JPH08156250A - Ink jet head - Google Patents

Abstract

PURPOSE: To ensure printing quality by preventing the lowering of the particle amt. and particle speed of ink in an ink jet head wherein an elastic member is provided to the intermediate part of a wall member and to shorten the filling time of ink to correspond to high speed printing. CONSTITUTION: An ink jet head is equipped with a nozzle plate 12 having nozzle orifices 9 emitting particles of ink 6, a pressure plate 18 pushing out the ink 6, a wall member 14 connecting the nozzle plate 12 and the pressure plate 18 and having an intermediate part constituted of at least one kind of an elastic member 17 and having an ink supply port 16, a pressure chamber 13 formed from the nozzle plate 12, the wall member 14 and the pressure plate 18 and receiving the supply of the ink 6 from the ink supply port 16 and the actuator 18 driving the pressure plate 18. The pressure plate 18 is driven by the actuator 8 to emit the ink 6 supplied to the pressure chamber 13 from the nozzle orifices 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head of an ink jet printer, and more particularly to an ink jet head having an elastic member in an intermediate portion of a wall member.

Recently, an ink jet printer for directly recording fine particles of ink onto a print medium for recording has no limitation on the print medium, high-speed printing is possible, low noise, and easy colorization. It is spreading rapidly.

In the ink jet head of this ink jet printer, for example, a pressure chamber is formed by a nozzle plate having a nozzle, a wall member and a pressure plate, and the pressure chamber filled with ink is displaced by electric strain of the piezoelectric element via the pressure plate. Is applied to eject ink from a nozzle to form a dot print.

However, a phenomenon occurs in which a desired pressure is not obtained in the pressure chamber due to the bending of the wall member at the time of driving, and print dots are not recorded at a predetermined position. This problem is solved and further high speed printing is supported. A method that can do it is desired.

[0005]

2. Description of the Related Art FIG. 7 shows an outline of an ink jet printer. As shown in the figure, a guide shaft 3 is fitted to a carrier 2 having an inkjet head (hereinafter referred to as a print head) 1, and a feed screw 4 is screwed to the carrier 2.
The feed screw 4 is connected to a motor (not shown). The carrier 2 is arranged on the front surface of the platen 5, and is moved in parallel with the platen 5 in the directions of arrows A and B by the feed screw 4 by the forward and reverse rotations of the motor.

The print head 1 is composed of a head portion 10 and a pressure circuit portion 11. The head portion 10 faces the platen 5 with a predetermined gap and has a plurality of nozzle holes described later at its tip. The pressure circuit section 11 is a circuit that selectively transmits a drive signal to the head section 10 based on print data, and is connected to the control section by a flexible cable (not shown).

Therefore, while the carrier 2 is moving, the print head 1 ejects the ink 6a from the nozzle holes to print the print paper 7.
A print is formed by matrix dots. The printing paper 7 is fed in the direction of arrow C by driving a moving mechanism (not shown) and rotating the platen 5.

Next, the head portion 10 will be described with reference to FIGS. As shown in FIGS. 8 and 9, the head unit 10 includes piezoelectric elements 8 ₁ , 8 ₂ , ... And nozzle holes 9 ₁ , 9 ₂ ,.
Nozzle plates 12 _1, 12 ₂ , ..., Pressure chambers each provided with 50 μm)
13 ₁ , 13 ₂ , ..., Wall members 14 ₁ , 14 ₂ , ... Having ink supply ports 16 ₁ , 16 ₂ , ... And vibration plates 15 ₁ , 15 ₂ ,.

The piezoelectric elements 8 ₁ , 8 ₂ , ... Are rectangular plate-shaped, one end surface of which is adhered to the outside of the vibrating plates 15 ₁ , 15 ₂ , ... And electrodes are provided on both surfaces. Further, the nozzle plates 12 ₁ , 12 ₂ , ... And the vibration plate 15 ₁ ,
The wall members 14 ₁ , 14 ₂ , ... Are arranged between 15 ₂ , ..., And the pressure chambers 13 ₁ , 13 ₂ ,. The ink supply ports 16 ₁ , 16 ₂ , ... Are connected to an ink tank (not shown).

Actually, the nozzle plates 12 ₁ , 12 ₂ , ..., The wall member 14
_The diaphragms ₁ , 14 ₂ , ... And the diaphragms 15 ₁ , 15 ₂ , ... Are integrally formed and joined by electrostatic bonding (or diffusion bonding) or an adhesive agent.

Therefore, a voltage is selectively applied to the piezoelectric elements 8 ₁ , 8 ₂ , ... And the vibration plates 15 ₁ , 15 are caused by the amount of displacement of the electric strain.
By vibrating the positions corresponding to ₂ , ...
Ink 6a supplied from the ink supply ports 16 ₁ , 16 ₂ , ... by applying pressure to 13 ₁ , 13 ₂ , ... causes nozzle holes 9 ₁ , 9 ₂ , ... as described above.
Jet from.

The diaphragms 15 ₁ , 15 ₂ , ... And the wall members 14 ₁ , 14 ₂ ,
, Or the nozzle plates 12 ₁ , 12 ₂ , ... And the wall members 14 ₁ , 14 ₂ , ... Are integrally formed, for example, there is also a head portion formed by an electroforming method. Further, there is also a head portion using a nozzle plate formed by etching a stainless steel plate or a photosensitive glass, a wall member and a vibrating plate.

Although such a head portion 10 is generally used, a voltage is applied to the piezoelectric elements 8 ₁ , 8 ₂ , ...
When vibrating 15 ₁ , 15 ₂ , ..., The force generated by the piezoelectric elements 8 ₁ , 8 ₂ , ... Is the sum of the force for pushing out the ink 6a and the force for bending the vibrating plates 15 ₁ , 15 ₂ ,. .

[0014] However, the vibration plate 15 _1, 15 _2, ... surrounding the wall member 14 _1, 14 _2, because it is fixed to ..., diaphragm 15 _1, 15 _2, ...
A large force is required to bend the. as a result,
The force for pushing out the ink 6a is reduced. Therefore, the piezoelectric element
8 _1, 8 _2, is poor conversion efficiency ... to the extrusion force of the ink 6a for generating force.

Further, the diaphragms 15 ₁ , 15 ₂ , ... And the wall members 14 ₁ , 14 ₂ ,
A large stress is generated in the connection portion of ... And this stress may cause fatigue fracture and the connection portion may be broken. There is a problem.

In order to solve this problem, the method of Japanese Patent Application No. 6-059872 by the present applicant has been proposed. The outline will be described with reference to FIG. Head part 10a
Are the piezoelectric elements 8 ₁ , 8 ₂ , ..., The nozzle holes 9 ₁ , 9 ₂ ,.
_1, 12 _2, ..., a pressure chamber 13 _1, 13 _2, ..., wall members 14 _1, 14 _2, ..., the pressing plate 18 _1, 18 _2, ..., the elastic member 17 _1, 17 _2, ..., and an ink supply port 16
_{It has 1} , 16 ₂ , ... The pressure chambers 13 ₁ , 13 ₂ , ... And the wall member 14
_{, 1} , 14 ₂ , ... Are made of a material having high rigidity (metal or resin having Young's modulus of about 1 × 10 ¹⁰ Pa).

The pressure chambers 13 ₁ , 13 ₂ , ... Include nozzle plates 12 ₁ , 12 ₂ ,
..., wall members 14 ₁ , 14 ₂ , ..., elastic members 17 ₁ , 17 ₂ , ... and pressure plate
It is formed by 18 ₁ , 18 ₂ , .... The pressure plates 18 ₁ , 18 ₂ , ... Are integrally formed.

The elastic members 17 ₁ , 17 ₂ , ... Have a Young's modulus of 1 × 10.
Wall members 14 ₁ , 14 ₂ , ... And pressure plates 18 ₁ , formed of rubber or resin (for example, dry film) of about ⁵ to 1 × 10 ⁹ Pa
It is located between 18 ₂ , ... The elastic members 17 ₁ , 17 ₂ , ... Are formed of liquid one-component silicone rubber or two-component silicone rubber by a printing method such as screen printing.
Wall members 14 _1, 14 _2, formed on ... one end of the pressing plate 18 _1, 18 _2, after aligning the ..., cured at room temperature or elevated temperatures (about 120 ° C), is formed in a plate-like member.

Piezoelectric elements 8 ₁ , 8 ₂ , are provided outside the pressure plates 18 ₁ , 18 ₂ ,.
One end surface of ... is glued. Therefore, the piezoelectric elements 8 ₁ , 8 ₂ ,
A voltage is applied to the pressure plate by the amount of displacement of the electric strain.
18 _1, 18 _2, ... when pressed, the elastic member 17 _1, 17 _2, the pressure chamber 13 ₁ by deforming by pressing the ..., 13 _2, ... ink
By increasing the pressure of 6a, more stable operation is possible.

[0020]

According to the above-mentioned conventional method, the volume of the ink particles ejected from the nozzle and the flight speed thereof are determined by the volume change and pressure change in the pressure chamber transmitted via the diaphragm, respectively. To be done. Therefore, in order to eject ink particles having appropriate particle characteristics, both volume change and pressure change in the pressure chamber are large under the same voltage application state, and it is necessary that each change amount satisfies the required amount.

However, in the case of the head described with reference to FIG. 10, the volume change transmitted through the pressure chamber outer wall and the magnitude of the pressure change have a reciprocal relation with respect to the rigidity of the pressure chamber outer wall,
In order to increase either amount, it is necessary to increase the rigidity of the outer wall of the pressure chamber. In addition, in order to obtain a flying characteristic having straightness as the particle characteristics of the ink so that the printing quality becomes good with the configuration shown in the drawing in consideration of the ink injection property into the pressure chamber,
The depth of the pressure chamber in the ink ejection direction must be set to some extent.

This will be described with reference to FIGS. 11 and 12. FIG. 11 shows a case of a pressure chamber in which the depth in the ink jet direction is not sufficiently obtained by the conventional method, and FIGS.
Shows the time series at the time of injection. When the depth of the pressure chamber in the ink ejection direction is small as shown in this figure, the flight direction does not go straight and the ink is not recorded at a predetermined position on the recording medium.

Therefore, from the above, in order to efficiently generate the ink particles, it is necessary to increase the rigidity of the pressure chamber and to increase the depth in the ink ejecting direction to some extent.
However, in the conventional methods, since the elastic member is bonded to the vibration plate and exists, when the depth in the ink ejection direction in the pressure chamber is increased as shown in FIG. 12A, the pressure chamber is formed. The distance between the wall members becomes large, and even when the same pressure is generated, the wall members are excessively bent as shown in FIG. 12 (b), and there is a problem that the volume amount to be injected is insufficient. Therefore, the energy efficiency, which is the product of pressure and volume change, decreases.

Further, when the ink particles are ejected, the ink flows backward from the ink supply port, which causes a pressure drop in the ink in the pressure chamber and lowers the energy efficiency, and also to the pressure chamber after the ink is ejected. The refilling amount of ink is the sum of the ejection amount of ink particles and the reverse flow rate from the ink supply port, and the refilling time becomes long. There is a problem.

The present invention provides an ink jet head capable of preventing the drop of the ink particle amount and the particle speed, ensuring the printing quality, and shortening the ink filling time to cope with high speed printing. It is an object.

[0026]

FIG. 1 is a principle diagram of the present invention (corresponding to claim 1). In the figure, 6 is ink, 9 is a nozzle hole, 17 is an elastic member, 12 is a nozzle plate having nozzle holes 9 for ejecting particles of the ink 6, 18 is a pressure plate for pushing out the ink 6, and 14 is at least one intermediate part. A wall member that is composed of elastic members 17 of various types, connects the nozzle plate 12 and the pressure plate 18, and has an ink supply port 16, 13 is the nozzle plate 12,
A pressure chamber formed by the wall member 14 and the pressure plate 18 to which the ink 6 is supplied from the ink supply port 16, and an actuator 8 for driving the pressure plate 18.

Accordingly, the pressure plate is applied by the actuator 8.
18 is driven to eject the ink 6 supplied to the pressure chamber 13 from the nozzle hole 9. Next, the means of claims 2 to 5 will be described.

According to a second aspect, in the first aspect, the elastic member 17 is formed in a bellows shape. In the third aspect, the elastic member 17 constitutes at least a part of the ink supply port 16 in the first or second aspect.

According to a fourth aspect of the present invention, in the first, second or third aspect, the wall member 14 partially has a reinforcing portion formed of a material having higher rigidity than other portions. According to claim 5, in any one of claims 1, 2, 3 and 4, the wall member 14 has a cross-section having a smaller second moment of inertia as it goes from the nozzle plate 12 and the pressure plate 18 side toward the central portion. So that the wall thickness is thin.

[0030]

As shown in FIG. 1, by forming the intermediate portion of the wall member 14 with the elastic member 17, the length of the wall member 14 is divided and shortened, and when the pressure plate 18 is driven by the actuator 8. Bending of the wall member 14 is prevented, volume loss of the pressure chamber 13 can be suppressed, pressure loss is also suppressed, and energy efficiency is increased. Therefore, it is possible to prevent the pressure in the pressure chamber 13 from decreasing, and it is possible to secure the print quality without a decrease in the particle amount and particle speed of the ink 6.

Next, the operation of claims 2 to 5 will be described. According to the second aspect, since the elastic member 17 is formed in a bellows shape, soft elasticity can be obtained even if a material having a high elastic modulus is used.

In the third aspect, the elastic member 17 is the ink supply port.
By configuring at least a part of 16, the ink supply port 16 is narrowed when the pressure plate 18 is driven and the elastic member 17 is compressed, and the backflow of the ink 6 from the ink supply port 16 is restricted. The pressure drop in the pressure chamber 13 is prevented, the pressure is effectively used for ejecting the ink 6, and the refilling amount of the ink 6 after ink ejection is small, so that the filling time can be shortened. It is possible to support high speed printing.

According to the fourth aspect of the present invention, by forming a part of the wall member 14 with a material having higher rigidity than other parts, it is possible to further reduce the deflection of the wall member 14 when the pressure plate 18 is driven. The effects of claim 1, claim 2 or claim 3 can be further enhanced.

In the fifth aspect, the wall member 14 is formed so that the second moment of area becomes smaller as it goes from the nozzle plate 12 and the pressure plate 18 side toward the central portion.
It is possible to further reduce the deflection of the wall member 14 when it is driven, and it is possible to further enhance the effects of claim 1, claim 2, claim 3, or claim 4.

[0035]

EXAMPLES Examples 1 to 1 of the present invention will be described below with reference to FIGS.
Example 3 will be described. The same reference numerals denote the same objects throughout the drawings.

1) Description of Embodiment 1 (corresponding to claim 1 and claim 3) Embodiment 1 will be described with reference to FIGS. 2 is a partially cutaway perspective view showing the first embodiment of the present invention, FIG. 3 is an explanatory view of the first embodiment, and FIG. 4 is a side view showing the operation of the first embodiment.

FIG. 2 shows a portion corresponding to one nozzle hole of the head portion having a plurality of nozzle holes described in the conventional example. The piezoelectric element 8 ₁ (8 _2, ...) In FIG. 2 corresponds to the actuator 8 in FIG.

As shown in FIG. 2, in the pressure chamber 13A ₁ ,
The wall member 14 formed of the dry film described in the conventional example
₁ is divided into wall members 14A ₁ and 14B ₁ substantially equally, and an elastic member 17A ₁ made of silicone rubber is sandwiched between them.

In the ink supply port 16A ₁ , the side surface parallel to the pressure plate 18 ₁ is the side surface of the wall members 14A ₁ and 14B ₁ , and the side surface orthogonal to the pressure plate 18 ₁ is the side surface of the elastic member 17A _1. Has been done.

Here, the elastic member 17A ₁ is connected to the wall members 14A ₁ and 14B ₁
The reason for placing it between will be explained. Although the wall member 14 ₁ of the pressure chamber 13A ₁ described in the conventional example covers the four sides, it is regarded as a cantilever from the pressure plate 18 ₁ for simplicity, as shown in FIG. Assuming that a uniformly distributed load having a magnitude q of load per unit length acts on this cantilever, the deflection w of the tip is expressed by the following equation.

W = qL ⁴ / 8EI where L is the length of the cantilever, E is the Young's modulus of the cantilever,
I is the second moment (I = BH ^3/12: However, B
Is the width of the beam and H is the thickness).

Therefore, since the deflection w of the cantilever is proportional to the fourth power of the length L of the cantilever, if the length of the cantilever is halved, the deflection is 1/2 ⁴ (= 1/16). It is understood that it can be suppressed to). Accordingly, the pressure chambers 13 ₁ of the height, i.e., the wall member 14
Wall members 14A ₁ to ₁ of a length to 2 minutes, and the 14B ₁ (Note, since the actual pressure chamber is constituted by four surfaces, deformation degree at the time of pressure application is as simple as a cantilever However, the pressure chamber has a rectangular cross section in the plane orthogonal to the axial direction of the nozzle, and the wall surface in the long axis direction is considered to be in a plane strain state.
Considered as a two-dimensional problem, if the height of the beam is shorter than the length of the beam, the above formula can be used approximately).

Since it has such a structure, FIG.
(c), the pressing plate applies a voltage to the piezoelectric element 8 ₁
Even when the pressure of the ink 6a in the pressure chamber 13A ₁ increases when the 18 ₁ is driven, the wall members 14A ₁ and 14B ₁ are divided in length, so that the wall members 14A ₁ and 14B ₁ are significantly bent. Reduced pressure chamber
Volume loss at 13A ₁ can be suppressed, and pressure loss can also be suppressed.

When the pressure plate 18 ₁ is driven, the elastic member 17
Since A ₁ is compressed and the ink supply port 16A ₁ is narrowed, and the backflow of the ink 6a from the ink supply port 16A ₁ is limited, the pressure drop in the pressure chamber 13A ₁ is prevented and the pressure of the ink 6a is reduced. It is effectively used for injection. Moreover, the ink after jetting
When refilling 6a, the ink replenishment amount is small, and the filling time can be shortened.

2) Description of Embodiment 2 (Claims 1 and 3)
Example 2 will be described with reference to FIG. The difference between the first embodiment described with reference to FIGS. 2 to 4 and the second embodiment shown in FIG. 5 is that reinforcing members are provided on both sides of the elastic member.

That is, as shown in FIG. 5, in the pressure chamber 13A ₁ ′, a material having a higher rigidity than the wall members 14A ₁ ′ and 14B ₁ ′ between the wall members 14A ₁ ′ and 14B ₁ ′ and the elastic member 17A _1. For example, the reinforcing members 19a and 19b formed of a thin plate (or nickel material) of stayless steel (219 giga Pa) are provided.

With this structure, the pressure plate 18 ₁
Even when the pressure of the ink 6a in the pressure chamber 13A ₁ ′ is increased when the drive is driven, the rigidity of the reinforcing members 19a and 19b makes it possible to suppress the bending as compared with the case of the first embodiment. Therefore, the pressure loss in the pressure chamber 13A ₁ ′ can be further reduced,
Further, since the volume loss can be suppressed, the effect of the first embodiment can be further enhanced.

3) Description of Example 3 (claims 1 and 2)
(Corresponding to claim 5) Embodiment 3 will be described with reference to FIG. The difference between Example 1 described in FIGS. 2 to 4 and Example 2 described in FIG. 5 and Example 3 in FIG. 6 is that the elastic member is formed in a bellows shape, and the wall member is arranged in the direction of the elastic member. That is, it was made thinner toward the outside.

That is, as shown in FIG. 6, in the pressure chamber 13A ₁ ″, the elastic member 17A ₁ ′ is formed in a bellows shape. Further, the wall members 14A ₁ ″ and 14B ₁ ″ are elastically pressed from the pressure plate 18 _1. The cross-sectional shape is such that the second moment of area becomes smaller in the direction of the member 17A ₁ ′, that is, the wall thickness is gradually reduced. The elastic member 17A ₁ ′ constitutes a part of the ink supply port 16A ₁ ′.

With such a structure, by changing the cross-sectional shape, it is possible to eliminate a portion where stress concentration is likely to occur due to a pressure change in the pressure chamber 13A ₁ ″, and it is possible to reduce bending due to pressure. , Pressure chamber
The pressure loss in 13A ₁ ″ can be reduced and the volume loss can be suppressed. In addition, the overall durability can be increased.

Further, since the elastic member 17A ₁ ′ is formed in a bellows shape, soft elasticity can be obtained even if a material having a high elastic modulus is used. In this way, by providing the elastic member in the intermediate portion of the wall member of the pressure chamber, it is possible to reduce the deflection of the wall member when the pressure plate is driven, so that the pressure loss is reduced and the volume loss is suppressed. In addition, it is possible to prevent the reduction of energy efficiency, and it is possible to secure the print quality without the drop of the ink particle amount and particle speed.

Further, since the elastic member constitutes a part of the ink supply port, backflow of ink from the ink supply port is suppressed during driving, less replenishment ink is required, ink replenishment time is shortened, and high speed printing is performed. Can correspond to.

Further, by providing a material having high rigidity between the wall member and the elastic member, or by forming the wall member so that the second moment of area in the direction from the pressure plate to the elastic member is reduced, the wall at the time of driving can be reduced. The bending of the member can be further reduced, and the life can be extended.

[0054]

As described above, according to the present invention, in the first aspect, the length of the wall member is divided and becomes shorter respectively,
When the pressure plate is driven by the actuator, bending of the wall member is prevented, volume loss of the pressure chamber can be suppressed, pressure loss is also suppressed, and energy efficiency is increased.
Therefore, it is possible to prevent the pressure in the pressure chamber from decreasing, and to ensure the print quality without a decrease in the ink particle amount and particle speed.

According to the second aspect, even if a material having a high elastic modulus is used, soft elasticity can be obtained. In the third aspect, since the ink supply port is narrowed when the pressure plate is driven and the backflow of the ink from the ink supply port is limited, the pressure drop in the pressure chamber is prevented, and the pressure is effectively used for ejecting the ink. In addition, since the replenishment amount is small when refilling the ink after the ink is ejected, the filling time can be shortened and high-speed printing can be supported.

According to the fourth aspect, it is possible to further reduce the deflection of the wall member when the pressure plate is driven. According to the fifth aspect, it is possible to further reduce the deflection of the wall member when the pressure plate is driven, and it is possible to improve the durability and prolong the service life. There is an effect.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a perspective view showing a first embodiment of the present invention with a part thereof cut away.

FIG. 3 is an explanatory diagram of the first embodiment.

FIG. 4 is a side view showing the operation of the first embodiment.

FIG. 5 is a perspective view showing a second embodiment of the present invention partially broken away.

FIG. 6 is a configuration diagram showing a third embodiment of the present invention.

FIG. 7 is a perspective view showing an outline of an inkjet printer.

FIG. 8 is a perspective view showing a part of the head portion by breaking.

FIG. 9 is a configuration diagram showing a head unit of a conventional example.

FIG. 10 is a configuration diagram showing a head unit of a different conventional example.

FIG. 11 is an explanatory view (1) showing problems of different conventional examples.

FIG. 12 is an explanatory diagram (part 2) showing problems of different conventional examples.

[Explanation of symbols]

6,6a is ink, 8 is actuator,
8 ₁ and 8 ₂ are piezoelectric elements, 9 and 9 ₁ and 9 ₂ are nozzle holes, 10 and 10a are head parts, 12 and 12 ₁ and 12 ₂ are nozzle plates, and 13 13 _{1 1} 13 ₂ 1
3A ₁ , 13A ₁ ′, 13A ₁ ″ are pressure chambers, 14 _1, 14 ₂ , 14A ₁ , 14B ₁ , 14
A ₁ ′, 14B ₁ ′, 14A ₁ ″, 14B ₁ ″ is a wall member, 16 ₁ , 16 ₂ , 16A ₁ is an ink supply port, 17,17 ₁ , 17 ₂ , 17A ₁ , 17A ₁ ′ is an elastic member,
18,18 ₁ and 18 ₂ are pressure plates, 19a and 19b are reinforcing members

Claims (5)

[Claims] 1. A nozzle plate having nozzle holes for ejecting ink particles, a pressure plate for pushing out ink, the nozzle plate and the pressure plate are connected, and an intermediate portion is composed of at least one kind of elastic member, A wall member having an ink supply port, a pressure chamber formed of a nozzle plate, a wall member and a pressure plate, to which ink is supplied from the ink supply port, and an actuator for driving the pressure plate, are provided by the actuator. An ink jet head characterized in that a pressure plate is driven to eject ink supplied to the pressure chamber from the nozzle hole. 2. The ink jet head according to claim 1, wherein the elastic member is formed in a bellows shape. 3. The ink jet head according to claim 1, wherein the elastic member constitutes at least a part of the ink supply port. 4. The ink jet head according to claim 1, wherein the wall member has a reinforcing portion formed in part of a material having higher rigidity than other portions. 5. The wall member is formed so that the second moment of area becomes smaller as it goes from the nozzle plate and the pressure plate side toward the central portion. The inkjet head according to claim 2, claim 3, or claim 4.