JP7545873B2 - Coating device nozzle - Google Patents

Description

The present invention relates to a nozzle for a coating device.

A known example of an applicator is an inkjet applicator that ejects ink to record an image on a recording medium. Inkjet applicators are generally equipped with a liquid ejection head that has an applicator nozzle for ejecting ink.

As an example of such a nozzle for an application device, Patent Document 1 describes an inkjet nozzle for printing in which at least the tip surface of the metallic ink nozzle and the inner surface of the ink nozzle's ejection hole are coated with a carbon film. This is said to reduce ink leakage and improve the straightness of the ejected ink, thereby improving the accuracy of the ink spot placement position and size when printed.

Japanese Patent Application Publication No. 60-54858

In recent years, there has been a demand for technology to paint vehicles using coating devices such as inkjet printers in order to improve the design of vehicles. However, when painting vehicles using inkjet printers, the distance between the inkjet nozzle and the vehicle to be printed is greater than when printing on paper, and the ink may be used at a high viscosity to prevent dripping, so ink must be ejected at high pressure. Furthermore, from the perspective of painting accuracy, there is a demand for nozzles with smaller diameters than the spray guns typically used for painting vehicles.

However, when using a nozzle such as that described in Patent Document 1, it has become clear that there is a problem in that when ink is ejected from a small-diameter nozzle at high pressure, the nozzle wears out due to inorganic components such as the pigment contained in the ink and the luster materials used in metallic paints.

Therefore, the present invention aims to provide a nozzle for a coating device that has excellent wear resistance.

The inventors of the present invention have conducted extensive research to solve the above problems. As a result, they discovered that the amount of wear on the nozzle can be reduced by providing a layer containing diamond crystal grains on at least the surface of the nozzle's discharge hole, and have completed the present invention.

That is, the present invention is a nozzle for a coating device for coating a fluid onto a substrate, characterized in that a layer containing diamond crystal grains is formed on at least the surface of the discharge hole that comes into contact with the fluid.

According to the nozzle for an applicator of the present invention, a layer of diamond crystal grains, which is harder than the components contained in high-viscosity ink, is provided at least on the surface of the ejection hole that comes into contact with a fluid such as ink. This makes it possible to obtain a nozzle for an applicator with excellent abrasion resistance.

1 is a schematic diagram showing an ink ejection head equipped with a nozzle according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a nozzle according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration in which conductive diamond crystal grains are bonded together by a conductive binder in a layer containing diamond crystal grains. FIG. 2 is a schematic diagram showing an apparatus for measuring wear resistance. FIG. 2 is a schematic diagram showing a measuring device for resistivity and surface temperature. FIG. 2 is a graph showing the relationship between the average grain size of diamond crystal grains and the surface roughness of a sintered compact containing diamond crystal grains. FIG. 1 is a graph showing the relationship between the surface roughness of a sintered compact containing diamond crystal grains and the pressure loss obtained by liquid simulation.

The present invention is a nozzle for a coating device for coating a fluid onto a substrate, characterized in that a layer containing diamond crystal grains is formed on at least the surface of the discharge hole that comes into contact with the fluid.

In the technology described in Patent Document 1 above, a nozzle made of metal such as stainless steel is used in the inkjet nozzle for printing in office equipment. However, when painting a vehicle, in addition to the distance between the nozzle and the vehicle to be painted being large, it is necessary to use a high-viscosity ink as the paint to prevent dripping. Therefore, although there is no problem with the wear resistance of the nozzle under the application conditions of the inkjet nozzle for printing in office equipment, it was found that the wear resistance is insufficient under the application conditions of the application device for vehicles, which applies high-viscosity ink under high-pressure conditions.

In contrast, in the nozzle for application device of the present invention, a layer containing diamond crystal grains is formed at least on the surface of the discharge hole that comes into contact with the fluid. Diamond crystal grains are harder than inorganic components such as pigments and luster materials contained in high-viscosity inks such as inks for vehicle painting. Diamond crystal grains are also harder than cemented carbide such as stainless steel and WC. Therefore, by forming a layer containing diamond crystal grains on the surface of the discharge hole of the nozzle, the wear resistance of the nozzle can be increased.

In addition, diamond crystal grains are resistant to oxidation and have excellent thermal conductivity, so providing a layer containing diamond crystal grains can prevent oxidation and deterioration of the nozzle. Also, since the heat capacity of the ink can be suppressed, deterioration of the ink pigment can be prevented.

The following describes an embodiment of the present invention with reference to the drawings, but the technical scope of the present invention is not limited to the following form. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

[Nozzle for coating device]
The present invention relates to a nozzle for a coating device for coating a fluid onto a substrate, in which a layer containing diamond crystal grains is formed at least on the surface of the discharge hole that comes into contact with the fluid.

As an example of the applicator, an inkjet applicator can be used. Inkjet applicators are generally equipped with an ink ejection head for ejecting ink.

Figure 1 shows an outline of an ink ejection head 1 according to one embodiment. The mechanism by which the ink ejection head 1 ejects ink may be a mechanism that uses an ink chamber 3 that is deformable by a piezoelectric element 2. The ink chamber 3 is provided with a liquid supply path 4 through which ink flows as a fluid, and a nozzle (nozzle plate) 5 equipped with an ink ejection hole 8 that ejects ink. The arrows in the figure indicate the direction of flow of ink as a fluid. When the volume of the ink chamber 3 contracts, ink is ejected as droplets 6 from the ink ejection hole 8, and when the volume of the ink chamber expands, ink is introduced into the ink chamber 3 from the liquid supply path 4.

Figure 2 shows a cross-sectional view through the ink ejection hole 8 in the nozzle (nozzle plate) 5 of this embodiment. As shown in Figure 2, the nozzle (nozzle plate) 5 may have a conical ejection hole upstream portion 8a upstream of the ink ejection hole 8 and a cylindrical ejection hole downstream portion 8b downstream in order to optimize the flow of ink. The nozzle plate may have multiple ink ejection holes that are through holes, and these through holes may be arranged, for example, in a matrix at equal intervals in the nozzle plate (not shown).

In the nozzle of this embodiment, a layer containing diamond crystal grains is formed at least on the surface of the nozzle outlet that comes into contact with the fluid. The layer containing diamond crystal grains may be formed at least on the surface of the nozzle outlet, and for example, as shown in FIG. 2(a), the entire nozzle plate 5 may be a layer containing diamond crystal grains 7a. Also, as shown in FIG. 2(b), a layer containing diamond crystal grains 7b may be formed on the surface of the upstream part 8a of the outlet hole and the surface of the downstream part 8b of the outlet hole. Also, as shown in FIG. 2(c), a layer containing diamond crystal grains 7c may be formed on the surface of the downstream part 8b of the outlet hole. One preferred embodiment is a form in which a layer containing diamond crystal grains is formed in the most downstream part of the downstream part 8b of the outlet hole.

In the nozzle of the present invention, the ink ejection hole preferably includes a cylindrical structure as shown in the ejection hole downstream portion 8b. The cylindrical structure preferably has an inner diameter of 0.03 to 1.0 mm, more preferably 0.05 to 0.1 mm. The cylindrical structure also preferably has a length (height) of 10 μm to 1 mm.

The layer containing diamond crystal grains is not particularly limited, but may be a layer containing polycrystalline diamond (PCD). The polycrystalline diamond may be, for example, a synthetic polycrystalline diamond material containing 88% by volume or more, preferably 90% by volume or more, of diamond crystal grains. The synthetic polycrystalline diamond material may be prepared by a conventional method. For the specific form of polycrystalline diamond, see, for example, JP 2012-528780 A. As the polycrystalline diamond, for example, conductive (EC)-PCD-synthetic diamond powder may be used.

The average grain size of the diamond crystal grains is not particularly limited, but is preferably 0.01 to 100 μm, and more preferably 0.1 to 60 μm. As described below, the surface roughness of the layer containing diamond crystal grains can be controlled by adjusting the average grain size of the diamond crystal grains. According to one embodiment, it is preferable for the average grain size of the diamond crystal grains to be 10 μm or less, since this reduces the surface roughness and the pressure loss.

The volume ratio of the diamond crystal grains in the layer containing the diamond crystal grains is preferably 50 volume % or more, and more preferably 70 volume % or more. If it is in the above range, the wear resistance can be further improved.

For example, in the nozzle of this embodiment, the entire nozzle plate 5 may be layer 7a containing diamond crystal grains, as shown in FIG. 2(a) above. When the entire nozzle plate 5 is a layer containing diamond crystal grains, the volume ratio of diamond crystal grains in the nozzle of this embodiment is preferably 50 volume % or more. If it is in the above range, the wear resistance can be further improved. As shown in FIG. 2(b) and (c) above, even when the nozzle plate 5 has layers 7b and 7c containing diamond crystal grains on the surface that contacts the fluid, the wear resistance can be further improved if the volume ratio of diamond crystal grains in the layers 7b and 7c containing diamond crystal grains is 50 volume % or more.

In addition, in the nozzle of this embodiment, it is preferable that the volume ratio of diamond crystal grains increases from the upstream part to the downstream part of the surface that contacts the fluid. Taking the nozzle shown in Figures 2 (a) to (c) as an example, the flow rate of ink as a fluid introduced into the discharge hole 8 of the nozzle (nozzle plate) 5 is relatively higher in the downstream discharge hole downstream part 8b, which is the downstream part, than in the upstream discharge hole upstream part 8a, which is the upstream part. Therefore, by increasing the volume ratio of diamond crystal grains on the surface of the downstream discharge hole downstream part 8b, which is the downstream part, and increasing the hardness, sufficient wear resistance can be more effectively ensured even when the fluid contacts the surface at a high flow rate. In addition, it is more effective in preventing oxidation deterioration of the nozzle. As a preferred embodiment, as shown in Figure 2 (c), a structure in which a layer having diamond crystal grains is not provided on the surface of the discharge hole upstream part 8a, and a layer having diamond crystal grains 7c is provided on the surface of the discharge hole downstream part 8b.

The surface roughness of the layer containing diamond crystal grains is not particularly limited, but it is preferable that the surface roughness of the surface of the ejection hole in contact with the fluid (the inner surface of the ink ejection hole of the nozzle) is 0.3 μm or less. The smaller the surface roughness of the surface of the ejection hole in contact with the fluid, the more the pressure loss when ejecting the ink, which is the fluid, can be suppressed. In the nozzle of this embodiment, if the surface roughness is 0.3 μm or less, the pressure loss between the inlet and outlet of the ink ejection hole of the nozzle can be sufficiently reduced even when high-viscosity ink is used as the fluid. As a result, the ink flow is improved and it can be suitably used for applying high-viscosity ink. The surface roughness Ra of the layer containing diamond crystal grains can be adjusted by the average particle size of the diamond crystal grains (or conductive diamond crystal grains) constituting the layer containing diamond crystal grains, as shown in FIG. 3, and the smaller the average particle size, the smaller the surface roughness tends to be. In one embodiment, it is preferable that the average particle size of the diamond crystal grains is 10 μm or less, because the surface roughness in the above range can be easily obtained. The lower limit of the surface roughness of the layer containing diamond crystal grains is not particularly limited, but is substantially 0.1 μm or more, and preferably 0.16 μm or more. The surface roughness of the layer containing diamond crystal grains can be determined, for example, by image analysis of a scanning electron microscope photograph.

The layer containing diamond crystal grains is preferably a layer containing conductive diamond crystal grains that generate heat when exposed to external electrical energy. When the layer containing diamond crystal grains generates heat when exposed to external electrical energy, the layer containing diamond crystal grains acts as a heating element to heat the fluid and reduce the viscosity of the fluid. This makes it possible to eject high-viscosity ink without clogging the nozzle. It also makes it possible to reduce the heat capacity of the droplets. And since the ink is quickly cooled after ejection and returns to its high viscosity, dripping when applied to a vertical surface can be prevented, and a smooth coating surface can be obtained.

An example of the conductive diamond crystal grains is boron-doped diamond. The specific form of the boron-doped diamond is not particularly limited, and conventionally known knowledge can be appropriately adopted.

The means for externally applying electrical energy to the layer containing conductive diamond crystal grains is not particularly limited, and a terminal can be attached to the layer containing conductive diamond crystal grains and connected to a DC power source to apply a voltage and pass a current. The magnitude of the current is preferably within a range in which the layer containing conductive diamond crystal grains generates heat and the ink can be heated to reduce its viscosity, and can be adjusted according to the shape of the nozzle, the resistivity of the layer containing conductive diamond crystal grains, the composition of the ink, etc.

In this case, the layer containing conductive diamond crystal grains preferably has a resistivity of 0.1 to 100 Ω·cm, more preferably 5 to 90 Ω·cm. When the resistivity of the layer containing conductive diamond crystal grains is 0.1 Ω·cm or more, it generates heat when a current is passed through the layer containing conductive diamond crystal grains, and is excellent in the effect of reducing the viscosity of the ink. On the other hand, when the resistivity of the layer containing conductive diamond crystal grains is 100 Ω·cm or less, the heat generation temperature does not become too high, so that the ink pigment is less likely to deteriorate. The resistivity of the layer containing conductive diamond crystal grains can be adjusted by changing the type and amount of the conductive diamond dopant, the volume ratio of the conductive diamond crystal grains in the layer containing conductive diamond crystal grains, and the type and amount of the conductive binder, if used, as described below. The resistivity can also be adjusted by changing the average particle size of the conductive diamond crystal grains. The smaller the average particle size of the conductive diamond crystal grains, the larger the area of the contact interface between the diamond particles and the conductive binder, and therefore the larger the resistivity. The resistivity of the layer containing conductive diamond crystal grains can be measured by the method described in the examples.

(Conductive binder)
The layer containing conductive diamond grains preferably contains a conductive binder that binds the conductive diamond grains together. As shown in Fig. 3, in one embodiment of the present invention, the conductive binder 12 exists between the particles of the conductive diamond grains 11, and binds the conductive diamond grains 11 together. By using the conductive binder 12, the conductivity of the layer containing conductive diamond grains can be appropriately adjusted. This makes it easier to adjust the temperature when heating the layer containing conductive diamond grains by current, and the viscosity of the ink can be adjusted more effectively.

The conductive binder is not particularly limited, but may be, for example, particles of Co, Si, Ni, Cr, Mo, Ti, B, WC, Cu, or Sn. Two or more types of binder may be used. By appropriately selecting the type of conductive binder, the resistivity of the layer containing the conductive diamond crystal grains can be adjusted, and the conductivity can be adjusted. The average particle size of the conductive binder is not particularly limited, but is preferably smaller than the average particle size of the conductive diamond crystal grains, for example, 0.01 to 30 μm, and preferably 0.1 to 10 μm.

In the layer containing conductive diamond crystal grains, the volume ratio of the conductive diamond crystal grains to the conductive binder is not particularly limited. For example, the volume ratio of the conductive diamond crystal grains to the total amount of the conductive diamond crystal grains and the conductive binder is 30 to 100 volume%, preferably 50 volume% or more, and more preferably 50 to 90 volume%. If the volume ratio of the conductive diamond crystal grains is 30 volume% or more, particularly 50 volume% or more, the wear resistance is excellent. In addition, the larger the volume ratio of the conductive diamond crystal grains, the higher the resistivity becomes, and the heat can be generated with a small current to heat the fluid, so the volume ratio of the conductive diamond crystal grains is preferably 30 volume% or more, and more preferably 50 volume% or more. When two or more types of conductive binders are used, the total amount is preferably within the above range.

When the layer containing conductive diamond crystal grains contains conductive diamond crystal grains and a conductive binder, the combined amount of the conductive diamond crystal grains and the conductive binder is preferably 90 volume % or more, more preferably 95 volume % or more, and even more preferably 99 volume % or more, of the total volume of the layer containing diamond crystal grains.

(Method of making a nozzle including a layer having diamond grains)
There is no particular restriction on the method of producing a nozzle including a layer having diamond crystal grains. For example, a powder of diamond crystal grains is prepared and mixed with a conductive binder as necessary. This is placed in a suitable mold and sintered in an ultra-high pressure and high temperature generating device to produce a nozzle. There is no particular restriction on the sintering conditions, but for example, conditions of heating and holding at 1300 to 1500°C and holding at a pressure of 5 to 6 GPa for 15 to 50 minutes can be adopted.

When a layer containing diamond crystal grains is formed on the surface of the ink ejection hole of a nozzle, for example, a method using CVD coating can be adopted. For example, a nozzle plate made of cemented carbide is prepared, and a layer containing diamond crystal grains can be coated on the surface of the ink ejection hole of the nozzle using a hot filament type CVD device. The conditions such as temperature and pressure at this time are not particularly limited. As an example, the conditions include a base material temperature of 650 to 800°C, a gas pressure of 500 Pa, and a gas flow rate ratio of H ₂ :CH ₄ = 100:1, and the material is maintained for 24 hours. When a layer containing boron-doped diamond is formed as a layer containing conductive diamond crystal grains, a boron compound such as trimethylboron can be further used as the raw material gas. The thickness of the layer containing diamond crystal grains is also not particularly limited. At this time, the volume ratio of diamond crystal grains in the layer containing diamond crystal grains can be adjusted to a desired value by changing the gas composition and the flow rate ratio of each component.

(ink)
The ink as a fluid to be applied using the application device having the nozzle of the present embodiment is not particularly limited as long as it can be applied to a substrate. Known inks such as water-based inks, oil-based inks, and emulsion inks can be used.

The ink may contain a resin such as an acrylic resin, a polyester resin, or an epoxy resin, and a solvent. If necessary, colorants, luster materials, additives such as surfactants, neutralizers, stabilizers, thickeners, defoamers, surface conditioners, UV absorbers, and antioxidants, and inorganic fillers such as silica may be further blended. Examples of colorants include inorganic pigments such as titanium oxide, carbon black, iron oxide, chromium oxide, and Prussian blue, organic pigments such as azo pigments, anthracene pigments, perylene pigments, quinacridone pigments, indigo pigments, and phthalocyanine pigments, and dyes. Examples of luster materials include aluminum flakes and mica. The luster materials are not particularly limited, but are preferably flake-shaped particles with an average particle size of about 10 μm to 1 mm and an average thickness of about 0.1 to 15 μm, and may be used in an amount of 20 to 40% by mass based on the total amount of ink.

There are no particular limitations on the viscosity of the ink, but the effects of the present invention can be more pronounced with a high-viscosity ink, for example, with a viscosity of 70 mPa·s or more at 25°C, preferably 90 mPa·s or more.

The nozzle of the present invention can be suitably used in coating devices for coating objects such as, but not limited to, automobiles, motorcycles, and other motor vehicles or parts thereof, large vehicles such as trucks, buses, construction machinery, and railroad cars, and other parts thereof.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

Example 1
As the conductive diamond grains, EC-PCD-synthetic diamond powder (boron-doped diamond) with an average grain size of 5 μm was prepared. Co powder (average grain size 1.5 μm) was used as the conductive binder, and the EC-PCD-synthetic diamond powder and Co powder were sintered and bonded at a volume ratio of 50% by volume by 50% by volume under high temperature and high pressure to obtain a sintered body with a diameter of 30 mm and a thickness of 1 mm. Specifically, the EC-PCD-synthetic diamond powder and the conductive binder were mixed and inserted into a mold, and heated and held in an ultra-high pressure and high temperature generating device at 1300 to 1500 ° C and a pressure of 5 to 6 GPa for 15 to 50 minutes.

(Examples 2 to 6, 8, 9, and 11)
Except for changing the EC-PCD-synthetic diamond powder and conductive binder as shown in Table 1 below, a φ30 mm×1 mmt sintered body was obtained in the same manner as in Example 1. In Example 5, Co powder (average particle size 1.5 μm) and Si powder (average particle size 1.5 μm) were mixed at Co:Si=9:1 (volume ratio) as the conductive binder.

(Example 7)
A 20μm thick boron-doped polycrystalline diamond film was formed by CVD on a carbide (WC) substrate with 5% Co, φ30mm×1mmt. CVD coating was performed using a carbide substrate in a hot filament CVD apparatus with the substrate temperature at 650-800°C, gas pressure at 500Pa, and gas flow ratio _H2 : _CH4 =100:1 for 24 hours. Boron was added to the diamond by supplying 6000ppm of trimethylboron B( _CH3 ) ₃ diluted with hydrogen to 1000ppm with respect to the methane supply.

The resulting boron-doped polycrystalline diamond film had a volume ratio of diamond crystal grains of 100% by volume.

Example 10
A 20μm thick boron-doped polycrystalline diamond film was formed by CVD on a carbide (WC) substrate with 5% Co, φ30mm×1mmt. CVD coating was performed using a carbide substrate in a hot filament CVD apparatus with the substrate temperature at 650-800°C, gas pressure at 500Pa, and gas flow ratio _H2 : _CH4 =100:5 for 24 hours. Boron was added to the diamond by supplying 6000ppm of trimethylboron B( _CH3 ) ₃ diluted with hydrogen to 1000ppm with respect to the methane supply.

The resulting boron-doped polycrystalline diamond film had a diamond crystal grain volume ratio of 50% by volume. The remaining 50% by volume was a diamond-like carbon film component that contained graphite (SP2) that had not completely crystallized into diamond (SP3).

(Comparative Example 1)
A sample of φ30 mm×1 mmt was cut out from a SUS304 plate.

(Comparative Example 2)
A sample of φ30 mm × 1 mm thickness was cut out from a φ30 mm round bar of cemented carbide (WC).

(Wear resistance test)
The wear resistance test was carried out by the ball-on-disk method. The ball used was made of copper, φ3/8 inch, with a surface roughness Ra of 0.1 μm. The disks used were the samples prepared in the above examples and comparative examples. A load was applied to the ball as shown in FIG. 4, and the disk was rotated to measure the specific wear rate of the disk. The test conditions and evaluation method were as follows:
Test conditions Load: 10N
Rotation speed: 1000 rpm
Temperature: 30°C
Test time: 300 min
Evaluation method: specific wear rate.

The evaluation results of the wear resistance test are shown in Table 1 below. As shown in Table 1, it was found that all of Examples 1 to 11, which have a layer containing diamond crystal grains, were able to significantly reduce the amount of wear compared to the stainless steel of Comparative Example 1 and the cemented carbide of Comparative Example 2. Furthermore, a comparison of Examples 1, 3, 4, and 5 showed that, if the average grain size of the diamond crystal grains is the same, the larger the volume ratio of the diamond crystal grains, the higher the wear resistance tends to be, and that a volume ratio of diamond crystal grains of 50 volume % or more is preferable.

(Measurement of resistivity and surface temperature)
The resistivity and surface temperature of the layer containing diamond crystal grains were measured by disk heating test.The sample prepared in the above-mentioned embodiment was used as the disk.As shown in FIG.5, polyester resin organic solvent-based paint, which is made by adding aluminum flakes with an average particle size of 30 μm and an average thickness of 2.0 μm to polyester resin in an amount of about 30 mass% relative to the total amount of paint, was applied to the surface of the disk with an application amount of 2 μL.

(Measurement of resistivity)
The contact resistance was measured when a current of 2 A was passed over a distance of 1 cm on the surface of the disk sample, and the specific resistance was calculated according to the following formula:
Specific resistance ρ = (contact resistance R x cross-sectional area S) / length L
Here, the contact resistance R is the electrical resistance measured by the four-terminal method, the cross-sectional area S is the cross-sectional area of the disk, and the length L is the length of the disk.

(Measurement of heating temperature)
The surface temperature of the disk was measured using a thermocouple after 5 seconds when a current of 2 A, 4 A, and 6 A was applied. Here, the initial surface temperature of the disk was 10° C., and the viscosity of the paint was 135 mPa·s.

The results are shown in Table 2. In Table 2, the paint viscosity when 6A was applied was calculated based on the disk surface temperature measured above, by measuring the change in viscosity of the paint with respect to the temperature in advance. The evaluation criteria for paint viscosity when 6A was applied are as follows:
◯: Viscosity decreases due to a stable temperature rise. △: The temperature is unstable and the viscosity is difficult to reduce, or the temperature rise is so great that there is a risk of the ink pigment deteriorating.

As shown in Table 2 above, in Examples 1 to 11, the layer containing diamond crystal grains is a layer containing boron-doped diamond and conductive diamond crystal grains that generate heat when exposed to external electrical energy. It was confirmed that such a layer containing conductive diamond crystal grains generates heat when exposed to electrical energy, heating the paint and reducing the viscosity of the paint.

Even when the layer containing conductive diamond crystal grains is bonded with a conductive binder as in Examples 1 to 6, 8, 9, and 11, heat is generated by electrical energy, and the paint is heated, resulting in a decrease in viscosity of the paint. Even when the layer containing conductive diamond crystal grains is coated on the surface of the substrate as in Examples 7 and 10, heat is generated by electrical energy, and the paint is heated, resulting in a decrease in viscosity of the paint.

In particular, it was found that in Examples 1 to 9, in which the resistivity of the layer containing conductive diamond crystal grains is 0.1 to 100 Ω·cm, as in Examples 1 to 8, a stable temperature rise leads to a sufficient viscosity reduction. It was also found that the pigment is less likely to deteriorate due to an excessive temperature rise. In contrast, in Example 10, in which the resistivity exceeds 100 Ω·cm, it is difficult to achieve a stable temperature rise, and the viscosity of the paint is less likely to decrease. Also, in Example 11, in which the resistivity is below 0.1 Ω·cm, the temperature rise is too large, which may cause deterioration of the ink pigment.

In addition, when the volume ratio of diamond crystal grains in the layer containing diamond crystal grains is 50 volume % or more as in Examples 1 to 8, the electrical conductivity is excellent and the effect of reducing the viscosity of the paint is high.

(Average diamond grain size, surface roughness and pressure loss)
The average grain size of diamond crystal grains was changed, and sintered compacts were produced using a conductive binder in the same manner as in the above examples. The surface roughness Ra of the produced sintered compacts was measured, and the relationship between the average grain size of diamond crystal grains and the surface roughness Ra was obtained. The surface roughness was obtained by image analysis of scanning electron microscope photographs. Figure 6 shows the upper and lower limits of the surface roughness relative to the average grain size. From Figure 6, for example, when the average grain size is 10 μm, it can be said that the surface roughness Ra is in the range of 0.16 to 0.3 μm.

The viscosity of the high-viscosity ink was 100 mPa·s, the length of the cylindrical ink ejection hole was 300 μm, the diameter (inner diameter) of the ink ejection hole was 30 μm, the inlet pressure was 100 kPa, and the friction coefficient was the surface roughness Ra. The pressure loss between the inlet and outlet when the friction coefficient was changed was obtained from a fluid simulation. A nozzle shape model was created using the flow analysis software star-ccm+ manufactured by Siemens, and the surface roughness (friction coefficient) of the ink ejection hole was changed to obtain the pressure loss between the inlet and outlet of the ink ejection hole. The results are shown in FIG. 7. If the pressure loss is 80 kPa or less, it can be said that the pressure loss is sufficiently small and the ink flow is better. The surface roughness Ra that satisfies the pressure loss of 80 kPa or less was 0.3 μm or less. Table 3 shows the surface roughness of the layer containing diamond crystal grains of the samples prepared in each example and the results of the pressure loss obtained from the fluid simulation. In Table 3, the evaluation criteria for pressure loss are as follows:
◯: Pressure loss is 80 kPa or less.
Δ: Pressure loss exceeds 80 kPa.

As shown in Table 3 and Figures 6 and 7, it was found that by controlling the surface roughness Ra of the layer containing diamond crystal grains to 0.3 μm or less, the pressure loss in the nozzle can be reduced when using high viscosity ink.

1 ink ejection head,
2 Piezoelectric element,
3 ink chamber,
4 liquid supply passage,
5. Coating device nozzle (nozzle plate),
6 droplets,
7a, 7b, 7c layers containing diamond grains;
8 ink ejection hole (ejection hole),
8a upstream of the discharge hole,
8b downstream of the discharge hole,
11 conductive diamond grains,
12 conductive binder,
Ra: surface roughness.

Claims (6)

A nozzle for a coating device for coating a fluid onto a substrate, the nozzle having a layer including diamond grains formed on at least a surface of a discharge hole that comes into contact with the fluid ,
A nozzle for a coating device , wherein the layer containing diamond crystal grains is a layer containing conductive diamond crystal grains that generate heat by electrical energy from an outside source. The nozzle for a coating apparatus according to claim 1 , wherein the layer containing the conductive diamond crystal grains contains a conductive binder that binds the conductive diamond crystal grains together. 3. The nozzle for a coating apparatus according to claim 1 , wherein the layer containing the conductive diamond crystal grains has a resistivity of 0.1 to 100 Ω·cm. The nozzle for a coating apparatus according to any one of claims 1 to 3 , wherein a volume ratio of said diamond crystal grains in said layer containing said diamond crystal grains is 50 volume % or more. A nozzle for a coating device for coating a fluid onto a substrate, the nozzle having a layer including diamond grains formed on at least a surface of a discharge hole that comes into contact with the fluid,
A nozzle for an applicator, wherein the volume ratio of the diamond crystal grains increases from an upstream portion to a downstream portion of the surface in contact with the fluid . The nozzle for a coating apparatus according to any one of claims 1 to 5 , wherein the layer containing diamond crystal grains has a surface roughness Ra of 0.3 µm or less.