JP2008222977A - Inkjet ink and inkjet recording system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inkjet ink having a high tinting strength and fixing properties and to provide an inkjet recording system. <P>SOLUTION: The inkjet recording system is equipped with an inkjet recording head 21 in which a part of the wall surfaces of pressure chambers 2 furnished with nozzles 3 is composed of piezoelectric elements 8, a pressure wave is applied to ink by the piezoelectric elements 8 and ink droplets are discharged from the nozzles 3 uses a polymer particle containing a colorant as a color material in the ink to be used. The polymer particle satisfies formula (1) (wherein a is an absorbance to the maximum absorption wavelength in a visible light region of the colorant in the ink at a certain concentration of the colorant containing the polymer particle; b is an absorbance to the maximum absorption wavelength in a visible light region of the colorant in the ink at the same concentration of the colorant as that of (a) containing no polymer particle; and c is the weight ratio of the colorant to the polymer particle including the colorant). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet ink excellent in coloring power and fixability and an ink jet recording system using the same.

  Conventionally, solvent-based inks are not used for ink jet printers used in offices, homes, and the like from the viewpoint of environmental safety, and water-based inks using water-soluble dyes as color materials are generally used. However, further improvement is required in view of insufficient water resistance and light resistance of the image. For this reason, proposals have been made to use pigments that exceed the reliability of recorded matter, such as water resistance and light resistance, as colorants for ink-jet inks. Further, in order not to pollute the use environment, proposals have been made for a long time to make ink by dispersing a colorant pigment in an aqueous medium. In this way, pigments with excellent light resistance have been proposed and widely used as color materials to replace water-soluble dyes, but from the viewpoint of performing fine printing with the mechanism of an ink jet printing apparatus, the above color is used. In order to use the material as a water-based ink, there is a problem that it is necessary to stably disperse the material in an aqueous medium.

  In order to solve such problems, various methods have been proposed in which a colorant is contained in a polymer from the viewpoint of fixability and dispersion stability of the pigment. For example, Patent Document 1 discloses a method in which a monomer is added to a pigment dispersion to produce a vinyl polymer, and Patent Document 2 discloses a method in which a water-insoluble colorant is dispersed with a polymerizable surfactant and encapsulated with a photopolymerization initiator. Has been proposed. However, in such a method of stochastically containing the colorant in the polymer, the concentration of the colorant in the particles is not uniform, and there is a high possibility that polymer particles not containing the colorant are also present. On the other hand, Patent Document 3 proposes a method in which a polymer and a colorant are kneaded and adhered in a liquid. However, as in Patent Documents 1 and 2, the concentration of the colorant is not uniform, and further, no colorant is contained. Polymer particles are also likely to be present.

This uneven colorant concentration, especially the presence of particles with low colorant concentration or particles that do not contain colorant, does not contribute to the coloring power of the ink, but increases the viscosity of the ink and ejects droplets. Increases the energy required. That is, when the same solid content is added, there is a problem that the coloring power is lowered even if the fixing property and fastness are good. In addition, Non-Patent Document 1 proposes a method in which a polymerization initiator is introduced into the pigment particle surface and then polymerized together with the monomer. However, there is a high degree of certainty regarding the inclusion of a colorant in the polymer particles. Since the structure of the pigment surface changes, there is a problem that the color tone and light resistance are insufficient.
JP 2005-54043 A JP 2004-91729 A JP 2002-256166 A H.Ueno, T.Ogasawara, M.Kobayashi, T.Iida, N, Tsubokawa, “Color Material Association Magazine”, Vol. 69, p. 743 (issued in 1996)

  An object of the present invention is to provide an ink-jet ink having high coloring power and high fixability and an ink-jet recording system using the same.

（式中、ａ：ポリマー粒子を含有した所定の着色剤濃度におけるインクの、前記着色剤の可視光域における最大吸収波長に対する吸光度、ｂ：ポリマー粒子を含まないａと同じ着色剤濃度におけるインクの、前記着色剤の可視光域における最大吸収波長に対する吸光度、ｃ：着色剤を含めたポリマー粒子に対する着色剤の重量比率である。）
（２）前記着色剤を含有するポリマー粒子は、着色剤の含有量の少ないポリマー粒子を減少させることにより得られるポリマー粒子であることを特徴とする（１）に記載のインクジェット用インク。
（３）前記着色剤を含有するポリマー粒子は、前記着色剤が特定波長に吸収領域をもち、前記ポリマー粒子を含有する分散液を流路上方から流下させて前記特定波長のレーザー光を照射することにより、前記特定波長に吸収領域をもつ着色剤を高濃度に含有する高着色ポリマー粒子を、光泳動によりレーザーの照射方向に移動させて、前記流路の下流に配設され、前記流路を流れ方向に２分するように配設された分離板により隔てられた一方の高着色ポリマー粒子分散液回収槽に回収し、前記着色剤を低濃度に含有する低着色ポリマー粒子分散液を他方の低着色ポリマー粒子分散液回収槽に回収して分離することにより得られるポリマー粒子であることを特徴とする（２）に記載のインクジェット用インク。
（４）ノズルが設けられた加圧室の壁面の一部が圧電素子で形成され、前記圧電素子を作動・変形させて前記加圧室の中のインクに圧力波を作用させて、前記ノズルからインク滴を吐出させるインクジェット記録ヘッドを備えたインクジェット記録システムであって、前記インクは（１）〜（３）のいずれかに記載のインクを用いたことを特徴とするインクジェット記録システム。
（５）前記インクジェット記録ヘッドは、前記ノズル数を１インチ当り６６０個以上有し、駆動周波数が１５ｋＨｚ以上であることを特徴とする（４）に記載のインクジェット記録システム。
（６）前記インクジェット記録ヘッドを、記録媒体の搬送方向に対して直交する水平方向に２個以上配置してなることを特徴とする（４）または（５）に記載のインクジェット記録システム。 As a result of intensive studies to solve the above-mentioned problems, the present inventor reduced the polymer particles containing the colorant at a low concentration in the ink using the polymer particles containing the colorant as the coloring material, The new fact that the fixing property and fastness are high and the deterioration of the coloring power can be prevented by satisfying a predetermined relationship between the absorbance of the agent with respect to a specific absorption wavelength and the weight ratio of the colorant in the polymer particles. The headline and the present invention were completed.
That is, the inkjet ink of the present invention and the inkjet recording system using the inkjet ink have the following configurations.
(1) An ink for ink jet using polymer particles containing a colorant as a coloring material, wherein the polymer particles satisfy the following formula (1).

(Wherein, a: the absorbance of the ink at a predetermined colorant concentration containing polymer particles with respect to the maximum absorption wavelength in the visible light region of the colorant, b: the ink at the same colorant concentration as a without polymer particles) The absorbance with respect to the maximum absorption wavelength in the visible light region of the colorant, and c: the weight ratio of the colorant to the polymer particles including the colorant.)
(2) The ink-jet ink according to (1), wherein the polymer particles containing the colorant are polymer particles obtained by reducing polymer particles having a small content of colorant.
(3) The polymer particles containing the colorant are irradiated with laser light of the specific wavelength by causing the colorant to have an absorption region at a specific wavelength and causing the dispersion containing the polymer particle to flow down from above the flow path. Thus, the highly colored polymer particles containing the colorant having the absorption region at the specific wavelength in a high concentration are moved in the laser irradiation direction by photophoresis, and are disposed downstream of the flow path. Is collected in one highly colored polymer particle dispersion collecting tank separated by a separating plate arranged to divide into two in the flow direction, and the other low colored polymer particle dispersion containing the colorant in a low concentration is collected. (2) The ink-jet ink according to (2), wherein the ink is a polymer particle obtained by collecting and separating in a low-colored polymer particle dispersion collecting tank.
(4) A part of the wall surface of the pressurizing chamber provided with the nozzle is formed of a piezoelectric element, and the piezoelectric element is actuated and deformed to cause a pressure wave to act on the ink in the pressurizing chamber. An ink jet recording system comprising an ink jet recording head for discharging ink droplets from the ink, wherein the ink according to any one of (1) to (3) is used.
(5) The inkjet recording system according to (4), wherein the inkjet recording head has 660 or more nozzles per inch and a driving frequency of 15 kHz or more.
(6) The ink jet recording system according to (4) or (5), wherein two or more of the ink jet recording heads are arranged in a horizontal direction orthogonal to the conveyance direction of the recording medium.

  Since the ink of the present invention uses polymer particles containing a colorant as a coloring material and reduces the polymer particles having a small content of the colorant, the polymer particles satisfy the above formula (1). Since the polymer particles with a small content of the agent are reduced, and the polymer particles are mainly composed of a polymer with a large content of the colorant, an ink jet recording system having high fixability and fastness and little reduction in coloring power can be realized. Moreover, this effect can be expressed stably.

  The ink-jet ink and ink-jet recording system according to the present invention will be described in detail below.

(ink)
The ink in the present invention comprises at least water, a coloring material, and an organic solvent containing a surfactant. In addition, a pH adjuster, an antiseptic and fungicide can be added as necessary.
The coloring material of the present invention comprises polymer particles containing a colorant, and the polymer particles satisfy the above formula (1) by reducing the polymer particles having a low content of the colorant. If a / b in the above formula (1) is within the range of the above formula (1), since the color material is composed of polymer particles, the fixing property and fastness are excellent, the bronze phenomenon can be prevented, and the color material is colored. The polymer particles (hereinafter referred to as “low-colored polymer particles”) having a low content of the colorant are reduced, and mainly composed of polymer particles (hereinafter referred to as “highly-colored polymer particles”) having a high content of the colorant. Can be suppressed.

  However, when a / b in the above formula (1) exceeds 0.95, the tinting strength is improved, but the bronze phenomenon occurs. On the other hand, if a / b is less than 1.05 times the weight ratio c of the colorant in the polymer particles, the coloring power is lowered, which is not preferable.

A dispersion in which low-colored polymer particles are reduced can be prepared by the method described below.
FIG. 4 shows an outline of the configuration of a separation processing apparatus for separating low-colored polymer particles.
First, a dispersion 42 in which the low color polymer particles 40 and the high color polymer particles 20 are mixed is supplied from the stock solution tank 22 to the dispersion liquid supply port 23. Next, the dispersion 42 is supplied into the separation channel 28 from the dispersion supply port 23. At this time, the polymer particles in the dispersion liquid 42 are irradiated with laser light oscillated from the laser oscillator 24 through the slit glass 25, for example, converged to a diameter of 100 μm of 593 nm and 1 W, and received propulsive force by the laser light. The separation channel 28 is pushed to the opposite side from the surface of the slit glass 25. That is, the colorant of the polymer particles absorbs the laser beam, thereby obtaining a migration speed (movement speed) and moving in the dispersion liquid 42. And this movement speed is so large that the density | concentration of a coloring agent is high. On the other hand, the separation channel 28 has a depth of 200 μm in the horizontal direction from the surface of the slit glass 25, and includes a separation plate 29 at a position below the slit glass 25 at a distance of 100 μm from the surface of the slit glass 25. ing. The separation plate 29 extends to the bottom surface downstream of the flow path, and the low color polymer particle dispersion recovery tank 26 on the slit glass 25 side disposed on the bottom surface and the high color polymer particle dispersion on the opposite side thereof. The liquid recovery tank 27 is isolated. Among the polymer particles pushed by the laser light, the polymer particles 20 having a high colorant concentration with a high moving speed and the polymer particles originally flowing on the opposite side of the slit glass 25 collect the highly colored polymer particle dispersion liquid 47. It flows into the highly colored polymer particle dispersion recovery tank 27 and is recovered. In the case of a laser having a wavelength of 593 nm, for example, in the case of a cyan pigment having absorption at this wavelength, the movement speed of the polymer particles containing this in a high concentration is particularly high. The proportion of polymer particles having a high concentration is increased. When processing polymer particles of other colors, laser light having a wavelength that is absorbed by each colorant may be used. On the other hand, the polymer particles 40 having a low colorant concentration with a low moving speed and the particles originally flowing down the slit glass 25 flow into the low color polymer particle dispersion recovery tank 26 for recovering the low color polymer particle dispersion 46 and are recovered. Is done. And the obtained highly colored polymer particle dispersion liquid 47 is returned again to the stock solution tank 22, and the low colored polymer particle 40 in a dispersion liquid can be reduced by repeating the process shown above.
As the laser oscillator 24, for example, ORANGE manufactured by Xiton Photonics can be used, but is not particularly limited thereto.

  The phenomenon in which the polymer particles containing the colorant move by receiving a driving force by laser light in the dispersion is due to the interaction between the light and the fine particles, and the fine particles are dispersed in the dispersion by absorbing the laser light. . Regarding this laser electrophoresis, for example, non-patent literature [A. Hirai, H. Monjushiro, and H. Watarai, "Laser-Photophoresis of a Single Droplet in o / w Emulsions", Langmuir, 12, 5570-5575 (1997 )] Describes the principle and the like.

(Coloring agent)
The components of the colorant of the present invention include, as organic colorants, azo, phthalocyanine, anthraquinone, quinacridone, metal complex, dioxazine, indigo, thioindigo, berylene, isoindolenone, aniline black, Examples include azomethine pigments. Examples of the inorganic colorant include rhodamine B lake pigment and carbon black. For example, carbon black manufactured by Mitsubishi Chemical Corporation includes # 20B, # 40, MA100, and the like. Examples of carbon black manufactured by Degussa include Color Black FW18, Color Black S170, Special Black 250, and the like. Examples of carbon black manufactured by Columbia Carbon include Conductex SC and Raven 1255. Examples of carbon black manufactured by Cabot include Monarch 700, Monarch 880, and Elftex 12.

(Polymer particles)
The polymer particles of the present invention contain the colorant and are used as a coloring material. The component of the polymer particles is not particularly limited. For example, styrene resin, styrene-acrylic resin, polyester resin, polyacrylic resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyamide resin, polyurethane resin. And thermoplastic resins such as polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Of course, if necessary, other resins may be used in combination with these resins, or two or more of these resins may be used.

  Examples of the method for incorporating the colorant into the polymer particles include a method in which the colorant and the polymer particles are mixed using a ball mill, a sand mill, a roll mill, an agitator, an ultrasonic homogenizer, a wet jet mill, a paint shaker, or the like. .

  As for the average particle diameter of the polymer particle containing the coloring agent in this invention, 30-300 nm is preferable, More preferably, it is 50-200 nm. The average particle size can be measured using, for example, a dynamic light scattering type particle size distribution measuring device (LB-550, manufactured by HORIBA).

  In the present invention, a nonionic surfactant can be contained for adjusting the surface tension. Examples of such nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyerylene alkyl allyl ethers, polyoxyethylene polyoxypropylene glycols, glycerin esters, sorbitan esters, sucrose esters, polyoxyethylene ethers of glycerin esters, Examples include sorbitan ester polyoxyethylene ether, sorbitol ester polyoxyethylene ether, fatty acid alkanolamide, polyoxyethylene fatty acid amide, amine oxide, and polyoxyethylene alkylamine.

  In the present invention, water (preferably purified water) is used as the aqueous medium used in the ink. It is preferable to add a water-soluble organic solvent to the water. Specific examples of the water-soluble organic solvent include, for example, glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; glycerin; diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, Of polyhydric alcohols such as ethylene glycol monobutyl ether, methyl carbitol, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, diethyl carbitol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and propylene glycol monomethyl ether Ethers; acetates; thiodiglycol; N-methyl-2-pyrrolidone; , 3-dimethyl imidazolidinone, formamide, nitrogen-containing compounds such as dimethylformamide; dimethyl sulfoxide and the like.

(Preparation of ink)
Next, an ink preparation method will be described. The ink of the present invention can be obtained by dispersing polymer particles containing at least a colorant and a dispersant for the polymer particles in an aqueous medium, and diluting the obtained dispersion with an aqueous medium.
Dispersion treatment and dilution can be performed according to a conventionally known method. Examples of the disperser used in the dispersion treatment include a disperser such as a ball mill, a roll mill, and a sand mill. Among these, a high-speed sand mill is preferable. For example, a super mill, a sand grinder, a bead mill, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all trade names) are preferably used. The obtained high-concentration dispersion is usually diluted 2 to 10 times to obtain a recording ink having a desired concentration.

  An example of the proportion of each component in the recording ink will be given. That is, the ratio of the colorant is 40 to 90% by weight, preferably 70 to 85% by weight, based on the polymer particles including the colorant, and the ratio of the nonionic surfactant is usually 0.01 relative to the total amount of the ink. -10 wt%, preferably 0.1-5 wt%, and the proportion of the water-soluble organic solvent is usually 1-40 wt%, preferably 3-30 wt%, based on the total amount of the ink.

(Recording head)
In an example of the recording head 21 of the present invention, FIG. 1 shows a state before a piezoelectric actuator including a laminated piezoelectric element 8 and individual electrodes 9 is attached.
The recording head in the illustrated example has a plurality of dot forming portions including a pressurizing chamber 2 and a nozzle 3 communicating therewith arranged on a single substrate 1.
2A is an enlarged cross-sectional view showing one dot forming portion in a state where the piezoelectric actuator is attached in the ink jet recording head of the above example, and FIG. 2B is a diagram showing one dot forming portion. It is a perspective view which shows the overlapping state of each part which comprises. FIG. 3 is an enlarged view of the vicinity of the nozzle 3 in FIG.

The nozzles 3 of the dot forming section are arranged in a plurality of rows in the main scanning direction (printing medium conveyance direction) indicated by white arrows in FIG. In the example shown in the figure, the lines are arranged in four rows, and the pitch between the dot forming portions in the same row is 150 dpi, and the recording head as a whole realizes 600 dpi.
Each dot forming portion is formed on the upper surface side of the substrate 1 in FIG. 2A and has a center at the center in the width direction of the rectangular portion, the diameter is equal to the width length, and the horizontal sectional shape is semicircular. The pressurizing chamber 2 having a flat plate shape with the end portions being at both ends in the longitudinal direction of the rectangular portion, and the semicircle and center of the end portion on the one end side of the pressurizing chamber 2 on the lower surface side of the substrate 1 Are connected to each other through a cylindrical nozzle passage 4 having the same diameter and the same center as the semicircle of the end portion, and the end on the other end side of the pressurizing chamber 2. A configuration in which the pressurizing chamber 2 is connected to a common flow path 6 formed in the substrate 1 so as to communicate with each dot forming portion via a cylindrical supply port 5 having the same center as the semicircle of the portion; It has become.

In the example shown in the figure, each of the above parts includes a first substrate 1a in which the pressurizing chamber 2 is formed, a second substrate 1b in which an upper portion 4a of the nozzle channel 4 and a supply port 5 are formed, and a lower portion 4b of the nozzle channel 4. The third substrate 1c on which the common flow path 6 is formed and the fourth substrate 1d on which the nozzle 3 is formed as a nozzle plate are stacked and integrated in this order.
In addition, as shown in FIG. 3, the nozzle 3 has an opening 30 at the tip on the ink droplet ejection side formed in a circle on the lower surface 1e of the fourth substrate 1d, which is the lower surface side of the substrate 1. At the same time, the nozzle 3 is formed in a tapered shape (conical shape) so that the opening 30 on the distal end side is smaller than the opening 31 on the pressurizing chamber 2 side.

  As shown in FIG. 1, the first substrate 1 a and the second substrate 1 b are connected to a common flow path 6 formed in the third substrate 1 c with piping from an ink cartridge (not shown) on the upper surface side of the substrate 1. The through-hole 11a for comprising the joint part 11 for doing is formed. Furthermore, each board | substrate 1a-1d consists of resin, a metal, etc., for example, and is formed with the plate-shaped body which has the through-hole used as said each part by the etching etc. which used the photolithographic method, and has predetermined thickness.

  On the upper surface side of the substrate 1, the laminated piezoelectric element 8 having a planar shape and a transverse vibration mode having a common electrode 7 having the same size as that of the substrate 1, and the addition of each dot forming portion. The piezoelectric actuator AC is configured by laminating individual electrodes 9 having the same plane shape, which are substantially rectangular and are individually provided at positions overlapping the central portion of the pressure chamber 2 in this order.

  Both the common electrode 7 and the individual electrode 9 are formed of a metal foil excellent in conductivity such as gold, silver, platinum, copper, and aluminum, a plating film made of these metals, a vacuum deposition film, or the like.

  As a piezoelectric material for forming the piezoelectric element 8, for example, lead zirconate titanate (PZT), or one or more oxides of lanthanum, barium, niobium, zinc, nickel, manganese, etc. are added to the PZT. Examples thereof include PZT-based piezoelectric materials such as PLZT. In addition, lead magnesium niobate (PMN), lead nickel niobate (PNN), lead zinc niobate, lead manganese niobate, lead antimony stannate, lead titanate, barium titanate, etc. You can also.

  The piezoelectric element 8 is formed by, for example, bonding and fixing a chip having a predetermined planar shape obtained by sintering a sintered body formed by sintering the above piezoelectric material into a thin plate shape at a predetermined position, or a so-called sol-gel method. (Or by the MOD method), a paste formed from an organometallic compound that is the basis of the piezoelectric material is printed in a predetermined planar shape, and formed through drying, pre-baking, and firing steps, or a reactive sputtering method, It can be formed by forming a thin film of a piezoelectric material into a predetermined planar shape by a vapor phase growth method such as a reactive vacuum deposition method or a reactive ion plating method.

  The surface roughness of the piezoelectric element 8 can be obtained by accelerating particle growth under firing conditions, surface processing using mechanical polishing, etching, or the like. The surface roughness of the piezoelectric element 8 is measured using, for example, an optical interference type surface roughness measuring device (Wyko NT1100 manufactured by Veeco) and can be evaluated as an average surface roughness Ra.

  In order to drive the piezoelectric element 8 in the transverse vibration mode, for example, the polarization direction of the piezoelectric material is oriented in the thickness direction of the piezoelectric element 8, more specifically in the direction from the individual electrode 9 to the common electrode 7. For this purpose, conventionally known polarization methods such as a high temperature polarization method, a room temperature polarization method, an alternating electric field superposition method, and an electric field cooling method can be employed. Moreover, you may age-treat the piezoelectric element 8 after polarization.

  The piezoelectric element 8 in which the polarization direction of the piezoelectric material is oriented in the above-described direction contracts in a plane orthogonal to the polarization direction by applying a positive drive voltage from the individual electrode 9 with the common electrode 7 grounded. To do. For this reason, the force when the bending occurs is transmitted to the ink in the pressurizing chamber 2 as a pressure wave, and the ink in the supply port 5, the pressurizing chamber 2, the nozzle flow path 4, and the nozzle 3 is transmitted by this pressure wave. Causes vibration. As a result of the vibration speed going outward from the nozzle 3, the ink meniscus in the nozzle 3 is pushed out from the opening 30 at the tip on the ink droplet ejection side to form an ink column. The vibration speed will eventually go in the nozzle, but the ink column will continue to move in the outward direction, so it will be separated from the ink meniscus and gathered into one or two ink drops that will fly in the direction of the paper. To form dots on the paper.

  The amount of ink that has decreased due to the flying ink droplets is reduced from the ink cartridge by the ink meniscus surface tension in the nozzle 3, the piping of the ink cartridge, the joint portion 11, the common flow path 6, the supply port 5, and the pressure chamber 2, and the nozzle 3 is refilled via the nozzle flow path 4.

  On the lower surface 1e of the fourth substrate 1d, which is the lower surface side of the substrate 1, as described above, an area A1 having a predetermined planar shape that is not subjected to water repellent treatment is provided at the tip of the nozzle 3 on the ink droplet ejection side. It is provided so as to overlap with the circular opening 30. That is, the water repellent layer 12 is laminated on the other surface 1e except the region A1, and the surface of the fourth substrate 1d is exposed without forming the water repellent layer 12 in the region A1. Thus, the water-repellent treatment is not performed.

  Although the thickness of the water repellent layer 12 is not specifically limited, It is preferable that it is 0.5-2 micrometers. If the thickness of the water-repellent layer 12 is less than this range, the water repellency is lowered, and there is a possibility that ink droplet ejection failure due to ink adhesion may occur. Further, the water repellent layer 12 having a film thickness exceeding 2 μm is not easily formed, and even if it can be formed, there is a possibility that no further effect can be obtained.

  The ink jet recording head of the present invention draws the ink meniscus in the nozzle by deforming the piezoelectric element 8 in the direction of expanding the capacity of the pressurizing chamber 2 immediately before the dot formation, and then reduces the capacity of the pressurizing chamber 2. By deforming the piezoelectric element 8 in the direction of reduction, the piezoelectric element 8 is deformed in the direction of reducing the capacity of the pressurizing chamber 2 when the ink droplet is separated from the ink meniscus and ejected, and at the time of dot formation. Thus, the ink meniscus in the nozzle 3 is pushed out, and then the piezoelectric element is deformed in the direction of expanding the capacity of the pressurizing chamber 2, thereby drawing the ink meniscus and separating the ink droplets from the ink meniscus and ejecting them. It may be driven by any driving method of the push type.

In the ink jet recording system of the present invention, in order to achieve high-speed printing, the recording head has 660 or more nozzles, preferably 1000 to 3000 nozzles, a driving frequency of 15 kHz or more, and the recording head 21. Are two or more, preferably 2 to 8, more preferably 2 to 4 in a horizontal direction perpendicular to the recording medium conveyance direction. Moreover, it can be used as a line head by connecting a plurality more than the width of the recording medium.
In the initial filling of the ink into the ink jet recording head, as shown in FIG. 1, the ink is pumped (not shown) between a pipe from an ink cartridge (not shown) and a joint portion 11 for connecting the pipe. The recording head is supplied through the joint portion 11. The pump can be used according to the purpose, such as a tube pump, a gear pump, or an electromagnetic pump.

  In the case of color printing, the ink is combined with the recording head to form a multicolor set, and usually an ink set including four colors of yellow, magenta, cyan, and black is formed. It is preferable that the image forming apparatus is a combination of the ink and the recording head.

  Hereinafter, the ink and inkjet recording system of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

First, a dispersion having polymer particles containing a colorant was prepared according to the following formulation.
(Preparation of dispersions A to C)
(1) Dispersion A: 25 parts by weight of styrene, 5 parts by weight of lauryl methacrylate, 30 parts by weight of methoxypolyethylene glycol methacrylate [manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-40G], and styrene-acrylonitrile copolymer A copolymer comprising 10 parts by weight of a macromer (manufactured by Toa Gosei Co., Ltd., trade name: AN-6, styrene content: 70% by weight, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group) 1). The weight average molecular weight of the obtained polymer 1 was 12,000.
300 g of a methyl ethyl ketone solution of polymer 1 (amount of polymer 1: 50% by weight), 450 g of chromofine blue 4920 (B-15: 3, β-type copper phthalocyanine) manufactured by Dainichi Seika as a colorant, and 500 g of methyl ethyl ketone at 25 ° C. with a disper, Mixing for 60 minutes gave a mixture of colorant and polymer. The viscosity of the mixture was 2000 mPa · s (25 ° C.).
The obtained mixture was dispersed with a shear stress of 1.2 × 10 ⁶ Pa under the following conditions using a three-roll mill (manufactured by Noritake Company, trade name: NR-84A).
Roll peripheral speed difference: 6m / s
Clearance between rolls: 10 μm
Number of treatments: 5 passes The obtained dispersion has polymer particles with an average particle size of 0.15 μm containing a colorant, a sharp particle size distribution, no aggregates, and stable dispersibility over a long period of time. Indicated. This is dispersion A.
(2) Dispersion B: Prepared in the same manner as Dispersion A, except that 200 g of the methyl ethyl ketone solution of polymer 1 (amount of polymer 1: 50% by weight) was changed to 400 g of chromofine blue 4920 manufactured by Dainichi Seika.
(3) Dispersion C: A dispersion C was prepared in the same manner as Dispersion A, except that 140 g of the methyl ethyl ketone solution of Polymer 1 (amount of Polymer 1: 50% by weight) and 400 g of Chromofine Blue 4920 manufactured by Dainichi Seika Co., Ltd. were used.

(Preparation of dispersion 1)
After removing methyl ethyl ketone from the dispersion A obtained above by vacuum distillation and adjusting the concentration of the polymer particles containing the colorant to 25%, the mixture was filtered with a membrane filter having an average pore diameter of 5 μm. A180 g could be filtered and the filterability was good. This was designated as Dispersion Liquid 1.

(Preparation of dispersion 2)
As a colorant, 20 parts by weight of Chromofine Blue 4920 (manufactured by Dainichi Seika), 1 part by weight of a dispersing agent (Emulgen 420 made by Kao) and 59 parts by weight of ion-exchanged water are placed in a sand mill and dispersed for 3 hours. To prepare a colorant dispersion. This was designated as Dispersion Liquid 2.

(Preparation of dispersions 3 to 16)
The dispersions A, B, and C were subjected to low-colored polymer particle separation treatment under the processing conditions shown in Table 1 using the above-described separation processing apparatus, and then the concentration of polymer particles containing a colorant was changed to 23.4 for dispersion B. %, Dispersion C was prepared in the same manner as Dispersion 1 except that Dispersion C was adjusted to 22.06%. However, the separation treatment was performed after 10-fold dilution with methyl ethyl ketone. In addition, about the dispersion liquids 7 and 12, the said separation process was not performed.
Table 1 shows the treatment conditions of each dispersion and the weight ratio of the colorant in the polymer particles. The flow-down speed in Table 1 is the speed at which the dispersion 42 in the separation flow path 28 flows down in the separation processing apparatus of FIG.

[Example 1]
It was obtained by mixing 6 parts by weight of glycerin, 1 part by weight of acetylene glycol / polyethylene oxide adduct [Orphine E1010 (manufactured by Nissin Chemical Industry)] and 73 parts by weight of ion-exchanged water with respect to 20 parts by weight of dispersion 4. The mixed liquid was filtered through a membrane filter having an average pore diameter of 0.5 μm to remove coarse particles, whereby the ink of Example 1 was produced.

[Examples 2-6, Comparative Examples 1-9]
Inks of Examples 2 to 6 and Comparative Examples 1 to 9 were prepared in the same manner as the ink of Example 1, except that the dispersion shown in Table 2 was used.

(Measurement of absorbance)
The absorbance of the ink was measured at a wavelength of 610 nm when the ink obtained above was diluted 1500 times with ion-exchanged water. A U-3000 Spectrometer manufactured by Hitachi, Ltd. was used as the absorbance measurement apparatus.

(Preparation of recording head)
1 and 2 (a) and 2 (b). The dimensions are as follows: the area of the pressurizing chamber 2 is 0.2 mm ² , the width is 2200 μm, the depth is 100 μm, and the nozzle channel 4 The diameter is 200 μm, the length is 800 μm, the diameter of the supply port 5 is 30 μm, the length is 40 μm, the length of the nozzle 3 is 30 μm, and the shapes of the ink discharge side opening 30 and the pressure chamber 2 side opening 31 are radii. A recording head having a circular shape of 10 μm and 20 μm, and having 166 dot forming portions composed of these portions per row and 664 dot forming portions in total (4 rows) arranged on the substrate 1 is used. It was.
The pitch between the dot forming portions in the same row was 150 dpi, and the adjacent rows were shifted by ½ pitch to make 600 dpi as a whole.

(Evaluation methods)
Using the ink and the recording head 21 obtained above, each ink was filled in an ink jet recording head, and a solid image of 1 cm × 1 cm was printed on a copy paper (CC90 manufactured by Xerox) at the time of filling. Was measured with RD-19I manufactured by Gretag Machbeth, and the reflection density was evaluated. Moreover, bronze property evaluation was performed visually.
The evaluation results are shown in Table 2. FIG. 5 is a graph showing the relationship between a / b and reflection density.

(Evaluation results)
As shown in Table 2, Examples 1 to 6, which are within the scope of the present invention, had a good reflection density without a reduction in coloring power. Moreover, no bronze phenomenon occurred.
On the other hand, when a / b is less than 1.05 × c, it can be seen that the reflection density decreases and the coloring power decreases (Comparative Examples 1, 3, 4, 6, 7, and 9). On the other hand, when a / b exceeded 0.95, the reflection density was good, but bronzing occurred (Comparative Examples 2, 5, and 8).
In FIG. 5, broken lines La, Lb, and Lc are values of the left side (1.05 × c) of the above formula (1) for the dispersions A, B, and C, respectively, and Lu is a value of the right side of the above formula (1). Is shown. FIG. 5 shows that the reflection density is increased by reducing the low-colored polymer particles 40 even when the same dispersion is used. However, the higher the reflection density, the better, but bronzing occurs when a / b exceeds 0.95. This is thought to be because the amount of polymer was reduced too much. In addition, the slope of the reflection density is gentler on the right side than the left side values (La, Lb, and Lc) corresponding to the respective dispersions. That is, the effect of reducing the low-colored polymer particles 40 is a region that is easily and stably expressed, and it is desirable to use in this region in consideration of the mass productivity of the ink.

1 is a plan view showing an embodiment of an ink jet recording head according to the present invention. (A) is a partially enlarged longitudinal sectional view of the ink jet recording head according to the present invention, and (b) is a bottom view of (a). It is an enlarged view of the nozzle part of Fig.2 (a). It is the schematic which shows the structure of the separation processing apparatus of the low coloring polymer particle which concerns on this invention. It is a graph which shows the relationship between a / b and reflection density which concern on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Pressurization chamber 3 Nozzle 4 Ink flow path 5 Supply port 6 Common flow path 7 Common electrode 8 Piezoelectric element 9 Individual electrode 11 Joint part 12 Water repellent layer 20 Highly colored polymer particle 21 Recording head 22 Stock solution tank 23 Dispersion liquid supply Mouth 24 Laser heating device 25 Slit glass 26 Low colored polymer particle dispersion recovery tank 27 High colored polymer particle dispersion recovery tank 28 Separation flow path 29 Separation plate 40 Low colored polymer particles

Claims (6)

An ink for ink jet using polymer particles containing a colorant as a colorant, wherein the polymer particles satisfy the following formula (1).

(Wherein, a: the absorbance of the ink at a predetermined colorant concentration containing polymer particles with respect to the maximum absorption wavelength in the visible light region of the colorant, b: the ink at the same colorant concentration as a without polymer particles) The absorbance with respect to the maximum absorption wavelength in the visible light region of the colorant, and c: the weight ratio of the colorant to the polymer particles including the colorant.)   2. The ink-jet ink according to claim 1, wherein the polymer particles are polymer particles obtained by reducing polymer particles having a small colorant content.   The polymer particles have an absorption region at a specific wavelength, and the polymer particles are absorbed at the specific wavelength by irradiating the dispersion liquid containing the polymer particles from above the flow path and irradiating the laser light with the specific wavelength. Highly colored polymer particles containing a colorant having a region in a high concentration are moved in the laser irradiation direction by photophoresis and arranged downstream of the flow path so that the flow path is divided into two in the flow direction. Is recovered in one highly colored polymer particle dispersion recovering tank separated by a separation plate disposed in the same, and the low colored polymer particle dispersion containing the colorant in a low concentration is recovered in the other low colored polymer particle dispersion. 3. The ink-jet ink according to claim 2, wherein the ink-jet ink is polymer particles obtained by collecting and separating in a tank.   A part of the wall surface of the pressurizing chamber provided with the nozzle is formed of a piezoelectric element, and the piezoelectric element is operated and deformed to cause a pressure wave to act on the ink in the pressurizing chamber. An ink jet recording system comprising an ink jet recording head for discharging ink, wherein the ink according to claim 1 is used as the ink.   5. The ink jet recording system according to claim 4, wherein the ink jet recording head has 660 or more nozzles per inch and a driving frequency of 15 kHz or more.   6. The ink jet recording system according to claim 4, wherein two or more ink jet recording heads are arranged in a horizontal direction perpendicular to the conveyance direction of the recording medium.

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