JP2002361859A - Inkjet head - Google Patents

Abstract

(57) Abstract: The present invention provides an ink jet head for performing high-speed, high-density, high-resolution recording. An ink jet head (1) supplies ink from a common ink liquid chamber (11) to a pressure chamber (10) through an ink supply path (12), pressurizes the inside of the pressure chamber (10) by displacement of a vibration plate (5), and causes the ink in the pressure chamber (10) to move. Are ejected and fly as ink droplets 20 from the nozzle holes 9 through the ink communication grooves 13. Then, the diameter of the inscribed circle of the ink communication groove 13 in the direction orthogonal to the ink flow direction is formed to be 30 μm or more, and the diameter of the opening on the ejection side of the nozzle hole 9 is determined by the diameter of the inscribed circle of the ink communication groove 13. It is formed small. Therefore, high-speed operation can be performed by low-voltage driving and high integration, and a high-definition image can be formed.

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, and more particularly, to an ink-jet head mounted on a high-speed, high-density, high-resolution drop-on-demand (DOD) type ink jet recording apparatus.

[0002]

2. Description of the Related Art Ink-jet heads have recently become widespread because they have many advantages such as extremely low noise during recording and the use of inexpensive plain paper with a high degree of freedom of ink.

[0003] In particular, a drop-on-demand (DOD) type ink jet head that discharges ink only when necessary is used in an ink jet recording apparatus such as a printer, a facsimile, a copying machine, etc. A plurality of nozzle holes for ejecting ink droplets, a pressure chamber to which the nozzle holes are connected and the ink is pressurized, and energy generating means for pressurizing the ink in the pressure chamber (for example, a piezoelectric element, an electrostatic element, etc. By using an inkjet head equipped with an electromechanical transducer, a thermomechanical transducer such as a thermal resistor (heater), ink droplets are ejected and fly out of the nozzle holes only when a recording signal is input. Perform high-resolution recording.

[0004] As described above, the ink jet head performs recording by driving the energy generating means such as the thermal resistor and the piezoelectric element at an arbitrary frequency to eject and fly the ink droplets formed from the nozzle holes. In addition, the shape of the nozzle hole and the diameter of the discharge port affect the ejection performance of the ink droplet.

[0005] In recent years, many images output by an ink jet recording apparatus have a high definition of 1200 dpi or more. This is because the size of an ink droplet per pixel is reduced to 10 picoliter or less. This is largely due to the fact that it has become possible. In order to eject and fly such minute ink droplets, a method of changing a driving pulse applied to the energy generating means or reducing the diameter of the ejection opening of the nozzle hole has been adopted.

On the other hand, as the energy generating means, first, a thermo-mechanical conversion element on which a thermal resistor is mounted, that is, after converting electric energy into thermal energy by the thermal resistor, the ink is stored in the ink chamber in the pressure chamber. There is an element that generates air bubbles and converts it into mechanical energy for discharging ink.

This thermo-mechanical conversion element is generally characterized in that bubbles are generated in an ink reservoir, and a thermal resistor can be manufactured by an existing silicon semiconductor process. ,
A high-density arrangement of about 600 dpi is possible. Also,
The thermomechanical conversion element can arbitrarily set the size of the bubble by the thermal energy to be converted, so that the discharge energy can be increased, and a relatively large discharge energy can be obtained as compared with the electromechanical conversion element. It has the advantage that.

On the other hand, the thermomechanical transducer requires a long time to cool the ink inside the pressure chamber and cool the thermal resistor after the ink is ejected, so that the ejection bit can be driven at a high frequency or a large number of bits exceeding several hundred bits can be obtained. Are difficult to drive at once. as a result,
The thermomechanical conversion element has a disadvantage that the advantage of high-density arrangement is negated, and electrical energy is converted into thermal energy by a thermal resistor, so that the heat generation and power consumption of the ink jet recording apparatus are remarkably increased. have. In particular, the increase in heat generation and power consumption is a disadvantage from the viewpoint of environmental issues that are currently attracting attention.

The second energy generation means includes a piezoelectric conversion element using a piezo element as an energy generation element, and an electromechanical conversion element utilizing electrostatic attraction between electrodes (hereinafter also referred to as an electrostatic conversion element). There is. Each of the piezoelectric conversion element and the electromechanical conversion element has a vibration plate on an arbitrary surface of the pressure chamber, and vibrates the vibration plate to transmit energy to ink in the pressure chamber, thereby causing ink droplets to be discharged from the nozzle holes. Discharge and fly. The piezoelectric element is directly connected (generally bonded) to the diaphragm to electrically displace the piezoelectric element and vibrate the diaphragm in accordance with a drive pulse. As an arbitrary electrode having opposite properties, an opposing electrode is arranged in an opposing state, a potential difference (generally a driving voltage) is generated between the two electrodes, and an electrostatic attraction and / or an electrostatic repulsion is generated between the electrodes. The electrostatic conversion element vibrates the diaphragm by applying a drive voltage in a pulsed manner (generally, a drive pulse).

A piezo element in a piezoelectric conversion element is generally formed by a print transfer method, or a lump of stacked piezo elements is divided by a dicing method. As an array, 20
The arrangement of about 0 dpi is the limit of the current high-density arrangement.

On the other hand, in the electrostatic conversion element, since electrodes are formed by a silicon semiconductor process, 600
An array that is miniaturized to about dpi is possible. In addition, since both the piezoelectric conversion element and the electrostatic conversion element generate negligible heat as compared with the thermo-mechanical conversion element, the ejection bit can be driven at a high frequency or a large number of bits exceeding several hundred bits can be used. Can be driven at once. Furthermore, the piezoelectric conversion element and the electrostatic conversion element are also smaller in power consumption than the thermo-mechanical conversion element. In particular, since the electrostatic conversion element only changes the electrostatic potential, Significantly less consumption.

However, in the case of a piezoelectric transducer, due to the limit of vibration displacement of a piezo element, in the case of an electrostatic transducer,
There is a problem that the energy for ejecting ink droplets is smaller than that of the thermo-mechanical transducer due to the limit of the distance between the electrodes and the thickness / strength of the diaphragm.

The results of the above study can be represented as shown in FIG. 16. As can be seen from FIG. 16, due to the advantages of high-speed operation and power consumption, a future drop-on demand (DO)
In consideration of the performance required of the D) type ink jet recording apparatus, particularly, low energy loss, high speed, and high definition, the ink jet head has a fine nozzle hole diameter, and It is desirable that an electromechanical conversion element, in particular, an electrostatic conversion element be used as the energy generating means.

However, an ink jet head using an electrostatic conversion element has a relatively small ejection energy as compared with a thermomechanical conversion element, and in particular, the element arrangement is 150 dpi.
It becomes remarkable when it becomes finer than the above.

As a conventional ink jet head, there is an edge shooter type ink jet head described in Japanese Patent No. 2607308. As shown in FIG. 17, a side cross-sectional view, and FIG. 18, a front view as viewed from the ink ejection side, in the inkjet head 100, the vibration plate 102 vibrates by the piezoelectric body 101, and the pressure chamber 103
The ink in the inside is pressurized, passed through an ink communication groove 105 formed of silicon having a (100) plane as a surface plane orientation, and having a triangular cross-section, and ejecting ink from an ejection port 106.

In this prior art, a piezoelectric body 101 which is a piezoelectric conversion element is used as an energy generating means.
Other prior art uses a thermal resistor.

Japanese Patent Application Laid-Open No. 9-48126 discloses that
A discharge energy generating means for generating discharge energy in the recording liquid; and a liquid flow path forming substrate for forming a liquid flow path for flowing the recording liquid toward a discharge port. The side of the liquid flow path is made of single crystal silicon (1
A liquid jet recording head has been proposed which includes a 10) surface and a pair of (111) surfaces perpendicular to the 10) surface. That is, in this liquid jet recording head, a top plate is formed of silicon having a (110) plane as a surface plane direction, using a thermomechanical conversion element formed of a thermal resistor as an energy generating unit.

In each of the above-described ink jet heads, the ejection port from which ink is ejected is formed of the same member as the top plate, and no nozzle forming member is provided.

Further, as a conventional technique using an electrostatic conversion element as an energy generating means, Japanese Patent Application Laid-Open No. H11-999 discloses a plurality of nozzle holes and a plurality of independent discharge chambers communicating with each of the nozzle holes. A diaphragm formed on the lower surface of the discharge chamber, and an individual electrode facing the diaphragm with a gap, and applying a voltage between the diaphragm and the individual electrode to deform the diaphragm. As an inkjet head that ejects ink droplets from the nozzle holes, there has been proposed an inkjet head in which the height of the partition wall of the ejection chamber is set in the range of 100 μm to 160 μm.

That is, this ink jet head has:
It is a side shooter type in which the direction of pressurization by the diaphragm and the direction of ejection are the same, and there is no ink communication groove.

[0021]

However, such a conventional ink jet head discharges ink at a high density, at a high speed and with a high degree of accuracy to form an image with good image quality at a high speed. Therefore, there was still a need for improvement.

That is, in order to perform high-speed printing of the head, it is necessary to arrange the element rows in a highly integrated manner of 150 dpi or more, and to increase the definition of the image, the volume of the ink droplets must be 10 picoliters or less. It is required to be.

In the case of the conventional edge shooter type, it is necessary to reduce the width and height of the ink communication groove. That is, it is necessary to reduce the inscribed circle of the ink communication groove.

However, as described above, as the energy generating means, it is required to use an electrostatic conversion element from the advantages of high-speed operation and power consumption. There is a problem that the pressure loss during the passage of the ink increases and the driving voltage of the inkjet head increases.

Further, as described in Japanese Patent Application Laid-Open No. 11-993, the conventional technique using an electrostatic conversion element as an energy generating means is a side shooter type.
There is a problem that the size of the ink jet head becomes larger than that of the edge shooter type.

Therefore, according to the first aspect of the present invention, an ink flow path for supplying ink to at least each pressure chamber and an ink for discharging ink from each pressure chamber are provided on one surface of the plurality of pressure chambers filled with ink. The top plate member in which the communication groove is formed is joined, and the diaphragm provided in a part of each pressure chamber is vibrated by electrostatic attraction with an electrostatic conversion element, and ink in the pressure chamber is vibrated.
Through the ink communication groove, a direction perpendicular to the ink flow direction of the ink communication groove of the ink jet head, which is formed on a nozzle forming member formed as a member separate from the top plate member and is ejected from a nozzle hole communicating with the ink communication groove. The diameter of the inscribed circle is formed to be 30 μm or more, and the diameter of the opening on the discharge side of the nozzle hole is formed smaller than the diameter of the inscribed circle of the ink communication groove. In this case, it is possible to suppress the increase in the driving pulse voltage for obtaining the sufficient ink droplet ejection performance, to enable high-speed operation by low-voltage driving and high integration, and to make the ejection port small and small in volume. It is an object of the present invention to provide an ink jet head capable of ejecting ink droplets and forming a high-definition image.

According to a second aspect of the present invention, the cross section of the ink communication groove in a direction orthogonal to the ink flow direction is formed to be substantially square, so that the ink communication groove has the same ink communication groove width as that of the triangular shape. It is an object of the present invention to provide an ink-jet head that can further reduce the pressure loss of the ink communication groove, and can perform high-speed operation by low-voltage driving and high integration.

According to a third aspect of the present invention, the nozzle forming member is formed of a metal member manufactured by an electroforming method, and the nozzle hole has a sectional shape in a direction perpendicular to the ink flow direction from the ink discharge side. Towards the inflow side,
By forming a shape in which the angle between the tangential direction of the inner wall surface of the nozzle hole and the ink ejection direction continuously increases, the pressure loss in the nozzle forming member is suppressed as compared with the straight shape, and the electrostatic conversion element is formed. In the case of using the energy generating means, it is possible to suppress the increase of the driving pulse voltage for obtaining sufficient ink droplet ejection performance, to enable high-speed operation by low voltage driving and high integration, and to make the ejection port small. Accordingly, it is an object of the present invention to provide an ink jet head capable of discharging an ink droplet having a small volume and improving the definition of an image.

[0029]

According to a first aspect of the present invention, there is provided an ink jet head comprising: a plurality of pressure chambers filled with ink; an ink flow path for supplying ink to at least each of the pressure chambers; A top plate member formed with an ink communication groove for discharging the ink and joined to one surface of each of the pressure chambers; and a nozzle hole formed of a member separate from the top plate member and communicating with the ink communication groove. A nozzle forming member, and an electrostatic conversion element that vibrates a diaphragm provided in a part of each of the pressure chambers by electrostatic attraction to discharge ink in the pressure chamber from the nozzle hole through the ink communication groove,
Wherein the ink communication groove has an inscribed circle having a diameter of 30 μm or more in a direction perpendicular to the ink flow direction, and the nozzle hole has an ink ejection side opening having a diameter of 30 μm or more. The above object is achieved by making the diameter smaller than the diameter of the inscribed circle of the ink communication groove.

According to the above configuration, an ink flow path for supplying ink to at least each pressure chamber and an ink communication groove for discharging ink in each pressure chamber are formed on one surface of the plurality of pressure chambers filled with ink. The top plate member is joined, and the vibrating plate disposed in a part of each pressure chamber is vibrated by electrostatic attraction by an electrostatic conversion element, and ink in the pressure chamber is passed through the ink communication groove, and the top plate member is The diameter of an inscribed circle in a direction perpendicular to the direction of ink flow in the ink communication groove of the ink jet head, which is formed on a nozzle forming member formed as a member separate from the nozzle hole and is ejected from the nozzle hole communicating with the ink communication groove, is 30 μm.
m, and the diameter of the opening on the discharge side of the nozzle hole is formed smaller than the diameter of the inscribed circle of the ink communication groove.
An increase in the drive pulse voltage for obtaining sufficient ink droplet ejection performance can be suppressed, enabling high-speed operation by low-voltage drive and high integration, and a small ejection port to reduce the volume. Ink droplets can be ejected, and a high-definition image can be formed.

In this case, for example, as described in claim 2, the ink communication groove may be formed to have a substantially quadrangular cross section in a direction orthogonal to the ink flow direction.

According to the above configuration, since the cross-sectional shape of the ink communication groove in the direction orthogonal to the ink flow direction is formed in a substantially square shape, the ink communication groove has the same width as the triangular shape. However, the pressure loss in the ink communication groove can be further reduced, and the high-speed operation can be performed by lower voltage driving and higher integration.

Further, for example, as set forth in claim 3, the nozzle forming member is formed of a metal member manufactured by an electroforming method, and the nozzle hole is formed in a direction orthogonal to the ink flow direction. The cross-sectional shape may be formed such that the angle between the tangential direction of the inner wall surface of the nozzle hole and the ink discharge direction continuously increases from the ink discharge side toward the inflow side.

According to the above configuration, the nozzle forming member is formed of a metal member manufactured by the electroforming method, and the nozzle hole is formed such that a cross-sectional shape in a direction orthogonal to the ink flow direction is from the ink discharge side to the ink inflow side. In order to reduce the pressure loss in the nozzle forming member as compared with the straight shape, since the angle formed between the tangential direction of the inner wall surface of the nozzle hole and the ink ejection direction continuously increases. In the case where the electrostatic conversion element is used as the energy generating means, it is possible to suppress the increase in the driving pulse voltage for obtaining sufficient ink droplet ejection performance, thereby enabling high-speed operation by low voltage driving and high integration. In addition, by reducing the size of the ejection port, an ink droplet having a small volume can be ejected, and the image can be made high definition.

[0035]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

FIGS. 1 to 13 are views showing an embodiment of the ink jet head of the present invention. FIG. 1 is a side sectional view of the ink jet head 1 to which the embodiment of the ink jet head of the present invention is applied. , FIG. 2 is a front view of the ink ejection side of the inkjet head 1 of FIG. 1, and FIG.
FIG. 2 is a cross-sectional view of the inkjet head 1 of FIG.

In FIG. 1, the ink jet head 1
Uses an electrostatic conversion element as an energy generating means. An electrode 3 is formed for each element on a substrate 2 formed of a low-conductivity silicon semiconductor substrate. The diaphragm 5 is disposed with a space therebetween. The diaphragm 5 is made of a conductive metal or metal compound, for example,
It is formed of silicon, ITO (an oxide film of indium and tin) or the like, and is connected to a common potential, for example, a ground potential.

A liquid chamber member 6 is stacked on the upper portion of the diaphragm 5, and a top plate member 7 is stacked on the liquid chamber member 6.
A nozzle forming member 8 is joined to the front side surface of the substrate 2, the vibration plate 3, the liquid chamber member 6, and the top plate member 7, and the nozzle forming member 8 has a nozzle as shown in FIGS. A hole 9 is formed.

The liquid chamber member 6 is a member in which the pressure chamber 10 is formed, and is usually made of silicon whose surface has a (110) plane orientation. The top plate member 7 includes a common ink chamber 11, an ink supply path 12, and an ink communication groove 1.
The member is formed of silicon, resin, or a silicon oxide film having a (100) plane orientation as a surface. Note that (10)
0) In the case where silicon having the surface orientation as the surface is used, the ink communication groove 13 is generally formed by a wet etching method using a KOH solution. In this case, the ink communication groove 13 is formed as shown in FIG. It is formed in such a triangular shape.

The nozzle forming member 8 is made of a metal such as nickel or a nickel-cobalt alloy formed by an electroforming method, a resin, a stainless steel alloy, or the like. When the nozzle forming member 8 is formed of a metal such as nickel or a nickel-cobalt alloy formed by an electroforming method, it is general to form a nozzle hole 9 by forming a resist type by a lithography technique. When formed of resin, the nozzle hole 9 is formed by an excimer laser method or a YAG laser method.
Is generally formed, and when it is occasionally formed of a stainless alloy, the nozzle hole 9 is formed by a press working method.
Is generally formed. Although not shown, an ink-repellent surface layer is formed on the ink ejection side surface of the nozzle forming member 8.

In the ink jet head 1, ink is supplied to the pressure chamber 10 from the common ink liquid chamber 11 through the ink supply path 12, and the inside of the pressure chamber 10 is pressurized by the displacement of the vibration plate 5. Ink communication groove 1
The ink droplet 20 is ejected from the ejection opening of the nozzle hole 9 through the nozzle hole 9 and flies. The ejection and flying of the ink droplets 20 are performed by vibrating the diaphragm 5 due to an electrostatic attraction generated by a potential difference applied between the electrode 3 and the diaphragm 5 to pressurize the ink in the pressure chamber 10. As a result, pressure is propagated in the nozzle hole 9 to generate the pressure.

In FIGS. 1 to 3, the top plate member 7 of the ink jet head 1 is made of silicon having the (100) plane orientation as the surface.
Formed by a wet etching method using a KOH solution,
Ink communication groove 13, as shown in FIG. 3, but is formed in a triangular shape, the ink communication groove may be formed by a dry etching method using a CF ₄ / O ₂ gas, in this case, FIG. 4 to 6, particularly, as shown in FIG. 6, the ink communication groove 30 is formed in a square shape. In addition, FIG.
6, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals.

Next, the operation of the present embodiment will be described. In the ink jet head 1 of the present embodiment, ink flows occur as shown by arrows in FIG. That is, FIG.
The force F1 for pressurizing the ink generated by the potential difference (hereinafter referred to as a driving voltage) applied between the electrodes 3 is attenuated due to the pressure loss until the ink is discharged, and becomes the ink discharging force F2. The process is shown schematically.

In FIG. 7, the ink jet head 1
Receives the electrostatic force generated by the drive voltage V and
When the force F1 is generated, a pressure loss indicated by R1 occurs first due to the material, strength, and film thickness of the diaphragm 5.
Further, due to the density and viscosity of the ink, the pressure chamber 1
Even within 0, a pressure loss represented by R3 occurs, and
A pressure loss of R2 occurs due to the ink flowing in the direction of flowing backward to the ink supply path 12. Due to the size and shape of the ink communication groove 13, R4
The pressure loss shown by occurs. It should be noted that the prior art inkjet head having no nozzle forming member 8 has a high integration, particularly, 150 d
When the density is higher than pi, or when the size of the ejection part is reduced to reduce the size of the ink droplet, the pressure loss R4 significantly affects the ejection performance.

The ink jet head 1 has a nozzle hole 9 inside the nozzle hole 9 and in the vicinity of the nozzle hole 9.
, A pressure loss R5 occurs.
The pressure loss R5 in the nozzle hole 9 becomes remarkable when the discharge port diameter of the nozzle hole 9 is reduced to, for example, 25 μm or less. In order to improve the ink discharge performance, the pressure loss R5 must be suppressed. It is also important. The pressure loss in the top plate member 7 and the liquid chamber member 6 forming the pressure chamber 10 is expressed by a force F1 when the top plate member 7 and the liquid chamber member 6 are made of a metal such as silicon. Since it has rigidity that does not deform upon receiving and is considered to be negligibly small, it is omitted.

Next, the pressure loss R4 in the ink communication groove 13 and the ink communication groove 30 will be described with reference to FIGS. 8 shows a cross-sectional shape of the ink communication groove 13 of the ink-jet head 1 of FIGS. 1 to 3, and FIG. 9 shows a cross-sectional shape of the ink communication groove 30 of the ink-jet head 1 of FIGS. Is shown.

FIG. 8 shows a case where silicon having the (100) plane orientation as the surface is used as the top plate member 7 as described above, and the ink communication groove 13 is formed by a wet etching method using a KOH solution. It is formed into a triangular shape due to the difference in etching rate depending on the plane orientation. The width Y of the ink communication groove 13 and the diameter X of the inscribed circle are represented by X =
Represented by ^{(6 1/2 -2 1/2) Y /} 2.

FIG. 9 shows a case where silicon or a silicon oxide film is used as the top plate member 7 as described above. The ink communication groove 30 is formed by a dry etching method and has a substantially square shape. Is formed. The width Y and the inscribed circle diameter X of the ink communication groove 30 are represented by X = Y.

In FIGS. 8 and 9, the pressure loss R4 is
This is a pressure loss caused by the dimensions of the ink communication grooves 13 and 30, and can be substantially defined by a resistance value as an ink fluid flowing in a circular tube of an inscribed circle of the ink communication grooves 13 and 30.

As shown in FIG. 10, the flow rate Q of the fluid flowing in the circular tube is L (the pressure loss R4 corresponds to the length L of the ink communication grooves 13, 30 in the pressure loss R4). ,
The radius of the circular tube is r ₀ (corresponding to 1/2 of the diameter X of the inscribed circle of the ink communication grooves 13 and 30 in the pressure loss R4), and the viscosity coefficient is μ (in the pressure loss R4, the viscosity of the ink is If the pressure drop is ΔP, it can be calculated by the Hagen-Poiseuille equation shown below.
In FIG. 10, circles indicate the broken pipes of the ink communication grooves 13 in FIG. 8 and the broken pipes of the ink communication grooves 30 in FIG. 9.

[0051]

(Equation 1) Then, πr ₀ ⁴ / 8μ of expression of the Hagen-Poiseuille
The reciprocal of L represents the resistance in the circular pipe and corresponds to the pressure loss R4. From the Hagen-Poiseuille equation, it can be seen that the pressure loss R4 increases rapidly as the inscribed circle diameter X decreases.

The calculated resistance value of the ink fluid with respect to the inscribed circle diameter X of the ink communication grooves 13 and 30 is as follows:
As shown in FIG. 11, this resistance value corresponds to the pressure loss R4 in the ink communication grooves 13 and 30. The ink communication grooves 13 and 30 are generally divided by a dicing method from the silicon wafer of the ink jet head 1.
The longer the length of 30 is, the more the variation of the pressure loss R4 between the inkjet heads 1 can be suppressed. Therefore, usually, the ink communication grooves 13 and 30 are
It is generally formed with a length of 100 μm or more.
FIG. 11 shows a case where the length of the ink communication grooves 13 and 30 is 100 μm, and a pigment ink having a viscosity of 2.5 mPa · sec, which is the average viscosity of a general ink, is used as the ink. It can be seen from FIG. 11 that when the inscribed circle diameter of the communication grooves 13 and 30 is less than 30 μm, the pressure loss R4 in the ink communication grooves 13 and 30 rapidly increases.

Therefore, as in the case of the ink jet head 1 of the present embodiment, when the vibration plate 3 which is an electrostatic conversion element is used as energy generating means and the area for generating pressure by integrating the element array is small. The force F1 generated by the diaphragm 3 decreases, so that the pressure loss R4
As described above, especially when the diameter of the inscribed circle of the ink communication grooves 13 and 30 is 30 μm or less, the adverse effect on the ejection performance becomes remarkable. As a result, the diameter of the inscribed circle of the ink communication grooves 13 and 30 is desirably 30 μm or more.

Next, the pressure loss R5 inside the nozzle hole 9 and in the vicinity of the nozzle hole 9 will be described with reference to FIGS. FIG. 12 is a sectional view of the nozzle hole 9 of the ink jet head 1 according to the present embodiment, and FIG.
FIG. 4 is a cross-sectional view of a nozzle hole of a conventional inkjet head.

First, in the ink jet head 1 according to the present embodiment shown in FIG. 12, the tangential direction of the inner wall surface of the nozzle hole 9 and the ink discharge direction are formed from the ink discharge port side of the nozzle hole 9 to the inflow side. The angle θ1 is formed in a shape that continuously increases. The pressure loss R5 is a pressure loss caused by the size and shape of the nozzle hole 9, and is represented by the resistance value Ra as an ink fluid and the smoothness of ink flow.

Therefore, as shown in FIG. 12, the shape of the nozzle hole 9, that is, the cross-sectional shape of the nozzle hole 9 is such that the inner wall surface tangential direction of the nozzle hole 9 and the ink discharge direction from the ink discharge port toward the inflow port. When the angle θ1 is formed so as to increase continuously, there is no rapid change in the ink flow, the ink inlet increases, and the resistance as the ink fluid decreases.

On the other hand, the conventional nozzle hole 200 shown in FIG.
Is formed straight from the ink inlet to the discharge port, and extends from the ink communication groove 201 to the nozzle hole 20.
The flow of the ink flowing into 0 changes rapidly, and the resistance as an ink fluid rapidly increases. In FIG. 13, reference numeral 202 denotes a nozzle forming member in which the nozzle holes 200 are formed, 203 denotes a top plate member, and 204 denotes a liquid chamber member.

When the electrostatic conversion elements are used as energy generating means and the element rows are arranged in a highly integrated array of 150 dpi or more as in the prior art, the diameter of the inscribed circle of the ink communication groove 201 is set to 30 μm or more, and the ink communication groove 201 is formed. If the pressure loss R4 of 201 is not reduced, the injection performance will be reduced. Therefore, the diameter of the inscribed circle of the ink communication groove 201 is set to 3
When the ink droplet is ejected with the end of the ink communication groove 201 as the ejection port, the volume of the ink droplet is 0 μm or more,
When it is 10 picoliters or more, it is difficult to reduce the size of droplets, and it is difficult to increase the definition of an image.

However, as in the ink jet head 1 of the present embodiment, the diameter of the inscribed circle of the ink communication grooves 13 and 30 is set to 30 μm or more to reduce the pressure loss R4 of the ink communication grooves 13 and 30 and to reduce the ink loss. A nozzle forming member 8 having a nozzle hole 9 for discharging ink is formed on an end surface of each of the grooves 13 and 30 as a separate member from the top plate member 7.
If the diameter of the discharge port is smaller than the diameter of the inscribed circle of the ink communication grooves 13 and 30, an ink droplet of 10 picoliters or less can be discharged, and high-definition image output can be performed.

That is, when the pressure loss R4 in the ink communication grooves 13 and 30 increases, the drive voltage for obtaining the target ejection speed v increases regardless of the drive frequency. An upper limit value of the drive voltage is determined by a drive control circuit for supplying the potential, and a target discharge speed v cannot be obtained because of the drive voltage having the determined upper limit value. FIG.
The force F2 for ejecting the ink shown in (1) decreases, and in order to make this force F2 a force at which the desired ejection speed v is obtained, it is necessary to increase the force F1 for pressurizing the ink. Then, in order to increase the force F1 for pressing the ink, it is necessary to increase the driving voltage. Regarding the decrease in the ejection performance due to the increase in the pressure loss R4, the impedance increases in accordance with the increase in the pressure loss R4 at the time of high frequency operation of 10 kHz or more, so that the fluid resistance (corresponding to the pressure loss R2 in the ink supply path 12). ) May be lost and the injection speed may be reduced.

Therefore, particularly, the ink communication grooves 13, 3
It is important that the diameter of the inscribed circle of 0 is 30 μm or more. The pressure loss R4 varies depending on the viscosity of the ink, but the viscosity of the ink generally used at present is about 1.5 to 3.5 mPa · sec. By setting the diameter of the inscribed circle to 30 μm or more, it is possible to reduce the deterioration of the injection performance.

[0062]

Next, an embodiment of the ink jet head of the present invention will be described. Note that the nozzle forming members of Examples 1 and 2 described below are made of nickel manufactured by an electroforming method.

<Example 1> An ink jet head similar to the ink jet head 1 shown in FIGS. 1 to 3 was used. The top plate member was made of silicon having a (100) plane as the surface, and the ink communication groove was formed of a KOH liquid. Was formed into a triangular shape by a wet etching method. In this case, the width Y of the ink communication groove and the diameter X of the inscribed circle are X = ( ^{61 /} 2-21 ^/ 2) Y
/ 2, and the length L of the ink communication groove is 100
μm.

The sectional shape of the ink communication groove viewed from the ink ejection direction is the same as that shown in FIG.
The element rows were arranged in a 150 dpi array (inter-element pitch of about 169 μm) instead of 0 to 100 μm.

As in the conventional case, the shape of the nozzle hole is circular when viewed from the front and the cross-sectional shape is straight, and the shape of the nozzle hole is circular when viewed from the front and the cross-sectional shape flows from the discharge port side. Toward the inlet side, a case where the angle θ1 between the tangential direction of the inner wall surface of the nozzle hole and the ink discharge direction continuously increases, and both are created, and the diameter of the discharge port is
20 μm and 25 μm. Thickness L of nozzle forming member
Used a 30 μm nozzle forming member. In addition,
For comparison with the conventional example shown in FIGS. 17 and 18, an ink jet head having no nozzle forming member was also manufactured.

An ink jet head similar to the ink jet head 1 shown in FIGS.
7 and the conventional inkjet heads shown in FIG. 18 were evaluated for ejection performance. The ink used was a pigment ink having a viscosity of 2.5 mPa · sec, which is the average viscosity of a general ink.

<Embodiment 2> An ink jet head similar to the ink jet head 1 shown in FIGS. 4 to 6 was formed by using a silicon oxide film as a top plate member, and drying the ink communication grooves with CF ₄ / O ₂ gas. The ink communication groove was formed in an approximately square shape by etching. In this case, the width Y of the ink communication groove and the diameter X of the inscribed circle are represented by X = Y, and the length L of the ink communication groove is 100 μm.

The sectional shape of the ink communication groove viewed from the ink ejection direction is the same as that shown in FIG.
The element rows were arranged in a 300 dpi array (inter-element pitch of about 84.5 μm) instead of 0 to 60 μm.

As in the conventional case, the shape of the nozzle hole is a circular shape when the discharge port is viewed from the front and the cross-sectional shape is straight, and the shape of the nozzle hole is circular when viewed from the front and the cross-sectional shape is from the discharge port to the inlet. And the case where the angle θ1 formed between the tangential direction of the inner wall surface of the nozzle hole and the ink discharge direction continuously increases, and the diameter of the discharge port is set to 20
μm and 25 μm. As the film thickness L of the nozzle forming member, a 20 μm nozzle forming member was used. FIG.
For comparison with the related art shown in FIGS. 7 and 18, an ink jet head having no nozzle forming member was also prepared.

An ink jet head similar to the ink jet head 1 shown in FIGS.
7 and the conventional inkjet heads shown in FIG. 18 were evaluated for ejection performance. The ink used was a pigment ink having a viscosity of 2.5 mPa · sec, which is the average viscosity of a general ink. Further, in the second embodiment, since the size of the diaphragm is smaller than that of the first embodiment, the force F1 obtained from the electrostatic conversion element as the energy generating means is relatively small.

<Evaluation Results> In the first and second embodiments, the calculated value of the pressure loss R4 as the ink fluid in the ink communication groove portion of the ink jet head of each structure, the volume of the ejected ink droplet, and the drive for obtaining normal ejection Comprehensive evaluation of voltage and injection performance resulted in the results shown in FIGS.

In FIGS. 14 and 15, the driving voltage is
The drive voltage for achieving the target ejection speed is indicated by whether or not it falls within a design allowable value, and if it is, it is indicated by ◎ (large allowance) and （(small allowance), and if not, it is indicated by x. . The ejection performance is as follows: when the size of the ink droplet is at least 10 to 20 picoliters and the driving voltage is ◎ or ○,
When it was 0 picoliter or less and the driving voltage was ◎ or ○, it was marked as ◎.

As can be seen from FIGS. 14 and 15, when the ink communication groove has a triangular shape, if the width is smaller than 60 μm, that is, if the inscribed circle of the ink communication groove is 30 μm or less, the ink communication groove portion is formed. , The pressure loss R4 increases, and normal injection cannot be obtained. Further, since the nozzle shape of the nozzle hole 9 of the ink jet head of the present embodiment has a smaller pressure loss than that of the straight shape, normal ejection can be easily obtained.
Further, in the case of the conventional ink jet head shown in FIGS. 17 and 18, if the width of the ink communication groove is reduced, normal ejection cannot be obtained due to the pressure loss R4 in the ink communication groove, and the width of the ink communication groove is increased. Then, the ink droplet becomes large, and normal ejection cannot be performed.

Further, as for the shape of the ink communication groove, the inscribed circle with the same width of the ink communication groove can be made larger in the case of the square shape than in the case of the triangle shape, and the pressure loss 4 can be reduced. And miniaturization of the ink jet head.

As described above, in the ink jet head 1 of the present embodiment, the diameter of the inscribed circle in the direction perpendicular to the ink flow direction of the ink communication grooves 13 and 30 is formed to be 30 μm or more. The diameter of the opening on the ejection side is smaller than the diameter of the inscribed circle of the ink communication grooves 13 and 30.

Therefore, when the electrode 3 and the vibration plate 5 which are electrostatic conversion elements are used as energy generating means, an increase in driving pulse voltage for obtaining a sufficient ink droplet ejection performance is suppressed, and a low voltage driving is performed. In addition, high-speed operation can be realized by high integration, and the ink ejection port of the nozzle hole 9 can be made small, so that a small-volume ink droplet can be ejected, and a high-definition image can be formed. it can.

In the ink jet head 1 of the present embodiment, the cross section of the ink communication groove 30 in the direction perpendicular to the ink flow direction is formed in a substantially square shape in FIGS.

Therefore, as compared with the triangular shape of the ink communication groove 13 in the case of the ink jet head 1 shown in FIGS. 1 to 3, the pressure loss of the ink communication groove can be further reduced even with the same ink communication groove width. Accordingly, high-speed operation can be performed by lower voltage driving and higher integration.

Further, in the ink jet head 1 of the present embodiment, the nozzle forming member 8 is formed of a metal member manufactured by the electroforming method, and the nozzle hole 9 is formed.
Is formed so that the cross-sectional shape in the direction perpendicular to the ink flow direction is such that the angle between the tangential direction of the inner wall surface of the nozzle hole 9 and the ink discharge direction continuously increases from the ink discharge side to the inflow side. are doing.

Therefore, compared to the straight shape,
The pressure loss in the nozzle forming member 8 can be suppressed, and when the electrode 3 and the vibration plate 5 which are electrostatic conversion elements are used as energy generating means, a driving pulse voltage for obtaining sufficient ink droplet ejection performance is obtained. It is possible to suppress the increase and enable high-speed operation by low-voltage driving and high integration, and to make the ejection port small, thereby ejecting small-sized ink droplets to achieve high-definition images. Can be.

As described above, the invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

[0082]

According to the ink jet head of the first aspect of the present invention, at least one surface of the plurality of pressure chambers filled with ink is provided with an ink flow path for supplying ink to at least each pressure chamber and the inside of each pressure chamber. A top plate member formed with an ink communication groove for discharging ink is joined, and a vibration plate provided in a part of each pressure chamber is vibrated by an electrostatic attraction by an electrostatic conversion element to discharge ink in the pressure chamber. A direction orthogonal to the direction of ink flow in the ink communication groove of the ink jet head, which is formed on a nozzle forming member formed as a member separate from the top plate member through the ink communication groove and is ejected from a nozzle hole communicating with the ink communication groove. The diameter of the inscribed circle of 30 μm or more,
Since the diameter of the opening on the ejection side of the nozzle hole is formed smaller than the diameter of the inscribed circle of the ink communication groove, sufficient ejection performance of ink droplets is obtained when the electrostatic conversion element is used as energy generating means. The increase of the drive pulse voltage for
High-speed operation by low-voltage driving and high integration can be enabled, and the ejection openings can be made small to eject small-sized ink droplets, whereby a high-definition image can be formed.

According to the ink jet head of the second aspect of the invention, since the cross-sectional shape of the ink communication groove in the direction perpendicular to the ink flow direction is formed to be substantially quadrangular, it is the same as the triangular shape. Even if the ink communication groove width is, the pressure loss of the ink communication groove can be further reduced,
High-speed operation can be performed by lower voltage driving and higher integration.

According to the third aspect of the present invention, the nozzle forming member is formed of a metal member manufactured by an electroforming method, and the nozzle hole is formed.
The cross-sectional shape in a direction orthogonal to the ink flow direction is formed so that the angle between the tangential direction of the inner wall surface of the nozzle hole and the ink discharge direction continuously increases from the ink discharge side to the inflow side. Therefore, compared to the straight shape, it is possible to suppress the pressure loss in the nozzle forming member,
When the electrostatic conversion element is used as the energy generating means, it is possible to suppress the increase in the driving pulse voltage for obtaining sufficient ink droplet ejection performance, and to enable high-speed operation by low-voltage driving and high integration. In addition, by reducing the size of the ejection port, a small-volume ink droplet can be ejected, and the image can be made high definition.

[Brief description of the drawings]

FIG. 1 is a side cross-sectional view of an inkjet head to which an embodiment of an inkjet head of the present invention is applied.

FIG. 2 is a front view of an ink ejection side of the inkjet head of FIG.

FIG. 3 is a cross-sectional view of the inkjet head 1 of FIG.

FIG. 4 is a side cross-sectional view of the ink-jet head in a case where the ink communication groove of the ink-jet head of FIG. 1 is rectangular.

FIG. 5 is a front view of the ink ejection side of the inkjet head of FIG. 4;

FIG. 6 is a cross-sectional view of the inkjet head 1 of FIG.

FIG. 7 is a side cross-sectional view of the ink jet head of FIG. 1 and FIG. 4, showing ink flow and generated pressure loss.

FIG. 8 is a cross-sectional view of the ink communication groove of the ink jet head of FIGS.

FIG. 9 is a sectional view of an ink communication groove of the ink jet head of FIGS. 4 to 6;

FIG. 10 is a schematic diagram of a fluid flowing between circles inscribed in the ink communication grooves of FIGS. 8 and 9;

FIG. 11 is a diagram illustrating a calculated resistance value of an ink fluid with respect to a diameter of an inscribed circle of an ink communication groove.

FIG. 12 is a sectional view of a nozzle hole of the inkjet head of FIGS. 1 to 3 and FIGS. 4 to 6;

FIG. 13 is a sectional view of a nozzle hole of a conventional inkjet head.

FIG. 14 is a diagram showing a calculated value of the pressure loss of the ink fluid in the ink communication groove, the volume of the ejected ink droplet, the volume of the ejected ink droplet, and the drive for obtaining the normal ejection of the ink communication grooves of the ink jet heads of the first and second embodiments and the conventional ink jet head. The figure which shows the comprehensive evaluation result of voltage and injection performance.

FIG. 15 shows a calculated value of the pressure loss of the ink fluid in the ink communication groove, the volume of the ejected ink droplet, the volume of the ejected ink droplet, and the drive for obtaining the normal ejection of the ink communication grooves of the ink jet heads according to the first and second embodiments. The figure which shows the continuation of the comprehensive evaluation result of voltage and injection performance.

FIG. 16 is a diagram showing a comparison result of high-density arrangement, high-speed operation, power consumption, and discharge energy in a piezoelectric conversion element and an electrostatic conversion element of a conventional thermo-mechanical conversion element and an electro-mechanical conversion element.

FIG. 17 is a side sectional view of a conventional edge shooter type ink jet head.

18 is a front view of the inkjet head of FIG. 17 as viewed from the ink ejection side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink-jet head 2 Substrate 3 Electrode 4 Gap 5 Vibration plate 6 Liquid chamber member 7 Top plate member 8 Nozzle forming member 9 Nozzle hole 10 Pressure chamber 11 Common ink liquid chamber 12 Ink supply path 13, 30 Ink communication groove 20 Ink droplet

Claims (3)

[Claims] A plurality of pressure chambers filled with ink;
The top plate member formed with an ink flow path for supplying ink to at least each of the pressure chambers and an ink communication groove for discharging ink in each of the pressure chambers and joined to one surface of each of the pressure chambers, and the top plate member A nozzle forming member formed of a separate member and having a nozzle hole communicating with the ink communication groove, and a diaphragm provided in a part of each of the pressure chambers are vibrated by electrostatic attraction to form ink in the pressure chamber. And an electrostatic conversion element for discharging the ink from the nozzle hole through the ink communication groove, wherein the ink communication groove has an inscribed circle having a diameter of 3 in a direction orthogonal to the ink flow direction.
An ink jet head, wherein the diameter of the nozzle hole is smaller than the diameter of an inscribed circle of the ink communication groove. 2. An ink jet head according to claim 1, wherein said ink communication groove has a substantially quadrangular cross section in a direction orthogonal to a flow direction of said ink. 3. The nozzle forming member is formed of a metal member manufactured by an electroforming method, and the nozzle hole has a cross-sectional shape in a direction orthogonal to a flow direction of the ink from an ink discharge side to an ink inflow side. 3. The ink jet head according to claim 1, wherein an angle between a tangential direction of an inner wall surface of the nozzle hole and an ink ejection direction is continuously increased.