Inkjet recording method and inkjet recording apparatus

Abstract

To provide an inkjet recording method which suppresses discharge deviation and enables recording an image having high optical density even when performing recording using an inkjet recording device having a large capacity ink storage part and aqueous ink containing a pigment over a long period of time.SOLUTION: There is provided an inkjet recording method for recording an image on a recording medium using an inkjet recording device which includes an ink storage part capable of replenishing aqueous ink containing a pigment, a recording head 20 and cleaning means. The aqueous ink contains first ink and second ink, a plurality of discharge port arrays include a first discharge port array 3 for discharging first ink and a second discharge port array 4 for discharging second ink, the second ink contains a predetermined surfactant such as a sulfonic acid type surfactant, and the cleaning means is means for wiping the second discharge port array 4 and the first discharge port array 3 in this order by one motion in a direction 5 crossing arrangement directions of the discharge port arrays 3 and 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus. [Background technology]

[0002] Inkjet recording is a method of converting input image data into an output image using liquid ink. This method involves ejecting ink from minute nozzles in a recording head and applying the ink to a recording medium to record an image. With this method, minute ink droplets (e.g., mist) other than the ink involved in recording the image may float in the atmosphere. These minute ink droplets may then adhere to the periphery of the nozzles of the recording head. When such unwanted ink adheres to the periphery of the nozzles, the ejected ink droplets may be distorted, resulting in a distorted image (discharge distortion). To address this issue, inkjet recording devices are now being used that employ a so-called cleaning mechanism, which wipes the nozzle face of the recording head with a wiping member (wiper) made of an elastic material such as rubber to remove any deposits.

[0003] In recent years, inkjet recording methods have been increasingly used for recording business documents containing characters, charts, and other information using plain paper as a recording medium. Such applications require the ability to record images with high density and excellent water resistance, so pigment inks are often used. Furthermore, there is a demand for a greater number of printable pages to achieve high productivity. To meet these demands, there is a trend toward larger ink reservoirs for supplying ink to the print head. Furthermore, ink reservoirs are being used that allow ink to be refilled (injected) through an ink supply port at the top of the reservoir, without the need for replacement.

[0004] Even when an inkjet recording apparatus equipped with a large-capacity ink storage unit is used for long-term recording, it is required that the wiper properly wipes the nozzle surface of the recording head, and that normal ejection is restored even if irregular ejection occurs. To meet this requirement, for example, an inkjet recording apparatus has been proposed in which the wiping performance of the nozzle surface of the recording head is improved by using an ink containing oleic acid (Patent Document 1). Also, an inkjet recording apparatus has been proposed in which the continuous recording stability is improved by using an ink storage unit that can be refilled with ink containing trimethylglycine (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-201220 [Patent Document 2] Japanese Patent Application Publication No. 2018-109119 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors incorporated a large-capacity ink storage unit into the inkjet recording device proposed in Patent Document 1, recorded images over a long period of time, and evaluated the wiping performance of the ejection port surface. As a result, they found that with repeated recording, the amount of ink remaining on the ejection port surface increased, causing the ink ejection direction to change, making it difficult to record high-quality images. Furthermore, when the inkjet recording device proposed in Patent Document 2 was used, they found that while the wiping performance improved, the color development of the recorded images deteriorated.

[0007] Therefore, an object of the present invention is to solve the problems that arise when an inkjet recording apparatus equipped with a large-capacity ink reservoir is used to record over a long period of time using a water-based ink containing a pigment. That is, an object of the present invention is to provide an inkjet recording method that can suppress uneven ejection and record images with high optical density even when using the inkjet recording apparatus. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an inkjet recording method comprising: an inkjet recording apparatus including: an ink reservoir provided with an openable / closable ink inlet and capable of being refilled with a pigment-containing aqueous ink; a recording head having a recording element substrate on which a plurality of ejection port arrays are formed, each of which has a plurality of ejection port arrays for ejecting the aqueous ink, the plurality of ejection port arrays being arranged in a predetermined direction; and a cleaning means for wiping the surface of the recording element substrate on which the ejection port arrays are formed; and a step of applying the aqueous ink ejected from the ejection ports to a recording medium to record an image, wherein the aqueous ink includes a first ink and a second ink, and the plurality of ejection port arrays include a first ejection port array for ejecting the first ink and a second ejection port array for ejecting the second ink, and the second ink is a surfactant selected from the group consisting of a sulfonic acid surfactant, a carboxylic acid surfactant, and Phosphate surfactant Drug? and the cleaning means is a means for wiping the surface on which the ejection port arrays are formed in a direction intersecting with the arrangement directions of the first ejection port array and the second ejection port array, in the order of the second ejection port array and the first ejection port array, in a single operation. [Effects of the Invention]

[0009] According to the present invention, it is possible to solve the problems that arise when an inkjet recording apparatus equipped with a large-capacity ink storage unit is used to record over a long period of time using a water-based ink containing a pigment. That is, according to the present invention, it is possible to provide an inkjet recording method that suppresses uneven ejection and is capable of recording images with high optical density, even when using the inkjet recording apparatus. Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus used in this inkjet recording method. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of a recording head and a cleaning unit. [Figure 2] 1 is a perspective view schematically illustrating the appearance of an inkjet recording apparatus according to an embodiment of the present invention. [Figure 3] 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating an example of an ink supply system. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience, it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0012] Compared to ink storage units in the form of ink cartridges, increasing the capacity of the ink storage unit reduces the labor required for ink storage unit replacement, thereby improving productivity. However, because the ink storage unit does not need to be replaced, the pigment in the ink tends to gradually settle in large-capacity ink storage units, increasing the pigment concentration of the ink in the lower part of the ink storage unit. Furthermore, in large-capacity ink storage units with openable inlets, the ink in the ink storage unit tends to be exposed to air for a longer period of time, which makes the pigment more likely to aggregate and increase the amount of pigment that settles compared to ink storage units with smaller capacities. On the other hand, ink storage units in the form of ink cartridges do not have openable inlets and are less likely to experience problems such as pigment settling.

[0013] One method is to remove ink with a high pigment concentration due to pigment sedimentation by suctioning the ink from the nozzle surface of the print head. However, when using a large-capacity ink storage unit, attempting to remove the ink with a high pigment concentration consumes a large amount of ink, so printing will continue for a long period of time with the pigment concentration remaining high. It has been newly discovered that if printing continues for a long period of time with the pigment concentration remaining high, the wiping ability of the wiper on the nozzle surface of the print head will decrease, making it more likely that irregular ejection will occur.

[0014] In the ink inside the ink storage unit, settled pigment particles approach each other, and the electrostatic repulsion is eliminated by the compression of the electric double layer, making the pigment more likely to aggregate. When ink containing aggregated pigment is ejected from the print head, a mist containing the aggregated pigment adheres to the nozzle surface, and the mist is transferred to the wiper by wiping. Because the electrostatic repulsion of the aggregated pigment is reduced, it easily adheres to the nozzle surface of the print head and the wiper. Furthermore, repeated wiping causes the aggregated pigment to accumulate on the wiper, reducing its flexibility. A wiper with reduced flexibility has difficulty conforming to the shape of the nozzle surface of the print head, reducing wiping performance. As a result, pigment that could not be wiped away remains around the nozzles of the print head, which is thought to cause irregular ejection.

[0015] The present inventors have investigated ink compositions and wiping conditions to solve the above-mentioned problems that arise when using an inkjet recording apparatus equipped with a large-capacity ink storage unit, and have found that the following configuration makes it possible to record images with high optical density and high-quality images with suppressed irregular ejection over a long period of time.

[0016] The inkjet recording method of the present invention uses aqueous inks containing two types of inks (first ink and second ink) each containing a pigment as a coloring material, and one of the inks (second ink) contains at least one surfactant selected from the surfactant group described below. [Surfactants that make up the surfactant group] Sulfonic acid surfactants Carboxylic acid surfactants Phosphate surfactants Polyoxyethylene alkyl ether Ethylene oxide adduct of saturated polyhydric alcohol Ethylene oxide-propylene oxide block copolymer Perfluoroalkyl ethylene oxide adducts

[0017] FIG. 1 is a schematic diagram showing an example of a recording head and a cleaning device. In the inkjet recording method of the present invention, an image is recorded on a recording medium using an inkjet recording device equipped with a recording head 20 and a cleaning device as shown in FIG. 1. The recording head 20 is provided with a recording element substrate 2 on which a plurality of ejection port arrays are formed, each of which has a plurality of ejection port arrays for ejecting ink arranged in a predetermined direction. The cleaning device includes a wiper 10 that wipes the ejection port surface of the recording element substrate 2. The ejection port arrays include a second ejection port array 4 for ejecting the second ink and a first ejection port array 3 for ejecting the first ink. The wiper 10 is a member that wipes the second ejection port array 4 and the first ejection port array 3 in a single motion in a direction 5 intersecting the arrangement direction of the ejection port arrays.

[0018] When the wiper 10 wipes the second ejection port array 4 and the first ejection port array 3 in the direction of the arrow, the wiper 10 first wipes away excess ink adhering to the periphery of the second ejection port array 4. The second ink contains the predetermined surfactant. The pigment in the aqueous ink is dispersed by the action of the hydrophilic groups of the resin dispersant and the hydrophilic groups bonded to the pigment particle surface. However, there are also portions of the pigment particle surface that are not covered by the hydrophilic groups (hydrophobic portions). The hydrophobic portions of the predetermined surfactant easily adsorb to the hydrophobic portions of the pigment particle surface due to hydrophobic interactions. The pigment with the surfactant adsorbed thereto maintains a stable dispersion state due to the action of the hydrophilic groups of the surfactant, making it less likely to aggregate. Therefore, even if the pigment in the ink settles in the ink storage section, aggregation of the pigment particles is suppressed. Therefore, ink adhering to the vicinity of the ejection ports or to the wiper is easily removed by wiping, preventing a decrease in wiping performance. Furthermore, the unnecessary ink adhering around the second ejection port array 4 is pushed toward the first ejection port array 3 by wiping, where it mixes with the unnecessary ink adhering around the first ejection port array 3. As a result, the surfactant in the second ink is adsorbed to the pigment in the first ink, making it difficult for the pigment in the unnecessary ink adhering around the first ejection port array 4 to aggregate, making it easier to wipe off by wiping. As a result, wiping performance is not reduced, uneven ejection is less likely to occur, and image quality can be improved.

[0019] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention includes a step of recording an image on a recording medium using an inkjet recording device equipped with an ink reservoir, a recording head, and a cleaning device. The ink reservoir is a member provided with an openable / closable ink inlet and capable of being refilled with aqueous ink containing a pigment. The recording head has a recording element substrate on which multiple nozzle arrays are formed, each of which has multiple nozzles for ejecting the aqueous ink arranged in a predetermined direction. The cleaning device is a device for wiping the surface of the recording element substrate on which the nozzle arrays are formed. The inkjet recording method of the present invention includes a step of applying aqueous ink ejected from the nozzles of the recording head to a recording medium to record an image. The aqueous ink includes a first ink and a second ink, and the multiple nozzle arrays include a first nozzle array for ejecting the first ink and a second nozzle array for ejecting the second ink. The second ink includes at least one surfactant selected from the group of surfactants described below (hereinafter, for convenience, also referred to simply as a "predetermined surfactant"). The cleaning means is a means for wiping the surface on which the ejection port arrays are formed in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array in a single operation in the order of the second ejection port array and the first ejection port array. [Surfactants that make up the surfactant group] Sulfonic acid surfactants Carboxylic acid surfactants Phosphate surfactants Polyoxyethylene alkyl ether Ethylene oxide adduct of saturated polyhydric alcohol Ethylene oxide-propylene oxide block copolymer Perfluoroalkyl ethylene oxide adducts

[0020] The inkjet recording apparatus of the present invention includes an ink storage unit, a recording head, and a cleaning unit. The ink storage unit is a member provided with an openable / closable ink inlet and capable of being refilled with aqueous ink containing a pigment. The recording head has a recording element substrate on which a plurality of ejection port arrays are formed, each of which has a plurality of ejection port arrays arranged in a predetermined direction for ejecting the aqueous ink. The cleaning unit is a unit for wiping the surface of the recording element substrate on which the ejection port arrays are formed. The aqueous ink contains a first ink and a second ink, and the plurality of ejection port arrays include a first ejection port array for ejecting the first ink and a second ejection port array for ejecting the second ink. The second ink contains at least one surfactant selected from the surfactant group. The cleaning unit is a unit for wiping the surface on which the ejection port arrays are formed, in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array, in the second ejection port array and the first ejection port array, in a single operation.

[0021] (Inkjet recording device) Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, parts having the same function are given the same reference numerals, and their description may be omitted. FIG. 2 is a perspective view that schematically shows one embodiment of an inkjet recording device of the present invention. The inkjet recording device 1 of the embodiment shown in FIG. 2 comprises a housing 11 and a large-capacity ink storage section 12 disposed inside the housing 11. The ink storage section 12 contains (is filled with) ink, which is the liquid to be applied to a recording medium.

[0022] FIG. 3 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus according to the present invention. The inkjet recording apparatus of this embodiment is a so-called serial inkjet recording apparatus that performs a recording operation by reciprocating a recording head in the X direction (main scanning direction). A recording medium 101 is intermittently transported in the Y direction (sub-scanning direction) by a transport roller 107. A recording unit 102 mounted on a carriage 103 is reciprocally scanned in the X direction (main scanning direction), which is perpendicular to the Y direction, the transport direction of the recording medium 101. A recording operation is performed by transporting the recording medium 101 in the Y direction and reciprocating scanning of the recording unit 102 in the X direction. The recording unit 102 is comprised of an inkjet recording head 203 (FIG. 4) that ejects supplied ink from ejection openings, and a sub-tank 202 (FIG. 4) that serves as a second ink container, and is mounted on the carriage 103. The carriage 103 is supported so as to be movable along a guide rail 105 arranged along the X direction, and is fixed to an endless belt 106 that moves parallel to the guide rail 105. The endless belt 106 moves back and forth by the driving force of a motor, thereby causing the carriage 103 to scan back and forth in the X direction.

[0023] A main tank 201 serving as a first ink storage section is housed inside the main tank storage section 108. The main tank 201 of the main tank storage section 108 and a sub-tank 202 of the recording unit 102 are connected by an ink supply tube 104, which is an ink supply path. Ink is supplied from the main tank 201 to the sub-tank 202 (FIG. 4) via the ink supply tube 104, and then ejected from the ejection openings of the recording head 203. The number of main tanks 201, ink supply tubes 104, and sub-tanks 202 can all be provided in accordance with the type of ink.

[0024] An ink inlet 205 is provided at the top of the main tank 201 for injecting ink into the main tank 201 from outside the inkjet recording device. When using the inkjet recording device for the first time or when the ink level has decreased, ink is injected from an ink bottle into the main tank while it is placed inside the inkjet recording device. In other words, the main tank is left inside the inkjet recording device and is not replaced itself.

[0025] 4 is a schematic diagram showing an example of an ink supply system. Ink (shown hatched) stored in a main tank 201 is supplied to a sub-tank 202 via an ink supply tube 104, and then supplied to a print head 203. A gas introduction tube 204, which serves as an atmosphere communication part, is connected to the main tank 201. When printing is performed and ink is consumed, ink is supplied from the main tank 201 to the sub-tank 202, and the ink in the main tank 201 decreases. Then, air is introduced into the main tank 201 from the gas introduction tube 204, one end of which is open to the atmosphere, and the internal negative pressure for retaining ink in the ink supply system is maintained at a substantially constant level.

[0026] To increase the number of recordable sheets and thereby achieve high productivity, it is preferable that the main tank 201 has a large maximum ink capacity V1 (mL). Specifically, the maximum ink capacity V1 (mL) of the main tank 201 is preferably 100 mL or more and 300 mL or less, and more preferably 100 mL or more and 200 mL or less. Furthermore, it is preferable that the initial ink filling amount of the main tank 201 be approximately 95% of the maximum ink capacity.

[0027] It is also preferable that the subtank 202 have a large maximum ink capacity V2 (mL) to reduce the frequency of ink supply from the main tank 201 and to ensure a stable ink supply to the print head 203. However, for example, assuming a serial system in which the subtank 202 is mounted on the carriage 103 as shown in FIG. 3, it is preferable that the maximum ink capacity V2 (mL) of the subtank 202 not be too large. In other words, if too much ink is stored in the subtank 202, the printing unit 102 will become larger, the movement speed of the carriage 103 will decrease, and the strength of the endless belt 106 and motor that move the carriage 103 will need to be increased. Therefore, it is preferable that the maximum ink capacity V2 (mL) of the subtank 202 be 1 mL or more and 20 mL or less, and more preferably 2 mL or more and 10 mL or less.

[0028] The housings of the main tank 201 and the subtank 202 are made of thermoplastic resins such as polyester, polycarbonate, polyethylene, polypropylene, polystyrene, polyphenylene ether, and mixtures or modifications of these materials. An ink absorber capable of generating negative pressure to retain ink may be disposed inside the housing. Compressed fibers of polypropylene, polyurethane, or the like are preferable as the ink absorber. Alternatively, ink may be stored directly inside the housing without the ink absorber.

[0029] The recording unit 102 is composed of a recording head 203 and a subtank 202. The subtank 202 may be attached to the recording unit 102, which is a head cartridge incorporating the recording head 203, and the recording unit 102 with the attached subtank 202 may be attached to the carriage 103. Furthermore, the recording unit 102 integrally configured with the subtank 202 and recording head 203 may be attached to the carriage 103. Of these, as shown in FIGS. 3 and 4, it is preferable that the recording unit 102 in cartridge form, in which the subtank 202 and recording head 203 are integrally configured, be attached to the carriage 103. Furthermore, it is preferable that the subtank is a housing made of thermoplastic resin, and that the recording element substrate equipped with the recording head is directly bonded to the subtank without any intervening member such as a heat sink.

[0030] The ink supply tube 104 is connected to a sub-tank 202 that constitutes the recording unit 102 mounted on the carriage 103. Therefore, the ink supply tube 104 is routed within the device in response to the reciprocating scanning of the carriage 103. Therefore, the material that constitutes the ink supply tube 104 must be selected to be flexible enough to withstand the frequent reciprocating scanning of the carriage 103. For this reason, the ink supply tube 104 is made of a resin material.

[0031] The ink supply tube is a component formed by molding a resin material into a tubular shape. The resin material constituting the tube may be a single resin material or a combination of two or more resin materials. It may also be a resin material blended with various additives. The tube may have a single-layer structure or a multi-layer structure. Thermoplastic elastomers are preferred as resin materials because of their excellent moldability, rubber elasticity, and flexibility. Examples of thermoplastic elastomers include olefin-based, urethane-based, ester-based, styrene-based, and vinyl chloride-based resins. Among these, styrene-based thermoplastic elastomers are preferred because of their particularly excellent flexibility and rubber elasticity. Examples of additives blended into the resin material include softeners, lubricants, surfactants, antioxidants, antiaging agents, adhesion promoters, and pigments.

[0032] The inner diameter and wall thickness of the tube are appropriately set in consideration of productivity such as molding, bending rigidity when routed through a recording device, ink supply performance, gas barrier properties, etc. The inner diameter of the tube is preferably 1 mm or more and 5 mm or less, and more preferably 1 mm or more and 3 mm or less. The wall thickness of the tube is preferably 0.5 mm or more and 5 mm or less, and more preferably 0.5 mm or more and 3 mm or less.

[0033] When the amount of ink contained in the main tank 201 decreases, the first valve 206 is operated to close the ink supply tube 104, and then the ink inlet 205 of the main tank 201 is opened to inject ink into the main tank 201. If the ink inlet 205 is opened without operating the first valve 206 and closing the ink supply tube 104, the negative pressure required to retain the ink is lost, causing ink to leak from the nozzles of the print head 203. When injecting ink into the main tank 201, the second valve 207 can be operated to close the gas introduction tube 204, and then the ink inlet 205 can be opened. This configuration prevents ink from flowing from the main tank 201 toward the gas introduction tube 204. Operating the first valve 206 and the second valve 207 in conjunction with each other more reliably prevents ink leakage.

[0034] The ink inlet 205 is preferably provided at the top of the main tank 201. The top of the main tank 201 is not limited to the top surface of the main tank 201 as shown in FIG. 4, but may be at the side or other location as long as it is located at a position that is greater than half of the maximum ink capacity of the main tank 201. Injecting ink from the top of the main tank 201 is excellent in usability. However, in this case, it is difficult to sufficiently mix ink containing settled pigment even with the convection that occurs when the ink is injected, and it is more difficult to eliminate pigment concentration gradients than when ink is injected from the bottom of the main tank.

[0035] Large inkjet recording devices used in industrial printing and other applications often incorporate measures to prevent ink settling. Examples of such mechanisms include an agitation mechanism that circulates ink within the ink reservoir; an ink flow mechanism that circulates ink within a circulation path via an ink flow channel; and a mechanism that supplies ink from the top and bottom of the ink reservoir. Recording devices equipped with such mechanisms do not encounter the problems addressed by the present invention. However, for small inkjet recording devices used in offices and homes, there is strong market demand for smaller and more cost-effective devices. To address these demands, recording devices used in offices and homes typically do not incorporate a mechanism to prevent ink settling, and the inkjet recording device of the present invention does not incorporate such a mechanism.

[0036] (wiping means) As shown in FIG. 1 , the wiper 10 wipes the second ejection port array 4 and the first ejection port array 3 in a single operation in a direction 5 intersecting the arrangement direction of the ejection port arrays. Specifically, wiping must be initiated so that the second ejection port array 4, which ejects the second ink containing a predetermined surfactant, is first. By starting wiping so that the second ejection port array 4 is first, the wiper 10 is covered with the second ink, in which the pigment is stably dispersed. Therefore, even if the first ejection port array ejecting the first ink containing agglomerated pigment is wiped later, the agglomerated pigment is less likely to adhere to the wiper 10, thereby maintaining good wiping performance. In contrast, if wiping is initiated so that the first ejection port array 3, which ejects the first ink substantially free of the predetermined surfactant, is first, the wiper 10 is likely to be covered with the agglomerated pigment, making it difficult to maintain good wiping performance. Furthermore, wiping in a direction parallel to the arrangement direction of the ejection port arrays prevents the second ink from coming into contact with the first ink adhering to the periphery of the first ejection port array. As a result, the specific surfactant in the second ink does not mix with the first ink, and aggregated pigment tends to remain unwiped.

[0037] The wiper is preferably a blade-shaped wiper from the viewpoint of wiping the ejection orifice surface. Furthermore, it is preferable to wipe the ejection orifice surface by sliding the blade-shaped wiper against the ejection orifice surface. The wiper is preferably made of a material having rubber elasticity. Specific examples of the wiper material include rubber materials formed from urethane resin (urethane rubber, ethylene propylene diene rubber [EPDM]). The thickness of the wiper is preferably 0.1 mm or more and 1.0 mm or less. The wiper movement speed during wiping is preferably 1 mm / sec or more and 150 mm / sec or less. Furthermore, the wiper preferably has a width that includes the length of the ejection orifice array of the recording element substrate, and more preferably has a width that covers the recording element substrate.

[0038] (recording head) The print head has a print element substrate on which multiple nozzle arrays are formed, each array having multiple nozzles for ejecting ink, each array being arranged in a predetermined direction. The number of print element substrates arranged in one print head is not particularly limited. The print head is preferably a serial print head (serial head) rather than a so-called line head, in which the nozzle array width is extended to the maximum width of the print medium. Line heads can achieve faster printing speeds than serial heads, but are often disadvantageous in terms of miniaturization and cost of the inkjet printing apparatus itself. Furthermore, when printing an image with a line head, the number of ink droplets ejected per nozzle is smaller than when printing an image with a serial head, so wiping is less frequent and problems such as poor wiping performance are less likely to occur.

[0039] A recording element substrate disposed in the recording head has multiple parallel ejection port arrays, each ejecting two or more types of ink. The recording element substrate may further include an ejection port array (a third ejection port array, a fourth ejection port array, ..., an nth ejection port array) other than the first and second ejection port arrays, arranged parallel to the first and second ejection port arrays. The cleaning device (wiper) preferably wipes the surface on which the ejection port arrays are formed in a single operation in a direction intersecting the arrangement direction of the ejection port arrays, in the order of the nth ejection port array, ..., the fourth ejection port array, the third ejection port array, the second ejection port array, and the first ejection port array. It is assumed that the ink ejected from the third ejection port array is the third ink, the ink ejected from the fourth ejection port array is the fourth ink, ..., and the ink ejected from the nth ejection port array is the nth ink. In this case, each ink (except the first ink) preferably contains a predetermined surfactant. As a result, even when a print head having a print element substrate on which a large number of ejection port arrays are formed is used, the ejection port surface has excellent wiping properties, and high-quality images can be printed for a long period of time.

[0040] The ink ejection method of the print head 203 can be a method of applying mechanical energy to the ink or a method of applying thermal energy to the ink. The print head may eject ink using either method.

[0041] (Recording process) The inkjet recording method of the present invention includes a step of recording an image using the inkjet recording device described above (recording step). Specifically, in the recording step, ink ejected from the ejection openings of a recording head is applied to a recording medium to record an image. Any recording medium may be used as the target for recording an image. In particular, it is preferable to use a recording medium without a coating layer, such as plain paper or uncoated paper, or a recording medium with a coating layer, such as glossy paper or art paper. Examples of the substrate for a recording medium with a coating layer include paper and paper with a resin layer provided on at least one side thereof. Apart from using the inkjet recording device described above, the recording step may be any known method.

[0042] (water-based ink) The ink used in the inkjet recording method of the present invention is an aqueous inkjet ink containing a colorant. The components used in the ink are described in detail below. When there is no need to distinguish between the first ink and the second ink, they are collectively referred to simply as "ink." The first ink and the second ink do not need to react with each other. Therefore, the first ink and the second ink do not need to contain a so-called "reactant." Furthermore, neither the first ink nor the second ink needs to be cured by irradiation with active energy rays. Therefore, the first ink and the second ink do not need to contain a "polymerization initiator" or a component that cures by irradiation with active energy rays (polymerizable component).

[0043] [Colorant] Pigments are used as colorants. The total amount (mass %) of pigment in the ink is preferably 0.50% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink. Examples of pigment types include inorganic pigments such as carbon black, calcium carbonate, and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, and perinone. Dyes may be used in combination for purposes such as color matching.

[0044] The pigment of the first ink is preferably carbon black. The pigment of the second ink is preferably an organic pigment. That is, the first ink is preferably a black ink and the second ink is preferably a color ink. Examples of color inks include inks of the basic colors of subtractive color mixing, such as cyan, magenta, and yellow. Carbon black has a structure composed of multiple primary particles, and therefore has a larger specific surface area and is more susceptible to aggregation than organic pigments used as color pigments. For this reason, inks containing carbon black tend to adhere to the wiper and around the nozzle array of the print head. Therefore, it is preferable to wipe the surface on which the nozzle arrays are formed in the order of the second nozzle array, which ejects the second ink containing an organic pigment that is less susceptible to aggregation, and the first nozzle array, which ejects the first ink containing carbon black, which is more susceptible to aggregation. This order further improves wiping performance.

[0045] The pigment dispersion method is not particularly limited. For example, resin-dispersed pigments dispersed with a resin dispersant, pigments dispersed with a surfactant, and microencapsulated pigments in which at least a portion of the pigment particle surface is coated with a resin or the like can be used. Self-dispersed pigments in which functional groups containing hydrophilic groups such as anionic groups are bonded to the pigment particle surface, and pigments in which organic groups containing polymers are chemically bonded to the pigment particle surface (resin-bonded self-dispersed pigments) can also be used. Pigments with different dispersion methods may also be used in combination.

[0046] Self-dispersing pigments can be used in which an anionic group is bonded to the particle surface of the pigment directly or via another atomic group (-R-). Examples of anionic groups include -COOM, -SO3M, and -PO3M2. Each M can independently represent a hydrogen atom, an alkali metal, ammonium (NH4), or an organic ammonium. Examples of other atomic groups (-R-) include an alkylene group, an arylene group, an amide group, a sulfonyl group, an imino group, a carbonyl group, an ester group, an ether group, or a combination of these groups.

[0047] The pigment in the first ink is preferably a self-dispersing pigment. In the case of a resin-dispersed pigment, interactions between dispersants can sometimes require time for a specific surfactant to orient on the pigment particle surface. This can make it difficult for the pigment to stably disperse in the short time it takes for the first and second inks to mix by wiping, making it difficult to efficiently improve wiping performance. Furthermore, the pigment tends to sink into the recording medium along with the liquid components, which can result in a slight decrease in optical density. It is particularly preferable that the pigment in the first ink be carbon black with anionic groups bonded to its particle surface directly or via other atomic groups.

[0048] The amount of anionic groups in the self-dispersing pigment in the first ink is preferably 0.05 mmol / g or more and 1.50 mmol / g or less. If the amount of anionic groups in the self-dispersing pigment is less than 0.05 mmol / g, the charge repulsion of the pigment particles is small, and the proportion of the pigment particle surface exposed is likely to be high. This may result in the pigment being more likely to aggregate or adhere to the wiper or the nozzle array, resulting in a slight decrease in wiping performance. On the other hand, if the amount of anionic groups in the self-dispersing pigment is more than 1.50 mmol / g, the pigment is more likely to aggregate, and this may accelerate pigment aggregation due to evaporation of liquid components. This may result in an increase in the amount of pigment adhering to the wiper or the nozzle array, resulting in a slight decrease in wiping performance. The amount of anionic groups in the self-dispersing pigment (mmol / g) is expressed as the number of moles of anionic groups per unit mass of the self-dispersing pigment.

[0049] The amount of anionic groups in a self-dispersed pigment can be calculated from the surface charge measured by colloid titration. In the examples described below, the surface charge of the self-dispersed pigment in a pigment dispersion was measured by colloid titration using potential difference using an automatic potentiometric titrator (product name "AT-510" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). More specifically, the pigment dispersion was diluted approximately 300 times (by mass) with pure water, and the pH was adjusted to approximately 10 with potassium hydroxide as needed. Potentiometric titration was then performed using 5 mmol / L methyl glycol chitosan as a titration reagent. It is also possible to measure the surface charge using a pigment extracted from ink by an appropriate method.

[0050] The resin dispersant used in the resin-dispersed pigment may be a resin, particularly a water-soluble resin, as described below. When a resin-dispersed pigment is used, the pigment content (mass %) in the ink is preferably 0.3 to 10.0 times the mass of the resin dispersant content (mass %). It is particularly preferred that the pigment in the second ink is an organic pigment that can be dispersed by a resin dispersant.

[0051] [resin] The ink preferably contains a resin. Resins can be added to the ink (i) to stabilize the pigment dispersion, i.e., as a resin dispersant or its auxiliary. They can also be added to the ink (ii) to improve various properties of the printed image. The resin in the ink may be dissolved in an aqueous medium or dispersed as resin particles in the aqueous medium. In this specification, "water-soluble resin" means that when the resin is neutralized with an alkali equivalent to its acid value, it does not form particles whose particle size can be measured by a measurement method such as dynamic light scattering. The content (mass %) of the resin in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, and more preferably 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the ink.

[0052] Examples of the resin include acrylic resins, polyester resins, urethane resins, urea resins, polysaccharides, and polypeptides. Among these, acrylic resins are preferred from the viewpoint of ejection characteristics from the ejection orifices of the recording head. Preferred acrylic resins have as their constituent units a unit having an anionic group and a unit not having an anionic group. Examples of the form of the acrylic resin include random copolymers, block copolymers, graft copolymers, and combinations thereof.

[0053] Examples of monomers that become units constituting the acrylic resin upon polymerization include monomers having an anionic group and monomers having no anionic group. Usually, a monomer having an anionic group becomes a hydrophilic unit upon polymerization, and a monomer having no anionic group becomes a hydrophobic unit upon polymerization.

[0054] Examples of the monomer having an anionic group include a monomer having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anhydrides and salts of these monomers; and examples of the cation constituting the salt of the monomer having an anionic group include a lithium cation, a sodium cation, a potassium cation, an ammonium cation, and an organic ammonium cation.

[0055] Examples of the monomer having no anionic group include monomers having an aromatic group, such as styrene, α-methylstyrene, benzyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole; and (meth)acrylic acid esters, such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso)propyl (meth)acrylate, (n-, iso-, and t-)butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0056] Among these, acrylic resins having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer are preferred. In particular, acrylic resins having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a styrene and an α-methylstyrene monomer are preferred. These acrylic resins are likely to interact with pigments, and therefore can be suitably used as resin dispersants for dispersing pigments.

[0057] The urethane resin contains, for example, a unit derived from a polyisocyanate having no acid groups, a unit derived from a polyol having no acid groups, and a unit derived from a polyol having acid groups. The urethane resin can be obtained by reacting a polyisocyanate having no acid groups, a polyol having no acid groups, and a polyol having acid groups. The urethane resin may also be one that has been further reacted with a polyamine, a crosslinking agent, a chain extender, or the like.

[0058] [Aqueous medium] The ink is an aqueous ink containing at least water as the aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, any solvent that can be used in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, based on the total mass of the ink. Deionized water or ion-exchanged water is preferably used as the water. The content (mass %) of water in the ink is preferably 50.00% by mass or more and 95.00% by mass or less, based on the total mass of the ink.

[0059] [Surfactants] The second ink contains at least one surfactant (predetermined surfactant) selected from the surfactant group described below. All surfactants included in the surfactant group described below have a compact molecular shape. These surfactants have less steric hindrance than surfactants commonly used in aqueous inkjet inks, such as acetylene glycol-based surfactants, and are more likely to orient quickly on the pigment particle surface. Therefore, by using a second ink containing at least one surfactant selected from the surfactant group described below, pigment aggregation can be suppressed and excellent wiping properties can be maintained. Furthermore, high-density, high-quality images can be obtained even when recording for a long period of time. On the other hand, if a surfactant not included in the surfactant group described below is used, steric hindrance prevents the pigment from orienting on the particle surface, and the effect of improving wiping properties cannot be effectively achieved.

[0060] [Surfactants that make up the surfactant group] Sulfonic acid surfactants Carboxylic acid surfactants Phosphate surfactants Polyoxyethylene alkyl ether Ethylene oxide adduct of saturated polyhydric alcohol Ethylene oxide-propylene oxide block copolymer Perfluoroalkyl ethylene oxide adducts

[0061] Among the aforementioned surfactants, it is preferable to use at least one of sulfonic acid surfactants, carboxylic acid surfactants, and phosphoric acid surfactants as the specific surfactant. These surfactants have anionic groups. Surfactants with anionic groups adsorb to the pigment particle surface due to hydrophobic interaction between their hydrophobic groups and the pigment particle surface. The anionic groups of these surfactants increase the thickness of the pigment's electric double layer, and the repulsion of electric charges facilitates stable maintenance of the pigment's dispersed state, thereby further suppressing ejection irregularities during long-term recording. Among these, sulfonic acid surfactants are more preferable. Sulfonic acid groups are highly acidic and easily dissociate. Therefore, when the hydrophobic groups of sulfonic acid surfactants adsorb to the pigment particle surface, the sulfonic acid groups further increase the thickness of the pigment's electric double layer, and the repulsion of electric charges facilitates more stable maintenance of the pigment's dispersed state.

[0062] Examples of sulfonic acid surfactants include compounds represented by the following general formula (1). R1-R2-SO3M (1) (In the general formula (1), R1 represents an alkyl group. R2 represents a single bond, an ether group, or -O-(CH2CH2O) a -R3-, where a is a number of 1 or more, R3 is an alkylene group, and M is a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0063] In general formula (1), R1 represents an alkyl group. The alkyl group is preferably linear and has 1 to 18 carbon atoms. R2 represents a single bond, an ether group, or -O-(CH2CH2O) a -R3-. When R2 is a single bond, it means that R1 and the sulfur atom are directly bonded. -O-(CH2CH2O) represented by R2 aIn -R3-, a represents a number of 1 or more, preferably 1 to 50. R3 represents an alkylene group. The alkylene group is preferably linear and has preferably 1 to 22 carbon atoms, more preferably 12 to 18 carbon atoms. When R2 is -O-(CH2CH2O) a When the group is -R3-, the water solubility is increased and the compound can be suitably used in aqueous inks. In this case, when a is 50 or less, the ink viscosity is not excessively increased and stable ink ejection properties can be maintained. M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among these, M is preferably a hydrogen atom or an alkali metal such as lithium, sodium, or potassium.

[0064] Examples of the carboxylic acid surfactant include compounds represented by the following general formula (2). R4-R5-COOM (2) (In the general formula (2), R3 represents an alkyl group. R4 represents a single bond, an ether group, or -O-(CH2CH2O) b -R5-, b is a number of 1 or more, R5 is an alkylene group, and M is a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0065] In the general formula (2), R4 represents an alkyl group. The alkyl group is preferably linear and has 1 to 18 carbon atoms. R5 represents a single bond, an ether group, or -O-(CH2CH2O) b -R6-. When R5 is a single bond, it means that R4 and the carbon atom are directly bonded. -O-(CH2CH2O) represented by R5 b In -R6-, b represents a number of 1 or more, preferably 1 to 10. R6 represents an alkylene group. The alkylene group is preferably linear and has preferably 1 to 22 carbon atoms, more preferably 12 to 18 carbon atoms. R5 is -O-(CH2CH2O) bWhen the group is -R6-, the water solubility is increased and the compound can be suitably used in aqueous inks. In this case, when b is 10 or less, the ink viscosity is not excessively increased and stable ink ejection properties can be maintained. M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among these, M is preferably a hydrogen atom or an alkali metal such as lithium, sodium, or potassium.

[0066] Examples of the phosphoric acid surfactant include compounds represented by the following general formula (3). R7-R8-PO(OM)2···(3) (In the general formula (3), R7 represents an alkyl group. R8 represents a single bond, an ether group, or —O—(CH2CH2O) c -R9-, c is a number of 1 or more, R9 is an alkylene group, and each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0067] In the general formula (3), R7 represents an alkyl group. The alkyl group is preferably linear and has 1 to 18 carbon atoms. R8 represents a single bond, an ether group, or -O-(CH2CH2O) c -R9-. When R8 is a single bond, it means that R7 is directly bonded to the phosphorus atom. -O-(CH2CH2O) represented by R8 c In -R9-, c represents a number of 1 or more, preferably 1 to 10. R9 represents an alkylene group. The alkylene group is preferably linear and has preferably 1 to 22 carbon atoms, more preferably 12 to 18 carbon atoms. R8 is -O-(CH2CH2O) c When the group is -R9-, the water solubility is increased and the group can be suitably applied to aqueous inks. In this case, when c is 10 or less, the ink viscosity is not excessively increased and the ink ejection properties can be stably maintained. Each M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Among these, M is preferably a hydrogen atom or an alkali metal such as lithium, sodium, or potassium.

[0068] Polyoxyethylene alkyl ether is a compound represented by the following general formula (4). R 10 -O-(CH2CH2O) d -H (4) (In the general formula (4), R 10 represents a hydrocarbon group, and d represents a number of 5 or more.

[0069] In general formula (4), R 10 represents a hydrocarbon group. Examples of the hydrocarbon group include alkyl groups and alkenyl groups, which are preferably linear and have 1 to 22 carbon atoms. d represents a number of 5 or more, preferably 5 to 50. When d is 5 or more, the water solubility is high and the compound can be suitably applied to aqueous inks. Furthermore, when d is 50 or less, the viscosity of the ink is not excessively increased, and stable ink ejection properties can be maintained.

[0070] The ethylene oxide adduct of a saturated polyhydric alcohol is a compound represented by the following general formula (5). R 11 -[O-(CH2CH2O) e ] f -H (5) (In the general formula (5), R 11 represents a residue of a saturated polyhydric alcohol other than a hydroxy group, and e represents a number of 1 or more.

[0071] In general formula (5), R 11 represents a residue of a saturated polyhydric alcohol other than a hydroxy group. The valence of the saturated polyhydric alcohol is equal to f and is preferably 3 to 10. e represents a number of 1 or more and is preferably 1 to 20. The total of e in the ethylene oxide adduct of the saturated polyhydric alcohol is preferably 3 to 60, and more preferably 3 to 30.

[0072] An example of the ethylene oxide-propylene oxide block copolymer is a compound represented by the following general formula (6). HO-(CH2CH2O) g -(CH2CH(CH3)O) h -(CH2CH2O) i -H ···(6) (In the general formula (6), g, h, and i each independently represent a number of 1 or more.)

[0073] In general formula (6), g, h, and i each independently represent a number of 1 or more, and preferably 1 to 20. The hydrophilicity or hydrophobicity of the compound represented by general formula (6) can be adjusted by the balance between g+i and h.

[0074] Examples of the perfluoroalkylethylene oxide adduct include compounds represented by the following general formula (7). F-(CF2) j -(CH2CH2O) k -H (7) (In the general formula (7), j and k each independently represent a number of 1 or more.)

[0075] In general formula (7), j and k each independently represent a number equal to or greater than 1. j is preferably 2 to 12, and more preferably 2 to 6. Furthermore, k is preferably 2 to 13.

[0076] The content (mass %) of the predetermined surfactant in the second ink is preferably 5.00% by mass or less, and more preferably 0.10% by mass or more to 2.00% by mass, based on the total mass of the second ink. The content (mass %) of the predetermined surfactant in the second ink is preferably 0.02 times or more in mass relative to the content (mass %) of the pigment. By setting the mass ratio to 0.02 times or more, the predetermined surfactant can easily penetrate into gaps between aggregated pigments, making it easier to redisperse the aggregated pigments. Furthermore, wiping properties can be further improved, and ejection irregularities can be further suppressed even when recording for a long period of time. The content (mass %) of the predetermined surfactant in the second ink is preferably 0.30 times or less in mass relative to the content (mass %) of the pigment.

[0077] It is preferable that the first ink is substantially free of a specific surfactant selected from the group of surfactants described above. If a specific surfactant is present in the first ink, aggregation of the pigment in the first ink is suppressed, which may slightly reduce the color development of the printed image. Specifically, the content (mass %) of the specific surfactant in the first ink is preferably 0.01 mass % or less, and more preferably 0.00 mass %, based on the total mass of the first ink.

[0078] The second ink may further contain a surfactant (other surfactant) other than the predetermined surfactant. Examples of other surfactants include other anionic surfactants, cationic surfactants, and other nonionic surfactants. The second ink preferably contains an ethylene oxide adduct of acetylene glycol in addition to the predetermined surfactant. The first ink may also contain other surfactants. In particular, it is preferable that the first ink contains another surfactant that is different from the predetermined surfactant contained in the second ink. In particular, it is preferable that the first ink contains an ethylene oxide adduct of acetylene glycol. The content (mass %) of other surfactants in the ink is preferably 0.10% by mass or more and 5.00% by mass or less, and more preferably 0.10% by mass or more and 2.00% by mass or less, based on the total mass of the ink.

[0079] [Other ingredients] The ink may further contain water-soluble organic compounds that are solid at 25°C, such as urea or its derivatives, trimethylolpropane, and trimethylolethane. The content (mass %) of the water-soluble organic compounds in the ink is preferably 0.10 mass % or more and 10.00 mass % or less, based on the total mass of the ink. In addition to the above components, the ink may also contain various additives, such as antifoaming agents, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and antireducing agents, as needed.

[0080] [Ink properties] The pH of the ink at 25°C is preferably 7 or more and 10 or less. The pH of the second ink is preferably higher than the pH of the first ink. Generally, the higher the pH of the ink, the higher the degree of dissociation of the anionic groups, and the easier it is to maintain a stable dispersion state of the pigment. Therefore, when the unwanted ink adhering to the periphery of the second ejection port array that has been swept away by wiping mixes with the unwanted ink adhering to the periphery of the first ejection port array, the pH of the unwanted ink adhering to the periphery of the first ejection port array increases. This makes it easier for the aggregated pigment to be redispersed, further improving wiping performance and further suppressing uneven ejection even when recording for a long period of time. [Example]

[0081] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0082] <Preparation of pigment dispersion> (Amount of anionic groups in self-dispersing pigment) The amount of anionic groups in the self-dispersing pigment in the pigment dispersion was measured by potentiometric titration using 5 mmol / L methyl glycol chitosan as the titration reagent using an automatic potentiometric titrator equipped with a streaming potential titration unit (PCD-500). The automatic potentiometric titrator used was the "AT-510" (manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0083] (Pigment dispersions 1 to 5) A solution of 5.0 g of concentrated hydrochloric acid dissolved in 5.5 g of water was cooled to 5°C, and in this state, 4-aminophthalic acid was added in the amount shown in Table 1. The container containing this solution was placed in an ice bath, and while stirring to maintain the temperature of the solution at 10°C or below, a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of 5°C ion-exchanged water was added. After stirring for 15 minutes, carbon black (specific surface area 220 m) was added. 26.0 g of carbon black (10.0 g / g, DBP oil absorption 105 mL / 100 g) was added under stirring and stirred for an additional 15 minutes to obtain a slurry. The resulting slurry was filtered through filter paper (trade name "Standard Filter Paper No. 2" manufactured by Advantec), and the particles were thoroughly washed with water and dried in an oven at 110°C. Sodium ions were then replaced with potassium ions using ion exchange to obtain a self-dispersing pigment in which -CH-(COOK) groups were bonded to the surface of the carbon black particles. An appropriate amount of water was added to adjust the pigment content, yielding Pigment Dispersions 1 to 5 with a pigment content of 15.0%. The amounts of anionic groups in the self-dispersing pigments in the resulting Pigment Dispersions 1 to 5 are shown in Table 1.

[0084] TIFF0007822756000001.tif57170

[0085] (Pigment dispersion 6) Carbon black (specific surface area 220m 2 The carbon black (carbon black with a 10.0% CO₂ content of 1.0%) was pre-dispersed in ion-exchanged water and then subjected to ozone treatment for 8 hours. The pH of the mixture was then adjusted to approximately 7 by adding potassium hydroxide, while the mixture was circulated for 3 hours using a liquid-liquid collision disperser. The mixture was then purified by ultrafiltration. The pH was then adjusted to 10.0 using an aqueous potassium hydroxide solution, yielding a self-dispersible pigment with -COOK groups bonded to the surface of the carbon black particles. An appropriate amount of water was added to adjust the pigment content, yielding Pigment Dispersion 6 with a pigment content of 15.0%. The amount of anionic groups in the self-dispersible pigment in the resulting Pigment Dispersion 6 was 0.40 mmol / g.

[0086] (Pigment dispersion 7) A styrene-acrylic acid copolymer with an acid value of 160 mgKOH / g and a weight-average molecular weight of 10,000 was neutralized with a 10% aqueous solution of potassium hydroxide. Carbon black (specific surface area 220 m) 2A mixture was obtained by mixing 10.0 parts of a styrene-acrylic acid copolymer (solids content: 105 mL / 100 g), 3.0 parts of neutralized styrene-acrylic acid copolymer, and 85.0 parts of ion-exchanged water. The resulting mixture was dispersed using a sand grinder for 1 hour and then centrifuged to remove coarse particles. The mixture was then filtered under pressure using a 3.0 μm pore size microfilter (Fujifilm) to obtain Pigment Dispersion 7, in which carbon black was dispersed in water by the resin. The pigment content in Pigment Dispersion 7 was 15.0%, and the resin dispersant content was 4.5%.

[0087] (Pigment dispersion 8) Pigment Dispersion 8 was obtained in the same manner as for Pigment Dispersion 7, except that the pigment was changed to CI Pigment Blue 15:3. The pigment content in Pigment Dispersion 8 was 15.0%, and the resin dispersant content was 4.5%.

[0088] (Pigment Dispersion 9) Pigment Dispersion Liquid 9 was obtained in the same manner as for Pigment Dispersion Liquid 7, except that the pigment was changed to CI Pigment Red 122. The pigment content in Pigment Dispersion Liquid 9 was 15.0%, and the resin dispersant content was 4.5%.

[0089] (Pigment Dispersion 10) Pigment Dispersion 10 was obtained in the same manner as for Pigment Dispersion 7, except that the pigment was changed to CI Pigment Yellow 74. The pigment content in Pigment Dispersion 10 was 15.0%, and the resin dispersant content was 4.5%.

[0090] <Preparation of dye aqueous solution> Aqueous dye solutions 1 and 2 containing dye 1 (CI Direct Black 195) and dye 2 (CI Direct Yellow 132), respectively, were obtained. The dye contents in the obtained aqueous dye solutions 1 and 2 were each 10.0%.

[0091] <Preparation of acrylic resin> Acrylic resin 1 was synthesized by copolymerizing 81.0 parts of styrene and 19.0 parts of acrylic acid using a conventional method. The carboxylic acid groups were neutralized with potassium hydroxide in an amount equimolar to the acid value of acrylic resin 1, and an appropriate amount of pure water was added to obtain a liquid containing acrylic resin 1 with a resin content of 20.00%. The acid value of acrylic resin 1 was 148 mgKOH / g, and the weight-average molecular weight measured by gel permeation chromatography was 10,000.

[0092] <Preparation of surfactant> The surfactants shown in Table 2 were prepared.

[0093] TIFF0007822756000002.tif144170

[0094] <Ink Preparation> The components (unit: %) shown in the upper rows of Tables 3-1 to 3-4 were mixed and thoroughly stirred. The pH was then adjusted using a 1 mol / L aqueous potassium hydroxide solution. Each ink was prepared by pressure filtration using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm. In Tables 3-1 to 3-4, "Betafin BP20" is the trade name for trimethylglycine manufactured by DuPont. The lower rows of Tables 3-1 to 3-4 show the pH of the ink at 25°C. The pH of the ink was measured using a pH meter (manufactured by Horiba, Ltd.).

[0095] TIFF0007822756000003.tif233170

[0096] TIFF0007822756000004.tif244170

[0097] TIFF0007822756000005.tif246170

[0098] TIFF0007822756000006.tif231170

[0099] <Recording head configuration> A print head was prepared that ejects ink by applying thermal energy. The print head has a print element substrate with an array of 512 ejection ports arranged at a density of 600 dpi. The mass of an ink droplet ejected from one ejection port is approximately 5.5 ng. As shown in Figure 1, the print head is a serial print head 20 with a print element substrate 2 arranged on it. This print element substrate 2 has a first ejection port array 3 and a second ejection port array 4 formed thereon, which eject two types of ink, respectively.

[0100] <Inkjet recording device> The inkjet recording devices (Recording Devices 1 to 4) listed in Table 4 were used. The ink inlet provided in the ink storage unit of Recording Devices 1 to 3 was an openable inlet, while the ink storage unit of Recording Device 4 was in the form of a removable cartridge and did not have an openable ink inlet. Furthermore, the ink storage units of all recording devices were equipped with a communication port that allowed communication with the outside air. A blade-shaped wiper made of urethane resin and 0.5 mm thick was used to clean the nozzle surface. This wiper had a width that included the lengths of the first and second nozzle arrays of the recording element substrate. The wiper movement speed during wiping was 100 mm / sec. The wipers of Recording Devices 1 and 4 wiped the second nozzle array and then the first nozzle array in a single motion, in a direction intersecting the nozzle array arrangement direction. The wiper of Recording Device 2 wiped in a single motion in a direction parallel to the nozzle array arrangement direction. The wiper of the recording device 3 wipes the first and second ejection port rows in a single operation in a direction intersecting the arrangement direction of the ejection port rows. In these inkjet recording devices, the recording duty of an image recorded under the condition that two ink droplets are applied to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as 100%.

[0101] TIFF0007822756000007.tif89170

[0102] <Evaluation> The following evaluations were carried out using the inkjet recording device. In the present invention, the following evaluation criteria were used: "AA", "A", and "B" were acceptable levels, and "C" was unacceptable. The evaluation results are shown in Table 5.

[0103] (wiping ability) The ink reservoir of the recording device shown in Table 5 was filled with the inks shown in Table 5 to the respective amounts. After filling, the device was left for two months at a temperature of 40°C and a humidity of 15% to allow the ink pigments in the ink reservoir to settle. At a temperature of 15°C and a relative humidity of 10%, a pump was used to draw 10 g of each ink from the printhead nozzles, and a solid image (18 cm x 2 cm) was printed at 100% print duty. 1,500 images were printed, with cleaning performed once after each image was printed, and the head was cleaned 1,500 times. After that, to check the print quality from each nozzle, 20 drops of ink were ejected in a straight line from one nozzle to print a ruled line. Glossy paper (product name "Gloss Gold GL-101" manufactured by Canon) was used as the print medium. After recording 1,500 images (cleaning 1,500 times), the recorded ruled lines were visually inspected for any bending or breaks, and the wiping properties were evaluated according to the following evaluation criteria. If the ink is ejected unevenly, the ruled lines will bend or break, so if continuous, straight ruled lines are recorded, the wiping properties can be said to be good. AAA: Ink was ejected normally from all ejection ports. AA: Wrinkling occurred in more than 0% and less than 5% of the ejection ports. A: Wrinkles occurred in 5% or more but less than 10% of the outlets. B: Wrinkles occurred in 10% or more but less than 15% of the discharge ports. C: Wrinkles occurred in 15% or more of the outlets.

[0104] (Color development) Using the inkjet recording device described above, 3 cm x 2 cm solid images were recorded on two types of recording media (plain paper). Recording was performed under conditions where approximately 22 ng of black ink and approximately 11 ng of cyan, magenta, and yellow inks were applied per 1 / 600 inch x 1 / 600 inch unit area. The recording media used were "CS-680" (Canon) and "Bright White" (Hewlett-Packard). Recording conditions were a temperature of 25°C and a relative humidity of 50%. After leaving the recorded solid images for one day under a temperature of 25°C and a relative humidity of 50%, the optical density of the images was measured using a fluorescence spectrodensitometer (FD-7, Konica Minolta). The average optical density was calculated, and color development was evaluated according to the following evaluation criteria. The reference optical density values ​​were 1.37 for black ink and 1.08 for color inks (cyan, magenta, and yellow). A: The average optical density was 0.02 or more higher than the standard value. B: The average optical density was within ±0.01 of the reference value. C: The average optical density was 0.02 or more lower than the standard value.

[0105] TIFF0007822756000008.tif255166

[0106] Reference Examples 1 to 4 are examples using an ink storage unit in the form of a cartridge, without an openable / closable ink inlet. The devices used in Reference Examples 1 to 4 had a smaller ink storage capacity in the ink storage unit than the devices used in the other Examples and Comparative Examples, so problems due to pigment settling in the ink did not occur. Therefore, wiping performance was not impaired, but the ink storage unit (ink cartridge) had to be replaced multiple times to record the same number of images as in the other Examples, resulting in poor productivity. In Reference Example 5, ink containing a dye was used as the colorant, so the colorant did not settle, and wiping performance did not deteriorate.

[0107] Example 27 A print head was prepared, each having a first nozzle array, a second nozzle array, a third nozzle array, and a fourth nozzle array, each of which ejects four types of ink. The wiping sequence with the wiper was, from the upstream side, the fourth nozzle array, the third nozzle array, the second nozzle array, and the first nozzle array. The wiping performance was evaluated under the conditions that ink 1 was ejected from the first nozzle array, ink 14 from the second nozzle array, ink 15 from the third nozzle array, and ink 16 from the fourth nozzle array. As a result, the print head was rated as "AAA" rank, as in Example 1.

Claims

1. an inkjet recording method comprising: a step of applying the water-based ink ejected from the ejection ports to a recording medium to record an image, using an inkjet recording apparatus comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with a water-based ink containing a pigment; a recording head having a recording element substrate on which a plurality of ejection port arrays are formed, each of which has a plurality of ejection ports for ejecting the water-based ink arranged in a predetermined direction; and cleaning means for wiping a surface of the recording element substrate on which the ejection port arrays are formed, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, and phosphoric acid surfactants; an inkjet recording method, characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting an arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

2. An inkjet recording method using an inkjet recording device comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with pigment-containing aqueous ink; a recording head having a recording element substrate on which a plurality of ejection port rows are formed, each of which has a plurality of ejection port rows arranged in a predetermined direction for ejecting the aqueous ink; and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed; and the inkjet recording method comprising the steps of: applying the aqueous ink ejected from the ejection port rows to a recording medium to record an image; the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the first ink does not contain the surfactant, an inkjet recording method, characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting an arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

3. An inkjet recording method using an inkjet recording device equipped with an ink storage section provided with an openable / closable ink inlet and capable of being refilled with pigment-containing aqueous ink, a recording head having a recording element substrate on which a plurality of ejection port rows are formed, with a plurality of ejection port rows for ejecting the aqueous ink arranged in a predetermined direction, and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed, and comprising the step of applying the aqueous ink ejected from the ejection port rows to a recording medium to record an image, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the first ink is a black ink and the second ink is a color ink; an inkjet recording method, characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting an arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

4. An inkjet recording method using an inkjet recording device comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with pigment-containing aqueous ink; a recording head having a recording element substrate on which a plurality of ejection port rows are formed, each of which has a plurality of ejection port rows arranged in a predetermined direction for ejecting the aqueous ink; and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed; and the inkjet recording method comprising the steps of: applying the aqueous ink ejected from the ejection port rows to a recording medium to record an image; the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the pigment in the first ink is a self-dispersing pigment having an anionic group bonded to the particle surface thereof directly or via another atomic group, an inkjet recording method, characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting an arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

5. An inkjet recording method using an inkjet recording device equipped with an ink storage section provided with an openable / closable ink inlet and capable of being refilled with pigment-containing aqueous ink, a recording head having a recording element substrate on which a plurality of ejection port rows are formed, with a plurality of ejection port rows for ejecting the aqueous ink arranged in a predetermined direction, and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed, and comprising the step of applying the aqueous ink ejected from the ejection port rows to a recording medium to record an image, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the pH of the second ink is higher than the pH of the first ink; an inkjet recording method, characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting an arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

6. 6. The inkjet recording method according to claim 1, wherein the content (mass %) of the surfactant in the second ink is 0.02 times or more the mass ratio of the content (mass %) of the pigment in the second ink.

7. 7. The inkjet recording method according to claim 1, wherein the content (mass %) of the surfactant in the second ink is 0.30 or less times the content (mass %) of the pigment in terms of mass ratio.

8. 8. The ink jet recording method according to claim 2, wherein the surfactant is at least one selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, and phosphoric acid surfactants.

9. 8. The ink jet recording method according to claim 1, wherein the surfactant is a sulfonic acid surfactant.

10. 10. The inkjet recording method according to claim 1, wherein the content (mass %) of the surfactant in the second ink is 0.10 mass % or more and 2.00 mass % based on the total mass of the ink.

11. 11. The ink jet recording method according to claim 1, wherein the first ink does not contain the surfactant.

12. 12. The ink jet recording method according to claim 1, wherein the first ink is a black ink and the second ink is a color ink.

13. 13. The ink jet recording method according to claim 1, wherein the pigment in the first ink is a self-dispersing pigment having an anionic group bonded to the particle surface thereof directly or via another atomic group.

14. 14. The inkjet recording method according to claim 13, wherein the amount of anionic groups in the self-dispersion pigment in the first ink is 0.05 mmol / g or more and 1.50 mmol / g or less.

15. 15. The inkjet recording method according to claim 13, wherein the pigment in the first ink is carbon black.

16. 16. The inkjet recording method according to claim 1, wherein the content (mass %) of the pigment in the first ink is 0.50 mass % or more and 15.00 mass % or less based on the total mass of the ink.

17. 17. The inkjet recording method according to claim 1, wherein the pigment in the second ink is dispersed with a resin dispersant.

18. 18. The inkjet recording method according to claim 1, wherein the pigment in the second ink is an organic pigment.

19. 19. The inkjet recording method according to claim 1, wherein the content (mass %) of the pigment in the second ink is 0.50 mass % or more and 15.00 mass % or less based on the total mass of the ink.

20. 20. The inkjet recording method according to claim 1, wherein the pH of the first ink is 7 or more and 10 or less.

21. 21. The inkjet recording method according to claim 1, wherein the second ink has a pH of 7 or more and 10 or less.

22. 22. The ink jet recording method according to claim 1, wherein the second ink has a higher pH than the first ink.

23. 23. The ink jet recording method according to claim 1, wherein the recording head is a serial type recording head.

24. 24. The ink jet recording method according to any one of claims 1 to 23, wherein the cleaning means is a blade-shaped wiper.

25. An inkjet recording apparatus comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with a pigment-containing aqueous ink; a recording head having a recording element substrate on which a plurality of ejection port arrays are formed, each of which has a plurality of ejection port arrays arranged in a predetermined direction for ejecting the aqueous ink; and a cleaning device for wiping a surface of the recording element substrate on which the ejection port arrays are formed, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, and phosphoric acid surfactants; an inkjet recording apparatus characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

26. An inkjet recording device comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with aqueous ink containing a pigment; a recording head having a recording element substrate on which a plurality of ejection port rows are formed, each row having a plurality of ejection ports for ejecting the aqueous ink arranged in a predetermined direction; and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the first ink does not contain the surfactant, an inkjet recording apparatus characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

27. ​​An inkjet recording device comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with aqueous ink containing a pigment; a recording head having a recording element substrate on which a plurality of ejection port rows are formed, each row having a plurality of ejection ports for ejecting the aqueous ink arranged in a predetermined direction; and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the first ink is a black ink and the second ink is a color ink; an inkjet recording apparatus characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

28. An inkjet recording device comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with aqueous ink containing a pigment; a recording head having a recording element substrate on which a plurality of ejection port rows are formed, each row having a plurality of ejection ports for ejecting the aqueous ink arranged in a predetermined direction; and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the pigment in the first ink is a self-dispersing pigment having an anionic group bonded to the particle surface thereof directly or via another atomic group, an inkjet recording apparatus characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

29. An inkjet recording device comprising: an ink storage section provided with an openable / closable ink inlet and capable of being refilled with aqueous ink containing a pigment; a recording head having a recording element substrate on which a plurality of ejection port rows are formed, each row having a plurality of ejection ports for ejecting the aqueous ink arranged in a predetermined direction; and cleaning means for wiping the surface of the recording element substrate on which the ejection port rows are formed, the aqueous ink includes a first ink and a second ink, and the plurality of ejection opening arrays include a first ejection opening array that ejects the first ink and a second ejection opening array that ejects the second ink, the second ink contains at least one surfactant selected from the group consisting of sulfonic acid surfactants, carboxylic acid surfactants, phosphoric acid surfactants, polyoxyethylene alkyl ethers, ethylene oxide adducts of saturated polyhydric alcohols, ethylene oxide-propylene oxide block copolymers, and perfluoroalkyl ethylene oxide adducts; the pH of the second ink is higher than the pH of the first ink; an inkjet recording apparatus characterized in that the cleaning means is a means for wiping a surface on which the ejection port arrays are formed in a direction intersecting the arrangement direction of the first ejection port array and the second ejection port array, in a single operation in the order of the second ejection port array and the first ejection port array.

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