Inkjet head and image forming apparatus

Abstract

To provide a share-mode type inkjet head, which can suppress ink from contacting electric wiring and an electrode, so as to improve durability, and an image forming device.SOLUTION: The inkjet head comprises a first substrate configured so that a plurality of wall parts that are applied with voltages from electric wiring arranged along wall surfaces to deform form a pressure chamber whose volumes can be varied, and a second substrate having a through-hole, which is made to adhere to the first substrate, at a position where the through-hole is communicated with the pressure chamber, between the adjacent wall parts, where a protective film is formed on an inside surface of the pressure chamber. An adhesive making the first substrate adhere to the second substrate protrudes, along the surface at the pressure chamber side of the second substrate, toward the through-hole more than the wall parts, and the protruding adhesive forms corner parts of the pressure chamber into fillet shapes.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] As an inkjet head for ejecting ink, there is a piezoelectric inkjet head, which changes the volume of a pressure chamber provided in the inkjet head by applying a voltage to a piezoelectric member (piezo element) to introduce and eject ink. Among them, a shear mode inkjet head is known as an inkjet head that has good driving efficiency and can form high-quality images at high speed. In a shear mode inkjet head, a piezoelectric member forms the wall of the pressure chamber of the inkjet head, and these expand and bend to change the volume of the pressure chamber and eject ink.

[0003] For example, Patent Document 1 discloses an inkjet head in which an actuator unit having electrodes formed on the inner surface of a piezoelectric member forming the wall of an ink chamber and a substrate including a drive circuit electrically connected to each electrode and having a through hole formed therein with a diameter larger than the width between the walls of the ink chamber are bonded together. According to Patent Document 1, the adhesive filled between the actuator unit and the substrate can prevent ink from leaking out of the ink chamber or the through hole.

[0004] In recent years, in image forming devices equipped with such share mode inkjet heads, there has been a demand for a large number of nozzles arranged at high density in order to form high quality images at high speed. To achieve this, it is necessary to reduce the diameter of the flow path for introducing ink into the pressure chamber and to arrange electrical wiring for driving the piezoelectric member on part of the wall surface of the pressure chamber (piezoelectric member).

[0005] For example, Patent Document 2 discloses a method for manufacturing a liquid ejection device having a pressure chamber for storing liquid, an air chamber, and a piezoelectric body provided between the pressure chamber and the air chamber, and a liquid ejection head that ejects liquid from the ejection port by expanding and contracting a wall constituting the pressure chamber. Patent Document 2 describes that the liquid ejection device is manufactured by bonding the liquid ejection head to a wiring board having a through hole with a cross-sectional area smaller than the opening cross-sectional area of ​​the pressure chamber with an adhesive film. Patent Document 2 also describes that the manufacturing method makes it possible to prevent an adhesive from entering the pressure chamber or ink flow path of the liquid ejection device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-86741 A [Patent Document 2] JP 2014-24325 A Summary of the Invention [Problem to be solved by the invention]

[0007] Thus, various types of shear mode inkjet heads are known. FIG. 1A is a side cross-sectional view showing a schematic configuration of a main part of a conventional shear mode inkjet head, and FIG. 1B is a partial enlarged view of the α part in FIG. 1A. In FIGS. 1A and 1B, electrical wiring (not shown) for driving the piezoelectric member is arranged on a part of the wall surface (piezoelectric member) of the pressure chamber C1. Also, in FIGS. 1A and 1B, the wiring board C6 and the piezoelectric member C4 are bonded with an adhesive C5. In a shear mode inkjet head such as that in Patent Document 2, a protective film C2 is formed on the inner surface of the pressure chamber C1 and the inner surface of the ink flow path to prevent ink from contacting the electrical wiring and electrodes arranged on the piezoelectric member. At this time, since the corner C3 of the pressure chamber C1 is bent (FIG. 1A), fine foreign matter is likely to remain at the corner C3 before the protective film C2 is formed, and is difficult to remove. Therefore, even if the protective film C2 is formed, when the inkjet head is used repeatedly, defects C7 will occur in the protective film C2 starting from the above-mentioned foreign matter (FIG. 1B), and ink will leak from the protective film C2 with the defects C7. The leaked ink will come into contact with the electrical wiring and electrodes arranged on the piezoelectric member C4, causing electrical leakage and corrosion of the electrodes, resulting in failure of the inkjet head or a decrease in the durability of the inkjet head.

[0008] Therefore, the inventors thought that when bonding the substrate and the piezoelectric member, by overflowing the adhesive and covering the corners of the pressure chamber where foreign matter is likely to remain with adhesive, and by making the curvature of the corners gentler, foreign matter would be less likely to accumulate.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide an inkjet head and an image forming apparatus in a share mode type inkjet head that can prevent ink from coming into contact with electrical wiring and electrodes, thereby improving durability. [Means for solving the problem]

[0010] In order to solve the above problem, an inkjet head according to one embodiment of the present invention comprises a first substrate which forms a variable volume pressure chamber by a plurality of wall portions which deform upon application of a voltage from electrical wiring arranged along the wall surfaces, and a second substrate which has a through hole having a diameter smaller than the width between the adjacent wall portions and is bonded to the first substrate at a position between the adjacent wall portions where the through hole communicates with the pressure chamber, wherein an adhesive which bonds the first substrate and the second substrate together extends beyond the wall portions toward the through hole along the surface of the second substrate facing the pressure chamber, and the corners of the pressure chamber are formed into a fillet shape by the adhesive which bonds the first substrate and the second substrate together.

[0011] Further, in order to solve the above problem, an image forming apparatus according to one embodiment of the present invention is an image forming apparatus including the above inkjet head. Effect of the Invention

[0012] The present invention provides an inkjet head that can prevent ink from coming into contact with electrical wiring or electrodes in a share mode inkjet head and can improve durability. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a main part of a conventional share mode type ink jet head. [Diagram 2] FIG. 2 is a schematic diagram showing the overall configuration of an image forming apparatus according to one embodiment of the present invention. [Diagram 3] FIG. 3 is an exploded perspective view showing an outline of an ink-jet head according to one embodiment of the present invention. [Figure 4] Fig. 4A is a cross-sectional view taken along line AA in the head chip of Fig. 3. Fig. 4B is a partially enlarged view of a β portion in Fig. 4A. [Diagram 5] FIG. 5A is a side cross-sectional view of an ink-jet head in which the corners of a pressure chamber are curved, and FIG. 5B is an enlarged view of a portion δ in FIG. 5A. [Figure 6] FIG. 6 is a plan view of the γ portion in FIG. 4B as viewed from the second substrate side. [Figure 7] FIG. 7 is a side cross-sectional view of a head chip of an ink-jet head according to a modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0015] (Image forming device) FIG. 2 is a diagram showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention.

[0016] As shown in FIG. 2, the image forming apparatus 100 includes an inkjet head 1, an ink supply device 110, a conveying device 120, and a main tank .

[0017] The inkjet head 1 has a plurality of nozzles for ejecting ink droplets onto a recording medium M such as paper that is a printing substrate. For example, the inkjet head 1 is configured so that a plurality of different colored inks are each supplied to a specific nozzle. The inkjet head 1 is disposed, for example, so as to be capable of scanning in a direction transverse to a transport direction D of the recording medium M on which an image is to be formed. The configuration of the inkjet head 1 will be described in detail later.

[0018] In this embodiment, the type of ink ejected by the inkjet head 1 is not particularly limited, and may be, for example, a water-based ink.

[0019] 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 is composed of a plurality of rotatable pulleys 121a and an endless belt 121b stretched around the pulleys 121a. The feed roller 122 is disposed at a position facing the pulley 121a on the upstream side in the transport direction D of the recording medium M so as to sandwich the recording medium M with the belt 121b and send out the recording medium M onto the belt 121b.

[0020] The ink supply device 110 is disposed integrally with the inkjet head 1. The ink supply device 110 is disposed for each type of ink. For example, when four colors of ink, Y (yellow), M (magenta), C (cyan) and K (black), are used, four ink supply devices 110 are disposed on the inkjet head 1.

[0021] Each ink supply device 110 is supplied with ink from the main tank 130 via a pipe 151 and a valve 152 connected to the main tank 130. Each ink supply device 110 also communicates with a common ink chamber 2 (described later) of the inkjet head 1 via a pipe 154, and is connected so as to be able to supply ink of each color to an ink supply port 2a of a desired common ink chamber 2.

[0022] The inkjet head 1 is also connected to the main tank 130 by a bypass pipe 153 branching off from the above-mentioned pipe 151. At the branching point between the pipe 151 and the bypass pipe 153, a valve 152 capable of switching and setting the ink flow path to one or both of the pipe 151 and the bypass pipe 153 is disposed. The pipe 151, the pipe 154, and the bypass pipe 153 are all, for example, flexible tubes. The valve 152 is, for example, a three-way valve.

[0023] The main tank 130 is a tank for storing ink to be supplied to the inkjet head 1. The main tank 130 is disposed separately from the inkjet head 1. The main tank 130 has, for example, a stirring device (not shown). The main tank 130 can be appropriately determined depending on 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 / s, the main tank 130 may be formed in a size of 100 mm. 2 / min, the capacity of the main tank 130 is, for example, 1 L.

[0024] (Inkjet head) 3 is an exploded perspective view showing an outline of the inkjet head 1 used in the above-mentioned image forming apparatus 100. As shown in FIG 2, the inkjet head 1 has a common ink chamber 2, a holding portion 3, and a head chip 4.

[0025] The common ink chamber 2 is formed in a hollow, substantially rectangular parallelepiped shape, and is open on one side facing the holding portion 3. An ink supply port 2a for supplying ink from the ink supply device 110 and an ink discharge port 2b for discharging ink to the ink supply device 110 are provided on the side of the common ink chamber 2 facing the opening. A porous body 2c, which will be described later, is provided in the ink discharge port 2b. The common ink chamber 2 has an internal filter that removes foreign matter from the ink supplied from the ink supply port 2a and finely breaks up any air bubbles contained in the ink.

[0026] The holding portion 3 is formed in a substantially flat plate shape having an opening 3a substantially in the center, and is disposed so as to cover the opening of the common ink chamber 2. As a result, the common ink chamber 2 is connected to one surface of the holding portion 3 so as to cover the opening 3a. Moreover, the head chip 4 is connected to the other surface of the holding portion 3 so as to cover the opening 3a. The holding portion 3 communicates between the common ink chamber 2 and the head chip 4 via the opening 3a.

[0027] An insertion hole 3b is provided on the outer periphery of the holding portion 3. A flexible wiring board 5 is inserted into the insertion hole 3b. One end of the flexible wiring board 5 is connected to a head chip 4 described below. The other end of the flexible wiring board 5 is inserted through the insertion hole 3b provided in the holding portion 3 from the other surface of the holding portion 3 and drawn out to the common ink chamber 2 side.

[0028] Fig. 4A is a cross-sectional view taken along line AA in head chip 4 in Fig. 3. Fig. 4B is a partial enlarged view of portion β in Fig. 4A.

[0029] 4A and 4B, the head chip 4 in the inkjet head 1 has a first substrate 10, a second substrate 20 bonded to the first substrate 10, a third substrate 30 bonded to the first substrate 10, and a fourth substrate 40 bonded to the third substrate 30. In this embodiment, the head chip 4 is stacked in the order of the fourth substrate 40, the third substrate 30, the first substrate 10, and the second substrate 20 from the ejection surface side of the inkjet head.

[0030] The first substrate 10 has walls 11 of the pressure chambers 12 of the inkjet head 1, and is deformed by application of a voltage from electrical wiring arranged along the wall surfaces of the walls 11. That is, the first substrate 10 functions as a piezoelectric member that expands or bends the multiple walls 11 when a voltage is applied, changing the volume of the pressure chambers 12. This allows ink to be ejected into the ejection ports 41. The material contained in the first substrate 10 is not particularly limited, and is, for example, PZT (lead zirconate titanate).

[0031] Electrical wiring (not shown) is arranged along the wall surface of the wall portion 11 of the first substrate 10. In addition, electrodes (not shown) to which the electrical wiring is connected are formed on parts of the surface of the first substrate 10. The material contained in the electrodes (not shown) is not particularly limited, and may be, for example, nickel or aluminum. From the viewpoints of workability and cost reduction, the material contained in the electrodes is preferably aluminum.

[0032] The pressure chamber 12 is a liquid chamber for storing ink. In this embodiment, the pressure chamber 12 is formed surrounded by a wall portion 11 of the first substrate 10, a second substrate 20 (described later), a third substrate 30 (described later), and an adhesive 60 (described later). The pressure chamber 12 has a corner 12a. Although details will be described later, in this embodiment, the corner 12a of the pressure chamber 12 forms a fillet with the adhesive 60.

[0033] The corner portion 12a is a corner of the pressure chamber 12. In this embodiment, the pressure chamber 12 has the corner portion 12a, which is formed into a fillet shape by the adhesive 60, on the second substrate 20 side. In addition, the pressure chamber 12 has the corner portion 12b, which is a joint portion between the wall portion 11 and the third substrate 30, on the third substrate side.

[0034] In the inkjet head 1, a protective film 50 is formed on the inner surface of the pressure chamber 12. The inner surface of the pressure chamber 12 is a collective term for the surfaces of the parts of the first substrate 10 and the second substrate 20 (described later) that constitute the pressure chamber 12 and the surfaces of the corners 12a that are fillets. The protective film 50 can prevent ink from coming into contact with the electrical wiring and electrodes arranged in the wall portion 11, and can improve the durability of the inkjet head 1. As shown in FIG. 4B, in this embodiment, the protective film 50 is formed on the inner surface of the pressure chamber 12 and the surface of the through hole 21. The compound contained in the wall portion 11 and the protective film 50 is not particularly limited, and is, for example, paraxylylene. The protective film 50 may be formed on the surface of the through hole 21 or between the first substrate 10 and the third substrate 30. In this embodiment, the protective film 50 is formed on the inner surface of the pressure chamber 12, the gap between the first substrate 10 and the third substrate 30, and the surface of the through hole 21.

[0035] The second substrate 20 is a substrate having a through hole 21, and is bonded to the first substrate 10 between adjacent wall portions 11 at a position where the through hole 21 communicates with the pressure chamber 12. In this embodiment, the second substrate 20 is disposed upstream of the pressure chamber 12 in the direction in which the ink is ejected (arrow B in FIG. 4B). The material contained in the second substrate 20 is not particularly limited, but is preferably glass from the viewpoints of insulation and processability. In the second substrate 20, the through hole 21 can be formed by sandblasting, etching, or the like.

[0036] The through holes 21 function as ink flow paths for introducing ink into the pressure chambers. The arrangement of the through holes 21 is not particularly limited as long as they are in a position that communicates with the pressure chambers 12.

[0037] The edge 21a of the through hole 21 on the pressure chamber 12 side (hereinafter simply referred to as the edge 21a of the through hole 21) may be disposed on the pressure chamber 12 side or on the air chamber 70 (described later) side with respect to the wall portion 11, but is preferably disposed on the pressure chamber 12 side. According to the present inventors, a defect may occur in the protective film 50 at the edge 21a of the through hole 21 on the pressure chamber 12 side (hereinafter simply referred to as the edge 21a of the through hole 21), causing ink to leak out. Therefore, by disposing the edge 21a of the through hole 21 on the pressure chamber 12 side with respect to the wall portion 11, it is possible to make it difficult for ink to reach the electrode even if ink leaks from the defect.

[0038] From the above viewpoint, the distance (La in FIG. 6) between the end 21b of the edge 21a of the through hole 21 on the wall 11 side (hereinafter simply referred to as the end 21b of the through hole 21) and the center 11b of the joint between the wall 11 and the second substrate 20 is preferably 45 μm or more, more preferably 45 μm to 200 μm, more preferably 60 μm to 200 μm, and even more preferably 65 μm to 200 μm. When the distance is 45 μm or more, the distance between the edge 21a of the through hole 21 and the first substrate 10 can be more sufficiently secured, and the ink can be prevented from contacting the electrode. Also, when the distance is 200 μm or less, the inkjet heads 1 can be arranged at a high density. In FIG. 6, for the sake of explanation, the center 11b of the joint between the wall 11 and the second substrate 20 and the end 21b of the through hole are covered with black circles.

[0039] The shape of the through hole 21 is not particularly limited, but it is preferable that the diameter increases toward the pressure chamber 12, and more preferably that the diameter increases continuously toward the pressure chamber 12. By having the through hole 21 have such a shape, it is possible to reduce pressure loss caused by a sudden expansion of the flow path diameter when ink flows from the through hole 21 to the pressure chamber 12. In this embodiment, the through hole 21 has a tapered shape whose diameter is smaller than the width between the wall portions 11 (X in FIG. 4B) and whose diameter increases continuously toward the pressure chamber 12.

[0040] As described above, the second substrate 20 is bonded to the first substrate 10 with the adhesive 60 at a position between adjacent wall portions 11 where the through holes 21 communicate with the pressure chambers 12. The adhesive 60 protrudes along the surface of the second substrate 20 on the pressure chamber 12 side toward the through holes 21 beyond the wall portions 11, and the protruding adhesive 60 forms the corners 12a of the pressure chambers 12 into a fillet shape.

[0041] FIG. 5A is a side cross-sectional view of the inkjet head 1 in the case where the corner 12a of the pressure chamber 12 is bent, and FIG. 5B is an enlarged view of the δ portion in FIG. 5A. In the inkjet head 1, when the corner 12a of the pressure chamber 12 is bent on the surface of the wall 11 and the inner wall of the through hole 21 (FIG. 5A), fine foreign matter is likely to remain in the bent portion of the corner 12a before the protective film 50 is formed, and is difficult to remove. Even if the protective film 50 is formed with the foreign matter remaining, when the inkjet head 1 is used repeatedly, a defect 51 occurs in the protective film 50 starting from the foreign matter (FIG. 5B), and ink leaks from the defective protective film 50. The leaked ink comes into contact with the electrical wiring or electrodes arranged on the wall 11, causing electric leakage or corrosion of the electrodes, which causes the inkjet head 1 to break down or the durability of the inkjet head 1 to decrease.

[0042] Therefore, the inventors of the present invention thought that the above-mentioned foreign matter would be less likely to remain if the adhesive 60 that bonds the first substrate 10 and the second substrate 20 were allowed to protrude from the joint between the first substrate 10 and the second substrate 20, the corners 12a were covered with the adhesive 60, the bending of the corners 12a was eliminated, and the corners 12a were curved, so that the foreign matter would be less likely to remain. Then, the inventors found that by forming a fillet at the corners 12a of the pressure chambers 12 using the adhesive 60, the bent portion of the corners 12a could be eliminated, and the above-mentioned foreign matter could be less likely to remain, so that defects in the protective film 50 would be less likely to occur even if the inkjet head 1 is used repeatedly. The above-mentioned fillet is a concave curved surface of the adhesive 60 that protrudes from the joint between the first substrate 10 and the second substrate 20. That is, by making the concave curved surface of the adhesive 60 the corners 12a of the pressure chambers 12, a fillet can be formed at the corners 12a of the pressure chambers 12. This makes it possible to make it less likely for ink to leak from the protective film 50. Even if ink leaks from the protective film 50, the adhesive 60 is arranged along the corners 12a, and therefore the adhesive 60 can prevent the leaked ink from reaching the electrical wiring or electrodes. As a result, leakage current and corrosion of the electrodes can be suppressed, and the durability of the inkjet head 1 can be improved.

[0043] The type of adhesive 60 is not particularly limited as long as it is liquid and has fluidity, and examples of such adhesives include epoxy adhesives, acrylic adhesives, fluorine adhesives, rubber adhesives, urethane adhesives, and silicone adhesives. The method of making the corners 12a into fillets with the adhesive 60 is not particularly limited. In this embodiment, the adhesive 60 is applied to the second substrate 20, and pressed in parallel when adhering to the first substrate 10, so that the adhesive 60 overflows uniformly from the entire area of ​​the gap between the first substrate 10 and the second substrate 20, thereby forming a fillet. In this way, the overflowing adhesive 60 is applied along the surface of the wall portion 11 and the second substrate on the pressure chamber side, and the excess covers the corners 12a, forming a concave curved surface.

[0044] FIG. 6 is a plan view of the γ portion in FIG. 4B as viewed from the second substrate 20 side. In FIG. 6, the first substrate 10 is shown by a broken line for the sake of explanation. The arrangement of the adhesive 60 is not particularly limited, but as shown in FIG. 6, it is preferable that the adhesive 60 overflows onto the through hole 21 side over the entire width (Y in FIG. 6) of the joint between the wall portion 11 and the second substrate 20 as viewed from the second substrate side. It is also preferable that a fillet is formed over the entire width. As a result, the adhesive 60 is filled and present in the area surrounded by the corner portion 12a, the wall portion 11, and the second substrate 20, so that even if ink leaks from the protective film 50, the ink is unlikely to come into contact with the electrical wiring or the electrodes. In this case, the adhesive 60 is applied to the second substrate 20, and pressed in parallel when adhering to the first substrate 10, and the adhesive 60 is made to overflow uniformly from the entire area of ​​the gap between the first substrate 10 and the second substrate 20, so that a fillet can be formed even over the entire width (Y in FIG. 6) of the joint.

[0045] The longer the overflow length of the overflowing adhesive 60, the more preferable. Here, in this specification, the "overflow length" means the length of the adhesive 60 overflowing from the first substrate 10 in the width direction between the walls 11. By increasing the overflow length of the adhesive 60, the fillet of the corner 12a can be made into a more gently curved surface, so that the remaining of foreign matter at the corner 12a can be suppressed, and the formed protective film 50 can be made less likely to have defects. Even if a defect occurs in the protective film 50, the distance from the corner 12a to the first substrate 10 can be secured, and the adhesive 60 exists between them, so that the ink can be prevented from contacting the electrical wiring or the electrodes.

[0046] In addition, it is preferable that the protruding length (Lb in FIG. 6) of the adhesive 60 at the center 11b of the joint between the wall 11 and the second substrate 20 is shorter than the distance (La in FIG. 6) between the end 21b of the through hole 21 and the center 11b of the joint between the wall 11 and the second substrate 20. This makes it possible to prevent the adhesive 60 from blocking the through hole 21, making it easier to ensure ink ejection stability. From the above viewpoint, it is more preferable that the end 60a of the protruding adhesive 60 is located closer to the wall 11 than the through hole 21. Here, the "end 60a of the adhesive 60" means the end of the protruding adhesive 60 that is located closest to the through hole 21.

[0047] Table 1 shows the influence of the ratio of the distance (La) between the end 21b of the through-hole 21 and the center 11b of the joint between the wall portion 11 and the second substrate 20, and the protruding length (Lb) at the center 11b of the joint, on the durability of the inkjet head 1. In this embodiment, for the "durability results" shown in Table 1, the inkjet head 1 was filled with water-based ink, and the ink was ejected until defects occurred in the protective film 50. The number of times the ink was ejected (pulses) when defects occurred in the protective film 50 was evaluated according to the following criteria. ×: Less than 10 billion pulses △: 10 billion to 50 billion pulses ○: 50 billion to 100 billion pulses ◎: 100 billion pulses or more

[0048] [Table 1]

[0049] As shown in Table 1, in inkjet heads No. 1 to No. 5, the corners 12a were fillets, and thus the durability evaluation was good. Furthermore, in inkjet heads No. 2 to No. 4, La was 45 μm or more, and thus the durability of the inkjet head 1 was further improved. This is believed to be because, as described above, by ensuring the distance from the edge 21a of the through-hole 21 to the electrode of the first substrate 10, it was possible to prevent ink flowing out from defects in the edge 21a of the through-hole 21 from contacting the electrode. Furthermore, in inkjet head No. 5, the durability was further improved as a result of the increase in La. This is believed to be because the fillet of the corners 12a could be made into a more gently curved surface, making it difficult for defects to occur in the formed protective film 50, and thus the durability of the inkjet head 1 was further improved.

[0050] Moreover, it is preferable that the protruding length (Lc in FIG. 6) of the adhesive 60 at the end 11a of the joint between the wall 11 and the second substrate 20 is longer than the protruding length (Lb in FIG. 6) at the center 11b of the joint. This allows the adhesive 60 to be applied over a wider area while satisfying the relationship La>Lb, so that the ink can be more sufficiently prevented from contacting the electrodes. Note that in FIG. 6, for the sake of explanation, a black circle is added to the end 11a of the joint.

[0051] The third substrate 30 is a substrate having a communication hole 31, and is bonded to the first substrate 10 on the opposite side of the pressure chamber 12 to the second substrate 20 at a position where the communication hole 31 communicates with the pressure chamber 12 between adjacent wall portions 11. The material contained in the third substrate 30 is not particularly limited, and may be, for example, silicone, a resin-based material, or the like.

[0052] The method for bonding the third substrate 30 and the first substrate 10 is not particularly limited, and they may be bonded with a liquid adhesive or with an adhesive film.

[0053] The communication hole 31 has a diameter smaller than the width between adjacent wall portions 11, and is a hole that communicates between the pressure chamber 12 and the ejection port 41 of the fourth substrate 40. The shape of the communication hole 31 is not particularly limited.

[0054] The fourth substrate 40 is a substrate having an outlet 41, and is bonded to the third substrate 30 at a position where the outlet 41 communicates with the communication hole 31. The material contained in the fourth substrate 40 is not particularly limited, and is, for example, silicone or a resin-based material.

[0055] The method by which the fourth substrate 40 and the third substrate 30 are bonded together is not particularly limited, and they may be bonded together using a liquid adhesive or an adhesive film.

[0056] The ejection port 41 functions as a nozzle that ejects ink from the pressure chamber 12 to the outside of the inkjet head 1 through the communication hole 31. The shape of the ejection port 41 is not particularly limited as long as it has the above-mentioned function. In this embodiment, the ejection port 41 is shaped so that the diameter gradually decreases from the communication hole 31 toward the outside where the ink is ejected.

[0057] In this embodiment, the head chip 4 of the inkjet head 1 has an air chamber 70. The air chamber 70 is a gap formed on both sides of the pressure chamber 12 in the head chip 4. With this configuration, the first substrate 10 is disposed between the pressure chamber 12 and the air chamber 70, so that even if the first substrate 10 expands or bends, it is possible to eject ink without affecting the volume of another pressure chamber 12.

[0058] In the inkjet head 1 having such a configuration, ink stored in the common ink chamber 2 passes through the through hole 21 and flows into the pressure chamber 12. Then, when a voltage is applied to the electrodes arranged on the wall, the wall 11 expands or bends, changing the volume of the pressure chamber 12. This generates pressure in the pressure chamber 12 for ejecting ink. Due to the generation of this pressure, the ink in the pressure chamber 12 is pushed out to the communication hole 31 and the ejection port 41, and ejected towards the recording medium M.

[0059] [Variations] As shown in FIG. 7, in this embodiment, the pressure chamber 12 has two filleted corners 12a on the through hole 21 side, but the present invention is not limited thereto. The first substrate 10 and the third substrate 30 may be bonded with an adhesive 60, and the adhesive 60 may be caused to protrude toward the communicating hole 31 side from the wall portion 11 along the surface of the third substrate 30 on the pressure chamber 12 side, and the corners 12b may be formed into a fillet shape by the protruding adhesive 60. This allows the corners 12b to be curved gently, and the curved portions in the entire pressure chamber 12 to be reduced. Therefore, it is possible to further suppress the remaining of foreign matter before the formation of the protective film 50, and further suppress the leakage of ink due to defects in the protective film 50. Even if ink leaks from the protective film 50, the adhesive 60 is arranged so as to follow the corners 12b, so that the leaked ink can be prevented from contacting electrical wiring or electrodes. [Industrial Applicability]

[0060] According to the inkjet head and image forming apparatus of the present invention, it is possible to suppress ink leakage from the pressure chamber of the inkjet head, and therefore it is possible to increase the durability of the inkjet head and the image forming apparatus, which is useful in, for example, the field of image formation. [Explanation of symbols]

[0061] 1 Inkjet head 2 Common ink chamber 3 Holding part 4 Head Chip 5 Flexible wiring board 10 First board 11 Wall 12 Pressure Chamber 20 Second board 21 Through hole 30 Third board 31 Communication hole 40 4th board 41 Discharge port 50 Protective film 60 Adhesive 70 Air chamber

Claims

1. a first substrate that defines a pressure chamber having a variable volume by a plurality of walls that are deformed by application of a voltage from electrical wiring arranged along the wall surface; a second substrate having a through hole and bonded to the first substrate at a position between the adjacent wall portions where the through hole communicates with the pressure chamber; A protective film is formed on the inner surface of the pressure chamber, an adhesive that bonds the first substrate and the second substrate together extends along a surface of the second substrate facing the pressure chamber toward the through hole beyond the wall portion; The corners of the pressure chamber are formed into a fillet shape by the protruding adhesive. Inkjet head.

2. The second substrate is disposed upstream of the pressure chamber in a direction in which ink is ejected.

2. The ink-jet head according to claim 1.

3. The inkjet head according to claim 1 , wherein an edge of the through hole on the side of the pressure chamber is disposed on the pressure chamber side with respect to the wall portion.

4. The inkjet head according to any one of claims 1 to 3, wherein the adhesive protrudes toward the through hole over the entire width of the joint between the wall portion and the second substrate when viewed from the second substrate side.

5. The ink jet head according to claim 4 , wherein the adhesive forms a fillet across an entire width of a joint between the wall portion and the second substrate when viewed from the second substrate side.

6. An inkjet head as described in claim 4 or 5, wherein the adhesive has an overhang length at the center of the joint between the wall portion and the second substrate, when viewed from the second substrate side, which is shorter than the distance between the end of the edge of the through hole on the wall portion side and the center of the joint.

7. The inkjet head according to claim 1 , wherein the adhesive has a protruding length at an end of a joint between the wall portion and the second substrate that is longer than a protruding length at a center of the joint.

8. 8. The inkjet head according to claim 1, wherein an end of the protruding adhesive is located closer to the wall portion than the through hole.

9. An inkjet head according to any one of claims 1 to 8, wherein the distance between the end of the through hole on the wall side at the edge on the pressure chamber side and the center of the joint between the wall and the second substrate is 45 μm or more.

10. 10. The inkjet head according to claim 1, wherein the through hole has a shape in which a diameter increases toward the pressure chamber.

11. a third substrate having a communication hole with a diameter smaller than a width between the adjacent wall portions, the third substrate being bonded to the first substrate on the opposite side to the second substrate with respect to the pressure chamber at a position between the adjacent wall portions where the communication hole communicates with the pressure chamber, an adhesive that bonds the first substrate and the second substrate together extends along a surface of the third substrate that faces the pressure chamber toward the communication hole beyond the wall portion; The overflowing adhesive forms a fillet shape at the corners of the pressure chamber. The ink-jet head according to any one of claims 1 to 10.

12. 12. The inkjet head according to claim 1, wherein the adhesive is an epoxy adhesive.

13. The inkjet head according to any one of claims 1 to 12, which ejects a water-based ink.

14. The inkjet head according to any one of claims 1 to 13, wherein the second substrate includes glass.

15. The protective film includes paraxylylene. The ink-jet head according to any one of claims 1 to 14.

16. The inkjet head according to any one of claims 1 to 15, wherein an electrode is disposed on a surface of the first substrate, the electrode including aluminum.

17. An image forming apparatus comprising the inkjet head according to any one of claims 1 to 16.

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