Inkjet head

Abstract

The inkjet head includes: a nozzle that ejects ink; a pressure chamber communicating with the nozzle; a reservoir chamber communicating with the pressure chamber via the throttle portion; a vibration plate having a portion forming a part of the pressure chamber; and a pressure fluctuation unit that causes the vibration plate to vibrate so as to fluctuate the pressure of the ink in the pressure chamber, and causes the ink to be discharged from the pressure chamber to the outside via the nozzle. The storage chamber has a flexural portion that deforms more easily than a portion of the diaphragm.

Description

Technical Field

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

[0002] Patent Document 1 discloses a drop-on-demand inkjet head.

[0003] The inkjet head of Patent Document 1 is a piezoelectric inkjet head, and a voltage is applied to a piezoelectric element to cause it to expand and reduce the volume of a pressure chamber. Thus, the inkjet head applies pressure to ink in the pressure chamber and ejects the ink to the outside through a nozzle.

[0004] In addition, the piezoelectric element contracts and the volume of the pressure chamber is restored, thereby raising the liquid surface (so-called meniscus) of the ink in the nozzle, thereby cutting off the liquid ligament of the ejected ink.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-159514 Summary of the invention

[0008] An inkjet head according to one embodiment of the present invention comprises: a nozzle that ejects ink; a pressure chamber that is connected to the nozzle; a storage chamber that is connected to the pressure chamber via a throttling portion; a vibration plate that has a portion that forms a part of the pressure chamber; and a pressure changing portion that vibrates the vibration plate in a manner that causes the pressure of the ink in the pressure chamber to change, thereby ejecting the ink from the pressure chamber through the nozzle to the outside, the storage chamber having a flexure that is easier to deform than the portion of the vibration plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is an exploded perspective view of an inkjet head according to an exemplary embodiment.

[0010] Figure 2 It is a schematic plan view for explaining the ink flow path in the inkjet head according to the embodiment.

[0011] Figure 3 It is a partial cross-sectional view of an inkjet head according to an exemplary embodiment.

[0012] Figure 4 yes Figure 3 II sectional view.

[0013] Figure 5 This is a diagram for explaining the amount of expansion of the pressure changing portion during the ink ejection operation.

[0014] Figure 6 It is a graph showing the relationship between ink viscosity and shear rate.

[0015] Figure 7 It is a partial cross-sectional view of a pressure changing unit and a vibration plate included in the inkjet head according to the embodiment.

[0016] Figure 8 It is a partial plan view of a vibration plate included in the inkjet head according to the embodiment.

[0017] Fig. 9 This is a diagram showing changes in pressure near the nozzle in the pressure chamber during the ink ejection operation performed by the inkjet head according to the embodiment.

[0018] Fig.10 It is a partial cross-sectional view of a pressure changing unit and a vibration plate included in an inkjet head of a comparative example.

[0019] Fig.11 It is a partial plan view of a vibration plate included in an inkjet head of a comparative example.

[0020] Fig.12 This is a diagram showing changes in pressure near the nozzle in the pressure chamber during the ink ejection operation performed by the inkjet head of the comparative example.

[0021] Fig.13 This is a partial plan view of a vibration plate included in the inkjet head of Modification 1.

[0022] Fig.14 This is a partial plan view of a vibration plate included in the inkjet head of Modification 2. DETAILED DESCRIPTION

[0023] Even for the same ink, the lower the ink flow rate (so-called shear velocity), the greater the ink viscosity. During the period when the volume of the pressure chamber is restored by the contraction of the piezoelectric element, the ink shear velocity decreases. The inkjet head of Patent Document 1 cuts off the liquid line when the ink viscosity increases, so the liquid line is difficult to cut and tends to become longer.

[0024] When the liquid line of ink is long, the liquid line and the main droplet of ink are separated, and spray as floating ink is easily generated. In order to improve the printing performance of the inkjet head, it is necessary to suppress the generation of spray.

[0025] An object of the present invention is to provide an inkjet head having improved printing performance.

[0026] Hereinafter, various embodiments and various modifications of the present invention will be described with reference to the accompanying drawings. In the present invention, an orthogonal coordinate system (X, Y, Z) is used for description. Figure 1 As shown by the arrows in FIG. 1 , the Z-axis direction is the height direction of the inkjet head 1 , the Y-axis direction is the length direction of the inkjet head 1 , and the X-axis direction is the width direction of the inkjet head 1 .

[0027] [Implementation Method]

[0028] First, use Figure 1 The overall structure of the inkjet head 1 according to the first embodiment will be described. Figure 1 It is an exploded perspective view illustrating the inkjet head 1 according to the embodiment.

[0029] like Figure 1 As shown in FIG. 1 , the inkjet head 1 includes a main body 10 and a plurality of pressure changing parts 61 (see FIG. 1 ). Figure 3 ) is a pressure changing element unit 60. A plurality of nozzles 41 are formed on the ejection surface S of the main body 10. The plurality of nozzles 41 are provided, for example, in a manner forming a plurality of nozzle rows.

[0030] The main body 10 includes a casing 20, a flow path plate 30, a nozzle plate 40, and a vibration plate 50. The main body 10 is formed by stacking the nozzle plate 40, the flow path plate 30, the vibration plate 50, and the casing 20 in this order.

[0031] The housing portion 20 is formed in, for example, a rectangular parallelepiped shape, and constitutes an upper portion of the main body portion 10. The housing portion 20 is formed by, for example, cutting alloy steel such as stainless steel.

[0032] The flow path plate 30 is formed in a rectangular parallelepiped shape, for example, and constitutes the lower portion of the main body 10. The flow path plate 30 is formed with a plurality of pressure chambers 31 (see FIG. 1 ) for storing ink ejected to the outside. Figure 4 ). The flow channel plate 30 is formed by laminating stainless steel plates formed by etching or pressing by bonding or diffusion bonding.

[0033] The nozzle plate 40 is disposed on the bottom surface of the flow channel plate 30 so that its plate surface is perpendicular to the Z-axis direction, and constitutes the bottom surface of the main body 10. The nozzle plate 40 is formed by, for example, molding a stainless steel plate by etching, pressing, or laser processing.

[0034] The vibration plate 50 is disposed between the housing 20 and the flow path plate 30 in such a manner that its plate surface is orthogonal to the Z-axis direction. The vibration plate 50 is a thin plate-shaped elastic body. Figure 1 As shown, the vibration plate 50 may be composed of, for example, two plate members disposed separately from each other. The vibration plate 50 is formed of, for example, a stainless steel plate or a nickel electroformed plate.

[0035] Next, use Figure 2~Figure 4 The structure of the inkjet head 1 will be described in detail. Figure 2 It is a schematic plan view for explaining the ink flow path in the inkjet head 1 . Figure 3 It is a partial cross-sectional view illustrating the inkjet head 1 and is a cross-sectional view based on the ZX plane. Figure 4 yes Figure 3It should be noted that the inkjet head 1 of the present embodiment is an inkjet head of an ink circulation type.

[0036] <Casing 20>

[0037] like Figure 2 As shown, the shell portion 20 is provided with an ink supply path 21, upstream common flow paths 22a, 22b, downstream supply flow paths 23a, 23b, 23c, 23d, ink discharge paths 24a, 24b and storage spaces 25a, 25b, 25c, 25d.

[0038] The ink supply path 21 is connected to, for example, an ink tank (not shown) serving as an ink supply source. The ink supply path 21 extends along the Z-axis direction and is provided at the center of the case 20 in the X-axis direction and the Y-axis direction.

[0039] The upstream common flow paths 22a and 22b are connected to the ink supply path 21. The upstream common flow paths 22a and 22b extend from the ink supply path 21 toward the negative end and the positive end of the case portion 20 in the Y-axis direction, respectively.

[0040] The downstream supply flow paths 23 a and 23 b are provided, for example, on both sides of the upstream common flow path 22 a in the X-axis direction, and extend toward the negative end of the case portion 20 in the Y-axis direction.

[0041] The downstream supply flow paths 23 c and 23 d are provided, for example, on both sides of the upstream common flow path 22 b in the X-axis direction, and extend toward the positive side end of the case portion 20 in the Y-axis direction.

[0042] The ink discharge passages 24a and 24b are respectively arranged at both ends of the housing 20 in the Y-axis direction. The ink discharge passage 24a is connected to the downstream supply passages 23a and 23b. The ink discharge passage 24a is, for example, provided at the center of the housing 20 in the X-axis direction and extends along the Z-axis direction. The ink discharge passage 24b is connected to the downstream supply passages 23c and 23d. The ink discharge passage 24b is, for example, provided at the center of the housing 20 in the X-axis direction and extends along the Z-axis direction.

[0043] The accommodation spaces 25a, 25b, 25c, and 25d are spaces for accommodating a plurality of pressure changing parts 61, respectively, and extend along the Y-axis direction. For example, the accommodation space 25a is provided between the upstream common flow path 22a and the downstream supply flow path 23a, and the accommodation space 25b is provided between the upstream common flow path 22a and the downstream supply flow path 23b. In addition, the accommodation space 25c is provided between the upstream common flow path 22b and the downstream supply flow path 23c, and the accommodation space 25d is provided between the upstream common flow path 22b and the downstream supply flow path 23d.

[0044] The ink is supplied from the ink tank to the plurality of pressure chambers 31 arranged on the negative side of the storage space 25a and the storage space 25b in the Z-axis direction via the ink supply path 21 and the upstream common flow path 22a. In addition, the ink is supplied to the plurality of pressure chambers 31 arranged on the negative side of the storage space 25c and 25d in the Z-axis direction via the ink supply path 21 and the upstream common flow path 22b.

[0045] Ink is discharged from the plurality of pressure chambers 31 disposed on the negative side of the accommodating spaces 25a and 25b in the Z-axis direction via the downstream supply flow paths 23a and 23b and the ink discharge path 24a to the outside of the inkjet head 1. In addition, ink is discharged from the plurality of pressure chambers 31 disposed on the negative side of the accommodating spaces 25c and 25d in the Z-axis direction via the downstream supply flow paths 23c and 23d and the ink discharge path 24b to the outside of the inkjet head 1.

[0046] <Flow path plate 30>

[0047] like Figure 4 As shown in the figure, the flow channel plate 30 has a plurality of ejection units 301 arranged in a one-to-one correspondence with the plurality of nozzles 41. That is, the number of the nozzles 41 is the same as the number of the ejection units 301. The ejection unit 301 is composed of a pressure chamber 31, a first upstream reservoir chamber 32, a second upstream reservoir chamber 33, a first downstream reservoir chamber 34, and a second downstream reservoir chamber 35.

[0048] The pressure chamber 31 is configured, for example, in the shape of a rectangular parallelepiped with its long side extending in the X-axis direction. Figure 3 As shown, the pressure chamber 31 is in communication with the nozzle 41 .

[0049] The first upstream storage chamber 32 is provided on the positive side in the X-axis direction of the pressure chamber 31. A first upstream throttle portion 36 is provided between the pressure chamber 31 and the first upstream storage chamber 32, and the first upstream storage chamber 32 communicates with the pressure chamber 31 via the first upstream throttle portion 36. The first upstream throttle portion 36 has a smaller dimension in the Z-axis direction than the pressure chamber 31 and the first upstream storage chamber 32.

[0050] The second upstream storage chamber 33 is provided on the positive side in the X-axis direction of the first upstream storage chamber 32. A second upstream throttle portion 37 is provided between the first upstream storage chamber 32 and the second upstream storage chamber 33. The second upstream storage chamber 33 is communicated with the upstream common flow path 22a, and is communicated with the first upstream storage chamber 32 via the second upstream throttle portion 37. The second upstream throttle portion 37 is smaller in size in the Z-axis direction than the first upstream storage chamber 32 and the second upstream storage chamber 33.

[0051] The first upstream throttle portion 36 and the second upstream throttle portion 37 are provided so that the first upstream storage chamber 32 becomes a substantially closed space. In addition, the second upstream throttle portion 37 is provided at a position different from that of the first upstream throttle portion 36 in the Z-axis direction. Figure 3 In the Z-axis direction, the first upstream throttle portion 36 is provided at the upper wall of the first upstream storage chamber 32, and the second upstream throttle portion 37 is provided at the lower wall. Therefore, it is easy to block the pressure wave in the first upstream storage chamber 32.

[0052] The ink is supplied from the upstream common flow path 22 a to the pressure chamber 31 via the second upstream reservoir chamber 33 , the second upstream throttle portion 37 , the first upstream reservoir chamber 32 , and the first upstream throttle portion 36 .

[0053] The first downstream storage chamber 34 is provided on the negative side in the X-axis direction of the pressure chamber 31. A first downstream throttle portion 38 is provided between the pressure chamber 31 and the first downstream storage chamber 34, and the first downstream storage chamber 34 communicates with the pressure chamber 31 via the first downstream throttle portion 38. The first downstream throttle portion 38 has a smaller dimension in the Z-axis direction than the pressure chamber 31 and the first downstream storage chamber 34.

[0054] The second downstream storage chamber 35 is provided on the negative side in the X-axis direction of the first downstream storage chamber 34. A second downstream throttle portion 39 is provided between the first downstream storage chamber 34 and the second downstream storage chamber 35. The second downstream storage chamber 35 communicates with the downstream supply flow path 23a, and communicates with the first downstream storage chamber 34 via the second downstream throttle portion 39. The second downstream throttle portion 39 has a smaller dimension in the Z-axis direction than the first downstream storage chamber 34 and the second downstream storage chamber 35.

[0055] The first downstream throttle portion 38 and the second downstream throttle portion 39 are provided so that the first downstream storage chamber 34 becomes a substantially closed space. In addition, the second downstream throttle portion 39 is provided at a position different from that of the first downstream throttle portion 38 in the Z-axis direction. Figure 3 In the Z-axis direction, the first downstream throttle portion 38 is disposed near the upper wall of the first downstream storage chamber 34, and the second downstream throttle portion 39 is disposed near the lower wall. Therefore, it is easy to block the pressure wave of the ink in the first downstream storage chamber 34.

[0056] The ink in the pressure chamber 31 is discharged to the downstream supply flow path 23 a through the first downstream throttle portion 38 , the first downstream reservoir chamber 34 , the second downstream throttle portion 39 , and the second downstream reservoir chamber 35 .

[0057] <Nozzle plate 40>

[0058] A plurality of nozzles 41 are formed on the nozzle plate 40. The nozzles 41 are holes through which ink passes when the ink is ejected, and penetrate the nozzle plate 40. The nozzles 41 are cylindrical in shape. It should be noted that the nozzles 41 may also be formed in a tapered shape.

[0059] The larger the diameter of the nozzle 41, the larger the volume of the ejected ink droplets, and the smaller the diameter of the nozzle 41, the smaller the droplet volume, so the diameter of the nozzle 41 is set according to the desired droplet volume. In this embodiment, the diameter of the nozzle 41 is, for example, 7 μm or more and 200 μm or less.

[0060] The longer the size of the nozzle 41 in the Z-axis direction, the more the straightness of the ink droplet improves. On the other hand, the fluid resistance when the nozzle 41 passes increases, so it is difficult to eject the ink. In this embodiment, the size of the nozzle 41 in the Z-axis direction is, for example, 5 μm or more and 500 μm or less.

[0061] <Vibration plate 50>

[0062] The vibration plate 50 constitutes a part of the pressure chamber 31, the first upstream storage chamber 32, and the first downstream storage chamber 34. In the present embodiment, the vibration plate 50 constitutes the upper wall of the pressure chamber 31, the first upstream storage chamber 32, and the first downstream storage chamber 34. The vibration plate 50 is formed by, for example, overlapping a lower plate member 51 and an upper plate member 52. For example, the lower plate member 51 and the upper plate member 52 have the same thickness. It should be noted that the lower plate member 51 and the upper plate member 52 may also have different thicknesses from each other.

[0063] The lower plate member 51 covers the pressure chamber 31, the first upstream reservoir chamber 32, and the first downstream reservoir chamber 34 from the side opposite to the discharge surface S. The second upstream reservoir chamber 33 and the second downstream reservoir chamber 35 of the lower plate member 51 are open on the positive side in the Z axis direction.

[0064] The lower plate member 51 is thinner than the flow path plate 30, and has a thickness that is, for example, one-third or less of the flow path plate 30. Therefore, the lower plate member 51 is less rigid than the flow path plate 30 and is easily deformed.

[0065] The upper plate member 52 is composed of a reinforcing portion 52a and a pressed portion 52b.

[0066] The reinforcing portion 52 a is disposed in the lower plate member 51 at a position other than the positive side in the Z-axis direction of the pressure chamber 31 , the first upstream reservoir chamber 32 , the first downstream reservoir chamber 34 , the first upstream throttle portion 36 , and the first downstream throttle portion 38 .

[0067] Therefore, the upper walls of the first upstream storage chamber 32 and the first downstream storage chamber 34 are constituted only by the lower plate member 51. In the following description, the portions of the vibration plate 50 that constitute the upper walls of the first upstream storage chamber 32 and the first downstream storage chamber 34 are referred to as "upstream flexure 72" and "downstream flexure 73", respectively.

[0068] The pressed portion 52 b is disposed in a predetermined region of the upper surface of a portion of the lower plate member 51 that covers the pressure chamber 31 , and is pressed by the pressure changing portion 61 .

[0069] Therefore, the upper wall of the pressure chamber 31 (hereinafter referred to as the "central bending portion 70") is composed of a portion consisting only of the lower plate member 51 (hereinafter referred to as the "thin plate portion") and a portion consisting of the lower plate member 51 and the pressed portion 52b (hereinafter referred to as the "thick plate portion") .

[0070] <Pressure Changing Section 61>

[0071] The plurality of pressure changing parts 61 are arranged in the Y direction in each accommodation space so as to be separated from each other. The pressure changing parts 61 are arranged on the pressed part 52b in a one-to-one correspondence with the sets of the nozzles 41 and the ejection units 301. That is, in the inkjet head 1, the same number of pressure changing parts 61 as the number of sets of the nozzles 41 and the ejection units 301 are provided.

[0072] The pressure changing portion 61 expands and contracts in the Z-axis direction when a voltage is applied via the electrodes. In response thereto, the central flexible portion 70 deforms so as to reduce or restore the volume of the pressure chamber 31 .

[0073] When the volume of the pressure chamber 31 decreases, the pressure chamber 31 becomes a positive pressure state, and the ink in the pressure chamber 31 is ejected from the nozzle 41 to the outside. Hereinafter, the action of extending the pressure changing portion 61 is referred to as a "pushing action". In addition, when the pressure changing portion 61 contracts and returns to the volume of the pressure chamber 31, the pressure chamber 31 becomes a negative pressure state, and the meniscus in the nozzle 41 is pulled up to the positive side in the Z-axis direction. Hereinafter, the action of contracting the pressure changing portion 61 is referred to as a "pulling action".

[0074] <Relationship between ink shear rate and viscosity>

[0075] Figure 5 2 is a diagram for explaining the shear velocity of ink during the ink ejection operation. Figure 5 In FIG. 1 , the vertical axis represents the amount of expansion of the pressure changing portion 61 , and the horizontal axis represents time. Figure 6 This is a graph showing the relationship between the viscosity of ink and the shear rate. Figure 5 The time period of ΔTH is a time period during which the shear velocity of the ink is relatively high, and the time period of ΔTL is a time period during which the shear velocity of the ink is relatively low.

[0076] While the pressure changing portion 61 is extending, the shearing speed of the ink increases, and the shearing speed reaches a maximum at the timing of ink ejection. Thereafter, the shearing speed decreases due to the contraction (restoration) of the pressure changing portion 61.

[0077] like Figure 6As shown in FIG. 1 , the viscosity of the ink changes according to the shear rate of the ink. Specifically, the higher the shear rate of the ink, the lower the viscosity of the ink.

[0078] Generally, the lower the viscosity of the ink, the easier it is to cut the liquid line of the ejected ink. On the other hand, the higher the viscosity of the ink, the harder it is to cut and the easier it is to lengthen the liquid line.

[0079] In this embodiment, the vibration plate 50 has an upstream flexure 72 and a downstream flexure 73, and the upstream flexure 72 and the downstream flexure 73 are easier to deform than the central flexure 70. The liquid line can be cut off during a period of time when the ink viscosity is low by the action of the upstream flexure 72 and the downstream flexure 73. The action of the embodiment is described in detail below in comparison with the comparative example.

[0080] <Ink ejection according to the embodiment>

[0081] Figure 7 It is a partial cross-sectional view of the pressure changing unit 61 and the vibration plate 50 included in the inkjet head 1 . Figure 7 d1 is the thickness of the upstream flexure 72 and the downstream flexure 73 . Figure 8 It is a partial plan view of the vibration plate 50 included in the inkjet head 1 . Figure 8 W1 is the depth of the upstream bending portion 72 and the downstream bending portion 73, Figure 8 L1 is the length of the width of the upstream flexure 72 and the downstream flexure 73 .

[0082] The upstream flexible portion 72 and the downstream flexible portion 73 function to maintain the pressure chamber 31 in a negative pressure state of a certain value or more for a certain period of time or more.

[0083] More specifically, the upstream flexure 72 receives the positive pressure transmitted from the pressure chamber 31 to the first upstream storage chamber 32 and deforms during the period from the start of the pushing action to the start of the pulling action. As a result, since it takes more than a certain time for the pressure to be reflected from the first upstream storage chamber 32 to the pressure chamber 31, during this period, the function is performed in a manner such that the time integral value of the negative pressure value of the ink in the pressure chamber 31 becomes greater than a specified value. In addition, the downstream flexure 73 receives the positive pressure transmitted from the pressure chamber 31 to the first downstream storage chamber 34 and deforms during the period from the start of the pushing action to the start of the pulling action. As a result, since it takes more than a certain time for the pressure to be reflected from the first downstream storage chamber 34 to the pressure chamber 31, during this period, the function is performed in a manner such that the time integral value of the negative pressure value of the ink in the pressure chamber 31 (hereinafter referred to as the "negative pressure time integral value") becomes greater than a specified value. It should be noted that the negative pressure time integral value is described later. Fig. 9 The area of ​​the shaded portion.

[0084] The upstream flexure 72 and the downstream flexure 73 are easier to deform than the central flexure 70. Specifically, the upstream flexure 72 and the downstream flexure 73 have a deformation parameter δ greater than that of the central flexure 70. It should be noted that the deformation parameter δ is a value indicating the ease of deformation in the Z-axis direction, and when the force applied along the Z-axis direction is set to F and the displacement in the Z-axis direction when F is applied is set to Δz, there is a relationship of Δz=δF.

[0085] The deformation parameter δ can be expressed by the following formula (1) when Young's modulus is E, the dimension in the minor axis direction of the dimensions in the X-axis and Y-axis directions is Ls, the dimension in the major axis direction is R, and the dimension in the Z-axis direction is d.

[0086] [Formula 1]

[0087]

[0088] When viewed from above, when the central bending portion 70, the upstream bending portion 72 and the downstream bending portion 73 are rectangular, the dimension in the short axis direction refers to the shorter dimension of the width or depth, and the dimension in the long axis direction refers to the longer dimension of the width or depth.

[0089] For example, when the central flexible portion 70 , the upstream flexible portion 72 , and the downstream flexible portion 73 are elliptical in a plan view, the dimension in the short axis direction is the diameter in the short axis direction, and the dimension in the long axis direction is the diameter in the long axis direction.

[0090] Furthermore, when the central flexible portion 70 , the upstream flexible portion 72 , and the downstream flexible portion 73 are circular in plan view, the dimension in the short-axis direction and the dimension in the long-axis direction are the diameters of the circles.

[0091] According to formula (1), the smaller the Young's modulus and the thickness d are, the larger δ is. In addition, the longer the dimension Ls in the minor axis direction is, the larger δ is. In addition, the longer the dimension R in the major axis direction is, the larger δ is.

[0092] In the present embodiment, the deformation parameter δ1 of the upstream flexure 72 and the deformation parameter δ2 of the downstream flexure 73 are larger than the deformation parameter δ0 of the central flexure 70. More preferably, δ1 and δ2 are both 1.5 times or more and 100 times or less of δ0.

[0093] In this embodiment, if Figure 8 As shown, the upstream flexible portion 72 and the downstream flexible portion 73 have the same shape, so δ1=δ2 holds.

[0094] Fig. 9 1 is a diagram showing changes in the pressure of the ink near the nozzle 41 in the pressure chamber 31 during the ink ejection operation by the inkjet head 1 . Fig. 9 The solid line represents the time variation of the pressure of the ink near the nozzle 41 in the pressure chamber 31, and the dotted line represents the time variation of the extension amount of the pressure changing portion 61. Hereinafter, unless otherwise specified, the ink in the pressure chamber 31 refers to the ink near the nozzle 41 in the pressure chamber 31. It should be noted that Fig. 9 In the diagram, when the ink pressure shows a positive value, the pressure chamber 31 is in a positive pressure state, and when it shows a negative value, it is in a negative pressure state.

[0095] By applying a voltage to the pressure changing portion 61, the pressure changing portion 61 expands in the Z-axis direction ( Fig. 9 The pressed portion 52b is pressed toward the negative side in the Z-axis direction. As a result, the central flexure 70 is deformed so as to reduce the volume of the pressure chamber 31, and the pressure of the ink in the pressure chamber 31 increases ( Fig. 9 At the timing when the extension amount of the pressure changing portion 61 reaches the maximum value (time t10), the ink is ejected from the nozzle 41 to the outside, and moves toward the negative side in the Z-axis direction while forming a liquid line.

[0096] Immediately after the pressure of the ink in the pressure chamber 31 increases, the pressure fluctuation in the pressure chamber 31 propagates to the first upstream storage chamber 32 and the first downstream storage chamber 34 via the first upstream throttle portion 36 and the first downstream throttle portion 38. In addition, the upstream flexure 72 and the downstream flexure 73 are deformed so as to increase the volumes of the first upstream storage chamber 32 and the first downstream storage chamber 34.

[0097] Due to the reaction of the ink ejection, the pressure of the ink in the pressure chamber 31 decreases and becomes a negative pressure at time t11. As a result, the curved liquid surface in the nozzle 41 begins to be pulled up to the positive side in the Z-axis direction. In addition, the upstream flexure 72 and the downstream flexure 73 are formed to be easily deformed, so it takes a relatively long time from the beginning of deformation to the restoration of the original shape. Therefore, after the ink is ejected, the ink in the pressure chamber 31 is maintained in a negative pressure state for a relatively long time (after time t11 and before time t12). That is, the negative pressure time integral value during the negative pressure period immediately after the ink ejection time t10 (after time t11 and before time t12) is greater than the specified value. As a result, during the negative pressure period immediately after the ejection time t10, the liquid line of the ink is cut off.

[0098] This cutting timing is before the time t13 when the pressure changing portion 61 starts to contract, and is a timing when the ink viscosity is low. Therefore, the liquid line is easily cut.

[0099] In addition, in the present embodiment, the time from the ejection time t10 to the time when the liquid line is cut can be made relatively short. Therefore, the liquid line is cut before it becomes longer.

[0100] After that, the deformed upstream flexure 72 and the downstream flexure 73 are restored, and the volumes of the first upstream storage chamber 32 and the second upstream storage chamber 33 are restored. As a result, the pressure of the ink in the first upstream storage chamber 32 and the first downstream storage chamber 34 increases. This pressure change is transmitted to the pressure chamber 31 via the first upstream throttle portion 36 and the first downstream throttle portion 38. In addition, the pressure of the ink in the pressure chamber 31 increases, and at time t12, the pressure changes from negative pressure to positive pressure. As a result, the ink in the pressure chamber 31 starts to move toward the ejection end of the nozzle 41.

[0101] After time t11, the meniscus of the ink in the nozzle 41 is pulled up toward the positive side in the Z-axis direction, so the meniscus at time t12 is located on the positive side in the Z-axis direction relative to the discharge end of the nozzle 41. That is, air exists between the discharge end of the nozzle 41 and the meniscus.

[0102] Therefore, after time t12, the ink in the pressure chamber 31 begins to move toward the ejection end of the nozzle 41, so that the atmosphere in the nozzle 41 is squeezed by the ink from the ejection surface S to the negative side in the Z-axis direction. The squeezed atmosphere is blown toward the flying liquid line of the ink. Therefore, the liquid line is pushed toward the negative side in the Z-axis direction by the atmosphere, so it is accelerated in the direction of travel and easily converges with the main droplet located at the front. That is, it is difficult for the liquid line to separate from the main droplet and it is difficult to generate a spray. In addition, the overall flying speed of the droplets is increased by the blowing of the atmosphere, so the landing position of the ink is difficult to fluctuate.

[0103] When the pressure changing portion 61 starts to contract at time t13 , the central flexible portion 70 restores the volume of the pressure chamber 31 , and the pressure of the ink in the pressure chamber 31 decreases to become a negative pressure.

[0104] <Discharge of Comparative Example>

[0105] First, use Figure 10~Figure 11 The structure of the inkjet head 2 of the comparative example will be described mainly in terms of differences from the inkjet head 1 .

[0106] Fig.10 It is a partial cross-sectional view of the pressure changing section 61 and the vibration plate 50 included in the inkjet head 2 of the comparative example. Fig.11 It is a partial plan view of the vibration plate 50 provided in the inkjet head 2 of the comparative example. Fig.11 182 is an upper wall of the first upstream storage chamber 32 , and 183 is an upper wall of the first downstream storage chamber 34 .

[0107] The upper plate member 52 of the comparative example has the reinforcing portion 152a, and the reinforcing portion 152a is also arranged on the positive side in the Z-axis direction of the first upstream storage chamber 32 and the first downstream storage chamber 34. Therefore, the upper wall 182 of the first upstream storage chamber 32 and the upper wall 183 of the first downstream storage chamber 34 are entirely constituted by the lower plate member 51 and the reinforcing portion 152a.

[0108] In the comparative example, the deformation parameters of the upper wall 182 and the upper wall 183 are smaller than that of the central bending portion 70 .

[0109] Fig.12 1 is a diagram showing changes in the pressure of ink near the nozzle in the pressure chamber 31 during the ink ejection operation performed by the inkjet head 2 of the comparative example. Fig.12 The solid line represents the temporal change in the pressure of the ink in the pressure chamber 31 , and the dotted line represents the temporal change in the amount of expansion of the pressure changing portion 61 .

[0110] By applying a voltage to the pressure changing portion 61, the pressure changing portion 61 expands in the Z-axis direction ( Fig.12 The pressed portion 52b is pressed toward the negative side in the Z-axis direction. As a result, the central flexure 70 is deformed so as to reduce the volume of the pressure chamber 31, and the pressure of the ink in the pressure chamber 31 increases ( Fig.12 At the timing when the extension amount of the pressure changing portion 61 reaches the maximum value (time t20), the ink is ejected from the nozzle 41 to the outside, and moves toward the negative side in the Z-axis direction while forming a liquid line.

[0111] The pressure of the ink in the pressure chamber 31 increases, and the pressure change in the pressure chamber 31 propagates to the first upstream storage chamber 32 and the first downstream storage chamber 34 via the first upstream throttle portion 36 and the first downstream throttle portion 38. As a result, the pressure of the ink in the first upstream storage chamber 32 and the first downstream storage chamber 34 increases. Along with this, the pressure of the ink in the pressure chamber 31 decreases and becomes a negative pressure at time t21.

[0112] However, the upper wall 182 and the upper wall 183 are not deformed so much as to increase the volume of the first upstream storage chamber 32 and the first downstream storage chamber 34, so the pressure of the ink in the first upstream storage chamber 32 and the first downstream storage chamber 34 immediately starts to decrease. And, along with this pressure change, the pressure in the pressure chamber 31 increases and becomes a positive pressure at time t22.

[0113] The first negative pressure period after the ink ejection time t20 ( Fig.12 The negative pressure time integral value during the negative pressure period immediately after the ink is ejected is relatively small and is below the specified value. Therefore, during this negative pressure period, although the meniscus in the nozzle 41 begins to be pulled up toward the positive side in the Z-axis direction, the liquid line is difficult to be cut off.

[0114] Thereafter, the pressure changes of the ink in the pressure chamber 31 and the first upstream storage chamber 32 and the first downstream storage chamber 34 affect each other, and the pressure of the ink in the pressure chamber 31 repeatedly increases and decreases, and repeatedly changes between a positive pressure state and a negative pressure state.

[0115] At time t23, when the pressure changing portion 61 starts to contract, the central flexure 70 recovers so as to increase the volume of the pressure chamber 31. Along with this, at time t24, the ink in the pressure chamber 31 becomes in a negative pressure state, and the meniscus is pulled up to the positive side in the Z-axis direction. The negative pressure period after time t24 lasts for a relatively long time, so the liquid line of the ejected ink is cut off.

[0116] In the comparative example, the liquid line is cut off after time t24. Time t24 is a time later than time t23 when the pressure changing portion 61 starts to contract, so it can be said that the ink viscosity is relatively high. Therefore, the liquid line is difficult to be cut off, and the liquid line is easy to be elongated. In addition, the period from the ink ejection time t20 to the liquid line being cut off is relatively long, so the liquid line is further easy to be elongated.

[0117] It should be noted that, in the embodiment, δ1=δ2 may not necessarily hold. For example, the areas of the first upstream storage chamber 32 and the first downstream storage chamber 34 in the XY plane may be different from each other. Alternatively, one of the upstream flexure 72 and the downstream flexure 73 may have a portion formed by the reinforcement portion 52a and the lower plate member 51.

[0118] In the embodiment, the larger the values ​​of δ1 and δ2, the larger the deformation of the upstream flexure 72 and the downstream flexure 73, so the negative pressure period immediately after the ink ejection becomes longer, and the negative pressure time integral value of the negative pressure period becomes larger. In addition, the pressure increase of the ink in the pressure chamber 31 after the liquid line is cut off becomes larger, so the blowing intensity of the atmosphere on the flying liquid line becomes larger, and the flying speed of the ink becomes higher. Furthermore, the fluctuation of the landing position of the ink becomes smaller, and the printing performance is easily improved.

[0119] On the other hand, as described above, δ1 and δ2 are preferably 100 times or less of δ0. The reason for setting the upper limit is that when δ1 and δ2 are too large, the pressure increase in the pressure chamber 31 accompanying the recovery of the upstream flexure 72 and the downstream flexure 73 is too large, and ink may be blown out.

[0120] It should be noted that, when only the blowing of the atmosphere to the cut liquid line is considered, the larger the area of ​​the upstream flexible portion 72 and the downstream flexible portion 73 in the XY plane is, the more effective it is.

[0121] The upstream and downstream flexures 72 and 73 may have a smaller Young's modulus E than the central flexure 70. By appropriately selecting the materials for forming the upstream and downstream flexures 72 and 73, the upstream and downstream flexures 73 can be deformed more easily than the central flexure 70.

[0122] In addition, the upstream flexure 72 and the downstream flexure 73 may be configured to have a smaller dimension d in the Z-axis direction than the central flexure 70. By appropriately selecting the dimension d in the Z-axis direction of the upstream flexure 72, the downstream flexure 73, and the central flexure 70, the upstream flexure 72 and the downstream flexure 73 can be deformed more easily than the central flexure 70.

[0123] In addition, the upstream flexure 72 and the downstream flexure 73 may be configured to have a dimension Ls in the short axis direction larger than that of the central flexure 70. By appropriately selecting the dimension Ls in the short axis direction of the upstream flexure 72, the downstream flexure 73, and the central flexure 70, the upstream flexure 72 and the downstream flexure 73 can be made to deform more easily than the central flexure 70.

[0124] In addition, the upstream flexure 72 and the downstream flexure 73 may be configured to have a larger dimension R in the long axis direction than the central flexure 70. By appropriately selecting the dimension R in the long axis direction of the upstream flexure 72, the downstream flexure 73 and the central flexure 70, the upstream flexure 72 and the downstream flexure 73 can be deformed more easily than the central flexure 70.

[0125] As described above, the inkjet head 1 of the embodiment includes: a nozzle 41 that ejects ink; a pressure chamber 31 that is connected to the nozzle 41; first storage chambers 32 and 34 that are connected to the pressure chamber 31 via a first throttle portion; a vibration plate 50 that has a portion (central flexure 70) that forms a part of the pressure chamber 31; and a pressure changing portion 61 that vibrates the vibration plate 50 in a manner that causes the pressure of the ink in the pressure chamber 31 to change, thereby causing the ink to be ejected from the pressure chamber 31 to the outside via the nozzle 41.

[0126] The first storage chambers 32 and 34 have the flexible portions 72 and 73 that are more easily deformed than the portion of the vibration plate 50 (the central flexible portion 70 ).

[0127] Thus, the pressure of the ink near the nozzle 41 in the pressure chamber 31 can be maintained at a negative pressure for a relatively long time immediately after the ink is ejected. Therefore, the liquid line of the ejected ink can be cut off at a time when the ink viscosity is low. In addition, the liquid line is cut off at a relatively early time from the time when the ink is ejected. Therefore, the liquid line can be shortened, so that spray is less likely to occur, and the printing performance can be improved.

[0128] In addition, after the liquid line is cut, the air in the nozzle 41 can be blown toward the flying liquid line of the ink, so that the liquid line is easily merged with the main droplet, and the generation of spray can be suppressed. In addition, the flying speed of the ink becomes higher, so the fluctuation of the landing position is suppressed. As a result, the printing performance is further improved.

[0129] The bending parts 72 and 73 are formed by the vibration plate 50. Therefore, the printing performance can be improved with a relatively simple structure.

[0130] The flexible portions 72 and 73 and the pressure changing portion 61 deform to increase the volumes of the first storage chambers 32 and 34 in accordance with the increase in the pressure of the ink in the pressure chamber 31 , thereby making the pressure of the ink in the pressure chamber 31 negative.

[0131] By operating in this way, the ink in the pressure chamber 31 is maintained in a negative pressure state for a relatively long time immediately after the ink is ejected, and the liquid line is cut off at this timing.

[0132] The flexible portions 72 and 73 increase the volumes of the first storage chambers 32 and 34 and then restore the volumes of the first storage chambers 32 and 34 to their original values, thereby making the pressure of the ink in the pressure chamber 31 a positive pressure.

[0133] By this operation, the atmosphere is blown toward the liquid line of the ejected ink.

[0134] The flow channel plate 30 includes two first storage chambers 32 and 34 for one pressure chamber 31. The set of the pressure chamber 31, the pressure changing unit 61, and the two first storage chambers 32 and 34 corresponds to the nozzle 41 in a one-to-one manner.

[0135] In this way, the pressure chamber 31, the pressure changing section 61, and the two first storage chambers 32 and 34 are arranged in a one-to-one correspondence with the nozzle 41. Thus, by controlling the pressure of the ink near the nozzle 41 in the pressure chamber 31 using the plurality of first storage chambers 32 and 34, the liquid line can be effectively cut off and the liquid line can be blown by the atmosphere.

[0136] The deformation parameters δ1 and δ2 of the upstream flexible portion 72 and the downstream flexible portion 73 indicating the ease of deformation are 1.5 times or more and 100 times or less the deformation parameter δ0 of the central flexible portion 70 .

[0137] By setting the deformation parameters δ1 and δ2 to be 1.5 times or more of δ0, the liquid line can be cut off and the air can be blown to the liquid line more effectively.

[0138] In addition, by setting the deformation parameters δ1 and δ2 to be less than 100 times of δ0, the increase in the ink pressure in the pressure chamber 31 caused by the restoration of the upstream flexure 72 and the downstream flexure 73 can be suppressed, and the ink can be prevented from being ejected when the liquid line is blown to the atmosphere. In addition, in the design of the inkjet head 1, the dimensions in the X, Y and Z axis directions are limited to a certain extent, so the deformation parameters δ1 and δ2 are also substantially limited. That is, by setting a certain upper limit for δ1 and δ2, the inkjet head 1 can be designed in reality. For example, it is possible to prevent the thickness d of the upstream flexure 72 and the downstream flexure 73 from being too thin and being damaged during deformation.

[0139] The smaller the Young's modulus E and the thickness d of the upstream flexure 72 and the downstream flexure 73 are, the larger the deformation parameters δ1 and δ2 are. The longer the dimension Ls in the minor axis direction and the dimension R in the major axis direction are, the larger the deformation parameters δ1 and δ2 are.

[0140] It should be noted that the vibration plate 50 may also be composed of a single plate member, and the thickness may vary depending on the location. In addition, the vibration plate 50 may also have a uniform thickness, and the material, that is, the Young's modulus, may be changed depending on the location. For example, the upstream flexure 72 and the downstream flexure 73 may also be formed of a material having a smaller Young's modulus than the central flexure 70.

[0141] [Variant 1]

[0142] Hereinafter, regarding Modification 1, points different from the embodiment will be mainly described. Fig.13 It is a diagram illustrating a vibration plate 50 according to Modification 1.

[0143] In the embodiment, the entire downstream flexible portion 73 is constituted by only the lower plate member 51 , but in Modification 1, a part of the downstream flexible portion 73 is constituted by the lower plate member 51 and the reinforcing portion 52 a .

[0144] The downstream bending portion 73 is composed of a thin plate portion 191 composed only of the lower plate member 51 and a thick plate portion 192 composed of the lower plate member 51 and the reinforcement portion 52a. The width length L2 of the thin plate portion 191 is shorter than the width length L1 of the downstream bending portion 73 of the embodiment.

[0145] In the first modification, the deformation parameter δ2 of the downstream flexible portion 73 is smaller than the deformation parameter δ1 of the upstream flexible portion 72 .

[0146] Even if the deformation parameter δ2 of the downstream flexure 73 is smaller than the deformation parameter δ1 of the upstream flexure 72 as in the first modification, the deformation parameter δ1 is 1.5 to 100 times the deformation parameter δ0 of the central flexure 70 , and thus the same effects as those of the embodiment can be obtained.

[0147] However, as described above, when δ2 is large, the negative pressure period of the pressure chamber 31 immediately after the ink is ejected becomes longer, and the negative pressure time integral value becomes large, which makes it easy to cut off the liquid line. In addition, when δ2 is large, the atmosphere in the nozzle 41 can be blown strongly to the flying liquid line.

[0148] In the first modification, even if the structure of the downstream flexible portion 73 is made the same as that of the embodiment and the structure of the upstream flexible portion 72 is changed so that δ1 is smaller than that of the embodiment, the same effect can be obtained.

[0149] [Variant 2]

[0150] Hereinafter, regarding Modification Example 2, points different from Modification Example 1 will be mainly described. Fig.14 It is a diagram illustrating a vibration plate 50 according to a second modification.

[0151] In modification example 1, the downstream flexure 73 is formed by the thin plate portion 191 formed only by the lower plate member 51 and the thick plate portion 192 formed by the lower plate member 51 and the reinforcement portion 52a, but in modification example 2, the downstream flexure 73 is entirely formed by the lower plate member 51 and the reinforcement portion 52a.

[0152] In Modification 2, the deformation parameter δ2 of the downstream flexure 73 is smaller than the deformation parameter δ0 of the central flexure 70. However, the deformation parameter δ1 of the upstream flexure 72 is 1.5 to 100 times the deformation parameter δ0 of the central flexure 70, so the same effects as those of the embodiment can be obtained.

[0153] However, controlling the ink pressure in the pressure chamber 31 using both the upstream flexure 72 of the first upstream reservoir 32 and the downstream flexure 73 of the first downstream reservoir 34 as in the embodiment is advantageous in terms of cutting off the liquid line and blowing the atmosphere to the liquid line.

[0154] [Other modifications]

[0155] In each of the above-described embodiments and modifications, the second upstream reservoir chamber 33 and the second downstream reservoir chamber 35 are provided in the flow channel plate 30 . However, the second upstream reservoir chamber 33 and the second downstream reservoir chamber 35 may not be provided.

[0156] That is, the flow channel plate 30 may be configured such that ink is directly supplied from the upstream common flow channel 22a to the first upstream common flow channel 22a via the second upstream throttle portion 37 and is directly discharged from the first downstream reservoir 34 to the downstream common flow channel 23a via the second downstream throttle portion 39 .

[0157] The inkjet head 1 may be other than the ink circulation type, that is, the first downstream throttle portion 38 , the first downstream reservoir chamber 34 , the second downstream throttle portion 39 , and the second downstream reservoir chamber 35 may not be formed in the flow channel plate 30 .

[0158] In addition, a storage chamber that contributes to the pressure adjustment in the pressure chamber 31 may be provided separately from the ink supply path. For example, the first upstream storage chamber 32 and the second upstream storage chamber 33 may be formed integrally, the second downstream throttle portion 39 and the second downstream storage chamber 35 may not be formed, and the ink pressure in the pressure chamber 31 may be adjusted using only the downstream flexure 73 of the second downstream storage chamber 35.

[0159] It should be noted that, instead of the upper wall or a part thereof of the first storage chambers 32 and 34, the portion located on the positive side of the second throttle portion 37 and 39 in the Z-axis direction and the side wall of the first storage chamber 32 and 34 may be formed as the upstream bending portion and the downstream bending portion, respectively. In this case, the portion may be formed into a hollow shape in order to ensure the flow path length of the second throttle portion 37 and 39 and increase the deformation parameter.

[0160] The present invention also includes various modifications that can be conceived by those skilled in the art to the above-mentioned embodiments and modifications, and arbitrarily combining the components and functions in the above-mentioned embodiments without departing from the gist of the present invention.

[0161] According to the present invention, it is possible to provide an inkjet head having improved printing performance.

[0162] Industrial Applicability

[0163] The present invention can be suitably applied to an inkjet head in which a reservoir chamber communicating with a pressure chamber is formed.

[0164] Description of Reference Numerals

[0165] 1.2 Inkjet Head

[0166] 10 Main body

[0167] 20 Housing

[0168] 21 Ink supply path

[0169] 22a, 22b Upstream common flow path

[0170] 23a, 23b, 23c, 23d Downstream supply flow path

[0171] 24a, 24b Ink discharge path

[0172] 25a, 25b, 25c, 25d Containment Space

[0173] 30 Manifold board

[0174] 31 Pressure Chamber

[0175] 32 First upstream storage chamber

[0176] 33 Second upstream storage room

[0177] 34 First downstream storage chamber

[0178] 35 Second downstream storage room

[0179] 36 First upstream throttle

[0180] 37 Second upstream throttle

[0181] 38 First downstream throttle

[0182] 39 Second downstream throttling section

[0183] 40 Nozzle Plate

[0184] 41 Nozzle

[0185] 50 Vibration Plate

[0186] 51 Lower plate member

[0187] 52 Upper plate member

[0188] 52a Reinforcement

[0189] 52b Pressed down

[0190] 60 Pressure variable element unit

[0191] 61 Pressure change part

[0192] 70 Central flexure

[0193] 72 Upstream flexure

[0194] 73 Downstream flexure

[0195] 152a Reinforcement

[0196] 182, 183 upper wall

[0197] 191 Thin Plate Department

[0198] 192 Thick Plate Department

[0199] S ejection surface.

Claims

1. An inkjet head, wherein: The inkjet head comprises: a nozzle that ejects ink; a pressure chamber in communication with the nozzle; a storage chamber connected to the pressure chamber via a throttle portion; a vibrating plate having a portion forming a portion of the pressure chamber; as well as a pressure changing unit that vibrates the vibration plate so as to change the pressure of the ink in the pressure chamber, thereby causing the ink to be ejected from the pressure chamber to the outside through the nozzle, The storage chamber has a flexible portion that is more easily deformed than the portion of the vibration plate.

2. The inkjet head according to claim 1, wherein: The flexure is formed by the vibration plate.

3. The inkjet head according to claim 1 or 2, wherein: Two storage chambers are provided for one pressure chamber. The set consisting of the pressure chamber, the pressure changing portion, and the two storage chambers corresponds one-to-one to the nozzles.

4. The inkjet head according to claim 1 or 2, wherein: The flexure portion has a smaller Young's modulus than the portion of the vibration plate.

5. The inkjet head according to claim 1 or 2, wherein: The bending portion is thinner than the portion of the vibration plate.

6. The inkjet head according to claim 1 or 2, wherein: The bending portion has a larger dimension in the short-axis direction than the portion of the vibration plate.

7. The inkjet head according to claim 1 or 2, wherein: The bending portion has a larger dimension in the long-axis direction than the portion of the vibration plate.

8. The inkjet head according to claim 1 or 2, wherein: A parameter indicating the ease of deformation of the flexure is 1.5 to 100 times greater than a deformation parameter of the portion of the vibration plate.

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