WO2009104487A1

WO2009104487A1 - Inkjet head

Info

Publication number: WO2009104487A1
Application number: PCT/JP2009/052146
Authority: WO
Inventors: 奈帆美久保
Original assignee: コニカミノルタホールディングス株式会社
Priority date: 2008-02-19
Filing date: 2009-02-09
Publication date: 2009-08-27
Also published as: JPWO2009104487A1

Abstract

Provided is an inkjet head which suppresses generation of satellite droplets even when a nozzle having a jetting port having a diameter of 10μm or less is used. The inkjet head is provided with a nozzle having a jetting port having a diameter of 10μm or less, a pressure chamber connected to the nozzle, an inlet for introducing an ink into the pressure chamber, and an actuator for generating pressure to the ink by changing the volume of the pressure chamber. The shapes of the nozzle, the pressure chamber and the inlet are set so that an inequality of f1≤f2 is satisfied, where, f1 is a number of characteristic frequency of a meniscus in the nozzle, and f2 is a number of characteristic frequency of the pressure chamber.

Description

Inkjet head

The present invention relates to an inkjet head.

A general inkjet head has a nozzle having a discharge port for discharging droplets, a pressure chamber communicating with the nozzle, an inlet for introducing ink into the pressure chamber, and a volume of the pressure chamber is changed. And a piezoelectric element as an actuator for generating pressure on the ink.

Then, for example, a part of the pressure chamber is formed so as to be easily deformed and used as a diaphragm, and this is elastically displaced by a piezoelectric element to generate a pressure for ejecting ink droplets from the nozzle ejection port.

When a driving voltage is applied to the piezoelectric element of such an ink jet head, the diaphragm is flexed and deformed by the piezoelectric effect to excite a pressure wave in the fluid in the flow path. When the pressure wave is transmitted to the nozzle, a liquid column (meniscus) is formed, and the liquid column is separated to discharge a droplet.

At this time, extra droplets called satellites may be formed in addition to the main droplets, which causes a reduction in image quality.

As a countermeasure against such a problem, in Japanese Patent Application Laid-Open No. H10-228707, the liquid discharge is characterized in that the resonance frequency f [kHz] of the discharge unit and the liquid discharge speed v [m / s] satisfy the relationship f> 31 × v + 80. A head has been proposed.
JP 2007-223231 A

There are two possible satellite generation mechanisms.

(1) When the droplet is separated while the liquid column has grown more than necessary due to excess of input energy, the satellite is separated at the tail portion of the droplet.

(2) A surface wave having a wavelength smaller than the droplet diameter is generated and grows on the surface of the liquid column, resulting in a break of the liquid column and separation of satellites.

The inventor conducted intensive research on the relationship between the behavior of the meniscus in the nozzle and the occurrence of satellite in the above (2), and as a result, the following was found.

The inkjet head has multiple fluid vibration modes. One of them is the natural vibration of the pressure chamber, conventionally called Helmholtz vibration. In addition, there is a natural vibration caused by the free surface of the meniscus in the nozzle (hereinafter referred to as a meniscus natural vibration).

The vibration excited in a plurality of modes is superimposed on the meniscus, so that it grows as a surface wave of the liquid column and becomes a break of the liquid column, resulting in satellite generation. In particular, the meniscus natural vibration is greatly related to the generation of satellites, and when the natural vibration of the meniscus with a higher frequency occurs due to the natural vibration of the pressure chamber excited by the actuator, the natural vibration of the pressure chamber The meniscus's natural vibration is superimposed during the half cycle, which causes the generation of satellites during ejection.

In the conventional head as in Patent Document 1, the diameter of the discharge port in the nozzle is larger than 10 μm. When the nozzle diameter is large in this way, the impedance of the nozzle becomes small and the frequency of the natural vibration of the meniscus is reduced. Becomes lower. As a result, the frequency of the natural vibration of the meniscus tends to be lower than the frequency of the natural vibration of the pressure chamber, so that satellites due to the above (2) are unlikely to occur.

That is, the technique disclosed in Patent Document 1 suppresses the growth and separation of the liquid column more than necessary by limiting the droplet discharge speed, and prevents the occurrence of satellites due to the above (1). It is thought that. In Patent Document 1, since the liquid discharge speed is limited by the resonance frequency of the discharge unit, for example, in a head having a low resonance frequency, there is also a problem that the liquid drop discharge speed is reduced and image quality is deteriorated.

On the other hand, when the diameter of the discharge port is small, the impedance of the nozzle increases rapidly and the frequency of the natural vibration of the meniscus increases. As a result, the frequency of the natural vibration of the meniscus tends to be higher than the frequency of the natural vibration of the pressure chamber, so that satellites due to (2) are likely to occur.

Also, when looking at the energy balance, when the diameter of the discharge port is large, the kinetic energy of the droplets becomes much more dominant than the surface energy. Therefore, the kinetic energy of the meniscus was almost converted into the kinetic energy of the droplet, and it was easy to separate the droplet from the liquid column.

On the other hand, when the diameter of the discharge port is reduced, the energy balance is reversed, and it is necessary to supply the kinetic energy of the meniscus more than the kinetic energy for forming the droplet. For example, the energy when ejecting ink corresponding to the ejection orifice diameter at an initial droplet velocity of 10 m / s using ink having a surface tension of 50 × 10 ⁻³ [N / m] and a viscosity of 3 × 10 ⁻³ [Pa · s]. This graph is as shown in FIG. FIG. 8 shows that the difference decreases as the diameter of the discharge port decreases from around 10 μm, and the kinetic energy and the surface energy are reversed around 6 μm.

In this case, extra energy must be supplied to the meniscus to form and discharge droplets. For this purpose, the flow velocity of the meniscus must be increased. As a result, the liquid column grows greatly with respect to the discharge port diameter, and satellites are likely to be generated.

In recent years, there has been an increasing demand for reducing the diameter of dots formed by ink droplets in order to improve image quality. To reduce the size of dots, it is effective to reduce the diameter of the discharge port in the nozzle. It is necessary to take measures to suppress the generation of satellites in the head.

An object of the present invention is to solve these problems in the prior art, and to provide an ink jet head capable of suppressing the generation of satellites even when a nozzle having a discharge port having a diameter of 10 μm or less is used. And

The above object is achieved by the following invention.

1.
A nozzle having a discharge port having a diameter of 10 μm or less, a pressure chamber communicating with the nozzle, an inlet for introducing ink into the pressure chamber, and generating a pressure in the ink by changing the volume of the pressure chamber An ink jet head including an actuator, wherein the frequency of the natural vibration of the meniscus in the nozzle is f1, and the frequency of the natural vibration of the pressure chamber is f2, so that f1 ≦ f2. An ink jet head in which the shape of a nozzle, the pressure chamber, and the inlet is set.

2.
When the inertance component of the nozzle is Ln, the capacitive component is Cn, the inertance component of the pressure chamber is Lc, the capacitive component is Cc, the inertance component of the inlet is Li, and the capacitive component of the actuator is Ca, formula (1) 2. The ink jet head according to 1, wherein:

In the present invention, when the frequency of the meniscus natural vibration (mode 1 vibration) in the nozzle is f1, and the frequency of the pressure chamber natural vibration (mode 2 vibration) is f2, f1 ≦ f2. Since the shapes of the nozzle, the pressure chamber, and the inlet are set, the meniscus rises due to the natural vibration of the pressure chamber excited by the actuator, but the vibration period of mode 1 is higher than the vibration period of mode 2. Therefore, the generation of satellites can be suppressed even when a nozzle having a discharge port with a diameter of 10 μm or less is used without getting on the vibration node of mode 2. Thereby, a high-quality recorded matter can be obtained.

It is a figure which shows typically an example of the inkjet head which concerns on embodiment of this invention. It is an equivalent circuit of an inkjet head. This is an equivalent circuit in which elements that do not affect the characteristics are omitted. It is an equivalent circuit separated into two vibration modes. 1 is a diagram schematically illustrating an example of an ink jet head according to an embodiment of the present invention, disassembled for each component. It is a figure which shows the joining process of a nozzle plate and a body plate. It is a figure which shows the adhesion process of a piezoelectric element. It is a graph which shows the relationship between the diameter of a discharge outlet, and energy.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nozzle plate 101 Nozzle 110 Borosilicate glass thick film 2 Body plate 201 Ink supply port 202 Common ink chamber 203 Inlet 204 Pressure chamber 3 Piezoelectric element 4 DC high voltage power supply

Hereinafter, the present invention will be described with reference to the illustrated embodiment, but the present invention is not limited to the embodiment.

As shown in FIG. 1, the inkjet head according to the present embodiment includes a nozzle having a discharge port for discharging droplets, a pressure chamber communicating with the nozzle, an inlet for introducing ink into the pressure chamber, A piezoelectric element as an actuator that generates pressure on the ink by changing the volume of the pressure chamber, and a common ink chamber for storing ink introduced into each channel are provided.

The ejection port means an opening at the tip of the ink ejection side of the nozzle, and the diameter of the ejection port refers to the diameter when the opening is circular. The opening shape is not limited to a circular shape, and may be a polygonal shape or a star shape instead of the circular shape. When the shape is not a circle, the diameter when the area is replaced with a circle having the same area is defined as the diameter of the discharge port.

A plurality of vibration modes and resonance points thereof, that is, the frequency f1 of the natural vibration of the meniscus in the nozzle and the frequency f2 of the natural vibration of the pressure chamber can be obtained by numerical calculation or experiment.

When it is determined by experiment, it can be calculated from the meniscus bulge amount at that time by sweeping and inputting a sinusoidal drive voltage waveform to the pressure generator (actuator). When the frequency of the sine wave versus the amount of uplift (or flow rate) is plotted, the frequency at which the amount of uplift reaches the maximum value becomes the resonance point, which is the frequency of the natural vibration.

In the case of numerical calculation, analysis can be performed using general-purpose numerical analysis software, or if it can be approximated to a simple model, it can be easily calculated without using software.

Here, a calculation method using the equivalent circuit method will be described.

When one channel in the inkjet head shown in FIG. 1 is replaced with an equivalent circuit, the result is as shown in FIG. In FIG. 2, symbol L is an inertance component [kg / m ⁴ ], La is an inertance component in the actuator, Ln is an inertance component in the nozzle, Li is an inertance component in the inlet, and Lc is an inertance component in the pressure chamber. Symbol R is a resistance component [N · s / m ⁵ ], Ra is a resistance component in the actuator, Rn is a resistance component in the nozzle, Ri is a resistance component in the inlet, and Rc is a resistance component in the pressure chamber. Symbol C is a capacitive component [m ⁵ / N], Ca is a capacitive component in the actuator, Cn is a capacitive component in the nozzle, Ci is a capacitive component in the inlet, and Cc is a capacitive component in the pressure chamber.

Here, the inertance component L in each part is given by equation (2), where S [m ² ] is the cross-sectional area of the flow path, l [m] is the flow path length, and ρ [kg / m ³ ] is the ink density. It is done. Here, α is a shape factor determined by the cross-sectional shape of the flow path, and is about 1.3 when the cross-section is circular or rectangular.

Further, the resistance component R in each part is given by the equation (3) when the ink viscosity is η [Pa · s] and the diameter is d [m] when the flow path cross section is circular.

And the capacity component C in each part is as follows.

Cc and Ca, which are terms related to the compression inside the fluid, are V [m ³ ] for the pressure chamber volume, ρ [kg / m ³ ] for the ink density, and c [m / s] for the sound velocity of the ink. It is given by equation (4).

Cn, which is a term related to the fluid free surface, is given by equation (5) where the surface tension σ [N / m] of the ink and the diameter of the ejection port are d [m].

In the normal design range, the elements Ci, Ra, and La that have little influence on the characteristics are approximately set to 0, and the remaining elements are synthesized to obtain a circuit as shown in FIG.

When the vibration mode is separated from the circuit of FIG. 3, the vibration mode is separated into two of FIGS. 4 (a) and 4 (b).
The vibration mode (a) is mode 1, the resonance point is f1, the vibration mode (b) is mode 2, and the resonance point is f2.

Vibration mode 1 is the natural vibration of the meniscus that occurs on the surface of the meniscus. The vibration mode 2 is a natural vibration of the pressure chamber caused by pressure fluctuation in the pressure chamber, and the meniscus rises when this is transmitted to the nozzle. This is conventionally called Helmholtz vibration.

The natural frequency f1 of the meniscus is expressed by the following equation (6).

The natural frequency f2 of the pressure chamber is expressed by the following equation (7).

At this time, the behavior at the time of droplet discharge differs depending on the magnitude relationship between f1 and f2.

When f1> f2, the natural vibration of the mode 1 meniscus having a higher frequency is generated along with the natural vibration of the mode 2 pressure chamber excited by the actuator. Then, the natural vibration of the meniscus is superimposed on the half cycle of the natural vibration of the pressure chamber, which causes satellite generation during discharge.

In particular, when the diameter of the discharge port of the nozzle is reduced, the inertance component Ln and the resistance component Rn of the nozzle increase as is apparent from the equations (2) and (3), so that the impedance of the nozzle increases and the meniscus is increased. The frequency f1 of the natural vibration becomes higher. This tends to satisfy f1> f2, so satellites are likely to occur.

When f1 ≦ f2, the meniscus rises with the natural vibration of the pressure chamber excited by the actuator, but because the vibration period of mode 1 is longer than the vibration period of mode 2, it rides on the vibration node of mode 2. Even when a nozzle having a discharge port with a diameter of 10 μm or less is used, the generation of satellites can be suppressed. Thereby, a high-quality recorded matter can be obtained.

As can be seen from the equations (6) and (7), the parameters governing f1 and f2 are only the inertance component and the capacitance component of each part. That is, f1 and f2 are determined by the combination of the inertance component and the capacitance component of each part.

Here, as can be seen from the equations (2), (4), and (5), when the density ρ of the ink to be used, the sound velocity c of the ink, and the surface tension σ are determined, the parameters governing f1 and f2 are , Only the shape of each part.

That is, in order to suppress the occurrence of satellites with respect to a head using a nozzle having a discharge port having a diameter of 10 μm or less, f1 ≦ f2 is satisfied with respect to the ink used, that is, the expression (1) It is important to set the shape of each part so as to satisfy the above.

However, conventionally, since the design concept based on the viewpoint of optimizing the balance between f1 and f2 has not been known, according to the analysis result of the inventor according to this application, a discharge port having a diameter of 10 μm or less is provided. There is no head designed to satisfy f1 ≦ f2 with respect to the head using the nozzle having the nozzle.

FIG. 5 schematically shows an example of the ink jet head according to the embodiment of the present invention disassembled for each component, and the ink jet head HD has a nozzle plate 1, a body plate 2 and a piezoelectric element 3.

The nozzle plate 1 has a plurality of nozzles 101 for discharging ink.

The body plate 2 is joined by covering the nozzle plate 1 with the pressure plate groove 204 serving as a pressure chamber, an inlet groove 203 serving as an inlet, a common ink chamber groove 202 serving as a common ink chamber, and an ink supply port. 201 is formed.

Then, the nozzle plate 1 and the body plate 2 are joined so that the nozzle 101 of the nozzle plate 1 and the pressure chamber groove 204 of the body plate 2 correspond one-to-one.

Furthermore, the piezoelectric element 3 is bonded to a position corresponding to each pressure chamber 204 on the surface opposite to the surface to be joined to the nozzle plate 1 of the body plate 2. The piezoelectric element 3 is an actuator made of PZT (lead zirconate titanate), and is deformed when a drive voltage is applied through drive electrodes provided on both sides, thereby generating pressure by changing the volume of the pressure chamber. The ink in the pressure chamber is ejected from the nozzle 101.

In the following description, a chamber formed by the pressure chamber groove 204 and the nozzle plate 1 is referred to as a pressure chamber 204, a chamber formed by the inlet groove 203 and the nozzle plate 1 is referred to as an inlet 203, and a common ink chamber. A chamber formed by the groove 202 and the nozzle plate 1 is referred to as a common ink chamber 202.

Next, creation of the inkjet head HD will be described.

The manufacturing method of the nozzle plate 1 is performed by a procedure of forming the nozzle 101 by using a silicon substrate as a base material and using, for example, a known photolithography technique (resist coating, exposure, development) and an etching technique. . The diameter of the discharge port of the nozzle 101 is 10 μm or less.

The body plate 2 uses a silicon substrate having a thickness of about 200 to 500 μm as a base material in the same way as the nozzle plate 1 is manufactured. For example, a known photolithography technique (resist application, exposure, development), an etching technique, etc. Is used to form a pressure chamber groove 204 which is a plurality of pressure chambers which communicate with the nozzle 101 included in the nozzle plate 1 and which is formed with the nozzle plate 1 described above, and a plurality of inlets which respectively communicate with the pressure chamber. An inlet groove 203, a common ink chamber groove 202 serving as a common ink chamber communicating with the inlet, and an ink supply port 201 are formed.

The size of the groove formed here may be determined as appropriate as long as the shape of each part after completion of the head satisfies the above-described formula (1). In the head as an example of the present embodiment, for example, the pressure chamber groove 204 has a width of about 50 μm to 350 μm, a height of about 10 μm to 200 μm, a length of about 50 μm to 3000 μm, and the inlet groove 203 has a width of about 10 μm to 150 μm. The common ink chamber groove 202 is a through-hole having a diameter of about 400 μm to 1500 μm and a common ink chamber groove 202 having a width of about 400 μm to 1000 μm, a depth of about 50 μm to 200 μm, and a diameter φ of about 400 μm to 1500 μm. Similarly, for the nozzle, for example, the diameter of the ink discharge port is 1 μm to 10 μm, and the length of the nozzle is about 1 μm to 100 μm.

The etching method for the silicon substrate is preferably a silicon (Si) anisotropic dry etching method that can perform an etching process perpendicular to the surface of the body plate. Regarding the silicon (Si) anisotropic dry etching method, Sangyo Tosho Co., Ltd. “Semiconductor dry etching technology” can be referred to.

Next, the nozzle plate 1 and the body plate 2 processed by the method described so far are bonded using an anodic bonding technique. This will be described below.

FIG. 6 is a diagram showing a joining process between the nozzle plate 1 and the body plate 2. FIG. 6A shows a nozzle plate 1 in which nozzles (not shown) are processed using a silicon substrate as a base material. In addition, the body plate 2 in which the grooves such as the pressure chamber grooves 204 are formed by the processing described above is shown.

The nozzle plate 1 and the body plate 2 are joined by anodic bonding. When two substrates are bonded using an anodic bonding technique, silicon is used as a material constituting one of the substrates, and the other is silicon with a glass material containing mobile ions, typically sodium ions (Na ⁺ ). It is preferable to use a material having a linear expansion coefficient relatively similar to (Si) (the linear expansion coefficient of silicon is about 4.2 × 10 ⁻⁶ / ° C.), for example, borosilicate glass is used. .

Here, as borosilicate glass containing mobile ions (hereinafter referred to as borosilicate glass), Pyrex (registered trademark), Corning (USA) or Tempax Float (registered trademark), except for Japan, BOROFLOAT (registered trademark) ) And Shot Japan Co., Ltd. from the viewpoint of these linear expansion coefficients (both Pyrex (registered trademark) and Tempax Float (registered trademark) have a linear expansion coefficient of about 3.2 × 10 ⁻⁶ / ° C.). More preferred.

Also, since silicon is finer and easier to process than borosilicate glass, a silicon substrate is used instead of borosilicate glass as a base material. Then, a borosilicate glass film is formed on the bonding surface of the silicon substrate as the base material to form a borosilicate glass surface. The film thickness in this case may be a film thickness that can be strongly bonded by anodic bonding, and is 0.5 μm from the viewpoint of the density and uniformity of the film and the heating and applied voltage of the bonding surface required during anodic bonding described later. The range of ˜3 μm is preferable, and the range of 1 μm to 2 μm is more preferable.

Further, in this case, the borosilicate glass film may be formed by any one of a vacuum deposition method, a radio frequency (RF) magnetron sputtering method, and an ion plating method, and the substrate temperature is easily formed at the time of film formation. It is preferable to heat to 250 ° C. or higher. The upper limit of the temperature is not particularly defined, but is preferably about 400 ° C. from the viewpoint of a substrate mounting jig, a substrate temperature control device during film formation, and the like.

In the ink jet head which is an example of the present embodiment, the base material of the nozzle plate 1 and the body plate 2 are both silicon substrates because of the ease of fine processing. Therefore, it is necessary to make one of the joint surfaces of the nozzle plate 1 and the body plate 2 the surface of the borosilicate glass described above.

Temporarily, when a borosilicate glass film is provided on the body plate 2 side, it is predicted that deformation due to deposition of the film will occur in the already formed fine shape due to the film thickness forming the surface of the borosilicate glass. Also, the bottom of the pressure chamber 204 is thickened by this film, so that the structure of the pressure chamber 204 itself is strengthened and distortion due to the piezoelectric element 3 cannot be sufficiently generated. As a result, ink cannot be discharged sufficiently or the piezoelectric element 3 There is a risk that a problem arises that the drive power must be increased.

Accordingly, the surface side of the nozzle plate 1 shown in FIG. 6B covering the body plate is a borosilicate glass surface, and the nozzle plate 1 is a substrate, and the surface side of the substrate covering the body plate is 0.5 μm to 3 μm. A borosilicate glass thick film 110 having a relatively thick film thickness in the range of is provided.

Next, the nozzle plate 1 and the body plate 2 formed with the borosilicate glass film described above are overlapped and fixed in an appropriate positional relationship as shown in FIG. Is subjected to anodic bonding by applying a voltage using a DC high voltage power source 4. Below, it demonstrates concretely regarding anodic bonding of the nozzle plate 1 and the body plate 2. FIG.

The polarity of the voltage applied when anodic bonding is performed is positive (+) on the silicon substrate side and negative (-) on the borosilicate glass substrate side. If it does in this way, an electric current will flow at the same time that a joining interface closely_contact | adheres by electrostatic attraction, and both board | substrates will be strongly anodically bonded.

In the recording head which is an example of the present embodiment, it is sufficient to apply a voltage that is positive (+) for the body plate 2 and negative (−) for the nozzle plate 1 having the borosilicate glass thick film 110.

The high temperature state at the time of joining is in the range of 300 ° C. to 550 ° C. Using a constant temperature bath capable of maintaining such an atmospheric temperature or a simple method using a hot plate having good insulation with a built-in ceramic heater or the like. What is necessary is just to heat the junction part of the nozzle plate 1 and the body plate 2.

When the bonding is performed beyond the above temperature range, there is a tendency that the bonding cannot be performed or the bonding is not sufficient. For example, at 550 ° C. or more, although depending on the applied voltage, mobile ions may flow out at a stretch, resulting in deterioration such as the borosilicate glass film becoming cloudy or the film density becoming rough, and as a result, strong bonding may not be possible. is there. At 300 ° C. or lower, the movable ions are difficult to move, and in order to make it easier to move, it is necessary to increase the applied voltage. As a result of increasing the applied voltage, a short circuit occurs between the nozzle plate 1 and the body plate 2, and as a result, anodic bonding may not be sufficient.

Further, the electric field strength of the DC voltage applied between the nozzle plate 1 and the body plate 2 by the DC high voltage power source 4 is preferably in the range of 30 kV / mm to 200 kV / mm. For example, if the thickness of the borosilicate glass is 0.5 μm, the applied voltage range is 15 to 100 V, and if it is 3 μm, it is 90 to 600 V.

Normally, when a voltage exceeding 1 kV is used, it is necessary to ensure the capacity of the DC high-voltage power supply 4 that generates the voltage and the insulation withstand voltage of the auxiliary device related to voltage application. The device becomes expensive and cumbersome. Therefore, it is preferable to set the appropriate film thickness so that the voltage applied during anodic bonding is less than 1 kV, which is easy to handle.

The piezoelectric element 3 is bonded to the combined body A of the nozzle plate 1 and the body plate 2 joined by anodic bonding in this way.

FIG. 7 shows a process of bonding the piezoelectric element 3 made of PZT to the body plate 2.

The piezoelectric element 3 is bonded to the body plate 2 by transfer bonding as described below.

As shown in FIG. 7b, a dry film 33 is laminated on a glass plate 30 having a foam release sheet 31 and a PZT bulk plate 32 adhered in this order (shown in FIG. 7a), and foamed by a known photolithography technique. The release sheet 31, the PZT bulk plate 32, and the dry film 33 are patterned to form the piezoelectric element group 300 (FIG. 7c). After the surface of the piezoelectric element group 300 is sandblasted, the dry film 33 is peeled off (FIG. 7d).

Next, the resin sheet 34 having the adhesive layer 35 is bonded to the piezoelectric element group 300 (FIGS. 7e and 7f), the resin sheet 34 is isolated (FIG. 7g), and the piezoelectric element group 300 is attached from the adhesive layer 35 side. It adheres to the body plate 2 held by the jig 40, and the glass plate 30 and the piezoelectric element group 300 are heated by a hot plate (FIG. 7h).

The foam release sheet 31 is melted and removed by heating, the glass plate 30 is separated from the body plate 2 and the piezoelectric element group 300, and the ink jet head is completed.

In the above embodiment examples, the case where the present invention is applied to a Kaiser-type inkjet head has been described. However, the pressure of the ink is generated by changing the volume of the pressure chamber by the actuator, and ink droplets are ejected from the nozzles. As long as it is an inkjet head, it is not limited to a Kaiser type inkjet head.

Moreover, although the inkjet head provided with several pressure chambers, nozzles, and inlets was used, even when the inkjet head provided with one pressure chamber, nozzles, and inlets is used, this invention does not impair the effect. .

In this example, an inkjet head similar to the inkjet head HD shown in the above embodiment was manufactured according to the above manufacturing method, and the occurrence of satellites was observed when ink droplets were discharged from the discharge ports of the inkjet head. .

First, both the nozzle plate and the body plate were made of silicon, and a plurality of ink jet heads with variously changed pressure chambers, inlets, and nozzle shapes were produced. Specifically, the pressure chamber and the inlet were formed in a rectangular parallelepiped shape, and the width, length, and height were changed as shown in Table 1. The nozzle was cylindrical, and the diameter of the discharge port and the length of the nozzle were changed as shown in Tables 2 and 3. The shape of the pressure chamber, inlet, and nozzle between the channels in one inkjet head was the same.

Thereafter, a driving voltage was applied to the piezoelectric element, and two types of inks having different surface tensions shown in Tables 2 and 3 below were discharged. The density ρ of each ink was 10 ³ [kg / m ³ ] and the viscosity η was 3 × 10 ⁻³ [Pa · s]. The state of satellite generation at the time of discharge was observed with a microscope, and the case where there was no satellite was evaluated as ◯, and the case where there was a satellite was evaluated as ×.

Tables 2 and 3 below show the relationship between discharge port diameter, nozzle length, flow path shape, and satellite generation. In Tables 2 and 3, the frequency f1 of the natural vibration of the meniscus in the nozzle and the frequency f2 of the natural vibration of the pressure chamber were calculated from the equations (6) and (7), respectively, as described above.

As shown in Tables 2 and 3, when f1 ≦ f2, no satellite was observed in any ink. From the above, it is useful to set the shape of the nozzle, the pressure chamber, and the inlet so that f1 ≦ f2 in order to suppress the generation of satellites when a nozzle having a discharge port having a diameter of 10 μm or less is used. It can be seen that it is.

Claims

A nozzle having a discharge port having a diameter of 10 μm or less, a pressure chamber communicating with the nozzle, an inlet for introducing ink into the pressure chamber, and generating a pressure in the ink by changing the volume of the pressure chamber An ink jet head including an actuator, wherein the frequency of the natural vibration of the meniscus in the nozzle is f1, and the frequency of the natural vibration of the pressure chamber is f2, so that f1 ≦ f2. An ink jet head in which the shape of a nozzle, the pressure chamber, and the inlet is set.
When the inertance component of the nozzle is Ln, the capacitive component is Cn, the inertance component of the pressure chamber is Lc, the capacitive component is Cc, the inertance component of the inlet is Li, and the capacitive component of the actuator is Ca, formula (1) The inkjet head according to claim 1, wherein: