Inkjet printing method

Abstract

In an inkjet printing method for discharging ink from a liquid discharge head, the ink contains titanium oxide, and the precipitation rate of titanium oxide in the ink is 1.0 * 10-11 m / s or more on the basis of the Stokes equation, and the precipitation rate of titanium oxide in the ink is 1.0 * 10-11 m / s or more on the basis of the Stokes equation. The liquid discharge head includes a discharge port, a pressure chamber, an energy generating element for discharging ink, 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 in which the liquid is discharged from the pressure chamber. The ink circulates in the order of the upstream flow channel, the pressure chamber, the downstream flow channel, and the upstream flow channel, and the ratio Q / S [m / s] of the flow rate Q of the ink in the circulation path to the maximum cross-sectional area S of the circulation path is higher than the deposition rate.

Description

Technical Field

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

[0002] In recent years, when outputting advertisements and exhibits using printing media such as paper and resin films, inkjet printing devices have been widely used. For example, in order to express a vivid color image also 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 ​​a transparent printing medium containing an area where an image is to be printed to perform background color processing, and color ink is applied thereon. Alternatively, a printing method (so-called reverse color printing) of applying inks in reverse order is performed.

[0003] As a colorant for white ink, titanium oxide is widely used because it is low in cost and also has excellent properties required for white ink, such as whiteness and concealment. However, titanium oxide has the problem of easy precipitation. Therefore, from the perspective of inhibiting the precipitation of titanium oxide in white ink, a method of improving dispersion stability by surface treating titanium oxide has been studied. For example, PCT Japanese Laid-Open Patent Publication No. 2017-521348 proposes a method for preparing a dried titanium oxide product, wherein a portion of the silane coupling agent is covalently bonded to the surface of the titanium oxide particles by surface treating the titanium oxide with silicon dioxide, and then further surface treating the titanium oxide with a silane coupling agent and drying.

[0004] International Publication No. WO 2018 / 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 Laid-Open Patent Publication No. 2017-521348 and International Publication No. WO 2018 / 190848, attempts have been made to achieve stable discharge of white ink and suppress the occurrence of image unevenness in a printed image by using white ink in which precipitation of titanium oxide is suppressed.

[0006] The present inventors considered that as a method for achieving stable discharge of ink in an inkjet printing method using ink (e.g., white ink containing titanium oxide that is easily precipitated), titanium oxide particles having high redispersibility are used instead of composing the ink so as to suppress precipitation of titanium oxide. In addition, the present inventors considered composing a liquid discharge head so that the particles can be redispersed even if they are precipitated.

[0007] Therefore, the present disclosure provides an inkjet printing method that enhances the redispersibility of an ink containing titanium oxide and improves the discharge stability of the ink. Summary of the invention

[0008] In order to solve the above-mentioned problems, the present invention discloses an inkjet printing method for discharging ink from a liquid discharge head, wherein the ink contains titanium oxide, and the precipitation rate of titanium oxide in the ink is 1.0×10 -11 m / s or above; 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, the pump is connected to the upstream flow channel and the downstream flow channel and forms 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; and the ratio Q / S [m / S] of the flow velocity Q of the ink in the circulation path to the maximum cross-sectional area S of the circulation path is higher than the sedimentation rate.

[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 It 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 It 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 8B This is a three-dimensional diagram of the appearance of the circulation pump.

[0020] Fig. 9 yes Fig. 8AA cross-sectional view along line IX-IX of the circulating pump shown in FIG.

[0021] Figures 10A to 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] Figures 14A to 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 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 18B is a diagram showing a flow channel configuration of a liquid discharge head.

[0030] Fig.19 It 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 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] There is no particular limitation on the print medium, 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 absorbency, such as a resin film. Applying ink to a unit area of ​​the print medium can be a multi-pass printing in which a relative scan is performed multiple times on the print head and the print medium. In particular, white ink and colored ink can be applied to the unit area by different relative scans. Therefore, the time required until various inks contact each other becomes longer, which tends to inhibit their mixing. The unit area can be set to an arbitrary area, such as a pixel or a band.

[0037] The present inventors first studied a method for improving the redispersibility when the ink containing titanium oxide has been 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 must be 1.0×10 -11 The sedimentation velocity based on the Stokes equation refers to the velocity when the drag and buoyancy forces exerting an upward force on the particles are balanced with the gravity exerting a downward force on the particles, so that the particles move at a constant speed.

[0038] However, when such an ink having high redispersibility is used, the titanium oxide in the ink itself tends to precipitate. Therefore, if the flow rate of the ink flow generated by the circulation is higher than the precipitation rate of the ink, the redispersion of the ink is promoted. In order to achieve stable discharge through the discharge port 13, it is desired that the ink in which the titanium oxide particles are fully dispersed flows into the pressure chamber. Therefore, in the present disclosure, the liquid discharge head has a mechanism for circulating the ink in a circulation path in the discharge head, and allows the ink with a uniform pigment concentration to flow into the pressure chamber by promoting the redispersion of the ink in the circulation path by the circulation flow, so as to improve the discharge stability of the ink.

[0039] Reference Figure 5 The circulation of ink in the liquid discharge head is described. Figure 5 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.

[0040] Figure 5 The liquid discharge head 1 shown in the figure 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 connected to each other 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.

[0041] In order to promote the redispersion of titanium oxide by the flow of ink, it is sufficient that the flow of ink is higher than or equal to the precipitation speed of titanium oxide particles even at the area where the flow speed is the slowest in the circulation path. It is considered that the flow speed acting on the titanium oxide particles in the ink by circulation is expressed by Q / S using the circulation flow speed Q and the maximum cross-sectional area S of the circulation path. It can be inferred that when Q / S [m / S] is greater than the precipitation speed, redispersion is promoted.

[0042] Here, the cross-sectional area in the circulation path is the area of ​​a plane orthogonal to the liquid flow direction. Since the increase in the maximum cross-sectional area S increases the circulation flow rate Q required for redispersion of the ink, the maximum cross-sectional area is preferably 500 mm 2 Below, more preferably 350mm 2 the following.

[0043] (1) Liquid discharge equipment

[0044] 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 following present embodiment 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 solution of the present disclosure. The same components are given the same figure marks. In the present embodiment, a thermal system that discharges liquid by generating bubbles by an electrothermal conversion element will be described as an example of a discharge element for discharging liquid, but the discharge element is not limited to this. A liquid discharge head that uses a discharge system or other discharge system that uses a piezoelectric element (piezo) to discharge liquid can also be applied. In addition, the pump, pressure control device, etc. described below are not limited to the configurations described in the embodiments and the accompanying drawings.

[0045] Liquid discharge equipment

[0046] Figure 1A and 1B 2 is a diagram for explaining a liquid discharge apparatus and is an enlarged view of a liquid discharge head of the liquid discharge apparatus and its vicinity. Figure 1A and 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 tandem type inkjet printing apparatus that performs printing on a printing medium P by discharging ink as liquid while scanning the liquid discharge head 1.

[0047] The liquid discharge head 1 is loaded on the carriage 60. The carriage 60 reciprocates along the guide shaft 51 in the main scanning direction (X direction). The printing medium P is conveyed to the sub-scanning direction (Y direction) intersecting (in this example, orthogonal) with the main scanning direction by conveying rollers 55, 56, 57 and 58. That is, the liquid discharge head 1 is configured to discharge liquid while scanning in a direction orthogonal to the conveying direction of the printing medium to which ink is to be applied. In each of the figures cited below, the Z direction represents the vertical direction and intersects (in this example, orthogonal) with the XY plane defined by the X direction and the Y direction. The liquid discharge head 1 is configured to be detachable and attached to the carriage 60 by the user.

[0048] By including the circulation unit 54 and the discharge unit 3 (see Figure 2 ) to constitute the liquid discharge head 1. Although the 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 emits discharge energy for discharging the liquid through each discharge port.

[0049] The liquid discharge device 50 is provided with an ink tank 2 (liquid storage portion) as a supply source of ink, and an external pump 21 , and the ink stored in the ink tank 2 is supplied to the circulation unit 54 through the ink supply tube 59 by the driving force of the external pump 21 .

[0050] The liquid discharge device 50 forms a prescribed image on the print medium P by repeating a print scan and a conveying operation of conveying the print medium P to the sub-scanning direction, in which 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 in the present embodiment is configured to be able to discharge 4 types of ink, including ink containing titanium oxide. However, the structure of the inkjet printing device in the present disclosure is not limited to the structure of discharging 4 types of liquids. For example, a structure capable of discharging 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 by 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 amount of liquid discharged from the liquid discharge head are not limited.

[0051] The liquid discharge device 50 is provided with a cap member (not shown) that can cover the discharge port surface of the liquid discharge head where the discharge port is formed at a position deviated in the X direction from the conveying path of the printing medium P. The cap member covers the discharge port surface of the liquid discharge head 1 during a non-printing operation, and serves to prevent the discharge port from drying and to protect the discharge port, the ink suction operation performed through the discharge port, and the like.

[0052] Figure 1A The liquid discharge head 1 shown in FIG. 1 is an example in which four circulation units 54 corresponding to four types of ink are provided in the liquid discharge head 1, and it is sufficient to set the circulation unit 54 according to the type of liquid to be discharged. A plurality of circulation units 54 may be provided for one type of liquid. That is, the liquid discharge head 1 may be configured to include one or more circulation units. This configuration may be used to circulate only at least one ink containing titanium oxide, rather than to circulate all four types of ink.

[0053] 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. When the CPU 103 performs processing, the RAM 102 is used as a work area, 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 controls 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, for example, a motor driver 105A of a carriage motor 105 for moving the carriage 60 and a motor driver 104A of a conveying motor 104 for conveying the 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 the processing may be performed by the liquid discharge device 50 without depending on the data from the host device 400 .

[0054] Basic structure of liquid discharge head

[0055] Figure 2 It is an exploded perspective view of the liquid discharge head 1 of this embodiment. Figure 3A yes Figure 2 2 is a cross-sectional view of the liquid discharge head 1 shown in FIG. 1 taken along line IIIA-IIIA. Figure 3A is an overall vertical sectional view of the liquid discharge head 1, Figure 3B yes Figure 3AAn enlarged view of the discharge module 300 is shown in FIG. Figure 1A and Figure 1B In the case of Figure 2 as well as Figure 3A and Figure 3B While focusing on the above, the basic configuration of the liquid discharge head 1 in this embodiment will be described.

[0056] like Figure 2 As 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 by 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 to perform printing on the printing medium P.

[0057] The ink supply tube 59 is provided on the external pump 21 (see Figure 1A ), the external pump is connected to the ink tank 2 as the ink supply source. 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 this embodiment, since 4 types 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 various inks respectively, and 4 ink supply paths corresponding to various inks are independently formed. Therefore, the liquid discharge device 50 of this embodiment includes an ink supply system, and ink is supplied to the ink supply system from the ink tank 2 provided outside the liquid discharge head 1. The liquid discharge device 50 of this 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 ink in the liquid discharge head 1 in the ink tank 2. The liquid connector insertion port 53a is provided for each ink.

[0058] 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 structure, and when the circulation units are not particularly distinguished, they are all collectively referred to as circulation units 54 in this embodiment.

[0059] exist Figure 2 and Figure 3A In 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 in FIG. 1 , 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 an electrical wiring formed on the silicon substrate 310 by a film forming technology.

[0060] 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 collecting channel 19 are formed. In addition, in the silicon substrate 310, a supply connection channel 323 communicating between the common supply channel 18 and each pressure chamber 12, and a collection connection channel 324 communicating between the common collecting channel 19 and each pressure chamber 12 are formed. In the construction of this embodiment, one discharge module 300 performs the discharge of 2 types of ink. That is, in Figure 3A In the two discharge modules shown in the figure, the discharge module 300 located on the left side of the figure performs the discharge of the first ink and the second ink, and the discharge module 300 located on the right side of the figure performs the discharge of the third ink and the fourth ink. This combination is an example, and the inks can be any combination. A structure in which one discharge module discharges one type of ink may be adopted, or a structure in which one discharge module discharges three or more types of ink may be adopted. The two discharge modules 300 do not need to discharge the same number of types of ink. A structure including one discharge module 300 may be adopted, or a structure including three or more discharge modules 300 may be adopted. In addition, in Figure 3A and 3BIn the example shown in , two discharge port arrays extending in the Y direction are formed for one type of ink. A pressure chamber 12, a common supply channel 18, and a common collection channel 19 are formed for each of a plurality of discharge ports 13 constituting each discharge port array.

[0061] 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.

[0062] The ink supply port and the ink collection port mentioned here refer to openings for supplying and collecting ink during the ink circulation in the forward direction described later. That is, in the ink circulation in the forward direction, 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 can also be performed. 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.

[0063] like Figure 3A As shown in FIG. , the rear surface ( Figure 3A The top surface of the first support member 4 is adhered and fixed to one surface ( Figure 3A bottom surface in the middle).

[0064] The first supporting member 4 is formed with an ink supply channel 48 and an ink collection channel 49 penetrating from one surface to the other surface thereof. 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 type of ink.

[0065] The second supporting member 7 is adhered and fixed to one surface of the first supporting member 4 ( Figure 3A The second support member has an opening 7a (see Figure 2 ).

[0066] 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 for discharging ink to the discharge module 300. The electrical connection between the discharge module 300 and the electric wiring member 5 is sealed by a sealing material (not shown), and is protected from corrosion caused by ink and external impact.

[0067] 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 to 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.

[0068] In addition, the joint member 8 ( Figure 3A ) is disposed between the first support member 4 and the circulation unit 54. The joint member 8 is formed with a supply port 88 and a collection port 89 for each type of ink. The supply port 88 and the collection port 89 communicate between the ink supply channel 48 and the ink collection channel 49 of the first support member 4 and 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.

[0069] The opening at one end 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 adapted to the ink supply port and the ink collection port in the silicon substrate 310. In contrast, the opening at the other end of each of the ink supply channel 48 and the ink collection channel 49 of the first support member 4 has a shape with an increased opening area, which is the same as the large opening area of ​​the joint member 8 formed to accommodate the flow channel of the circulation unit 54. In this configuration, the increase in the flow channel resistance of the ink collected from each collection channel can be suppressed. However, the shape of the openings at one end and the other end of each of the ink supply channel 48 and the ink collection channel 49 is not limited to the above example.

[0070] 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 driving 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.

[0071] Components of a circulation unit

[0072] Figure 4 1 is a schematic diagram of the appearance of a circulation unit 54 corresponding to one type of ink applied to the printing device of this embodiment. In addition to the circulation pump 500, the circulation unit 54 may 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 6 The ink shown in FIG. 1 is connected to each flow channel, and constitutes a circulation path that performs supply and collection of ink to the discharge module 300 in the liquid discharge head 1 .

[0073] Circulation path in liquid discharge head

[0074] Figure 5 1 is a vertical cross-sectional view schematically showing a circulation path for one type of ink (one color of ink) configured in the liquid discharge head 1. In order to more clearly illustrate the circulation path, the Figure 5 The relative position of each component in the pressure control device 120, the second pressure control device 150 and the circulation pump 500 is different from the relative position of each component described later. Fig.19 The structure in . Figure 6 It is schematically shown Figure 5 A block diagram of the loop path shown in . Figure 5 and 6 As shown in FIG. 1 , 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.

[0075] The configuration is made so that the ink flows in the pressure chamber 12 (discharge element 15) at a flow rate according to the pressure difference between the pressures in the first pressure regulating device 120 and the second pressure regulating device 150. Reference will now be made to Figure 5 and 6 Description is given of the circulation path and the flow of ink in the circulation path in the liquid discharge head 1. The arrow in each figure indicates the direction in which the ink flows.

[0076] The connection state of each component in the liquid discharge head 1 will be described.

[0077] The external pump 21 is connected to the circulation unit 54 through the ink supply tube 59 ( FIG. 1 ), and pumps the ink stored in the ink tank 2 ( FIG. 1 ) provided outside the liquid discharge head 1. Figure 6) is sent to the liquid discharge head 1. The ink flow passage (inlet flow passage) located upstream of the circulation unit 54 is provided with a filter 110. The ink supply path (inlet flow passage) 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, which can be connected by Figure 5 The valve 190A shown in FIG. 1 opens and closes. The inlet flow channel is a flow channel that flows into the liquid discharge head 1 and is used to supply the liquid in the ink tank 2 provided outside the liquid discharge head 1 to the pressure chamber 12 .

[0078] 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, which is connected by Figure 5 Valve 190B is shown open and closed. Figure 5 and 6 An example is shown in which 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.

[0079] 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.

[0080] Subsequently, the flow of ink in the liquid discharge head 1 having the above-described configuration will be described. Figure 6 As shown in FIG. 1 , 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.

[0081] 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 decreases due to pressure loss when passing through the filter 110, the pressure of the ink is in a positive pressure state at this stage. 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 switches from a positive pressure state to a negative pressure state due to pressure loss when passing through the communication port 191A.

[0082] Then, 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 driving the pump. Although the details will be described later, in this embodiment, as a circulation pump that can send liquid, a piezoelectric diaphragm pump is used, which uses a piezoelectric element attached to a diaphragm as a driving source. The piezoelectric diaphragm pump is a pump that sends liquid by applying a driving voltage to the piezoelectric element to change the volume of the pump chamber and thereby causing two check valves to move alternately through pressure changes.

[0083] The ink flowing into the supply channel 130 passes through the common supply channel 18 and flows into the pressure chamber 12 through the ink supply port of the discharge module 300, and a part of the ink is discharged from the discharge port 13 by the driving (heat generation) of the discharge element 15. The remaining ink not used in the discharge process 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.

[0084] 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 by the driving of the circulation pump 500. The ink sucked into the circulation pump 500 is sent 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 flow into the circulation pump 500. Then, the ink is sent from the circulation pump 500 to the first pressure control chamber 122. Thus, circulation of the ink in the circulation path is performed.

[0085] 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 increase in the viscosity of the ink and the accumulation of the precipitated components of the colorant ink in the discharge module 300 can be suppressed, and the fluidity of the ink in the discharge module 300 and the discharge characteristics in the discharge port can be maintained in a good state.

[0086] Since the circulation path in the present embodiment adopts a structure 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 performed with a small-sized circulation pump (such as a piezoelectric pump). In particular, in the present disclosure, since the reciprocating movement of the liquid discharge head suppresses the precipitation of particles in the ink and promotes the redispersion of the ink, it is easy to maintain the dispersibility of the ink even with a small circulation pump.

[0087] 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 miniaturization of the entire device can be achieved. In addition, the reduction in the number of tubes can reduce the change in ink pressure 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, when the configuration is performed to allow the liquid to circulate in the liquid discharge device 50, miniaturization and cost reduction can be achieved.

[0088] The flow rate for circulating the reaction liquid (circulation flow rate) is preferably 1.0 mL / min to 10.0 mL / min, more preferably 2.0 mL / min to 10.0 mL / min, further preferably 2.0 mL / min to 5.0 mL / min.

[0089] Pressure control device

[0090] Fig. 7A , 7B 7C are diagrams showing examples of pressure control devices. Figures 7A to 7C , the configuration and function of the pressure control devices (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 substantially the same configuration. Therefore, hereinafter, the first pressure control device 120 will be described as an example, and regarding the second pressure control device 150, Figures 7A to 7C In 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 .

[0091] 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 the 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 flow of ink through the communication port 191 is disconnected. 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 center 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 ink flow through the communication port 191 is blocked by the valve 190 is referred to as a "closed state", and a state in which the ink flows through the communication port 191 is referred to as an "open state".

[0092] The opening 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 as the flexible member 230 is displaced. The materials of the pressing plate 210 and the flexible member 230 are not particularly limited. For example, the pressing plate 210 may be composed of a resin molded product, and the flexible member 230 may be composed of a resin film. In this case, the pressing plate 210 may be fixed to the flexible member 230 by thermal welding.

[0093] The pressure adjustment spring 220 (biasing member) is provided between the pressing plate 210 and the partition 123. Fig. 7A As shown in FIG. 1 , the pressing plate 210 and the flexible member 230 are urged in a direction in which the internal volume of the first pressure control chamber 122 increases by the biasing force of the pressure adjusting spring 220 .

[0094] When the pressure in the first pressure control chamber 122 decreases, the pressing plate 210 and the flexible member 230 are displaced against the pressure of the pressure regulating spring 220, so that the internal volume of the first pressure control chamber 122 decreases. When the internal volume of the first pressure control chamber 122 decreases to a certain volume, the pressing 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 overcomes the biasing force of the valve spring 200 and moves together with the valve shaft 190a, and separates from the partition 123. Therefore, the communication port 191 becomes an open state ( Figure 7B status shown in ).

[0095] 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.

[0096] Therefore, when the communication port 191 becomes the 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 pressing plate 210 so that the internal volume of the first pressure control chamber 122 increases. As a result, the pressing plate 210 is separated from the valve shaft 190a of the valve 190, the valve 190 is in close contact with the partition 123 by the biasing force of the valve spring 200, and the communication port 191 becomes the closed state ( Figure 7C status shown in ).

[0097] 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, the configuration is made 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 keep the pressure within a certain range.

[0098] The pressure of the first pressure control chamber 122 will then be described in more detail.

[0099] As described above, considering the open state of the communication port 191 ( Figure 7B ), in which the flexible member 230 and the pressing plate 210 are displaced in response to the pressure of the first pressure control chamber 122 and the pressing plate 210 abuts against the valve shaft 190a. In this case, the relationship of the force acting on the pressing plate 210 is expressed by the following equation 1:

[0100] P2×S2+F2+(P1-P2)×S1+F1=0Equation 1.

[0101] Furthermore, rearranging equation 1, we obtain with respect to P2:

[0102] P2 = -(F1 + F2 + P1 × S1) / (S2 - S1) Equation 2.

[0103] P1: pressure of the first valve chamber 121 (gauge pressure);

[0104] P2: pressure of the first pressure control chamber 122 (gauge pressure);

[0105] F1: Spring force of valve spring 200;

[0106] F2: Spring force of the pressure regulating spring 220;

[0107] S1: the pressure receiving area of ​​valve 190; and

[0108] S2: The pressure receiving area of ​​the pressing plate 210 .

[0109] 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 pressing plate 210 ( Figures 7A to 7C The leftward direction in the first valve chamber 121 is defined as a positive direction. The configuration is made so that the pressure P1 in the first valve chamber 121 and the pressure P2 in the first pressure control chamber 122 have a relationship of P1 ≥ P2.

[0110] When the communication port 191 becomes the open state, the pressure P2 in the first pressure control chamber 122 is determined by Equation 2, and is configured so that when the communication port 191 becomes the open state, the 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.

[0111] In contrast, Figure 7C As shown in , when the pressing plate 210 is not in contact with the valve shaft 190a and the communication port 191 becomes a closed state, the relationship of the force acting on the pressing plate 210 is expressed by Equation 3:

[0112] P3×S3+F3=0 Equation 3.

[0113] Here, rearranging equation 3, we get about P3:

[0114] P3 = -F3 / S3 Equation 4.

[0115] F3: spring force of the pressure regulating spring 220 when the pressing plate 210 and the valve shaft 190a are not in contact with each other;

[0116] P3: the pressure (gauge pressure) of the first pressure control chamber 122 when the pressing plate 210 and the valve shaft 190a are not in contact with each other; and

[0117] S3: The pressed area of ​​the pressing plate 210 when the pressing plate 210 and the valve 190 are in the non-contact area.

[0118] here, Figure 7C The state in which the pressing plate 210 and the flexible member 230 are displaced to the right in the figure until the limit of possible displacement is shown. 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 pressing plate 210 change according to the amount of displacement until the pressing plate 210 and the flexible member 230 are displaced to the right. Figure 7C Specifically, when the pressing plate 210 and the flexible member 230 are in contact with each other, Figure 7C Compared with the Figure 7B , the pressure area S3 of the pressing 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 in the Figure 7C During the state shown in , the pressure in the first pressure control chamber 122 gradually increases according to equations 2 and 4 (i.e., the negative pressure becomes weaker and approaches the positive pressure side). That is, the pressing plate 210 and the flexible member 230 gradually shift toward the left direction from the state in which 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 of possible displacement. That is, the negative pressure weakens.

[0119] Circulation pump

[0120] Then refer to Fig. 8A , 8B 9 describe in detail the configuration and function of the circulation pump 500 built in the above-described liquid discharge head 1.

[0121] Fig. 8A and 8B It is a perspective view of the appearance of the circulation pump 500. Fig. 8A 2 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 .

[0122] 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 adhered and fixed to the outer surface of the housing body 505a. A pair of through holes that are connected to each other are provided at two different positions in 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 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.

[0123] Fig. 9 yes Fig. 8A 500 shown in FIG. 506 is a cross-sectional view along line IX-IX of the circulation pump 500. The diaphragm 506 is bonded to the inner surface of the pump housing 505, and the pump chamber 503 is formed between the diaphragm 506 and the recessed portion formed on the inner surface of the pump housing 505. The pump chamber 503 is communicated with the pump supply hole 501 and the pump discharge hole 502 formed in the pump housing 505. The check valve 504a is arranged at the middle part of the pump supply hole 501, and the check valve 504b is arranged at the middle part 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 the space 512a partially formed at the middle part 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 the space 512B partially formed at the middle part of the pump discharge hole 502.

[0124] When the pressure in the pump chamber 503 decreases due to the increase in the volume of the pump chamber 503 caused by the displacement of the diaphragm 506, 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 that allows the ink in the pump supply hole 501 to flow. Since the displacement of the diaphragm 506 causes the volume of the pump chamber 503 to decrease and the pump chamber 503 is pressurized, the check valve 504a is in close contact with the wall around the opening of the pump supply hole 501. Therefore, the state becomes a closed state in which the flow of ink in the pump supply hole 501 is blocked.

[0125] 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., moves to the right side in the figure), and ink can flow in the pump discharge hole 502.

[0126] 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 elastomer, or a film or sheet of polypropylene, etc. However, the material of the check valve is not limited thereto.

[0127] As described above, the pump chamber 503 is formed by combining the pump housing 505 and the diaphragm 506. Therefore, the pressure in the pump chamber 503 is changed by the deformation of the diaphragm 506. For example, the diaphragm 506 is displaced to the pump housing 505 side (in the figure, it is displaced to the right side) to reduce the volume of the pump chamber 503, and the pressure in the pump chamber 503 is thereby increased. Therefore, the check valve 504b arranged to face the pump discharge hole 502 becomes an open state, 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.

[0128] On the contrary, when the diaphragm 506 is displaced in the direction of expansion of the pump chamber 503, the pressure in the pump chamber 503 is reduced. 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. In this case, 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.

[0129] Therefore, in the circulation pump 500, the diaphragm 506 is deformed to change the pressure in the pump chamber 503, thereby performing the suction and discharge of ink. In this case, if bubbles penetrate into the pump chamber 503, even when the diaphragm 506 is displaced, the pressure change in the pump chamber 503 becomes smaller due to the expansion and contraction of the bubbles, thereby reducing the liquid feed amount. Therefore, the pump chamber 503 is arranged parallel to gravity so that the bubbles that penetrate into the pump chamber 503 tend 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 ability to discharge bubbles inside the pump can be improved, and the flow rate can be stabilized.

[0130] Flow of liquid in the discharge head

[0131] Figures 10A to 10E 2 is a diagram for explaining the flow of ink in a liquid discharge head. Figures 10A to 10E , the ink circulation in the liquid discharge head 1 will be described. In order to more clearly describe the ink circulation path, the ink circulation path is simplified. Figures 10A to 10E The relative positions of the components in the pressure control device (such as the first pressure control device 120, the second pressure control device 150 and the circulation pump 500). Therefore, the relative position of each component is different from that described later. Fig.19 The construction shown in . Fig. 10A The flow of ink when performing a printing operation by discharging ink from the discharge port 13 is schematically shown. The arrows in the figure represent 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 association with each other, but can also be driven individually and independently.

[0132] During the printing operation, the circulation pump 500 is in the "ON" state (driven 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 is then supplied to the second pressure control chamber 152.

[0133] 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, and 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 performed.

[0134] 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 increase in the viscosity of the ink near the discharge port in the discharge module 300. In the circulation unit 54 corresponding to the ink containing titanium oxide, the pressure difference is further set so that Q / S [m / s] represented by using the circulation flow rate Q and the maximum cross-sectional area S of the circulation path is higher than the precipitation rate of titanium oxide. 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 the pressure in the first pressure control chamber decreases. 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 this reduction in the internal volume of the first pressure control chamber 122, the communication port 191A becomes an open state, and ink is supplied from the first valve chamber 121 to the first pressure control chamber 122. When the 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 the positive pressure state to the 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 the communication port 191A being in a closed state. 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.

[0135] Fig. 10B The ink flow immediately after the printing operation ends and the circulation pump 500 is changed 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, and then through the collection channel 140 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 to the second pressure control chamber 152 also continuously occurs.

[0136] 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 in a certain amount, which 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. According to 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 pressing 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, the pressure P2 in the first pressure control chamber 122 maintains the same pressure as the control pressure during the printing operation.

[0137] In contrast, the pressure in the second pressure control chamber 152 changes with time in response to the change in the internal volume caused by the inflow of ink from the first pressure control chamber 122. Specifically, Fig. 10B to the state shown in Fig. 10C During the state shown in (where the second valve chamber 151 and the second pressure control chamber 152 are not communicated with each other because the communication port 191 is in a closed state), the pressure in the second pressure control chamber 152 changes according to Equation 2. Subsequently, the pressing 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 in FIG. 4 , ink flows from the collecting channel 140 into the second pressure control chamber 152. This inflow of ink displaces the pressing plate 210a and the flexible member 230, and the pressure in the second pressure control chamber 152 changes, i.e., increases, according to Equation 4 until the internal volume of the second pressure control chamber 152 reaches a maximum value.

[0138] When the status changes to Fig. 10C , 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 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 movement of ink stops.

[0139] When 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 in may vary depending on the shape and size of the flow channel and the characteristics of the ink, but is approximately 1 to 2 minutes. Fig. 10D The state in which the ink shown in FIG. 1 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 pressing plate 210 are displaced in the expansion direction. When the circulation pump 500 is continuously driven, as shown in FIG. Fig. 10A As shown in , the state changes in the cycle path.

[0140] In the above description, although Fig. 10A Although described as an example of a printing operation, the circulation of ink can be performed without a printing operation as described above. Also, in this case, Figures 10A to 10E The ink flow shown in FIG. 5 occurs in response to the operation and stop of the circulation pump 500 .

[0141] Here, when the stop state of the circulation pump 500 continues for a long time (for example, when the power supply of the main body is in the OFF state), it can be inferred that the titanium oxide particles in the ink are not redispersed and precipitated. It can also be inferred that the concentration and viscosity of the ink increase due to the evaporation of the ink from the discharge port 13, and the negative pressure in the liquid discharge head is weakened due to the air infiltration and invasion 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 suction and discharge process can be performed by sucking and discharging the thickened ink and air bubbles together with the ink from the discharge port 13 of the liquid discharge head 1 using the above-mentioned cap member, etc., to update the ink in the discharge port 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.

[0142] 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 pressing 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 first pressure control chamber 122 and the second pressure control chamber 152 have a larger volume than other parts in the circulation path, and are areas where ink in the liquid discharge head is easily precipitated. In this case, it can be inferred that the precipitated ink (titanium oxide particles) inhibits the displacement of the flexible member 230 and the pressing plate 210, and an appropriate negative pressure cannot be maintained.

[0143] Therefore, in the circulation path, the pressure control chambers (the first pressure control chamber 122 and the second pressure control chamber 152) are connected to other flow channels (in Figures 10A to 10E In the embodiment of the present invention, the portion in communication with the pressure control chamber (250, 260, 280, 240 and 270) can be arranged vertically below the pressure control chamber. Therefore, during the suction and discharge process, the precipitated ink in the pressure control chamber can be effectively discharged to the outside of the liquid discharge head. 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.

[0144] That is, the portion (hole) communicating with the supply channel 130 or the collection channel 140 can be arranged at a position where 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. Figures 10A to 10E In the figure, the connection part 250 with the supply channel 130 of the first pressure control chamber 122 and the connection part 270 with 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).

[0145] 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 where ink in the circulation flow settles and is difficult to circulate, is eliminated.

[0146] In the above description, "vertically below the pressure control chamber" in the posture of the liquid discharge head arranged during printing may be within half of the length of the pressure control chamber from the lower end in the vertical direction, or may be within 1 / 4 of the length of the pressure control chamber from the lower end in the vertical direction.

[0147] In addition, the flow channel in the discharge unit 3 may 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 or inclined to the vertical direction. Therefore, the effect obtained is that 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 are sucked into the supply channel 130 or the collection channel 140 and the ink is easily discharged from the discharge port 13. Fig.22A and 22B is a cross-sectional view of another example of the liquid discharge head 1 . Fig.22A is a cross-sectional view showing a connection portion between the circulation unit 54 and the discharge unit 3 on the liquid supply side, Fig. 22B : is a cross-sectional view showing the connection portion between the circulation unit 54 and the discharge unit 3 on the liquid collection side.

[0148] Fig.22A and 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 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 circulation of the ink is stopped, 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. Hereinafter, the bypass flow channel 160 and its function will be described in detail.

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

[0151] An example will now be described in which the bypass flow channel 160 is provided to prevent the discharge module 300 from being affected by a negative pressure greater than a predetermined value. For example, the characteristics of the ink (e.g., viscosity) may change in response to a change in ambient temperature. If the viscosity of the ink changes, the pressure loss in the circulation path also changes. 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 certain driving amount increases so that the flow rate flowing in the discharge module 300 increases. At the same time, since the discharge module 300 is maintained 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 does not change. 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 greater than the predetermined value, thereby destroying the meniscus of the discharge port 13, and the external air is sucked into the circulation path, resulting in the risk of not being able to perform normal discharge. Even if the meniscus is not broken, the negative pressure of the pressure chamber 12 becomes larger than a predetermined value, which may affect the discharge.

[0152] Therefore, in the present embodiment, the bypass flow channel 160 is formed in the circulation path. When the negative pressure becomes greater 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 remains in a closed state even during the period when the circulation pump 500 is driven, and the control pressure in the second pressure control device can be set so that when the negative pressure is greater than a predetermined value, the communication port 191 of the second pressure control device 150 becomes an open state. That is, during the period when the circulation pump 500 is driven, even when the pump flow rate changes due to a change in viscosity caused by an environmental change, the communication port 191B can be in a closed state as long as the meniscus does not collapse, or as long as the predetermined negative pressure is maintained.

[0153] An example will now be described in which the bypass flow channel 160 is provided for supplying ink to the pressure chamber 12 from both sides of the supply channel 130 and the collection channel 140. The discharge operation of the discharge element 15 may also cause a pressure change in the circulation path. This is because the discharge operation generates a force that sucks the ink into the pressure chamber.

[0154] Now, a point will be described where the ink supplied to the pressure chamber 12 is supplied from both the supply channel 130 side and the collection channel 140 side when high duty printing is continued. Although the definition of the duty ratio may vary due to various conditions, the state of printing a 4 pL ink droplet on a 1200 dpi grid is regarded as 100% here. For example, high duty ratio printing is printing performed at a duty ratio 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, the negative pressure in the second pressure control chamber 152 becomes strong, 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 strong 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 further high duty cycle printing is continued, the amount flowing from the pressure chamber 12 into the second pressure control chamber 152 through the collecting channel 140 decreases, and conversely, the amount flowing through the bypass flow channel 160 and into the second pressure control chamber 152 from the communication port 191B increases. When this state further develops, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the collecting channel 140 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 into the pressure chamber 12 from the second pressure control chamber 152 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] Such backflow occurring when the printing duty ratio is high is a phenomenon caused by providing the bypass flow passage 160. In the above, although an example has been described in which the communication port 191B in the second pressure regulating device becomes an open state in response to the backflow of ink, the backflow of ink may occur when the communication port 191B in the second pressure regulating device is in an open state.

[0158] Furthermore, 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] Discharge unit structure

[0160] Fig.11A and 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 taken from the first supporting member 4 side of the discharge unit 3, Fig. 11B 3 is an exploded perspective view taken from the discharge module 300 side of the discharge unit 3. The arrows "IN" and "OUT" in the figure indicate the ink flow. The ink flow will be described only for one color, but the flow of other colors is the same. Fig.11A and 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 description will now be given of a path from when the ink passes through the joint member 8 until the ink returns to the joint member 8. In the following drawings, 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 further includes a discharge port forming member 320. The discharge element substrate 340, the opening plate 330, and the discharge port forming member 320 overlap and combine with each other so that the flow channels of each ink 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 rows of discharge port arrays, each row of the discharge port arrays is composed of a plurality of discharge ports 13, and the discharge port forming member 320 discharges a portion of the ink supplied through the ink flow channel in the discharge module 300 from the discharge port 13. Undischarged ink is collected from the ink flow channel in the discharge module 300.

[0164] like Fig.11A , 11B As shown in FIGS. 1 and 12, 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 14A As shown in FIG. 14C , 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 supply channel 48 and the ink collection channel 49 (see FIG. 14C ) provided in the first support member 4 are connected to each other. Figure 3A ) and the flow channel provided in the discharge module 300 to form the ink flow channel in the discharge unit 3. 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 passing through the supporting member supply port 211 in the ink supply channel 48 is passed through the ink supply channel 48 (see Figure 3A ) and the ink supply port 311 of the opening plate 330 are supplied to the common supply channel 18 of the discharge element substrate 340, and enter 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 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 into the ink collection channel 49 of the first support member 4 through the ink collection port 312 of the opening plate 330, 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. The first support member 4 does not include an opening in this area. When the discharge module 300 and the first support member 4 are combined with each other, such an area is used as an adhesive area.

[0168] exist Fig.12 In the embodiment, the opening plate 330 is provided with a plurality of columns of openings, each column of openings is composed of a plurality of openings arranged in the X direction and arranged in the Y direction, wherein the openings are arranged so that the supply (IN) openings and the collection (OUT) openings are alternately arranged in the Y direction so as to be offset by half a pitch in the X direction. Fig.13 In the discharge element substrate 340, the common supply channel 18 connected to the plurality of supply connection channels 323 arranged in the Y direction and the common collection channel 19 connected to the plurality of collection connection channels 324 arranged in the Y direction are alternately arranged in 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 common collection channels 19 to be arranged is determined according to the number of discharge port arrays of each color. The supply connection channels 323 and the collection connection channels 324 are also arranged in a number corresponding to the number of the discharge ports 13. It is not necessary to correspond one to one, 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 the discharge element substrate 340 overlap and combine with each other so that the flow channels of each ink communicate with each other to form the discharge module 300, and are supported by the first support member 4 to form the ink flow channel including the above-mentioned supply channel and collection channel.

[0170] Figures 14A to 14C 2 are cross-sectional views 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 in which 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 of FIG. 1 , and shows a cross section of a portion in the discharge unit 3 where the ink collection channel 49 and the ink collection port 312 communicate with each other. Fig. 14C It is along Fig.11A 1 is a cross section taken along line XIVC-XIVC of , 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 in FIG. 1 , ink is supplied from a portion where the ink supply channel 48 of the first support member 4 and the ink supply port 311 of the opening plate 330 overlap and communicate with each other. In the collection channel for collecting ink, as shown in FIG. Fig. 14B As shown in , ink is collected from a portion where the ink collection channel 49 of the first support member 4 and the ink collection port 312 of the opening plate 330 overlap and communicate with each other. Fig. 14C As shown in FIG. 3 , 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, no ink is supplied and collected between the discharge element substrate 340 and the first support member 4. Fig.14A As shown in FIG. 1 , ink is supplied in a region where the ink supply port 311 is provided, and as shown in FIG. Fig. 14B , ink is collected in the area where the ink collection port 312 is provided. In the present embodiment, although an example of a configuration using the opening plate 330 has been described, the configuration may be a configuration that does not use the opening plate 330. In the 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 15B is a cross-sectional view showing the vicinity of the discharge port 13 in the discharge module 300, Fig.16A and 16B 1 is a cross-sectional view showing a discharge module as a comparative example, the discharge module having a configuration in which the common supply channel 18 and the common collection channel 19 are widened in the X direction. Fig.15A , 15B The thick arrows shown in the common supply channel 18 and the common collection channel 19 of 16A and 16B represent ink fluctuations 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 tandem type liquid discharge apparatus 50, when the ink thus circulated is discharged, the discharge of the ink is greatly affected by the ink fluctuation in the ink flow channel caused by 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 16BAs shown in , when the common supply channel 18 and the common collecting channel 19 have a cross-sectional shape that is wider in the X direction that is the main scanning direction, the ink in the common supply channel 18 and the common collecting channel 19 tends to be subjected to the inertial force in the main scanning direction, and a large fluctuation occurs in the ink. As a result, the fluctuation of the ink may affect the discharge of the ink from the discharge port 13. If the common supply channel 18 and the common collecting channel 19 are widened in the X direction, the distance between the colors is widened, which may reduce the printing efficiency.

[0174] Therefore, the common supply channel 18 and the common collection channel 19 of the present embodiment are configured to Fig.15A and 15B In the cross section shown in , it extends in the Y direction and also extends in the Z direction perpendicular to the X direction which is the main scanning direction. In this construction, the flow channel width of each of the common supply channel 18 and the common collecting channel 19 in the main scanning direction can be reduced. By reducing the width of each flow channel of each of the common supply channel 18 and the common collecting channel 19 in the main scanning direction, the ink fluctuation caused by the inertial force (thick black arrow in the figure) acting on the ink in the common supply channel 18 and the common collecting channel 19 during scanning to the opposite side of the main scanning direction can be reduced. Therefore, the influence of the ink fluctuation on the discharge can be suppressed. In addition, the cross-sectional area is increased by extending the common supply channel 18 and the common collecting channel 19 in the Z direction, and the flow channel pressure loss is thereby reduced.

[0175] As described above, the configuration is made to reduce the ink fluctuation in the common supply channel 18 and the common collection channel 19 during the main scanning by reducing the flow channel width of each of the common supply channel 18 and the common collection channel 19 in the main scanning direction, but this does not mean that the fluctuation will disappear. Therefore, in the present invention, in order to suppress the occurrence of the discharge difference of each type of ink (which may still occur due to the reduced fluctuation), the configuration is made so that the common supply channel 18 and the common collection channel 19 are arranged to overlap in the X direction.

[0176] As described above, in the present embodiment, the supply connection channel 323 and the collection connection channel 324 are provided corresponding to the discharge port 13, and the supply connection channel 323 and the collection connection channel 324 are arranged in a corresponding relationship with the discharge port 13 being located therebetween in the X direction. Therefore, the common supply channel 18 and the common collection channel 19 have a portion that does not overlap 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 in the X direction are affected. When the influence of ink fluctuation is added, the discharge of ink from each discharge port may be affected.

[0177] 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 approximately equal at any position in the Y direction where the discharge port 13 is arranged. As a result, the pressure difference between the common supply channel 18 side and the common collecting channel 19 side appearing in the pressure chamber 12 does not vary significantly, and stable discharge can be performed.

[0178] In some structures 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 and the pressure chamber 12 are connected to each other, the pressure chamber 12 and the collecting connection channel 324 are connected to each other, and the ink is discharged from the discharge port 13 of the pressure chamber 12. That is, the structure is made so that the pressure chamber 12, which is a path for connecting 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 easily affected by the evaporation of the ink through the discharge port 13.

[0179] 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, ink can also be supplied from these two flow channels. That is, compared with the configuration in which the supply and collection of ink are performed with only one flow channel, the configuration in this embodiment has the advantage of being able to circulate the ink efficiently and also being able to cope with high flow rate discharge.

[0180] In addition, when the common supply channel 18 and the common collection channel 19 are arranged closer to each other in the X direction, the influence caused by the fluctuation of the ink is less likely to occur. Ideally, the distance between the flow channels is 75 μm to 100 μm.

[0181] 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 provided by the discharge element 15 in the pressure chamber 12 flows into the common collection channel 19, the ink having a relatively high temperature relative to the temperature of the ink in the common supply channel 18 flows. In this case, in the comparative example, as Fig.17In the α portion surrounded by the dotted line in FIG, there is a portion where only the common collecting channel 19 exists in a portion of the discharge element substrate 340 in the X direction. In this case, the temperature locally rises at this portion, resulting in uneven temperature in the discharge module 300, which may affect the discharge.

[0182] In the common supply channel 18, ink having a relatively low temperature relative to the temperature of 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 the increase in temperature. Therefore, the common supply channel 18 and the common collection channel 19 may have approximately equal lengths, exist at positions overlapping in the X direction, and be adjacent to each other.

[0183] Fig.18A and 18B 1 is a diagram showing the flow channel configuration of the liquid discharge head 1 corresponding to three types of ink. Fig.18A As shown in FIG. 1 , the liquid discharge head 1 has a circulation flow channel for various types of inks. The pressure chamber 12 is arranged along the X direction which is the main scanning direction of the liquid discharge head 1. Fig.18B As shown in FIG. 1 , 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 in the Y direction and sandwich the discharge port array therebetween.

[0184] Connection between the main body and the liquid discharge head

[0185] Fig.19 2 is a schematic configuration diagram showing in more detail the connection state of the ink tank 2 and the external pump 21 with 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 in the present embodiment has a configuration in which, when a malfunction occurs in the liquid discharge head 1, only the liquid discharge head 1 can be easily replaced. Specifically, the liquid discharge device 50 includes a liquid connection component 700 that can easily perform connection and disconnection between the ink supply tube 59 connected to the external pump 21 and the liquid discharge head 1. Therefore, it is possible to easily attach and detach only the liquid discharge head 1 to and from the liquid discharge device 50.

[0186] like Fig.19As shown in FIG. 1 , the liquid connection part 700 includes a liquid connector insertion port 53a provided in a protruding state on the head housing 53 of the liquid discharge head 1, and a cylindrical liquid connector 59a that can be inserted into the liquid connector insertion port 53a. The liquid connector insertion port 53a is fluidly connected to an 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 connector 59a is provided at the end of the ink supply tube 59 connected to the external pump 21, which pressurizes the ink in the ink tank 2 and supplies it to the liquid discharge head 1.

[0187] The liquid connection part 700 can be easily connected, removed and replaced Fig.19 The above-mentioned liquid discharge head 1 shown in FIG. However, when the sealing performance 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 liquid leakage adheres to the circulation pump 500, etc., there is a risk of causing electrical system failure. Therefore, in the present embodiment, the circulation pump, etc. are arranged as follows.

[0188] Arrangement of circulation pumps, etc.

[0189] like Fig.19 As shown in, in the present embodiment, in order to prevent the ink leaking from the liquid connection part 700 from adhering to the circulation pump 500, the circulation pump 500 is arranged above the liquid connection part 700 in the direction of gravity. That is, the circulation pump 500 is arranged above the liquid connector insertion port 53a in the direction of gravity, and the liquid connector insertion port is the inlet port of the liquid in the liquid discharge head 1. In addition, the circulation pump 500 is arranged at a position where it does not contact the components constituting the liquid connection part 700. Therefore, even if the ink leaks from the liquid connection part 700, since the ink flows in the horizontal direction (which is the opening direction of the liquid connector 59a) or flows downward in the direction of gravity, it is possible to prevent the ink from reaching the circulation pump 500 located above in the direction of gravity. In addition, since the circulation pump 500 is located at a position away from the liquid connection part 700, the risk of the ink traveling through the components and reaching the circulation pump 500 is also reduced.

[0190] 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 part 700 in the gravity direction. Therefore, the risk of ink from the liquid connection part 700 causing electrical failure can be reduced.

[0191] 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 member 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.

[0192] Fig. 20 The ink circulation system in this embodiment is shown. In this embodiment, the ink is supplied from the ink tank 2 to the liquid discharge head 1 under pressure using the external pump 21 through the liquid connection part 700. The external pump 21 has the function of sucking ink from the ink tank 2 and supplying the ink to the liquid discharge head 1 under pressure.

[0193] The flow channel 591 is provided between the external pump 21 and the liquid connecting part 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 also be stirred in the flow channel outside the liquid discharge head 1 of the liquid discharge device 50.

[0194] here, Fig.21 An ink circulation system of a comparative example is shown. An external pump 21 is used to send ink from an ink tank 2 to a sub-tank 25. Subsequently, the ink is circulated (stirred) in the sub-tank 25 and the liquid discharge head 1 and the entire flow channel therebetween by a supply pump 23 and a collection pump 24. In this case, since the ink must 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 relatively higher capacity than the pump of the present embodiment. In addition, since the liquid discharge head 1 requires two system connection components (a liquid connection component 700a for supply and a liquid connection component 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 result in a reduction in the quality of the printed image. In addition, in the tandem 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. Fig. 20The effect 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 in . 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, the excessive increase in equipment manufacturing cost and the increase in equipment size can be suppressed, while obtaining a greater effect of suppressing the precipitation of ink containing titanium oxide. The total volume of ink flowing in only 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. That is, 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.

[0195] As mentioned above, in Fig. 20 In the ink circulation system shown in , both reduction in size of the liquid discharge device and improvement in quality of printed images can be achieved.

[0196] (2) Ink

[0197] The ink that can be used in 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 in the form of dissociated ions, but is expressed as "containing salt" for convenience. Titanium oxide and titanium oxide particles may be referred to as "pigment" for short. Aqueous ink for inkjet printing may be referred to as "ink" for short. 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 for color ink. In this case, the image can be printed by applying color ink (such as black, cyan, magenta and yellow ink) so that it overlaps at least a portion of the area to which white ink is applied. Alternatively, 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 color ink is applied.

[0198] Water-based ink and method for producing water-based ink

[0199] The ink disclosed herein is an ink containing titanium oxide. Since titanium oxide is a white pigment, this 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 disclosed herein does not need to be a so-called "curable ink". Therefore, the ink disclosed herein 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 disclosed herein, the physical properties of the ink, the manufacturing method, etc. will now be described in detail.

[0200] Colorants

[0201] 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 construction of the liquid discharge device, the content (mass %) of the titanium oxide particles in the ink can be easily increased, and based on the total mass of the ink may be greater than 5.00 mass % and less than 20.00 mass %.

[0202] 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.

[0203] The cumulative 50% particle size based on volume 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% particle size based on volume of the titanium oxide particles may be 200 nm or more and 400 nm or less.

[0204] The volume-based cumulative 50% particle size (D50) of titanium oxide particles is the particle diameter when the total volume of the measured particles is accumulated from the small particle size side to 50% in the particle size accumulation curve. The D50 of titanium oxide particles can be measured under the following conditions: 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, etc. are not limited to the above.

[0205] Titanium oxide surface-treated with aluminum oxide and silicon dioxide can be used. The surface treatment is intended 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,

[0206] "Silica" is a general term for silicon dioxide and materials composed of silicon dioxide. The alumina and silica coated with titania are mainly present in the form of silicon dioxide and alumina, respectively.

[0207] 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. The mass ratio of the proportion (mass %) of aluminum oxide in the titanium oxide particles to the proportion (mass %) of silicon dioxide needs to be 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 silicon dioxide in the titanium oxide particles may be 1.00 mass % or more and 4.00 mass % or less. When the proportion (mass %) of silicon dioxide is less than 1.00 mass %, the affinity with the compound represented by the general formula (1) cannot be fully obtained, and the discharge stability of the ink may become insufficient. When the ratio (mass %) of silicon dioxide is greater than 4.00 mass %, even if surface treatment is performed with aluminum oxide, the amount of the compound represented by the general formula (1) adsorbed to 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.

[0208] An example of a method for measuring the ratio of aluminum oxide and silicon dioxide in titanium oxide particles (i.e., the coating amount of aluminum oxide and silicon dioxide) 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 covering the surface are oxides and converting the obtained amounts of aluminum and silicon into their oxides (i.e., aluminum oxide and silicon dioxide). The mass ratio of the ratio (mass %) of the aluminum element in the titanium oxide particles obtained by inductively coupled plasma 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 silicon dioxide), the mass ratio of the ratio (mass %) of aluminum oxide in the titanium oxide particles to the ratio (mass %) of silicon dioxide is 0.50 times or more and 1.00 times or less.

[0209] The example of the method for the surface treatment of titanium oxide includes wet treatment and dry treatment. For example, the surface treatment can be carried out by dispersing titanium oxide in a liquid medium and then reacting it with a surface treatment agent (such as sodium aluminate and sodium silicate). The desired characteristics 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, in addition to aluminum oxide and silicon dioxide, inorganic oxides (such as zinc oxide and zirconium oxide) or organic materials (such as polyols) can also be used for surface treatment.

[0210] As long as the effect of the present disclosure is not impaired, the ink may contain other pigments except titanium oxide. In such a case, the ink may be any color except 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.

[0211] The compound represented by the general formula (1)

[0212] The ink may include a compound represented by the following general formula (1) as a dispersant for dispersing titanium oxide particles. The content (mass %) of the compound represented by the general 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.

[0213]

[0214] (In the general formula (1), R1, R2 and R3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R4 are each independently an alkylene group having 2 to 4 carbon atoms; X is a single bond or an alkylene 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).

[0215] In the general formula (1), R1, R2 and R3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of alkyl 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 alkyl group may be a methyl group. When R1, R2 and R3 are each an alkyl 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, and "b" representing the number of R2 is 0 to 2, 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.

[0216] In the general 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-propenyl, isopropenyl, and n-butenyl. In particular, the alkylene group may be vinyl. The number of OR4, i.e., n representing the number (average value) of alkyl oxides, is 6 to 24. When n is less than 6, since the length of the alkyl oxide 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 alkyl oxide 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 cannot be suppressed. Therefore, the titanium oxide particles cannot be stably dispersed, and the discharge stability of the ink cannot be obtained.

[0217] In the general 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 and OR4 are directly bonded to each other. 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 can be n-propenyl. When X is an alkylene group having more than 6 carbon atoms, the hydrophobicity of the compound represented by the general formula (1) becomes too high, the titanium oxide particles cannot be stably dispersed, and the discharge stability of the ink cannot be obtained.

[0218] The compound represented by the general formula (1) as a dispersant for titanium oxide particles may be a compound represented by the following general formula (2). In the compound represented by the general formula (2), since the number of OR1 bonded to the silicon atom is three, a part thereof is hydrolyzed in an aqueous medium, and three hydroxyl groups bonded to the silicon atom may be formed to increase the site having affinity with the titanium oxide particles. The compound represented by the following general formula (2) has a repeating structure of an ethylene oxide group. Therefore, the ethylene oxide chain is appropriately elongated in an aqueous medium, and repulsion may be obtained due to steric hindrance.

[0219]

[0220] (In the general formula (2), R1 and R3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and m is 8 to 24).

[0221] The mass ratio of the content (mass %) of the compound represented by the general 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 the general formula (1) is too high, and condensation (self-condensation) tends to occur between the molecules of the compound represented by the general formula (1). Therefore, the compound represented by the general formula (1) is consumed and cannot play the role of a dispersant, the function of stably dispersing the titanium oxide particles is weak, and the discharge stability of the ink may become insufficient.

[0222] The compound represented by the general formula (1) forms a hydrogen bond with the surface hydroxyl group of the titanium oxide particles, and it is inferred that a part of it forms a covalent bond through a dehydration reaction. However, in the present disclosure, the compound represented by the general formula (1) can disperse the titanium oxide particles even if it does not form a covalent bond with the titanium oxide particles. That is, the amount of the compound represented by the general formula (1) that forms a covalent bond with the titanium oxide particles is very small and can be ignored. Therefore, the compound represented by the general formula (1) that is covalently bonded to the titanium oxide particles is not included in the content of the titanium oxide particles. As a result of the research of the present inventors, it was found that if the amount of the compound represented by the general formula (1) that is covalently bonded to the titanium oxide particles is too large, the discharge stability of the ink is reduced.

[0223] The reason for the above situation is inferred as follows. Since electrostatic attraction generally becomes less effective in a liquid medium (such as water) with a high dielectric constant, the titanium oxide particles move freely without being significantly affected by the surrounding environment. However, if the compound represented by the general formula (1) is covalently bonded to the titanium oxide particles, the hydrophilic portion (OR4 portion) in the structure of the general formula (1) forms a hydrogen bond with the water molecule. 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, such as during discharge in inkjet printing, the above characteristics manifest as a difference in discharge characteristics. Therefore, the amount (mass %) of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles as a mass ratio relative to the content (mass %) of the titanium oxide particles can be 0.001 times or less. When the mass ratio is greater than 0.001 times, the discharge stability of the ink may become insufficient. The mass ratio can be 0.0001 times or less. The amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles can be calculated by thermogravimetric analysis, etc.

[0224] Wax particles

[0225] In the present disclosure, the ink may contain wax particles. The wax may be a composition including 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.

[0226] In a narrow sense, wax is an ester of a higher monovalent or divalent alcohol that is insoluble in water and fatty acids, and includes animal wax and plant wax, but does not include oil and fat. In a broad sense, it includes high melting point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the printing method disclosed in the present invention, waxes in a broad sense can be used without any restrictions. Waxes in a broad sense can be divided into natural waxes, synthetic waxes, blends thereof (composite waxes) and modified products thereof (modified waxes).

[0227] Examples of natural waxes include animal waxes, such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes, such as tree wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes, such as montan wax; and petroleum waxes, such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes, such as Fischer-Tropsch wax and polyolefin waxes (e.g., polyethylene wax and polypropylene wax). Composite wax is a mixture of the above-mentioned various waxes. Modified wax is obtained by modifying the above-mentioned various waxes (such as oxidation, hydrogenation, alcohol modification, acrylic acid modification, and urethane modification). 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 various types of waxes or a blend of petroleum wax and synthetic wax.

[0228] The wax may be solid at room temperature (25°C). The melting point of the wax is preferably 40°C to 120°C or less, and further preferably 50°C or more and 100°C or less. The melting point of the wax may be measured according to the test method described in 5.3.1 (melting point test method) in JIS K2235:1991 (petroleum wax). When the wax is microcrystalline wax, petrolatum, or a mixture of multiple types of waxes, the melting point may be measured more accurately using the test method described in 5.3.2. The melting point of the wax is easily affected by its properties, such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the straight chain has a high melting point, but the presence of a branched chain reduces the melting point), 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 properties, the wax may have a desired melting point.

[0229] Resin

[0230] 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, and particularly preferably 5.00 mass % or more and 15.00 mass % or less.

[0231] The ink may contain resins in the application to improve various properties of the printed image, such as wear 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 resin particles dispersed in an aqueous medium. The resin particles do not need to contain a colorant.

[0232] In this specification, "resin is water-soluble" means that when the resin is neutralized with an alkali in an amount equal 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) is prepared, and the resin is neutralized with an alkali (such as sodium hydroxide and potassium hydroxide) in an amount equal to the acid value. Subsequently, the prepared liquid is diluted 10 times (based on volume) with pure water to prepare a sample solution.

[0233] The particle size of the resin in the sample solution is measured by a dynamic light scattering method. When no particles with a certain particle size are observed, it can be judged that the resin is water-soluble. The measurement conditions in this case can be set to, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. As a particle size distribution measuring device, a particle size analyzer using 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.

[0234] The acid value of the water-soluble resin is preferably 80 mg KOH / g or more and 250 mg KOH / g or less, and more preferably 100 mg KOH / g or more and 200 mg KOH / g or less. When resin particles are used, the acid value may be 0 mg KOH / g or more and 50 mg KOH / 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).

[0235] Aqueous medium

[0236] 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.

[0237] There is no particular limitation on the water-soluble organic solvent as long as it is water-soluble (for example, dissolved in water at any ratio at 25°C). Specifically, monovalent or divalent 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 will adhere to the inkjet printing device, and sufficient anti-adhesion 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.

[0238] Other additives

[0239] In addition to the above-mentioned additives, the ink may contain surfactants, pH regulators, corrosion inhibitors, preservatives, antifungal agents, antioxidants, reductive inhibitors, evaporation promoters, chelating agents, etc. as needed. In particular, the ink may contain surfactants. 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 surfactants are used to adjust the various physical properties of the ink, the surfactant may be a nonionic surfactant that has a low affinity for titanium oxide particles and shows an effect in a small amount.

[0240] Physical properties of ink

[0241] Because the ink is 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 value 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 due to the hydrolysis of the compound represented by the general formula (1) proceeds, so the weak affinity between the titanium oxide particles and the compound represented by the general formula (1) is effectively exhibited. The pH value of the ink can be measured with an ordinary pH meter loaded with a glass electrode.

[0242] Example

[0243] The present disclosure will now be described in further 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 the gist thereof. Unless otherwise specified, "parts" and "%" regarding the amount of components are based on mass. The dispersion of titanium oxide particles is referred to as a "pigment dispersion".

[0244] Preparation of titanium oxide

[0245] Commercially available rutile titanium oxide particles that had been surface treated in advance were used. The cumulative 50% particle size (D ) of the titanium oxide particles based on volume was measured by a dynamic light scattering method using a particle size analyzer (trade name: Nanotrac WaveII-EX150, manufactured by Microtrac BEL). 50 ). Table 1 shows the characteristics of each titanium oxide particle.

[0246] Table 1: Characteristics of titanium oxide particles

[0247]

[0248] Preparation of pigment dispersions

[0249] Pigment dispersion 1

[0250] A styrene-methyl methacrylate-methacrylic acid copolymer (resin 1) having an acid value of 150 mg KOH / g and a weight-average molecular weight of 10,000 is provided. An aqueous solution of resin 1 is prepared by neutralizing 20.0 parts of resin 1 with potassium hydroxide in an amount equimolar to the acid value of the resin and adding an appropriate amount of pure water thereto, wherein the content (solid content) of the resin 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 so that the total amount of each component is 100.0 parts, and a homogenizer is used for preliminary dispersion. Subsequently, a dispersion treatment (main treatment) is performed in a paint vibrator 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%.

[0251] Pigment dispersion 2

[0252] Pigment Dispersion 2 was prepared by 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%.

[0253] Ink preparation

[0254] 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 AG) to prepare Ink 1. Ink 2 was prepared by the same procedure as that for Ink 1 except that Pigment Dispersion 2 was used instead of Pigment Dispersion 1.

[0255] The details of each mixed component are shown below:

[0256] Acrylic resin particles (trade name: Vinyblan 2685, manufactured by Nissin Chemical Industries, Ltd., resin particle content: 30%): 20.0 parts;

[0257] Diethylene glycol: 10.0 parts;

[0258] Diethylene glycol isobutyl ether: 10.0 parts;

[0259] Fluorinated surfactant (trade name: Capstone FS-3100, manufactured by Chemours): 1.0 part; and

[0260] Ion exchange water: 34.0 parts.

[0261] The viscosity (Pa·s) of Ink 1 and Ink 2 and the density (g / cm 3 ) are 8Pa·s and 1.16g / cm 3 . By using these values, the sedimentation rate of each ink was calculated. The result was that 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.

[0262] The precipitation rate was calculated by the following equation (Stokes equation), where ν is the precipitation rate, D is the particle size of titanium oxide, and ρ is 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.

[0263]

[0264] Liquid discharge head

[0265] Head 1

[0266] Figures 2 to 5 The liquid discharge head shown in FIG. 1 is set as head 1. The maximum cross-sectional area S of the circulation path in head 1 is 300 mm 2 .

[0267] evaluate

[0268] The ink 1 was placed in an inkjet printing device equipped with the head 1, and the ink was discharged in an environment with a temperature of 25°C and a relative humidity of 50%. The circulation flow rate was set to 4.0 mL / min. That is, Q / S was 2.2×10 -6 m / s. As a result, it was confirmed that the effect of the present disclosure was sufficiently obtained.

[0269] According to the present disclosure, it is possible to provide an inkjet printing method that improves discharge stability of ink containing titanium oxide.

[0270] 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. Based on the Stokes equation, the precipitation rate of titanium oxide 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 passage for supplying liquid to the pressure chamber; a downstream flow passage in communication with the pressure chamber; and a pump which communicates with the upstream flow channel and the downstream flow channel and forms 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, and The ratio Q / S [m / s] of the flow velocity Q of the ink in the circulation path to the maximum cross-sectional area S of the circulation path is higher than the sedimentation velocity.

2. The inkjet printing method according to claim 1, wherein: The flow rate Q is the flow rate in the pump.

3. The inkjet printing method according to claim 1, wherein: The flow rate Q is greater than or equal to 2.0 mL / min and less than or equal to 10 mL / min.

4. The inkjet printing method according to claim 1, wherein: The volume of the ink flowing in the circulation path is 5.0 mL or more and 30 mL or less.

5. The inkjet printing method according to claim 1, wherein: The liquid discharge head is configured to discharge liquid while scanning in a direction orthogonal to a conveyance direction of a printing medium to which ink is to be applied.

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 be able 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 pressing plate and a first biasing member, wherein a portion of the surface of the first pressing plate is formed by a first flexible member configured to be displaceable and can be displaced in conjunction with the first flexible member, the first biasing member applies a force to the first pressing plate in a direction in which the volume of the first pressure control chamber increases, and is configured to enable the first valve to open and close in response to the displacement of the first pressing 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: The first communication port is arranged vertically below the first pressure control chamber, and the first pressure control chamber communicates with the upstream flow channel 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 includes: a discharge unit including an element substrate, which includes the discharge port and the pressure chamber; and A circulation unit, comprising the pump, wherein the circulation unit is configured to circulate liquid between the discharge unit and the circulation unit, wherein: In a portion where the discharge unit is in fluid contact with the circulation unit, a wall of a flow channel in which the fluid in the discharge unit is connected to the circulation unit is perpendicular 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.

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