Patent Description:
In recent years, increased performance has been required for inkjet heads, and it has become issues how to achieve high speed ink ejection and increase the amount of ejected droplets. For example, a shear mode shared wall type inkjet head has high power and is suitable for ejecting high-viscosity ink or large droplets. In a shear mode shared wall type inkjet head, a so-called three-cycle drive is generally used in which the same drive column is shared by two pressure chambers and only one-third of the plurality of arranged pressure chambers is simultaneously driven during an ejection operation. Furthermore, an independent drive head has been developed in which one pressure chamber is driven by two independent drive columns, with dummy pressure chambers being provided on both sides of the driven pressure chamber. In some examples, a structure has been developed in which a large number of grooves are formed in a piezoelectric body, but the inlets and outlets are closed every other groove, the grooves where the inlets and outlets are not closed are used as pressure chambers, the closed grooves are used as air chambers (dummy chambers), and the grooves can be independently driven.

In such an inkjet head, ink is replenished from a common liquid chamber after the ink droplets are ejected. At this time, a phenomenon occurs in which the meniscus rises due to overshooting by the nozzle. The smaller the fluid resistance along the flow path from the common liquid chamber to the nozzle, the larger the overshoot, and if this overshoot is too large, the next ink ejection cannot be performed with a stable meniscus. Therefore, in order to increase the speed in the inkjet head, it is required to quickly mitigate the rise of the meniscus and ensure stable ejection characteristics.

<CIT> discloses a chevron type printhead with dummy chambers and pressure chambers arranged alternately.

It is therefore provided a liquid ejection according to claim <NUM>.

In other words, the length in the second direction of a part of a lateral surface of the aperture overlapping the side wall is longer than a part of the lateral surface of the aperture which does not overlap the side wall (outside the side wall).

In some embodiments, a fluid resistance in the apertures is higher than a fluid resistance in the pressure chambers.

In some embodiments, the pair of covers fully cover both ends of each of the dummy chambers in the second direction.

In some embodiments, the pair of covers are made of a photosensitive resin.

In some embodiments, the first length is <NUM>% or more of a sum of the first and second lengths.

In some embodiments, the first length is <NUM>% or more of the sum of the first and second lengths.

In some embodiments, each of the nozzles is arranged at a position corresponding to a center of the corresponding pressure chamber in the second direction.

In some embodiments, the liquid is ejected towards a third direction intersecting the first and second directions.

In some embodiments, a width of each of the apertures in the first direction is smaller than a width of each of the pressure chambers in the first direction.

In some embodiments, the second length is equal to or less than a width of each of the pressure chambers in the first direction.

It is further provided a liquid ejecting device. The liquid ejecting device comprises a conveyer configured to convey a medium along a predetermined conveyance path. The liquid ejecting device also comprises a liquid ejecting head of a side shooter type, including a plate including a plurality of nozzles arranged along a first direction and through which liquid is ejected toward the medium. The liquid ejecting head also includes an actuator including: a plurality of pressure chambers each communicating with a corresponding one of the nozzles, a plurality of dummy chambers each disposed between two of the pressure chambers that are adjacent to each other, and a plurality of sidewalls separating the pressure and dummy chambers along the first direction and deformable to change a volume of each of the pressure chambers according to a drive signal. The liquid ejecting head also includes a pair of covers having a plurality of apertures and partly covering both ends of each of the pressure chambers in a second direction intersecting the first direction such that the pressure chambers communicate with a common chamber at both ends thereof through the apertures, wherein each of the covers includes a first portion on and between the sidewalls and a second portion other than the first portion, and a first length in the second direction of the first portion is equal to or greater than a second length in the second direction of the second portion.

Embodiments provide a liquid ejection head with stable liquid ejection characteristics.

In general, according to one embodiment, a liquid ejection head of a side shooter type includes a plate including a plurality of nozzles arranged along a first direction and through which liquid is ejected. The liquid ejection head further includes an actuator including a plurality of pressure chambers each communicating with a corresponding one of the nozzles, a plurality of dummy chambers each disposed between two of the pressure chambers that are adjacent to each other, and a plurality of sidewalls separating the pressure and dummy chambers along the first direction and deformable to change a volume of each of the pressure chambers according to a drive signal. The liquid ejection head further includes a pair of covers having a plurality of apertures and partly covering both ends of each of the pressure chambers in a second direction intersecting the first direction such that the pressure chambers communicate with a common chamber at both ends thereof through the apertures. Each of the covers includes a first portion on and between the sidewalls and a second portion other than the first portion, and a first length in the second direction of the first portion is equal to or greater than a second length in the second direction of the second portion.

Hereinafter, a configuration of an inkjet head <NUM> which is a liquid ejection head will be described with reference to <FIG>. <FIG> is a perspective view showing the inkjet head <NUM>, and <FIG> is an exploded perspective view of a part of the inkjet head <NUM>. <FIG> and <FIG> are enlarged cross-sectional views showing a part the inkjet head <NUM>. <FIG> and <FIG> are diagrams of apertures of the inkjet head <NUM> according to Example <NUM> and an inkjet head according to Comparative Example <NUM>, and <FIG> is a table showing the measured values of the apertures of Example <NUM> and Comparative Example <NUM>. <FIG> are an diagrams showing apertures according to Example <NUM>, Example <NUM>, and Example <NUM>, respectively. <FIG> is a diagram showing an aperture unit according to Comparative Example <NUM>. In this disclosure, the direction along which nozzles <NUM> and pressure chambers <NUM> of the inkjet head <NUM> are arranged is defined as the X axis, the extension direction of each pressure chamber <NUM> is defined as the Y axis, and the liquid ejection direction is defined as the Z axis for illustration purpose.

As shown in <FIG>, the inkjet head <NUM> is a so-called side shooter type, shear mode shared wall type inkjet head. The inkjet head <NUM> is a device for ejecting ink and is mounted inside, for example, an inkjet printer. For example, the inkjet head <NUM> is an independently driven inkjet head in which pressure chambers <NUM> and dummy chambers <NUM> are alternately arranged. The dummy chamber <NUM> is an air chamber to which ink is not supplied and does not communicate with any nozzle <NUM>.

The inkjet head <NUM> includes an actuator base <NUM>, a nozzle plate <NUM>, and a frame <NUM>. In the actuator base <NUM>, an ink chamber <NUM> to which ink as an example of a liquid is supplied is formed inside the inkjet head <NUM>.

Further, the inkjet head <NUM> includes parts such as a circuit board <NUM> that controls the inkjet head <NUM> and a manifold <NUM> that forms a part of a path between the inkjet head <NUM> and the ink tank.

As shown in <FIG>, the actuator base <NUM> includes a substrate <NUM>, a pair of actuator members <NUM>, and a cover unit <NUM>.

The substrate <NUM> is formed of ceramics such as alumina in a rectangular plate shape. The substrate <NUM> has a flat mounting surface. A pair of actuator members <NUM> are joined to the mounting surface of the substrate <NUM>. A plurality of supply holes <NUM> and discharge holes <NUM> are formed on the substrate <NUM>.

As shown in <FIG>, a pattern wiring <NUM> is formed on the substrate <NUM> of the actuator base <NUM>. The pattern wiring <NUM> is formed of, for example, a nickel thin film. The pattern wiring <NUM> has common patterns and individual patterns and is configured in a predetermined pattern shape connected to an electrode layer <NUM> formed on the actuator member <NUM>.

The supply holes <NUM> are provided in the central portion of the substrate <NUM> between the pair of actuator members <NUM> side by side along the longitudinal direction of the actuator members <NUM>. The supply hole <NUM> communicates with the ink supply portion of the manifold <NUM>. The supply hole <NUM> is connected to the ink tank via the ink supply portion. Through the supply hole <NUM>, the ink is supplied from the ink tank to the ink chamber <NUM>.

The discharge holes <NUM> are provided side by side in two rows with the supply holes <NUM> and the pair of actuator members <NUM> interposed therebetween. The discharge hole <NUM> communicates with the ink discharge portion of the manifold <NUM>. The discharge hole <NUM> is connected to the ink tank via the ink discharge portion. Through the discharge hole <NUM>, the ink is discharged from the ink chamber <NUM> into the ink tank.

The pair of actuator members <NUM> adhere to the mounting surface of the substrate <NUM>. The pair of actuator members <NUM> are provided on the substrate <NUM> side by side in two rows with the supply holes <NUM> interposed therebetween. Each actuator member <NUM> is formed of, for example, two plate-shaped piezoelectric bodies formed of lead zirconate titanate (PZT). The two piezoelectric bodies are bonded so that the polarization directions are opposite to each other in the thickness direction. The actuator member <NUM> is adhered to the mounting surface of the substrate <NUM> with, for example, a thermosetting epoxy adhesive. As shown in <FIG>, the actuator members <NUM> are arranged side by side in parallel in the ink chamber <NUM> corresponding to the nozzles <NUM> arranged in two rows. The actuator member <NUM> divides the ink chamber <NUM> into a first common chamber <NUM> in which the supply hole <NUM> opens and two second common chambers <NUM> in which the discharge hole <NUM> opens.

The pair of actuator members <NUM> are arranged along the longitudinal direction (first direction), and an orthogonal cross section is formed in a trapezoidal shape. The side surface portion <NUM> of the actuator member <NUM> has an inclined surface that is inclined with respect to the second direction (Y-axis direction) and the third direction (Z-axis direction). That is, the actuator member <NUM> is configured to have a trapezoidal shape in the cross-sectional view orthogonal to the second direction. The top of the actuator member <NUM> adheres to the nozzle plate <NUM>. The actuator member <NUM> includes a plurality of pressure chambers <NUM> and a plurality of dummy chambers <NUM>. The actuator member <NUM> includes a plurality of sidewalls <NUM> and includes grooves forming the pressure chamber <NUM> and the dummy chamber <NUM> between the sidewalls <NUM>. In other words, the sidewall <NUM> operates as a driving element between the grooves forming the pressure chamber <NUM> and the dummy chamber <NUM>. The plurality of pressure chambers <NUM> and the dummy chamber <NUM> are composed of grooves that open at both ends in the second direction and on one side in the third direction.

As shown in <FIG>, a bottom surface portion of the groove and the main surface of the substrate <NUM> are connected by the inclined side surface portion <NUM>. The pressure chambers <NUM> and the dummy chambers <NUM> are alternately placed. The pressure chambers <NUM> and the dummy chambers <NUM> extend in a direction intersecting the longitudinal direction of the actuator member <NUM> (X-axis in the drawings) and are arranged in parallel along the longitudinal direction of the actuator member <NUM>.

The shape of the pressure chamber <NUM> and the shape of the dummy chamber <NUM> may be different. The sidewall <NUM> is formed between the pressure chamber <NUM> and the dummy chamber <NUM> and deforms in response to a drive signal to change the volume of the pressure chamber <NUM>.

The plurality of pressure chambers <NUM> communicate with the plurality of nozzles <NUM> of the nozzle plate <NUM> joined to the top thereof. Both ends of the pressure chamber <NUM> in the second direction communicate with the ink chamber <NUM>. That is, one end opens to the first common chamber <NUM> of the ink chamber <NUM>, and the other end opens to the second common chamber <NUM> of the ink chamber <NUM>. Therefore, the ink flows in from one end of the pressure chamber <NUM>, and the ink flows out from the other end. At both ends of the pressure chamber <NUM>, aperture units <NUM> having a fluid resistance larger than the inside of the pressure chamber <NUM> are formed.

The dummy chamber <NUM> is closed by the nozzle plate <NUM> having one side joined to the top <NUM> in the third direction. Further, both ends of the plurality of dummy chambers <NUM> in the second direction are closed (blocked) by the cover unit <NUM>, for example. That is, the cover units <NUM> are arranged between the first common chamber <NUM> and one end of the dummy chamber <NUM> of the ink chamber <NUM>, and between the other end of the dummy chamber <NUM> and the second common chamber <NUM>, respectively, and both ends of the dummy chamber <NUM> are separated from the ink chamber <NUM>. Therefore, the dummy chamber <NUM> forms an air chamber in which ink does not flow in.

The electrode layer <NUM> is provided in each of the pressure chambers <NUM> and the dummy chambers <NUM> of the actuator base <NUM>. The electrode layer <NUM> is formed of, for example, a nickel thin film. The electrode layer <NUM> reaches from the inner surface of the groove onto the substrate <NUM> and is connected to the pattern wiring <NUM>. The electrode layer <NUM> is formed on the inner wall of the groove. For example, the electrode layer <NUM> is formed on the side surface portion and the bottom surface portion of the sidewall <NUM>.

The cover units <NUM> are provided at both ends in the second direction of the grooves forming the plurality of pressure chambers <NUM> and the dummy chamber <NUM>. The cover unit <NUM> is made of, for example, a photosensitive resin. The cover unit <NUM> is a cover formed in a predetermined shape having a slit-shaped opening by being exposed and developed after the film of the photosensitive resin is formed, or by being exposed, developed, and machined after the film of the photosensitive resin is formed. That is, on the inner surface of the sidewall <NUM> on the pressure chamber side, which forms both side surfaces of the pressure chamber <NUM>, a protrusion protruding toward the pressure chamber side is formed.

The cover unit <NUM> is configured in a predetermined shape to close both ends of the groove forming the dummy chamber <NUM> and a part of both ends of the groove forming the pressure chamber <NUM> by performing a developing process in which photosensitive resin is applied to the inlets on both sides of the pressure chamber <NUM>, the target portion is cured by exposure, and unnecessary unexposed resin is washed away with a developing solution.

The cover unit <NUM> includes a plurality of protrusions <NUM> that close the ends of the dummy chamber <NUM> in the second direction and are formed on both side surfaces in the first direction of each end of the pressure chamber <NUM> in the second direction. The protrusions <NUM> are formed on both side surfaces of the pressure chamber <NUM>, for example.

The pair of protrusions <NUM> formed at the end of each pressure chamber <NUM> may be formed over the entire length in the third direction, which is the depth direction of the groove of the pressure chamber <NUM>, or may be partially formed in the third direction. For example, each of the pair of protrusions <NUM> is formed in a rectangular shape long in the third direction.

The protrusion <NUM> forms the aperture unit <NUM> that has a fluid resistance larger than the inside of the pressure chamber by narrowing the opening of the pressure chamber <NUM>.

That is, the groove forming the pressure chamber <NUM> is not completely covered by the protrusions <NUM>, and an aperture <NUM> that communicates the pressure chamber <NUM> with the first common chamber <NUM> and the second common chamber <NUM> between the pair of protrusions <NUM> is formed. The aperture <NUM> has a slit shape extending in the third direction, which is the depth direction of the pressure chamber <NUM> and is configured to be smaller than the flow path cross-sectional area of the pressure chamber <NUM> by the opening width in the first direction being smaller than the width inside the pressure chamber <NUM> in the first direction. That is, the protrusion <NUM> partially closes the communication ports at both ends in the second direction to form the aperture unit <NUM> in which the flow path resistance increases. The aperture unit <NUM> is formed by being exposed and developed after the film of the photosensitive resin is formed, or by being exposed, developed, and machined after the film of the photosensitive resin is formed. For example, the aperture unit <NUM> is configured in a predetermined shape by performing a developing process in which a photosensitive resin is applied to the inlets on both sides of the pressure chamber <NUM>, the target portion forming the protrusion <NUM> is cured by exposure, and unnecessary unexposed resin is washed away with a developing solution. Alternatively, the aperture <NUM> may be formed by applying a photosensitive resin to the pressure chamber <NUM>, the photosensitive resin at predetermined positions of the communication ports on both sides is cured by the exposure process and development process, and then machining such as dicing is performed.

If the fluid resistance of the aperture unit <NUM> is too large, the replenishment of ink to the pressure chamber <NUM> after ink droplet ejection is delayed, which hinders high speed. Further, the rise of the meniscus differs depending on the ink viscosity, the ejection volume, the drive frequency, and the like. Therefore, the shape of the protrusion <NUM> and the dimension and position of the aperture <NUM> of the aperture unit <NUM> are set to have a flow path resistance according to the ink replenishment condition and the characteristics of the rise of the meniscus.

The cover unit <NUM> includes a first portion <NUM> formed in a gap between the sidewalls <NUM>, and a second portion <NUM> located outside the pressure chamber <NUM> from the sidewall <NUM> in the second direction. That is, the aperture <NUM> formed by the protrusion <NUM> formed as a part of the cover unit <NUM> integrally has the first portion <NUM> on the sidewall <NUM> and the second portion <NUM> extending to the outside of the pressure chamber <NUM> in the second direction from the sidewall <NUM>. Here, the dimensions of the cover unit <NUM>, the protrusions <NUM>, and the aperture <NUM> in the second direction are such that the portion on or between the sidewalls <NUM> is longer than the portion formed on the outside of the sidewalls <NUM>.

In Example <NUM>, the first portion <NUM> is configured to be larger than the second portion <NUM> in the second direction. That is, <NUM>% or more of the cover unit <NUM> in the thickness direction or the second direction are between the sidewalls <NUM>. The dimension of the first portion <NUM> of the protrusion <NUM> in the second direction is <NUM>% or more of the total length of the protrusion <NUM> in the second direction. That is, the length of the first portion is longer than that of the second portion. In other words, the dimension of the first portion <NUM> of the aperture <NUM> in the second direction, which is the flow path length of the aperture <NUM> composed of the protrusion <NUM> is <NUM>% or more of the total length of the aperture <NUM> in the second direction. That is, the length of the first portion <NUM> is longer than that of the second portion <NUM>.

<FIG> is a diagram showing the aperture unit <NUM> according to Example <NUM>, and <FIG> is a diagram showing the aperture unit <NUM> according to Comparative Example <NUM>. <FIG> is a table showing the dimension of the width "a" at the outlet <NUM> on the pressure chamber <NUM> side, which is the inside of the aperture <NUM>, and the dimension of the width "b" at the inlet <NUM> on the ink chamber <NUM> side, which is the outside of the aperture <NUM>, in the design values for Example <NUM> and Comparative Example <NUM>. In <FIG>, in five different pressure chambers <NUM> according to Example <NUM> and Comparative Example <NUM>, the measured values of the width "a" and the width "b," the average value, and the standard deviation are shown. Both Example <NUM> and Comparative Example <NUM> show the measured values in the five pressure chambers <NUM> if a slit, which becomes the aperture <NUM>, is formed by dicing after the cover unit <NUM> is applied. In both Example <NUM> and Comparative Example <NUM>, the design values are set for the aperture length, that is, the total length of the aperture <NUM> in the second direction to be <NUM>, for the aperture width, that is, the dimension of the slit which is the aperture <NUM> in the first direction to be <NUM>, and for the width of the groove, that is, the dimension of the pressure chamber <NUM> in the first direction to be <NUM>.

In Example <NUM>, the lengths of the first portion <NUM> and the second portion <NUM> are set to <NUM>% of the aperture length in the second direction. In Example <NUM>, the width "a" of the aperture <NUM> inside the pressure chamber <NUM> was <NUM> on average, and the standard deviations of the widths of the openings inside and outside the aperture unit <NUM> were about <NUM> and <NUM>.

In Comparative Example <NUM>, the lengths of the first and second portions <NUM> and <NUM> are set to <NUM>% and <NUM>% of the aperture length in the second direction. In Comparative Example <NUM>, the width "a" of the aperture <NUM> inside the pressure chamber <NUM> was <NUM> on average, and the width "b" of the aperture <NUM> outside of the pressure chamber <NUM> was <NUM> on average. Further, the standard deviations of the width dimensions of the openings inside and outside the aperture unit <NUM> were <NUM> and <NUM>. As shown in <FIG>, in the case of Comparative Example <NUM>, the widths of the slit as the aperture <NUM> formed by machining are greatly different between the first portion <NUM> on the sidewall <NUM> and the second portion <NUM> formed outside the sidewall <NUM>, and the variation in the width dimension of the outer inlet <NUM> for each pressure chamber <NUM> becomes particularly large.

<FIG> is a diagram showing the aperture unit <NUM> according to Example <NUM>. In Example <NUM>, the design values are set for the aperture length, that is, the total length of the aperture <NUM> in the second direction to be <NUM>, for the aperture width, that is, the dimension of the slit-shaped aperture <NUM> in the first direction to be <NUM>, and for the width of the pressure chamber <NUM>, that is, the dimension of the pressure chamber <NUM> in the first direction to be <NUM>. For example, in Example <NUM>, <NUM>% or more of the total thickness, which is the dimension of the cover unit <NUM> in the second direction, is configured to be between the sidewalls <NUM>. That is, in the aperture <NUM> composed of the protrusion <NUM>, the dimension of the first portion <NUM> is <NUM>% or more of the total length of the aperture <NUM> in the second direction. Further, in Example <NUM>, the dimension of the second portion in the second direction is based on the width dimension of the pressure chamber <NUM> in the first direction so that the thickness of the second portion in the second direction is the same as or less than the width dimension of the pressure chamber <NUM> in the first direction, or equal to or less than the width dimension of the pressure chamber <NUM> in the first direction, and the width dimension of the first portion <NUM> is set to be <NUM>% or more of the total length of the aperture <NUM> in the second direction.

<FIG> is a diagram showing the aperture unit <NUM> according to Example <NUM>. In Example <NUM>, the design value is set for the aperture length, that is, the total length of the aperture <NUM> in the second direction to be <NUM>, for the aperture width, that is, the dimension of the slit forming the aperture <NUM> in the first direction to be <NUM>, and for the width of the groove, that is, the dimension of the pressure chamber <NUM> in the first direction to be <NUM>. For example, in Example <NUM>, <NUM>% or more of the total thickness, which is the dimension of the cover unit <NUM> in the second direction, is set as the first portion <NUM> on the sidewall <NUM>. That is, in the aperture <NUM> composed of the protrusion <NUM>, the dimension of the first portion <NUM> is set to <NUM>% or more of the total length of the aperture <NUM> in the second direction. In Example <NUM>, the dimension of the second portion <NUM> in the second direction is equal to or less than the thickness of the protrusion <NUM> formed on the sidewall <NUM>, that is, the thickness dimension of the protrusion <NUM> in the first portion <NUM> in the first direction. In the present example, the thickness in the pressure chamber <NUM> is <NUM>, which is (groove width <NUM> - slit width <NUM>) / <NUM>. The length of the first portion <NUM> is <NUM>, that is, <NUM>% of the total length. In this example, based on this thickness, the thickness of the second portion <NUM> in the second direction is set to be equal to or less than the thickness of the first portion <NUM> in the pressure chamber <NUM> or to be equal to or less than the thickness. As an example, the thickness of the second portion <NUM> in the second direction is set to be the thickness of the thinnest portion or less, or equal to or less than the thickness of the thinnest portion based on that of the thinnest portion among the thickness of the bottom surface portion and the side surface portion in the pressure chamber <NUM> of the first portion <NUM>. In the present example, the dimension of the first portion <NUM> is set to be <NUM>% or more of the total length of the aperture <NUM> in the second direction.

<FIG> is a diagram showing the aperture unit <NUM> according to Example <NUM>. In Example <NUM>, the design values are set for the aperture length, that is, the total length of the aperture <NUM> in the second direction to be <NUM>, for the aperture width, that is, the dimension of the slit forming the aperture <NUM> in the first direction to be <NUM>, and for the width of the groove, that is, the dimension of the pressure chamber <NUM> in the first direction to be <NUM>. In Example <NUM>, the entire cover unit <NUM> and protrusion <NUM> are formed to be in the space between the sidewalls <NUM> or the inner wall of the sidewall <NUM>. That is, there is no second portion <NUM>. In the present example, <NUM>% of the total thickness of the cover unit <NUM> is the first portion <NUM>.

The nozzle plate <NUM> is formed of, for example, a rectangular film made of polyimide. The nozzle plate <NUM> faces the mounting surface of the actuator base <NUM>. A plurality of nozzles <NUM> are formed in the nozzle plate <NUM> to penetrate the nozzle plate <NUM> in the thickness direction.

A plurality of nozzles <NUM> are provided in the same number as the pressure chambers <NUM> and are arranged to face the pressure chambers <NUM>. A plurality of nozzles <NUM> are arranged along the first direction and are arranged in two rows corresponding to the pair of actuator members <NUM>. Each nozzle <NUM> is configured in a cylindrical shape whose axis extends in the third direction. For example, the nozzle <NUM> may have a constant diameter or may have a shape in which the diameter is reduced toward the central portion or the tip portion. The nozzles <NUM> are arranged to face the extension direction of the corresponding pressure chambers <NUM> formed in the pair of actuator members <NUM> and communicate with the pressure chambers <NUM>. One nozzle <NUM> is arranged in the central portion of each pressure chamber <NUM> in the longitudinal direction.

The frame <NUM> is formed of, for example, a nickel alloy in a rectangular frame shape. The frame <NUM> is interposed between the mounting surface of the actuator base <NUM> and the nozzle plate <NUM>. The frame <NUM> is adhered to the mounting surface of the actuator base <NUM> and the nozzle plate <NUM>. That is, the nozzle plate <NUM> is attached to the actuator base <NUM> via the frame <NUM>.

The manifold <NUM> is joined to the actuator base <NUM> on the side on which the nozzle plate <NUM> is not joined. Inside the manifold <NUM>, an ink supply portion, which is a flow path communicating with the supply hole <NUM>, and an ink discharge portion, which is a flow path communicating with the discharge hole <NUM>, are formed.

The circuit board <NUM> is a film carrier package (FCP). The circuit board <NUM> includes a resin film <NUM> having flexibility and a plurality of wirings formed therein, and drive IC chips <NUM> connected to the plurality of wirings of the film <NUM>. Each drive IC chip <NUM> is electrically connected to the electrode layer <NUM> via the wiring of the film <NUM> and the pattern wiring <NUM>.

Inside the inkjet head <NUM> configured as described above, the ink chamber <NUM> surrounded by the actuator base <NUM>, the nozzle plate <NUM>, and the frame <NUM> is formed. That is, the ink chamber <NUM> is formed between the actuator base <NUM> and the nozzle plate <NUM>. For example, the ink chamber <NUM> is divided into three sections in the second direction by the two actuator members <NUM>, and includes the two second common chambers <NUM> as common chambers in which the discharge holes <NUM> open, and the first common chamber <NUM> as a common chamber in which the supply holes <NUM> open. The first common chamber <NUM> and the second common chambers <NUM> communicate with the pressure chambers <NUM>.

In the inkjet head <NUM> configured as described above, ink circulates between the ink tank and the ink chamber <NUM> through the supply hole <NUM>, the pressure chamber <NUM>, and the discharge hole <NUM>. For example, the drive IC chip <NUM> applies a drive voltage to the electrode layer <NUM> of the pressure chamber <NUM> via the wiring of the film <NUM> in response to a signal input from the controller of the inkjet printer to create a potential difference between the electrode layer <NUM> of the pressure chamber <NUM> and the electrode layer <NUM> of the dummy chamber <NUM>, whereby the sidewalls <NUM> are selectively deformed in the shear mode. The volume of the pressure chamber <NUM> is changed by deforming the sidewall <NUM> formed between the pressure chamber <NUM> and the dummy chamber <NUM> in response to the drive signal.

If the sidewall <NUM> is deformed in the shear mode, the volume of the pressure chamber <NUM> provided with the electrode layer <NUM> increases, and the pressure decreases. As a result, the ink in the ink chamber <NUM> flows into the pressure chamber <NUM>.

With the volume of the pressure chamber <NUM> increased, the drive IC chip <NUM> applies a reverse potential drive voltage to the electrode layer <NUM> of the pressure chamber <NUM>. As a result, the sidewall <NUM> is deformed in the shear mode, the volume of the pressure chamber <NUM> provided with the electrode layer <NUM> is reduced, and the pressure increases. As a result, the ink in the pressure chamber <NUM> is pressurized and ejected from the nozzle <NUM>.

The manufacturing method of the inkjet head <NUM> will be described. First, a piezoelectric member forming a plurality of grooves is attached to the plate-shaped substrate <NUM> with an adhesive or the like, and machined using a dicing saw, a slicer, or the like to form the actuator member <NUM> having an outer shape in a predetermined shape. For example, a block-shaped base member having a thickness corresponding to a plurality of sheets may be formed in advance and then divided to manufacture a plurality of actuator bases <NUM> having a predetermined shape.

Subsequently, the electrode layer <NUM> and the pattern wiring <NUM> are formed on the inner surface of the groove forming the pressure chamber <NUM> and the dummy chamber <NUM>, and the surface of the substrate <NUM>. As described above, the electrode layer <NUM> and the pattern wiring <NUM> are formed at predetermined positions on the surface of the actuator base <NUM>. Subsequently, the cover unit <NUM> is formed of the photosensitive resin. For example, the cover unit <NUM> is formed by a filling process of filling the communication ports which are the inlets and outlets on both sides of the groove constituting the dummy chamber <NUM> and the pressure chamber <NUM> with a photosensitive resin material and closing the communication ports at both ends with the photosensitive resin, and a molding process for molding the photosensitive resin into a predetermined shape. As an example, the aperture <NUM> having a predetermined shape is opened by a developing process in which after a photosensitive resin material is filled in the communication ports on both sides of the grooves constituting the dummy chamber <NUM> and the pressure chamber <NUM>, an exposure mask having an exposure pattern in which a portion forming an opening to be the aperture <NUM> is uncured is overlapped and exposed to cure the portion other than the portion not to be cured which becomes the aperture <NUM>, and the uncured portion is washed away with a developing solution. As a result, the photosensitive resin material is formed into a predetermined shape, and the aperture unit <NUM> is formed. That is, the cover unit <NUM> having a pair of protrusions <NUM> with the aperture <NUM> formed therebetween is formed.

Further, as another example, if sufficient resolution cannot be obtained by forming an aperture pattern of a photosensitive resin by exposure depending on the conditions, the aperture <NUM> may be formed by machining to form the protrusion <NUM>. As the filling treatment, the photosensitive resin material is applied and filled in both ends of the dummy chamber <NUM> and the pressure chamber <NUM>, and the filled photosensitive resin material is cured by the exposure treatment and the development treatment to close the communication ports of the dummy chamber <NUM> and the pressure chamber <NUM> with a wall of a photosensitive resin, and then the aperture <NUM> is formed by machining using a dicer having a desired width as a molding process. As a result, the cover unit <NUM> having the protrusion <NUM> having a predetermined shape is formed.

Further, the actuator base <NUM> is assembled to the manifold <NUM>, and the frame <NUM> is attached to one surface of the substrate <NUM> of the actuator base <NUM> with an adhesive sheet of thermoplastic resin.

Then, the assembled frame <NUM>, the top <NUM> of the sidewall <NUM> of the actuator member <NUM>, and the facing surface of the protrusion <NUM> facing the nozzle plate <NUM> are polished to be flush with each other. Then, the nozzle plate <NUM> is adhered and attached to the top <NUM> of the sidewall <NUM>, the frame <NUM>, and the facing surface of the protrusion <NUM>, which were polished. At this time, positioning is performed so that the nozzle <NUM> faces the pressure chamber <NUM>. Further, as shown in <FIG>, the inkjet head <NUM> is completed by connecting the drive IC chip <NUM> and the circuit board <NUM> to the pattern wiring <NUM> formed on the main surface of the substrate <NUM> via the flexible printed circuit board.

Hereinafter, an example of the inkjet printer <NUM> including the inkjet head <NUM> will be described with reference to <FIG>. The inkjet printer <NUM> includes a housing <NUM>, a medium supply unit <NUM>, an image forming unit <NUM>, a medium discharge unit <NUM>, a conveyer <NUM>, and a controller <NUM>.

The inkjet printer <NUM> is a liquid ejection device that performs image forming processing on paper P by ejecting a liquid such as ink or the like while conveying, for example, paper P as a recording medium which is an ejection target, along a predetermined conveyance path A from the medium supply unit <NUM> to the medium discharge unit <NUM> through the image forming unit <NUM>.

The housing <NUM> houses the components of the inkjet printer <NUM>. A discharge port for discharging the paper P to the outside is provided at a predetermined position on the housing <NUM>.

The medium supply unit <NUM> is provided with a plurality of paper feed cassettes and is configured to be able to hold a plurality of sheets P of various sizes.

The medium discharge unit <NUM> includes a sheet discharge tray configured to hold the paper P discharged from the discharge port.

The image forming unit <NUM> includes a support unit <NUM> that supports the paper P, and a plurality of head units <NUM> that are arranged to face the support unit <NUM> above the support unit <NUM>.

The support unit <NUM> includes a conveying belt <NUM> provided in a loop shape in a predetermined area for image formation, a support plate <NUM> that supports the conveying belt <NUM> from the backside, and a plurality of belt rollers <NUM> provided on the backside of the conveying belt <NUM>.

At the time of image formation, the support unit <NUM> supports the paper P on the holding surface which is the upper surface of the conveying belt <NUM>, and feeds the conveying belt <NUM> at a predetermined timing by the rotation of the belt roller <NUM> to convey the paper P to the downstream side.

The head unit <NUM> includes a plurality of (e.g., four color) inkjet heads <NUM>, an ink tank <NUM> as a liquid tank mounted on each inkjet head <NUM>, a connection flow path <NUM> connecting the inkjet head <NUM> and the ink tank <NUM>, and a circulation pump <NUM>. The head unit <NUM> is a circulation-type head unit that constantly circulates liquid in the ink tank <NUM>, the pressure chamber <NUM>, the dummy chamber <NUM>, and the ink chamber <NUM>, built inside the inkjet head <NUM>.

In the example of <FIG>, the inkjet head <NUM> of four colors of cyan, magenta, yellow, and black, and the ink tank <NUM> for storing the ink of each color are provided. The ink tank <NUM> is connected to the inkjet head <NUM> by the connection flow path <NUM>. The connection flow path <NUM> includes a supply flow path connected to the supply port of the inkjet head <NUM> and a collection flow path connected to the discharge port of the inkjet head <NUM>.

Further, a negative pressure control device such as a pump (not shown) is connected to the ink tank <NUM>. Then, the negative pressure control device applies to the inside of the ink tank <NUM> a negative pressure corresponding to the head values of the inkjet head <NUM> and the ink tank <NUM>, so that the ink supplied to each nozzle <NUM> of the inkjet head <NUM> forms a meniscus in a predetermined shape.

The circulation pump <NUM> is a liquid feed pump composed of, for example, a piezoelectric pump. The circulation pump <NUM> is provided in the supply flow path. The circulation pump <NUM> is connected to the drive circuit of the controller <NUM> by wiring and is configured to be controllable by the control by a Central Processing Unit (CPU). The circulation pump <NUM> circulates the liquid in a circulation flow path including the inkjet head <NUM> and the ink tank <NUM>.

The conveyer <NUM> conveys the paper P along the conveyance path A from the medium supply unit <NUM> to the medium discharge unit <NUM> through the image forming unit <NUM>. The conveyer <NUM> includes a plurality of guide plate pairs <NUM> arranged along the conveyance path A, and a plurality of conveying rollers <NUM>.

Each of the plurality of guide plate pairs <NUM> includes a pair of plate members arranged to face each other with the paper P to be conveyed interposed therebetween, and guides the paper P along the conveyance path A.

The conveying roller <NUM> is driven by the controller <NUM> and rotates to feed the paper P to the downstream side along the conveyance path A. Sensors for detecting the sheet conveyance status are arranged in various places on the conveyance path A.

The controller <NUM> includes a processor such as a CPU, a Read Only Memory (ROM) that stores various programs, a Random Access Memory (RAM) that temporarily stores various variable data and image data, and a network interface circuit for inputting data from the outside and outputting data to the outside.

In the inkjet printer <NUM> configured as described above, if a print instruction is detected by the operation through the operation input unit by the user, for example, the controller <NUM> drives the conveyer <NUM> to convey the paper P and outputs a print signal to the head unit <NUM> at the predetermined timing, thereby driving the inkjet head <NUM>. As an ejection operation, the inkjet head <NUM> sends a drive signal to the IC by an image signal corresponding to the image data, applies a drive voltage to the electrode layer <NUM> of the pressure chamber <NUM> via wiring, selectively drives the sidewalls <NUM> of the actuator member <NUM>, ejects ink from the nozzle <NUM> to form an image on the paper P held on the conveying belt <NUM>. Further, as a liquid ejection operation, the controller <NUM> drives the circulation pump <NUM> to circulate the liquid in the circulation flow path passing through the ink tank <NUM> and the inkjet head <NUM>. By the circulation operation, the circulation pump <NUM> is driven so that the ink in the ink tank <NUM> passes through the ink supply portion of the manifold <NUM> and supplied to the first common chamber <NUM> of the ink chamber <NUM> from the supply hole <NUM>. This ink is supplied to the plurality of pressure chambers <NUM> and the plurality of dummy chambers <NUM>, of the pair of actuator members <NUM>. The ink flows into the second common chamber <NUM> of the ink chamber <NUM> through the pressure chamber <NUM> and the dummy chamber <NUM>. This ink is discharged from the discharge hole <NUM> to the ink tank <NUM> through the ink discharge portion of the manifold <NUM>.

According to the above-described examples, it is possible to provide a liquid ejection head and a method for manufacturing a liquid ejection head with stable ejection characteristics. That is, in the inkjet head <NUM> according to the above examples, by providing the cover unit <NUM> in the pressure chamber <NUM>, the flow path resistance of the inlet and outlet of the pressure chamber <NUM> is larger than those of the inside of the pressure chamber <NUM>, the first common chamber <NUM>, and the second common chamber <NUM>. As a specific example, the opening that opens into the first common chamber <NUM> and the second common chamber <NUM>, which are the common chambers of the pressure chamber <NUM>, has a flow path cross-sectional area smaller than that of the pressure chamber <NUM>. Therefore, the rise of the meniscus if the liquid is ejected by the inkjet head <NUM> is reduced. Therefore, the meniscus returns quickly, the influence on the next droplet can be reduced, and the ejection stability can be improved.

<FIG> show the inkjet head <NUM> having the aperture unit <NUM> according to Test Example <NUM> and the inkjet head <NUM> having no aperture according to Test Example <NUM>. <FIG> shows the frequency characteristics of the inkjet head <NUM> having the aperture unit <NUM> according to Test Example <NUM>, and <FIG> shows the frequency characteristics of the inkjet head <NUM> having no aperture as Test Example <NUM>. <FIG> show the relationship between the ejection speed of each nozzle and the frequency in the cases in which <NUM> drop and <NUM> drops are ejected at once, respectively.

The inkjet head <NUM> according to Test Example <NUM> is a side shooter type in which both sides of the pressure chamber <NUM> in the second direction, which is the extension direction, communicate with the common chamber, and the nozzle <NUM> opens in the middle of the extension direction of the pressure chamber <NUM>.

As shown in <FIG>, in the inkjet head <NUM> according to Test Example <NUM>, the ejection speed is flat in the low frequency region, but the ejection speed tends to decrease as the frequency increases, and there is a difference in ejection speed between the low frequency region and the high frequency region. In the case in which <NUM> drop is ejected by the inkjet head <NUM> according to Test Example <NUM>, the ejection speed is flat up to <NUM>, but the ejection speed tends to decrease as the frequency increases at <NUM> or higher. Further, in the case in which <NUM> drops are ejected by the inkjet head <NUM> according to Test Example <NUM>, the ejection speed is flat up to <NUM>, but the ejection speed tends to decrease as the frequency increases at <NUM> or higher. Therefore, the landing position shifts depending on the printing pattern. If the difference in ejection speed is large as described above, it takes time for the rise of the meniscus to settle, which causes deterioration of print quality, and therefore high-speed driving cannot be performed.

On the other hand, as shown in <FIG>, in the inkjet head <NUM> having the aperture unit <NUM>, the ejection speed tends to be flat in both cases of <NUM> drop and <NUM> drops. This is because the fluid resistance between the common liquid and the nozzle increases, and the rise of the meniscus decreases.

Further, <FIG> shows the simulation results of meniscus return in Test Example <NUM> in which the pressure chamber <NUM> has the aperture unit <NUM>, and Test Example <NUM> in which the pressure chamber has no aperture. According to <FIG>, in the meniscus state of the nozzle at low frequency, there is sufficient time from the ejection of the ink droplet to the ejection of the next droplet, and ink droplets can be ejected in a stable state after waiting for the meniscus to return regardless of the presence of an aperture. On the other hand, in the case of high frequency, since the time from the ejection of dots (e.g. a series of ink droplets for printing one image pixel or the like) to the ejection of the next droplet is short, the ejection of the next droplet starts before the meniscus returns. Therefore, in the case of the inkjet head <NUM> without the aperture unit <NUM>, the rise of the meniscus is large after ejection, and the meniscus cannot be restored by the time the next droplet is ejected, and the ejection speed decreases. On the other hand, if the aperture unit <NUM> is provided, the rise of the meniscus becomes smaller, and thus, the meniscus returns faster and the influence on the next droplet can be reduced. Therefore, from these simulation results, it can be said that providing the aperture unit <NUM> between the pressure chamber <NUM> and the common chamber leads to improvement in the ejection stability of the inkjet head <NUM>.

<FIG> are diagrams of a side shooter type inkjet head <NUM> as Test Example <NUM> and a shear mode shared wall type end shooter type inkjet head <NUM> as Test Example <NUM> in which an ink inlet and outlet is formed at one end and a nozzle <NUM> is formed at the other end.

<FIG> are diagrams comparing simulation characteristics if the aperture unit <NUM> is provided in each of the end shooter type inkjet head <NUM> of Test Example <NUM> and the side shooter type inkjet head <NUM> of Test Example <NUM>. <FIG> shows the drive waveform, <FIG> shows the nozzle flow velocity vibration, <FIG> shows the ejection volume, and <FIG> shows the return characteristics of the meniscus.

Further, the inkjet head <NUM> according to Test Example <NUM> is an end shooter type in which one end side of the pressure chamber <NUM> in the second direction, which is the extension direction, communicates with the common chamber, the other end is closed, and the nozzle opens at the end of the flow path. That is, the inkjet head <NUM> forms a flow path that flows from one side of the second direction toward the nozzle <NUM>.

If the end shooter type inkjet head <NUM> supplied from one side as Test Example <NUM> and the side shooter type inkjet head <NUM> supplied on both sides as Test Example <NUM> have the same ejection volume, nozzle flow velocity vibration, and meniscus return characteristics, the drive voltage is the lowest in the side shooter type configuration of supply on both sides, and thus, it can be said that the supply on both sides has a high advantage over the supply on one side from the viewpoint of drive efficiency. That is, the so-called side shooter type inkjet head <NUM>, which has the nozzle <NUM> in the center of the pressure chamber and ink inlets and outlets at both ends, has better ejection efficiency than the end shooter type inkjet head <NUM>.

In general, in a shear mode shared wall type inkjet head, for example, since a pressure chamber is composed of fine grooves formed by a diamond cutter in the piezoelectric body, it is difficult to reduce the cross-section of a part of the pressure chamber. According to the above examples, however, it is easy to design the shape of the aperture unit <NUM> with high accuracy by setting the first portion <NUM> sandwiched between the sidewalls <NUM> to <NUM>% or more of the aperture <NUM>. Further, by reducing the size of the second portion <NUM> protruding from the sidewall <NUM> to the outside of the pressure chamber <NUM>, it is possible to reduce dimensional variation and stabilize the flow path resistance of the aperture <NUM>. Further, in the above examples, since the side surface portion <NUM> of the actuator member <NUM> forms an inclined surface, restrictions on the exposure direction are less, and the exposure and development processes are facilitated. In addition, by using machining together, finer patterning can be realized with high accuracy.

Further, in Example <NUM>, the first portion <NUM> sandwiched between the sidewalls <NUM> is set to <NUM>% or more of the aperture <NUM>, and the dimension of the second portion <NUM> protruding to the outside of the pressure chamber <NUM> is set to be equal to or less than the width dimension of the pressure chamber <NUM>, whereby it is possible to reduce the generation of bubbles larger than the inside of the pressure chamber <NUM>. Therefore, the dimensions of the aperture <NUM> can be set with high accuracy, and the flow path resistance of the aperture <NUM> can be stabilized.

Further, in Example <NUM>, the first portion <NUM> sandwiched between the sidewalls <NUM> is set to <NUM>% or more of the aperture <NUM>, and the dimension of the second portion <NUM> protruding to the outside of the pressure chamber <NUM> is set to be equal to or less than the thickness of the pressure chamber <NUM>, whereby the influence of swelling and the like can be reduced. That is, even if swelling occurs depending on the type of ink, if the thickness is less than or equal to the thickness of the pressure chamber, swelling can be reduced to a small extent as compared with the case where the thickness of the second portion is larger as shown in <FIG> as Comparative Example <NUM>. Therefore, the dimensions of the aperture <NUM> can be set with high accuracy, and the flow path resistance of the aperture <NUM> can be stabilized.

Further, in the inkjet head <NUM> according to the above examples, an aperture is partially formed at the communication port which is the inlet or outlet of the pressure chamber <NUM>, which makes it easier to secure the volume of the pressure chamber <NUM> than the configuration of reducing the width of the pressure chamber <NUM> as a whole. Therefore, there are fewer restrictions on the size of the nozzle and the droplet as compared with the configuration in which the width of the pressure chamber is reduced as a whole, and it is easy to maintain the ejection performance.

The present invention is defined by the scope of the appendend claims.

In the above examples, the first common chamber <NUM> is arranged on one side of the pressure chamber <NUM>, the second common chamber <NUM> is arranged on the other side, and the fluid flows in from one side of the pressure chamber and flows out to the other side, but the present disclosure is not limited thereto. For example, the common chambers on both sides of the pressure chamber <NUM> may be on the supply side and may be configured to flow in from both sides. That is, the fluid may flow in from both sides of the pressure chamber <NUM> and flow out from the nozzle <NUM> arranged in the center of the pressure chamber <NUM>. Even in this case, the fluid resistance can be increased and the ejection efficiency can be improved by providing an aperture at the inlet portions on both sides of the pressure chamber <NUM>.

Further, in the above examples, the aperture unit <NUM> for increasing the flow path resistance is configured to have a pair of protrusions <NUM> formed on the wall surfaces of the sidewalls <NUM> on both sides of the pressure chamber <NUM>, but the shape of the aperture unit <NUM> is not limited thereto. For example, the aperture <NUM> has a slit shape extending in the third direction, which is the depth direction of the pressure chamber, but may extend in another direction, or may have another shape including a circle or an oval. Further, the shape, position, and size of the aperture units <NUM> provided on both sides can be set according to the flow path resistance, and may be configured under the same conditions on both sides, or may be configured under conditions in which the aperture units <NUM> on one side and the other side are different.

In the above examples, the actuator member <NUM> having a plurality of grooves is arranged on the main surface portion of the substrate <NUM> is shown, but the present disclosure is not limited thereto. For example, an actuator may be provided on the end surface of the substrate <NUM>. Further, the number of nozzle rows is not limited to two, and one row or three or more rows may be provided.

Further, in the above examples, the actuator base <NUM> provided with the stacked piezoelectric body made of the piezoelectric member on the substrate <NUM> is exemplified, but the present disclosure is not limited thereto. For example, the actuator member <NUM> may be formed only by the piezoelectric member without using a substrate. Further, one piezoelectric member may be used instead of the two piezoelectric members. Further, the dummy chamber <NUM> may communicate with the first common chamber <NUM> and the second common chamber <NUM>, which are common chambers. Further, the supply side and the discharge side may be reversed or may be configured to be switchable.

Further, in the above examples, a circulation-type inkjet head was exemplified in which one side of the pressure chamber <NUM> is the supply side and the other side is the discharge side, and the fluid flows in from one side of the pressure chamber and flows out from the other side, but the present disclosure is not limited thereto. For example, a non-circular type may be used. Further, for example, the common chambers on both sides of the pressure chamber <NUM> may be the supply side, and the fluid may flow in from both sides. That is, the fluid may flow in from both sides of the pressure chamber <NUM> and flow out from the nozzle <NUM> arranged in the center of the pressure chamber <NUM>. Even in such a case, the fluid resistance can be increased and the ejection efficiency can be improved by providing the aperture unit <NUM> in the communication ports which are the inlets on both sides of the pressure chamber <NUM>. For example, a non-circulating configuration may be provided by not providing a flow path on the discharge side or by closing the flow path on the discharge side. For example, a non-circulating configuration may be provided in which the supply hole <NUM> may be provided instead of the discharge hole <NUM>, or the flow path on the discharge side is open only at the time of ink replenishment or maintenance and closed at the time of printing.

For example, the liquid to be ejected is not limited to the ink for printing and may be, for example, a liquid containing conductive particles for forming a wiring pattern of a printed wiring board.

Further, in the above examples, the inkjet head is used for a liquid ejection device such as an inkjet printer, but the present disclosure is not limited thereto. The inkjet head can be also used for, for example, a 3D printer, an industrial manufacturing machine, and a medical application, and it is possible to reduce the size, weight, and cost.

According to at least one example described above, it is possible to provide a liquid ejection head and a method for manufacturing a liquid ejection head with stable ejection characteristics.

Claim 1:
A liquid ejection head of a side shooter type, comprising:
a plate (<NUM>) including a plurality of nozzles (<NUM>) arranged along a first direction (X) and through which liquid is ejected;
an actuator (<NUM>) including:
a plurality of pressure chambers (<NUM>) each communicating with a corresponding one of the nozzles,
a plurality of dummy chambers (<NUM>) each disposed between two of the pressure chambers that are adjacent to each other, and
a plurality of sidewalls (<NUM>) separating the pressure and dummy chambers along the first direction and deformable to change a volume of each of the pressure chambers according to a drive signal,
characterized in that the liquid ejection head further comprises a pair of covers (<NUM>) having a plurality of apertures (<NUM>) and partly covering both ends of each of the pressure chambers in a second direction (Y) intersecting the first direction such that a pair of protrusions (<NUM>) protruding relative to the side walls in the first direction (X) are formed and such that the pressure chambers communicate with a common chamber at both ends thereof through the apertures (<NUM>) formed by the pair of protrusions, wherein
each of the covers includes a first portion (<NUM>) on and between the sidewalls and a second portion (<NUM>) other than the first portion, and a first length in the second direction of the first portion is equal to or greater than a second length in the second direction of the second portion.