JP7802268B2 - Droplet ejection head, droplet ejection device, and method of manufacturing droplet ejection head - Google Patents

Description

The present invention relates to a droplet ejection head in which a bearing supporting a valve element for opening and closing a nozzle is diffusion-welded to a housing, a droplet ejection device, and a method for manufacturing a droplet ejection head.

As a droplet ejection device that ejects droplets from nozzles, for example, the device described in Patent Document 1 (JP 2021-151767 A) is known. A nozzle plate with multiple nozzles formed in it is arranged in the housing of the droplet ejection head of such a device.

Needle-shaped valve bodies are arranged inside the nozzle plate 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 valve body opens and closes when the driver expands and contracts (vibrates) in the longitudinal direction, and the moment the valve body opens, high-pressure ink is sprayed from the nozzle in the form of droplets.

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 components contained in the liquid (ink) may deteriorate the adhesive and cause the bearing to peel off from the housing.

The present invention therefore aims to provide a droplet ejection head in which there is no risk of bearings peeling off.

To solve the above problem, the droplet ejection head of the present invention comprises a housing in which a liquid flow path is formed, a nozzle plate disposed on one surface of the housing, a valve body disposed within the housing so as to be capable of reciprocating in a direction transverse to the flow path to open and close a nozzle formed in the nozzle plate, and a bearing disposed in a receiving hole inside the housing to guide the reciprocating movement of the valve body, wherein the bearing is bonded to the inner surface of the receiving hole by diffusion bonding.

This invention can prevent bearings from peeling off.

FIG. 1 is a perspective view showing the appearance of a droplet ejection head according to an embodiment of the present invention. 1 is an overall cross-sectional view of a droplet ejection head according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a droplet ejection module. FIG. 3 is a cross-sectional view of the periphery of a bearing of the droplet ejection head according to the first embodiment before bonding. 4 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. FIG. FIG. 4 is a cross-sectional view of the periphery of the bearing of the droplet ejection head according to the first embodiment after bonding. 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. 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. 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. 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. FIG. 10 is a cross-sectional view of the periphery of a bearing of the droplet ejection head according to the second embodiment after bonding. 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. FIG. 10 is a cross-sectional view of the completed state of the periphery of the bearing of the droplet ejection head according to the second embodiment. FIG. 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 1 before bonding. 10 is a cross-sectional view of the droplet ejection head according to Comparative Example 1, in the vicinity of the bearing, when pressurized and heated. FIG. 10 is a cross-sectional view of the bearing periphery of the droplet ejection head according to Comparative Example 1 after bonding. FIG. FIG. 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. 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 2 when bonded. FIG. 10 is a cross-sectional view of the periphery of a bearing of a droplet ejection head according to Comparative Example 2 after bonding. 10 is a cross-sectional view of the droplet ejection head according to the modified embodiment, in which the periphery of the bearing is pressurized and heated. FIG. FIG. 1 is a perspective view of a droplet ejection device. FIG. 2 is a perspective view of a driving unit of the droplet ejection device.

(● Droplet ejection head)
An embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a perspective view of the appearance of a droplet ejection head 1, Fig. 2 is a cross-sectional view taken along the line S1 in Fig. 1, and Fig. 3 is a cross-sectional view of one droplet ejection module of the droplet ejection head.

The droplet ejection head 1 has multiple droplet ejection modules 100 arranged in one or more rows within a housing 10. Pressurized liquid is supplied to each droplet ejection module 100 from the outside via a supply port 11, and any unejected liquid is recovered to the outside via a recovery port 12. The housing 10 also has a connector 2.

The droplet ejection module 100 includes a nozzle plate 101 on which nozzles 111 for ejecting liquid are formed, a flow path 112 to which the nozzles 111 communicate and through which pressurized liquid is supplied, a needle-shaped valve element 113 that opens and closes the nozzle 111, and a piezoelectric element 114 that drives the valve element 113.

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

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.

The piezoelectric element 114 is housed in the piezoelectric element housing 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 115b of the holding member 115.

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

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 tip end portion 115b side where the valve body 113 is attached, and the spring portion 116b is located on the rear end portion 115c side, opposite the tip end portion 115b side where the valve body 113 is attached.

Spring sections 116a and 116b have alternating slits in the short direction perpendicular to the long direction, leaving them in a crank shape, giving them a spring function. In this embodiment, the spring constants of spring sections 116a and 116b are approximately the same (including being the same).

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

As a result, when the piezoelectric element 114 contracts in the longitudinal direction, the retaining leaf spring 116 also contracts in the longitudinal direction, causing a biasing force to act on the valve body 113 in the direction of opening the nozzle 111.

Here, when voltage is applied by the voltage application means 200, the piezoelectric element 114 operates in d31 mode, driving the valve body 113 in the direction that opens the nozzle 111. In other words, when voltage is applied to the piezoelectric element 114, the valve body 113 is driven in the direction that opens the nozzle 111.

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, no liquid is ejected from the nozzle 111.

Then, when a voltage is applied 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.

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

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

(● Diffusion bonding of bearings)
Next, the bearing 121 disposed in the lower housing 10b of the droplet ejection head 1 and the method of 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 are disposed above and below the lower housing 10b to apply pressure to the bearing 121. These pressure plates 20 and 30 are made of ceramic members with a very high degree of flatness, for example, 0.005/100 mm.

Figures 4A to 4E are cross-sectional views of the area around the bearing 121 of the droplet ejection head 1 according to the first embodiment, sequentially illustrating the process of diffusion bonding the bearing 121 to the lower housing 10b. Also, Figures 5A to 5E are cross-sectional views of the area around the bearing 121 of the droplet ejection head 1 according to the second embodiment, sequentially illustrating the process 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 Figures 4E and 5E.

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

The bearing 121 of the second embodiment is cylindrical as shown in Figures 5A to 5E, but the bearing 121 of the first embodiment has a rib 121e formed as a protrusion on the outer periphery of the bearing as shown in Figures 4A to 4E. Inside the bearing 121, a through-hole 121b through which the valve body 113 is inserted vertically and a horizontal through-hole 121c for the ink flow path are formed.

In the first and second embodiments, the material of the bearing 121 is SUS304, which has a linear expansion coefficient of 17.3×10 ⁻⁶ /° C. The material of the lower housing 10b is also SUS304, which has a linear expansion coefficient of 9.9×10 ⁻⁶ /° C. The reason for setting the linear expansion coefficients in this manner is to allow the pressure applied to the bearing 121 during diffusion bonding to be applied effectively, as will be described later.

(First embodiment)
4A, a liquid (ink) flow path 112 extending in the left-right direction is formed inside the lower housing 10b. A housing hole for fitting and housing 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.

Ribs 121e are formed as protrusions on the outer periphery of the bearing 121. These ribs 121e can be formed to protrude radially from multiple locations on the outer periphery of the bearing 121.

Meanwhile, a step 10b1 is formed on the inner peripheral surface 10b4 of the accommodation hole, with the diameter expanded on the lower side (towards the nozzle plate 101 or nozzle 111). 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 completely disappears due to the thermal expansion of the bearing 121 and the movement of the metal grain boundaries during diffusion bonding.

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

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 surface 10b4 of the receiving hole, and before joining, the dished head 50a is loosely fitted into the inner surface 10b4 of the receiving hole (for example, a minimum gap of 0 mm and a maximum gap of 0.4 mm).

Here, the vertical thickness of the rib 121e of the bearing 121 is A, and the depth of the step portion 10b1 relative to 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.

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

4A, with the lower housing 10b sandwiched between pressure plates 20 and 30 from above and below, a vacuum hot press (FVHP-R-750, FRET-300, manufactured by Fuji Dempa Kogyo) is used to apply a pressure (20 MPa) to the pressure plates 20 and 30 as shown by the arrows under a vacuum of 1.0 x ^10-4 Pa. 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.

This heating causes thermal expansion of the lower housing 10b, positioning pin 50, and bearing 121. This thermal expansion causes the dished head 50a of the positioning pin 50 to expand in diameter, creating a light interference fit with the inner 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 the specified position in the lower housing 10b.

Due to the difference in linear expansion coefficients mentioned above, the amount of thermal expansion at this time is greater for bearing 121 than for lower housing 10b. For this reason, as shown in Table 1, the bottom surface of bearing 121 tends to protrude 0.002 mm below the bottom surface of lower housing 10b. This downward expansion of 0.002 mm is pushed back upward by pressure plate 20, resulting in an axial press-fit of 0.002 mm.

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.

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. This prevents the bonding interface from deteriorating or peeling due to chemical attack by corrosive components of the fluid (ink) flowing through the flow path 112.

Once the bearing 121 has been diffusion bonded to the lower housing 10b, the lower housing 10b and 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 bearing 121 to shrink.

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

The nozzle plate 101 will be diffusion bonded to the underside 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.

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 body 113, as shown in Figure 4D. Then, the upper housing 10a is placed on top of the lower housing 10b. At this time, the upper end of the positioning pin 40 is inserted into the through-hole 10a1 in the upper housing 10a for inserting the valve body.

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 and lower housings 10a and 10b are not limited to being diffusion bonded, and can also be fastened with screws.

Figure 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 Figure 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.

Now, by applying a voltage to the piezoelectric element 114 using the voltage application means 200 in Figure 3, the valve body 113 can be driven upward in a direction that opens the nozzle 111. Furthermore, by releasing the voltage application to the piezoelectric element 114, the valve body 113 can be driven downward in a direction that closes the nozzle 111.

(● Second embodiment)

In the second embodiment, the bearing 121 is cylindrical, as shown in Figures 5A to 5E. It does not have the rib 121e that was present in the first embodiment described above. Furthermore, the accommodation hole in the lower housing 10b is cylindrical and extends in the axial direction of the nozzle 111, and does not have the step 10b1 that was present 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 in the lower housing 10b, but this small gap disappears completely during diffusion bonding due to the radial thermal expansion of the bearing 121 and the movement of metal grain boundaries.

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

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 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 surface 10b4 of the receiving hole, and before joining, the dished head 50a is loosely fitted into the inner surface 10b4 of the receiving hole (for example, a minimum gap of 0 mm and a maximum gap of 0.1 mm).

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.

Amount of radial press-fit of bearing 121 when pressurized and heated: C1-D1=0.009 mm
Radial depression of bearing 121 after joining: C2-D2=0 mm

As shown in Figure 5A, with the lower housing 10b sandwiched between pressure plates 20 and 30 from above and below, a vacuum hot press (FVHP-R-750, FRET-300, manufactured by Fuji Dempa Kogyo) is used to apply a pressure (20 MPa) 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.

This heating causes thermal expansion of the lower housing 10b, positioning pin 50, and bearing 121. This thermal expansion causes the dished head 50a of the positioning pin 50 to expand in diameter, creating a light interference fit with the inner 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 the specified position in the lower housing 10b.

Due to the difference in linear expansion coefficients mentioned above, the amount of thermal expansion at this time is greater for the bearing 121 than for the lower housing 10b. 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 accommodating hole by 0.009 mm.

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 surface 121g of the bearing 121 is pressed against the inner 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 surface 121g of the bearing 121 can be diffusion-bonded to the inner surface 10b2 of the accommodation hole.

This diffusion bonding completely eliminates the minute uneven gaps that existed between the outer surface 121g of the bearing 121 and the inner surface 10b2 of the accommodating hole before bonding due to the movement of metal crystal grain boundaries. This prevents the bonding interface from peeling off due to corrosive components of the fluid (ink) flowing through the flow path 112.

Once the diffusion bonding of the bearing 121 to the lower housing 10b is complete, the lower housing 10b and 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 5C. This cooling causes the lower housing 10b and bearing 121 to shrink.

In this case, although there is a difference in the linear expansion coefficients of the two as mentioned above, the outer surface 121g of the bearing 121 and the inner 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).

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

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 top of 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.

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 lower housing 10b are not limited to being diffusion bonded, and can also be fastened with screws.

Figure 5E shows the state after the upper and lower housings 10a, 10b and 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 Figure 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.

Now, by applying a voltage to the piezoelectric element 114 using the voltage application means 200 in Figure 3, the valve body 113 can be driven upward in a direction that opens the nozzle 111. Furthermore, by releasing the voltage application to the piezoelectric element 114, the valve body 113 can be driven downward in a direction that closes the nozzle 111.

(●Comparative Example 1)

Next, Comparative Example 1 will be described with reference to Figures 6A to 6C. In this 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 as SUS304 (linear expansion coefficient: 17.3 x ^10-6 /°C). Other aspects are the same as those of the first embodiment.

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

In this comparative example 1, the lower end surface 121a of the bearing 121 protrudes slightly downward (G-H) 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.

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

(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 accommodating hole) of the second embodiment are changed from C to 4.0 ^-0.04 _-0.05 and D to 4.0 ^-0.01 ₀ , and the outer surface of the bearing 121 is bonded to the inner surface of the accommodating hole of the lower housing 10b using an adhesive. The material of the bearing 121 and the lower housing 10b is the same SUS304 (linear expansion coefficient of 17.3 x 10 ^-6 /°C). Other aspects are the same as those of the second embodiment.

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

(Third embodiment)
Next, a third embodiment will be described with reference to Fig. 8. In this third embodiment, a rib 121h serving as a protrusion of the bearing 121 is formed on the upper end of the bearing 121 in the axial direction.

The upper surface 121d of this rib 121h is made to protrude slightly upward before diffusion bonding. Instead of making the upper surface 121d of the rib 121h not protrude upward, a protrusion 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 may be disposed in place of the protrusion. The material of the bearing 121 and the lower housing 10b is the same SUS304 (linear expansion coefficient: 17.3×10 ⁻⁶ /°C). The rest is the same as in the first embodiment. Note that 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.

The lower surface 121i of the rib 121h abuts against the step portion 10b3 of the accommodation hole in the lower housing 10b. In this state, the lower end surface 121a of the bearing 121 also abuts against the pressure plate 20.

If it is difficult to accurately match the dimensions E1 and F1 described below, E1 is made slightly shorter (E1<F1). Then, as shown in Figure 8, the lower housing 10b and bearing 121 are sandwiched between upper and lower pressure plates 20, 30 and pressure and heat are applied, thereby diffusion-bonding the lower surface 121i of the rib 121h of the bearing 121 to the step portion 10b3 of the receiving hole in the lower housing 10b.

Here, E1 is the length from the underside 121i of rib 121h to the bearing lower end surface 121a, and F1 is the length from step 10b3 of lower housing 10b to the housing lower surface. Because the linear expansion coefficients of bearing 121 and lower housing 10b are the same, the relationship E1 = F1 holds true before bonding, during pressure and heating, and after bonding. If E1 < F1, the bearing lower end surface 121a will be slightly recessed, but as described below, this will not have a significant impact on the surface precision of the nozzle plate 101.

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

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 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 is used as the reference, was measured using the 3D surface profile measuring machine. If the size of the step was between -15 and 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."

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 bond between the nozzle plate 101 and lower housing 10b was then observed using a VHX-6000 digital microscope for any peeling.

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 bearing peeling.

(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 section of the droplet ejection device 500.

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

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.

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 unit (DB unit) 807 is connected to the information processing device 806, which records and saves information about the printing object 700, such as its shape and size.

The frame unit 802 comprises upper, lower, left, and right frame members 808, 809, 810, and 811 formed from 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 enable the frame unit 802 to stand on its own. The movable unit 813, which is bridged between the left and right frame members 810 and 811, is configured to be able to move up and down while supporting the drive unit 803.

The printing object 700 is positioned perpendicular to the liquid ejection 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 positioned at the specified position where printing is to be performed, for example, by suction-holding the back side of the printing area of the printing object 700 using a chuck attached to the tip of the arm of an articulated arm robot. Using an articulated arm robot makes it possible to accurately position the printing object 700 at the printing position, and also makes it possible to change the orientation of the printing object 700 as needed.

As shown in Figure 10, the drive unit 803 is arranged so that it can move back and forth horizontally (in the X direction) on the movable unit 813. The movable unit 813 is composed of a rail 830 arranged horizontally across 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 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 the pinion gear unit 833, and a rotary encoder 835 for detecting the printing point position.

By driving the motor 834 (forward or reverse), the droplet discharge unit 501 moves to the right or left along the movable unit 813. The drive unit 803 functions as an X-direction drive mechanism for the droplet discharge unit 501. Limit switches 837a and 837b are attached to both sides of the housing of the reducer 836.

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

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 the 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.

Although the above describes an embodiment of the present invention, the present invention is not limited to the above embodiment and various modifications are possible based on the technical concept described in the claims. For example, the shape of the bearing 121 may be any shape as long as it is capable of guiding the axial reciprocating motion of the valve body 113. As mentioned above, the bearing 121 may have ribs 121e and 121h protruding radially outward, may be cylindrical without ribs, or may have a conical shape tapering toward the nozzle 111, or may have a conical shape tapering toward the opposite side of the nozzle 111.

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 in place of the piezoelectric element 114.

1: droplet ejection head 2: connector 10: housing 10a: upper housing 10a1: through hole 10b: lower housing 10b1: step portion of accommodating hole 10b2: inner peripheral surface of accommodating hole 10b3: step portion of accommodating hole 11: supply port 12: recovery port 20, 30: pressure plate 40, 50: positioning pin 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 portion 115c: rear end portion 116: holding leaf spring 116a, 116b: spring portion 121: bearing 121a: lower end surface 121b: through hole 121c: through hole 121d: upper surface 121e, 121h: Ribs 121f: Upper surface 121g: Outer circumferential 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 target 802: Frame unit 803: Drive section 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

Japanese Patent Application Laid-Open No. 2021-151767

Claims (7)

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. The droplet ejection head of claim 1, characterized in that 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. 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. A droplet ejection head according to any one of claims 1 to 3, characterized in that the linear expansion coefficient of the bearing is greater than the linear expansion coefficient of the housing. A droplet ejection device comprising the droplet ejection head of any one of claims 1 to 4. 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. 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.