negative polarity to the color material particles. It is desired. Color material particles coated with a color material with a resin can be formed by coating a color material with a resin to form a colored mixture, and then dispersing the colored mixture in a non-aqueous solvent. However, in the normal dispersion, coarse color material particles are generated, or fine color material particles of 0.2 μm or less are generated, and the average particle size is about 0.3 to 4 μm and the particle sizes are uniform. In fact, it is difficult to obtain a dispersion with a small amount of fine color material particles of 0.2 μm or less by dispersion.
Japanese Patent Laid-Open No. 9-193389 JP 10-138493 A

The first object of the present invention is to provide a method for producing an ink-jet ink composition capable of printing dots with high density and little bleeding at high speed because the colorant particles in the ink have a high positive specific conductivity. Is to provide.
The second object of the present invention is an ink jet ink composition which is excellent in dryness on a transfer medium such as recording paper, water resistance and light resistance of recorded images, and has high-speed fixing properties and scratch resistance. It is to provide a manufacturing method.
The third object of the present invention is to provide a method for producing an ink-jet ink composition capable of stably printing for a long period of time because the charge amount of the colorant particles can be stably maintained for a long period of time.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the problem is solved by the following configuration.
That is, the present invention is as follows.
(1) In a method for producing an ink composition for an ink jet recording apparatus comprising at least a non-aqueous solvent, a color material coated with a resin insoluble in the non-aqueous solvent, and a dispersant, the resin insoluble in the non-aqueous solvent 5 to 50 parts by mass of the dispersant is used with respect to 100 parts by mass of the color material coated with, and the color material coated with a resin insoluble in the non-aqueous solvent in the non-aqueous solvent together with the dispersant. A method for producing an inkjet ink composition, wherein the dispersion is dispersed in a temperature range of 10 to 50 ° C.
(2) The average particle diameter of the color material particles coated with a resin insoluble in the non-aqueous solvent is in the range of 0.3 to 4 μm, and the ratio of the color material particles of 0.2 μm or less is 5% on a volume basis. The method for producing an ink-jet ink composition as described in (1) above, wherein:

(3) In the method for producing an ink composition for an electrostatic inkjet recording apparatus, comprising at least a non-aqueous solvent, a color material coated with a resin insoluble in the non-aqueous solvent, a dispersant, and a charge control agent, The dispersant was used in an amount of 5 to 50 parts by mass with respect to 100 parts by mass of the color material coated with a resin insoluble in a non-aqueous solvent, and the non-aqueous solvent was coated with a resin insoluble in the non-aqueous solvent. A method for producing an electrostatic ink-jet ink composition, comprising: dispersing a colorant together with the dispersant in a temperature range of 10 to 50 ° C.
(4) The average particle diameter of the color material particles coated with a resin insoluble in the non-aqueous solvent is in the range of 0.3 to 4 μm, and the ratio of the color material particles of 0.2 μm or less is 5% on a volume basis. The method for producing an electrostatic ink-jet ink composition as described in (3) above, wherein:
(5) The volume resistivity at 25 ° C. of the ink composition is 10 ⁸ Ω · cm or more, and the particle conductivity in the ink composition is 100 pS / cm or more. A method for producing an electrostatic inkjet ink composition.
(6) The average particle diameter of the colorant particles containing at least a nonaqueous solvent, a colorant coated with a resin insoluble in the nonaqueous solvent and a dispersant, and coated with a resin insoluble in the nonaqueous solvent is An ink-jet ink composition, wherein the ratio of colorant particles in the range of 0.3 to 4 μm and not more than 0.2 μm is 5% or less on a volume basis.
(7) At least a non-aqueous solvent, a color material coated with a resin insoluble in the non-aqueous solvent, a dispersant and a charge control agent, and a color material particle coated with a resin insoluble in the non-aqueous solvent An electrostatic inkjet ink composition, wherein the average particle diameter is in the range of 0.3 to 4 μm, and the ratio of the colorant particles of 0.2 μm or less is 5% or less on a volume basis.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the inkjet ink composition which can print a dot with a high density | concentration and few bleeding at high speed is provided because the color material particle in ink has high positive polarity specific conductivity. The
Further, according to the present invention, an ink-jet ink composition having excellent dryability on a transfer medium such as recording paper, water resistance and light resistance of a recorded image, and having high-speed fixability and scratch resistance. A method is provided.
The present invention also provides a method for producing an ink-jet ink composition capable of stably printing for a long period of time because the charge amount of the colorant particles can be stably maintained for a long period of time.

The present invention is described in detail below.
The non-aqueous solvent used in the present invention is preferably a non-polar insulating solvent having a relative dielectric constant of 1.5 to 20 and a surface tension of 15 to 60 mN / m (at 25 ° C.), having low toxicity and flammability. It is good to have less odor and less odor. Examples of such non-aqueous solvents include solvents selected from linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, petroleum naphtha, halogen substitution products thereof, and the like. It is done. For example, hexane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, Isopar E from Exxon, Isopar G, Isopar H, Isopar L, Saltol from Philippe Petroleum, IP Solvent from Idemitsu Petrochemical, Petroleum Naphtha Then, S. of Shell Petrochemical Co., Ltd. B. R. A solvent selected from Shellzol 70, Shellzol 71, Mobil Petroleum Begazole, etc. is used alone or in combination.

Preferable hydrocarbon solvents include high-purity isoparaffinic hydrocarbons having a boiling point in the range of 150 to 350 ° C., and commercially available products such as Isopar G, H, L, M, and V (manufactured by Exxon Chemical Co., Ltd.) Name), Noper 12, 13, 15 (trade name), IP Solvent 1620, 2028 (trade name) manufactured by Idemitsu Petrochemical, Isosol 300,400 (trade name) manufactured by Nippon Petrochemical, Amsco OMS, Amsco 460 solvent ( Amsco; a brand name of Spirits). These products are highly saturated aliphatic saturated hydrocarbons, the viscosity at 25 ° C. is 3 cSt or less, the surface tension at 25 ° C. is 22.5 to 28.0 mN / m, and the specific resistance at 25 ° C. is 10 ¹⁰ Ω. -It is cm or more. In addition, it is characterized by low reactivity and stability, low toxicity, high safety, and low odor.
There are fluorocarbon solvents as halogen-substituted hydrocarbon solvents, for example, perfluoroalkanes represented by C _n F _{2n + 2} such as C ₇ F ₁₆ and C ₈ F ₁₈ (“Fluorinert PF5080” manufactured by Sumitomo 3M, "Fluorinert PF5070" (trade name), etc., fluorinated inert liquids (such as "Fluorinert FC series" (trade name) manufactured by Sumitomo 3M), fluorocarbons ("Crytox GPL series" manufactured by DuPont Japan Limited) (trade name) )), CFCs ("HCFC-141b" (trade name) manufactured by Daikin Industries, Ltd.), iodine such as [F (CF ₂ ) ₄ CH ₂ CH ₂ I], [F (CF ₂ ) ₆ I] Fluorocarbons ("I-1420", "I-1600" (trade name), etc., manufactured by Daikin Fine Chemical Laboratory), etc.).

As the non-aqueous solvent used in the present invention, higher fatty acid esters and silicone oil can also be used. Specific examples of silicone oil include low-viscosity synthetic dimethylpolysiloxane, and commercially available products include KF96L (trade name) manufactured by Shin-Etsu Silicone, SH200 (trade name) manufactured by Toray Dow Corning Silicone, and the like. .
The silicone oil is not limited to these specific examples. These dimethylpolysiloxanes are available in a very wide viscosity range depending on the molecular weight, but it is preferable to use those in the range of 1 to 20 cSt. These dimethylpolysiloxanes, like isoparaffinic hydrocarbons, have a volume resistivity of 10 ¹⁰ Ω · cm or more, and are characterized by high stability, high safety, and odorlessness. These dimethylpolysiloxanes are characterized by low surface tension and have a surface tension of 18 to 21 mN / m.

  Solvents that can be used in combination with these organic solvents include alcohols (eg, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, fluorinated alcohol), ketones (eg, acetone, methyl ethyl ketone, cyclohexanone, etc.), carvone Acid esters (eg, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, etc.), ethers (eg, diethyl ether, dipropyl ether, tetrahydrofuran, dioxane, etc.) and halogenated hydrocarbons ( Examples thereof include methylene dichloride, chloroform, carbon tetrachloride, dichloroethane, methyl chloroform, and the like.

Next, the color material used in the present invention will be described in detail.
The coloring material is not particularly limited, and all commercially available organic pigments and inorganic pigments, or those obtained by dispersing a pigment in a resin insoluble in a dispersion medium, or a resin on the pigment surface. A grafted product can be used. Moreover, what dye | stained the resin particle with dye can be used.
Specific examples of organic pigments and inorganic pigments include, for example, C.I. I. Pigment Yellow 1 (Fast Yellow G etc.), C.I. I. Monoazo pigments such as CI Pigment Yellow 74; I. Pigment Yellow 12 (disaji yellow AAA, etc.), C.I. I. Disazo pigments such as CI Pigment Yellow 17; I. Non-benzidine azo pigments such as CI Pigment Yellow 180; I. An azo lake pigment such as C.I. Pigment Yellow 100 (eg Tartrazine Yellow Lake); I. Condensed azo pigments such as CI Pigment Yellow 95 (Condensed Azo Yellow GR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Yellow 115 (such as quinoline yellow lake); I. Basic dye lake pigments such as CI Pigment Yellow 18 (Thioflavin Lake, etc.), anthraquinone pigments such as Flavantron Yellow (Y-24), isoindolinone pigments such as Isoindolinone Yellow 3RLT (Y-110), and quinophthalone yellow Quinophthalone pigments such as (Y-138), isoindoline pigments such as isoindoline yellow (Y-139), C.I. I. Nitroso pigments such as CI Pigment Yellow 153 (nickel nitroso yellow, etc.); I. And metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.).

  As a magenta color, C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as C.I. Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment Red 53: 1 (Lake Red C, etc.) and C.I. I. Azo lake pigments such as CI Pigment Red 57: 1 (Brilliant Carmine 6B); I. Condensed azo pigments such as CI Pigment Red 144 (condensed azo red BR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Red 174 (Phloxine B Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Red 81 (Rhodamine 6G 'lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Red 177 (eg, dianthraquinonyl red); I. Thioindigo pigments such as C.I. Pigment Red 88 (Thioindigo Bordeaux, etc.); I. Perinone pigments such as C.I. Pigment Red 194 (perinone red, etc.); I. Perylene pigments such as C.I. Pigment Red 149 (perylene scarlet, etc.); I. Quinacridone pigments such as C.I. Pigment Red 122 (quinacridone magenta, etc.); I. Isoindolinone pigments such as C.I. Pigment Red 180 (isoindolinone red 2BLT, etc.); I. And alizarin lake pigments such as CI Pigment Red 83 (Mada Lake, etc.).

  As a pigment exhibiting a cyan color, C.I. I. Disazo pigments such as C.I. Pigment Blue 25 (Dianisidine Blue, etc.); I. Phthalocyanine pigments such as C.I. Pigment Blue 15 (phthalocyanine blue, etc.); I. Acidic dye lake pigments such as C.I. Pigment Blue 24 (Peacock Blue Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Blue 1 (such as Viclotia Pure Blue BO Lake); I. Anthraquinone pigments such as C.I. Pigment Blue 60 (Indantron Blue, etc.); I. And alkali blue pigments such as CI Pigment Blue 18 (Alkali Blue V-5: 1).

  Examples of black pigments include organic pigments such as aniline black pigments such as BK-1 (aniline black), iron oxide pigments, and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. . Specific examples of the carbon black pigment include MA-8, MA-10, MA-11, MA-100, MA-220, # 25, # 40, # 260, # 2600, # 2700B, manufactured by Mitsubishi Chemical Corporation. # 3230B, CF-9, MA-100R, MA-200RB, Degussa Printex 75, 90, Cabot Monarch 800, 1100, and the like. Also, metal powder can be used for color reproduction of gold, silver, copper and the like.

  In addition, a processed pigment in which pigment fine particles are dispersed in a rosin ester resin, vinyl chloride-vinyl acetate resin, or the like is commercially available and may be used. Specific examples of commercially available processed pigments include microlith pigments manufactured by Ciba Specialty Chemicals, and preferred examples of processed pigments include Microlith-T pigments in which the pigment is coated with a rosin ester resin.

  In the present invention, the concentration of the coloring material (pigment) is preferably 0.5 to 20% by mass, particularly preferably 2 to 15% by mass, based on the total amount of the ink composition. A sufficient printing density can be obtained by setting the density of the color material to 0.5% by mass or more. Further, when the concentration of the color material is 20% by mass or less, stable ink ejection can be performed without significantly increasing the viscosity of the ink composition.

Next, the resin insoluble in the nonaqueous solvent will be described.
As the resin insoluble in the non-aqueous solvent, various known natural or synthetic resins can be used. For example, there are acrylic resin, epoxy resin, polyester resin, ethylene-vinyl acetate resin, vinyl chloride-vinyl acetate resin, styrene-butadiene resin, styrene-acrylic resin and the like. As a method for dispersing the pigments in these resins, various known methods such as those found in the production process of electrophotographic toner may be used.
In addition, colorant particles coated with a commercially available resin can be used, and specific examples include Microlith-T pigment in which the pigment is coated with the above-mentioned rosin ester resin.

  As a preferable resin, a resin having a function of adsorbing to a pigment and being well dispersed in a non-aqueous solvent, a part that is solvated in a solvent, a part that is difficult to solvate in a solvent, and a part that has a polar group Is preferred. For example, examples of the monomer that solvates with a solvent after polymerization include lauryl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate, and cetyl methacrylate. Examples of monomers that are difficult to solvate with the solvent after polymerization include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, styrene, and vinyl toluene. Monomers containing polar groups include acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, styrene sulfonic acid or alkali salts thereof, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, vinyl pyridine, vinyl Examples include basic group monomers such as pyrrolidine, vinylpiperidine, and vinyllactam.

  Color material particles (color material resin particles) coated with a pigment or the like with a resin insoluble in a non-aqueous solvent are coated with a binder resin to form a color mixture, and the color mixture is described below. It can be formed by dispersing in the form of fine particles in a non-aqueous solvent by the dispersion treatment step. First, a process of making a color mixture by coating a color material with a binder resin will be described. The colored mixture is prepared by the following method, for example.

(1) A pigment or the like (coloring material) and a binder resin are melt-kneaded at a temperature equal to or higher than the softening point of the binder resin using a kneader such as a roll mill, a Banbury mixer, or a kneader, and crushed after cooling to obtain a colored mixture. How to get.
(2) Dissolve the binder resin in a solvent, add a colorant, wet disperse with a ball mill, attritor, sand grinder, etc., evaporate the solvent to obtain a colored admixture, or disperse the dispersion of the binder resin. A method of pouring into a non-solvent and precipitating to obtain an admixture, followed by drying to obtain a colored admixture.
(3) A method in which a water-containing pigment paste (wet cake) is kneaded with a resin or a resin solvent by a flushing method, water is replaced with a resin or a resin solution, and then the water and the solvent are dried under reduced pressure to obtain a colored mixture.

  Next, a dispersion step in which the colored admixture described above is dry-ground and then wet-dispersed with a dispersant in a non-aqueous solvent, which is a feature of the present invention, will be described. In the dispersion step of the present invention, 5 to 50 parts by mass of a dispersant is used for 100 parts by mass of the color material coated with a resin insoluble in a non-aqueous solvent, and the resin is insoluble in the non-aqueous solvent in the non-aqueous solvent. The coated color material is dispersed together with the dispersant in a temperature range of 10 to 50 ° C.

  There is no restriction | limiting in particular as a disperser used at a dispersion | distribution process, A commercially available wet disperser can be used. For example, a ball mill, a sand mill, an attritor, etc., and a sealed type is generally used to prevent evaporation of the solvent. Sand mills have a vertical type and a horizontal type, and are dispersed by rotating a shaft on which a disk or a pin is attached at a peripheral speed of 3 to 15 m / s. By arranging several continuous sand mills in series and changing the diameter of the media according to the degree of dispersion, the ink composition can be efficiently produced. Further, when a pigment having a large particle size is dispersed by a continuous sand mill, pre-dispersion is required. In this case, a disperser, a ball mill, a batch sand mill, or the like is used as a pre-dispersing machine.

  Specific examples of horizontal sand mills include Dino Mill, Dino Mill ECM (WAB, Switzerland), Pearl Mill, DCP (Dreis, Germany), Agitator Mill (Necche, Germany), Super Mill (Susmeier, Belgium), Cobol Mill (Switzerland, Freema), spike mill (Inoue Seisakusho), and the like.

Various media such as zirconia, titania, alumina, glass, steel, silicon nitride can be used as media for ball mills and sand mills. In accordance with the viscosity of the dispersion, the degree of pre-dispersion, and the like, the material of the media is selected from the viewpoint of the specific gravity of the media, wear resistance, and the like.
The media diameter is not particularly limited, but for example, media having a diameter of about 0.1 mm to 10 mm can be used. In general, the larger the media, the wider the particle size distribution, and the smaller the media, the smaller the particle size tends to be dispersed. Also, the media filling rate is not particularly limited, but a media filling rate of 50% to 90% is preferable. There is a close relationship between the filling rate of media and the dispersion performance, and it is generally known that the dispersion efficiency can be improved if the filling rate can be increased. In the case of a horizontal mill, it is preferable to set the filling rate to 80 to 85% with respect to the vessel capacity because there is no media locking phenomenon at the start-up as compared with the vertical mill.

In the present invention, as described above, 5 to 50 parts by mass of the dispersant is used with respect to 100 parts by mass of the color material coated with the resin insoluble in the non-aqueous solvent, and insoluble in the non-aqueous solvent in the non-aqueous solvent. It is characterized in that the color material coated with a resin is dispersed together with a dispersant in a temperature range of 10 to 50 ° C. The method for controlling the liquid temperature of the dispersion is not particularly limited.For example, a jacket is provided around the disperser and cooled with a refrigerant such as cold water, or a heat exchanger is provided on the discharge side of the disperser, and the temperature of the dispersion is controlled. The liquid temperature of the dispersion liquid can be controlled by monitoring and controlling the temperature of the refrigerant according to the change of the dispersion liquid temperature.
As a method for controlling the dispersion temperature, the temperature of the refrigerant in the dispersion process may be set to be constant and adjusted to the target dispersion temperature, or the dispersion temperature may be increased several times to increase the target temperature. The dispersion temperature may be adjusted.

By using 5 parts by mass or more of the dispersant with respect to 100 parts by mass of the color material coated with a resin insoluble in a non-aqueous solvent, coarse particles are not generated and good dispersion stability is obtained. In addition, when the dispersant is 50 parts by mass or less, the proportion of fine color material particles of 0.2 μm or less can be reduced, and good ejection stability can be obtained.
Further, by setting the dispersion treatment temperature to 10 ° C. or higher, the ratio of minute color material particles of 0.2 μm or less can be reduced, and good ejection stability can be obtained. Further, by performing dispersion treatment at a dispersion temperature of 50 ° C. or less, coarse particles are not generated, and colorant particles having a target average particle diameter range can be obtained.
A more preferable use ratio of the dispersant is 5 to 40 parts by weight, particularly 5 to 30 parts by weight with respect to 100 parts by weight of the color material coated with a resin insoluble in a non-aqueous solvent, and a more preferable dispersion treatment temperature. Is 15 to 45 ° C., for example, 2 to 12 hours in residence time.

  The range of the average particle diameter of the formed color material particles is preferably 0.3 to 4 μm, more preferably 0.3 to 3 μm, and particularly preferably 0.4 to 2 μm. Further, the proportion of fine color material particles of 0.2 μm or less is preferably 5% or less, more preferably 4% or less, and particularly preferably 3% or less in terms of volume.

In the dispersion treatment step, a dispersant is used in order to disperse the color material particles in the form of fine particles and stabilize the dispersion in the non-aqueous solvent. As a method of using the dispersant, for example, the following method is available.
1. Add and disperse pigment composition premixed with color admixture and dispersant in non-aqueous solvent;
2. Add and disperse colored admixture and dispersant separately in non-aqueous solvent;
Any of these methods can achieve the intended effect.

As the dispersant used in the present invention, a general pigment dispersant applied in the non-aqueous solvent can be used.
For example, any dispersant may be used as long as it is compatible with the non-aqueous solvent and can stably disperse fine particles of a pigment or the like. Specific examples include sorbitan fatty acid esters (sorbitan monooleate, sorbitan monolaurate, sorbitan sesquioleate, sorbitan trioleate, etc.), polyoxyethylene sorbitan fatty acid esters (polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan). Monooleate, etc.), polyethylene glycol fatty acid esters (polyoxyethylene monostearate, polyethylene glycol diisostearate, etc.), polyoxyethylene alkyl phenyl ethers (polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, etc.), Nonionic surfactants such as aliphatic diethanolamides and polymer dispersants include polymer compounds having a molecular weight of 1000 or more. For example, styrene-maleic acid resin, styrene-acrylic resin, rosin, BYK-160, 162, 164, 182 (urethane polymer compound manufactured by Big Chemie), EFKA-47, LP-4050 (manufactured by EFKA) Urethane dispersant), Solsperse 24000 (polyester polymer compound manufactured by Zeneca), Solsperse 17000 (aliphatic diethanolamide from Zeneca), and the like.

  In addition to the above, the polymeric dispersants include monomers such as lauryl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate, and cetyl methacrylate that are solvated in a solvent, and methyl methacrylate, ethyl methacrylate, and isopropyl methacrylate that are difficult to solvate in a solvent. , A random copolymer comprising a monomer having a polar group and a monomer such as styrene and vinyltoluene, or a graft copolymer disclosed in JP-A-3-188469. Examples of the monomer containing a polar group include an acidic group monomer such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, styrene sulfonic acid or an alkali salt thereof, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and vinylpyridine. And basic group monomers such as vinylpyrrolidine, vinylpiperidine, and vinyllactam. In addition to this, a styrene-butadiene copolymer, a block copolymer of styrene and a long-chain alkyl methacrylate disclosed in JP-A-60-10263, and disclosed in JP-A-6-95436. Examples thereof include block copolymers. Further, it is soluble in the graft copolymer disclosed in JP-A-4-350669 and JP-A-5-188657, and in the non-aqueous solvent containing a graft group disclosed in JP-A-11-43638. Random copolymers, partially crosslinked polymers disclosed in JP-A-10-316920, partially crosslinked polymers containing graft groups at the main chain ends disclosed in JP-A-10-316920, etc. As an agent. Preferred examples of the dispersant for pigment include graft copolymers disclosed in JP-A-3-188469, JP-A-4-350669, and JP-A-5-188657. However, the pigment dispersant is not limited to these.

  As for the usage-amount of the dispersing agent used at a dispersion treatment process, 5-50 mass parts is preferable with respect to 100 mass parts of colored admixtures. A more preferable amount of the dispersant used is 5 to 40 parts by mass, and a particularly preferable amount is 5 to 30 parts by mass with respect to 100 parts by mass of the colored mixture. When the added amount of the dispersant is 5 parts by mass or more, the pigment dispersion effect is exhibited, and when the amount is 50 parts by mass or less, the effect of reducing the proportion of fine particles is obtained.

    Next, as a charge control agent that can be used in the present invention, conventionally known charge control agents can be used. For example, metal salts of fatty acids such as naphthenic acid, octenoic acid, oleic acid, stearic acid, metal salts of sulfosuccinic acid esters, Japanese Patent Publication No. 45-556, Japanese Patent Publication No. 52-37435, Japanese Patent Publication No. 52-37049 Oil-soluble sulfonic acid metal salts disclosed in Japanese Patent Publication No. 45-9594, phosphoric acid ester metal salts disclosed in Japanese Patent Publication No. 45-9594, abietic acid or hydrogenated abietin disclosed in Japanese Patent Publication No. 48-25666 Metal salts of acids, alkylbenzene sulfonic acid Ca salts disclosed in Japanese Patent Publication No. 55-2620, JP-A 52-107837, 52-38937, 57-90643, and 57-139753 Nonionics such as aromatic carboxylic or sulfonic acid metal salts, polyoxyethylated alkylamines, etc. Surfactant, fats and oils such as lecithin and linseed oil, polyvinyl pyrrolidone, organic acid ester of polyhydric alcohol, phosphate ester type surfactant disclosed in JP-A-57-210345, JP-B-56-24944 The sulfonic acid resin etc. which are shown by gazette gazette can be used. In addition, amino acid derivatives described in JP-A-60-21056 and 61-50951 can also be used. Moreover, the copolymer etc. which contain the maleic acid half amide component described in each gazette of Unexamined-Japanese-Patent No. 60-173558 and 60-179750 are mentioned. Further, quaternized amine polymers described in JP-A-54-31739 and JP-B-56-24944 can be given.

  Among these, preferred are a metal salt of naphthenic acid, a metal salt of dioctylsulfosuccinic acid, a copolymer containing the maleic acid half amide component, lecithin, and the amino acid derivative. As these charge control agents, two or more compounds can be used in combination. The concentration of the charge control agent as described above is preferably in the range of 0.0001 to 2.0% by weight with respect to the total amount of ink. By making the concentration of the charge control agent more than 0.0001% by weight, it is possible to impart high specific conductivity to the colorant particles, and by making it less than 2.0% by weight, the volume resistivity of the ink is lowered. Therefore, the necessary print density can be maintained.

  The basic constituent materials in the present invention are as described above, but various additives may be added to the ink composition of the present invention as desired. The ink composition is arbitrarily selected depending on the material and structure of the ink jet system or the ink jet discharge head, the ink supply unit, and the ink circulation unit, and is contained as an ink composition. For example, additives described in Takeshi Amari “Inkjet Printer Technology and Materials”, Chapter 17, published by CMC Co., Ltd. (1998) are used.

  Specifically, fatty acids (for example, C6-C32 monocarboxylic acid, polybasic acid; for example, 2-ethylhexynoic acid, dodecenyl succinic acid, butyl succinic acid, 2-ethylcaproic acid, lauric acid, palmitic acid, elaidin Acid, linolenic acid, ricinoleic acid, oleic acid, stearic acid, enanthic acid, naphthenic acid, ethylenediaminetetraacetic acid, abietic acid, dehydroabietic acid, hydrogenated rosin etc.), resin acid, alkylphthalic acid, alkylsalicylic acid, etc. (As metals of metal ions, Na, K, Li, B, Al, Ti, Ca, Pb, Mn, Co, Zn, Mg, Ce, Ag, Zr, Cu, Fe, Ba, etc.), surface active compounds (For example, as an organic phosphoric acid or a salt thereof, a mono-, di- or trialkylphosphorus composed of an alkyl group having 3 to 18 carbon atoms Organic sulfonic acids or salts thereof such as long chain aliphatic sulfonic acids, long chain alkylbenzene sulfonic acids, dialkylsulfosuccinic acids, etc. or metal salts thereof, amphoteric surface active compounds such as phospholipids such as lecithin and kephalin) , Alkyl group-containing surfactants containing fluorine atoms and / or dialkylsiloxane bonding groups, aliphatic alcohols (for example, higher alcohols comprising branched alkyl groups having 9 to 20 carbon atoms, benzyl alcohol, phenethyl alcohol) Cyclohexyl alcohol, etc.), polyhydric alcohols {for example, alkylene glycols having 2 to 18 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-he Sundiol, dodecanediol, etc.)}; alkylene ether glycols having 4 to 1000 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, etc.); fats having 5 to 18 carbon atoms Cyclic diols (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.); C12-C23 bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) C2-C18 alkylene oxides (ethylene oxide) , Propylene oxide, butylene oxide, α-olefin oxide, etc.) adducts, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol Polyols such as sorbitol; trihydric to octahydric or higher phenols (trisphenol PA, phenol novolac, cresol novolac, etc.); C2-C18 alkylene oxide adducts (additions) of the above trivalent or higher polyphenols 2-20), polyhydric alcohol ether derivatives (polyglycol alkyl ethers, alkylaryl polyglycol ethers, etc.), polyhydric alcohol fatty acid ester derivatives, polyhydric alcohol ether oleate derivatives (eg, ethylene glycol) Monoethyl acetate, diethylene glycol monobutyl acetate, propylene glycol monobutyl propiolate, sorbitan monomethyl dioxalto), alkyl naphthalene sulfonate, alkyl aryl sulfonate It compounds such bets, and the like, but not limited thereto. The amount of each additive used is preferably adjusted so that the surface tension of the ink composition is 15 to 60 mN / m (at 25 ° C.) and the viscosity is 1.0 to 40 cP.

The ink composition obtained in the present invention is particularly useful as an ink for an electrostatic ink jet recording apparatus. Any electrostatic ink jet printer can be used as long as it uses ink using color material particles, without being limited to a particular method. A preferable example is a color material concentration discharge type electrostatic ink jet printer. In this embodiment, the volume resistivity of the ink composition at 25 ° C. is preferably 10 ⁸ Ω · cm or more, and the particle conductivity in the ink composition is preferably 100 pS / cm or more. By satisfying these conditions, excellent printing performance can be imparted to the ink composition.

  A color material concentration discharge type electrostatic ink jet printer will be further described. 1 and 2 are schematic diagrams for explaining an example of an ejection head. FIG. 1 is a diagram showing a configuration of a line scanning type multi-channel inkjet head, and shows a cross section of ejection electrodes corresponding to recording dots. In the drawing, ink 100 is supplied between a head substrate 102 and a discharge electrode substrate 103 from a circulation mechanism 111 including a pump through an ink supply channel 112 connected to the head block 101, and the ink formed in the head block 101 is also the same. The ink is recovered by the ink circulation mechanism 111 through the recovery channel 113. The discharge electrode substrate 103 includes an insulating substrate 104 having a through hole 107 and a discharge electrode 109 formed on the recording medium side around the through hole 107. On the other hand, a convex ink guide 108 is disposed on the head substrate 102 at a substantially central position of the through hole 107. The convex ink guide 108 is made of an insulating member such as plastic resin or ceramics, and is arranged at the same row interval and pitch so that the center is equal to the through hole 107, and is held on the head substrate 102 by a predetermined method. Yes. Each convex ink guide 108 has a shape in which the tip of a flat plate having a constant thickness is cut into a triangle or a trapezoid, and the tip becomes the ink droplet flying position 110. Each convex ink guide 108 may form a slit-like groove from its tip, and the ink supply to the ink flying position 110 is smoothly performed by the capillary action of the slit, thereby improving the recording frequency. it can. In addition, any surface of the ink guide may have conductivity as necessary. In that case, the conductive portion is electrically floated so that the ink can be effectively applied with a small voltage applied to the ejection electrode. An electric field can be formed at the flight position. Each convex ink guide 108 protrudes in the ink droplet flying direction by a predetermined distance substantially perpendicularly from each through hole. A recording medium 121, which is a recording sheet, is disposed opposite to the tip of the convex ink guide 108, and a counter electrode that also serves as a platen for guiding the recording medium 121 on the back surface of the recording medium 121 opposite to the head substrate 102. 122 is arranged. In addition, an electrophoretic electrode 140 is formed at the bottom of the space formed between the head substrate 102 and the discharge electrode substrate 103, and a predetermined voltage is applied to the electrophoretic electrode 140 so that the ink guides in the ink guide in the discharge position direction. Charged particles can be electrophoresed to increase ejection responsiveness. Next, a specific configuration example of the discharge electrode substrate 103 will be described with reference to FIG. FIG. 2 is a view of the discharge electrode substrate 103 as viewed from the recording medium 121 side. A plurality of discharge electrodes are arranged in an array in two rows in the main scanning direction, and a through hole 107 is formed at the center of each discharge electrode. In addition, individual discharge electrodes 109 are formed around the through-holes 107, respectively. In the present embodiment, the inner diameter of the discharge electrode 109 is slightly larger than the diameter of the through hole 107, but it may be the same as the diameter of the through hole 107. Here, the insulating substrate 104 is made of polyimide with a thickness of about 25 to 200 μm, the discharge electrode 109 is made of copper foil with a thickness of about 10 to 100 μm, and the inner diameter of the through hole 107 is about 150 to 250 μmφ.

  Next, the recording operation of the electrostatic ink jet recording apparatus will be described. Here, a case where ink containing a negatively charged color material is used will be described as an example, but the present invention is not limited to this example. At the time of recording, the ink 100 supplied from the ink circulation mechanism 111 via the ink supply channel 112 is supplied from the through hole 107 to the ink flying position 110 at the tip of the convex ink guide 108, and a part of the ink recovery channel. The ink is recovered by the ink circulation mechanism 111 through 113. Here, a voltage of −1.5 kV, for example, is always applied as a bias from the bias voltage source 123 to the ejection electrode 109, and a pulse of −500 V is applied to this as a signal voltage corresponding to the image signal from the signal voltage source 124. The voltage is superimposed on the ejection voltage 109. At this time, a voltage of −1.8 kV is applied to the migration electrode 140. On the other hand, the counter electrode 122 provided on the back surface of the recording medium 121 is set to a ground voltage of 0 V as shown in the figure. In some cases, the recording medium 121 side may be charged to, for example, −1.5 kV to obtain a bias voltage. In this case, an insulating layer is provided on the surface of the counter electrode 122, the recording medium is charged by a corona charger, a scorotron charger, a solid ion generator or the like, and the discharge electrode 109 is grounded, for example, and a signal voltage source 124 is connected thereto. As a signal voltage corresponding to the image signal from, for example, a pulse voltage of −500 V is superimposed on the ejection voltage 109 at the time of ON. At this time, a voltage of −200 V is applied to the migration electrode 140. Now, when the discharge voltage 109 is in an ON state (a state in which −500 V is applied) and a voltage of a total of −2 kV in which a pulse voltage of −500 V is superimposed on a bias DC of −1.5 kV is applied, the tip of the convex electrode 108 is applied. An ink droplet 115 is ejected from the ink droplet flying position 110 and pulled toward the counter electrode 122 to fly toward the recording medium 121 to form an image. In order to improve the accuracy of landing on the recording medium by precisely controlling the flying of the ink droplets after the flight, an intermediate electrode is provided between the ejection electrode and the recording medium, or a guard electrode for suppressing electric field interference between the ejection electrodes. Of course, measures such as providing the above are used, but it is needless to say that the present embodiment can be suitably used in this example. Further, a porous body may be provided between the head base 28 plate 102 and the discharge electrode substrate 103. In this case, the influence of the change in the internal pressure of the ink due to the movement of the ink jet head or the like can be prevented, and the through hole after the ink droplet is discharged Ink liquid supply to 107 parts is quickly achieved. Therefore, the flying of the ink droplet 115 is stabilized, and a good image with a stable density can be recorded on the recording medium 121 at high speed.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further, this invention is not limited to these examples.

Example 1: Ink composition IJ-1
100 parts by mass of Linol Blue FG-7350 (Pigment Blue 15: 3 manufactured by Toyo Ink Co.) as a blue pigment, Styrene / vinyltoluene / lauryl methacrylate / butyl acrylate / trimethylammonium ethyl methacrylate (anion, p-toluenesulfonic acid ion) as a resin A table-type kneader PBV (Irie) was prepared by preliminarily grinding and mixing 200 parts by mass of a copolymer (25/27/2/27/18 mass ratio, weight average molecular weight 11,000) with a trioblender and then mixing well. Melt kneading (120 minutes). The pigment kneaded product (colored mixture) was pulverized with a pin mill. Next, 10 parts by mass of the pulverized pigment kneaded product, 80 parts by mass of Isopar G, 12.5 parts by mass of a 20% by mass solution prepared by heating and dissolving the following pigment dispersant D-1 in Isopar G, and 3G- After pre-dispersing for 30 minutes with a paint shaker (Toyo Seiki KK) together with 350 parts by mass of X glass beads, using a thermostat NESLAB RTE7 (MS Equipment Co., Ltd.) at 3000 rpm in a Dynomill KDL type (Shinmaru Enterprise Co., Ltd.) The dispersion was wet-dispersed for 10 hours while controlling the liquid temperature of the dispersion at 35 ° C. After completion of dispersion, the volume average particle size of pigment resin particles (color material coated with an unnecessary resin in a non-aqueous solvent) in the dispersion was measured with an ultracentrifugal automatic particle size distribution analyzer CAPA700 (Horiba). 0.97 μm. The proportion of fine particles of 0.2 μm or less was 0.6% on a volume basis.

The pigment resin particle dispersion from which the glass beads were removed by filtration was diluted with Isopar G so that the pigment resin particle component would be 7.0%. Next, an ink composition IJ-1 was prepared by adding an octadecene-half-maleic acid octadecylamide copolymer as a charge control agent so as to be 0.032% by mass. The viscosity of the obtained ink composition is 1.37 cP (E-type viscometer, measured at a temperature of 25 ° C.), the surface tension is 23 mN / m (automatic surface tension meter manufactured by Kyowa Interface Science Co., Ltd., measured at a temperature of 25 ° C.), The relative dielectric constant was 2.48 (LCR meter, measured by Ando Electric Co., Ltd. AG-4311). The ink composition IJ-1 has a total specific conductivity of 841 pS / cm, a volume resistivity at 25 ° C. of 1.2 × 10 ⁹ Ω · cm, and a blue resin exhibiting a clear positive charge. The particles exhibited a particle conductivity of 467 pS / cm. It was also found that the overall specific conductivity of the ink composition after forced aging at 45 ° C. for one week and the particle conductivity of the pigment resin particles were extremely stable with almost no change in charge amount.
The charge amount of the ink composition was measured by using the above-described LCR meter and liquid electrode (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.) and the specific conductivity measured under conditions of an applied voltage of 5 V and a frequency of 1 kHz. The particle conductivity of the pigment resin particles is obtained by subtracting the specific conductivity of the supernatant obtained by centrifuging the ink composition from the total specific conductivity of the ink composition, and the volume resistivity is the total specific conductivity. Obtained by reciprocal degree. Centrifugation was performed for 30 minutes using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd. SRX-201) under conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C.

As the ink jet apparatus, a 100 dpi 64 channel electrostatic ink jet head having the head structure shown in FIG. 1 was used, and the ink composition IJ-1 was filled in the ink tank. After removing dust on the surface of the coated recording paper as a recording medium by air pump suction, the ejection head was brought close to the coated recording paper to the drawing position, and ink was ejected and drawn at a drawing resolution of 600 dpi. At this time, the drawing was performed while adjusting the pulse voltage and changing the dot area in 16 steps within a dot diameter range of 15 μm to 60 μm. The drawn image was stably printed with uniform dots without blurring, and gave a clear image of good quality with a satisfactory density. The ejection stability from the ink head was also good, there was no clogging, and stable dot-shaped printing was possible even during long-term continuous image drawing. Next, a full solid pattern was printed, the printed matter was dried and fixed, and then the solid portion was subjected to a tape peeling test. As a result, it was found that there was no missing portion and extremely excellent scratch resistance and fixability.
Furthermore, when drawing was similarly performed using the ink composition after forced aging at 45 ° C. for one week, the drawn image gave a clear image of good quality with satisfactory density with uniform dots without bleeding, and stable ejection. The dot shape was also stable, and even with long-term continuous image drawing, stable dot-shaped printing was possible.

Example 2: Ink composition IJ-2
In Example 1, wet dispersion was performed in the same manner as in Example 1 except that the dispersion was dispersed for 5 hours while controlling the liquid temperature at 45 ° C. The volume average particle size of the pigment resin particles in the dispersion was 1.04 μm, and the proportion of fine particles of 0.2 μm or less was 1.3% on a volume basis. Next, the obtained pigment resin particle dispersion was prepared in the same manner as in Example 1 to prepare ink composition IJ-2.
Ink composition IJ-2 had a surface tension of 23 mN / m, a viscosity of 1.34 cp, and a relative dielectric constant of 2.31. Ink composition IJ-2 has a total specific conductivity of 771 pS / cm, a volume resistivity at 25 ° C. of 1.3 × 10 ⁹ Ω · cm, and a blue resin particle exhibiting a clear positive charge The particle conductivity was 655 pS / cm, and most of the charge amount of the ink composition was in the pigment resin particles. It was also found that the overall specific conductivity of the ink composition after forced aging at 45 ° C. for one week and the particle conductivity of the pigment resin particles were extremely stable with almost no change in charge amount.
When the drawing performance of the ink composition IJ-2 was evaluated in the same manner as in Example 1, the ejection stability from the ink head was good, the clogging did not occur, and the dot shape was stable even during long-term continuous image drawing. Was printed. The obtained drawn image was free of bleeding, had a sufficient image density, and was high quality and clear. Further, after printing a solid pattern and drying and fixing the printed matter, the solid part was subjected to a tape peeling test. As a result, it was found that there was no missing part and extremely excellent scratch resistance and fixability. Furthermore, when drawing was similarly performed using the ink composition after forced aging at 45 ° C. for one week, the drawn image could be satisfied with uniform dots without bleeding.

Comparative Example 1: Comparative ink composition IJR-1
In Example 1, wet dispersion was performed in exactly the same manner as in Example 1 except that the dispersion was dispersed for 5 hours while controlling the liquid temperature at 55 ° C. The volume average particle diameter of the pigment resin particles in the dispersion was 1.64 μm. However, since there were many coarse particles and precipitates were formed over time, they could not be used for the next ink composition.

Example 3: Ink composition IJ-3
The pigment kneaded material was obtained by melt-kneading in exactly the same manner as in Example 1. Next, 30 parts by mass of the pulverized pigment kneaded material, 45.7 parts by mass of Isopar G, 12.5 parts by mass of a 20% by mass solution prepared by dissolving the above pigment dispersant D-1 in Isopar G by heating, and 3G -After pre-dispersing with 300 parts by mass of glass beads for 30 minutes with a paint shaker, using a constant temperature bath NESLAB RTE7 at 3000 rpm in a Dynomill KDL type, wet dispersion was performed for 7 hours while controlling the liquid temperature of the dispersion at 25 ° C. . After the completion of dispersion, the volume average particle size of the pigment resin particles in the dispersion was 1.04 μm, and the proportion of fine particles of 0.2 μm or less was 0.6% on a volume basis.
Next, the ink composition IJ- was exactly the same as Example 1 except that 0.002% by mass of the charge control agent octadecene-half-maleic acid octadecylamide copolymer was added to the obtained pigment resin particle dispersion. 3 was prepared. The ink composition IJ-3 has a surface tension of 23 mN / m, a viscosity of 1.47 cp, a relative dielectric constant of 2.40, an overall specific conductivity of 450 pS / cm, and a volume resistivity at 25 ° C. of 2.2. The blue resin particles having × 10 ⁹ Ω · cm and showing a clear positive charge had a particle conductivity of 379 pS / cm, and most of the charge amount of the ink composition was related to the pigment resin particles. It was also found that the overall specific conductivity of the ink composition after forced aging at 45 ° C. for one week and the particle conductivity of the pigment resin particles were extremely stable with almost no change in charge amount.

  When the drawing performance of the ink composition IJ-3 was evaluated in the same manner as in Example 1, the ejection stability from the ink head was good, the clogging did not occur, and the dot shape was stable even during long-term continuous image drawing. Was printed. The obtained drawn image was free of bleeding, had a sufficient image density, and was high quality and clear. Further, after printing a solid pattern and drying and fixing the printed matter, the solid part was subjected to a tape peeling test. As a result, it was found that there was no missing part and extremely excellent scratch resistance and fixability. Furthermore, when drawing was similarly performed using the ink composition after forced aging at 45 ° C. for one week, the drawn image could be satisfied with uniform dots without bleeding.

Comparative Example 2: Comparative ink composition IJR-2
In Example 3, wet dispersion was performed in the same manner as in Example 3, except that the dispersion was dispersed for 7 hours while controlling the liquid temperature to 5 ° C. The volume average particle diameter of the pigment resin particles in the dispersion was 0.42 μm, and the proportion of fine particles of 0.2 μm or less was 11.4% on a volume basis.
Next, a comparative ink composition was prepared in the same manner as in Example 3 except that 0.002% by mass of the charge control agent octadecene-half-maleic acid octadecylamide copolymer was added to the obtained pigment resin particle dispersion. IJR-2 was prepared. The comparative ink composition IJR-2 has a surface tension of 23 mN / m, a viscosity of 1.51 cp, a relative dielectric constant of 2.32, an overall specific conductivity of 590 pS / cm, and a clear positive charge. The blue resin particles had a particle conductivity of 565 pS / cm.
The drawing performance of the comparative ink composition IJR-2 was evaluated in the same manner as in Example 3. As a result, ink ejection became unstable within one hour and clogging at the head portion occurred.

  From Examples 1 to 3, the ink composition dispersed while controlling the liquid temperature of the dispersion liquid to 10 to 50 ° C. as in the present invention has a small proportion of fine particles of 0.2 μm or less, so that the ink composition has a high concentration of bleeding. It can be seen that a small number of dots can be printed stably at a high speed, and good ejection performance can be obtained. On the other hand, in Comparative Example 1 in which dispersion treatment was performed while controlling the liquid temperature of the dispersion liquid to 55 ° C., good dispersion was not possible, and in Comparative Example 2 in which dispersion treatment was performed while controlling the liquid temperature of the dispersion liquid at 5 ° C., It can be seen that good ejection performance cannot be obtained because the proportion of fine particles of 0.2 μm or less is as large as 11.4%.

Examples 4 to 6: Ink compositions IJ-4 to IJ-6
In the same manner as in Example 3, melt-kneading was performed to obtain a pigment kneaded product. Next, using 30 parts by mass of the pulverized pigment kneaded material, 8.3 parts by mass and 16.7 parts by mass of the pigment dispersant D-1 (20% by mass solution of Isopar G) are respectively added to 100 parts by mass of the pigment kneaded material. 25 parts by mass, and the dispersions of Examples 4 to 6 were prepared so that the concentration of the pigment kneaded material in Isopar G was 35% by mass. Next, wet dispersion was performed for 6 to 12 hours while controlling the liquid temperature of the dispersion at 30 ° C. Table A shows the volume average particle diameter of the pigment resin particles in the dispersion after completion of dispersion and the proportion of fine particles of 0.2 μm or less. Next, in the same manner as in Example 3, the obtained pigment resin particle dispersion was added with octadecene-half-maleic acid octadecylamide copolymer as a charge control agent to prepare ink compositions IJ-4 to IJ-6. The surface tensions of the ink compositions IJ-4 to IJ-6 are 23 to 24 mN / m, the viscosity, the relative dielectric constant, the overall specific conductivity, the particle conductivity, and the volume resistivity are shown in Table 1.
When the drawing performance of the ink compositions IJ-4 to IJ-6 was evaluated in the same manner as in Example 3, the ejection stability from the ink head was good, no clogging occurred, and even continuous image drawing for a long period of time. Stable dot-shaped printing was possible. The obtained drawn image was free of bleeding, had a sufficient image density, and was high quality and clear. Further, after printing a solid pattern and drying and fixing the printed matter, the solid part was subjected to a tape peeling test. As a result, it was found that there was no missing part and extremely excellent scratch resistance and fixability. Furthermore, when drawing was similarly performed using the ink compositions IJ-4 to IJ-6 after forced aging at 45 ° C. for one week, the drawn image could be satisfied with uniform dots without bleeding.

Comparative Examples 3 and 4: Comparative ink compositions IJR-3 and IJR-4
In Example 4, the amount of the pigment dispersant D-1 (20% by mass solution of Isopar G) used was 4.2 parts by mass and 100 parts by mass with respect to 100 parts by mass of the pigment kneaded product, respectively. Comparative Example 3 and Comparative Example 4 were carried out in the same manner as in Example 4. In Comparative Example 3, wet dispersion was performed for 3 hours while controlling the liquid temperature of the dispersion at 30 ° C., and in Comparative Example 4, 15 hours. Table 1 shows the volume average particle diameter of the pigment resin particles in the dispersion after the completion of dispersion and the ratio of fine particles having a size of 0.2 μm or less. Further, in the same manner as in Example 4, the charge control agent octadecene-half-maleic acid octadecylamide copolymer was added to prepare comparative ink compositions IJR-3 and IJR-4. Table 1 shows the results of the comparative ink compositions IJR-3 and IJR-4 with the surface tension of 23 mN / m, viscosity, relative dielectric constant, overall specific conductivity, particle conductivity, and volume resistivity. In Comparative Example 3, since the dispersion was poor and aggregates were generated, it could not be used for the next ink composition.
When the drawing performance of the comparative ink composition IJR-4 was evaluated in the same manner as in Example 4, the ejection of ink became unstable within one hour and clogging at the head portion occurred.

  From Examples 4 to 6 and Comparative Examples 3 and 4, as in the present invention, the liquid temperature of the dispersion was controlled at 30 ° C., and the dispersant was added to 100 parts of the pigment admixture (color material coated with resin). Since the ink composition dispersed using 5 to 50 parts has a small proportion of fine particles of 0.2 μm or less, it can stably print dots with high density and little bleeding at high speed, and good ejection performance can be obtained. I understand. On the other hand, in Comparative Example 3, since the amount of the dispersant used is as small as 4.2 parts, good dispersion cannot be achieved. In Comparative Example 4, the amount of the dispersant used is as large as 100 parts, so that it is 0.2 μm or less. It can be seen that the fine particle ratio increases to 9.6%, and therefore good discharge performance cannot be obtained.

It is a figure for demonstrating the structure of a line scanning type multi-channel inkjet head. FIG. 3 is a diagram of an ejection electrode viewed from a recording medium side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Ink 101 Head block 102 Head substrate 103 Discharge electrode substrate 104 Insulating substrate 107 Through-hole 108 Convex ink guide 109 Discharge electrode 110 Ink droplet flight position 111 Circulation mechanism 112 Supply channel 113 Collection channel 115 Ink droplet 121 Recording medium 122 Counter electrode 123 Bias voltage source 124 Signal voltage source 140 Electrophoresis electrode

Claims (7)

  In a method for producing an ink composition for an ink jet recording apparatus comprising at least a nonaqueous solvent, a colorant coated with a resin insoluble in the nonaqueous solvent, and a dispersant, the ink composition is coated with a resin insoluble in the nonaqueous solvent. 5 to 50 parts by mass of the dispersant is used with respect to 100 parts by mass of the colorant, and in the nonaqueous solvent, the colorant coated with a resin insoluble in the nonaqueous solvent is dispersed together with the dispersant. A method for producing an inkjet ink composition, wherein the dispersion treatment is carried out in a temperature range of 10 to 50 ° C.   The average particle diameter of the color material particles coated with the resin insoluble in the non-aqueous solvent is in the range of 0.3 to 4 μm, and the ratio of the color material particles of 0.2 μm or less is 5% or less on a volume basis. The method for producing an inkjet ink composition according to claim 1.   In the method for producing an ink composition for an electrostatic ink jet recording apparatus, comprising at least a non-aqueous solvent, a color material coated with a resin insoluble in the non-aqueous solvent, a dispersant and a charge control agent, the non-aqueous solvent 5 to 50 parts by mass of the dispersant is used with respect to 100 parts by mass of the color material coated with an insoluble resin, and the color material coated with the resin insoluble in the non-aqueous solvent in the non-aqueous solvent. A method for producing an electrostatic ink-jet ink composition, wherein the dispersion is dispersed in a temperature range of 10 to 50 ° C. together with the dispersant.   The average particle diameter of the color material particles coated with the resin insoluble in the non-aqueous solvent is in the range of 0.3 to 4 μm, and the ratio of the color material particles of 0.2 μm or less is 5% or less on a volume basis. The method for producing an electrostatic inkjet ink composition according to claim 3. 4. The electrostatic inkjet ink according to claim 3, wherein the volume resistivity at 25 ° C. of the ink composition is 10 ⁸ Ω · cm or more and the particle conductivity in the ink composition is 100 pS / cm or more. A method for producing the composition.   At least the non-aqueous solvent, the color material coated with the resin insoluble in the non-aqueous solvent, and the dispersant, and the average particle size of the color material particles coated with the resin insoluble in the non-aqueous solvent is 0.3. An ink-jet ink composition, characterized in that the proportion of colorant particles in the range of ˜4 μm and not more than 0.2 μm is 5% or less on a volume basis.   The average particle diameter of the colorant particles coated with a non-aqueous solvent, a colorant coated with a resin insoluble in the non-aqueous solvent, a dispersant, and a charge control agent, and coated with a resin insoluble in the non-aqueous solvent The electrostatic ink-jet ink composition is characterized in that the ratio of colorant particles having a particle size of not more than 0.3 to 4 μm and not more than 0.2 μm is 5% or less on a volume basis.

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