Inkjet recording method, and inkjet recording device

Abstract

To provide an inkjet recording method which can record a high quality image suppressing positional deviation of ruled lines using a circulation serial head, and can suppress a color tone change of an image due to color mixture of ink even during long-term use.SOLUTION: An inkjet recording method discharges ink from a recording head having a plurality of discharge ports, discharge elements, and first flow channels and second flow channels each of which communicate 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; a flowing step of causing the ink to flow in the first flow channel different from the discharge step to the second flow channel; and a step of heating the ink in the recording head. The recording head is a serial system that comprises a plurality of discharge port arrays in which the plurality of discharge ports are arrayed in a predetermined direction, and that scans in a direction crossing an array direction of the discharge port arrays. The first flow channel and the second flow channel are arranged in parallel with the direction in 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 upstream of the ink flowing direction, and a second discharge port array for discharging second ink downstream thereof. Static surface tension γs1 of the first ink and static surface tension γs2 of the second ink satisfy a relation of γs1≥γs2.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus. [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. In addition, it is 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, 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, and to reduce the frequency of recovery operations to suppress deterioration of ejection properties due to thickening of the ink or bubbles, and it becomes a challenge to achieve both of these while improving image quality.

[0005] When an image is recorded by one-pass recording in which multiple inks are applied to the recording medium in one printhead scan, the difference in the amount of ink discharged between the nozzles is more likely to affect the image quality than in multi-pass recording. When there is a difference in the frequency of ink discharge between the nozzles, the ink viscosity increases at the nozzles with low frequency of ink discharge, and when the preliminary ejection operation to prevent this is reduced, the decrease in the amount of ink discharged becomes even more noticeable. In addition, when there is a difference in temperature between the nozzles in the printhead due to the frequency of use between the nozzles or the environment around the printhead, a difference in the viscosity of the ink occurs, which causes a fluctuation in the amount of ink discharged. Both of these factors cause the amount of ink discharged between the nozzles to vary, and in particular, cause deviations due to variations in dot position in ruled lines recorded in one pass.

[0006] As a method for improving the ink ejection stability while reducing the frequency of preliminary ejection operations, for example, a liquid ejection head has been proposed that can prevent solids in the liquid from remaining around the edges of the ejection port even after the ejection operation has been paused for a certain period of time (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-124608 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] In addition, in order to achieve both a higher printing speed and a smaller printing device while still achieving higher image quality, the inventors have investigated the use of a mechanism for heating the ink in the above-mentioned circulating serial head (ink heating mechanism) to print images in one pass. As a result, it has been found that the ink heating mechanism reduces the difference in ink viscosity due to the difference in temperature between the ejection ports, and the accompanying fluctuation in the ejection volume is suppressed, thereby suppressing the variation in the ejection volume and making it possible to print high-quality images with suppressed misalignment of ruled lines. However, it has been found that when images are printed over a long period of time, the color tone of the printed image may change due to ink mixing.

[0010] Therefore, an object of the present invention is to provide an inkjet recording method that can record high-quality images with reduced misalignment of ruled lines using a circulation serial head, and can also suppress changes in color tone of the images caused by ink mixing even after long-term use. Another object of the present invention is to provide an inkjet recording apparatus used 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; a flow step, which is separate from the ejection step, of causing the ink in the first flow path to flow into the second flow path; and a heating step of heating the ink in the recording head, the recording head including an ejection element substrate having a plurality of ejection port arrays in which the plurality of ejection ports are arranged in a predetermined direction. the first flow path and the second flow path are arranged parallel to the direction in which the recording head scans, and the ink flow direction is the same; the multiple nozzle arrays include a first nozzle array that ejects a first ink and a second nozzle array that ejects a second ink, the first nozzle array is arranged upstream and the second nozzle array is arranged downstream with respect to the ink flow direction; and a static surface tension γs1 of the first ink and a static surface tension γs2 of the second ink satisfy the relationship γs1≧γs2. Effect of the Invention

[0012] According to the present invention, it is possible to provide an inkjet recording method that can record high-quality images with reduced misalignment of ruled lines by using a circulation serial head and that can suppress changes in color tone of the images caused by ink mixing even after long-term use. Also, according to the present invention, it is possible to provide an inkjet recording apparatus used 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 ruled line recorded with the two inks may be simply referred to as "ruled line". 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. Furthermore, the inkjet recording apparatus of the present invention includes a flow means that causes the ink in the first flow path to flow to the second flow path, which is separate from the ejection element, and a mechanism that heats the ink in the recording head. 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, a flow step that causes the ink in the first flow path to flow to the second flow path, which is separate from the ejection step, and a heating step of the ink in the recording head.

[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] By configuring an inkjet recording method using a serial type recording head (circulating serial head) that generates the above-mentioned circulating flow, even if there is a difference in ejection frequency between the ejection ports, it is possible to suppress variations in the ejection amount without performing recovery through a preliminary ejection operation.

[0018] The inkjet recording apparatus of the present invention also includes a mechanism for heating the ink in the recording head (ink heating mechanism). The inkjet recording method of the present invention includes, for example, a step of heating the ink in the recording head (heating step) using an inkjet recording apparatus including the ink heating mechanism. The heating 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 so as to be 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. It is preferable that the temperature of the ink in the recording head is adjusted to a range of 40° C. or more and 60° C. or less. By this heating means, the temperature between the ejection ports can be made uniform, thereby suppressing the variation in the ejection amount.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] As described above, in an image recorded in one pass using a serial head that causes the ink to flow and a process of heating the ink in the head, it is possible to suppress fluctuations in the ejection amount due to differences in ejection frequency and temperature between the ejection ports without performing a recovery operation by preliminary ejection. However, even with the above-mentioned configuration, it has been found that a change in the color tone of the image may occur due to ink mixing over a long period of use. The inventors speculate on this phenomenon as follows.

[0027] FIG. 5 is a schematic diagram for explaining the flow state of ink in the print head when the print head scans. When printing is started using a circulation serial head, the meniscus 12 at the ejection port 1 is stable as shown in FIG. 5(a) when the print head scans from the home position in the forward direction and switches from the forward direction to the backward direction and scans the print medium. Thereafter, immediately after the print head switches from the backward direction to the forward direction, that is, when the print head stops instantaneously near the home position, it is considered that an inertial force acts on the ink near the ejection port 1 in the same direction as the circulating flow. At that time, it is considered that the meniscus at the ejection port 1 is destroyed by the inertial force as shown in FIG. 5(b), and the ink overflows downstream of the circulating flow. After this, the overflowing ink is quickly drawn into the ejection port 1 in a short time.

[0028] However, when the ink is heated, the viscosity of the ink decreases, which makes the meniscus more likely to fluctuate, making overflow more likely, and the ink dries faster, which makes it easier for components such as coloring materials to precipitate at the overflow area. In this way, in an inkjet recording method using a circulation serial head and having an ink flow process and a heating process, it is thought that components such as coloring materials are more likely to precipitate downstream of the circulation flow of the ejection port. The ink is more likely to remain in the area where the components such as coloring materials have precipitated, and the precipitation of components such as coloring materials due to drying is promoted, so that the range of ink overflowing is thought to expand. With long-term use, the range of ink overflowing reaches the ejection port array located downstream from the ejection port array located upstream in the ink flow direction, causing the ink ejected from the ejection port array located downstream to mix with the ink ejected from the ejection port array located upstream. It is speculated that the mixed ink on the upstream side remains on the meniscus at the ejection port 1 or its surroundings, or continuously enters the flow path from the ejection port array located downstream due to the circulation flow, causing a change in color tone.

[0029] 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.

[0030] In order to suppress the change in color tone of an image due to ink mixing during long-term use, the inventors have focused on the relationship between the ink flow direction and the static surface tension of the inks ejected from the two ejection port arrays. In the ink mixing, the ink with a relatively low static surface tension is likely to enter the ink with a relatively high static surface tension. For this reason, the static surface tension γs1 of the first ink ejected from the first ejection port array arranged on the upstream side and the static surface tension γs2 of the second ink ejected from the second ejection port array arranged on the downstream side are set to a relationship of γs1 ≧ γs2 with respect to the ink flow direction. By setting the relationship of γs1 ≧ γs2, when the first ink of the first ejection port array overflowing from the upstream side comes into contact with the second ink in the vicinity of the second ejection port array and inside the ink flow path, it is possible to suppress the first ink of the first ejection port array from mixing with the second ink of the second ejection port array. This makes it possible to suppress the change in color tone of an image due to ink mixing by reducing the change in color tone and making the color mixing less noticeable.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] As shown in FIG. 7, a pressure adjustment mechanism H is connected to the common inflow channel 211, and a pressure adjustment mechanism L is connected to the common outflow channel 212, so that a pressure difference occurs between the inflow channel 6 and the outflow channel 7. This also causes a pressure difference between the inlet 8 (FIG. 6) communicating with the inflow channel 6 and the outlet 9 (FIG. 6) communicating with the outflow channel 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 to be 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, an increase in the viscosity of the ink near the outlet when the ejection operation is paused for a certain period of time is suppressed, which makes it easier to improve the ejection stability of the ink and further suppress the misalignment of the ruled lines. On the other hand, when the ink flow velocity is 100.0 mm / s or less, the stability of the meniscus at the ejection port is likely to be improved, the overflow of ink from the ejection port due to inertial force is likely to be suppressed, and changes in color tone of the image over long-term use are likely to be further suppressed.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] In the inkjet recording method of the present invention, the scanning speed of the recording head when recording an image, i.e., the moving speed when the recording head scans, can be preferably 30 inches / second or more, more preferably 35 inches / second or more, from the viewpoint of increasing the recording speed. In addition, the moving speed when the recording head scans is preferably 70 inches / second or less. By making the moving speed when the recording head scans 70 inches / second or less, the inertial force when the recording head stops is suppressed, and ink is less likely to overflow from the ejection openings. As a result, it is easier to suppress color tone changes in images when used for a long period of time.

[0045] 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 arranged densely, which makes it easier to achieve miniaturization and high image quality, but the inks tend to mix. When the distance between the first and second ejection port arrays is 1.8 mm or less, the static surface tension γs1 of the first ink and the static surface tension γs2 of the second ink satisfy the relationship γs1≧γs2, so that the color tone change of the image due to the ink mixing can be suppressed even during long-term use. 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.

[0046] 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.

[0047] 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, by reducing the effect of the temperature increase, the above heating step may be omitted in order to easily suppress the color tone change of the image due to the ink mixture even during long-term use.

[0048] (Cleaning process) The inkjet recording method of the present invention preferably further includes a cleaning step of wiping the nozzle surface on which a plurality of nozzle rows of the recording head are arranged in a predetermined direction. The cleaning step can be performed, for example, by using an inkjet recording device equipped with a cleaning means for wiping the nozzle surface. Examples of wiping methods include a method of wiping the nozzle surface by bringing a wiper member made of an elastic member such as rubber into contact with the nozzle surface and moving it, and a method of pressing an absorbent member such as a nonwoven fabric against the nozzle surface to absorb the ink. In the present invention, the wiping method is preferably a method of moving the wiper member in a direction parallel to the arrangement direction of the nozzle rows, or a method of pressing a nonwoven fabric against the nozzle surface to absorb the ink. By performing wiping using these methods, overflow of ink and precipitated coloring material between adjacent nozzle rows can be efficiently removed, and color tone changes in images due to color mixing can be suppressed even during long-term use.

[0049] <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 in the ink flow direction, and a second ink ejected from an ejection opening array (second ejection opening array) on the downstream side. Furthermore, the static surface tension γs1 of the first ink and the static surface tension γs2 of the second ink satisfy the relationship γs1≧γs2.

[0050] The static surface tension of the ink can be appropriately controlled by adjusting the type and amount of the surfactant and water-soluble organic solvent contained in the ink, which will be described later. The static surface tension of the ink may be adjusted by using a surfactant and a water-soluble organic solvent in combination. The static surface tension of the ink can be measured by a plate method using a platinum plate. In the examples described later, the static surface tension of the ink was measured using an automatic surface tensiometer (product name "CBVP-Z type", manufactured by Kyowa Interface Science).

[0051] In the range in which the static surface tension γs1 of the first ink and the static surface tension γs2 of the second ink satisfy the relationship γs1≧γs2, the values ​​of γs1 and γs2 are preferably 24 mN / m or more and 42 mN / m or less. The difference between the static surface tensions of the first ink and the second ink (γs1-γs2) is preferably 3 mN / m or less, more preferably 2 mN / m or less, and is 0 mN / m or more.

[0052] The components constituting the first ink and the second ink and the physical properties of the inks will be described in detail below.

[0053] (Colorant) The coloring material contained in the ink may be a pigment or a dye. Among them, a pigment is preferable. The content (mass %) of the coloring material in the ink is preferably 0.10 mass % or more and 15.00 mass % or less, and more preferably 0.30 mass % or more and 10.00 mass % or less, based on the total mass of the ink.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] It is preferable to use a dye having an anionic group. Specific examples of the dye include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes.

[0059] (resin) The ink may contain a resin. The content (mass %) of the resin in the ink is preferably from 0.10% to 20.00% by mass, and more preferably from 0.50% to 15.00% by mass, based on the total mass of the ink.

[0060] 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.

[0061] 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

[0062] 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.

[0063] 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.

[0064] Examples of the resin include acrylic resins, urethane resins, olefin resins, etc. Among these, acrylic resins and urethane resins are preferred.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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".

[0074] 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.

[0075] 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.

[0076] [Resin particles] The ink preferably contains resin particles. In the present invention, it is preferable to use an ink containing resin particles having a glass transition temperature Tg higher than the heating temperature of the recording head as the resin particles. In particular, it is more preferable that the first ink contains resin particles having a glass transition temperature Tg higher than the heating temperature of the recording head. When the ink is dried, the resin particles can reduce the aggregation of color materials and suppress precipitation on the discharge port surface, thereby suppressing color tone changes in the image due to ink mixing. Examples of the resin particles include acrylic resin particles, olefin resin particles, and urethane resin particles. The glass transition temperature of the resin particles can be measured for the resin particles themselves using a thermal analysis device such as a differential scanning calorimeter (DSC).

[0077] [Water-soluble urethane resin] The ink preferably contains a water-soluble urethane resin. Among water-soluble resins, water-soluble urethane resins rapidly interact with each other in the vicinity of the meniscus and form a stable molecular film. Therefore, by using an ink containing a water-soluble urethane resin, it becomes easier to prevent the ink from overflowing from the ejection port due to inertial force, and it becomes easier to prevent color tone changes in images during long-term use.

[0078] [Block copolymer] The ink preferably contains a block copolymer. A block copolymer usually has a structure in which a plurality of blocks derived from monomers having the same or similar properties are arranged. Block copolymers generally used in aqueous inkjet inks have the following structures. For example, there is an AB block structure having a hydrophobic block (A block) and an ionic hydrophilic block (B block); an ABC block structure in which a nonionic hydrophilic block (C block) is further added to this AB block structure; and the like. That is, since the block copolymer has a structure in which the hydrophilic block and the hydrophobic block are each localized, it has high surface activity and is quickly oriented in the vicinity of the meniscus. For this reason, when an ink containing a block copolymer is used, the meniscus is stabilized, and it becomes easier to suppress the occurrence of ink overflowing from the ejection port due to inertial force, and it is easy to suppress the color tone change of the image during long-term use.

[0079] The block copolymer can be synthesized by a conventional synthesis method such as anionic living polymerization, cationic living polymerization, group transfer polymerization, atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization, etc. The block copolymer is preferably a water-soluble resin rather than a resin particle.

[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] Among the ethylene oxide adducts of acetylene glycol, it is particularly preferable to use a compound represented by the following general formula (1). The first ink preferably contains a compound represented by the following general formula (1). The second ink may also contain a compound represented by the following general formula (1).

[0083] TIFF2024178106000001.tif59170 (in the general formula (1), x and y each independently represent a number of 0 or more, and x+y is 0 or more and 50 or less)

[0084] The compound represented by general formula (1) has a high speed of orientation to the interface. Therefore, when the ink dries, it is quickly oriented and adsorbed to the coloring material, and precipitation can be suppressed, so that the color tone change of the image due to the ink mixing during long-term use can be suppressed. In general formula (1), x and y each independently represent a number of 0 or more, and are preferably 1 or more. In addition, in general formula (1), x+y is 0 or more and 50 or less, preferably 1 or more and 50 or less, and more preferably 1.3 or more and 10 or less. The content (mass %) of the compound represented by general formula (1) in the ink is preferably 0.05% by mass or more and 5.00% by mass or less, and more preferably 0.10% by mass or more and 3.00% by mass or less, based on the total mass of the ink.

[0085] (aqueous medium) The ink used in the inkjet recording method of the present invention is preferably an aqueous ink containing at least water as an aqueous medium. The ink may 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 50.00% by mass or more and 95.00% by 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 3.00% by mass or more and 48.00% by 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.

[0086] (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.

[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 the lightness of the second ink. Ink mixing is more noticeable when the ink with a lower lightness of the two inks mixes with the ink with a higher lightness, and is less noticeable when the ink with a higher lightness mixes with the ink with a lower lightness. Therefore, it is preferable that the lightness of the first ink of the first ejection port array located upstream in the ink flow direction of the inks ejected from two adjacent ejection port arrays is higher than the lightness of the second ink located downstream. This allows the ink with a higher lightness to mix with the ink with a lower lightness even when color mixing occurs, thereby reducing color tone changes in the image and making color mixing less noticeable, and further suppressing color tone changes in the image due to ink mixing.

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

[0090] (specific gravity) It is preferable that the specific gravity d1 of the first ink and the specific gravity d2 of the second ink satisfy the relationship d1 ≧ d2. When the recording head is arranged so that ink is discharged downward from the nozzle row, the ink mixture occurs when the first ink moves in the opposite direction to gravity into the nozzle of the second ink after reaching the nozzle of the second ink. Here, when the specific gravity d1 of the first ink is lower than the specific gravity d2 of the second ink, the first ink is relatively likely to move in the opposite direction to gravity, and the ink mixture is likely to be promoted by entering the nozzle. On the other hand, when the specific gravity d1 of the first ink is higher than the specific gravity d2 of the second ink, the ink mixture caused by the movement of the first ink into the nozzle of the second ink can be further suppressed even when the first ink reaches the nozzle of the second ink. The specific gravity of the ink can be measured using a float type or vibration type hydrometer. EXAMPLES

[0091] 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.

[0092] <Resin preparation> (Resin Dispersant) A styrene-ethyl acrylate-acrylic acid copolymer (water-soluble resin) with an acid value of 150 mgKOH / g and a weight-average molecular weight of 8,000 was prepared for use as a resin dispersant. 20.0 parts of the resin were 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 resin dispersant with a resin (solid content) content of 20.00%.

[0093] (Resin particles 1-3) 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, a monomer mixture was prepared by mixing 159.4 mL of water with monomers of the types and amounts (g) shown in Table 1, 1.6 g of isooctylthioglycolate as a chain transfer agent, and 9.98 g of a 30% aqueous solution of an emulsifier. 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 the contents were cooled to ambient temperature, they were filtered through a 200 mesh filter and deionized water was added to obtain a dispersion of resin particles 1 to 3 (resin content 30.00%). The composition of the resin particles in the obtained dispersion is shown in Table 1. The meanings of the abbreviations of the monomers in Table 1 are as follows: αMSt: α-methylstyrene St: styrene ·BzA: Benzyl acrylate ·MAA: Methacrylic acid

[0094] (glass transition temperature) A liquid containing resin particles was dried at 60°C to obtain 2 mg of resin particles, which were then placed in an aluminum container and sealed to prepare a sample for measurement. The prepared sample was subjected to thermal analysis using a differential scanning calorimeter (product name "Q1000", manufactured by TA instruments) according to the temperature program shown below to create a temperature rise curve. In the created temperature rise curve (horizontal axis: temperature, vertical axis: heat amount), the temperature at the intersection of a straight line extended from the low-temperature side curve to the high-temperature side through two points on the curve on the horizontal axis, and a tangent drawn at the point where the gradient of the step-like change in the curve is maximum was determined as the "glass transition temperature (Tg) of the resin (particle)". The Tg of resin particles 1 to 3 is shown in Table 1. [Temperature Program]: (1) Heat up to 200°C at 10°C / min (2) Decrease temperature from 200°C to -50°C at 5°C / min. (3) Heat from -50°C to 200°C at 10°C / min

[0095] TIFF2024178106000002.tif44170

[0096] (urethane resin) A four-neck flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux tube was prepared. 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 added to the flask. Then, the mixture was reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Then, an appropriate amount of methanol was added, and the mixture was reacted at 80°C until the weight average molecular weight reached 12,000. 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. Methyl ethyl ketone was distilled off from the resin solution under heating and reduced pressure to prepare an aqueous solution of urethane resin having a resin (solid content) content of 20.00%.

[0097] <Preparation of pigment dispersion> (Pigment dispersion 1) A mixture was obtained by mixing 10.0 parts of pigment (CI Pigment Blue 15:3), 15.0 parts of the aqueous solution of the resin dispersant prepared earlier, and 75.0 parts of pure water. 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 pigment dispersion 1 with a pigment content of 10.00% and a resin dispersant (resin) content of 3.00%.

[0098] (Pigment dispersion 2) To a solution of 5.0 g of concentrated hydrochloric acid in 5.5 g of water, 1.6 g of 4-amino-1,2-benzenedicarboxylic acid was added at 5°C. To the solution obtained above, a solution of 1.8 g of sodium nitrite in 9.0 g of water was added while stirring in an ice bath to maintain the temperature at 10°C or less. After stirring for 15 minutes, the specific surface area was 220 m 2 6.0 g of carbon black with a DBP oil absorption of 105 mL / 100 g was added and mixed. After stirring for 15 minutes, the obtained slurry was filtered with filter paper (standard filter paper No. 2, manufactured by Advantec), the carbon black was thoroughly washed with water, and dried in an oven at a temperature of 110°C. Water was added to the obtained carbon black to obtain a pigment dispersion (pigment content 10.00%) in which a self-dispersing pigment in which -C6H3-(COONa)2 groups were bonded to the particle surface of the carbon black was dispersed in water. Then, the sodium ions in the pigment dispersion were replaced with potassium ions using an ion exchange method to obtain pigment dispersion 2.

[0099] (Pigment dispersion 3) An appropriate amount of ion-exchanged water was added to a commercially available pigment dispersion (product name "CAB-O-JET250C", manufactured by Cabot) to prepare pigment dispersion 3 with a pigment content of 10.00%. The pigment in pigment dispersion 3 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.

[0100] (Pigment Dispersion 4) The pigment type is carbon black (specific surface area 220 m 2 Pigment dispersion 4 with a pigment content of 10.00% and a resin dispersant (resin) content of 3.00% was obtained in the same manner as in Pigment Dispersion 1 described above, except that the DBP oil absorption was changed to 10.00% (10.00 mL / 100 g, and DBP oil absorption was 105 mL / 100 g).

[0101] (Pigment Dispersion 5) Pigment dispersion 5 having a pigment content of 10.00% and a resin dispersant (resin) content of 3.00% 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 Red 122.

[0102] (Pigment Dispersion 6) Except for changing the type of pigment to CI Pigment Yellow 74, the same procedure as for the above-mentioned Pigment Dispersion 1 was used to obtain Pigment Dispersion 6 having a pigment content of 10.00% and a resin dispersant (resin) content of 3.00%.

[0103] <Ink Preparation> The components (unit: %) shown in the upper part of Table 2 (Table 2-1 to Table 2-3) were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each ink. "Acetylenol E60", "Acetylenol E100", and "Acetylenol E40" are the trade names of surfactants manufactured by Kawaken Fine Chemicals, and the values ​​of "x+y" in the general formula (1) are "6", "10", and "4", respectively. "Zonyl FS-3100" is the trade name of a fluorine-based nonionic surfactant manufactured by DuPont. The lower part of Table 2 shows the static surface tension (mN / m) and specific gravity of the ink. The static surface tension of the ink was measured at 25° C. using an automatic surface tensiometer (trade name "CBVP-Z type", manufactured by Kyowa Interface Science). The specific gravity of the ink was measured using a digital specific gravity meter (trade name "Portable Density Meter DMA35", manufactured by Anton Paar) based on a vibration type measurement method.

[0104] TIFF2024178106000003.tif135170

[0105] TIFF2024178106000004.tif137170

[0106] TIFF2024178106000005.tif136170

[0107] <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 ruled lines recorded in the following evaluations were 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 inks (ink set of the first ink and the second ink) and the nozzle rows (symbols in FIG. 4) used were recorded under the conditions described in Table 3 (Table 3-1 and Table 3-2). 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 were recorded under the conditions described in Table 4 (Table 4-1 and Table 4-2). The ink in the recording head was heated so that the temperature of the ink was 60° C. Furthermore, a preliminary ejection operation was not performed outside the recording medium area of ​​the recording head. Furthermore, a heating process was not performed on the recording medium to which the ink was applied. Table 3 also shows the magnitude relationship between the static surface tension γs1 of the first ink and the static surface tension γs2 of the second ink, and the magnitude relationship between the specific gravity d1 of the first ink and the specific gravity d2 of the second ink.

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[0110] TIFF2024178106000008.tif142170

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[0112] (Disordered lines) Using the above inkjet recording device, the recording head was scanned back and forth to record "Pattern 1" having a ruled line of 25 cm length in the same direction as the ejection port row direction at the center of the recording medium shown in FIG. 10 using the first ink in one pass on 10 sheets. The recording medium used was "High-quality dedicated paper HR-101SA4" (manufactured by Canon). The recorded ruled lines were visually checked, and the disturbance of the ruled lines was evaluated as the image quality due to the misalignment of the ruled lines according to the following evaluation criteria. In the present invention, "A" and "B" were defined as acceptable levels and "C" was defined as an unacceptable level in the following evaluation criteria. The results are shown in Table 5 (Table 5-1 and Table 5-2). A: There was no disorder in the lines on all 10 sheets. B: Disordered lines were found on 1 or 2 sheets out of 10. C: Disordered lines were found on 3 or more sheets out of 10.

[0113] (mixed colors) In this embodiment, a solid image recorded under the condition that two ink droplets with a mass of 8 ng per droplet are applied to an area of ​​1 / 600 inch x 1 / 600 inch is defined as having a recording duty of 100%. A single-color solid image with a recording duty of 100% was recorded using the second ink. The obtained image was used as evaluation image 1. After that, the ejection port surface was wiped once, and then 20 secondary color solid images (pattern 2 shown in FIG. 10) were continuously recorded using the first ink and the second ink so that the recording duty of each ink was 50% and the total recording duty was 100%, and then a pause was given for one minute. A series of operations of wiping, continuous recording, and pause was repeated a predetermined number of times, and then a single-color solid image with a recording duty of 100% was recorded using the second ink again, and used as evaluation image 2. A4-sized plain paper (product name "CS-068", manufactured by Canon) was used as the recording medium, and the solid image of pattern 2 was recorded on the A4-sized recording medium with a margin of 2 cm around the periphery.

[0114] The wiping method was as follows. In Examples 1 to 20, 23 to 32, Comparative Examples 1 to 6, and Reference Example 1, wiping was performed by moving a blade-shaped wiper made of urethane resin in a direction parallel to the arrangement direction of the ejection port array. In Example 21, wiping was performed by pressing a nonwoven fabric against the ejection port surface to absorb the ink. In Examples 22 and 33, wiping was performed by moving a blade-shaped wiper made of urethane resin in a direction perpendicular to the arrangement direction of the ejection port array.

[0115] Evaluation image 1 and evaluation image 2 were visually observed, and evaluated according to the following evaluation criteria to see whether a color change due to color mixing was observed in evaluation image 2. In the present invention, "A" and "B" were defined as acceptable levels, and "C" and "D" were defined as unacceptable levels. The results are shown in Table 5 (Table 5-1 and Table 5-2). A: Even after repeating the series of actions 800 times, no color mixing occurred in evaluation image 2. B: When the series of actions was repeated 600 to less than 800 times, color mixing occurred in evaluation image 2. C: When the series of actions was repeated 400 times or more but less than 600 times, color mixing occurred in evaluation image 2. D: The series of actions was performed less than 400 times, and color mixing occurred in evaluation image 2.

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[0118] In Comparative Examples 3 to 5, since the ink was not heated, it is considered that even if the recording head was reciprocated to record an image, no change in color tone of the image due to ink mixing did not occur. However, the ejection stability was insufficient, and a preliminary ejection operation was required. Reference Example 1 is an example in which a line-type recording head having a width equivalent to the width of the recording medium was used as the recording head. In Reference Example 1, since an image was recorded without reciprocating the recording head, no deterioration in color tone due to color mixing occurred. In Reference Example 1, the recording head was larger than a serial-type recording head, and the recording device could not be made smaller.

[0119] 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; and heating the ink in the recording head. 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, an ink jet recording method, wherein a static surface tension γs1 of the first ink and a static surface tension γs2 of the second ink satisfy the relationship γs1≧γs2; (Method 2) The inkjet recording method according to Method 1, wherein the first ink contains a compound represented by the following general formula (1):

[0120] TIFF2024178106000012.tif59170 (In the general formula (1), x and y each independently represent a number of 0 or more, and x+y is 0 or more and 50 or less.)

[0121] (Method 3) The inkjet recording method according to Method 1 or 2, wherein the first ink contains resin particles having a glass transition temperature Tg higher than a heating temperature of the recording head. (Method 4) The inkjet recording method according to any one of Methods 1 to 3, wherein the lightness of the first ink is higher than the lightness of the second ink. (Method 5) The ink jet recording method according to any one of Methods 1 to 4, wherein a specific gravity d1 of the first ink and a specific gravity d2 of the second ink satisfy the relationship d1≧d2. (Method 6) further comprising a cleaning step of wiping an ejection port face on which the plurality of ejection port arrays are arranged in a predetermined direction, The inkjet recording method according to any one of methods 1 to 5, wherein the wiping method is a method of moving a wiper member in a direction parallel to the arrangement direction of the nozzle row, or a method of pressing a nonwoven fabric against the nozzle face to absorb the ink. (Method 7) The inkjet recording method according to any one of Methods 1 to 6, wherein the moving speed of the recording head during the scanning is 70 inches / second or less. (Method 8) The inkjet recording method according to any one of Methods 1 to 7, 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 9) The inkjet recording method according to any one of Methods 1 to 8, 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; a mechanism for heating the ink in the recording head, 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, an ink jet recording apparatus, wherein a static surface tension γs1 of the first ink and a static surface tension γs2 of the second ink satisfy the relationship γs1≧γs2;

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; and heating the ink in the recording head. 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 static surface tension γs of the first ink １ and the static surface tension γs of the second ink ２ But, γs １ ≧γs ２ The ink jet recording method according to the present invention is characterized in that the above relationship is satisfied.

2. The inkjet recording method according to claim 1 , wherein the first ink contains a compound represented by the following general formula (1): (In the general formula (1), x and y each independently represent a number of 0 or more, and x+y is 0 or more and 50 or less.)

3. 2. The ink jet recording method according to claim 1, wherein the first ink contains resin particles having a glass transition temperature Tg higher than a heating temperature of the recording head.

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

5. Specific gravity d of the first ink １ and the specific gravity d of the second ink ２ But, d １ ≧d ２ The ink jet recording method according to claim 1 , wherein the following relationship is satisfied:

6. a cleaning step of wiping an ejection port face on which the plurality of ejection port rows are arranged in a predetermined direction, 2. The ink jet recording method according to claim 1, wherein the wiping method is a method of moving a wiper member in a direction parallel to the arrangement direction of the nozzle row, or a method of pressing a nonwoven fabric against the nozzle face to absorb the ink.

7. 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.

8. 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.

9. 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.

10. 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; a mechanism for heating the ink in the recording head, 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 static surface tension γs of the first ink １ and the static surface tension γs of the second ink ２ But, γs １ ≧γs ２ The ink jet recording apparatus is characterized in that the above relationship is satisfied.

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