Inkjet printing method

Abstract

The invention relates to an ink-jet printing method. In an inkjet printing method for discharging ink from a liquid discharge head, the ink contains titanium oxide, and the precipitation rate in the ink based on the Stokes equation is 1.0 * 10-11 m / s or more. The liquid discharge head includes a discharge port, a pressure chamber, an energy generating element, an upstream flow passage for supplying liquid to the pressure chamber, a downstream flow passage communicating with the pressure chamber, and a pump communicating with the upstream flow passage and the downstream flow passage and forming a circulation path, the ink circulates in the circulation path in the order of the upstream flow channel, the pressure chamber, the downstream flow channel, and the upstream flow channel, and the liquid discharge head is configured to perform reciprocating scanning, and a scanning speed in a region where the liquid discharge head scans at a constant speed is higher than a deposition speed.

Description

Technical Field

[0001] The present disclosure relates to an inkjet printing method. Background Art

[0002] In recent years, inkjet printing devices have been widely used when outputting advertisements and exhibits using printing media such as paper and resin films. For example, in order to depict a clear color image even on a transparent printing medium, not only black and basic color inks (hereinafter, these inks may be collectively referred to as color inks) are used, but also white ink is used in combination. Specifically, white ink is applied in advance to an area of ​​the transparent printing medium including a range where an image is to be printed to implement background color processing, and color ink is applied to the area. Alternatively, a printing method of applying inks in reverse order (so-called reverse color printing) is implemented.

[0003] As a colorant for white ink, titanium oxide is widely used because of its low cost and excellent properties required for white ink (such as whiteness and concealment). However, titanium oxide has the problem of easy precipitation. Therefore, from the viewpoint of inhibiting the precipitation of titanium oxide in white ink, methods for improving dispersion stability by surface treatment of titanium oxide have been studied. For example, PCT Japanese Translation Patent Publication No. 2017-521348 proposes a method for manufacturing a dry titanium dioxide product, in which titanium oxide is surface treated with silica, and then surface treated and dried with a silane coupling agent, so that part of the silane coupling agent is covalently bonded to the surface of the titanium oxide particles.

[0004] International Publication No. WO2018 / 190848 proposes an ink containing titanium oxide surface-treated with aluminum oxide, a monovalent metal salt, and aluminum oxide fine particles.

[0005] That is, in PCT Japanese Patent Publication No. 2017-521348 and International Publication No. WO2018 / 190848, attempts have been made to stably discharge white ink and suppress the occurrence of image unevenness in printed images by using white ink that suppresses precipitation of titanium oxide.

[0006] The inventors of the present invention considered, as a method for achieving stable discharge of ink in an inkjet printing method using ink (for example, white ink containing titanium oxide that easily precipitates), using titanium oxide particles with high redispersibility and configuring a liquid discharge head so that even precipitated particles will redisperse without constituting an ink that inhibits the precipitation of titanium oxide.

[0007] Therefore, the present disclosure provides an inkjet printing method in which the redispersibility of an ink containing titanium oxide is enhanced and the discharge stability of the ink is improved. Summary of the invention

[0008] The present disclosure for solving the above-mentioned problems is an inkjet printing method for discharging ink from a liquid discharge head, wherein the ink contains titanium oxide; and the precipitation rate based on the Stokes equation in the ink is 1.0×10 -11 m / s or more; the liquid discharge head includes a discharge port for discharging ink, a pressure chamber for supplying ink to the discharge port, an energy generating element for generating energy for discharging ink, an upstream flow channel for supplying liquid to the pressure chamber, a downstream flow channel connected to the pressure chamber, and a pump connected to the upstream flow channel and the downstream flow channel to form a circulation path, in which the ink circulates in the order of the upstream flow channel, the pressure chamber, the downstream flow channel and the upstream flow channel; the liquid discharge head is configured to scan reciprocally in a direction orthogonal to the conveying direction of the printing medium to which the ink is applied; and the scanning speed in the area where the liquid discharge head scans at a constant speed is higher than the sedimentation speed.

[0009] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1A It is a perspective view for explaining the liquid discharge device.

[0011] Figure 1B is a block diagram showing a control system of the liquid discharge apparatus.

[0012] Figure 2 is an exploded perspective view of the liquid discharge head.

[0013] Figure 3A A vertical cross section of the liquid discharge head is shown.

[0014] Figure 3B is an enlarged cross-sectional view of the discharge module.

[0015] Figure 4 This is a schematic diagram of the appearance of the cycle unit.

[0016] Figure 5 is a vertical cross-sectional view showing the circulation path.

[0017] Figure 6 is a block diagram schematically illustrating a cycle path.

[0018] Figures 7A to 7C is a cross-sectional view showing an example of a pressure regulating device.

[0019] Fig. 8A and Figure 8B This is a perspective view of the circulation pump.

[0020] Fig. 9 yes Fig. 8AA cross-sectional view of the circulation pump is shown taken along line IX-IX.

[0021] FIG. 10A to FIG. 10E It is a diagram for explaining the flow of ink in the liquid discharge head.

[0022] Fig.11A and 11B is a schematic diagram showing a circulation path in the discharge unit.

[0023] Fig.12 3 is a diagram showing the opening plate 330 .

[0024] Fig.13 It is a diagram showing a discharge element substrate.

[0025] FIG. 14A to FIG. 14C is a cross-sectional view showing the flow of ink in the discharge unit.

[0026] Fig.15A and 15B is a cross-sectional view showing the vicinity of the discharge port.

[0027] Fig.16A and Fig. 16B It is a cross-sectional view showing a comparative example near a discharge port.

[0028] Fig.17 It is a diagram showing a comparative example of a discharge element substrate.

[0029] Fig.18A and Fig.18B is a diagram showing a flow channel configuration of a liquid discharge head.

[0030] Fig.19 is a diagram showing a connection state of a main body portion of a liquid discharge apparatus and a liquid discharge head.

[0031] Fig. 20 is a diagram showing an ink circulation system.

[0032] Fig.21 is a diagram showing an ink circulation system.

[0033] Fig.22A and Fig. 22B It is a cross-sectional view of the connection portion between the circulation unit and the discharge unit. DETAILED DESCRIPTION

[0034] Inkjet printing method

[0035] The inkjet printing method of the present disclosure is a method of printing an image on a printing medium by discharging ink described later from a print head of an inkjet system.

[0036] The print medium is not particularly limited, and a transparent or colored print medium can be used. The print medium can be a poorly absorbent medium (non-absorbent medium) with low liquid absorption capacity, such as a resin film. The unit area of ​​the print medium to which the ink is applied can be a multi-pass printing in which the relative scanning of the print head and the print medium is performed multiple times. In particular, the application of white ink and the application of colored ink to the unit area can be implemented by different relative scanning. Therefore, the time for which the inks are in contact with each other becomes longer, which tends to inhibit their mixing. The unit area can be set to an arbitrary area, such as 1 pixel or 1 band.

[0037] The present inventors first studied a method for improving the redispersibility when an ink (hereinafter also referred to as "ink") containing titanium oxide (e.g., white ink) is precipitated. As a result of the present inventors' study, it was found that in order to improve the redispersibility of the ink, the precipitation velocity (terminal velocity in precipitation) based on the Stokes equation needs to reach 1.0×10 -11 The sedimentation velocity based on the Stokes equation is the velocity at which the particles move at a constant speed due to the balance between the drag and buoyancy forces exerting an upward force on the particles and the gravity forces exerting a downward force on the particles.

[0038] However, when such an ink having high redispersibility is used, titanium oxide itself in the ink tends to precipitate. Therefore, a liquid discharge head that handles such a white ink requires a mechanism for circulating the ink.

[0039] The present inventors have studied and found that it is difficult to redisperse the precipitated titanium oxide in some cases by simply providing a mechanism for circulating the ink. Therefore, it has been found that the titanium oxide can be sufficiently redispersed by a liquid discharge head having a mechanism for circulating the ink, the mechanism being configured so that scanning is performed in a direction orthogonal to the conveying direction of the print medium.

[0040] Figure 1A : is a perspective view schematically showing a liquid discharge device using a liquid discharge head 1. The device is configured so that a carriage 60 loaded with the liquid discharge head 1 reciprocates in the main scanning direction along a guide shaft 51. In the present disclosure, it is considered that the precipitation of ink in the liquid discharge head 1 is suppressed by shaking the ink by utilizing the acceleration motion and uniform motion caused by the reciprocating motion of the carriage 60. In addition, in the present disclosure, since the entire circulation mechanism of the ink in the liquid discharge head is arranged on the carriage, the precipitation suppression effect caused by the reciprocating motion affects all the ink in the circulation path. That is, in the present disclosure, the liquid discharge head has a mechanism for circulating the ink in the circulation path in the liquid discharge head, and the reciprocating motion of the carriage relative to the ink in the circulation path further promotes redispersion and allows the ink with uniform pigment concentration to flow into the pressure chamber to improve the discharge stability of the ink.

[0041] Will refer to Figure 5The circulation of ink in the liquid discharge head is described. Figure 5 It is a cross-sectional view showing the vicinity of a discharge port 13 in an example of a liquid discharge head of the present disclosure described later.

[0042] Figure 5 The liquid discharge head 1 shown includes: a discharge port 13 for discharging a reaction liquid; a pressure chamber 12 including a discharge element 15 for generating energy for discharging the reaction liquid; and a common supply channel 18 (upstream flow channel) and a common collection channel 19 (downstream flow channel) which are interconnected between the discharge port 13 and the discharge element 15 and in which the reaction liquid flows. The reaction liquid passes between the discharge port 13 and the discharge element 15 and flows to the common supply channel 18 and the common collection channel 19 (downstream flow channel). Figure 5 ). In addition, the liquid discharge head 1 includes a pump 500 configured to allow the liquid in the common collecting channel 19 to flow in the common supply channel 18. Therefore, in the liquid discharge head 1, a circulation path is formed in which the ink circulates in the order of the common supply channel 18, the pressure chamber 12, the common collecting channel 19, and the common supply channel 18.

[0043] In the present disclosure, the redispersion of titanium oxide in the ink is promoted by the reciprocating motion of the carriage 60 and the liquid discharge head 1. In a liquid discharge device including a serial type liquid discharge head, generally, the carriage 60 performs printing by repeating constant speed scanning near the center of the scanning area and accelerating and decelerating at both ends of the scanning area. The scanning speed in the area where the carriage 60 performs constant speed scanning can be higher than the sedimentation speed of the ink. Therefore, since the titanium oxide particles in the ink are accelerated in a direction inclined to the direction of gravity, it takes a longer time for the titanium oxide particles to settle to the bottom of the flow channel. That is, the ink is less likely to settle. In addition, the acceleration in the acceleration and deceleration motion area of ​​the carriage 60 can be higher than the acceleration of gravity. Therefore, since the acceleration in the direction inclined to the direction of gravity can be applied to the titanium oxide particles every time the direction is changed while the carriage movement direction is changed, the effect of easily promoting the redispersion of the ink can be obtained.

[0044] The scanning speed of the carriage 60 can be changed according to the pattern to be printed or the ink (liquid type) to be used. For example, the constant scanning speed is set to 30 ips (inches / second) when printing ink that requires drying time (such as white ink containing titanium oxide), and the constant scanning speed is set to 60 ips when printing a reaction liquid or another ink. Therefore, when at least one of a color ink containing no titanium oxide or a titanium oxide concentration lower than that of a white ink and a reaction liquid is discharged from the liquid discharge head, it can be considered to set the scanning speed of the liquid discharge head when discharging white ink to be slower than the scanning speed of the liquid discharge head when discharging color ink or reaction liquid. When discharging a liquid that requires a shorter drying time than white ink, it is possible to print more efficiently by increasing the scanning speed compared to when discharging white ink. When the constant scanning speed of the carriage 60 changes according to the ink type, the acceleration of the acceleration and deceleration motion of the carriage 60 at both ends of the scanning area can also be changed correspondingly to the constant scanning speed. For example, consider a configuration such that when the constant scanning speed of the carriage 60 is 0 ips to 45 ips, the carriage 60 is scanned at 10 m / s 2 Acceleration and deceleration are implemented, and when the constant scanning speed of the carriage 60 is 45 ips to 60 ips, the speed is 6 m / s. 2 Implement acceleration and deceleration.

[0045] (1) Liquid discharge equipment

[0046] With respect to a liquid discharge device (inkjet printing device) that can be used in the inkjet printing method of the present disclosure, a suitable embodiment of the present disclosure will now be described in detail with reference to the accompanying drawings. The present embodiment below does not limit the subject matter of the present disclosure, and not all combinations of the features described in the present embodiment are necessary for the scheme of the present disclosure. The same components are given the same figure numerals. In the present embodiment, an example of a thermal system that discharges liquid by generating bubbles through an electrothermal conversion element as a discharge element for discharging liquid will be described, but the discharge element is not limited to this. A liquid discharge head that uses a discharge system or other discharge system that discharges liquid using a piezoelectric element (piezo) can also be applied. In addition, the pump, pressure control device, etc. described later are not limited to the structures described in the embodiments and the accompanying drawings.

[0047] Liquid discharge equipment

[0048] Figure 1A and Figure 1B 1 is a diagram for explaining a liquid discharge device and an enlarged view of a liquid discharge head of the liquid discharge device and its vicinity. Figure 1A and Figure 1B A schematic configuration of a liquid discharge apparatus 50 according to the present embodiment is described. Figure 1Ais a perspective view schematically showing a liquid discharge apparatus using the liquid discharge head 1. The liquid discharge apparatus 50 of the present embodiment constitutes a serial type inkjet printing apparatus that performs printing on a printing medium P by discharging ink as liquid while scanning the liquid discharge head 1.

[0049] The liquid discharge head 1 is loaded on the carriage 60. The carriage 60 reciprocates in the main scanning direction (X direction) along the guide shaft 51. The print medium P is transported by the transport rollers 55, 56, 57 and 58 to the sub-scanning direction (Y direction) intersecting (orthogonal in this example) the main scanning direction. In each of the drawings referred to below, the Z direction indicates the vertical direction and intersects (orthogonal in this example) the XY plane defined by the X direction and the Y direction. The liquid discharge head 1 is configured to be detachable from and attached to the carriage 60 by a user.

[0050] The liquid discharge head 1 is formed by including a circulation unit 54 and a discharge unit 3 (see Figure 2 Although a specific configuration will be described later, the discharge unit 3 is provided with a plurality of discharge ports and an energy generating element (hereinafter referred to as a discharge element) that generates discharge energy for discharging the liquid through each discharge port.

[0051] The liquid discharge device 50 forms a prescribed image on the print medium P by repeating the printing scan and the conveying operation of conveying the print medium P to the sub-scanning direction. During the repeated printing scan, the liquid discharge head 1 loaded on the carriage 60 performs printing by discharging ink while moving in the main scanning direction. The liquid discharge head 1 of the present embodiment is configured to be able to discharge 4 kinds of inks including ink containing titanium oxide. However, the configuration of the inkjet printing device in the present disclosure is not limited to the configuration of discharging 4 kinds of liquids. For example, a configuration that can discharge black (K), cyan (C), magenta (M), yellow (Y) and white (W) inks can be exemplified. In this case, a full-color image can be printed with these inks. However, the ink that can be discharged from the liquid discharge head 1 is not limited to the above 5 types. The present disclosure can be applied to liquid discharge heads for discharging other types of inks, reaction liquids other than inks, etc. That is, the type and quantity of liquid discharged from the liquid discharge head are not limited.

[0052] The liquid discharge device 50 is provided with a cap member (not shown) capable of covering a discharge port surface of the liquid discharge head where the discharge port is formed at a position deviated from the conveying path of the print medium P in the X direction. The cap member covers the discharge port surface of the liquid discharge head 1 during a non-printing operation and is used to prevent the discharge port from drying and protect the discharge port, perform an ink suction operation through the discharge port, and the like.

[0053] Figure 1AThe illustrated liquid discharge head 1 is an example in which four circulation units 54 corresponding to four types of inks are provided in the liquid discharge head 1, and it is sufficient to provide the circulation units 54 according to the type of liquid to be discharged. A plurality of circulation units 54 for one type of liquid may be provided. That is, the liquid discharge head 1 may also be configured to include more than one circulation unit. This configuration may be used to circulate only at least one ink containing titanium oxide, rather than to circulate all four types of inks.

[0054] Figure 1B 1 is a block diagram showing a control system of the liquid discharge device 50. The CPU 103 is used as a control device for controlling the operation of each part of the liquid discharge device 50 based on a program such as a processing program stored in the ROM 101. The RAM 102 is used as a work area when the CPU 103 implements processing, etc. The CPU 103 receives image data from a host device 400 outside the liquid discharge device 50 to control the head driver 1A and control the driving of the discharge element provided in the discharge unit 3. The CPU 103 also controls the drivers of various actuators provided in the liquid discharge device. For example, the CPU 103 controls a motor driver 105A such as a carriage motor 105 for moving the carriage 60 and a motor driver 104A for a conveying motor 104 for conveying the print medium P. In addition, the CPU 103 controls, for example, a pump driver 500A for driving a circulation pump 500 described later and a pump driver 21A for driving an external pump 21. Figure 1B A configuration for performing processing on image data from the host device 400 is shown, but processing may be performed by the liquid discharge device 50 without relying on data from the host device 400 .

[0055] Basic Configuration of Liquid Discharge Head

[0056] Figure 2 is an exploded perspective view of the liquid discharge head 1 of the present embodiment. Figure 3A yes Figure 2 A cross-sectional view of the liquid discharge head 1 taken along line IIIA-IIIA is shown. Figure 3A is an overall vertical sectional view of the liquid discharge head 1, Figure 3B yes Figure 3A FIG. 3 is an enlarged view of the discharge module 300 shown in FIG. Figure 1A and Figure 1B In the case of Figure 2 and Figure 3A as well as Figure 3B Focusing on the above, the basic configuration of the liquid discharge head 1 in the present embodiment will be described.

[0057] like Figure 2As shown in FIG. 1 , the liquid discharge head 1 is constituted by including a circulation unit 54 and a discharge unit 3 for discharging ink supplied from the circulation unit 54 onto a printing medium P. The liquid discharge head 1 according to the present embodiment is fixed to and supported by the carriage 60 through a positioning device (not shown) and an electrical contact provided on the carriage 60 of the liquid discharge device 50. The liquid discharge head 1 is moved along the carriage 60 together with the carriage 60. Figure 1A The ink is discharged while moving in the main scanning direction (X direction) shown in FIG. 1 , so that printing is performed on the printing medium P.

[0058] The ink supply tube 59 is provided to the external pump 21, and the external pump 21 is connected to the ink tank 2 (liquid storage portion) as a supply source of ink (see Figure 1A ). The end of the ink supply tube 59 is provided with a liquid connector (not shown). When the liquid discharge head 1 is loaded on the liquid discharge device 50, the liquid connector provided at the end of the ink supply tube 59 is airtightly connected to the liquid connector insertion port 53a, which is an inlet port for liquid provided in the head housing 53 of the liquid discharge head 1. Therefore, an ink supply path starting from the ink tank 2, passing through the external pump 21 and reaching the liquid discharge head 1 is formed. In the present embodiment, since 4 kinds of ink are used, 4 groups of ink tanks 2, external pumps 21, ink supply tubes 59 and circulation units 54 are provided so as to correspond to the inks respectively and independently form 4 ink supply paths corresponding to the corresponding inks. Therefore, the liquid discharge device 50 of the present embodiment includes an ink supply system, to which ink is supplied from the ink tank 2 provided outside the liquid discharge head 1. The liquid discharge device 50 of the present embodiment does not include an ink collection system for collecting ink in the liquid discharge head 1 in the ink tank 2. Therefore, the liquid discharge head 1 includes a liquid connector insertion port 53a for connecting the ink supply tube 59 of the ink tank 2, but does not include a connector insertion port for connecting a tube for collecting the ink in the liquid discharge head 1 in the ink tank 2. The liquid connector insertion port 53a is provided for each ink.

[0059] exist Figure 3A , 54A represents a circulation unit for the first ink, 54B represents a circulation unit for the second ink, 54C represents a circulation unit for the third ink, and 54D represents a circulation unit for the fourth ink. Among these inks (the first, second, third and fourth inks), when at least one ink contains titanium oxide, the present disclosure can be appropriately used. These circulation units have substantially the same configuration, and when the circulation units are not particularly distinguished, they are all collectively referred to as circulation units 54 in this embodiment.

[0060] exist Figure 2 and Figure 3AIn the embodiment, the discharge unit 3 includes two discharge modules 300, a first support member 4, a second support member 7, an electrical wiring member (electrical wiring tape) 5 and an electrical contact substrate 6. Figure 3B As shown, the discharge module 300 includes a silicon substrate 310 having a thickness of 0.5 mm to 1 mm and a plurality of discharge elements 15 provided on one surface of the silicon substrate 310. The discharge element 15 in this embodiment is composed of an electrothermal conversion element (heater) that generates heat energy as discharge energy for discharging liquid. Electricity is supplied to each discharge element 15 through electrical wiring formed on the silicon substrate 310 by film forming technology.

[0061] The discharge port forming member 320 is formed on the surface ( Figure 3B In the discharge port forming member 320, a plurality of pressure chambers 12 corresponding to a plurality of discharge elements 15 and a plurality of discharge ports 13 for discharging ink are formed by photolithography technology. In addition, in the silicon substrate 310, a common supply channel 18 and a common collection channel 19 are formed. In addition, a supply connection channel 323 that connects the common supply channel 18 with each pressure chamber 12 and a collection connection channel 324 that connects the common collection channel 19 with each pressure chamber 12 are formed in the silicon substrate 310. In the configuration of this embodiment, one discharge module 300 implements the discharge of two types of ink. That is, in Figure 3A Of the two discharge modules shown, the discharge module 300 located on the left side of the figure implements the discharge of the first ink and the second ink, and the discharge module 300 located on the right side of the figure implements the discharge of the third ink and the fourth ink. This combination is an example, and the inks can be any combination. A configuration in which one discharge module discharges one ink may be adopted, or a configuration in which one discharge module discharges three or more inks may be adopted. The two discharge modules 300 do not need to discharge the same number of types of inks. A configuration including one discharge module 300 may be adopted, or a configuration including three or more discharge modules 300 may be adopted. In addition, in Figure 3A and Figure 3B In the example shown, two discharge port arrays extending in the Y direction are formed for one ink. A pressure chamber 12, a common supply channel 18, and a common collection channel 19 are formed for each of the plurality of discharge ports 13 constituting each discharge port array.

[0062] An ink supply port and an ink collection port described later are formed on the rear surface ( Figure 3B The ink supply port supplies ink from the ink supply channel 48 to the plurality of common supply channels 18, and the ink collection port collects ink from the plurality of common collection channels 19 into the ink collection channel 49.

[0063] The ink supply port and the ink collection port mentioned here refer to openings for supplying and collecting ink during the forward circulation of ink described later. That is, in the forward ink circulation, ink is supplied from the ink supply port to each common supply channel 18, and ink is collected from each common collection channel 19 to the ink collection port. However, an ink circulation in which the ink flows in the reverse direction may also be implemented. In this case, ink is supplied from the above-mentioned ink collection port to the common collection channel 19, and ink is collected from the common supply channel 18 to the ink supply port.

[0064] like Figure 3A As shown, the rear surface ( Figure 3A The top surface of the first support member 4 is bonded and fixed to one surface ( Figure 3A bottom surface in the middle).

[0065] The first supporting member 4 is formed with an ink supply channel 48 and an ink collection channel 49 passing through from one surface thereof to the other surface. One opening of the ink supply channel 48 communicates with the above-mentioned ink supply port of the silicon substrate 310, and one opening of the ink collection channel 49 communicates with the above-mentioned ink collection port of the silicon substrate 310. The ink supply channel 48 and the ink collection channel 49 are independently provided for each ink.

[0066] The opening 7a (see Figure 2 ) is bonded and fixed to one surface of the first supporting member 4 ( Figure 3A top surface in the ).

[0067] The second supporting member 7 holds the electric wiring member 5 electrically connected to the discharge module 300. The electric wiring member 5 is a member for applying an electric signal to the discharge module 300 to discharge ink. The electrical connection portion between the discharge module 300 and the electric wiring member 5 is sealed with a sealing material (not shown), and is protected from ink corrosion and external impact.

[0068] The electric contact substrate 6 is thermocompression-bonded to the end portion 5a of the electric wiring member 5 using an anisotropic conductive film (not shown). Figure 2 ) to electrically connect the electric wiring member 5 and the electric contact substrate 6. The electric contact substrate 6 includes an external signal input terminal (not shown) for receiving an electric signal from the liquid discharge device 50.

[0069] In addition, a joint member 8 ( Figure 3A ). The joint member 8 is formed with a supply port 88 and a collection port 89 for each ink. The supply port 88 and the collection port 89 allow the ink supply channel 48 and the ink collection channel 49 of the first support member 4 to communicate with the flow channel formed in the circulation unit 54. Figure 3A, the supply port 88A and the collection port 89A correspond to the first ink, the supply port 88B and the collection port 89B correspond to the second ink, the supply port 88C and the collection port 89C correspond to the third ink, and the supply port 88D and the collection port 89D correspond to the fourth reaction liquid.

[0070] The opening at one end portion of each of the ink supply channel 48 and the ink collection channel 49 of the first support member 4 has a small opening area that accommodates the ink supply port and the ink collection port in the silicon substrate 310. In contrast, the shape of the opening of the other end portion of each of the ink supply channel 48 and the ink collection channel 49 of the first support member 4 has an enlarged opening area that is the same as the large opening area of ​​the joint member 8, and the large opening area is formed to accommodate the flow channel of the circulation unit 54. In such a configuration, it is possible to suppress an increase in the flow channel resistance to the ink collected from each collection channel. However, the opening shapes of the one end portion and the other end portion of each of the ink supply channel 48 and the ink collection channel 49 are not limited to the above examples.

[0071] In the liquid discharge head 1 having the above-described configuration, the ink supplied to the circulation unit 54 passes through the supply port 88 of the joint member 8 and the ink supply channel 48 of the first support member 4 and flows into the common supply channel 18 through the ink supply port of the discharge module 300. Subsequently, the ink flows from the common supply channel 18 into the pressure chamber 12 through the supply connection channel 323, and a portion of the ink flowing into the pressure chamber is discharged from the discharge port 13 by the drive of the discharge element 15. The remaining ink that is not discharged flows out of the pressure chamber 12, passes through the collection connection channel 324 and the common collection channel 19, and flows into the ink collection channel 49 of the first support member 4 through the ink collection port. The ink that has flowed into the ink collection channel 49 then flows into the circulation unit 54 through the collection port 89 of the joint member 8 and is collected.

[0072] Components of a circulation unit

[0073] Figure 4 1 is a schematic diagram of the appearance of a circulation unit 54 corresponding to one ink applied to the printing device of this embodiment. In addition to the circulation pump 500, the circulation unit 54 may also include a filter 110, a first pressure control device 120 and a second pressure control device 150. These components are as follows: Figure 5 and Figure 6 The ink discharge module 300 shown is connected to each flow channel and constitutes a circulation path for performing supply and collection of ink to the discharge module 300 in the liquid discharge head 1.

[0074] Circulation path in the liquid discharge head

[0075] Figure 51 is a vertical cross-sectional view schematically showing a circulation path for one ink (one color ink) configured in the liquid discharge head 1. In order to more clearly explain the circulation path, Figure 5 The relative positions of the various components (such as the first pressure control device 120, the second pressure control device 150 and the circulation pump 500) are simplified. Therefore, the relative positions of the various components are different from those described later. Fig.19 The configuration is different. Figure 6 It is schematically shown Figure 5 The block diagram of the loop path shown in Figure 5 and Figure 6 As shown, the first pressure control device 120 includes a first valve chamber 121 and a first pressure control chamber 122. The second pressure control device 150 includes a second valve chamber 151 and a second pressure control chamber 152. The first pressure control device 120 is configured so that the control pressure is relatively higher than the control pressure of the second pressure control device 150. In this embodiment, circulation within a certain pressure range is achieved in the circulation path by using these two pressure control devices 120 and 150.

[0076] The configuration is such that the ink flows in the pressure chamber 12 (discharge element 15) at a certain flow rate according to the pressure difference between the pressure in the first pressure regulating device 120 and the pressure in the second pressure regulating device 150. Figure 5 and Figure 6 Description is given of a circulation path and the flow of ink in the circulation path in the liquid discharge head 1. Arrows in the respective drawings indicate the direction in which the ink flows.

[0077] The connection state of each component in the liquid discharge head 1 will be described.

[0078] The ink tank 2 ( Figure 6 ) is connected to the circulation unit 54 through the ink supply pipe 59 (FIG. 1). The ink flow path (inlet flow path) located upstream of the circulation unit 54 is provided with a filter 110. The ink supply path (inlet flow path) located downstream of the filter 110 is connected to the first valve chamber 121 of the first pressure control device 120. The first valve chamber 121 is connected to the first pressure control chamber 122 through the communication port 191A, and the communication port can be connected to the first pressure control chamber 122. Figure 5 The valve 190A shown opens and closes. The inlet flow channel is a flow channel into the liquid discharge head 1 for supplying liquid in the ink tank 2 provided outside the liquid discharge head 1 to the pressure chamber 12 .

[0079] The first pressure control chamber 122 is connected to the supply channel 130, the bypass flow channel 160, and the pump outlet channel 180 of the circulation pump 500. The supply channel 130 is connected to the common supply channel 18 through the above-mentioned ink supply port provided in the discharge module 300. The bypass flow channel 160 is connected to the second valve chamber 151 provided in the second pressure control device 150. The second valve chamber 151 is connected to the second pressure control chamber 152 through the communication port 191B, and the communication port is connected to the second pressure control chamber 152. Figure 5 Valve 190B is shown opened and closed. Figure 5 and Figure 6 In the illustrated example, one end of the bypass flow passage 160 is connected to the first pressure control chamber 122 of the first pressure control device 120, and the other end of the bypass flow passage 160 is connected to the second valve chamber 151 of the second pressure control device 150. One end of the bypass flow passage 160 may be connected to the supply passage 130, and the other end of the bypass flow passage may be connected to the second valve chamber 151.

[0080] The second pressure control chamber 152 is connected to the collection channel 140. The collection channel 140 is connected to the common collection channel 19 through the above-mentioned ink collection port provided in the discharge module 300. In addition, the second pressure control chamber 152 is connected to the circulation pump 500 through the pump inlet channel 170. Figure 5 , 170a represents an inlet port of the pump inlet passage 170.

[0081] Next, the ink flow in the liquid discharge head 1 having the above-described configuration will be described. Figure 6 As shown, the ink stored in the ink tank 2 is pressurized by the external pump 21 provided in the liquid discharge apparatus 50 and is supplied to the circulation unit 54 of the liquid discharge head 1 as a positive-pressure ink flow.

[0082] The ink supplied to the circulation unit 54 passes through the filter 110 to remove foreign matter such as dust and bubbles, and then flows into the first valve chamber 121 provided in the first pressure control device 120. Although the pressure of the ink is reduced due to pressure loss when passing through the filter 110, the ink pressure at this stage is in a positive pressure state. Subsequently, when the valve 190A is in an open state, the ink flowing into the first valve chamber 121 passes through the communication port 191A and flows into the first pressure control chamber 122. The ink flowing into the first pressure control chamber 122 is switched from a positive pressure state to a negative pressure state due to the pressure loss when passing through the communication port 191A.

[0083] Next, the ink flow in the circulation path will be described. The circulation pump 500 operates to send the ink sucked from the pump inlet channel 170 on the upstream side to the pump outlet channel 180 on the downstream side. Therefore, the ink supplied to the first pressure control chamber 122 flows into the supply channel 130 and the bypass flow channel 160 together with the ink sent from the pump outlet channel 180 by the drive pump. Although the details will be described later, in this embodiment, as a circulation pump that can transport liquid, a piezoelectric diaphragm pump is used, which uses a piezoelectric element attached to a diaphragm as a driving source. The piezoelectric diaphragm pump transports liquid by applying a driving voltage to the piezoelectric element to change the pump chamber volume and thereby alternately moving two check valves under the action of pressure changes.

[0084] The ink flowing into the supply channel 130 flows into the pressure chamber 12 through the common supply channel 18 and the ink supply port of the discharge module 300, and part of the ink is discharged from the discharge port 13 under the action of the driving (heating) of the discharge element 15. The remaining ink not used at the time of discharge flows in the pressure chamber 12, passes through the common collection channel 19, and then flows into the collection channel 140 connected to the discharge module 300. The ink flowing into the collection channel 140 flows into the second pressure control chamber 152 of the second pressure regulating device 150.

[0085] In contrast, the ink flowing into the bypass flow channel 160 from the first pressure control chamber 122 flows into the second valve chamber 151, then passes through the communication port 191B, and flows into the second pressure control chamber 152. The ink flowing into the second pressure control chamber 152 through the bypass flow channel 160 and the ink collected from the collection channel 140 are sucked into the circulation pump 500 through the pump inlet channel 170 under the driving action of the circulation pump 500. The ink sucked into the circulation pump 500 is transported to the pump outlet channel 180 and flows into the first pressure control chamber 122 again. Thereafter, the ink flowing into the second pressure control chamber 152 from the first pressure control chamber 122 through the supply channel 130 and then through the discharge module 300, and the ink flowing into the second pressure control chamber 152 through the bypass flow channel 160 both flow into the circulation pump 500. Then, the ink is transported from the circulation pump 500 to the first pressure control chamber 122. Thus, circulation of the ink in the circulation path is implemented.

[0086] As described above, in the present embodiment, the liquid can be circulated along the circulation path formed in the liquid discharge head 1 by the circulation pump 500. Therefore, the viscosity increase of the ink in the discharge module 300 and the accumulation of the precipitated components of the colorant ink can be suppressed, and the fluidity of the ink in the discharge module 300 and the good state of the discharge characteristics in the discharge port can be maintained.

[0087] Since the circulation path in the present embodiment adopts a configuration completed in the liquid discharge head 1, the length of the circulation path can be significantly shortened compared to when the ink circulates between the ink tank 2 provided outside the liquid discharge head and the liquid discharge head 1. Therefore, the circulation of the ink can be implemented using a small-sized circulation pump such as a piezoelectric pump. In particular, in the present disclosure, since the reciprocating motion of the liquid discharge head suppresses the precipitation of particles in the ink and promotes the redispersibility of the ink, it is easy to maintain the dispersibility of the ink even with a small-sized circulation pump.

[0088] In addition, the connection channel of the liquid discharge head 1 and the ink tank 2 is configured to include only a flow channel for supplying ink. That is, the adopted configuration does not require a flow channel for collecting ink from the liquid discharge head 1 to the ink tank 2. Therefore, it is only necessary to provide a tube for supplying ink that connects the ink tank 2 and the liquid discharge head 1, and no tube for collecting ink is required. Therefore, the interior of the liquid discharge device 50 can adopt a simple configuration in which the number of tubes is reduced and the size reduction of the overall device can be achieved. In addition, the reduction in the number of tubes can reduce the ink pressure change caused by the tube oscillation caused by the main scanning of the liquid discharge head 1. The oscillation of the tube during the main scanning of the liquid discharge head 1 becomes a driving load of the carriage motor that drives the carriage 60. Therefore, the reduction in the number of tubes reduces the driving load of the carriage motor, and the main scanning mechanism including the carriage motor can be simplified. In addition, since it is not necessary to collect ink from the liquid discharge head to the ink tank, the size of the external pump 21 can also be reduced. Therefore, according to the present embodiment, while being configured to allow liquid to circulate in the liquid discharge device 50, size reduction and cost reduction can be achieved.

[0089] The flow rate (circulation flow rate) for circulating the reaction solution is preferably 1.0 mL / min to 10.0 mL / min, more preferably 2.0 mL / min to 10.0 mL / min, and further preferably 2.0 mL / min to 5.0 mL / min.

[0090] Pressure control device

[0091] Fig. 7A , 7B 7C are diagrams showing examples of pressure control devices. 7A to 7C , the configuration and function of the pressure control device (the first pressure control device 120 and the second pressure control device 150) built into the above-mentioned liquid discharge head 1 will be described in more detail. The first pressure control device 120 and the second pressure control device 150 have basically the same configuration. Therefore, hereinafter, the first pressure control device 120 will be described as an example, and with respect to the second pressure control device 150, 7A to 7CIn the second pressure control device 150 , the first valve chamber 121 to be described below is replaced by a second valve chamber 151 , and the first pressure control chamber 122 is replaced by a second pressure control chamber 152 .

[0092] The first pressure regulating device 120 includes 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 from each other by a partition 123 provided in the cylindrical housing 125. However, the first valve chamber 121 is communicated with the first pressure control chamber 122 through a communication port 191 formed in the partition 123. The first valve chamber 121 is provided with a valve 190 that switches communication and closing 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 is configured to be in close contact with the partition 123 by the biasing force of the valve spring 200. When the valve 190 is in close contact with the partition 123, the ink flow through the communication port 191 is cut off. In order to enhance the tightness with the partition 123, the contact portion of the valve 190 with the partition 123 may be formed of an elastic material. The valve shaft 190a inserted into the communication port 191 is provided in a protruding state at the central portion of the valve 190. The valve 190 is separated from the partition 123 by pressing the valve shaft 190a against the biasing force of the valve spring 200, and ink can flow in the communication port 191. Hereinafter, a state in which the flow of ink through the communication port 191 is blocked by the valve 190 is referred to as a "closed state", and a state in which ink flows through the communication port 191 is referred to as an "open state".

[0093] The opening portion of the cylindrical housing 125 is blocked by the flexible member 230 and the pressing plate 210. The flexible member 230, the pressing plate 210, the surrounding wall of the housing 125 and the partition 123 form the first pressure control chamber 122. The pressing plate 210 is configured to be displaceable with the displacement of the flexible member 230. The materials of the pressing plate 210 and the flexible member 230 are not particularly limited. For example, the pressing plate 210 may be configured by a resin molded product, and the flexible member 230 may be configured by a resin film. In this case, the pressing plate 210 may be fixed to the flexible member 230 by thermal fusion.

[0094] A pressure adjustment spring 220 (biasing member) is provided between the pressure plate 210 and the partition 123. Fig. 7A As shown, the pressure plate 210 and the flexible member 230 are urged by the biasing force of the pressure adjustment spring 220 in the direction of increasing the internal volume of the first pressure control chamber 122 .

[0095] When the pressure in the first pressure control chamber 122 decreases, the pressure plate 210 and the flexible member 230 are displaced, so that 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 volume, the pressure plate 210 abuts against the valve shaft 190a of the valve 190. Subsequently, when the internal volume of the first pressure control chamber 122 decreases, the valve 190 moves together with the valve shaft 190a against the biasing force of the valve spring 200 and separates from the partition 123. Therefore, the communication port 191 becomes an open state ( Figure 7B status shown).

[0096] In the present embodiment, the connection in the circulation path is set so that the pressure of the first valve chamber 121 is higher than the pressure of the first pressure control chamber 122 when the communication port 191 is in the open state.

[0097] Therefore, when the communication port 191 becomes an open state, ink flows from the first valve chamber 121 into the first pressure control chamber 122. This ink flow displaces the flexible member 230 and the pressure plate 210, so that the internal volume of the first pressure control chamber 122 increases. As a result, the pressure plate 210 is separated from the valve shaft 190a of the valve 190, the valve 190 is in close contact with the partition 123 under the biasing force of the valve spring 200, and the communication port 191 becomes a closed state ( Figure 7C status shown).

[0098] Therefore, in the first pressure regulating device 120 of the present embodiment, when the pressure in the first pressure control chamber 122 decreases below a certain pressure (for example, when the negative pressure becomes stronger), the ink flows from the first valve chamber 121 into the first pressure control chamber 122 through the communication port 191. Therefore, it is configured so that the pressure of the first pressure control chamber 122 does not decrease further. Therefore, the first pressure control chamber 122 is controlled to maintain the pressure within a certain range.

[0099] The pressure of the first pressure control chamber 122 will then be described in more detail.

[0100] As described above, considering the open state of the communication port 191 ( Figure 7B In the open state, the flexible member 230 and the pressure plate 210 are displaced in response to the pressure of the first pressure control chamber 122, and the pressure plate 210 abuts against the valve shaft 190a. In this case, the relationship of the forces acting on the pressure plate 210 is expressed by the following equation 1:

[0101] P2×S2+F2+(P1-P2)×S1+F1=0Equation 1.

[0102] Furthermore, organization of equation 1 with respect to P2 gives the following:

[0103] P2 = -(F1 + F2 + P1 × S1) / (S2 - S1) Equation 2.

[0104] P1: pressure of the first valve chamber 121 (gauge pressure);

[0105] P2: pressure of the first pressure control chamber 122 (gauge pressure);

[0106] F1: Spring force of valve spring 200;

[0107] F2: Spring force of the pressure regulating spring 220;

[0108] S1: the pressure receiving area of ​​valve 190; and

[0109] S2: The pressure-bearing area of ​​the pressure plate 210 .

[0110] Here, the spring force F1 of the valve spring 200 and the spring force F2 of the pressure regulating spring 220 press the valve 190 and the pressure plate 210 ( Figures 7A to 7C The left direction in the first valve chamber 121 is defined as positive. The pressure P1 in the first valve chamber 121 and the pressure P2 in the first pressure control chamber 122 are configured so that the pressure P1 ≥ P2 has a relationship.

[0111] The pressure P2 in the first pressure control chamber 122 when the communication port 191 becomes the open state is determined by Equation 2, and is configured so that when the communication port 191 becomes the open state, a relationship of P1 ≥ P2 is established. Therefore, 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 no longer decreases, and the pressure P2 is maintained within a certain range.

[0112] In contrast, Figure 7C As shown, when the pressure plate 210 is not in contact with the valve shaft 190a and the communication port 191 becomes closed, the relationship of the force acting on the pressure plate 210 is expressed by Equation 3:

[0113] P3×S3+F3=0 Equation 3.

[0114] Here, the organization of equation 3 with respect to P3 gives the following:

[0115] P3=-F3 / S3 Equation 4.

[0116] F3: Spring force of the pressure regulating spring 220 when the pressure plate 210 and the valve shaft 190a are not in contact with each other;

[0117] P3: the pressure (gauge pressure) of the first pressure control chamber 122 when the pressure plate 210 and the valve shaft 190a are not in contact with each other; and

[0118] S3: The pressure area of ​​the pressure plate 210 when the pressure plate 210 and the valve 190 are in a non-contact area.

[0119] here, Figure 7C The pressure P3 in the first pressure control chamber 122, the spring force F3 of the pressure regulating spring 220, and the pressure receiving area S3 of the pressure plate 210 change according to the displacement amount until the pressure plate 210 and the flexible member 230 are displaced to the right in the figure until the limit of the displacement is reached. Figure 7C Specifically, when the pressing plate 210 and the flexible member 230 are in contact with each other, Figure 7C The pressure plate and the flexible member are located in Figure 7B As shown in the right side, the pressure area S3 of the pressure plate 210 decreases, and the spring force F3 of the pressure regulating spring 220 increases. As a result, the pressure P3 in the first pressure control chamber 122 decreases according to the relationship of equation 4. Figure 7B The status shown changes to Figure 7C During the state shown, the pressure in the first pressure control chamber 122 gradually decreases (i.e., the negative pressure weakens and approaches the positive pressure side) according to Equations 2 and 4. That is, the pressure plate 210 and the flexible member 230 gradually shift to the left direction from the state where the communication port 191 is in the open state, and the pressure in the first pressure control chamber gradually increases until the internal volume of the first pressure control chamber 122 finally reaches the limit that can be shifted. That is, the negative pressure weakens.

[0120] Circulation pump

[0121] Next, we will refer to Fig. 8A , 8B 9 describe in detail the configuration and function of the circulation pump 500 built in the above-mentioned liquid discharge head 1.

[0122] Fig. 8A and Figure 8B It is a perspective view of the appearance of the circulation pump 500. Fig. 8A is a perspective view showing the front appearance of the circulation pump 500, Figure 8B 1 is a perspective view showing the appearance of the rear side of the circulation pump 500 .

[0123] 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 channel connecting member 505b bonded and fixed to the outer surface of the housing body 505a. A pair of through holes that are interconnected are provided at two different positions of each of the housing body 505a and the flow channel connecting member 505b. A pair of through holes provided at one position forms a pump supply hole 501, and a pair of through holes provided at another position forms a pump discharge hole 502. The pump supply hole 501 is connected to the pump inlet channel 170, which is connected to the second pressure control chamber 152, and the pump discharge hole 502 is connected to the pump outlet channel 180 connected to the first pressure control chamber 122. The ink supplied from the pump supply hole 501 passes through the pump chamber 503 described later (see Fig. 9 ) and is discharged from the pump discharge hole 502.

[0124] Fig. 9 yes Fig. 8A 1. A cross-sectional view of the circulation pump 500 shown along line IX-IX. A diaphragm 506 is bonded to the inner surface of the pump housing 505, and a pump chamber 503 is formed between the diaphragm 506 and a recessed portion formed on the inner surface of the pump housing 505. The pump chamber 503 is communicated with 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 portion of the pump supply hole 501, and a check valve 504b is provided in the middle portion of the pump discharge hole 502. Specifically, the check valve 504a is arranged so that it can move to the left side in the figure in a space 512a, which is partially formed at the middle portion of the pump supply hole 501. The check valve 504b is arranged so that it can move to the right side in the figure in a space 512b, which is partially formed at the middle portion of the pump discharge hole 502.

[0125] When the displacement of the diaphragm 506 causes the volume of the pump chamber 503 to increase and the pressure in the pump chamber 503 to decrease, the check valve 504a is separated from the opening of the pump supply hole 501 in the space 512a (i.e., moves to the left in the figure). By separating the check valve 504a from the opening of the pump supply hole 501 in the space 512a, the state becomes an open state in which the ink in the pump supply hole 501 is allowed to flow. Since the displacement of the diaphragm 506 causes the volume of the pump chamber 503 to decrease, the check valve 504a is in close contact with the wall around the opening of the pump supply hole 501 under the action of the pressurization of the pump chamber 503. Therefore, the state becomes a closed state in which the flow of ink in the pump supply hole 501 is blocked.

[0126] On the contrary, by reducing the pressure in the pump chamber 503, the check valve 504b is brought into close contact with the wall around the opening of the pump housing 505, and the state becomes a closed state in which the flow of ink in the pump discharge hole 502 is blocked. When pressure is applied to the pump chamber 503, the check valve 504b is separated from the opening of the pump housing 505 and moves to the space 512b side (i.e., to the right side in the figure), and ink can flow in the pump discharge hole 502.

[0127] Check valves 504a, 504b may be made of any material that can deform in response to the pressure in pump chamber 503, and may be formed of, for example, elastic materials such as EPDM and elastomers, or films or sheets of polypropylene, etc. However, the material of the check valve is not limited thereto.

[0128] As described above, the pump chamber 503 is formed by bonding the pump housing 505 and the diaphragm 506. Therefore, the pressure in the pump chamber 503 changes due to the deformation of the diaphragm 506. For example, the diaphragm 506 shifts toward the pump housing 505 side (in the figure, shifted to the right side) to reduce the volume of the pump chamber 503, thereby increasing the pressure in the pump chamber 503. As a result, the check valve 504b arranged to face the pump discharge hole 502 becomes open, and the ink in the pump chamber 503 is discharged. In this case, since the check valve 504a arranged to face the pump supply hole 501 is in close contact with the wall around the pump supply hole 501, the ink is prevented from flowing back from the pump chamber 503 to the pump supply hole 501.

[0129] On the contrary, when the diaphragm 506 is displaced in the direction in which the pump chamber 503 expands, the pressure in the pump chamber 503 decreases. Therefore, the check valve 504a arranged to face the pump supply hole 501 becomes an open state to supply ink to the pump chamber 503. At this time, the check valve 504b arranged in the pump discharge hole 502 is in close contact with the wall around the opening formed in the pump housing 505 to block the opening. Therefore, the ink is prevented from flowing back from the pump discharge hole 502 to the pump chamber 503.

[0130] Therefore, in the circulation pump 500, the diaphragm 506 is deformed to change the pressure in the pump chamber 503, thereby implementing the suction and discharge of ink. At this time, if bubbles penetrate into the pump chamber 503, even if the diaphragm 506 is displaced, the pressure change in the pump chamber 503 caused by the expansion and contraction of the bubbles will become smaller to reduce the amount of liquid inflow. Therefore, the pump chamber 503 is arranged parallel to gravity, so that the bubbles that penetrate into the pump chamber 503 are easy to gather at the top of the pump chamber 503, and the pump discharge hole 502 is arranged above the center of the pump chamber 503. Therefore, the discharge capacity of the bubbles in the pump can be improved, and the flow rate can be stabilized.

[0131] Flow of liquid in the discharge head

[0132] FIG. 10A to FIG. 10E2 is a diagram for explaining the flow of ink in a liquid discharge head. Figures 10A to 10E , the circulation of ink in the liquid discharge head 1 will be described. In order to more clearly describe the ink circulation path, Fig. 10A and Fig.10E The relative positions of the components (such as the first pressure control device 120, the second pressure control device 150 and the circulation pump 500) are simplified. Fig.19 The configuration shown is different. Fig. 10A The flow of ink when the printing operation is performed by discharging ink from the discharge port 13 is schematically shown. The arrows in the figure indicate the flow of ink. In the present embodiment, when the printing operation is performed, both the external pump 21 and the circulation pump 500 begin to be driven. In a state where the printing operation is not performed, the external pump 21 and the circulation pump 500 can be driven. The external pump 21 and the circulation pump 500 can be driven in conjunction with each other, but can also be driven separately and independently.

[0133] During the printing operation, the circulation pump 500 is in the "ON" state (driving state), and the ink flowing out of the first pressure control chamber 122 flows into the supply channel 130 and the bypass flow channel 160. The ink flowing into the supply channel 130 passes through the discharge module 300, then flows into the collection channel 140, and then is supplied to the second pressure control chamber 152.

[0134] On the other hand, the ink flowing into the bypass flow channel 160 from the first pressure control chamber 122 flows into the second pressure control chamber 152 through the second valve chamber 151. The ink flowing into the second pressure control chamber 152 passes through the pump inlet channel 170, the circulation pump 500, and the pump outlet channel 180, and then flows into the first pressure control chamber 122 again. In this case, based on the relationship of the above equation 2, the control pressure of the first valve chamber 121 is set to be higher than the control pressure in the first pressure control chamber 122. Therefore, the ink in the first pressure control chamber 122 is supplied to the discharge module 300 again through the supply channel 130 without flowing into the first valve chamber 121. The ink flowing into the discharge module 300 passes through the collection channel 140, the second pressure control chamber 152, the pump inlet channel 170, the circulation pump 500, the pump outlet channel 180, and then flows into the first pressure control chamber 122 again. As described above, the ink circulation completed in the liquid discharge head 1 is implemented.

[0135] In the above-mentioned ink circulation, the circulation amount (flow rate) of the ink in the discharge module 300 is determined by the pressure difference between the control pressures of the first pressure control chamber 122 and the second pressure control chamber 152. The pressure difference is set to a circulation amount that can suppress the viscosity increase of the ink near the discharge port in the discharge module 300. The amount of ink consumed by printing is supplied from the ink tank 2 to the first pressure control chamber 122 through the filter 110 and the first valve chamber 121. The mechanism for supplying the consumed ink will be described in detail. The ink in the circulation path reduces the amount of ink consumed by printing, so that the pressure in the first pressure control chamber is reduced. As a result, the ink in the first pressure control chamber 122 is also reduced. The reduction of the ink in the first pressure control chamber 122 causes the internal volume of the first pressure control chamber 122 to decrease. Due to the reduction in the internal volume of the first pressure control chamber 122, the communication port 191A becomes open, and ink is supplied from the first valve chamber 121 to the first pressure control chamber 122. When ink passes through the communication port 191A from the first valve chamber 121, a pressure loss is generated in the supplied ink, and the ink flows into the first pressure control chamber 122 to switch the ink from a positive pressure state to a negative pressure state. Then, the ink flows from the first valve chamber 121 into the first pressure control chamber 122 to increase the pressure in the first pressure control chamber, which increases the internal volume of the first pressure control chamber, resulting in a closed state of the communication port 191A. Therefore, the open state and the closed state of the communication port 191A are repeated according to the consumption of the ink. When the ink is not consumed, the communication port 191A remains in a closed state.

[0136] Fig. 10B The flow of ink after the printing operation has just ended and the circulation pump 500 has been switched to the "OFF" state (stop state) is schematically shown. When the printing operation ends and the circulation pump 500 is switched to "OFF", the pressure in the first pressure control chamber 122 and the pressure in the second pressure control chamber 152 are both the control pressures during the printing operation. Therefore, according to the pressure difference between the pressure of the first pressure control chamber 122 and the pressure of the second pressure control chamber 152, the following occurs: Fig. 10B Specifically, the flow of ink from the first pressure control chamber 122 through the supply channel 130 to the discharge module 300, then through the collection channel 140 and to the second pressure control chamber 152 continuously occurs. In addition, the flow of ink from the first pressure control chamber 122 through the bypass flow channel 160 and the second valve chamber 151 and to the second pressure control chamber 152 also continuously occurs.

[0137] Ink is supplied from the ink tank 2 to the first pressure control chamber 122 through the filter 110 and the first valve chamber 121, and the amount of ink supplied is the amount of ink moved from the first pressure control chamber 122 to the second pressure control chamber 152 by the flow of the above-mentioned ink. Therefore, the internal volume of the first pressure control chamber 122 remains constant. As can be seen from the relationship of the above-mentioned equation 2, when the internal 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 area S1 of the valve 190, and the pressure area S2 of the pressure plate 210 remain constant. Therefore, the pressure in the first pressure control chamber 122 is determined in response to the change of the pressure (gauge pressure) P1 in the first valve chamber 121. Therefore, when the pressure P1 in the first valve chamber 121 does not change, during the printing operation, the pressure P2 in the first pressure control chamber 122 is kept equal to the control pressure.

[0138] In contrast, the pressure in the second pressure control chamber 152 changes over time in response to the change in the internal volume caused by the inflow of ink from the first pressure control chamber 122. Fig. 10B The status shown is as follows Fig. 10C During the state in which the second valve chamber 151 and the second pressure control chamber 152 are not communicated with each other due to the closed state of the communication port 191, the pressure in the second pressure control chamber 152 changes according to Equation 2. Subsequently, the pressure plate 210 and the valve shaft 190a are not in contact with each other, and the communication port 191 becomes a closed state. Fig. 10D As shown, ink flows from the collection channel 140 into the second pressure control chamber 152. This ink inflow displaces the pressure plate 210 and the flexible member 230, and the pressure in the second pressure control chamber 152 changes according to Equation 4, i.e., increases, until the internal volume of the second pressure control chamber 152 reaches a maximum value.

[0139] When the state changes to Fig. 10C In the state shown, the flow of ink from the first pressure control chamber 122 to the second pressure control chamber 152 through the bypass flow channel 160 and the second valve chamber 151 does not occur. Therefore, only the flow of ink supplied from the first pressure control chamber 122 to the discharge module 300 through the supply channel 130 and then passing through the collection channel 140 and reaching the second pressure control chamber 152 occurs. As described above, the movement of ink from the first pressure control chamber 122 to the second pressure control chamber 152 occurs in response 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 and the pressure in the first pressure control chamber 122 become equal, the ink movement stops.

[0140] 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 Fig. 10D When the second pressure control chamber 152 is Fig. 10D When the circulation pump 500 is expanded, a storage portion capable of storing ink is formed in the second pressure control chamber 152. Fig. 10D The time of the state shown may vary depending on the shape and size of the flow channel and the properties of the ink, but is approximately 1 to 2 minutes. Fig. 10D The state in which the ink is stored in the storage portion drives the circulation pump 500, and the ink in the storage portion is supplied to the first pressure control chamber 122 by the circulation pump 500. Fig.10E As shown in FIG. 1 , the amount of ink in the first pressure control chamber 122 increases, and the flexible member 230 and the pressure plate 210 are displaced in the expansion direction. Fig. 10A As shown, the conditions in the cycle path change.

[0141] In the above description, although Fig. 10A This is explained as an example of a printing operation, but as described above, the circulation of ink can be implemented without performing a printing operation. Also in this case, Figures 10A to 10E The ink flow shown occurs in response to the operation and stopping of the circulation pump 500.

[0142] Here, when the stop state of the circulation pump 500 continues for a long period of time (for example, when the power of the main body is turned off), it is inferred that the titanium oxide particles in the ink are not dispersed and precipitated again. It is also inferred that the concentration and viscosity of the ink increase due to the evaporation of the ink from the discharge port 13, and it is also inferred that the negative pressure in the liquid discharge head is weakened due to the infiltration and invasion of the air into the liquid discharge head housing. If the printing operation is performed under these conditions, the quality of the printed image may be reduced. Therefore, the ink in the discharge port can be refreshed by sucking and discharging viscous ink and bubbles and ink from the discharge port 13 of the liquid discharge head 1 using the above-mentioned cap member, etc. to maintain and restore the ink discharge performance. The suction and discharge process sucks and discharges the precipitated ink to eliminate the precipitation in the liquid discharge head.

[0143] As described above, the first pressure control device 120 and the second pressure control device 150 in the present embodiment are configured so that the flexible member 230 and the pressure plate 210 receive the pressure in the liquid discharge head 1 and are displaced. From the perspective of negative pressure design, a pressure receiving area of ​​a certain size is required. Therefore, the volume of the first pressure control chamber 122 and the second pressure control chamber 152 is larger than that of other parts in the circulation path and is an area where ink in the liquid discharge head is easily precipitated. In this case, it is inferred that the precipitated ink (titanium oxide particles) hinders the displacement of the flexible member 230 and the pressure plate 210 and cannot maintain an appropriate negative pressure.

[0144] Therefore, in the circulation path, the pressure control chambers (the first pressure control chamber 122 and the second pressure control chamber 152) and other flow channels ( Figures 10A to 10E , 250, 260, 280, 240 and 270) can be arranged vertically below the pressure control chamber. Therefore, the ink deposited in the pressure control chamber can be effectively discharged to the outside of the liquid discharge head during the suction and discharge process. The ink is sucked through the discharge port 13 by the suction and discharge process so that the ink flows toward the discharge port 13 in the supply channel 130 and the collection channel 140. The ink in the pressure control chamber passes through the supply channel 130 and the collection channel 140 and is discharged from the discharge port 13.

[0145] That is, the portion (hole) communicating with the supply channel 130 or the collection channel 140 can be arranged at a position where the ink is easily precipitated in the pressure control chamber of the pressure control device. Therefore, the precipitated ink easily flows into the supply channel 130 or the collection channel 140, and can be sucked and discharged from the discharge port 13. FIG. 10A to FIG. 10E In the figure, the connection part 250 connected to the supply channel 130 of the first pressure control chamber 122 and the connection part 270 connected to the collection channel 140 of the second pressure control chamber 152 are respectively arranged vertically below the pressure control chambers (the first pressure control chamber and the second pressure control chamber).

[0146] Furthermore, the connection portion 260 between the first pressure control chamber 122 and the bypass flow passage 160 and the connection portion 280 between the first pressure control chamber 122 and the pump outlet passage 180 are also arranged vertically below the first pressure control chamber 122, and the connection portion 240 between the second pressure control chamber 152 and the pump inlet passage 170 is also arranged vertically below the second pressure control chamber 152. Therefore, in the pressure control chamber in the circulation path, a bag-like stagnant area, which becomes a dead point in the circulation flow, in which the ink settles and is difficult to circulate, is eliminated.

[0147] The arrangement of "vertically below the pressure control chamber" in the above description can be within half of the length of the pressure control chamber from the downward end in the vertical direction in the posture of the liquid discharge head during printing, or within 1 / 4 of the length of the pressure control chamber from the downward end in the vertical direction.

[0148] In addition, the flow channel in the discharge unit 3 may also have a structure in which the ink deposited in the circulation path is easily discharged from the discharge port 13 to the outside and in the connection between the circulation unit 54 and the discharge unit 3, the walls of the flow channels 301, 302 may be perpendicular to or inclined to the vertical direction. That is, in the portion where the discharge unit 3 and the circulation unit 54 are in fluid contact, the wall of the flow channel in the discharge unit 3 that is fluidly connected to the circulation unit 54 may be perpendicular to the vertical direction or inclined to the vertical direction. Therefore, the following effect is obtained: in the connection between the supply port 88 and the support member supply port 211 and the connection between the collection port 89 and the support member collection port 212, the ink components deposited in the circulation unit 54 can be sucked into the supply channel 130 or the collection channel 140 and the ink can be easily discharged from the discharge port 13. Fig.22A and Fig. 22B is a cross-sectional view of another example of the liquid discharge head 1 . Fig.22A is a cross-sectional view showing the connection between the circulation unit 54 and the discharge unit 3 on the liquid supply side, Fig. 22B 3 is a cross-sectional view showing the connection between the circulation unit 54 and the discharge unit 3 on the liquid collection side. Fig.22A and Fig. 22B A configuration is shown in which the walls of the flow channels 301 , 302 in the connection between the circulation unit 54 and the discharge unit 3 are perpendicular to the vertical direction or inclined to the vertical direction.

[0149] As described above, the present embodiment uses an example in which the communication port 191B in the second pressure regulating device 150 becomes an open state when the circulation pump 500 is driven to circulate the ink and becomes a closed state when the ink circulation stops, but is not limited thereto. The control pressure may be set so that the communication port 191B in the second pressure regulating device 150 is in a closed state even when the circulation pump 500 is driven to circulate the ink. The bypass channel 160 and its function will be described in detail below.

[0150] The bypass flow channel 160 connected between the first pressure control device 120 and the second pressure control device 150 is provided, for example, to prevent the discharge module 300 from being affected by a negative pressure stronger than a predetermined value generated in the circulation path. The bypass flow channel 160 can also be provided to supply ink to the pressure chamber 12 from both sides of the supply channel 130 and the collection channel 140.

[0151] An example of providing the bypass flow channel 160 to prevent the discharge module 300 from being affected by a negative pressure stronger than a predetermined value will now be described. For example, the characteristics of the ink (e.g., viscosity) may change in response to changes in ambient temperature. If the viscosity of the ink changes, the pressure loss in the circulation path will also change. For example, if the viscosity of the ink decreases, the amount of pressure loss in the circulation path also decreases. As a result, the flow rate of the circulation pump 500 driven by a specific drive amount increases to increase the flow rate flowing into the discharge module 300. At the same time, 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 remains constant even if the ambient temperature changes. The flow rate of the ink flowing in the discharge module 300 increases, while the viscosity of the ink in the discharge module 300 remains unchanged. Therefore, the negative pressure in the discharge module 300 is enhanced due to the flow resistance. Therefore, the negative pressure in the discharge module 300 becomes stronger than the predetermined value to destroy the meniscus of the discharge port 13, and external air is sucked into the circulation path, resulting in the risk of not being able to implement normal discharge. Even if the meniscus is not broken, the negative pressure of the pressure chamber 12 becomes stronger than a predetermined value, which may affect the discharge.

[0152] Therefore, in the present embodiment, the bypass channel 160 is formed in the circulation path. When the negative pressure becomes stronger than a predetermined value by providing the bypass flow channel 160, the pressure in the discharge module 300 can be kept constant because the ink also flows in the bypass flow channel 160. Therefore, for example, the control pressure can be set so that the communication port 191B in the second pressure control device 150 is kept in a closed state even during the driving of the circulation pump 500, and the control pressure in the second pressure control device can be set so that the communication port 191 of the second pressure control device 150 becomes an open state when the negative pressure is stronger than a predetermined value. That is, if the meniscus does not collapse even when the pump flow rate changes due to a change in viscosity caused by an environmental change, or a predetermined negative pressure is maintained, the communication port 191B can be in a closed state during the driving of the circulation pump 500.

[0153] An example will now be described in which the bypass flow channel 160 is provided to supply ink to the pressure chamber 12 from both sides of the supply channel 130 and the collection channel 140. Pressure changes in the circulation path can also occur by the discharge operation of the discharge element 15. This is because the discharge operation generates a force that draws ink into the pressure chamber.

[0154] Now, the main point of supplying the ink to be supplied to the pressure chamber 12 from both the supply channel 130 side and the collection channel 140 side when high duty cycle printing is continued will be described. Although the definition of the duty cycle may vary depending on various conditions, the state of printing one 4pL ink droplet on a 1200dpi grid is regarded as 100% here. For example, high duty cycle printing refers to printing at a duty cycle of 100%.

[0155] When high duty cycle printing is continued, the amount of ink flowing from the pressure chamber 12 through the collecting channel 140 into the second pressure control chamber 152 is reduced. On the other hand, since the circulation pump 500 sends out a certain amount of ink, the balance between the inflow and outflow in the second pressure control chamber 152 is destroyed, the ink in the second pressure control chamber 152 is reduced, and the negative pressure in the second pressure control chamber 152 becomes stronger, and the second pressure control chamber 152 contracts. The amount of ink flowing into the second pressure control chamber 152 through the bypass flow channel 160 increases due to the strengthening of the negative pressure in the second pressure control chamber 152, and the second pressure control chamber 152 is stabilized in a state where the outflow and inflow are balanced. Therefore, as a result, the negative pressure in the second pressure control chamber 152 becomes stronger according to the duty cycle. As described above, in the configuration in which the communication port 191B is in a closed state during the operation of the circulation pump 500, the communication port 191B becomes an open state according to the duty cycle, and ink flows from the bypass flow channel 160 into the second pressure control chamber 152.

[0156] When the high duty cycle printing is further continued, the amount of ink flowing from the pressure chamber 12 through the collecting channel 140 into the second pressure control chamber 152 decreases, and instead, the amount flowing into the second pressure control chamber 152 through the bypass flow channel 160 and from the communication port 191B increases. When this state further develops, the amount of ink flowing from the pressure chamber 12 through the collecting channel 140 into the second pressure control chamber 152 becomes zero, and all the ink flowing out to the circulation pump 500 is the ink flowing in through the communication port 191B. When this state further develops, at this time, the ink flows back from the second pressure control chamber 152 into the pressure chamber 12 through the collecting channel 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 pass through the bypass flow channel 160 and flow into the second pressure control chamber 152 from the communication port 191B through the bypass flow channel 160. In this case, the ink in the supply channel 130 and the ink in the collecting channel 140 fill the pressure chamber 12 and discharge is performed.

[0157] This backflow that occurs when the printing duty ratio is high is a phenomenon caused by providing the bypass flow channel 160. In the above, although an example is described in which the communication port 191B in the second pressure regulating device becomes an open state in response to the ink backflow, when the communication port 191B in the second pressure regulating device is in an open state, the ink backflow may occur.

[0158] In addition, in a configuration in which the second pressure regulating device is not provided, the backflow of ink can occur by providing the bypass flow channel 160 .

[0159] Configuration of the discharge unit

[0160] Fig.11A and Fig. 11B : is a schematic diagram showing a circulation path for ink of one color in the discharge unit 3 of the present embodiment. Fig.11A is an exploded perspective view viewed from the first supporting member 4 side of the discharge unit 3, Fig. 11B 3 is an exploded perspective view viewed from the discharge module 300 side of the discharge unit 3. The in and out arrows in the figure indicate the ink flow. The ink flow is described only for one color, but the flow of other colors is the same. Fig.11A and Fig. 11B , the second supporting member 7 and the electric wiring member 5 are omitted, and their description is also omitted in the following description of the configuration of the discharge unit. Fig.11A The first support member 4 is along Figure 3A The discharge module 300 includes a discharge element substrate 340 and an opening plate 330 . Fig.12 is a diagram showing an opening plate 330, Fig.13 3 is a diagram showing the discharge element substrate 340 .

[0161] From the circulation unit 54 through the joint member 8 (see Figure 3A ) supplies ink to the discharge unit 3. A path from the joint member 8 until the joint member 8 through which the ink passes and reaches will now be described. In the following figures, the joint member 8 is omitted.

[0162] The discharge module 300 includes a discharge element substrate 340 and an opening plate 330 constituting a silicon substrate 310, and also includes a discharge port forming member 320. The discharge element substrate 340, the opening plate 330, and the discharge port forming member 320 are overlapped and bonded to each other so that flow channels of various inks communicate with each other to form the discharge module 300, and are supported by the first supporting member 4.

[0163] The discharge module 300 is supported by the first support member 4 to form the discharge unit 3. The discharge element substrate 340 includes a discharge port forming member 320, and the discharge port forming member 320 includes a plurality of discharge port arrays in a plurality of rows, each row being composed of a plurality of discharge ports 13 and discharging a portion of the ink supplied through the ink flow channel in the discharge module 300 from the discharge ports 13. The ink that is not discharged is collected from the ink flow channel in the discharge module 300.

[0164] like Fig.11A , Fig. 11B and Fig.12 As shown, the opening plate 330 includes a plurality of arranged ink supply ports 311 and a plurality of arranged ink collection ports 312. Fig.13 and FIG. 14A to FIG. 14CAs shown, the discharge element substrate 340 includes a plurality of arranged supply connection channels 323 and a plurality of arranged collection connection channels 324. The discharge element substrate 340 also includes a common supply channel 18 communicating with the plurality of supply connection channels 323 and a common collection channel 19 communicating with the plurality of collection connection channels 324. The ink flow channel in the discharge unit 3 is connected by the ink supply channel 48 and the ink collection channel 49 (see FIG. 4 ) provided in the first support member 4. Figure 3A ) and a flow channel provided in the discharge module 300 are connected to each other. The support member supply port 211 is a cross-sectional opening forming the ink supply channel 48, and the support member collection port 212 is a cross-sectional opening forming the ink collection channel 49.

[0165] The ink to be supplied to the discharge unit 3 is supplied from the circulation unit 54 (see Figure 3A ) side is supplied to the ink supply channel 48 of the first supporting member 4 (see Figure 3A The ink supplied through the supporting member supply port 211 in the ink supply channel 48 flows through the ink supply channel 48 (see Figure 3A ) and the ink supply port 311 of the opening plate 330 is supplied to the common supply channel 18 of the discharge element substrate 340 and enters the supply connection channel 323. The channel up to this point is the supply side flow channel. Subsequently, the ink passes through the pressure chamber 12 of the discharge port forming member 320 (see Figure 3B ) and flows to the collection connection channel 324 of the collection side flow channel. The details of the ink flow in the pressure chamber 12 will be described in detail later.

[0166] In the collection side flow channel, the ink entering the collection connection channel 324 flows into the common collection channel 19. Subsequently, the ink flows from the common collection channel 19 through the ink collection port 312 of the opening plate 330 into the ink collection channel 49 of the first support member 4, passes through the support member collection port 212 and is collected in the circulation unit 54.

[0167] The area in which the ink supply port 311 and the ink collection port 312 do not exist in the opening plate 330 corresponds to an area on the first support member 4 for separating the support member supply port 211 and the support member collection port 212 from each other. This area does not include the first support member 4 and the opening. When the discharge module 300 and the first support member 4 are bonded to each other, such an area serves as an adhesion area.

[0168] exist Fig.12 In the embodiment, the opening plate 330 is provided with a plurality of rows, each row consisting of a plurality of openings arranged in the X direction and in the Y direction, wherein the openings are arranged so that the supply (inlet) openings and the collection (outlet) openings are alternately arranged in the Y direction and offset by half a pitch in the X direction. Fig.13, in the discharge element substrate 340, the common supply channel 18 communicating with the plurality of supply connection channels 323 arranged along the Y direction and the common collection channel 19 communicating with the plurality of collection connection channels 324 arranged along the Y direction are alternately arranged along the X direction. The common supply channel 18 and the common collection channel 19 are separated according to the type of ink, and the number of the common supply channels 18 and the number of the common collection channels 19 to be arranged are determined according to the number of discharge port arrays of each color. The number of arrangement of the supply connection channels 323 and the collection connection channels 324 also corresponds to the number of the discharge ports 13. It is not necessary to be one-to-one correspondence, and one supply connection channel 323 and one collection connection channel 324 may correspond to a plurality of discharge ports 13.

[0169] The above-mentioned opening plate 330 and discharge element substrate 340 overlap and bond with each other so that the flow channels of each ink are connected to each other to form the discharge module 300, and are supported by the first support member 4 to form the ink flow channel, which includes the above-mentioned supply channel and collection channel.

[0170] FIG. 14A to FIG. 14C 2 is a cross-sectional view showing the flow of ink in the discharge unit 3 at three different portions of the discharge unit 3 . Fig.14A It is along Fig.11A 4 is a cross section taken along the line XIVA-XIVA of , and shows a cross section of a portion where the ink supply passage 48 and the ink supply port 311 communicate with each other in the discharge unit 3 . Fig. 14B It is along Fig.11A XIVB-XIVB is a cross section taken along the line XIVB-XIVB and shows a cross section of a portion where the ink collection channel 49 and the ink collection port 312 communicate with each other in the discharge unit 3. Fig. 14C It is along Fig.11A XIVC-XIVC is a cross section taken along the line XIVC-XIVC of FIG. 4 and shows a cross section of a portion where the ink supply port 311 and the ink collection port 312 are not in communication with the flow channel of the first supporting member 4 .

[0171] In the supply channel for supplying ink, as Fig.14A As shown, ink is supplied from the portion where the ink supply channel 48 of the first support member 4 overlaps and communicates with the ink supply port 311 of the opening plate 330. In the collection channel for collecting ink, as shown in FIG. Fig. 14B As shown, ink is collected from the portion where the ink collection channel 49 of the first support member 4 overlaps and communicates with the ink collection port 312 of the opening plate 330. Fig. 14C As shown, in a portion of the discharge unit 3, the opening plate 330 also includes an area where no opening is provided. In such an area, ink is not supplied and collected between the discharge element substrate 340 and the first support member 4. Fig.14AAs shown, ink is supplied in the area where the ink supply port 311 is provided, and as shown in FIG. Fig. 14B As shown, ink is collected in the area provided with the ink collection port 312. In the present embodiment, although an example of a configuration using the opening plate 330 has been described, the configuration may be a configuration not using the opening plate 330. In this example of the configuration, flow channels corresponding to the ink supply channel 48 and the ink collection channel 49 may be formed in the first supporting member 4, and the discharge element substrate 340 may be bonded to the first supporting member 4.

[0172] Fig.15A and Fig. 15B is a cross-sectional view showing the vicinity of the discharge port 13 in the discharge module 300, Fig.16A and Fig. 16B : is a cross-sectional view showing a discharge module having a configuration in which the common supply channel 18 and the common collecting channel 19 are widened in the X direction as a reference example. Fig.15A , Fig. 15B , Fig.16A and Fig. 16B The thick arrows shown in the common supply channel 18 and the common collection channel 19 represent the fluctuation of the ink in the configuration using the serial type liquid discharge device 50. The ink that passes through the common supply channel 18 and the supply connection channel 323 and is supplied to the pressure chamber 12 is discharged from the discharge port 13 by driving the discharge element 15. When the discharge element 15 is not driven, the ink is collected from the pressure chamber 12 to the common collection channel 19 through the collection connection channel 324 as a collection channel.

[0173] In the configuration using the serial type liquid discharge apparatus 50, when discharging the ink thus circulated, the discharge of the ink is greatly affected by the fluctuation of the ink in the ink flow channel due to the main scanning of the liquid discharge head 1. Specifically, the influence of the ink fluctuation in the ink flow channel may appear as a difference in the discharge amount of the ink and a deviation in the discharge direction. Fig.16A and Fig. 16BAs shown, when the common supply channel 18 and the common collection channel 19 have a cross-sectional shape that is wider in the X direction, which is the main scanning direction, the ink in the common supply channel 18 and the common collection channel 19 tends to be subjected to the inertial force in the main scanning direction, and the ink will fluctuate greatly. In the present embodiment, the supply connection channel 323 and the collection connection channel 324 are arranged to correspond to the discharge port 13, and the supply connection channel 323 and the collection connection channel 324 are arranged in a corresponding relationship so that the discharge port 13 is located between the two in the X direction. Therefore, the common supply channel 18 and the common collection channel 19 have a non-overlapping portion in the X direction, and if the corresponding relationship between the supply connection channel 323 and the collection connection channel 324 in the X direction is destroyed, the flow and discharge of the ink in the pressure chamber 12 along the X direction are affected. When the influence of the ink fluctuation is added, the discharge of the ink from each discharge port may be affected.

[0174] Therefore, by arranging the common supply channel 18 and the common collecting channel 19 to overlap in the X direction, the ink fluctuations in the common supply channel 18 and the common collecting channel 19 during the main scan are substantially the same at any position where the discharge port 13 is arranged in the Y direction. Therefore, the pressure difference between the common supply channel 18 side and the common collecting channel 19 side occurring in the pressure chamber 12 does not significantly change, and stable discharge can be implemented.

[0175] In some configurations of liquid discharge heads for circulating ink, the flow channel for supplying ink to the liquid discharge head and the flow channel for collecting ink are the same. However, in the present embodiment, the common supply channel 18 and the common collecting channel 19 are different flow channels. The supply connection channel 323 is interconnected with the pressure chamber 12, the pressure chamber 12 is interconnected with the collecting connection channel 324, and the ink is discharged from the discharge port 13 of the pressure chamber 12. That is, the pressure chamber 12 configured as a connection path between the supply connection channel 323 and the collecting connection channel 324 includes the discharge port 13. Therefore, in the pressure chamber 12, an ink flow from the supply connection channel 323 side to the collecting connection channel 324 side is generated, and the ink in the pressure chamber 12 is effectively circulated. By effectively circulating the ink in the pressure chamber 12, the ink in the pressure chamber 12 can be kept in a fresh state, while the ink in the pressure chamber 12 is often affected by the evaporation of the ink through the discharge port 13.

[0176] If it is necessary to discharge at a high flow rate by making the two flow channels of the common supply channel 18 and the common collection channel 19 communicate with the pressure chamber 12, it is also possible to supply ink from these two flow channels. That is, compared with a configuration in which the supply and collection of ink are implemented using only one flow channel, the configuration of this embodiment has the advantages of being able to circulate ink efficiently and being able to discharge corresponding to a high flow rate.

[0177] Fig.17 FIG. 3 is a diagram showing a discharge element substrate 340 as a comparative example. Fig.17 , the supply connection channel 323 and the collection connection channel 324 are omitted. Since the ink receiving the heat energy through the discharge element 15 in the pressure chamber 12 flows into the common collection channel 19, the ink with a higher temperature than the ink in the common supply channel 18 flows. In this case, in the comparative example, as Fig.17 In the α portion surrounded by the dotted line in FIG, there is a portion where only the common collecting channel 19 exists in the portion along the X direction of the discharge element substrate 340. In this case, the temperature at this portion locally rises, resulting in uneven temperature in the discharge module 300, which may affect the discharge.

[0178] In the common supply channel 18, ink having a lower temperature than the ink in the common collection channel 19 flows. Therefore, when the common supply channel 18 and the common collection channel 19 are adjacent to each other, in the vicinity thereof, the temperatures in the common supply channel 18 and the common collection channel 19 cancel each other to suppress a temperature increase. Therefore, the common supply channel 18 and the common collection channel 19 may have substantially the same length, exist at a position overlapping in the X direction, and be adjacent to each other.

[0179] Fig.18A and Fig.18B : is a diagram showing the flow channel configuration of the liquid discharge head 1 corresponding to three types of inks. Fig.18A As shown in FIG. 1 , the liquid discharge head 1 has a circulation flow channel for the corresponding type of ink. The pressure chamber 12 is provided along the X direction which is the main scanning direction of the liquid discharge head 1. Fig.18B As shown, the common supply channel 18 and the common collection channel 19 are provided along the discharge port array of the arranged discharge ports 13 so as to extend along the Y direction and sandwich the discharge port array therebetween.

[0180] Connection between the main body and the liquid discharge head

[0181] Fig.19 700 is a schematic configuration diagram showing in more detail the connection state of the ink tank 2 and the external pump 21 connected to the liquid discharge head 1 provided in the main body portion of the liquid discharge device 50 of the present embodiment, and the arrangement of the circulation pump and the like. The liquid discharge device 50 of the present embodiment has a configuration in which only the liquid discharge head 1 can be easily replaced when a failure occurs in the liquid discharge head 1. Specifically, the liquid discharge device 50 includes: a liquid connection portion 700 that can easily implement connection and disconnection between the ink supply tube 59 connected to the external pump 21 and the liquid discharge head 1. Therefore, only the liquid discharge head 1 can be easily attached to and detached from the liquid discharge device 50.

[0182] like Fig.19 As shown, the liquid connection portion 700 includes a liquid connection member insertion port 53a provided in a protruding state to the head housing 53 of the liquid discharge head 1 and a cylindrical liquid connection member 59a that can be inserted into the liquid connection member insertion port 53a. The liquid connection member insertion port 53a is fluidly connected to the ink supply channel (inlet flow channel) formed in the liquid discharge head 1, and is connected to the first pressure control device 120 through the above-mentioned filter 110. The liquid connection member 59a is provided at the end of the ink supply tube 59 connected to the external pump 21, and the external pump pressurizes and supplies the ink in the ink tank 2 to the liquid discharge head 1.

[0183] Can be easily attached, removed and replaced via liquid connection 700 Fig.19 The above-mentioned liquid discharge head 1 shown. However, when the sealing between the liquid connector insertion port 53a and the liquid connector 59a is reduced, the ink supplied by the external pump 21 under pressure may leak from the liquid connection part 700. If the ink of the leaked liquid adheres to the circulation pump 500 and the like, there is a risk of causing a pneumatic system failure. Therefore, in the present embodiment, the circulation pump and the like are arranged as follows.

[0184] Arrangement of circulation pumps, etc.

[0185] like Fig.19 As shown, in the present embodiment, in order to prevent the ink leaking from the liquid connection 700 from adhering to the circulation pump 500, the circulation pump 500 is arranged above the liquid connection 700 in the direction of gravity. That is, the circulation pump 500 is arranged above the liquid connection insertion port 53a, which is the liquid inlet port in the liquid discharge head 1, in the direction of gravity. In addition, the circulation pump 500 is arranged at a position where it does not contact the member constituting the liquid connection 700. Therefore, even if the ink leaks from the liquid connection 700, since the ink flows in the horizontal direction (i.e., along the opening direction of the liquid connection 59a) or flows downward in the direction of gravity, it is possible to prevent the ink from reaching the circulation pump 500 positioned above in the direction of gravity. In addition, since the circulation pump 500 is located at a position away from the liquid connection 700, the risk of the ink passing through the member and reaching the circulation pump 500 is also reduced.

[0186] The electrical connection portion 515 for electrically connecting the circulation pump 500 and the electrical contact substrate 6 via the flexible wiring member 514 is disposed above the liquid connection 700 in the gravity direction. Therefore, the risk of electrical failure caused by ink from the liquid connection 700 can be reduced.

[0187] In this embodiment, since the wall 52 b of the head housing 53 is provided, even if ink is ejected from the opening 59 b of the liquid connecting portion 700 , the ink can be blocked and the risk of the ink reaching the circulation pump 500 or the electrical connecting portion 515 can be reduced.

[0188] Fig. 20 The ink circulation system in this embodiment is shown.

[0189] In the present embodiment, the ink is pressure-supplied from the ink tank 2 to the liquid discharge head 1 through the liquid connection 700 using the external pump 21. The external pump 21 functions to extract the ink from the ink tank 2 and pressure-supply the ink to the liquid discharge head 1.

[0190] The flow channel 591 is provided between the external pump 21 and the liquid connection portion 700 in parallel with the ink supply tube 59. The second external pump 22 is provided in the flow channel 591 and is configured to circulate the ink in the range from the downstream of the external pump (first external pump) 21 to the carriage 60. Therefore, the ink can be stirred also in the flow channel outside the liquid discharge head 1 of the liquid discharge device 50.

[0191] here, Fig.21 An ink circulation system of a comparative example is shown. An external pump 21 is used to deliver ink from the ink tank 2 to the sub-tank 25. Subsequently, the supply pump 23 and the collection pump 24 circulate (stir) the ink in the sub-tank 25 and the liquid discharge head 1 and the entire flow channel between them. In this case, since it is necessary to make the ink flow from the sub-tank 25 to the liquid discharge head 1 and flow in the entire liquid discharge device 50, the supply pump 23 and the collection pump 24 are required to have a higher capacity than the pump of the present embodiment. In addition, since the liquid discharge head 1 requires two system connections, namely, the liquid connection 700a for supply and the liquid connection 700b for discharge, the size of the liquid discharge head 1 tends to increase. In addition, since the collection pump 24 and the discharge unit 3 are directly fluidically connected, the pulsation of the collection pump 24 tends to propagate to the discharge unit 3 and may cause the quality of the printed image to deteriorate. In addition, in the serial type liquid discharge head 1, since both the ink supply tube 59 and the ink collection tube 591 fluctuate due to scanning, the pressure change caused by the fluctuation of the ink collection tube tends to propagate to the liquid discharge unit 3 and may cause the quality of the printed image to deteriorate.

[0192] Even when using Fig. 20The effects of the present disclosure can also be fully obtained in the ink circulation system and inkjet printing method of the liquid discharge device of the flow channel 591 and the second external pump 22 shown. The flow channel 591 and the second external pump 22 can be applied only to the ink circulation system for ink containing titanium oxide. In this case, it is possible to suppress the excessive increase in equipment manufacturing cost and the increase in equipment size, while obtaining a greater effect of suppressing the precipitation of ink containing titanium oxide. The total volume of ink flowing only in one circulation path including the circulation pump 500 in the liquid discharge head 1 is preferably 30 mL or less, more preferably 15 mL or less, and preferably 5 mL or more. In other words, the volume of the liquid flowing in the circulation path is preferably 5 mL or more and 30 mL or less, and further preferably 5 mL or more and 15 mL or less.

[0193] As mentioned above, in Fig. 20 In the ink circulation system shown, reduction in size of the liquid discharge device and improvement in quality of printed images can be achieved.

[0194] (2) Ink

[0195] The ink that can be used for the inkjet printing method of the present disclosure will now be described in detail by citing examples. In the present disclosure, when the compound is a salt, the salt in the ink exists as a dissociated ion, but is expressed as "containing a salt" for convenience. Titanium oxide and titanium oxide particles are referred to as "pigment". Aqueous ink for inkjet printing can be referred to as "ink". Unless otherwise specified, physical values ​​are values ​​at room temperature (25°C). When printing an image of white ink, white ink can be used for background color processing of color ink. In this case, the image can be printed by applying color ink (e.g., black, cyan, magenta, and yellow ink) so that it overlaps at least a portion of the area to which the white ink is applied. Optionally, the ink can also be used in reverse color printing, in which white ink is applied so that it overlaps at least a portion of the area to which the color ink is applied.

[0196] Water-based ink and method for producing water-based ink

[0197] The ink of the present disclosure is a white ink containing titanium oxide. Since titanium oxide is a white pigment, the ink can be a white ink. However, as long as it contains titanium oxide, the present disclosure can be used for inks other than white. The ink of the present disclosure does not need to be a so-called "curable ink". Therefore, the ink of the present disclosure does not need to contain a compound that can be polymerized by applying external energy (such as heat and light), such as a polymerizable compound. The components constituting the ink of the present disclosure, the physical properties of the ink, the manufacturing method, etc. will now be described in detail.

[0198] Colorants

[0199] The ink contains titanium oxide as a colorant (pigment). The titanium oxide may be titanium oxide particles surface-treated with a specific inorganic oxide. That is, the ink may contain titanium oxide particles, which are titanium oxide particles whose surfaces are coated with a specific inorganic oxide. Based on the total mass of the ink, the content (mass %) of the titanium oxide particles in the ink may be greater than 0.10 mass % and less than 20.00 mass %. Based on the total mass of the ink, the content (mass %) of the titanium oxide particles in the ink may be greater than 1.00 mass % and less than 20.00 mass %. In addition, in the present disclosure, since the redispersibility of the ink is improved by the configuration of the liquid discharge device, the content (mass %) of the titanium oxide particles in the ink can be easily increased and may be greater than 5.00 mass % and less than 20.00 mass % based on the total mass of the ink.

[0200] Titanium oxide is a white pigment and has three crystal forms: rutile, anatase, and brookite. In particular, the titanium oxide may be rutile titanium oxide. Examples of industrial production methods of titanium oxide include a sulfuric acid method and a chlorine method, and the titanium oxide used in the present disclosure may be produced by any production method.

[0201] The cumulative 50% volume-based particle size of the titanium oxide particles (hereinafter also referred to as the average particle size) may be 200 nm or more and 500 nm or less. In particular, the cumulative 50% volume-based particle size of the titanium oxide particles may be 200 nm or more and 400 nm or less.

[0202] The volume-based cumulative 50% particle size (D50) of titanium oxide particles is the particle diameter of 50% in the particle size accumulation curve when the total volume of the measured particles is accumulated from the small particle size side. The D50 of titanium oxide particles can be measured under the conditions of, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: non-spherical, and refractive index: 2.60. As a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method can be used. The measurement conditions and the like are not limited to the above.

[0203] Titanium oxide surface-treated with alumina and silica can be used. The surface treatment is expected to suppress photocatalytic activity and improve dispersibility. In this specification, "alumina" is a general term for aluminum oxides such as aluminum oxide. In this specification, "silica" is a general term for silicon dioxide and materials composed of silicon dioxide. Alumina and silica coated with titanium oxide mainly exist in the form of silica and aluminum oxide, respectively.

[0204] Based on the total mass of the titanium oxide particles, the proportion (mass %) of titanium oxide in the titanium oxide particles may be 90.00 mass % or more. Based on the total mass of the titanium oxide particles, the proportion (mass %) of titanium oxide in the titanium oxide particles may be 98.50 mass % or less. It is required that the mass ratio of the proportion (mass %) of aluminum oxide in the titanium oxide particles to the proportion (mass %) of silica is 0.50 times or more and 1.00 times or less. When the mass ratio is less than 0.50 times or greater than 1.00 times, the ink cannot obtain discharge stability. Based on the total mass of the titanium oxide particles, the proportion (mass %) of silica in the titanium oxide particles may be 1.00 mass % or more and 4.00 mass % or less. When the proportion (mass %) of silica is less than 1.00 mass %, the affinity with the compound represented by formula (1) cannot be fully obtained, and the discharge stability of the ink may become insufficient. When the ratio (mass %) of silica is greater than 4.00 mass %, even if surface treatment with aluminum oxide is performed, the amount of the compound represented by formula (1) adsorbed on the titanium oxide particles cannot be suppressed, and the discharge stability of the ink may become insufficient. The ratio (mass %) of aluminum oxide in the titanium oxide particles may be 0.50 mass % or more and 4.00 mass % or less based on the total mass of the titanium oxide particles.

[0205] An example of a method for measuring the ratio of aluminum oxide and silica in titanium oxide particles, that is, the coating amount of aluminum oxide and silica, includes quantitative analysis of aluminum and silicon elements by inductively coupled plasma (ICP) optical emission spectroscopy. In this case, the ratio can be calculated by assuming that all atoms on the coating surface are oxides and converting the obtained amounts of aluminum and silicon into their oxides (i.e., aluminum oxide and silica). The mass ratio of the ratio (mass %) of the aluminum element in the titanium oxide particles obtained by inductively coupled plasma optical emission spectroscopy to the ratio (mass %) of the silicon element is 0.57 times or more and 1.13 times or less. When this value is converted into its oxide, i.e., aluminum oxide and silica, the mass ratio of the ratio (mass %) of aluminum oxide in the titanium oxide particles to the ratio (mass %) of silica is 0.50 times or more and 1.00 times or less.

[0206] Examples of 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 (e.g., sodium aluminate and sodium silicate) to implement surface treatment. The desired properties can also be adjusted by appropriately changing the ratio of these surface treatment agents. As long as the effect of the present disclosure is not impaired, surface treatment can also use inorganic oxides such as zinc oxide and zirconium oxide or organic substances such as polyols in addition to aluminum oxide and silica.

[0207] As long as the effect of the present disclosure is not impaired, the ink may also contain other pigments other than titanium oxide. In this case, the ink may be any color ink other than white ink. Based on the total mass of the ink, the content (mass %) of the pigment other than titanium oxide in the ink is preferably 0.10 mass % or more and 5.00 mass % or less, more preferably 0.10 mass % or more and 1.00 mass % or less.

[0208] Compound represented by formula (1)

[0209] The ink may contain a compound represented by the following formula (1) as a dispersant for dispersing titanium oxide particles. The content (mass %) of the compound represented by formula (1) in the ink is preferably 0.01 mass % or more and 1.00 mass % or less, and more preferably 0.02 mass % or more and 0.50 mass % or less, based on the total mass of the ink.

[0210]

[0211] (In formula (1), R1, R2 and R3 are each independently a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms; R4 is each independently a hydrocarbon ethylene group having 2 to 4 carbon atoms; X is a single bond or a hydrocarbon ethylene group having 1 to 6 carbon atoms; n is 6 to 24; and a is 1 to 3, b is 0 to 2, and a+b=3).

[0212] In formula (1), R1, R2 and R3 are each independently a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. Examples of hydrocarbon groups having 1 to 4 carbon atoms include methyl, ethyl, n-propyl, isopropyl, and n-butyl. In particular, from the perspective of easy hydrolysis, the hydrocarbon group may be a methyl group. When R1, R2 and R3 are each a hydrocarbon group having more than 4 carbon atoms, it is difficult to form a silanol group by hydrolysis, and affinity with titanium oxide particles cannot be obtained. Therefore, titanium oxide particles cannot be stably dispersed, and discharge stability of the ink cannot be obtained. "a" representing the number of R1O is 1 to 3, "b" representing the number of R2 is 0 to 2, and a+b=3. In particular, "a" can represent 3, and "b" can represent 0, that is, all three substituents of the silicon atom can be R1O.

[0213] In formula (1), R4 is independently an alkylene group having 2 to 4 carbon atoms. Examples of alkylene groups having 2 to 4 carbon atoms include vinyl, n-propylene, isopropylene and n-butylene. In particular, the alkylene group may be vinyl. The number of OR4, i.e., n representing the number (average value) of oxyalkylene groups, is 6 to 24. When n is less than 6, since the length of the oxyalkylene chain is too short, the repulsive force generated by steric hindrance cannot be fully obtained, and the discharge stability of the ink cannot be obtained. When n is greater than 24, since the length of the oxyalkylene chain is too long, the affinity increases, which makes it easier to release into an aqueous medium. Therefore, sufficient affinity with the surface hydroxyl groups of the titanium oxide particles cannot be obtained, and the aggregation of the titanium oxide particles can be suppressed. Therefore, the titanium oxide particles cannot be stably dispersed, and the discharge stability of the ink cannot be obtained.

[0214] In formula (1), X is a single bond or an alkylene group having 1 to 6 carbon atoms. When X is a single bond, it means that the silicon atom is directly bonded to OR4. Examples of alkylene groups having 1 to 6 carbon atoms include methylene, vinyl, n-propenyl, isopropenyl, n-butenyl, n-pentenyl, and n-hexenyl. In particular, the alkylene group may be n-propenyl. When X is an alkylene group having more than 6 carbon atoms, the hydrophobicity of the compound represented by formula (1) becomes too high, the titanium oxide particles cannot be stably dispersed, and the discharge stability of the ink cannot be obtained.

[0215] The compound represented by formula (1) as a dispersant for titanium oxide particles can be a compound represented by the following formula (2). In the compound represented by formula (2), since the number of OR1 bonded to the silicon atom is 3, a part of it is hydrolyzed in an aqueous medium to form three hydroxyl groups bonded to the silicon atom to increase the sites having affinity with the titanium oxide particles. The compound represented by the following formula (2) has a repeating structure of ethylene oxide groups. Therefore, the ethylene oxide chain is approximately elongated in an aqueous medium, and a repulsive force due to steric hindrance can be obtained.

[0216]

[0217] (In formula (2), R1 and R3 are each independently a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms; and m is 8 to 24).

[0218] The mass ratio of the content (mass %) of the compound represented by formula (1) to the titanium oxide particles in the ink can be 0.002 times or more and 0.10 times or less. When the mass ratio is less than 0.002 times, the function of stably dispersing the titanium oxide particles is weakened, and the discharge stability of the ink may become insufficient. When the mass ratio is greater than 0.10 times, the proportion of the compound represented by formula (1) is too high, and condensation (self-condensation) is likely to occur between the molecules of the compound represented by formula (1). Therefore, the compound represented by formula (1) is consumed and cannot act as a dispersant, the function of stably dispersing the titanium oxide particles is weakened, and the discharge stability of the ink may become insufficient.

[0219] The compound represented by formula (1) forms hydrogen bonds with the surface hydroxyl groups of the titanium oxide particles, and it is inferred that a part of it forms covalent bonds through dehydration reaction. However, in the present disclosure, the compound represented by formula (1) can disperse the titanium oxide particles even if it does not form covalent bonds with the titanium oxide particles. That is, the amount of the compound represented by formula (1) that forms covalent bonds with the titanium oxide particles is very small and can be ignored. Therefore, the compound represented by formula (1) that is covalently bonded to the titanium oxide particles is not included in the content of the titanium oxide particles. According to the research results of the inventors, it was found that if the amount of the compound represented by formula (1) that is covalently bonded to the titanium oxide particles is too much, the discharge stability of the ink is reduced. The reason is presumed to be as follows. Since electrostatic attraction generally becomes less effective in liquid media with high dielectric constants such as water, the titanium oxide particles move freely without being significantly affected by the surrounding environment. However, if the compound represented by formula (1) is covalently bonded to the titanium oxide particles, the hydrophilic part (OR4 part) of the structure of formula (1) forms hydrogen bonds with water molecules. As a result, the movement of the titanium oxide particles may be affected. Therefore, in the case where the liquid is deformed due to instantaneous pressure (for example, during the discharge process of inkjet printing), the above-mentioned characteristics manifest as differences in discharge characteristics. Therefore, as a mass ratio of the content (mass %) of the titanium oxide particles, the content (mass %) of the compound represented by formula (1) covalently bonded to the titanium oxide particles may be 0.001 times or less. When the mass ratio is greater than 0.001 times, the discharge stability of the ink may be insufficient. The mass ratio may be 0.0001 times or less. The amount of the compound represented by formula (1) covalently bonded to the titanium oxide particles can be calculated by methods such as thermogravimetric analysis.

[0220] Wax particles

[0221] In the present disclosure, the ink may contain wax particles. The wax may be a composition containing components other than the wax, or may be the wax itself. The wax particles may be dispersed in a dispersant such as a surfactant and a resin.

[0222] Wax in a narrow sense is an ester of a higher monohydric or dihydric alcohol that is insoluble in water and fatty acids, including animal wax and plant wax, but excluding oil and fat. In a broad sense, it includes high melting point fats, mineral wax, petroleum wax, and blends and modified products of various waxes. In the printing method disclosed in the present invention, wax in a broad sense can be used without any restrictions. Wax in a broad sense can be divided into natural wax, synthetic wax, blends thereof (composite wax) and modified products thereof (modified wax).

[0223] Examples of natural waxes include animal waxes (e.g., beeswax, spermaceti, wool wax (lanolin)), vegetable waxes (e.g., tree wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax), mineral waxes (e.g., montan wax), and petroleum waxes (e.g., paraffin wax, microcrystalline wax, vaseline). Examples of synthetic waxes include hydrocarbon waxes (e.g., Fischer-Tropsch wax) and polyolefin waxes (e.g., polyethylene wax and polypropylene wax). Composite wax is a mixture of the above-mentioned various waxes. Modified wax is obtained after modification treatments such as oxidation, hydrogenation, alcohol modification, acrylic acid modification, and urethane modification of the above-mentioned various waxes. The wax may be at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified products and blends thereof. In particular, the wax may be a blend of multiple types of waxes or a blend of petroleum wax and synthetic wax.

[0224] The wax may be solid at room temperature (25°C). The melting point of the wax is preferably above 40°C and below 120°C, and further preferably above 50°C and below 100°C. The melting point of the wax can be measured according to the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). When the wax is microcrystalline wax, vaseline or a mixture of multiple waxes, the melting point can be measured more accurately by the test method described in 5.3.2. The melting point of the wax is easily affected by its characteristics, such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (straight chain has a high melting point, but with branched chains, the melting point is lowered), crystallinity (the higher the crystallinity, the higher the melting point) and density (the higher the density, the higher the melting point). Therefore, by controlling these characteristics, the wax can have a desired melting point.

[0225] Resin

[0226] The ink may contain a resin. Examples of the resin include acrylic resins, polyurethane resins, and urea resins. In particular, the resin may be an acrylic resin. Based on the total mass of the ink, the content (mass %) of the resin in the ink is preferably 1.00 mass % or more and 25.00 mass % or less, further preferably 3.00 mass % or more and 15.00 mass % or less, particularly preferably 5.00 mass % or more and 15.00 mass % or less.

[0227] The ink may contain a resin in the application to improve various properties of the printed image, such as abrasion resistance and concealment. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles dispersed in an aqueous medium. The resin particles do not need to contain a colorant.

[0228] In this specification, "the resin is water-soluble" means that when the resin is neutralized with an alkali in an amount equivalent to the acid value, the resin exists in an aqueous medium without forming particles whose particle size can be measured by a dynamic light scattering method. Whether the resin is water-soluble can be judged by the following method. A liquid containing a resin (resin solid content: 10% by mass) neutralized with an alkali (e.g., sodium hydroxide and potassium hydroxide) equivalent to the acid value is prepared. Subsequently, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution.

[0229] The particle size of the resin in the sample solution is measured by a dynamic light scattering method. When no particles with a particle size are observed, it can be judged that the resin is water-soluble. The measurement conditions in this case can be set, for example, to SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. As a particle size distribution measuring device, a particle size analyzer by a dynamic light scattering method (for example, trade name: UPA-EX150, manufactured by Nikkiso Co., Ltd.) can be used. The particle size distribution measuring device, measurement conditions, etc. are not limited to the above.

[0230] The acid value of the water-soluble resin is preferably 80 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 200 mgKOH / g or less. When resin particles are used, the acid value thereof may be 0 mgKOH / g or more and 50 mgKOH / g or less. The weight average molecular weight of the resin is preferably 1,000 or more and 30,000 or less, and more preferably 5,000 or more and 15,000 or less. The weight average molecular weight of the resin is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0231] Aqueous medium

[0232] The ink is an aqueous ink containing water as an aqueous medium. The ink may contain an aqueous medium, which is water or a solvent mixture of water and a water-soluble organic solvent. As water, deionized water (ion exchange water) may be used. Based on the total mass of the ink, the content (mass %) of water in the ink may be 50.00 mass % or more and 95.00 mass % or less.

[0233] There is no particular limitation on the water-soluble organic solvent, as long as it is water-soluble (for example, soluble in water at any ratio at 25°C). Specifically, monohydric or dihydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc. can be used. Based on the total mass of the ink, the content (mass %) of the water-soluble organic solvent in the ink is preferably 3.00 mass % or more and 50.00 mass % or less, and further preferably 10.00 mass % or more and 40.00 mass % or less. When the content (mass %) of the water-soluble organic solvent is less than 3.00 mass %, the ink adheres to the inkjet printing device, and sufficient anti-stickiness may not be obtained. When the content (mass %) of the water-soluble organic solvent is greater than 50.00 mass %, poor ink supply may occur.

[0234] Other additives

[0235] In addition to the above-mentioned additives, the ink may also contain surfactants, pH regulators, corrosion inhibitors, preservatives, mildew inhibitors, antioxidants, reduction inhibitors, evaporation promoters, chelating agents, etc. as needed. In particular, the ink may contain a surfactant. Based on the total mass of the ink, the content (mass %) of the surfactant in the ink is preferably 0.10 mass % or more and 5.00 mass % or less, and further preferably 0.10 mass % or more and 2.00 mass % or less. Examples of surfactants include anionic surfactants, cationic surfactants and nonionic surfactants. In particular, since the surfactant is used to adjust the various physical properties of the ink, the surfactant can be a nonionic surfactant that has low affinity with the titanium oxide particles and can show an effect in a small amount.

[0236] Physical properties of ink

[0237] Since the ink is an ink applied to an inkjet system, its physical properties can be appropriately controlled. The surface tension of the ink at 25°C is preferably 10 mN / m or more and 60 mN / m or less, and further 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. The viscosity of the ink at 25°C can be 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C can be 7.0 or more and 9.0 or less. When the pH of the ink is within the above range, the process of generating silanol groups by hydrolysis of the compound represented by formula (1) is in progress, so the weak affinity between the titanium oxide particles and the compound represented by formula (1) is effectively exhibited. The pH of the ink can be measured using an ordinary pH meter equipped with a glass electrode.

[0238] Example

[0239] The present disclosure will now be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited in any way to the following examples unless it exceeds its purport. Unless otherwise specified, "parts" and "%" regarding the amount of components are mass references. The dispersion of titanium oxide particles is referred to as "pigment dispersion".

[0240] Preparation of titanium oxide

[0241] Commercially available rutile titanium oxide particles that had been surface treated in advance were used. The cumulative 50% particle size (D50) based on volume of the titanium oxide particles was measured by dynamic light scattering using a particle size analyzer (trade name: Nanotrac WaveII-EX150, manufactured by Microchip Biotech). Table 1 shows the properties of each titanium oxide particle.

[0242] Table 1: Characteristics of titanium oxide particles

[0243]

[0244] Preparation of pigment dispersions

[0245] Pigment dispersion 1

[0246] A styrene-methyl methacrylate-methacrylic acid copolymer (resin 1) is provided, which has an acid value of 150 mgKOH / g and a weight-average molecular weight of 10,000. An aqueous solution of resin 1 is prepared by neutralizing 20.0 parts of resin 1 with potassium hydroxide in an equimolar amount to the resin acid value and adding an appropriate amount of pure water, wherein the resin content (solid content) is 20.0%. Ion exchange water is mixed with 40.0 parts of titanium oxide particles 1 and 40.0 parts of an aqueous solution of resin 1 to make the total amount of the components 100.0 parts, and a homogenizer is used for pre-dispersion. Subsequently, a dispersion treatment (main treatment) is performed in a paint shaker at 25°C for 12 hours using 0.5 mm zirconium beads. The zirconium oxide beads are removed by filtration, and an appropriate amount of ion exchange water is added to the filtrate as needed to prepare a pigment dispersion 1, wherein the content of titanium oxide particles is 40.0% and the content of the resin dispersion (resin 1) is 8.0%.

[0247] Pigment dispersion 2

[0248] Pigment Dispersion 2 was prepared according to the same procedure as Pigment Dispersion 1, except that the pigment was changed to Titanium Oxide Particles 2, in which the content of the titanium oxide particles was 40.0% and the content of the resin dispersion (Resin 1) was 8.0%.

[0249] Ink preparation

[0250] A mixture of 25.0 parts of Pigment Dispersion 1 and the components shown below was stirred. Subsequently, pressure filtration was performed with a membrane filter having a pore size of 5.0 μm (manufactured by Sartorius) to prepare Ink 1. Ink 2 was prepared by the same procedure as Ink 1 except that Pigment Dispersion 2 was used instead of Pigment Dispersion 1.

[0251] The details of each mixing component are as follows:

[0252] Acrylic resin particles (trade name: Vinyblan 2685, manufactured by Nissin Chemical Industry Co., Ltd., resin particle content: 30%): 20.0 parts;

[0253] Diethylene glycol: 10.0 parts;

[0254] Diethylene glycol isobutyl ether: 10.0 parts;

[0255] Fluorine-containing surfactant (trade name: Capstone FS-3100, manufactured by Chemours): 1.0 part; and

[0256] Ion exchange water: 34.0 parts.

[0257] Viscosities (Pa·s) and densities (g / cm2) of inks 1 and 2 3 ) are 8Pa·s and 1.16g / cm 3 The sedimentation rate of each ink was calculated using these values. As a result, the sedimentation rate of ink 1 was 1.2×10 -11 m / s. The sedimentation rate of ink 2 is 8.5×10 -12 m / s.

[0258] The precipitation rate is calculated by the following formula (Stokes equation), where ν is the precipitation rate, D is the particle size of titanium oxide, and ρ p is the density of titanium oxide particles, ρ f is the density of ion-exchanged water, g is the acceleration due to gravity, and η is the density of ion-exchanged water.

[0259]

[0260] Liquid discharge head

[0261] Head 1

[0262] Figures 2 to 5 The liquid discharge head shown is set as head 1. The maximum cross-sectional area of ​​the circulation path in head 1 is 300 mm 2 .

[0263] Evaluate

[0264] The ink 1 was set into a serial inkjet printing apparatus loaded with the head 1, and the ink was discharged under an environment of a temperature of 25°C and a relative humidity of 50% while the ink was circulated in the head 1. The carriage loaded with the head 1 was operated at a constant scanning speed of 30 ips and 10 m / s during acceleration and deceleration. 2 As a result, it was confirmed that the effect of the present disclosure was fully obtained.

[0265] According to the present disclosure, it is possible to provide an inkjet printing method that improves the discharge stability of ink containing titanium oxide.

[0266] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An inkjet printing method for discharging ink from a liquid discharge head, wherein The ink contains titanium oxide, and the precipitation rate in the ink based on the Stokes equation is 1.0×10 -11 m / s or more, The liquid discharge head comprises: a discharge port for discharging ink; a pressure chamber for supplying ink to the discharge port; an energy generating element for generating energy for discharging ink; an upstream flow passage for supplying liquid to the pressure chamber; a downstream flow passage in communication with the pressure chamber; as well as a pump that communicates with the upstream flow channel and the downstream flow channel and forms a circulation path in which ink circulates in the order of the upstream flow channel, the pressure chamber, the downstream flow channel, and the upstream flow channel, The liquid discharge head is configured to perform reciprocating scanning, and The scanning speed in the area where the liquid discharge head scans at a constant speed is higher than the deposition speed.

2. The inkjet printing method according to claim 1, wherein: The liquid discharge head reciprocates and scans so that an acceleration / deceleration rate during acceleration and deceleration in the reciprocating scanning is greater than the gravitational acceleration.

3. The inkjet printing method according to claim 1, wherein: The ink is white ink.

4. The inkjet printing method according to claim 3, wherein: At least one of a color ink that does not contain titanium oxide or a color ink whose concentration of titanium oxide is lower than that of white ink and a reaction liquid is discharged from the liquid discharge head; and the scanning speed of the liquid discharge head when discharging white ink is slower than the scanning speed of the liquid discharge head when discharging color ink or reaction liquid.

5. The inkjet printing method according to claim 1, wherein: The volume of the ink flowing in the circulation path is 5 mL or more and 30 mL or less.

6. The inkjet printing method according to claim 1, wherein: The liquid discharge head further includes a first pressure regulating device configured to adjust the pressure of the liquid in the upstream flow channel.

7. The inkjet printing method according to claim 6, wherein: The first pressure regulating device includes a first valve chamber, a first pressure control chamber, a first opening communicating between the first valve chamber and the first pressure control chamber, and a first valve configured to open and close the first opening.

8. The inkjet printing method according to claim 7, wherein: The first pressure control chamber includes: a first pressure plate, a portion of a surface of the first pressure plate is formed by a first flexible member configured to be displaceable, and the first pressure plate can be displaced in conjunction with the first flexible member; and a first biasing member, the first biasing member applies a force to the first pressure plate in a direction to increase the volume of the first pressure control chamber and is configured to enable the first valve to open and close in response to the displacement of the first pressure plate and the first flexible member.

9. The inkjet printing method according to any one of claims 1 to 8, wherein: The liquid discharge head further includes a second pressure regulating device configured to adjust the pressure of the liquid in the downstream flow channel.

10. The inkjet printing method according to claim 9, wherein: The second pressure regulating device includes a second valve chamber, a second pressure control chamber, a second opening communicating between the second valve chamber and the second pressure control chamber, and a second valve configured to be able to open and close the second opening.

11. The inkjet printing method according to claim 7 or 8, wherein: A first communication port is arranged vertically below the first pressure control chamber, and the first pressure control chamber communicates with the upstream flow passage through the first communication port.

12. The inkjet printing method according to claim 10, wherein: The second communication port is arranged vertically below the first pressure control chamber, and the second pressure control chamber communicates with the downstream flow passage through the second communication port.

13. The inkjet printing method according to claim 1, wherein The liquid discharge head comprises: a discharge unit, the discharge unit comprising an element substrate, the element substrate comprising the discharge port and the pressure chamber; and a circulation unit, the circulation unit including the pump, configured to circulate the liquid between the discharge unit and the circulation unit, wherein In a portion where the discharge unit and the circulation unit are in fluid contact, a wall of a flow channel in the discharge unit fluidly connected to the circulation unit is perpendicular to a vertical direction or inclined to a vertical direction.

14. The inkjet printing method according to claim 1, wherein: The liquid storage portion is connected to the liquid discharge head through a tube configured to supply ink to the liquid discharge head.

15. The inkjet printing method according to claim 1, wherein: The pump is a piezoelectric pump.

16. The inkjet printing method according to claim 1, wherein: The concentration of titanium oxide in the ink is 5.00 mass % or more and 20.00 mass % or less.

17. The inkjet printing method according to claim 1, wherein: The liquid discharge head is configured to reciprocate and scan in a direction orthogonal to a conveyance direction of a printing medium to which ink is applied.

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