JP2010155377A - Inkjet head unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head unit that can suppress influence of a thermal expansion coefficient increased by polarization processing to thereby suppress a thermal expansion coefficient of an entire head, and can prevent interfacial separation between an adhesive and an end portion of the head due to thermosetting. <P>SOLUTION: An end portion of a head chip 11 in a direction perpendicular to a polarization direction of an actuator layer of the head chip 11 and a protection cover member 6 are fixed to each other with an adhesive 8. An actuator substrate of the head chip 11 is so constituted that a thermal expansion coefficient of a base layer is smaller than that of the actuator layer in a direction perpendicular to the polarization direction of the actuator layer, and a thermal expansion coefficient of a cover substrate is smaller than that of the actuator layer in the direction perpendicular to the polarization direction of the actuator layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inkjet head unit that ejects ink droplets from nozzles.

  In recent years, an inkjet method using a shear mode deformation of a piezoelectric material has been proposed in printers and industrial applications. This method uses an electrode formed on both sides of an ink channel wall made of piezoelectric material (hereinafter referred to as “channel wall”) to generate an electric field in a direction perpendicular to the polarization direction of the piezoelectric material. The channel wall is deformed in the mode, and ink droplets are ejected by using pressure wave fluctuations generated at that time, which is suitable for increasing the density of the nozzle, reducing the power consumption, and increasing the driving frequency.

  In recent years, the use of ink jet heads utilizing this shear mode deformation for industrial purposes has become active. In response to the development of such a wide range of applications, ink-jet drawing requires higher definition and higher quality image quality, and ink droplets ejected from nozzle holes for high-precision printing. Must be landed on the substrate with high accuracy.

  In the conventional ink jet head using the shear mode deformation, as shown in FIG. 6, the piezoelectric substrate 135 in which a plurality of ink chambers 134 are formed by channel walls and the top plate in which the common ink chamber 133 is formed are bonded. In order to reduce warpage and undulation, the material for the cover substrate 136 is the same as that of the piezoelectric substrate 135, so that the thermal expansion coefficient is matched to prevent warpage and undulation. In addition, the piezoelectric substrate 135 on which the channel wall is formed is polarized in the thickness direction, and the thermal expansion coefficient changes between the thickness direction treated by the polarization treatment and the untreated direction. Thus, the same polarization treatment is applied to the piezoelectric material to be the cover substrate 136 to match the thermal expansion coefficient (see, for example, Japanese Patent Laid-Open No. 2001-10038 (Patent Document 1)).

  On the other hand, in order to realize stable ink ejection, it is necessary to maintain the ink so that there is no residual ink in the ejected nozzle holes and the surface, so that maintenance is performed in accordance with ink ejection. For maintenance, removal by wiping is generally used, so a protective cover for protecting the head is used around the inkjet head, and the gap generated in the protective cover and the head is filled with resin and sealed. A configuration is used. In the case of ink having a resin component such as pigment ink, the viscosity of the residual ink increases, and if the thickened ink is carried to the nozzle portion by wiping, the landing accuracy may be deteriorated. It is important that the ink is completely sealed so that the removed ink does not remain.

  However, the conventional configuration has the following problems. That is, when an ink jet head having a conventional configuration was prepared, the cover member serving as the holding member and the resin filled between the head serving as the fixing member and the head interface, in particular, the end portion in the head longitudinal direction that is the channel row direction Alternatively, peeling frequently occurred on the end surface of the cover member facing the end portion in the longitudinal direction. The present inventors inferred this cause as follows. In order to seal and cure the gap with resin, heat treatment is generally performed after filling the gap with resin. In this cooling after heat curing (return to normal temperature), shrinkage occurs according to the thermal expansion coefficient of each material.

  FIGS. 7A to 7C show a mechanism in which the conventional ink jet head structure peels off at the head end portion and the adhesive interface inferred by the present inventors.

  FIG. 7A is a diagram showing a state in which a protective cover member 106 is formed around a head chip 111 that is an inkjet head, and a gap between the head chip 111 and the protective cover member 106 is filled with an adhesive 108. After the gap 108 is filled with the adhesive 108, heat treatment is performed to cure the adhesive 108. In the cooling after the heating, as shown in FIG. 7B, the shrinkage corresponding to the thermal expansion coefficient of each material is performed. Will occur. As the thermal expansion coefficient of each material, the protective cover member 106 is α≈11 ppm, the adhesive 108 is α≈25 to 40 ppm, the piezoelectric substrate 135 and the cover substrate 136 are α≈0.5 ppm in the polarization direction, and relative to the polarization direction. The configuration has a value of α≈7 ppm in the orthogonal direction.

  Due to the above configuration, when the adhesive 108 is cooled from the heated state for curing the adhesive 108 to room temperature using the inkjet head, the adhesive 108 contracts due to the contraction of the contact surface of the protective cover member 106 with the adhesive 108. The amount increases. That is, the adhesive 108 contracts by cooling, but the protective cover member 106 has a smaller contraction amount, and thus is pinned (attached) at the interface with the protective cover member 106. That is, the peeling force 182 is generated in a form in which the shrinkage of the resin is inhibited by the protective cover member 106. On the other hand, since the end of the head chip 111 also tends to shrink in the direction of the arrow 183 by cooling, the adhesive 108 is pulled to the protective cover member 106 and the end of the head chip 111, and the peeling force 184 is generated. .

  Since the contraction amount of the head chip 111 is larger in the longitudinal direction, as shown in FIG. 7C, peeling is performed at the end portion 181 in the longitudinal direction where the head contraction amount is large or the end surface 180 of the protective cover member 106 facing the longitudinal end portion. Is likely to occur.

  When peeling occurs as described above, it becomes easy to collect ink on the head ejection surface, ejection failure due to adhesion of the thickened ink to the nozzle, and damage to the wipe blade due to adhesion of the thickened ink to the nozzle surface There was a problem.

The peeling as described above becomes larger as the shrinkage amount of the inkjet head is larger, that is, as the thermal expansion coefficient in the longitudinal direction of the head is larger.
JP 2001-10038 A

  Therefore, an object of the present invention is to prevent the peeling of the interface between the adhesive and the head end due to heat-curing by reducing the influence of the thermal expansion coefficient that increases on the polarization treatment and suppressing the thermal expansion coefficient of the entire head. An object of the present invention is to provide an inkjet head unit that can be used.

In order to solve the above problems, an inkjet head unit of the present invention is
A base layer and an actuator layer are laminated, and an actuator substrate having a plurality of grooves separated by a partition wall formed on the opposite side of the actuator layer to the base layer, and an upper surface of the partition wall of the actuator substrate are bonded. An inkjet head having a cover substrate that forms an ink chamber with the plurality of grooves of the actuator layer;
A holding member for holding the inkjet head;
A fixing member for fixing the holding member and the end of the ink jet head on the side orthogonal to the polarization direction of the actuator layer;
The actuator layer of the actuator substrate is made of a piezoelectric material that is polarized in the thickness direction and changes its shape by an electric field,
The thermal expansion coefficient of the base layer is smaller than the thermal expansion coefficient in the direction perpendicular to the polarization direction of the actuator layer of the actuator substrate, and
The thermal expansion coefficient of the cover substrate is smaller than the thermal expansion coefficient in a direction orthogonal to the polarization direction of the actuator layer of the actuator substrate.

  According to the above configuration, the end of the inkjet head in the direction orthogonal to the polarization direction of the actuator layer is fixed to the holding member via the fixing member. Due to thermal contraction during the cooling process, a tensile stress acts on the interface between the fixing member and the inkjet head. The thermal expansion coefficient of the base layer is smaller than the thermal expansion coefficient of the actuator substrate in the direction orthogonal to the polarization direction of the actuator layer, and the thermal expansion in the direction orthogonal to the polarization direction of the actuator layer of the actuator substrate is performed. By this configuration that the thermal expansion coefficient of the cover substrate is smaller than the coefficient, the thermal contraction of the inkjet head itself is smaller than the conventional configuration, so that the tensile stress generated at the interface between the inkjet head and the fixing member can be reduced, A highly reliable ink jet head unit with a low risk of cracking can be produced.

Moreover, in the inkjet head unit of one embodiment,
The holding member is disposed so as to surround the inkjet head, and the nozzle surface and the ejection side surface of the inkjet head are substantially on the same plane,
A gap between the inkjet head and the holding member is sealed with the fixing member.

  According to the above embodiment, the nozzle surface of the inkjet head is substantially flush with the discharge-side surface of the holding member, and the fixing member is filled in the gap between the inkjet head and the holding member. A maintenance operation such as wiping the nozzle surface or removing bubbles in the inkjet head does not leave ink on the nozzle surface of the inkjet head, and a highly reliable drawing operation can be maintained for a long time.

Moreover, in the inkjet head unit of one embodiment,
The fixing member includes a resin material as a main component.

  According to the above embodiment, since the fixing member is made of a resin material, the gap between the ink jet head and the holding member can be filled with high reproducibility through a simple process, so that the reliability of the ink jet head can be improved. it can.

Moreover, in the inkjet head unit of one embodiment,
The base layer of the actuator substrate is made of a piezoelectric material that has not been polarized.

  According to the embodiment, since the base layer is not polarized, the thermal expansion coefficient in the direction orthogonal to the polarization direction of the actuator layer can be made smaller than that of the actuator layer. As a result, the thermal expansion coefficient of the entire inkjet head can be reduced, so that the risk of peeling between the inkjet head and the fixing member can be reduced, and the reliability of the inkjet head unit can be increased. In addition, since the actuator layer and the base layer are piezoelectric materials and only the distinction between polarization and non-polarization is made, the actuator substrate can be easily created, and the cost of creating the inkjet head can be reduced.

Moreover, in the inkjet head unit of one embodiment,
The cover substrate has substantially the same thermal expansion coefficient as the base layer of the actuator substrate.

  According to the above-described embodiment, since the cover substrate and the base layer have substantially the same thermal expansion coefficient, there is very little application of stress due to the thermal history due to the processing process of the inkjet head and the accompanying deformation is extremely small. Reliability can be improved, and deterioration of droplet discharge characteristics due to stress can be prevented.

Moreover, in the inkjet head unit of one embodiment,
The cover substrate is made of a piezoelectric material that has not been polarized.

  According to the above embodiment, since the cover substrate is not polarized, the thermal expansion coefficient in the direction orthogonal to the polarization direction of the actuator layer can be made smaller than that of the actuator layer. As a result, the thermal expansion coefficient of the entire inkjet head can be reduced, so that the risk of peeling between the inkjet head and the fixing member can be reduced, and the reliability of the inkjet head unit can be increased. In addition, since the cover substrate and the actuator layer are piezoelectric materials, and only a distinction is made between polarization and non-polarization, it is easy to create the cover substrate and the actuator substrate, and it is possible to reduce the cost of creating the inkjet head.

  As is clear from the above, according to the ink jet head unit of the present invention, the influence of the thermal expansion coefficient that increases with respect to the polarization treatment is reduced, and the thermal expansion coefficient of the entire head is suppressed, whereby the adhesive by heat curing is used. Can be prevented, and an ink jet head unit free from structural defects can be realized.

  Hereinafter, the ink jet head unit of the present invention will be described in detail with reference to the illustrated embodiments.

  1A and 1B show an embodiment of an ink jet head unit according to the present invention.

  The inkjet head unit 1 includes a protective cover member 6, a base unit 2, and a filter unit 3 as an example of a holding member. The protective cover member 6 is disposed so as to cover the surface on the ink discharge side of the head chip support portion 4 constituted by the base unit 2 and the filter unit 3 coupled to each other.

  A head chip 11 as an example of an inkjet head is disposed so as to penetrate an opening 6 a provided in the protective cover member 6. A gap between the protective cover member 6 and the head chip 11 is filled with an adhesive 8 as an example of a fixing member. The adhesive 8 prevents ink from accumulating in the gap between the protective cover member 6 and the head chip 11 and further prevents the accumulated ink from dropping inadvertently. 1A shows a state in which the protective cover member 6 is attached to the head chip support portion 4 composed of the base unit 2 and the filter unit 3, and FIG. 6 shows a state where it is removed.

  Then, the structure of the base unit 2 and the filter unit 3 is shown using FIG.

  The base unit 2 includes a head base 13, a chip mount 12, a head chip 11, a flexible substrate 26, a driver substrate 9, and manifolds 14A and 14B.

  The head chip 11 has a polyparaxylylene film formed as a protective film 10 on the outer peripheral surface and inside. In addition, a nozzle plate 7 in which a plurality of discharge ports are linearly provided at predetermined intervals is bonded to the discharge side end face of the head chip 11.

  The filter unit 3 includes two housings 161 and 162 made of PEEK (polyether ether ketone). A filter plate (not shown) for filtering the liquid is disposed so as to separate the liquid chambers formed inside the housings 161 and 162. In the liquid chamber of the housing 161, an introduction port is formed through which liquid is introduced from a first liquid storage portion (not shown) that supplies ink. A flow path to be communicated with the first opening 57A in the manifold 14A is formed in the liquid chamber of the housing 162. Further, a vent channel (not shown) to be communicated with the first opening 56A of the manifold 14B is formed in the housing 162. The vent channel is connected to a second liquid storage unit that accumulates discharged ink via a vent channel formed in the housing 161.

  As shown in FIG. 2, grooves 16A and 16B are formed in the manifolds 14A and 14B, respectively. The grooves 16A and 16B are filled with an adhesive when the manifolds 14A and 14B and the filter unit 6 are attached. It is preferable to use an adhesive having a linear expansion coefficient close to the material of the filter unit 6 and the manifolds 14A and 14B for the grooves 16A and 16B. In this embodiment, the grooves 16A and 16B are filled with an epoxy adhesive. FIG. 1B shows a state in which the filter unit 3 and the manifolds 14A and 14B are bonded with an adhesive.

  Next, FIG. 3 shows an embodiment of the head chip 11 of the present invention.

  As shown in FIG. 3, the head chip 11 is formed with an actuator substrate 29 using zircon zinc titanate (PZT) as a material. The actuator substrate 29 includes a base layer 30 that has not been subjected to polarization treatment, and an upper surface thereof. Further, an actuator layer 31 polarized in the thickness direction is laminated. A partition wall made up of a plurality of grooves 35 is formed in the actuator layer 31, and a driving electrode film (not shown) is formed on the side wall of the groove 35, and an ink chamber 34 is formed by the partition wall. The actuator layer 31 has a height (thickness) equivalent to the height of the partition wall forming the ink chamber 34. In the present embodiment, the actuator layer 31 is formed with a thickness of 240 μm, which is the height of the partition wall.

  As described in the subject of the present invention, in the configuration shown in FIG. 4, in the piezoelectric material, the coefficient of thermal expansion increases in the direction 51 orthogonal to the polarization direction. Since it causes peeling at the interface 81 of the adhesive 8, it is desirable to make the actuator layer 31 as thin as possible. In addition, an insulating layer made of polyparaxylylene or a derivative thereof is formed on substantially the entire inside and outside of the head chip 11.

  In this embodiment, the thermal expansion coefficient of unpolarized PZT is α≈2, and the thermal expansion coefficient of PZT subjected to polarization is α≈0.5 in the polarization direction, with respect to the polarization direction. The value is α≈7 in the orthogonal direction.

  FIG. 5 shows a result of peeling of the interface 81 between the short-side end portion of the head chip 11 and the adhesive 8 depending on the stacking ratio of the actuator layer 31 in the configuration of the actuator substrate 29. As shown in FIG. 5, the interface 81 can be prevented from peeling by setting the actuator layer 31 to a lamination ratio of 40% or less. However, this lamination ratio is a result of verification by the piezoelectric material used in the embodiment of the present invention, and other piezoelectric materials are not limited to the above ratio.

  The cover substrate 32 uses the same type of PZT as the actuator substrate 29 and is not subjected to polarization treatment. A common ink chamber 33 is formed on the cover substrate 32 so as to communicate with the ink chamber 34, and the cover substrate 32 is bonded to the upper wall surface of the partition formed on the actuator layer 31 with an adhesive. In the present embodiment, an epoxy adhesive is used as the adhesive, and is bonded by heat curing.

  As shown in FIG. 4, the head chip 11 has an ink chamber 33 in which a cover substrate 32 is bonded to an actuator substrate 29 composed of an actuator layer 31 and a base layer 30 as described with reference to FIG. It is the structure which forms. The nozzle plate 7 is bonded to the surface of the head chip 11. A nozzle hole 40 is disposed in the nozzle plate 7 at a position corresponding to the ink chamber 33 so as to communicate with the ink chamber 33. A protective cover member 6 is formed around the head chip 11, and a gap formed by the head chip 11 and the protective cover member 6 is filled with an adhesive 8 to seal the gap. SUS316 is used as the material of the protective cover member 6, and the surface is coated with a fluororesin such as PTFE (polytetrafluoroethylene) in order to improve ink removability by wiping. An epoxy adhesive is used for the adhesive 8 that seals the gap, and the adhesive 8 is cured by heating after filling. In this embodiment, heating is performed at 75 ° C. for a predetermined time. With this configuration, the head chip 11 is protected during maintenance of the surface of the nozzle plate 7, and ink droplets can be removed by wiping.

  As described above, according to the ink jet head unit according to the present embodiment, the actuator substrate 29 that forms the head chip 11 includes the actuator layer 31 and the base layer 30 and is equivalent to the height of the partition wall that forms the ink chamber 34. By stacking the actuator layer 31 on the base layer 30 with a thickness of 2 mm, it becomes possible to reduce the influence of the thermal expansion coefficient in the direction 51 orthogonal to the polarization direction increased by the polarization treatment, and the adhesive 8 In the used peripheral sealing structure, peeling of the interface 81 between the head chip 11 and the adhesive 8 is prevented, and a stable sealing process can be realized. Further, in the wiping in the maintenance, the structure that does not cause the ink residue is generated, and the reliable maintenance can be realized.

  Further, as described above, in the present embodiment, the cover substrate and the actuator layer and the base layer constituting the actuator substrate are made of a piezoelectric material mainly composed of lead zirconate titanate. Therefore, uneven wear does not occur in the cutting process and polishing process of the head chip, and no step is generated on the cut surface and the polished surface. For this reason, when nozzle bonding is performed, the nozzle plate can be bonded without being distorted, and thereby high landing accuracy can be realized.

  According to the inkjet head unit having the above-described configuration, the influence of the thermal expansion coefficient that increases with respect to the polarization process is reduced, and the thermal expansion coefficient of the entire head chip 11 is suppressed, whereby the adhesive and the head end portion due to heat curing are reduced. Interfacial peeling can be prevented, and an ink jet head unit free of structural defects can be realized.

  The nozzle surface of the head chip 11 is substantially flush with the discharge-side surface of the protective cover member 6, and the gap between the head chip 11 and the protective cover member 6 is filled with the adhesive 8. Therefore, a maintenance operation such as wiping the nozzle surface or removing bubbles in the head chip 11 does not cause ink to remain on the nozzle surface of the head chip 11, and a highly reliable drawing operation can be maintained for a long time. it can.

  In addition, since the adhesive 8 is made of a resin material, the gap between the head chip 11 and the protective cover member 6 can be filled with high reproducibility by a simple process, so that the reliability of the head chip 11 is improved. Can do.

  In addition, by making the actuator layer 31 as thick as the height of the partition wall that actually contributes to the droplet discharge operation, the thickness of the actuator layer 31 can be minimized, The influence of the large thermal expansion coefficient of the actuator layer 31 on the thermal expansion coefficient of the entire head chip 11 can be minimized.

  Further, since the base layer 30 is not polarized, the thermal expansion coefficient in the direction orthogonal to the polarization direction of the actuator layer 31 can be made smaller than that of the actuator layer 31. As a result, the thermal expansion coefficient of the entire head chip 11 can be reduced, so that the risk of separation of the head chip 11 and the adhesive 8 can be reduced, and the reliability of the inkjet head unit can be increased. Further, since the actuator layer 31 and the base layer 30 are piezoelectric materials, and only the distinction between polarization and non-polarization, the actuator substrate 29 can be easily created, and the cost of creating the head chip 11 can be reduced.

  In addition, since the actuator layer 31 and the base layer 30 are made of the same main component piezoelectric material, the actuator layer 31 and the base layer 30 can be processed in the same manner in cutting and polishing of the head chip 11. As a result, there is no step due to uneven wear and the like, the shape stability of the head chip 11 and the flatness of the nozzle bonding surface can be maintained, and an ink jet head unit having excellent landing characteristics can be manufactured.

  In addition, since the cover substrate 32 and the base layer 30 have substantially the same thermal expansion coefficient, the application of stress due to the thermal history in the processing process of the head chip 11 and the accompanying deformation are extremely small. Reliability can be improved, and deterioration of droplet discharge characteristics due to stress can be prevented.

  Further, since the cover substrate 32 is not polarized, the thermal expansion coefficient in the direction orthogonal to the polarization direction of the actuator layer 31 can be made smaller than that of the actuator layer 31. As a result, the thermal expansion coefficient of the entire head chip 11 can be reduced, so that the risk of separation of the head chip 11 and the adhesive 8 can be reduced, and the reliability of the inkjet head unit can be increased. In addition, since the cover substrate 32 and the actuator layer 31 are piezoelectric materials, and only the distinction between polarization and non-polarization is made, it is easy to create the cover substrate 32 and the actuator substrate 29 and reduce the production cost of the head chip 11. Can do.

  Further, since the cover substrate 32 is made of the same main component piezoelectric material as the actuator layer 31, the actuator layer 31 and the cover substrate 32 can be processed in the same manner in the cutting and polishing of the head chip 11. As a result, there is no step due to uneven wear and the like, the shape stability of the head chip 11 and the flatness of the nozzle bonding surface can be maintained, and an ink jet head unit having excellent landing characteristics can be manufactured.

  In addition, since the cover substrate 32 is made of the same principal component piezoelectric material as the actuator substrate 29 (actuator layer 31 and base layer 30), the actuator substrate 29 and the cover substrate are cut or polished in the head chip 11. 32 can be processed in the same manner, so that no step due to uneven wear or the like occurs, so that the shape stability of the head chip 11 and the flatness of the nozzle bonding surface can be maintained, and the ink jet head having excellent landing characteristics Units can be made.

  In the above embodiment, zircon zinc titanate (PZT) is used as the material of the base layer 30 and the cover substrate 32, but the material of the base layer and the cover substrate is not limited to this, and the polarization direction of the actuator layer of the actuator substrate As long as the thermal expansion coefficient of the base layer is smaller than the thermal expansion coefficient in the orthogonal direction, the thermal expansion coefficient of the cover substrate is higher than the thermal expansion coefficient in the direction orthogonal to the polarization direction of the actuator layer of the actuator substrate. As long as the material is small.

  The description of the above-described embodiment is an example in all respects and is not restrictive. The scope of the present invention is shown not by the above-described embodiments but by the claims.

FIG. 1A is a diagram showing a configuration of an inkjet head unit according to an embodiment of the present invention. FIG. 1B is a diagram illustrating a state where the protective cover member of the inkjet head unit is removed. FIG. 2 is a diagram illustrating a state in which the base unit and the filter unit are disassembled. FIG. 3 is a diagram showing the configuration of the head chip of the inkjet head unit. FIG. 4 is a view showing a peripheral sealing configuration of the head chip. FIG. 5 is a table showing the effect of the head chip configuration of the head chip. FIG. 6 is a diagram showing a configuration of a head chip of a conventional inkjet head unit. FIG. 7A is a diagram showing a peeling mechanism of the head chip. FIG. 7B is a diagram showing a peeling mechanism of the head chip. FIG. 7C is a diagram showing a peeling mechanism of the head chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Inkjet head unit 2 ... Base unit 3 ... Filter unit 6 ... Protective cover member 7 ... Nozzle plate 8 ... Peripheral sealing adhesive 9 ... Driver board 10 ... Protective film 11 ... Head chip (inkjet head)
DESCRIPTION OF SYMBOLS 12 ... Chip mount 13 ... Head base 14A, 14B ... Manifold 16A, 16B ... Groove 26 ... Flexible substrate 29 ... Actuator substrate 30 ... Base layer 31 ... Actuator layer 32 ... Cover substrate 33 ... Common ink chamber 34 ... Ink chamber 35 ... Groove 40 ... Nozzle hole

Claims (6)

A base layer and an actuator layer are laminated, and an actuator substrate having a plurality of grooves separated by a partition wall formed on the opposite side of the actuator layer to the base layer, and an upper surface of the partition wall of the actuator substrate are bonded. An inkjet head having a cover substrate that forms an ink chamber with the plurality of grooves of the actuator layer;
A holding member for holding the inkjet head;
A fixing member for fixing the holding member and the end of the ink jet head on the side orthogonal to the polarization direction of the actuator layer;
The actuator layer of the actuator substrate is made of a piezoelectric material that is polarized in the thickness direction and changes its shape by an electric field,
The thermal expansion coefficient of the base layer is smaller than the thermal expansion coefficient in the direction perpendicular to the polarization direction of the actuator layer of the actuator substrate, and
The ink jet head unit according to claim 1, wherein a thermal expansion coefficient of the cover substrate is smaller than a thermal expansion coefficient in a direction orthogonal to a polarization direction of the actuator layer of the actuator substrate. The inkjet head unit according to claim 1,
The holding member is disposed so as to surround the inkjet head, and the nozzle surface and the ejection side surface of the inkjet head are substantially on the same plane,
A gap between the inkjet head and the holding member is sealed with the fixing member. The inkjet head unit according to claim 1 or 2,
The fixing member includes a resin material as a main component, and an ink jet head unit. In the inkjet head unit according to any one of claims 1 to 3,
The ink jet head unit according to claim 1, wherein the base layer of the actuator substrate is made of a piezoelectric material not subjected to polarization treatment. In the inkjet head unit according to any one of claims 1 to 4,
The inkjet head unit, wherein the cover substrate has substantially the same thermal expansion coefficient as the base layer of the actuator substrate. In the inkjet head unit according to claim 5,
The ink jet head unit according to claim 1, wherein the cover substrate is made of a piezoelectric material not subjected to polarization treatment.

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