阅读说明：本技术 液体喷出头及喷墨装置 (Liquid ejection head and ink jet apparatus ) 是由 中谷修平 入江一伸 于 2020-10-22 设计创作，主要内容包括：本发明提供液体喷出头及喷墨装置,其为能够抑制液体中包含的颗粒等所导致的喷嘴堵塞、或流路及振动板表面上的颗粒附着,实现长期稳定的喷出的液体喷出头及喷墨装置。喷墨头具备：喷嘴,喷出液体；压力室,与喷嘴连通；独立流路,经由节流部与压力室连通；共用流路,与独立流路连通；能量产生元件,产生能量；以及振动板,将能量传递至压力室,在喷嘴、压力室、节流部、振动板和独立流路各自的内壁上,形成有对液体具有亲液性的单分子膜。(The invention provides a liquid ejection head and an ink jet device, which can inhibit nozzle blockage caused by particles contained in liquid and the like or particle adhesion on a flow path and a vibrating plate surface and realize stable ejection for a long time. The ink jet head includes: a nozzle that ejects liquid; a pressure chamber in communication with the nozzle; an independent flow path communicating with the pressure chamber via the throttle portion; a common flow path communicating with the independent flow paths; an energy generating element that generates energy; and a vibration plate for transmitting energy to the pressure chamber, wherein a monomolecular film having lyophilic to liquid is formed on the inner wall of each of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the independent flow path.)

1. A liquid ejecting head is provided with:

a nozzle that ejects liquid;

a pressure chamber in communication with the nozzle;

an independent flow path communicating with the pressure chamber via a throttle portion;

a common flow path communicating with the independent flow paths;

an energy generating element that generates energy; and

a vibration plate that transmits the energy to the pressure chamber,

a monomolecular film having lyophilic property to the liquid is formed on each inner wall of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the independent flow path.

2. A liquid ejection head according to claim 1,

the monomolecular film is a self-assembled monomolecular film.

3. A liquid ejection head according to claim 1 or 2,

the thickness of the monomolecular film is 50nm or less.

4. A liquid ejection head according to claim 1 or 2,

the monomolecular film is provided so as to cover the metal oxide film.

5. A liquid ejection head according to claim 1 or 2,

the static contact angle of the inner walls of the nozzle, the pressure chamber, the throttle section, and the independent channel with respect to the liquid is larger than the receding contact angle.

6. A liquid ejection head according to claim 1 or 2,

the surface of the outer side of the nozzle has liquid repellency to the liquid.

7. A liquid ejection head according to claim 6,

the receding contact angle of the surface of the outer side of the nozzle with respect to the liquid is 30 degrees or more.

8. An inkjet apparatus, comprising:

a liquid ejection head according to any one of claims 1 to 6;

a drive control section that generates a drive voltage signal to be applied to the energy generating element and controls an ink ejection operation of the liquid ejection head; and

and a transport unit that moves the liquid discharge head and the drawing medium relative to each other.

Technical Field

The present invention relates to a liquid ejection head and an ink jet apparatus.

Background

Conventionally, as an example of a liquid ejection head, a drop-on-demand (drop-on-demand) ink jet head capable of applying a desired amount of ink as needed in accordance with an input signal is known. For example, a piezoelectric drop-on-demand ink jet head generally includes: an ink supply flow path; a plurality of pressure chambers connected to the ink supply flow path and having nozzles; and a piezoelectric element for applying pressure to the ink filled in the pressure chamber.

Here, an example of a conventional large-capacity ink jet head will be described with reference to fig. 1A and 1B. Fig. 1A and 1B are schematic diagrams showing a cross-sectional structure of a conventional large-capacity ink jet head. Fig. 1A shows a state before voltage is applied, and fig. 1B shows a state when voltage is applied.

As shown in fig. 1A and 1B, a conventional large-capacity inkjet head includes: a plurality of nozzles 100 for ejecting droplets of ink; a pressure chamber 110 communicating with the nozzle 100 and filled with ink; a partition wall 111 partitioning the pressure chamber 110 corresponding to the adjacent nozzle 100; a vibration plate 112 constituting a part of the pressure chamber 110; a piezoelectric element 130 that vibrates the vibrating plate 112; and a piezoelectric member 140 supporting the piezoelectric element 130 and the partition 111. Although not shown, the conventional large-capacity ink jet head includes a common electrode for applying a voltage to the piezoelectric element 130 and an ink inlet.

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

The conventional large-capacity ink jet head configured as described above operates as follows.

When a voltage is applied between the common electrode (not shown) on the back surface side of the piezoelectric element 130 and the piezoelectric element 130, the piezoelectric element 130 is deformed from the state shown in fig. 1A to the state shown in fig. 1B. Specifically, in fig. 1B, the lower portion of the second piezoelectric element 130 from the left side is deformed. As a result, the volume of the pressure chamber 110 is reduced, the ink in the pressure chamber 110 is pressurized, and droplets (not shown) of the ink are ejected from the nozzle 100.

The above description has been made of an example of a conventional large-capacity ink jet head.

Further, an inkjet head is known which has an ink inlet and an ink outlet and discharges ink while circulating the ink. The effect obtained by circulating the ink will be described below.

The ink near the nozzle is always in contact with the atmosphere. Since the contact area between the ink and the atmosphere is very small, evaporation of the solvent of the ink cannot be ignored. When the solvent of the ink evaporates, the solid content concentration of the ink increases. As a result, the viscosity of the ink increases, and normal ink ejection may be difficult.

Therefore, by circulating the ink, the ink near the nozzles can be constantly replaced, and the ink near the nozzles can be constantly maintained at a normal viscosity. As a result, clogging of the nozzle can be suppressed, and normal discharge can be stably performed.

In addition, a thin film type ink jet head using a thin film piezoelectric element is known. An example of the thin film type ink jet head will be described below with reference to fig. 2A and 2B. Fig. 2A and 2B are schematic diagrams showing a cross-sectional structure of a conventional thin film type inkjet head. Fig. 2A shows a state before voltage is applied, and fig. 2B shows a state when voltage is applied.

As shown in fig. 2A and 2B, the conventional film-type ink jet head includes: a nozzle 200 for ejecting droplets of ink; a pressure chamber 210 communicating with the nozzle 200 and filled with ink; a vibration plate 212 constituting a part of the pressure chamber 210; a thin film piezoelectric element 220 provided on the upper portion of the diaphragm 212 to vibrate the diaphragm 212; and a common pressure chamber 230 that supplies ink to the pressure chambers 210.

The conventional thin film type ink jet head configured as described above operates as follows.

When a voltage is applied to the thin-film piezoelectric element 220, the thin-film piezoelectric element 220 is deformed from the state shown in fig. 2A to the state shown in fig. 2B. The volume of the pressure chamber 210 is reduced by the deformation of the thin film piezoelectric element 220, and the liquid in the pressure chamber 210 is pressurized, so that a droplet (not shown) of ink is ejected from the nozzle 200.

The above description has explained an example of a conventional film-type ink jet head.

For example, patent document 1 discloses an ink jet head in which the surface of a nozzle has a property of repelling ink (lyophobic property) in order to suppress adhesion of discharged ink, and the inner wall of the nozzle has a property of wetting with ink (lyophilic property) in order to suppress retention of air bubbles in the ink.

Here, the processing steps for rendering the nozzle lyophobic and lyophilic disclosed in patent document 1 will be described with reference to fig. 3. Fig. 3 is a schematic sectional view showing a process of processing a nozzle plate of the ink jet head disclosed in patent document 1.

First, as shown in the upper diagram of fig. 3, the surface of the nozzle plate 60 and the inner wall of the nozzle hole 51 are subjected to hydrogen termination treatment (X).

Next, as shown in the middle diagram of fig. 3, light energy 61 is applied to the surface of nozzle plate 60 to activate the reaction of the surface of nozzle plate 60. Then, the lyophobic film raw material is brought into contact with the surface of the nozzle plate 60, thereby lyophobic the surface of the nozzle plate 60 (Y).

Next, as shown in the lower drawing of fig. 3, thermal energy 62 is applied to the inner wall of the nozzle hole 51, and the lyophilic film raw material is brought into contact with the inner wall of the nozzle hole 51, whereby the inner wall of the nozzle hole 51 is hydrophilized (Z).

The surface of the nozzle plate 60 is lyophobic through the above processing steps, and therefore, the adhesion of ink can be suppressed. Further, the inner wall of the nozzle hole 50 has lyophilic properties, and therefore accumulation of air bubbles can be suppressed.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2011-68095

However, in the ink jet head of patent document 1, the lyophilic property of the ink liquid contact portion (for example, the inner wall surface of the flow path or the pressure chamber) other than the nozzles cannot be secured. Therefore, in the inkjet head of patent document 1, when an ink containing particles made of an inorganic compound, a binder component, or the like (hereinafter referred to as "particles or the like") is used, the particles or the binder component may adhere to and accumulate on an ink contact portion other than the nozzles, and may cause clogging. In particular, the binder component is a material composed of an organic compound, and is easily attached to an ink contact portion composed of a metal such as stainless steel.

For example, in a portion of the flow path of the ink jet head where the independent flow path communicates with the pressure chamber, a throttle portion, which is a flow path having a narrower width than the independent flow path, is provided in order to prevent the pressure wave in the pressure chamber from dissipating. A large shear stress is applied to the throttle portion during the ink flow. Therefore, particles and the like in the ink are easily aggregated, and the particles and the like are easily attached to the wall surface of the flow path to cause clogging.

In addition, the diaphragm vibrates at a high speed in accordance with the frequency of the ejection. For example, the diaphragm vibrates about 1000 to 50000 times in 1 second according to a frequency of about 1kHz to 50 kHz. This vibration causes a shearing force to be applied to the ink at high speed. This may break the dispersion state of the particles in the ink, cause aggregation, and adhere to the surface of the diaphragm.

Disclosure of Invention

An object of one embodiment of the present invention is to provide a liquid ejection head and an ink jet apparatus that can suppress clogging of nozzles due to particles contained in a liquid or adhesion of particles to a flow path and a vibrating plate surface, and realize stable ejection over a long period of time.

Means for solving the problems

A liquid ejection head according to an aspect of the present invention includes: a nozzle that ejects liquid; a pressure chamber in communication with the nozzle; an independent flow path communicating with the pressure chamber via a throttle portion; a common flow path communicating with the independent flow paths; an energy generating element that generates energy; and a vibration plate for transmitting the energy to the pressure chamber, wherein a monomolecular film having lyophilic property to the liquid is formed on each inner wall of the nozzle, the pressure chamber, the throttle portion, the vibration plate, and the independent flow path.

An inkjet device according to an aspect of the present invention includes: a liquid ejection head according to one aspect of the present invention; a drive control section that generates a drive voltage signal to be applied to the energy generating element and controls an ink ejection operation of the liquid ejection head; and a transport unit that moves the liquid ejection head and the drawing medium relative to each other.

Effects of the invention

According to the present invention, clogging due to particles and the like contained in the liquid can be suppressed, and stable discharge over a long period of time can be achieved.

Drawings

Fig. 1A is a schematic cross-sectional view showing a state before voltage is applied to a conventional large-capacity ink jet head.

Fig. 1B is a schematic cross-sectional view showing a state when a voltage is applied to a conventional large-capacity ink jet head.

Fig. 2A is a schematic cross-sectional view showing a state before voltage is applied to a conventional thin film type ink jet head.

Fig. 2B is a schematic cross-sectional view showing a state when a voltage is applied to the conventional thin film type ink jet head.

Fig. 3 is a schematic sectional view showing a process of processing a nozzle plate of the ink jet head of patent document 1.

Fig. 4A is a schematic sectional view showing the structure of an ink jet head according to an embodiment of the present invention.

Fig. 4B is an XY cross-sectional view of fig. 4A.

Fig. 4C is a plan view showing the arrangement of the common flow path in the entire inkjet head according to the embodiment of the present invention.

Fig. 5A is a graph showing the change with time of the contact angle after the hydrophilization treatment in example 1.

Fig. 5B is a graph showing the change with time of the contact angle after the hydrophilization treatment in comparative example 1.

Fig. 6A is a view showing a flight process of the droplets of the ink of example 2.

Fig. 6B is a view showing the flight angle of the ink droplets of example 2.

Fig. 7A is a diagram showing a flight process of the droplets of the ink of comparative example 2.

Fig. 7B is a view showing the flight angle of the droplets of the ink of comparative example 2.

Description of the reference numerals

51 nozzle hole

60 nozzle plate

61 light energy

62 heat energy

100 nozzle

110 pressure chamber

111 spacer wall

112 vibration plate

130 piezoelectric element

140 piezoelectric element

200 spray nozzle

210 pressure chamber

212 vibrating plate

220 thin film piezoelectric element

230 common pressure chamber

300 ink jet head

312 nozzle

314 pressure chamber

315 independent flow path

317 vibration plate

320 throttle part

330 piezoelectric element

340 monomolecular film

350 lyophobic film

351 share a flow path

353 supply port

354 discharge port

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

< ink jet head 300>

The structure of the ink jet head 300 according to the embodiment of the present invention will be described with reference to fig. 4A, 4B, and 4C.

Fig. 4A is a schematic sectional view showing the structure of an ink jet head 300 according to this embodiment. In addition, FIG. 4A shows the AA' cross-section of FIG. 4C. Fig. 4B is an XY cross-sectional view of fig. 4A. Fig. 4C is a plan view showing the arrangement of the common channel 351 of the entire inkjet head 300.

In the present embodiment, the case where the liquid ejection head is the ink jet head 300 that ejects ink is described as an example, but the present invention is not limited thereto. The liquid ejection head may eject liquid other than ink.

The inkjet head 300 includes: the nozzle 312, the pressure chamber 314, the piezoelectric element 330, the vibrating plate 317, the orifice 320, the independent channel 315, the common channel 351, the monomolecular film 340, and the lyophobic film 350.

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 μm to 50 μm. The nozzle 312 is formed, for example, by laser machining, etching, or punching.

A liquid repellent film 350 having a property of repelling ink (liquid repellent property) is provided on the surface of the nozzle 312. The lyophobic film 350 is formed by spin coating a liquid of a lyophobic material. By forming the liquid repellent film 350, the surface of the nozzle 312 has liquid repellency. The receding contact angle (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.

The piezoelectric element 330 (an example of an energy generating element) is provided so as to correspond to the pressure chamber 314, and is displaced by application of a voltage. As the piezoelectric element 330, for example, a multilayer piezoelectric element of d33 mode or d31 mode, or a piezoelectric element using shear mode can be used. Alternatively, an electrostatic actuator, a heat generating element, or the like may be used as the energy generating element instead of the piezoelectric element.

The vibrating plate 317 is disposed adjacent to the piezoelectric element 330, and is deformed 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 thereto. The thickness of the vibrating plate 317 is preferably 5 μm to 50 μm, for example.

When the displacement of the piezoelectric element 330 is transmitted to the vibration plate 317, the vibration plate 317 is deformed. This changes the volume of the pressure chamber 314, and a droplet of ink is ejected from the nozzle 312. Therefore, the amount of deformation of the vibration plate 317 is very important, and since the rigidity of the vibration plate 317 is related to the amount of deformation and the variation thereof affects the ejection characteristics, it is required to make the rigidity of the vibration plate 317 uniform.

The pressure chamber 314 communicates with the nozzle 312. The pressure chamber 314 communicates with the independent flow passage 315 via the throttle portion 320. The volume of the pressure chamber 314 changes due to the deformation of the vibration plate 317. The ink is ejected from the nozzle 312 due to the change in the volume. The resonance period of the ink changes depending on the volume of the pressure chamber 314 or the flow path resistance of the orifice 320, and the volume and speed of the ejected ink change. Thus, the volume of the pressure chamber 314 and the like need to be optimally adjusted as necessary.

The independent channel 315, the common channel 351, and the orifice 320 are channels of ink. The common flow path 351 communicates with the individual flow path 315. The independent flow passage 315 communicates with the pressure chamber 314 via a throttle portion 320. The throttle section 320 has a width narrower than that of the independent flow passage 315. This makes it difficult for the pressure wave in the pressure chamber 314 to escape to the independent flow passage 315.

A lyophilic monomolecular film 340 is formed on the inner walls of each of the nozzle 312, the pressure chamber 314, the orifice 320, the vibration plate 317, and the independent flow path 315. Details of the monolayer 340 will be described later. Further, the monolayer 340 may be formed on the inner wall of the common channel 351.

The nozzle 312, the pressure chamber 314, the independent channel 315, the vibration plate 317, the common channel 351, and the orifice 320 are formed by, for example, thermally diffusion bonding a plurality of metal plates subjected to processing such as etching, or etching a silicon material.

< monolayer 340>

As shown in fig. 4A, a monomolecular film 340 containing an organic compound having wettability (lyophilic, hereinafter also referred to as "wettability") to ink is formed on the inner walls of each of the nozzle 312, the pressure chamber 314, the orifice 320, the vibration plate 317, and the independent flow path 315.

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

Examples of the material of the monolayer 340 include a material having a silanol group at a molecular terminal and a plurality of molecular chains having a hydrophilic group extending from a main skeleton. As such a material, for example, a super-hydrophilic coating material (specifically, LAMBIC-771W) manufactured by genuine chemical Co. Therefore, the monomolecular film 340 can be said to be a film made of the following molecules: a molecule having a silanol group at a molecular terminal and a plurality of molecular chains having a hydrophilic group extending from a main skeleton.

Here, the monomolecular film refers to a film in which molecules are arranged in a thin film having a thickness corresponding to exactly one molecule. Further, the monomolecular film is also referred to as a "monomolecular layer".

When a higher fatty acid or a higher alcohol is dissolved in a volatile solvent such as benzene and dropped on a water surface, a monomolecular film can be formed after the solvent is volatilized. At this time, the following arrangement is made: the hydroxyl and carboxyl groups of the alcohol are hydrophilic groups and thus face the direction of water, whereas the long-chain alkyl groups of the hydrophobic groups are arranged on the side facing away from water (in the air). The molecules are arranged without gaps, and a film of a single molecule having a thickness corresponding to the length of the long-chain alkyl group (plus hydrophilic group) can be obtained.

The material of the monolayer 340 has a characteristic that molecules are arranged in a self-assembly manner, and reactive silanol groups chemically react with and are adsorbed on the surface of the substrate. The presence of a functional group for activating a silanol group on the surface of the substrate is required.

For example, a silicon oxide film is desirably formed on the surface of the substrate, and the hydroxyl group is desirably exposed. In addition, as long as the hydroxyl group is exposed on the surface of the substrate, the film formed on the surface of the substrate is not limited to silicon oxide. For example, instead of silicon oxide, aluminum oxide (Al) may be used₂O₃) Or titanium dioxide (TiO)₂) And the like. The monomolecular film 340 is provided so as to cover a silicon oxide film or a metal oxide film formed on the surface of the substrate.

The surface of the monolayer material that is capable of chemisorption is fixed and therefore does not sterically adsorb further onto it once adsorbed. By this principle, a monomolecular film is formed by self-assembly. The thickness of the film is controlled to be very thin 5nm to 30 nm. This thickness is very important when forming a film on the inner wall of the nozzle 312 or the pressure chamber 314. When a coating agent exhibiting lyophilic properties is used, it is difficult to control the thickness, and the thickness is on the order of several μm to several tens of μm. If the thickness is thick, the throttle portion 320 or the nozzle 312 is filled with a lyophilic film, thereby causing clogging. In addition, the thickness is also very important in the case of the film formed on the surface of the vibration plate 317. This is because the thickness of the diaphragm 317 is about 10 μm, and therefore, if a thick film is applied to the surface of the diaphragm 317, the rigidity of the diaphragm 317 changes greatly, and the vibration characteristics transmitted from the piezoelectric element 330 change greatly. The material of the monolayer 340 is not limited to the above-mentioned materials, as long as it is a material that completes the reaction in a monolayer thickness in a self-assembly manner.

As described above, the monolayer 340 can be said to be a self-assembled monolayer. The self-assembled monolayer can be formed by the following method: a self-assembled monolayer is formed by placing a suitable material in a solution or vapor of organic molecules to cause the organic molecules to be chemically adsorbed on the surface of the material, and forming a monolayer having a thickness of 1nm to 2nm and a uniform orientation of the organic molecules. The self-assembled monolayer can be easily produced by simply immersing the substrate in a solution of molecules having functional groups bonded to the substrate, and has high orientation and stability, and various functions can be introduced from the terminal functional groups. The self-assembled monolayer is also referred to as a "self-assembled monolayer".

The receding contact angle of a film formed from such a self-assembly 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.

Here, the receding contact angle and the static contact angle will be described.

When a liquid is dropped onto a solid surface, the liquid is rounded by the surface tension of the liquid itself, and the relationship shown in the following formula (1) is established. Equation (1) is referred to as the "Young's (Young) equation".

γs＝γL×cosθ+γSL…(1)

γ s: surface tension of solid

γ L: surface tension of liquid

γ SL: interfacial tension of solid and liquid

The angle θ formed by the tangent to the liquid droplet and the solid surface at this time is referred to as "contact angle". Herein, a contact angle at which a liquid is stationary on a solid surface and reaches an equilibrium state is referred to as a "static contact angle".

On the other hand, the contact angles in the state of interfacial movement between a liquid and a solid, that is, in the dynamic state of interfacial movement of a liquid droplet are referred to as an "advancing contact angle" and a "receding contact angle". Here, the receding contact angle, i.e. the dynamic contact angle after the solid surface has been wetted with a liquid, is of interest.

The monomolecular film 340 shown in FIG. 4A has a static contact angle with respect to ink of 30 degrees or more. The receding contact angle of the monolayer 340 shown in FIG. 4A with respect to the ink is 20 degrees or less. The meaning thereof is as follows.

In a dry state of the nozzle 312, the independent channel 315, and the like, the static contact angle when the ink first contacts the monolayer 340 formed on the inner wall of the nozzle 312, the independent channel 315, and the like is 50 degrees or more, and the contact angle is relatively large.

As shown in FIG. 4A, the monolayer 340 is not formed on the inner wall of the common channel 351. Therefore, the wettability of the material is exhibited in the common channel 351. For example, when stainless steel is used as the material of the common channel 351, the static contact angle is 50 degrees or more.

In such a case, a difference in wettability with respect to ink hardly occurs between the common channel 351 and the individual channel 315. Therefore, when the ink is filled in each flow path, a wetting failure such as entrainment of bubbles does not occur during the flow of the ink.

If there is a large difference in wettability between the common channel 351 and the individual channels 315 during the ink flow, the flow varies irregularly at that portion, and bubbles may be entrained. The presence of bubbles in the ink often causes ejection failure, and it is important to try to remove the bubbles in the ink.

When the monolayer 340 is formed also in the common channel 351, the static contact angle is not limited to the above angle, and may be a small angle of 30 degrees or less.

On the other hand, the receding contact angle of the monolayer 340 is in a small state of 20 degrees or less. When the monolayer 340 is wetted with the ink, hydrophilic groups in the monolayer 340 are developed, and high lyophilic properties are exhibited. In this case, the following states are obtained: the solvent component in the ink covers the inner wall surfaces of each of the nozzle 312, the pressure chamber 314, the throttle 320, and the independent flow path 315. In this state, even if particles or a binder in the ink adhere to each inner wall, the particles or the binder flows away without adhering due to the coating of the solvent.

In fig. 4A, only one nozzle 312 and its corresponding components (for example, the pressure chamber 314, the throttle 320, the independent flow path 315, the piezoelectric element 330, and the like) are shown, but as shown in fig. 4B, a plurality of nozzles 312 and its corresponding components are provided along the Y direction.

As shown in fig. 4B, the common flow path 351 is connected to each of the plurality of pressure chambers 314 via each of the independent flow paths 315 and each of the orifices 320.

The common channel 351 is connected to an ink reservoir (not shown). The ink reservoir is connected to an ink supply tank (not shown) as a supply source of ink. The ink reservoir may be considered to be 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 nozzles 312 can be controlled, and the ink can be discharged in an appropriate state.

As shown in fig. 4C, the common channel 351 communicates with the supply port 353 and the discharge port 354. Ink flows from the ink reservoir into one of the common channels 351 through the supply port 353, and flows from the common channel 351 into the pressure chambers 314 through the individual channels 315 and the orifice portions 320. The ink flowing from each pressure chamber 314 to the other common channel 351 is discharged from the discharge port 354. The discharged ink is collected by an ink recovery tank connected to the ink supply tank, and flows into the ink supply tank again.

By providing a pressure difference between the ink supply tank and the ink recovery tank, ink flows from the ink recovery tank to the ink supply tank. By adopting such an ink circulation system, new ink can be continuously supplied to each pressure chamber 314, and an increase in viscosity due to evaporation of the solvent of the ink at a portion in contact with the atmosphere near the nozzle 312 can be prevented. This enables stable ink ejection over a long period of time.

< ink jet device >

The ink jet head 300 may be provided in an ink jet device. The inkjet device includes, for example, a drive control unit and a transport unit in addition to the inkjet head 300. 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 to be drawn (which may also be referred to as a "printing target") on which the droplets of ink land.

< evaluation of examples and comparative examples >

Next, the evaluation of each example and comparative example will be described.

The contact angle was evaluated in comparison between the case where the monolayer 340 was formed on the stainless steel plate and the case where the monolayer 340 was not formed on the stainless steel plate (example 1 and comparative example 1 described later). The contact angle was measured using a contact angle measuring instrument DSA100 (manufactured by KRUSS).

Further, comparative evaluation of the ejection characteristics of the ink was performed for the case where the monolayer 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 independent channel 315, and for the case where the monolayer 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 independent channel 315 (example 2 and comparative example 2 described later).

The evaluation method is as follows.

The flying of the liquid droplets is observed by discharging ink from the nozzle 312, irradiating the liquid droplets (hereinafter, simply referred to as "liquid droplets") with flash light in synchronization with the timing of application of the drive waveform, and observing the liquid droplets with a camera. Further, the time of flash emission was delayed, so that the droplets at two different times, that is, at two time points were observed, and the position coordinates of the droplets at the two time points were measured, and the angle in the flight direction of the droplets was evaluated.

The ink used for the evaluation was an ink having a viscosity of 8 mPas and a surface tension of 33 mN/m. The viscosity was measured by using a viscometer AR-G2(TA instruments). The surface tension was measured by using a surface tensiometer DSA100 (manufactured by KRUSS). In addition, titanium oxide having a particle size of 1 μm and a binder material composed of an organic compound were added to the ink used for the evaluation.

(example 1)

In example 1, first, a film of silicon oxide of about 20nm was formed on the surface of a stainless steel plate. A method called "atomic layer deposition" is used for this film formation.

Then, the stainless steel sheet on which the silicon oxide film was formed was immersed in a liquid material (for example, a super-hydrophilic coating material manufactured by genuine chemical Co., Ltd.) as a raw material of the monolayer 340 for about 10 seconds. Thereafter, the immersed stainless steel plate was dried at 80 ℃ for 15 minutes using a heating furnace, thereby forming a monomolecular film 340.

Further, the change with time of the contact angle of the ink with the stainless steel plate on which the monomolecular film 340 was formed was evaluated. The evaluation results are shown in fig. 5A.

As shown in fig. 5A, the static contact angle at the initial stage (when the ink first contacts) was 95 degrees, and the static contact angle after 20 days of immersion in the ink was 90 degrees. From this, it was found that the static contact angle hardly changed with time.

As shown in fig. 5A, the initial receding contact angle was 10 degrees, and the receding contact angle was 12 degrees after immersion in ink for 20 days. From this, it was found that the receding contact angle hardly changed with time.

It is considered that in example 1, the monomolecular film 340 was formed on the stainless steel plate, whereby the adhesion of particles or a binder in the ink was suppressed, and the surface of the stainless steel plate was stabilized.

Comparative example 1

In comparative example 1, as in example 1, first, a silicon oxide film of about 20nm was formed on the surface of a stainless steel plate by atomic layer deposition.

Further, the change with time of the contact angle with ink of the stainless steel plate on which only the silicon oxide film was formed was evaluated. The evaluation results are shown in fig. 5B.

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, which showed a large change with time.

As shown in fig. 5B, the initial receding contact angle was 16 degrees, whereas the receding contact angle after 20 days of immersion in ink was 12 degrees.

It is considered that, in example 2, since the monomolecular film 340 was not formed on the stainless steel plate, particles or a binder in the ink adhered to the surface of the stainless steel plate during the ink immersion process, and the contact angle was largely changed.

(example 2)

In example 2, first, a film of silicon oxide was formed on the inner walls of each of the nozzle 312, the pressure chamber 314, the throttle 320, and the independent flow path 315 by atomic layer deposition. Here, the material constituting each of the nozzle 312, the pressure chamber 314, the throttle portion 320, the vibration plate 317, and the independent flow path 315 is stainless steel.

Then, a monolayer 340 was formed on the inner walls of the nozzle 312, the pressure chamber 314, the orifice 320, the vibration plate 317, and the independent channel 315 in the same manner as in example 1.

As described above, the observation of the flight process and the evaluation of the angle of the flight direction were performed for the liquid droplets discharged from the nozzle 312.

The flight of the droplets is shown in fig. 6A. As shown in fig. 6A, the liquid droplets flying from the nozzle 312 were observed to fly in a cylindrical shape with the tail portions thereof being tapered. In addition, it was confirmed that the tail was extended straight during flight. If the tail is curved, the subsequent droplet also flies curved instead of straight, and the accuracy of the landing position of the droplet is lowered. If the accuracy of the landing position is lowered, the droplet cannot be applied to the target position, resulting in a reduction in print quality.

Fig. 6B shows the flight angle of the liquid droplets ejected from the plurality of nozzles 312. In fig. 6B, the horizontal axis represents each nozzle, and the vertical axis represents the flight angle of the liquid droplet. In fig. 6B, when the liquid droplet flies straight in the vertical direction of the nozzle 312, the flight angle is 0 degree, and the larger the value of the flight angle, the larger the degree of curvature of the liquid droplet when flying.

When expressed by a triple standard deviation (3 σ), the deviation of the flight angle of each droplet ejected from the hundreds of nozzles 312 is 17 mrad. This value means that if the distance between the nozzle 312 and the object to be printed is 1mm, the deviation of the landing position of the droplet is 17 μm.

It is assumed that the ink is applied in such a manner that the diameter of the landed droplet is about 60 μm and the semicircles of the droplet overlap each other. In this case, if the landing position is separated by 30 μm or more, an uncoated region where the droplets do not overlap with each other is generated. Therefore, the target value of the accuracy of the landing position is set to be within 30 μm. Further, it was confirmed that in example 2, the target value of the landing position was achieved.

Comparative example 2

In comparative example 2, as in example 2, first, a silicon oxide film was formed on the inner walls of each of the nozzle 312, the pressure chamber 314, the throttle section 320, and the independent flow channel 315 by atomic layer deposition. Here, the material constituting each of the nozzle 312, the pressure chamber 314, the throttle portion 320, the vibration plate 317, and the independent flow path 315 is stainless steel.

As described above, the observation of the flight process and the evaluation of the angle of the flight direction were performed for the liquid droplets discharged from the nozzle 312.

The flight of the droplets is shown in fig. 7A. As shown in fig. 7A, the liquid droplets flying from the nozzle 312 were observed to fly in a cylindrical shape with the tail portions thereof being tapered. In addition, it was confirmed that the tail was bent during flying. It is believed that particles or binder in the ink adhere to the inner walls of the nozzle 312, causing the tail to bend. As described above, if the tail is curved, the subsequent droplet also flies curved instead of straight, and the accuracy of the landing position of the droplet is lowered. As a result, the droplets cannot be applied to the target position, resulting in a reduction in print quality.

Fig. 7B shows the flight angle of the liquid droplets ejected from the plurality of nozzles 312. The horizontal and vertical axes of fig. 7B are the same as those of fig. 6B. In fig. 7B, similarly to fig. 6B, when the liquid droplet flies straight in the vertical direction of the nozzle 312, the flight angle is 0 degree, and the larger the value of the flight angle, the larger the degree of curvature of the liquid droplet when flying.

When expressed by a triple standard deviation (3 σ), the deviation of the flight angle of each droplet ejected from the hundreds of nozzles 312 is 86 mrad. From this, it is understood that the deviation of the flying angle of each droplet is very large. This value means that if the distance between the nozzle 312 and the object to be printed is 1mm, the landing position deviation of the droplets is 86 μm. That is, the droplets may undesirably overlap each other, or produce a portion that is not overlapped at all but not printed, resulting in a reduction in print quality.

As described above, the inkjet head 300 according to the present embodiment includes: a nozzle 312 for ejecting liquid; a pressure chamber 314 in communication with the nozzle 312; an independent flow path 315 communicating with the pressure chamber 314 via a throttle portion 320; a common flow path 351 communicating with the independent flow path 315; an energy generating element (e.g., piezoelectric element 330) that generates energy; and a vibration plate 317 for transmitting energy to the pressure chamber 314, wherein a monomolecular film 340 having lyophilic property to the liquid is formed on the inner wall of each of the nozzle 312, the pressure chamber 314, the orifice 320, the vibration plate 317, and the independent flow path 315.

With the above feature, it is possible to suppress adhesion of particles, an adhesive, or the like contained in the ink in the nozzle 312, the pressure chamber 314, the throttle portion 320, the vibration plate 317, and the independent flow path 315. This can suppress clogging due to particles, a binder, or the like, and realize stable discharge over a long period of time. As a result, the print quality can be improved.

The present invention is not limited to the description of the above embodiments, and various modifications can be made without departing from the gist thereof.

Industrial applicability

The liquid ejection head and the ink jet apparatus of the present invention are useful for applications of ejecting, for example, the following inks: white ink containing titanium oxide, conductive ink containing metal nanoparticles, quantum dot luminescent ink containing quantum dot semiconductor particles, bio-ink containing cells and the like, and the like.