Method of manufacturing liquid ejection 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 technology]

[0002] A drop-on-demand inkjet head, which can apply the required amount of ink when required in response to an input signal, has been known as a conventional example of a liquid ejection head. For example, a piezoelectric drop-on-demand inkjet head generally has an ink supply channel, a plurality of pressure chambers connected to the ink supply channel and having nozzles, and a piezoelectric element that applies pressure to the ink filled in the pressure chambers.

[0003] An example of a conventional bulk-type inkjet head will now be described with reference to Figures 1A and 1B. Figures 1A and 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 when voltage is applied.

[0004] 1A and 1B, a conventional bulk inkjet head has 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 that correspond 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 shown, the conventional bulk inkjet head also has a common electrode that applies a voltage to the piezoelectric element 130, and an ink inlet.

[0005] The piezoelectric members 140 are obtained by separating one 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 nozzles 100 is, for example, 100 to 400.

[0006] The conventional bulk ink jet head configured as above operates as follows.

[0007] When a voltage is applied between the piezoelectric element 130 and a common electrode (not shown) on the back side of the piezoelectric element 130, the piezoelectric element 130 deforms from the state shown in Fig. 1A to the state shown in Fig. 1B. Specifically, in Fig. 1B, the lower part of the second piezoelectric element 130 from the left deforms. This reduces the volume of the pressure chamber 110, applies pressure to the ink in the pressure chamber 110, and ejects ink droplets (not shown) from the nozzle 100.

[0008] An example of a conventional bulk type ink jet head has been described above.

[0009] Inkjet heads are also known that have an ink inlet and an ink outlet and eject ink while circulating the ink. The effects obtained by circulating the ink will be described below.

[0010] The ink near the nozzle is constantly exposed to the air. Because the contact area between the ink and the air is extremely small, evaporation of the ink solvent cannot be ignored. When the ink solvent evaporates, the ink's solids concentration increases. As a result, the ink's viscosity increases, which can make it difficult to eject the ink normally.

[0011] Therefore, by circulating the ink, the ink near the nozzles can be constantly replaced and the ink near the nozzles can be kept at a normal viscosity, which prevents nozzle clogging and enables regular, normal ejection.

[0012] Also known is a thin-film inkjet head that uses a thin-film piezoelectric element. An example of this 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 application, and Figure 2B shows the state when voltage is applied.

[0013] As shown in Figures 2A and 2B, a conventional thin-film inkjet head has a nozzle 200 that ejects ink droplets, a pressure chamber 210 that communicates with the nozzle 200 and is filled with ink, a vibration plate 212 that forms part of the pressure chamber 210, a thin-film piezoelectric element 220 that is provided on top of the vibration plate 212 and vibrates the vibration plate 212, a piezoelectric member 140 that supports the piezoelectric element 130 and the partition wall 111, and a common pressure chamber 230 that supplies ink to the pressure chamber 210.

[0014] The conventional thin film ink jet head configured as above 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 Fig. 2A to the state shown in Fig. 2B. This deformation of the thin film piezoelectric element 220 reduces the volume of the pressure chamber 210, applying pressure to the liquid in the pressure chamber 210, and causing a droplet of ink (not shown) to be ejected from the nozzle 200.

[0016] An example of a conventional thin film ink jet head has been described above.

[0017] Furthermore, for example, Patent Document 1 discloses an inkjet head in which the surface of the nozzle has ink-repellent properties (liquid repellency) to prevent the ejected ink from adhering to the surface, and the inner wall of the nozzle has ink-adaptable and wettable properties (lyophilicity) to prevent air bubbles from remaining in the ink.

[0018] Here, the processing steps for making the nozzles liquid-repellent and liquid-philic, which are disclosed in Patent Document 1, will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view showing the processing steps for the nozzle plate of the inkjet head disclosed in Patent Document 1.

[0019] First, as shown in the upper diagram of FIG. 3, the surface of the nozzle plate 60 and the inner walls of the nozzle holes 51 are subjected to a hydrogen termination treatment (X).

[0020] 3, light energy 61 is applied to the surface of the nozzle plate 60 to reactively activate the surface of the nozzle plate 60. Then, a liquid-repellent film material is brought into contact with the surface of the nozzle plate 60, thereby making the surface of the nozzle plate 60 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 lyophilic film material is brought into contact with the inner wall of the nozzle hole 51, thereby making the inner wall of the nozzle hole 51 lyophilic (Z).

[0022] The above processing steps make the surface of the nozzle plate 60 liquid-repellent, which can prevent ink from adhering to it. In addition, the inner walls of the nozzle holes 50 are lyophilic, which can prevent air bubbles from accumulating. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-68095 Summary of the Invention [Problem to be solved by the invention]

[0024] However, the inkjet head of Patent Document 1 does not guarantee the lyophilicity of ink-contacting parts other than the nozzles (for example, the inner wall surfaces of the flow paths and pressure chambers). Therefore, when ink containing particles or binder components made of inorganic compounds (hereinafter referred to as particles, etc.) is used in the inkjet head of Patent Document 1, the particles or binder components may adhere to and accumulate on ink-contacting parts other than the nozzles, causing clogging. In particular, binder components are made of organic compounds and are prone to adhering to ink-contacting parts made of metals such as stainless steel.

[0025] For example, in the flow paths of an inkjet head, a throttle section, which is a flow path narrower than the individual flow paths, is provided at the portion where the individual flow paths communicate with the pressure chambers to make it difficult for pressure waves in the pressure chambers to escape. This throttle section is subjected to a large shear stress as the ink flows. This makes it easy for particles in the ink to aggregate, and the particles tend to adhere to the wall surfaces of the flow paths, causing clogging.

[0026] The diaphragm also vibrates at high speed according to the frequency of the ejection. For example, the diaphragm vibrates at 1,000 to 50,000 times per second according to a frequency of about 1 to 50 kHz. This vibration causes high-speed shearing force to be applied to the ink. This can cause the dispersion of ink particles to break down, leading to aggregation and the risk of the particles adhering to the surface of the diaphragm.

[0027] An object of one aspect of the present disclosure is to provide a method for manufacturing a liquid ejection head that can suppress clogging of nozzles due to particles contained in the liquid and adhesion of particles to the flow path and vibration plate surface, thereby achieving stable ejection over time. [Means for solving the problem]

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

[0029] According to the present disclosure, clogging due to particles contained in the liquid can be suppressed, and stable ejection over time can be achieved. [Brief explanation of the drawings]

[0030] [Figure 1A] Schematic cross-sectional view showing the state before voltage application in a conventional bulk-type inkjet head [Figure 1B] Schematic cross-sectional view showing the state when voltage is applied to a conventional bulk-type inkjet head [Figure 2A] Schematic cross-sectional view showing the state before voltage application in a conventional thin-film inkjet head [Figure 2B] Schematic cross-sectional view showing the state when voltage is applied to a conventional thin-film inkjet head [Figure 3] Schematic cross-sectional view showing the process of processing the nozzle plate of the inkjet head in Patent Document 1 [Figure 4A] 1 is a cross-sectional view illustrating a configuration of an inkjet head according to an embodiment of the present disclosure; [Figure 4B] XY cross section of Figure 4A [Figure 4C] FIG. 1 is a plan view showing the arrangement of common flow paths in an entire inkjet head according to an embodiment of the present disclosure. [Figure 5A] FIG. 1 is a graph showing the change over time in contact angle after hydrophilic treatment according to Example 1. [Figure 5B] FIG. 10 is a graph showing the change over time in contact angle after hydrophilic treatment according to Comparative Example 1. [Figure 6A] FIG. 10 is a diagram showing the flight process of ink droplets according to Example 2. [Figure 6B] FIG. 10 is a diagram showing the flight angle of ink droplets according to Example 2. [Figure 7A] FIG. 10 is a diagram showing the flight process of ink droplets according to Comparative Example 2. [Figure 7B] FIG. 10 is a diagram showing the flight angle of ink droplets according to Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that common components in the drawings are denoted by the same reference numerals, and descriptions thereof will be omitted as appropriate.

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

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

[0034] In the present embodiment, the liquid ejection head will be described as an inkjet head 300 that ejects ink, but the present invention is not limited to this. The liquid ejection head may also eject a liquid other than ink.

[0035] The inkjet head 300 includes a nozzle 312 , a pressure chamber 314 , a piezoelectric element 330 , a vibration plate 317 , a throttle portion 320 , an individual flow channel 315 , a common flow channel 351 , a monolayer 340 , and a liquid-repellent film 350 .

[0036] Nozzles 312 are through holes for ejecting ink, and communicate with pressure chambers 314. The diameter of nozzles 312 is, for example, about 5 to 50 μm. Nozzles 312 are formed by, for example, laser processing, etching, or punching.

[0037] A liquid-repellent film 350 having ink-repellent properties (liquid repellency) is provided on the surface of the nozzle 312. The liquid-repellent film 350 is formed by spin-coating a liquid made of a liquid-repellent raw material. The formation of the liquid-repellent film 350 makes the surface of the nozzle 312 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] Piezoelectric element 330 (an example of an energy generating element) is provided corresponding to pressure chamber 314 and is displaced by application of a voltage. For example, a stacked piezoelectric element of d33 mode or d31 mode, or a piezoelectric element utilizing a shear mode can be used as the piezoelectric element 330. Alternatively, an electrostatic actuator or a heating element may be used as an energy generating element instead of such a piezoelectric element.

[0039] Diaphragm 317 is disposed so as to be in contact with piezo element 330, and is deformed by the displacement of piezo element 330. Diaphragm 317 is made of, for example, but not limited to, a metal such as nickel or a resin such as polyimide. The thickness of diaphragm 317 is preferably, for example, 5 to 50 μm.

[0040] When the displacement of the piezo element 330 is transmitted to the vibration plate 317, the vibration plate 317 is deformed. This changes the volume of the pressure chamber 314, causing a droplet of ink to be ejected from the nozzle 312. Therefore, the amount of deformation of the vibration plate 317 is very important, and since variations in the rigidity of the vibration plate 317 related to this affect the ejection characteristics, it is necessary to make the rigidity of the vibration plate 317 uniform.

[0041] The pressure chamber 314 communicates with the nozzle 312. The pressure chamber 314 also communicates with an individual flow path 315 via a throttle portion 320. The volume of the pressure chamber 314 changes due to the deformation of the vibration plate 317. This change in volume causes ink to be ejected from the nozzle 312. The resonance period of the ink changes depending on the volume of the pressure chamber 314 and the flow path resistance of the throttle portion 320, and the volume and speed of the ejected ink change. Therefore, it is necessary to optimally adjust the volume of the pressure chamber 314, etc., as needed.

[0042] The individual flow paths 315, the common flow path 351, and the throttle section 320 are flow paths for ink. The common flow path 351 communicates with the individual flow paths 315. The individual flow paths 315 communicate with the pressure chambers 314 via the throttle sections 320. The throttle sections 320 have a width narrower than that of the individual flow paths 315. This makes it difficult for pressure waves in the pressure chambers 314 to escape to the individual flow paths 315.

[0043] A lyophilic monolayer 340 is formed on the inner wall of each of the nozzle 312, the pressure chamber 314, the throttle portion 320, the vibration plate 317, and the individual flow path 315. Details of this monolayer 340 will be described later. In addition, the monolayer 340 may be formed on the inner wall of the common flow path 351.

[0044] The nozzles 312, pressure chambers 314, individual flow paths 315, vibration plate 317, common flow path 351, and throttle portion 320 described above are fabricated, for example, by thermal diffusion bonding of multiple metal plates processed by etching or the like, or by etching a silicon material.

[0045] <Monomolecular Film 340> As shown in FIG. 4A, a monolayer 340 made of an organic compound having a property of being easily wetted by ink (lyophilic, hereinafter also referred to as wettability) is formed on the inner walls of each of the nozzle 312, the pressure chamber 314, the throttle section 320, the vibration plate 317, and the individual flow path 315.

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

[0047] An example of a material for the monolayer 340 is a material having silanol groups at the molecular end and multiple molecular chains with hydrophilic groups extending from the main skeleton. Such a material can be, for example, a superhydrophilic coating material (specifically, LAMBIC-771W) manufactured by Junsei Chemical Co., Ltd. Therefore, the monolayer 340 can be said to be a film made of a molecule having silanol groups at the molecular end and multiple molecular chains with hydrophilic groups extending from the main skeleton.

[0048] Here, a monomolecular film refers to a thin film with a thickness equivalent to just one molecule, in which molecules are aligned. A monomolecular film is also called a monomolecular layer.

[0049] When higher fatty acids or higher alcohols are dissolved in a volatile solvent such as benzene and dropped onto the water surface, a monomolecular film can be formed after the solvent evaporates. At this time, the hydroxyl and carboxyl groups of the alcohol are hydrophilic groups, so they face toward the water, while the hydrophobic long-chain alkyl groups line up away from the water (into the air). When the molecules are arranged without gaps, a monomolecular film is obtained whose thickness is exactly the length of the long-chain alkyl groups (plus the hydrophilic groups).

[0050] The material of the monolayer 340 has the characteristic of self-organizing molecular arrangement, and active silanol groups react with the substrate surface and are adsorbed. The substrate surface must have functional groups that activate the silanol groups.

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

[0052] Because monolayer materials have a specific surface on which they can chemically adsorb, once adsorbed, they do not adsorb three-dimensionally. This principle allows for the self-organization of monolayer-order films. The thickness is controlled to be extremely thin, between 5 and 30 nm, but this thickness is extremely important when forming films on the inner walls of the nozzle 312 and pressure chamber 314. If a lyophilic coating agent is used, controlling the thickness becomes difficult, resulting in thicknesses on the order of several micrometers to several tens of micrometers. If the thickness becomes too large, the throttle section 320 and nozzle 312 will be filled with the lyophilic film and become clogged. The thickness of the film formed on the surface of the diaphragm 317 is also extremely important. Because the thickness of the diaphragm 317 is approximately 10 μm, a thick film on the surface of the diaphragm 317 significantly changes the rigidity of the diaphragm 317, significantly altering the vibration characteristics transmitted from the piezoelectric element 330. The material of the monolayer 340 is not limited to the above-mentioned materials, as long as it is a material that can self-assemble and complete the reaction at a thickness on the order of a monolayer.

[0053] From the above, it can be said that the monolayer 340 is a self-assembled monolayer. A self-assembled monolayer can be formed by placing an appropriate material in a solution or vapor of organic molecules, chemically adsorbing the organic molecules to the material surface, and forming a monolayer of organic molecules with a thickness of 1 to 2 nm, with uniform orientation. A self-assembled monolayer can be easily created by simply immersing a substrate in a solution of molecules with functional groups that bond with it. Furthermore, it has high orientation and stability, and various functions can be introduced through the terminal functional groups. A self-assembled monolayer is also called a self-assembled monolayer.

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

[0055] Here, the receding contact angle and static contact angle will be explained.

[0056] When a drop of liquid is dropped onto a solid surface, the liquid becomes round due to its own surface tension, and the relationship shown in the following equation (1) holds. Equation (1) is called Young's equation. γs = γL × cosθ + γSL (1) γs: Surface tension of the solid γL: Surface tension of the liquid γSL: Interfacial tension between solid and liquid

[0057] The angle θ between the tangent of the droplet and the solid surface 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 static contact angle.

[0058] On the other hand, when the interface between the liquid and the solid is moving, i.e., when the interface of the droplet is moving, the contact angle in a dynamic situation is called the advancing contact angle and the receding contact angle. Here, we focus on the receding contact angle, which is the dynamic contact angle after the solid surface has been wetted with the liquid.

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

[0060] When the nozzle 312, the individual flow channel 315, etc. are in a dry state and the ink first comes into contact with the monolayer 340 formed on the inner wall thereof, the static contact angle is 50 degrees or more, which is a relatively high state.

[0061] 4A, no monolayer 340 is formed on the inner wall of the common flow channel 351. Therefore, the common flow channel 351 exhibits the wettability of the material that it is made of. For example, if stainless steel is used as the material for the common flow channel 351, the static contact angle will be 50 degrees or more.

[0062] In such a case, there is almost no difference in wettability with respect to ink between the common flow path 351 and the individual flow paths 315. Therefore, ink fills each flow path without causing poor wetting such as air bubbles getting caught in the ink as it flows.

[0063] If there is a large difference in wettability between the common flow path 351 and the individual flow paths 315 as the ink flows, the flow may change irregularly at that point, causing air bubbles to get caught in. The presence of air bubbles in the ink often causes ejection defects, so it is important to find a way to remove air bubbles from the ink. When the monolayer 340 is also formed on the common flow 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 spread, exhibiting high lyophilicity. At this time, the solvent component in the ink covers the inner wall surfaces of the nozzle 312, pressure chamber 314, throttle portion 320, and individual flow channel 315. In this state, even if the particles and binder in the ink try to adhere to each inner wall, they flow away without adhering because they are covered by the solvent.

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

[0066] As shown in FIG. 4B, the common flow path 351 is connected to each of the pressure chambers 314 via each of the individual flow paths 315 and each of the throttle portions 320 .

[0067] 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 is an ink supply source. The ink reservoir can be considered a second ink supply tank located between the common flow path 351 and the ink supply tank. By pressurizing or depressurizing this ink reservoir, the pressure applied to the nozzles 312 can be controlled, allowing ink to be ejected under appropriate conditions.

[0068] 4C, the common flow path 351 communicates with a supply port 353 and a discharge port 354. Ink flows from the ink reservoir into one common flow path 351 via the supply port 353, and then flows from the common flow path 351 into each pressure chamber 314 via each individual flow path 315 and each throttle portion 320. The ink that flows from each pressure chamber 314 into the other common flow path 351 is discharged from the discharge port 354. The discharged ink is collected 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 using this type of ink circulation system, fresh ink can be constantly supplied to each pressure chamber 314, and an increase in viscosity due to evaporation of the ink solvent at the location near the nozzle 312 that comes into contact with the atmosphere can be prevented. This makes it possible to achieve stable ink ejection over a long period of time.

[0070] <Inkjet device> The inkjet head 300 described above may be included 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 to be 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 a medium (which may also be called an object to be printed) on which ink droplets land.

[0071] <Evaluation of 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 carried out between a case where the monomolecular film 340 was formed on a stainless steel plate and a case where 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] In addition, a comparative evaluation of the ink ejection characteristics was carried out between a case where the monomolecular film 340 was formed on the inner walls of the nozzle 312, the pressure chamber 314, the throttle section 320, the vibration plate 317, and the individual flow path 315, and a case where the monomolecular film 340 was not formed on the inner walls of the nozzle 312, the pressure chamber 314, the throttle section 320, the vibration plate 317, and the individual flow path 315 (Example 2 and Comparative Example 2, which will be described later).

[0074] The evaluation method is as follows.

[0075] Ink was ejected from the nozzle 312, and a strobe was emitted in synchronization with the application timing of the drive waveform, irradiating ink droplets (hereinafter simply referred to as droplets), which were then observed with a camera to observe the droplet flight process. In addition, by delaying the timing of the strobe emission, droplets were observed at two different times, and the position coordinates of the droplets at the two points were measured to evaluate the angle of the droplet flight direction.

[0076] The ink used for the evaluation had a viscosity of 8 mPa·s and a surface tension of 33 mN / m. The viscosity was measured using a viscometer AR-G2 (manufactured by TA Instruments). The surface tension was measured using a surface tensiometer DSA100 (manufactured by KRUSS). The ink used for the evaluation also contained titanium oxide with a particle diameter of 1 μm and a binder material made of an organic compound.

[0077] Example 1 In Example 1, first, a silicon oxide film was formed on the surface of a stainless steel plate to a thickness of about 20 nm by a method called atomic layer deposition.

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

[0079] Then, the change over time in the contact angle of the ink on the stainless steel plate on which the monomolecular film 340 was formed was evaluated, and the evaluation results are shown in FIG.

[0080] As shown in Figure 5A, the initial static contact angle (when the ink first came into contact) was 95 degrees, and the static contact angle after 20 days of immersion in the ink was 90 degrees. This indicates that there is 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 after immersion in ink for 20 days, the receding contact angle was 12 degrees, indicating that there was almost no change in the receding contact angle over time.

[0082] In Example 1, it is believed that the monomolecular film 340 formed on the stainless steel plate prevents particles and binders in the ink from adhering to the surface of the stainless steel plate, stabilizing the surface of the stainless steel plate.

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

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

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

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

[0087] In Example 2, since the monolayer 340 was not formed on the stainless steel plate, it is believed that the particles and binder in the ink adhered to the surface of the stainless steel plate during ink immersion, causing a large change in the contact angle.

[0088] Example 2 In Example 2, first, a silicon oxide film was formed by atomic layer deposition on the inner walls of each of the nozzle 312, the pressure chamber 314, the throttle portion 320, and the individual flow path 315. Here, the material of each of the nozzle 312, the pressure chamber 314, the throttle portion 320, the diaphragm 317, and the individual flow path 315 was stainless steel.

[0089] Next, in the same manner as in Example 1, a monomolecular film 340 was formed on the inner walls of the nozzle 312, the pressure chamber 314, the throttle portion 320, the vibration plate 317, and the individual flow channel 315, respectively.

[0090] Then, as described above, the flight process of the droplets discharged from the nozzle 312 was observed and the angle of the flight direction was evaluated.

[0091] Figure 6A shows the droplet flight process. As shown in Figure 6A, the droplet ejected from the nozzle 312 was observed to elongate into a cylindrical shape with a tapered tail as it flew. It was also found that the tail flew straight. If the tail bends, the subsequent droplets also do not fly straight, but rather fly in a curved manner, reducing the accuracy of the droplet landing position. If the accuracy of the landing position decreases, the droplets cannot be applied to the targeted position, resulting in 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 droplet. In Figure 6B, when a droplet flies straight relative to the vertical direction of the nozzle 312, the flight angle is 0 degrees, and the larger the flight angle, the more curved the droplet is in flight.

[0093] The variation in the flight angle of each droplet ejected from the hundreds of nozzles 312 was expressed as three times the standard deviation (3σ), which was 17 mrad. This value means that if the distance between the nozzle 312 and the printing object is 1 mm, the variation in the landing position of the droplets will be 17 μm.

[0094] The diameter of the impacted droplets is approximately 60 μm, and the ink is applied so that the semicircular droplets overlap. In this case, if the impact positions are separated by more than 30 μm, the droplets will not overlap and an area will be left uncoated. Therefore, the target value for the accuracy of the impact position is set to within 30 μm. It was found that the target value for the impact position was achieved in Example 2.

[0095] (Comparative Example 2) In Comparative Example 2, similarly to Example 2, first, a silicon oxide film was formed by atomic layer deposition on the inner walls of each of the nozzle 312, the pressure chamber 314, the throttle portion 320, and the individual flow path 315. Here, the material of each of the nozzle 312, the pressure chamber 314, the throttle portion 320, the diaphragm 317, and the individual flow path 315 was stainless steel.

[0096] Then, as described above, the flight process of the droplets discharged from the nozzle 312 was observed and the angle of the flight direction was evaluated.

[0097] Figure 7A shows the droplet flight process. As shown in Figure 7A, the droplet ejected from the nozzle 312 was observed to elongate into a cylindrical shape with a tapered tail as it flew. It was also found that the tail was curved as it flew. It is believed that the tail was curved due to particles or binder in the ink adhering to the inner wall of the nozzle 312. As mentioned above, when the tail is curved, the subsequent droplets also do not fly straight, but rather fly in a curved manner, reducing the accuracy of the droplet landing position. As a result, the droplets cannot be applied to the targeted position, 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 those in Figure 6B. Also, in Figure 7B, as in Figure 6B, when a droplet flies straight relative to the vertical direction of the nozzle 312, the flight angle is 0 degrees, and the larger the flight angle value, the more curved the droplet is in flight.

[0099] The variation in the flight angle of each droplet ejected from the hundreds of nozzles 312, expressed in 3σ, was 86 mrad. This shows that the variation in the flight angle of each droplet is extremely large. This value means that if the distance between the nozzle 312 and the printing target is 1 mm, the variation in the landing position of the droplets will be 86 μm. In other words, droplets will unintentionally overlap or will not overlap at all, resulting in unprinted areas, which will reduce print quality.

[0100] As described above, the inkjet head 300 of this embodiment comprises a nozzle 312 that ejects liquid, a pressure chamber 314 that communicates with the nozzle 312, an individual flow path 315 that communicates with the pressure chamber 314 via a throttling section 320, a common flow path 351 that communicates with the individual flow path 315, an energy generating element (e.g., a piezoelectric element 330) that generates energy, and a vibration plate 317 that transmits the energy to the pressure chamber 314, and is characterized in that a monomolecular film 340 that is lyophilic with respect to the liquid is formed on the inner walls of each of the nozzle 312, the pressure chamber 314, the throttling section 320, the vibration plate 317, and the individual flow path 315.

[0101] This feature makes it possible to suppress adhesion of particles and binders contained in the ink to the nozzles 312, pressure chambers 314, throttle sections 320, diaphragms 317, and individual flow paths 315. This prevents clogging due to particles and binders, and allows for stable ejection over time. As a result, it is possible to achieve high print quality.

[0102] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. [Industrial Applicability]

[0103] The method for manufacturing a liquid ejection head according to the present disclosure is also useful for ejecting, for example, white ink containing titanium oxide, conductive ink containing metal nanoparticles, quantum dot luminescent ink containing quantum dot semiconductor particles, and biological ink containing cells, etc. [Explanation of symbols]

[0104] 51 nozzle hole 60 nozzle plate 61 Light Energy 62 Thermal Energy 100 nozzles 110 Pressure Chamber 111 Bulkhead 112 Diaphragm 130 Piezoelectric element 140 Piezoelectric member 200 nozzles 210 Pressure Chamber 212 Diaphragm 220 Thin-film piezoelectric element 230 Common Pressure Chamber 300 Inkjet Head 312 Nozzle 314 Pressure Chamber 315 Individual Channel 317 Diaphragm 320 Constriction section 330 Piezoelectric element 340 Monolayer 350 Liquid repellent film 351 Common flow path 353 Supply Inlet 354 Outlet

Claims

1. A method for manufacturing a liquid ejection head, comprising: The liquid ejection head includes: a nozzle for discharging a liquid; a pressure chamber communicating with the nozzle; an individual flow channel communicating with the pressure chamber via a throttle portion; a common flow path communicating with the individual flow paths; an energy generating element that generates energy; a vibration plate that transmits the energy to the pressure chamber, a film having lyophilicity with respect to the liquid is formed on an inner wall of each of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the individual flow path; forming a metal oxide film on the surface of an inner wall of each of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the individual flow path; forming a film having lyophilicity to the liquid so as to cover the metal oxide film; A method for manufacturing a liquid ejection head.

2. a static contact angle of the liquid on the inner walls of the nozzle, the pressure chamber, the throttle portion, and the individual flow path is greater than a receding contact angle; The method for manufacturing a liquid ejection head according to claim 1 .

3. The outer surface of the nozzle is liquid-repellent to the liquid. The method for manufacturing a liquid ejection 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; The method for manufacturing a liquid ejection head according to claim 3 .

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