Liquid discharge head, inkjet device, and method for manufacturing liquid discharge head

Abstract

The present application provides a liquid ejection head and an inkjet device, which are capable of inhibiting clogging of a nozzle or adhesion of particles on a flow path and a surface of a vibration plate caused by particles contained in a liquid, and achieving long-term stable ejection. The inkjet head includes a nozzle that ejects a liquid, a pressure chamber that communicates with the nozzle, an independent flow path that communicates with the pressure chamber via a throttle portion, a common flow path that communicates with the independent flow path, an energy generating element that generates energy, and a vibration plate that transmits the energy to the pressure chamber. A monomolecular film having a lyophilic property with respect to the liquid is formed on inner walls of each of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the independent flow path.

Description

[0001] This application is a divisional application of patent application No. 202011142167.3, filed on October 22, 2020, entitled "Liquid ejector head and inkjet device". Technical Field

[0002] This invention relates to liquid ejector heads and inkjet devices. Background Technology

[0003] Previously, as an example of a liquid ejector head, a drop-on-demand inkjet head is known that can apply the required amount of ink when needed based on an input signal. For example, a piezoelectric drop-on-demand inkjet head generally has: an ink supply path; multiple pressure chambers connected to the ink supply path and having nozzles; and a piezoelectric element that applies pressure to the ink filled in the pressure chambers.

[0004] Here, use Figure 1A , Figure 1B An example of a previous high-capacity inkjet head will be explained. Figure 1A and Figure 1B This is a schematic diagram showing the cross-sectional structure of a conventional high-capacity inkjet head. Figure 1A This indicates the state before the voltage is applied. Figure 1B This indicates the state when a voltage is applied.

[0005] like Figure 1A and Figure 1B As shown, a conventional high-capacity inkjet head includes: multiple nozzles 100 that eject ink droplets; a pressure chamber 110 connected to the nozzles 100 and filled with ink; a spacer wall 111 that separates the pressure chambers 110 corresponding to adjacent nozzles 100; a vibrating plate 112 that forms part of the pressure chamber 110; a piezoelectric element 130 that vibrates the vibrating plate 112; and a piezoelectric component 140 that supports the piezoelectric element 130 and the spacer wall 111. Additionally, although not shown in the figure, a conventional high-capacity inkjet head includes a common electrode for applying voltage to the piezoelectric element 130 and an ink inlet.

[0006] The piezoelectric component 140 is a component formed by cutting a piezoelectric component. The nozzle 100 has a diameter of 10 μm to 50 μm. The nozzles 100 are arranged at intervals of 100 μm to 500 μm. The number of nozzles 100 is, for example, 100 to 400.

[0007] The conventional high-capacity inkjet head, constructed in this way, operates as follows.

[0008] If a voltage is applied between the common electrode (not shown) on the back side of the piezoelectric element 130 and the piezoelectric element 130, the piezoelectric element 130 will... Figure 1AThe state shown is transformed to Figure 1B The state shown. Specifically, in Figure 1B In the middle, the lower part of the second piezoelectric element 130 from the left is deformed. As a result, the volume of the pressure chamber 110 decreases, the ink in the pressure chamber 110 is pressurized, and ink droplets (not shown) are ejected from the nozzle 100.

[0009] The above provides an example of a previous high-capacity inkjet head.

[0010] In addition, an inkjet head is known that has an ink inlet and an ink outlet, and that ejects ink while circulating it. The effect of circulating the ink will be explained below.

[0011] The ink near the nozzle is constantly in contact with the atmosphere. Since the contact area between the ink and the atmosphere is very small, the evaporation of the ink solvent cannot be ignored. If the ink solvent evaporates, the concentration of the ink's solid components increases. As a result, the ink viscosity increases, which may make normal ink ejection difficult.

[0012] Therefore, by circulating the ink, the ink near the nozzle can be continuously replaced, maintaining the ink near the nozzle at a normal viscosity. As a result, nozzle clogging can be suppressed, and stable, normal ejection can be achieved.

[0013] In addition, thin-film inkjet printheads that utilize piezoelectric elements are known. Below, we will use... Figure 2A , Figure 2B An example of this thin-film inkjet head will be described. Figure 2A and Figure 2B This is a schematic diagram showing the cross-sectional structure of a conventional thin-film inkjet head. Figure 2A This indicates the state before the voltage is applied. Figure 2B This indicates the state when a voltage is applied.

[0014] like Figure 2A and Figure 2B As shown, a conventional thin-film inkjet head includes: a nozzle 200 that ejects droplets of ink; a pressure chamber 210 that communicates with the nozzle 200 and is filled with ink; a vibrating plate 212 that forms part of the pressure chamber 210; a thin-film piezoelectric element 220 that is disposed on the upper part of the vibrating plate 212 to vibrate the vibrating plate 212; and a common pressure chamber 230 that supplies ink to the pressure chamber 210.

[0015] The conventional thin-film inkjet head, constructed in this way, operates as follows.

[0016] If a voltage is applied to the thin-film piezoelectric element 220, the thin-film piezoelectric element 220 will... Figure 2A The state shown is transformed to Figure 2BThe state shown. Due to the deformation of the thin-film piezoelectric element 220, the volume of the pressure chamber 210 decreases, the liquid in the pressure chamber 210 is pressurized, and droplets of ink (not shown) are ejected from the nozzle 200.

[0017] The above describes an example of a conventional thin-film inkjet head.

[0018] In addition, for example, Patent Document 1 discloses an inkjet head in which the surface of the nozzle has ink-repellent properties (liquid-repellent) in order to suppress the adhesion of the ejected ink, and the inner wall of the nozzle has ink-friendly and wetting properties (liquid-friendly) in order to suppress the retention of air bubbles in the ink.

[0019] Here, use Figure 3 The processing steps for making the nozzle liquefied and liquefied, as disclosed in Patent Document 1, will be described. Figure 3 This is a cross-sectional schematic diagram showing the processing steps of the nozzle plate of the inkjet head disclosed in Patent Document 1.

[0020] First, such as Figure 3 As shown in the figure above, hydrogen termination treatment (X) is applied to the surface of the nozzle plate 60 and the inner wall of the nozzle orifice 51.

[0021] Next, as Figure 3 As shown in the middle figure, light energy 61 is applied to the surface of the nozzle plate 60 to activate the reaction on the surface of the nozzle plate 60. Furthermore, the surface of the nozzle plate 60 is made liquefied (Y) by bringing the liquefying film material into contact with the surface of the nozzle plate 60.

[0022] Next, as Figure 3 As shown in the figure below, thermal energy 62 is applied to the inner wall of the nozzle orifice 51, thereby making the inner wall of the nozzle orifice 51 liquefied (Z) by bringing the hydrophilic film material into contact with the inner wall of the nozzle orifice 51.

[0023] Through the above processing steps, the surface of the nozzle plate 60 becomes hydrophobic, thus inhibiting ink adhesion. In addition, the inner wall of the nozzle orifice 50 becomes hydrophilic, thus inhibiting air bubble accumulation.

[0024] Existing technical documents

[0025] Patent documents

[0026] Patent Document 1: Japanese Patent Application Publication No. 2011-68095

[0027] However, in the inkjet head of Patent Document 1, the hydrophilicity of the ink receiving portion other than the nozzle (e.g., the inner wall of the flow path or pressure chamber) cannot be guaranteed. Therefore, in the inkjet head of Patent Document 1, when using ink containing particles composed of inorganic compounds or binder components (hereinafter referred to as "particles, etc."), the particles or binder components adhere to and accumulate on the ink receiving portion other than the nozzle, potentially causing clogging. In particular, the binder component is a material composed of organic compounds, which readily adheres to ink receiving portions made of metals such as stainless steel.

[0028] For example, in the flow path of an inkjet head, where the independent flow path connects to the pressure chamber, a throttling section is provided that is narrower than the independent flow path to prevent pressure waves from dissipating from the pressure chamber. During ink flow, significant shear stress is applied to this throttling section. Therefore, ink particles tend to agglomerate and adhere to the walls of the flow path, causing blockage.

[0029] Furthermore, the vibrating plate vibrates at a high speed corresponding to the ejection frequency. For example, the vibrating plate vibrates at a frequency of approximately 1 kHz to 50 kHz, performing approximately 1,000 to 50,000 vibrations per second. This vibration is the cause of the high-speed shearing force applied to the ink. As a result, the dispersion state of the ink particles may be disrupted, causing agglomeration, which then adheres to the surface of the vibrating plate. Summary of the Invention

[0030] One aspect of the present invention aims to provide a liquid ejector head and inkjet device capable of suppressing nozzle clogging or particle adhesion on the surface of the flow path and vibrating plate caused by particles contained in the liquid, thereby achieving long-term stable ejection.

[0031] Solution to the problem

[0032] One embodiment of the liquid ejector head of the present invention comprises: a nozzle for ejecting liquid; a pressure chamber communicating with the nozzle; an independent flow path communicating with the pressure chamber via a throttling portion; a common flow path communicating with the independent flow path; an energy generating element for generating energy; and a vibrating plate for transmitting the energy to the pressure chamber, wherein a monomolecular film having hydrophilicity to the liquid is formed on the inner wall of the nozzle, the pressure chamber, the throttling portion, the vibrating plate, and the independent flow path, respectively.

[0033] One embodiment of the inkjet apparatus of the present invention includes: a liquid ejector head according to the present invention; a drive control unit that generates a drive voltage signal applied to the energy generating element to control the ink ejection operation of the liquid ejector head; and a transport unit that moves the liquid ejector head relative to the medium being painted.

[0034] Invention Effects

[0035] According to the present invention, blockages caused by particles or the like contained in the liquid can be suppressed, and long-term stable ejection can be achieved. Attached Figure Description

[0036] Figure 1A This is a cross-sectional diagram showing the state of a conventional high-capacity inkjet head before voltage is applied.

[0037] Figure 1B This is a cross-sectional diagram showing the state of the applied voltage in a conventional high-capacity inkjet head.

[0038] Figure 2A This is a cross-sectional schematic diagram showing the state of a conventional thin-film inkjet head before voltage is applied.

[0039] Figure 2B This is a cross-sectional schematic diagram showing the state of an applied voltage in a conventional thin-film inkjet head.

[0040] Figure 3 This is a cross-sectional schematic diagram showing the processing steps of the nozzle plate of the inkjet head in Patent Document 1.

[0041] Figure 4A This is a cross-sectional schematic diagram showing the structure of the inkjet head according to an embodiment of the present invention.

[0042] Figure 4B yes Figure 4A XY cross-sectional view.

[0043] Figure 4C This is a top view showing the configuration of the common flow path of the inkjet head as an embodiment of the present invention.

[0044] Figure 5A This is a graph showing the change of the contact angle over time after hydrophilization treatment in Example 1.

[0045] Figure 5B This is a graph showing the change of the contact angle of Comparative Example 1 after hydrophilization treatment over time.

[0046] Figure 6A This is a diagram illustrating the flight process of ink droplets in Example 2.

[0047] Figure 6B This is a diagram showing the flight angle of the ink droplets in Example 2.

[0048] Figure 7A This is a diagram showing the flight process of ink droplets in Comparative Example 2.

[0049] Figure 7B This is a diagram showing the flight angle of the ink droplets in Comparative Example 2.

[0050] Explanation of reference numerals in the attached figures

[0051] 51 Nozzle Orifice

[0052] 60 nozzle plate

[0053] 61 light energy

[0054] 62 thermal energy

[0055] 100 nozzles

[0056] 110 pressure chamber

[0057] 111 partition wall

[0058] 112 Vibrating Plate

[0059] 130 piezoelectric element

[0060] 140 piezoelectric components

[0061] 200 nozzles

[0062] 210 pressure chamber

[0063] 212 Vibrating Plate

[0064] 220 Thin Film Piezoelectric Element

[0065] 230 shared pressure chamber

[0066] 300 inkjet heads

[0067] 312 nozzle

[0068] 314 pressure chamber

[0069] 315 independent flow path

[0070] 317 Vibrating Plate

[0071] 320 throttling section

[0072] 330 piezoelectric element

[0073] 340 monolayer

[0074] 350 liquid-repellent film

[0075] 351 shared flow path

[0076] 353 Supply Port

[0077] 354 discharge outlet Detailed Implementation

[0078] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the same constituent elements in each drawing are labeled with the same reference numerals, and their descriptions are omitted where appropriate.

[0079] <Inkjet Head 300>

[0080] use Figure 4A , Figure 4B , Figure 4C The structure of the inkjet head 300 according to an embodiment of the present invention will be described.

[0081] Figure 4A This is a cross-sectional schematic diagram showing the structure of the inkjet head 300 according to this embodiment. Additionally, Figure 4A It indicates Figure 4C AA' section in the middle. Figure 4B yes Figure 4A XY cross-sectional view. Figure 4C This is a top view showing the configuration of the common flow path 351 of the entire inkjet head 300.

[0082] Furthermore, this embodiment is described using the case where the liquid ejector head is an inkjet head 300 that ejects ink as an example, but it is not limited to this. The liquid ejector head may also eject liquids other than ink.

[0083] The inkjet head 300 includes: a nozzle 312, a pressure chamber 314, a piezoelectric element 330, a vibrating plate 317, a throttling section 320, an independent flow path 315, a common flow path 351, a monomolecular membrane 340, and a hydrophobic membrane 350.

[0084] Nozzle 312 is a through-hole for ejecting ink and is connected to pressure chamber 314. The diameter of nozzle 312 is, for example, about 5μm to 50μm. Nozzle 312 is formed, for example, by laser processing, etching or perforation.

[0085] A hydrophobic film 350 with ink-repellent properties (liquidity) is provided on the surface of the nozzle 312. The hydrophobic film 350 is formed by spin-coating a liquid hydrophobic raw material. By forming the hydrophobic film 350, the surface of the nozzle 312 becomes hydrophobic. The receding contact angle of the hydrophobic film 350 to the ink is, for example, 30 degrees or more. The static contact angle of the hydrophobic film 350 to the ink is, for example, 50 degrees or more.

[0086] The piezoelectric element 330 (an example of an energy-generating element) is arranged in a manner corresponding to the pressure chamber 314 and is displaced by the application of voltage. For example, a stacked piezoelectric element in d33 or d31 mode, or a piezoelectric element employing a shear mode, can be used as the piezoelectric element 330. Alternatively, an electrostatic actuator or a heating element may be used instead of these piezoelectric elements as the energy-generating element.

[0087] The vibrating plate 317 is arranged adjacent to the piezoelectric element 330 and deforms by the displacement of the piezoelectric element 330. The vibrating plate 317 is made of, for example, a metal such as nickel or a resin such as polyimide, but is not limited to these. The thickness of the vibrating plate 317 is preferably, for example, 5 μm to 50 μm.

[0088] If the displacement of the piezoelectric element 330 is transmitted to the vibrating plate 317, the vibrating plate 317 deforms. As a result, the volume of the pressure chamber 314 changes, and ink droplets are ejected from the nozzle 312. Therefore, the amount of deformation of the vibrating plate 317 is very important, and the rigidity of the vibrating plate 317 is related to the amount of deformation. Its deviation will affect the ejection characteristics, so it is required to make the rigidity of the vibrating plate 317 uniform.

[0089] Pressure chamber 314 is connected to nozzle 312. Additionally, pressure chamber 314 is connected to independent flow path 315 via throttling section 320. The volume of pressure chamber 314 changes due to the deformation of vibrating plate 317. This change in volume causes ink to be ejected from nozzle 312. Depending on the volume of pressure chamber 314 or the flow path resistance of throttling section 320, the resonance period of the ink changes, resulting in variations in the volume and velocity of the ejected ink. Therefore, optimal adjustment of the volume of pressure chamber 314 and other parameters is necessary as required.

[0090] Independent flow path 315, common flow path 351, and throttling section 320 constitute the ink flow path. Common flow path 351 is connected to independent flow path 315. Independent flow path 315 is connected to pressure chamber 314 via throttling section 320. Throttling section 320 has a width narrower than that of independent flow path 315. Therefore, pressure waves within pressure chamber 314 are less likely to dissipate into independent flow path 315.

[0091] A hydrophilic monomolecular film 340 is formed on the inner wall of each of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315. Details of this monomolecular film 340 will be described later. Alternatively, the monomolecular film 340 may be formed on the inner wall of the common flow path 351.

[0092] The nozzle 312, pressure chamber 314, independent flow path 315, vibrating plate 317, common flow path 351, and throttling section 320 described above can be manufactured, for example, by thermally diffusing and connecting multiple metal plates after etching or other processing, or by etching silicon material.

[0093] <Monopolymer 340>

[0094] like Figure 4AAs shown, a monomolecular film 340 containing an organic compound that has a wettable property (hydrophilicity, hereinafter also referred to as "wetting property") to ink is formed on the inner wall of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317 and independent flow path 315.

[0095] The thickness of the 340 monolayer is, for example, about 5 nm to 50 nm.

[0096] As a material for the monomolecular membrane 340, examples include materials having silanol groups at the molecular ends and multiple hydrophilic groups extending from the main backbone. For example, a superhydrophilic coating material manufactured by Junko Chemical Co., Ltd. (specifically, LAMBIC-771W) can be used as such a material. Therefore, the monomolecular membrane 340 can be described as a membrane made of molecules having silanol groups at the molecular ends and multiple hydrophilic groups extending from the main backbone.

[0097] Here, a monomolecular membrane refers to a relatively thin membrane in which molecules are arranged in a manner that is exactly the thickness of one molecule. Furthermore, a monomolecular membrane is also called a "monoderm".

[0098] If higher fatty acids or higher alcohols are dissolved in a volatile solvent such as benzene and allowed to settle on a water surface, a monomolecular membrane can be formed after the solvent evaporates. In this case, the hydroxyl and carboxyl groups of the alcohol are hydrophilic and therefore face towards the water, while the hydrophobic long-chain alkyl groups are arranged on the side away from the water (in the air). This seamless arrangement of molecules results in a monomolecular membrane with a thickness exactly equivalent to the length of the long-chain alkyl groups (plus the hydrophilic groups).

[0099] The monolayer 340 material is characterized by its self-assembled molecular arrangement, where active silanol groups undergo chemical reactions and adsorb onto the substrate surface. Functional groups that activate the silanol groups are required to be present on the substrate surface.

[0100] For example, it is desirable to form a silicon oxide film on the surface of a substrate, with hydroxyl groups exposed. Furthermore, as long as the hydroxyl groups are exposed on the substrate surface, the film formed on the substrate surface is not limited to silicon oxide. For example, metal oxides such as aluminum oxide (Al₂O₃) or titanium dioxide (TiO₂) can be used instead of silicon oxide. The monomolecular film 340 is provided in a manner that covers the silicon oxide film or the metal oxide film formed on the substrate surface.

[0101] The surface on which monomolecular membrane materials can chemically adsorb is fixed, so once adsorbed, further stereoadsorption will not occur. Based on this principle, monomolecular-level membranes are self-assembled. The membrane thickness is controlled to be very thin, ranging from 5 nm to 30 nm. This thickness is crucial when forming a membrane on the inner wall of nozzle 312 or pressure chamber 314. If a hydrophilic coating agent is used, thickness control becomes difficult, resulting in thicknesses in the range of several μm to tens of μm. If the thickness is too thick, the throttling section 320 or nozzle 312 will be filled with the hydrophilic membrane, leading to blockage. Furthermore, the thickness of the membrane formed on the surface of the vibrating plate 317 is also very important. This is because the thickness of the vibrating plate 317 is approximately 10 μm; therefore, if a thicker membrane is applied to the surface of the vibrating plate 317, the rigidity of the vibrating plate 317 will change significantly, thereby significantly altering the vibration characteristics transmitted from the piezoelectric element 330. Furthermore, the material of the monomolecular film 340 can be any material that is self-assembled and whose reaction ends with a film thickness at the monomolecular level, and is not limited to the materials mentioned above.

[0102] Based on the above, the monomolecular film 340 can be considered a self-assembled monomolecular film. A self-assembled monomolecular film can be formed by placing a suitable material in a solution or vapor of organic molecules, causing the organic molecules to chemically adsorb onto the material surface. This process forms a monomolecular film with a thickness of 1 nm to 2 nm and consistent orientation of the organic molecules, thus creating a self-assembled monomolecular film. Self-assembled monomolecular films can be easily fabricated simply by immersing a substrate in a solution of molecules having functional groups that bind to the substrate. Furthermore, they exhibit high orientation and stability, and various functions can be introduced through the terminal functional groups. In addition, self-assembled monomolecular films are also called "self-organizing monomolecular films."

[0103] Preferably, the receding contact angle of the film generated using such a self-assembled material is 20 degrees or less, more preferably 15 degrees or less. Furthermore, the static contact angle is preferably 25 degrees or more, more preferably 30 degrees or more.

[0104] Here, the retreat contact angle and static contact angle will be explained.

[0105] If a liquid is dripped onto a solid surface, the liquid will become round due to its own surface tension, and the relationship shown in equation (1) holds. Equation (1) is called the "Young equation".

[0106] γs=γL×cosθ+γSL···(1)

[0107] γs: Surface tension of a solid

[0108] γL: Surface tension of the liquid

[0109] γSL: Interfacial tension between solid and liquid

[0110] The angle θ between the tangent of the droplet and the solid surface at this point is called the "contact angle". Among them, the contact angle when the liquid is at rest and in equilibrium on the solid surface is called the "static contact angle".

[0111] On the other hand, the contact angle under the dynamic state of interfacial activity between liquid and solid, i.e., the interfacial activity of droplets, is called the "advancing contact angle" and the "receding contact angle". Here, we are concerned with the receding contact angle, which is the dynamic contact angle after the solid surface has been wetted by the liquid.

[0112] Figure 4A The static contact angle of the monolayer 340 shown to the ink is greater than 30 degrees. Figure 4A The monolayer 340 shown has a receding contact angle of less than 20 degrees with the ink. The meaning of this is as follows.

[0113] When the nozzle 312 and independent flow path 315 are dry, the static contact angle when the ink first comes into contact with the monomolecular film 340 formed on the inner wall of the nozzle 312 and independent flow path 315 is more than 50 degrees, which is a relatively large contact angle.

[0114] like Figure 4A As shown, no monolayer 340 is formed on the inner wall of the common flow path 351. Therefore, the original wettability of the material is exhibited in the common flow path 351. For example, when stainless steel is used as the material of the common flow path 351, its static contact angle is 50 degrees or more.

[0115] Under these conditions, there is almost no difference in ink wetting between the common flow path 351 and the independent flow path 315. Therefore, when ink fills each flow path, there will be no poor wetting conditions such as air bubbles being trapped during ink flow.

[0116] During ink flow, if there is a significant difference in wettability between the common flow path 351 and the independent flow path 315, the flow will change irregularly in that area, sometimes carrying air bubbles. The presence of air bubbles in the ink often causes poor ejection, so it is important to remove the air bubbles from the ink.

[0117] When a monolayer 340 is also formed in the common flow path 351, the static contact angle is not limited to the angle mentioned above, and can also be a smaller angle of less than 30 degrees.

[0118] On the other hand, the receding contact angle of the monolayer 340 is relatively small, less than 20 degrees. Once the monolayer 340 is wetted by ink, the hydrophilic groups in the monolayer 340 unfold, exhibiting high hydrophilicity. At this time, the solvent component in the ink covers the inner wall surfaces of the nozzle 312, pressure chamber 314, throttling section 320, and independent flow path 315. In this state, even if particles or binders in the ink try to adhere to the inner walls, they will not adhere and will flow away due to the solvent coverage.

[0119] In addition, Figure 4A The image shows only one nozzle 312 and its corresponding components (e.g., pressure chamber 314, throttling section 320, independent flow path 315, piezoelectric element 330, etc.), but as shown in the image... Figure 4B As shown, a plurality of nozzles 312 and their corresponding constituent elements are arranged along the Y direction.

[0120] like Figure 4B As shown, the common flow path 351 is connected to each of the plurality of pressure chambers 314 via each independent flow path 315 and each throttling section 320.

[0121] The common flow path 351 is connected to an ink reservoir (not shown). The ink reservoir is connected to an ink supply tank (not shown), which serves as the ink supply source. The ink reservoir can be considered as a second ink supply tank existing between the common flow path 351 and the ink supply tank. By pressurizing or depressurizing the ink reservoir, the pressure applied to the nozzle 312 can be controlled, allowing the ink to be ejected in an appropriate state.

[0122] like Figure 4C As shown, the common flow path 351 is connected to the supply port 353 and the discharge port 354. Ink flows from the ink reservoir into one side of the common flow path 351 through the supply port 353, and from the common flow path 351 into each pressure chamber 314 through each independent flow path 315 and each throttling section 320. Ink flowing from each pressure chamber 314 into the other side of the common flow path 351 is discharged from the discharge port 354. The discharged ink is recovered by an ink recovery tank connected to the ink supply tank and flows back into the ink supply tank.

[0123] A pressure difference is established between the ink supply tank and the ink recovery tank, thereby causing ink to flow from the ink recovery tank to the ink supply tank. By employing such an ink circulation system, new ink can be continuously supplied to each pressure chamber 314, preventing viscosity increases due to solvent evaporation near the nozzle 312 in contact with the atmosphere. This enables stable ink ejection over a long period.

[0124] <Inkjet device>

[0125] The inkjet head 300 described above can also be provided in an inkjet apparatus. In addition to the inkjet head 300, the inkjet apparatus may also include, for example, a drive control unit and a transport unit. The drive control unit generates a drive voltage signal applied to the piezoelectric element 330 to control the ink ejection operation of the inkjet head 300. The transport unit moves the inkjet head 300 relative to the medium being depicted (also referred to as the "printed object") upon which the ink droplets land.

[0126] <Evaluation of Examples and Comparative Examples>

[0127] The following is an evaluation of the various embodiments and comparative examples.

[0128] The contact angles were compared and evaluated for cases where the monomolecular film 340 was formed on a stainless steel plate and cases where the monomolecular film 340 was not formed on a stainless steel plate (Example 1 and Comparative Example 1 described later). The contact angles were measured using a DSA100 contact angle measuring instrument (made by KRUSS).

[0129] Furthermore, comparative evaluations of ink ejection characteristics were conducted for cases where the monomolecular film 340 was formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315, and for cases where the monomolecular film 340 was not formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315 (Example 2 and Comparative Example 2 described later).

[0130] The evaluation method is as follows.

[0131] Ink was ejected from nozzle 312, and a flash was emitted synchronously with the application of the drive waveform to illuminate the ink droplets (hereinafter referred to as "droplets"). This illumination was then observed using a camera, thus allowing for the observation of the droplet's flight process. Furthermore, by delaying the flash emission, droplets were observed at two different times, and the position coordinates of the droplets at these two times were measured to evaluate the angle of the droplet's flight direction.

[0132] The ink used in the evaluation had a viscosity of 8 mPa·s and a surface tension of 33 mN / m. The viscosity was measured using an AR-G2 viscometer (manufactured by TA Insruments). The surface tension was measured using a DSA100 surface tension meter (manufactured by KRUSS). Additionally, the ink used in the evaluation contained titanium dioxide with a particle size of 1 μm and a binder material composed of organic compounds.

[0133] (Example 1)

[0134] In Example 1, a silicon oxide film of approximately 20 nm was first formed on the surface of a stainless steel plate. This film formation was performed using a method known as "atomic layer deposition".

[0135] Next, the stainless steel sheet with the silicon oxide film formed is immersed in a liquid material (for example, a superhydrophilic coating material manufactured by Junko Chemical Co., Ltd., more specifically, LAMBIC-771W) as a raw material for the monomolecular film 340 for about 10 seconds. Afterward, the immersed stainless steel sheet is dried at 80°C for 15 minutes using a heating furnace, thereby forming the monomolecular film 340.

[0136] Furthermore, the change in the contact angle of the stainless steel plate with the formed monolayer 340 to the ink over time was evaluated. The evaluation results are as follows: Figure 5A As shown.

[0137] like Figure 5A As shown, the initial static contact angle (when the ink first comes into contact) is 95 degrees, and the static contact angle after immersion in the ink for 20 days is 90 degrees. Therefore, it can be seen that the static contact angle hardly changes over time.

[0138] In addition, such as Figure 5A As shown, the initial retraction contact angle was 10 degrees, and the retraction contact angle after immersion in ink for 20 days was 12 degrees. Therefore, it can be seen that the retraction contact angle hardly changed over time.

[0139] It can be considered that in Example 1, the monomolecular film 340 is formed on the stainless steel plate, thereby inhibiting the adhesion of particles or adhesives in the ink and stabilizing the surface of the stainless steel plate.

[0140] (Comparative Example 1)

[0141] In Comparative Example 1, similar to Example 1, a silicon oxide film of about 20 nm was first formed on the surface of a stainless steel plate by atomic layer deposition.

[0142] Furthermore, the change in the contact angle of ink with respect to stainless steel plates with only a silica film formed over time was evaluated. The evaluation results are as follows: Figure 5B As shown.

[0143] like Figure 5B As shown, the initial static contact angle is 25 degrees, while the static contact angle after immersion in ink for 20 days is 70 degrees, showing a significant change over time.

[0144] In addition, such as Figure 5B As shown, the initial retraction contact angle was 16 degrees, compared to 12 degrees after immersion in ink for 20 days.

[0145] It can be assumed that in Example 2, since a monomolecular film 340 was not formed on the stainless steel plate, particles or adhesives in the ink adhered to the surface of the stainless steel plate during the ink impregnation process, resulting in a significant change in the contact angle.

[0146] (Example 2)

[0147] In Example 2, firstly, a silicon oxide film is formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, and independent flow path 315 by atomic layer deposition. Here, the material constituting each of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315 is stainless steel.

[0148] Next, using the same method as in Example 1, monomolecular films 340 were formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315.

[0149] Furthermore, as described above, the flight process of the droplets ejected from nozzle 312 was observed and the angle of their flight direction was evaluated.

[0150] Figure 6A The image shows the flight process of a droplet. For example... Figure 6A As shown, it was observed that the droplets ejected from nozzle 312 extended into a cylindrical shape, tapering at the end, as they flew. Furthermore, it was confirmed that the end of the droplet extended straight during flight. It should be noted that if the end were curved, subsequent droplets would also fly in a curved path instead of a straight one, thus reducing the accuracy of the droplet's landing position. If the accuracy of the landing position decreases, the droplet cannot be applied to the target location, resulting in a reduction in print quality.

[0151] Figure 6B The image shows the flight angle of droplets ejected from multiple nozzles 312. Figure 6B In the diagram, the horizontal axis represents each nozzle, and the vertical axis represents the droplet's flight angle. Figure 6B If the droplet flies straight relative to the vertical direction of the nozzle 312, the flight angle is 0 degrees. The larger the value of the flight angle, the greater the curvature of the droplet during flight.

[0152] When expressed as three standard deviations (3σ), the deviation of the flight angle of each droplet ejected from hundreds of nozzles 312 is 17 mrad. This value means that, assuming the distance between the nozzle 312 and the object being printed is 1 mm, the deviation of the droplet's landing position is 17 μm.

[0153] Assuming the ink is coated in a manner where the diameter of the falling droplets is approximately 60 μm and the semicircles of the droplets overlap each other, then if the landing position is more than 30 μm away, areas will be created where the droplets do not overlap and are therefore uncoated. Therefore, the target value for the accuracy of the landing position is set to within 30 μm. Furthermore, it was confirmed that the target value for the landing position was achieved in Example 2.

[0154] (Comparative Example 2)

[0155] In Comparative Example 2, similarly to Example 2, firstly, a silicon oxide film was formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, and independent flow path 315 by atomic layer deposition. Here, the material constituting each of the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315 is stainless steel.

[0156] Furthermore, as described above, the flight process of the droplets ejected from nozzle 312 was observed and the angle of their flight direction was evaluated.

[0157] Figure 7A The image shows the flight process of a droplet. For example... Figure 7A As shown, it was observed that the droplets ejected from nozzle 312 extended into a cylindrical shape, tapering at the tip, as they flew. Furthermore, it was confirmed that the tip was curved during flight. It can be assumed that particles or adhesives in the ink adhered to the inner wall of nozzle 312, causing the tip to curve. As mentioned above, if the tip is curved, subsequent droplets will also fly in a curved path instead of a straight one, thus reducing the accuracy of the droplet's landing position. Consequently, the droplets cannot be coated onto the target location, leading to a decrease in print quality.

[0158] Figure 7B The image shows the flight angle of droplets ejected from multiple nozzles 312. Figure 7B The horizontal and vertical axes and Figure 6B Same. Also, with Figure 6B Similarly, in Figure 7B If the droplet flies straight relative to the vertical direction of the nozzle 312, the flight angle is 0 degrees. The larger the value of the flight angle, the greater the curvature of the droplet during flight.

[0159] When expressed as three standard deviations (3σ), the deviation in the flight angle of each droplet ejected from hundreds of nozzles 312 is 86 mrad. This indicates a very large deviation in the flight angle of each droplet. This value means that, assuming the distance between the nozzle 312 and the object being printed is 1 mm, the droplet landing position deviation is 86 μm. That is, droplets may unexpectedly overlap each other, or produce completely non-overlapping, unprinted portions, leading to a decrease in print quality.

[0160] As explained above, the inkjet head 300 of this embodiment is characterized by comprising: a nozzle 312 for ejecting liquid; a pressure chamber 314 communicating with the nozzle 312; an independent flow path 315 communicating with the pressure chamber 314 via a throttling section 320; a common flow path 351 communicating with the independent flow path 315; an energy generating element (e.g., a piezoelectric element 330) for generating energy; and a vibrating plate 317 for transferring energy to the pressure chamber 314. A monomolecular film 340 having hydrophilicity to the liquid is formed on the inner walls of the nozzle 312, the pressure chamber 314, the throttling section 320, the vibrating plate 317, and the independent flow path 315.

[0161] Through the aforementioned features, the adhesion of particles or adhesives contained in the ink can be suppressed in the nozzle 312, pressure chamber 314, throttling section 320, vibrating plate 317, and independent flow path 315. This suppresses clogging caused by particles or adhesives, enabling long-term stable ejection. Consequently, high-quality printing can be achieved.

[0162] Furthermore, the present invention is not limited to the description of the above embodiments, and various modifications can be made without departing from its essential points.

[0163] Industrial applicability

[0164] The liquid ejector head and inkjet device of the present invention are also useful for applications such as ejecting inks containing: white ink containing titanium oxide, conductive ink containing metal nanoparticles, quantum dot luminescent ink containing quantum dot semiconductor particles, and bio-ink containing cells, etc.

Claims

1. A liquid ejector head, characterized in that, have: Nozzle, spraying liquid; The pressure chamber is connected to the nozzle; An independent flow path is connected to the pressure chamber via a throttling section; Shared flow path, connected to the independent flow path; Energy-generating components produce energy; as well as The vibrating plate transfers the energy to the pressure chamber. A metal oxide film is formed on the inner wall of each of the nozzle, the pressure chamber, the throttling section, the vibrating plate, and the independent flow path. Hydroxyl groups are exposed from the metal oxide film.

2. The liquid ejector head as described in claim 1, wherein, The liquid nozzle also has a hydrophilic membrane. The hydrophilic membrane covers the metal oxide film.

3. The liquid ejector head as described in claim 2, wherein, The hydrophilic membrane is a monomolecular membrane.

4. The liquid ejector head as described in claim 3, wherein, The monomolecular membrane is a self-assembled monomolecular membrane.

5. The liquid ejector head as described in claim 3, wherein, The thickness of the monolayer is less than 50 nm.

6. The liquid ejector head as claimed in claim 1, wherein, The static contact angle of the inner wall of each of the nozzle, the pressure chamber, the throttling section, and the independent flow path with the liquid is larger than the recoil contact angle.

7. The liquid ejector head as claimed in claim 1, wherein, The outer surface of the nozzle is hydrophobic to the liquid.

8. The liquid ejector head as claimed in claim 7, wherein, The outer surface of the nozzle has a recoil contact angle of 30 degrees or more with the liquid.

9. An inkjet device, characterized in that, have: The liquid ejector head according to claim 1; The drive control unit generates a drive voltage signal applied to the energy generating element to control the ink ejection action of the liquid ejector head; as well as The delivery unit causes the liquid nozzle to move relative to the medium being depicted.

10. A method for manufacturing a liquid ejector head, characterized in that, The liquid ejector head includes: Nozzle, spraying liquid; The pressure chamber is connected to the nozzle; An independent flow path is connected to the pressure chamber via a throttling section; Shared flow path, connected to the independent flow path; Energy-generating components produce energy; as well as The vibrating plate transfers the energy to the pressure chamber. A metal oxide film is formed on the inner wall of each of the nozzle, the pressure chamber, the throttling section, the vibrating plate, and the independent flow path. Hydroxyl groups are exposed from the metal oxide film.

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