JP7766245B2 - Inkjet head, inkjet head manufacturing method and printing device - Google Patents

Description

The present invention relates to an inkjet head, a method for manufacturing an inkjet head, and a printing device.

Inkjet printing devices that eject droplets from the nozzles of an inkjet head to form an image on a recording medium are known. When droplets are ejected from the nozzles of an inkjet head, ink can sometimes adhere to the periphery of the nozzle's ejection opening. This can cause the droplets to be ejected at a curved angle.

For example, in Patent Document 1, a nozzle plate is formed by forming a silicone resin layer on an organic film using a silane coupling agent, an alkoxysilane compound, and a fluoroalkylsilane compound, and then forming a fluororesin layer on the silicone resin layer using a fluororesin.

JP 2007-230061 A

Since the liquid-repellent properties of the nozzle surface are essential for stable droplet ejection, the liquid-repellent film must be stable over time. However, conventional liquid-repellent films, such as those shown in Patent Document 1, have had the problem of poor stability over time when exposed to ink. In particular, the liquid-repellent properties of conventional liquid-repellent films quickly deteriorate when exposed to ink containing dispersed particles of inorganic compounds such as titanium oxide. This is because titanium oxide particles are hard and have an abrasive effect, which can wear away the liquid-repellent film.

The present invention was made in light of these issues, and aims to provide an inkjet head that maintains stable liquid repellency over time, even when using ink containing inorganic compounds.

An inkjet head according to one aspect of the present disclosure includes a nozzle plate having nozzles formed therein, a pressure chamber communicating with the nozzles, a pressurizing unit that pressurizes the pressure chamber, and a diaphragm that transmits energy generated by the pressurizing unit to the pressure chamber. The outer surface of the nozzle plate is coated with a liquid-repellent film made of a diamond-like carbon film doped with fluorine.

A printing device according to another aspect of the present disclosure includes the inkjet head described above, a control unit that controls the ejection operation of the inkjet head, and a transport unit that moves the inkjet head and the print medium relative to each other.

Another aspect of the present disclosure relates to a method for manufacturing an inkjet head that ejects droplets from nozzles formed in a nozzle plate and causes the droplets to land on a print medium, and includes a liquid-repellent film process for forming a liquid-repellent film made of a fluorine-doped diamond-like carbon film on the outer surface of the nozzle plate, and a nozzle process for forming the nozzles in the nozzle plate on which the liquid-repellent film has been formed.

According to the present disclosure, a liquid-repellent film made of a fluorine-doped diamond-like carbon film is formed on the outer surface of the nozzle plate. This allows stable liquid repellency to be maintained over time, even when ejecting liquid containing inorganic compounds from the inkjet head.

Schematic cross-sectional view showing the structure of an inkjet head 1B is a schematic cross-sectional view showing the detailed positional relationship between the liquid-repellent film and the nozzle in FIG. 1A; 1A, a cross-sectional view taken along line AA of FIG. View of the inkjet head from the print medium side FIG. 1B shows another example of the configuration of an inkjet head. FIG. 1B shows another example of the configuration of an inkjet head. FIG. 10 is a diagram showing an example of the fluorine concentration of the liquid-repellent film of an inkjet head. FIG. 10 is a diagram showing an example of the contact angle of the liquid-repellent film of an inkjet head. Flowchart for explaining a manufacturing method of an inkjet head FIG. 10 is a diagram showing the contact angle of the liquid-repellent film of the inkjet head according to the first embodiment. FIG. 10 is a diagram showing the contact angle of the liquid-repellent film of the inkjet head according to Comparative Example 1. FIG. 1 is a diagram showing a droplet ejection state of an inkjet head according to a first embodiment; 1B according to another embodiment. FIG. 10 is a diagram showing the state of droplet ejection from the inkjet head when a chip occurs. FIG. 1 is a plan view showing the configuration of a printing device; A side view showing the configuration of a printing device

Embodiments of the present disclosure will be described below with reference to the drawings. Note that each embodiment described below represents a preferred specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, component placement and connection configurations, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Therefore, among the components in the following embodiments, components that are not recited in the independent claims that represent the superordinate concept of the present disclosure will be described as optional components.

<Inkjet head>
FIG. 1 (FIGS. 1A to 1D) shows an example of the configuration of an inkjet head 10. In FIG.

The inkjet head 10 of the present disclosure ejects ink droplets from nozzles formed in the nozzle plate 11, causing the droplets to land on a print medium. The ink to be ejected is not particularly limited. For example, (1) quantum dot luminescent ink containing quantum dot semiconductor particles or white decorative ink containing titanium oxide, (2) functional ink for constructing perovskite solar cells, (3) conductive ink containing metal nanoparticles, (4) biological ink containing cells, etc. may be ejected. Note that the inkjet head 10 may also eject liquids other than ink.

The inkjet head 10 comprises a nozzle plate 11 in which one or more nozzles 12 are formed, a pressure chamber 14, a pressure unit 30, and a vibration plate 17. The inkjet head 10 is used to cause ink droplets 70 (see Figure 7) ejected from the nozzles 12 to land on a print medium (not shown).

In the following description, the longitudinal direction of the inkjet head 10 is referred to as the Y direction, and the width direction perpendicular to the longitudinal direction is referred to as the X direction. Furthermore, the direction perpendicular to the X and Y directions is referred to as the Z direction. In this disclosure, the nozzle plate 11 is arranged along the X and Y directions.

- Nozzle plate -
As described above, the nozzle plate 11 is formed with nozzles 12 for ejecting ink contained in the pressure chambers 14 as droplets. The material of the nozzle plate 11 is not particularly limited, but is, for example, a metal such as stainless steel. The nozzles 12 are through-holes that are circular in plan view and are formed to penetrate the nozzle plate 11 in the Z direction.

The diameter R of the nozzle 12 is, for example, approximately 5 to 50 μm. The nozzle 12 is formed using methods such as laser processing, etching, or punching.

The shape of the nozzle 12 does not have to be straight in cross section as shown in Figure 1B. For example, as shown in the cross section of Figure 1E, the nozzle 12 may have a so-called "cone-shaped" opening that tapers gradually toward the outlet 12a. Also, as shown in the cross section of Figure 1F, the nozzle 12 may have a so-called "funnel-shaped" opening that tapers gradually toward the outlet 12a before becoming straight in cross section. The shapes of Figures 1E and 1F can be suitably achieved by forming the nozzle 12 using laser processing.

Also, as shown in Figure 1A, the nozzle plate 11 may form part of the outer wall that defines the pressure chamber 14.

-Water-repellent film-
The nozzle plate 11 has a liquid-repellent film 50 formed on its outer surface 11a (hereinafter simply referred to as the outer surface 11a) that faces the print medium, the liquid-repellent film 50 having ink-repellent properties (liquid-repellency).

The liquid-repellent film 50 is made of a diamond-like carbon film containing fluorine. There are no particular limitations on the thickness of the liquid-repellent film 50, but it is, for example, approximately 50 nm to 300 nm. If the liquid-repellent film 50 is too thin, the liquid repellency will be poor. On the other hand, if the liquid-repellent film 50 is too thick, the film stress will be large and the nozzle plate 11 will warp. In this warped state, it will be difficult to adhere to other components (e.g., the flow path plate 16) when assembling the inkjet head 10. Using a diamond-like carbon film containing fluorine as the liquid-repellent film 50 provides excellent abrasion resistance.

Some inks contain particles of inorganic compounds such as titanium oxide. In conventional technology, titanium oxide can scrape away the liquid-repellent film, degrading the liquid-repellent properties. If the liquid-repellent properties around the nozzle are impaired, the ink will spread around the nozzle, preventing the formation of an appropriate meniscus. This will prevent the inkjet head 10 from ejecting ink stably. In contrast, the inkjet head 10 of this embodiment uses a diamond-like carbon film, which gives the liquid-repellent film 50 abrasion resistance, eliminating the problems associated with the conventional technology described above.

As shown in Figures 1B and 1D, the liquid-repellent film 50 is formed with a gap secured to the nozzle 12. In other words, the liquid-repellent film 50 is not formed within a certain distance L around the ejection port 12a of the nozzle 12. In other words, a step 60 is provided between the outer surface 11a of the nozzle plate 11 and the surface 50a of the liquid-repellent film 50 at the ejection port of the nozzle 12.

The gap is not particularly limited, but is, for example, approximately 10 nm to 500 nm, and more preferably 200 nm or less. The gap is set to approximately 500 nm because if the gap is too large, the wettability around the nozzle 12 increases, and there is a risk of the ink spreading.

The liquid-repellent film 50 has a gradient in fluorine concentration in the depth direction D (Z direction). Specifically, the fluorine concentration is higher at the surface 50a of the liquid-repellent film 50 and decreases as one approaches the bottom surface (the surface in contact with the nozzle plate 11). For example, the fluorine concentration present in the liquid-repellent film 50 is approximately 1.0 atom% to 2.0 atom% near the surface and approximately 0.2 atom% to 0.5 atom% near the bottom surface.

Figure 2 shows the results of measuring the fluorine concentration of the liquid-repellent film 50. The fluorine concentration was measured using energy dispersive X-ray spectroscopy (EDX). As shown in Figure 2, it was found that fluorine was present at a concentration of 1.4 atomic % (atom%) near the surface of the liquid-repellent film 50 and at a concentration of 0.3 atomic % (atom%) near the bottom.

By providing the above-described fluorine concentration gradient, it is possible to improve adhesion between the outer surface 11a of the nozzle plate 11 and the bottom surface of the liquid-repellent film 50 while ensuring liquid repellency on the surface 50a of the liquid-repellent film 50. It also allows for more stable formation of the ink meniscus in the nozzle 12.

The relationship between the contact angles α, β, and γ with respect to the ink droplet 70 is expressed by Equation 1. The contact angle α is the contact angle of the ink droplet 70 with the surface 50a of the liquid-repellent film 50. The contact angle β is the contact angle of the ink droplet 70 with the side surface 50b of the liquid-repellent film 50. The contact angle γ is the contact angle of the ink droplet 70 with the outer surface 11a of the nozzle plate 11.
[Formula 1]
Contact angle α > Contact angle β > Contact angle γ

There are two types of contact angles: static angle and receding angle. The static angle and receding angle are explained below.

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 [Equation 2] holds. [Equation 2] is called Young's equation.
[Formula 2]
γs=γL×cosθ+γSL
γs: Surface tension of solid γL: Surface tension of liquid γSL: Interfacial tension between solid and liquid

The angle θ between the tangent of the ink droplet 70 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 angle of rest.

On the other hand, contact angles when the interface between the liquid and solid is moving, i.e., in a dynamic situation where the interface of a droplet is moving, are called the "advancing angle" and "receding angle." Here, we focus on the receding angle, which is the dynamic contact angle after the solid surface has been wetted with liquid. The receding angle of the liquid-repellent film 50 relative to the ink is, for example, 30 degrees or more.

Figure 3 shows an example comparing the values of the aforementioned contact angles α, β, and γ using specific inks as examples. In Figure 3, Ink X is an ink in which titanium oxide particles are dispersed in a solvent whose main component is water. Ink Y is an ink in which titanium oxide is dispersed in a liquid resin whose main component is acrylic monomer.

As shown in Figure 3, the relationship between contact angles α, β, and γ is as shown in Equation 1 above for both inks X and Y. This prevents liquid from adhering to the nozzle surface, enabling good droplet ejection. Note that ink X has a larger contact angle overall than ink Y, indicating low wettability (difficulty wetting).

- Pressure chamber -
Returning to FIG. 1 , the pressure chamber 14 communicates with the nozzle 12. The pressure chamber 14 also communicates with the individual flow path 15 via the throttle section 20. The volume of the pressure chamber 14 changes due to the deformation of the vibration plate 17. This change in volume causes ink to be ejected from the nozzle 12. The resonance period of the ink changes depending on the volume of the pressure chamber 14 and the flow path resistance of the throttle section 20, and the ejection volume and ejection speed of the ejected ink droplets 70 change. Therefore, it is necessary to optimally adjust the volume of the pressure chamber 14, etc., as necessary.

-Pressure section-
The pressure unit 30 is provided corresponding to the pressure chamber 14 and is displaced by application of a voltage. For example, a stacked piezoelectric element of d33 mode or d31 mode, or a piezoelectric element using a shear mode, can be used as the pressure unit 30. Furthermore, instead of the above-mentioned piezoelectric element, an energy generating element such as an electrostatic actuator or a heat generating element can be used as the pressure unit 30.

-Vibration plate-
The diaphragm 17 transmits energy generated by the pressure applying unit 30 to the pressure chamber 14. In FIG. 1, the diaphragm 17 is disposed between the pressure applying unit 30 and the pressure chamber 14 so as to be in contact with the pressure applying unit 30. The diaphragm 17 is deformed by the displacement of the pressure applying unit 30. There are no particular limitations on the material that constitutes the diaphragm 17, but it may be made of, for example, a metal such as nickel or stainless steel, or a resin such as polyimide. There are no particular limitations on the thickness of the diaphragm 17, but it is preferably 5 to 50 μm, for example.

Note that while Figure 1A shows only one nozzle 12 and its corresponding components (e.g., pressure chamber 14, throttle section 20, individual flow path 15, pressurizing section 30, etc.), multiple of these components are provided along the Y direction, as shown in Figure 1C.

- Ink flow path -
The common flow path 51, the individual flow paths 15, and the throttle portion 20 are ink flow paths.

Figure 1C is a schematic cross-sectional view showing the arrangement of the nozzles 12 and ink flow paths of the inkjet head 10.

As shown in FIG. 1C, the common flow path 51 communicates with the individual flow paths 15. The individual flow paths 15 communicate with the pressure chambers 14 via the throttle sections 20. In other words, the common flow path 51 is connected to each of the pressure chambers 14 via each individual flow path 15 and each throttle section 20.

The common flow path 51 is connected to an ink reservoir (not shown). The ink reservoir is connected to an ink supply tank (not shown), which is the ink supply source. The ink reservoir can be considered a second ink supply tank located between the common flow path 51 and the ink supply tank. By pressurizing or depressurizing this ink reservoir, it is possible to control the circulating flow rate of ink flowing through the common flow path 51 and individual flow paths 15 within the inkjet head 10. Furthermore, the pressure applied to the nozzles 12 can be controlled to eject ink under appropriate conditions.

In Figure 1C, one of the common flow paths 51 provided on the left and right sides of the drawing is connected to a supply port (not shown), and the other is connected to an outlet port (not shown). Ink flows from the ink reservoir mentioned above into one common flow path 51 via the supply port, and from the common flow path 51 flows into each pressure chamber 14 via each individual flow path 15 and each throttle section 20. Ink that flows from each pressure chamber 14 into the other common flow path 51 is discharged from the outlet port. The discharged ink is recovered in an ink recovery tank connected to the ink supply tank and flows back into the ink supply tank.

The throttle portion 20 is narrower than the width of the individual flow path 15. This makes it difficult for the pressure waves generated in the pressure chamber 14 by the deformation of the vibration plate 17 to escape to the individual flow path 15. As a result, the ink in the pressure chamber 14 is ejected from the nozzle 12 as ink droplets 70.

<Inkjet head manufacturing method>
The method for manufacturing the inkjet head 10 will be specifically described below with reference to the flowchart of FIG.

A flat nozzle plate material is used as the base of the nozzle plate 11. The nozzle plate material is made of stainless steel, nickel, or other metal materials, polyimide resin material, other organic materials, or silicon material.

In step S1, a liquid-repellent film 50 made of a fluorine-containing diamond-like carbon film is formed on the outer surface 11a of the nozzle plate material. The diamond-like carbon film is formed (deposited) using a CVD (Chemical Vapor Deposition) method (e.g., thermal CVD, photo-assisted CVD, or plasma CVD). CVD involves vaporizing a gas or liquid. The gas is then given energy by heat or light, or the gas is converted into plasma by high-frequency waves, thereby converting the source material into radicals that are adsorbed and deposited on the substrate.

To incorporate fluorine, for example, a hydrocarbon gas such as acetylene (C2H2) and a gas containing fluorine may be used as the source gas. Alternatively, after deposition of the diamond-like carbon film, the surface of the film may be treated with a gas containing fluorine to modify the surface of the diamond-like carbon film with fluorine. It is preferable to deposit the liquid-repellent film 50 by gradually increasing the fluorine concentration in the source gas during the deposition process.

In the next step S2, nozzles 12 are formed in the nozzle plate material on which the liquid-repellent film 50 has been formed, to form the nozzle plate 11.

The method for forming the nozzle 12 is not particularly limited, and the following methods can be used, for example. For example, the nozzle 12 may be formed by laser processing the nozzle plate material. Alternatively, the nozzle 12 may be formed by punching a hole in the nozzle plate material and then polishing the area around the hole. Alternatively, the nozzle 12 may be formed by etching.

In the next step S3, the inkjet head 10 is assembled.

Specifically, the above-mentioned pressure chambers 14, individual flow paths 15, diaphragm 17, common flow path 51, and throttle portion 20 (hereinafter collectively referred to as "components") are fabricated, for example, by thermal diffusion bonding of multiple metal plates processed by etching or the like. These components may also be fabricated by etching a silicon material or the like.

The nozzle plate 11 is bonded to a flow path plate 16, which has individual flow paths 15 and throttle sections 20 formed therein. The flow path plate 16 is also bonded to a vibration plate 17. The housing 18, which forms the housing of the inkjet head 10, is then bonded to the structure formed by the above bonding. The housing 18 is provided with a common flow path 51. The inkjet head 10 is then completed by bonding a pressure section 30 to the vibration plate 17.

In summary, the method for manufacturing an inkjet head 10 according to the present disclosure includes a liquid-repellent film process in which a liquid-repellent film 50 made of a fluorine-doped diamond-like carbon film is formed on the outer surface 11a of the nozzle plate 11, and a nozzle process in which nozzles 12 are formed in the nozzle plate 11 on which the liquid-repellent film 50 has been formed.

In this way, by forming the liquid-repellent film 50 on the nozzle plate 11 and then forming the nozzle 12, an area is formed around the nozzle 12 where the liquid-repellent film 50 is not formed. This improves the straightness of the flight of the ink droplets 70.

<Printing device>
The inkjet head 10 described above may be included in a printing device 9 shown in FIGS. 10 and 11 . The printing device 9 includes a transport unit. The configuration of the transport unit is not particularly limited, but may include, for example, a base 1, a guide 2 arranged on the base 1, a movable unit 7 movable along the guide 2, a transport table 3 connected to the movable unit 7 and transporting the substrate in the scanning direction, a portal gantry 4 arranged on the base 1, and a line head 5 attached to the portal gantry 4. The line head 5 is a single unit formed by arranging a plurality of inkjet heads 10 side by side. Although not shown, the printing device 9 also includes a control unit. The control unit controls the ejection operation of the inkjet head 10. The control unit may include, for example, a CPU (processor) and a memory for storing information such as programs for operating the CPU and processing results of the CPU.

Specifically, the control unit generates a drive voltage signal to be applied to the pressure unit 30. The control unit uses this drive voltage signal to control the pressure application operation of the pressure unit 30. Because the pressure unit 30 and the vibration plate 17 are bonded together, control of the pressure unit 30 is synonymous with control of the vibration plate 17, and the ejection operation of the inkjet head 10 can be controlled by controlling the pressure unit 30.

The transport table 3 moves the inkjet head 10 relative to the printing medium 6 onto which the ink droplets 70 land.

<Evaluation of Examples and Comparative Examples Depending on the Type of Liquid-Repellent Film>
The evaluation of each of the Examples and Comparative Examples will be described below.

Here, the durability of the liquid repellency was evaluated by comparative evaluation of the contact angle of the liquid repellent film 50. In Example 1, a fluorine-containing diamond-like carbon film was used as the liquid repellent film 50. In contrast, in the Comparative Example, instead of the above liquid repellent film 50, a film formed by a dehydration condensation reaction using silane coupling, as described in Patent Document 1, was used as the liquid repellent film. Apart from the liquid repellent film, the Example and Comparative Example had the same configuration.

In this comparative evaluation, contact angles were measured using a contact angle meter DSA100 (manufactured by KRUSS). Durability was evaluated by measuring the initial contact angle of the liquid-repellent film 50 and the contact angle after wiping the surface of the liquid-repellent film 50 with a cloth 300 times with water-based ink containing titanium oxide attached (hereinafter referred to as the contact angle after the friction test). The particle size of the titanium oxide was approximately 1 μm.

Example 1
In the first embodiment, an inkjet head was used in which the liquid-repellent film 50 made of a diamond-like carbon film containing fluorine was formed on the outer surface 11a of the nozzle plate 11 by CVD.

In Example 1, a liquid-repellent film 50 was formed on the outer surface of the nozzle plate 11 by CVD, and then the nozzles 12 were formed by laser processing. During this manufacturing process, a step 60 was created as shown in Figure 1. The film thickness of the water-repellent film 50 was 120 nm, and the gap L between the water-repellent film 50 and the nozzles 12 was 170 nm.

Figure 5 shows the contact angle of the liquid-repellent film 50 of Example 1. As shown by the bar graph on the left side of Figure 5, in the initial state, the static angle was 97° and the receding angle was 82°. Furthermore, as shown by the bar graph on the right side of Figure 5, the contact angles after the friction test were 95° and 61°, respectively.

The inventors have found that a receding contact angle of 40° or more is required for stable ejection of ink droplets 70.

In Example 1, it was found that by adopting the configuration of this embodiment, the liquid-repellent film 50 was scraped off by the titanium oxide, reducing the contact angle, but droplets could be ejected stably over time.

Figure 6 shows the flight state of ink droplets 70 when they are ejected using the inkjet head 10 of Example 1. The meniscus of the ink droplets 70 is stably formed from the outer surface 11a of the nozzle plate 11, where the liquid-repellent film 50 is not formed, to the side surface 50b of the liquid-repellent film 50. This demonstrates that the ink droplets 70 fly in a straight line with good flight characteristics.

(Comparative Example 1)
In Comparative Example 1, an inkjet head was used in which, instead of the liquid-repellent film 50 of Example 1, a liquid-repellent film formed by a dehydration condensation reaction using silane coupling was formed on the outer surface 11a of the nozzle plate 11 by a spin coating method.

Figure 6 shows the contact angle of the liquid-repellent film of Comparative Example 1. As shown by the bar graph on the left side of Figure 6, in the initial state, the static angle was 83° and the receding angle was 82°. Furthermore, as shown by the bar graph on the right side of Figure 6, the contact angles after the friction test were 62° and 5°, respectively.

Titanium oxide is extremely hard and has an abrasive effect. Therefore, depending on the type of liquid-repellent film, titanium oxide can wear away the film, reducing its liquid-repellent properties. Although not shown, in Comparative Example 1, it was confirmed that titanium oxide wore away most of the liquid-repellent film, significantly reducing the contact angle.

Here, with a sweepback angle of 5°, the ink is not repelled, and instead spreads wet on the liquid-repellent film 50. In this state, it is difficult for the meniscus formed at the nozzle 12 to remain stable, making it difficult for droplets to fly accurately.

As described above, the inkjet head 10 according to this embodiment comprises a nozzle plate 11 in which nozzles 12 are formed, pressure chambers 14 that communicate with the nozzles 12, a pressure unit 30 that pressurizes the pressure chambers 14, and a vibration plate 17 that transmits energy generated by the pressure unit 30 to the pressure chambers 14. Furthermore, a liquid-repellent film 50 made of a diamond-like carbon film doped with fluorine is formed on the outer surface 11a of the nozzle plate 11.

In this embodiment, a liquid-repellent film 50 made of a diamond-like carbon film is formed on the outer surface 11a of the inkjet head 10, maintaining sufficient reliability and durability. This prevents ink from adhering to the outer surface 11a, allowing for good droplet ejection. The same effect can be achieved with a printing device using the above-mentioned inkjet head 10.

In addition, in the above embodiment, an area where the liquid-repellent film 50 is not formed is provided within a certain distance (e.g., 10 nm to 500 nm) around the nozzle outlet, i.e., an area where the liquid-repellent film 50 is not formed. In other words, at the outlet 12a of the nozzle 12, a step portion 60 is provided between the outer surface 11a of the nozzle plate 11 and the surface 50a of the liquid-repellent film 50.

This further improves the reliability and durability of the inkjet head 10. This will be explained in more detail in the "Other Embodiments" section below, providing specific examples.

In the above embodiment, the relationship between the contact angle α of the surface 50a of the liquid-repellent film 50 with the ink droplets 70 ejected from the nozzles 12, the contact angle β of the side surface 50b of the liquid-repellent film 50 with the ink droplets 70 ejected from the nozzles 12, and the contact angle γ of the outer surface 11a of the nozzle plate 11 with the ink droplets 70 ejected from the nozzles 12 is expressed by the relationship in [Equation 1] described above.

This prevents particles and binders contained in the ink from adhering to the nozzle, thereby preventing clogging caused by particles and binders and achieving stable ejection over time. As a result, higher quality printing can be achieved.

<Other embodiments>
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.

For example, in the above embodiment, an example was described in which a non-forming area in which the liquid-repellent film 50 is not formed is provided within a certain distance L around the ejection port 12a of the nozzle 12, but this is not limited to this.

For example, it is possible to eliminate the need for an area around the outlet 12a of the nozzle 12 where the liquid-repellent film 50 is not formed. In other words, as shown in Figure 8, the inner wall surface 12b of the nozzle 12 and the side surface of the liquid-repellent film 50 may be configured to be substantially flush with each other.

In this case, too, if the contact angle of the ink on the surface 50a of the liquid-repellent film 50 is α, the contact angle of the side surface 50b of the liquid-repellent film 50 is β, and the contact angle of the ink on the inner wall surface 12b of the nozzle 12 is θ, the relationship between the contact angles α, β, and θ is as shown in [Equation 3].
[Formula 3]
Contact angle α > Contact angle β > Contact angle θ

This prevents the liquid from adhering to the nozzle surface, allowing for good droplet ejection. Furthermore, the meniscus of the ink droplet 70 is stably formed from the inner wall surface 12b of the nozzle 12 to the side surface 50b of the liquid-repellent film 50. This allows the ink droplet 70 to fly in a straight line with good propulsion.

In the configuration of Figure 8, after forming the nozzles 12 on the nozzle plate 11, it is recommended to form a liquid-repellent film 50 made of a diamond-like carbon film containing fluorine using the CVD method.

When forming the liquid-repellent film 50, it is possible to form the liquid-repellent film 50 while masking the nozzle 12, thereby preventing the liquid-repellent film 50 from being formed inside the nozzle 12.

In this case, as shown in Figure 8, unlike in Example 1 described above, the liquid-repellent film 50 is formed right up to the periphery of the nozzle 12's ejection port. As a result, as shown in Figure 9, chipping may occur in the corners of the liquid-repellent film 50 (diamond-like carbon film) around the nozzle 12's ejection port 12a due to friction with the print medium.

Figure 9 shows the flight state of an ink droplet 70 when it is ejected using an inkjet head 10 in which a chip has occurred in the liquid-repellent film 50. When a chip occurs as shown in Figure 9, the meniscus becomes asymmetrical on the liquid-repellent film 50, impairing the straightness of the ink droplet 70. In contrast, as shown in Example 1 above, by providing an area in which the liquid-repellent film 50 is not formed around the ejection port 12a of the nozzle 12, it is possible to make the liquid-repellent film 50 less likely to chip. This can further improve the reliability and durability of the inkjet head 10.

As described above, the inkjet head, inkjet head manufacturing method, and printing device disclosed herein are useful for ejecting, for example, quantum dot luminescent ink containing quantum dot semiconductor particles, white decorative ink containing titanium oxide, functional ink for constructing perovskite solar cells, conductive ink containing metal nanoparticles, and biological ink containing cells, and have high industrial applicability.

9 Printing device 10 Inkjet head 11 Nozzle plate 12 Nozzle 14 Pressure chamber 17 Vibration plate 30 Pressurizing unit 50 Liquid-repellent film

Claims (6)

a nozzle plate in which nozzles are formed;
a pressure chamber communicating with the nozzle;
a pressurizing unit that pressurizes the pressure chamber;
a vibration plate that transmits energy generated by the pressure unit to the pressure chamber,
a liquid-repellent film made of a diamond-like carbon film containing fluorine is formed on the outer surface of the nozzle plate;
the liquid-repellent film is not formed within a certain distance around the ejection port of the nozzle,
The fixed distance is 10 nm to 500 nm.
Inkjet head. An inkjet head as described in claim 1, wherein the fluorine concentration of the liquid-repellent film decreases with increasing depth from the surface. An inkjet head according to claim 1 or 2, wherein a step is provided between the outer surface of the nozzle plate and the surface of the liquid-repellent film at the nozzle outlet. A method for manufacturing an inkjet head that ejects droplets from nozzles formed in a nozzle plate and causes the droplets to land on a print medium, comprising:
a liquid-repellent film process for forming a liquid-repellent film made of a fluorine-doped diamond-like carbon film on the outer surface of the nozzle plate;
a nozzle step of forming the nozzle in the nozzle plate on which the liquid-repellent film is formed,
the liquid-repellent film is not formed within a certain distance around the ejection port of the nozzle,
The fixed distance is 10 nm to 500 nm.
A method for manufacturing an inkjet head. The method for manufacturing an inkjet head according to claim 4 , wherein the nozzle step comprises forming the nozzles by irradiating the nozzle plate with a laser. The inkjet head according to any one of claims 1 to 3 ;
a control unit that controls an operation of discharging droplets from the inkjet head;
A printing device including a transport unit that moves the inkjet head and the print medium relative to each other.