Inkjet recording method, ink set, and inkjet recording device

Abstract

This invention provides an inkjet recording method that enables the recording of images with minimal misalignment of grid lines, even when recording images using a recording head having overlapping sections where the end ejection ports of adjacent ejection port rows overlap. [Solution] An inkjet recording method comprising the step of discharging aqueous ink from end discharge ports constituting an overlapping portion, allocated to a first discharge port row and a second discharge port row, to record an image on a recording medium, wherein the viscosity of the aqueous ink is 4.0 mPa·s or more, and the water-soluble organic solvent contains a water-soluble organic solvent (A) with a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) with a vapor pressure of 1.000 Pa or more at 25°C, wherein the content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass ratio to the content (mass%) of water-soluble organic solvent (B).

Description

[Technical Field]

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

[0002] In recent years, inkjet technology, which applies ink to recording media when outputting text and diagrams, has become widely used. When recording text and diagrams, there is a demand for images with high optical density and excellent line quality. Furthermore, the need to record large amounts of images in a short time necessitates faster recording speeds.

[0003] To record images with high optical density and excellent line quality, pigment inks that exhibit excellent color development in the recorded images are widely used, and various studies have been conducted to date. Patent Document 1 describes a study on improving color development using an ink containing resin particles formed from acrylic resin and pigments. Patent Document 2 describes a study on improving line quality using an ink containing a highly hydrophobic surfactant.

[0004] Furthermore, to increase recording speed, elongated recording heads are widely used, which are created by arranging multiple ejection port rows in a predetermined direction with a slight offset. In such recording heads, if the boundaries between the offset ejection port rows are discontinuous, streaks may appear in the image. Therefore, measures have been proposed to suppress the appearance of streaks in images in recording heads having multiple ejection port rows. Patent Document 3 proposes an inkjet recording apparatus equipped with a recording head in which the ejection port rows are arranged so that parts of the multiple ejection port rows overlap. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-048994 [Patent Document 2] Japanese Patent Publication No. 2015-117332 [Patent Document 3] Japanese Patent Publication No. 2024-000522 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present inventors recorded an image using the inkjet recording method proposed in Patent Document 3, using the inks proposed in Patent Documents 1 and 2, in order to record an image with excellent line quality at high speed. As a result, while high-speed recording was possible, it was found that the line quality was insufficient. Upon analysis of the recorded image, it was found that a misalignment occurred in the grid lines of the recorded image at the boundary between the portion recorded in the "overlapping portion" where the ends of the ejection port rows overlap and the portion recorded in the "non-overlapping portion" where the ends of the ejection port rows do not overlap.

[0007] Therefore, an object of the present invention is to provide an inkjet recording method that can record images in which line misalignment is less likely to occur, even when recording an image using a recording head having overlapping portions where the end discharge ports of adjacent discharge port rows overlap. Another object of the present invention is to provide an ink set and an inkjet recording apparatus to be used in the above-described inkjet recording method. [Means for solving the problem]

[0008] The above objective is achieved by the present invention as follows. That is, according to the present invention, an inkjet recording device is used which comprises an aqueous ink containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent, and a recording head having a plurality of discharge port rows configured such that a plurality of discharge ports for discharging aqueous ink are arranged in a predetermined direction, and a first discharge port row and a second discharge port row are arranged offset from each other in a predetermined direction such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting the predetermined direction, and the end discharge ports forming the overlapping portion are allocated to the first discharge port row and the second discharge port row and the aqueous ink An inkjet recording method is provided, comprising the step of ejecting ink to record an image on a recording medium, wherein the viscosity of the aqueous ink is 4.0 mPa·s or more, and the water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C, wherein the content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass relative to the content (mass%) of water-soluble organic solvent (B). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an inkjet recording method that can record images in which line misalignment is less likely to occur, even when recording an image using a recording head having an overlapping portion where the end discharge ports of adjacent discharge port rows overlap. Another object of the present invention is to provide an ink set and an inkjet recording apparatus for use in the above-mentioned inkjet recording method. [Brief explanation of the drawing]

[0010] [Figure 1] This figure schematically shows an example of an inkjet recording device equipped with the serial head of the present invention, where (a) is a perspective view of the main part of the inkjet recording device and (b) is a perspective view of the head cartridge. [Figure 2] This is a schematic diagram showing an example of the arrangement of the output port rows in a serial head. [Figure 3]It is a schematic diagram showing another example of the arrangement pattern of the ejection port row in the serial head. [Figure 4] It is a cross-sectional view schematically showing an embodiment of an ink cartridge. [Figure 5] It is an image diagram for recording an image by the line head of the present invention. [Figure 6] It is a schematic diagram showing an example of an inkjet recording apparatus provided with the line head of the present invention. [Figure 7] It is a diagram schematically showing an example of a line head, where (a) is a perspective view and (b) is an exploded perspective view. [Figure 8] It is a schematic diagram showing an example of the arrangement pattern of the ejection port row in the line head. [Figure 9] It is a schematic diagram showing another example of the arrangement pattern of the ejection port row in the line head. [Figure 10] It is a diagram showing an example of a recovery mechanism in the line head, where (a) is a perspective view and (b) is a schematic diagram. [Figure 11] It is a schematic diagram showing an example of a supply mechanism for supplying ink to the line head. [Figure 12] It is a schematic diagram showing the arrangement pattern of the ejection ports of the ejection port row constituting the recording head 1. [Figure 13] It is a schematic diagram showing the arrangement pattern of the ejection ports of the ejection port row constituting the recording head 3. [Figure 14] It is a schematic diagram showing the arrangement pattern of the ejection ports of the ejection port row constituting the recording head 5. [Figure 15] It is a schematic diagram showing the arrangement pattern of the ejection ports of the ejection port row constituting the recording head 10.

Embodiments for Carrying Out the Invention

[0011] The present invention will be described in more detail below with reference to preferred embodiments. Furthermore, water-based ink for inkjet printing may be simply referred to as "ink." Unless otherwise specified, physical properties are given at room temperature (25°C). In the present invention, a "unit" constituting the resin means a repeating unit derived from one monomer.

[0012] In this invention, "chromatic color" refers to a color that has three properties: "lightness," "hue," and "saturation." "Achromatic color" refers to a color that only has "lightness," such as white, black, and intermediate gray. It should be noted that achromatic inks used in practice do not completely lack hue, as the colorants themselves have a slight tint. However, achromatic inks are L * C * In the h color space, L * Since it is a color near the axis, it can be treated as having virtually no hue. "Having virtually no hue" means, for example, |C * The value must be ≤ 20. The "lightness," "hue," and "chroma" of the ink can be measured using a spectrophotometer or similar device. In this case, the physical properties of each can be measured for a sample prepared by appropriately diluting the ink with water (ion-exchanged water, deionized water, etc.).

[0013] The inventors have conducted a detailed analysis of the cause of line misalignment in images recorded at the boundary between overlapping and non-overlapping sections of the ejection port row. Normally, when recording a line image, ink droplets are ejected from the ejection port of the recording head so that two or more ink droplets overlap on the recording medium. For lines recorded in the non-overlapping section, ink droplets are ejected from the ejection port located at the position corresponding to the non-overlapping section so that they overlap. In this case, the time difference in the application of the ink droplet ejected first (also referred to as the "preceding ink droplet") and the ink droplet ejected later (also referred to as the "subsequent ink droplet") to the recording medium is the time required for the recording head to move by the distance between the ink droplets. Therefore, since the subsequent ink droplet is applied to the recording medium relatively soon after the preceding ink droplet is applied, there is no significant difference in the penetration and evaporation behavior of the preceding and subsequent ink droplets to the recording medium, and the pigment is uniformly distributed and fixed.

[0014] On the other hand, the ejection port located in the overlapping area is present in any of the adjacent ejection port rows. Therefore, in the overlapping area of ​​the ejection port rows, the ink is usually distributed and ejected using the adjacent ejection port rows. Consequently, the time difference between the application of the preceding ink droplet and the succeeding ink droplet to the recording medium is the distance between the ink droplets plus the time required for the recording head to move the distance between the adjacent ejection port rows. As a result, the time difference between the application of the preceding ink droplet to the recording medium and the application of the succeeding ink droplet is longer than the time difference between the application of ink droplets from the ejection port corresponding to the non-overlapping area. Therefore, penetration and evaporation of the preceding ink droplet into the recording medium occur before the succeeding ink droplet is applied. When the succeeding ink droplet is applied so as to overlap at least a portion with the preceding ink droplet, the preceding ink droplet maintains a certain degree of fluidity while having a higher pigment concentration. When the succeeding ink droplet is applied, the pigment concentration of the preceding ink droplet is higher than that of the succeeding ink droplet. This gradient in pigment concentration causes the pigment to flow from the preceding ink droplet to the succeeding ink droplet, resulting in a higher concentration of pigment in the succeeding droplet and an uneven distribution of pigment during fixation. Thus, while images recorded in non-overlapping areas had uniformly distributed and fixed pigment, images recorded in overlapping areas had an uneven distribution of pigment, and it was found that this unevenness in pigment concentration was visible as misalignment of the grid lines.

[0015] Based on the above findings, the inventors investigated the constituent materials of the ink in order to reduce the occurrence of line misalignment caused by uneven pigment distribution in overlapping areas. As a result, they found that by satisfying the requirements (i) to (iii) below, it is possible to record images with excellent line quality and less line misalignment even when using a recording head having overlapping areas where the end ejection ports of adjacent ejection port rows overlap. (i) The water-based ink comprises a pigment, a silicone-based surfactant, a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. (ii) The content (mass%) of water-soluble organic solvent (A) is 0.30 times or more in mass ratio to the content (mass%) of water-soluble organic solvent (B). (iii) The viscosity of the water-based ink is 4.0 mPa·s or higher.

[0016] The inventors speculate that satisfying the above requirements (i) to (iii) makes it less likely for the grid lines of the recorded image to be misaligned as follows.

[0017] If the vapor pressure of the water-soluble organic solvent in the ink is low, the water-soluble organic solvent will have low volatility, and therefore its migration speed to the gas-liquid interface is likely to be slow.

[0018] On the other hand, if the vapor pressure of the water-soluble organic solvent in the ink is high, the water-soluble organic solvent will have high volatility, and therefore its migration speed to the gas-liquid interface is considered to be fast. Water-soluble organic solvent (A) with a vapor pressure of 0.200 Pa or less has low volatility and tends to remain at the gas-liquid interface, but its migration speed to the gas-liquid interface is relatively slow, so it takes time to localize at the gas-liquid interface. Water-soluble organic solvent (B) with a vapor pressure of 1.000 Pa or more moves relatively quickly to the gas-liquid interface and tends to localize quickly at the gas-liquid interface, but because it is highly volatile, it is easily released into the atmosphere and does not tend to remain at the gas-liquid interface.

[0019] Furthermore, while silicone-based surfactants can lower the surface tension of ink, their migration speed to the gas-liquid interface is relatively slow, so it takes time for them to localize at the gas-liquid interface.

[0020] When a silicone-based surfactant with these properties is combined with a water-soluble organic solvent (A) and a water-soluble organic solvent (B), the interaction between them changes the migration speed to the gas-liquid interface. In particular, the interaction of water-soluble organic solvent (B) with the silicone-based surfactant and water-soluble organic solvent (A) increases the migration speed of the silicone-based surfactant and water-soluble organic solvent (A) to the gas-liquid interface due to the faster migration speed of water-soluble organic solvent (B). As a result, after the ink is applied to the recording medium, the silicone-based surfactant and water-soluble organic solvent (A) can quickly localize at the gas-liquid interface between the ink droplet on the recording medium and the atmosphere (i.e., on the surface of the ink droplet). Note that since the pigment has a larger mass compared to the water-soluble organic solvent (B), localization at the gas-liquid interface due to interaction with the water-soluble organic solvent (B) is less likely to occur.

[0021] This mechanism suggests that when a preceding ink droplet is applied to the recording medium, the silicone-based surfactant and water-soluble organic solvent (A) are quickly localized at the gas-liquid interface. The surface tension of the ink droplet where the silicone-based surfactant is localized is relatively low, while the surface tension of the ink droplet where the water-soluble organic solvent (A) is localized is relatively high. On the surface of the same ink droplet, non-uniformity of surface tension occurs between areas where the water-soluble organic solvent (A) is localized and areas where the silicone-based surfactant is localized, causing convection by the silicone-based surfactant and organic solvent (A) on the ink droplet surface. This convection makes it easier for the pigment to move effectively into the interior of the ink droplet, thus mitigating the pigment concentration gradient at the interface between the preceding and succeeding ink droplets when the subsequent ink droplet comes into contact with the preceding ink droplet. As a result, it is hypothesized that the flow of pigment into the subsequent ink droplet is suppressed. From the above, it is hypothesized that the pigment is uniformly distributed even in images recorded in overlapping areas, and as a result, the pigment is uniformly distributed in both non-overlapping and overlapping areas, making it less likely for line misalignment to occur.

[0022] The water-soluble organic solvent (A) has a vapor pressure of 0.030 Pa or higher. If the vapor pressure of the water-soluble organic solvent (A) is less than 0.030 Pa, the migration speed to the gas-liquid interface will be even slower. Therefore, even when used in combination with the water-soluble organic solvent (B), localization will take longer, and the pigment will have difficulty retreating into the ink droplet. As a result, it will not be possible to prevent misalignment of the lines.

[0023] Furthermore, the content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass ratio to the content (mass%) of water-soluble organic solvent (B). If the content (mass%) of water-soluble organic solvent (A) is less than 0.30 times by mass ratio to the content (mass%) of water-soluble organic solvent (B), the amount of water-soluble organic solvent (A) localized at the gas-liquid interface of the preceding ink droplet will decrease. This reduces the difference in surface tension on the surface of the preceding ink droplet, making convection less likely to occur, and thus the pigment does not retreat into the interior of the ink droplet. For this reason, it is not possible to suppress misalignment of the lines.

[0024] Furthermore, the ink viscosity is 4.0 mPa·s or higher. This viscosity suppresses the penetration and evaporation of the preceding ink droplet into the recording medium, thereby preventing an increase in the pigment concentration of the preceding ink droplet and mitigating the pigment concentration gradient at the interface between the preceding and succeeding ink droplets. As a result, ink flow is suppressed, making line misalignment less likely.

[0025] In deriving the above requirements (i) to (iii), the inventors investigated using acetylene glycol-based surfactants instead of silicone-based surfactants, but were unable to reduce the likelihood of line misalignment. The reason for this is speculated as follows: Generally, acetylene glycol-based surfactants do not tend to lower the surface tension of the ink as much as silicone-based surfactants. Therefore, it is speculated that because uneven surface tension is less likely to occur on the surface of the preceding ink droplet, convection is less likely to occur, and the pigment is less likely to retreat into the interior of the ink droplet.

[0026] Furthermore, the inventors investigated using a fluorine-based surfactant instead of a silicone-based surfactant, but were unable to reduce the likelihood of line misalignment. The reason for this is speculated as follows: Generally, fluorine-based surfactants interact less readily with water-soluble organic solvents than silicone-based surfactants. Therefore, because fluorine-based surfactants do not interact readily with water-soluble organic solvents (B), it takes time for them to localize at the gas-liquid interface. As a result, it is speculated that uneven surface tension is less likely to occur on the surface of the ink droplets of the preceding ink, making convection less likely to occur and preventing the pigment from retreating into the interior of the ink droplets.

[0027] <Inkjet recording method, inkjet recording device, and ink set> The present invention uses an inkjet recording apparatus comprising an aqueous ink and a recording head having a plurality of nozzle rows configured in which a plurality of nozzles for ejecting the aqueous ink are arranged in a predetermined direction. The aqueous ink contains a pigment, a silicone-based surfactant, and a water-soluble organic solvent. The viscosity of the aqueous ink is 4.0 mPa·s or higher. The water-soluble organic solvent includes a water-soluble organic solvent (A) with a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) with a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass relative to the content (mass%) of water-soluble organic solvent (B). The present invention also includes a step of recording an image on a recording medium using this inkjet recording apparatus (hereinafter also referred to as the "recording step"). Multiple nozzle rows include a first nozzle row and a second nozzle row, which are arranged offset from each other in a predetermined direction such that the end nozzles of adjacent nozzle rows overlap in a direction that intersects with a predetermined direction (the direction in which the nozzles are arranged). In the recording process, water-based ink is dispensed from the end nozzles that constitute the overlapping section, allocated to the first nozzle row and the second nozzle row.

[0028] The ink set of the present invention comprises achromatic ink and chromatic ink. The achromatic ink and chromatic ink each contain a pigment, a silicone-based surfactant, and a water-soluble organic solvent. The viscosity of the achromatic ink and chromatic ink is 4.0 mPa·s or higher. The water-soluble organic solvent includes a water-soluble organic solvent (A) with a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) with a vapor pressure of 1.000 Pa or higher at 25°C. The content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass relative to the content (mass%) of water-soluble organic solvent (B). The ink set of the present invention is used in the above-described inkjet recording method. The inkjet recording method first has a plurality of nozzle rows configured in which a plurality of nozzles for ejecting achromatic ink and chromatic ink, respectively, are arranged in a predetermined direction. Furthermore, the ink set includes a first and second row of discharge ports, which are arranged offset from each other in a predetermined direction, such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting a predetermined direction. Preferably, it also includes a third row of discharge ports, which is arranged to overlap the second row of discharge ports in a direction intersecting a predetermined direction, and is located on the opposite side of the first row of discharge ports, with the second row of discharge ports in between. The ink set of the present invention can also be used in an inkjet recording method that includes a step of recording an image on a recording medium using an inkjet recording device equipped with a recording head including the first to third rows of discharge ports. In this case, achromatic ink is discharged from the first and second rows of discharge ports, and chromatic ink is discharged from the third row of discharge ports. Achromatic ink is allocated and discharged from the end discharge ports that form the overlapping portion to the first and second rows of discharge ports.

[0029] Furthermore, the inkjet recording apparatus of the present invention is a device suitably used in the above-described inkjet recording method, and comprises an aqueous ink and a recording head. The aqueous ink contains a pigment, a silicone-based surfactant, and a water-soluble organic solvent. The viscosity of the aqueous ink is 4.0 mPa·s or higher. The water-soluble organic solvent includes a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass ratio to the content (mass%) of water-soluble organic solvent (B). The inkjet recording apparatus of the present invention includes a first and second discharge port row, in which a plurality of discharge port rows are arranged offset from each other in a predetermined direction such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting a predetermined direction (the direction of arrangement of discharge ports). Then, water-based ink is dispensed from the end outlets that make up the overlapping section, allocated to the first and second outlet rows.

[0030] (Inkjet recording device) Examples of inkjet recording heads found in inkjet recording devices include serial heads and line heads. A serial head is a recording head that records an image by transporting the recording medium in the sub-scanning direction while moving back and forth in the main scanning direction. A line head is a recording head that records an image by transporting the recording medium without moving itself.

[0031] Methods for ejecting ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. Among these, it is preferable to adopt a method that imparts mechanical energy to the ink to eject it.

[0032] The details of the inkjet recording device equipped with a serial head and the inkjet recording device equipped with a line head will be described below with reference to the drawings.

[0033] Figure 1 is a schematic diagram showing an example of an inkjet recording apparatus equipped with a serial head used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus 10 is provided with a transport means (not shown) for transporting the recording medium 11 and a carriage shaft 12. A head cartridge 13 can be mounted on the carriage shaft 12. The head cartridge 13 comprises recording element substrates 14 and 15 and is configured to accommodate an ink cartridge 40, which will be described later. While the head cartridge 13 is transported along the carriage shaft 12 in the main scanning direction, ink (not shown) is ejected from the recording element substrates 14 and 15 toward the recording medium 11. Then, the recording medium 11 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 11.

[0034] Figure 2 is a schematic diagram showing an example of the arrangement of ejection port rows in a serial head. As shown in Figure 2, a serial head, which is an example of a recording head constituting the inkjet recording apparatus of the present invention, comprises recording element substrates 21 and 22. The recording element substrate 21 has a first ejection port row 23 configured with a plurality of ejection ports for ejecting ink arranged in a predetermined direction. The recording element substrate 22 has a second ejection port row 24 configured with a plurality of ejection ports for ejecting ink arranged in a predetermined direction. The adjacent first ejection port row 23 and second ejection port row 24 are arranged offset from each other in a predetermined direction such that their end ejection ports have an overlapping portion D1 in a direction intersecting the predetermined direction (the direction of arrangement of the ejection ports). The end ejection ports (overlapping portion ejection ports) in the first ejection port row 23, located in the overlapping portion, and the end ejection ports (overlapping portion ejection ports) in the second ejection port row 24, also located in the overlapping portion, are configured to eject aqueous ink, which is allocated to the first and second ejection port rows.

[0035] Figure 3 is a schematic diagram showing another example of the arrangement of nozzle rows in a serial head. As shown in Figure 3, a serial head, which is another example of a recording head constituting the inkjet recording apparatus of the present invention, comprises recording element substrates 31, 32, and 33. The recording element substrate 31 has a first nozzle row 34 configured with a plurality of nozzles for ejecting ink arranged in a predetermined direction. The recording element substrate 32 has a second nozzle row 35 configured with a plurality of nozzles for ejecting ink arranged in a predetermined direction. The recording element substrate 33 has a third nozzle row 36 configured with a plurality of nozzles for ejecting ink arranged in a predetermined direction. The adjacent first nozzle row 34 and second nozzle row 35 are arranged offset from each other in a predetermined direction such that their end nozzles overlap in a direction intersecting the predetermined direction (the direction of nozzle arrangement). The adjacent second nozzle row 35 and third nozzle row 36 are arranged to overlap in parallel in a direction intersecting the predetermined direction (the direction of nozzle arrangement). The third nozzle row 36 is arranged so as to be on the opposite side of the first nozzle row 34, with the second nozzle row 35 in between, in a direction intersecting a predetermined direction (the direction in which the nozzles are arranged). In the case of a serial head, the direction intersecting the predetermined direction is the main scanning direction of the recording head. In the case of a line head, the direction intersecting the predetermined direction is the transport direction of the recording medium. The first nozzle row and the second nozzle row are configured to eject achromatic ink, while the third nozzle row ejects chromatic ink. In the overlapping section, the end nozzles that constitute part of the overlapping section in the first nozzle row and the end nozzles that constitute part of the overlapping section in the second nozzle row are configured to eject achromatic ink, allocated to the first nozzle row and the second nozzle row, respectively.

[0036] Figure 4 is a schematic cross-sectional view showing one embodiment of an ink cartridge. The ink cartridge 40 comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the water-based ink described above. As shown in Figure 4, an ink supply port 41 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge 40. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 42 and an absorbent storage chamber 43, which are connected via a communication port 44. The absorbent storage chamber 43 is also connected to the ink supply port 41. Liquid ink 45 is stored in the ink storage chamber 42, and absorbent materials 46 and 47 that hold the ink in an impregnated state are stored in the absorbent storage chamber 43. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0037] Figure 5 is an illustrative diagram showing how an image is recorded by a line head. Figure 6 is a schematic diagram showing an example of an inkjet recording device equipped with the line head of the present invention. In the recording device M4000 shown in Figure 6, the line head (recording head H1000) is fixed to the recording device body, and a method is employed in which the recording medium 51 is transported in the direction of the arrow 52 to record.

[0038] The recording device M4000 includes, for example, a recording head H1000Y for yellow ink, a recording head H1000M for magenta ink, a recording head H1000C for cyan ink, and a recording head H1000Bk for black ink (Figure 5). The ink colors are not limited to those listed above; at least one ink color may be a water-based ink, as described later. Also, as shown in Figure 6, the recording device M4000 may include a recording head H1000R for the reaction solution.

[0039] The recording heads H1000Y, H1000M, H1000C, H1000Bk, and H1000R shown in Figure 6 are fixed by a recording head holder 53 mounted on the recording device M4000. Figures 5 and 6 show a configuration in which yellow, magenta, cyan, and black inks, as well as reaction liquids, are ejected from separate recording heads. Alternatively, an image may be recorded by ejecting multiple inks and reaction liquids from each of multiple ejection port rows provided on a single recording element substrate.

[0040] The paper feed cassette 54 is detachably attached to the main body of the device, and the recording media 51 are stored inside the paper feed cassette 54. The pickup roller 55 is a component that feeds out the topmost sheet of the recording media 51 stored inside the paper feed cassette 54. The transport roller 56 is a component that transports the recording media 51 fed out by the pickup roller 55 to the transport path 57. In addition, the transport roller 58, which is located on the exit side of the transport path 57, is a component that transports the recording media 51 in the direction of the recording head H1000 while it is resting on the transport belt 59.

[0041] Figure 7 is a schematic diagram of an example of a line head, where (a) is a perspective view and (b) is an exploded perspective view. As shown in Figure 7, the line head (recording head H1000) comprises a recording element unit H1400 and an ink supply unit H1500, which is a liquid supply unit for supplying ink to the recording element unit H1400. The ink supply unit H1500 includes a connection part H1700 with a connection port H1710 formed therein for connecting to the outside in order to supply ink from an external source such as a recording device to an ink chamber (not shown). The recording element unit H1400 is composed of a recording element substrate H1100, a support substrate H1200, and a wiring member H1300.

[0042] The support substrate H1200 is a component that holds and fixes the recording element substrate H1100 and the wiring member H1300, and has ink supply holes H1210 formed therein that supply ink supplied from the ink supply unit H1500 to the recording element substrate H1100. Multiple recording element substrates H1100 are arranged and fixed on the main surface of the support substrate H1200 with predetermined positional accuracy. Furthermore, the multiple recording element substrates H1100 are arranged in a staggered pattern on the support substrate H1200 such that the discharge ports are arranged continuously along the direction of the discharge port row between adjacent recording element substrates H1100. By arranging the recording element substrates H1100 in this way, with the end discharge ports of the joints of adjacent recording element substrates H1100 overlapping, it is possible to correct the effect on the image due to misalignment of the recording element substrates, and a line head with a long recording width is formed.

[0043] The wiring member H1300 is electrically connected to the recording element board H1100 in order to transmit electrical signals and power to drive the recording elements provided on the recording element board H1100 from outside the recording head H1000 (recording device) to the recording element board H1100. A flexible printed circuit board, such as a flexible wiring board, is used as the wiring member H1300. The flexible wiring member H1300 is bent to facilitate electrical connection between the recording element board H1100 and the recording device, and is fixed to the ink supply unit H1500.

[0044] Figure 8 is a schematic diagram showing an example of the arrangement of nozzle rows in a line head. As shown in Figure 8, a line head, which is an example of a recording head constituting the inkjet recording apparatus of the present invention, comprises recording element substrates H1100 and H1105. The recording element substrate H1100 has a first nozzle row 81 configured in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction. The recording element substrate H1105 has a second nozzle row 82 configured in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction. The adjacent first nozzle row 81 and second nozzle row 82 are arranged offset from each other in a predetermined direction such that their end nozzles form an overlapping portion in a direction intersecting the predetermined direction (the direction of nozzle arrangement). The plurality of recording element substrates, including the recording element substrate H1100 having the first nozzle row 81 and the recording element substrate H1105 having the second nozzle row 82, are all held on a support substrate H1200. In the overlapping section, the end outlets (overlapping section outlets) that constitute a part of the overlapping section in the first outlet row and the end outlets (overlapping section outlets) that constitute a part of the overlapping section in the second outlet row are configured to dispense water-based ink, which is then allocated to the first and second outlet rows.

[0045] The arrangement of the recording element substrates is not particularly limited. For example, the recording element substrates can be arranged in a staggered pattern as shown in Figures 2 and 8. Alternatively, a combination of a staggered arrangement and a parallel arrangement, as shown in Figure 3, may be used. Furthermore, as shown in Figure 9, multiple recording element substrates, including a recording element substrate H1110 having a first discharge port row 91 and a recording element substrate H1115 having a second discharge port row 92, may be arranged in a line.

[0046] The inkjet recording apparatus used in the inkjet recording method of the present invention may further include a recovery mechanism for restoring the adhesion of ink at the discharge port of the line head and the wet state of the discharge port surface. Figure 10 shows an example of a recovery mechanism, where (a) is a perspective view and (b) is a schematic diagram. As shown in Figure 10, the wiper W1001 is held by a clip member W1002, and the clip member W1002 is held by a connecting member W1003. The clip member W1002 is attached to a wipe base W1011 that can move along the slide rail W1006. The wipe base W1011 can move along the slide rail W1006 by driving a timing belt W1007 through the connecting member W1003. The timing belt W1007 is supported by a driven pulley W1004 and a drive pulley W1005, and the shaft of a drive motor W1010 that drives the timing belt W1007 is connected to the drive pulley W1005. In addition, to control the position of the wiper W1001 during the recovery operation, photosensors W1008 and W1009 are provided at both ends of the slide rail W1006. During the recovery operation by wiping, the wiper W1001 slides and moves on the slide rail W1006, causing the wiper W1001 to flex and wipe the ejection port surface H1001 of the recording element substrate H100 of the recording head H10.

[0047] The inkjet recording apparatus used in the inkjet recording method of the present invention may further include a supply mechanism for supplying liquids such as ink or reaction solution to the line head. Figure 11 is a schematic diagram showing an example of a supply mechanism for supplying ink to the line head. As shown in Figure 11, ink is supplied from the sub-tank T2 to the line head H1000 by the pump P1. Ink or reaction solution that overflows from the line head H1000 is returned to the sub-tank T2. Valve V1 is provided for switching between pressurizing or releasing the ink liquid chamber inside the line head during recovery operation. When pressurizing is restored, valve V1 is closed and pressurized by pump P1, thereby removing some of the bubbles in the ink or reaction solution supply path and the flow path of the ink or reaction solution. The liquid level of the ink or reaction solution in the sub-tank T2 is configured to maintain a head difference with respect to the discharge port surface of the line head H1000 within a certain range, thereby maintaining the negative pressure on the discharge port surface of the line head H1000 within an appropriate range. If the ink or reaction solution in sub-tank T2 becomes insufficient, pump P2 will send ink or reaction solution from main tank T1 to sub-tank T2. To pressurize and flow the ink or reaction solution in the recording element substrate H100, valve V1 is closed and valve V2 is opened, and pressurization is applied by pump P1. This causes the thickened ink or reaction solution to be discharged from the recording element substrate H100 of the line head H1000. On the other hand, to suction and flow the ink or reaction solution in the recording element substrate H100, valve V1 is closed and valve V2 is open, and cap C10 is tightly sealed to the discharge port surface H1001, and suction is applied by pump P3. This causes the thickened ink or reaction solution (waste ink or waste reaction solution 75) to be discharged from the recording element substrate H100 of the line head H1000. The temperature of each tank and the ink or reaction solution contained therein depends on the ambient temperature in which the inkjet recording device is installed, but is preferably in the range of 15 to 45°C, for example.

[0048] (Recording medium) While known recording media can be used to record images using the inkjet recording method of the present invention, it is preferable to use an ink-absorbing recording media. Examples of ink-absorbing recording media include paper-based recording media such as glossy paper, art paper, and plain paper. An ink-absorbing recording media is defined as follows: In the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51, "Test Method for Liquid Absorption of Paper and Paperboard," from the start of contact for 30 msec 1 / 2 Up to 10 mL / m² of water absorption capacity 2 It is an ultra-high-performance recording medium.

[0049] <ink> The inkjet recording method of the present invention uses an aqueous ink containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent. The components of the ink used in the inkjet recording method of the present invention will be described in detail below.

[0050] (Pigment) Ink contains pigments as colorants. Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, imidazolon pigments, diketopyrrolopyrrole pigments, and dioxazine pigments.

[0051] Methods for dispersing pigments in ink include resin-dispersed pigments, which use resin as a dispersant, and self-dispersing pigments, in which hydrophilic groups are bonded to the surface of the pigment particles. Additionally, resin-bonded pigments, in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments, in which the surface of the pigment particles is coated or encapsulated with resin, can be used. Furthermore, it is possible to use pigments with different dispersion methods in combination.

[0052] As a resin (resin dispersant) for dispersing pigments in an aqueous medium, a resin having hydrophilic units and hydrophobic units as constituent units is preferred. The resin dispersant is preferably an acrylic resin having acrylic components such as units derived from (meth)acrylic acid or units derived from (meth)acrylic esters, and is even more preferably a water-soluble acrylic resin. Among these, a water-soluble acrylic resin in the form of a random copolymer is particularly preferred. Hereinafter, "(meth)acrylic" means "acrylic" and "methacrylic," and "(meth)acrylate" means "acrylate" and "methacrylate."

[0053] Hydrophilic units are units having hydrophilic groups such as acidic groups and hydroxyl groups. Hydrophilic units can be formed, for example, by polymerizing monomers having hydrophilic groups. Specific examples of monomers having hydrophilic groups include: acidic monomers having carboxylic acid groups such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; acidic monomers having sulfonic acid groups such as styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 3-sulfopropyl (meth)acrylate; anionic monomers such as anhydrides and salts of these acidic monomers; monomers having hydroxyl groups such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; monomers having ethylene oxide groups such as methoxy(mono, di, tri, poly)ethylene glycol (meth)acrylate; and so on. Cationic ions that constitute salts of anionic monomers include lithium, sodium, potassium, ammonium, and organic ammonium ions. The acid value of the resin used as a resin dispersant is preferably 50 mg KOH / g or more and 200 mg KOH / g or less.

[0054] As self-dispersing pigments, oxidized self-dispersing carbon black (oxidized carbon black), carboxylic acid groups, and sulfonic acid groups can be used. In addition, pigments in which anionic groups such as phosphonic acid groups are directly bonded to the surface of the pigment particles or via other atomic groups (-R-) can be used. Oxidized carbon black can be obtained by oxidizing carbon black particles. As an example of a method for oxidizing carbon black, one can treat the surface of the raw material carbon black with ozone, hypochlorous acid and its salts, and persulfuric acid and its salts to oxidize the carbon black.

[0055] The anionic group may be either an acidic or salty form, and if it is a salty form, it may be partially dissociated or completely dissociated. When the anionic group is a salty form, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium. Specific examples of other atomic groups (-R-) include linear or branched alkylene groups with 1 to 12 carbon atoms, arylene groups such as phenylene and naphthylene groups, carbonyl groups, imino groups, amide groups, sulfonyl groups, ester groups, and ether groups. Combinations of these groups are also acceptable.

[0056] (Silicone-based surfactant) The ink contains a silicone-based surfactant. The silicone-based surfactant is preferably a compound represented by any of the following general formulas (1) to (3). In the following general formulas (1) to (3), "C2H4O" represents an ethylene oxide unit and "C3H6O" represents a propylene oxide unit. The ethylene oxide unit and the propylene oxide unit may be arranged in either a random state or a blocked state.

[0057] "Each unit is placed in a random state" means that each unit is placed irregularly. On the other hand, "Each unit is placed in a block state" means that the blocks formed by the collection of each unit are placed in a regular manner.

[0058] [ka]

[0059] (In the above general formula (1), R1 represents an alkylene group, R2 represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, a represents an integer of 1 or more, and b represents an integer of 0 or more.)

[0060] [ka]

[0061] (In the above general formula (2), R3 represents a hydrogen atom or an alkyl group, R4 represents an alkylene group, p represents an integer of 1 or more, c represents an integer of 1 or more, and d represents an integer of 0 or more.)

[0062] [ka]

[0063] (In the above general formula (3), R5 represents a hydrogen atom or an alkyl group, R6 represents an alkylene group, q and r each independently represent an integer of 1 or more, e represents an integer of 1 or more, and f represents an integer of 0 or more.)

[0064] (aqueous medium) The ink contains water and a water-soluble organic compound as an aqueous medium. It is preferable to use deionized water or ion-exchanged water as the water. The water content (mass%) in the aqueous ink is preferably 40.0% to 95.0% by mass, based on the total mass of the ink. The water-soluble organic compound includes a water-soluble organic solvent (A) with a vapor pressure of 0.030 Pa to 0.200 Pa at 25°C and a water-soluble organic solvent (B) with a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of water-soluble organic solvent (A) is preferably 0.30 times or more by mass compared to the content (mass%) of water-soluble organic solvent (B). Furthermore, it is preferable that the content (mass%) of water-soluble organic solvent (A) is 0.30 times or more by mass compared to the content (mass%) of water-soluble organic solvent (B). When the above mass ratio is 1.00 or less, the content of water-soluble organic solvent (A) is the same as or less than the content of water-soluble organic solvent (B). As a result, water-soluble organic solvent (B) is less likely to interact with water-soluble organic solvent (A) and more likely to interact with silicone-based surfactants. Therefore, convection is more likely to occur on the surface of the ink droplets of the preceding ink, and the effect of suppressing line misalignment is more likely to improve. In this specification, "vapor pressure" is the value at 25°C and 1 atmosphere. The vapor pressure at 25°C can be obtained by the static method. Alternatively, a value can be obtained by using commercially available calculation software (for example, product name "ACD / PhysChem Suite Version 12.00", manufactured by ACD / Labs).

[0065] Specific examples of water-soluble organic solvents (A) with a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C include, for example, glycerin (0.031 Pa), triethylene glycol monobutyl ether (0.072 Pa), and triethylene glycol (0.180 Pa). The numbers in parentheses above represent the vapor pressure (Pa) at 25°C.

[0066] Specific examples of water-soluble organic solvents (B) with a vapor pressure of 1,000 Pa or higher at 25°C include, for example, triethylene glycol monomethyl ether (1,300 Pa), diethylene glycol monobutyl ether (1,700 Pa), 1,4-butanediol (1,900 Pa), 3-methyl-1,5-pentanediol (1,900 Pa), 1,2-hexanediol (2,600 Pa), 1,3-pentanediol (3,700 Pa), 2-pyrrolidone (3,900 Pa), and 1,2-pentanediol (7,700 Pa). Examples include 1,3-butanediol (8,000 Pa), diethylene glycol monoethyl ether (9,800 Pa), 3-methyl-1,3-butanediol (10,400 Pa), ethylene glycol (11,700 Pa), propylene glycol (17,700 Pa), 1,2-butanediol (19,700 Pa), diethylene glycol monomethyl ether (26,700 Pa), ethylene glycol monobutyl ether (93,300 Pa), and 3-methoxy-1-butanol (98,400 Pa). The values ​​in parentheses above represent the vapor pressure (Pa) at 25°C. Furthermore, it is preferable that the water-soluble organic solvent (B) has a vapor pressure of 5,000 Pa or higher at 25°C. If the water-soluble organic solvent (B) has a vapor pressure of 5,000 Pa or higher at 25°C, the migration speed to the gas-liquid interface can be further increased. Therefore, the migration speed of the water-soluble organic solvent (A) and silicone-based surfactant to the gas-liquid interface is increased, and the effect of suppressing line misalignment can be further improved. There is no particular upper limit on the vapor pressure of the water-soluble organic solvent (B) at 25°C, but for example, it is preferable that the vapor pressure of the water-soluble organic solvent (B) at 25°C is 100,000 Pa or less. Furthermore, it is preferable that the water-soluble organic solvent (B) is an alkanediol having 4 or fewer carbon atoms. When the water-soluble organic solvent (B) is an alkanediol having 4 or fewer carbon atoms, the molecular weight is small, so the migration speed to the gas-liquid interface is fast. In addition, when the water-soluble organic solvent (B) is an alkanediol, a good balance between hydrophilicity and hydrophobicity is easily achieved, and it interacts easily with the water-soluble organic solvent (A) and silicone-based surfactant.Therefore, the migration speed of the water-soluble organic solvent (A) and silicone-based surfactant to the gas-liquid interface is increased, and the effect of suppressing line misalignment can be further improved. Furthermore, it is even more preferable that the water-soluble organic solvent (B) is 1,3-butanediol. Compared to other water-soluble organic solvents, 1,3-butanediol has a faster migration speed to the gas-liquid interface and readily interacts with the water-soluble organic solvent (A) and silicone-based surfactant. Therefore, by using 1,3-butanediol, ink flow can be effectively suppressed, and the effect of suppressing line misalignment can be further enhanced.

[0067] (Other ingredients) In addition to the components mentioned above, the ink may contain various other components as needed.

[0068] Other components may include various additives such as surfactants other than the silicone-based surfactants mentioned above, defoamers, pH adjusters, viscosity modifiers, rust inhibitors, preservatives, mold inhibitors, antioxidants, and reduction inhibitors. Examples of surfactants other than silicone-based surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. Examples of nonionic surfactants include hydrocarbon-based nonionic surfactants and fluorine-based nonionic surfactants.

[0069] (Ink properties) The ink is an aqueous ink for use in inkjet systems. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. The viscosity of the ink at 25°C is preferably 4.0 mPa·s or higher, and more preferably 6.0 mPa·s or higher. If the viscosity of the ink is less than 4.0 mPa·s, the fluidity of the ink is somewhat high, which may make it difficult to suppress the penetration and evaporation of the preceding ink into the recording medium. As a result, the pigment concentration gradient at the interface between the preceding and succeeding inks may not be easily mitigated, and the effect of suppressing line misalignment may decrease. There is no particular upper limit on the viscosity of the ink, but for example, it is preferable that the viscosity of the ink is 10.0 mPa·s or lower. The static surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less, and more preferably 25 mN / m or more and 45 mN / m or less. The pH of the ink at 25°C is preferably 7.0 or more and 10.0 or less. [Examples]

[0070] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0071] <Method for measuring physical properties> (Acid value of resin) Samples were prepared by dispersing or dissolving the resin in water. The prepared samples were potentiometrically titrated with methyl glycol chitosan 200 / N titrant using a potentiometric automatic titrator to calculate the number of anionic functional groups per gram of resin. The calculated number of anionic functional groups was converted to KOH mass to obtain the acid value of the resin (mgKOH / g). The potentiometric automatic titrator used was the "AT510" (manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0072] <Preparation of Pigment Dispersion> (Pigment dispersions 1-4) Each component shown in Table 1 and 85 parts of 0.3 mm zirconia beads were placed in a batch-type vertical sand mill (manufactured by AIMEX) and dispersed for 3 hours while water cooling. After that, the mixture was centrifuged to remove undispersed material containing coarse particles. Next, pigment dispersions 1 to 4 were prepared by pressure filtration through a 3.0 μm pore-size cellulose acetate filter (manufactured by Advantec). The components (in parts) of pigment dispersions 1 to 4 were as shown in Table 1. As a dispersant, a 20.0% acrylic resin aqueous solution was used, which was obtained by neutralizing a styrene-acrylic acid copolymer with an acid value of 170 mg KOH / g and a weight-average molecular weight of 8000 with a 10.0% potassium hydroxide aqueous solution to an acid value of 1 equivalent, and then diluting it with water. Details of the materials in Table 1 are shown below. • Carbon Black (product name "Black Pearls 880", made by Cabot) • CI Pigment Blue 15:3 (Product name "Hosta Palm Blue B2G", manufactured by Heubach) • Magenta solid solution pigment (solid solution of CI Pigment Red 202 and CI Pigment Violet 19, product name "Syncassia Magenta D4500J", manufactured by Sun Chemical Co., Ltd.) • CI Pigment Yellow 74 (product name "Fast Yellow 011", manufactured by Dainichi Seika Kogyo Co., Ltd.)

[0073] [Table 1]

[0074] (Pigment dispersion 5) A solution was prepared by dissolving 5.0g of concentrated hydrochloric acid in 5.5g of water and cooled to 5°C. 1.6g of 4-aminophthalic acid (treatment agent) was then added. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C. A solution prepared by dissolving 1.8g of sodium nitrite in 9.0g of ion-exchanged water at 5°C was then added. After stirring for 15 minutes, carbon black (specific surface area 260m²) was added. 26.0 g of the pigment was added under stirring, and the mixture was stirred for a further 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), the particles were thoroughly washed with water, and the mixture was dried in an oven at 110°C. After replacing the counterions from sodium ions to potassium ions by ion exchange, an appropriate amount of ion-exchanged water was added to adjust the pigment content. In this way, a pigment dispersion 5 was obtained containing a self-dispersing pigment with a pigment content of 20.00%, in which phthalate groups with potassium ions as counterions were bonded to the surface of carbon black particles.

[0075] <Preparation of resin particles> First, 43.9 parts of deionized water and 0.1 parts of potassium persulfate were mixed under a nitrogen atmosphere to obtain a solution. To the obtained solution, an emulsion was added dropwise, consisting of 34.0 parts of methyl methacrylate, 14.0 parts of n-butyl methacrylate, 2.0 parts of methacrylic acid, 3.0 parts of 1,4-butanediol dimethacrylate, and a reactive surfactant (product name "KH-05", manufactured by Daiichi Kogyo Seiyaku). The mixture was then stirred at 80°C for 10 hours to carry out the polymerization reaction. After cooling to 25°C, potassium hydroxide equivalent to the acid value of the resin and an appropriate amount of deionized water were added to obtain an aqueous dispersion of resin particles with a resin particle content of 20.0%.

[0076] <Preparation of water-soluble resin> A resin was synthesized in accordance with the preparation example of "Water-soluble resin 1" described in Japanese Patent Publication No. 2015-11733, and an aqueous solution with a water-soluble resin content of 15.0% was obtained. This water-soluble resin is a styrene / acrylic acid copolymer (mass ratio 87.5 / 12.5).

[0077] <Ink preparation> (Ink 1-46) Each component (in %) shown in the upper section of Tables 2-5 was mixed and thoroughly stirred. Then, inks 1-46 were prepared by pressure filtration through a 1.0 μm pore size polypropylene filter (manufactured by Advantec). The properties of the inks are shown in the lower section of Tables 2-5. The values ​​in parentheses in Tables 2-5 represent the vapor pressure (Pa) at 25°C.

[0078] The surfactants used to prepare the ink are listed below. • Product name "BYK-348", manufactured by BYK, silicone-based surfactant (meets formula (1)) • Product name "BYK-349", manufactured by BYK, silicone-based surfactant (meets formula (1)) • Product name "BYK-333", manufactured by BYK, silicone-based surfactant (meets formula (2)) • Product name "KF6017", manufactured by Shin-Etsu Chemical, silicone-based surfactant (meets formula (1)) • Product name "X-22-4952", manufactured by Shin-Etsu Chemical, silicone-based surfactant (meets formula (2)) • Product name "FZ-2231", manufactured by Dow Toray, silicone-based surfactant (meets formula (3)) • Product name: "Acetylenel E100", manufactured by Kawaken Fine Chemicals, acetylene glycol-based surfactant • Product name: Surfinol DF110D, manufactured by Nisshin Chemical, acetylene glycol-based surfactant. • Product name: Surfinol 104, manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol-based surfactant. • Product name: Surfinol 440, manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol-based surfactant. • Product name: "Orphine E1010", manufactured by Air Products, acetylene glycol-based surfactant • Product name: "Orphine EXP4300", manufactured by Air Products, acetylene glycol-based surfactant • Product name: "NIKKOL BC-20", manufactured by Nikko Chemicals, polyoxyethylene alkyl ether-based surfactant • Product name "Pluronic (registered trademark) L-31", manufactured by Adeka, polyoxyethylene-polyoxypropylene surfactant • Product name "FS-3100", manufactured by Chemours, fluorine-based surfactant

[0079] [Table 2]

[0080]

Table 3

[0081]

Table 4

[0082]

Table 5

[0083] <Preparation of Recording Medium> The following recording media were prepared. · Plain paper (product name "CS-064F A4", manufactured by Canon, water absorption from the start of contact in the Bristol method up to 30 msec 1 / 2 is 10 mL / m 2 exceeding)

[0084] <Configuration of Recording Head> The configurations of recording heads 1 to 10 used in this example, comparative example, and reference example are shown in Tables 6 and 7.

[0085] (Recording Head 1) A piezo inkjet recording head 1 that applies mechanical energy to eject ink was prepared. As shown in FIG. 2, recording head 1 is a serial head in which a plurality of recording element substrates 21 and 22 are arranged in a staggered pattern. The number of ejection ports per row of ejection port rows is 512, and as shown in FIG. 12, the number of overlapping ejection ports 200 per row of ejection port rows is 64.

[0086] (Recording Head 2) A piezo inkjet recording head 2 that applies mechanical energy to eject ink was prepared. As shown in FIG. 8, recording head 2 is a line head in which a plurality of recording element substrates H1100 and H1105 are arranged in a staggered pattern. The number of ejection ports per row of ejection port rows is 512, and as shown in FIG. 12, the number of overlapping ejection ports 200 per row of ejection port rows is 64.

[0087] (Recording head 3) A piezo-inkjet type recording head 3 was prepared, which ejects ink by applying mechanical energy. As shown in Figure 9, the recording head 3 is a line head in which multiple recording element substrates H1110 and H1115 are arranged in line. There are 512 ejection ports per row of ejection ports, and as shown in Figure 13, there are 16 overlapping ejection ports 220 per row of ejection ports.

[0088] (Recording head 4) A thermal inkjet recording head 4 was prepared, which ejects ink by applying thermal energy. As shown in Figure 2, the recording head 4 is a serial head in which multiple recording element substrates 21 and 22 are arranged in a staggered pattern. There are 512 ejection ports per row of ejection ports, and as shown in Figure 12, there are 64 overlapping ejection ports 200 per row of ejection ports.

[0089] (Recording head 5) A piezo-inkjet recording head 5 was prepared, which ejects ink by applying mechanical energy. As shown in Figure 14, the recording head 5 is a serial head having one recording element substrate H1120 in which two rows of ejection ports are arranged offset from each other. There are 512 ejection ports per row of ejection ports, and there are 64 overlapping ejection ports 240 per row of ejection ports.

[0090] (Recording head 6) A piezo-inkjet type recording head 6 was prepared, which ejects ink by applying mechanical energy. As shown in Figure 3, the recording head 6 is a serial head in which recording element substrates 31 and 32 are arranged in a staggered pattern, and recording element substrates 32 and 33 are arranged in parallel.

[0091] The number of discharge ports per discharge port row is 512, and as shown in Figure 12, the number of overlapping discharge ports 200 per discharge port row in the overlapping portion of recording element substrates 31 and 32 is 64. Also, the number of overlapping discharge ports per discharge port row in the overlapping portion of recording element substrates 32 and 33 is 512. In Table 7, the number on the left of the "Arrangement Configuration of Recording Element Substrates" column indicates the arrangement configuration of recording element substrates 31 and 32. Similarly, the number on the right indicates the arrangement configuration of recording element substrates 32 and 33. Also, in Table 7, the number on the left of the "Number of Overlapping Discharge Ports per Discharge Port Row" column indicates the number of overlapping discharge ports per discharge port row in recording element substrates 31 and 32. Similarly, the number on the right indicates the number of overlapping discharge ports per discharge port row in recording element substrates 32 and 33.

[0092] (Recording head 7) A piezo-inkjet type recording head 7 was prepared, which ejects ink by applying mechanical energy. As shown in Figure 2, the recording head 7 is a serial head in which multiple recording element substrates 21 and 22 are arranged in a staggered pattern. There are 512 ejection ports per row of ejection ports, and there are 0 overlapping ejection ports per row of ejection ports.

[0093] (Recording head 8) A piezo-inkjet type recording head 8 was prepared, which ejects ink by applying mechanical energy. As shown in Figure 8, the recording head 8 is a line head in which multiple recording element substrates H1100 and H1105 are arranged in a staggered pattern. There are 512 ejection ports per row of ejection ports, and there are 0 overlapping ejection ports per row of ejection ports.

[0094] (Recording head 9) A piezo-inkjet recording head 9 was prepared, which ejects ink by applying mechanical energy. As shown in Figure 9, the recording head 9 is a line head in which multiple recording element substrates H1110 and H1115 are arranged in line. There are 512 ejection ports per row of ejection ports, and there are 0 overlapping ejection ports per row of ejection ports.

[0095] (Recording head 10) A piezo-inkjet recording head 10 that ejects ink by applying mechanical energy was prepared. As shown in Figure 15, the recording head 10 is a serial head in which multiple recording element substrates 151 and 152 are arranged in parallel. 153 and 154 are ejection port rows. There are 512 ejection ports per ejection port row, and there are 512 overlapping ejection ports per ejection port row.

[0096] [Table 6]

[0097] [Table 7]

[0098] <Rating> Each ink obtained above was evaluated for the following items. Each adjusted ink was filled into an ink cartridge or ink tank of an inkjet recording device equipped with the recording head numbered as shown in the "Recording Head" section of Table 8. In the examples, comparative examples, and reference examples using recording heads 1, 4-7, and 10, the recording head was installed in the inkjet recording device shown in Figure 2 so that the ejection port row intersected the scanning direction of the recording head, and the ink was filled into the ink cartridge. In the inkjet recording device shown in Figure 2, images were recorded by the main scanning of the recording head and the transport of the recording medium in the sub-scanning direction.

[0099] In the examples and reference cases using recording heads 2, 3, 8, and 9, the recording heads were incorporated into the inkjet recording apparatus shown in Figure 6 so that the ejection port rows intersected the transport direction of the recording medium, and ink was filled into the ink tanks. Various types of ink were filled into the cartridges. In the inkjet recording apparatus shown in Figure 6, images were recorded by a single relative scan between the recording head and the recording medium.

[0100] In this invention, the following evaluation criteria were used, with "AA," "A," "B," and "C" representing acceptable levels and "D" representing an unacceptable level. The evaluation conditions and results are shown in Table 8.

[0101] (Misaligned lines) Using the inkjet recording device described above, a ruled line image with a recording resolution of 1200 dpi, a line width of 16 pixels, and a length of 100 mm was recorded on a recording medium with a recording duty cycle of 100%, such that the longitudinal direction of the ruled line intersects with a predetermined direction (the direction of the nozzle arrangement). In this embodiment, an image recorded under the condition of applying 8 droplets of 3.8 ng ± 10% ink to a unit area of ​​1 / 600 inch × 1 / 600 inch is defined as having a recording duty cycle of 100%. The boundary between the overlapping and non-overlapping parts of the nozzle rows in the recorded image was observed visually and under a microscope, and the misalignment of the ruled lines in the image was evaluated according to the evaluation criteria shown below. A digital microscope (model number "KH-3000", manufactured by Hirox) was used for the microscopic observation. AA: Almost no misalignment of the grid lines was observed visually. Furthermore, almost no misalignment of the grid lines was observed under microscopic observation. A: Almost no misalignment of the grid lines was observed visually, but slight misalignment was observed under microscopic observation. B: There was almost no misalignment of the grid lines when viewed with the naked eye, but significant misalignment of the grid lines was observed under a microscope. C: Slight misalignment of the grid lines was observed visually, and significant misalignment of the grid lines was observed under microscopic observation. D: Significant misalignment of the grid lines was observed both visually and under a microscope.

[0102] [Table 8]

[0103] Furthermore, the disclosure of embodiments of the present invention includes the following methods and configurations.

[0104] (Method 1) An inkjet recording method comprising an inkjet recording apparatus comprising: an aqueous ink containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent; a recording head having a plurality of discharge port rows configured such that a plurality of discharge ports for discharging the aqueous ink are arranged in a predetermined direction, and a first discharge port row and a second discharge port row are arranged offset from each other in the predetermined direction such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting the predetermined direction; wherein the inkjet recording method comprises the step of discharging the aqueous ink from the end discharge ports forming the overlapping portion and allocating it to the first discharge port row and the second discharge port row to record an image on a recording medium, The viscosity of the aforementioned water-based ink is 4.0 mPa·s or higher. The water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. An inkjet recording method characterized in that the content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more by mass ratio to the content (mass%) of the water-soluble organic solvent (B).

[0105] (Method 2) The inkjet recording method according to Method 1, wherein the content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more and 1.00 times or less in mass ratio to the content (mass%) of the water-soluble organic solvent (B).

[0106] (Method 3) The inkjet recording method according to method 1 or 2, wherein the water-soluble organic solvent (B) has a vapor pressure of 5,000 Pa or more at 25°C.

[0107] (Method 4) The inkjet recording method according to any one of methods 1 to 3, wherein the water-soluble organic solvent (B) is an alkanediol having 4 or fewer carbon atoms.

[0108] (Method 5) The inkjet recording method according to any one of methods 1 to 4, wherein the water-soluble organic solvent (B) is 1,3-butanediol.

[0109] (Method 6) The inkjet recording method according to any one of methods 1 to 5, wherein the viscosity of the aqueous ink is 6.0 mPa·s or more.

[0110] (Method 7) The inkjet recording method according to any one of methods 1 to 6, wherein the recording head further comprises a third row of ejection ports, the third row of ejection ports being arranged to overlap and be parallel to the second row of ejection ports in a direction intersecting the predetermined direction, and being located on the opposite side of the first row of ejection ports with the second row of ejection ports in between.

[0111] (Composition 1) An inkjet ink set having achromatic ink and chromatic ink, The achromatic ink and the chromatic ink are aqueous inks containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent. The viscosity of the aforementioned water-based ink is 4.0 mPa·s or higher. The water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more in mass ratio to the content (mass%) of the water-soluble organic solvent (B), The ink set is used in an inkjet recording method that includes a recording head comprising: a recording device having a plurality of nozzle rows configured such that a plurality of nozzles for ejecting the achromatic ink and the chromatic ink are arranged in a predetermined direction, the first nozzle row and the second nozzle row being arranged offset from each other in the predetermined direction such that the end nozzles of adjacent nozzle rows overlap in a direction intersecting the predetermined direction, and a third nozzle row being arranged to overlap with the second nozzle row in a direction intersecting the predetermined direction and to be located on the opposite side of the first nozzle row with the second nozzle row in between, and recording an image on a recording medium. The achromatic ink is ejected from the first and second nozzle rows, and the chromatic ink is ejected from the third nozzle row. An ink set characterized in that the achromatic ink is distributed and discharged from the end discharge ports constituting the overlapping portion to the first and second discharge port rows.

[0112] (Configuration 2) An inkjet recording apparatus comprising: an aqueous ink containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent; and a recording head having a plurality of discharge port rows configured such that a plurality of discharge ports for discharging the aqueous ink are arranged in a predetermined direction, and including a first discharge port row and a second discharge port row arranged offset from each other in the predetermined direction such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting the predetermined direction, The viscosity of the aforementioned water-based ink is 4.0 mPa·s or higher. The water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more in mass ratio to the content (mass%) of the water-soluble organic solvent (B), An inkjet recording apparatus characterized in that it dispenses the aqueous ink from the end discharge ports constituting the overlapping portion, allocating it to the first discharge port row and the second discharge port row, and records an image on a recording medium. [Explanation of Symbols]

[0113] 13 Head Cartridges 21, 22, 31, 32, 33 Recording element substrate H1100 Recording element substrate

Claims

1. An inkjet recording method comprising an inkjet recording apparatus comprising: an aqueous ink containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent; a recording head having a plurality of discharge port rows configured such that a plurality of discharge ports for discharging the aqueous ink are arranged in a predetermined direction, and a first discharge port row and a second discharge port row are arranged offset from each other in the predetermined direction such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting the predetermined direction; wherein the inkjet recording method comprises the step of discharging the aqueous ink from the end discharge ports forming the overlapping portion and allocating it to the first discharge port row and the second discharge port row to record an image on a recording medium, The viscosity of the aqueous ink is 4.0 mPa·s or higher. The water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. An inkjet recording method characterized in that the content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more by mass ratio to the content (mass%) of the water-soluble organic solvent (B).

2. The inkjet recording method according to claim 1, wherein the content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more and 1.00 times or less in mass ratio to the content (mass%) of the water-soluble organic solvent (B).

3. The inkjet recording method according to claim 1, wherein the water-soluble organic solvent (B) has a vapor pressure of 5,000 Pa or more at 25°C.

4. The inkjet recording method according to claim 1, wherein the water-soluble organic solvent (B) is an alkanediol having 4 or fewer carbon atoms.

5. The inkjet recording method according to claim 1, wherein the water-soluble organic solvent (B) is 1,3-butanediol.

6. The inkjet recording method according to claim 1, wherein the viscosity of the aqueous ink is 6.0 mPa·s or more.

7. The inkjet recording method according to claim 1, wherein the recording head further comprises a third row of ejection ports, the third row of ejection ports being arranged to overlap and be parallel to the second row of ejection ports in a direction intersecting the predetermined direction, and being positioned on the opposite side of the first row of ejection ports with respect to the second row of ejection ports.

8. An inkjet ink set having achromatic ink and chromatic ink, The achromatic ink and the chromatic ink are aqueous inks containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent. The viscosity of the aqueous ink is 4.0 mPa·s or higher. The water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more in mass ratio to the content (mass%) of the water-soluble organic solvent (B). The ink set is used in an inkjet recording method that includes a recording head comprising: a recording device having a plurality of nozzle rows configured such that a plurality of nozzles for ejecting the achromatic ink and the chromatic ink are arranged in a predetermined direction, the first nozzle row and the second nozzle row being arranged offset from each other in the predetermined direction such that the end nozzles of adjacent nozzle rows overlap in a direction intersecting the predetermined direction, and a third nozzle row being arranged to overlap with the second nozzle row in a direction intersecting the predetermined direction and to be located on the opposite side of the first nozzle row with the second nozzle row in between, and recording an image on a recording medium. The achromatic ink is ejected from the first and second nozzle rows, and the chromatic ink is ejected from the third nozzle row. An ink set characterized in that the achromatic ink is distributed and discharged from the end discharge ports constituting the overlapping portion to the first and second discharge port rows.

9. An inkjet recording apparatus comprising: an aqueous ink containing a pigment, a silicone-based surfactant, and a water-soluble organic solvent; and a recording head having a plurality of discharge port rows configured such that a plurality of discharge ports for discharging the aqueous ink are arranged in a predetermined direction, and including a first discharge port row and a second discharge port row arranged offset from each other in the predetermined direction such that the end discharge ports of adjacent discharge port rows form an overlapping portion in a direction intersecting the predetermined direction, The viscosity of the aqueous ink is 4.0 mPa·s or higher. The water-soluble organic solvent comprises a water-soluble organic solvent (A) having a vapor pressure of 0.030 Pa or more and 0.200 Pa or less at 25°C, and a water-soluble organic solvent (B) having a vapor pressure of 1.000 Pa or more at 25°C. The content (mass%) of the water-soluble organic solvent (A) is 0.30 times or more in mass ratio to the content (mass%) of the water-soluble organic solvent (B), An inkjet recording apparatus characterized in that it discharges the aqueous ink from the end discharge ports constituting the overlapping portion, allocating it to the first discharge port row and the second discharge port row, and records an image on a recording medium.

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