Droplet dispensing head, droplet dispensing unit, and droplet dispensing device

Abstract

To stabilize a fluid flow on an inlet side of nozzle holes, stabilize a flight direction of discharge droplets, and stabilize image quality.SOLUTION: A droplet discharge head 1 has a liquid channel 112 formed between a nozzle plate 101 having nozzle holes 111 and a housing 10 supporting a peripheral edge part of the nozzle plate 101, and discharges a liquid of the liquid channel 112 as droplets from the nozzle holes 111 by opening a valve body opened and closed by drive means, wherein the plurality of nozzle holes 111 are arranged in a longitudinal direction of the liquid channel 112, and the nozzle plate 101 and the housing 10 are connected to each other by a connection part 200 crossing the liquid channel 112 in a thickness direction, between the plurality of nozzle holes 111.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a droplet discharge head, a droplet discharge unit, and a droplet discharge device.

Background Art

[0002] As described in, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-131571), a droplet discharge device generates pressure in a pressure generation chamber by vibrating a diaphragm member with a piezoelectric member, and discharges droplets from fine nozzle holes formed in a nozzle plate with this pressure. In this case, since it is difficult to generate a large pressure in the pressure generation chamber, there is a restriction (upper limit) on the viscosity of the liquid to be used.

[0003] Therefore, as described in, for example, Patent Document 2 (Japanese Patent Application Laid-Open No. ********), a droplet discharge device has been developed in which high-pressure fluid flows inside a nozzle hole and the nozzle hole is opened and closed by a needle valve connected to a piezoelectric element. Such a droplet discharge device can handle a wide range of liquid viscosities. Droplet discharge devices are used in various fields, for example, to draw graphics or the like on the body of an automobile with high image quality, or to discharge a liquid resist or a DNA sample as droplets.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a droplet discharge device that uses high-pressure fluid, the fluid flow near the inlet of the nozzle hole is likely to affect the flight direction of the discharged droplets. In particular, when the nozzle holes 111 are arranged in a staggered pattern in order to achieve high image quality as shown in FIG. 2C(a) described later, since the nozzle holes are arranged close to each other, depending on the viscosity of the liquid used, the fluid flow near the inlet of the upstream nozzle hole greatly affects the fluid flow near the inlet of the downstream nozzle hole, and there is a problem that the flight direction of the discharged droplets may become unstable and the image quality may deteriorate.

[0005] Therefore, an object of the present invention is to stabilize the fluid flow on the inlet side of the nozzle hole, stabilize the flight direction of the discharged droplets, and stabilize the image quality. [Means for solving the problem]

[0006] To solve the aforementioned problems, the droplet dispensing head of the present invention is characterized in that a liquid flow path is formed between a nozzle plate having nozzle holes and a housing that supports the peripheral edge of the nozzle plate, and the liquid in the liquid flow path is discharged as droplets from the nozzle holes by opening a valve body which is opened and closed by a driving means, wherein a plurality of nozzle holes are arranged in the longitudinal direction of the liquid flow path, and the nozzle plate and the housing are connected between the plurality of nozzle holes by a connecting portion that crosses the liquid flow path. [Effects of the Invention]

[0007] This invention stabilizes the fluid flow at the nozzle inlet, thereby stabilizing the flight direction of the discharged droplets and improving image quality. [Brief explanation of the drawing]

[0008] [Figure 1A] This is a front view of the droplet dispensing head according to this embodiment. [Figure 1B] This is a perspective view of the droplet dispensing head according to this embodiment. [Figure 2A] This is a front view of the droplet dispensing head with the lower housing removed. [Figure 2B] This is a magnified perspective view of the lower end of the droplet dispensing head. [Figure 2C] This is a plan view of the nozzle plate of the droplet dispensing head. [Figure 3] This is a cross-sectional view of the liquid flow path of the droplet dispensing head. [Figure 4] (a) A cross-sectional view of the droplet dispensing head along the liquid flow path, and (b) and (c) a horizontal cross-sectional plan view of the lower end of the head. [Figure 5] This is a cross-sectional view along the liquid flow path of a modified droplet dispensing head. [Figure 6A] This is a horizontal cross-sectional plan view of a droplet dispensing head that is compatible with varying fluid viscosities. [Figure 6B]This diagram illustrates a method for designing droplet dispensing heads that can handle varying fluid viscosities. [Figure 6C] This is a plan view of the convex portion within the flow path. [Figure 7] This is a perspective view of a droplet dispensing device. [Figure 8] This is a perspective view of the drive unit of the droplet dispensing device. [Modes for carrying out the invention]

[0009] (● Droplet dispensing head) Embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1A is a front view of the droplet dispensing head 1, and Figure 1B is a perspective view of the droplet dispensing head 1 viewed from diagonally below.

[0010] The housing 10 of the droplet dispensing head 1 has an upper housing 10a and a lower housing 10b. The upper housing 10a and the lower housing 10b can also be formed integrally. A cover 20 is mounted on top of the upper housing 10a, and electrical components are arranged inside this cover 20. A connector portion 2 for the electrical components is provided at the upper end of the cover 20.

[0011] A nozzle plate 101 made of a corrosion-resistant metal such as stainless steel (SUS) is disposed on the lower surface of the lower housing 10b. Droplets are discharged from fine nozzle holes 111 formed in the nozzle plate 101.

[0012] A liquid flow path 112 is formed inside the lower housing 10b, as shown in Figure 3. One end of this flow path 112 is connected to the supply port 11, and the other end is connected to the recovery port 12.

[0013] The supply port 11 and the recovery port 12 are connected via a circulation passage L, and pressurized liquid pressurized by the pump P in the circulation passage L is supplied to the supply port 11. Pressurized liquid that is not discharged from the nozzle hole 111 is recovered from the recovery port 12 and then supplied back to the supply port 11 via the circulation passage L and pump P.

[0014] Since the liquid discharge head 1 of the present embodiment pressurizes the liquid supply pressure of the supply port 11 at a magnitude of several 100 kPa, the peripheral portion of the nozzle plate 101 and the housing 10 are firmly joined by an adhesive. When the liquid discharge head 1 is viewed from the bottom surface, conventionally, there has been a form without a connecting portion 200 described later.

[0015] However, the ink flowing into the flow path 112 has a high flow velocity, and if it is discharged from the recovery port 12 as it is, the flight direction of the discharged droplets from the nozzle holes 111 may be inclined. Further, when the nozzle holes 111 are formed in a double row or the number of nozzle holes is increased, the nozzle plate 101 becomes larger accordingly and its pressure receiving area increases.

[0016] Then, peeling may occur due to insufficient strength at the joint portion of the peripheral portion of the nozzle plate 101, and there has been a concern that ink may leak from the liquid chamber to the outside. Therefore, in the present embodiment, the nozzle plate 101 and the housing 10 are connected by a connecting portion 200 as described later.

[0017] When the aforementioned lower housing 10b is removed, the tip of the needle valve 113 as a shaft-like member is exposed from the bearing 121 on the lower surface of the upper housing 10a as shown in FIGS. 2A and 2B. The needle valve 113 is made of a metal such as corrosion-resistant SUS, and is very thin with a diameter of 1 mm or less at the thin portion and about 2 mm even at the thick portion. This thin needle valve 113 is exposed from the bearing 121 of the upper housing 10a with a length of, for example, 1 to 20 mm.

[0018] A valve body 113a for opening and closing the nozzle hole 111 is disposed at the tip of the needle valve 113. An O-ring 113b having elasticity as a seal member and a washer 113c for fixing the O-ring 113b to the needle valve 113 are disposed above the valve body 113a.

[0019] The peripheral edge of the nozzle plate 101 is joined to the housing 10 with a thermosetting resin or the like. Conventionally, the nozzle holes 111 of the nozzle plate 101 were often formed in a single row, as shown in Figure 2C(b), but in recent years, in order to improve image quality and make the device more compact, it is not uncommon for them to be formed in two or more rows, as shown in Figure 2C(a).

[0020] In other words, in the case of a nozzle plate 101 having a single row of nozzle holes 111 as shown in Figure 2C(b), the nozzle plate 101 must be arranged at a considerable angle with respect to the printing direction X in order to obtain the desired image quality. This results in limitations on the printable area, as shown in the shaded area, leading to decreased productivity due to an increase in the number of prints required by the user, as well as inconvenience during printing.

[0021] As shown in Figure 2C(a), in the case of a nozzle plate 101 having two rows of nozzle holes 111, by arranging the nozzle holes 111 in a staggered pattern, it is possible to achieve higher image quality, a more compact device, and improved production efficiency through an increased coating area without having to tilt the nozzle plate 101 with respect to the printing direction X.

[0022] The aforementioned example involves joining six nozzle plates 101, as shown in Figures 2C(a) and 2C(b), to a housing 10. However, a droplet dispensing unit may also be constructed by arranging six droplet dispensing heads 1, each with a housing joined to a nozzle plate 101. By configuring a droplet dispensing unit with multiple droplet dispensing heads 1 in this way, a liquid supply channel can be provided for each nozzle plate 101. This makes it possible to supply and dispense different liquids to each nozzle plate 101.

[0023] For example, if a different color of ink is supplied to each of the six nozzle plates 101 in Figure 2C(a), an image can be formed using six different colored inks with a single droplet ejection unit. Alternatively, by supplying liquids of different viscosities to the droplet ejection heads 1 that make up each of the six nozzle plates 101, droplets of different viscosities can be ejected with a single droplet ejection unit.

[0024] The droplet dispensing head 1 requires adjustment of its flow path design and driving method depending on the viscosity of the droplets to be dispensed. By configuring the droplet dispensing unit with multiple droplet dispensing heads 1, it is possible to combine droplet dispensing heads 1 designed to suit the viscosity of the liquids to be dispensed. This makes it possible to appropriately dispense multiple types of liquids with different viscosities using a single droplet dispensing unit.

[0025] (●Opening and closing drive of the needle valve) As shown in Figure 3, a needle valve 113 and a piezoelectric element 114 that drives the needle valve 113 are arranged in the upper housing 10a. The piezoelectric element 114 is held in the central space 115a of the holding member 115.

[0026] Spring portions are formed at both the upper and lower ends of the holding member 115, and these spring portions hold the piezoelectric element 114 in a compressed state in the axial direction (along the Z direction). The tip portion 115b of the holding member 115 and the rear end portion of the needle valve 113 are connected coaxially to the piezoelectric element 114 and the needle valve 113. As a result, when the piezoelectric element 114 contracts in the longitudinal direction (along the Z direction), the holding member 115 also contracts in the longitudinal direction (along the Z direction), allowing a biasing force to be applied to the needle valve 113 in the direction that opens the nozzle hole 111 (opposite to the Z direction).

[0027] The piezoelectric element 114 operates in d31 mode when a voltage is applied by the voltage application means, driving the needle valve 113 in the direction that opens the nozzle hole 111 (opposite to Z). In other words, the needle valve 113 is driven in the direction that opens the nozzle hole 111 (opposite to Z) when a voltage is applied to the piezoelectric element 114.

[0028] Therefore, when no voltage is applied to the piezoelectric element 114, the needle valve 113 blocks the nozzle hole 111. As a result, even if pressurized liquid is supplied to the flow path 112, no liquid is discharged from the nozzle hole 111.

[0029] Then, by applying a voltage to the piezoelectric element 114, the piezoelectric element 114 contracts and pulls the needle valve 113 via the holding member 115, causing the valve body 113a of the needle valve 113 to move away from the nozzle hole 111 and open the nozzle hole 111. As a result, the pressurized liquid supplied to the flow path 112 is discharged as droplets from the nozzle hole 111.

[0030] The piezoelectric element 114 can also be operated in d33 mode, in which it extends in the direction (Z direction) that closes the needle valve 113 when a voltage is applied. When the piezoelectric element operates in d33 mode, the valve body 113a of the needle valve 113 is pressed against the nozzle hole 111 side when a voltage is applied, thereby closing the nozzle hole 111.

[0031] When discharging droplets, the voltage applied to the piezoelectric element 114 is stopped or reduced, causing the valve body 113a of the needle valve 113 to move in the opening direction (opposite to Z) and open the nozzle hole 111. The d33 mode of the piezoelectric element 114 has high responsiveness and large displacement. Therefore, the d33 mode is suitable when it is desired to improve the responsiveness of the opening and closing operation of the needle valve 113 and reduce variations in the droplet speed and volume of the liquid discharged from the nozzle hole 111.

[0032] (● Up and down movement of the needle valve) The retaining member 115 is positioned within the upper housing 10a so as to be adjustable in the vertical direction (along the Z-axis) as shown in Figure 3. The rear end portion 115c of the retaining member 115 can be positioned and fixed to the upper housing 10a by a fixing screw 124. Female screw holes 115d are formed in the rear end portion 115c of the retaining member 115 in the axial direction (along the Z-axis) and the direction perpendicular to the X-axis, and the tip of the fixing screw 124 is screwed into these female screw holes 115d.

[0033] As shown in Figure 3, an elongated hole 30 is formed at the upper end of the upper housing 10a in the axial direction (along the Z-axis), and a fixing screw 124 is inserted through this elongated hole 30. When the fixing screw 124 is loosened, the retaining member 115 becomes movable up and down.

[0034] The fixing screw 124 is tightened and fixed to the elongated hole 30 at a position where a predetermined gap δ is formed between the valve body 113a and the nozzle hole 111, as shown in Figure 3. The droplet dispensing head 1 is delivered as a product in this state.

[0035] (● Droplet dispensing head) As shown in Figures 1B and 4, nozzle holes 111 are formed in the nozzle plate 101 along the flow path 112 from the supply port 11 to the recovery port 12. Figure 4(b) shows the case where two rows of nozzle holes 111 are formed, and Figure 4(c) shows the case where one row of nozzle holes 111 is formed. The nozzle holes 111 consist of four in a row, and these nozzle holes 111 are opened and closed by the valve body 113a at the tip of the needle valve 113. Note that 2a and 2b in Figure 4(a) are lead wires of the connector part 2.

[0036] Conventionally, the fluid flow near the inlet of the nozzle hole 111 has not been given particular consideration. However, the inventors of this invention have confirmed that the fluid flow near the inlet of the nozzle hole 111 is affected by the viscosity and pressure of the fluid used, which in turn affects the flight direction of the discharged droplets. In other words, it was found that the flight direction of the discharged droplets deviates from the axial direction of the nozzle hole 111 (the direction along Z) depending on the viscosity and pressure of the fluid. When the flight direction of the discharged droplets is deviated in this way, the quality of the image formed by the discharged droplets deteriorates.

[0037] Furthermore, insufficient consideration was given to reinforcing the nozzle plate 101 when using high-pressure fluid. In particular, when the nozzle holes 111 are arranged in two (or multiple) rows as shown in Figure 4(b), the width or volume of the flow path 112 increases, and the pressure-receiving area of ​​the nozzle plate 101 increases accordingly. As a result, an excessive peeling force acts on the joint portion of the peripheral edge of the nozzle plate 101 with respect to the lower housing 10b, making peeling and fluid leakage at the joint portion more likely.

[0038] (●Connection part) Therefore, in this embodiment, as shown in Figures 4(b) and 4(c), the inside of the nozzle plate 101 and the housing 10a are connected at the upstream and downstream sides of each nozzle hole 111 of the nozzle plate 101 by a connecting portion 200 that crosses the flow path 112 in the vertical direction (along the Z direction) as shown in Figure 4(a).

[0039] Figure 4(b) shows a configuration in which four nozzle holes 111 are arranged in a staggered pattern in two rows along the longitudinal direction (direction along the Y) of the flow path 112, with connecting parts 200 placed only upstream and downstream (upstream and downstream) of each nozzle hole 111 in each row. The connecting parts 200 are also formed in a staggered pattern, similar to the nozzle holes 111.

[0040] The longitudinal direction (along the Y-axis) of the flow path 112 is the direction in which the liquid flows from the supply port 11 to the recovery port 12. The connecting portion 200 has an elongated shape that extends along the longitudinal direction (along the Y-axis) of the flow path 112, and its upstream and downstream ends are sharpened so as not to obstruct the fluid flow.

[0041] The fluid flowing from the supply port 11 through the flow path 112 to the recovery port 12 forms a three-row flow as shown in Figure 4(b). The center of the three rows is the central liquid flow path, and no connecting portion 200 is formed in this central liquid flow path. This makes the flow velocity near the entrance of each nozzle hole 111 in the flow path 112 uniform, allowing a stable flow velocity of liquid to be supplied near the entrance of the nozzle holes 111, and thus stabilizing the flight direction of the discharged droplets.

[0042] Since there are connecting sections 200 between the three rows of flow, the inclination of the fluid into the nozzle hole 111 is suppressed. In addition, there are three rows of fluid flow, including the central liquid flow path, on both sides of each row of nozzle holes 111, that is, on both sides in the direction perpendicular to the flow (along the X direction).

[0043] This averages out the fluid flow state near the entrance of each nozzle hole 111, stabilizing the flight direction of the ejected droplets. Furthermore, since the ink flow velocity near the entrance of the nozzle hole 111 is suppressed, the range of ink viscosities that can be handled is wider compared to Figure 4(c), which will be explained next. Therefore, this is advantageous when supplying liquids of different viscosities to the six heads (nozzle plates 101) in Figure 2C.

[0044] Figure 4(c) shows a configuration in which four nozzle holes 111 are formed in a row along the longitudinal direction (along the Y-axis) of the flow path 112, with connecting parts 200 positioned on the upstream and downstream sides of each nozzle hole 111. Similar to Figure 4(b), the connecting parts 200 have an elongated shape extending along the longitudinal direction (along the Y-axis) of the flow path 112, and their upstream and downstream ends are sharpened so as not to obstruct the fluid flow.

[0045] In Figure 4(c), the fluid flowing from the supply port 11 through the flow path 112 to the recovery port 12 forms a two-tiered flow. Because there is a connecting section 200 between the two tiers of flow, the inclination of the fluid flowing into the nozzle hole 111 is suppressed.

[0046] This stabilizes the flight direction of the ejected droplets. Furthermore, fluid flow exists on both sides of each nozzle hole 111, that is, on both sides perpendicular to the flow (along the X direction). This averages out the fluid flow state near the entrance of each nozzle hole 111, stabilizing the flight direction of the ejected droplets. Compared to the configuration in Figure 4(b), it is less likely to suppress the ink flow velocity near the entrance of the nozzle hole 111, making it suitable for use with relatively high viscosity inks.

[0047] As shown in Figure 4(a), the aforementioned connecting portion 200 can be integrally formed with the upper housing 10a on the lower surface of the upper housing 10a facing the flow path 112. The lower end surface of the connecting portion 200 is joined to the upper surface of the nozzle plate 101 using a thermosetting resin or the like.

[0048] This allows for a flow path shape that is unaffected even if the viscosity changes depending on the ink color and intended use (usage environment). The length and width of the connecting section 200 can be determined arbitrarily.

[0049] The height of the outer periphery of the flow path 112 and the vertical (along the Z-axis) height of the connecting portion 200 can be set to be the same. This allows the lower end surface of the connecting portion 200 and the lower surface of the outer periphery of the flow path 112 to be positioned on the same plane, and the upper surface of the nozzle plate 101 to be joined to them without deformation and without any gaps.

[0050] The length and width of the connecting section 200 can be set arbitrarily, but it is preferable to make it as long and wide as possible without obstructing the flow in the channel 112. This increases the contact area between the nozzle plate 101 and the upper housing 10a.

[0051] In other words, the connecting portion 200 can improve the connecting force (pressure resistance of the nozzle plate 101) between the nozzle plate 101 and the upper housing 10a. Since the connecting force is proportional to the cross-sectional area of ​​the connecting portion 200, it is advantageous to form the connecting portion 200 as long and wide as possible along the flow path 112, as shown in Figure 5.

[0052] In this way, by supporting a portion of the liquid pressure acting on the nozzle plate 101 with the connecting portion 200, the peeling force caused by the liquid pressure acting on the peripheral joint portion of the nozzle plate 101 can be reduced, preventing peeling and liquid leakage at the joint portion. Furthermore, the connecting portion 200 can improve the pressure resistance of the nozzle plate 101, thereby maintaining the flatness of the nozzle plate 101 with high precision and increasing the joint strength. This makes it possible to suppress variations in the velocity and volume of liquid droplets from each nozzle hole 111.

[0053] The nozzle plate 101 and the upper housing 10a can be made of a material that has corrosion resistance to high-pressure liquids and sufficient strength. There are no particular restrictions on the material of the nozzle plate 101 and the upper housing 10a, and they can be appropriately selected according to the purpose.

[0054] The materials for the nozzle plate 101 and the upper housing 10a can be selected from, for example, stainless steel, Al, Bi, Cr, InSn, ITO, Nb, Nb2O5, NiCr, Si, SiO2, Sn, Ta2O5, Ti, W, ZAO(ZnO+Al2O3), Zn, etc. These may be used individually or in combination of two or more. Among these, stainless steel is preferred from the viewpoint of corrosion resistance.

[0055] When the nozzle plate 101 and the upper housing 10a are interconnected via the connecting portion 200 as described above, if the difference in the coefficient of thermal expansion between the nozzle plate 101 and the upper housing 10a is large, deformation may occur at the lower end joint of the connecting portion 10a1. Such deformation will adversely affect the flatness of the nozzle plate 101, reducing the droplet ejection accuracy (drawing accuracy) from the nozzle hole 111.

[0056] Therefore, it is desirable that the nozzle plate 101 and the upper housing 10a be made of the same material. If they are made of the same material, the amount of thermal shrinkage when the thermosetting resin cools and hardens at the lower end joint of the connecting part 200 will be the same for the nozzle plate 101 and the connecting part 200, which will allow the flatness of the nozzle plate 101 to be maintained with high precision and the joint strength to be increased. This makes it possible to suppress variations in droplet velocity and volume for each nozzle hole 111.

[0057] In this embodiment, the nozzle plate 101 and the upper housing 10a are made of stainless steel (SUS304). Instead of the connecting portion 200 of the upper housing 10a, a similar connecting portion may be integrally formed on the upper surface of the nozzle plate 101, and the upper end of the connecting portion may be joined to the lower surface of the upper housing 10a with a thermosetting resin.

[0058] Furthermore, as shown in Figure 5, it is also possible to arrange a connecting section 210 that is completely separate from the upper housing 10a and nozzle plate 101. In this case, the range of materials that can be selected for the connecting section 210 is expanded, and the connecting section 210 can be easily formed into a complex shape. As a result, even if the viscosity changes depending on the ink color and intended use (usage environment), the flow path shape can be made to be less affected by viscosity than the integrated connecting section 200 in Figure 4.

[0059] (● Distance between nozzle hole and connecting part) In Figure 4, the distance between the nozzle hole 111 and the flow path 112 of the connecting portion 200 in the longitudinal direction (along the Y direction) is approximately the same on the upstream and downstream sides of the nozzle hole 111. However, depending on the viscosity of the liquid (ink) used, the distance between the upstream and downstream sides of the nozzle hole 111 can be different.

[0060] Figures 6A(a) and (b) show examples where the spacing immediately upstream and immediately downstream of the nozzle hole 111 is different for low-viscosity and high-viscosity liquids. Figure 6A(a) shows the case when a low-viscosity liquid is used. Since the flow of a low-viscosity liquid is easily changed, the immediate upstream spacing A1 is made shorter than the immediate downstream spacing B1 (A1 <B1)。

[0061] In contrast, when using high-viscosity liquids, the immediate upstream spacing A2 is made longer than the immediate downstream spacing B2, as shown in Figure 6A(b) (A2>B2). Since the flow of high-viscosity liquids is relatively stable, it is not necessary to shorten the upstream spacing A2 as is done with low-viscosity liquids.

[0062] Conversely, if the immediate upstream distance A2 is made too short, it may obstruct the fluid flow into the nozzle hole 111. Therefore, the ratio A / B of the upstream distance A from the nozzle hole 111 to the immediate upstream connecting section 200 and the downstream distance B to the immediate downstream connecting section 200 increases as the viscosity of the liquid flowing through the liquid channel 112 increases. In this way, the arrangement of the connecting section 200 is changed for low-viscosity liquids (first liquid) and high-viscosity liquids (second liquid).

[0063] Figure 6B is a flowchart illustrating the flow path design method. In this flowchart, the size and shape of the protrusions (connecting parts 200) are changed depending on whether the viscosity of the liquid (ink) used is greater or less than the standard viscosity A.

[0064] Here, we assume that Figures 4(b) and 4(c) show the case where ink with standard viscosity A is used. In this case, the upstream distance from the nozzle hole 111 to the protrusion (connecting part 200) and the downstream distance are assumed to be the same. Also, the connecting part width W of the protrusion (connecting part 200) in the longitudinal direction of the flow path (along the Y direction) and the perpendicular direction (along the X direction) can be, for example, 1 mm.

[0065] When using an ink (first liquid) with viscosity B lower than standard viscosity A, • Increase the width W of the connecting section in the longitudinal direction (along the Y direction) and the perpendicular direction (along the X direction) of the flow path as shown in Figure 6C(a) (1 mm <W)。 • As shown in Figure 6A(a), shorten the upstream spacing A1 and lengthen the downstream spacing B1 (A1 <B1)。 • Smooth the surface of the protruding portion (connecting portion 200) as shown in Figure 6C(a). This stabilizes the flow velocity and flow direction near the nozzle hole 111 entrance in the flow path.

[0066] When using an ink (second liquid) with a viscosity C greater than the standard viscosity A, • Reduce the width W of the connecting section in the longitudinal direction (along the Y direction) and the perpendicular direction (along the X direction) of the flow path as shown in Figure 6C(a) (W < 1 mm). • As shown in Figure 6A(b), lengthen the upstream spacing A2 and shorten the downstream spacing B2 (B2 <A2)。 As shown in Figures 6C(b) and 6C(c), indentations (dimples) 200a and projections 200b are formed on the surface of the convex portion (connecting portion 200). The indentations 200a and projections 200b may be formed in combination. As a result, the flow velocity and flow direction near the nozzle hole 111 entrance in the flow path are stabilized.

[0067] The connection width W of the connection part 200 is in the plane direction of the nozzle plate 101 and Liquid channel is the width in the direction perpendicular to the longitudinal direction (the direction along Y) of 112 (the direction along X). As the viscosity of the liquid flowing through the liquid flow path 112 increases, the connection width W of this connection part 200 decreases.

[0068] The degree of the size (depth·height) of the recess 200a and the protrusion 200b is calculated based on the average value of the surface roughness of the connection part 200. As the calculation methods, "ten-point average roughness" and "arithmetic average roughness" can be used. In JIS, they are denoted as "Ra" and "RzJIS". The surface roughness (Ra) of the connection part 200 increases as the viscosity of the liquid flowing through the liquid flow path 112 increases.

[0069] (Regarding the interval AB, the connection width W, and the roughness Ra) The reason for setting the interval AB, the connection width W, and the roughness Ra as described above corresponding to the ink viscosity will be further explained below. [Interval AB] droplet When the ink viscosity used in the discharge head 1 increases (the second liquid), a boundary layer is generated on the surface of the nozzle hole 111 side on the downstream side of the connection part 200, and backflow occurs, resulting in a decrease in the flow velocity. Due to this decrease in the flow velocity, the amount and velocity of the droplets discharged from the downstream nozzle hole 111 decrease.

[0070] By increasing the distance from the connection part 200 to the nozzle hole 111 on the downstream side, the once-decreased flow velocity begins to accelerate. As a result, the amount and velocity of the droplets discharged from the nozzle hole 111 recover. Therefore, droplet when the ink viscosity used in the discharge head 1 increases (the second liquid), the upstream interval A2 is increased and the downstream interval B2 is decreased (B2 < A2). Thus, it is necessary to adjust to increase the distance from the connection part 200 to the downstream nozzle hole 111.

[0071] [Connection width W] dropletWhen the viscosity of the ink used in the discharge head 1 increases (second liquid), as described above, the decrease in flow velocity when the ink collides with the connecting part 200 becomes greater, and the inlet flow velocity of the downstream nozzle hole 111 slows down. This decrease in flow velocity reduces the amount and speed of the droplets discharged from the downstream nozzle hole 111. Therefore, when the viscosity of the ink used increases, the width W of the connecting part 200 is narrowed to reduce the fluid resistance caused by the connecting part 200, thereby increasing the inlet flow velocity of the downstream nozzle hole 111.

[0072] [Roughness Ra] droplet As the viscosity of the liquid used in the discharge head 1 increases (the second liquid), the inlet flow velocity of the nozzle hole 111 downstream of the connecting section 200 decreases, as described above. This decrease in flow velocity reduces the amount and speed of the droplets discharged from the downstream nozzle hole 111.

[0073] In this case, if the surface of the connecting portion 200 is a smooth surface without irregularities, a boundary layer will be generated along the surface of the connecting portion 200, causing a large vortex (backflow) to be generated downstream of the connecting portion 200, resulting in a greater decrease in flow velocity. Therefore, by creating irregularities on the surface of the connecting portion 200, a turbulent boundary layer is formed (boundary layer control), and the separation point of the surface of the connecting portion 200 is moved upstream, thereby suppressing the decrease in flow velocity.

[0074] Thus, droplet By optimizing the shape and arrangement of the connecting portion 200 of the droplet ejection head 1 according to the viscosity of the liquid ejected from the ejection head 1, stable ejection performance can be obtained for multiple liquids with different viscosities (a first liquid and a second liquid). In other words, a single droplet ejection unit can be constructed by combining a droplet ejection head (HB) appropriately designed for ink with viscosity B and a droplet ejection head (HC) appropriately designed for ink with viscosity C, for example, two or more liquids with different viscosities. This makes it possible to eject inks with different viscosities (at least viscosity B and viscosity C) with stable ejection performance using a single droplet ejection unit.

[0075] As mentioned above, by adjusting only one of the values ​​for the spacing AB, connecting section width W, and roughness Ra, it is possible to configure multiple droplet dispensing heads that are appropriately designed for two or more liquids with different viscosities. Similarly, by adjusting any combination of values ​​for spacing AB, connecting section width W, and roughness Ra, it is possible to configure multiple droplet dispensing heads that are appropriately designed for two or more liquids with different viscosities. By adjusting multiple values ​​for spacing AB, connecting section width W, and roughness Ra, it becomes possible to handle a wider range of fluid viscosities compared to adjusting only one value.

[0076] (Droplet discharge device) Next, an embodiment of the droplet dispensing device 500 using the droplet dispensing head 1 shown in Figure 1 will be described with reference to Figures 7 and 8. As mentioned above, the droplet dispensing head 1 has a connecting section configured to correspond to the viscosity of the liquid used. Figure 7 is a perspective view of the droplet dispensing device 500, and Figure 8 is a perspective view of the drive unit of the droplet dispensing device 500.

[0077] The droplet ejection device 500 includes a movable frame unit 802 that is installed facing a printed object 700 having a curved surface, such as the hood of a vehicle. A movable unit 813 is attached to the left and right frame members 810 and 811 that make up the frame unit 802, so as to span across the frame members 810 and 811, and is capable of moving up and down vertically (in the Y direction).

[0078] The movable unit 813 is equipped with a drive unit 803 that incorporates a motor and is arranged to move back and forth horizontally (along the X direction) on the movable unit 813, and a droplet ejection unit 501 that is attached to the drive unit 803 and ejects liquid toward the object to be printed 700.

[0079] The system also includes a controller 805, which acts as a control unit for controlling the discharge of liquid from the droplet dispensing unit 501, the reciprocating movement of the drive unit 803, and the raising and lowering of the movable unit 813, and an information processing device 806, such as a PC (personal computer), which gives instructions to the controller 805. A database unit (DB unit) 807 is connected to the information processing device 806 for recording and storing information about the print target object 700, such as its shape and size.

[0080] The frame unit 802 includes upper and lower left and right frame members 808, 809, 810, and 811 formed from metal columnar bodies or the like, and left and right leg members 812a and 812b attached perpendicularly and horizontally to both sides of the lower frame member 809 to allow the frame unit 802 to stand on its own. The movable unit 813, which is spanned 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.

[0081] The object to be printed 700 is positioned perpendicular to the liquid discharge direction (Z direction), that is, 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 object to be printed 700 can be positioned at a predetermined location to be printed, for example, by using a chuck attached to the tip of the arm of a multi-jointed robotic arm to hold the back side of the printing area of ​​the object to be printed 700 by suction. By using a multi-jointed robotic arm, it is possible to accurately position the object to be printed 700 at the print position, and the orientation of the object to be printed 700 can also be changed as needed.

[0082] As shown in Figure 7, the drive unit 803 is arranged to be able to reciprocate horizontally (along the X direction) on the movable unit 813. The movable unit 813 is composed of a rail 830 horizontally arranged so as to span across the left and right frame members 810 and 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 by sliding, a pinion gear unit 833 connected to the linear guide 832 and meshing with the rack gear 831, a motor 834 with a reduction gear 836 that rotationally drives the pinion gear unit 833, and a rotary encoder 835 for detecting the position of the printing point.

[0083] By driving the motor 834 (forward or reverse rotation), the droplet dispensing unit 501 is moved along the movable unit 813 in the rightward or leftward direction in the X direction of Figure 8. The drive unit 803 functions as a drive mechanism for the droplet dispensing unit 501 in the X direction. Limit switches 837a and 837b are mounted on both sides of the housing of the reduction gear 836.

[0084] The droplet dispensing unit 501 includes, for example, at least one droplet dispensing head 1 that dispenses liquids of black, cyan, magenta, yellow, and white, or a droplet dispensing head 1 having multiple nozzle rows. Each droplet dispensing head 1 or each nozzle row of the droplet dispensing head 1 of the droplet dispensing unit 501 is supplied under pressure from a liquid tank with liquid of each color. Since the droplet dispensing head 1 can be configured to correspond to the viscosity of the liquids used, even if the viscosities of each liquid are different, a single droplet dispensing unit 501 can appropriately dispense each liquid.

[0085] 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 required image onto the object to be printed 700. The aforementioned "droplet ejection device" is not limited to those in which meaningful images such as characters or figures are visualized by the ejected liquid. For example, it also includes those that form patterns or uniform paint films that do not have meaning in themselves, or those that create three-dimensional images.

[0086] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible based on the technical idea described in the claims. For example, the nozzle plate 101 and the lower housing 10b can be joined by methods other than adhesive, for example, the nozzle plate 101 and the lower housing 10b may be joined by diffusion bonding.

[0087] Furthermore, the liquid flow path 112 does not necessarily need to be connected to the circulation passage L, and the system can also be applied to droplet dispensing heads of a type that do not have a recovery port 12 and discharge all supplied liquid from the nozzle hole 111. In addition, the piezoelectric element 114 can be replaced with other drive bodies that extend and retract in the longitudinal direction. For example, a piston that extends and retracts in the longitudinal direction using an electromagnetic solenoid can be used instead of the piezoelectric element 114.

[0088] Furthermore, the droplet ejection device according to the present invention is not limited to the form of the printing apparatus described above. For example, the droplet ejection head of the present invention may be attached to the tip of a robotic arm of a multi-joint robot that has multiple joints that allow for free movement like a human arm. The present invention may also be applied to unmanned aerial vehicles such as drones, or to robots capable of climbing walls. droplet It may be equipped with a discharge head and take the form of an unmanned aerial vehicle capable of painting and spraying, or a climbing robot capable of painting and spraying.

[0089] <●Note> Preferred embodiments of the present invention are described below. <First aspect> The first embodiment is a droplet dispensing head in which a liquid flow path is formed between a nozzle plate having nozzle holes and a housing that supports the peripheral edge of the nozzle plate, and the liquid in the liquid flow path is discharged as droplets from the nozzle holes by opening a valve body that is opened and closed by a driving means, wherein a plurality of nozzle holes are arranged in the longitudinal direction of the liquid flow path, and the nozzle plate and the housing are connected between the plurality of nozzle holes by a connecting portion that crosses the liquid flow path. <Second aspect> The first embodiment is a droplet dispensing head characterized by comprising a supply port for supplying liquid to the liquid channel and a recovery port for discharging the liquid from the liquid channel, wherein the plurality of nozzle holes are arranged in a line along the direction in which the liquid flows from the supply port to the recovery port. <Third aspect> A third embodiment is a droplet dispensing head according to the first or second embodiment, characterized in that the nozzle holes are formed in a plurality of rows extending in the longitudinal direction of the liquid flow path, and the connecting portion is formed only upstream and downstream of the nozzle holes included in each of the plurality of rows. <Fourth aspect> The fourth embodiment is a droplet dispensing head according to the third embodiment, characterized in that the multiple rows of nozzle holes and the connecting portion are arranged in a staggered pattern. <Fifth aspect> The fifth embodiment is characterized in that the nozzle holes are formed in two rows extending in the longitudinal direction of the liquid flow path, and the connecting portion is formed between each of the nozzle holes in the two rows. Liquid channel This is a droplet dispensing head according to any one of the first to fourth embodiments, characterized in that it has a central liquid flow path formed between the rows of the two rows of nozzle holes. <Sixth aspect> The sixth embodiment is a droplet dispensing head according to the first or second embodiment, characterized in that the nozzle holes are formed in a single row extending in the longitudinal direction of the liquid flow path, and the connecting portion is formed between each of the nozzle holes in the single row. <Seventh aspect> The seventh embodiment is a droplet dispensing head according to any one of the first to sixth embodiments, characterized in that the connecting portion is formed integrally with the housing. <Eighth aspect> The eighth embodiment is a droplet dispensing head according to any one of the first to sixth embodiments, characterized in that the connecting portion is formed separately from the housing. <Ninth aspect> The ninth aspect is a droplet dispensing unit comprising a plurality of droplet dispensing heads according to any one of the first to eighth aspects, wherein the plurality of droplet dispensing heads dispense a first liquid droplet The nozzle plate is in the planar direction of the first liquid and includes a discharge head and a second droplet discharge head that discharges a second liquid having a higher viscosity than the first liquid. Liquid channel The droplet dispensing unit is characterized in that the width of the connecting portion in the direction perpendicular to the longitudinal direction of the unit is defined as the connecting portion width, and the connecting portion width of the first droplet dispensing head is greater than the connecting portion width of the second droplet dispensing head. <Tenth aspect> The tenth embodiment is a droplet dispensing unit comprising a plurality of droplet dispensing heads of the second embodiment, wherein the plurality of droplet dispensing heads dispense a first liquid droplet A droplet dispensing unit comprising a dispensing head and a second droplet dispensing head that dispensing a second liquid having a higher viscosity than the first liquid, wherein the upstream distance from the nozzle hole of the first droplet dispensing head to the immediately upstream connecting portion is shorter than the downstream distance from the nozzle hole to the immediately downstream connecting portion, and the upstream distance from the nozzle hole of the second droplet dispensing head to the immediately upstream connecting portion is longer than the downstream distance from the nozzle hole to the immediately downstream connecting portion. <11th aspect> The eleventh embodiment is a droplet dispensing unit comprising a plurality of droplet dispensing heads according to any one of the first to eighth embodiments, wherein the plurality of droplet dispensing heads dispense a first liquid dropletA droplet dispensing unit comprising a dispensing head and a second droplet dispensing head for dispensing a second liquid having a higher viscosity than the first liquid, wherein the surface roughness of the connecting portion of the first droplet dispensing head is smaller than the surface roughness of the connecting portion of the second droplet dispensing head. <Twelfth aspect> The twelfth embodiment is a droplet dispensing device characterized by including a droplet dispensing head according to any one of the first to eighth embodiments, or a droplet dispensing unit according to any one of the ninth to eleventh embodiments, and a control unit for controlling the driving means. [Explanation of symbols]

[0090] 1: Droplet dispensing head 2: Connector section 10: Housing 10a: Upper housing 10a1~10a5: Connecting section 10b: Lower housing 11: Supply port 12: Recovery port 20: Cover 30: Slot 101: Nozzle plate 111: Nozzle hole 112: Liquid flow path 113: Needle valve 113a: Valve body 113b: O-ring 113c: Washer 114: Piezoelectric element 115: Holding member 115a: Central space 115b: Tip 115c: Rear end 115d: Female threaded hole 121: Bearing 124: Fixing screw 200: Connecting part (protruding part) 210: Connecting part (protruding part) 500: Droplet dispensing device 501: Droplet ejection unit 700: Print target 802: Frame unit 803: Drive unit 805: Controller (control unit) 806: Information processing unit 807: Database section (DB section) 808~811: 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 836: Reducer 837a, 837b: Limit switch L: Circulation passage P: pump δ: gap A1, A2: Upstream spacing B1, B2: Downstream spacing W: Connection width [Prior art documents] [Patent Documents]

[0091] [Patent Document 1] Japanese Patent Publication No. 2011-131571 [Patent Document 2] Japanese Patent Publication No. 2020-023177

Claims

1. In a droplet dispensing head, a liquid channel is formed between a nozzle plate having nozzle holes and a housing supporting the peripheral edge of the nozzle plate, and by opening a valve body operated by a drive mechanism, the liquid in the liquid channel is discharged as droplets from the nozzle holes, A droplet dispensing head characterized in that a plurality of nozzle holes are arranged in the longitudinal direction of the liquid flow path, and the nozzle plate and the housing are connected between the plurality of nozzle holes by a connecting portion that crosses the liquid flow path.

2. The droplet dispensing head according to claim 1, comprising a supply port for supplying liquid to the liquid channel and a recovery port for discharging the liquid from the liquid channel, wherein the plurality of nozzle holes are arranged in a line along the direction in which the liquid flows from the supply port to the recovery port.

3. The droplet dispensing head according to claim 1, characterized in that the nozzle holes are formed in a plurality of rows extending in the longitudinal direction of the liquid flow path, and the connecting portion is formed only upstream and downstream of the nozzle holes included in each of the plurality of rows.

4. The droplet dispensing head of the 3rd, characterized in that the multiple rows of nozzle holes and the connecting portion are each arranged in a staggered pattern.

5. The droplet dispensing head according to claim 1, characterized in that the nozzle holes are formed in two rows extending in the longitudinal direction of the liquid flow path, the connecting portion is formed between each of the nozzle holes in the two rows, and the liquid flow path has a central liquid flow path formed between the rows of nozzle holes.

6. The droplet dispensing head according to claim 1, characterized in that the nozzle holes are formed in a single row extending in the longitudinal direction of the liquid flow path, and the connecting portion is formed between each nozzle hole in the single row.

7. The droplet dispensing head according to claim 1, characterized in that the connecting portion is formed integrally with the housing.

8. The droplet dispensing head according to claim 1, characterized in that the connecting portion is formed separately from the housing.

9. A droplet dispensing unit comprising a plurality of droplet dispensing heads according to claim 1, The plurality of droplet dispensing heads include a first droplet dispensing head for dispensing a first liquid and a second droplet dispensing head for dispensing a second liquid having a higher viscosity than the first liquid. The width of the connecting portion in the direction of the surface of the nozzle plate and perpendicular to the longitudinal direction of the liquid flow path is defined as the width of the connecting portion. A droplet dispensing unit characterized in that the width of the connecting portion of the first droplet dispensing head is greater than the width of the connecting portion of the second droplet dispensing head.

10. A droplet dispensing unit comprising a plurality of droplet dispensing heads according to claim 2, The plurality of droplet dispensing heads include a first droplet dispensing head for dispensing a first liquid and a second droplet dispensing head for dispensing a second liquid having a higher viscosity than the first liquid. The upstream distance from the nozzle hole of the first droplet dispensing head to the immediately upstream connecting portion is shorter than the downstream distance from the nozzle hole to the immediately downstream connecting portion. The upstream distance from the nozzle hole of the second droplet dispensing head to the immediately upstream connecting portion is longer than the downstream distance from the nozzle hole to the immediately downstream connecting portion. A droplet dispensing unit characterized by the following features.

11. A droplet dispensing unit comprising a plurality of droplet dispensing heads according to claim 1, The plurality of droplet dispensing heads include a first droplet dispensing head for dispensing a first liquid and a second droplet dispensing head for dispensing a second liquid having a higher viscosity than the first liquid. The surface roughness of the connecting portion of the first droplet dispensing head is smaller than the surface roughness of the connecting portion of the second droplet dispensing head. A droplet dispensing unit characterized by the following features.

12. A droplet dispensing head according to any one of claims 1 to 8, or a droplet dispensing unit according to any one of claims 9 to 11, A control unit that controls the drive means, A droplet dispensing device characterized by including the following:

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