Inkjet head

Abstract

The inkjet head includes: a plurality of nozzles capable of ejecting ink to the outside; a plurality of pressure chambers respectively communicating with the plurality of nozzles; a first common flow path communicating with the plurality of pressure chambers; a second common flow path communicating with the plurality of pressure chambers through a path different from the first common flow path; a first damper disposed in the first common flow path; and a second damper disposed in the second common flow path. The thickness of the first damper is larger than that of the second damper.

Description

Technical Field

[0001] The present invention relates to an ink jet head. Background Art

[0002] In the past, as an example of an inkjet head, there is a known drop-on-demand inkjet head (hereinafter referred to as a "DOD inkjet head") that can eject a desired amount of ink droplets to a printing object at a desired timing through high-frequency driving (for example, 50kHz). A piezoelectric DOD inkjet head generally includes an ink flow path, a pressure chamber connected to the ink flow path and storing ink, a piezoelectric element (piezoelectric element) that pressurizes the ink stored in the pressure chamber, and a nozzle connected to the pressure chamber. By energizing the piezoelectric element, the ink in the pressure chamber is pressurized, thereby ejecting ink droplets from the nozzle.

[0003] In a DOD inkjet head, after the ink droplets are ejected, residual vibration is generated at the period of the Helmholtz resonance. Therefore, if high-frequency ejection is performed in a DOD inkjet head, the ejection accuracy (fluctuation of the ejection angle and ejection speed) may be deteriorated due to the influence of the residual vibration after the droplets are ejected. In order to avoid this problem, it is important to suppress the residual vibration after the droplets are ejected at an early stage.

[0004] In order to suppress residual vibration at an early stage, it is effective to provide a damper in the ink flow path. For example, Patent Document 1 discloses an inkjet head in which a plurality of dampers with different elastic moduli are arranged in the ink flow path. In addition, Patent Document 2 discloses that in a circulation-type inkjet head, dampers with different cross-sectional areas are arranged in the ink supply flow path and the ink discharge flow path.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 4493965

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-165051 Summary of the invention

[0009] An inkjet head according to one embodiment of the present invention comprises:

[0010] a plurality of nozzles capable of ejecting ink to the outside;

[0011] a plurality of pressure chambers, which are respectively connected to the plurality of nozzles;

[0012] a first common flow path communicating with the plurality of pressure chambers;

[0013] a second common flow path communicating with the plurality of pressure chambers through a path different from that of the first common flow path;

[0014] a first damper disposed in the first common flow path; and

[0015] a second damper disposed in the second common flow path,

[0016] The thickness of the first damper is greater than the thickness of the second damper.

[0017] An inkjet head according to another embodiment of the present invention comprises:

[0018] a plurality of nozzles capable of ejecting ink to the outside;

[0019] a plurality of pressure chambers, which are respectively connected to the plurality of nozzles;

[0020] a first common flow path communicating with the plurality of pressure chambers;

[0021] a second common flow path communicating with the plurality of pressure chambers through a path different from that of the first common flow path;

[0022] a first damper disposed in the first common flow path; and

[0023] a second damper disposed in the second common flow path,

[0024] The Young's modulus of a material forming the first damper is greater than the Young's modulus of a material forming the second damper. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is an exploded perspective view showing the appearance of the inkjet head according to the embodiment.

[0026] Figure 2 1 is a cross-sectional view schematically showing an ink flow path of one nozzle in the inkjet head according to the embodiment.

[0027] Figure 3 It is a top view of the first stacked body forming the flow path plate.

[0028] Figure 4 It is a top view of the second stacked body forming the flow path plate.

[0029] Figure 5 It is a top view of the third stacked body forming the flow path plate.

[0030] Figure 6 It is a top view of the fourth stacked body forming the flow path plate.

[0031] Figure 7 It is a top view of the fifth stacked body forming the flow path plate.

[0032] Figure 8 It is an explanatory diagram showing an example of vibration of the upstream damper and the downstream damper.

[0033] Fig. 9 It is an explanatory diagram showing an example of pressure waves generated by vibrations of the upstream damper and the downstream damper.

[0034] Fig.10 It is a diagram for explaining the vibration of the upstream damper and the downstream damper in the thickness direction parallel to the Z-axis direction.

[0035] Fig.11 It is an explanatory diagram showing the volumes of the upstream common flow path and the downstream common flow path.

[0036] Fig.12 It is an explanatory diagram showing an example of pressure waves generated by vibrations of the upstream damper and the downstream damper.

[0037] Fig.13 It is an explanatory diagram showing an example of pressure waves generated by vibrations of the upstream damper and the downstream damper.

[0038] Fig.14 1 is a diagram showing the direction in which the upstream damper 121 and the downstream damper 122 squeeze ink.

[0039] Fig.15 It is a cross-sectional view showing an example of nozzle arrangement.

[0040] Fig.16 1 is a cross-sectional view schematically showing an ink flow path of one nozzle in an inkjet head according to a modified example.

[0041] Fig.17 1 is a cross-sectional view schematically showing an ink flow path of one nozzle in an inkjet head according to a modified example. DETAILED DESCRIPTION

[0042] In an inkjet head that requires high ejection accuracy, in addition to the residual vibration of the ink after ejection at the period of Helmholtz resonance, the pressure fluctuation caused by the vibration of the damper itself is also a cause of deterioration of the ejection accuracy and cannot be ignored. When the elastic deformation of the damper is increased to suppress the residual vibration of the ink, the pressure fluctuation caused by the vibration of the damper itself becomes larger, resulting in an increase in the residual vibration of the ink, which is a trade-off.

[0043] In particular, in an ink circulation type inkjet head, when a damper is arranged in the ink supply flow path and the ink discharge flow path, the pressure fluctuation waves caused by the vibration of the damper itself overlap near the nozzle, which may have a significant adverse effect on the ejection accuracy.

[0044] An object of the present invention is to provide an inkjet head capable of suppressing residual vibration after ink is ejected and achieving high ejection accuracy.

[0045] Hereinafter, an inkjet head 1 according to an embodiment of the present invention will be described with reference to the accompanying drawings. The inkjet head 1 is, for example, an ink circulation type inkjet head. In the present invention, an orthogonal coordinate system (X, Y, Z) is used for description. The negative direction of the Z axis is the ejection direction of the ink in the inkjet head 1, the direction along the Y axis is the arrangement direction of the nozzles 101, and the direction along the X axis is the flow direction of the ink relative to the pressure chamber 103. Hereinafter, the directions along the X axis, the Y axis, and the Z axis are referred to as "X axis direction", "Y axis direction", and "Z axis direction", respectively.

[0046] Figure 1 It is an exploded perspective view showing the appearance of the inkjet head 1 according to the embodiment.

[0047] like Figure 1 As shown, the inkjet head 1 includes a nozzle plate 10 , a flow path plate 20 , a vibration plate 30 , a housing 40 , and a pressure changing unit 50 .

[0048] The nozzle plate 10 is arranged so that the plate surface of the nozzle plate 10 is perpendicular to the Z axis. The nozzle plate 10 is formed of, for example, a stainless steel plate formed by etching or pressing. The thickness of the stainless steel plate is, for example, 100 μm. A plurality of nozzles 101 are provided through the nozzle plate 10 along the Y axis.

[0049] The flow path plate 20 is in a rectangular parallelepiped shape and is arranged on the positive side of the nozzle plate 10 in the Z-axis direction so that the plate surface of the flow path plate 20 is orthogonal to the Z-axis. The flow path plate 20 is sandwiched between the vibration plate 30 and the nozzle plate 10. The flow path plate 20 is, for example, a stack of a plurality of stainless steel plates formed by etching and stamping. The thickness of each stainless steel plate is, for example, 10 to 100 μm, and the number of stacked layers is, for example, 3 to 10 layers.

[0050] The vibration plate 30 is arranged on the positive side of the flow path plate 20 in the Z-axis direction so that the plate surface of the vibration plate 30 is perpendicular to the Z-axis. The vibration plate 30 is sandwiched between the housing 40 and the flow path plate 20. The vibration plate 30 is, for example, a thin film with a thickness of 5 to 50 μm, and is formed by, for example, electroplating of a nickel alloy.

[0051] The vibration plate 30 has a pressure receiving portion 31 (see Figure 2 ). The pressure receiving portion 31 and the plurality of pressure chambers 103 (refer to Figure 2 ) are respectively provided correspondingly, for example, formed to protrude toward the positive side in the Z-axis direction. In the vibration plate 30, the portion where the pressure receiving portion 31 is formed forms the upper wall of the pressure chamber 103 (the wall on the positive side in the Z-axis direction).

[0052] The housing 40 has a rectangular parallelepiped shape and is disposed on the positive side in the Z-axis direction of the vibration plate 30. The thickness of the housing 40 in the Z-axis direction is, for example, 1 cm. The housing 40 is formed by cutting alloy steel such as stainless steel, for example.

[0053] The pressure changing unit 50 is disposed in the pressure changing unit storage chamber (reference numeral omitted) of the housing 40, and pressurizes the ink stored in the pressure chamber 103 to generate pressure fluctuations. The pressure changing unit 50 includes a base 51, a control substrate 52, and a piezoelectric element 108 (see Figure 2 ). The base 51 holds the control substrate 52 and the piezoelectric elements 108. The control substrate 52 is, for example, a flexible printed substrate on which a control IC and the like are mounted. The control IC controls the voltage applied to the plurality of piezoelectric elements 108 individually.

[0054] The nozzle plate 10 and the flow path plate 20, the flow path plate 20 and the vibration plate 30, the vibration plate 30 and the housing 40, and the vibration plate 30 and the pressure change portion 50 are bonded and fixed by adhesives. For example, an epoxy adhesive having a thermosetting property is used as the adhesive. It should be noted that the adhesives used to bond the various components may be the same adhesive or different adhesives. For example, a rubber adhesive and an epoxy adhesive may be used in combination.

[0055] Each element of the inkjet head 1 is formed inside the nozzle plate 10 , the flow path plate 20 , the vibration plate 30 , the housing 40 , and the pressure changing section 50 , or is formed by combining these elements.

[0056] Figure 2 1 is a cross-sectional view schematically showing an ink flow path of one nozzle 101 in the inkjet head 1 .

[0057] like Figure 2 As shown, the inkjet head 1 includes a nozzle 101, a silo portion 102, a pressure chamber 103, an upstream individual flow path 104, a downstream individual flow path 105, an upstream common flow path 106, a downstream common flow path 107, a piezoelectric element 108, an ink supply path 109, and an ink discharge path 110. In addition, the inkjet head 1 includes an upstream damper 121, a downstream damper 122, a first space portion 123, and a second space portion 124.

[0058] The inkjet head 1 pressurizes the ink stored in the pressure chamber 103 by the piezoelectric element 108 to eject ink droplets from the nozzle 101. The nozzles 101 may be arranged in one row or in multiple rows along the Y axis. Figure 1 In FIG. 1 , the nozzles 101 are arranged in two rows along the Y axis.

[0059] It should be noted that, when the nozzles 101 are arranged in multiple rows, the pressure chambers 103, the upstream separate flow paths 104, and the downstream separate flow paths 105 are also formed in multiple rows corresponding to the nozzles 101. The upstream common flow path 106 and the downstream common flow path 107 can be provided for each row of the nozzles 101, respectively, or can be shared with respect to the nozzles 101 of multiple rows. In addition, the flow direction of the ink relative to the pressure chambers 103 belonging to different rows can be the same or opposite. The following describes a case where the flow direction of the ink relative to the pressure chamber 103 is the negative direction of the X-axis. That is, the positive side of the X-axis is set as the upstream of the flow direction of the ink, and the negative side is set as the downstream of the flow direction.

[0060] The nozzle 101 is a hole that penetrates the nozzle plate 10 in the Z-axis direction. The diameter of the nozzle 101 is, for example, 3 to 100 μm. Ink droplets are ejected to the outside through the nozzle 101 .

[0061] The pressure chamber 103 and the silo part 102 are provided one-to-one with respect to each of the plurality of nozzles 101. The pressure chamber 103 communicates with the nozzle 101 via the silo part 102.

[0062] The pressure chamber 103 is an ink storage space formed by the flow path plate 20 and the vibration plate 30. In the present embodiment, the upper surface (the surface on the positive side in the Z-axis direction) of the recessed portion formed in the flow path plate 20 is closed by the vibration plate 30, thereby forming the pressure chamber 103. The pressure chamber 103 has, for example, a rectangular parallelepiped shape extending along the X-axis. It should be noted that a step may also be formed on the inner surface of the pressure chamber 103.

[0063] The silo part 102 is formed along the Z axis and connects the pressure chamber 103 with the nozzle 101. The silo part 102 forms an ink storage space together with the pressure chamber 103. The silo part 102 may be, for example, cylindrical or quadrangular.

[0064] The upstream individual flow path 104 is an ink flow path that connects the pressure chamber 103 with the upstream common flow path 106. The upstream individual flow path 104 is disposed upstream of the pressure chamber 103 in the ink flow direction. The upstream individual flow path 104 is provided one-to-one with respect to each of the plurality of pressure chambers 103.

[0065] The downstream individual flow path 105 is an ink flow path that connects the pressure chamber 103 with the downstream common flow path 107. The downstream individual flow path 105 is disposed downstream of the pressure chamber 103 in the ink flow direction. The downstream individual flow path 105 is provided one-to-one with respect to each of the plurality of pressure chambers 103.

[0066] The upstream common flow path 106 is an ink flow path arranged upstream of the ink flow direction of the upstream individual flow path 104 (on the positive side of the upstream individual flow path 104 in the X-axis direction). The upstream common flow path 106 is provided in common with respect to the plurality of upstream individual flow paths 104. The upstream common flow path 106 includes a first upstream common flow path 106a formed in the flow path plate 20 and a second upstream common flow path 106b formed in the housing 40. The first upstream common flow path 106a and the second upstream common flow path 106b are connected via a filter 106c. The filter 106c can be said to form a part of the upstream common flow path 106.

[0067] The filter portion 106c is a portion of the vibration plate 30 corresponding to the first upstream common flow path 106a and the second upstream common flow path 106b, and has through holes arranged vertically and horizontally. The diameter of the through hole is set to allow ink to pass through and prevent particles that are to be prevented from flowing into the nozzle 101 from passing through. The diameter of the through hole is, for example, 5 to 30 μm.

[0068] The downstream common flow path 107 is an ink flow path arranged downstream of the downstream individual flow paths 105 in the ink flow direction. The downstream common flow path 107 is provided in common with respect to the plurality of downstream individual flow paths 105. The downstream common flow path 107 includes a first downstream common flow path 107a formed in the flow path plate 20 and a second downstream common flow path 107b formed in the housing 40. The first downstream common flow path 107a and the second downstream common flow path 107b are connected via an opening 107c formed in the vibration plate 30. The opening 107c can be said to form a part of the downstream common flow path 107.

[0069] A plurality of piezoelectric elements 108 are arranged on the bottom surface of the base 51, and are pressure sources for pressurizing the ink contained in the pressure chambers 103. The piezoelectric elements 108 are provided corresponding to the plurality of pressure chambers 103, and are in contact with the pressure receiving portion 31 of the vibration plate 30. The piezoelectric elements 108 are deformed, for example, in a manner of expansion and contraction in the Z-axis direction by applying a voltage. The piezoelectric elements 108 are, for example, stacked piezoelectric actuators of the D33 mode.

[0070] In the inkjet head 1, the ink supplied from the external ink supply tank (not shown) via the ink supply path 109 is discharged from the ink discharge path 110 via the upstream common flow path 106, the upstream individual flow path 104, the pressure chamber 103, the downstream individual flow path 105, and the downstream common flow path 107. The discharged ink is circulated to the ink supply tank by, for example, a circulation pump (not shown). By circulating the ink without stagnation, it is possible to prevent the ink from stagnation in the pressure chamber 103 or the nozzle 101 and causing nozzle clogging.

[0071] In the ink circulation type inkjet head 1, the pressure of the ink supply tank (not shown) connected to the ink supply path 109 is set higher than the pressure of the ink discharge tank (not shown) connected to the ink discharge path 110. For example, the pressure difference can be controlled by making the positions of the ink supply tank and the ink discharge tank in the Z-axis direction (the height based on the pressure chamber 103) different. In addition, for example, the internal pressures of the ink supply tank and the ink discharge tank can be controlled separately by a regulator.

[0072] In the pressure changing section 50, when a voltage is applied to the piezoelectric element 108, the piezoelectric element 108 is deformed, for example, in a manner of extending in the Z-axis direction, and the pressure receiving portion 31 of the vibration plate 30 is pressed downward (to the negative side in the Z-axis direction). As a result, the upper wall of the pressure chamber 103 is deformed, and pressure fluctuations are generated in the ink stored in the pressure chamber 103. The pressure fluctuations are propagated toward the nozzle 101 via the silo section 102, so that ink droplets are ejected toward the nozzle 101.

[0073] In addition, a portion of the liquid contact surface of the upstream common flow path 106 that contacts the ink is formed by a deformable upstream damper 121. Specifically, the bottom wall surface of the upstream common flow path 106 (first upstream common flow path 106a) on the negative side in the Z-axis direction is formed by the upstream damper 121. The upstream damper 121 is formed, for example, using one layer of the laminated body constituting the flow path plate 20. The thickness of the upstream damper 121 is, for example, 2 to 30 μm.

[0074] A first space 123 that allows deformation of the upstream damper 121 is provided on the opposite side of the liquid contact surface of the upstream damper 121. The thickness of the first space 123 may be sufficient to allow elastic deformation of the upstream damper 121, and is, for example, 10 to 200 μm.

[0075] The upstream damper 121 has a thin film shape that can be elastically deformed in accordance with the pressure fluctuation of the upstream common flow path 106, and suppresses the pressure fluctuation of the upstream common flow path 106. Specifically, after the ink is ejected, the pressure of the ink propagates to the upstream common flow path 106 via the pressure chamber 103, and is reflected in the upstream common flow path 106 and propagates to the pressure chamber 103. The upstream damper 121 deforms toward the first space portion 123 side in accordance with the pressure fluctuation propagated from the pressure chamber 103 to the upstream common flow path 106, so that the pressure fluctuation propagated to the pressure chamber 103 by reflection becomes smaller. Therefore, by providing the upstream damper 121 in the upstream common flow path 106, the residual vibration of the ink after the ink is ejected is suppressed.

[0076] In addition, a portion of the liquid contact surface of the downstream common flow path 107 that contacts the ink is formed by the vibration plate 30. In the vibration plate 30, a portion 122 that forms the liquid contact surface of the downstream common flow path 107 functions as a downstream damper (hereinafter referred to as "downstream damper 122"). The thickness of the downstream damper 122 is equal to or less than that of the vibration plate 30, for example, 2 to 30 μm.

[0077] A second space 124 that allows deformation of the downstream damper 122 is provided on the opposite side of the liquid contact surface of the downstream damper 122. The thickness of the second space 124 may be sufficient to allow elastic deformation of the downstream damper 122, and is, for example, 10 to 200 μm.

[0078] It should be noted that the portion of the vibration plate 30 that functions as the downstream damper 122 may be processed to be thinner by forming a recessed portion, etc., in order to facilitate elastic deformation. In addition, when the vibration plate 30 is sufficiently deformable to a degree that can suppress pressure fluctuations, the thickness of the portion that functions as the downstream damper 122 may not be processed to be thinner.

[0079] The downstream damper 122 has a thin film shape that can be elastically deformed in accordance with the pressure fluctuation of the downstream common flow path 107, and suppresses the pressure fluctuation of the downstream common flow path 107. Specifically, after the ink is ejected, the pressure fluctuation of the ink propagates to the downstream common flow path 107 via the pressure chamber 103, and is reflected in the downstream common flow path 107 and propagates to the pressure chamber 103. The downstream damper 122 deforms toward the second space portion 124 side in accordance with the pressure fluctuation propagated from the pressure chamber 103 to the downstream common flow path 107, so that the pressure fluctuation propagated to the pressure chamber 103 by reflection becomes smaller. Therefore, by providing the downstream damper 122 in the downstream common flow path 107, the residual vibration of the ink after the ink is ejected is suppressed.

[0080] Reference Figure 3~Figure 7 An example of the stacked structure of the flow channel plate 20 will be described. Figure 3~Figure 7 FIG. 2 is a top view of each stacked body forming the stacked structure of the flow path plate 20. Figure 3~Figure 7 , the structure of the first stack 21 to the fifth stack 25 forming the flow path plate 20 is shown in a plan view when viewed from the positive side in the Z-axis direction.

[0081] The flow channel plate 20 is formed by stacking the first stack 21, the second stack 22, the third stack 23, the fourth stack 24 and the fifth stack 25 in order from the negative side in the Z-axis direction. The first stack 21 to the fifth stack 25 have openings penetrating in the Z-axis direction.

[0082] The first stacked body 21 is Figure 3As shown, it has an opening 21A forming the silo portion 102 and an opening 21B forming the first space portion 123. The thickness of the first stack 21 is, for example, 80 μm. The opening 21A has a circular shape, for example, when viewed from the Z-axis direction, and is formed in plurality along the Y-axis direction. The opening 21B has a rectangular shape extending in the Y-axis direction, for example, when viewed from the Z-axis direction, and is formed on the positive side of the opening 21A in the X-axis direction. It should be noted that the opening 21B can be as follows Figure 3 Although one opening is shown, it may be divided into a plurality of openings to maintain strength. For example, in the Y-axis direction, the opening 21B may be divided every time 10 openings 21A are formed, and one opening 21B may be provided for each 10 openings 21A.

[0083] The second stacked body 22 is Figure 4 As shown in FIG. 1 , the second stack 22 has an opening 22A forming the silo portion 102. The thickness of the second stack 22 is, for example, 25 μm. The opening 22A corresponds to the opening 21A of the first stack 21. That is, the shape, size, and position of the opening 22A when viewed from the Z-axis direction are the same as those of the opening 21A of the first stack 21. On the other hand, in the region 22B (represented by Figure 4 No opening is formed in the area surrounded by the dotted line (hereinafter referred to as the “solid area 22B”).

[0084] The third stacked body 23 is Figure 5 As shown, it has an opening 23D that forms the pressure chamber 103, an opening 23B that forms the first upstream common flow path 106a, and an opening 23C that forms the first downstream common flow path 107a. The thickness of the third stack 23 is, for example, 100 μm. The opening 23D has a rectangular shape, for example, when viewed from above when observed from the Z-axis direction, and is formed one-to-one with the opening 22A of the second stack 22. The opening 23B corresponds to the opening 21B of the first stack 21. That is, the shape, size and position of the opening 23B when viewed from the Z-axis direction are the same as those of the opening 21B of the first stack 21. In addition, the opening 23C is formed symmetrically with the opening 23B with respect to the opening 23D. It should be noted that the opening 23B and the opening 23C can be as follows. Figure 5 Although it is one opening as shown, it can also be divided into multiple openings to maintain strength. For example, it can also be that the opening 23B and the opening 23C are divided every time 10 openings 23D are formed in the Y-axis direction, and one opening 23B and one opening 23C are provided for each of the 10 openings 23D.

[0085] The fourth stacked body 24 is as follows Figure 6As shown, it has an opening 24E forming the pressure chamber 103, the upstream individual flow path 104, and the downstream individual flow path 105. The thickness of the fourth stack 24 is, for example, 30 μm. The opening 24E is formed to have a length that bridges the openings 23B and 23C of the third stack 23 in the X-axis direction.

[0086] The fifth stacked body 25 is as follows Figure 7 As shown, it has an opening 25D that forms the pressure chamber 103, an opening 25B that forms the first upstream common flow path 106a, an opening 25C that forms the first downstream common flow path 107a, and an opening 25F that forms the second space portion 124. The thickness of the fifth stack 25 is, for example, 80 μm. The openings 25D, 25B, and 25C correspond to the openings 23D, 23B, and 23C of the third stack 23, respectively. That is, the shape, size, and position of the openings 25D, 25B, and 25C when viewed from the Z-axis direction are the same as those of the openings 23D, 23B, and 23C of the third stack 23. It should be noted that the openings 25B, 25C, and 25F can be as follows Figure 7 Although it is one opening as shown, it can also be divided into multiple openings to maintain strength. For example, it can also be that the opening 25B, the opening 25C and the opening 25F are divided every time 10 openings 25D are formed in the Y-axis direction, and one opening 25B, one opening 25C and one opening 25F are provided for each of the 10 openings 25D.

[0087] The upstream damper 121 is formed by stacking the first stack 21 to the third stack 23. Specifically, the solid area 22B of the second stack 22 is sandwiched between the opening 21B of the first stack 21 and the opening 23B of the third stack 23 in the Z-axis direction. Therefore, the portion corresponding to the solid area 22B of the second stack 22 becomes the upstream damper 121.

[0088] The silo section 102 is formed by stacking the first stack 21 to the third stack 23. The first upstream common flow path 106a and the first downstream common flow path 107a are formed by stacking the third stack 23 to the fifth stack 25. The upstream individual flow path 104 and the downstream individual flow path 105 are formed by the opening 24E of the fourth stack 24.

[0089] The first space portion 123 is formed by bonding the nozzle plate 10 to the negative side of the flow path plate 20 in the Z-axis direction and closing the opening 21B of the first stacked body 21 with the nozzle plate 10 .

[0090] The pressure chamber 103 and the second space 124 are formed by joining the vibration plate 30 to the positive side of the flow path plate 20 in the Z-axis direction and closing the openings 25D and 25F of the fifth stack 25 with the vibration plate 30. In addition, the opening 25B of the fifth stack 25 is closed by the filter 106c provided on the vibration plate 30.

[0091] Furthermore, by joining the housing 40 to the positive side of the vibration plate 30 in the Z-axis direction, the portion of the vibration plate 30 sandwiched between the second downstream common flow path 107 b and the second space portion 124 functions as the second damper 122 .

[0092] In the inkjet head 1 having the above-described structure, after the ink is ejected, pressure fluctuations are generated at the period of the Helmholtz resonance, and the pressures of the upstream common flow path 106 and the downstream common flow path 107 are increased. The pressure fluctuations are attenuated by the elastic deformation of the upstream damper 121 and the downstream damper 122. Therefore, the pressure fluctuations reflected in the upstream common flow path 106 and the downstream common flow path 107 and propagated to the pressure chamber 103 are reduced, and the residual vibration of the ink is suppressed.

[0093] On the other hand, due to the vibration caused by the elastic deformation of the upstream damper 121 and the downstream damper 122 themselves, the pressure fluctuation propagates to the pressure chamber 103. When the phases of the pressure fluctuation waves (hereinafter referred to as "pressure waves") are consistent, in the pressure chamber 103, the first pressure wave P1 propagating from the upstream and the second pressure wave P2 propagating from the downstream overlap, and the pressure fluctuation in the pressure chamber 103 increases. Although the pressure fluctuation amount at this time is smaller than the pressure fluctuation amount caused by the Helmholtz resonance after the ink is ejected, it may cause unacceptable adverse effects in the inkjet head requiring high precision ejection accuracy.

[0094] That is, when the first pressure wave P1 generated by the vibration of the upstream damper 121 and the second pressure wave P2 generated by the vibration of the downstream damper 122 are in the same phase, the pressure fluctuation caused by the first pressure wave P1 and the second pressure wave P2 in the pressure chamber 103 becomes larger than when the phase of the first pressure wave P1 and the second pressure wave P2 is offset, and the ejection speed and ejection volume of the ink may fluctuate at a level that cannot be ignored. In particular, when ejecting in a high frequency band, the fluctuation of the ejection speed and ejection volume caused by the difference in ejection frequency becomes larger.

[0095] Therefore, in the present embodiment, the vibration period of the upstream damper 121 in the thickness direction is shorter than the vibration period of the downstream damper 122 in the thickness direction, so that the phase of the first pressure wave P1 generated by the vibration of the upstream damper 121 is offset from the phase of the second pressure wave P2 generated by the vibration of the downstream damper 122. It should be noted that, in the embodiment, the thickness directions of the upstream damper 121 and the downstream damper 122 are parallel to the ejection direction of the ink, but they may not be parallel to the ejection direction of the ink. In addition, hereinafter, the first pressure wave P1 and the second pressure wave P2 are sometimes collectively referred to as "pressure waves P1, P2".

[0096] Figure 8 1 is an explanatory diagram showing vibrations V1 and V2 of the upstream damper 121 and the downstream damper 122. Figure 8 , the pressure change generated in the pressure chamber 103 reaches the upstream damper 121 at the same time as the downstream damper 122. Figure 8 In FIG. 1 , the displacement in the direction in which the upstream damper 121 and the downstream damper 122 press the ink back, that is, the displacement on the positive side in the Z-axis direction is shown as positive.

[0097] When the pressure fluctuation generated in the pressure chamber 103 propagates and the pressure in the upstream common flow path 106 and the downstream common flow path 107 increases, Figure 8 At timing t1, the upstream damper 121 and the downstream damper 122 are pushed by the ink and start elastically deforming toward the negative side in the Z-axis direction.

[0098] Figure 8 The timing t2 is the time when the displacement of the vibration V1 of the upstream damper 121 reaches a maximum value. The timing t3 is the time when the displacement of the vibration V2 of the downstream damper 122 reaches a maximum value. When the vibration period of the upstream damper 121 is shorter than the vibration period of the downstream damper 122, the timing t2 is earlier than the timing t3.

[0099] Fig. 9 1 is an explanatory diagram showing pressure waves P1 and P2 in the pressure chamber 103 . Fig. 9 The pressure wave P1 and the pressure wave P2 shown are pressure waves generated by the vibration of the upstream damper 121 and the downstream damper 122, respectively. Fig. 9 In the figure, it is shown that based on Figure 8 The illustrated case is a situation where the pressure waves P1 , P2 of the vibrations V1 , V2 propagate to the pressure chamber 103 with the same propagation time.

[0100] Fig. 9 The timing t4 is the time when the pressure waves P1 and P2 reach the pressure chamber 103, and Figure 8The timing t5 is the time when the pressure wave P1 reaches a local maximum, and the timing t6 is the time when the pressure wave P2 reaches a local maximum.

[0101] like Figure 8 , Fig. 9 As shown in FIG. 1 , the waveforms of the pressure waves P1 and P2 are substantially the same as the vibrations V1 and V2 of the upstream damper 121 and the downstream damper 122. That is, when the vibration periods of the upstream damper 121 and the downstream damper 122 are shifted, the phases of the maximum values ​​of the pressure waves P1 and P2 propagating to the pressure chamber 103 are shifted accordingly. As a result, it is possible to avoid the overlap of the pressure waves P1 and P2, thereby suppressing the pressure fluctuations generated in the pressure chamber 103.

[0102] Specifically, the thickness of the upstream damper 121 is set larger than that of the downstream damper 122. In this embodiment, the thickness of the upstream damper 121 is set to 15 μm, and the thickness of the downstream damper 122 is set to 5 μm. The difference in thickness between the upstream damper 121 and the downstream damper 122 is preferably 8 μm or more.

[0103] In addition, the Young's modulus of the material forming the upstream damper 121 is larger than the Young's modulus of the material forming the downstream damper 122. In the present embodiment, the upstream damper 121 is formed of a stainless steel material, and the downstream damper 122 is formed of a nickel alloy. The Young's modulus of the stainless steel material is about 200 GPa, and the Young's modulus of the nickel alloy is about 160 GPa. It should be noted that the Young's modulus of these materials can be adjusted by a manufacturing method, a composition ratio, etc.

[0104] Fig.10 It is a diagram for explaining the vibration of the upstream damper 121 and the downstream damper 122 in the thickness direction parallel to the Z-axis direction.

[0105] The upstream damper 121 and the downstream damper 122 have a thin film structure, so the vibration in the thickness direction can be considered using a beam model. Fig.10 As shown in FIG. 1 , a beam model in which a load m is added to the center of a simple beam having a length L, a width b, and a thickness h is used for explanation. The spring coefficient k of the upstream damper 121 and the downstream damper 122 is obtained by using the length L, the width b, the thickness h, and the Young's modulus E of the forming material using the following formula (1). In addition, the larger the spring coefficient k, the shorter the vibration period of the upstream damper 121 and the downstream damper 122.

[0106]

[0107] According to formula (1), the spring coefficient k can be adjusted by using the thickness h of the upstream damper 121 and the downstream damper 122, so that the phase of the vibration of the upstream damper 121 and the downstream damper 122 is shifted. It should be noted that the spring coefficient k can also be adjusted by using the length L and width b of the upstream damper 121 and the downstream damper 122, but it is difficult to greatly shift the values ​​of the length L and the width b due to the size of the inkjet head 1. Therefore, it is preferred to adjust the spring coefficient k by using the thickness of the upstream damper 121 and the downstream damper 122.

[0108] Furthermore, according to the formula (1), the spring constant k can be adjusted using the Young's modulus E of the materials forming the upstream damper 121 and the downstream damper 122 , so that the phases of the vibrations of the upstream damper 121 and the downstream damper 122 can be shifted.

[0109] In the upstream damper 121 and the downstream damper 122 , when the spring constant k is adjusted using both the thickness h and the Young's modulus E, the spring constant k can be adjusted more easily than when the spring constant k is adjusted using only one of them.

[0110] In the present embodiment, the thickness of the upstream damper 121 is greater than the thickness of the downstream damper 122, and the Young's modulus of the material forming the upstream damper 121 is greater than the Young's modulus of the material forming the downstream damper 122. Since the spring constant of the upstream damper 121 is greater than the spring constant of the downstream damper 122, the vibration period of the upstream damper 121 is shorter than the vibration period of the downstream damper 122. That is, the phases of the vibrations of the upstream damper 121 and the downstream damper 122 are shifted. Therefore, the pressure fluctuation generated in the pressure chamber 103 due to the propagation of the two pressure waves P1 and P2 caused by the vibration of the damper itself is suppressed.

[0111] The upstream common flow path 106 and the downstream common flow path 107 preferably have different volumes. In the present embodiment, the volume of the upstream common flow path 106 is smaller than the volume of the downstream common flow path 107. "The volume of the upstream common flow path 106" and "the volume of the downstream common flow path 107" refer to the volumes of the same space where ink exists continuously.

[0112] The first downstream common flow path 107a and the second downstream common flow path 107b forming the downstream common flow path 107 are connected via the opening 107c of the vibration plate 30. Therefore, ink exists continuously between the first downstream common flow path 107a and the second downstream common flow path 107b. Therefore, the pressure change propagated from the pressure chamber 103 propagates in the same manner to the first downstream common flow path 107a, the second downstream common flow path 107b and the opening 107c of the vibration plate 30. That is, when considering the influence of the pressure change propagated between the pressure chamber 103 and the downstream common flow path 107, the entire downstream common flow path 107 becomes the object. In short, the "volume of the downstream common flow path 107" refers to the volume of the first downstream common flow path 107a and the second downstream common flow path 107b combined.

[0113] On the other hand, the first upstream common flow path 106a and the second upstream common flow path 106b forming the upstream common flow path 106 are connected via a filter section 106c having a through hole. In the filter section 106c, the through hole allows the ink to circulate, but the ink is reflected in the part outside the through hole. Therefore, it can also be considered that the pressure change propagated from the pressure chamber 103 is difficult to propagate to the second upstream common flow path 106b, and only propagates to the first upstream common flow path 106a. That is, when examining the influence of the pressure change propagated between the pressure chamber 103 and the upstream common flow path 106, the first upstream common flow path 106a and the second upstream common flow path 106b are regarded as different spaces, and only the first upstream common flow path 106a becomes the object. In short, the "volume of the upstream common flow path 106" refers to the volume of the first upstream common flow path 106a.

[0114] When the lengths of the upstream common flow path 106 and the downstream common flow path 107 along the Y axis are the same, as shown in FIG. Fig.11 As shown by the thick line in the figure, the respective volumes can be controlled by using the cross-sectional areas parallel to the XZ plane of the upstream common flow path 106 and the downstream common flow path 107. It should be noted that, when it is difficult to make the cross-sectional areas of the upstream common flow path 106 and the downstream common flow path 107 different due to size constraints, the cross-sectional areas may be made the same, and the respective volumes may be controlled by using the lengths of the upstream common flow path 106 and the downstream common flow path 107 along the Y axis.

[0115] Since the upstream common flow path 106 is disconnected by interposing the filter unit 106c between the first upstream common flow path 106a and the second upstream common flow path 106b, the cross-sectional area of ​​the upstream common flow path 106 parallel to the XZ plane becomes smaller than when the first upstream common flow path 106a and the second upstream common flow path 106b form the same space. Therefore, compared with the case where the volume of the upstream common flow path 106 is reduced by using the cross-sectional area of ​​the first upstream common flow path 106a or the second upstream common flow path 106b parallel to the XZ plane and the length along the Y-axis direction, the volume of the upstream common flow path 106 can be easily reduced.

[0116] Most of the pressure change components generated by the vibration of the upstream damper 121 first propagate to the entire same space portion including the upstream damper 121, that is, the entire upstream common flow path 106, and then propagate to the pressure chamber 103. Similarly, most of the pressure change components generated by the vibration of the downstream damper 122 first propagate to the entire same space portion including the downstream damper 122, that is, the entire downstream common flow path 107, and then propagate to the pressure chamber 103.

[0117] Therefore, the larger the volume of the upstream common flow path 106 and the downstream common flow path 107 is, the later the propagation time until the pressure waves P1 and P2 based on the vibration of the upstream damper 121 and the downstream damper 122 reach the pressure chamber 103 is.

[0118] When the volume of the upstream common flow path 106 is set smaller than the volume of the downstream common flow path 107 as in the present embodiment, the first pressure wave P1 based on the vibration of the upstream damper 121 having a shorter vibration period appears at a higher maximum value earlier than the second pressure wave P2 based on the vibration of the downstream damper 122 having a longer vibration period (see Fig. 9 ), on this basis, it reaches the pressure chamber 103 earlier by the difference in propagation time Δt (refer to Fig.12 ). That is, Fig.12 As shown in the figure, the phase difference between the two pressure waves P1 and P2 (the time between timing t5 and t6) is Fig. 9 The phase difference in the case shown is large. Therefore, the pressure fluctuation in the pressure chamber 103 caused by the propagation of the two pressure waves P1 and P2 due to the vibration of the damper itself is reliably suppressed.

[0119] On the other hand, when the volume of the upstream common flow path 106 is set larger than the volume of the downstream common flow path 107, the pressure wave P1 based on the vibration of the upstream damper 121 having a shorter vibration period appears at a higher maximum value earlier than the pressure wave P2 based on the vibration of the downstream damper 122 having a longer vibration period (see Fig. 9 ), but arrives at the pressure chamber 103 later by a difference in propagation time Δt (refer to Fig.13). In this case, if Fig.13 As shown, the two pressure waves P1 and P2 are in phase with each other and their maximum values ​​overlap, and there is a possibility that the effect of suppressing the pressure fluctuation generated in the pressure chamber 103 cannot be obtained.

[0120] Therefore, when making the volumes of the upstream common flow path 106 and the downstream common flow path 107 different, it is preferred to set the volume of the upstream common flow path 106 equipped with the upstream damper 121 having a shorter vibration period to be smaller than the volume of the downstream common flow path 107 equipped with the downstream damper 122 having a longer vibration period.

[0121] Fig.14 1 is a diagram showing the direction in which the upstream damper 121 and the downstream damper 122 squeeze ink.

[0122] like Fig.14 As shown in FIG. 1 , the upstream damper 121 extrude ink from the liquid contact surface with the ink toward the extrusion direction D1 which is the positive direction (vertically upward) of the Z axis. The upstream connecting portion 111 connecting the upstream common flow path 106 and the upstream individual flow path 104 is located on the positive side in the Z axis direction relative to the liquid contact surface of the upstream damper 121. That is, the direction from the liquid contact surface of the upstream damper 121 toward the upstream connecting portion 111 is the same as the extrusion direction D1. This structure is called a "direct reflection structure". In the direct reflection structure, the first pressure wave P1 caused by the vibration of the upstream damper 121 is mainly directly propagated to the pressure chamber 103.

[0123] The downstream damper 122 extrude ink from the liquid contact surface with the ink toward the extrusion direction D2 which is the positive direction (vertically upward) of the Z axis. The downstream connecting portion 112 connecting the downstream common flow path 107 with the downstream individual flow path 105 is located on the negative side in the Z axis direction compared to the liquid contact surface of the downstream damper 122. That is, the direction from the liquid contact surface of the downstream damper 122 toward the downstream connecting portion 112 is opposite to the extrusion direction D2. This structure is called an "indirect reflection structure". In the indirect reflection structure, the second pressure wave P2 caused by the vibration of the downstream damper 122 is mainly propagated toward the pressure chamber 103 through reflection at the wall surface of the downstream common flow path 107 which is opposite to the downstream damper 122 in the extrusion direction D2.

[0124] In the direct reflection structure in the upstream common flow path 106, the upstream individual flow path 104 exists in the squeezing direction D1 of the upstream damper 121, whereas in the indirect reflection structure in the downstream common flow path 107, the downstream individual flow path 105 does not exist in the squeezing direction D2 of the downstream damper 122. Therefore, in the indirect reflection structure, the pressure fluctuation component directly propagating from the downstream damper 122 to the downstream individual flow path 105 is smaller than in the direct reflection structure. That is, the second pressure wave P2 caused by the vibration of the downstream damper 122 reaches the pressure chamber 103 later than the first pressure wave P1 caused by the vibration of the upstream damper 121. It can be said that the positional relationship between the first damper 121 and the pressure chamber 103 and the positional relationship between the second damper 122 and the pressure chamber 103 are set so that a first propagation time for the first pressure wave P1 generated by the vibration of the first damper 121 to reach the pressure chamber 103 is shorter than a second propagation time for the second pressure wave P2 generated by the vibration of the second damper 122 to reach the pressure chamber 103.

[0125] By setting the upstream common flow path 106 where the upstream damper 121 having a shorter vibration period is arranged as a direct reflection structure, and setting the downstream common flow path 107 where the downstream damper 122 having a longer vibration period is arranged as an indirect reflection structure, the phase shift of the two pressure waves P1 and P2 propagating to the pressure chamber 103 is increased. Therefore, the pressure fluctuation generated in the pressure chamber 103 due to the propagation of the two pressure waves P1 and P2 caused by the vibration of the damper itself is more reliably suppressed.

[0126] In addition, the pressure wave P1 propagating from the upstream common flow path 106 to the pressure chamber 103 advances in the same direction as the circulation direction of the ink, whereas the pressure wave P2 propagating from the downstream common flow path 107 to the pressure chamber 103 moves in the reverse direction relative to the circulation direction of the ink. That is, the circulation of the ink becomes a resistance to the pressure wave P2 caused by the vibration of the downstream damper 122, so the pressure wave P2 is less likely to propagate to the pressure chamber 103 than the pressure wave P1 caused by the vibration of the upstream damper 121. Therefore, the phase shift of the two pressure waves P1 and P2 propagating to the pressure chamber 103 can be increased more effectively.

[0127] Fig.15 1 is a diagram showing an example of the arrangement of the nozzles 101 in the pressure chamber 103 .

[0128] The pressure fluctuation propagated from the pressure chamber 103 after the ink is ejected from the nozzle 101 is absorbed by the upstream damper 121 and the downstream damper 122, but a part of the pressure fluctuation component is reflected by the wall surface of the upstream common flow path 106 and the downstream common flow path 107, and is not absorbed by the upstream damper 121 and the downstream damper 122, but returns to the pressure chamber 103. In the indirect reflection structure in the downstream common flow path 107, the path length from the pressure chamber 103 to the downstream damper 122 is longer than the direct reflection structure in the upstream common flow path 106, so the pressure fluctuation component that is not absorbed by the downstream damper 122 and returns to the pressure chamber 103 is larger. Therefore, in the indirect reflection structure, the effect of suppressing the residual vibration that vibrates with a period close to the Helmholtz resonance after the ink is ejected from the nozzle 101 is smaller than that of the direct reflection structure.

[0129] Therefore, in this embodiment, the residual vibration generated after the ink is ejected and vibrates with a period close to the Helmholtz resonance is propagated more to the upstream common flow path 106 of the direct reflection structure than to the downstream common flow path 107 of the indirect reflection structure. Specifically, Fig.15 As shown, the nozzle 101 is arranged offset from the center of the pressure chamber 103 in the ink flow direction so as to be close to the downstream common flow path 107. When the flow path lengths of the upstream individual flow path 104 and the downstream individual flow path 105 are the same, it can be said that the first path length from the upstream common flow path 106 to the nozzle 101 is longer than the second path length from the downstream common flow path 107 to the nozzle 101.

[0130] The first path length is represented by, for example, the shortest distance from the nozzle 101 along the liquid contact surface of the silo part 102, the pressure chamber 103, and the upstream individual flow path 104 to the upstream common flow path 106. Similarly, the second path length is represented by, for example, the shortest distance from the nozzle 101 along the liquid contact surface of the silo part 102, the pressure chamber 103, and the downstream individual flow path 105 to the downstream common flow path 107.

[0131] In this case, when the pressure fluctuation generated in the pressure chamber 103 due to the operation of the piezoelectric element 108 propagates to the downstream common flow path 107 via the downstream individual flow path 105, it also propagates to the nozzle 101 via the silo section 102 that connects the nozzle 101 and the pressure chamber 103. That is, the pressure fluctuation component generated in the pressure chamber 103 is distributed to the downstream individual flow path 105 and the silo section 102. On the other hand, when the pressure fluctuation generated in the pressure chamber 103 propagates to the upstream common flow path 106 via the upstream individual flow path 104, the pressure fluctuation component is not distributed. Therefore, the pressure fluctuation component propagated to the downstream common flow path 107 is smaller than the pressure fluctuation component propagated to the upstream common flow path 106.

[0132] Therefore, in the downstream common flow path 107 of the indirect reflection structure, although the effect of suppressing the residual vibration after the ink is ejected is small, the propagated pressure fluctuation component is also small, so the residual vibration can be sufficiently suppressed.

[0133] In such Fig.15 When the nozzle 101 is arranged as shown, the pressure change component propagating to the upstream common flow path 106 is not distributed to the nozzle 101, etc., so it is different from the case where the nozzle 101 is arranged at the center of the pressure chamber 103 (see Figure 2 ), the nozzles 101 adjacent in the Y-axis direction may easily generate pressure crosstalk. However, the path length from the upstream common flow path 106 to the nozzle 101 is also longer, and the flow path resistance is increased, so the influence of pressure crosstalk is suppressed.

[0134] It should be noted that the flow path length of the upstream individual flow path 104 may be longer than the flow path length of the downstream individual flow path 105 to increase the first path length from the nozzle 101 to the upstream common flow path 106 to increase the flow path resistance.

[0135] As described above, the upstream damper 121 is manufactured inside the flow path plate 20 by stacking the first stack 21 to the third stack 23 of the flow path plate 20. In addition, by joining the flow path plate 20, the vibration plate 30 and the housing 40, a part of the vibration plate 30 is formed as the downstream damper 122. That is, the upstream damper 121 and the downstream damper 122 are formed by joining a plurality of members. Compared with the case where the upstream damper 121 and the downstream damper 122 with a thickness of several μm to several tens of μm are manufactured inside one molded part, it is possible to easily form them.

[0136] Here, when the flow path plate 20 and the vibration plate 30 are bonded using a thermosetting adhesive, expansion or contraction due to the influence of heat occurs in the flow path plate 20 and the vibration plate 30. Specifically, when the adhesive is heated to cure, the flow path plate 20 and the vibration plate 30 are thermally expanded and bonded in a thermally expanded state. After the heating is completed, the flow path plate 20 and the vibration plate 30 shrink as an integral component in a bonded state.

[0137] If the thermal expansion coefficients of the flow path plate 20 and the vibration plate 30 are different, thermal stress will be generated respectively during contraction. And after the thermal stress is balanced, a stable bonding state is achieved. At this time, one of the flow path plate 20 and the vibration plate 30 expands compared to before heating, and the other shrinks compared to before heating. Therefore, the degree of tension between the upstream damper 121 and the downstream damper 122 is different, and the fluctuation of the ejection speed and ejection volume may increase. In particular, the degree of tension of the damper is prone to fluctuation depending on the position in the longitudinal direction (Y-axis direction).

[0138] Therefore, the flow path plate 20 and the vibration plate 30 preferably have the same thermal expansion coefficient. Specifically, the difference in thermal expansion coefficient is preferably within 30%. As a result, the damper functions of the upstream damper 121 and the downstream damper 122 become uniform, thereby suppressing fluctuations in the ejection speed and ejection volume. In the present embodiment, the upstream damper 121 is formed of a stainless steel material, and the thermal expansion coefficient is 18ppm. On the other hand, the downstream damper 122 is formed of a nickel alloy, and the thermal expansion coefficient is 16ppm. In this case, the difference in thermal expansion coefficient becomes approximately 12%.

[0139] Thus, the inkjet head 1 of the embodiment includes: a plurality of nozzles 101 capable of ejecting ink to the outside; a plurality of pressure chambers 103 respectively communicating with the plurality of nozzles 101; an upstream common flow path 106 (first common flow path) communicating with the plurality of pressure chambers 103; a downstream common flow path 107 (second common flow path) communicating with the plurality of pressure chambers 103 through a different path from the upstream common flow path 106; an upstream damper 121 (first damper) disposed in the upstream common flow path 106; and a downstream damper 122 (second damper) disposed in the downstream common flow path 107. In the inkjet head 1, the vibration period of the upstream damper 121 in the thickness direction is shorter than the vibration period of the downstream damper 122 in the thickness direction.

[0140] According to the inkjet head 1, the elastic deformation of the upstream damper 121 and the downstream damper 122 can be used to suppress the residual vibration of the ink in the periodic vibration of the Helmholtz resonance after the ink is ejected. In addition, the phase shift of the pressure waves P1 and P2 generated by the vibration of the upstream damper 121 and the downstream damper 122 can suppress the pressure change caused by the propagation of the pressure waves P1 and P2. Therefore, the inkjet head 1 can maximize the damper effect and eject ink droplets at high frequency and high precision even when there are constraints on size and productivity. In addition, in an inkjet device equipped with the inkjet head 1 of the present invention, it is possible to achieve an improvement in the printing generation beat and productivity.

[0141] Specifically, in the inkjet head 1, the thickness of the upstream damper 121 (first damper) is greater than the thickness of the downstream damper 122 (second damper). Thus, the phases of the pressure waves P1 and P2 generated by the vibration of the upstream damper 121 and the downstream damper 122 can be easily shifted by simply adjusting the thickness of the upstream damper 121 and the downstream damper 122, and the pressure fluctuation caused by the propagation of the pressure waves P1 and P2 can be suppressed.

[0142] In addition, in the inkjet head 1, the Young's modulus of the material forming the upstream damper 121 is larger than the Young's modulus of the material forming the downstream damper 122. For example, by making the material forming the upstream damper 121 and the material forming the downstream damper 122 different materials, the Young's modulus of the upstream damper 121 and the downstream damper 122 can be easily made different. Thus, the phases of the pressure waves P1 and P2 generated by the vibration of the upstream damper 121 and the downstream damper 122 can be easily shifted by adjusting the Young's modulus of the material forming the upstream damper 121 and the downstream damper 122, and the pressure fluctuation caused by the propagation of the pressure waves P1 and P2 can be suppressed.

[0143] In particular, in the inkjet head 1, the thickness of the upstream damper 121 (first damper) is greater than the thickness of the downstream damper 122 (second damper), and the Young's modulus of the material forming the upstream damper 121 is greater than the Young's modulus of the material forming the downstream damper 122. Thus, the pressure fluctuation caused by the propagation of the pressure waves P1 and P2 can be more effectively suppressed.

[0144] In addition, in the inkjet head 1, the volume of the first upstream common flow path 106a (first common flow path) is smaller than the volume of the downstream common flow path 107 (second common flow path). As a result, a difference is also generated between the propagation time until the pressure wave P1 generated by the vibration of the upstream damper 121 reaches the pressure chamber 103 and the propagation time until the pressure wave P2 generated by the vibration of the upstream damper 121 reaches the pressure chamber 103. Therefore, the phase shift of the pressure waves P1 and P2 in the pressure chamber 103 increases, and the pressure fluctuation generated in the pressure chamber 103 due to the propagation of the two pressure waves P1 and P2 caused by the vibration of the damper itself can be more reliably suppressed.

[0145] In addition, in the inkjet head 1, at least a part of the wall surface of the first upstream common flow path 106a (first common flow path) is formed by a filter portion 106c having a plurality of openings, and the first upstream common flow path 106a is connected to the second upstream common flow path 106b (ink flow path of different space) via the filter portion 106c. Thus, the upstream common flow path 106 is divided into the first upstream common flow path 106a and the second upstream common flow path 106b, so that the volume of the upstream common flow path 106 can be easily reduced compared to the case where the volume of the upstream common flow path 106 is reduced by using the cross-sectional area of ​​the first upstream common flow path 106a or the second upstream common flow path 106b parallel to the XZ plane and the length along the Y-axis direction.

[0146] In addition, the inkjet head 1 includes: an upstream individual flow path 104 (first individual flow path) connecting the pressure chamber 103 and the upstream common flow path 106 (first common flow path); and a downstream individual flow path 105 (second individual flow path) connecting the pressure chamber 103 and the downstream common flow path 107 (second common flow path). The upstream common flow path 106 is connected to the upstream individual flow path 104 through a connecting portion 111 (first connecting portion), and the downstream common flow path 107 is connected to the downstream individual flow path 105 through a connecting portion 112 (second connecting portion). The direction from the liquid contact surface of the upstream damper 121 (first damper) toward the connecting portion 111 is opposite to the ink ejection direction, and the direction from the liquid contact surface of the downstream damper 122 toward the connecting portion 112 is the same as the ejection direction. As a result, the upstream common flow path 106 in which the upstream damper 121 having a shorter vibration period is arranged becomes a direct reflection structure, and the downstream common flow path 107 in which the upstream damper 122 having a longer vibration period is arranged becomes an indirect reflection structure. Therefore, the phase shift of the two pressure waves P1 and P2 propagating to the pressure chamber 103 increases, and the pressure fluctuation generated in the pressure chamber 103 due to the propagation of the two pressure waves P1 and P2 caused by the vibration of the damper itself can be more reliably suppressed.

[0147] In addition, in the inkjet head 1, the upstream common flow path 106 (first common flow path) is arranged upstream of the pressure chamber 103, and the downstream common flow path 107 (second common flow path) is arranged downstream of the pressure chamber 103. As a result, the pressure wave P1 propagating from the upstream common flow path 106 to the pressure chamber 103 advances in the same direction as the circulation direction of the ink, while the pressure wave P2 propagating from the downstream common flow path 107 to the pressure chamber 103 moves in the reverse direction relative to the circulation direction of the ink. Therefore, the phase shift of the two pressure waves P1 and P2 propagating to the pressure chamber 103 can be increased more effectively.

[0148] In addition, in the inkjet head 1, the nozzle 101 is arranged in a manner offset in the direction of ink flow with the center of the pressure chamber 103 as a reference so as to be close to the downstream common flow path 107 (second common flow path). As a result, the residual vibration generated after the ink is ejected and vibrates with a period close to the Helmholtz resonance is propagated more to the upstream common flow path 106 of the direct reflection structure than to the downstream common flow path 107 of the indirect reflection structure. Therefore, in the downstream common flow path 107 of the indirect reflection structure, although the effect of suppressing the residual vibration after the ink is ejected is small, the propagated pressure change component is also small, so the residual vibration can be fully suppressed.

[0149] In addition, in the inkjet head 1, the first path length from the upstream common flow path 106 (first common flow path) to the nozzle 101 is longer than the second path length from the downstream common flow path 107 (second common flow path) to the nozzle 101. As a result, the path length from the upstream common flow path 106 to the nozzle 101 is also longer, and the flow path resistance increases. Therefore, even if the pressure change component propagating to the upstream common flow path 106 is larger than that of the downstream common flow path 107, the influence of pressure crosstalk on the nozzles 101 adjacent in the Y-axis direction can be suppressed.

[0150] In the inkjet head 1, the flow path plate 20 (first member) forming the upstream damper 121 (first damper) and the vibration plate 30 (second member) forming the downstream damper 122 (second damper) are bonded by a thermosetting adhesive, and the difference in thermal expansion coefficient between the flow path plate 20 and the vibration plate 30 is 30% or less. Thus, even when the flow path plate 20 and the vibration plate 30 are bonded by a thermosetting adhesive, the damper functions of the upstream damper 121 and the downstream damper 122 become uniform, so that fluctuations in the ejection speed and the ejection volume can be suppressed.

[0151] As mentioned above, the invention completed by the present inventors has been specifically described based on the embodiments. However, the present invention is not limited to the above-mentioned embodiments, and can be modified within the scope not departing from the gist thereof.

[0152] For example, the structure of the upstream damper and the structure of the downstream damper may be opposite. That is, in the embodiment, the thickness of the upstream damper 121 and the downstream damper 122 and the Young's modulus of the forming material are set in such a way that the vibration period of the upstream damper 121 is shorter than the vibration period of the downstream damper 122, but the thickness of the upstream damper 121 and the downstream damper 122 and the Young's modulus of the forming material may be set in such a way that the vibration period of the upstream damper 121 is longer than the vibration period of the downstream damper 122. That is, the thickness of the downstream damper 122 may be thicker than the thickness of the upstream damper 121, and the Young's modulus of the forming material of the downstream damper 122 may be larger than the Young's modulus of the forming material of the upstream damper 121. In addition, the upstream damper 121 may be formed by the vibration plate 30, and the downstream damper 122 may be formed inside the flow path plate 20.

[0153] You can also Fig.16As in the inkjet head 2 shown in FIG. 1 , the upstream damper 121 and the downstream damper 122 are formed inside the flow path plate 20, and the first space portion 123 and the second space portion 124 are formed by joining the nozzle plate 10 and the flow path plate 20. In this case, the vibration periods of the pressure waves P1 and P2 generated by the vibration of the upstream damper 121 and the downstream damper 122 can be made different by making the thickness of the upstream damper 121 and the downstream damper 122 different and the Young's modulus of the forming material. It should be noted that even if it is difficult to make the forming material of the laminate constituting the flow path plate 20 different, it is easy to make the thicknesses of the respective dampers different by constituting the upstream damper 121 with a single-layer laminate and forming the downstream damper 122 with a two-layer laminate.

[0154] In addition, you can also Fig.17 As in the inkjet head 3 shown in FIG. 1 , the upstream damper 121 and the downstream damper 122 are formed by the vibration plate 30, and the first space portion 123 and the second space portion 124 are formed by joining the flow path plate 20 and the vibration plate 30. In this case, the vibration periods of the pressure waves P1 and P2 generated by the vibration of the upstream damper 121 and the downstream damper 122 can be made different by making the thickness of the upstream damper 121 and the downstream damper 123 different. This is effective in the case where it is difficult to form a damper structure on the flow path plate 20 due to size constraints, etc. It should be noted that, in the case where the upstream damper 121 is formed by the vibration plate 30, an opening is formed in the area corresponding to the filter portion 106c.

[0155] Furthermore, the upstream common flow path 106 and the downstream common flow path 107 may be divided in the Y-axis direction. In this case, the rigidity of the flow path plate 20 forming the upstream common flow path 106 and the downstream common flow path 107 is improved, so the processability is improved, and the production yield can be improved.

[0156] The embodiments disclosed this time should be considered as illustrative and non-restrictive in all aspects. The scope of the present invention is indicated by the patent claims rather than the above description, and is intended to include all changes within the meaning and scope equivalent to the patent claims.

[0157] According to the present invention, it is possible to suppress residual vibration after ink is ejected and realize high ejection accuracy.

[0158] Industrial Applicability

[0159] The present invention can be widely used in an inkjet head and a printing device equipped with the inkjet head.

[0160] Description of Reference Numerals

[0161] 1~3 inkjet head

[0162] 10 Nozzle plate

[0163] 20 Manifold board

[0164] 30 Vibration Plate

[0165] 40 Shell

[0166] 50 Pressure fluctuation part

[0167] 101 Nozzle

[0168] 102 Silo Department

[0169] 103 Pressure Chamber

[0170] 104 Upstream single flow path

[0171] 105 Downstream separate flow path

[0172] 106 Upstream common flow path

[0173] 107 Downstream common flow path

[0174] 108 Piezoelectric element

[0175] 121 Upstream damper

[0176] 122 Downstream damper.

Claims

1. An inkjet head, wherein: The inkjet head comprises: a plurality of nozzles capable of ejecting ink to the outside; a plurality of pressure chambers, which are respectively connected to the plurality of nozzles; a first common flow path communicating with the plurality of pressure chambers; a second common flow path communicating with the plurality of pressure chambers through a path different from that of the first common flow path; a first damper disposed in the first common flow path; as well as a second damper disposed in the second common flow path, The thickness of the first damper is greater than the thickness of the second damper.

2. An inkjet head, wherein: The inkjet head comprises: a plurality of nozzles capable of ejecting ink to the outside; a plurality of pressure chambers, which are respectively connected to the plurality of nozzles; a first common flow path communicating with the plurality of pressure chambers; a second common flow path communicating with the plurality of pressure chambers through a path different from that of the first common flow path; a first damper disposed in the first common flow path; as well as a second damper disposed in the second common flow path, The Young's modulus of a material forming the first damper is greater than the Young's modulus of a material forming the second damper.

3. The inkjet head according to claim 1 or 2, wherein: The volume of the first common flow path is smaller than the volume of the second common flow path.

4. The inkjet head according to claim 3, wherein: At least a portion of a wall surface of the first common flow path is formed by a filter portion having a plurality of openings, and the first common flow path communicates with ink flow paths in different spaces via the filter portion.

5. The inkjet head according to claim 1 or 2, wherein: The positional relationship between the first damper and the pressure chamber and the positional relationship between the second damper and the pressure chamber are set so that a first propagation time for a first pressure wave generated by the vibration of the first damper to reach the pressure chamber is shorter than a second propagation time for a second pressure wave generated by the vibration of the second damper to reach the pressure chamber.

6. The inkjet head according to claim 5, wherein: The first pressure wave propagates directly toward the pressure chamber, The second pressure wave is reflected and propagates toward the pressure chamber.

7. The inkjet head according to claim 6, wherein: The inkjet head comprises: a first separate flow path connecting the pressure chamber and the first common flow path; and a second separate flow path connecting the pressure chamber and the second common flow path, The first common flow path is connected to the first individual flow path via a first connection portion. The second common flow path is connected to the second individual flow path via a second connection portion. The direction from the liquid contact surface of the first damper toward the first connecting portion is opposite to the ejection direction of the ink. A direction from the liquid contact surface of the second damper toward the second connection portion is the same as the discharge direction.

8. The inkjet head according to claim 1 or 2, wherein: The first common flow path is arranged upstream of the pressure chamber. The second common flow path is arranged downstream of the pressure chamber.

9. The inkjet head according to claim 1 or 2, wherein: The nozzle is arranged offset from the center of the pressure chamber so as to be close to the second common flow path in the flow direction of the ink.

10. The inkjet head according to claim 1 or 2, wherein: A first path length from the first common flow path to the nozzle is longer than a second path length from the second common flow path to the nozzle.

11. The inkjet head according to claim 1 or 2, wherein: The first member on which the first damper is formed and the second member on which the second damper is formed are bonded together using a thermosetting adhesive. A difference in thermal expansion coefficient between the first member and the second member is 30% or less.

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