JP2000079688A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low power consumption ink jet recorder where an ink drop is made to fly by utilizing ultrasonic radiation pressure. SOLUTION: An ultrasonic wave generating source, i.e., a piezoelectric element 1, comprises a laminate of n layers (n>=2) of substantially the same thickness arranged while alternating the direction of polarization and the piezoelectric elements 1 are arranged in series acoustically. Respective piezoelectric layers are also arranged in series electrically by forming electrodes 2, 3 on the opposite end faces in the direction of lamination.

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 recording an image by forming liquid ink into droplets and flying on a recording medium, and more particularly to a sound pressure of an ultrasonic beam radiated by a piezoelectric element. The present invention relates to an ink jet recording apparatus that ejects ink droplets on a recording medium by ejecting ink droplets on the recording medium.

[0002]

2. Description of the Related Art An apparatus for recording an image by forming an image point by making liquid ink into small particles called droplets and flying the recording medium has been put to practical use as an ink jet printer. This inkjet printer is
Compared to other recording methods, it has the advantage of less noise and does not require processing such as development and fixing, and is widely used as plain paper recording technology.

[0003] A number of ink jet printer systems have been devised so far. In particular, a system in which ink droplets are ejected by the pressure of steam generated by the heat of a heating element (for example, JP-B-56-9429 and JP-B-61-59911) ), And a method in which an ink droplet is caused to fly by a pressure pulse due to displacement of a piezoelectric body (for example, Japanese Patent Publication No. 53-12138).

[0004] These ink jet printers fly ink from the tip of a nozzle. For this reason, the nozzle type inkjet printer has a problem that local concentration of the ink occurs due to evaporation and volatilization of the solvent in the ink, and the nozzle is clogged. Further, it is difficult for the conventional ink jet printer to reduce the particle diameter of the ink droplet to be ejected (diameter of 20 μm or less), and it is not easy to increase the resolution.

In order to overcome these drawbacks, IBM TDB, Vol. 16, Vol. 16 discloses a method in which ink is ejected from an ink surface using the sound pressure of an ultrasonic beam generated by a piezoelectric element formed as a thin film piezoelectric layer. No.4, pp.1168 (1973-10),
USP-4308547 (1981), JP-A-63-166548, JP-A-63-312
157, JP-A-2-84443 and the like have been proposed. However, these methods have a problem that the image recording speed cannot be increased.

Therefore, the present inventors have attempted to increase the printing speed by sequentially moving a plurality of element groups of a piezoelectric element array formed by a plurality of individual electrodes by switching electronic switches. He proposed Japanese Patent Application No. Hei 6-238102 and others. However, a piezoelectric element with high ultrasonic transmission efficiency generally has a large dielectric constant, and a large current flows when a constant voltage necessary for flying a droplet is applied, resulting in increased power consumption. However, there was a problem that it was damaged.

[0007]

As described above, the ink jet recording apparatus using ultrasonic waves can achieve high image quality without nozzle clogging, and according to the proposal of the present inventors, it is possible to increase the printing speed. Although it can be achieved, there is a problem that the power consumption is large when applying a constant voltage necessary for flying a droplet, and particularly in the case of a piezoelectric element array, the power consumption is large.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an ink jet recording apparatus in which power consumption is reduced by laminating piezoelectric elements.

[0009]

According to the present invention, a plurality of piezoelectric layers having substantially the same thickness are stacked so that the polarization directions of the adjacent piezoelectric layers in the thickness direction are opposite to each other. One end face of the multilayer piezoelectric element array having a common electrode and the other end face forming an individual electrode, ink, and ultrasonic waves radiated from at least a part of the multilayer electrode array of the multilayer piezoelectric element array near the ink liquid level. This is an inkjet recording apparatus provided with a converging means for converging. Further, according to the present invention, a plurality of piezoelectric layers having substantially the same thickness are stacked so that the polarization directions of the adjacent piezoelectric layers in the thickness direction are opposite to each other, and one end surface in the thickness direction is a common electrode, and the other end surface. Provided with a laminated piezoelectric element array having individual electrodes formed thereon, ink, and a focusing means for focusing ultrasonic waves radiated from at least a part of the laminated electrode array of the laminated piezoelectric element array in the vicinity of the ink liquid surface. This is an inkjet recording apparatus. Further, the present invention provides a laminated piezoelectric element array in which laminated piezoelectric elements are arranged at a predetermined pitch perpendicular to the thickness direction, ink, and ultrasonic waves radiated from at least a part of the laminated electrode array of the laminated piezoelectric element array. An ink jet recording apparatus comprising a converging means for converging near the ink liquid surface. Further, an acoustic matching layer for acoustic matching between the laminated piezoelectric element or the laminated piezoelectric element array and the ink may be formed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an ink jet recording apparatus using a laminated piezoelectric element array according to the present invention, and its structure will be described. In FIG. 1, a plurality of ultrasonic wave generating elements in which electrodes formed on both end surfaces of two laminated piezoelectric layers are arranged in an array form are used. To fly. The plurality of elements at this time are referred to as a simultaneous drive element group. This group of simultaneous driving elements may be provided at a plurality of places instead of one place. A common electrode 2 and an individual electrode 3 are formed on both end surfaces of the laminate of the two piezoelectric layers 1,
This is formed on the backing material 8. The laminate, the common electrode 2 and the individual electrodes 3 are collectively referred to as a laminated piezoelectric element. In the case of piezoelectric ceramics such as zircon / lead titanate or lead titanate, the laminating method is an integral firing in which an internal electrode (not shown) is formed on a green sheet of the piezoelectric ceramic by screen printing or the like and a plurality of sheets are stacked and fired. The method is mainly used for bonding with a bonding method using an adhesive (not shown).
The layers may be sequentially laminated by the D method or the like. In FIG. 1, a laminated piezoelectric element manufactured by an integral firing method or an adhesive method is formed on a backing material 8 on which individual electrodes 7 are formed, using an adhesive (not shown). Accordingly, both the individual electrode 3 formed on the piezoelectric layer 1 and the individual electrode 7 formed on the backing material 8 are aligned and adhered, and the individual electrode 3 and the individual electrode 7 are conducted. When a laminated piezoelectric element is formed by a sputtering method or a CVD method, since the piezoelectric element is formed directly on the individual electrode 7 formed on the backing material 8, the individual electrode 3 becomes unnecessary. An acoustic matching layer / acoustic lens 4 is formed on the common electrode 2, and a groove based on the Fresnel zone theory is formed in parallel with the main scanning direction to also serve as an acoustic lens. The ink liquid chamber 5 is formed by the acoustic matching layer / acoustic lens 4, the side wall, and a portion surrounded by a slit.
Ink 6 is full. The drive circuit 9 is formed on the backing material 8 and is connected to the common electrode 2 and the individual electrodes 7, that is, the individual electrodes 3 via a wiring pattern (not shown).

FIG. 2 is a sectional view in a direction (sub-scanning direction) perpendicular to the arrangement direction (main scanning direction) of the laminated piezoelectric element array of FIG. FIGS. 2 (a) and 2 (b) show the case where there is no acoustic matching layer in a laminated structure of two layers and three layers, respectively, and FIGS. 2 (c) and 2 (d) show the case where the acoustic matching layer is formed. FIG.
And FIG. 4 show a modified example of the ultrasonic focusing means in the sub-scanning direction.
Represents a concave piezoelectric element, and FIG. 4 represents a concave acoustic lens.
5 and 6 are cross-sectional views of only the laminated piezoelectric element and the acoustic lens portion in the main scanning direction. FIG. 5 shows an array type in which only the electrodes are divided and the piezoelectric body is integrated, and FIG. 6 also separates the piezoelectric element. Configuration. FIGS. 7 and 8 are perspective views showing another configuration of the ink jet recording apparatus according to the present invention, in which one droplet of ink is ejected from one piezoelectric element. Fig. 7
(a) and (b) show a case where a piezoelectric element is formed on a supporting substrate (backing material), (a) shows a case of a Fresnel lens, and (b) shows a case of a concave lens. 8 (a) and 8 (b) show an acoustic lens component also serving as a support substrate, and FIG. 8 (a) shows a Fresnel lens configuration,
(b) shows the case of a concave lens configuration. FIG. 9 is a cross-sectional view of an ink jet recording apparatus configured to fly one drop of ink from one piezoelectric element as shown in FIGS.
(b) is BB ′ of the Fresnel lens configuration of FIG. 8 (a), FIG. 9 (c),
(d) shows a surface cut by CC ′ of the concave lens configuration of FIG. 8 (b). FIG. 7B is a cross-sectional view taken along the line AA ′ in FIG.

The present inventors have made various evaluations, such as printing quality and printing speed, using a prototype ink jet recording apparatus. As a result, in the case of a single-layer piezoelectric element, for example, in the case of an array configuration as shown in FIG. 1, the power consumption of the piezoelectric element increases, and in some cases, the acoustic matching layer / acoustic lens is peeled off by heat, ink It was recognized that the instability of the droplet flight became remarkable. So far, lead titanate-based piezoelectric ceramics with a relative dielectric constant of about 200 have been used, but in order to reduce power consumption, lithium niobate and piezoelectric polymers with a small dielectric constant have been studied. However, it has been found that the flying efficiency of the ink droplets is deteriorated and the load on the drive circuit is increased, for example, the drive voltage must be increased. Therefore, we examined the flight conditions of the ink droplets again, and found that the flight efficiency of the ink droplets depends on the sound pressure of the ultrasonic waves radiated into the ink when the beam width and the driving frequency near the focal point are fixed. . Further studies have led to the discovery that the multilayer piezoelectric element shown below is effective as a configuration having both low power consumption in the piezoelectric element and radiation sound pressure required for ink droplet flying. The configuration is such that all the piezoelectric layers have substantially the same thickness, the polarization directions of the adjacent layers are reversed, and electrodes are formed on both end surfaces. That is, an n-layer piezoelectric body having substantially the same thickness t is electrically and acoustically connected in series. In this case, the resonance frequency is equal to that of a single-layer piezoelectric body having a thickness t, whereas
The impedance becomes n times. It was confirmed that when a drive signal as shown in FIG. 10 was applied to the ink jet recording apparatus composed of the laminated piezoelectric elements, the same drive voltage would produce almost the same sound pressure as in the case of the one-layer configuration. That is, it was found that the flying efficiency of ink droplets did not change even though the power consumption of the piezoelectric element was reduced to 1 / n.

The material of the piezoelectric layer 1 is not particularly limited.
For example, the dielectric constant, the frequency constant, the workability, the manufacturing method (growing method), etc. are determined in consideration of the ultrasonic frequency and the size of the element. Specifically, zircon / lead titanate (P
Ceramics such as ZT) and lead titanate (PT), and polymers such as copolymers of vinylidene fluoride and ethylene trifluoride;
Single crystals such as lithium niobate and piezoelectric semiconductors such as zinc oxide are used. The electrodes formed on the piezoelectric element may be formed by a thin film method using Ti, Ni, Al, Cu, Au, or the like by vapor deposition or sputtering, or a printing method using screen printing in which glass frit is mixed with a silver paste or the like. When stacking piezoelectric ceramics by integral firing, it is necessary to form internal electrodes, but basically, a high melting point metal,
Specifically, noble metals such as Pt, Ag-Pd, Ni, W and the like are used. In the case of forming by adhesion, a low-viscosity adhesive is more desirable in order to reduce the influence of the adhesive layer thickness,
Epoxy resin or the like is used.

In order to achieve acoustic matching between the piezoelectric element and the ink, it is desirable to form an acoustic matching layer. The acoustic impedance of the acoustic matching layer is close to the square root of the product of the acoustic impedance Zp of the piezoelectric element and the ink Zi. As the matching material, an epoxy resin, a polyimide, a material mixed with fibers for changing the acoustic impedance, or a mixture with an alumina powder or a tungsten powder is used. Further, a SiO2 film or the like may be formed by a sputtering method, a CVD method, or the like. The thickness tm is given by the following equation, and before and after the thickness tm is allowed within a range not departing from the gist of the present invention, specifically, within ± 20%.

[0016]

(Equation 1) Here, n is an integer equal to or greater than zero, and λm is a wavelength in the acoustic matching layer determined by the ultrasonic frequency. However, in the case of the matching layer constituting the Fresnel lens, the following expression is almost satisfied.

[0017]

(Equation 2) Where λink is the wavelength of the ultrasonic wave in the ink.

Next, the present invention will be described based on embodiments.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Specific examples will be described below. The piezoelectric material is a lead titanate-based ceramic having a relative dielectric constant of 200, and the frequency is 50 MHz (the thickness of one layer is 50 μm).
A layer structure was adopted. First, a Ti / Au electrode was sputtered on both sides of a piezoelectric material with a length of 11 cm and a thickness of about 0.3 mm to a thickness of 0.05 mm.
μm and 0.5 μm, and polarization treatment was performed by applying an electric field of 2 kV / mm. Two identical products were prepared and bonded with an epoxy resin so that the polarization directions were opposite.
Thereafter, one of the layers was polished to a thickness of 50 μm.
Subsequently, a Ti / Au electrode was formed by sputtering, and an individual electrode was formed by etching, and the width of one element was 65 μm,
The electrode spacing was set to 20 μm (the arrangement pitch of the individual electrodes was 85 μm). The number of individual electrodes is 1250 elements corresponding to A6 size horizontal. This laminate was bonded to a backing material 8 made of glass with an epoxy resin. Then, the thicker piezoelectric body is polished to a thickness of 50 μm, and the effective aperture is 2 mm and the Ti / A
The u common electrodes were formed by sputtering so that their thicknesses were 0.05 μm and 0.5 μm, respectively. Backing material (glass) at both ends in the main scanning direction
Was connected to the wiring pattern formed on the substrate to conduct electricity.
A mixture of epoxy resin and alumina powder was used for the acoustic matching layer and acoustic lens formed in the next step. First, the mixing ratio was adjusted so that the sound speed was around 3 × 10 ³ m / s, the density was 2.20 × 10 ³ kg / m ³ , and the sound speed was 2.95 × 1.
0 ³ m / s was obtained. This was applied to the common electrode surface, cured, and polished to a thickness of 45 μm. Thereafter, a groove having a depth of 1/2 wavelength (about 30 μm) was formed in the main scanning direction so as to have a focal length of 2.7 mm, thereby forming a Fresnel lens. Further, as shown in FIG. 1, an ink chamber was formed so that the distance between the ultrasonic wave emitting surface and the ink liquid surface was approximately 2.7 mm, and a drive circuit was formed to complete an ink jet recording apparatus.

A printing experiment was performed using this ink jet recording apparatus. 16 simultaneous driving elements, 2.7m focal length
Assuming m, the grouping can be expressed as 0 and π, representing signals with opposite phases, respectively, as “π0 π0 ππ0000ππ0 π0
π ”. When A6 size large solid printing was performed,
The power consumption of the piezoelectric element was about 9W, and printing was possible without any problem.
On the other hand, as a comparative example, a single-layer ink jet recording apparatus was manufactured and a similar printing experiment was performed. At the same printing speed, part of the acoustic matching layer / acoustic lens was peeled off from the electrode, making it impossible to print. The power consumption of the piezoelectric element at this time was about 20 W. Solid printing was possible by using another single-layer type ink jet recording apparatus produced in the same manner and reducing the printing speed to about 1/2.

Example 2 Next, an integrally fired laminated piezoelectric material comprising six layers of zirconate / lead titanate piezoelectric ceramics having a relative dielectric constant of 1300 was used. In manufacturing, a green sheet having a thickness in consideration of a shrinkage ratio after firing was used. For the internal electrode
About 10% of co-fabric (zirconic acid / lead titanate powder) in Pt
The mixed paste was printed. The external electrodes were formed by sputtering Ti / Au in the same manner as in Example 1. As shown in FIG. 11, the configuration of the external electrode and the internal electrode was such that the end portions were electrically connected with a conductive paste, and the respective layers were electrically connected in parallel. Polarization was performed in this state, and the rear end was cut so that the piezoelectric layers were electrically connected in series. The thickness of the laminated piezoelectric body was about 0.3 mm.
After that, individual electrodes are formed in the same manner as in the first embodiment,
It was bonded to a backing material made of glass with an epoxy resin. Subsequently, an inkjet recording apparatus was manufactured in the same process as in Example 1.

Next, a printing experiment was performed. The number of simultaneous driving elements and the focal length were 16 and 2.7 m, respectively, as in the case of the first embodiment.
m. When solid printing of A6 size was performed, the piezoelectric element was able to print well with power consumption of about 10 W.

Although the effectiveness of the present invention has been confirmed as described above, when there is no concave piezoelectric body, concave lens, or acoustic matching layer which is a modification of the present invention, not only the electrodes but also the piezoelectric elements are separated to form a gap. Similar effects can be obtained when resin is filled.

[0024]

As described above, in the present invention, a plurality of (n) piezoelectric bodies having substantially the same thickness are stacked so that the polarization directions of adjacent layers are reversed, and electrodes are formed on both end faces. In this case, a laminated piezoelectric body having the same resonance frequency as that of the single-layer configuration can be formed by electrically forming the series configuration. Further, by using this laminated piezoelectric material, substantially the same transmission sound pressure can be obtained at the same driving voltage as in the single-layer structure. Therefore, it is possible to provide an ink jet recording apparatus having the same flying efficiency with n times the impedance, which is extremely effective in reducing power consumption. In other words, as compared with a single-layer structure having the same frequency, the ink droplet ejection cycle can be shortened, so that the printing speed can be increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an ink jet recording apparatus according to the present invention.

FIG. 2 is a sectional view in the sub-scanning direction of the ink jet recording apparatus shown in FIG.

FIG. 3 is a modification of the sub-scanning direction ultrasonic focusing means shown in FIG. 2;

FIG. 4 is a modification of the sub-scanning direction ultrasonic focusing means shown in FIG. 2;

5 is a cross-sectional view of the inkjet recording apparatus shown in FIG. 1 in the main scanning direction (only a laminated piezoelectric element and an ultrasonic focusing unit).

6 is a modification of the cross section in the main scanning direction shown in FIG. 5 (only the laminated piezoelectric element and the ultrasonic focusing means).

FIG. 7 is a perspective view of another ink jet recording apparatus according to the present invention.

FIG. 8 is a perspective view of another ink jet recording apparatus according to the present invention.

FIG. 9 is a sectional view in the sub-scanning direction of another inkjet recording apparatus according to the present invention.

FIG. 10 is a diagram showing an example of a drive signal according to the present invention.

FIG. 11 is a diagram showing an example of an electrode configuration when a body-fired laminated piezoelectric body is manufactured in another ink jet recording apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric layer, 2 ... Common electrode, 3 ... Individual electrode formed in piezoelectric element, 4 ... Sound matching layer and acoustic lens, 5 ... Ink chamber, 6 ... Ink, 7 ... Individual electrode formed in backing material, 8 ... Backing material, 9 ... Drive circuit, 10 ... Polarization direction, 11 ... Acoustic matching layer, 12 ... Fresnel type acoustic lens, 13 ... Filling material, 14 ... Concave surface acoustic lens, 15 ...
Concave surface acoustic lens and support material, 16 ... Fresnel lens type single head, 17 ... Concave lens type single head, 1
8: Fresnel lens type acoustic lens and support material, 19: laminated piezoelectric element, 20: inner and outer electrodes of integrally fired piezoelectric body

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kenichi Mori 1st address, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term (reference) 2C056 EA01 EA25 FA04 2C057 AF03 AF54 AG44 AG48 AG62

Claims (4)

[Claims] 1. A plurality of piezoelectric layers having substantially the same thickness are stacked so that the polarization directions of the adjacent piezoelectric layers in the thickness direction are opposite to each other, and electrodes are formed on both end surfaces in the thickness direction. An ink jet recording apparatus comprising: a laminated piezoelectric element; ink; and a focusing unit for focusing ultrasonic waves radiated from the laminated piezoelectric element in the vicinity of the ink liquid level. 2. A plurality of piezoelectric layers having substantially the same thickness are stacked so that the directions of polarization of the adjacent piezoelectric layers in the thickness direction are opposite to each other, and one end face in the thickness direction has a common electrode, etc. A laminated piezoelectric element array having individual electrodes on the end faces, ink,
An ink jet recording apparatus, comprising: focusing means for focusing ultrasonic waves radiated from at least a part of the laminated electrode array of the laminated piezoelectric element array near the ink liquid surface. 3. A multilayer piezoelectric element array in which the multilayer piezoelectric elements according to claim 1 are arranged at a predetermined pitch in a main scanning direction perpendicular to a thickness direction, ink, and at least a part of the multilayer piezoelectric element array. An ink jet recording apparatus comprising a focusing means for focusing ultrasonic waves radiated from the laminated electrode array in the vicinity of the ink liquid level. 4. An acoustic matching layer for performing acoustic matching between the laminated piezoelectric element or the laminated piezoelectric element array according to claim 1 and ink and ink is formed on the laminated piezoelectric element or on the laminated piezoelectric element. The ink jet recording apparatus according to claim 1, wherein: