Inkjet recording method, inkjet recording device, and ink set

Abstract

To provide an inkjet recording method that can record a high quality image in which color unevenness in reciprocal recording of a secondary color recorded by a plurality of ink using a circulation serial head is reduced.SOLUTION: An inkjet recording method discharges ink from a recording head having a plurality of discharge ports, discharge elements, and a first flow channel and a second flow channel which are communicated with each other between the discharge ports and the discharge elements and allow ink to distribute therein, and records an image. The method includes a discharge step of discharging ink from the discharge ports, and a flowing step of flowing the ink in the first flow channel different from the discharge step to the second flow channel. The recording head is a serial system such that it has a plurality of discharge port arrays in which the plurality of discharge ports are arrayed in a predetermined direction, and it scans in a direction crossing the array directions of the discharge port arrays. The first flow channel and the second flow channel are arranged in parallel with the direction at which the recording head scans, and the ink flowing directions thereof are the same. The plurality of discharge port arrays include a first discharge port array for discharging first ink on the upstream side with respect to the ink flowing direction, and a second discharge port array for discharging second ink on the downstream side thereto. The first ink and the second ink are aqueous ink containing a pigment. A molar fraction R1 of water of the first ink and a molar fraction R2 of water of the second ink satisfy a relation of R1≥R2.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Inkjet recording methods make it possible to record images such as photographs and documents on various recording media. In addition, various inks have been proposed depending on the application, such as inks suitable for recording photographic quality images on glossy paper and inks suitable for recording documents on plain paper.

[0003] In recent years, inkjet recording methods have been used to record business documents, including characters and charts, on recording media such as plain paper, and the frequency of use for such applications has increased dramatically. There is a demand for the ability to record documents at higher speeds than before. In addition, there is a strong demand for inkjet recording devices to be more compact due to restrictions on installation space, etc.

[0004] There are two types of print head systems for inkjet printing devices: serial and line. From the viewpoint of miniaturization, serial print heads (serial heads) are advantageous. In order to improve the printing speed using a serial head, it is necessary to increase the scanning speed of the print head. It is also necessary to reduce the frequency of so-called preliminary ejection operations, which are a type of recovery process performed between scans of the print head, and to perform one-pass printing, in which multiple inks are applied to a unit area in one relative scan of the print head and the print medium.

[0005] As a method for reducing the frequency of preliminary ejection operations, for example, a liquid ejection head has been proposed that can prevent solid matter in the liquid from accumulating near the edges of the ejection port even after the ejection operation has been paused for a certain period of time (Patent Document 1).

[0006] On the other hand, in the inkjet recording method, an inkjet recording device may be used in which the ejection ports of two or more types of ink in a recording head are capped with a single cap. When multiple inks are used in this inkjet recording device, there is a problem that uneven recording occurs at the beginning of recording after a long period of non-use. In response to this problem, inkjet inks have been proposed that can suppress uneven recording by aligning the molar fraction of water in multiple dye inks (Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-124608 A [Patent Document 2] JP 2006-070257 A Summary of the Invention [Problem to be solved by the invention]

[0008] In order to achieve both high-speed printing and compact printing apparatus, the inventors of the present invention have investigated printing images in one pass using a serial type print head (circulating serial head) that employs a mechanism for flowing ink near the ejection ports, as proposed in Patent Document 1. As a result, the ink ejection stability has improved even after the ejection operation has been paused for a certain period of time, and the frequency of preliminary ejection operations performed between scans of the print head has been reduced.

[0009] Next, the inventors of the present invention have studied printing an image in one pass by mounting a plurality of pigment inks, the relationship of which has been adjusted for the molar fraction of water, on a circulation serial head, with reference to Patent Document 2. As a result, they have found that, under certain combinations of scanning conditions and inks of a specific composition, a new problem arises in that the color tone changes between forward printing and backward printing in a secondary color image printed with a plurality of inks, and color unevenness may occur.

[0010] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording high-quality images with reduced color unevenness during reciprocating recording of secondary colors recorded with a plurality of inks using a circulation serial head. Another object of the present invention is to provide an inkjet recording apparatus and an ink set for use in the inkjet recording method. [Means for solving the problem]

[0011] That is, according to the present invention, there is provided an inkjet recording method for recording an image by ejecting ink from a recording head having a plurality of ejection ports for ejecting ink, ejection elements for generating energy for ejecting the ink, and a first flow path and a second flow path communicating between the ejection ports and the ejection elements and through which the ink flows, the method comprising: an ejection step of ejecting the ink from the ejection ports; and a flow step, separate from the ejection step, of causing the ink in the first flow path to flow into the second flow path, the recording head comprising an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and a flow path intersecting the arrangement direction of the ejection port arrays. the first flow path and the second flow path are arranged parallel to the scanning direction of the print head and have the same ink flow direction; the multiple nozzle rows include a first nozzle row for ejecting a first ink and a second nozzle row for ejecting a second ink, the first nozzle row is arranged upstream and the second nozzle row is arranged downstream with respect to the ink flow direction; the first ink and the second ink are aqueous inks containing a pigment; and a molar fraction R1 of water in the first ink and a molar fraction R2 of water in the second ink satisfy the relationship R1≧R2. Effect of the Invention

[0012] According to the present invention, it is possible to provide an inkjet recording method capable of recording high-quality images with reduced color unevenness during reciprocating recording of secondary colors using a circulation serial head, and an inkjet recording apparatus and an ink set for use in the inkjet recording method. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic diagram showing a state in the vicinity of an ejection port of a print head. [Diagram 2] 1 is a perspective view illustrating an embodiment of an inkjet recording apparatus. [Diagram 3] FIG. 1 is a schematic diagram illustrating an internal configuration of an inkjet recording apparatus. [Figure 4] 3A and 3B are schematic diagrams showing an example of the arrangement of ejection port arrays in a print head and an example of the circulating flow direction of ink. [Diagram 5] 5A and 5B are schematic diagrams illustrating the state of ink in the print head when the print head is scanning. [Figure 6] FIG. 2 is a perspective view showing a cross section of a discharge element substrate. [Figure 7] FIG. 2 is a schematic diagram showing an ink supply system. [Figure 8] 5A and 5B are schematic diagrams illustrating the flow state of ink in the vicinity of an ejection port. [Figure 9] FIG. 2 is a cross-sectional view partially illustrating an example of a recording head. [Figure 10] 5A to 5C are schematic diagrams illustrating image patterns recorded in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, the aqueous ink for inkjet printing may be simply referred to as "ink." The first flow path and the second flow path may be collectively referred to as "flow path." Similarly, the first ink and the second ink may be collectively referred to as "ink." The secondary color image recorded with the two inks may be simply referred to as "image." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0015] <Inkjet recording method and inkjet recording apparatus> The inkjet recording apparatus of the present invention includes a recording head having a plurality of ejection ports for ejecting ink, an ejection element that generates energy for ejecting ink, and a first flow path and a second flow path through which ink flows by communicating between the ejection ports and the ejection element. The recording head includes an ejection element substrate having a plurality of ejection port arrays in which a plurality of ejection ports are arranged in a predetermined direction, and is a serial type recording head (serial head) that scans in a direction intersecting the arrangement direction of the ejection port arrays. The first flow path and the second flow path in the recording head are arranged parallel to the direction in which the recording head scans, and the ink flows in the same direction. Furthermore, the inkjet recording apparatus of the present invention includes a flow means, separate from the ejection element, for causing the ink in the first flow path to flow to the second flow path. The inkjet recording method of the present invention is, for example, a method of ejecting ink from the above-mentioned recording head using the above-mentioned inkjet recording apparatus to record an image. That is, the inkjet recording method of the present invention includes an ejection step of ejecting ink from the ejection ports, and a flow step, separate from the ejection step, of causing the ink in the first flow path to flow to the second flow path. The ink set of the present invention is an ink set containing a first ink and a second ink that are used in the above-mentioned inkjet recording method.

[0016] FIG. 1 is a schematic diagram showing the state near the ejection port of a recording head. The recording head shown in FIG. 1 includes an ejection port 1 for ejecting ink, an ejection element 4 for generating energy for ejecting ink, and a first flow path 17 and a second flow path 18 that communicate between the ejection port 1 and the ejection element 4 and through which ink flows. As will be described later in the description of the ejection element substrate in the recording head, the ejection port 1 is formed in an ejection port forming member 5, and the ejection element 4 is disposed on a substrate 3. The ink flows from the first flow path 17 to the second flow path 18 (in the direction of the arrow in FIG. 1) through between the ejection port 1 and the ejection element 4. If the ink does not flow, evaporation of water from the ink meniscus 12 at the ejection port 1 progresses, and the ink present between the ejection port 1 and the ejection element 4 gradually thickens. For this reason, if the ejection pause time is long, the fluid resistance of the ink increases at the time of the next ejection operation, and ejection may become difficult. In contrast, if the ink flows in the direction of the arrow in Figure 1, even if water evaporates from the meniscus 12, ink will be continuously supplied between the ejection port 1 and the ejection element 4 due to the circulating flow, thereby suppressing the ink from thickening and making it less likely to become difficult to eject.

[0017] The inventors combined multiple inks in a serial type recording head (circulating serial head) that generates a circulating flow as shown in FIG. 1, and discharged the inks from the discharge ports to record an image. As a result, the ink discharge stability was improved even after the discharge operation was stopped for a certain period of time, and the frequency of the preliminary discharge operation performed during the scan of the recording head could be reduced. However, it was found that a new problem occurred in that a color tone change may occur in a secondary color image recorded with multiple inks under certain specific scanning conditions. After a detailed investigation into the reason for the color tone change in the secondary color image, it was found that the following phenomenon occurs.

[0018] An inkjet recording device equipped with a circulating serial head will be described. Fig. 2 is a perspective view showing a schematic diagram of an embodiment of an inkjet recording device 1000. A feeding unit 200 is capable of loading a plurality of recording media, and feeds the recording media by a feeding roller (not shown). The recording medium P (see Fig. 3) of this embodiment will be described taking as an example a cut sheet of paper cut to a predetermined size, but is not limited to this and can also be used in a form in which recording is performed on rolled paper.

[0019] The recording medium fed by the feeding unit 200 is transported in the Y direction (transport direction) by a transport unit including a transport roller (not shown) to a recording position facing an ejection unit (recording head) 300 (see FIG. 3(b)) that ejects ink. The carriage 100 is equipped with the ejection unit (recording head) 300, and is driven by a carriage motor 400 to reciprocate along a guide shaft 700 via a timing belt 600 in an X direction (main scanning direction) that intersects with the Y direction.

[0020] When an image for a unit area is recorded by the movement of the carriage 100 in the X direction and the ink discharge operation by the discharge unit (recording head) 300, the recording medium is transported in the Y direction by the transport unit. The unit area can be arbitrarily set, such as the arrangement width of the discharge port array arranged along the Y direction in the discharge unit 300, "one band" that can be recorded by one movement of the discharge unit 300 in the X direction, or "one" pixel corresponding to the resolution of the recording head. In the serial method, an image can be recorded over the entire recording medium by a recording operation that repeats the ink discharge operation for one band and intermittent transport operation. In this embodiment, the X direction and the Y direction are orthogonal to each other.

[0021] A platen 500 that supports the recording medium from below in the vertical direction is disposed in a recording area facing the discharge unit (recording head) 300 where recording is performed by the discharge unit (recording head) 300. The platen 500 maintains a predetermined distance between the recording surface of the recording medium and a discharge port surface 2 (FIG. 3) of the discharge unit (recording head) 300 on which discharge ports for discharging ink are arranged.

[0022] FIG. 3 is a schematic diagram showing the internal configuration of an embodiment of an inkjet recording apparatus 1000 of the present invention. FIG. 3(a) is a schematic top view of the recording apparatus 1000 when viewed from above, and FIG. 3(b) is a schematic side view of the recording apparatus 1000 when viewed from the front. The carriage 100 detachably mounts an ink cartridge that contains ink to be supplied to the discharge unit (recording head) 300. A plurality of ink cartridges 111, 112, 113, and 114 correspond to the discharge port arrays 21, 22, 23, and 24 (see FIG. 4), respectively, and supply ink to each discharge port array. For example, discharge port arrays and ink cartridges corresponding to each of the inks of cyan, magenta, yellow, and black (CMYK) are provided.

[0023] Furthermore, within the movement area of ​​the carriage 100, outside the area (printing area) through which the recording medium P passes, a cap 302 for capping the discharge port surface 2 of the discharge unit (printing head) 300 is disposed. The position of the carriage 100 (discharge unit (printing head) 300) where the discharge port surface 2 of the discharge unit (printing head) 300 faces the cap 302 is also referred to as the home position 301. The cap 302 is connected to suction means (not shown), and by driving the suction means with the discharge port surface 2 capped, ink is sucked from the discharge unit (printing head) 300.

[0024] FIG. 4 is a schematic diagram showing an example of the arrangement of the ejection port arrays in the ejection unit (recording head) 300 and an example of the circulating flow direction, which is the flow direction of the ink. FIG. 4 shows the ejection unit (recording head) 300 shown in FIG. 3(b) as viewed from the recording medium P side. As shown in FIG. 4, the ejection unit (recording head) 300 is a serial type recording head that includes an ejection element substrate 10 having four ejection port arrays 21, 22, 23, and 24, and scans in the X direction intersecting the arrangement direction of the ejection port arrays 21 to 24. The circulating flow directions of the four ejection port arrays 21 to 24 are all the same direction from right to left, and are parallel to the X direction (scanning direction). The ejection unit (recording head) 300 reciprocates in the forward direction from left to right and the return direction from right to left, so that the scanning direction and the circulating flow direction are the same direction in the return direction, and are opposite directions in the forward direction.

[0025] Next, the location where the color tone change occurred in the secondary color image recorded by a plurality of inks and the reason for the occurrence will be described. The inventors used the above-mentioned inkjet recording device to record a secondary color solid image on a recording medium in one pass using two ejection port arrays 23 and 24 (the ejection port array 24 arranged relatively upstream with respect to the ink flow direction, and the ejection port array 23 arranged downstream). Specifically, while scanning the ejection unit (recording head) 300 back and forth, recording was performed as follows. First, in the forward direction of the X direction, an image of one band was recorded on the recording medium in the order of the ejection port array 24 and the ejection port array 23, and then the recording medium was conveyed by one band in the Y direction, and the operation of recording on the recording medium in the order of the ejection port array 23 and the ejection port array 24 in the return direction of the X direction was repeated. As a result, when the secondary color solid image was recorded, there were cases where color unevenness occurred in which the color tone changed between the forward direction and the return direction. The inventors closely observed the secondary color solid image recorded on the recording medium using pigment ink. As a result, it was found that the cause of the color unevenness is that, in forward printing, the dots formed by the ink droplets ejected from the upstream ejection port array 24 may be smaller than the dots formed by the ink droplets ejected from the downstream ejection port array. The inventors speculate as follows about the reason for this phenomenon.

[0026] 5 is a schematic diagram for explaining the state of ink ejected from the ejection port 1 of the downstream ejection port array 23 and the state of ink ejected from the ejection port 1 of the upstream ejection port array 24 with respect to the ink flow direction (circulation flow direction) in the print head when the print head is scanning. FIG. 5(a) is a schematic diagram for explaining the state of ink ejected from the ejection port 1 of the downstream ejection port array 23 when the print head is scanned in the forward direction, and FIG. 5(b) is a schematic diagram for explaining the state of ink ejected from the ejection port 1 of the upstream ejection port array 24 when the print head is scanned in the forward direction. FIG. 5(c) is a schematic diagram for explaining the state of ink ejected from the ejection port 1 of the downstream ejection port array 23 when the print head is scanned in the backward direction, and FIG. 5(d) is a schematic diagram for explaining the state of ink ejected from the ejection port 1 of the upstream ejection port array 24 when the print head is scanned in the backward direction.

[0027] 5(a) and (b), when the scanning direction of the print head and the circulating flow direction of the ink are opposite, the contact time between the ink of the meniscus and the air in the printing device, which has a relatively lower humidity than the vicinity of the print head, becomes longer, particularly in the ejection port array 24 that is ejected first. Therefore, water in the ink may evaporate from the meniscus of the upstream ejection port array 24, and the effect of suppressing thickening by the circulating flow of the ink may decrease. As a result, the volume of the ink droplets ejected from the upstream ejection port array 24 tends to be smaller than that of the ink ejected from the downstream ejection port array 23.

[0028] On the other hand, as shown in Figures 5(c) and (d), when the scanning direction of the print head and the circulating flow direction of the ink are the same, there is little difference in the amount of water evaporated from the meniscus among the multiple ejection port arrays, and there is little difference in the amount of ink droplets ejected between ejection port array 23 and ejection port array 24. As described above, it is believed that color unevenness occurs during reciprocating printing of secondary colors due to the difference in the ejection amount between the ejection port arrays in forward and backward printing. It was found that such color unevenness is difficult to recognize in dye ink, but occurs significantly in pigment ink.

[0029] The present inventors have studied a method for suppressing color unevenness during reciprocating printing of the above-mentioned secondary colors. Specifically, they have studied suppressing a reduction in the amount of ink ejected from the upstream nozzle array that first comes into contact with air when the ink circulating flow direction and the print head scanning direction are reversed when the print head scans in the forward direction. As a result, they have found that color unevenness during reciprocating printing of secondary colors can be suppressed by making the molar fraction of water in the ink ejected from the upstream nozzle array, which comes into contact with air, equal to or greater than the molar fraction of water in the ink ejected from the downstream nozzle array with respect to the ink flow direction.

[0030] In this specification, of the multiple ejection port arrays in a print head, the ejection port array on the upstream side with respect to the ink flow direction may be referred to as the "first ejection port array," and the ink ejected from the first ejection port array may be referred to as the "first ink." Also, the ejection port array on the downstream side with respect to the ink flow direction may be referred to as the "second ejection port array," and the ink ejected from the second ejection port array may be referred to as the "second ink." In multiple ejection port arrays, the "upstream side" and "downstream side" with respect to the ink flow direction refer to the relative relationship between the two ejection port arrays being compared.

[0031] As described above, the inventors speculate as follows about the reason why it is possible to print high-quality images with reduced color unevenness during reciprocating printing of secondary colors by satisfying the relationship of the water molar fraction R1 of the first ink ≧ the water molar fraction R2 of the second ink.

[0032] When the water molar fraction R1 of the first ink is equal to or greater than the water molar fraction R2 of the second ink, the first ink has the same or relatively higher water molar fraction in the ejected ink droplets. Therefore, the humidity of the air near the first ejection port array is more likely to be higher than the humidity near the second ejection port array during the ejection operation. It is believed that the occurrence of such a relative humidity difference makes it difficult for the above-mentioned ejection volume difference to occur due to the moisturizing effect near the ejection ports of the first ink on the upstream side in the ink circulation flow direction during forward printing.

[0033] FIG. 6 is a perspective view showing a cross section of the discharge element substrate. As shown in FIG. 6, the discharge element substrate 10 includes a discharge port forming member 5 in which a discharge port 1 is formed, and a substrate 3 in which a discharge element (not shown) is arranged. The discharge port forming member 5 and the substrate 3 are laminated to form a first flow path 17 and a second flow path 18 through which ink flows. The first flow path 17 is a region from an inlet 8 through which ink flows in the inflow path 6 to a portion between the discharge port 1 and the discharge element (liquid chamber 213 in FIG. 7). The second flow path 18 is a region from a portion between the discharge port 1 and the discharge element (liquid chamber 213 in FIG. 7) to an outlet 9 through which ink flows out to the outlet path 7. For example, if a pressure difference is provided between the inlet 8 and the outlet 9, such as the inlet 8 having a high pressure and the outlet 9 having a low pressure, the ink can flow from the high pressure side to the low pressure side (in the direction of the arrow in FIG. 6). The ink that has passed through the inflow path 6 and the inlet 8 enters the first flow path 17. Then, the ink that has passed through the portion between the ejection port 1 and the ejection element (the liquid chamber 213 in FIG. 7) passes through the second flow path 18 and the outlet port 9, and flows into the outlet path 7.

[0034] The flowing step of causing the ink in the first flow path to flow to the second flow path is a separate step (different step) from the ejection step of ejecting ink from the ejection port. In addition, the flow of ink from the first flow path to the second flow path in the flowing step is preferably performed separately from filling the space between the ejection port and the ejection element with ink. The flowing step is preferably a step of causing the ink in the first flow path to flow to the second flow path without discharging the ink from the ejection port. Discharging the ink from the ejection port includes a recovery operation such as preliminary ejection or suction. During a recovery operation of the recording head, the flow of ink from the first flow path to the second flow path may be stopped. In addition, in the flowing step, it is preferable to cause the ink to flow from the first flow path to the second flow path by a flowing means other than the ejection element.

[0035] Hereinafter, the inkjet recording method and the inkjet recording apparatus of the present invention will be described in further detail, taking as an example a thermal type recording head that uses a discharge element that generates thermal energy to generate bubbles to discharge ink. However, the inkjet recording method and the inkjet recording apparatus of the present invention can be applied to a piezo type recording head or a recording head that employs another discharge method. Here, an example in which ink is circulated between an ink storage section and a recording head will be described, but other forms may also be used. For example, a form in which two ink storage sections are provided on the upstream side and downstream side of a recording head, and ink flows from one ink storage section to the other ink storage section may also be used. Furthermore, an example in which a recording head incorporating a discharge element substrate in which four discharge port rows capable of discharging four colors of ink, CMYK, are arranged will be described, but a recording head having discharge port rows capable of discharging two or more types of ink may also be used. In the present invention, it is particularly preferable to use a recording head that discharges ink by a thermal method.

[0036] In the flow process, it is preferable to flow the ink continuously or intermittently. Hereinafter, the method of flowing the ink continuously and the method of flowing the ink intermittently will be described in detail. First, the method of flowing the ink continuously will be described with reference to FIG. 7. FIG. 7 is a schematic diagram showing an ink supply system. The discharge unit (recording head) 300 shown in FIG. 7 is connected to a first circulation pump (high pressure side) 1001, a first circulation pump (low pressure side) 1002, a sub-tank 1003, a second circulation pump 1004, and the like. For the sake of simplicity, FIG. 7 shows only a path through which ink of one color flows, but in reality, flow paths for four colors of CMYK are provided in each of the discharge units (recording heads) 300.

[0037] The sub-tank 1003, which is connected to the main tank 1006 that is an ink storage section, has an air communication port (not shown) and is capable of discharging air bubbles mixed in the ink to the outside. The sub-tank 1003 is also connected to a refill pump 1005. Ink is consumed in the discharge unit (print head) 300 by discharging (discharging) ink from the discharge port for image recording, suction recovery, etc. The refill pump 1005 transfers an amount of ink corresponding to the consumed amount from the main tank 1006 to the sub-tank 1003.

[0038] The first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002 cause the ink in the discharge unit (recording head) 300, which has flowed out from the connection part 1110, to flow into the sub tank 1003. As the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002, it is preferable to use a positive displacement pump having a quantitative liquid delivery capability. Specific examples of such a positive displacement pump include a tube pump, a gear pump, a diaphragm pump, and a syringe pump. When the discharge unit 300 is driven, the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002 can cause the ink to flow into the common inflow channel 211 and the common outflow channel 212.

[0039] The negative pressure control unit 230 includes two pressure adjustment mechanisms with mutually different control pressures set thereto. The pressure adjustment mechanism (high pressure side) H and the pressure adjustment mechanism (low pressure side) L are respectively connected to a common inflow channel 211 and a common outflow channel 212 in the ejection unit 300 via a supply unit 220 provided with a filter 221 that removes foreign matter from the ink.

[0040] The supply unit 220 and the discharge unit (recording head) 300 are connected by an ink supply tube (not shown) which is an ink supply path. Since the discharge unit (recording head) 300 scans back and forth inside the inkjet recording device, the ink supply tube is made of a resin material having flexibility that can withstand the back and forth scanning.

[0041] The discharge unit 300 is provided with a common inflow path 211, a common outflow path 212, and an inflow path 6 and an outflow path 7 that communicate with a liquid chamber 213 that is a portion between the discharge port 1 and the discharge element (not shown). Since the inflow path 6 and the outflow path 7 communicate with the common inflow path 211 and the common outflow path 212, a flow (arrow in FIG. 7) occurs in which a portion of the ink flows from the common inflow path 211 through the inside of the liquid chamber 213 to the common outflow path 212. The arrow in FIG. 6 indicates the flow of ink inside the liquid chamber 213. That is, as shown in FIG. 6, the ink in the first flow path 17 flows to the second flow path 18 through between the discharge port 1 and the discharge element.

[0042] As shown in FIG. 7, a pressure adjustment mechanism H is connected to the common inflow path 211, and a pressure adjustment mechanism L is connected to the common outflow path 212, so that a pressure difference occurs between the inflow path 6 and the outflow path 7. As a result, a pressure difference also occurs between the inlet 8 (FIG. 6) communicating with the inflow path 6 and the outlet 9 (FIG. 6) communicating with the outflow path 7. When the ink is made to flow by the pressure difference between the inlet and the outlet, it is preferable to control the flow velocity (mm / s) of the ink during the flow to 1.0 mm / s or more and 100.0 mm / s or less. When the ink flow velocity is 1.0 mm / s or more, the effect of suppressing thickening due to the circulating flow of the ink is easily achieved, and color unevenness during reciprocating recording of secondary colors is easily suppressed. On the other hand, when the ink flow velocity is 100.0 mm / s or less, evaporation of water from the ejection port is suppressed, and color unevenness during reciprocating recording of secondary colors is easily suppressed.

[0043] In the inkjet recording method of the present invention, the ink in the first flow path may be caused to flow to the second flow path even during a recovery operation of the recording head. When the ink flows during a recovery operation of the recording head, the ink flows steadily. When the ink flows steadily, water is more likely to evaporate, and the concentration of the circulating ink is more likely to increase. In order to suppress the increase in the ink concentration, it is preferable to provide the inkjet recording device with a mechanism that adds water to the ink after a certain period of time has elapsed. Furthermore, it is preferable to provide the inkjet recording device with a detector that detects the ink concentration, and add water to the ink in conjunction with the detected increase in the ink concentration.

[0044] FIG. 8 is a schematic diagram for explaining the flow state of ink in the vicinity of the ejection port. The flow state of ink in the vicinity of the ejection port is roughly divided into two types. The first type is a flow state in which no circulating flow occurs in the vicinity of the meniscus 12 of the ejection port 1 as shown in FIG. 8(a). The second type is a flow state in which a circulating flow occurs in the vicinity of the meniscus 12 of the ejection port 1 as shown in FIG. 8(b). Even if the flow speed of the ink in the flow path is the same, the flow state of the ink in the vicinity of the meniscus 12 may not be constant. It is considered that which flow state the ink will be in depends on the thickness (c) of the ejection port forming member 5, the height (d) of the flow path (first flow path 17 and second flow path 18), and the diameter (e) of the ejection port 1, rather than the flow speed of the ink in the flow path. For example, when the height (d) of the flow path and the diameter (e) of the ejection port 1 are the same, if the thickness (c) of the ejection port forming member 5 is large, a circulating flow is likely to occur in the vicinity of the meniscus 12 as shown in FIG. 8(b).

[0045] Next, a method for intermittently flowing ink will be described with reference to FIG. 9. FIG. 9 is a cross-sectional view partially showing an example of a recording head. As shown in FIG. 9, ink flowing in from an inlet 210 flows in the direction of the arrow by the action of a circulation pump 206, which is an ink flow means, and flows out from an outlet 214. The circulation pump 206 is a pump that can intermittently flow ink. Therefore, by driving the circulation pump 206, ink can be intermittently flowed between the ejection port 1 and the ejection element 4.

[0046] The inkjet recording apparatus of the present invention preferably includes a means for adjusting the temperature of the ink in the recording head. The inkjet recording method of the present invention may further include a step of heating the ink in the recording head. The temperature of the ink in the recording head can be adjusted, for example, by a means for controlling the temperature of the recording head. Examples of the means for controlling the temperature of the recording head include a heater for temperature adjustment provided in direct contact with the recording head and a heater for ink ejection. In order to control (heat or warm) the temperature of the recording head by the heater for ink ejection, for example, it is sufficient to repeatedly pass a current that does not eject ink. The temperature of the recording head and the ink in the recording head can be read, for example, by a temperature sensor provided in the recording head. The temperature of the ink in the recording head is preferably adjusted to a range of 40°C to 60°C.

[0047] When the ink is heated, the viscosity of the ink tends to decrease as the temperature rises, and the ink is less likely to thicken even when the water evaporates, making it easier to suppress color unevenness when recording secondary colors back and forth.

[0048] In the inkjet recording method of the present invention, the scanning speed of the recording head when recording an image, i.e., the movement speed when the recording head is scanned, can be set to preferably 30 inches / second or more, more preferably 35 inches / second or more, from the viewpoint of increasing the recording speed. In addition, the movement speed when the recording head is scanned is preferably 70 inches / second or less. By setting the movement speed when the recording head is scanned at 70 inches / second or less, it is easy to suppress evaporation of water from the ejection openings, and it is easy to suppress evaporation of water during forward recording of the first ink. As a result, it is easy to suppress color unevenness during forward recording of the secondary color.

[0049] In the recording head used in the inkjet recording method of the present invention, the distance between the first and second ejection port arrays can be 1.8 mm or less. Another ejection port array may be arranged between the first and second ejection port arrays, or the first and second ejection port arrays may be adjacent to each other. If the distance between the ejection port arrays is short, the ejection port arrays can be densely arranged, which makes it easier to achieve miniaturization and high image quality. Also, if the distance between the ejection port arrays is short, the humidity in the vicinity of the ejection port arrays is likely to increase. When the distance between the first and second ejection port arrays is 1.8 mm or less, the molar fraction R1 of water in the first ink and the molar fraction R2 of water in the second ink satisfy the relationship R1≧R2, thereby further suppressing color unevenness during reciprocating recording of secondary colors. The distance between the first and second ejection port arrays is preferably 0.1 mm or more, and more preferably 0.5 mm or more.

[0050] The inkjet recording method of the present invention includes a step of recording an image using the inkjet recording device (recording step). Specifically, in the recording step, ink discharged from the discharge port 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 permeable paper such as 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.

[0051] The inkjet recording method of the present invention may not have a step (heating step) of heating the recording medium to which the ink has been applied in the recording step. When the recording medium to which the ink has been applied is heated, the temperature inside the device body increases with the heating step, and it is considered that the evaporation of water from the meniscus of the recording head is likely to proceed. Therefore, the above heating step may not be performed in order to easily suppress color unevenness during reciprocating recording of secondary colors by reducing the effect of the temperature increase.

[0052] <Ink> The inkjet recording method and inkjet recording apparatus of the present invention include a process for recording an image by using a plurality of inks and applying the inks ejected from the ejection openings of a recording head to a recording medium. The plurality of inks (ink set) include a first ink ejected from an ejection opening array (first ejection opening array) on the upstream side with respect to the ink flow direction, and a second ink ejected from an ejection opening array (second ejection opening array) on the downstream side. In addition, both the first ink and the second ink are aqueous inks containing a pigment. Furthermore, the molar fraction R1 of water in the first ink and the molar fraction R2 of water in the second ink satisfy the relationship R1≧R2.

[0053] In the range where the molar fraction R1 of water in the first ink and the molar fraction R2 of water in the second ink satisfy the relationship R1≧R2, it is preferable that the values ​​(%) of R1 and R2 are each 90.0% or more. It is preferable that the molar fractions of water in the first ink and the second ink satisfy the relationship R1>R2. It is more preferable that the difference (R1-R2) between the molar fractions of water in the first ink and the second ink satisfies the relationship 0.5(%)≦R1-R2≦5.0(%), and even more preferable that it satisfies the relationship 1.0(%)≦R1-R2≦3.0(%).

[0054] The molar fraction of water in the present invention is a value calculated based on the components (compounds) present in the ink. The molar fraction of water is preferably 85.0% or more and 99.5% or less, and more preferably 90.0% or more and 99.0% or less. Specifically, the molar fraction of water in the ink is calculated according to the formula [(moles of water) / (moles of water+moles of compounds present in the ink)]×100(%) in the ink. The number of moles can be calculated using molecular weight, and in the case of polymers such as water-soluble resins, weight average molecular weight can be used. In addition, for compounds such as pigments whose molecular weight is large on the order of several million, the molecular weight can be calculated as a predetermined value such as "million" for convenience. This is because compounds with a sufficiently large molecular weight are less likely to affect the molar fraction of water in aqueous inkjet inks.

[0055] The components constituting the first ink and the second ink and the physical properties of the inks will be described in detail below.

[0056] (Colorant) A pigment is used as the coloring material contained in the ink. The content (mass %) of the pigment in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, and more preferably 0.3 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

[0057] Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide, and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, etc. Of these, carbon black and organic pigments are preferred.

[0058] As a pigment dispersion method, resin-dispersed pigments using a resin as a dispersant, self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface, etc. can be used. In addition, resin-bonded pigments in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microcapsule pigments in which the pigment particle surface is coated with a resin, etc. can be used. Among them, resin-dispersed pigments are more preferable from the viewpoint of ejection properties.

[0059] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of anionic groups. As the resin dispersant, a resin as described below, particularly a water-soluble resin, can be used. The content (mass%) of the pigment in the ink is preferably 0.3 times or more and 10.0 times or less in mass ratio to the content of the resin dispersant.

[0060] As the self-dispersing pigment, an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group can be used, which is bonded to the particle surface of the pigment directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. In addition, it may be a group that is a combination of these groups.

[0061] (resin) The ink may contain a resin. The content (mass %) of the resin in the ink is preferably from 0.1% to 20.0% by mass, and more preferably from 0.5% to 15.0% by mass, based on the total mass of the ink.

[0062] The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, the resin can be added to the ink (ii) to improve various properties of the recorded image. Examples of the form of the resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. The resin particles do not need to encapsulate a colorant. When a resin is used as a dispersant for dispersing the pigment, it is preferable to further contain another resin in addition to the resin as the dispersant.

[0063] The first ink and the second ink preferably contain a water-soluble resin, and more preferably, the content A1 (mass%) of the water-soluble resin in the first ink and the content A2 (mass%) of the water-soluble resin in the second ink satisfy the relationship A1 ≧ A2. When the content A1 of the water-soluble resin in the first ink is equal to or greater than the content A2 of the water-soluble resin in the second ink, evaporation of water from the first ink is easily suppressed, and color unevenness during reciprocal recording of secondary colors is easily suppressed. The resins (water-soluble resins, resin particles) contained in each ink may be the same or different.

[0064] In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali of equimolar amount to the acid value, it exists in an aqueous medium in a state in which it does not form particles whose particle size can be measured by dynamic light scattering. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if particles having a particle size are not measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, as follows. [Measurement conditions] SETZERO: 30 seconds Number of measurements: 3 Measurement time: 180 seconds

[0065] As the particle size distribution measuring device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150" manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and the measurement conditions to be used are not limited to those described above.

[0066] The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 mgKOH / g or less. The acid value of the resin constituting the resin particles is preferably 5 mgKOH / g or more and 100 mgKOH / g or less. In this specification, the acid value of the resin can be a value measured by a potentiometric titration device using a potassium hydroxide-methanol titrant. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 2,000,000 or less. In this specification, the weight average molecular weight of the resin can be measured as a polystyrene-equivalent value measured by gel permeation chromatography (GPC). The volume average particle diameter of the resin particles measured by dynamic light scattering is preferably 100 nm or more and 500 nm or less.

[0067] Examples of the resin include acrylic resins, urethane resins, olefin resins, etc. Among these, acrylic resins and urethane resins are preferred.

[0068] The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit as constituent units. Among them, a resin 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 is preferred. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of styrene and α-methylstyrene is preferred. These resins are easily interacted with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

[0069] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not having a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having a hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0070] The urethane resin can be obtained, for example, by reacting a polyisocyanate with a component that reacts with it (such as a polyol or a polyamine). In addition, it may be obtained by further reacting a crosslinking agent or a chain extender.

[0071] Polyisocyanates are compounds that have two or more isocyanate groups in their molecular structure. Examples of polyisocyanates that can be used include aliphatic polyisocyanates and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0072] Specific examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

[0073] A polyol can be used as a component that becomes a unit constituting a urethane resin by reacting with the above-mentioned polyisocyanate. In the present invention, "polyol" means a compound having two or more hydroxyl groups in the molecule. Specifically, polyols having no acid group, such as polyether polyol, polyester polyol, and polycarbonate polyol; polyols having an acid group; and the like can be mentioned.

[0074] Examples of polyols having no acid group include long-chain polyols having a number average molecular weight of about 450 to 4,000, such as polyether polyols, polyester polyols, and polycarbonate polyols.

[0075] Examples of polyols having an acid group include polyols containing an acid group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group in the structure. In particular, it is preferable to use a water-soluble urethane resin synthesized by further using a polyol having an acid group such as dimethylolpropionic acid or dimethylolbutanoic acid in addition to a polyol having no acid group. The acid group may be in the form of a salt. Examples of cations constituting the salt include ions of lithium, sodium, potassium, ammonium, and organic ammonium. When the water-soluble urethane resin has an acid group, it usually exhibits water solubility by neutralizing the acid group with a neutralizing agent such as a hydroxide of an alkali metal (lithium, sodium, potassium, etc.) or ammonia water.

[0076] Examples of polyamines include monoamines having multiple hydroxyl groups, such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines, such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; and trifunctional or higher polyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, and polyethylenepolyimine. For convenience, compounds having multiple hydroxyl groups and one "amino group, imino group" are also listed as "polyamines".

[0077] When synthesizing a urethane resin, a crosslinking agent or a chain extender can be used. Usually, a crosslinking agent is used when synthesizing a prepolymer, and a chain extender is used when carrying out a chain extension reaction on a prepolymer that has been synthesized in advance. Basically, the crosslinking agent or the chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. depending on the purpose, such as crosslinking or chain extension. As the chain extender, one that can crosslink the urethane resin can also be used.

[0078] Examples of olefin-based resins include α-olefin polymers such as polyethylene and polypropylene. The α-olefin polymers have α-olefin units such as ethylene units and propylene units as main constituent units. The α-olefin polymers may be homopolymers of ethylene or propylene, or may be copolymers of α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-pentene. Examples of copolymers include random copolymers, block copolymers, graft copolymers, and combinations of these copolymers.

[0079] [Resin particles] The first ink and the second ink preferably contain resin particles, and more preferably the content B1 (mass%) of the resin particles in the first ink and the content B2 (mass%) of the resin particles in the second ink satisfy the relationship B1≦B2. When the content B1 of the resin particles in the first ink is equal to or less than the content B2 of the resin particles in the second ink, thickening of the first ink when water evaporates is easily suppressed, and color unevenness during reciprocal recording of secondary colors is easily suppressed. Examples of resin particles include acrylic resin particles, olefin resin particles, and urethane resin particles.

[0080] (Surfactant) The ink preferably contains a surfactant. The surfactant is oriented at the gas-liquid interface with the hydrophobic group facing the atmosphere and the hydrophilic group facing the ink, so that the meniscus can be further stabilized. Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Among them, it is preferable to use a nonionic surfactant from the viewpoint of the reliability of the ink.

[0081] Examples of the nonionic surfactant include hydrocarbon surfactants such as ethylene oxide adducts of acetylene glycol and polyoxyethylene alkyl ethers, fluorine-based surfactants such as perfluoroalkyl ethylene oxide adducts, silicone surfactants such as polyether-modified siloxane compounds, etc. Among these, hydrocarbon surfactants are preferred, and ethylene oxide adducts of acetylene glycol are more preferred.

[0082] (aqueous medium) The ink used in the inkjet recording method of the present invention is an aqueous ink containing at least water as an 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, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, the content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 3.0 mass% or more and 48.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used.

[0083] The first ink and the second ink preferably contain resin particles and a water-soluble organic solvent. It is more preferable that the pigment content C1, resin particle content B1, and water-soluble organic solvent content D1 in the first ink, and the pigment content C2, resin particle content B2, and water-soluble organic solvent content D2 in the second ink satisfy the relationship of the following formula (1). By satisfying the following formula (1), it is easy to suppress thickening of the first ink when water evaporates, and it is easy to suppress color unevenness during reciprocal recording of the secondary color. Note that the unit of each of the above contents is mass % based on the total mass of the ink. (C1+B1) / D1≦(C2+B2) / D2 (1)

[0084] (Other additives) In addition to the above components, the ink may contain various additives, such as an antifoaming agent, other surfactants, a pH adjuster, a viscosity adjuster, an antirust agent, an antiseptic, an antifungal agent, an antioxidant, and an antireducing agent, as necessary.

[0085] (viscosity) The viscosity of the ink is preferably 3.0 mPa·s or more, and more preferably 10.0 mPa·s or less. By making the viscosity of the ink 3.0 mPa·s or more, a stable meniscus can be formed. The viscosity of the ink can be measured using a rotational viscometer or the like.

[0086] In the inks used in the inkjet recording method and inkjet recording apparatus of the present invention, it is preferable that the viscosity η1 of the first ink and the viscosity η2 of the second ink satisfy the relationship η1 ≧ η2. When the viscosity η1 of the first ink is equal to or greater than the viscosity η2 of the second ink, evaporation of water in the first ink is easily suppressed, and color unevenness during reciprocating recording of secondary colors is easily suppressed.

[0087] (brightness) In the inks used in the inkjet recording method and inkjet recording apparatus of the present invention, the lightness of the first ink is preferably higher than that of the second ink. By having the lightness of the first ink higher than that of the second ink, color change caused when water in the first ink evaporates is easily suppressed, and color unevenness during reciprocating recording of secondary colors is easily suppressed.

[0088] The ink brightness relationship can be calculated by measuring the brightness of ink diluted with water at an appropriate ratio using a spectrophotometer so that the absorbance value is suitable for measurement, but the ink brightness relationship may change depending on the content of coloring material in the ink. When comparing the brightness of multiple inks, it is necessary to dilute the multiple inks with water to the same ratio.

[0089] The first ink and the second ink may be of different hues or the same hue, or any combination of hues may be used. In particular, it is preferable that the first ink and the second ink are of different hues. When the hues are different, the order of brightness of the basic colors of the aqueous inks used in the inkjet recording method is usually black, cyan, magenta, and yellow, from lowest to highest. EXAMPLES

[0090] 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 without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0091] <Preparation of pigment dispersion> (Pigment dispersion 1) A styrene-ethyl acrylate-acrylic acid copolymer (resin) with an acid value of 150 mgKOH / g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of the resin were neutralized with potassium hydroxide in an amount equimolar to the acid value, and an appropriate amount of pure water was added to prepare a resin aqueous solution 1 with a resin (solid content) content of 20.0%. 20.0 parts of a pigment (CI Pigment Yellow 74), 25.0 parts of the resin aqueous solution 1, and 55.0 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of zirconia beads with a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex), dispersed for 5 hours while cooling with water, and then centrifuged to remove coarse particles. The mixture was filtered under pressure with a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare a pigment dispersion 1 with a pigment content of 20.0% and a resin dispersant (resin) content of 5.0%.

[0092] (Pigment dispersion 2) Pigment dispersion 2 with a pigment content of 20.0% and a resin dispersant (resin) content of 5.0% was obtained in the same manner as in the above-mentioned pigment dispersion 1, except that the type of pigment was changed to CI Pigment Blue 15:3.

[0093] (Pigment dispersion 3) Except for changing the type of pigment to CI Pigment Red 122, the same procedure as for the above-mentioned Pigment Dispersion 1 was used to obtain Pigment Dispersion 3 having a pigment content of 20.0% and a resin dispersant (resin) content of 5.0%.

[0094] (Pigment Dispersion 4) The pigment type is carbon black (specific surface area 220 m 2 Pigment dispersion 4, which has a pigment content of 20.0% and a resin dispersant (resin) content of 5.0%, was obtained in the same manner as pigment dispersion 1 described above, except that the DBP oil absorption was changed to 105 mL / 100 g and the DBP oil absorption was changed to 105 mL / 100 g.

[0095] (Pigment Dispersion 5) A commercially available pigment dispersion (product name "CAB-O-JET270Y", manufactured by Cabot) was concentrated to prepare Pigment Dispersion 5 with a pigment content of 20.0%. The pigment in Pigment Dispersion 5 is a self-dispersing pigment in which sulfonic acid groups are bonded to the particle surface of the pigment (CI Pigment Yellow 74) via benzene rings.

[0096] (Pigment Dispersion 6) A commercially available pigment dispersion (product name "CAB-O-JET250C", manufactured by Cabot) was concentrated to prepare Pigment Dispersion 6 with a pigment content of 20.0%. The pigment in Pigment Dispersion 6 is a self-dispersing pigment in which sulfonic acid groups are bonded to the particle surface of the pigment (CI Pigment Blue 15:4) via benzene rings.

[0097] (Pigment Dispersion 7) A commercially available pigment dispersion (product name "CAB-O-JET265M", manufactured by Cabot) was concentrated to prepare Pigment Dispersion 7 with a pigment content of 20.0%. The pigment in Pigment Dispersion 7 is a self-dispersing pigment in which sulfonic acid groups are bonded to the particle surface of the pigment (CI Pigment Red 122) via benzene rings.

[0098] (Pigment Dispersion 8) A commercially available pigment dispersion (product name "CAB-O-JET200", manufactured by Cabot) was concentrated to prepare pigment dispersion 8 with a pigment content of 20.0%. The pigment in pigment dispersion 8 is a self-dispersing pigment in which sulfonic acid groups are bonded to the particle surface of the pigment (carbon black) via benzene rings.

[0099] <Preparation of resin aqueous solution> (acrylic resin solution) A styrene-ethyl acrylate-acrylic acid copolymer (resin) was prepared with an acid value of 150 mgKOH / g and a weight average molecular weight of 8,000. 20.0 parts of the resin was neutralized with potassium hydroxide in an amount equal to the acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of the acrylic resin with a resin (solid content) content of 20.0%.

[0100] (Aqueous solution of urethane resin) In a four-neck flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux tube, 29 parts of isophorone diisocyanate, 39 parts of polypropylene glycol having a number average molecular weight of 2,000, 12 parts of dimethylolpropionic acid, 0.02 parts of dibutyltin dilaurate, and 120 parts of methyl ethyl ketone were charged and reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Then, an appropriate amount of methanol was added, and the reaction was continued at 80°C until the weight average molecular weight reached the desired size. After the reaction, the mixture was cooled to 40°C, ion-exchanged water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer. The resin solution was heated under reduced pressure to distill off methyl ethyl ketone, and an aqueous solution of urethane resin with a resin (solid content) content of 20.0% was prepared.

[0101] <Synthesis of resin particles> 1,160 mL of water was heated to 90°C in a reactor. In addition, 1.39 g of potassium persulfate was mixed with 160 mL of water as a polymerization initiator to prepare an initiator solution. 32 mL of the prepared initiator solution was added to the reactor and stirred. Separately, 183 g of α-methylstyrene, 80 g of benzyl acrylate, 1.5 g of methacrylic acid, 1.6 g of isooctylthioglycolate as a chain transfer agent, and 9.98 g of a 30% aqueous solution of an emulsifier were mixed with 159.4 mL of water to prepare a monomer mixture. As the emulsifier, a product name "RHODAFAC RS 710" (manufactured by RHODIA NOVECARE) was used. The prepared monomer mixture was dropped into the reactor over 30 minutes, and at the same time, 129.4 g of the initiator solution was dropped into the reactor over 30 minutes and stirred. The resulting reactant was stirred and maintained at 90°C for 3 hours. After cooling to 50°C, a 50% aqueous potassium hydroxide solution was added to adjust the pH to 8.5. After cooling the contents to ambient temperature, the contents were filtered through a 200 mesh filter, and deionized water was added to obtain an aqueous dispersion of resin particles (resin content 25.0%).

[0102] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the upper part of Table 1 (Table 1-1 to Table 1-5), thoroughly stirring, and then filtering under pressure with a cellulose acetate filter (Advantec) with a pore size of 3.0 μm. The numerical value attached to polyethylene glycol indicates the number average molecular weight. "Acetylenol E60" is the trade name of a surfactant manufactured by Kawaken Fine Chemicals. The lower part of Table 1 shows the molar fraction R (%) of water in the ink, the pigment content C (%) in the ink, the water-soluble resin content A (%), the resin particle content B (%), the water-soluble organic solvent content D (%), the value of (C+B) / D, and the viscosity η (mPa·s). The viscosity of each ink was measured using an E-type viscometer (trade name "RE-80L", manufactured by Toki Sangyo) at a temperature of 25°C and 50 rpm.

[0103] TIFF2024178119000001.tif158170

[0104] TIFF2024178119000002.tif159170

[0105] TIFF2024178119000003.tif158170

[0106] TIFF2024178119000004.tif158170

[0107] TIFF2024178119000005.tif157170

[0108] <Evaluation> Using an inkjet recording device having the main parts shown in Fig. 2 and Fig. 3, the ink cartridge shown in Fig. 3 was filled with ink, and the following evaluations were performed in an environment of temperature 25°C and relative humidity 50%. A serial type recording head (circulating serial head) having the configuration shown in Fig. 4 was used as the recording head. This recording head has a first flow path and a second flow path that communicate between the ejection port and the ejection element for each ejection port, and uses a pump to make the ink in the first flow path flow to the second flow path. The number of ejection ports per ejection port array is 256, the ejection port density is 600 dpi, and the ink ejection amount per ejection port is 8 ng. The solid image recorded in the following evaluation was recorded using two ejection port arrays under the condition that one ink droplet was applied from each ejection port array to an area of ​​1 / 600 inch x 1 / 600 inch. The images were recorded under the conditions listed in Table 2 for the inks (ink set of the first ink and the second ink) and the ejection port arrays (symbols in Fig. 4). In addition, images were recorded under the conditions shown in Table 3, including the presence or absence of a flow process (circulation flow) in the recording head, the ink flow speed, the scanning method, the scanning speed, the distance between the nozzle rows, and the presence or absence of heating of the ink in the recording head. The ink in the recording head was heated so that the temperature of the ink was 60°C. In addition, no preliminary ejection operation was performed outside the recording medium area of ​​the recording head. Furthermore, no heating process was performed on the recording medium to which the ink was applied. Table 2 shows the magnitude relationship between the molar fraction R1 of the water in the first ink and the molar fraction R2 of the water in the second ink, and the value of R1-R2 (%). Table 2 also shows the magnitude relationship between the viscosities η1 and η2, the water-soluble resin contents A1 and A2, the resin particle contents B1 and B2, and the ratios (C1+B1) / D1 and (C2+B2) / D2) of the total content of the pigment and the resin particles to the water-soluble organic solvent content for both inks.

[0109] TIFF2024178119000006.tif246170

[0110] TIFF2024178119000007.tif250170

[0111] (Color unevenness when printing secondary colors back and forth) Using the above-mentioned inkjet recording device, the recording head was scanned back and forth to record in one pass using the first ink and the second ink. Specifically, a solid image of the secondary color (see FIG. 10) was recorded in one pass so that the recording duty of each ink was 50% and the total recording duty was 100%. The recording medium used was "High-quality dedicated paper HR-101SA4" (Canon). The solid image was measured for the area recorded by the forward scan of the recording head and the area recorded by the backward scan using a fluorescent spectrodensitometer (FD-7, Konica Minolta) under conditions of a light source of D50 and a visual field of 2°, and the color difference ΔE between the two areas was calculated. The color difference ΔE is calculated based on the L * a * b * L in color space * , a * , and b * Based on this, ΔE={(ΔL) 2 +(Δa) 2 +(Δb) 2} 1 / 2 The color difference ΔE was calculated based on the formula. The color unevenness during reciprocal printing of secondary colors was evaluated from the obtained color difference ΔE according to the following evaluation criteria. In the present invention, in the following evaluation criteria, "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. The results are shown in Table 4. A: The color difference ΔE was less than 2.0. B: The color difference ΔE was 2.0 or more and less than 3.0. C: The color difference ΔE was 3.0 or more.

[0112] TIFF2024178119000008.tif249170

[0113] Comparative Examples 2 and 3 are examples in which recording was performed under conditions in which a flow process, separate from the ejection process, in which the ink in the first flow path is caused to flow to the second flow path is not performed. In this case, since there is no reference ink flow direction, the ejection port array and the ink are not defined as "first" and "second", but for convenience, the ejection port array and the ink are assigned as shown in Table 2. In Comparative Examples 2 and 3, ejection stability was insufficient, and a preliminary ejection operation was required. Reference Example 1 is an example in which a line-type recording head equivalent to the width of the recording medium was used as the recording head. In Reference Example 1, an image was recorded without reciprocating motion of the recording head, so color unevenness of the secondary color did not occur during reciprocating recording. From Reference Examples 2 and 3, when dye inks were used, color unevenness of the secondary color did not occur during reciprocating recording, regardless of the magnitude relationship between the water molar fraction R1 of the first ink and the water molar fraction R2 of the second ink.

[0114] The disclosure of this embodiment includes the following methods and configurations. (Method 1) An inkjet recording method for recording an image by ejecting ink from a recording head including a plurality of ejection ports for ejecting ink, ejection elements for generating energy for ejecting the ink, and first and second flow paths communicating between the ejection ports and the ejection elements and through which the ink flows, comprising: a discharge step of discharging the ink from the discharge port; a flowing step, separate from the ejection step, for causing the ink in the first flow path to flow into the second flow path, the print head is a serial print head that includes an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and that scans in a direction intersecting the arrangement direction of the ejection port arrays, the first flow path and the second flow path are arranged parallel to a scanning direction of the recording head, and the ink flows in the same direction; the plurality of ejection port arrays include a first ejection port array that ejects a first ink and a second ejection port array that ejects a second ink, the first ejection port array being disposed on an upstream side and the second ejection port array being disposed on a downstream side with respect to a flow direction of the ink, the first ink and the second ink are aqueous inks containing a pigment, an ink jet recording method, wherein a molar fraction R1 of water in the first ink and a molar fraction R2 of water in the second ink satisfy the relationship R1≧R2. (Method 2) The inkjet recording method according to Method 1, wherein the molar fraction R1 of water in the first ink and the molar fraction R2 of water in the second ink satisfy the relationship: 0.5≦R1−R2≦5.0. (Method 3) The inkjet recording method according to Method 1 or 2, wherein the lightness of the first ink is higher than the lightness of the second ink. (Method 4) The ink jet recording method according to any one of Methods 1 to 3, wherein the viscosity η1 of the first ink and the viscosity η2 of the second ink satisfy the relationship η1≧η2. (Method 5) The inkjet recording method described in any one of Methods 1 to 4, wherein the first ink and the second ink contain a water-soluble resin, and a content A1 (mass %) of the water-soluble resin in the first ink and a content A2 (mass %) of the water-soluble resin in the second ink satisfy the relationship A1≧A2. (Method 6) The inkjet recording method described in any one of Methods 1 to 5, wherein the first ink and the second ink contain resin particles, and a content B1 (mass %) of the resin particles in the first ink and a content B2 (mass %) of the resin particles in the second ink satisfy the relationship B1≦B2. (Method 7) The inkjet recording method described in any one of Methods 1 to 6, wherein the first ink and the second ink contain resin particles and a water-soluble organic solvent, and the pigment content C1 (mass %), the resin particle content B1 (mass %), and the water-soluble organic solvent content D1 (mass %) in the first ink, and the pigment content C2 (mass %), the resin particle content B2 (mass %), and the water-soluble organic solvent content D2 (mass %) in the second ink satisfy the relationship of the following formula (1). (C1+B1) / D1≦(C2+B2) / D2 (1) (Method 8) The inkjet recording method according to any one of Methods 1 to 7, further comprising the step of heating the ink in the recording head. (Method 9) The inkjet recording method according to any one of Methods 1 to 8, which does not include a step of heating the recording medium to which the ink has been applied. (Method 10) The inkjet recording method according to any one of Methods 1 to 9, wherein the flow velocity of the ink during the flow is 1.0 mm / s or more and 100.0 mm / s or less. (Method 11) The inkjet recording method according to any one of Methods 1 to 10, wherein the moving speed of the recording head during the scanning is 70 inches / second or less. (Method 12) The inkjet recording method according to any one of Methods 1 to 11, wherein the distance between the first ejection port row and the second ejection port row is 1.8 mm or less. (Configuration 1) An inkjet recording device including a recording head having a plurality of ejection ports for ejecting ink, ejection elements for generating energy for ejecting the ink, and first and second flow paths communicating between the ejection ports and the ejection elements and through which the ink flows, a flow means for causing the ink in the first flow path to flow into the second flow path, the flow means being separate from the ejection element; the print head is a serial print head that includes an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and that scans in a direction intersecting the arrangement direction of the ejection port arrays, the first flow path and the second flow path are arranged parallel to a scanning direction of the recording head, and the ink flows in the same direction; the plurality of ejection port arrays include a first ejection port array that ejects a first ink and a second ejection port array that ejects a second ink, the first ejection port array being disposed on an upstream side and the second ejection port array being disposed on a downstream side with respect to a flow direction of the ink, the first ink and the second ink are aqueous inks containing a pigment, an ink jet recording apparatus, wherein a molar fraction R1 of water in the first ink and a molar fraction R2 of water in the second ink satisfy the relationship R1≧R2. (Configuration 2) An ink set including a first ink and a second ink for use in an inkjet recording method for recording an image by ejecting the ink from a recording head including a plurality of ejection ports for ejecting ink, an ejection element for generating energy for ejecting the ink, and a first flow path and a second flow path communicating between the ejection ports and the ejection elements and through which the ink flows, the inkjet recording method includes a discharge step of discharging the ink from the discharge port, and a flow step, which is separate from the discharge step, of causing the ink in the first flow path to flow into the second flow path, the print head is a serial print head that includes an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and that scans in a direction intersecting the arrangement direction of the ejection port arrays, the first flow path and the second flow path are arranged parallel to a scanning direction of the recording head, and the ink flows in the same direction; 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 first ejection opening array being disposed on an upstream side and the second ejection opening array being disposed on a downstream side with respect to a flow direction of the ink, the first ink and the second ink are aqueous inks containing a pigment, an ink set, wherein a molar fraction R1 of water in the first ink and a molar fraction R2 of water in the second ink satisfy the relationship R1≧R2.

Claims

1. An inkjet recording method for recording an image by ejecting ink from a recording head including a plurality of ejection ports for ejecting ink, ejection elements for generating energy for ejecting the ink, and first and second flow paths communicating between the ejection ports and the ejection elements and through which the ink flows, comprising: a discharge step of discharging the ink from the discharge port; a flowing step, separate from the ejection step, for causing the ink in the first flow path to flow into the second flow path, the print head is a serial print head that includes an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and that scans in a direction intersecting the arrangement direction of the ejection port arrays, the first flow path and the second flow path are arranged parallel to a scanning direction of the recording head, and the ink flows in the same direction; the plurality of ejection opening arrays include a first ejection opening array that ejects a first ink and a second ejection opening array that ejects a second ink, the first ejection opening array being disposed on an upstream side and the second ejection opening array being disposed on a downstream side with respect to a flow direction of the ink, the first ink and the second ink are aqueous inks containing a pigment, The mole fraction R of water in the first ink １ and the molar fraction R of water in the second ink. ２ But, R １ ≧R ２ The ink jet recording method according to the present invention is characterized in that the above relationship is satisfied.

2. The mole fraction R of water in the first ink １ and the molar fraction R of water in the second ink. ２ And, 0.5≦R １ -R ２ The ink jet recording method according to claim 1, wherein the relationship of ≦5.0 is satisfied.

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

4. The viscosity η of the first ink １ and the viscosity η of the second ink ２ And, η １ ≧η ２ The ink jet recording method according to claim 1 , wherein the following relationship is satisfied:

5. The first ink and the second ink each contain a water-soluble resin, and the content A of the water-soluble resin in the first ink １ (mass%), and the content A of the water-soluble resin in the second ink ２ (mass%) and A １ ≧A ２ The ink jet recording method according to claim 1 , wherein the following relationship is satisfied:

6. The first ink and the second ink contain resin particles, and the content B of the resin particles in the first ink １ (mass%), and the content B of the resin particles in the second ink ２ (mass%) and B １ ≦B ２ The ink jet recording method according to claim 1 , wherein the following relationship is satisfied:

7. The first ink and the second ink contain resin particles and a water-soluble organic solvent, and the content C of the pigment in the first ink is １ (mass%), the content B of the resin particles １ (mass%), and the content D of the water-soluble organic solvent １ (mass%) and the content C of the pigment in the second ink ２ (mass%), the content B of the resin particles ２ (mass%), and the content D of the water-soluble organic solvent ２ The ink jet recording method according to claim 1 , wherein (% by mass) satisfies the following formula (1): (C １ +B １ ) / D １ ≦(C ２ +B ２ ) / D ２ ・・・(1)

8. 2. The ink jet recording method according to claim 1, further comprising the step of heating the ink in the recording head.

9. The ink-jet recording method according to claim 1, which does not include a step of heating the recording medium to which the ink has been applied.

10. 2. The ink jet recording method according to claim 1, wherein the flow velocity of the ink during the flow is 1.0 mm / s or more and 100.0 mm / s or less.

11. 2. The ink jet recording method according to claim 1, wherein the moving speed of the recording head during the scanning is 70 inches / second or less.

12. 2. The ink jet recording method according to claim 1, wherein the distance between the first ejection port array and the second ejection port array is 1.8 mm or less.

13. An inkjet recording apparatus including a recording head having a plurality of ejection ports for ejecting ink, ejection elements for generating energy for ejecting the ink, and first and second flow paths communicating between the ejection ports and the ejection elements and through which the ink flows, a flow means for causing the ink in the first flow path to flow into the second flow path, the flow means being separate from the ejection element; the print head is a serial print head that includes an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and that scans in a direction intersecting the arrangement direction of the ejection port arrays, the first flow path and the second flow path are arranged parallel to a scanning direction of the recording head, and the ink flows in the same direction; the plurality of ejection opening arrays include a first ejection opening array that ejects a first ink and a second ejection opening array that ejects a second ink, the first ejection opening array being disposed on an upstream side and the second ejection opening array being disposed on a downstream side with respect to a flow direction of the ink, the first ink and the second ink are aqueous inks containing a pigment, The mole fraction R of water in the first ink １ and the molar fraction R of water in the second ink. ２ But, R １ ≧R ２ The ink jet recording apparatus is characterized in that the above relationship is satisfied.

14. an ink set including a first ink and a second ink for use in an inkjet recording method, which records an image by ejecting the ink from a recording head including a plurality of ejection ports for ejecting ink, ejection elements for generating energy for ejecting the ink, and first and second flow paths communicating between the ejection ports and the ejection elements and through which the ink flows, the ink jet recording method includes a discharge step of discharging the ink from the discharge port, and a flow step, which is separate from the discharge step, of causing the ink in the first flow path to flow into the second flow path, the print head is a serial print head that includes an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction, and that scans in a direction intersecting the arrangement direction of the ejection port arrays, the first flow path and the second flow path are arranged parallel to a scanning direction of the recording head, and the ink flows in the same direction; 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 first ejection opening array being disposed on an upstream side and the second ejection opening array being disposed on a downstream side with respect to a flow direction of the ink, the first ink and the second ink are aqueous inks containing a pigment, The mole fraction R of water in the first ink １ and the molar fraction R of water in the second ink. ２ But, R １ ≧R ２ The ink set is characterized in that the following relationship is satisfied:

Images