Droplet ejection head, droplet ejection device, and method of manufacturing droplet ejection head

Abstract

To provide a droplet discharge head which makes a bearing unlikely to be peeled.SOLUTION: A droplet discharge head includes: a housing 10b formed with a liquid passage 112; a nozzle plate 101 disposed on one surface of the housing 10b; a valve body which is disposed in the housing 10b in a manner that the valve body may reciprocate in a direction that crosses the passage to open and close a nozzle 111 formed on the nozzle plate 101; and a bearing 121 which is disposed in a housing hole within the housing 10b and guides reciprocating motion of the valve body. The bearing 121 is joined to an inner surface of the housing hole by diffusion junction.SELECTED DRAWING: Figure 4C

Description

[Technical Field]

[0001] The present invention relates to a droplet discharge head in which a bearing that supports a valve element for opening and closing a nozzle is diffusion-welded to a housing, a droplet discharge device, and a method for manufacturing a droplet discharge head. [Background technology]

[0002] As a droplet ejection device that ejects droplets from a nozzle, for example, the device described in Patent Document 1 (JP 2021-151767 A) is known. A nozzle plate having a plurality of nozzles formed therein is disposed in a housing of a droplet ejection head of such a device.

[0003] Inside the nozzle plate, needle-shaped valve bodies are arranged to open and close each nozzle individually. A driver (actuator) such as a piezoelectric element that expands and contracts in the longitudinal direction of the valve body is connected to the rear end of this valve body. The driver expands and contracts (vibrates) in the longitudinal direction to open and close the valve body, and the moment the valve body opens, high-pressure ink is sprayed from the nozzle as droplets. Summary of the Invention [Problem to be solved by the invention]

[0004] The needle-shaped valve element is slidably supported by a bearing fixed inside the housing. Conventional bearings are fixed inside the housing with adhesive, so there is a risk that the adhesive may deteriorate depending on the components contained in the liquid (ink), causing the bearing to peel off from the housing.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a droplet ejection head in which there is no risk of the bearings peeling off. [Means for solving the problem]

[0006] In order to solve the above problem, the droplet ejection head of the present invention is a droplet ejection head having a housing in which a liquid flow path is formed, a nozzle plate arranged on one surface of the housing, a valve body arranged to be able to move back and forth within the housing in a direction transverse to the flow path to open and close a nozzle formed in the nozzle plate, and a bearing arranged in a storage hole inside the housing to guide the reciprocating movement of the valve body, characterized in that the bearing is joined to the inner surface of the storage hole by diffusion bonding. [Effects of the Invention]

[0007] The present invention can prevent the bearing from peeling off. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing the appearance of a droplet ejection head according to an embodiment of the present invention. [Figure 2] 1 is an overall cross-sectional view of a droplet ejection head according to an embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view of a droplet ejection module. [Figure 4A] FIG. 2 is a cross-sectional view of the periphery of a bearing of the droplet ejection head according to the first embodiment before bonding. [Figure 4B] FIG. 3 is a cross-sectional view of the periphery of the bearing of the droplet ejection head according to the first embodiment when pressure and heat are applied. [Figure 4C] FIG. 4 is a cross-sectional view of the bearing periphery of the droplet ejection head according to the first embodiment after bonding. [Figure 4D] 3 is a cross-sectional view showing the joining of upper and lower housings of the droplet ejection head according to the first embodiment. FIG. [Figure 4E] FIG. 3 is a cross-sectional view of the completed state of the periphery of the bearing of the droplet ejection head according to the first embodiment. [Figure 5A] FIG. 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to a second embodiment before bonding. [Figure 5B] FIG. 10 is a cross-sectional view of the periphery of the bearing of the droplet ejection head according to the second embodiment when pressure and heat are applied. [Figure 5C] FIG. 10 is a cross-sectional view of the bearing periphery of the droplet ejection head according to the second embodiment after bonding. [Figure 5D] FIG. 10 is a cross-sectional view showing the joining of upper and lower housings of a droplet ejection head according to a second embodiment. [Figure 5E] FIG. 10 is a cross-sectional view of the completed state of the periphery of a bearing of the droplet ejection head according to the second embodiment. [Figure 6A] 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 1 before bonding. FIG. [Figure 6B] 10 is a cross-sectional view of the periphery of the bearing of the droplet ejection head according to Comparative Example 1 when pressure and heat are applied. FIG. [Figure 6C] 10 is a cross-sectional view of the bearing periphery of the droplet ejection head according to Comparative Example 1 after bonding. FIG. [Figure 7A] 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 2 before bonding. FIG. [Figure 7B] 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 2 when being bonded. FIG. [Figure 7C] 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 2 after bonding. FIG. [Figure 8] FIG. 10 is a cross-sectional view of the vicinity of the bearing of the droplet ejection head according to the modified embodiment when pressure and heat are applied. [Figure 9] FIG. 1 is a perspective view of a droplet ejection device. [Figure 10] FIG. 2 is a perspective view of a driving unit of the droplet ejection device. DETAILED DESCRIPTION OF THE INVENTION

[0009] (● Droplet ejection head) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is an external perspective view of a droplet ejection head 1, Fig. 2 is a cross-sectional view taken along section S1 in Fig. 1, and Fig. 3 is a cross-sectional view of one droplet ejection module of the droplet ejection head.

[0010] The droplet ejection head 1 has a plurality of droplet ejection modules 100 arranged in one or more rows inside a housing 10. Pressurized liquid is supplied to each droplet ejection module 100 from the outside via a supply port 11, and any liquid not ejected is recovered to the outside via a recovery port 12. The housing 10 is also provided with a connector 2.

[0011] The droplet ejection module 100 includes a nozzle plate 101 having nozzles 111 formed therein for ejecting liquid, a flow path 112 to which the nozzles 111 are connected and through which pressurized liquid is supplied, a needle-shaped valve body 113 for opening and closing the nozzles 111, and a piezoelectric element 114 for driving the valve body 113.

[0012] The nozzle plate 101 and the housing 10 are joined together. The flow path 112 is a flow path common to the multiple droplet ejection modules 100 formed in the housing 10, and as described above, pressurized liquid is supplied through the supply port 11 and the liquid is recovered from the recovery port 12.

[0013] An elastic body 113a is provided at the tip of the valve body 113, which reliably closes the nozzle 111 when pressed against the nozzle plate 101. A bearing 121 is provided between the valve body 113 and the housing 10, and a sealing member 122 such as an O-ring is provided between the bearing 121 and the valve body 113.

[0014] The piezoelectric element 114 is accommodated in the piezoelectric element accommodating space 123 of the housing 10. The piezoelectric element 114 is held in the central space 115a of the holding member 115, which also serves as the first biasing means. The piezoelectric element 114 and the valve body 113 are coaxially connected via the tip end 115b of the holding member 115.

[0015] The holding member 115 has a central space 115a that houses the piezoelectric element 114. A tip end 115b of the holding member 115 is connected to the valve body 113, and a rear end 115c is fixed by a piezoelectric element fixing shaft 124 attached to the housing 10.

[0016] The holding member 115 has a holding leaf spring 116 as a first biasing means. The holding leaf spring 116 has elastically deformable spring portions 116a and 116b at both ends in the longitudinal direction, which corresponds to the expansion and contraction direction of the piezoelectric element 114. The spring portion 116a is located on the side of the tip portion 115b to which the valve body 113 is attached, and the spring portion 116b is located on the side of the rear end portion 115c opposite the side of the tip portion 115b to which the valve body 113 is attached.

[0017] The spring portions 116a and 116b have slits formed alternately in the widthwise direction perpendicular to the lengthwise direction, and are left in a crank shape to provide a spring function. In this embodiment, the spring constants of the spring portions 116a and 116b are approximately the same (including being the same).

[0018] Here, the length of central space 115a of holding member 115 (the axial length of valve body 113) is shorter than the length of piezoelectric element 114. Therefore, when piezoelectric element 114 is fitted into central space 115a of holding member 115, spring portions 116a and 116b of holding leaf spring 116 are in an extended state.

[0019] As a result, when the piezoelectric element 114 contracts in the longitudinal direction, the holding plate spring 116 also contracts in the longitudinal direction, and a biasing force in the direction in which the nozzle 111 opens can be applied to the valve body 113 .

[0020] Here, when a voltage is applied by the voltage application means 200, the piezoelectric element 114 operates in the d31 mode and drives the valve body 113 in the direction to open the nozzle 111. In other words, when a voltage is applied to the piezoelectric element 114, the valve body 113 is driven in the direction to open the nozzle 111.

[0021] Therefore, when no voltage is applied to the piezoelectric element 114, the valve body 113 closes the nozzle 111. Therefore, even if pressurized liquid is supplied to the flow path 112, the liquid is not ejected from the nozzle 111.

[0022] Then, by applying a voltage to the piezoelectric element 114, the piezoelectric element 114 contracts and pulls the valve body 113 via the holding member 115, causing the valve body 113 to move away from the nozzle 111 and open the nozzle 111. As a result, the pressurized liquid supplied to the flow path 112 turns into droplets and is ejected from the nozzle 111.

[0023] The piezoelectric element 114 can also be operated in a d33 mode in which it expands in a direction to close the valve element 113 when a voltage is applied. When the piezoelectric element operates in the d33 mode, the valve element 113 is pressed against the nozzle 111 while a voltage is applied, thereby closing the nozzle 111. When a droplet is to be ejected, the application of voltage to the piezoelectric element 114 is stopped or reduced, thereby moving the valve element 113 in a direction to open the nozzle 111 and opening the nozzle 111.

[0024] The d33 mode of the piezoelectric element 114 has high responsiveness and a large displacement. Therefore, the d33 mode is suitable when it is desired to increase the responsiveness of the opening and closing operation of the valve body 113 and reduce variations in the droplet speed and droplet volume of the liquid ejected from the nozzle 111.

[0025] (● Diffusion bonding of bearings) Next, the bearing 121 disposed in the lower housing 10b of the droplet ejection head 1 and a method for diffusion bonding the bearing 121 to the lower housing 10b will be described with reference to Figures 4A to 8. Pressure plates 20 and 30 for applying pressure to the bearing 121 are disposed above and below the lower housing 10b. The pressure plates 20 and 30 are made of ceramic members with a very high flatness, for example, 0.005 / 100 mm.

[0026] 4A to 4E are cross-sectional views of the vicinity of the bearing 121 of the droplet ejection head 1 according to the first embodiment, sequentially showing the steps of diffusion-bonding the bearing 121 to the lower housing 10b. Also, FIGS. 5A to 5E are cross-sectional views of the vicinity of the bearing 121 of the droplet ejection head 1 according to the second embodiment, sequentially showing the steps of diffusion-bonding the bearing 121 to the lower housing 10b. After the bearing 121 is diffusion-bonded to the lower housing 10b, the nozzle plate 101 is disposed on the underside of the lower housing 10b, as shown in FIGS. 4E and 5E.

[0027] The nozzle plate 101 can be made of inorganic materials such as stainless steel or nickel. If the nozzle plate is not diffusion bonded, organic materials such as polyphenylene sulfide, polyimide, polyether ether ketone, polyetherimide, and polyethylene can also be used in addition to the inorganic materials mentioned above. The surface of the nozzle plate 101 can be subjected to a water-repellent treatment as needed, taking into account wettability with the ink liquid.

[0028] While the bearing 121 of the second embodiment is cylindrical as shown in Figures 5A to 5E, the bearing 121 of the first embodiment has ribs 121e formed as protrusions on the outer periphery of the bearing as shown in Figures 4A to 4E. Inside the bearing 121, a through-hole 121b into which the valve body 113 is inserted in the vertical direction and a through-hole 121c in the horizontal direction for the ink flow path are formed.

[0029] In the first and second embodiments, the material of the bearing 121 is SUS304, and its linear expansion coefficient is 17.3×10 -6 / °C. The material of the lower housing 10b is SUS304, and its linear expansion coefficient is 9.9×10 -6 / ° C. The reason why the linear expansion coefficients are set to large and small values ​​in this manner is to allow the pressure to be effectively applied to the bearing 121 during diffusion bonding, as will be described later.

[0030] (First embodiment) 4A, a liquid (ink) flow path 112 extending in the left-right direction is formed inside the lower housing 10b. A receiving hole for fitting and receiving a bearing 121 is formed so as to cross this flow path 112 in the up-down direction. In the illustrated example, the peripheral gap of the bearing 121 is exaggerated and shown larger than it actually is.

[0031] Ribs 121e as protrusions are formed on the outer periphery of the bearing 121. The ribs 121e can be formed in a shape that protrudes in the radial direction from a plurality of locations on the outer periphery of the bearing 121.

[0032] Meanwhile, a step 10b1 is formed on the inner peripheral surface 10b4 of the accommodation hole, with the diameter expanded on the lower side (the nozzle plate 101 side or the nozzle 111 side). The step 10b1 and the upper surface of the rib 121e face each other across a small gap in the axial direction of the nozzle 111. This small gap disappears completely due to the thermal expansion of the bearing 121 and the movement of the metal grain boundaries during diffusion bonding.

[0033] To diffusion-bond bearing 121 to the receiving hole (step portion 10b1) of lower housing 10b, first, bearing 121 and lower housing 10b are degreased and cleaned using a solvent such as acetone. Then, as shown in FIG. 4A, bearing 121 and lower housing 10b are placed on lower pressure plate 20. At this time, the lower surface of lower housing 10b and lower end surface 121a of bearing 121 abut against pressure plate 20 and become flush (horizontal).

[0034] Next, the positioning pin 50 is inserted from above into the through hole 121b of the bearing 121. The positioning pin 50 has a dished head 50a. The outer diameter of the dished head 50a is slightly smaller than the inner diameter of the inner circumferential surface 10b4 of the receiving hole, and before joining, the dished head 50a is clearance-fitted to the inner circumferential surface 10b4 of the receiving hole (for example, a minimum gap of 0 mm and a maximum gap of 0.4 mm).

[0035] Here, the vertical thickness of the rib 121e of the bearing 121 is A, and the depth of the step portion 10b1 based on the lower surface of the lower housing 10b is B. The dimensions of A and B before diffusion bonding, during pressure and heat application, and after bonding are as shown in Table 1 below. [Table 1] Axial press-fit amount of bearing 121 when pressurized and heated: A1-B1=0.002 mm Axial recession of bearing 121 after joining: B2-A2=0.013 mm

[0036] As shown in FIG. 4A, the lower housing 10b was sandwiched between pressure plates 20 and 30 from above and below, and a vacuum pressure of 1.0×10 was applied using a vacuum hot press (FVHP-R-750, FRET-300 manufactured by Fuji Dempa Kogyo). -4 Under a pressure of 20 Pa, a pressure (20 MPa) is applied to the pressure plates 20 and 30 as shown by the arrows. At the same time, the lower housing 10b and bearing 121, including the pressure plates 20 and 30, are heated to approximately 1000°C. This pressurized and heated state is maintained for approximately 10 minutes to 1 hour.

[0037] This heating causes thermal expansion of the lower housing 10b, the positioning pin 50, and the bearing 121. This thermal expansion causes the dish-shaped head 50a of the positioning pin 50 to expand in diameter, resulting in a light interference fit with the inner circumferential surface 10b4 of the receiving hole that does not result in diffusion bonding. This interference fit allows the bearing 121 to be positioned (centered) in a predetermined position in the lower housing 10b.

[0038] At this time, the amount of thermal expansion of bearing 121 is greater than that of lower housing 10b due to the difference in linear expansion coefficients described above. For this reason, the bottom surface of bearing 121 tends to protrude downward by 0.002 mm from the bottom surface of lower housing 10b, as shown in Table 1. This downward expansion of 0.002 mm that tends to protrude is pushed back upward by pressure plate 20, resulting in an axial press-fit of 0.002 mm.

[0039] As a result, the upper surface 121f of the rib 121e is pressed against the step portion 10b1 of the receiving hole with the aforementioned pressure (20 MPa). By maintaining this pressed state at a high temperature (approximately 1000°C) for a predetermined time (approximately 10 minutes to 1 hour), the rib 121e can be diffusion-bonded to the step portion 10b1.

[0040] This diffusion bonding completely eliminates the minute uneven gaps that existed between the rib 121e and the step portion 10b1 before bonding due to the movement of the metal crystal grain boundaries, thereby preventing the bonding interface from deteriorating or peeling due to chemical attack by corrosive components of the fluid (ink) flowing through the flow path 112.

[0041] After the diffusion bonding of the bearing 121 to the lower housing 10b is completed, the lower housing 10b and the bearing 121 are cooled to room temperature in an argon gas atmosphere, and then the pressure plates 20 and 30 are removed as shown in Figure 4C. This cooling causes the lower housing 10b and the bearing 121 to shrink.

[0042] At this time, due to the difference in the linear expansion coefficients of the two, bearing 121 contracts more than lower housing 10b. As a result, as shown in Table 1, lower end surface 121a of bearing 121 is recessed by 0.013 mm (B2-A2) from the lower surface of lower housing 10b.

[0043] The nozzle plate 101 will be diffusion bonded to the lower surface of the lower housing 10b in a later process, but even if the gap exists on the lower end surface 121a of the bearing 121, as long as the gap is approximately 0.013 mm, it will have almost no effect on the flatness of the nozzle plate 101, as will be described later in Table 4.

[0044] After the bearing 121 is diffusion-bonded to the lower housing 10b as shown in Figure 4C, a ceramic positioning pin 40 with a diameter of 1.5 mm is inserted into the through-hole 121b for inserting the valve disc 113 as shown in Figure 4D. Then, the upper housing 10a is placed on the lower housing 10b. At this time, the upper end of the positioning pin 40 is inserted into the through-hole 10a1 of the upper housing 10a for inserting the valve disc.

[0045] This allows the axis of the through hole 121b of the bearing 121 to be aligned with the axis of the through hole 10a1 of the upper housing 10a. In this state, pressure is applied to the pressure plates 20 and 30 to diffusion bond the upper and lower housings 10a and 10b and the nozzle plate 101. Note that the upper housing 10a and the lower housing 10b are not limited to being diffusion bonded, and they may also be fastened by screws.

[0046] 4E shows the state after the upper and lower housings 10a, 10b and the nozzle plate 101 have been diffusion bonded together and the pressure plates 20, 30 have been removed. From this state, the valve body 113 shown in FIG. 3 is inserted into the through-hole 10a1 of the upper housing 10a and the through-hole 121b of the bearing 121, and the upper end of this valve body 113 is connected to the holding member 115 of the piezoelectric element 114.

[0047] 3 applies a voltage to the piezoelectric element 114, the valve element 113 can be driven upward in a direction to open the nozzle 111. In addition, by releasing the voltage application to the piezoelectric element 114, the valve element 113 can be driven downward in a direction to close the nozzle 111.

[0048] (Second embodiment)

[0049] In the second embodiment, the bearing 121 is cylindrical as shown in Figures 5A to 5E. There is no rib 121e as in the first embodiment described above. The accommodation hole of the lower housing 10b is cylindrical and extends in the axial direction of the nozzle 111, and there is no step 10b1 as in the first embodiment described above. A small gap is formed between the outer peripheral surface 121g of the bearing 121 and the inner peripheral surface 10b2 of the accommodation hole of the lower housing 10b, but this small gap disappears completely due to radial thermal expansion of the bearing 121 and movement of metal grain boundaries during diffusion bonding.

[0050] To diffusion-bond bearing 121 to the receiving hole of lower housing 10b, first clean bearing 121 and lower housing 10b using a solvent such as acetone. Then, place bearing 121 and lower housing 10b on lower pressure plate 20 as shown in Fig. 5A. At this time, the lower surface of lower housing 10b and lower end surface 121a of bearing 121 abut against pressure plate 20 and become flush (horizontal).

[0051] Next, the positioning pin 50 is inserted from above into the through hole 121b of the bearing 121. This positioning pin 50 is also made of a ceramic material. The positioning pin 50 has a dished head 50a. The outer diameter of the dished head 50a is slightly smaller than the inner diameter of the inner circumferential surface 10b4 of the receiving hole, and before joining, the dished head 50a is loosely fitted into the inner circumferential surface 10b4 of the receiving hole (for example, a minimum gap of 0 mm and a maximum gap of 0.1 mm).

[0052] Here, the outer diameter of the bearing 121 is C, and the inner diameter of the receiving hole of the lower housing 10b is D. The dimensions of C and D before diffusion bonding, during pressure and heat application, and after bonding are as shown in Table 2 below. [Table 2] Radial press-fit amount of bearing 121 when pressurized and heated: C1-D1=0.009 mm Radial depression of bearing 121 after joining: C2-D2=0 mm

[0053] As shown in Figure 5A, lower housing 10b is sandwiched between pressure plates 20 and 30 from above and below, and a vacuum hot press (FVHP-R-750, FRET-300, manufactured by Fuji Dempa Kogyo) is used to apply a pressure (20 MPa) to pressure plates 20 and 30 as shown by the arrows. At the same time, lower housing 10b and bearing 121, including pressure plates 20 and 30, are heated to approximately 1000°C. This pressurized and heated state is maintained for approximately 10 minutes to 1 hour.

[0054] This heating causes thermal expansion of the lower housing 10b, the positioning pin 50, and the bearing 121. This thermal expansion causes the dish-shaped head 50a of the positioning pin 50 to expand in diameter, resulting in a light interference fit with the inner circumferential surface 10b4 of the receiving hole that does not result in diffusion bonding. This interference fit allows the bearing 121 to be positioned (centered) in a predetermined position in the lower housing 10b.

[0055] At this time, the amount of thermal expansion of the bearing 121 is greater than that of the lower housing 10b due to the difference in linear expansion coefficients described above. For this reason, as shown in Table 2, the outer diameter C of the bearing 121 tends to protrude radially beyond the inner diameter D of the receiving hole by 0.009 mm.

[0056] This 0.009 mm of expansion that would otherwise protrude is restricted by the accommodation hole in the lower housing 10b. As a result, the outer peripheral surface 121g of the bearing 121 is pressed against the inner peripheral surface 10b2 of the accommodation hole. By maintaining this pressed state at a high temperature (approximately 1000°C) for a predetermined time (approximately 10 minutes to 1 hour), the outer peripheral surface 121g of the bearing 121 can be diffusion-bonded to the inner peripheral surface 10b2 of the accommodation hole.

[0057] This diffusion bonding completely eliminates minute uneven gaps that existed between the outer peripheral surface 121g of the bearing 121 and the inner peripheral surface 10b2 of the accommodation hole before bonding due to the movement of metal crystal grain boundaries. Therefore, it is possible to prevent peeling of the bonding interface due to corrosive components of the fluid (ink) flowing through the flow path 112.

[0058] After the diffusion bonding of bearing 121 to lower housing 10b is completed, lower housing 10b and bearing 121 are cooled to room temperature in an argon gas atmosphere, and then pressure plates 20 and 30 are removed as shown in Figure 5C. This cooling causes lower housing 10b and bearing 121 to shrink.

[0059] In this case, although there is a difference in the linear expansion coefficients of the two as mentioned above, the outer peripheral surface 121g of the bearing 121 and the inner peripheral surface 10b2 of the accommodating hole are integrated by diffusion bonding, so no gap occurs between the bearing 121 and the accommodating hole as shown in Table 2 (C2-D2=0).

[0060] Nozzle plate 101 will be diffusion bonded to the lower surface of lower housing 10b in a later process, but since lower end surface 121a of bearing 121 is flush with the lower surface of lower housing 10b at the stage shown in Figure 5B, the flatness of nozzle plate 101 is not affected at all.

[0061] After the bearing 121 is diffusion-bonded to the lower housing 10b as shown in Figure 5C, the positioning pin 40 is then inserted into the through-hole 121b for inserting the valve body 113 as shown in Figure 5D. Then, the upper housing 10a is placed on the lower housing 10b. At this time, the upper end of the positioning pin 40 is inserted into the through-hole 10a1 of the upper housing 10a for inserting the valve body.

[0062] This allows the axis of the through hole 121b of the bearing 121 to be aligned with the axis of the through hole 10a1 of the upper housing 10a. In this state, pressure is applied to the pressure plates 20 and 30 to diffusion bond the upper and lower housings 10a and 10b and the nozzle plate 101 together. The upper and lower housings 10a and 10b and the nozzle plate 101 are diffusion bonded together. Note that the upper housing 10a and the lower housing 10b are not limited to being diffusion bonded, and they can also be fastened by screws.

[0063] 5E shows the state after the upper and lower housings 10a, 10b and the nozzle plate 101 have been diffusion bonded together and the pressure plates 20, 30 have been removed. From this state, the valve body 113 of FIG. 3 is inserted into the through-hole 10a1 of the upper housing 10a and the through-hole 121b of the bearing 121, and the upper end of this valve body 113 is connected to the holding member 115 of the piezoelectric element 114.

[0064] 3 applies a voltage to the piezoelectric element 114, the valve element 113 can be driven upward in a direction to open the nozzle 111. In addition, by releasing the voltage application to the piezoelectric element 114, the valve element 113 can be driven downward in a direction to close the nozzle 111.

[0065] (Comparative Example 1)

[0066] Next, Comparative Example 1 will be described with reference to FIGS. 6A to 6C. In Comparative Example 1, the dimensions A and B of the first embodiment are changed from A to G and from B to H as shown in Table 3 below. In addition, the material of the bearing 121 and the lower housing 10b is the same SUS304 (linear expansion coefficient is 17.3×10 -6 / °C). The rest is the same as in the first embodiment. [Table 3] Protrusion amount of bearing 121 when pressurized and heated: G1-H1=0.005 mm Protrusion amount of bearing 121 after joining: G2-H2=0.005 mm

[0067] In this comparative example 1, the lower end surface 121a of the bearing 121 protrudes slightly downward (GH) before bonding, as shown in Figure 6A. This protrusion increases (G1-H1) to 0.005 mm during pressure and heat application for diffusion bonding. Therefore, diffusion bonding is performed with the pressure of the pressure plates 20 and 30 acting between the rib 121e and the step portion 10b1.

[0068] After this diffusion bonding, nozzle plate 101 is then diffusion bonded to the underside of lower housing 10b as shown in Figure 6C in the same manner as in Figure 4D. However, because lower end surface 121a of bearing 121 protrudes downward (G2-H2) below the underside of lower housing 10b, the surface precision of nozzle plate 101 deteriorates.

[0069] (Comparative Example 2) Next, Comparative Example 2 will be described with reference to Figures 7A to 7C. In Comparative Example 2, the dimensions C (outer diameter of the bearing) and D (inner diameter of the receiving hole) of the second embodiment are changed from C to 4.0. -0.04 -0.05 , D⇒4.0 -0.01 0, and the outer circumferential surface of the bearing 121 is bonded to the inner circumferential surface of the receiving hole of the lower housing 10b with an adhesive. The material of the bearing 121 and the lower housing 10b is the same SUS304 (linear expansion coefficient is 17.3 × 10 -6 / °C). The rest is the same as in the second embodiment.

[0070] The adhesive used was a thermosetting epoxy adhesive (IW2460, manufactured by 3M Japan). The adhesive was applied to the outer surface of bearing 121 using a dispenser (MS-1D, manufactured by Musashi Engineering Co., Ltd.), and bearing 121 was fitted into the receiving hole of lower housing 10b as shown in Figure 7A. After that, in the state shown in Figure 7B, it was left to stand for 1 hour in an oven (DX302, manufactured by Yamato Scientific Co., Ltd.) set to 120°C, and then cured for 24 hours.

[0071] (● Third Embodiment) Next, the third embodiment will be described with reference to FIG. 8. In this third embodiment, a rib 121h as a protruding portion of the bearing 121 is formed at the upper end portion in the axial direction of the bearing 121.

[0072] The upper surface 121d of this rib 121h is slightly protruded upward before diffusion bonding. Instead of not protruding the upper surface 121d of the rib 121h upward, a convex portion that abuts against the upper surface 121d of the rib 121h may be formed on the lower surface of the pressure plate 30, or a plate material that substitutes for the convex portion may be arranged. The materials of the bearing 121 and the lower housing 10b are made of common SUS304 (linear expansion coefficient is 17.3×10 -6 / °C). Other aspects are the same as those of the first embodiment. Instead of the positioning pin 50 described above, positioning protrusions for the bearing 121 may be formed on the surfaces of the pressure plates 20 and 30.

[0073] The lower surface 121i of the rib 121h is made to abut against the stepped portion 10b3 of the accommodation hole of the lower housing 10b. In this state, the lower end surface 121a of the bearing 121 is also made to abut against the pressure plate 20.

[0074] When it is difficult to exactly match the dimensions E1 and F1 to be described later, make E1 slightly shorter (E1 < F1). Then, as shown in FIG. 8, by sandwiching the lower housing 10b and the bearing 121 between the upper and lower pressure plates 20 and 30 and applying pressure and heating, the lower surface 121i of the rib 121h of the bearing 121 is diffusion bonded to the stepped portion 10b3 of the accommodation hole of the lower housing 10b.

[0075] Here, let the length from the lower surface 121i of the rib 121h to the lower end surface 121a of the bearing be E1, and the length from the stepped portion 10b3 of the lower housing 10b to the lower surface of the housing be F1. Since the linear expansion coefficients of the bearing 121 and the lower housing 10b are the same, the relationship of E1 = F1 holds at any time before bonding, during pressure application and heating, and after bonding. When E1 < F1, the lower end surface 121a of the bearing is slightly recessed, but as described below, it does not have a great influence on the surface accuracy of the nozzle plate 101.

[0076] (Comparison between the embodiment and the comparative example) When the above-described embodiments and comparative examples are compared in terms of surface precision of the nozzle plate 101 and reliability against bearing detachment, the results are as shown in Table 4 below. [Table 4]

[0077] A 3D surface profile measuring machine VR-5000 (manufactured by Keyence) was used to evaluate the surface precision of the nozzle plate 101 bonding surface of the lower housing 10b. The maximum value of the step between the lower end surface 121a of the bearing 121 and the lower surface of the lower housing 10b, when the lower surface of the lower housing 10b was used as a reference, was measured using the 3D surface profile measuring machine. If the size of the step was -15 to 0 μm, it was judged to be "good," and if it was greater than 0 μm or less than -15 μm, it was judged to be "poor."

[0078] The bonded sample (bearing 121 and lower housing 10b) was immersed in each test solvent (pure water, acetone, ethyl acetate, toluene) at a temperature of 30°C and left to stand for two months. The sample was then removed from the test solvent, washed to remove the solvent, and dried. The presence or absence of peeling at the bonded portion between the nozzle plate 101 and lower housing 10b was observed using a VHX-6000 digital microscope.

[0079] If there was no peeling, it was judged as "good", and if there was peeling, it was judged as "bad". As shown in Table 4, it was confirmed that diffusion bonding of the bearing is effective in maintaining the surface precision of the nozzle plate and preventing peeling of the bearing.

[0080] (Droplet discharge device) Next, an embodiment of a droplet ejection device 500 using the droplet ejection head 1 of Fig. 1 will be described with reference to Fig. 9 and Fig. 10. Fig. 9 is a perspective view of the droplet ejection device 500, and Fig. 10 is a perspective view of a drive unit of the droplet ejection device 500.

[0081] The droplet discharge device 500 is equipped with a movable frame unit 802 that is installed facing a printing target 700 having a curved surface, such as a vehicle hood. A movable unit 813 is attached to left and right frame members 810 and 811 that make up the frame unit 802 so as to span the frame members 810 and 811 and be capable of moving up and down in the vertical direction (Y direction).

[0082] The movable unit 813 is equipped with a drive unit 803 incorporating a motor that is arranged so that it can move back and forth horizontally (X direction) on the movable unit 813, and a droplet ejection unit 501 that is attached to this drive unit 803 and ejects liquid toward the printing object 700.

[0083] The printer also includes a controller 805 that controls the ejection of liquid from the droplet ejection unit 501, the reciprocating movement of the drive unit 803, and the elevation of the movable unit 813, and an information processing device 806 such as a PC (personal computer) that issues instructions to the controller 805. A database section (DB section) 807 that records and saves information about the print target 700, such as its shape and size, is connected to the information processing device 806.

[0084] The frame unit 802 includes upper, lower, left, and right frame members 808, 809, 810, and 811 formed of metal pillars or the like, and left and right leg members 812a and 812b attached horizontally and at right angles to both sides of the lower frame member 809 to make the frame unit 802 self-standing. A movable unit 813 is bridged between the left and right frame members 810 and 811 and is configured to be able to move up and down while supporting the drive unit 803.

[0085] The printing object 700 is placed perpendicular to the liquid discharge direction (Z direction), i.e., facing the plane formed by the top, bottom, left, and right frame members 808, 809, 810, and 811 of the frame unit 802. In this case, the printing object 700 can be placed at a predetermined position where printing is to be performed, for example, by suction-holding the back side of the printing area of ​​the printing object 700 with a chuck attached to the tip of the arm of an articulated arm robot. Using an articulated arm robot makes it possible to accurately place the printing object 700 at the printing position, and also makes it possible to change the orientation of the printing object 700 as needed.

[0086] 10, the drive unit 803 is arranged so as to be able to move back and forth in the horizontal direction (X direction) on the movable unit 813. The movable unit 813 is composed of a rail 830 arranged horizontally so as to span between the left and right frame members 810, 811 of the frame unit 802, a rack gear 831 arranged parallel to the rail 830, a linear guide 832 fitted onto a part of the rail 830 and moving while sliding, a pinion gear unit 833 connected to the linear guide 832 and meshing with the rack gear 831, a motor 834 with a reducer 836 that rotates and drives the pinion gear unit 833, and a rotary encoder 835 for detecting the printing point position.

[0087] By driving the motor 834 (forward or reverse), the droplet discharge unit 501 is moved rightward or leftward along the movable unit 813. The drive section 803 functions as a drive mechanism for the droplet discharge unit 501 in the X direction. Limit switches 837a and 837b are attached to both sides of the housing of the reducer 836.

[0088] The droplet discharge unit 501 includes a plurality of droplet discharge heads 1 that discharge liquid of each color, for example, black, cyan, magenta, yellow, and white, or a droplet discharge head 1 that has a plurality of nozzle rows. Liquid of each color is supplied under pressure from a liquid tank to each droplet discharge head 1 or each nozzle row of the droplet discharge head 1 of the droplet discharge unit 501.

[0089] In this droplet ejection device 500, the movable unit 813 is moved in the Y direction, and the droplet ejection unit 501 is moved in the X direction, to print a desired image on the printing object 700. The aforementioned "droplet ejection device" is not limited to devices that visualize meaningful images such as letters and figures using ejected liquid. For example, it also includes devices that form meaningless patterns or uniform paint films, and devices that create three-dimensional images.

[0090] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications are possible based on the technical ideas described in the claims. For example, the shape of bearing 121 is arbitrary as long as it can guide the axial reciprocating motion of valve element 113. As described above, bearing 121 may have ribs 121e and 121h protruding radially outward, may be cylindrical without ribs, or may have a conical shape tapered toward nozzle 111 or a conical shape tapered away from nozzle 111.

[0091] Furthermore, the piezoelectric element 114 can be replaced with another driving body that expands and contracts in the longitudinal direction. For example, a piston that expands and contracts in the longitudinal direction using an electromagnetic solenoid can be used instead of the piezoelectric element 114. [Explanation of symbols]

[0092] 1: Droplet ejection head 2: Connector 10: Housing 10a: Upper housing 10a1: Through hole 10b: Lower housing 10b1: Step portion of the receiving hole 10b2: Inner peripheral surface of the receiving hole 10b3: Step of the receiving hole 11: Supply port 12: Collection port 20, 30: Pressure plate 40, 50: Positioning pins 100: Droplet ejection module 101: Nozzle plate 111: Nozzle 112: Flow path 113: Valve body 113a: Elastic body 114: Piezoelectric element 115: Holding member 115a: Central space 115b: Tip 115c: Rear end 116: Retaining leaf spring 116a, 116b: Spring portion 121: Bearing 121a: Lower end surface 121b: Through hole 121c: Through hole 121d: Top surface 121e, 121h: Ribs 121f: Top surface 121g: Outer surface 121i: Lower surface 122: Sealing member 123: Piezoelectric element accommodating space 124: Piezoelectric element fixing shaft 200: Voltage application means 500: Droplet ejection device 501: droplet ejection unit 700: printing object 802: Frame unit 803: Drive unit 805: Controller 806: Information processing device 807: Database section 808, 809, 810, 811: Frame members 812a, 812b: Leg members 813: Movable unit 830: Rail 831: Rack gear 832: Linear guide 833: Pinion gear unit 834: Motor 835: Rotary encoder 836: Reducer 837a, 837b: Limit switch [Prior art documents] [Patent documents]

[0093] [Patent Document 1] Patent Publication No. 2021-151767

Claims

1. A droplet ejection head having a housing in which a liquid flow path is formed, a nozzle plate disposed on one surface of the housing, a valve body disposed in the housing so as to be capable of reciprocating in a direction crossing the flow path to open and close a nozzle formed in the nozzle plate, and a bearing disposed in an accommodating hole inside the housing to guide the reciprocating movement of the valve body, The droplet ejection head is characterized in that the bearing is joined to the inner surface of the accommodation hole by diffusion bonding.

2. 2. The droplet ejection head according to claim 1, wherein the accommodation hole extends cylindrically in the axial direction of the nozzle, and the outer peripheral surface of the bearing is diffusion-bonded to the inner peripheral surface of the cylindrical accommodation hole.

3. The droplet ejection head of claim 1, characterized in that the accommodating hole extends cylindrically in the axial direction of the nozzle and has a stepped portion with an enlarged diameter on the nozzle side, and a protrusion formed on the outer periphery of the bearing is diffusion-bonded to the stepped portion.

4. 4. The droplet ejection head according to claim 1, wherein the bearing has a linear expansion coefficient greater than that of the housing.

5. A droplet ejection device comprising the droplet ejection head according to any one of claims 1 to 4.

6. A method for manufacturing a droplet ejection head having a housing in which a liquid flow path is formed, a nozzle plate disposed on one surface of the housing, a valve body disposed in the housing so as to be able to reciprocate in a direction crossing the flow path to open and close a nozzle formed in the nozzle plate, and a bearing disposed in an accommodating hole inside the housing to guide the reciprocating movement of the valve body, The linear expansion coefficient of the bearing is set to be larger than the linear expansion coefficient of the housing, an outer peripheral surface of the bearing is fitted onto an inner peripheral surface of the receiving hole, the receiving hole extending cylindrically in the axial direction of the nozzle; a nozzle plate provided on the housing and an end face of the bearing are aligned with each other, and the housing and the bearing are heated to diffusion bond the inner peripheral surface of the accommodating hole and the outer peripheral surface of the bearing together; A method for manufacturing a droplet ejection head, comprising diffusion bonding the nozzle plate to one surface of the housing.

7. A method for manufacturing a droplet ejection head having a housing in which a liquid flow path is formed, a nozzle plate disposed on one surface of the housing, a valve body disposed in the housing so as to be able to reciprocate in a direction crossing the flow path to open and close a nozzle formed in the nozzle plate, and a bearing disposed in an accommodating hole inside the housing to guide the reciprocating movement of the valve body, The linear expansion coefficient of the bearing is set to be larger than the linear expansion coefficient of the housing, an outer peripheral surface of the bearing is fitted into an inner peripheral surface of the accommodation hole, which extends cylindrically in the axial direction of the nozzle, and a protrusion formed on the outer periphery of the bearing is opposed to a stepped portion, the diameter of which is enlarged on the nozzle side of the accommodation hole, with a predetermined gap in the axial direction of the nozzle; By heating the housing and the bearing in a state where the surface of the housing on which the nozzle plate is disposed is aligned with the end surface of the bearing, the predetermined gap is filled by the difference in linear expansion coefficient between the bearing and the housing, and the step portion of the accommodating hole and the protruding portion of the bearing are diffusion-bonded together, and then A method for manufacturing a droplet ejection head, comprising diffusion bonding the nozzle plate to one surface of the housing.

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