JP2005097349A - Method for producing ink for inkjet recording and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing ink for inkjet recording with which ink droplets can stably be jetted without causing clogging in an ink circulating system and an image of high image quality can be formed over a long period and to provide an inkjet recording apparatus. <P>SOLUTION: The method for producing the ink for electrostatic inkjet recording containing at least a dispersion medium, a colorant and a dispersing agent is carried out as follows. A magnetic field is made to act after at least one step after a dispersing step or after an ink preparing step to remove substances captured in the magnetic field. In the method for production, the content of magnetic powder in the ink is ≤0.010 mass%. The inkjet recording apparatus is equipped with a magnetic powder-removing apparatus designed to make a magnetic field act on at least one site of an ink circulation system 111 provided with an ink feeding line 112 having a pump 3 and leading from an ink tank 1 through the pump to a jetting head 2 and an ink recovering line 113 and capture the magnetic powder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing ink for inkjet recording. In particular, the present invention relates to a method for producing oil-based ink for use in an electrostatic ink jet recording apparatus that ejects ink and forms characters and images on a transfer medium such as recording paper, and the ink jet recording apparatus.

  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, there has been a problem that print density is reduced, blurred, or show-through easily occurs.

  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.
However, as a result of intensive investigations on the necessary conditions for stably ejecting ink droplets without clogging, it was found that the presence of magnetic powder in the ink significantly hinders stable ejection in addition to the above physical property values. This magnetic powder is generated in ink materials such as pigments and various resins, or in the process of manufacturing ink as described below.
The ink is generally produced by the following method. Forming colorant particles (colored mixture) coated with a colorant with a resin insoluble in the dispersion medium, and then dispersing the colored mixture in a dispersion medium containing a dispersant to form fine particles. Can do. In this dispersion step, a commercially available wet disperser can be used. For example, a ball mill, a sand mill, an attritor or the like. However, metal powder (iron powder, iron scrap, magnetic foreign matter, etc.) generated by abrasion during dispersion is generated. Recently, ceramic dispersers and media represented by zirconia, which can reduce the metal contamination, have been used. As a result, the metal contamination is considerably reduced, but the present situation is that the discharge stability has not been reduced to a level at which there is no problem. It has also been found that the method of removing magnetic powder generated during dispersion and the absolute amount of magnetic powder contained in the ink are not suppressed.

Japanese Patent Laid-Open No. 9-193389 JP 10-138493 A

  The present invention has been made for the purpose of stably ejecting ink droplets without clogging in an ink circulation system, for example, a head, a pump, and a piping system, for long-time inkjet recording. An object of the present invention is to provide an ink jet recording ink manufacturing method and an ink jet recording apparatus capable of forming an image for a long time.

The present invention relates to the following means, whereby the above-described problems can be solved.
(1) In a method for producing an ink containing at least a dispersion medium, a colorant, and a dispersant, a magnetic field is applied to the magnetic field after the dispersion step or after at least one of the ink preparation steps. A method for producing an electrostatic ink jet recording ink, wherein the material is produced by removing a substance to be captured.
(2) In a method for producing an ink containing at least a dispersion medium, a colorant, and a dispersant, a magnetic field is applied to the magnetic field after the dispersion step or after at least one of the ink preparation steps. A method for producing an electrostatic ink jet recording ink, wherein the amount of magnetic powder in an ink for ink jet recording produced by removing a substance to be captured is 0.010% by mass or less.
(3) An ink tank for storing ink in which at least a colorant is dispersed in a dispersion medium, an ejection head for ejecting ink in accordance with an input signal, and supplying ink in the ink tank to the ejection head An ink supply system that includes a pump and passes through the pump from the ink tank to the discharge head; and ink recovery from the discharge head to the ink tank for recovering ink from the discharge head to the ink tank. An ink jet recording apparatus having an ink circulation system comprising: a magnetic powder removing device that captures magnetic powder by applying a magnetic field to at least one of the ink circulation systems. Type ink jet recording apparatus.

  In the production of an ink containing at least a dispersion medium, a colorant, and a dispersant, a substance that is trapped in the magnetic field is applied by applying a magnetic field after at least one of the dispersion process or the ink preparation process. By removing the ink, it is possible to provide an oil-based ink capable of stably printing high-density dots with less bleeding and without ink clogging for a long time.

The present invention is described in detail below.
The dispersion medium used in the inkjet recording ink of the present invention is a nonpolar insulating solvent, and preferably has a relative dielectric constant of 1.5 to 20 and a surface tension of 15 to 60 mN / m (at 25 ° C.). . Further desirable properties are low toxicity, low flammability, and low odor.

  Examples of such a dispersion medium include solvents selected from linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, petroleum naphtha, halogen substitution products thereof, and the like. 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, Shell Petrochemical's S. B. R. Solvents selected from Shellzol 70, Cielzol 71, Mobil Petroleum Company's Vegazole and the like can be 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) (product) name), etc.), CFCs (manufactured by Daikin Industries, Ltd. "HCFC-141b" (trade name), _{etc.), [F (CF 2)} 4 CH 2 CH 2 I], such as _{[F (CF 2) 6 I} ] And iodinated fluorocarbons ("I-1420", "I-1600" (trade name), etc., manufactured by Daikin Fine Chemical Laboratory).

As the dispersion medium used in the present invention, higher fatty acid esters and silicone oils 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 colorant will be described in detail.
The colorant is not particularly limited, and includes all organic pigments and inorganic pigments that are generally commercially available.

  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. Metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.) are conceivable.

  As a magenta color, C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as CI Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment red 53: 1 (such as lake red C) and C.I. I. Pigment red 57: 1 (brilliant carmine 6B), an azo lake pigment such as C.I. I. Condensed azo pigments such as C.I. 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 (such as Thioindigo Bordeaux); 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. Pigment Red 180 (isoindolinone red 2BLT, etc.), isoindolinone pigments such as C.I. I. An alizarin lake pigment such as CI Pigment Red 83 (Mada Lake, etc.) is conceivable.

  As a pigment exhibiting a cyan color, C.I. Disazo pigments such as CI Pigment Blue 25 (dianisidine blue, etc.); I. Phthalocyanine pigments such as CI 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 (Viclotia Pure Blue BO Lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Blue 60 (Indantron Blue, etc.); I. An alkaline blue pigment such as pigment blue 18 (alkali blue V-5: 1) is conceivable.

As pigments exhibiting a black color, 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 are considered. .
In addition, application of metal powder is also conceivable for color reproduction of gold, silver, copper and the like.

The colorant used in the ink for inkjet recording is usually subjected to a surface treatment.
As the surface treatment method of the colorant, methods such as rosin treatment, polymer treatment, grafting treatment, and plasma treatment described in Chapter 5 of “Pigment Dispersion Technology” published by the Technical Information Association can be applied.

  “Rosin treatment” refers to a method of mechanically kneading the pigment and rosin to treat the rosin on the pigment surface, or adding an alkaline aqueous solution of rosin to the aqueous pigment slurry and then adding an alkaline earth salt or acid to the rosin. For example, a method of precipitating a slightly soluble salt or a free acid on the pigment particle surface. In the rosin treatment, rosin of about several to 20% of the pigment is usually used. (1) A fine and highly transparent pigment is obtained due to the effect of preventing crystal growth of the pigment, and (2) Dry aggregation of the particles is weak. Therefore, it is easy to disperse mechanically, and (3) it has a great effect in improving the wetting of oily vehicles by increasing the oleophilicity of the pigment surface, and it is widely used especially in the field of printing inks. .

  “Grafting treatment” refers to the grafting reaction between carbon black and inorganic fine particles such as silica and titanium oxide, as well as functional groups such as hydroxyl groups, carboxyl groups and amino groups present on the surface of organic pigments and polymers. Is what you do. In the grafting reaction of the polymer to the pigment surface, (1) the vinyl monomer is polymerized using a polymerization initiator in the presence of pigment fine particles, and the growth polymer produced in the system is converted into functional groups on the pigment particle surface. A method by stopping, (2) a method of growing a graft chain from a polymerization initiating group introduced to the surface of the pigment fine particle, and (3) a method by a polymer reaction between a functional group on the surface of the pigment fine particle and a functional group at the end of the polymer There is.

“Plasma treatment” is a modification of the pigment powder surface by low-temperature plasma or thermal plasma. Specific examples of the treatment of the pigment surface with low-temperature plasma include (1) modification by plasma irradiation of non-polymerizable gas such as oxygen and nitrogen, (2) modification by plasma polymerized film formation using polymerizable gas, ( 3) Modification by plasma-initiated graft polymerization reaction, which consists of a two-stage process of 1st stage in which active species are formed on the substrate surface by plasma irradiation and 2nd stage in which post-irradiation monomer is brought into contact with post-irradiation to proceed with graft polymerization. Etc.
In order to improve the dispersibility of the pigment, the polymer treatment described below is preferable.

  As a typical method of polymer treatment, a chemical method using an in-situ polymerization method described in “Pigment Dispersion Technology” on page 99 and later published by the Technical Information Association, a method using a phase separation method (coacervation), The method of processing with a mechanical force at the time of pigment dispersion etc. is mentioned.

  As an in-situ polymerization method, a method of dispersing a pigment and a polymer, followed by suspension polymerization, dispersing the pigment in an aqueous system in the presence of a dispersant, adding a polar polymer, a vinyl polymer, and a polyfunctional crosslinking polymer. And a method in which the monomer in which the pigment is dispersed is bulk polymerized, and then suspension polymerization or emulsion polymerization is performed to sufficiently adsorb the pigment.

The phase separation method (coacervation) is a chemical method (in-situ method) in which a pigment is dispersed in a polymer solution and then the solubility of the polymer is lowered by some method to precipitate the polymer from the solution system onto the pigment particles. Compared with the polymerization method), a wide range of polymers can be selected. Add a non-solvent to the pigment-dispersed resin solution to deposit the resin on the pigment surface, or finely disperse the pigment in the water-soluble polymer or water-soluble resin solution, then adjust the pH to deposit them on the pigment surface This method is widely used including rosin treatment. After dispersing the pigment in an acid solution of acid-soluble nitrogen-containing acrylic resin, increasing the pH to insolubilize the polymer on the pigment surface will prevent aggregation in paints and printing inks, improve fluidity, gloss, and coloring power. The effect is seen.
Exemplifying the method of polymer processing by mechanical force, after mixing the polymer and pigment in advance so that the pigment content is 5 to 95%, knead with a kneader, three rolls, etc. while heating and pulverize with a pin mill etc. To do. A method called a flushing resin treatment is also included in the mechanical polymer treatment method.

  The resin used for the polymer treatment is not particularly limited as long as it has a function of improving the dispersibility of the pigment in the dispersion medium.

  As a preferred resin, a resin having a function of adsorbing to a colorant and being well dispersed in a dispersion medium, a part that solvates with a solvent, a part that is difficult to solvate with 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.

  Specific examples of the resin used for polymer treatment include olefin polymers and copolymers (for example, polyethylene, polypropylene, polyisobutylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-methacrylate copolymer, ethylene -Methacrylic acid copolymer, etc.), polymers of styrene and its derivatives and copolymers (eg butadiene-styrene copolymer, isoprene-styrene copolymer, styrene-methacrylate copolymer, styrene-acrylate copolymer, etc.) ), Acrylate polymers and copolymers, methacrylate polymers and copolymers, itaconic acid diester polymers and copolymers, maleic anhydride copolymers, rosin resins, hydrogenated rosin resins, petroleum resins, Hydrogenated petroleum resin, maleic acid tree , Terpene resins, hydrogenated terpene resins, chroman - indene resins, cyclized rubber - methacrylic acid ester copolymers, cyclized rubber - like acrylic acid ester copolymer.

  The ratio of the resin used for the colorant and polymer treatment of the present invention is usually in the range of 95/5 to 5/95, preferably in the range of 80/20 to 10/90, as the mass ratio of the colorant / resin. .

  In addition, commercially available processed pigments can also be used as the surface-treated colorant. 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 dispersion step in the present invention, the surface-treated colorant is dispersed in the form of fine particles in a dispersion medium.
In the dispersion step, it is preferable to use a dispersant in order to disperse the surface-treated colorant in the form of fine particles and stabilize the dispersion in a dispersion medium.

  As the dispersant that can be used in the present invention, a general pigment dispersant applied in the dispersion medium can be used. Any pigment dispersant may be used as long as it is compatible with the dispersion medium and can stably disperse the pigment in fine particles.

  Specific examples of the dispersant for pigment 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), polyethylene glycol fatty acid ester (polyoxyethylene monostearate, polyethylene glycol diisostearate, etc.), polyoxyethylene alkylphenyl ether (polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl) Ethers), nonionic surfactants such as aliphatic diethanolamides, and polymer dispersants are polymers having a molecular weight of 1000 or more. The compound is good, for example, styrene-maleic acid resin, styrene-acrylic resin, rosin, BYK-160, 162, 164, 182 (urethane polymer compound manufactured by BYK Chemie), EFKA-47, LP-4050 (EFKA) Urethane dispersants manufactured by the company), Solsperz 24000 (polyester polymer compound manufactured by Zeneca), Solsperse 17000 (aliphatic diethanolamide from Zeneca), and the like.

  In addition to the above, the polymeric pigment 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 that are difficult to solvate in a solvent. Examples thereof include random copolymers composed of monomers having a polar group and monomers such as methacrylate, styrene and vinyltoluene, and graft copolymers 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. Other examples include styrene-butadiene copolymers and block copolymers of styrene and long-chain alkyl methacrylate disclosed in JP-A-60-10263. Preferred examples of the dispersant for pigment include a graft copolymer disclosed in JP-A-3-188469.

  The amount of the pigment dispersant used is preferably 0.1 to 300 parts by mass with respect to 100 parts by mass of the pigment. When the addition amount of the pigment dispersant is less than 0.1 parts by mass, the pigment dispersion effect is small and not preferable. Moreover, even if it uses more than 300 mass parts, the effect of the used part will not be acquired.

  In the dispersion step in which the surface-treated colorant is dispersed in the dispersion medium in the form of fine particles, as a method of using the pigment dispersant, for example, there are the following methods. Is obtained.

  The above is the basic constituent material dispersion medium, colorant, and dispersant in the present invention. 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.
Further, it is preferable to add a charge adjusting agent in order to control the polarity of the ink particles and the charge amount thereof. Suitable as the charge control agent are metal salts of organic carboxylic acids such as zirconium naphthenate and zirconium octenoate, ammonium salts of organic carboxylic acids such as tetramethylammonium stearate, sodium dodecylbenzenesulfonate, dioctylsulfosuccinate Side chains of organic sulfonic acid metal salts such as magnesium salts, organic sulfonic acid ammonium salts such as toluene sulfonic acid tetrabutylammonium salt, polymers containing carboxylic acid groups modified with amines of copolymers of styrene and maleic anhydride A polymer having a carboxylic acid group, a polymer having a carboxylic acid anion group in the side chain such as a copolymer of stearyl methacrylate and a tetramethylammonium salt of methacrylic acid, and a nitrogen in the side chain of a copolymer of styrene and vinylpyridine. Have atoms That polymers, methacrylic acid Buchioru and N- (2-methacryloyloxyethyl) -N, N, polymers having an ammonium group in the side chain of the copolymer of N- trimethylammonium tosylate. A particularly preferred charge control agent is octadecene and a half maleic acid octadecylamide copolymer. The charge applied to the particles may be positive or negative.

  Next, the method for producing the ink for inkjet recording of the present invention will be described in detail. Colorant particles (colorant resin particles) coated with a colorant with a resin that is insoluble in the dispersion medium form a color mixture by coating the colorant with a binder resin, and then the color mixture is dispersed in the dispersion medium. It can be formed by dispersing fine particles. First, a process of making a color mixture by coating a colorant with a binder resin will be described. The colored mixture is prepared by the following method, for example.

(1) A method in which a colorant and a binder resin are melt-kneaded using a kneader such as a roll mill, a Banbury mixer, or a kneader at a temperature equal to or higher than the softening point of the binder resin, and pulverized after cooling to obtain a colored mixture.
(2) Dissolve the binder resin in a solvent, add a colorant, and wet-disperse with a ball mill, attritor, sand grinder, etc., and evaporate the solvent to obtain a colored mixture, 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 process in which the color mixture described above is dry-ground and then wet-dispersed with a dispersant in a dispersion medium will be described. The disperser used in this dispersion step is not particularly limited, and 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, the media locking phenomenon at the time of start-up does not occur at all as compared with the vertical mill, so that the filling rate is preferably 80 to 85% with respect to the vessel capacity.
The volume average diameter of the colorant particles in the dispersion medium obtained by the dispersion process as described above is 0.01 to 10 μm. A more preferred volume average diameter is 0.2 to 5 μm.

In the method for producing an ink for ink jet recording of the present invention, a step of removing a substance trapped in the magnetic field by applying a magnetic field after at least one of the steps after the dispersion step or the ink preparation step is provided. It is characterized by.
The ink preparation process is a process for preparing a final product by diluting the dispersion obtained in the dispersion process and adding charge adjustment.
As the dispersion medium used for dilution, the same dispersion medium as in the dispersion step is used. As the charge adjusting agent, those already described are used.
In the step of removing a substance trapped in the magnetic field by applying the magnetic field of the present invention (hereinafter also referred to as a magnetic field treatment step), as a specific means thereof, in the dispersion obtained in the dispersion step or the preparation step A means for removing the substance by putting the magnet directly for a predetermined time or applying the magnet to the outside of the container containing the dispersion for a predetermined time can be mentioned. The strength of the magnetic field is appropriately set, but is usually 40 to 800 kA / m, preferably 80 to 250 kA / m. Further, the application time of the magnetic field is appropriately selected and may be continuous or discontinuous. In the latter case, it is preferable to use again after once removing the traps collected on the magnetic pole.
Examples of the jig used in the magnetic field treatment step include those shown in FIGS. The jig shown in FIG. 6 is a container 13 provided with a dispersion flow inlet 14 and a dispersion flow outlet 15, and a pair of permanent magnets 12 is provided therein. While the dispersion flowing in from the dispersion flow inlet 14 passes through A, B or C between the permanent magnet pair and is discharged from the dispersion flow outlet 15, the captured matter is captured by the permanent magnet. The dispersed flow inlet 14 and the dispersed flow outlet 15 may be a closed circulation system in communication with a pipe and a pump.
The jig shown in FIG. 7 arranges two pairs of permanent magnets 12 as shown in the modification of FIG. 6 and increases the contact time of the magnetic field and improves the capture efficiency by bypassing the flow path of the dispersion. It is what. This example may be a closed circulation system as described above.

In the present invention, the trap is a magnetic substance (iron or the like), and usually the form is mainly magnetic powder.
The amount of magnetic powder in the ink that is effective for clogging is 0.010% by mass or less, more preferably 0.005% by mass or less, and particularly preferably 0.001% by mass or less.
In the present invention, the magnetic powder amount is defined by a value obtained from values W1 to W0 measured by the following measuring method.
50 g of ink having an ink particle concentration of 7% by mass is put into a 100 ml glass screw tube, and KANETEC CO. , LTD MAGNETIC HOLDER (MB-PB) is placed, the magnetic field is taken for 24 hours, and after removing the magnetic powder, the total nonvolatile content concentration is W0 (mass%), and the magnetic powder is also removed. When the total non-volatile content concentration of the ink that is not used is W1 (mass%), the amount (mass%) of the magnetic powder in the ink that is not subjected to the magnetic powder removal process is W1-W0.
It is clear that the magnetic powder in the ink when the magnetic powder is processed for 24 hours is completely removed and is 0% by mass.
Therefore, it is clear that the amount of magnetic powder in the ink can be easily adjusted by applying the magnetic field.

Next, an electrostatic ink jet recording method in which the ink for ink jet recording produced according to the present invention is suitably used will be described.
FIG. 1 is a diagram showing a configuration example of a line scanning type multi-channel ink jet head used in an electrostatic ink jet recording method, and shows a section of ejection electrodes corresponding to recording dots. In the drawing, ink 100 is supplied from an ink circulation system 111 including a pump through an ink supply system 112 connected to the head block 101 between the head substrate 102 and the discharge electrode substrate 103, and the ink formed on the head block 101 is also the same. The ink is recovered by the ink circulation system 111 through the recovery system 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 the tip thereof, 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. I can do it. In addition, any surface of the ink guide may have conductivity as required. 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, a migration electrode 140 is formed at the bottom of the space formed between the head substrate 102 and the ejection electrode substrate 103. By applying a predetermined voltage to the migration electrode 140, the migration of the ink in the ink guide in the ejection position direction is performed. Charged particles can be electrophoresed to increase ejection responsiveness.

  Next, a specific configuration example of the discharge electrode substrate 103 will be described. 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. Individual discharge electrodes 109 are formed around the through hole 107, respectively. ing. Here, the insulating substrate 104 is made of polyimide having a thickness of about 25 to 200 μm, the discharge electrode 109 is made of copper foil having 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 positively charged ink 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 system 111 via the ink supply flow path 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 collection system 113. After that, the ink is recovered by the ink circulation system 111. Here, a voltage of, for example, +1.5 kV is applied as a bias from the bias voltage source 123 to the ejection electrode 109, and a pulse voltage of, for example, +500 V is applied as a signal voltage corresponding to the image signal from the signal voltage source 124 to the discharge electrode 109. Superposed on the discharge 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 2 kV in total, in which a 500 V pulse voltage is superimposed on the bias DC 1.5 kV, is applied, the ink droplet flying position 110 at the tip of the convex electrode 108 is applied. Then, the ink droplet 115 is ejected, pulled in the direction of the counter electrode 122, and ejected 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, a means such as providing the above is used, but it should be understood that the present embodiment can be suitably used in this embodiment as needed. Further, a porous body may be provided between the head base plate 102 and the discharge electrode substrate 103. In this case, it is possible to prevent the influence of the change in the ink internal pressure due to the movement of the ink jet head or the like and 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.

FIG. 2 shows a configuration example of an ink circulation system of the ink jet recording apparatus of the present invention.
The ink circulation system 111 includes a sealed ink tank 1 that stores ink in which at least a colorant is dispersed in a dispersion medium, an ejection head 2 that ejects ink according to an input signal, and ink in the ink tank. A pump 3 for supplying to the discharge head; an ink supply system 112 extending from the ink tank to the discharge head through the pump; and the ink for collecting ink from the discharge head to the ink tank, In the present invention, there is provided a magnetic powder removing device that captures magnetic powder by applying a magnetic field to at least one of the ink circulation systems. .
There are two types of pump 3, a positive displacement type and a centrifugal type. In the positive displacement type, there are a reciprocating type, a rotary type, and other methods. A reciprocating type includes a diaphragm pump, a bi-mole pump, a plunger pump, a valveless pump, and the like. The rotary type includes an external gear pump, an internal gear pump, and a tubing pump. Another method is a finger pump. Centrifugal types include centrifugal pumps and mixed flow pumps. Whichever pump is used, clogging is likely to occur if magnetic powder is present in the ink. Among them, the gear pump and the centrifugal pump are classified, and in the case of the magnet drive system, the magnetic powder in the ink adheres to the magnet drive unit, causing clogging at an early stage. Therefore, when the magnetic powder is removed from the dispersion or ink, there is a remarkable improvement effect particularly in the case of the gear pump and the spiral pump and the magnet drive system.
The ink supply system 112 includes a filter 4, an ink concentration detector 6, an accumulator 5, and the like.
The ink circulation system 111 includes a replenishment ink container 8 including a container 8 containing dark ink and a container 9 containing thin ink, and a level detector 11 so that the ink tank is appropriately replenished via a valve 10. It is configured.

Next, the magnetic powder removing device provided in the ink circulation system will be specifically described with reference to the drawings.
FIG. 3 shows a magnetic powder removing device in which a permanent magnet 12 is installed in the ink tank 1.
FIG. 4 shows a magnetic powder removing device in which the permanent magnet 12 is installed in the ink recovery system 113. FIG. 5 shows details of the magnet installation portion of FIG. 4 and shows an example in which the permanent magnet 12 is installed inside the piping tube 113a. In addition, you may install the permanent magnet 12 in the outer side of the piping tube 113a.

Example 1 Ink IJ-1
100 parts by mass of linole blue FG-7350 (Pigment blue 15: 3, manufactured by Toyo Ink Co., Ltd.) as a blue pigment, styrene / vinyl toluene / lauryl methacrylate / butyl acrylate / trimethylammonium ethyl methacrylate (anion, p-toluenesulfonic acid) as a resin A table-type kneader PBV (Irie) which was heated to 85 ° C. after 200 parts by mass of a copolymer (25/27/2/27/18, mass, mass average molecular weight 11,000) was pre-ground with a trioblender and mixed well. Melt-kneaded (120 minutes). The pigment kneaded product was pulverized with a pin mill. Next, 20 parts by mass of the pulverized pigment kneaded product, 93 parts by mass of Isopar G, 25 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 400 parts by mass of X glass beads, a thermostatic bath NESLABRTE7 (MS Equipment Co., Ltd.) at 2000 rpm in a dynomill KDL type (Shinmaru Enterprise) with a hardened disc ) For 4 hours while controlling the liquid temperature of the dispersion at 25 ° C. The volume average diameter of the pigment resin particles in the dispersion was measured by an ultracentrifugal automatic particle size distribution analyzer CAPA700 (Horiba Seisakusho), and was 0.49 μm.

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 was prepared by adding an octadecene-half-maleic acid octadecylamide copolymer as a charge control agent so as to be 0.054% by mass. The viscosity of the obtained ink is 1.5 mPa · sec (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 2.30 (measured with LCR meter, AG-4311 manufactured by Ando Electric Co., Ltd.). Further, the ink IJ-1 showed an overall specific conductivity of 1200 pS / cm and a clear positive charge. The charge amount of ink was measured under the conditions of an applied voltage of 5 V and a frequency of 1 kHz using the above LCR meter and liquid electrode (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.). Next, 50 g of this ink was transferred to a glass container, and KANETEC CO. , LTD MAGNETIC HOLDER (MB-PB) was placed, and when a magnetic field was applied for 1 hour, a lot of magnetic powder (metal powder) was adhered, so that the adhering component was removed to prepare ink IJ-1. The amount of magnetic powder in IJ-1 after removing the magnetic powder was 0.005% by mass.
As the ink jet recording apparatus, a 100 dpi 64 channel electrostatic ink jet head having the head structure shown in FIG. 1 is specified, ink IJ-1 is filled in an ink tank, and ink is supplied to the head portion by an external gear pump manufactured by Chuo Rika Co., Ltd. The solution was sent and circulated. 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. 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 with continuous drawing for 1 hour.
[Comparative Example 1] Comparative ink IJR-1
In Example 1, a comparative ink IJR-1 in which magnetic powder (metal powder) was mixed was prepared without performing treatment with MAGNETIC HOLDER (MB-PB). The amount of magnetic powder in this ink was 0.15% by mass.
As a result of discharging under the same conditions as in Example 1, the drawing image was stably printed with uniform dots without bleeding at the initial stage of discharging, and a clear image with a satisfactory density was obtained. However, after 1 hour, foreign matter started to adhere to the tip of the head, ink clogging gradually occurred, and drawing became impossible at all. As a result of disassembling the external gear pump, it was found that the ink powder was clogged because the magnetic powder (metal powder) in the ink adhered and accumulated inside the gear pump.

[Example 2] Ink IJ-2
Toner BG (Clariant) press cake as a blue pigment and styrene / vinyltoluene / lauryl methacrylate / trimethylammonium ethyl methacrylate (anion, p-toluenesulfonic acid) copolymer (29/66/2/3) as a resin , Mass ratio, mass average molecular weight 17,000) of a 33% toluene solution with respect to the blue pigment, and after stirring with a flasher, it is heated and depressurized to remove water and solvent to have a water content of 1% by mass. A blue mass was obtained. The blue lump was vacuum dried to completely remove moisture, and then pulverized with a sample mill to obtain a blue powder of 0.1 to 0.01 mm.
Next, wet dispersion was performed for 2 hours in the same manner as in Example 1 while controlling the liquid temperature of the dispersion at 25 ° C. The volume average particle size of the pigment resin particles in the dispersion was 0.45 μm. Next, when a bar magnet was directly inserted into this dispersion, magnetic powder (metal powder) adhered. The process was repeated until the magnetic powder did not adhere. The dispersion from which the magnetic powder was removed was diluted with Isopar G so that the pigment resin particle component would be 7.0%, and then the octadecene-half maleic acid octadecylamide copolymer was added to 0.060% by mass as a charge control agent. Was added to prepare ink IJ-2. The surface tension of the ink was 23 mN / m, the viscosity was 1.55 mPa · sec, and the relative dielectric constant was 2.30. Ink IJ-2 showed an overall specific conductivity of 750 pS / cm and a clear positive charge. The amount of magnetic powder in IJ-2 after removing the magnetic powder was 0.001% by mass.
When the drawing performance of the ink IJ-2 was evaluated in the same manner as in Example 1, the ejection stability from the ink head was good, there was no clogging, and the dot shape was stable even after 1 hour of continuous image drawing. I was able to print. The obtained drawn image was free from bleeding, had a sufficient image density, and was high-quality and clear.

[Comparative Example 2] Comparative ink IJR-2
In Example 2, a comparative ink IJR-2 in which magnetic powder (metal powder) was mixed was produced without performing the treatment of inserting a bar magnet into the dispersion. A comparative ink IJR-2 having the same formulation was prepared by adding 7.0% of a pigment resin particle component and 0.06% by mass of a charge control agent (octadecene-half-maleic acid octadecylamide copolymer). The comparative ink IJR-2 had a surface tension of 23 mN / m, a viscosity of 1.60 mPa · sec, and a relative dielectric constant of 2.33. Ink IJ-2 had an overall specific conductivity of 790 pS / cm. The amount of magnetic powder in the ink was 0.02% by mass.
When the drawing performance of the ink IJR-2 was evaluated in the same manner as in Example 2, the drawn image was stably printed with uniform dots without bleeding at the initial stage of ejection, and the density was satisfactory. Although a clear image of good quality was obtained, the flow rate began to decrease after 1 hour, ink clogging occurred after 3 hours, and the drawing became unstable. As a result of disassembling the external gear pump, it was found that the ink powder was clogged because the magnetic powder (metal powder) in the ink adhered and accumulated inside the gear pump.

It is a figure which shows the structural example of the line scanning type | mold multichannel inkjet head used for an electrostatic inkjet recording method, and has shown the cross section of the discharge electrode corresponding to a recording dot. 2 shows an example of the configuration of an ink circulation system of an ink jet recording apparatus of the present invention. An example of a magnetic powder removing device is shown. An example of a magnetic powder removing device is shown. It shows the details of the magnet installation part of FIG. The example of the jig | tool used at a magnetic field processing process is shown. The example of the jig | tool used at a magnetic field processing process is shown.

Explanation of symbols

  1: ink tank, 2: discharge head, 3: pump, 4: filter, 5: accumulator, 6: ink density detector, 7: replenishment ink container, 8: container containing dark ink, 9: contains light ink 10: valve, 11: level detector, 12: permanent magnet, 13: container, 14: dispersion flow inlet, 15: dispersion outflow, 100: ink, 102: head substrate, 103: discharge electrode substrate, 109 : Ejection electrode, 110: ink droplet flight position, 111: ink circulation system, 112: ink supply system, 113: ink recovery system, 123: bias electrode, 124: signal voltage source

Claims (3)

  In a method for producing an ink containing at least a dispersion medium, a colorant, and a dispersant, a magnetic field is applied after the dispersion step or after at least one step after the ink preparation step and is captured by the magnetic field. A method for producing an ink for electrostatic ink jet recording, wherein the ink is produced by removing a substance.   In a method for producing an ink containing at least a dispersion medium, a colorant, and a dispersant, a magnetic field is applied after the dispersion step or after at least one step after the ink preparation step and is captured by the magnetic field. A method for producing an ink for electrostatic ink jet recording, wherein the amount of magnetic powder in the ink for ink jet recording produced by removing the substance is 0.010% by mass or less.   An ink tank for storing ink in which at least a colorant is dispersed in a dispersion medium; an ejection head for ejecting ink in accordance with an input signal; and a pump for supplying ink in the ink tank to the ejection head. An ink supply system extending from the ink tank to the discharge head through the pump, and an ink recovery system extending from the discharge head to the ink tank for recovering ink from the discharge head to the ink tank. An ink jet recording apparatus having an ink circulation system comprising: a magnetic powder removing apparatus that captures magnetic powder by applying a magnetic field to at least one of the ink circulation systems apparatus.

Images