JP3139142B2 - Ink jet recording apparatus, ink jet head, and method of measuring ink ejection characteristics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus for ejecting ink droplets only when recording is required and attaching the ink droplets to recording paper.

[0002]

2. Description of the Related Art An ink jet recording apparatus is required to have extremely low noise at the time of recording, capable of high-speed printing,
It has many advantages, such as the use of inexpensive plain paper with high ink flexibility. Among them, the so-called ink-on-demand method, which discharges ink droplets only when printing is necessary, is the type that has received the most attention because it does not require the number of drops of ink that is unnecessary for printing. This ink-on-demand method is described in, for example,
As shown in Japanese Patent No. 734, a print head has nozzle holes arranged in a plurality of rows for discharging ink droplets,
A plurality of independent discharge chambers each communicating with each nozzle hole and part of one wall being a vibration plate, a piezoelectric element as electromechanical conversion means mounted on each vibration plate, and It consists of a common ink cavity for supplying ink, mechanically deflects the diaphragm to reduce the volume of the discharge chamber, and instantaneously increases the pressure in the chamber, so that the ink droplets from the nozzle hole To the recording paper.

[0003]

However, in such a structure of the conventional ink jet recording apparatus, the operation of attaching the piezoelectric element to the outside of the discharge chamber via a glass plate, a plastic plate, or the like constituting a vibration plate is extremely complicated. It takes a lot of time. Also, in general, the piezoelectric element has a large thickness variation, and a thickness variation of the adhesive to the diaphragm also occurs.
The size and speed of ink droplets ejected from the nozzles are different. For this reason, voltage adjustment was performed while performing actual ink ejection evaluation to maintain stable ejection. As a method of evaluating the vibration variation of the diaphragm, there is a displacement measurement by a laser Doppler method. However, in the case of the ink jet recording apparatus, the reflectance of the piezoelectric element is small and the measurement is difficult and cannot be used. Also, measurement from the ink cavity side was difficult when the ink was filled in the cavity.

Further, in order to improve the problem of the ink jet printing apparatus using the above-described piezoelectric element, the above-described diaphragm suction method using static electricity has been applied for a patent (Japanese Patent Application No. 3-23453).
7) Yes. Among them, when an opaque electrode was used, evaluation of the vibration characteristics of the diaphragm from the back side could not be performed by an optical measurement method such as a laser Doppler measurement apparatus.

Accordingly, an object of the present invention is to provide a stable discharge mechanism in a structure employing a driving method utilizing electrostatic force instead of the above-described method using a piezoelectric element as a driving means for a diaphragm in a discharge chamber. The characteristics can be evaluated by a very simple method using a light measuring instrument, etc., and the discharge voltage can be fed back. In addition, it is possible to observe when foreign substances are mixed between the diaphragm and the electrode or when defects due to electric discharge occur, so that the inspection efficiency is improved. Accordingly, an object of the present invention is to provide an ink jet recording apparatus having a structure excellent in mass productivity and inspection efficiency, for example, greatly improving the recording efficiency.

[0006]

A plurality of nozzle holes, a plurality of independent discharge chambers communicating with each of the nozzle holes, and a part of at least one wall of the discharge chamber undergoes mechanical deformation. A diaphragm, a driving unit for driving the diaphragm, and an inkjet head having a common ink cavity for supplying ink to the plurality of ejection chambers, by applying an electric pulse to the driving unit, An electrode substrate formed below the diaphragm is formed by deforming the diaphragm corresponding to the driving unit in a direction in which the pressure of the discharge chamber increases to discharge ink droplets from the nozzle holes toward recording paper. The electrode is made of a transparent conductive film on a transparent substrate.

In the method of manufacturing an ink jet head according to the present invention, a silicon single crystal substrate is subjected to anisotropic etching to form respective main parts (cavities and the like). Then, gold sputtering is performed on the entire surface, and pattern etching is performed by photolithographic etching to form a gap between the diaphragm and the substrate.

In this case, the gap can be formed by etching silicon without etching the glass, or the gap can be formed by other means such as film coating or sputtering. A transparent conductive film is patterned in the recess, and anodic bonding with the silicon is performed.

Further, since the electrode is formed of an ITO or Nesa film, an electrode having a low resistance can be formed, and the responsiveness and the discharge property are greatly improved.

The ink-jet head manufactured in this manner has a transparent substrate on the lower side of the diaphragm and electrodes, so that even if ink is filled in the ink cavity, the vibration characteristics of the diaphragm can be easily evaluated by laser Doppler measurement or the like. it can.

Further, by forming the diaphragm with a transparent electrode, it is possible to easily observe bubbles in the cavity, dust, and other defects.

[0012]

The substrate on which the ink cavity and the like of the present invention are formed is suitably a silicon substrate, and the electrode substrate is suitably borosilicate glass. The reason is that silicon is a single crystal, so that anisotropic etching is possible. For example, when the (100) plane is etched, it can be regularly etched in the direction of 55 °. On the (111) plane, etching can be performed in the 90 ° direction. Therefore, by using this characteristic, it is possible to accurately form main parts such as a nozzle hole, a discharge chamber, an orifice, and a cavity. Finally, the silicon substrate and the electrode substrate are stacked and heated at 300 to 500 degrees Celsius, and a voltage of several hundred volts is applied by using the silicon side as the anode and the electrode substrate side as the cathode to perform anodic bonding. At this time, the glass having a thermal expansion coefficient close to that of silicon is borosilicate glass, and if the thermal expansion coefficient is not close, the substrate cracks due to cooling after anodic bonding.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

(Embodiment 1) FIG. 1 is an exploded perspective view showing a main part of an ink jet recording apparatus according to a first embodiment of the present invention, and a partial cross-sectional view. This embodiment shows an example of an edge inkjet type in which ink droplets are ejected from a nozzle hole at an end of a substrate. FIG. 2 is a cross-sectional side view of the assembled apparatus, and FIG.
It is an arrow A view.

As shown in these drawings, an ink jet head 12 which is a main part of the ink jet recording apparatus 10 is provided.
Has a laminated structure in which three substrates 1, 2, and 3 having a structure described in detail below are stacked and joined.

The intermediate substrate 2 is a silicon substrate, and has a plurality of nozzle grooves 21 formed at equal intervals in parallel from one end on the surface of the intermediate substrate 2 forming the plurality of nozzle holes 4. A concave portion 22 that forms the discharge chamber 6 having the communication bottom wall as the vibration plate 5, a narrow groove 23 for the ink inlet that forms the orifice 7 provided at the rear of the concave portion 22, It has a concave portion 24 that constitutes a common ink cavity 8 for supplying ink to each ejection chamber 6. In addition, a concave portion 25 that constitutes the vibration chamber 9 for mounting an electrode to be described later is provided below the vibration plate 5. The pitch of the nozzle grooves 21 is 0.9 mm, and the width is 70 microns.

The upper substrate 1 bonded to the upper surface of the intermediate substrate 2 is made of borosilicate glass. The nozzle hole 4, the discharge chamber 6, the orifice 7, and the ink cavity 8 are formed by joining the substrate 1. The upper substrate 1 was provided with an ink supply port 14 communicating with the ink cavity 8. The ink supply port 14 is connected to an ink tank (not shown) via a connection pipe 16 and a tube 17.

The lower substrate 3 bonded to the lower surface of the intermediate substrate 2 is made of borosilicate glass. The vibration chamber 9 is formed by bonding the substrates 3 and the lower substrate 3 is connected to the vibration plate 5. At each of the corresponding positions, ITO was sputtered in a shape similar to the shape of the diaphragm by 0.1 μm, and an ITO pattern was formed in the same shape as the shape of the diaphragm 5 to form an electrode 31. The electrode 31 has a lead portion 32 and a terminal portion 33. Further, the terminal portion was sputtered with gold to form an electrode terminal portion 33.
Further, a borosilicate glass sputtered film was coated on the entire surface except for the electrode terminals by 0.2 μm to form an insulating layer 34 for preventing dielectric breakdown and short circuit during driving.

Next, the substrate 1 and the intermediate substrate 2 are set at 300 degrees Celsius,
Anodizing was performed by applying 500 V, and the substrate 2 and the substrate 3 were bonded under the same conditions, thereby assembling an ink jet head as shown in FIG. Further, an oscillation circuit 26 is connected between the intermediate substrate 2 and the terminal portion 33 of the electrode 31, respectively.
0 was configured. The ink 11 is supplied from an ink tank (not shown) to the inside of the intermediate substrate 2 from an ink supply port, and fills the ink cavity 8, the ejection 6, and the like.

In FIG. 2, reference numeral 13 denotes an ink droplet ejected from the nozzle hole 4, and reference numeral 15 denotes a recording paper.

The operation of the embodiment evaluated this time will be described.
When a pulse voltage of 0 V to 100 V is applied to the electrode 31 by the oscillation circuit 26, and the surface of the electrode 31 is positively charged, the corresponding lower surface of the diaphragm 5 is charged to a negative potential. Therefore, the diaphragm 5 bends downward due to the electrostatic attraction. Next, when the electrode 31 is turned off, the diaphragm 5
Is bent downward, so that the ink 11 is supplied from the ink cavity 8 into the ejection chamber 6 through the orifice 7.

Here, when the diaphragm 5 is driven by the electrostatic force as described above, the amount of displacement of the diaphragm 5
The drive voltage and the discharge amount are obtained.

As shown in FIG. 10A, the diaphragm 5 has a short side length 2a and a long side length b, and is supported on four sides by surrounding walls. Displacement w of this thin plate under pressure P
When the aspect ratio (b / 2a) is large, the coefficient approaches 0.5, and the displacement amount depends on a.

W = 0.5 × Pa ⁴ / Eh ³ (1) where w: displacement (m) P: pressure (N / m ³ ) a: half length of short side (m) h: thickness (m) E: Young's modulus (N / m ² , silicon 11 × 10 ¹⁰ N / m)
² ) Adsorption pressure by electrostatic force is P = 1/2 × ε × (V / t) ² where ε: dielectric constant (F / m, dielectric constant in vacuum 8.8)
× ^10-12 F / m) V: Voltage (V) t: The drive voltage V for obtaining the required discharge pressure is V = t (2P / ε) ^1/2 ... (2) Next, in order to obtain the discharge amount, a volume of a kamaboko shape as shown in FIG. 10B is obtained.

Since the volume S = 4/3 × abw, w = 3/4 × S / ab (3) From the equation (1), the equation (3) is obtained by P = 2w × Eh ³ / a ⁴ Substituting P = 3/2 × SEh ³ / a ⁵ b (4) Further, substituting equation (4) into equation (2), V = t × (3Eh ³ S / εb) ^1/2 × (1 / a ⁵ ) ^1/2 (5) That is, Expression (5) is a driving voltage for obtaining the ink ejection amount.

Here, for example, from equations (2) and (5),
When the ink dischargeable area is obtained, the result is as shown in FIG. FIG. 11A shows the short side length 2a (mm) when the long side length b of the silicon diaphragm shown in FIG. 11B is 5 mm, the plate thickness h is 80 microns, and the distance c between the diaphragm and the electrode is 1 micron.
The relationship between the driving voltage (V) and the driving voltage (V) is shown. When the discharge pressure P is 0.3 atm, the dischargeable area 30 is a range indicated by oblique lines in the drawing.

The larger the width of the diaphragm is, the more advantageous it is. However, considering the miniaturization and high density, the width of the nozzle in the pitch direction is as follows.
About 0.004 to 2.0 mm is appropriate. The length of the vibration plate is determined by calculating from the target ink discharge amount, the Young's modulus of silicon, the discharge pressure, and the plate thickness from Expression (4).

As for the thickness of the diaphragm, the width is 1 m.
In the case of about m, about 50 μm or more is required in consideration of the discharge speed. If the thickness is much larger than that, the driving voltage becomes abnormally high as can be seen from the equation (5). If the thickness is too small, the spring property of the diaphragm becomes small, which is disadvantageous for ejecting ink. Actually, it is manufactured by setting appropriate conditions based on the planned nozzle density and driving voltage.

The ink jet head having such a mechanism is ejected by driving at 10 kHz, and FIG.
The laser beam 51 is applied from the back to the diaphragm 5 in the arrangement shown in FIG.
, And the amplitude of the diaphragm was measured with a laser Doppler measuring device 50. When the voltage is changed while ink is ejected, it has become possible to measure the amplitude amount and the change in the ejection amount at the time of ink filling, which were conventionally difficult. As a result, the correlation between the amplitude amount and the ejection amount became clear, so that the voltage setting for stable ejection of ink droplets from each nozzle can be set only by measuring the amplitude amount.

(Embodiment 2) This embodiment shown in FIG. 5 is an edge ink jet type lower substrate 3 like the first embodiment.
Is etched at a position similar to the shape of the diaphragm at each position corresponding to the diaphragm 5 to a depth of 0.7 μm, a Nesa film is formed by CVD, and a Nesa film pattern is formed in the groove to form an electrode 31; A 0.3 micron borosilicate glass sputtered film was formed as an insulating film. Thereafter, assembly was performed in the same manner as in Example 1 to complete an ink jet head, and vibration evaluation was performed.

(Embodiment 3) FIG. 6 is an exploded perspective view showing a main part of an ink jet recording apparatus according to a third embodiment of the present invention, and is a partially sectional view. This embodiment shows an example of a face ink jet type in which ink droplets are ejected from a nozzle plate hole in a surface portion of a substrate. FIG. 7 is a cross-sectional side view of the assembled overall device, FIG.
FIG. 8 is a view taken along line AA of FIG. 7.

As shown in these figures, an ink jet head 42 which is a main part of the ink jet recording apparatus 40 is provided.
Are three substrates 61 and 62 having a structure described in detail below,
It has a laminated structure in which 63 are overlapped and joined.

The intermediate substrate 62 is a (110) silicon substrate having a plane orientation of 280 μm in thickness. The bottom wall made of a transparent conductive film of 5 μm is used as the diaphragm 5 in the discharge chamber 6 of the substrate 62. A narrow groove 23 for forming an orifice 7 provided at the rear of the concave portion 22 for an ink inlet, and a common groove for supplying ink to each ejection chamber 6. Ink cavity 8
Has a concave portion 24. Also, the substrate 6
In FIG. 3, a concave portion 25 that forms a vibration chamber 9 for mounting an electrode described later is provided below the vibration plate 5. Upper substrate 61 bonded to the upper surface of intermediate substrate 62
Used a nozzle plate with a thickness of 100 microns having nozzle holes 4 for discharging SUS ink. The upper substrate 62 has an ink supply port 1 communicating with the ink cavity 8.
4 were provided. The ink supply port 14 is connected to an ink tank (not shown) via a connection pipe 16 and a tube 17.

The lower substrate 63 bonded to the lower surface of the intermediate substrate 62 is made of borosilicate glass. The vibration chamber 9 is formed by bonding this substrate 63, and the lower substrate 63 is attached to the vibration plate 5. At each corresponding position, a shape similar to the shape of the diaphragm is etched by 0.5 μm in depth, and I
The electrode 31 was formed by sputtering TO and forming an ITO pattern in the groove. The electrode 31 has a lead portion 32 and a terminal portion 33. Further, the terminal portion is sputtered with gold, and the electrode terminal portion 33 is formed.
And Further, a borosilicate glass sputtered film was coated on the entire surface except for the electrode terminals by 0.2 μm to form an insulating layer 34 for preventing dielectric breakdown and short circuit during driving.

Next, the intermediate substrate 62 and the terminal portion 33 of the electrode 31
The oscillation circuits 26 were connected between them, thereby forming the ink jet recording apparatus 10.

In this manner, an ink jet head capable of observing the inside of the ink jet head from both the front and rear surfaces of the ink jet head was manufactured.

The ink 11 is supplied from an ink tank (not shown) to the inside of the intermediate substrate 62 from an ink supply port, and fills the ink cavity 8, the discharge chamber 6, and the like.

In FIG. 7, 13 is an ink droplet ejected from the nozzle hole 4, and 15 is a recording paper.

Next, a pulse voltage of 0 V to 100 V is applied to the electrode 31 by the oscillation circuit 26 as in the first embodiment.
The inkjet head was able to be driven.

In this embodiment, by making the diaphragm and the electrode transparent, it is possible to observe the cause of ink ejection instability during ink ejection, and to understand the sedimentation state and the like in the case of pigment-dispersed color ink. .

(Embodiment 4) FIG. 7 shows an improved embodiment when the specific resistance of the transparent conductive film is large. That is, the diaphragm 5
Only the lower electrode portion 70 is made of a transparent conductive film, and the other is a metal wiring 71 having a low resistance such as gold, which particularly leads to improvement in frequency response and ink droplet ejection speed.

[0042]

The effects of the present invention are as follows.

A plurality of nozzle holes, a plurality of independent discharge chambers communicating with each of the nozzle holes, and a diaphragm in which at least one wall of the discharge chamber undergoes mechanical deformation. A driving unit for driving the vibration plate, and an inkjet head having a common ink cavity for supplying ink to the plurality of ejection chambers, and the driving unit corresponds to the driving unit by applying an electric pulse to the driving unit. Deforming the diaphragm in a direction in which the pressure of the discharge chamber increases,
In the one in which ink droplets are ejected from the nozzle hole toward recording paper, the electrode substrate formed under the diaphragm is a transparent substrate, and the electrode uses a transparent conductive film, so that a stable ejection characteristic can be obtained by an optical measuring device or the like. Can be evaluated by a very simple method, the discharge voltage can be fed back, and even if a foreign substance is mixed between the diaphragm and the electrode or a defect due to electric discharge is observed, the inspection efficiency is greatly improved. An inkjet recording apparatus having a structure excellent in mass productivity and inspection efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a main part of an ink jet recording apparatus according to a first embodiment of the present invention, with a part thereof broken away.

FIG. 2 is a sectional side view after assembling of the ink jet recording apparatus according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional side view taken along the line AA of the assembled ink jet recording apparatus according to the first embodiment of the present invention.

FIG. 4 is a sectional side view showing a measurement state after assembling the ink jet recording apparatus according to the first embodiment of the present invention.

FIG. 5 is a sectional side view after assembling of an ink jet recording apparatus according to a second embodiment of the present invention.

FIG. 6 is an exploded perspective view showing a main part of an ink jet recording apparatus according to a third embodiment of the present invention, partially cut away.

FIG. 7 is a sectional side view after assembling of an ink jet recording apparatus according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional side view taken along the line AA of the assembled ink jet recording apparatus according to the third embodiment of the present invention.

FIG. 9 is a sectional side view after assembling an ink jet recording apparatus according to a fourth embodiment of the present invention.

FIG. 10A is an explanatory diagram of a dimensional relationship of a rectangular diaphragm. (B) is an explanatory diagram for obtaining a discharge pressure and a discharge amount.

FIG. 11A is a diagram illustrating a relationship between a short side length of the diaphragm and a drive voltage in the case of the diaphragm dimensions illustrated in FIG.
(B) is a diaphragm dimensional diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper substrate 2 Intermediate substrate 3 Lower substrate 4 Nozzle hole 5 Vibration plate 6 Discharge chamber 7 Orifice 8 Ink cavity 9 Vibration chamber 10 Ink jet recording device 11 Ink 12 Ink jet head 13 Ink droplet 14 Ink supply port 15 Paper 16 Connection pipe 17 Tube Reference Signs List 21 nozzle groove 22 concave portion 23 narrow groove 24 concave portion 25 concave portion 26 oscillation circuit 30 dischargeable region 31 electrode 32 lead portion 33 terminal portion 34 insulating film 35 connection line 40 inkjet recording device 42 inkjet head 50 laser Doppler measuring device 51 laser light 61 nozzle Plate 62 Intermediate substrate 63 Lower substrate 70 ITO 71 Metal film

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Yotsuya 3-5-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (56) References JP-A-2-289351 (JP, A) JP-A Sho 56-105777 (JP, A) JP-A-56-118872 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (14)

(57) [Claims] A plurality of nozzle holes, a plurality of independent discharge chambers communicating with each of the nozzle holes, and an ink cavity for supplying ink to each of the discharge chambers through an orifice; An ink jet recording apparatus that ejects ink droplets by deformation of a diaphragm that forms a part of at least one wall of a discharge chamber due to electrostatic force, wherein a transparent electrode for generating an electrostatic force faces the diaphragm. And an ink jet recording apparatus formed on a transparent substrate. A plurality of nozzle holes, a plurality of independent ejection chambers communicating with each of the nozzle holes, and an ink cavity for supplying ink to each of the ejection chambers through an orifice; An ink jet recording apparatus that ejects ink droplets by deformation of a diaphragm that forms a part of at least one wall of a discharge chamber due to electrostatic force, wherein a transparent electrode for generating an electrostatic force faces the diaphragm. and it is formed on a transparent substrate, an ink jet recording apparatus to the surface of the discharge chamber-side surface of the opposite side and characterized by being configured so as to be observed from the transparent substrate side of the diaphragm. 3. The ink jet recording apparatus according to claim 1, wherein the transparent substrate is made of borosilicate glass. In the ink jet recording apparatus according to any one of claims 4] claims 1 to 3, an ink jet recording apparatus, wherein the transparent electrode is made of ITO or Nesa film. 5. The ink jet recording apparatus according to claim 1, wherein said diaphragm is made of a transparent conductive film. 6. An intermediate substrate having a first concave portion forming a part of a discharge chamber; an upper substrate joined to the intermediate substrate and forming the discharge chamber together with the first concave portion; A lower substrate, which is provided with an electrode which is joined and is substantially parallel to the diaphragm formed at the bottom of the first concave portion via a gap, and which is provided with a voltage between the diaphragm and the electrode; A driving unit for deforming the vibration plate by the obtained electrostatic force, an ink jet recording apparatus that ejects ink droplets from nozzle holes by deformation of the vibration plate, wherein the electrode is a transparent electrode, An ink jet recording apparatus, wherein the lower substrate is a transparent substrate. 7. An intermediate substrate having a first concave portion forming a part of a discharge chamber; an upper substrate joined to the intermediate substrate and forming the discharge chamber together with the first concave portion; A lower substrate, which is provided with an electrode which is joined and is substantially parallel to the diaphragm formed at the bottom of the first concave portion via a gap, and which is provided with a voltage between the diaphragm and the electrode; A driving unit for deforming the vibration plate by the obtained electrostatic force, an ink jet recording apparatus that ejects ink droplets from nozzle holes by deformation of the vibration plate, wherein the electrode is a transparent electrode, An ink jet recording apparatus, wherein the lower substrate is a transparent substrate, and the diaphragm is configured to be observable from the lower substrate side. 8. The ink jet recording apparatus according to claim 6, wherein said lower substrate is made of borosilicate glass. In the ink jet recording apparatus according to any one of claims 9 claims 6 to 8, wherein the electrode is ITO
Alternatively, an ink jet recording apparatus comprising a Nesa film. 10. The ink jet recording apparatus according to claim 6, wherein said diaphragm is made of a transparent conductive film. 11. The ink jet recording apparatus according to claim 6, wherein a portion of the electrode facing the diaphragm is a transparent conductive film, and the other portion is a metal wiring. Inkjet recording apparatus. 12. An ink jet head used in the ink jet recording apparatus according to claim 1. 13. The discharge characteristic of the ink jet head according to claim 12, wherein the diaphragm is irradiated with laser light from an electrode provided opposite to the diaphragm, and the amplitude of the diaphragm is measured by the reflected light. A method for measuring ink ejection characteristics, characterized in that the method is evaluated by: 14. An ink jet recording apparatus, wherein a voltage of each nozzle is set based on a result evaluated by the ink discharge characteristic measuring method according to claim 13.