Method for manufacturing a liquid dispensing head

Abstract

To achieve stable discharge over time by suppressing clogging of a nozzle due to particles or the like contained in a liquid and adhesion of the particles to a flow path and a diaphragm surface.SOLUTION: A method of manufacturing a liquid ejection head includes the steps of: forming a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, an individual flow path communicating with the pressure chamber through a throttle portion, a common flow path communicating with the individual flow path, and an energy generating element for generating energy; and forming a film having lyophilicity to the liquid on an inner wall of each of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the individual flow path, and forming a metal oxide film on a surface of the inner wall of each of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the individual flow path.SELECTED DRAWING: Figure 4A

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for manufacturing a liquid ejection head.

BACKGROUND ART

[0002] Conventionally, as an example of a liquid ejection head, a drop-on-demand inkjet head that can apply a required amount of ink when required according to an input signal is known. For example, a piezoelectric drop-on-demand inkjet head generally includes an ink supply flow path, a plurality of pressure chambers connected to the ink supply flow path and provided with nozzles, and a piezoelectric element that applies pressure to the ink filled in the pressure chambers.

[0003] Here, an example of a conventional bulk-type inkjet head will be described with reference to Figure 1A and Figure 1B. Figure 1A and Figure 1B are schematic diagrams showing the cross-sectional structure of a conventional bulk-type inkjet head. Figure 1A shows the state before voltage application, and Figure 1B shows the state during voltage application.

[0004] As shown in Figure 1A and Figure 1B, the conventional bulk-type inkjet head includes a plurality of nozzles 100 that eject ink droplets, pressure chambers 110 that communicate with the nozzles 100 and are filled with ink, partition walls 111 that separate the pressure chambers 110 corresponding to adjacent nozzles 100, a vibration plate 112 that forms part of the pressure chambers 110, a piezoelectric element 130 that vibrates the vibration plate 112, and a piezoelectric member 140 that supports the piezoelectric element 130 and the partition walls 111. Although not illustrated, the conventional bulk-type inkjet head further includes a common electrode for applying a voltage to the piezoelectric element 130, and an ink introduction port.

[0005] The piezoelectric member 140 is obtained by separating a single piezoelectric member by dicing. The diameter of the nozzles 100 is 10 μm to 50 μm. The nozzles 100 are arranged at intervals of 100 μm to 500 μm. The number of the nozzles 100 is, for example, 100 to 400.

[0006] A conventional bulk inkjet head configured in this way operates as follows:

[0007] When 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 deforms from the state shown in Figure 1A to the state shown in Figure 1B. Specifically, in Figure 1B, the lower part of the second piezoelectric element 130 from the left deforms. As a result, the volume of the pressure chamber 110 decreases, pressure is applied to the ink in the pressure chamber 110, and ink droplets (not shown) are ejected from the nozzle 100.

[0008] The above describes an example of a conventional bulk-type inkjet head.

[0009] Furthermore, inkjet heads are known that have ink inlet and outlet ports and eject ink while circulating it. The effects obtained by circulating the ink are explained below.

[0010] The ink near the nozzle is constantly exposed to the atmosphere. Because the contact area between the ink and the atmosphere is extremely small, the evaporation of the ink solvent cannot be ignored. When the solvent evaporates, the solid content concentration of the ink increases. As a result, the viscosity of the ink increases, which can make normal ink ejection difficult.

[0011] Therefore, by circulating the ink, the ink near the nozzle can be constantly replaced, and the ink near the nozzle can be kept at the normal viscosity at all times. As a result, nozzle clogging is suppressed, and normal ink ejection can be performed on a regular basis.

[0012] Furthermore, thin-film inkjet heads using thin-film piezoelectric elements are known. An example of such a thin-film inkjet head will be described below with reference to Figures 2A and 2B. Figures 2A and 2B are schematic diagrams showing the cross-sectional structure of a conventional thin-film inkjet head. Figure 2A shows the state before voltage is applied, and Figure 2B shows the state when voltage is applied.

[0013] As shown in Figures 2A and 2B, a conventional thin-film inkjet head includes a nozzle 200 for ejecting ink droplets, a pressure chamber 210 communicating with the nozzle 200 and filled with ink, a diaphragm 212 forming part of the pressure chamber 210, a thin-film piezoelectric element 220 provided above the diaphragm 212 for vibrating the diaphragm 212, a piezoelectric member 140 supporting the piezoelectric element 130 and the partition wall 111, and a common pressure chamber 230 for supplying ink to the pressure chamber 210.

[0014] A conventional thin-film inkjet head configured in this way operates as follows:

[0015] When a voltage is applied to the thin-film piezoelectric element 220, the thin-film piezoelectric element 220 deforms from the state shown in Figure 2A to the state shown in Figure 2B. This deformation of the thin-film piezoelectric element 220 reduces the volume of the pressure chamber 210, pressurizing the liquid inside the pressure chamber 210, and causing ink droplets (not shown) to be ejected from the nozzle 200.

[0016] The above describes an example of a conventional thin-film inkjet head.

[0017] Furthermore, for example, Patent Document 1 discloses an inkjet head in which the surface of the nozzle has properties that repel ink (liquid-repellent) in order to suppress the adhesion of ejected ink, and the inner wall of the nozzle has properties that allow it to become wet with ink (hydrophilic) in order to suppress the accumulation of air bubbles in the ink.

[0018] Here, the processing steps for making the nozzle liquefy-repellent and hydrophilic, as disclosed in Patent Document 1, will be explained using Figure 3. Figure 3 is a schematic cross-sectional view showing the processing steps for the nozzle plate of an inkjet head disclosed in Patent Document 1.

[0019] First, as shown in the upper diagram of Figure 3, hydrogen termination treatment (X) is applied to the surface of the nozzle plate 60 and the inner wall of the nozzle hole 51.

[0020] Next, as shown in the middle diagram of Figure 3, 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. Then, by bringing the liquid-repellent film raw material into contact with the surface of the nozzle plate 60, the surface of the nozzle plate 60 is made liquid-repellent (Y).

[0021] Next, as shown in the lower diagram of Figure 3, thermal energy 62 is applied to the inner wall of the nozzle hole 51, and the hydrophilic film material is brought into contact with the inner wall of the nozzle hole 51, thereby causing the inner wall of the nozzle hole 51 to become hydrophilic (Z).

[0022] Through the above processing steps, the surface of the nozzle plate 60 becomes liquid-repellent, thereby suppressing ink adhesion. In addition, the inner wall of the nozzle hole 50 becomes lipophilic, thereby suppressing the accumulation of air bubbles. [Prior art documents] [Patent Documents]

[0023] [Patent Document 1] Japanese Patent Publication No. 2011-68095 [Overview of the project] [Problems that the invention aims to solve]

[0024] However, the inkjet head described in Patent Document 1 does not guarantee the hydrophilicity of parts other than the nozzles that come into contact with the ink (for example, the inner walls of the flow path and pressure chamber). Therefore, when using the inkjet head described in Patent Document 1 with ink containing particles or binder components made of inorganic compounds (hereinafter referred to as "particles, etc."), clogging may occur due to the particles or binder components adhering to and accumulating on parts other than the nozzles that come into contact with the ink. In particular, binder components are made of organic compounds and tend to adhere to parts of the ink that come into contact with the ink, such as stainless steel, which are made of metal.

[0025] For example, in a portion of the flow path of an inkjet head where an individual flow path and a pressure chamber communicate with each other, a throttle portion, which is a flow path narrower than the individual flow path, is provided to make it difficult for pressure waves in the pressure chamber to escape. A large shear stress is applied to this throttle portion in the process of ink flowing. As a result, particles and the like in the ink tend to aggregate, and the particles and the like easily adhere to the wall surface of the flow path to cause clogging.

[0026] Further, the vibration plate vibrates at high speed in accordance with the ejection frequency. For example, the vibration plate vibrates about 1000 to 50000 times per second in accordance with a frequency of about 1 to 50 kHz. This vibration causes a high-speed shear force to be applied to the ink. Accordingly, the dispersed state of the particles in the ink may be disrupted, causing aggregation and adhesion to the surface of the vibration plate.

[0027] An object of one aspect of the present disclosure is to provide a method for manufacturing a liquid ejection head that can suppress nozzle clogging caused by particles and the like contained in a liquid, and adhesion of particles on the surfaces of flow paths and a vibration plate, and can realize stable ejection over time. [Means for Solving the Problems]

[0028] In a method for manufacturing a liquid ejection head according to one aspect of the present disclosure, the liquid ejection head includes: a nozzle configured to eject a liquid; a pressure chamber communicating with the nozzle; an individual flow path communicating with the pressure chamber via a throttle portion; a common flow path communicating with the individual flow path; an energy generating element configured to generate energy; and a vibration plate configured to transmit the energy to the pressure chamber, wherein a film having lyophilicity to the liquid is formed on each inner wall of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the individual flow path, and the method includes forming a metal oxide film on the surface of each inner wall of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the individual flow path, and forming the film having lyophilicity to the liquid so as to cover the metal oxide film. [Effects of the Invention]

[0029] According to this disclosure, clogging caused by particles contained in the liquid can be suppressed, and stable dispensing over time can be achieved. [Brief explanation of the drawing]

[0030] [Figure 1A] A schematic cross-sectional diagram showing the state of a conventional bulk-type inkjet head before voltage is applied. [Figure 1B] A schematic cross-sectional diagram showing the state of a conventional bulk-type inkjet head when voltage is applied. [Figure 2A] A schematic cross-sectional diagram showing the state of a conventional thin-film inkjet head before voltage is applied. [Figure 2B] A schematic cross-sectional diagram showing the state of a conventional thin-film inkjet head when voltage is applied. [Figure 3] A schematic cross-sectional diagram showing the processing steps for the nozzle plate of the inkjet head described in Patent Document 1. [Figure 4A] A schematic cross-sectional view showing the configuration of an inkjet head according to an embodiment of this disclosure. [Figure 4B] XY cross-sectional view (Figure 4A) [Figure 4C] Plan view showing the arrangement of the common flow path for the entire inkjet head according to the embodiment of this disclosure. [Figure 5A] Figure showing the change in contact angle over time after hydrophilic treatment according to Example 1. [Figure 5B] Figure showing the change in contact angle over time after hydrophilic treatment in Comparative Example 1. [Figure 6A] Diagram showing the flight process of ink droplets according to Example 2 [Figure 6B] Diagram showing the flight angle of ink droplets in Example 2 [Figure 7A] Diagram showing the flight process of ink droplets in Comparative Example 2 [Figure 7B] Diagram showing the flight angle of ink droplets in Comparative Example 2 [Modes for carrying out the invention]

[0031] The embodiments of this disclosure will be described below with reference to the drawings. Common components in each drawing are denoted by the same reference numerals, and their descriptions will be omitted as appropriate.

[0032] <Inkjet head 300> The configuration of the inkjet head 300 according to the embodiment of this disclosure will be explained with reference to Figures 4A, 4B, and 4C.

[0033] Figure 4A is a schematic cross-sectional view showing the configuration of the inkjet head 300 in this embodiment. Figure 4A also shows the AA' cross-section in Figure 4C. Figure 4B is an XY cross-sectional view of Figure 4A. Figure 4C is a plan view showing the arrangement of the common flow path 351 of the entire inkjet head 300.

[0034] In this embodiment, the example given is that the liquid ejection head is an inkjet head 300 that ejects ink, but the invention is not limited to this. The liquid ejection head may eject a liquid other than ink.

[0035] The inkjet head 300 includes a nozzle 312, a pressure chamber 314, a piezoelectric element 330, a diaphragm 317, an aperture section 320, individual channels 315, a common channel 351, a monolayer 340, and a liquid-repellent film 350.

[0036] The nozzle 312 is a through-hole for ejecting ink and communicates with the pressure chamber 314. The diameter of the nozzle 312 is, for example, about 5 to 50 μm. The nozzle 312 is formed by methods such as laser processing, etching, or punching.

[0037] The surface of the nozzle 312 is provided with a liquid-repellent film 350 that has the property of repelling ink (liquid repellency). The liquid-repellent film 350 is formed by spin-coating a liquid raw material that has liquid-repellent properties. By forming the liquid-repellent film 350, the surface of the nozzle 312 becomes liquid-repellent. The receding contact angle of the liquid-repellent film 350 with respect to the ink is, for example, 30 degrees or more. The static contact angle of the liquid-repellent film 350 with respect to the ink is, for example, 50 degrees or more.

[0038] The piezoelectric element 330 (an example of an energy generating element) is provided in correspondence with the pressure chamber 314 and is displaced by the application of voltage. As the piezoelectric element 330, for example, a stacked piezoelectric element of d33 mode or d31 mode, or a piezoelectric element that utilizes the shear mode can be used. Alternatively, an electrostatic actuator or a heating element may be used as an energy generating element instead of these piezoelectric elements.

[0039] The diaphragm 317 is positioned in contact with the piezoelectric element 330 and deforms due to the displacement of the piezoelectric element 330. The diaphragm 317 is made of, for example, a metal such as nickel or a resin such as polyimide, but is not limited to these materials. The thickness of the diaphragm 317 is preferably, for example, 5 to 50 μm.

[0040] When the displacement of the piezoelectric element 330 is transmitted to the diaphragm 317, the diaphragm 317 deforms. This changes the volume of the pressure chamber 314, causing ink droplets to be ejected from the nozzle 312. Therefore, the amount of deformation of the diaphragm 317 is very important, and variations in the rigidity of the diaphragm 317, which are related to this deformation, affect the ejection characteristics. Thus, it is necessary to make the rigidity of the diaphragm 317 uniform.

[0041] The pressure chamber 314 is in communication with the nozzle 312. The pressure chamber 314 is also in communication with the individual flow path 315 via the throttling section 320. The volume of the pressure chamber 314 changes due to the deformation of the diaphragm 317. This change in volume causes ink to be ejected from the nozzle 312. The volume of the pressure chamber 314 and the flow path resistance of the throttling section 320 change the resonance period of the ink, which in turn changes the volume and velocity of the ejected ink. Therefore, it is necessary to optimally adjust the volume of the pressure chamber 314 and other parameters as needed.

[0042] The individual channel 315, the common channel 351, and the diaphragm 320 are ink channels. The common channel 351 communicates with the individual channel 315. The individual channel 315 communicates with the pressure chamber 314 via the diaphragm 320. The diaphragm 320 has a width narrower than the width of the individual channel 315. This makes it difficult for pressure waves in the pressure chamber 314 to escape into the individual channel 315.

[0043] A hydrophilic monolayer 340 is formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual channel 315. Details of this monolayer 340 will be described later. A monolayer 340 may also be formed on the inner wall of the common channel 351.

[0044] The nozzle 312, pressure chamber 314, individual flow channels 315, diaphragm 317, common flow channel 351, and throttling section 320 described above are manufactured, for example, by thermal diffusion bonding of multiple metal plates processed by etching, or by etching of silicon material.

[0045] <Monolayer 340> As shown in Figure 4A, a monolayer 340 made of an organic compound having good wetting properties (hydrophilic; hereinafter also referred to as wettability) is formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual flow channels 315.

[0046] The thickness of the monolayer 340 is, for example, about 5 to 50 nm.

[0047] Examples of materials for monolayer 340 include materials that have silanol groups at their molecular ends and multiple hydrophilic molecular chains extending from the main skeleton. For example, a superhydrophilic coating material (specifically LAMBIC-771W) manufactured by Junsei Chemical Co., Ltd. can be used as such a material. Therefore, monolayer 340 can be said to be a film made of molecules that have silanol groups at their molecular ends and multiple hydrophilic molecular chains extending from the main skeleton.

[0048] Here, a monolayer refers to a thin film whose thickness corresponds to exactly one molecule, formed when molecules are aligned in that manner. A monolayer is also called a monolayer.

[0049] When higher fatty acids or higher alcohols are dissolved in a highly volatile solvent such as benzene and dropped onto a water surface, a monolayer can be formed after the solvent evaporates. In this case, the hydroxyl and carboxyl groups of the alcohol are hydrophilic and face the water, while the hydrophobic long-chain alkyl groups are aligned away from the water (into the air). When the molecules are arranged without gaps, a monolayer film is obtained whose thickness is exactly equal to the length of the long-chain alkyl group (plus the hydrophilic group).

[0050] The monolayer 340 material has the characteristic of self-assembling molecular arrangement, and active silanol groups are adsorbed onto the substrate surface through a chemical reaction. Functional groups that activate the silanol groups must be present on the substrate surface.

[0051] For example, it is desirable that a silicon oxide film is formed on the substrate surface and that hydroxyl groups are exposed. However, since it is sufficient for hydroxyl groups to be exposed on the substrate surface, the film formed on the substrate surface is not limited to silicon oxide. For example, metal oxides such as alumina (Al2O3) or titania (TiO2) may be used instead of silicon oxide. The monolayer 340 is provided by coating the substrate surface with the silicon oxide film or metal oxide film formed thereon.

[0052] Because monomolecular film materials have a limited surface on which they can chemically adsorb, once adsorbed, they do not adsorb three-dimensionally onto that surface. This principle allows for the self-organization of films on the order of single molecules. The thickness is controlled to be very thin, between 5 and 30 nm, but this thickness is crucial when forming films on the inner walls of nozzles 312 and pressure chambers 314. If hydrophilic coating agents are used, controlling the thickness becomes difficult, resulting in thicknesses on the order of several micrometers to tens of micrometers. If the thickness is too high, the diaphragm 320 and nozzle 312 will become filled with the hydrophilic film, causing clogging. Furthermore, the thickness of the film formed on the surface of the diaphragm 317 is also extremely important. Since the diaphragm 317 is about 10 μm thick, if a thick film is attached to the surface of the diaphragm 317, the rigidity of the diaphragm 317 will change significantly, and the vibration characteristics transmitted from the piezoelectric element 330 will change drastically. Furthermore, the material for the monolayer 340 can be any material that self-assembles to complete the reaction at a thickness on the order of a single molecule, and is not limited to the materials mentioned above.

[0053] From the above, it can be said that monolayer 340 is a self-assembled monolayer. Self-assembled monolayers can be formed by placing a suitable material in a solution or vapor of organic molecules, allowing the organic molecules to be chemically adsorbed onto the material surface, and in the process forming a monolayer with a thickness of 1-2 nm in which the orientation of the organic molecules is uniform. Self-assembled monolayers can be easily created by simply immersing a substrate in a solution of molecules that have functional groups to bond with it, and they have high orientation and stability, and various functions can be introduced by terminal functional groups. Self-assembled monolayers are also called self-assembled monolayers.

[0054] The recessed contact angle of a film produced by such a self-assembled material is preferably 20 degrees or less, and more preferably 15 degrees or less. The static contact angle is preferably 25 degrees or more, and more preferably 30 degrees or more.

[0055] Here, we will explain the receding contact angle and the stationary contact angle.

[0056] When a liquid is dropped onto a solid surface, the liquid bends into a ball due to its own surface tension, and the relationship shown in equation (1) below holds true. Equation (1) is known as Young's equation. γs = γL × cosθ + γSL ···(1) γs: Surface tension of a solid γL: Surface tension of a liquid γSL: Interfacial tension between solid and liquid

[0057] The angle θ between the tangent of the liquid droplet and the solid surface at this time is called the contact angle. In particular, the contact angle when the liquid is stationary on the solid surface and has reached equilibrium is called the stationary contact angle.

[0058] On the other hand, the contact angles in a dynamic state where the interface between a liquid and a solid is in motion, that is, when the interface of a liquid droplet is moving, are called the advancing contact angle and the receding contact angle. Here, we will focus on the receding contact angle, which is the dynamic contact angle after a solid surface has been wetted with a liquid.

[0059] The static contact angle of the monolayer 340 with respect to the ink, as shown in Figure 4A, is 30 degrees or more. The receding contact angle of the monolayer 340 with respect to the ink, as shown in Figure 4A, is 20 degrees or less. This means the following:

[0060] When the nozzle 312 and individual channels 315 are dry, the static contact angle when the ink first comes into contact with the monomolecular film 340 formed on their inner walls is 50 degrees or more, which is a relatively high condition.

[0061] As shown in Figure 4A, a monolayer 340 is not formed on the inner wall of the common channel 351. Therefore, the common channel 351 exhibits the conventional wettability of its material. If, for example, stainless steel is used as the material for the common channel 351, its static contact angle will be 50 degrees or more.

[0062] In such cases, there is virtually no difference in wettability for the ink between the common channel 351 and the individual channels 315. Therefore, ink is filled into each channel without wetting defects such as air bubbles getting trapped during the ink flow process.

[0063] If there is a significant difference in wettability between the common channel 351 and the individual channels 315 during the ink flow process, the flow may change irregularly at that point, potentially causing air bubbles to become trapped. The presence of air bubbles in the ink often causes ejection problems, making it crucial to remove them effectively. If a monolayer 340 is also formed in the common channel 351, the static contact angle is not limited to the above and may be as low as 30 degrees or less.

[0064] On the other hand, the receding contact angle of the monolayer 340 is low, at 20 degrees or less. Once the monolayer 340 is wetted with ink, the hydrophilic groups in the monolayer 340 expand, exhibiting high hydrophilicity. At this time, the solvent components in the ink cover the inner wall surfaces of the nozzle 312, pressure chamber 314, throttling section 320, and individual flow channels 315. In this state, even if particles and binders in the ink try to adhere to each inner wall, they are covered with solvent and therefore flow away without adhering.

[0065] Although Figure 4A shows only one nozzle 312 and its corresponding components (e.g., pressure chamber 314, throttling section 320, individual flow path 315, piezoelectric element 330, etc.), multiple nozzles are provided along the Y direction, as shown in Figure 4B.

[0066] As shown in Figure 4B, the common flow path 351 is connected to each of the multiple pressure chambers 314 via each individual flow path 315 and each throttling section 320.

[0067] The common channel 351 is connected to an ink reservoir (not shown). The ink reservoir is connected to an ink supply tank (not shown), which is the source of the ink. The ink reservoir can be considered a second ink supply tank located between the common channel 351 and the ink supply tank. By pressurizing or depressurizing this ink reservoir, the pressure on the nozzle 312 can be controlled, allowing ink to be ejected in an appropriate state.

[0068] As shown in Figure 4C, the common channel 351 is in communication with the supply port 353 and the discharge port 354. Ink flows from the ink reservoir through the supply port 353 into one of the common channels 351, and from the common channel 351 into each individual channel 315 and each throttling section 320 into each pressure chamber 314. Ink that flows from each pressure chamber 314 into the other common channel 351 is discharged from the discharge port 354. The discharged ink is recovered in an ink recovery tank connected to the ink supply tank and flows back into the ink supply tank.

[0069] A pressure difference is created between the ink supply tank and the ink recovery tank, causing ink to flow from the ink recovery tank to the ink supply tank. By employing such an ink circulation system, fresh ink can be constantly supplied to each pressure chamber 314, and the increase in viscosity due to the evaporation of the ink solvent at the point in contact with the atmosphere near the nozzle 312 can be prevented. This enables stable ink discharge over a long period of time.

[0070] <Inkjet printer> The inkjet head 300 described above may be provided in an inkjet device. In addition to the inkjet head 300, the inkjet device includes, 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 and controls the ink ejection operation of the inkjet head 300. The transport unit moves the inkjet head 300 relative to the medium to be printed on (which may also be called the object to be printed) onto which the ink droplets land.

[0071] <Evaluation of the Examples and Comparative Examples> The evaluation of each of the examples and comparative examples will be described below.

[0072] A comparative evaluation of the contact angle was performed in two cases: when the monomolecular film 340 was formed on a stainless steel plate and when the monomolecular film 340 was not formed on a stainless steel plate (Example 1 and Comparative Example 1 described later). The contact angle was measured using a contact angle meter DSA100 (manufactured by KRUSS).

[0073] Furthermore, a comparative evaluation of ink ejection characteristics was conducted when the monolayer 340 was formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual channel 315, and when the monolayer 340 was not formed on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual channel 315 (see Example 2 and Comparative Example 2 below).

[0074] The evaluation method is as follows:

[0075] Ink was ejected from nozzle 312, and a strobe light was emitted in synchronization with the timing of the application of the drive waveform, illuminating the ink droplets (hereinafter simply referred to as droplets). The droplets were then observed with a camera to observe their flight path. By delaying the timing of the strobe light emission, droplets were observed at two different time points, and the position coordinates of the two droplets were measured to evaluate the angle of the droplet's flight direction.

[0076] The ink used for evaluation had a viscosity of 8 mPa·s and a surface tension of 33 mN / m. Viscosity was measured using a viscometer AR-G2 (TA Instruments). Surface tension was measured using a surface tension meter DSA100 (KRUSS). The ink used for evaluation also contained titanium dioxide with a particle size of 1 μm and a binder material consisting of an organic compound.

[0077] (Example 1) In Example 1, a silicon oxide film of approximately 20 nm was first deposited on the surface of a stainless steel plate. This film deposition was performed using a method called atomic layer deposition.

[0078] Next, the stainless steel plate on which the silicon oxide film was deposited was immersed for approximately 10 seconds in a liquid material that would serve as the raw material for monolayer 340 (for example, a superhydrophilic coating material manufactured by Junsei Chemical Co., Ltd., more specifically, LAMBIC-771W). After that, the immersed stainless steel plate was dried at 80°C for 15 minutes using a heating furnace to deposit the monolayer 340.

[0079] Next, the change in the contact angle between the stainless steel plate on which the monomolecular film 340 was formed and the ink over time was evaluated. The evaluation results are shown in Figure 5A.

[0080] As shown in Figure 5A, the initial static contact angle (when the ink first made contact) was 95 degrees, and the static contact angle after immersion in ink for 20 days was 90 degrees. Therefore, it was found that there was almost no change in the static contact angle over time.

[0081] Furthermore, as shown in Figure 5A, the initial receding contact angle was 10 degrees, and the receding contact angle after immersion in ink for 20 days was 12 degrees. Therefore, it was found that there was almost no change in the receding contact angle over time.

[0082] In Example 1, the formation of the monolayer 340 on the stainless steel plate is thought to suppress the adhesion of particles and binders in the ink, thereby stabilizing the surface of the stainless steel plate.

[0083] (Comparative Example 1) In Comparative Example 1, similar to Example 1, a silicon oxide film of approximately 20 nm was first deposited on the surface of a stainless steel plate by atomic layer deposition.

[0084] Next, the change in the contact angle between a stainless steel plate, on which only a silicon oxide film was formed, and the ink over time was evaluated. The evaluation results are shown in Figure 5B.

[0085] As shown in Figure 5B, the initial static contact angle was 25 degrees, while the static contact angle after immersion in ink for 20 days was 70 degrees, indicating a significant change over time.

[0086] Furthermore, as shown in Figure 5B, the initial receding contact angle was 16 degrees, while the receding contact angle after immersion in ink for 20 days was 12 degrees.

[0087] In Example 2, because the monomolecular film 340 was not formed on the stainless steel plate, it is thought that during ink immersion, particles and binders in the ink adhered to the surface of the stainless steel plate, causing a significant change in the contact angle.

[0088] (Example 2) In Example 2, first, a silicon oxide film was deposited on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, and individual channel 315 by atomic layer deposition. Here, the materials for the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual channel 315 are stainless steel.

[0089] Next, a monolayer 340 was deposited on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual channel 315 using the same method as in Example 1.

[0090] As described above, the flight process of the droplets ejected from the nozzle 312 was observed, and the angle of their flight direction was evaluated.

[0091] Figure 6A shows the flight process of the droplet. As shown in Figure 6A, the droplet ejected from the nozzle 312 was observed to elongate into a cylindrical shape, tapering towards the tail as it flew. It was also found that the tail extended straight during flight. If the tail bends, the subsequent droplets will not fly straight, but will curve, reducing the accuracy of the droplet's landing position. Reduced accuracy of the landing position makes it impossible to apply the droplet to the intended location, leading to a decrease in print quality.

[0092] Figure 6B shows the flight angles of droplets ejected from multiple nozzles 312. In Figure 6B, the horizontal axis represents each nozzle, and the vertical axis represents the flight angle of the droplets. In Figure 6B, when a droplet flies straight relative to the vertical direction of the nozzle 312, the flight angle is 0 degrees, and a larger value for the flight angle indicates that the droplet is flying in a curved path.

[0093] The variation in the flight angle of each droplet ejected from several hundred nozzles 312 was expressed as 3 times the standard deviation (3σ), resulting in 17 mrad. This value means that, assuming a distance of 1 mm between the nozzle 312 and the object to be printed, the variation in the droplet's landing position would be 17 μm.

[0094] The diameter of the impacted droplets is approximately 60 μm, and the ink is applied so that the semicircles of the droplets overlap. In this case, if the impact points are more than 30 μm apart, areas will not be coated because the droplets do not overlap. Therefore, the target value for the accuracy of the impact point was set to within 30 μm. In Example 2, it was found that the target value for the impact point was achieved.

[0095] (Comparative Example 2) In Comparative Example 2, similar to Example 2, a silicon oxide film was first deposited on the inner walls of the nozzle 312, pressure chamber 314, throttling section 320, and individual channel 315 by atomic layer deposition. Here, the materials for the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual channel 315 are stainless steel.

[0096] As described above, the flight process of the droplets ejected from the nozzle 312 was observed, and the angle of their flight direction was evaluated.

[0097] Figure 7A shows the flight process of the liquid droplet. As shown in Figure 7A, the droplet ejected from the nozzle 312 was observed to elongate into a cylindrical shape, with a tapering tail as it flew. It was also found that the tail was curved during flight. It is thought that particles and binder in the ink adhered to the inner wall of the nozzle 312, causing the tail to bend. As mentioned above, when the tail is curved, subsequent droplets also do not fly straight, but curve, reducing the accuracy of the droplet's landing position. As a result, it becomes impossible to apply the droplet to the intended location, leading to a decrease in print quality.

[0098] Figure 7B shows the flight angles of droplets ejected from multiple nozzles 312. The horizontal and vertical axes in Figure 7B are the same as in Figure 6B. Also, as in Figure 6B, in Figure 7B, if the droplet flies straight relative to the vertical direction of the nozzle 312, the flight angle is 0 degrees, and a larger value for the flight angle indicates that the droplet is flying in a curved path.

[0099] The variation in the flight angle of each droplet ejected from several hundred nozzles 312, expressed as 3σ, was 86 mrad. Therefore, it was found that the variation in the flight angle of each droplet was very large. This value means that if the distance between the nozzle 312 and the object to be printed is 1 mm, the variation in the landing position of the droplets will be 86 μm. In other words, droplets may unintentionally overlap, or areas may not overlap at all and not be printed, resulting in a decrease in print quality.

[0100] As described above, the inkjet head 300 of this embodiment comprises a nozzle 312 for ejecting liquid, a pressure chamber 314 communicating with the nozzle 312, individual flow channels 315 communicating with the pressure chamber 314 via a diaphragm 320, a common flow channel 351 communicating with the individual flow channels 315, an energy generating element (for example, a piezoelectric element 330) for generating energy, and a diaphragm 317 for transmitting energy to the pressure chamber 314. The inner walls of the nozzle 312, pressure chamber 314, diaphragm 320, diaphragm 317, and individual flow channels 315 are each formed with a monomolecular film 340 that is hydrophilic to the liquid.

[0101] This feature suppresses the adhesion of particles and binders contained in the ink to the nozzle 312, pressure chamber 314, throttling section 320, diaphragm 317, and individual flow paths 315. Therefore, clogging caused by particles and binders is suppressed, and stable ejection over time can be achieved. As a result, higher print quality can be achieved.

[0102] This disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from its spirit. [Industrial applicability]

[0103] The method for manufacturing a liquid dispensing head described herein is also useful for dispensing, for example, white ink containing titanium dioxide, conductive ink containing metal nanoparticles, quantum dot luminescent ink containing quantum dot semiconductor particles, and bio-ink containing cells, etc. [Explanation of symbols]

[0104] 51 Nozzle holes 60 Nozzle Plates 61 Light Energy 62 Thermal Energy 100 nozzles 110 Pressure Chamber 111 Bulkhead 112 Diaphragm 130 Piezoelectric element 140 Piezoelectric component 200 nozzles 210 Pressure Chamber 212 Diaphragm 220 Thin-film piezoelectric element 230 Common pressure chamber 300 inkjet heads 312 Nozzles 314 Pressure Chamber 315 Individual channel 317 Diaphragm 320 Aperture section 330 Piezo elements 340 Monolayer 350 Liquid repellent film 351 Common channel 353 Supply port 354 Outlet

Claims

1. A method for manufacturing a liquid dispensing head, The aforementioned liquid dispensing head is A nozzle for dispensing liquid, A pressure chamber communicating with the nozzle, Individual flow paths communicating with the pressure chamber via a throttling section, A common channel that communicates with the individual channels, An energy generating element that generates energy, The system comprises a diaphragm that transmits the aforementioned energy to the pressure chamber, A film having hydrophilic properties with respect to the liquid is formed on the inner walls of the nozzle, the pressure chamber, the throttling section, the diaphragm, and the individual flow channels. Forming a metal oxide film on the inner wall surface of the nozzle, the pressure chamber, the throttling section, the diaphragm, and each of the individual flow channels, A film having hydrophilic properties with respect to the liquid is formed so as to cover the metal oxide film. and, including A method for manufacturing a liquid dispensing head.

2. In the inner walls of the nozzle, the pressure chamber, the throttling section, and the individual flow channels, the static contact angle of the hydrophilic film coating the metal oxide film with respect to the liquid is greater than the receding contact angle. A method for manufacturing a liquid dispensing head as described in claim 1.

3. The outer surface of the nozzle is liquid-repellent to the liquid. A method for manufacturing a liquid dispensing head according to claim 1 or 2.

4. The receding contact angle of the outer surface of the nozzle with respect to the liquid is 30 degrees or more. A method for manufacturing a liquid dispensing head according to claim 3.

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