JP5580874B2 - Recording liquid and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a recording liquid for use in an ink jet recording head, which contains at least a colorant and a specific penetrant in water and has a specific viscosity, and an image forming apparatus using the same.

  2. Description of the Related Art In recent years, apparatuses that form an image on a recording medium by causing an aqueous liquid containing a color material to fly from a recording head have been rapidly spread due to advantages such as low noise and low running cost. Along with this, improvements in high-definition images and printing speed have been desired. In order to improve the printing speed, there is a method of increasing the number of nozzles and ejecting more recording liquid droplets per unit time of one head. Therefore, the drive frequency is desired to be 15 kHz or more, and the recording liquid used per unit time of one head must be supplied from the cartridge to the nozzles without excess or deficiency.

  On the other hand, since the recording liquid is an aqueous liquid containing a color material, non-ejection occurs due to clogging of the recording liquid when the nozzle portion of the recording head is left in the open state for a long time. This is considered to be due to the increase in the viscosity of the recording liquid or the precipitation or aggregation of the coloring material due to the evaporation of the moisture of the recording liquid in the nozzle portion. Therefore, in order to improve the ejection failure of the recording liquid such as non-ejection and flying curve, a cleaning device is generally provided. The cleaning device is, for example, moved with respect to the discharge port forming surface with a wiper blade, and removes precipitates or aggregates of the coloring material adhering to the discharge port forming surface while the wiping portion is in contact with and rubbed. . Therefore, for example, in Patent Document 1, the cleaning property of the nozzle forming surface of the recording head is defined by the recording liquid and foreign matter adhering state on the nozzle forming surface of the head, the recording liquid physical properties, and the contact amount of the wiper blade with respect to the nozzle forming surface. For example, a plurality of wiper blades having different characteristics have been proposed.

  In addition, in order to improve the high-definition image and the printing speed, the recording liquid to be ejected tends to be reduced in size, and therefore the nozzle diameter tends to be reduced. However, at present, it is difficult to achieve both the reduction in diameter and various characteristics of the recording liquid. Therefore, in Patent Document 2, in order to achieve high-speed stable ejection using an inkjet head including a filter as a component, the viscosity of the ink at 25 ° C. is set to 6 to 13 mPa · s, and between the ink supply unit and the ink ejection unit. Proposals have been made to define the fluid resistance of the filter placed in the box.

  Further, in order to improve the high-definition image and the printing speed, the recording liquid does not cause color bleeding or feathering on the recording medium, and needs to be dry so as not to stain the fingers even when rubbed after output. Therefore, Patent Document 3 proposes to increase the permeability to a recording medium by containing 2,4-diethyl-1,5-pentanediol in an aqueous recording liquid, that is, to prevent image deterioration by osmotic drying. I am doing. In Patent Document 4, in order to prevent clogging in the recording head tip and the recording ink flow path caused by vaporization of components constituting the recording liquid and to improve the uniformity of the recording liquid, 2, 4 It has been proposed to contain -diethyl-1,5-pentanediol.

JP 2005-224975 A JP 2006-150954 A JP 2003-253167 A JP 2002-309136 A

  However, the remaining wiping of the discharge port formation surface by the wiper blade in Patent Document 1 is difficult to remove even if the recording liquid dries with time and rubs with the wiper blade. Further, when the power is turned off, capping is performed to prevent the nozzle portion and the formation surface thereof from drying, but the recording liquid thickened in the capping portion, color material precipitates, and aggregates accumulate over time. For this reason, a nozzle part and its formation surface will be soiled, and discharge failure will be caused.

  Further, as in Patent Document 2, even if a filter is disposed between the ink supply unit and the ink discharge unit and the fluid resistance is defined, the filter itself may be clogged during long-term use.

  In addition, in an inkjet image forming apparatus, non-ejection and bending of recording droplets become noticeable during long-term use, leading to image degradation. Therefore, the recording head is reciprocated perpendicularly to the conveyance direction of the recording medium. There is a system generally called a serial head that performs printing by operating. This method is also used in Patent Documents 3 and 4. Here, the ejection defect can be compensated by wiping the ejection surface during the reciprocating operation of the recording head. However, since it is necessary to reciprocate the recording head, high-speed printing cannot be achieved even if the drive frequency is increased.

In order to achieve high-speed printing, high-speed printing can be achieved by mounting a line head having at least 1 inch wide and 500 or more nozzles as a recording head, and further connecting two or more recording heads. . However, it is difficult for the line head to make up for the discharge defects for each reciprocating operation performed serially from the viewpoint of high-speed printing.
Therefore, when the recording liquids of Patent Documents 3 and 4 are used for a high-speed printing line head, since the viscosity of the recording liquid is not considered in Patent Documents 3 and 4, ejection from the head becomes unstable. .

  An object of the present invention is to provide an ink jet recording head front end portion in an image forming apparatus having an ink jet recording head that discharges liquid droplets from a nozzle by causing a pressure wave to act on a recording liquid in a pressure chamber by operation and deformation of a piezoelectric element. In addition, there is provided a recording liquid suitable for high-speed printing and an image forming apparatus equipped with a line head using the recording liquid, which can obtain a high-definition image by high-speed printing without clogging or dirt in the head flow path. To do.

  As a result of intensive studies to solve the above problems, the present inventor has developed an image including an inkjet recording head containing a recording liquid containing at least a coloring material, a wetting agent, and a specific penetrating agent and having a viscosity in a predetermined range. By using it in a forming device, there is no clogging or contamination of the recording liquid, and the recording liquid can be supplied in an appropriate amount without excess or deficiency during high-speed printing to suppress ejection defects, and high-definition images can be obtained with high-speed printing. As a result, the present invention has been completed.

That is, the recording liquid of the present invention and the image forming apparatus using the same have the following configuration.
(1) Contains water, a coloring material, a wetting agent, 2,4-diethyl-1,5-pentanediol as a penetrating agent, and triethylene glycol monobutyl ether or hexylene glycol. A recording liquid having a surface tension of 10 to 35% by mass with respect to the total liquid medium and having a surface tension of 40 mN / m or less at a lifetime of 10 msec.
(2) The recording liquid according to (1), wherein the wetting agent is glycerin.
(3) 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 recording liquid in the pressurizing chamber. An image forming apparatus comprising an ink jet recording head for discharging recording droplets from a nozzle, wherein the recording liquid is the recording liquid described in (1) or (2).
(4) The ink jet recording head has a width of 1 inch or more, 500 or more nozzles, and two or more ink jet recording heads arranged in a horizontal direction perpendicular to the recording medium conveyance direction. The image forming apparatus according to (3), further comprising: a line head.
(5) The ink jet recording head is characterized in that an appropriate amount of liquid discharged from the nozzle is 1 to 30 pL, a droplet speed is 5 to 15 m / s, a maximum driving frequency is 20 kHz or more, and a resolution is 600 dpi or more. The image forming apparatus according to (3) or (4).

  According to the present invention, in an image forming apparatus for forming an image on a recording medium by discharging an aqueous recording liquid containing a color material from an ink jet recording head, the image forming apparatus includes a specific penetrant and has a predetermined range of viscosity. Since the recording liquid is used, there is no clogging or dirt in the head tip or the ink jet recording head flow path even if the unused period is long, and the recording liquid is supplied without excess or deficiency during high-speed printing. A high-definition image can be obtained by high-speed printing over a long period of time.

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).

(Recording liquid)
In the recording liquid of the present invention, a part of the wall surface of the pressurizing chamber provided with the nozzle is formed of a piezoelectric element, and the pressure wave acts on the recording liquid in the pressurizing chamber by operating and deforming the piezoelectric element. And used in an image forming apparatus having an ink jet recording head for discharging recording droplets from the nozzle, and water, a coloring material, a wetting agent, and 2,4-diethyl-1,5-pentane as a penetrating agent. And a viscosity of 3.0 to 6.0 mPa · s.

  According to the present invention, by including 2,4-diethyl-1,5-pentanediol as a penetrant in the recording liquid, even if the water in the recording liquid evaporates, Clogging and dirt can be prevented. This is because 2,4-diethyl-1,5-pentanediol used for the recording liquid has a high boiling point and a low freezing point, and thus becomes liquid in a wide temperature range, so that the water of the recording liquid evaporates. This is because clogging does not occur in the leading end of the recording head or in the flow path. The content of 2,4-diethyl-1,5-pentanediol in the total liquid medium is 0.1 to 3% by mass, preferably 0.5 to 2% by mass, and more preferably 0.5 to 1% by mass. It is. By setting the content of 2,4-diethyl-1,5-pentanediol within the above range, it is possible to effectively prevent clogging and contamination as described above.

  The recording liquid of the present invention preferably further contains triethylene glycol monobutyl ether or hexylene glycol as the penetrant. The recording liquid containing 2,4-diethyl-1,5-pentanediol has a low surface tension of 40 mN / m or less at a lifetime of 10 msec, and is subjected to water repellency treatment using not only the inner wall of the nozzle but also Teflon (registered trademark). The nozzle surface may get wet. In this case, a thin recording liquid film is formed on the nozzle surface even after the recording liquid thickened by a wiper blade or the like is removed. When a thin recording liquid film is formed on the nozzle surface, the trailing edge of the main droplet discharged from the nozzle by the pressure wave is pulled by the recording liquid film on the nozzle surface, and the main liquid droplet When the droplet discharge speed is slowed down or landed on the recording medium, the trailing edge of the droplet scatters around the main droplet and is recognized as a satellite. Further, when continuous discharge is performed, the rear end portion of the first droplet and the second main droplet collide with each other and the landing position is shifted, so that a high-definition image cannot be obtained. There was a case where a problem occurred in the discharge property.

Therefore, in order to improve the ink repellency on the nozzle surface while improving the wettability on the inner wall of the nozzle, it may be effective to further contain triethylene glycol monobutyl ether or hexylene glycol as a penetrant. It was revealed. The content of triethylene glycol monobutyl ether or hexylene glycol in the total liquid medium is 1 to 15% by mass, preferably 2 to 12% by mass, and more preferably 4 to 12% by mass. By setting the content of triethylene glycol monobutyl ether in the above range, the ink repellency on the nozzle surface can be effectively improved while the wettability on the nozzle inner wall is improved.
In place of triethylene glycol monobutyl ether or hexylene glycol, a water-soluble organic solvent such as triethylene glycol monomethyl ether described later may be used.

  The viscosity of the recording liquid of the present invention is 3.0 to 6.0 mPa · s, preferably 3.0 to 5.0 mPa · s. If the viscosity is out of the above range, the viscosity of the recording liquid is reduced or increased, so that the supply of the recording liquid becomes excessive or insufficient, and the ejection becomes unstable and defective ejection occurs. As a result, density unevenness occurs.

  The recording liquid in the present invention can obtain a desired viscosity by adjusting the amount of a water-soluble organic solvent to be described later. The viscosity of the recording liquid can be measured by using a viscometer such as a vibration viscometer (manufactured by A & D Co., Ltd., SV-10).

  The recording liquid of the present invention preferably has a surface tension of 40 mN / m or less at a lifetime of 10 msec. During production, when the nozzle is formed on the nozzle plate, some burrs and irregularities remain on the inner wall of the nozzle, which adversely affects the continuous high-speed discharge performance. In other words, the meniscus of the recording liquid is oscillating on the inner wall of the nozzle during ejection, and when the surface tension of the recording liquid at a lifetime of 10 msec is higher than 40 mN / m, the wettability of the recording liquid with respect to the inner wall of the nozzle is deteriorated. This will cause discharge and flying bends. On the other hand, if the surface tension at a lifetime of 10 msec is 40 mN / m or less, continuous high-speed ejection performance can be improved. The surface tension at a lifetime of 10 msec can be reduced to 40 mN / m or less by, for example, containing 2,4-diethyl-1,5-pentanediol.

  In the present invention, the surface tension with respect to the surface lifetime, that is, the surface tension at a lifetime of 10 msec is measured by a dynamic surface tension measurement method using a capillary represented by a bubble pressure method. Specifically, bubbles are generated in the liquid from the capillary, the surface tension is measured from the pressure applied to the bubbles, and the dynamic surface tension is measured by changing the bubble frequency (for example, 0.01 to 10 Hz). can do.

  The recording liquid according to the present invention mainly comprises a coloring material (colorant), a water-soluble organic solvent containing a wetting agent, and a surfactant in addition to the penetrating agent, and a pH adjuster and antiseptic as necessary. An antifungal agent or the like can be added.

As the coloring material, any of direct dyes, acid dyes, basic dyes and the like and pigments can be used. In the present invention, a pigment is preferably used from the viewpoints of high optical density, water resistance, light resistance and the like.
As pigment components, colorant pigment components such as insoluble azo pigments, soluble azo pigments, phthalocyanine blue, isoindolinone, quinacridone, dioxazine violet, organic pigments such as verinone betalin, carbon black, titanium dioxide and other inorganic pigments And extender pigments such as white clay, talc, clay, diatomaceous earth, calcium carbonate, barium sulfate, titanium oxide, alumina white, silica, kaolin, and aluminum hydroxide.

Specific organic pigments are exemplified below. Examples of magenta pigments include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.
As content with respect to the whole liquid medium of a pigment, 1-10 mass% is preferable, More preferably, it is 2-8 mass%.

Further, a water-soluble resin is used to disperse the pigment in the recording liquid solvent, and preferably a styrene-acryl-acrylic acid alkyl ester copolymer, a styrene-acrylic acid copolymer, a styrene-maleic acid copolymer, styrene. -Maleic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-alkyl methacrylate copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl It is a water-soluble resin such as naphthalene-maleic acid copolymer.
As content with respect to the whole liquid medium of water-soluble resin, 0.1-10 mass% is preferable, More preferably, it is 1-5 mass%. Two or more of these water-soluble resins can be used in combination.

As a method for dispersing the pigment, a ball mill, a sand mill, a roll mill, an agitator, an ultrasonic homogenizer, a wet jet mill, a paint shaker, or the like can be used.
The pigment dispersion of the present invention is preferably subjected to filtration using a centrifugal separator or a filter in order to remove foreign matters, dust, coarse particles and the like during dispersion.

  The average particle size of the pigment particles according to the present invention is preferably 30 to 300 nm, more preferably 50 to 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).

  Examples of the water-soluble organic solvent according to the present invention include ethylene glycol monobutyl ether, triethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monomethyl ether, triethylene glycol, hexylene glycol, octanediol, thiodiglycol, 2-butyl- 2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-methyl-1,3-propanediol, 2,4-pentanediol, 1,5-pentanediol 2,2-dimethyl-1,3-propanediol trimethylolpropane, 2-methyl-1,3-propanediol, diethylene glycol, propylene glycol, butanediol, ethylene glycol, glycerin, 2 Pyrrolidone, and the like, can be added the required material in accordance with the recording liquid.

  The recording liquid in the present invention preferably uses glycerin as a wetting agent. The content of the wetting agent relative to the total liquid medium is 5 to 45% by mass, preferably 10 to 35% by mass, and more preferably 10 to 25% by mass.

  Examples of the surfactant used in the recording liquid in the present invention include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene / polyoxypropylene block copolymers. An agent is preferably used.

  In addition to the components described above, the recording liquid in the present invention is, as necessary, within a range that does not impair the effects of the present invention, for example, a viscosity adjuster, a pH adjuster, or antiseptic / antifungal properties during storage. Various additives such as a bactericidal agent can be contained.

(Image forming device)
Next, an image forming apparatus suitable for using the recording liquid of the present invention will be described below. FIG. 1 shows an example of an ink jet recording head in an image forming apparatus according to the present invention before a piezoelectric actuator including a laminated piezoelectric element 8 and individual electrodes 9 is attached. The ink jet recording head 21 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 partial cross-sectional view showing one dot forming portion in a state where the piezoelectric actuator AC is attached in the ink jet recording head 21 of the above example, and FIG. It is a bottom view of a). 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 ink jet recording head 21 as a whole realizes 600 dpi.

  Each dot forming section includes a pressurizing chamber 2 having a flat plate shape formed on the upper surface side of the substrate 1, a nozzle 3 on the lower surface side of the substrate 1, and a nozzle channel 4 for communicating these. The pressurizing chamber 2 has ends at the center in the width direction of the rectangular portion, the diameter is equal to the width length, and the horizontal cross-sectional shape is semicircular at both ends in the longitudinal direction of the rectangular portion. ing. The pressurizing chamber 2 communicates with the common flow path 6 via a cylindrical supply port 5 having the same center as the semicircle of the end portion on the other end side of the pressurizing chamber 2. The nozzle 3 has a truncated cone shape with the same center as the semicircle of the end portion on the one end side of the pressurizing chamber 2. The nozzle channel 4 has a cylindrical shape having the same diameter and the same center as the semicircle of the end. The common flow path 6 is formed in the substrate 1 so as to communicate with each dot forming portion.

  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 recording droplet discharge side formed in a circular shape 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 1a and the second substrate 1b have a common flow path 6 formed in the third substrate 1c on the upper surface side of the substrate 1 and piping from a recording liquid cartridge (not shown). A through hole 11a for forming the joint part 11 for connection 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, a piezoelectric actuator AC is configured by laminating a laminated piezoelectric element 8 having a planar shape and a transverse vibration mode, and individual electrodes 9 having the same substantially rectangular shape in this order. It is. The laminated piezoelectric element 8 is approximately the same size as the substrate 1 and has a common electrode 7 therein. The individual electrodes 9 are individually provided at positions overlapping the central portion of the pressurizing chamber 2 of each dot forming portion.

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 plane shape, and is formed through drying, pre-baking, and baking processes. Alternatively, 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 sputtering method, 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 as a pressure wave to the recording liquid in the pressurizing chamber 2, and by this pressure wave, the supply port 5, the pressurizing chamber 2, the nozzle flow path 4, and the nozzle 3 The recording liquid vibrates. As a result, the speed of the vibration is directed to the outside of the nozzle 3, whereby the recording liquid meniscus in the nozzle 3 is pushed out from the opening 30 at the tip on the recording liquid droplet ejection side to form a recording liquid column. Is done. The speed of vibration will eventually go in the nozzle, but since the recording liquid column will continue to move outward, it will be separated from the recording liquid meniscus and gathered in about 1 to 2 drops, which is the direction of the paper surface. Flying to form dots on the paper.

  Due to the surface tension of the recording liquid meniscus in the nozzle 3, the recording liquid corresponding to the amount of the recording liquid that has been reduced due to flying is removed from the recording liquid cartridge by the piping of the recording liquid cartridge, the joint portion 11, the common channel 6, and the supply port. 5, the nozzle 3 is refilled via the pressurizing chamber 2 and 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 formed at the tip of the nozzle 3 on the recording droplet discharge side. The circular opening 30 is provided so as to overlap. That is, the water repellent layer 12 is laminated on the surface 1e other than the region A1 to perform water repellent treatment. In the region A1, the water repellent layer 12 is not formed, and the surface of the fourth substrate 1d is exposed, so that 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 a recording droplet ejection failure due to adhesion of the recording liquid 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 21 may be driven by either a pulling type or a pushing type driving method. In the pulling type, the recording liquid meniscus in the nozzle 3 is drawn by deforming the piezoelectric element 8 in a direction to expand the capacity of the pressurizing chamber 2 immediately before dot formation. After that, the piezoelectric element 8 is deformed in a direction to reduce the capacity of the pressurizing chamber 2, whereby the recording droplet is separated from the recording liquid meniscus and ejected. In the punching type, the recording liquid meniscus in the nozzle 3 is pushed out by deforming the piezoelectric element 8 in the direction of reducing the capacity of the pressurizing chamber 2 at the time of dot formation. Next, by deforming the piezoelectric element in the direction in which the capacity of the pressurizing chamber 2 is expanded, the recording liquid meniscus is drawn, and the recording liquid droplets are separated from the recording liquid meniscus and ejected.

  In the image forming apparatus of the present invention, in order to achieve high-speed printing, the inkjet recording head 21 has 500 or more nozzles, has a width of 1 inch or more, and is perpendicular to the conveyance direction of the recording medium and horizontally. Two or more, preferably 2 to 8, more preferably 2 to 4 may be arranged. In addition, it is preferable to use a line head by arranging a plurality of the recording medium more than the width of the recording medium. The ink jet recording head 21 preferably has an appropriate amount of liquid discharged from the nozzle 3 of 1 to 30 pL, a droplet speed of 5 to 15 m / s, a maximum driving frequency of 20 kHz or more, and a resolution of 600 dpi or more. Further, the conveyance speed of the recording medium is preferably 60 to 100 mm / s.

  When performing color printing, the recording liquid is combined with the ink jet recording head 21 to form a multicolor set, and usually a recording liquid set including four colors of yellow, magenta, cyan, and black is formed. The set is preferably an image forming apparatus in which the recording liquid and the inkjet recording head 21 are combined.

  Hereinafter, the recording liquid and the image forming apparatus 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.

(Preparation of recording liquid)
As the colorant contained in the recording liquid of the present invention, C.I. I. Pigment Red 122 was used and a water-soluble resin was used to prepare a pigment dispersion as follows.
(Pigment dispersion)
C. I. Pigment Red 122 30% by mass
Jonkrill 61 (acrylic-styrene resin, manufactured by Johnson) 15% by mass
Glycerin 10% by mass
Ion-exchanged water 45% by mass
The mixture was mixed with the above composition, 0.5 mm zirconia beads were used, and dispersed with a ball mill until the average particle size became 100 nm. The average particle size was confirmed by diluting the pigment dispersion with ion-exchanged water 5 times and using a dynamic light scattering type particle size distribution analyzer (LB-550, manufactured by HORIBA).

  The above magenta pigment dispersion was used, mixed with the composition shown in Table 1, and after sufficient stirring, recording liquid No. 1 was filtered using a filter having a pore size of 5 μm. Recording liquids 1 to 10 were obtained. As the surfactant, Olphine E1010 [EO (ethylene oxide) adduct of acetylenic diol, manufactured by Nissin Chemical Industry Co., Ltd.] was used.

The viscosity and surface tension of the recording liquid in this example shown in Table 1 were measured by the following methods.
(Viscosity measurement)
The viscosity of the recording liquid was measured using a vibration type viscometer (manufactured by A & D Co., Ltd., SV-10).
(surface tension)
The surface tension of the recording liquid was determined by measuring the surface tension at 25 ° C. according to JIS K 3362 using an automatic surface tension meter (“BP-D4” manufactured by Kyowa Interface Science Co., Ltd.) and calculating the surface tension at a lifetime of 10 msec. .

(Preparation of inkjet recording head)
1 and 2 (a) and 2 (b), and the area of the pressurizing chamber 2 is 0.2 mm ² , the width is 200 μm, the depth is 100 μm, the diameter of the nozzle channel 4 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, the shape of the opening 30 is circular and the radius is 10 μm. An ink jet recording head in which 166 dot forming portions per row and 664 dot forming portions in total (4 rows) were arranged on the substrate 1 was used.
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 method)
The recording liquid droplets were ejected onto a recording medium and evaluated using the image forming apparatus equipped with the recording liquid obtained above and the inkjet recording head 21. Evaluation was performed as follows. That is, the recording liquid No. Any one of 1 to 10 was initially filled into the ink jet recording head 21 from a recording liquid tank using a gear pump at a pressure of 150 kPa. Thereafter, in an environment of 25 ° C. and 50% RH, excess recording liquid coming out of the nozzle forming surface is cleaned with a wipe blade, the distance between the nozzle surface of the inkjet recording head 21 and the recording medium is fixed to 1 mm, and the driving frequency The recording liquid was discharged onto the recording medium at 20 kHz, and the following four evaluation items were evaluated. The evaluation results are shown in Table 2.

Evaluation 1: In order to observe the influence of clogging and dirt inside the nozzle 3, the excess recording liquid was not wiped with a wipe blade but wiped with clean soft cotton containing ion exchange water. Then, a vertical line of 1 dot 1 space in the width direction of the ink jet recording head 21 and continuous 500 dots in the transport direction is printed, and the pitch of 1 dot vertical line and the continuity of 1 continuous dot are based on the following criteria: evaluated.
A: The pitch of 1 dot vertical line is constant, and all continuous 1 dot lines have continuity.
Δ: The pitch of the 1-dot vertical line is constant, and the continuous 1-dot line is not continuous.
X: The pitch of the 1-dot vertical line is not constant, and the continuous 1-dot line has no continuity.

Evaluation 2: To see the influence of wetting and dirt outside the nozzle 3, the excess recording liquid was cleaned with a wipe blade, and as in the evaluation item 1, 1 dot 1 space in the width direction of the jet recording head 21; A vertical line of 500 dots was printed in the transport direction, and the pitch of 1 vertical line and the continuity of 1 continuous dot were evaluated according to the following criteria.
A: The pitch of 1 dot vertical line is constant, and all continuous 1 dot lines have continuity.
Δ: The pitch of the 1-dot vertical line is constant, and the continuous 1-dot line is not continuous.
X: The pitch of the 1-dot vertical line is not constant, and the continuous 1-dot line has no continuity.

Evaluation 3: All solid images in which all nozzles 3 were discharged simultaneously were printed in 1000 dots in the transport direction, and the recording liquid supply performance was evaluated according to the following criteria.
○: A uniform concentration is maintained from the beginning to the end, and there is no white streak.
(Triangle | delta): A uniform density | concentration is maintained from the head to the terminal, and there are some white stripes.
X: Density gradually faded from the beginning, with white streaks.

Evaluation 4: After printing 1000 dots in the transport direction for all solid images discharged from all nozzles 3 at the same time, a horizontal 1 dot line is printed in the width direction of the inkjet recording head 21, and the linearity of the horizontal 1 dot line is Evaluation was made according to the following criteria.
◯: There is linearity within one pixel deviation in one horizontal dot line.
Δ: The horizontal one dot line has linearity within 2 pixel deviation.
X: There is no linearity in a horizontal 1 dot line.

(Evaluation results)
As shown in Table 2, Examples 1 to 5 having viscosities within the scope of the present invention and containing the penetrant of the present invention have a pitch of 1 dot vertical line and continuity of 1 continuous dot (Evaluation 1). 2), recording liquid supply performance (evaluation 3), and horizontal one-dot-line linearity (evaluation 4) show good results, and recording liquid can be supplied without excess or deficiency during high-speed printing. I was able to get an image.

  On the other hand, when the recording liquid does not contain the penetrant of the present invention, the pitch of 1-dot vertical line and the continuity of 1-dot (evaluation 1, 2) and the linearity of 1-dot line (evaluation 4) are It was defective (Comparative Examples 2 and 3). When the viscosity of the recording liquid is smaller than the range of the present invention and does not contain the penetrating agent of the present invention, the pitch of 1 dot vertical line, the continuity of 1 continuous dot (Evaluation 1, 2), and the linearity of 1 horizontal dot line (Evaluation 4) was poor (Comparative Example 1). Further, when the viscosity of the recording liquid is out of the range of the present invention, even if the specific penetrant of the present invention is contained, the recording liquid supply ability (evaluation 3) is poor, or the horizontal 1 dot line The linearity (Evaluation 4) was poor (Comparative Examples 4 and 5).

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Pressurization chamber 3 Nozzle 4 Nozzle 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 21 Inkjet recording head 30 Recording liquid discharge side opening A1 Area AC Piezoelectric actuator

Claims (5)

  Contains water, a coloring material, a wetting agent, 2,4-diethyl-1,5-pentanediol as a penetrating agent, and triethylene glycol monobutyl ether or hexylene glycol. And a surface tension at a lifetime of 10 msec is 40 mN / m or less.   The recording liquid according to claim 1, wherein the wetting agent is glycerin.   A part of the wall 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 recording liquid in the pressurizing chamber, thereby recording from the nozzle. An image forming apparatus comprising an ink jet recording head for discharging droplets, wherein the recording liquid is the recording liquid according to claim 1.   The ink jet recording head has a width of 1 inch or more, has 500 or more nozzles, and has two or more ink jet recording heads arranged in a horizontal direction perpendicular to the conveyance direction of the recording medium. The image forming apparatus according to claim 3, further comprising:   4. The ink jet recording head has an appropriate amount of liquid ejected from the nozzle of 1 to 30 pL, a droplet speed of 5 to 15 m / s, a maximum driving frequency of 20 kHz or more, and a resolution of 600 dpi or more. Or the image forming apparatus of 4.

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