Nozzle plate, inkjet head, and image forming apparatus

Abstract

Provided is a nozzle plate having a nozzle hole for discharging droplets, wherein the nozzle hole has a first flow path and a second flow path disposed downstream of the first flow path with respect to the discharge direction of the droplets so as to communicate with the first flow path. In the first flow path, the cross-sectional area orthogonal to the discharge direction on the most upstream side of the discharge direction is greater than the cross-sectional area orthogonal to the discharge direction on the most downstream side, and the first flow path includes the center axis of the nozzle hole. In a cross section parallel to the discharge direction, the incline, with respect to the discharge direction, of a straight line joining the most upstream end and the most downstream end of the wall surface of the second flow path disposed on one side in relation to the center axis is less than the incline, with respect to the discharge direction, of a straight line joining the most upstream end and the most downstream end of the wall surface of the first flow path disposed on said one side, and the minimum cross-sectional area SA of the first flow path and the minimum cross-sectional area SB of the second flow path satisfy the relationship of formula (1).　Formula (1): SA > 13SB

Description

[Technical Field]

[0001] The present invention relates to a nozzle plate, an inkjet head, and an image forming apparatus. [Background technology]

[0002] Inkjet heads used in inkjet printers and the like have a nozzle plate on the surface from which the liquid droplets (ink) are ejected, which is equipped with numerous tiny nozzle holes.

[0003] Such a nozzle plate, as described in Patent Document 1, for example, has a flow path having a tapered shape and a flow path having a wall surface parallel to the direction of droplet discharge. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-267951 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when an inkjet head using a conventional nozzle plate, as described in Patent Document 1, is driven continuously, air may be drawn into the inkjet head during the ink retraction process that occurs just before ink ejection, potentially leading to a decrease in ejection stability.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a nozzle plate, an inkjet head, and an image forming apparatus that can suppress the entrapment of air inside the inkjet head. [Means for solving the problem]

[0007] A nozzle plate according to an embodiment of the present invention for solving the above problems is a nozzle plate having nozzle holes for discharging droplets, wherein the nozzle holes have a first flow path and a second flow path arranged on the downstream side of the first flow path with respect to the droplet discharge direction and communicating with the first flow path. The first flow path has a cross-sectional area perpendicular to the discharge direction on the most upstream side of the discharge direction that is larger than the cross-sectional area perpendicular to the discharge direction on the most downstream side, and includes the central axis of the nozzle hole. In a cross-section parallel to the discharge direction, the inclination of a straight line connecting the most upstream end and the most downstream end of the wall surface of the second flow path arranged on one side with respect to the central axis with respect to the discharge direction is smaller than the inclination of a straight line connecting the most upstream end and the most downstream end of the wall surface of the first flow path arranged on the one side with respect to the discharge direction, and the minimum cross-sectional area S A of the first flow path and the minimum cross-sectional area S B of the second flow path satisfy the relationship of formula (1). S A > 13S B (1)

[0008] An inkjet head according to an embodiment of the present invention for solving the above problems has the above nozzle plate. [

[0009] [ [ An image forming apparatus according to an embodiment of the present invention for solving the above problems has the above inkjet head. [

Advantages of the Invention

[0010] [ [ The present invention provides a nozzle plate, an inkjet head, and an image forming apparatus capable of improving discharge stability. [

Brief Description of the Drawings

[0011] [ [ [Figure 1] [ FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention. [ [Figure 2] [ FIG. 2 is an exploded perspective view showing the outline of an inkjet head according to an embodiment of the present invention. [Figure 3] Figure 3A is a cross-sectional view of the head tip shown in Figure 2, along line AA. Figure 3B is a cross-sectional view of the head tip shown in Figure 2, along line BB. [Figure 4] Figure 4 is a magnified view of area C in Figure 3A. [Figure 5] Figures 5A and 5B are schematic cross-sectional views illustrating the droplet drawing process in a conventional inkjet head equipped with a nozzle plate. [Figure 6] Figure 6A is a schematic cross-sectional view showing the droplet drawing process in an inkjet head equipped with a nozzle plate according to one embodiment of the present invention. Figure 6B is a cross-sectional view showing the cross-sectional areas SA and SB of the nozzle plate according to one embodiment of the present invention. [Figure 7] Figures 7A-7C are schematic diagrams illustrating an example of a method for manufacturing nozzle plates by punching. [Figure 8] Figure 8 is a cross-sectional view of the punch, including its central axis and parallel to the direction in which the punch is pressed into the plate. [Figure 9] Figure 9 is a cross-sectional view showing a nozzle plate according to Modification 1 in this embodiment. [Figure 10] Figure 10 is a cross-sectional view showing a nozzle plate according to a modified example 2 of this embodiment. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. Common components in each figure are denoted by the same reference numerals. Furthermore, the present invention is not limited to the following embodiments.

[0013] (Image forming apparatus) Figure 1 is a schematic diagram showing the configuration of an image forming apparatus 100 according to Embodiment 1.

[0014] As shown in Figure 1, the image forming apparatus 100 includes an inkjet head 1, an ink supply device 110, a transport device 120, and a main tank 130.

[0015] The inkjet head 1 has multiple nozzles for ejecting ink droplets onto a recording medium M, such as paper, which is the material to be printed on. For example, the inkjet head 1 is configured so that multiple types of ink of different colors are supplied to specific nozzles. The inkjet head 1 is arranged to be scannable in a direction that crosses the transport direction D of the recording medium M on which the image is to be formed, for example, by a scanning method. Details of the configuration of the inkjet head 1 will be described later. Note that the inkjet head 1 may also be arranged in a line configuration.

[0016] In this embodiment, the type of ink ejected by the inkjet head 1 is not particularly limited and may include, for example, active-ray curing ink, solvent-based ink, water-based ink, or hot-melt ink.

[0017] The transport device 120 is a device for transporting the recording medium M to the inkjet head 1. The transport device 120 includes, for example, a belt conveyor 121 and a rotatable feed roller 122. The belt conveyor 121 consists of a plurality of rotatable pulleys 121a and an endless belt 121b stretched over the pulleys 121a. The feed roller 122 is positioned opposite the upstream pulley 121a in the transport direction D of the recording medium M, and is arranged to grip the belt 121b and the recording medium M, and to feed the recording medium M onto the belt 121b.

[0018] The ink supply unit 110 is integrated with the inkjet head 1. The ink supply units 110 are arranged according to the type of ink. For example, when using four inks, Y (yellow), M (magenta), C (cyan), and K (black), four ink supply units 110 are arranged on the inkjet head 1.

[0019] Each ink supply device 110 is supplied with ink from the main tank 130 via a pipe 141 and valve 142 connected to the main tank 130. Each ink supply device 110 is also connected via a pipe 144 to a common ink chamber 2 of the inkjet head 1 (described later), and is connected to supply ink of each color to the desired ink supply port 2a of the common ink chamber 2.

[0020] The inkjet head 1 is also connected to the main tank 130 by a bypass pipe 143 that branches off from the pipe 141. At the branching point between pipe 141 and the bypass pipe 143, a valve 142 is positioned in one or both of these pipes 141 and the bypass pipe 143 to switch and set the ink flow path. Pipes 141, 144, and the bypass pipe 143 are, for example, all flexible tubes. The valve 142 is, for example, a three-way valve.

[0021] The main tank 130 is a tank for containing the ink to be supplied to the inkjet head 1. The main tank 130 is located separately from the inkjet head 1. The main tank 130 has, for example, a stirring device (not shown). The size of the main tank 130 can be appropriately determined according to the image forming performance and size of the image forming apparatus 100. For example, if the image forming speed of the image forming apparatus is 1 to 3 m 2 If the rate is per minute, the capacity of the main tank 130 is, for example, 1 liter.

[0022] (Inkjet head) Figure 2 is an exploded perspective view showing an overview of the inkjet head 1 used in the image forming apparatus 100 described above. As shown in Figure 2, the inkjet head 1 has a common ink chamber 2, a holding section 3, and a head chip 4.

[0023] The common ink chamber 2 is formed in a hollow, roughly rectangular parallelepiped shape, with one side facing the holding section 3 being open. On the side of the common ink chamber 2 facing the opening, there is an ink supply port 2a for supplying ink from the ink supply device 110, and an ink discharge port 2b for discharging the ink to the ink supply device 110. The common ink chamber 2 is equipped with a filter inside, which removes foreign matter from the ink supplied from the ink supply port 2a and also finely crushes any air bubbles contained in the ink.

[0024] The holding portion 3 is formed in a substantially flat shape with an opening 3a in the approximate center, and is positioned to cover the opening of the common ink chamber 2. As a result, the common ink chamber 2 is connected to one side of the holding portion 3 so as to cover the opening 3a. The head chip 4 is connected to the other side of the holding portion 3 so as to cover the opening 3a. The holding portion 3 connects the common ink chamber 2 and the head chip 4 through the opening 3a.

[0025] An insertion hole 3b is provided on the outer periphery of the retaining part 3. The flexible wiring board 5 is inserted through the insertion hole 3b. One end of the flexible wiring board 5 is connected to the head chip 4, which will be described later. The other end of the flexible wiring board 5 is inserted through the insertion hole 3b provided in the retaining part 3 from the other side of the retaining part 3 and pulled out towards the common ink chamber 2.

[0026] Figure 3A is a cross-sectional view along line AA in Figure 2, showing an overview of the head chip 4 of the inkjet head 1 described above, and Figure 3B is a cross-sectional view along line BB in Figure 2, showing an overview of the head chip 4 of the inkjet head 1 described above.

[0027] The print head chip 4 includes a nozzle plate 10, a pressure chamber forming plate 20, a drive plate 30, and a wiring board 40. The print head chip 4 is stacked in the following order from the ink ejection side: nozzle plate 10, pressure chamber forming plate 20, drive plate 30, and wiring board 40.

[0028] Multiple nozzle holes 11 are formed in the nozzle plate 10. The nozzle holes 11 penetrate from one surface to the other of the nozzle plate 10. These nozzle holes 11 discharge droplets of ink (hereinafter simply referred to as droplets) supplied from the common ink chamber 2 to the outside through the discharge port. Multiple nozzle holes 11 (for example, 500 to 2000) are provided on the nozzle plate 10 and arranged in a matrix. These nozzle holes 11 communicate with the pressure chamber 21 formed in the pressure chamber forming plate 20. In this embodiment, the nozzle holes 11 may be composed of two substrates, as shown in Figure 9 (described later).

[0029] A liquid-repellent film 14 is formed on the ink-discharging surface of the nozzle plate 10. The material contained in the liquid-repellent film 14 is not particularly limited, but for example, it is a fluororesin. The thickness of the liquid-repellent film 14 is not particularly limited, but for example, it is between 1 nm and less than 100 nm.

[0030] The pressure chamber forming plate 20 has a plurality of pressure chambers 21 and a diaphragm 22. The pressure chambers 21 are provided at positions corresponding to the nozzle holes 11 of the nozzle plate 10. The pressure chambers 21 also penetrate from one surface to the other of the pressure chamber forming plate 20. The pressure chambers 21 impart discharge pressure to the ink discharged from the nozzle holes 11 through the volume fluctuations of the pressure chambers 21. Partition walls 23 are formed between the plurality of pressure chambers 21. In this embodiment, the entire partition wall 23 is made of an electroplatable metal such as nickel (Ni). This increases the rigidity of the partition wall 23, making the inkjet head 1 less susceptible to damage from vibration and providing a stable structure. The nozzle plate 10 and the pressure chamber forming plate 20 may be bonded together.

[0031] The diaphragm 22 is positioned to cover the opening of the pressure chamber 21 on the side opposite to the nozzle plate 10. The diaphragm 22 is provided with a second communication hole 24 that communicates with the pressure chamber 21. A drive plate 30 is positioned on one side of the diaphragm 22 facing the pressure chamber 21 and on the opposite side.

[0032] The drive plate 30 has a space 31 and a third communication hole 32 that communicates with the second communication hole 24. The space 31 is positioned opposite the pressure chamber 21 with the diaphragm 22 in between. The actuator 50 is housed in the space 31.

[0033] The actuator 50 includes a piezoelectric element 51, a first electrode 52, and a second electrode 53. The first electrode 52 is laminated on one surface of the diaphragm 22. An insulating layer may be placed between the first electrode 52 and the diaphragm 22. The piezoelectric element 51 is laminated on the first electrode 52 and is positioned for each pressure chamber 21 (each channel) facing the pressure chamber 21 with the diaphragm 22 and the first electrode 52 in between.

[0034] The piezoelectric element 51 is made of a material that deforms when a voltage is applied, and is made of a ferroelectric material such as lead zirconate titanate (PZT). A second electrode 53 is laminated on the side of the piezoelectric element 51 opposite to the first electrode 52. The second electrode 53 is connected to a wiring layer 41 provided on a wiring substrate 40, which will be described later, via a bump 54. The film thickness of the piezoelectric element 51 is, for example, 10 μm or less.

[0035] The wiring board 40 has a wiring layer 41 and a silicon layer 42 on which the wiring layer 41 is formed on one surface. The wiring layer 41 is connected to a bump 54 provided on the second electrode 53 via solder 41a. The outer edge of the wiring layer 41 is connected to the flexible wiring board 5. Furthermore, the silicon layer 42 is arranged on one side of the wiring layer 41 opposite to the drive plate 30. The silicon layer 42 is bonded to the holding portion 3.

[0036] Furthermore, the wiring board 40 is provided with a fourth communication hole 43 that penetrates the wiring layer 41 and the silicon layer 42. This fourth communication hole 43 communicates with the common ink chamber 2 via the third communication hole 32 of the drive plate 30 and the opening 3a of the holding part 3.

[0037] In this embodiment, an inlet is formed by the fourth communication hole 43 of the interconnected wiring board 40, the third communication hole 32 of the drive plate 30, and the second communication hole 24 of the diaphragm 22, which are all interconnected, and this inlet serves as a flow path for supplying ink from the common ink chamber 2 to the pressure chamber 21. The inlet plays a role in reducing the flow resistance (flow rate) of the ink flowing from the common ink chamber 2 to the pressure chamber 21. Additionally, an outlet is formed by the nozzle hole 11 of the nozzle plate 10 for ejecting the ink from the pressure chamber 21 toward the recording medium 150.

[0038] In an inkjet head 1 with the above configuration, the ink contained in the common ink chamber 2 flows into the pressure chamber 21 through the inlet (i.e., the fourth communication hole 43, the third communication hole 32, and the second communication hole 24). When a voltage is applied between the first electrode 52 and the second electrode 53, the piezoelectric element 51 deforms (vibrates), and the diaphragm 22 deforms (vibrates) in conjunction with the deformation of the piezoelectric element 51. This deformation (vibration) of the diaphragm 22 generates pressure to eject the ink into the pressure chamber 21. Due to the generation of this pressure, the ink in the pressure chamber 21 is pushed out to the outlet (i.e., the nozzle hole 11) and ejected from the tip of the nozzle hole 11 (nozzle opening) toward the recording medium 150.

[0039] In this embodiment, the inkjet head 1 only needs to include a nozzle plate 10, and may be a piezoelectric inkjet head in which the piezoelectric element 51 constitutes the wall of the pressure chamber 21, or a thermal inkjet head.

[0040] (Nozzle plate) Figure 4 is a magnified view of area C in Figure 3A, showing the cross-sectional shape of the nozzle plate 10.

[0041] As shown in Figure 4, the nozzle hole 11 of the nozzle plate 10 has a first flow path 12 and a second flow path 13 that is downstream of the first flow path 12 and communicates with the first flow path 12 with respect to the droplet discharge direction (arrow E in Figure 4), and the cross-sectional area perpendicular to the discharge direction on the upstream side of the first flow path 12 is larger than the cross-sectional area on the downstream side. In this embodiment, the first flow path 12 and the second flow path 13 of the nozzle plate 10 are made by processing a single substrate.

[0042] Figures 5A and 5B are schematic cross-sectional views of the main parts of a conventional inkjet head 1 equipped with a nozzle plate C1, as described in Patent Document 1. In the inkjet head 1 (Figure 5A), a piezoelectric element 51 is vibrated to change the pressure in the pressure chamber 21 and eject ink droplets X. At this time, just before ejecting the ink droplets X, the pressure inside the pressure chamber 21 is reduced (the volume of the pressure chamber increases), so the ink is drawn in from the nozzle hole C2 towards the inside of the pressure chamber (Figure 5B). When the ink is drawn in, the surface tension of the ink forms a concave liquid surface (meniscus) Y inside the nozzle hole C2, so there is a risk of air Z being drawn into the inside of the pressure chamber 21 (Figure 5B). If air is drawn into the inside of the pressure chamber 21, when the droplet is ejected next, the force exerted by the piezoelectric element 51 to push out the ink inside the pressure chamber 21 (the force that contracts the volume of the pressure chamber 21) will be exerted on the air Z. In this case, if air bubbles are contained in the ink, attempting to eject the droplets in this state may lead to nozzle defects or disruption of the ejection process, resulting in reduced ejection stability, such as the droplets failing to land in the intended position.

[0043] Therefore, the inventors considered that by making the volume of the first channel 12 sufficiently large, it would be less likely for air to be drawn into the pressure chamber 21. As a result of diligent research, the inventors found that the minimum cross-sectional area S of the first channel 12 in a cross section parallel to the droplet discharge direction, including the central axis CA1 of the nozzle hole 11, is A And the minimum cross-sectional area S of the second channel 13. BBy satisfying the relationship of formula (1), it has been found that when the droplet is drawn in, it is possible to suppress the entrainment of air into the pressure chamber 21 and improve the discharge stability of the droplet (FIGS. 6A and B). Here, in this specification, the "central axis CA1 of the nozzle hole 11" means a straight line connecting the center (center of gravity) of the cross section of the first flow path 12 perpendicular to the droplet discharge direction and the center (center of gravity) of the cross section of the second flow path 13 perpendicular to the discharge direction. S A >13S B (1)

[0044] The reason why the air entrainment into the pressure chamber 21 can be suppressed by the first flow path 12 and the second flow path 13 satisfying the relationship of formula (1) is not clear, but it is considered as follows.

[0045] Since the cross-sectional area of the first flow path 12 perpendicular to the droplet discharge direction on the most upstream side in the droplet discharge direction is larger than the cross-sectional area perpendicular to the discharge direction on the most downstream side, the area of the cross section perpendicular to the discharge direction expands toward the pressure chamber 21. At this time, if the first flow path 12 has a size that satisfies formula (1), the area of the cross section of the first flow path 12 perpendicular to the discharge direction can be made sufficiently large, and it is considered that the volume sufficient to suppress the air Z entrained during the drawing of the droplet from reaching the inside of the pressure chamber 21 due to pressure loss can be ensured.

[0046] In addition, in a nozzle plate as described in Patent Document 1, when variations occur in the shape and dimensions of the flow path due to manufacturing and processing, the above-described air entrainment may become more likely to occur, and the discharge stability may further decrease.

[0047] In contrast, in the nozzle plate of this embodiment, the first flow path 12 and the second flow path 13 have shapes and sizes that satisfy equation (1), so that the volume of the first flow path 12 can be sufficiently secured. Therefore, the problems caused by air entrapment due to variations in shape and dimensions caused by the manufacturing and processing of the nozzle plate can be sufficiently compensated for by the first flow path 12 having sufficient volume. Accordingly, the decrease in discharge stability caused by variations in manufacturing and processing can be suppressed more effectively than with conventional nozzle plates.

[0048] As described above, the first channel 12 has a larger cross-sectional area perpendicular to the discharge direction on the upstream side of the droplet discharge direction than the same cross-sectional area perpendicular to the discharge direction on the downstream side. In this embodiment, the first channel 12 has a tapered shape in which the perpendicular cross-sectional area decreases by a constant rate toward the discharge direction. This makes it possible to increase the area of ​​the cross-section perpendicular to the discharge direction toward the pressure chamber 21 in the first channel 12. Furthermore, when droplets are discharged, the pressure in the first channel 12 is more easily applied evenly to the droplets, and irregularities in the shape of the droplets can be further suppressed. In addition, the tapered shape can sufficiently suppress the decrease in the robustness of the nozzle plate caused by variations in shape and dimensions during manufacturing and processing.

[0049] The shape of the cross-section of the first channel 12 perpendicular to the droplet discharge direction is not particularly limited and can be, for example, circular, elliptical, elongated, rectangular, or rhombic. In this embodiment, the shape of the cross-section of the first channel 12 perpendicular to the droplet discharge direction is elongated.

[0050] In a cross-section parallel to the droplet discharge direction and including the central axis CA1 of the nozzle hole 11, the straight line connecting the upstream end 12b and the downstream end 12c of the wall surface 12a of the first channel 12, which is located on one side of the central axis CA1, has an inclination with respect to the discharge direction. In this specification, the acute angle (θ1 in Figure 5) between the straight line P1 parallel to the droplet discharge direction and the straight line connecting the upstream end 12b and the downstream end 12c of the wall surface 12a of the first channel 12 is referred to as the "inclination of the wall surface 12a of the first channel 12".

[0051] The inclination of the wall surface 12a of the first channel 12 is preferably 5° or more and 20° or less. By having an inclination of 5° or more on the wall surface 12a of the first channel, the cross-sectional area perpendicular to the discharge direction on the upstream side of the droplet discharge direction can be made sufficiently larger than the cross-sectional area perpendicular to the same direction on the downstream side. This allows for more sufficient suppression of air entrainment into the pressure chamber 21 due to pressure loss, thereby further improving discharge stability. By having an inclination of 20° or less on the wall surface 12a of the first channel, the amount of droplet discharge can be adjusted more appropriately.

[0052] The length L of the first flow path 12 in the direction of droplet discharge. A The length L of the first flow path 12 in the discharge direction is not particularly limited, but is preferably 55 μm or more and 115 μm or less. A By having the above range, a sufficient distance can be secured from the tip of the nozzle hole 11 to the pressure chamber 21, making it less likely for air to be drawn into the pressure chamber 21 when droplets are drawn in, and also achieving space saving for the nozzle plate 10 in the inkjet head 1.

[0053] The minimum cross-sectional area S of the first flow path 12 in a cross-section parallel to the droplet discharge direction, including the central axis CA1 of the nozzle hole 11. A While not particularly limited as long as it satisfies equation (1), 1300 μm is preferred from the viewpoint of more sufficiently suppressing the entrapment of air into the pressure chamber 21. 2 More than 7000μm 2 Preferably, the following, 1600 μm2 More than 7000μm 2 The following is more preferable: 2400 μm 2 More than 5000μm 2 The following is even more preferable:

[0054] The second channel 13 is arranged to communicate with the first channel 12 downstream of the first channel 12 with respect to the droplet discharge direction. In addition, in a cross section parallel to the droplet discharge direction, including the central axis CA1 of the nozzle hole 11, the inclination of the straight line connecting the upstream end 13b and the downstream end 13c of the wall surface 13a of the second channel 13, which is located on one side of the central axis CA1, with respect to the discharge direction, is smaller than the inclination of the wall surface 12a of the first channel 12. In this specification, the acute angle between the straight line P1 parallel to the droplet discharge direction and the straight line connecting the upstream end 13b and the downstream end 13c of the wall surface 13a of the second channel 13 is referred to as the "inclination of the wall surface 13a of the second channel 13". In this embodiment, the inclination of the wall surface 12a of the first channel 12 is defined as angle θ1 in Figure 5, and the inclination of the wall surface 13a of the second channel 13 is defined as angle θ2 (not shown), and angles θ1 and θ2 satisfy the relationship θ1 > θ2. Also, in this embodiment, 0° < θ1 < 90° and 0° ≤ θ2 < 90°.

[0055] The inclination (angle θ2) of the wall surface 13a of the second channel 13 is not particularly limited as long as it is smaller than the inclination (angle θ1) of the wall surface 12a of the first channel 12, but it is preferably 0° or more and 10° or less, more preferably 0° or more and 5° or less, and even more preferably 0°. When the angle θ2 is within the above range, the ink flow direction in the second channel 13 is more likely to align with the droplet ejection direction, thereby further improving ejection stability. Also, when the angle θ2 is within the above range, variations in the droplet ejection angle caused by variations in the shape and dimensions of the channel due to manufacturing and processing can be more sufficiently suppressed. When the inclination of the wall surface 13a of the second channel 13 is 0°, the wall surface 13a of the second channel 13 is parallel to the droplet ejection direction, and the area of ​​the cross-section of the second channel 13 perpendicular to the ejection direction is constant toward the ejection direction. In this embodiment, the inclination (angle θ2) of the wall surface 13a of the second channel 13 is 0°.

[0056] The shape of the cross-section of the second channel 13 perpendicular to the droplet discharge direction is not particularly limited and can be, for example, circular, elliptical, rectangular, or rhombus. In this embodiment, the shape of the cross-section of the second channel 13 perpendicular to the droplet discharge direction is circular. That is, in this embodiment, the shape of the cross-section perpendicular to the discharge direction at the downstream end of the nozzle hole 11 in the droplet discharge direction is circular. In this embodiment, the minimum width R of the first channel 12 in the direction perpendicular to the discharge direction is Y Since this is the same as the diameter of the circle in the cross-section in the second channel 13, the downstream end 12c of the wall surface 12a of the first channel 12 in the discharge direction coincides with the upstream end 13b of the wall surface 13a of the second channel 13 in the discharge direction.

[0057] The length L of the second channel 13 in the direction of droplet discharge. B While not particularly limited, it is preferably 1 μm or larger, and preferably 5 μm or larger and 7 μm or smaller. B Having a diameter of 1 μm or more ensures that the length within the second channel 13 is sufficient to bring the ink flow direction closer to the droplet ejection direction, thereby further improving ejection stability.

[0058] The length L of the first flow path 12 in the direction of droplet discharge. A The length L of the droplet discharge direction in the second channel 13. B The sum of these is preferably 60 μm or more. This ensures a sufficient distance from the tip of the nozzle hole 11 to the pressure chamber 21, thereby reducing the inclination (angle θ1) of the wall surface 12a of the first flow path 12 and making it less likely for air to be drawn into the pressure chamber 21. From the above viewpoint, L A and L B The sum of these two values ​​is preferably between 60 μm and 120 μm. A value of 120 μm or less reduces pressure loss (fluid resistance), making it easier to eject the ink. In particular, when using a piezoelectric inkjet head, the voltage applied when ejecting the ink can be reduced.

[0059] Length L of the second channel in the direction of droplet discharge. B The length L of the first flow path in the discharge direction is A It is more preferable that it is 0.01 times or more and less than 0.1 times, and even more preferable that it is 0.01 times or more and less than 0.08 times. B is L A A ratio of 0.01 or more ensures sufficient length within the second flow path 13 to bring the ink flow direction closer to the droplet ejection direction. A ratio of less than 0.1 reduces the fluid resistance within the nozzle hole 11, making it easier to eject ink droplets.

[0060] The cross-sectional area S of the second flow path 13 in a cross-section parallel to the droplet discharge direction, including the central axis CA1 of the nozzle hole 11. B While not particularly limited as long as it satisfies equation (1), 100 μm is preferred from the viewpoint of more sufficiently suppressing the entrapment of air into the pressure chamber 21. 2 More than 400μm 2 The following is preferable, and 185 μm 2 More than 300μm 2 The following is more preferable: 200 μm 2 More than 250μm 2 The following is even more preferable:

[0061] In a cross-section parallel to the droplet discharge direction, including the central axis CA1 of the nozzle hole 11, the minimum width R of the second flow path 13 in the direction perpendicular to the discharge direction, on the downstream side in the discharge direction. X The size is not particularly limited, but is preferably 20 μm to 50 μm. Being within this range allows for more appropriate adjustment of the droplet discharge amount. In this embodiment, since the wall surface 13a of the second channel 13 is parallel to the droplet discharge direction, the minimum width R of the second channel 13 is... X The size is the minimum width R in the orthogonal direction at the downstream end of the first flow path 12 in the discharge direction. Y It is identical to [the other one].

[0062] In a cross-section parallel to the droplet discharge direction, including the central axis CA1 of the nozzle hole 11, the length L of the first flow path 12 in the discharge direction is defined. A The length L of the second flow path 13 in the discharge direction is... B And, in the second channel 13, the above R X Preferably, the relationship between equations (2) and (3) is satisfied. This reduces fluid resistance during ink ejection, making it easier to eject ink droplets. L A ≤2R X (2) L B <1 / 2R X (3)

[0063] The material included in the nozzle plate 10 is not particularly limited, but it is preferable that the downstream surface 15 of the nozzle plate 10 in the direction of droplet ejection is made of stainless steel. In this specification, the downstream surface 15 of the nozzle plate 10 in the ejection direction refers to the surface on the ink ejection side. If a liquid-repellent film is formed on the nozzle plate 10, it refers to the surface on the ink ejection side of the surface of the nozzle plate 10 to which the liquid-repellent film is applied. By making the downstream surface 15 of the nozzle plate 10 in the ejection direction out of stainless steel, it is possible to suppress damage to the nozzle holes 11 by wiping off the ink after using the inkjet head 1, thereby more effectively suppressing the decrease in ejection stability due to damage to the nozzle holes 11. Note that the nozzle plate 10 may be made of a material other than stainless steel except for the downstream surface 15.

[0064] The method for forming the first channel 12 and the second channel 13 is not particularly limited. Examples of methods for manufacturing the nozzle plate 10 include punching, etching, sandblasting, and laser processing.

[0065] Figures 7A to 7C are schematic diagrams illustrating an example of a method for manufacturing the nozzle plate 10 by punching.

[0066] As shown in Figures 7A to 7C, in the case of punching, for example, the nozzle plate 10 can be manufactured by pressing the punch 72 into the plate 71 placed on the die 70.

[0067] The die 70 functions as a receiving member for the punch 72. The material included in the die 70 is not particularly limited, but examples include stainless steel and aluminum.

[0068] The plate 71 is a substrate that serves as the base material for the nozzle plate 10. The downstream side of the plate 71 in the direction in which the punch 72 is pressed in is preferably made of stainless steel.

[0069] Figure 8 is a cross-sectional view of the punch 72, including its central axis CA2 and parallel to the direction in which the punch 72 is pressed into the plate 71.

[0070] The punch 72 has a first punch portion 72a and a second punch portion 72b. The first punch portion 72a has a cross-sectional area perpendicular to the direction of press-fitting the punch 72 into the plate 71 on the upstream side, which is larger than the cross-sectional area perpendicular to the direction of press-fitting on the downstream side. The second punch portion 72b is continuous with the first punch portion 72a downstream of the first punch portion with respect to the direction of press-fitting the punch 72 into the plate 71. The shape of the cross-section of the first punch portion 72a perpendicular to the direction of press-fitting the punch 72 is not particularly limited, but for example, it is an elongated hole shape.

[0071] The wall surface 72c of the first punch portion 72a, which is located on one side of the central axis CA2 in a cross section parallel to the direction of press-fitting and includes the central axis CA2 of the punch 72, has an inclination with respect to a straight line P2 parallel to the direction of press-fitting. In this specification, the acute angle (θ3 in Figure 5) between the straight line P2 and the straight line connecting the upstream end 72e and the downstream end 72f of the first punch portion 72a in the direction of press-fitting is referred to as the "inclination of the wall surface 72c of the first punch portion 72a". The angle θ3 is not particularly limited, but is preferably 3° or more and 30° or less.

[0072] In a cross-section parallel to the direction of press-fitting, including the central axis CA2 of the punch 72, the inclination of the wall surface 72d of the second punch portion 72b, which is positioned on one side of the central axis CA2, is smaller than the inclination of the wall surface 72c of the first punch portion 72a. In this specification, the acute angle between the straight line P2 parallel to the direction of press-fitting and the straight line connecting the upstream end 72g and the downstream end 72h of the wall surface 72d of the second punch portion in the direction of press-fitting is referred to as the inclination of the wall surface 72d of the second punch portion 72b. In this embodiment, the inclination of the wall surface 72d of the second punch portion 72b is θ4 (not shown), and the relationship θ3 > θ4 is satisfied between angles θ3 and θ4. Also, in this embodiment, 0° < θ3 < 90° and 0° ≤ θ4 < 90°.

[0073] The shape of the cross-section of the second punch portion 72b perpendicular to the direction in which the punch 72 is pressed in is not particularly limited, but is, for example, circular.

[0074] The inclination (angle θ4) of the wall surface 72d of the second punching section 72b is not particularly limited as long as it is smaller than the inclination of the wall surface 72c of the first punching section 72a, but it is preferably 0° or more and 10° or less, more preferably 0° or more and 5° or less, and even more preferably 0°. In this embodiment, the inclination of the wall surface 72d of the second punching section 72b is 0°.

[0075] The minimum cross-sectional area S of the first punch portion 72a is in a cross-section parallel to the direction of press-fitting, including the central axis CA2 of the punch 72. C And the minimum cross-sectional area S of the second punch portion 72b. D This satisfies the relationship in equation (4). S C >13S D (4)

[0076] The method for manufacturing the nozzle plate 10 by punching will be explained below, with reference to Figures 7A to 7C.

[0077] First, the second punch portion 72b of the punch 72 is pressed into the plate 71 placed on the die 70 (Figure 7A). Then, the first punch portion 72a is pressed into the interior of the plate 71 (Figure 7B), and when the punch 72 is removed from the plate 71, a first flow path 12, a second flow path 13, and a bottomed expansion portion 73 are formed in the plate 71. Finally, the expansion portion 73 is polished and removed to manufacture the nozzle plate 10 (Figure 7C).

[0078] [Example 1] Figure 9 is a cross-sectional view showing a nozzle plate 10 according to Modification 1 of this embodiment.

[0079] As shown in Figure 9, in this embodiment, the nozzle plate 10 may have a nozzle hole 11 comprising a first substrate 10a having a first flow path 12 and a second substrate 10b having a second flow path 13. In this case, the first flow path 12 is a through hole formed in the first substrate 10a, and the second flow path 13 is a through hole formed in the second substrate 10b. This allows the nozzle plate 10 to be manufactured by forming the first flow path 12 and the second flow path 13 separately and independently, thus enabling the simple formation of the first flow path 12 and the second flow path 13. Furthermore, compared to forming the first flow path 12 and the second flow path 13 as a single unit, the dimensions and shape of each flow path can be formed with greater precision, thus reducing variations due to manufacturing and processing.

[0080] The material included in the first substrate 10a is not particularly limited, but examples include stainless steel, copper, silicon, and polyimide resin.

[0081] The material included in the second substrate 10b is not particularly limited, but examples include stainless steel, copper, silicon, and polyimide resin. Of these, the second substrate 10b is preferably made of stainless steel. This suppresses damage to the nozzle holes 11 caused by the ink wiping process performed after using the inkjet head 1, thereby more effectively suppressing the decrease in ejection stability due to damage to the nozzle holes 11. From the above viewpoint, it is more preferable that the downstream side of the second substrate 10b in the droplet ejection direction is made of stainless steel.

[0082] [Differentiation 2] Figure 10 is a cross-sectional view showing a nozzle plate 10 according to a modified example 2 of this embodiment.

[0083] As shown in Figure 10, in this embodiment, the first channel 12 of the nozzle plate 10 may have a rounded shape such that the cross-sectional area perpendicular to the discharge direction on the upstream side of the droplet discharge direction is larger than the cross-sectional area perpendicular to the same direction on the downstream side. Having such a shape for the first channel 12 allows for a larger volume to be secured than when it has a tapered shape, so that air drawn in during droplet intake is less likely to reach the pressure chamber 21, thereby further improving discharge stability.

[0084] Such a nozzle plate 10 can be manufactured, for example, by punching, isotropic etching, sandblasting, laser processing, etc. [Examples]

[0085] (Evaluation of air entrainment) In this embodiment, a piezoelectric inkjet head using a nozzle plate 10 having first and second flow channels with the same shape as the nozzle plate 10 shown in Figure 4, and satisfying the conditions shown in Table 1, was simulated (Experiments No. 1-32) using general-purpose three-dimensional thermal fluid analysis software (FLOE-3D, manufactured by FLOW Sceince) to observe the behavior of air inside the nozzle during ink draw-in. The conditions for ink physical properties were set to a density of 980 kg / m³. 3 Viscosity of 0.010 kg / m·s, compressibility of 5.88 × 10 -10 In this simulation, the ink was not heated. The nozzle opening was positioned at z=0 in the ink droplet ejection direction, and the fluid distribution in the region z≧0 was calculated and visualized using the above simulation.

[0086] Based on the results obtained from the simulation, the air entrapment that occurs when ink is drawn into the nozzle hole was evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0087] (Evaluation Criteria) ○: Confirmed that air does not reach the inside of the pressure chamber when the ink is drawn in. ×: Confirmed that air reaches the inside of the pressure chamber when the ink is drawn in.

[0088] [Table 1]

[0089] (Evaluation of dispensing stability) A nozzle plate satisfying the conditions of Experiments No. 1, 2, 7, and 13 in Table 1 was obtained by press-fitting a punch having the same shape as punch 72 in this embodiment into a plate placed on a die, and then removing it from the plate. The expanded portion formed by the press-fitting of the punch was polished off to produce nozzle plates A to D. Nozzle plates A to D were attached to a piezoelectric inkjet head and bonded together.

[0090] The above inkjet head was filled with solvent-based ink (colorless, viscosity: 0.010 kg / m·s, manufactured by Konica Minolta Mechatronics Co., Ltd.), the ink droplet ejection speed was adjusted to 9 m / s, and then the piezoelectric element was driven at a frequency of 11.4 kHz for continuous ejection for 5 minutes.

[0091] The ink droplet ejection stability was evaluated according to the following criteria. ○ No ejection irregularities or nozzle defects were observed during ink droplet ejection, and the droplets landed in the designated positions. × During ink droplet ejection, ejection irregularities or nozzle defects were observed, preventing the droplets from landing in the designated location.

[0092] The evaluation results are shown in Table 2.

[0093] [Table 2] [Industrial applicability]

[0094] The nozzle plate, inkjet head, and image forming apparatus according to the present invention can improve droplet ejection stability, and are therefore useful, for example, in the field of image forming. [Explanation of symbols]

[0095] 1. Inkjet head 2. Common Ink Chamber 2a Ink supply port 2b Ink outlet 3 Holding part 3a opening 4 head tips 5 Flexible Wiring Board 10 Nozzle Plates 10a First substrate 10b Second board 11 Nozzle holes 12 First channel 12a, 13a Wall surfaces 13 Second channel 14 Liquid repellent film 20 Pressure chamber forming plate 21 Pressure Chamber 22 Diaphragm 23 Bulkhead 23a First partition member 23b Second bulkhead member 24 2nd communication hole 30 Drive Plate 31 Space section 32 3rd communication hole 40 Wiring board 41 Wiring layer 41a Handa 42 Silicon layer 43 4th communication hole 50 Actuators 51 Piezoelectric element 52 1st electrode 53 2nd electrode 100 Image forming apparatus 110 Ink supply device 120 Conveying device 121 Belt conveyor 122 Feed roller 123a Pulley 130 Main Tank 141, 144 tube 143 Bypass pipe 142 valves

Claims

1. A nozzle plate having nozzle holes for discharging droplets, The nozzle hole is The first channel and, It consists of a second channel arranged downstream of the first channel and in communication with the first channel with respect to the droplet discharge direction, The first flow path has a tapered shape such that the cross-sectional area perpendicular to the discharge direction decreases by a constant rate toward the discharge direction. The second flow path has a cross-sectional area perpendicular to the discharge direction that is constant in the direction of the discharge. In a cross-section including the central axis of the nozzle hole and parallel to the discharge direction, The inclination of the straight line connecting the upstream end and the downstream end of the wall surface of the second channel, which is located on one side with respect to the central axis, with respect to the discharge direction is smaller than the inclination of the straight line connecting the upstream end and the downstream end of the wall surface of the first channel, which is located on the one side, with respect to the discharge direction. Minimum cross-sectional area S of the first channel Ａ The minimum cross-sectional area S of the second channel. Ｂ And satisfy the relationship in equation (1), The length L A of the first channel in the discharge direction, the length L B of the second channel in the discharge direction, and the minimum width R X of the second channel in the direction perpendicular to the discharge direction at the downstream end in the discharge direction satisfy the relationship between equations (2) and (3). Nozzle plate. S Ａ >13S Ｂ (1) L A ≦2R X (2) L B <1 / 2R X (3)

2. The nozzle plate according to claim 1, wherein the shape of the cross-section perpendicular to the discharge direction at the downstream end of the nozzle hole in the direction of droplet discharge is circular.

3. The nozzle plate according to claim 1 or 2, wherein the first flow path has a tapered shape.

4. The nozzle plate according to any one of claims 1 to 3, wherein the area of ​​the cross-section perpendicular to the discharge direction is constant in the direction of discharge for the second flow path.

5. Length L of the first flow path in the discharge direction Ａ The length L of the second flow path in the discharge direction. Ｂ A nozzle plate according to any one of claims 1 to 4, wherein the sum of the two is 60 μm or more.

6. Length L of the second flow path in the discharge direction Ｂ The length L of the first flow path in the discharge direction is Ａ A nozzle plate according to any one of claims 1 to 5, wherein the ratio is less than 0.1 times.

7. The length L of the second flow path in the discharge direction Ｂ is 1 μm or more, and the nozzle plate according to any one of claims 1 to 6.

8. In a cross-section including the central axis of the nozzle hole and parallel to the discharge direction, The nozzle plate according to any one of claims 1 to 7, wherein the inclination of the wall surface of the first flow path is 5° or more and 20° or less.

9. The nozzle plate according to any one of claims 1 to 8, wherein the substrate including the downstream side in the discharge direction is made of stainless steel.

10. The nozzle plate according to any one of claims 1 to 9, wherein the first channel and the second channel are formed by processing a single substrate.

11. The first substrate having the first channel, The second substrate having the second channel, A nozzle plate according to any one of claims 1 to 9, having the following features.

12. A nozzle plate used in an inkjet head, according to any one of claims 1 to 11.

13. An inkjet head having a nozzle plate according to any one of claims 1 to 12.

14. An image forming apparatus having the inkjet head described in claim 13.

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