Inkjet recording method, inkjet recording device and aqueous ink

Abstract

To provide an inkjet recording method capable of suppressing an image unevenness even when recording in a multipath method.SOLUTION: An inkjet recording method records an image in multiple times of reciprocal scanning on a unit area of a storage medium through discharging aqueous ink from a plurality of discharge ports while reciprocally scanning a recording head in a direction intersecting a transportation direction of the recording medium. The recording head includes: a discharge unit having the plurality of discharge ports configured to discharge the aqueous ink, a pressure chamber communicating with the discharge port, and a discharge element arranged at the pressure chamber and configured to generate energy to discharge the aqueous ink from the plurality of discharge ports; and a circulation unit having a supply channel configured to supply the aqueous ink to the pressure chamber of the discharge unit, and a recovery channel configured to recover the aqueous ink from the pressure chamber of the discharge unit. The aqueous ink includes a particle with specific gravity of 3.8 g / cm3 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and a water-based ink. [Background technology]

[0002] In recent years, inkjet recording devices have come to be widely used when outputting advertisements and exhibits using recording media such as paper and resin film. In such applications, images that are eye-catching are required to be recorded, and therefore images that exhibit high color development are required. In order to record high-definition images such as photographic images, a so-called multi-pass recording method is advantageous in which ink is applied to a unit area by repeating the reciprocating scan of a recording head and the transport of a recording medium, and the ink is applied in multiple reciprocating scans.

[0003] Also, in order to improve ejection stability, which is a prerequisite for obtaining high-definition images, a recording head equipped with a mechanism for flowing ink in the vicinity of the ejection ports of the recording head has been proposed (see Patent Document 1). The recording head described in Patent Document 1 is a line-type recording head (line head) in which ejection ports are arranged across the entire width of the recording medium. In order to prevent the ejection stability from becoming unstable when a state in which ink is not ejected from such a recording head continues for a certain period of time, it has been proposed to use an ink containing a specific compound (see Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-118611 A [Patent Document 2] JP 2017-226209 A [Patent Document 3] JP 2017-101232 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have studied various characteristics when the ink circulation in a line head described in Patent Document 1 and the inks described in Patent Documents 2 and 3 are applied to a serial type print head. As a result, it was found that a certain degree of ejection stability can be obtained by using these technologies, but image unevenness occurs due to the use of a serial type print head. It was found that this image unevenness cannot be eliminated even by using the ink circulation described in Patent Document 1.

[0006] It is therefore an object of the present invention to provide an inkjet recording method capable of suppressing image unevenness even when recording is performed by a multi-pass method, and an inkjet recording apparatus and a water-based ink for use in the inkjet recording method. [Means for solving the problem]

[0007] The above object can be achieved by the present invention as described below. That is, the inkjet recording method according to the present invention is an inkjet recording method in which a recording head including: a plurality of ejection ports for ejecting water-based ink, a pressure chamber communicating with the ejection ports, and an ejection unit having an ejection element disposed in the pressure chamber and generating energy for ejecting the water-based ink from the plurality of ejection ports; and a circulation unit having a supply flow path for supplying the water-based ink to the pressure chamber of the ejection unit and a recovery flow path for recovering the water-based ink from the pressure chamber of the ejection unit, is scanned back and forth in a direction intersecting a transport direction of the recording medium, while ejecting the water-based ink from the plurality of ejection ports to record an image on a unit area of ​​the recording medium by scanning back and forth a plurality of times, the water-based ink having a specific gravity of 3.8 g / cm 3 The present invention is characterized in that the particle contains particles having the above properties. Effect of the Invention

[0008] According to the present invention, there is provided an inkjet recording method capable of suppressing image unevenness even when recording is performed by a multi-pass method. According to another embodiment of the present invention, there is provided an inkjet recording apparatus and a water-based ink for use in the inkjet recording method. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an inkjet recording apparatus. [Diagram 2] FIG. 2 is an exploded perspective view of the recording head. [Diagram 3] 3A and 3B are longitudinal and enlarged sectional views of a recording head and a discharge module, respectively. [Figure 4] FIG. 2 is a schematic view showing the appearance of a circulation unit. [Diagram 5] FIG. [Figure 6] FIG. 4 is a block diagram showing a schematic diagram of a circulation path. [Figure 7] FIG. 4 is a cross-sectional view showing an example of a pressure adjusting means. [Figure 8] FIG. 2 is an external perspective view of a circulation pump. [Figure 9] 9 is a cross-sectional view of the circulating pump shown in FIG. 8(a) taken along line IX-IX. [Figure 10] FIG. 2 is a diagram illustrating the flow of ink in a print head. [Figure 11] FIG. 4 is a schematic diagram showing a circulation path in the discharge unit. [Figure 12] FIG. 3 shows an aperture plate 330. [Figure 13] FIG. 2 is a diagram showing an example of a discharge element substrate. [Figure 14] 5A and 5B are cross-sectional views showing the ink flow in the ejection unit. [Figure 15] FIG. 4 is a cross-sectional view showing an example of the vicinity of a discharge port. [Figure 16] FIG. 11 is a cross-sectional view showing another example of the vicinity of the discharge port. [Figure 17] 11A and 11B are diagrams showing other examples of the ejection element substrate. [Figure 18]FIG. 2 is a diagram showing a flow path configuration of a recording head. [Figure 19] FIG. 2 is a diagram showing a connection state between a main body of the inkjet printing apparatus and a print head. [Figure 20] 1A to 1C are schematic diagrams showing differences in image unevenness due to different recording methods. [Figure 21] 5A and 5B are schematic diagrams showing the movement of solid components in the vicinity of a discharge port. [Figure 22] FIG. 2 is a perspective view of a line-shaped recording head. [Figure 23] FIG. 2 is a schematic diagram of an image recorded in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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". Titanium oxide and titanium oxide particles may be simply referred to as "pigment". Furthermore, water-based ink for inkjet printing may be simply referred to as "ink". Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

[0011] The present inventors applied the ink circulation described in Patent Document 1 to a serial type recording head, and investigated the cause of image unevenness when an image was recorded by ejecting ink containing oleic acid as the specific compound described in Patent Document 2 from this recording head. Specifically, the inventors confirmed the phenomenon that occurred near the ejection port of the recording head where image unevenness occurred. It is considered that oleic acid is easily precipitated when liquid components such as water in the ink evaporate, and is oriented in the meniscus part of the liquid surface of the ejection port. Therefore, it is considered that the precipitated oleic acid forms a film in the meniscus part of the ejection port, which suppresses further evaporation of liquid components such as water. As a result, it is considered that the increase in viscosity of the ink near the ejection port can be suppressed, and the decrease in ejection properties can be suppressed.

[0012] However, in reality, due to the influence of a slight increase in the viscosity of the ink and the presence of the film, a loss of ejection energy occurs when ejecting the ink, resulting in a decrease in the volume of the ejected ink droplets. In a recording method using a line head, the application of water-based ink to a unit area is performed by one relative scan of the recording head and the recording medium. Therefore, when a line head is used, the ejection volume per droplet is relatively large compared to the serial method, so even if the volume of the ejected ink droplets is slightly reduced, the effect is negligible. Therefore, even if the volume of the ink droplets is slightly reduced, it is not at a level that can be seen in the image, and image unevenness does not occur. On the other hand, when a serial type recording head is used, the effect of the reduction in the volume of the ink droplets occurs over a wide range, and may occur at a level that is recognized as image unevenness. Below, the phenomenon that occurs when a serial type recording head is used will be explained.

[0013] As shown in FIG. 20(a), an example will be described in which a pattern is printed in which an area (1) (right side of FIG. 20(a)) where a relatively large amount of ink is applied and an area (2) (left side of FIG. 20(a)) where a relatively small amount of ink is applied are adjacent to each other. Here, the print head is scanned in the X direction, and the print medium is transported in the Y direction (FIG. 20(a)). FIG. 20(b) is a schematic diagram showing the ink droplet application positions for printing the pattern of FIG. 20(a). Hereinafter, applying ink to a unit area by n relative scans of the print head and print medium will be described as n-pass printing. When printing by the line method, this is called 1-pass printing, and when printing by the serial method, any number of passes can be set. Increasing the number of printing passes slows down the printing speed, but there is a tendency for ink bleeding to be less likely to occur, so when printing a high-definition image, the number of printing passes is increased.

[0014] When the pattern in FIG. 20(a) is printed in one pass, as shown in FIG. 20(c), at the end of area (2) adjacent to area (1) in the scanning direction of the print head, the application interval is very short and there is almost no variation in the ejection amount. On the other hand, at the end of area (2) not adjacent to area (1) in the scanning direction of the print head, the ink droplet volume is slightly reduced due to the absence of application for a certain period of time, and the first droplet when ejection resumes is easily affected by this. However, the above-mentioned effect only affects the application of the first droplet after the application interval, and when printed in one pass, the affected area is very small and is not easily recognized as image unevenness. 201 in FIG. 20(c) is the affected area.

[0015] Next, consider the case where the above pattern is printed in four passes. The occurrence of ejection defects in the area applied in each printing pass is shown in Fig. 20(d) to (g). In Fig. 20(d) to Fig. 20(g), 201 is the location where the ejection defect occurs. The scanning direction of the print head in each printing pass is also shown by an arrow. Even when printing in four passes, there are areas that are affected by the reduction in the ejection volume. Furthermore, because ink is applied to a unit area by dividing it into multiple reciprocating scans of the print head, the affected area spreads, as is clear from a comparison between Fig. 20(c) and Fig. 20(g). It is believed that band-like image unevenness occurs for these reasons.

[0016] In view of the above phenomenon, the present inventors have investigated the composition of ink to suppress the volume reduction of ink droplets, and have found that the use of ink containing specific particles suppresses the volume reduction of ink droplets and solves the problem of image unevenness.

[0017] That is, the inkjet recording method of the present invention has the following features: First, the recording head is a recording head comprising: a discharge unit having a plurality of discharge ports for discharging water-based ink, a pressure chamber communicating with the discharge ports, and discharge elements disposed in the pressure chamber and generating energy for discharging the water-based ink from the plurality of discharge ports; and a circulation unit having a supply flow path for supplying water-based ink to the pressure chamber of the discharge unit and a recovery flow path for recovering the water-based ink from the pressure chamber of the discharge unit. The specific gravity of the water-based ink is 3.8 g / cm. 3 The recording head is scanned back and forth in a direction intersecting the transport direction of the recording medium, and the water-based ink is ejected onto a unit area of ​​the recording medium by a plurality of back and forth scans to record an image.

[0018] The inventors speculate that the mechanism by which the above configuration can suppress image unevenness is as follows: The print head includes a plurality of ejection ports for ejecting water-based ink, a pressure chamber communicating with the ejection ports, an ejection unit having ejection elements disposed in the pressure chamber and generating energy for ejecting the water-based ink from the plurality of ejection ports, and a circulation unit having a supply flow path for supplying water-based ink to the pressure chamber of the ejection unit, and a recovery flow path for recovering the water-based ink from the pressure chamber of the ejection unit. By using the above print head, it is possible to suppress a decrease in ejection stability due to localized evaporation of ink.

[0019] Water-based ink has a specific gravity of 3.8g / cm 3 The ink contains particles having a specific gravity of 0.01 to 0.01. These particles have a particularly high specific gravity among the components added to aqueous inkjet inks. Hereinafter, these particles will also be referred to as high specific gravity particles. When the recording head scans back and forth, inertial force acts on the high specific gravity particles during acceleration and deceleration during the back and forth scan, and the ink is thoroughly agitated. As a result, it is believed that image unevenness that could not be suppressed by ink circulation alone can be suppressed.

[0020] The mechanism of ink agitation by high specific gravity particles, which characterizes the present invention, will be described in detail below with reference to FIG. 21. FIG. 21(a) is a schematic diagram showing how high specific gravity particles in a flow path are agitated by reciprocating scanning of a carriage on which a recording head is arranged. The flow path 17 communicates with a pressure chamber 12 which corresponds to an area between the ejection port 1 and the ejection element 4. Here, an ink containing color material 13 and resin particles 14 as solid components in addition to high specific gravity particles 15 will be described as an example. Due to the circulation of the ink, the ink containing solid components flows in the pressure chamber 12 and flow path 17 in the direction indicated by 18.

[0021] When the ink continues to circulate, the solid components in the ink tend to remain in the area where the ink flow is relatively slow, such as the ejection port periphery 19. As a result, the concentration of the solid components in the ejection port periphery 19 increases, the viscosity increases locally, and the volume of the ink droplets decreases. On the other hand, as shown in FIG. 21(b), after the recording head scans in the forward direction, the carriage scans in the reverse direction (return direction) on the return path, so the direction of acceleration is exactly the opposite. Therefore, a force (inertia force) acts on the solid components in the ink in a direction that slows down the moving speed of the carriage. As a result, the solid components in the ink collide with the wall surface of the ejection port periphery 19. Among the solid components, the high specific gravity particles 15 are subject to a large impact due to the collision, and the ink around the ejection port can be sufficiently stirred. As a result, the increase in the viscosity of the ink around the ejection port is suppressed, and image unevenness can be suppressed.

[0022] If the water-based ink does not contain the high specific gravity particles as described above, the ink around the ejection port is not sufficiently stirred even if the ink is circulated or the ink is scanned back and forth, and image unevenness cannot be suppressed. Also, if the recording head is a line head, image unevenness cannot be recognized in the first place even if the ink is not scanned back and forth.

[0023] <Inkjet recording method, inkjet recording apparatus, and water-based ink> The inkjet recording method of the present invention is a method for ejecting water-based ink from an inkjet recording head by the action of thermal energy and applying it to a recording medium to record an image. The recording head includes a plurality of ejection ports for ejecting the water-based ink, a pressure chamber communicating with the ejection ports, an ejection unit having an ejection element disposed in the pressure chamber and generating energy for ejecting the water-based ink from the plurality of ejection ports, and a circulation unit having a supply flow path for supplying the water-based ink to the pressure chamber of the ejection unit and a recovery flow path for recovering the water-based ink from the pressure chamber of the ejection unit. The water-based ink is ejected from the plurality of ejection ports while scanning the recording head in a direction intersecting the transport direction of the recording medium, to record an image by performing a plurality of reciprocating scans on a unit area of ​​the recording medium. The water-based ink has a specific gravity of 3.8 g / cm.3 In the present invention, it is not necessary to provide a step of curing the image by irradiating it with active energy rays or the like.

[0024] The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which a water-based ink is ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image. The inkjet recording apparatus of the present invention is an apparatus that is suitably used in the above-mentioned recording method.

[0025] The aqueous ink of the present invention is an aqueous ink used in an inkjet recording method in which the ink is ejected from an inkjet recording head and applied to a recording medium to record an image, and is an aqueous ink that is suitably used in the above recording method.

[0026] The inkjet recording method and inkjet recording apparatus (hereinafter, simply referred to as "recording method and recording apparatus") of the present invention will be described in detail below. Here, in the following preferred embodiment, an example will be described in which a thermal method is adopted in which an electrothermal conversion element is used as an ejection element for ejecting ink to generate air bubbles, but the present invention is not limited to this. For example, the present invention can also be applied to a recording head that employs an ejection method that ejects ink using a piezoelectric element (piezo), or another ejection method. Furthermore, the pump and pressure adjustment means described below are not limited to the configurations shown in the preferred embodiment and drawings.

[0027] Fig. 1 is a diagram for explaining an inkjet recording apparatus, and is an enlarged view of a recording head of the inkjet recording apparatus and its surroundings. First, a schematic configuration of an inkjet recording apparatus 50 in this embodiment will be described with reference to Fig. 1. Fig. 1(a) is a perspective view that shows a schematic inkjet recording apparatus that uses a recording head 1. The inkjet recording apparatus 50 in this embodiment constitutes a serial type inkjet recording apparatus that performs recording on a recording medium P by ejecting ink as a liquid while scanning the recording head 1.

[0028] The recording head 1 is mounted on a carriage 60. The carriage 60 reciprocates along a guide shaft 51 in a main scanning direction (X direction). The recording medium P is transported by transport rollers 55, 56, 57, and 58 in a sub-scanning direction (Y direction) that intersects (orthogonal in this example) the main scanning direction. In each of the figures referred to below, the Z direction indicates the vertical direction, and intersects (orthogonal in this example) the XY plane defined by the X and Y directions. The recording head 1 is configured to be removable and attachable to the carriage 60 by the user.

[0029] The recording head 1 includes a circulation unit 54 and a discharge unit 3 (see FIG. 2) described later. The specific configuration will be described later, but the discharge unit 3 is provided with a plurality of discharge ports and energy generating elements (hereinafter referred to as discharge elements) that generate discharge energy for discharging ink from each discharge port.

[0030] The recording head 1 may be provided with a mechanism (temperature control mechanism) for heating the water-based ink ejected from the recording head. When the temperature control mechanism is provided, the heating temperature of the ink ejected from the recording head is preferably set to 35° C. or higher and 70° C. or lower.

[0031] The inkjet recording device 50 is also provided with an ink tank 2, which is an ink supply source, and an external pump 21, and the ink stored in the ink tank 2 is supplied to a circulation unit 54 via an ink supply tube 59 by the driving force of the external pump 21.

[0032] The inkjet recording device 50 records a predetermined image on the recording medium P by repeating a recording scan in which the recording head 1 mounted on the carriage 60 moves in the main scanning direction while ejecting ink to perform recording, and a transport operation in which the recording medium P is transported in the sub-scanning direction. That is, the recording head 1 is scanned back and forth in a direction intersecting the transport direction of the recording medium, and an image is recorded by ejecting water-based ink in a unit area of ​​the recording medium by multiple back and forth scans. Here, the unit area can be set as any area such as one pixel or one band. Note that the recording head 1 in this embodiment is capable of ejecting four types of ink, namely black (K), cyan (C), magenta (M), and yellow (Y), and full-color images can be recorded using these inks. However, the ink that can be ejected from the recording head 1 is not limited to the above four types of ink. The present disclosure is also applicable to a recording head for ejecting other types of ink. That is, the type and number of inks ejected from the recording head are not limited. Among them, white (W) ink using titanium oxide as a high specific gravity particle as a coloring material is preferable. Titanium oxide has a large particle size to achieve whiteness, and has a larger specific gravity than colorants typically used in inks. Even with such inks, image unevenness can be suppressed by using the recording head described above.

[0033] The moving speed of the recording head in reciprocating scanning (scanning speed, inches / s) is preferably 20 inches / s or more. More specifically, when recording, the speed at which the recording head moves relative to the recording medium P is preferably 20 inches / s or more. If the scanning speed is less than 20 inches / s, the inertial force acting on the high specific gravity particles becomes small and the ejection intervals become more likely to be large, so that image unevenness may not be sufficiently suppressed. The scanning speed is preferably 100 inches / s or less, and more preferably 80 inches / s or less. If the scanning speed exceeds 100 inches / s, ink foaming is likely to become significant, and ejection stability may not be sufficiently obtained. As a result, image unevenness may not be sufficiently suppressed.

[0034] Furthermore, the inkjet recording device 50 is provided with a cap member (not shown) capable of covering the ejection port surface on which the ejection ports of the recording head are formed, at a position offset in the X direction from the transport path of the recording medium P. The cap member covers the ejection port surface of the recording head 1 during non-recording operations, and is used to prevent the ejection ports from drying, to protect the ejection ports, and to suck ink from the ejection ports.

[0035] The recording head 1 shown in Fig. 1(a) shows an example in which the recording head 1 is provided with four circulation units 54 corresponding to four types of ink, but it is sufficient that the recording head 1 is provided with a circulation unit 54 corresponding to the type of ink to be ejected. Also, multiple circulation units 54 may be provided for the same type of ink. In other words, the recording head 1 can be configured to include one or more circulation units. It is also possible to have a configuration in which at least one ink is circulated rather than circulating all four types of ink.

[0036] FIG. 1B is a block diagram showing a control system of the inkjet recording apparatus 50. The CPU 103 functions as a control means for controlling the operation of each part of the inkjet recording apparatus 50 based on a program such as a processing procedure stored in the ROM 101. The RAM 102 is used as a work area when the CPU 103 executes processing. The CPU 103 receives image data from a host device 400 outside the inkjet recording apparatus 50, controls the head driver 1A, and controls the driving of the discharge elements provided in the discharge unit 3. The CPU 103 also controls the drivers of various actuators provided in the inkjet recording apparatus. For example, the CPU 103 controls a motor driver 105A of a carriage motor 105 for moving the carriage 60, and a motor driver 104A of a conveying motor 104 for conveying the recording medium P. The CPU 103 also controls a pump driver 500A for driving a circulation pump 500 described later, a pump driver 21A of an external pump 21, and the like. Although FIG. 1B shows a form in which processing is performed when image data is received from the host device 400, processing may be performed in the inkjet recording apparatus 50 independently of data from the host device 400.

[0037] <Basic configuration of recording head> Fig. 2 is an exploded perspective view of the recording head 1 of this embodiment. Fig. 3 is a cross-sectional view of the recording head 1 shown in Fig. 2 taken along line IIIA-IIIA. Fig. 3(a) is an overall vertical cross-sectional view of the recording head 1, and Fig. 3(b) is an enlarged view of the ejection module shown in Fig. 3(a). The basic configuration of the recording head 1 of this embodiment will be described below, mainly with reference to Fig. 2 and Fig. 3, and with appropriate reference to Fig. 1.

[0038] 2, the recording head 1 includes a circulation unit 54 and an ejection unit 3 for ejecting ink supplied from the circulation unit 54 onto a recording medium P. The recording head 1 in this embodiment is fixedly supported on a carriage 60 of an inkjet recording device 50 by positioning means and electrical contacts (not shown) provided on the carriage 60. The recording head 1 ejects ink while moving together with the carriage 60 in the main scanning direction (X direction) shown in FIG. 1, and performs recording on the recording medium P.

[0039] An ink supply tube 59 is provided on the external pump 21 connected to the ink tank 2 serving as the ink supply source (see FIG. 1). A liquid connector (not shown) is provided on the tip of the ink supply tube 59. When the recording head 1 is mounted on the inkjet recording device 50, the liquid connector provided on the tip of the ink supply tube 59 is airtightly connected to a liquid connector insertion port 53a, which is an ink inlet port provided on the head housing 53 of the recording head 1. As a result, an ink supply path is formed from the ink tank 2 to the recording head 1 via the external pump 21. In this embodiment, since four types of ink are used, four sets of the ink tank 2, the external pump 21, the ink supply tube 59, and the circulation unit 54 are provided corresponding to each ink, and four ink supply paths corresponding to each ink are independently formed. In this way, the inkjet recording device 50 of this embodiment is provided with an ink supply system to which ink is supplied from the ink tank 2 provided outside the recording head 1. Note that the inkjet recording device 50 of this embodiment is not provided with an ink recovery system that recovers the ink in the recording head 1 to the ink tank 2. Therefore, the recording head 1 is provided with a liquid connector insertion port 53a for connecting an ink supply tube 59 of the ink tank 2, but is not provided with a connector insertion port for connecting a tube for recovering the ink of the recording head 1 to the ink tank 2. A liquid connector insertion port 53a is provided for each ink.

[0040] 3, 54B indicates a circulation unit for black ink, 54C indicates a circulation unit for cyan ink, 54M indicates a circulation unit for magenta ink, and 54Y indicates an ink circulation unit for yellow ink. Each circulation unit has substantially the same configuration, and in this embodiment, when there is no need to distinguish between the circulation units, they are all referred to as circulation unit 54.

[0041] 2 and 3(a), the discharge unit 3 includes two discharge modules 300, a first support member 4, a second support member 7, an electric wiring member (electric wiring tape) 5, and an electric contact substrate 6. As shown in FIG. 3(b), the discharge module 300 includes a silicon substrate 310 having a thickness of 0.5 to 1 mm, and a plurality of discharge elements 15 provided on one side of the silicon substrate 310. In this embodiment, the discharge elements 15 are configured by electrothermal conversion elements (heaters) that generate thermal energy as discharge energy for discharging ink. Electric power is supplied to each discharge element 15 via electric wiring formed on the silicon substrate 310 by a film formation technique.

[0042] Further, an ejection port forming member 320 is formed on the surface (lower surface in FIG. 3(b)) of the silicon substrate 310. In the ejection port forming member 320, a plurality of pressure chambers 12 corresponding to a plurality of ejection elements 15 and a plurality of ejection ports 13 for ejecting ink are formed by photolithography. Furthermore, a common supply flow path 18 and a common recovery flow path 19 are formed in the silicon substrate 310. Further, in the silicon substrate 310, a supply connection flow path 323 that communicates the common supply flow path 18 with each pressure chamber 12, and a recovery connection flow path 324 that communicates the common recovery flow path 19 with each pressure chamber 12 are formed. In this embodiment, one ejection module 300 is configured to eject two types of ink. That is, of the two ejection modules shown in FIG. 3(a), the ejection module 300 located on the left side of the figure ejects black ink and cyan ink, and the ejection module 300 located on the right side of the figure ejects magenta ink and yellow ink. Note that this combination is an example, and any combination of inks may be used. One ejection module may be configured to eject one type of ink, or may be configured to eject three or more types of ink. The two ejection modules 300 do not have to eject the same number of types of ink. One ejection module 300 may be provided, or may be configured to include three or more ejection modules 300. Furthermore, in the example shown in FIG. 3, two ejection port arrays extending in the Y direction are formed for one color of ink. A pressure chamber 12, a common supply flow path 18, and a common recovery flow path 19 are formed for each of the multiple ejection ports 13 that constitute each ejection port array.

[0043] An ink supply port and an ink recovery port, which will be described later, are formed on the back surface (upper surface in FIG. 3(b)) of the silicon substrate 310. The ink supply port supplies ink from an ink supply flow path 48 to the multiple common supply flow paths 18, and the ink recovery port recovers ink from the multiple common recovery flow paths 19 to an ink recovery flow path 49.

[0044] The ink supply port and ink recovery port referred to here refer to openings that supply and recover ink during forward ink circulation, which will be described later. That is, during forward ink circulation, ink is supplied from the ink supply port to each common supply flow path 18, and ink is recovered from each common recovery flow path 19 to the ink recovery port. However, ink may also be circulated in the reverse direction. In this case, ink is supplied from the ink recovery port described above to the common recovery flow path 19, and ink is recovered from the common supply flow path 18 to the ink supply port.

[0045] As shown in FIG. 3(a), the back surface (upper surface in FIG. 3(a)) of the ejection module 300 is adhesively fixed to one surface (lower surface in FIG. 3(a)) of the first support member 4. An ink supply flow path 48 and an ink recovery flow path 49 are formed in the first support member 4, penetrating from one surface to the other surface. One opening of the ink supply flow path 48 communicates with the ink supply port in the silicon substrate 310, and one opening of the ink recovery flow path 49 communicates with the ink recovery port in the silicon substrate 310. The ink supply flow path 48 and the ink recovery flow path 49 are provided independently for each type of ink.

[0046] A second support member 7 having an opening 7a (see FIG. 2) through which the ejection module 300 is inserted is adhesively fixed to one surface of the first support member 4 (the upper surface in FIG. 3(a)). The second support member 7 holds an electrical wiring member 5 that is electrically connected to the ejection module 300. The electrical wiring member 5 is a member for applying an electrical signal to the ejection module 300 to eject ink. The electrical connection portion between the ejection module 300 and the electrical wiring member 5 is sealed with a sealant (not shown) and is protected from corrosion by ink and external impacts.

[0047] In addition, an electrical contact board 6 is thermocompression-bonded to an end 5a (see FIG. 2) of the electrical wiring member 5 using an anisotropic conductive film (not shown), and the electrical wiring member 5 and the electrical contact board 6 are electrically connected. The electrical contact board 6 has an external signal input terminal (not shown) for receiving an electrical signal from the inkjet recording device 50.

[0048] Furthermore, a joint member 8 (FIG. 3(a)) is provided between the first support member 4 and the circulation unit 54. A supply port 88 and a recovery port 89 are formed in the joint member 8 for each type of ink. The supply port 88 and the recovery port 89 communicate the ink supply flow path 48 and the ink recovery flow path 49 of the first support member 4 with the flow paths formed in the circulation unit 54. In FIG. 3(a), the supply port 88B and the recovery port 89B correspond to black ink, and the supply port 88C and the recovery port 89C correspond to cyan ink. Furthermore, the supply port 88M and the recovery port 89M correspond to magenta ink, and the supply port 88Y and the recovery port 89Y correspond to yellow ink.

[0049] The openings at one end of each of the ink supply flow passage 48 and the ink recovery flow passage 49 of the first support member 4 have a small opening area that matches the ink supply port and the ink recovery port in the silicon substrate 310. In contrast, the openings at the other end of each of the ink supply flow passage 48 and the ink recovery flow passage 49 of the first support member 4 have a shape that is expanded to the same opening area as the large opening area of ​​the joint member 8 formed to match the flow passage of the circulation unit 54. By adopting such a configuration, it is possible to suppress an increase in flow passage resistance to the ink collected from each recovery flow passage. However, the shapes of the openings at one end and the other end of each of the ink supply flow passage 48 and the ink recovery flow passage 49 are not limited to the above example.

[0050] In the recording head 1 having the above configuration, ink supplied to the circulation unit 54 passes through the supply port 88 of the joint member 8 and the ink supply flow path 48 of the first support member 4, and flows from the ink supply port of the ejection module 300 into the common supply flow path 18. The ink then flows from the common supply flow path 18 into the pressure chamber 12 through the supply connection flow path 323, and a portion of the ink that has flowed into the pressure chamber is ejected from the ejection port 13 by driving the ejection element 15. The remaining ink that has not been ejected passes from the pressure chamber 12 through the recovery connection flow path 324 and the common recovery flow path 19, and flows from the ink recovery port into the ink recovery flow path 49 of the first support member 4. The ink that has flowed into the ink recovery flow path 49 then flows into the circulation unit 54 through the recovery port 89 of the joint member 8, and is recovered.

[0051] <Components of the circulation unit> 4 is a schematic external view of one circulation unit 54 corresponding to one type of ink applied to the recording apparatus of this embodiment. In addition to the circulation pump 500, the circulation unit 54 preferably has a filter 110, a first pressure adjustment means 120, and a second pressure adjustment means 150. These components are connected by respective flow paths as shown in FIG. 5 and FIG. 6, and constitute a circulation path for supplying and recovering ink to the ejection module 300 in the recording head 1. The recording head 1 preferably has a circulation pump 500 that causes ink from the recovery flow path to flow into the supply flow path. In other words, the recording head 1 having the circulation pump is preferably fixed and supported on the carriage 60.

[0052] <Circulation path inside the recording head> FIG. 5 is a vertical cross-sectional view showing a circulation path of one type of ink (one color ink) in the recording head 1. In order to explain the circulation path more clearly, the relative positions of each component (first pressure adjustment means 120, second pressure adjustment means 150, circulation pump 500, etc.) in FIG. 5 are simplified. Therefore, the relative positions of each component are different from the configuration in FIG. 19 described later. FIG. 6 is a block diagram showing the circulation path shown in FIG. 5. As shown in FIG. 5 and FIG. 6, the first pressure adjustment means 120 includes a first valve chamber 121 and a first pressure control chamber 122. The second pressure adjustment means 150 includes a second valve chamber 151 and a second pressure control chamber 152. The first pressure adjustment means 120 is configured to have a relatively higher control pressure than the second pressure adjustment means 150. In this embodiment, the two pressure adjustment means 120 and 150 are used to achieve circulation within a certain pressure range in the circulation path. Also, the ink is configured to flow through the pressure chamber 12 (ejection element 15) at a flow rate according to the pressure difference between the first pressure adjustment means 120 and the second pressure adjustment means 150. Below, the circulation path in the recording head 1 and the flow of ink within the circulation path will be described with reference to Figures 5 and 6. The arrows in each figure indicate the direction of ink flow.

[0053] First, the connection state of each component in the recording head 1 will be described.

[0054] An external pump 21 that sends ink contained in an ink tank 2 (FIG. 6) provided outside the recording head 1 to the recording head 1 is connected to a circulation unit 54 via an ink supply tube 59 (FIG. 1). A filter 110 is provided in an ink flow path (inflow flow path) located upstream of the circulation unit 54. An ink supply path (inflow flow path) located downstream of the filter 110 is connected to a first valve chamber 121 of a first pressure adjustment means 120. The first valve chamber 121 communicates with a first pressure control chamber 122 via a first communication port 191A that can be opened and closed by a first valve 190A shown in FIG. 5. The inflow flow path is a flow path through which ink in an ink tank 2 provided outside the recording head 1 flows into the recording head 1 to be supplied to the pressure chamber 12.

[0055] The first pressure control chamber 122 is connected to the supply flow path 130, the bypass flow path 160, and the pump outlet flow path 180 of the circulation pump 500. The supply flow path 130 is connected to the common supply flow path 18 via the ink supply port provided in the ejection module 300. The bypass flow path 160 is connected to a second valve chamber 151 provided in the second pressure adjustment means 150. The second valve chamber 151 is connected to the second pressure control chamber 152 via a second communication port 191B that is opened and closed by a second valve 190B shown in FIG. 5. FIGS. 5 and 6 show an example in which one end of the bypass flow path 160 is connected to the first pressure control chamber 122 of the first pressure adjustment means 120, and the other end of the bypass flow path 160 is connected to the second valve chamber 151 of the second pressure adjustment means 150. One end of the bypass flow path 160 may be connected to the supply flow path 130, and the other end of the bypass flow path may be connected to the second valve chamber 151.

[0056] The second pressure control chamber 152 is connected to the recovery flow path 140. The recovery flow path 140 is connected to the common recovery flow path 19 via the ink recovery port provided in the ejection module 300. Furthermore, the second pressure control chamber 152 is connected to the circulation pump 500 via a pump inlet flow path 170. In FIG. 5, 170a denotes the inlet of the pump inlet flow path 170.

[0057] Next, a description will be given of the flow of ink in the recording head 1 having the above configuration. As shown in Fig. 6, the ink contained in the ink tank 2 is pressurized by an external pump 21 provided in the inkjet recording device 50, and is supplied to the circulation unit 54 of the recording head 1 as a positive pressure ink flow.

[0058] The ink supplied to the circulation unit 54 passes through the filter 110 to remove foreign matter such as dust and air bubbles, and then flows into the first valve chamber 121 provided in the first pressure adjustment means 120. The ink pressure decreases due to pressure loss when passing through the filter 110, but the ink pressure at this stage is positive. The ink that has flowed into the first valve chamber 121 then passes through the first communication port 191A and flows into the first pressure control chamber 122 when the first valve 190A is in the open state. Due to pressure loss when passing through the first communication port 191A, the ink that has flowed into the first pressure control chamber 122 switches from positive pressure to negative pressure.

[0059] Here, the pore size (μm) of the filter 110 is preferably 1 μm or more and 10 μm or less. If the pore size is less than 1 μm, particles such as coloring materials in the ink with a particle diameter of 1 μm or less will also be collected, and stable supply of the ink may not be sufficiently maintained. As a result, image unevenness may not be sufficiently suppressed. On the other hand, if the pore size exceeds 10 μm, it becomes difficult to remove impurities such as coarse particles in the ink. As a result, the above-mentioned impurities are likely to enter the ink flow path, and ejection stability may not be sufficiently obtained. As a result, image unevenness may not be sufficiently suppressed.

[0060] In order to suppress localized evaporation of the ink, the flow rate of the aqueous ink in the circulation path (circulation flow rate, mm / s) is preferably 10 mm / s or more and 30 mm / s or less. The circulation flow rate refers to the flow rate of the aqueous ink circulating in the circulation path. The circulation path refers to the region from the supply flow path to the recovery flow path. In the examples described later, the flow rate of the aqueous ink in the circulation path did not change even near the meniscus of the ejection port. If the circulation flow rate is less than 10 mm / s, ejection stability is likely to deteriorate due to the influence of localized evaporation of the ink. In addition, the circulation flow does not reach the vicinity of the ejection port sufficiently, and solid components are likely to remain. As a result, image unevenness in intermittent ejection may not be sufficiently suppressed. On the other hand, if the circulation flow rate is 30 mm / s or more, the change in the ejection amount of the ink becomes large when ejecting continuously, and normal ejection may not be performed. As a result, image unevenness in intermittent ejection may not be sufficiently suppressed. The circulation flow rate can be simply controlled by adjusting the difference between the pressure in the supply flow path and the pressure in the recovery flow path. In the examples described later, the circulation flow rate was adjusted by controlling the pressure in the first pressure control chamber 122 and the second pressure control chamber 152. In addition, it is preferable that the difference between the circulation flow rate and the scanning speed is large for the effect of stirring the ink near the ejection port by the high specific gravity particles in the present invention.

[0061] Next, the flow of ink in the circulation path will be described. The circulation pump 500 operates to pump ink sucked from the pump inlet flow path 170 on the upstream side to the pump outlet flow path 180 on the downstream side. Therefore, when the pump is driven, the ink supplied to the first pressure control chamber 122 flows into the supply flow path 130 and the bypass flow path 160 together with the ink sent from the pump outlet flow path 180. Although details will be described later, in this embodiment, a piezoelectric diaphragm pump using a piezoelectric element attached to a diaphragm as a drive source is used as a circulation pump capable of sending liquid. The piezoelectric diaphragm pump is a pump that changes the volume of the pump chamber by inputting a drive voltage to a piezoelectric element, and sends liquid by alternately moving two check valves due to pressure fluctuations.

[0062] The ink that has flowed into the supply flow channel 130 flows from the ink supply port of the ejection module 300 through the common supply flow channel 18 into the pressure chamber 12, and some of the ink is ejected from the ejection port 13 by driving (heat generation) the ejection element 15. The remaining ink that has not been used for ejection flows through the pressure chamber 12, passes through the common recovery flow channel 19, and then flows into the recovery flow channel 140 connected to the ejection module 300. The ink that has flowed into the recovery flow channel 140 flows into the second pressure control chamber 152 of the second pressure adjustment means 150.

[0063] On the other hand, the ink that has flowed from the first pressure control chamber 122 into the bypass flow path 160 flows into the second valve chamber 151, and then passes through the second communication port 191B and flows into the second pressure control chamber 152. The ink that has flowed into the second pressure control chamber 152 via the bypass flow path 160 and the ink that has been recovered from the recovery flow path 140 are sucked into the circulation pump 500 via the pump inlet flow path 170 by the operation of the circulation pump 500. Then, the ink that has been sucked into the circulation pump 500 is sent to the pump outlet flow path 180 and flows into the first pressure control chamber 122 again. Thereafter, the ink that has flowed into the second pressure control chamber 152 from the first pressure control chamber 122 via the supply flow path 130 through the ejection module 300 and the ink that has flowed into the second pressure control chamber 152 via the bypass flow path 160 flows into the circulation pump 500. Then, the ink is sent from the circulation pump 500 to the first pressure control chamber 122. In this manner, the ink is circulated in the circulation path.

[0064] As described above, in this embodiment, the circulation pump 500 can circulate the ink along the circulation path formed in the recording head 1. This makes it possible to suppress thickening of the ink and accumulation of ink sedimentation components (solid components) such as coloring materials in the ejection module 300, and makes it possible to maintain good ink fluidity in the ejection module 300 and ejection characteristics at the ejection ports.

[0065] The circulation path in this embodiment is configured to be completed within the print head 1, so the length of the circulation path can be significantly shortened compared to when ink is circulated between the print head 1 and an ink tank 2 provided outside the print head. This makes it possible to circulate the ink with a small circulation pump.

[0066] Furthermore, the connection flow path between the recording head 1 and the ink tank 2 is configured to include only a flow path for supplying ink. In other words, a configuration is adopted in which a flow path for recovering ink from the recording head 1 to the ink tank 2 is not required. Therefore, only a tube for supplying ink is required to connect the ink tank 2 to the recording head 1, and no tube for recovering ink is required. Therefore, the inside of the inkjet recording device 50 can be simplified with a reduced number of tubes, and the entire device can be made compact. Furthermore, by reducing the number of tubes, it is possible to reduce the pressure fluctuation of the ink caused by the oscillation of the tubes accompanying the main scanning of the recording head 1. In addition, the oscillation of the tubes during the main scanning of the recording head 1 becomes a driving load of the carriage motor that drives the carriage 60. Therefore, by reducing the number of tubes, the driving load of the carriage motor is reduced, and it is possible to simplify the main scanning mechanism including the carriage motor. Furthermore, since it is not necessary to recover ink from the recording head to the ink tank, the external pump 21 can also be made compact. Thus, according to this embodiment, it is possible to reduce the size and cost of the inkjet recording device 50.

[0067] <Pressure Adjustment Means> FIG. 7 is a diagram showing an example of a pressure adjusting means. The configuration and operation of the pressure adjusting means (first pressure adjusting means 120, second pressure adjusting means 150) built into the above-mentioned recording head 1 will be described in more detail with reference to FIG. 7. The first pressure adjusting means 120 and the second pressure adjusting means 150 have substantially the same configuration. For this reason, the first pressure adjusting means 120 will be described below as an example, and the second pressure adjusting means 150 will only be described with the reference numerals of the parts corresponding to the first pressure adjusting means in FIG. 7. In the case of the second pressure adjusting means 150, the first valve chamber 121 described below will be read as the second valve chamber 151, and the first pressure control chamber 122 will be read as the second pressure control chamber 152.

[0068] The first pressure adjustment means 120 has a first valve chamber 121 and a first pressure control chamber 122 formed in a cylindrical housing 125. The first valve chamber 121 and the first pressure control chamber 122 are separated by a partition wall 123 provided in the cylindrical housing 125. However, the first valve chamber 121 communicates with the first pressure control chamber 122 through a communication port 191 formed in the partition wall 123. The first valve chamber 121 is provided with a valve 190 that switches between communication and blocking between the first valve chamber 121 and the first pressure control chamber 122 at the communication port 191. The valve 190 is held at a position facing the communication port 191 by a valve spring 200, and has a configuration that allows it to come into close contact with the partition wall 123 by the biasing force of the valve spring 200. When the valve 190 comes into close contact with the partition wall 123, the flow of ink through the communication port 191 is blocked. To increase the close contact with the partition 123, it is preferable that the portion of the valve 190 that comes into contact with the partition 123 is made of an elastic material. Furthermore, a valve shaft 190a that is inserted into the communication port 191 protrudes from the center of the valve 190. By pressing this valve shaft 190a against the biasing force of a valve spring 200, the valve 190 moves away from the partition 123, allowing ink to flow through the communication port 191. Hereinafter, the state in which the valve 190 blocks the flow of ink through the communication port 191 is referred to as the "closed state," and the state in which ink can flow through the communication port 191 is referred to as the "open state."

[0069] The opening of the cylindrical housing 125 is closed by the flexible member 230 and the pressure plate 210. The first pressure control chamber 122 is formed by the flexible member 230, the pressure plate 210, the peripheral wall of the housing 125, and the partition wall 123. The pressure plate 210 is configured to be displaceable in accordance with the displacement of the flexible member 230. The materials of the pressure plate 210 and the flexible member 230 are not particularly limited, but for example, the pressure plate 210 can be configured from a resin molded part, and the flexible member 230 can be configured from a resin film. In this case, the pressure plate 210 can be fixed to the flexible member 230 by thermal welding.

[0070] A pressure adjustment spring 220 (biasing member) is provided between the pressure plate 210 and the partition wall 123. The pressure plate 210 and the flexible member 230 are biased by the biasing force of the pressure adjustment spring 220 in a direction in which the internal volume of the first pressure control chamber 122 expands, as shown in FIG. 7(a). When the pressure in the first pressure control chamber 122 decreases, the pressure plate 210 and the flexible member 230 are displaced in a direction in which the internal volume of the first pressure control chamber 122 decreases against the pressure of the pressure adjustment spring 220. When the internal volume of the first pressure control chamber 122 decreases to a certain amount, the pressure plate 210 abuts against the valve shaft 190a of the valve 190. When the internal volume of the first pressure control chamber 122 further decreases thereafter, the valve 190 moves together with the valve shaft 190a against the biasing force of the valve spring 200, and moves away from the partition wall 123. As a result, the communication port 191 is in an open state (the state shown in FIG. 7(b)).

[0071] In this embodiment, the connection in the circulation path is set so that the pressure in the first valve chamber 121 when the communication port 191 is in the open state is higher than the pressure in the first pressure control chamber 122. As a result, when the communication port 191 is in the open state, ink flows from the first valve chamber 121 to the first pressure control chamber 122. This ink flow causes the flexible member 230 and the pressure plate 210 to be displaced in a direction in which the internal volume of the first pressure control chamber 122 increases. As a result, the pressure plate 210 moves away from the valve shaft 190a of the valve 190, and the valve 190 is brought into close contact with the partition wall 123 by the biasing force of the valve spring 200, and the communication port 191 is in the closed state (the state of FIG. 7(c)).

[0072] In this manner, in the first pressure adjustment means 120 of this embodiment, when the pressure in the first pressure control chamber 122 decreases to a certain pressure or below (for example, when the negative pressure becomes stronger), ink flows in from the first valve chamber 121 via the communication port 191. This prevents the pressure in the first pressure control chamber 122 from decreasing any further. Therefore, the pressure in the first pressure control chamber 122 is controlled to be kept within a certain range.

[0073] Next, the pressure in the first pressure control chamber 122 will be described in more detail. As described above, the flexible member 230 and the pressure plate 210 are displaced in response to the pressure in the first pressure control chamber 122, and the pressure plate 210 comes into contact with the valve shaft 190a, opening the communication port 191 (as shown in FIG. 7(b)). At this time, the relationship of the forces acting on the pressure plate 210 is expressed by the following formula 1. P2×S2+F2+(P1-P2)×S1+F1=0...Equation 1

[0074] Furthermore, when equation 1 is rearranged for P2, it becomes as follows. P2=-(F1+F2+P1×S1) / (S2-S1)...Equation 2 P1: Pressure (gauge pressure) of the first valve chamber 121 P2: Pressure (gauge pressure) of the first pressure control chamber 122 F1: Valve spring force 200 F2: Spring force of the pressure adjusting spring 220 S1: Pressure receiving area of ​​valve 190 S2: Pressure receiving area of ​​the pressure plate 210

[0075] Here, the spring force F1 of the valve spring 200 and the spring force F2 of the pressure adjustment spring 220 are positive (leftward in FIG. 7) in the direction pressing the valve 190 and the pressure plate 210. In addition, the pressure P1 in the first valve chamber 121 and the pressure P2 in the first pressure control chamber 122 are configured so that P1 satisfies the relationship P1≧P2.

[0076] The pressure P2 in the first pressure control chamber 122 when the communication port 191 is open is determined by formula 2, and when the communication port 191 is open, due to the relationship P1≧P2, ink flows from the first valve chamber 121 into the first pressure control chamber 122. As a result, the pressure P2 in the first pressure control chamber 122 does not decrease any further, and P2 is maintained within a certain pressure range.

[0077] On the other hand, as shown in FIG. 7(c), when the pressure plate 210 is not in contact with the valve shaft 190a and the communication port 191 is closed, the relationship of the forces acting on the pressure plate 210 is expressed by Equation 3. P3×S3+F3=0...Equation 3

[0078] Here, if we rearrange Equation 3 for P3, we get the following: P3 = -F3 / S3 Equation 4 F3: The spring force of the pressure adjusting spring 220 when the pressure plate 210 and the valve shaft 190a are not in contact with each other P3: pressure (gauge pressure) in the first pressure control chamber 122 when the pressure plate 210 and the valve shaft 190a are not in contact with each other S3: The pressure-receiving area of ​​the pressure plate 210 when the pressure plate 210 and the valve 190 are not in contact with each other

[0079] Here, FIG. 7(c) shows a state in which the pressure plate 210 and the flexible member 230 are displaced to the right side of the figure to the limit of their displacement. The pressure P3 in the first pressure control chamber 122, the spring force F3 of the pressure adjustment spring 220, and the pressure receiving area S3 of the pressure plate 210 change according to the amount of displacement while the pressure plate 210 and the flexible member 230 are displaced to the state of FIG. 7(c). Specifically, when the pressure plate 210 and the flexible member 230 are in the right direction in FIG. 7 compared to FIG. 7(c), the pressure receiving area S3 of the pressure plate 210 becomes smaller, and the spring force F3 of the pressure adjustment spring 220 becomes larger. As a result, the pressure P3 in the first pressure control chamber 122 becomes smaller according to the relationship of Equation 4. Therefore, according to Equation 2 and Equation 4, the pressure in the first pressure control chamber 122 gradually increases from the state of FIG. 7(b) to the state of FIG. 7(c) (i.e., the negative pressure becomes weaker and approaches the positive pressure side). That is, from a state in which the communication port 191 is open, the pressure plate 210 and the flexible member 230 gradually displace to the left, and the pressure in the first pressure control chamber 122 gradually increases until the internal volume of the first pressure control chamber 122 finally reaches its limit of displacement. In other words, the negative pressure weakens.

[0080] <Circulation pump> Next, the configuration and operation of the circulation pump 500 built into the above-mentioned recording head 1 will be described in detail with reference to FIGS.

[0081] FIG. 8 is an external perspective view of the circulation pump 500. FIG. 8(a) is an external perspective view showing the front side of the circulation pump 500, and FIG. 8(b) is an external perspective view showing the rear side of the circulation pump 500. The outer shell of the circulation pump 500 is composed of a pump housing 505 and a cover 507 fixed to the pump housing 505. The pump housing 505 is composed of a housing body 505a and a flow path connecting member 505b adhesively fixed to the outer surface of the housing body 505a. The housing body 505a and the flow path connecting member 505b each have a pair of through holes communicating with each other at two different positions. The pair of through holes provided at one position forms a pump supply hole 501, and the pair of through holes provided at the other position forms a pump discharge hole 502. The pump supply hole 501 is connected to the pump inlet flow path 170 connected to the second pressure control chamber 152, and the pump discharge hole 502 is connected to the pump outlet flow path 180 connected to the first pressure control chamber 122. Ink supplied from pump supply hole 501 passes through a pump chamber 503 (see FIG. 9) described below, and is discharged from pump discharge hole 502.

[0082] FIG. 9 is a cross-sectional view of the circulating pump 500 shown in FIG. 8(a) taken along line IX-IX. A diaphragm 506 is joined to the inner surface of a pump housing 505, and a pump chamber 503 is formed between the diaphragm 506 and a recess formed on the inner surface of the pump housing 505. The pump chamber 503 is connected to a pump supply hole 501 and a pump discharge hole 502 formed in the pump housing 505. A check valve 504a is provided in the middle of the pump supply hole 501, and a check valve 504b is provided in the middle of the pump discharge hole 502. Specifically, the check valve 504a is arranged so that a part of the check valve 504a can move leftward in the figure in a space 512a formed in the middle of the pump supply hole 501. A part of the check valve 504b is arranged so that a part of the check valve 504b can move rightward in the figure in a space 512b formed in the middle of the pump discharge hole 502.

[0083] When diaphragm 506 is displaced to increase the volume of pump chamber 503 and reduce the pressure in pump chamber 503, check valve 504a moves away from the opening of pump supply hole 501 in space 512a (i.e., moves to the left in the figure). When check valve 504a moves away from the opening of pump supply hole 501 in space 512a, the check valve 504a enters an open state that allows the flow of ink through pump supply hole 501. When diaphragm 506 is displaced to decrease the volume of pump chamber 503 and reduce the pressure in pump chamber 503, check valve 504a comes into close contact with the wall surface surrounding the opening of pump supply hole 501. As a result, the check valve 504a enters a closed state that blocks the flow of ink through pump supply hole 501.

[0084] On the other hand, when the pump chamber 503 is depressurized, the check valve 504b comes into close contact with the wall surface surrounding the opening of the pump housing 505 and enters a closed state in which it blocks the flow of ink through the pump discharge hole 502. When the pump chamber 503 is pressurized, the check valve 504b moves away from the opening of the pump housing 505 toward the space 512b (i.e., moves to the right in the figure), allowing the flow of ink through the pump discharge hole 502.

[0085] The material of each check valve 504a, 504b may be any material that can deform in response to the pressure in the pump chamber 503, and may be made of, for example, an elastic material such as EPDM (ethylene propylene rubber) or elastomer, or a film or thin plate such as polypropylene, but is not limited to these.

[0086] As described above, pump chamber 503 is formed by joining pump housing 505 and diaphragm 506. Therefore, the pressure in pump chamber 503 changes as diaphragm 506 deforms. For example, when diaphragm 506 is displaced toward pump housing 505 (displaced to the right in the figure) and the volume of pump chamber 503 decreases, the pressure in pump chamber 503 increases. As a result, check valve 504b arranged opposite pump discharge hole 502 opens, and ink in pump chamber 503 is discharged. At this time, check valve 504a arranged opposite pump supply hole 501 is in close contact with the wall surface surrounding pump supply hole 501, so that the backflow of ink from pump chamber 503 to pump supply hole 501 is suppressed.

[0087] Furthermore, when the diaphragm 506 is displaced in a direction in which the pump chamber 503 widens, the pressure in the pump chamber 503 decreases. As a result, the check valve 504a arranged opposite the pump supply hole 501 opens, and ink is supplied to the pump chamber 503. At this time, the check valve 504b arranged at the pump discharge hole 502 comes into close contact with the wall surface surrounding the opening formed in the pump housing 505 to close the opening. As a result, the backflow of ink from the pump discharge hole 502 to the pump chamber 503 is suppressed.

[0088] In this way, in the circulation pump 500, the diaphragm 506 deforms, changing the pressure in the pump chamber 503, thereby sucking in and discharging ink. At this time, if bubbles get into the pump chamber 503, even if the diaphragm 506 is displaced, the bubbles expand and contract, reducing the pressure change in the pump chamber 503 and decreasing the amount of liquid delivered. Therefore, the pump chamber 503 is arranged parallel to gravity to make it easier for bubbles that get into the pump chamber 503 to gather above the pump chamber 503, and the pump discharge hole 502 is arranged above the center of the pump chamber 503. This makes it possible to improve the discharge of bubbles in the pump and stabilize the flow rate.

[0089] <Ink flow inside the print head> FIG. 10 is a diagram for explaining the flow of ink in the recording head. The circulation of ink in the recording head 1 will be explained with reference to FIG. 10. In order to more clearly explain the ink circulation path, the relative positions of each component (such as the first pressure adjustment means 120, the second pressure adjustment means 150, and the circulation pump 500) in FIG. 10 are simplified. Therefore, the relative positions of each component are different from the configuration in FIG. 19 described later. FIG. 10(a) is a schematic diagram showing the flow of ink when a recording operation is performed in which ink is discharged from the discharge port 13 to perform recording. The arrows in the figure indicate the flow of ink. In this embodiment, when a recording operation is performed, both the external pump 21 and the circulation pump 500 start to be driven. Regardless of the recording operation, the external pump 21 and the circulation pump 500 may be driven. In addition, the external pump 21 and the circulation pump 500 do not need to be driven in conjunction with each other, and may be driven independently.

[0090] During the recording operation, the circulation pump 500 is ON (driven), and the ink flowing out from the first pressure control chamber 122 flows into the supply flow path 130 and the bypass flow path 160. The ink that flows into the supply flow path 130 passes through the ejection module 300, then flows into the recovery flow path 140, and is then supplied to the second pressure control chamber 152.

[0091] On the other hand, the ink that has flowed from the first pressure control chamber 122 into the bypass flow path 160 flows into the second pressure control chamber 152 via the second valve chamber 151. The ink that has flowed into the second pressure control chamber 152 passes through the pump inlet flow path 170, the circulation pump 500, and the pump outlet flow path 180, and then flows into the first pressure control chamber 122 again. At this time, the control pressure by the first valve chamber 121 is set higher than the control pressure of the first pressure control chamber 122 based on the relationship of the above-mentioned formula 2. Therefore, the ink in the first pressure control chamber 122 is supplied to the ejection module 300 again via the supply flow path 130 without flowing into the first valve chamber 121. The ink that has flowed into the ejection module 300 flows into the first pressure control chamber 122 again via the recovery flow path 140, the second pressure control chamber 152, the pump inlet flow path 170, the circulation pump 500, and the pump outlet flow path 180. In this manner, the ink circulation that is completed within the recording head 1 is performed.

[0092] In the above ink circulation, the amount of ink circulating (flow rate) in the ejection module 300 is determined by the difference in the control pressure between the first pressure control chamber 122 and the second pressure control chamber 152. This pressure difference is set so as to be a circulation amount capable of suppressing thickening of ink near the ejection port in the ejection module 300. In addition, the ink consumed by the recording is supplied from the ink tank 2 to the first pressure control chamber 122 via the filter 110 and the first valve chamber 121. The mechanism by which the consumed ink is supplied will be described in detail. By reducing the ink from the circulation path by the amount of ink consumed by the recording, the pressure in the first pressure control chamber is reduced, and as a result, the ink in the first pressure control chamber 122 is also reduced. As the ink in the first pressure control chamber 122 is reduced, the internal volume of the first pressure control chamber 122 is reduced. Due to this reduction in the internal volume of the first pressure control chamber 122, the first communication port 191A is opened, and ink is supplied from the first valve chamber 121 to the first pressure control chamber 122. This supplied ink experiences a pressure loss when passing from first valve chamber 121 through first communication port 191A, and as it flows into first pressure control chamber 122, the ink changes from a positive pressure state to a negative pressure state. As ink flows from first valve chamber 121 into first pressure control chamber 122, the pressure inside the first pressure control chamber increases, increasing the internal volume of the first pressure control chamber and closing first communication port 191A. In this way, first communication port 191A alternates between an open state and a closed state depending on the consumption of ink. Furthermore, if no ink is consumed, first communication port 191A is maintained in a closed state.

[0093] FIG. 10B is a schematic diagram showing the flow of ink immediately after the recording operation is completed and the circulation pump 500 is turned off (stopped). When the recording operation is completed and the circulation pump 500 is turned off, the pressures of the first pressure control chamber 122 and the second pressure control chamber 152 are both at the control pressure during the recording operation. Therefore, the ink moves as shown in FIG. 10B according to the pressure difference between the pressures of the first pressure control chamber 122 and the second pressure control chamber 152. Specifically, the ink continues to flow from the first pressure control chamber 122 to the ejection module 300 via the supply flow path 130, and then to the second pressure control chamber 152 via the recovery flow path 140. The ink also continues to flow from the first pressure control chamber 122 to the second pressure control chamber 152 via the bypass flow path 160 and the second valve chamber 151.

[0094] The amount of ink that has moved from the first pressure control chamber 122 to the second pressure control chamber 152 by these ink flows is supplied to the first pressure control chamber 122 from the ink tank 2 via the filter 110 and the first valve chamber 121. Therefore, the content volume in the first pressure control chamber 122 is kept constant. From the relationship of the above-mentioned formula 2, if the content volume of the first pressure control chamber 122 is constant, the spring force F1 of the valve spring 200, the spring force F2 of the pressure adjustment spring 220, the pressure receiving area S1 of the valve 190, and the pressure receiving area S2 of the pressure plate 210 are kept constant. Therefore, the pressure in the first pressure control chamber 122 is determined according to the change in the pressure (gauge pressure) P1 in the first valve chamber 121. Therefore, if there is no change in the pressure P1 in the first valve chamber 121, the pressure P2 in the first pressure control chamber 122 is kept at the same pressure as the control pressure during the recording operation.

[0095] On the other hand, the pressure of the second pressure control chamber 152 changes over time according to the change in the content volume caused by the inflow of ink from the first pressure control chamber 122. Specifically, from the state of FIG. 10(b) until the communication port 191 is closed and the second valve chamber 151 and the second pressure control chamber 152 are not in communication with each other as shown in FIG. 10(c), the pressure of the second pressure control chamber 152 changes according to Equation 2. Thereafter, the pressure plate 210 and the valve shaft 190a are not in contact with each other and the communication port 191 is closed. Then, as shown in FIG. 10(d), ink flows from the recovery passage 140 into the second pressure control chamber 152. This ink inflow displaces the pressure plate 210 and the flexible member 230, and the pressure of the second pressure control chamber 152 changes according to Equation 4 until the internal volume of the second pressure control chamber 152 reaches its maximum. That is, it rises.

[0096] 10(c), no ink flows from the first pressure control chamber 122 to the second pressure control chamber 152 via the bypass flow path 160 and the second valve chamber 151. Therefore, after the ink in the first pressure control chamber 122 is supplied to the ejection module 300 via the supply flow path 130, only the ink flows to the second pressure control chamber 152 via the recovery flow path 140. As described above, the movement of ink from the first pressure control chamber 122 to the second pressure control chamber 152 occurs according to the pressure difference between the pressure in the first pressure control chamber 122 and the pressure in the second pressure control chamber 152. Therefore, when the pressure in the second pressure control chamber 152 becomes equal to the pressure in the first pressure control chamber 122, the movement of ink stops.

[0097] In addition, in a state where the pressure in the second pressure control chamber 152 is equal to the pressure in the first pressure control chamber 122, the second pressure control chamber 152 expands to a state shown in FIG. 10(d). When the second pressure control chamber 152 expands as shown in FIG. 10(d), a storage portion capable of storing ink is formed in the second pressure control chamber 152. The time from when the circulation pump 500 is stopped to when the state shown in FIG. 10(d) is transitioned to is about 1 to 2 minutes, which may vary depending on the shape and size of the flow path and the properties of the ink. When the circulation pump 500 is driven from the state shown in FIG. 10(d) where ink is stored in the storage portion, the ink in the storage portion is supplied to the first pressure control chamber 122 by the circulation pump 500. As a result, the amount of ink in the first pressure control chamber 122 increases as shown in FIG. 10(e), and the flexible member 230 and the pressure plate 210 are displaced in the expansion direction. Then, when the circulation pump 500 continues to be driven, the state inside the circulation path changes as shown in FIG. 10(a).

[0098] 10(a) is an example of the ink circulation during the printing operation, but as described above, the ink may be circulated without the printing operation. Even in this case, the ink flows as shown in FIGS. 10(a) to 10(e) according to the driving and stopping of the circulating pump 500.

[0099] As described above, in this embodiment, the second communication port 191B in the second pressure adjustment means 150 is in an open state when the circulation pump 500 is driven to circulate ink, and is in a closed state when the circulation of ink stops, but this is not limited to the above example. The control pressure may be set so that the second communication port 191B in the second pressure adjustment means 150 is in a closed state even when the circulation pump 500 is driven to circulate ink. The role of the bypass flow path 160 will be specifically described below.

[0100] The bypass flow path 160 connecting the first pressure adjustment means 120 and the second pressure adjustment means 150 is provided to prevent the negative pressure generated in the circulation path from being affected by the discharge module 300 when the negative pressure exceeds a predetermined value. The bypass flow path 160 is also provided to supply ink to the pressure chamber 12 from both sides of the supply flow path 130 and the recovery flow path 140.

[0101] First, an example will be described in which the bypass flow path 160 is provided to prevent the negative pressure from being influenced by the discharge module 300 when the negative pressure becomes stronger than a preset value. For example, the ink characteristics (e.g., viscosity) may change due to a change in the environmental temperature. When the ink viscosity changes, the pressure loss in the circulation path also changes. For example, when the ink viscosity decreases, the pressure loss in the circulation path decreases. As a result, the flow rate of the circulation pump 500 driven at a constant drive amount increases, and the flow rate through the discharge module 300 increases. On the other hand, since the discharge module 300 is kept at a constant temperature by a temperature adjustment mechanism (not shown), the viscosity of the ink in the discharge module 300 is maintained constant even if the environmental temperature changes. While the viscosity of the ink in the discharge module 300 does not change, the flow rate of the ink flowing through the discharge module 300 increases, and the negative pressure in the discharge module 300 is strengthened due to flow resistance. In this way, if the negative pressure in the discharge module 300 becomes stronger than the default value, the meniscus of the discharge port 13 may be destroyed, and external air may be drawn into the circulation path, preventing normal discharge. Even if the meniscus is not destroyed, the negative pressure in the pressure chamber 12 may become stronger than the default value, affecting discharge.

[0102] For this reason, in this embodiment, the bypass flow path 160 is formed in the circulation path. By providing the bypass flow path 160, when the negative pressure becomes stronger than a preset value, ink also flows through the bypass flow path 160, so that the pressure of the ejection module 300 can be kept constant. Therefore, for example, the second communication port 191B in the second pressure adjustment means 150 may be configured with a control pressure that maintains the closed state even when the circulation pump 500 is being driven. Then, the control pressure in the second pressure adjustment means may be set so that the second communication port 191B in the second pressure adjustment means 150 is in an open state when the negative pressure becomes stronger than a preset value. In other words, if the meniscus does not collapse even when the flow rate of the pump is changed due to a viscosity change such as an environmental change, or if a predetermined negative pressure is maintained, the second communication port 191B may be in a closed state when the circulation pump 500 is driven.

[0103] Next, an example will be described in which the bypass flow path 160 is provided to supply ink to the pressure chamber 12 from both the supply flow path 130 and the recovery flow path 140. Pressure fluctuations in the circulation path can also be caused by the ejection operation of the ejection element 15. This is because a force that draws ink into the pressure chamber is generated by the ejection operation.

[0104] Hereinafter, it will be described that when high duty printing is continued, the ink supplied to the pressure chamber 12 is supplied to both the supply flow path 130 side and the recovery flow path 140 side. The definition of duty can change depending on various conditions. As an example, an image printed under the condition of applying one ink droplet with a volume of 4 pL per droplet to a unit area of ​​1200 dpi x 1200 dpi will be treated as having a printing duty of 100%. High duty printing means, for example, printing performed at a duty of 100%.

[0105] If recording at a high duty continues, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the recovery flow path 140 decreases. On the other hand, since the circulation pump 500 causes a constant amount of ink to flow out, the balance between the inflow and outflow in the second pressure control chamber 152 is lost, the ink in the second pressure control chamber 152 decreases, the negative pressure in the second pressure control chamber 152 becomes stronger, and the second pressure control chamber 152 shrinks. Then, as the negative pressure in the second pressure control chamber 152 becomes stronger, the inflow amount of ink flowing into the second pressure control chamber 152 through the bypass flow path 160 increases, and the second pressure control chamber 152 becomes stable with the outflow and inflow balanced. As a result, the negative pressure in the second pressure control chamber 152 becomes stronger according to the duty. Furthermore, as described above, when the circulation pump 500 is driven, in a configuration in which the second communication port 191B is in a closed state, the second communication port 191B opens depending on the duty, and ink flows from the bypass flow path 160 into the second pressure control chamber 152.

[0106] Then, when recording at an even higher duty is continued, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the recovery flow passage 140 decreases, and instead the amount of ink flowing into the second pressure control chamber 152 from the second communication port 191B via the bypass flow passage 160 increases. If this state progresses further, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the recovery flow passage 140 becomes zero, and all ink flowing out to the circulation pump 500 becomes ink flowing in from the second communication port 191B. If this state progresses further, ink now flows back from the second pressure control chamber 152 into the pressure chamber 12 through the recovery flow passage 140. In this state, the ink flowing out from the second pressure control chamber 152 to the circulation pump 500 and the ink flowing out to the pressure chamber 12 flow into the second pressure control chamber 152 from the second communication port 191B through the bypass flow passage 160. In this case, the pressure chamber 12 is filled with ink from the supply flow passage 130 and ink from the recovery flow passage 140, and is ejected.

[0107] This backflow of ink that occurs when the recording duty is high is a phenomenon that occurs due to the provision of the bypass flow path 160. In addition, in the above, an example has been described in which the second communication port 191B in the second pressure adjustment means is opened in response to the backflow of ink, but backflow of ink may also occur when the second communication port 191B in the second pressure adjustment means is in the open state. Even in a configuration that does not include a second pressure adjustment means, the provision of the bypass flow path 160 may cause the above-mentioned backflow of ink.

[0108] <Configuration of the discharge unit> FIG. 11 is a schematic diagram showing a circulation path for one color of ink in the discharge unit 3 of this embodiment. FIG. 11(a) is an exploded perspective view of the discharge unit 3 seen from the first support member 4 side, and FIG. 11(b) is an exploded perspective view of the discharge unit 3 seen from the discharge module 300 side. The arrows indicated by IN and OUT in the figure indicate the flow of ink, and the flow of ink for only one color will be described, but the other colors flow in the same manner. Also, in FIG. 11, the second support member 7 and the electric wiring member 5 are omitted, and are also omitted in the following description of the configuration of the discharge unit. Also, the first support member 4 in FIG. 11(a) shows a cross section taken along line XI-XI in FIG. 3. The discharge module 300 includes a discharge element substrate 340 and an aperture plate 330. FIG. 12 is a diagram showing the aperture plate 330, and FIG. 13 is a diagram showing an example of the discharge element substrate 340.

[0109] Ink is supplied to the discharge unit 3 from the circulation unit 54 via a joint member 8 (see FIG. 3). The route of the ink from after the ink passes through the joint member 8 until it returns to the joint member 8 will be described. In the following drawings, the joint member 8 will be omitted from illustration.

[0110] The ejection module 300 includes an ejection element substrate 340, which is a silicon substrate 310, and an aperture plate 330, and further includes an ejection port forming member 320. The ejection element substrate 340, the aperture plate 330, and the ejection port forming member 320 are overlapped and joined together so that the ink flow paths communicate with each other to form the ejection module 300, which is supported by a first support member 4. The ejection module 300 is supported by the first support member 4 to form an ejection unit 3. The ejection element substrate 340 includes an ejection port forming member 320, which includes a plurality of ejection port rows in which a plurality of ejection ports 13 are arranged in a row, and ejects a portion of the ink supplied through the ink flow path in the ejection module 300 from the ejection port 13. Ink that is not ejected is collected through the ink flow path in the ejection module 300.

[0111] As shown in Figs. 11 and 12, the opening plate 330 has a plurality of arranged ink supply ports 311 and a plurality of arranged ink recovery ports 312. As shown in Figs. 13 and 14, the ejection element substrate 340 has a plurality of arranged supply connection channels 323 and a plurality of arranged recovery connection channels 324. Furthermore, the ejection element substrate 340 has a common supply channel 18 communicating with the plurality of supply connection channels 323 and a common recovery channel 19 communicating with the plurality of recovery connection channels 324. The ink flow channels in the ejection unit 3 are formed by communicating an ink supply channel 48 and an ink recovery channel 49 (see Fig. 3) provided in the first support member 4 with a flow channel provided in the ejection module 300. The support member supply port 211 is a cross-sectional opening that forms the ink supply channel 48, and the support member recovery port 212 is a cross-sectional opening that forms the ink recovery channel 49.

[0112] Ink supplied to the ejection unit 3 is supplied from the circulation unit 54 (see FIG. 3(a)) side to the ink supply flow path 48 (see FIG. 3(a)) of the first support member 4. The ink flowing through the support member supply port 211 in the ink supply flow path 48 is supplied to the common supply flow path 18 of the ejection element substrate 340 via the ink supply flow path 48 (see FIG. 3(a)) and the ink supply port 311 of the opening plate 330, and enters the supply connection flow path 323. This is the supply side flow path. After that, the ink flows through the pressure chamber 12 (see FIG. 3(b)) of the ejection port forming member 320 to the recovery connection flow path 324 of the recovery side flow path. The flow of ink in the pressure chamber 12 will be described in detail later.

[0113] In the recovery side flow path, the ink that has entered the recovery connection flow path 324 flows into the common recovery flow path 19. Thereafter, the ink flows from the common recovery flow path 19 through the ink recovery port 312 of the opening plate 330 to the ink recovery flow path 49 of the first support member 4, and then through the support member recovery port 212 to be recovered in the circulation unit 54.

[0114] The area of ​​the opening plate 330 without the ink supply port 311 or the ink recovery port 312 corresponds to the area for separating the support member supply port 211 and the support member recovery port 212 in the first support member 4. Moreover, this area does not have an opening in the first support member 4 either. Such an area is used as an adhesion area when the ejection module 300 and the first support member 4 are adhered to each other.

[0115] In FIG. 12, the aperture plate 330 has a plurality of rows of apertures arranged in the X direction, and the supply (IN) apertures and the recovery (OUT) apertures are arranged alternately in the Y direction so as to be shifted by half a pitch in the X direction. In FIG. 13, the ejection element substrate 340 has a common supply flow path 18 communicating with a plurality of supply connection flow paths 323 arranged in the Y direction, and a common recovery flow path 19 communicating with a plurality of recovery connection flow paths 324 arranged in the Y direction, arranged alternately in the X direction. The common supply flow paths 18 and the common recovery flow path 19 are separated by type of ink, and further, the number of common supply flow paths 18 and common recovery flow paths 19 is determined according to the number of ejection port rows of each color. In addition, the supply connection flow paths 323 and the recovery connection flow paths 324 are also arranged in the number corresponding to the ejection ports 13. It is not necessarily required that they correspond one-to-one, and one supply connection flow path 323 and one recovery connection flow path 324 may correspond to a plurality of ejection ports 13.

[0116] Such an opening plate 330 and an ejection element substrate 340 are overlapped and joined so that the flow paths of each ink are connected to form an ejection module 300, and by being supported by the first support member 4, an ink flow path having a supply flow path and a recovery flow path as described above is formed.

[0117] Fig. 14(a) to (c) are cross-sectional views showing ink flows in different parts of the discharge unit 3. Fig. 14(a) is a cross-section shown by XIVa-XIVa in Fig. 11(a) and shows a cross-section of a part where the ink supply flow path 48 and the ink supply port 311 in the discharge unit 3 communicate with each other. Fig. 14(b) is a cross-section shown by XIVb-XIVb in Fig. 11(a) and shows a cross-section of a part where the ink recovery flow path 49 and the ink recovery port 312 in the discharge unit 3 communicate with each other. Fig. 14(c) is a cross-section shown by XIVc-XIVc in Fig. 11(a) and shows a cross-section of a part where the ink supply port 311 and the ink recovery port 312 do not communicate with the flow path of the first support member 4.

[0118] In the supply flow path for supplying ink, as shown in FIG. 14(a), ink is supplied from a portion where the ink supply flow path 48 of the first support member 4 and the ink supply port 311 of the opening plate 330 overlap and communicate with each other. In the recovery flow path for recovering ink, as shown in FIG. 14(b), ink is recovered from a portion where the ink recovery flow path 49 of the first support member 4 and the ink recovery port 312 of the opening plate 330 overlap and communicate with each other. In addition, as shown in FIG. 14(c), in the ejection unit 3, there is also an area where the opening plate 330 does not have an opening. In such an area, ink is not supplied or recovered between the ejection element substrate 340 and the first support member 4. As shown in FIG. 14(a), ink is supplied in an area where the ink supply port 311 is provided, and as shown in FIG. 14(b), ink is recovered in an area where the ink recovery port 312 is provided. In the present embodiment, the configuration using the opening plate 330 has been described as an example, but a configuration without using the opening plate 330 may be used. For example, a configuration may be used in which flow paths corresponding to the ink supply flow path 48 and the ink recovery flow path 49 are formed in the first support member 4, and the ejection element substrate 340 is joined to the first support member 4.

[0119] 15(a) and (b) are cross-sectional views showing an example of the vicinity of the ejection port 13 in the ejection module 300, and FIG. 16 is a cross-sectional view showing an ejection module configured with the common supply flow path 18 and the common recovery flow path 19 expanded in the X direction. The thick arrows shown in the common supply flow path 18 and the common recovery flow path 19 in FIG. 15 and FIG. 16 indicate the oscillation of ink in a configuration using a serial type inkjet recording device 50. The ink supplied to the pressure chamber 12 via the common supply flow path 18 and the supply connection flow path 323 is ejected from the ejection port 13 by driving the ejection element 15. When the ejection element 15 is not driven, the ink is recovered from the pressure chamber 12 to the common recovery flow path 19 via the recovery connection flow path 324, which is a recovery flow path.

[0120] In the case of using the serial type inkjet recording device 50, when ink is discharged from the circulating ink, the ink discharge is influenced by the ink oscillation in the ink flow path caused by the main scanning of the recording head 1. As described above, the ink oscillation has the effect of suppressing the deterioration of the discharge characteristics, but a large oscillation may have an adverse effect on the discharge. Specifically, the influence of the ink oscillation in the ink flow path may appear as a difference in the ink discharge amount or a deviation in the discharge direction. As shown in FIG. 16, when the common supply flow path 18 and the common recovery flow path 19 have a cross-sectional shape that is wide in the X direction, which is the main scanning direction, the ink in the common supply flow path 18 and the common recovery flow path 19 is easily subjected to an inertial force in the main scanning direction, and the ink undergoes a large oscillation. As a result, the ink oscillation may affect the ink discharge from the discharge port 13. In addition, if the common supply flow path 18 and the common recovery flow path 19 are widened in the X direction, the distance between the colors will be increased, and the recording efficiency may decrease.

[0121] Therefore, in the cross section shown in FIG. 15, the common supply flow path 18 and the common recovery flow path 19 of this embodiment both extend in the Y direction, but are also configured to extend in the Z direction perpendicular to the X direction, which is the main scanning direction. With this configuration, the width of each flow path in the main scanning direction of the common supply flow path 18 and the common recovery flow path 19 can be reduced. By reducing the width of each flow path in the main scanning direction of the common supply flow path 18 and the common recovery flow path 19, the ink oscillation caused by the inertial force (indicated by the thick black arrow in the figure) acting on the ink in the common supply flow path 18 and the common recovery flow path 19 in the opposite direction to the main scanning direction during the main scanning is reduced. This makes it possible to suppress the effect of the ink oscillation on the ink ejection. In addition, the cross-sectional area is increased by extending the common supply flow path 18 and the common recovery flow path 19 in the Z direction, thereby reducing the flow path pressure loss.

[0122] As described above, by reducing the width of each of the common supply flow path 18 and the common recovery flow path 19 in the main scanning direction, the oscillation of ink in the common supply flow path 18 and the common recovery flow path 19 during main scanning is reduced, but the oscillation is not eliminated. Therefore, in order to suppress the occurrence of differences in ejection for each ink type that may still occur even with the reduced oscillation, in this embodiment, the common supply flow path 18 and the common recovery flow path 19 are configured to be disposed at positions that overlap with each other in the X direction.

[0123] As described above, in this embodiment, the supply connection flow path 323 and the recovery connection flow path 324 are provided corresponding to the ejection port 13, and the supply connection flow path 323 and the recovery connection flow path 324 are arranged side by side in the X direction with the ejection port 13 in between. Therefore, there are portions where the common supply flow path 18 and the common recovery flow path 19 do not overlap in the X direction, and if the corresponding relationship in the X direction between the supply connection flow path 323 and the recovery connection flow path 324 is lost, this will affect the flow and ejection of ink in the X direction in the pressure chamber 12. When the influence of ink fluctuation is added to this, it may further affect the ejection of ink from each ejection port.

[0124] Therefore, by arranging the common supply flow path 18 and the common recovery flow path 19 at positions where they overlap in the X direction, the ink oscillation during main scanning in the common supply flow path 18 and the common recovery flow path 19 becomes approximately equal at any position in the Y direction where the ejection ports 13 are arranged. As a result, the pressure difference between the common supply flow path 18 side and the common recovery flow path 19 side generated in the pressure chamber 12 does not vary greatly, and stable ejection can be performed.

[0125] In addition, in some recording heads that circulate ink, the flow path that supplies ink to the recording head and the flow path that recovers ink are configured as the same flow path, but in this embodiment, the common supply flow path 18 and the common recovery flow path 19 are configured as separate flow paths. The supply connection flow path 323 and the pressure chamber 12 are connected to each other, and the pressure chamber 12 and the recovery connection flow path 324 are connected to each other, and ink is discharged from the ejection port 13 of the pressure chamber 12. In other words, the pressure chamber 12, which is a path that connects the supply connection flow path 323 and the recovery connection flow path 324, is configured to have the ejection port 13. Therefore, an ink flow that flows from the supply connection flow path 323 side to the recovery connection flow path 324 side is generated in the pressure chamber 12, and the ink in the pressure chamber 12 is efficiently circulated. By efficiently circulating the ink in the pressure chamber 12, the ink in the pressure chamber 12, which is easily affected by the evaporation of ink from the ejection port 13, can be kept fresh.

[0126] Furthermore, since the two flow paths, the common supply flow path 18 and the common recovery flow path 19, are connected to the pressure chamber 12, if it becomes necessary to eject ink at a high flow rate, it is possible to supply ink from both flow paths. In other words, compared to a configuration in which ink supply and recovery are configured using only one flow path, the configuration of this embodiment has the advantage of not only being able to circulate ink efficiently, but also being able to handle ejection at a high flow rate.

[0127] Furthermore, the common supply flow path 18 and the common recovery flow path 19 are less susceptible to the influence of ink fluctuations when they are disposed close to each other in the X direction. It is preferable that the distance between the flow paths is 75 μm or more and 100 μm or less.

[0128] Fig. 17 is a diagram showing another example of the ejection element substrate 340. In Fig. 17, the supply connection flow path 323 and the recovery connection flow path 324 are omitted. Since ink that has received thermal energy from the ejection elements 15 in the pressure chambers 12 flows into the common recovery flow path 19, ink with a relatively high temperature flows compared to the temperature of the ink in the common supply flow path 18. At this time, as shown in the α portion surrounded by the dashed line in Fig. 17, there is a portion in the X direction of the ejection element substrate 340 where only the common recovery flow path 19 exists. In this case, the temperature locally increases in that portion, causing temperature unevenness in the ejection module 300, which may affect ejection.

[0129] In the common supply flow path 18, ink flows that is at a relatively low temperature relative to the common recovery flow path 19. Therefore, when the common supply flow path 18 and the common recovery flow path 19 are adjacent to each other, the temperatures in the common supply flow path 18 and the common recovery flow path 19 are partially offset in the vicinity thereof, suppressing a rise in temperature. Therefore, it is preferable that the common supply flow path 18 and the common recovery flow path 19 are adjacent to each other and have approximately the same length, and are positioned so as to overlap each other in the X direction.

[0130] 18(a) and (b) are diagrams showing the flow path configuration of the recording head 1 corresponding to three colors of ink: cyan (C), magenta (M), and yellow (Y). As shown in FIG. 18(a), the recording head 1 is provided with circulation paths for each type of ink. The pressure chambers 12 are provided along the X direction, which is the main scanning direction of the recording head 1. As shown in FIG. 18(b), the common supply flow path 18 and the common recovery flow path 19 are provided along the ejection port row in which the ejection ports 13 are arranged, and are provided extending in the Y direction so as to sandwich the ejection port row between the common supply flow path 18 and the common recovery flow path 19.

[0131] <Connection between the main body and the recording head> 19 is a schematic diagram showing in more detail the connection state between the ink tank 2 and external pump 21 provided in the main body of the inkjet recording device 50 of this embodiment and the recording head 1, and the arrangement of the circulation pump, etc. The inkjet recording device 50 of this embodiment is configured so that when a problem occurs in the recording head 1, only the recording head 1 can be easily replaced. Specifically, it has a liquid connection part 700 that can easily connect and disconnect the ink supply tube 59 connected to the external pump 21 and the recording head 1. This makes it possible to easily attach and detach only the recording head 1 to and from the inkjet recording device 50.

[0132] 19, the liquid connection part 700 has a liquid connector insertion port 53a protruding from the head housing 53 of the recording head 1, and a cylindrical liquid connector 59a into which the liquid connector insertion port 53a can be inserted. The liquid connector insertion port 53a is fluidly connected to an ink supply flow path (inflow flow path) formed in the recording head 1, and is connected to the first pressure adjustment means 120 via the above-mentioned filter 110. In addition, the liquid connector 59a is provided at the tip of an ink supply tube 59 connected to an external pump 21 that pressurizes and supplies ink from the ink tank 2 to the recording head 1.

[0133] 19, the recording head 1 can be easily attached, detached, and replaced by the liquid connection part 700. However, if the sealing performance between the liquid connector insertion port 53a and the liquid connector 59a is reduced, ink supplied under pressure by the external pump 21 may leak from the liquid connection part 700. If the leaked ink adheres to the circulation pump 500 or the like, a malfunction may occur in the electrical system. Therefore, in this embodiment, the circulation pump and the like are arranged as follows.

[0134] <Location of circulating pumps, etc.> As shown in FIG. 19, in this embodiment, in order to prevent ink leaking from the liquid connection part 700 from adhering to the circulation pump 500, the circulation pump 500 is disposed above the liquid connection part 700 in the direction of gravity. That is, the circulation pump 500 is disposed above the liquid connector insertion port 53a, which is the liquid inlet port of the recording head 1, in the direction of gravity. Furthermore, the circulation pump 500 is disposed at a position where it is not in contact with the members constituting the liquid connection part 700. As a result, even if ink leaks from the liquid connection part 700, the ink flows in the horizontal direction, which is the opening direction of the liquid connector 59a, or downward in the direction of gravity, so that it is possible to prevent the ink from reaching the circulation pump 500, which is located above in the direction of gravity. In addition, since the circulation pump 500 is disposed at a position away from the liquid connection part 700, the possibility that the ink will reach the circulation pump 500 by running down the members is also reduced.

[0135] Furthermore, the electrical connection part 515, which electrically connects the circulation pump 500 and the electrical contact board 6 via a flexible wiring member 514, is provided above the liquid connection part 700 in the direction of gravity. This makes it possible to reduce the possibility of electrical trouble caused by ink from the liquid connection part 700.

[0136] Furthermore, in this embodiment, since the wall portion 52b of the head housing 53 is provided, even if ink is ejected from the opening 59b of the liquid connection portion 700, the ink can be blocked, reducing the possibility of the ink reaching the circulation pump 500 or the electrical connection portion 515.

[0137] (Heating process) The recording method of the present invention may include a step of heating (heat treatment) the recording medium to which the ink has been applied. By heating the recording medium to which the ink has been applied, it is possible to promote drying and increase the strength of the image.

[0138] Examples of the means for heating the recording medium include known heating means such as a heater, air blowing means using air blowing such as a dryer, and a combination of these. Examples of the heating means include the above heating means, air blowing means, and a combination of these. Examples of the heat treatment method include a method of applying heat from the opposite side (back side) of the recording surface (ink application surface) of the recording medium using a heater, a method of applying warm or hot air to the recording surface of the recording medium, and a method of heating from the recording surface or back side using an infrared heater. A combination of these methods may also be used.

[0139] In order to enhance the abrasion resistance of the image, the heating temperature of the recording medium to which the ink and reaction liquid have been applied is preferably 50° C. or more and 90° C. or less. The heating temperature of the recording medium to which the ink has been applied may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined according to the type of ink and recording medium.

[0140] (Recording medium) In the recording method and recording device of the present invention, it is preferable to use a non-absorbent recording medium (a low to non-absorbent recording medium). A low to non-absorbent recording medium is one that is capable of being held in contact with the paper for 30 msec in the Bristow method described in JAPAN TAPPI Paper and Pulp Test Method No. 51 "Liquid Absorbency Test Method for Paper and Paperboard". 1 / 2 Water absorption up to 0mL / m 2 More than 10mL / m 2 In the present invention, a recording medium that satisfies the above-mentioned condition of water absorption amount is defined as a "low to non-absorbent recording medium". A recording medium for inkjet recording having a coating layer (ink receiving layer) formed of inorganic particles (glossy paper, matte paper, etc.) and plain paper having no coating layer have a water absorption amount of 10 mL / m 2 It is an "absorbent recording medium" that exceeds this.

[0141] Examples of low to non-absorbent recording media that can be used include plastic films, recording media in which a plastic film is bonded to the recording surface of a substrate, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Among these, plastic films are preferred, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred.

[0142] <Ink> The ink used in the recording method of the present invention has a specific gravity of 3.8 g / cm 3 The aqueous inkjet ink contains the above particles. Each component of the ink will be described in detail below.

[0143] (particle) The ink has a specific gravity of 3.8 g / cm 3 The particles contain particles with a specific gravity of 3.8 g / cm or more. These particles are a component with a high specific gravity compared to the components normally added to ink, and as mentioned above, are a component that can agitate the ink near the ejection port. The "particles" are 3 Any component may be used as long as it is equal to or greater than 3.8 g / cm. For example, it may be a pigment or resin particles, which will be described later. 3 In the following description, "particles having a specific gravity of 3.8 g / cm3 or more" may be used in combination. 3 The specific gravity of the above particles is 6.0 g / cm or more. 3 It is preferable that the density is 5.0 g / cm or less. 3 It is even more preferable that:

[0144] Here, the specific gravity of the particles, i.e., the true specific gravity of the particles, is the specific gravity determined by the structure of the particles. The specific gravity of the particles can be measured, for example, using a method conforming to JIS R 1620 (gas displacement method) or a method conforming to JIS Z 8807 (Gayerussac type pycnometer method). In the examples described below, the specific gravity of the liquid containing the coloring material is measured using the Gayerussac type pycnometer method, and then the specific gravity of components such as water and resin is also measured, and the specific gravity of each particle is calculated by taking the difference. The specific gravity may be measured using particles separated from the ink.

[0145] In order to efficiently agitate the ink near the ejection port, the particle content (mass %) in the aqueous ink is preferably 0.5% by mass or more and 20.0% by mass or less based on the total mass of the ink. If the particle content is less than 0.5% by mass, the amount of components contributing to agitation is too small, and image unevenness may not be sufficiently suppressed. On the other hand, if the particle content is more than 20.0% by mass, the content is too high, and the ink viscosity tends to increase, resulting in a decrease in agitation efficiency. As a result, image unevenness may not be sufficiently suppressed.

[0146] In order to efficiently exert the stirring action of the ink near the ejection port, the particle diameter of the particles is also an important factor. The volume-based cumulative 50% particle diameter (nm) of the particles is preferably 200 nm or more and 300 nm or less. The volume-based cumulative 50% particle diameter of the particles is the diameter of the particles that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in a particle diameter integration curve. The volume-based cumulative 50% particle diameter of the particles can be measured, for example, with a particle size analyzer and measurement conditions using the dynamic light scattering method described below. If the particle diameter is less than 200 nm, the particle size is too small, the stirring efficiency decreases, and image unevenness may not be sufficiently suppressed. On the other hand, if the particle diameter is more than 300 nm, the particle size is too large and tends to become unstable in the ink. As a result, image unevenness may not be sufficiently suppressed.

[0147] (Colorant) The ink preferably contains a coloring material. Pigments and dyes can be used as the coloring material. Of these, it is preferable to use pigments. The content (mass%) of the coloring material in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, based on the total mass of the ink, and more preferably 1.0% by mass or more and 20.0% by mass or less. Of these, it is particularly preferable that the content (mass%) of titanium oxide particles in the ink is 1.0% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0148] 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, and dioxazine.

[0149] As a method for dispersing the pigment, a resin-dispersed pigment using a resin as a dispersant, a self-dispersed pigment in which a hydrophilic group is bonded to the surface of the pigment particles, etc. can be used. In addition, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the surface of the pigment particles, and a microcapsule pigment in which the surface of the pigment particles is coated with a resin, etc. can be used. Among them, the pigment is preferably a self-dispersed pigment. If the pigment is dispersed with a resin (resin dispersant), the components that tend to remain in the dispersant increase, and the viscosity of the ink tends to increase, which may reduce the stirring efficiency. As a result, image unevenness may not be sufficiently suppressed.

[0150] 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.

[0151] 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.

[0152] The dye preferably has an anionic group. Specific examples of the dye include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes. The coloring material is preferably a pigment, and more preferably a resin-dispersed pigment.

[0153] As mentioned above, the particles may be color materials (pigments). Specifically, titanium oxide particles or zirconia particles are mixed with a material having a specific gravity of 3.8 g / cm 3 The particles can be any of the above. Among them, the particles are preferably titanium oxide particles. As described above, the titanium oxide particles are preferably not dispersed by a resin, and are preferably dispersed at least by the action of silica.

[0154] Inorganic oxides such as titanium oxide react with water molecules constituting the aqueous medium in the aqueous ink to generate hydroxyl groups (hereinafter, sometimes referred to as "surface hydroxyl groups") on the surface. For this reason, in the case of aqueous inkjet inks, in order to utilize the generated surface hydroxyl groups while further improving the storage stability of the ink, the ink is generally used in a state where the surface is treated with an inorganic oxide such as alumina or silica. The surface hydroxyl groups of titanium oxide particles have properties specific to the inorganic oxide corresponding to the inorganic compound used in the surface treatment, and the isoelectric point, which is an indicator of the strength of the acid, differs depending on the type of inorganic compound. Therefore, although titanium oxide itself is an inorganic oxide, the surface of titanium oxide particles shows the properties of an inorganic oxide corresponding to the inorganic compound used in the surface treatment, and the surface charge of titanium oxide particles is strongly dependent on the pH of the aqueous medium, the type of surface treatment agent, and the amount of the surface treatment agent used. In other words, "titanium oxide is dispersed at least by the action of silica" means that at least a part of the surface of the titanium oxide particles is covered with silica and dispersed by the action of its surface hydroxyl groups. However, if the water-soluble resin is contained in excess (for example, 0.01 times or more by mass ratio relative to the titanium oxide content), it is considered that the dispersion due to the action of silica is destabilized. Also, the addition of materials that assist dispersion is not excluded.

[0155] Titanium oxide is a white pigment, and has three crystal forms: rutile, anatase, and brookite. Among them, rutile titanium oxide is preferred. Titanium oxide can be industrially produced by the sulfuric acid method and the chlorine method, and the titanium oxide used in the present invention may be produced by either method.

[0156] The volume-based cumulative 50% particle diameter of the titanium oxide particles is preferably 200 nm or more and 500 nm or less, and more preferably 200 nm or more and 400 nm or less. The volume-based cumulative 50% particle diameter of the titanium oxide (D 50 ) is the diameter of the particle that is 50% of the total volume of the measured particles in the particle size accumulation curve, calculated from the small particle size side.50 can be measured under the following conditions: SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: aspheric, refractive index: 2.60. A particle size analyzer using a dynamic light scattering method can be used as the particle size distribution measuring device. Of course, the measurement conditions are not limited to those described above.

[0157] Titanium oxide may be surface-coated (surface-treated) with an inorganic oxide or an organic substance. In particular, titanium oxide surface-treated with alumina and silica is preferably used. The surface treatment is expected to suppress photocatalytic activity and improve dispersibility. In this specification, "alumina" is a general term for oxides of aluminum such as aluminum oxide. In this specification, "silica" is a general term for silicon dioxide or a substance composed of silicon dioxide. Most of the alumina and silica that coat titanium oxide are present in the form of silicon dioxide and aluminum oxide.

[0158] The ratio of alumina and silica in titanium oxide particles, i.e., the amount of alumina and silica coating, can be measured, for example, by quantitative analysis of aluminum and silicon elements by inductively coupled plasma (ICP) emission spectrometry. In this case, it is assumed that all atoms coating the surface are in the form of oxides, and the obtained values ​​of aluminum and silicon can be converted to the oxides, i.e., alumina and silica, to calculate the amount of alumina and silica.

[0159] Surface treatment methods for titanium oxide include wet treatment and dry treatment. For example, titanium oxide can be dispersed in a liquid medium and then reacted with a surface treatment agent such as sodium aluminate or sodium silicate to perform surface treatment, and the desired characteristics can be achieved by appropriately changing the ratio of these surface treatment agents. In addition to alumina and silica, inorganic oxides such as zinc oxide and zirconia, and organic substances such as polyols can also be used for surface treatment, as long as the effects of the present invention are not impaired.

[0160] Surface treatment methods for titanium oxide include wet treatment and dry treatment. For example, titanium oxide can be dispersed in a liquid medium, and then reacted with a surface treatment agent such as sodium aluminate or sodium silicate to perform surface treatment. The ratio of these surface treatment agents can be appropriately changed to adjust the desired characteristics. In addition to alumina and silica, inorganic oxides such as zinc oxide and zirconia, and organic substances such as polyols can be used for surface treatment, as long as the effects of the present invention are not impaired. As described above, titanium oxide particles are preferably dispersed at least by the action of silica, and therefore at least a part of the surface is preferably coated with silica.

[0161] The ink may contain other pigments in addition to titanium oxide. In this case, the ink may be of a color other than white ink. The content (mass %) of the other pigments in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 1.0% by mass or less, based on the total mass of the ink.

[0162] (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.

[0163] 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, and (ii) to improve various properties of the recorded image. Examples of the form of the resin include block copolymer, random copolymer, graft copolymer, 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.

[0164] [Resin composition] Examples of the resin include acrylic resins, urethane resins, olefin resins, etc. Among them, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

[0165] 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 monomer selected from the group consisting 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 monomer selected from the group consisting of styrene and α-methylstyrene is preferred. These resins are likely to interact with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

[0166] 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.

[0167] The urethane resin can be obtained by reacting, for example, polyisocyanate with a polyol. In addition, a chain extender may be further reacted with the urethane resin. Examples of the olefin resin include polyethylene and polypropylene.

[0168] [Resin properties] In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which it does not form particles whose particle size can be measured by a dynamic light scattering method. 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 a dynamic light scattering method, if no particles having a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. In addition, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used as a particle size distribution measuring device. Of course, the particle size distribution measuring device and the measuring conditions are not limited to those described above.

[0169] The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 mgKOH / g or less, and the weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

[0170] The acid value of the resin constituting the resin particles is preferably 5 mgKOH / g or more and 100 mgKOH / g or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 3,000,000 or less, and more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D 50 ) is preferably 50 nm or more and 500 nm or less. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particles that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in the particle diameter integration curve. The volume-based cumulative 50% particle diameter of the resin particles can be measured using the particle size analyzer and measurement conditions described above using the dynamic light scattering method. The glass transition temperature of the resin particles is preferably 40° C. or more and 120° C. or less, and more preferably 50° C. or more and 100° C. or less. The glass transition temperature (° C.) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not need to contain a coloring material. In addition, the resin particles are preferably formed of an acrylic resin, and it is preferable not to use a polyamide resin or the like.

[0171] (wax particles) The ink may contain particles formed of wax (wax particles). By using an ink containing wax particles, an image with improved abrasion resistance can be recorded. The wax may be a composition containing components other than wax, or may be the wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a water-soluble resin. The content (mass %) of the wax particles in the water-based ink is preferably 0.5 mass % or more and 5.0 mass % or less based on the total mass of the ink.

[0172] In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method of the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends thereof (blended waxes), and modified products thereof (modified waxes).

[0173] Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Among them, a blend of multiple types of wax is more preferable, and a blend of petroleum wax and synthetic wax is particularly preferable.

[0174] The wax particles are preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or more and 120°C or less, and more preferably 50°C or more and 100°C or less. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if it is linear, and the lower the melting point if it is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the crystallinity, the higher the melting point). Therefore, by controlling these characteristics, a wax having a desired melting point can be obtained.

[0175] (aqueous medium) The ink is an aqueous ink containing 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, it is preferable to use deionized water (ion-exchanged water). The content (mass %) of water in the ink is preferably 50.0 mass % or more and 95.0 mass % or less based on the total mass of the ink.

[0176] There are no particular limitations on the water-soluble organic solvent, so long as it is water-soluble (preferably soluble in water at 25°C in any proportion). Specifically, monohydric or polyhydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc. can be used. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less, and more preferably 10.0% by mass or more and 40.0% by mass or less, based on the total mass of the ink.

[0177] (Other additives) In addition to the above additives, the ink may contain various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, and chelating agents, as necessary. However, it is preferable that the ink does not contain a reactant to be contained in the reaction liquid described below. In particular, it is preferable that the ink contains a surfactant. The content (mass %) of the surfactant in the ink is preferably 0.1 mass % or more and 5.0 mass % or less, and more preferably 0.1 mass % or more and 2.0 mass % or less, based on the total mass of the ink. Examples of surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants. In particular, nonionic surfactants that are effective in small amounts are preferable because they are used to adjust various physical properties of the ink.

[0178] (Ink properties) Since the ink is applied to the inkjet method, it is preferable to appropriately control the physical properties of the ink. The surface tension of the ink at 25°C is preferably 10 mN / m or more and 60 mN / m or less, and more preferably 20 mN / m or more and 40 mN / m or less. The surface tension of the ink can be adjusted by appropriately determining the type and content of the surfactant in the ink. In addition, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.0 or less. The pH of the ink can be measured with a general pH meter equipped with a glass electrode or the like.

[0179] <Reaction solution> The recording method of the present invention preferably further comprises a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to the recording medium. Hereinafter, the aqueous reaction liquid is also simply referred to as the reaction liquid. By using the reaction liquid together with the ink, it is possible to record a high-quality image even on the non-absorbent recording medium described above. It is preferable that the reaction liquid is applied to the recording medium prior to the ink.

[0180] The reaction liquid reacts with the ink when it comes into contact with the ink, coagulating the components in the ink (components having anionic groups, such as resins and self-dispersing pigments), and contains a reactant. Examples of the reactant include cationic components such as polyvalent metal ions and cationic resins, and organic acids.

[0181] Examples of polyvalent metal ions include Ca. 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Sr 2+ , B.A. 2+ , and Zn 2+ Divalent metal ions such as Fe 3+ , Cr 3+ , Y 3+ , and Al 3+ In order to add a polyvalent metal ion to the reaction solution, a polyvalent metal salt (which may be a hydrate) formed by combining a polyvalent metal ion with an anion can be used. Examples of the anion include Cl. - , Br - , I - , ClO - , ClO2 - , ClO3 - , ClO4 - , NO2 - , NO3 - , SO4 2- , CO3 2- , HCO3 - , PO4 3- , HPO4 2- , and H2PO4 - Inorganic anions such as HCOO - , (COO - )2, COOH(COO - ), CH3COO - , CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 -When a polyvalent metal ion is used as the reactant, the content (mass %) of the polyvalent metal salt in the reaction solution is preferably 1.0 mass % or more and 20.0 mass % or less based on the total mass of the reaction solution.

[0182] The reaction liquid containing an organic acid has a buffering ability in the acidic range (less than pH 7.0, preferably pH 2.0 to 5.0), and thus efficiently converts the anionic groups of the components present in the ink into an acid form and causes them to aggregate. Examples of the organic acid include monocarboxylic acids and salts thereof, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furan carboxylic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and salts and hydrogen salts thereof, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and salts and hydrogen salts thereof, such as citric acid and trimellitic acid; and tetracarboxylic acids and salts and hydrogen salts thereof, such as pyromellitic acid. When an organic acid is used as the reactant, the content (mass %) of the organic acid in the reaction liquid is preferably 1.0 mass % or more and 50.0 mass % or less based on the total mass of the reaction liquid.

[0183] Examples of cationic resins include resins having a structure of primary to tertiary amines and resins having a structure of quaternary ammonium salts. Specific examples include resins having a structure of vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensate. In order to increase the solubility in the reaction solution, the cationic resin may be used in combination with an acidic compound or the cationic resin may be subjected to a quaternary treatment. When a cationic resin is used as a reactant, the content (mass%) of the cationic resin in the reaction solution is preferably 0.1 mass% or more and 10.0 mass% or less based on the total mass of the reaction solution. EXAMPLES

[0184] The present invention will be described in more detail below with reference to examples, comparative examples, and reference examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified. In addition, a dispersion of titanium oxide particles is referred to as a "pigment dispersion."

[0185] <Method of measuring physical properties> (Determining whether the resin is a resin particle or not, cumulative 50% particle size based on volume of resin particles and wax particles) The liquid containing the resin was diluted with ion-exchanged water to prepare a sample with a resin content of about 1.0%. The volume-based cumulative 50% particle diameter D of the resin particles was measured for this sample using a particle size distribution analyzer that uses dynamic light scattering under the following measurement conditions: 50 The particle size distribution meter used was a Nanotrac WAVEII-Q (manufactured by Microtrac Bell). When particles with a particle size were measured using this measurement method, the resin was determined to be a "resin particle" (a "water-dispersible resin"). On the other hand, when particles with a particle size were not measured using this measurement method, the resin was determined not to be a "resin particle" (a "water-soluble resin"). When measuring the particle size of wax particles, the same procedure as above was carried out except that a liquid containing wax particles was used instead of a liquid containing resin, and the cumulative 50% particle size D based on volume of the wax particles was measured. 50 was measured.

[0186] [Measurement conditions]: SetZero:30s Number of measurements: 3 Measurement time: 120 seconds ·Shape: true spherical Refractive index: 1.6 ·Density: 1.0

[0187] (Cumulative 50% particle size based on pigment volume) The pigment dispersion was diluted with ion-exchanged water to prepare a sample with a pigment content of about 0.01%. The average particle diameter D of the pigment was measured for this sample using the particle size distribution meter described above under the following measurement conditions. 50 (Cumulative 50% particle size on a volume basis) was measured.

[0188] [Measurement conditions]: SetZero:30s Number of measurements: 3 Measurement time: 120 seconds ·Shape: Non-spherical Refractive index: 1.5 (2.6 for titanium oxide particles) Density: 1.0 (4.0 for titanium oxide particles)

[0189] (Confirmation of surface treatment of titanium oxide particles) Using a liquid in which titanium oxide particles were added to nitric acid as a sample, quantitative analysis of aluminum and silicon elements was performed using an inductively coupled plasma (ICP) emission spectrometer. In this case, it was assumed that all atoms covering the surface were in the form of oxides, and the obtained values ​​of aluminum and silicon were converted to the oxides, i.e., alumina and silica, to calculate the mass ratio. In other words, if values ​​for aluminum and silicon were obtained, it means that the surface had been treated with alumina or silica.

[0190] (Melting point of wax particles) The melting point T of a wax made of a single component M The melting point (°C) was measured in accordance with the test method described in 5.3.1 (Melt point test method) of JIS K2235:1991 (petroleum wax). The melting point of a wax (wax mixture) composed of multiple components was measured in accordance with the test method described in 5.3.2 of JIS K2235:1991.

[0191] <Preparation of reaction solution> The components (unit: %) shown in Table 1 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (Advantec) with a pore size of 3.0 μm to prepare each reaction solution. In Table 1, "Catiomaster PDT-2" is an aqueous solution of cationic resin, and is the trade name of an aqueous solution of amine-epichlorohydrin condensation polymer (resin content: 60.0%) manufactured by Yokkaichi Chemicals. "Capstone FS3100" is the trade name of a fluorine-based nonionic surfactant manufactured by LEHVOSS Group, and "Proxel GXL(S)" is the trade name of a preservative manufactured by Arch Chemicals.

[0192] [Table 1]

[0193] <Preparation of pigment dispersion> A pigment dispersion was prepared according to the following procedure. The pigment properties are shown in Table 2.

[0194] (Pigment dispersions 1-3, 5, 6) 40.0 parts of the pigments shown in Table 2, 1.2 parts of 3-(methoxy(polyoxyethylene)9-12)propyltrimethoxysilane, and ion-exchanged water with a total of 100.0 parts of the components were mixed and pre-dispersed using a homogenizer. Then, dispersion treatment was carried out for 12 hours at 25°C using 0.5 mm zirconia beads in a paint shaker. The zirconia beads were filtered off, and an appropriate amount of ion-exchanged water was added as necessary to prepare pigment dispersions 1 to 3, 5, and 6 with a titanium oxide particle content of 40.0%.

[0195] (Pigment Dispersion 4) Zirconia beads with particle sizes of 0.1 mm and 0.5 mm (both trade names "TORECERAM Zirconia Beads", manufactured by Toray) were mixed at a mass ratio of 1:4. 1,080 parts of the resulting mixture and 300 parts of ion-exchanged water were placed in a batch-type bead mill (trade name "Easy Nano RMB", manufactured by AIMEX) and stirred at a peripheral speed of 8.4 m / s for 8 hours. After that, coarse components were filtered out using a membrane filter with a pore size of 1.0 μm (manufactured by Sartorius), and the concentration of the obtained filtrate was adjusted to obtain pigment dispersion 4 with a zirconia particle content of 30.0%. The D of the zirconia particles 50 (nm) was 295 nm.

[0196] (Pigment Dispersion 7) A water-soluble acrylic resin was synthesized by polymerizing 81.6 parts of butyl methacrylate and 18.4 parts of methacrylic acid by a conventional method. After adding ion-exchanged water containing potassium hydroxide in an amount equimolar to the acid value to neutralize the acid group, an appropriate amount of ion-exchanged water was further added to obtain an aqueous solution of a water-soluble resin with a resin content of 40.0%. The acid value of this water-soluble resin was 120.0 mg KOH / g. A pigment dispersion 7 with a titanium oxide particle content of 40.0% and a resin (water-soluble resin) content of 8.0% was prepared in the same manner as pigment dispersions 1 to 3 and 5, except that 1.2 parts of 3-(methoxy(polyoxyethylene)9-12)propyltrimethoxysilane was replaced with 20.0 parts of the aqueous solution of the water-soluble resin obtained above.

[0197] (Pigment Dispersion 8) A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) with an acid value of 150 mgKOH / g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide in an amount equimolar to the acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solid content) content of 20.0%. A mixture was obtained by mixing 15.0 parts of a pigment (carbon black, product name "MA-100", manufactured by Mitsubishi Chemical), 22.5 parts of the aqueous solution of resin 1, and 62.5 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) and dispersed for 5 hours while cooling with water. After centrifuging to remove coarse particles, the mixture was filtered under pressure using a cellulose acetate filter (Advantec) with a pore size of 3.0 μm to prepare pigment dispersion 8 having a pigment content of 15.0% and a resin dispersant (resin 1) content of 4.5%.

[0198] (Pigment Dispersion 9) A commercially available aqueous dispersion of colloidal silica (product name "Colloidal Silica MP-2040", colloidal silica content: 40.0%) was used as pigment dispersion 9.

[0199] [Table 2]

[0200] <Production of resin particles> Resin particles 1 to 3 were synthesized according to the following procedure. The specific gravity of each of resin particles 1 to 3 was 3.8 g / cm. 3 It was less than.

[0201] (Resin particles 1) In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 74.0 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, 24.0 parts of ethyl methacrylate, 1.5 parts of methacrylic acid, and 0.3 parts of a reactive surfactant were mixed to prepare an emulsion. As the reactive surfactant, "ADEKA REASOAP ER20" (manufactured by ADEKA, nonionic surfactant, number of moles of ethylene oxide group added: 20) was used. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and a polymerization reaction was carried out for 2 hours while stirring at 80°C. After cooling to 25°C, ion-exchanged water and an aqueous solution containing potassium hydroxide equimolar to the acid value of the resin particles were added to prepare an aqueous dispersion of resin particles 1 with a resin particle (solid content) content of 40.0%.

[0202] (Resin particles 2) In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 81.8 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, 16.1 parts of ethyl methacrylate, 1.6 parts of methoxypolyethylene glycol methacrylate, and 0.3 parts of the above reactive surfactant were mixed to prepare an emulsion. As the methoxypolyethylene glycol methacrylate, a product name "Blenmer PME1000" (manufactured by NOF Corp., number of moles of ethylene oxide groups added: about 23) was used. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and a polymerization reaction was carried out for 2 hours while stirring at 80°C. After cooling to 25°C, ion-exchanged water was added to prepare an aqueous dispersion of resin particles 2 with a resin particle (solid content) content of 40.0%.

[0203] (Resin particles 3) A 1-liter four-neck flask equipped with a stirrer, a temperature controller, a water divider, and a nitrogen gas inlet tube was charged with 112.5 parts (0.77 moles) of adipic acid and 16.9 parts of xylene, and heated to 50°C. Then, 308 parts (0.62 moles) of dimer diamine were gradually added, and the mixture was stirred at 150°C for 60 minutes. The mixture was then gradually heated to 175°C, and a dehydration reaction was carried out for 150 minutes to obtain a polyamide resin. 20 parts of the polyamide resin obtained above, 5 parts of polyoxyethylene-2-ethylhexyl ether, and 15 parts of propylene glycol monomethyl ether were mixed, and then heated to 120°C to dissolve the components. Then, 2 parts of N,N'-dimethylethanolamine were added and mixed. This mixture was gradually added to a 500-milliliter four-neck flask containing 203 parts of highly pure water heated to 40°C. The mixture was then stirred at 40° C. for 10 minutes and then allowed to stand in a thermostatic chamber at 80° C. for 24 hours to obtain an aqueous dispersion of resin particles 3 with a resin particle content of 10.0%.

[0204] <Preparation of wax particles> The components shown in Table 3 were mixed, and the temperature and pressure were appropriately adjusted to disperse the wax. An appropriate amount of pure water was added to dilute the mixture, to obtain aqueous dispersions of wax particles 1 to 3 each having a total wax and dispersant content of 30.0%. The dispersant used was an aqueous solution of an emulsifier (product name "Rhodafac RS-710", manufactured by Rhodia Novecare) to which an appropriate amount of ion-exchanged water was added, resulting in a dispersant content of 40.0%. The properties of the obtained wax particles are shown in Table 3. The specific gravity of wax particles 1 to 3 is all 3.8 g / cm. 3 It was less than.

[0205] [Table 3]

[0206] <Ink Preparation> The types and amounts of each component shown in the upper rows of Tables 4 to 5 were mixed and stirred. Then, pressure filtration was performed using a membrane filter (manufactured by Sartorius) with a pore size of 5.0 μm to prepare each ink. Acetylenol E60 (product name) is a nonionic surfactant manufactured by Kawaken Fine Chemicals. In addition, the product name "Hydran APX-101H" (manufactured by DIC) was used as the polyurethane resin. The content of high specific gravity particles in the ink is recorded in the "Particle content P (%)" column, and the "Particle D 50 In the "D (nm)" column, enter the D 50 Ink 18 to 20 do not contain particles with high specific gravity, so the "D 50 The "D (nm)" column shows the pigment's D 50 The following is stated.

[0207] [Table 4]

[0208] [Table 5]

[0209] <Recording Media> The following recording media were prepared. Recording medium 1: Product name "Graphical Indoor Ultra-Transparent PET with Adhesive Gloss GIY-0305", manufactured by Lintec Sign Systems, material = PET, 30 msec from the start of contact in the Bristow method 1 / 2 Water absorption up to = 0 mL / m 2 More than 10mL / m 2 below Recording medium 2: Product name "Recycled colored paper (Fresh Color) C-57 Bear (Dark Black)", manufactured by Daio Paper Corporation, size: wide roll, 30 msec from the start of contact in the Bristow method 1 / 2 Water absorption rate up to 10 mL / m 2 Super.

[0210] <Evaluation> Each of the prepared inks and reaction liquids was filled into an ink tank of an inkjet recording device having a recording head shown on the left side of Table 6. In Table 6, for the example with "1" in the recording head column, the ink was filled into the ink storage section of an inkjet recording device having the main part shown in Figure 1 (wherein the recording head scans back and forth in a direction intersecting the arrangement direction of the ejection port array).

[0211] In the example where "2" is entered in the recording head column, ink is filled in the ink storage section of an inkjet recording device in which the line head 800 shown in Fig. 20 is incorporated so that the ejection port array intersects with the transport direction of the recording medium. When recording on the recording medium P, the line head 800 does not move relative to the recording medium P.

[0212] The example with "3" in the recording head column is one in which the ink storage section of a recording head is filled with ink, and has a supply flow path that communicates between the ejection elements and through which ink flows, but does not have a recovery flow path. Here, Fig. 22 is a perspective view of a line-shaped recording head, and is a line head in which ejection element substrates 810, on which ejection port arrays are arranged, are linearly arranged.

[0213] Using an inkjet recording device having the above configuration, the following evaluations were performed under the conditions shown on the left side of Table 6. In the examples and comparative examples using recording head "1" or "3", the image pattern shown in Fig. 23 was recorded on the recording medium. 2303 in Fig. 23 reproduces the situation where ink is intermittently ejected by the multi-pass method, and if no image unevenness occurs in this area, it means that the intermittent ejection stability is excellent.

[0214] First, the reaction liquid was applied to the entire surface of the recording medium so that the recording duty was 20%. Then, as shown in FIG. 23, a 30 mm margin was provided on the left end along the conveying direction of the recording medium, and a solid image 2301 with a width of 30 mm and a length of 200 mm and an ink recording duty of 60% was recorded. Then, a pattern was recorded in which a solid image 2302 with a width of 1000 mm x 30 mm and an ink recording duty of 300% was provided five times with a gap of 10 mm adjacent to the solid image 2301 and a gap of 30 mm in the conveying direction of the recording medium. The recording environment was a temperature of 25° C. and a relative humidity of 50%. In this embodiment, an image recorded under the condition that one drop of 4.0 pL of ink is applied to a unit area of ​​1 / 1,200 inch x 1 / 1,200 inch is defined as having a recording duty of 100%. In Comparative Example 1, an image was recorded without operating the circulation pump 500 shown in FIG. 5.

[0215] In the reference example using the recording head "2", an image pattern was recorded on the recording medium by rotating the image pattern shown in FIG. 23 by 90 degrees clockwise. The image pattern was recorded in one pass by conveying the paper at 50 inches / second. In the reference example 3, assuming JP2017-101232A, the aforementioned image pattern was recorded using the recording head "2" and evaluated.

[0216] The obtained pattern was visually inspected for the presence or absence of image unevenness at the location 2303 in Fig. 23, and the suppression of image unevenness was evaluated according to the following evaluation criteria. In the present invention, in the evaluation criteria for each item shown below, "AA", "A" and "B" were considered to be acceptable levels, and "C" was considered to be an unacceptable level. The evaluation results are shown in Table 6. AA: No image unevenness was observed in the images recorded with any number of passes (8 passes, 16 passes, and 32 passes). A: Image unevenness was observed in the image recorded with 32 passes, but no image unevenness was observed in the images recorded with 8 passes and 16 passes. B: Image unevenness was observed in the images printed with 16 passes and 32 passes, but no image unevenness was observed in the image printed with 8 passes. C: Image unevenness was observed in images recorded with any number of passes (8 passes, 16 passes, and 32 passes).

[0217] [Table 6]

[0218] The evaluation result of Example 10 was the same as that of Example 1, ie, AA rank, but when these were compared, Example 1 was superior. [Explanation of symbols]

[0219] 1 Recording head 12 Pressure Chamber 15 Discharge element 120 First pressure adjustment means 130 Supply Channel 140 Recovery channel 160 Bypass flow path 500 Circulation Pump 800 Ejection element substrate

Claims

1. A plurality of ejection ports for ejecting the water-based ink; A pressure chamber communicating with the discharge port; and an ejection unit that is disposed in the pressure chamber and has an ejection element that generates energy for ejecting water-based ink from the plurality of ejection ports; a supply flow path for supplying the water-based ink to the pressure chamber of the ejection unit; and an inkjet recording method comprising: scanning a recording head, which includes a circulation unit having a recovery flow path for recovering the water-based ink from the pressure chamber of the discharge unit, back and forth in a direction intersecting a transport direction of the recording medium, while discharging the water-based ink from the plurality of discharge ports, thereby recording an image on a unit area of ​​the recording medium by the back and forth scan a plurality of times, The water-based ink has a specific gravity of 3.8 g / cm ３ An ink-jet recording method comprising the above particles.

2. 2. The ink jet recording method according to claim 1, wherein the particles have a volume-based cumulative 50% particle diameter (nm) of 200 nm or more and 300 nm or less.

3. the particles are titanium oxide particles at least a part of whose surface is coated with silica, 2. The ink-jet recording method according to claim 1, wherein the titanium oxide particles are dispersed at least by the action of silica.

4. The inkjet recording method according to claim 1, wherein a content (% by mass) of the particles in the aqueous ink is from 0.5% by mass to 20.0% by mass based on the total mass of the ink.

5. 2. The ink jet recording method according to claim 1, wherein a flow velocity (mm / s) of the water-based ink in the circulation path is 10 mm / s or more and 30 mm / s or less.

6. 2. The ink jet recording method according to claim 1, wherein the moving speed (inches / s) of the recording head during the reciprocating scan is 20 inches / s or more.

7. 2. The ink jet recording method according to claim 1, wherein the recording head further comprises a circulation pump for causing the aqueous ink in the recovery flow path to flow into the supply flow path.

8. the circulation unit has a first pressure adjusting means for adjusting the pressure in the supply flow path, the first pressure adjustment means has a first valve chamber, a first pressure control chamber, and a first opening that communicates the first valve chamber and the first pressure control chamber; 2. The ink jet recording method according to claim 1, wherein the first valve chamber includes a first valve that opens and closes the first opening in response to a pressure change in the first pressure control chamber.

9. the circulation unit further has a second pressure adjusting means for adjusting the pressure in the recovery flow path, the second pressure adjustment means has a second valve chamber, a second pressure control chamber, and a second opening that communicates the second valve chamber and the second pressure control chamber, 9. The ink jet recording method according to claim 8, wherein the second valve chamber includes a second valve that opens and closes the second opening in response to a pressure change in the second pressure control chamber.

10. The recording medium is １／２ The amount of water absorbed is 10 mL / m ２ The ink jet recording method according to claim 1, wherein:

11. A plurality of ejection ports for ejecting the water-based ink; A pressure chamber communicating with the discharge port; and an ejection unit that is disposed in the pressure chamber and has an ejection element that generates energy for ejecting water-based ink from the plurality of ejection ports; a supply flow path for supplying the water-based ink to the pressure chamber of the ejection unit; and an inkjet recording device that uses a recording head including a circulation unit having a recovery flow path for recovering the water-based ink from the pressure chamber of the discharge unit, while scanning the recording head back and forth in a direction intersecting a transport direction of the recording medium, to discharge the water-based ink from the plurality of discharge ports to record an image on the recording medium, The water-based ink has a specific gravity of 3.8 g / cm ３ An ink jet recording apparatus comprising the above particles.

12. A plurality of ejection ports for ejecting the water-based ink; A pressure chamber communicating with the discharge port; and an ejection unit that is disposed in the pressure chamber and has an ejection element that generates energy for ejecting water-based ink from the plurality of ejection ports; a supply flow path for supplying the water-based ink to the pressure chamber of the ejection unit; and a recording head including a circulation unit having a recovery flow path for recovering the water-based ink from the pressure chamber of the discharge unit, the water-based ink being discharged from the plurality of discharge ports while scanning the recording head back and forth in a direction intersecting a transport direction of the recording medium, the water-based ink being discharged from the plurality of discharge ports to record an image on the recording medium, The water-based ink has a specific gravity of 3.8 g / cm ３ A water-based ink comprising particles having the above structure.

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