Inkjet head and inkjet recording device

Abstract

The present invention enables stable discharge even when an inkjet head 100 is driven at higher speed and ink with lower viscosity is discharged.　The inkjet head 100 comprises: a plurality of nozzles 111 that inject ink; a plurality of pressure chambers 131 for changing the pressure of ink stored therein; an ink chamber 300 that stores ink to be supplied to the plurality of pressure chambers 131; a first flow path (through flow path 121) for individually communicating the nozzle 111 with the pressure chamber 131; and a second flow path (ink supply flow path 141) for individually communicating the pressure chamber 131 with the ink chamber 300. The flow path resistance RN of the nozzle 111, the flow path resistance RC of the pressure chamber 131, the flow path resistance RD of the first flow path, and the flow path resistance RU of the second flow path satisfy the following formula (1).　Formula (1): RU + RC + RD + RN ≥ 4.9 × 1013 Pa•s / m3

Description

[Technical Field]

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

[0002] Conventionally, when an inkjet head is driven at a short cycle (high speed) to eject low-viscosity ink, the ink overflows due to the protrusion of the meniscus. Crosstalk also occurs, causing fluctuations in droplet velocity. As a result, ink ejection from the nozzle becomes unstable.

[0003] In this regard, Patent Document 1 describes an inkjet head (droplet ejection head) in which the aspect ratio of the cross-sectional shape of the pressure chamber (ink flow path) is specified to increase the flow path resistance (viscous resistance), and the resonance frequency of the actuator (partition wall) is specified to reduce crosstalk. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-116571 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when driving an inkjet head at higher speeds and ejecting ink with lower viscosity, it is necessary to increase the flow path resistance, but it is not sufficient to simply specify the aspect ratio of the cross-sectional shape of the pressure chamber as described in Patent Document 1. Furthermore, if the cross-sectional shape of the pressure chamber is made too small in order to increase the flow path resistance, the acoustic resonance period of the ink flow path becomes large, which is a problem as it becomes impossible to drive at high speeds.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide an inkjet head and an inkjet recording apparatus that can perform stable ejection even when the inkjet head is driven at a higher speed and ejects ink with a lower viscosity. [Means for solving the problem]

[0007] In order to achieve the above object, the inkjet head according to claim 1 comprises: a plurality of nozzles for ejecting ink; a plurality of pressure chambers that change the pressure of the ink stored therein; an ink chamber that stores the ink to be supplied to the plurality of pressure chambers; a first flow path that individually connects the nozzle and the pressure chamber; a second flow path that individually connects the pressure chamber and the ink chamber; Equipped with a cross-sectional area of ​​the first flow path in a plane perpendicular to the ink ejection direction is larger than a cross-sectional area of ​​the pressure chamber in the plane; The flow resistance of the nozzle R N and the flow resistance R of the pressure chamber C and the flow path resistance R of the first flow path. D and the flow path resistance R of the second flow path. U satisfies the following formula (1). Formula (1):R U +R C +R D +R N ≧4.9×10 13 Pa·s / m 3

[0008] The inkjet head according to claim 2 is a plurality of nozzles for ejecting ink; a plurality of pressure chambers that change the pressure of the ink stored therein; an ink chamber that stores the ink to be supplied to the plurality of pressure chambers; a first flow path that individually connects the nozzle and the pressure chamber; a second flow path that individually connects the pressure chamber and the ink chamber; Equipped with a cross-sectional area of ​​the first flow path in a plane perpendicular to the ink ejection direction is larger than a cross-sectional area of ​​the pressure chamber in the plane; The flow resistance of the nozzle R N and the flow resistance R of the pressure chamber C and the flow path resistance R of the first flow path. D and the flow path resistance R of the second flow path. U satisfies the following formula (2). Formula (2):(R U +R C / 2)×(R C / 2+R D +R N ) / (R U +R C +R D +R N ) ≥ 1.1 × 10 13 Pa·s / m 3

[0009] The inkjet head according to claim 3 comprises: a plurality of nozzles for ejecting ink; a plurality of pressure chambers that change the pressure of the ink stored therein; an ink chamber that stores the ink to be supplied to the plurality of pressure chambers; a first flow path that individually connects the nozzle and the pressure chamber; a second flow path that individually connects the pressure chamber and the ink chamber; Equipped with a cross-sectional area of ​​the first flow path in a plane perpendicular to the ink ejection direction is larger than a cross-sectional area of ​​the pressure chamber in the plane; The flow resistance R of the nozzle N and the flow resistance R of the pressure chamber C and the flow path resistance R of the first flow path. D and the flow path resistance R of the second flow path. U satisfies the following formulas (1) and (2). Formula (1):R U +R C +R D +R N ≧4.9×10 13 Pa·s / m 3 Formula (2):(R U +R C / 2)×(R C / 2+R D +R N ) / (R U +RC +R D +R N ) ≥ 1.1 × 10 13 Pa·s / m 3

[0010] The invention described in claim 4 is the inkjet head according to any one of claims 1 to 3, The viscosity of the ink is 5 mPa·s or more and 7 mPa·s or less.

[0011] The invention described in claim 5 is the inkjet head according to any one of claims 1 to 4, The second flow path has a throttle portion whose cross-sectional area is smaller than that of other portions within the second flow path.

[0012] The invention described in claim 6 is the inkjet head described in claim 5, The second flow path has a two-stage restriction including the restriction portion.

[0013] The invention described in claim 7 is the inkjet head described in claim 5 or 6, The second flow path includes a tapered portion having a tapered shape.

[0014] The invention described in claim 8 is the inkjet head described in claim 7, In the tapered portion, the side with the larger flow path cross-sectional area is located on the ink chamber side, and the side with the smaller flow path cross-sectional area is located on the pressure chamber side.

[0015] The invention described in claim 9 is the inkjet head described in claim 7 or 8, The ratio of the area of ​​the outlet of the nozzle to the cross-sectional area of ​​the flow path in the throttle portion is 0.44 or more.

[0016] The invention described in claim 10 is the inkjet head according to any one of claims 1 to 9, The Helmholtz resonance period of the pressure chamber is not less than 3 μs and not more than 3.6 μs.

[0017] The invention described in claim 11 is the inkjet head according to any one of claims 1 to 10, a common partition wall made of a piezoelectric material is provided between adjacent pressure chambers; The inkjet head is a shear mode type that changes the volume of the pressure chamber by shearing the partition wall.

[0018] The inkjet recording apparatus according to claim 12, The inkjet head according to any one of claims 1 to 11 is provided. [Effects of the Invention]

[0019] According to the present invention, stable ejection can be achieved even when the inkjet head is driven at a higher speed and ink with a lower viscosity is ejected. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an inkjet recording apparatus. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a head unit. [Figure 3] FIG. 2 is a perspective view of an inkjet head. [Figure 4] FIG. 2 is an exploded perspective view of the main part of the inkjet head. [Figure 5] 5 is a diagram showing a cross section of the head chip taken along line AA in FIG. 4 and perpendicular to the Y direction. [Figure 6] FIG. 2 is a cross-sectional view of an ink ejection flow path. [Figure 7] FIG. 2 is a perspective view of an ink supply channel. [Figure 8] FIG. 2 is a perspective view of a connection portion between a pressure chamber and a through-flow channel. [Figure 9] FIG. [Figure 10] FIG. 10 is a diagram showing an example of the characteristics of normalized droplet velocity and drive period when driving an inkjet head. [Figure 11] FIG. 4 is a diagram showing an example of an equivalent circuit model of an ink ejection flow path as viewed from a nozzle. [Figure 12] FIG. 10 is a diagram showing the relationship between the first combined resistance and the rate of decrease in droplet velocity a. [Figure 13] 10 is a diagram showing an example of an equivalent circuit model of an ink ejection flow path viewed from the center of a pressure chamber. FIG. [Figure 14] 10 is a diagram showing the relationship between the second combined resistance and pixel deviation caused by variations in ink landing positions between the pressure chambers. FIG. [Figure 15] 10 is a diagram showing the relationship between the ratio of the area of ​​the nozzle ejection opening to the cross-sectional area of ​​the flow path in the first throttle portion and pixel deviation due to variations in the landing position of ink between the pressure chambers. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An inkjet head and an inkjet recording apparatus according to embodiments of the present invention will now be described with reference to the accompanying drawings.

[0022] <Configuration of Inkjet Recording Apparatus> FIG. 1 is a diagram showing a schematic configuration of an inkjet recording apparatus 1 according to an embodiment of the present invention. The inkjet recording apparatus 1 includes a transport unit 2, a head unit 3, and the like.

[0023] The transport unit 2 includes a ring-shaped transport belt 2c whose inner side is supported by two transport rollers 2a and 2b that rotate around a rotation axis extending in the X direction in Fig. 1. In the transport unit 2, with the recording medium M placed on the transport surface of the transport belt 2c, the transport roller 2a rotates in response to the operation of a transport motor (not shown), causing the transport belt 2c to move in a circular motion, thereby transporting the recording medium M in the movement direction of the transport belt 2c (transport direction; Y direction in Fig. 1).

[0024] The recording medium M may be a sheet of paper cut to a specific size. The recording medium M is supplied onto a conveyor belt 2c by a paper feeder (not shown), and after an image is recorded by ink being ejected from the head unit 3, the recording medium M is discharged from the conveyor belt 2c to a predetermined paper discharge section. Note that a long recording medium such as roll paper or continuous paper may also be used as the recording medium M. Furthermore, various media that can fix ink that has landed on the surface, such as paper such as plain paper or coated paper, fabric or sheet-like resin, may also be used as the recording medium M.

[0025] The head units 3 eject ink at appropriate timing based on image data onto the recording medium M transported by the transport unit 2 to record an image. In the inkjet recording device 1 of this embodiment, four head units 3 corresponding respectively to the four colors of ink, yellow (Y), magenta (M), cyan (C), and black (K), are arranged at predetermined intervals in the order of Y, M, C, and K from the upstream side in the transport direction of the recording medium M. The number of head units 3 may be three or less, or five or more.

[0026] 2 is a schematic diagram showing the configuration of the head unit 3, and is a plan view of the head unit 3 seen from the side facing the conveyance surface of the conveyor belt 2c. The head unit 3 has a plate-shaped base 3a and a plurality of (eight in this example) inkjet heads 100 fixed to the base 3a while fitting into through holes formed in the base 3a. The inkjet heads 100 are fixed to the base 3a with nozzle opening surfaces 112, on which openings of the nozzles 111 are formed, exposed in the -Z direction from the through holes in the base 3a.

[0027] In the inkjet head 100, a plurality of nozzles 111 are arranged at equal intervals in a direction intersecting the transport direction of the recording medium M (in this embodiment, the width direction perpendicular to the transport direction, i.e., the X direction). That is, each inkjet head 100 has a row of nozzles 111 (nozzle row) arranged one-dimensionally at equal intervals in the X direction. The inkjet head 100 may have multiple nozzle rows. In this case, the multiple nozzle rows are arranged with their positions in the X direction shifted from each other so that the positions of the nozzles 111 in the X direction do not overlap.

[0028] The eight inkjet heads 100 in the head unit 3 are arranged in a staggered pattern so that the arrangement range of the nozzles 111 in the X direction is continuous. The arrangement range in the X direction of the nozzles 111 included in the head unit 3 covers the width in the X direction of an area on the recording medium M transported by the transport belt 2c where an image can be recorded. The head unit 3 is used in a fixed position when recording an image, and ejects ink from the nozzles 111 to each position at predetermined intervals in the transport direction (transport direction intervals) as the recording medium M is transported, thereby recording an image by a single pass method.

[0029] <Inkjet head configuration> FIG. 3 is a perspective view of the inkjet head 100. As shown in FIG. The inkjet head 100 includes a housing 101 and an exterior member 102 that fits to the housing 101 at its bottom, with the main components housed inside the housing 101 and the exterior member 102. The exterior member 102 is provided with an inlet 103a through which ink is supplied from the outside, and outlets 103b and 103c through which ink is discharged to the outside. An ink chamber 300 (see FIG. 5) connected to the inlet 103a is also provided inside the exterior member 102. The exterior member 102 is also provided with a plurality of mounting holes 104 for mounting the inkjet head 100 to the base 3a of the head unit 3.

[0030] Next, the detailed configuration of the inkjet head 100 will be described. FIG. 4 is an exploded perspective view of the main part of the inkjet head 100. As shown in FIG. Fig. 4 shows the main components of the inkjet head 100 that are housed inside the exterior member 102. Specifically, Fig. 4 shows a nozzle substrate 11, a flow path substrate 12, a pressure chamber substrate 13, a head chip 10 having a wiring substrate 14, and an FPC 20 (Flexible Printed Circuit) electrically connected to the wiring substrate 14. 4, the nozzle opening surface 112 of the inkjet head 100 faces upward, that is, the components are drawn upside down from those in FIG.

[0031] As shown in FIG. 4, the head chip 10 has a structure in which a nozzle substrate 11, a flow path substrate 12, a pressure chamber substrate 13, and a wiring substrate 14 are laminated. The nozzle substrate 11, the flow path substrate 12, the pressure chamber substrate 13, and the wiring substrate 14 are all plate-like members having a substantially rectangular prism shape that is elongated in the X direction.

[0032] The nozzle substrate 11 is a polyimide substrate on which nozzles 111, which are holes penetrating in the thickness direction (Z direction), are arranged in a row along the X direction. The surface of the nozzle substrate 11 on the -Z direction side forms a nozzle opening surface 112 of the inkjet head 100.

[0033] The flow path substrate 12 is provided with a through flow path 121 (first flow path) that communicates with the nozzle 111, and individual discharge flow paths 122 that branch off from the through flow path 121. The pressure chamber substrate 13 is also provided with a pressure chamber 131 communicating with the through-flow channel 121, a common discharge flow channel 132 communicating with the individual discharge flow channel 122, and a vertical discharge flow channel 133 communicating with the common discharge flow channel 132. The wiring substrate 14 is also provided with an ink supply flow path 141 (second flow path) that communicates with the pressure chamber 131 via the second opening 1412, and a discharge hole 142 that communicates with the vertical discharge flow path 133.

[0034] The flow path substrate 12 and the pressure chamber substrate 13 are rectangular parallelepiped plate-like members whose shapes when viewed from the Z direction are substantially the same as those of the nozzle substrate 11. The flow path substrate 12 is made of, for example, a silicon substrate. The nozzle substrate 11 is bonded (fixed) to the surface of the flow path substrate 12 on the −Z direction side, and the pressure chamber substrate 13 is bonded (fixed) to the surface of the flow path substrate 12 on the +Z direction side, both of which are bonded (fixed) via an adhesive. The pressure chamber substrate 13 is made of a ceramic piezoelectric material (a material that deforms in response to the application of voltage). Examples of such piezoelectric materials include PZT (lead zirconate titanate), lithium niobate, barium titanate, lead titanate, and lead metaniobate. PZT is used for the pressure chamber substrate 13 of this embodiment. The wiring substrate 14 is a flat substrate having an area larger than the area of ​​the pressure chamber substrate 13, and is bonded via an adhesive to the surface on the +Z direction side of the pressure chamber substrate 13. The wiring substrate 14 may be made of, for example, glass, ceramics, silicon, plastic, or the like.

[0035] FIG. 5 is a cross-sectional view showing the configuration of the inkjet head 100. As shown in FIG. Fig. 5 is a diagram showing a cross section perpendicular to the Y direction at the position of line AA in Fig. 4. Hereinafter, the +Z direction will also be referred to as the upward direction, and the -Z direction will also be referred to as the downward direction. When the flow path substrate 12, the pressure chamber substrate 13, and the wiring substrate 14 are joined together, the through flow paths 121, the pressure chambers 131, and the ink supply flow paths 141 are connected together to form the ink channel 15. The ink channel 15 is provided at a position overlapping with the nozzle 111 when viewed from the Z direction, and is in communication with the nozzle 111. The ink channel 15 and the nozzle 111 form the ink ejection flow path 16. As shown in FIG. 5, the ink chamber 300 is disposed above (on the +Z direction side of) the opening formation surface 10a of the head chip 10 where the first opening 1411 is formed. The ink chamber 300 communicates with the ink channel 15 via a first opening 1411 formed in the opening formation surface 10a. This allows ink in the ink chamber 300 to be commonly supplied to multiple ink channels 15 and ejected from the nozzle 111.

[0036] Electrodes (not shown) are formed on the inner wall surfaces of the ink channels 15. The wall surfaces between the ink channels 15 (more specifically, the portions of the wall surfaces made of a piezoelectric material (partition walls 17) of the pressure chamber substrate 13) are displaced in response to the potential difference between drive signals applied to the electrodes of adjacent ink channels 15. As this wall surface undergoes repeated shear mode displacement, the pressure of the ink in the ink channels 15 fluctuates, and the volume of the pressure chamber changes in response to this pressure fluctuation, causing the ink in the ink channels 15 to be ejected from the nozzles 111. In other words, the inkjet head 100 of this embodiment performs shear mode ink ejection.

[0037] 4, in the flow path substrate 12, a first individual flow path 1221 branches off in the +Y direction from each of the plurality of through flow paths 121 (ink channels 15), and a second individual flow path 1222 that extends in the +Z direction and penetrates the flow path substrate 12 is connected to the end of the first individual flow path 1221 on the +Y direction side. The first individual flow path 1221 and the second individual flow path 1222 form an individual discharge flow path 122. A groove forming a common discharge flow path 132 extending in the X direction is provided on the bonding surface of the pressure chamber substrate 13 with the flow path substrate 12, in a range overlapping with the plurality of second individual flow paths 1222 when viewed from the Z direction. The common discharge flow path 132 is formed when the opening of the groove provided in the pressure chamber substrate 13 is blocked by the flow path substrate 12 in a state where the flow path substrate 12 and the pressure chamber substrate 13 are bonded together. Furthermore, when the flow path substrate 12 and the pressure chamber substrate 13 are bonded together, the common discharge flow path 132 is connected to the plurality of individual discharge flow paths 122. Furthermore, a vertical discharge channel 133 that penetrates the pressure chamber substrate 13 in the Z direction is connected to the end of the common discharge channel 132 on the +X direction side. The wiring substrate 14 is provided with a discharge hole 142 penetrating the wiring substrate 14 at a position overlapping the vertical discharge channel 133 when viewed from the Z direction. An opening 1421 of the discharge hole 142 communicates with the outlet 103b (or the outlet 103c).

[0038] An ink discharge flow path is formed by these individual discharge flow paths 122, common discharge flow path 132, vertical discharge flow path 133, and discharge hole 142. By providing the ink discharge flow path, a portion of the ink supplied from the ink chamber 300 to the ink channel 15 can be discharged to the outside of the inkjet head 100 via the ink discharge flow path. This allows air bubbles and foreign matter in the ink channel 15 to be discharged to the outside of the head chip 10 together with the ink.

[0039] A plurality of wirings 143 connected to the electrodes of the ink channels 15 are provided on the bonding surface of the wiring board 14 to the pressure chamber substrate 13. The FPC 20 is connected to the end of the wiring board 14 where the wirings 143 are provided, for example, via an ACF (anisotropic conductive film). A drive signal output from a drive circuit (not shown) is supplied to the electrodes of the ink channels 15 via the wirings 21 on the FPC 20 and the wirings 143.

[0040] FIG. 6 shows a cross-sectional view of the ink ejection flow path 16 taken perpendicular to the Y direction. As shown in Figures 5 and 6, ink in the ink chamber 300 is supplied to the ink supply channel 141 through the first opening 1411, and ink in the ink supply channel 141 is supplied to the pressure chamber 131 through the second opening 1412.

[0041] FIG. 7 shows a perspective view of the ink supply channel 141. 6 and 7, the ink supply flow path 141 is provided, between a first opening 1411 and a second opening 1412, with a first throttling section 1413 (throttling section) whose cross-sectional area in the XY plane perpendicular to the Z direction is smaller than that of the first opening 1411, and a second throttling section 1414 whose cross-sectional area in the XY plane is smaller than that of the second opening 1412. The ink supply flow path 141 is also provided, between the first throttling section 1413 and the second throttling section 1414, with an expansion section 1415 whose cross-sectional area in the XY plane is larger than that of the first throttling section 1413 and the second throttling section 1414. The shape of the first opening 1411 and the cross-sectional shape of the first throttle portion 1413 in the XY plane are circular, and the ink supply flow path 141 has a tapered flow path (tapered portion 1416) from the first opening 1411 to the first throttle portion 1413. The tapered portion 1416 is not limited to a truncated cone shape, and may have any tapered shape. Furthermore, the cross-sectional shape of the expansion section 1415 and the cross-sectional shape of the second throttle section 1414 in the XY plane are oval (or elliptical), and the ink supply channel 141 has a channel having an oblong truncated cone shape (or an elliptical truncated cone shape) from the expansion section 1415 to the second throttle section 1414. The second opening 1412 has an oval (or elliptical) shape, and the ink supply channel 141 has a channel that is shaped like an elongated truncated cone (or an elliptical truncated cone) from the second throttle portion 1414 to the second opening 1412. As shown in Figures 6 and 7, by providing two-stage throttling, a first throttling section 1413 and a second throttling section 1414, in the ink supply flow path 141, it is possible to sufficiently increase the flow path resistance without increasing the inertance, even when driving at a higher speed and ejecting ink with a lower viscosity.

[0042] FIG. 8 shows a perspective view of the connection portion between the pressure chamber 131 and the through-flow channel 121. 6 and 8, the pressure chamber 131 and the through-flow passage 121 are shaped like a rectangular parallelepiped. The cross-sectional area of ​​the through-flow passage 121 in the XY plane is larger than the cross-sectional area of ​​the pressure chamber 131 in the XY plane. Furthermore, the Helmholtz resonance period of the pressure chamber 131 in this embodiment is not less than 3 μs and not more than 3.6 μs.

[0043] FIG. 9 shows a perspective view of the nozzle 111. As shown in FIG. 9, the cross-sectional shape in the XY plane of a connection portion 1111 that connects to the through-channel 121 in the nozzle 111 is oval (or elliptical), and the cross-sectional shape in the XY plane of an ejection port 1112 that ejects ink is circular.

[0044] <Inkjet head drive> FIG. 10 shows an example of the characteristics of the normalized droplet velocity (normalized velocity) and drive period when driving an inkjet head. In the example shown in FIG. 10, the first narrowing portion 1413 has a diameter of 30 μm. As shown in Figure 10, the droplet velocity fluctuation period is long, resulting in a so-called undulating phenomenon. This is vibration mode A, in which the capillary force generated at the meniscus (the interface between ink and air) in the nozzle serves as the restoring force. In vibration mode A, the difference in droplet velocity between long-period (e.g., 15 to 30 [ / AL]) drive and short-period (e.g., 3 to 15 [ / AL]) drive becomes large, resulting in unstable ejection. Here, AL (Acoustic Length) is half the acoustic resonance period of the pressure wave in the pressure chamber 131. It is the pulse width at which the velocity is maximized when the velocity change is measured while the pulse width is varied with the peak value of a simple pulse-pulse waveform kept constant. Furthermore, for example, when the drive period is 7 [ / AL] or less (area surrounded by a dashed line), it can be seen that the droplet velocity fluctuates over a short fluctuation period. This is vibration mode B, which is centered on compliance, which is the elastic component of the pressure chambers 131. In vibration mode B, the influence of variations in the Helmholtz resonance period between the pressure chambers 131 becomes significant, which deteriorates the velocity distribution of the droplet velocity, and pixel shifts occur due to variations in the ink landing positions between the pressure chambers 131, resulting in unstable ejection.

[0045] <Total resistance of ink ejection flow path> In this embodiment, in order to suppress the effects of the vibration modes A and B, the ink ejection flow path 16 is configured as follows. In the ink ejection flow path 16 configured as shown in FIG. 6 to FIG. 9, the flow path resistance of the ink supply flow path 141 is set to R U , the flow resistance of the pressure chamber 131 is R C , the flow resistance of the through-flow path 121 is R D , the flow resistance of the nozzle 111 is R N In addition, the inertance of the ink supply channel 141 is set to L U , the inertance of the pressure chamber 131 is L C , the inertance of the through-flow passage 121 is LD , the inertance of the nozzle 111 is L N The compliance of the meniscus at the nozzle 111 is C N Let's say.

[0046] Here, the flow resistance R [Pa·s / m 3 ] is generally represented by the following formula (A1).

number

number

number

number

number

[0047] FIG. 11 shows an example of an equivalent circuit model of the ink ejection flow path 16 as viewed from the nozzle 111. In the example shown in FIG. 11, the first combined resistance R M is expressed by the following formula (1). Formula (1):R M =R U +R C +R D +R N

[0048] Figure 12 shows the first combined resistor R M 12 shows the relationship between the rate of decrease in droplet velocity a, which is the minimum droplet velocity, and the droplet velocity at which ejection is stable. In the example shown in Figure 12, the viscosity of the ink is 5 mPa·s or more and 7 mPa·s or less. In the example shown in FIG. 12, in order to suppress the influence of the vibration mode A and make the rate of decrease in the droplet velocity a at least −16% with a droplet velocity of 6 m / s as the reference, the ink ejection flow path 16 is configured to satisfy the following formula (2). Formula (2):R M ≧4.9×10 13 Pa·s / m 3 As a result, when the inkjet head 100 is driven at a high frequency, the drop in droplet speed can be suppressed more effectively than when the inkjet head 100 is driven at a low frequency. Specifically, R M =4.9×10 13 Pa·s / m 3When the resolution is 600 dpi, the drive frequency is 30 kHz, the distance between the recording medium M and the ejection opening 1112 of the nozzle 111 is 1 mm, and the conveyance speed of the recording medium M is 1.27 m / s, the landing deviation between a droplet with a droplet speed of 6 m / s and a droplet whose speed is reduced by 16% from the droplet speed of 6 m / s is 42.233 μm, which corresponds to one pixel at a resolution of 600 dpi. Therefore, the landing deviation of droplets in the ink ejection flow path 16 that satisfies formula (2) is a maximum of 42.233 μm, and ink can be ejected stably.

[0049] More preferably, in order to make the rate of decrease in the droplet velocity a at least −13% with respect to a droplet velocity of 6 m / s, the ink ejection flow path 16 is configured to satisfy the following formula (3). Formula (3):R M ≧5.8×10 13 Pa·s / m 3 R M =5.8×10 13 Pa·s / m 3 When the resolution is 600 dpi, the drive frequency is 30 kHz, the distance between the recording medium M and the ejection opening 1112 of the nozzle 111 is 1 mm, and the conveyance speed of the recording medium M is 1.27 m / s, the landing deviation between a droplet with a droplet speed of 6 m / s and a droplet whose speed is reduced by -13% from the droplet speed of 6 m / s is 0.75 pixels. Therefore, the landing deviation of droplets in the ink ejection flow path 16 that satisfies formula (3) is a maximum of 0.75 pixels, allowing for more stable ejection of ink.

[0050] More preferably, in order to make the rate of decrease in the droplet velocity a at least −9% with respect to a droplet velocity of 6 m / s, the ink ejection flow path 16 is configured to satisfy the following formula (4). Formula (4):R M ≧6.7×10 13 Pa·s / m 3 R M =6.7×10 13 Pa·s / m 3When the resolution is 600 dpi, the drive frequency is 30 kHz, the distance between the recording medium M and the ejection opening 1112 of the nozzle 111 is 1 mm, and the conveyance speed of the recording medium M is 1.27 m / s, the landing deviation between a droplet with a droplet speed of 6 m / s and a droplet whose speed is reduced by 9% from 6 m / s is 0.5 pixels. Therefore, the landing deviation of droplets in the ink ejection flow path 16 that satisfies formula (4) is a maximum of 0.5 pixels, and ink can be ejected even more stably.

[0051] Furthermore, in order to prevent an insufficient supply of ink to the ink ejection flow path 16 (insufficient refill), it is preferable that the ink ejection flow path 16 is configured to satisfy the following formula (5). Formula (5): R M ≦2.2×10 14 Pa·s / m 3 R M =2.2×10 14 Pa·s / m 3 When the resolution is 600 dpi, the drive frequency is 30 kHz, the distance between the recording medium M and the ejection opening 1112 of the nozzle 111 is 1 mm, and the conveyance speed of the recording medium M is 1.27 m / s, the drop rate of the droplet velocity a is 11%, and the landing deviation of the droplets is -0.5 pixels. Even in this case, the ink can be ejected stably.

[0052] In addition, the compliance of the pressure chamber 131 is C C 13 shows an example of an equivalent circuit model of the ink ejection flow path 16 as viewed from the center of the pressure chamber 131. In the example shown in FIG. 13, the second combined resistance R T is expressed by the following formula (6). Formula (6):R T =(R U +R C / 2)×(R C / 2+R D +R N ) / (R U +R C +R D +R N )

[0053] In Figure 14, the second combined resistor R T 14 shows the relationship between the difference in the ink viscosity and the pixel shift due to the variation in the landing position of ink (droplets) between the pressure chambers 131 in vibration mode B. In the example shown in Fig. 14, the ink viscosity is 5 mPa·s or more and 7 mPa·s or less. The example also shows the case where the resolution is 600 [dpi], the drive frequency is 30 [kHz], the distance between the recording medium M and the ejection opening 1112 of the nozzle 111 is 1 [mm], and the conveyance speed of the recording medium M is 1.27 [m / s]. In the example shown in FIG. 14, in order to suppress the influence of the vibration mode B, the ink ejection flow path 16 is configured to satisfy the following formula (7). Formula (7):R T ≧1.1×10 13 Pa·s / m 3 This makes it possible to suppress the speed fluctuations of each pressure chamber during high frequency driving due to the influence of crosstalk caused by variations in the Helmholtz resonance period between each pressure chamber 131, and to suppress pixel shifts caused by variations in the ink landing position between each pressure chamber 131 to 0.2 pixels or less.

[0054] More preferably, the ink ejection flow path 16 is configured to satisfy the following formula (8). Formula (8):R T ≧1.9×10 13 Pa·s / m 3 This makes it possible to suppress pixel deviation caused by variations in ink landing positions between the pressure chambers 131 to 0.1 pixel or less.

[0055] 15 shows the relationship between the ratio of the area of ​​the ejection opening 1112 of the nozzle 111 to the cross-sectional area of ​​the flow path in the first throttle portion 1413, and pixel shift due to variations in the landing position of ink between each pressure chamber 131. In the example shown in Fig. 15, the viscosity of the ink is 5 mPa·s or more and 7 mPa·s or less. The example also shows a case where the resolution is 600 [dpi], the drive frequency is 30 [kHz], the distance between the recording medium M and the ejection opening 1112 of the nozzle 111 is 1 [mm], and the conveyance speed of the recording medium M is 1.27 [m / s]. As shown in FIG. 15, in the ink ejection flow path 16 configured to suppress pixel shift due to variations in ink landing position between each pressure chamber 131 to 0.2 pixels or less, the ratio of the area of ​​the ejection port 1112 of the nozzle 111 to the flow path cross-sectional area in the first throttling section 1413 is 0.44 or more. The larger the ratio of the area of ​​the outlet 1112 of the nozzle 111 to the cross-sectional area of ​​the flow path in the first narrowing section 1413, the smaller the pixel shift will be, but if it is too large, the ink ejection efficiency will decrease, so it is desirable to keep it below 0.70.

[0056] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above embodiment, the ink ejection flow path 16 is configured to satisfy both the above formula (2) and the above formula (7), but this is not limiting. The ink ejection flow path 16 may be configured to satisfy either the above formula (2) or the above formula (7).

[0057] Furthermore, in the above embodiment, the shear mode inkjet head 100 has been described as an example, but the present invention is not limited to this, and may also be applied to a vent mode inkjet head in which ink is ejected by changing the pressure of the ink in the pressure chamber by deforming a piezoelectric element (pressure changing means) fixed to the wall surface of the pressure chamber serving as an ink storage section. However, due to production technology issues, it is difficult to design the pressure chamber of a shear mode inkjet head in a shape that significantly increases the flow path resistance while suppressing an increase in inertance, and therefore the present invention is more effective in shear mode inkjet heads.

[0058] As described above, the inkjet head 100 of this embodiment includes a plurality of nozzles 111 that eject ink, a plurality of pressure chambers 131 that vary the pressure of ink stored therein, an ink chamber 300 that stores ink to be supplied to the plurality of pressure chambers 131, a first flow path (through flow path 121) that individually connects the nozzles 111 and the pressure chambers 131, and a second flow path (ink supply flow path 141) that individually connects the pressure chambers 131 and the ink chamber 300, and the flow path resistance R of the nozzles 111 is N and the flow resistance R of the pressure chamber 131 C and the flow resistance of the first flow path R D and the flow resistance of the second flow path R U satisfies the following formula (1). Formula (1):R U +R C +R D +R N ≧4.9×10 13 Pa·s / m 3 Therefore, even when the inkjet head 100 is driven at a higher speed and ink with a lower viscosity is ejected, the influence of the vibration mode A can be suppressed, and stable ejection can be achieved.

[0059] The inkjet head 100 of this embodiment also includes a plurality of nozzles 111 that eject ink, a plurality of pressure chambers 131 that vary the pressure of the ink stored therein, an ink chamber 300 that stores ink to be supplied to the plurality of pressure chambers 131, a first flow path (through flow path 121) that individually connects the nozzles 111 and the pressure chambers 131, and a second flow path (ink supply flow path 141) that individually connects the pressure chambers 131 and the ink chamber 300, and a flow path resistance R of the nozzles 111 N and the flow resistance R of the pressure chamber 131 C and the flow resistance of the first flow path R D and the flow resistance of the second flow path R U satisfies the following formula (2). Formula (2):(R U +R C / 2)×(R C / 2+R D +R N ) / (R U +R C +RD +R N ) ≥ 1.1 × 10 13 Pa·s / m 3 Therefore, even when the inkjet head 100 is driven at a higher speed and ink with a lower viscosity is ejected, the influence of the vibration mode B can be suppressed, and stable ejection can be achieved.

[0060] The inkjet head 100 of this embodiment also includes a plurality of nozzles 111 that eject ink, a plurality of pressure chambers 131 that vary the pressure of the ink stored therein, an ink chamber 300 that stores ink to be supplied to the plurality of pressure chambers 131, a first flow path (through flow path 121) that individually connects the nozzles 111 and the pressure chambers 131, and a second flow path (ink supply flow path 141) that individually connects the pressure chambers 131 and the ink chamber 300, and a flow path resistance R of the nozzles 111 N and the flow resistance R of the pressure chamber 131 C and the flow resistance of the first flow path R D and the flow resistance of the second flow path R U satisfies the following formulas (1) and (2). Formula (1):R U +R C +R D +R N ≧4.9×10 13 Pa·s / m 3 Formula (2):(R U +R C / 2)×(R C / 2+R D +R N ) / (R U +R C +R D +R N ) ≥ 1.1 × 10 13 Pa·s / m 3 Therefore, even when the inkjet head 100 is driven at a higher speed and ink with a lower viscosity is ejected, the effects of the vibration modes A and B can be suppressed, and stable ejection can be achieved.

[0061] In the inkjet head 100 of this embodiment, the viscosity of the ink is 5 mPa·s or more and 7 mPa·s or less. Therefore, even when the viscosity of the ink is the above value, the influence of the vibration mode A and the vibration mode B can be suppressed, and stable ejection can be performed. Furthermore, even when the viscosity of the ink is not between 5 mPa·s and 7 mPa·s, the effect of stable ejection can be achieved by configuring the ink ejection flow path 16 to satisfy either or both of the above formulas (1) and (2). However, when the ink viscosity is greater than 7 mPa·s, if the ink ejection channel 16 is designed to satisfy either or both of the above formulas (1) and (2), the cross-sectional area of ​​the ink ejection channel 16 becomes too large. Furthermore, when the viscosity of the ink is less than 5 mPa·s, if the ink ejection flow path 16 is designed to satisfy either or both of the above formula (1) and formula (2), the cross-sectional area of ​​the ink ejection flow path 16 becomes too small, making the ink ejection flow path 16 prone to clogging. Therefore, the present invention is particularly effective when the viscosity of the ink is 5 mPa·s or more and 7 mPa·s or less.

[0062] In the inkjet head 100 of this embodiment, the second flow path has a throttle section (first throttle section 1413) whose flow path cross-sectional area is smaller than other parts in the second flow path, and is provided with a tapered section 1416. In the tapered section 1416, the side with the larger flow path cross-sectional area is located on the ink chamber 300 side, and the side with the smaller flow path cross-sectional area is located on the pressure chamber 131 side. Therefore, even when the ink is driven at a higher speed and ink with a lower viscosity is ejected, the flow path resistance of the second flow path can be made sufficiently large without increasing the inertance.

[0063] In the inkjet head 100 of this embodiment, the second flow path has a two-stage throttle including a throttle portion. Therefore, even when the ink is driven at a higher speed and ink with a lower viscosity is ejected, the flow path resistance can be made sufficiently large without increasing the inertance.

[0064] In the inkjet head 100 of this embodiment, the ratio of the area of ​​the ejection opening 1112 of the nozzle 111 to the cross-sectional area of ​​the flow path in the throttle portion is 0.44 or more. In this case, pixel deviation due to variations in ink landing positions between the pressure chambers 131 can be suppressed to 0.2 pixels or less, allowing stable ejection.

[0065] In the inkjet head 100 of this embodiment, the Helmholtz resonance period of the pressure chamber 131 is not less than 3 μs and not more than 3.6 μs. Therefore, stable ejection can be performed even in the inkjet head 100 in which the Helmholtz resonance period of the pressure chamber 131 is between 3 μs and 3.6 μs.

[0066] Furthermore, the inkjet head 100 of this embodiment is a shear mode inkjet head that has a common partition 17 made of a piezoelectric material between adjacent pressure chambers 131, and changes the volume of the pressure chambers 131 by shear deformation of the partition 17. The present invention is particularly effective in shear mode inkjet heads, since it is difficult from a production engineering standpoint to design the pressure chambers of shear mode inkjet heads in a shape that significantly increases flow path resistance while suppressing an increase in inertance.

[0067] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above embodiment, an example was described in which a vertical discharge flow path 133 is provided at one end of the common discharge flow path 132 and ink is discharged only from that one end, but this is not limited to this, and discharge flow paths may be provided at both ends of the common discharge flow path 132 and ink may be discharged from both ends of the common discharge flow path 132.

[0068] In the above embodiment, an example has been described in which the common discharge flow path 132 is configured by a groove provided on the surface of the pressure chamber substrate 13 facing the flow path substrate 12, but this is not limiting. For example, the common discharge flow path 132 may be formed across the flow path substrate 12 and the pressure chamber substrate 13.

[0069] Furthermore, the pressure chamber substrate 13 and the nozzle substrate 11 may be directly bonded together without providing the flow path substrate 12. In this case, the individual discharge flow paths and the common discharge flow path are provided in the pressure chamber substrate 13. In this configuration, the common discharge flow path can be formed by, for example, a groove provided on the surface of the pressure chamber substrate 13 facing the nozzle substrate 11.

[0070] Furthermore, in each of the above embodiments, an example has been described in which the recording medium M is transported by a transport unit 2 equipped with a transport belt 2c, but this is not intended to be limiting, and the transport unit 2 may, for example, hold and transport the recording medium M on the outer peripheral surface of a rotating transport drum.

[0071] Furthermore, in each of the above embodiments, the inkjet recording apparatus 1 of a single pass type has been described as an example, but the present invention may also be applied to an inkjet recording apparatus that records an image while scanning the inkjet head 100.

[0072] Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents. [Industrial Applicability]

[0073] The present invention can be used in an inkjet head and an inkjet recording apparatus. [Explanation of symbols]

[0074] 1. Inkjet recording device 2. Conveyor section 3 Head Unit 10 Head Chip 11 Nozzle board 111 Nozzle 1111 Connection 1112 Discharge port 112 Nozzle opening surface 12 Flow path substrate 121 Through passage (first passage) 122 Individual discharge flow path 1221 First individual channel 1222 Second individual channel 13 Pressure chamber substrate 131 Pressure Chamber 132 common discharge flow path 133 Vertical discharge channel 14 Wiring board 141 ink supply flow path (second flow path) 1411 First Opening 1412 Second Opening 1413 First throttle section (throttle section) 1414 Second throttle section 1415 Enlarged section 1416 Tapered section 15 ink channels 16 Ink discharge channel 17 Bulkhead 100 Inkjet head 101 Case 102 Exterior materials 103a Inlet 103b, 103c Outlet M Recording medium

Claims

1. a plurality of nozzles for ejecting ink; a plurality of pressure chambers that change the pressure of the ink stored therein; an ink chamber that stores the ink to be supplied to the plurality of pressure chambers; a first flow path that individually connects the nozzle and the pressure chamber; a second flow path that individually connects the pressure chamber and the ink chamber; Equipped with a cross-sectional area of ​​the first flow path in a plane perpendicular to the ink ejection direction is larger than a cross-sectional area of ​​the pressure chamber in the plane; The flow resistance R of the nozzle Ｎ and the flow resistance R of the pressure chamber. Ｃ and the flow path resistance R of the first flow path. Ｄ and the flow path resistance R of the second flow path. Ｕ An inkjet head that satisfies the following formula (1). Formula (1): R Ｕ + R Ｃ + R Ｄ + R Ｎ ≥ 4.9 × 10 １３ Pa·s / m ３

2. a plurality of nozzles for ejecting ink; a plurality of pressure chambers that change the pressure of the ink stored therein; an ink chamber that stores the ink to be supplied to the plurality of pressure chambers; a first flow path that individually connects the nozzle and the pressure chamber; a second flow path that individually connects the pressure chamber and the ink chamber; Equipped with a cross-sectional area of ​​the first flow path in a plane perpendicular to the ink ejection direction is larger than a cross-sectional area of ​​the pressure chamber in the plane; The flow resistance R of the nozzle Ｎ and the flow resistance R of the pressure chamber. Ｃ and the flow path resistance R of the first flow path. Ｄ and the flow path resistance R of the second flow path. Ｕ An inkjet head that satisfies the following formula (2). Formula (2): (R Ｕ + R Ｃ / 2) × (R Ｃ / 2 + R Ｄ + R Ｎ ) / (R Ｕ + R Ｃ + R Ｄ + R Ｎ ) ≥ 1.1 × 10 １３ Pa·s / m ３

3. a plurality of nozzles for ejecting ink; a plurality of pressure chambers that change the pressure of the ink stored therein; an ink chamber that stores the ink to be supplied to the plurality of pressure chambers; a first flow path that individually connects the nozzle and the pressure chamber; a second flow path that individually connects the pressure chamber and the ink chamber; Equipped with a cross-sectional area of ​​the first flow path in a plane perpendicular to the ink ejection direction is larger than a cross-sectional area of ​​the pressure chamber in the plane; The flow resistance R of the nozzle Ｎ and the flow resistance R of the pressure chamber. Ｃ and the flow path resistance R of the first flow path. Ｄ and the flow path resistance R of the second flow path. Ｕ An inkjet head that satisfies the following formulas (1) and (2). Formula (1): R Ｕ + R Ｃ + R Ｄ + R Ｎ ≥ 4.9 × 10 １３ Pa·s / m ３ Formula (2): (R Ｕ + R Ｃ / 2) × (R Ｃ / 2 + R Ｄ + R Ｎ ) / (R Ｕ + R Ｃ + R Ｄ + R Ｎ ) ≥ 1.1 × 10 １３ Pa·s / m ３

4. 4. The inkjet head according to claim 1, wherein the viscosity of the ink is 5 mPa.s or more and 7 mPa.s or less.

5. The inkjet head according to claim 1 , wherein the second flow path has a throttle portion whose cross-sectional area is smaller than that of other portions within the second flow path.

6. The inkjet head according to claim 5 , wherein the second flow path has a two-stage throttle including the throttle portion.

7. The inkjet head according to claim 5 or 6, wherein the second flow path has a tapered portion having a tapered shape.

8. 8. The ink jet head according to claim 7, wherein the tapered portion has a larger cross-sectional area on the ink chamber side and a smaller cross-sectional area on the pressure chamber side.

9. 9. The inkjet head according to claim 7, wherein a ratio of an area of ​​the ejection opening of the nozzle to a cross-sectional area of ​​the flow passage in the throttle portion is 0.44 or more.

10. 10. The inkjet head according to claim 1, wherein the Helmholtz resonance period of the pressure chamber is equal to or greater than 3 [mu]s and equal to or less than 3.6 [mu]s.

11. a common partition wall made of a piezoelectric material is provided between adjacent pressure chambers; 11. The inkjet head according to claim 1, wherein the inkjet head is a shear mode type inkjet head in which the partition wall is shear-deformed to change the volume of the pressure chamber.

12. An inkjet recording apparatus comprising the inkjet head according to any one of claims 1 to 11.

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