JP3469036B2 - Ink jet recording device - 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 recording an image by forming liquid ink into droplets and ejecting the liquid ink onto a recording medium, and in particular, the pressure of an ultrasonic beam emitted by a piezoelectric element is used. The present invention relates to an inkjet recording device that ejects ink droplets and causes them to fly onto a recording medium.

[0002]

2. Description of the Related Art An apparatus for forming image points by recording liquid ink into small particles called droplets and flying them on a recording medium for recording has been put to practical use. This ink jet printer has the advantages that it is less noisy than other recording methods and does not require processing such as development and fixing, and is attracting attention as a plain paper recording technology.

Many ink jet printer systems have been devised up to now, but 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, Japanese Patent Publication No. 56-9429 and Japanese Patent Publication No. 61-5991
No. 1), a method of ejecting ink droplets by a pressure pulse generated by displacement of a piezoelectric body (for example, Japanese Patent Publication No. 53-121).
No. 38) is a typical example.

In these ink jet printers, since the ink is ejected from the tip of the nozzle, there is a problem that the evaporation of the solvent in the ink liquid locally concentrates the ink and the nozzle is clogged. Further, in the conventional inkjet printer, it is difficult to reduce the particle diameter of the flying ink droplet (diameter is 20 μm or less), and it is difficult to increase the resolution.

In order to overcome these problems, a system has been proposed in which the pressure of an ultrasonic beam generated by a piezoelectric element composed of a thin film piezoelectric layer is used to fly an ink droplet from the ink surface (IBM). TDB, Vol. 1
6, No. 4, pp. 1168 (1973-10), U.S. Pat. No. 4,308,547, JP-A-63-166548.
Japanese Patent Laid-Open No. 63-121157). However, in this type of inkjet recording apparatus, since the depth of the ultrasonic beam generated is shallow, it is necessary to delicately control the ink liquid level, and there is a problem that the apparatus becomes complicated accordingly.

[0006]

SUMMARY OF THE INVENTION Therefore, according to the present invention, it is possible to easily increase the focusing depth of the ultrasonic beam, and thus the ink jet recording which does not require fine control of the ink liquid level without complicating the apparatus. An object is to provide a device.

[0007]

In order to solve the above-mentioned problems, the present invention is, firstly, a super structure comprising an ink holding chamber for holding an ink liquid and a piezoelectric element acoustically connected to the ink liquid. An ultrasonic wave focusing means, a driving means for driving the piezoelectric element, and an ultrasonic wave focusing formed on the ultrasonic wave generating means for focusing the ultrasonic waves generated from the ultrasonic wave generating means near the liquid surface of the ink liquid. In the ink jet recording apparatus including the means, the ultrasonic focusing means is composed of a Fresnel lens having a groove formed based on the Fresnel ring zone theory, and the Fresnel lens has the depth of the groove as d. At this time, there is provided an ink jet recording apparatus having a concave curved surface with a curvature R of 2 μm <R <d at the bottom.

Secondly, the present invention comprises an ink holding chamber for holding an ink liquid, an ultrasonic wave generating means composed of a piezoelectric element acoustically connected to the ink liquid, and a driving means for driving the piezoelectric element. An ultrasonic focusing unit that is formed on the ultrasonic generating unit and focuses the ultrasonic waves generated from the ultrasonic generating unit near the liquid surface of the ink liquid, The means is
An ink jet characterized by comprising a Fresnel lens having a groove formed based on the Fresnel ring zone theory, the Fresnel lens having a portion in which the width of the groove expands in the direction of the opening of the groove. A recording device is provided.

The present inventors, in an ink jet recording apparatus having a Fresnel lens as an ultrasonic wave focusing means for focusing the ultrasonic waves generated from the ultrasonic wave generating means, the Fresnel lens has a short focal length like the cylindrical lens. Since the depth becomes shallower, it is necessary to keep the ink level constant with accuracy. When the focal length becomes longer, the depth becomes deeper, but the ultrasonic wave is attenuated and the focusing efficiency of the ultrasonic wave becomes worse. . As a result of further research on this, it was concluded that it is essential to deepen the depth of the near focus lens in order to realize both ultrasonic focusing efficiency and simplification of ink level control at the same time. . In order to increase the depth, we thought that it could be achieved by stacking lenses with slightly different focal lengths, and we attempted to provide a part of the unevenness of the Fresnel lens with a part with a different delay time. It was found that a Fresnel lens with a deeper depth can be obtained by forming a concave curved surface with a specific curvature at the bottom of the or, or by sloping the sidewall of the groove, without lowering the sound wave focusing efficiency, and completes the present invention. Came to.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view showing an ink jet recording apparatus according to a first embodiment of the present invention. In this recording apparatus, the flat plate-shaped piezoelectric body 12 that constitutes the ultrasonic wave generating means is a support member (backing member) 1
1 is provided above. The piezoelectric body 12 is formed of a material that can generate ultrasonic waves in response to a predetermined drive signal applied to the piezoelectric body 12. Specifically, the piezoelectric body 12 is a ceramic piezoelectric material such as zircon / lead titanate (PZT) or lead titanate (PT), or a polymer piezoelectric material such as a copolymer of vinylidene fluoride and ethylene trifluoride. , A single crystal piezoelectric material such as lithium niobate, or a piezoelectric semiconductor material such as zinc oxide.

On the lower surface of the piezoelectric body 12, a plurality of individual electrodes 1
3 are arranged apart from each other in the length direction of the piezoelectric body 12. The piezoelectric body 12 is functionally divided into an array by these individual electrodes 13 to form a piezoelectric element array. That is, the piezoelectric element groups corresponding to some of the plurality of individual electrodes 13 of the plurality of individual electrodes 13 are simultaneously driven by the drive circuit described below to cause ink droplets to fly. On the other hand, a common electrode 14 is formed on the upper surface of the piezoelectric body 12. These electrodes 13 and 14 are usually made of Ti, N
A metal material such as i, Al, Cu or Au is formed as a thin film by vapor deposition or sputtering. Alternatively, these electrodes 1
3 and 14 are those in which glass frit is mixed with silver paste or the like and printed in a predetermined shape by a screen printing method,
It can also be formed by baking this.

A piezoelectric body 12 is provided on one end side of the support member 11.
A plurality of array electrodes 15 are formed at the same intervals as the individual electrodes 13 formed on the lower surface of the array electrode 15. Each array electrode 15 on the support member 11 and each individual electrode 13 formed on the lower surface of the piezoelectric body 12 are , Are aligned and crimped via a conductive adhesive (not shown), and are electrically connected. The array electrodes 15 on the support member 11 are connected to the drive circuits 16 arranged in the end regions of the support member 11 by the bonding wires 1
7, and the common electrode 14 formed on the upper surface of the piezoelectric body 12 is also connected to the drive circuit 16 by wiring not shown.

On the piezoelectric body 12 via the common electrode 14, a one-dimensional Fresnel lens 18 (which will be described further below) is provided as an acoustic lens that also serves as an acoustic matching layer. The Fresnel lens 18 is formed by providing at least two grooves 18a to 18f at a predetermined pitch based on the Fresnel ring theory. These grooves 18a to 18f are formed parallel to the arrangement direction (main scanning direction) of the piezoelectric elements sectioned by the individual electrodes 13. The positions where the grooves 18a to 18f are formed are determined by the radius r (a) of the Fresnel ring zone according to the following formula (1) or formula (2).

R (a) = [(2a-1) λ _i / 2 × {F + (2a-1) λ _i / 8}] ^1/2 (1) r (a) = (aλ _i F) ^{1 / 2} (2) In equations (1) and (2), λ _i is the wavelength of the ultrasonic wave in the ink liquid, F is the focal length (depth of the ink liquid), and a
Is an integer of 0 or more.

Then, the grooves 18a of the Fresnel lens 18 ...
Each depth d of 18f is given by the following equation (3). d = n · λ _m / 2 (3) In the formula (3), n is an integer of 0 or more, and λ _m is a wavelength in the Fresnel lens determined by the ultrasonic frequency.

By the way, in order to achieve acoustic matching between the piezoelectric element and the ink liquid, it is desirable that the Fresnel lens 18 also acts as an acoustic matching layer. The acoustic impedance of the Fresnel lens 18 as the acoustic matching layer is the acoustic impedance Z _p of the piezoelectric element and the ink Z _i.
Use a value close to the square root of the product of and. As such an acoustic matching material, an epoxy resin or polyimide, a material in which fibers or the like are mixed in order to change the acoustic impedance, or a mixture with alumina powder or powder such as tungsten is used. Further, a silicon dioxide film or the like may be formed by a sputtering method or a CVD method.

The thickness t _m of the Fresnel lens 18 as the acoustic matching layer, that is, the thickness from the lower surface to the upper surface of the Fresnel lens 18, and the groove bottom surface to the Fresnel lens 1
The thickness up to the lower surface of 8 is calculated by the formula: t _m = (2n +
1) It is preferable to satisfy λ _m / 4 (where n is an integer of 0 or more, and λ _m is the wavelength of the ultrasonic wave in the acoustic matching layer determined by the ultrasonic frequency). Actually, this calculated value ± 20
Thicknesses within% are acceptable.

The thickness t _m of the Fresnel lens 18 as the matching layer is expressed by the formula: t = 1 / (1
It is more preferable that / λ _ink −1 / λ _m ) = (2n + 1) λ _m / 2 (where the wavelength of the ultrasonic wave in the λ _ink ink liquid) is also satisfied.

Referring to FIG. 1 again, an ink holding chamber 19 which is in contact with the Fresnel lens 18 and accommodates the ink liquid 20 is provided on the support member 11. The ink holding chamber 19 has a slit 19a formed on its upper surface and extending in the lengthwise direction of the piezoelectric body 12. Ink drops are slits 19
The ink is ejected from the ink surface at a.

In the present invention, the groove of the Fresnel lens is 2 μm <R <d at the bottom, where d is the depth of the groove.
A concave curved surface is provided with a curvature R of. FIG. 2 is an enlarged cross-sectional view of each of the grooves 18a to 18f of the Fresnel lens 18 (collectively indicated by reference numeral 18n). The Fresnel lens 18 shown in FIG. 2 has a vertical side wall 31,
32 and a horizontal bottom surface 33, and the corner portions 33a and 33b formed by the side walls 31 and 32 and the bottom surface 33 are provided with R with the above curvature.

FIG. 3 is a sectional view showing another form of the groove of the Fresnel lens having the concave curved surface. The groove 18n of the Fresnel lens 18 has a concave surface 3 whose entire bottom surface has the above curvature.
It comprises 3 '.

FIG. 4 is a sectional view showing still another form of the groove of the Fresnel lens having the concave curved surface. The groove 18n of the Fresnel lens 18 has a concave curved surface with the above curvature only in the central portion of the bottom surface.

Now, as shown in FIGS. 2 to 4, by providing a concave curved surface portion with the above curvature on the bottom surface of the Fresnel lens,
It is possible to provide a lens having a deep depth without lowering the sound wave focusing efficiency.

In the present invention, the same effect can be obtained by providing the inclined portion on the side wall of the groove of the Fresnel lens so that the groove expands in the direction toward the opening of the groove. That is, as shown in FIG. 5, the groove 1 of the Fresnel lens 18
The 8n side walls 31 ', 32' are inclined such that the groove expands toward the groove opening (that is, the width b1 of the opening of the groove is larger than the width b2 of the bottom surface).

FIG. 6 is a sectional view showing another form of a Fresnel lens having an inclined portion. The Fresnel lens 18 shown in FIG. 6 has an inclined portion 33a at the corner formed by the vertical side walls 31 and 32 and the horizontal bottom surface 33 that form the groove 18n.
33b is provided.

In the ink jet recording apparatus shown in FIG. 1, the ultrasonic wave generating means is composed of a piezoelectric element array. However, the ultrasonic wave generating means of the present invention is not limited to this, and a so-called single head type is used. It may be one used in the inkjet recording apparatus. In that case,
As shown in FIG. 7, the Fresnel lens is formed in a disc shape, and the grooves 40a to 40c are formed concentrically with respect to the disc 40. The cross section of each groove can have the structure shown in FIGS.

In the ink jet recording apparatus of the present invention, the sound wave radiated from the piezoelectric element driven by the drive circuit is propagated in the ink liquid through the Fresnel lens which also serves as the acoustic matching layer, and the depth is almost the same as the focal length. The ink is condensed near the surface of the ink holding chamber formed so as to form a large pressure, and a large pressure is generated to fly the ink droplet. At this time, sound waves having a phase difference of 180 degrees are emitted from the surface of the Fresnel lens according to the unevenness of the groove, and the unevenness of the groove is formed in the vicinity of the focal point so that the phases of the waves match. Like a cylindrical lens, a Fresnel lens has a shallow depth with a lens having a short focal length, so it is necessary to control the ink surface to a constant level. Damping causes inefficiency, but by providing a concave curved surface on the bottom surface of the groove or sloping the side wall of the groove according to the present invention,
As the focusing depth of the Fresnel lens becomes deeper and the area where the ultrasonic beam becomes minimal becomes wider, the ink droplet flight efficiency does not decrease even if the ink surface height fluctuates to some extent, and stable ink droplet flight is achieved. Can be done.

[0028]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto. Example 1 In this example, an inkjet recording device having the structure shown in FIG. 1 was manufactured. The groove of the Fresnel lens had the structure shown in FIG.

That is, a PbTiO ₃ system piezoelectric ceramic having a relative dielectric constant of 200 is used as the piezoelectric body, and the frequency is 50M.
Hz (thickness 50 μm). Ti on both sides of this piezoelectric body
The thickness of each layer is 0.
Formed to have a thickness of 05 μm / 0.3 μm and 2 kV / m
A polarization process was performed by applying an electric field of m. Then, by etching, the width of one piezoelectric element is 65 μm and the electrode interval is two.
The individual electrodes were formed so as to be 0 μm (arrangement pitch of individual electrodes 85 μm).

The electrode width in the sub-scanning direction, that is, the diameter is 2 m.
m. This piezoelectric element was made into Ti by electron beam evaporation.
/ Au laminated electrode with each layer thickness 0.05μm / 0.3μ
After being formed so as to have a thickness of m, the thickness also serves as a backing member provided with an array electrode formed by etching.
It was attached to a 1 mm glass substrate with an epoxy adhesive. A mixture of epoxy resin and alumina powder is used to form a Fresnel lens that also serves as an acoustic matching layer on the surface of the piezoelectric body opposite to the individual electrodes, and the density is 2.20 × 1.
At 0 ³ kg / m 3 and a sound velocity of 2.95 m × 10 ³ / s, the groove is applied to the electrode so as to have a thickness of 45 μm and cured, and the groove is cut so that the focal length becomes 3.3 mm.
Considering the depth of the acoustic beam, the bottom of the recess has a curvature of 10
The curved surface was processed to have a thickness of μm. At this time, the depth of the groove was 30 μm. An ink holding chamber was provided in this element so that the height of the ink surface was 3.3 mm, and a drive circuit was connected to complete an ink jet recording head. In this recording head, ink droplet flight was confirmed when the high-frequency voltage applied to the piezoelectric body was 25V. Under these conditions, when the ink surface was gradually changed by about 20% with respect to the focal length of 3.3 mm, it was confirmed that the ink droplets were stably ejected in all cases. At this time, the average ink dot diameter is
The dot diameter was about 70 μm, and uniform dots were formed even with variations in the ink surface, and the dot diameter was the same as that of a head using a conventional Fresnel lens.

Example 2 In this example, an ink jet recording apparatus having the Fresnel lens shown in FIG. 7 was produced. The groove of the Fresnel lens had the cross-sectional shape shown in FIG.

That is, a PbTiO ₃ system piezoelectric ceramic having a relative dielectric constant of 200 is used as the piezoelectric body, and the frequency is 50M.
Hz (thickness 50 μm). Ti on both sides of this piezoelectric body
The thickness of each layer is 0.
Formed to have a thickness of 05 μm / 0.3 μm and 2 kV / m
A polarization process was performed by applying an electric field of m. Then, an electrode having a diameter of 2 mm for the signal lead-out line and the effective portion was formed on both surfaces by etching. This piezoelectric element was subjected to EB vapor deposition to form a Ti / Au laminated electrode with a thickness of each layer of 0.05 μm / 0.
1.1 mm that also serves as a backing member provided with an electrode formed by etching after being formed to have a thickness of 3 μm
It was pasted on a thick glass substrate with an epoxy adhesive.
In order to form a Fresnel lens on the surface of the piezoelectric body opposite to the electrode, a concentric pattern of an Al thin film mask was formed, and the glass was etched by RIE to form a Fresnel lens. The etching conditions such as gas composition and pressure were optimized so that a curved surface with a curvature of 5 μm could be processed at the bottom of the recess. The depth of the groove was 20 μm. An ink holding chamber was provided in this element so that the height of the ink surface was 5.4 mm, and a drive circuit was connected to complete an ink jet recording head. In this recording head, ink droplet flight was confirmed when the high-frequency voltage applied to the piezoelectric body was 35V. Under this condition, for a focal length of 5.4 mm,
When the ink surface was gradually changed by about 10%, it was confirmed that the ink droplets stably flew in all cases.

Example 3 In this example, an ink jet recording apparatus having the structure shown in FIG. 1 was produced. The grooves of the Fresnel lens had the cross-sectional shape shown in FIG.

[0034] That is, using a PbTi0 ₃ based piezoelectric ceramic of the specific dielectric constant 200 as the piezoelectric, frequency 50M
Hz (thickness 50 μm). Ti on both sides of this piezoelectric body
/ Au laminated electrode is sputtered and the thickness of each layer is 0.05μ
It was formed to have a thickness of m / 0.3 μm, and a polarization treatment was performed by applying an electric field of 2 kV / mm. After that, individual electrodes were formed by etching so that the width of one element was 65 μm and the electrode interval was 20 μm (arrangement pitch of individual electrodes 85 μm).

The electrode width in the sub-scanning direction, that is, the diameter is 2 m.
m. This piezoelectric element was made Ti / Au by EB vapor deposition.
Epoxy adhesive on a 1.1 mm thick glass substrate also serving as a backing material provided with individual electrodes formed by etching after forming laminated electrodes so that the thickness of each layer is 0.05 μm / 0.3 μm Pasted together. A mixture of epoxy resin and alumina powder was used to form a Fresnel lens that also functions as an acoustic matching layer on the surface of the piezoelectric body opposite to the individual electrodes, and the density was 2.20 × 10 ³ kg / m ³
, With a sound velocity of 2.95 × 10 ³ m / s and applied and cured on the electrode so as to have a thickness of 45 μm.
The groove is cut to 5 mm, but considering the depth of the acoustic wave beam, the width of the top of the recess is 10μ from the bottom.
It was processed so that it would be wider. The depth of the groove was 30 μm. The height of the ink surface is 2.
An ink holding chamber was provided so as to have a thickness of 5 mm, and a drive circuit was connected to complete an ink jet recording head. Under these conditions, when the ink surface was gradually changed by about 10% with respect to the focal length of 2.5 mm, it was confirmed that the ink droplets were stably ejected in all cases.

[0036]

As described above, according to the ink jet recording apparatus of the present invention, the bottom surface of the groove of the Fresnel lens for focusing the ultrasonic waves emitted from the piezoelectric element at a predetermined position on the ink surface is curved. It is possible to increase the depth of the sound wave beam by providing the above or by sloping the side wall of the groove, and it is possible to stably eject the ink droplets without finely controlling the ink liquid surface.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of an inkjet recording apparatus of the present invention.

FIG. 2 is a cross-sectional view showing a first form of a Fresnel lens used in the inkjet recording apparatus of the present invention.

FIG. 3 is a cross-sectional view showing a second form of a Fresnel lens used in the inkjet recording apparatus of the present invention.

FIG. 4 is a cross-sectional view showing a third form of a Fresnel lens used in the inkjet recording apparatus of the present invention.

FIG. 5 is a cross-sectional view showing a fourth form of a Fresnel lens used in the inkjet recording apparatus of the present invention.

FIG. 6 is a sectional view showing a fifth mode of a Fresnel lens used in the inkjet recording apparatus of the present invention.

FIG. 7 is a plan view showing a sixth mode of a Fresnel lens used in the inkjet recording apparatus of the present invention.

[Explanation of symbols]

11 ... Support member 12 ... Piezoelectric body, 13 ... Individual electrode 14 ... Common electrode 18 ... Fresnel lenses 18a-18f, 18n, 40a-40c ... Fresnel lens grooves

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriko Yamamoto 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Toshiba Research & Development Center Co., Ltd. (72) Inventor Hitoshi Yagi Komukai-shiba, Kawasaki-shi, Kanagawa No. 1 in Toshiba Research & Development Center Co., Ltd. (56) Reference JP-A-8-290587 (JP, A) JP-A-7-114393 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) B41J 2/175 B41J 2/015 G10K 11/30

Claims (2)

(57) [Claims] 1. An ink holding chamber for holding an ink liquid, an ultrasonic wave generating means comprising a piezoelectric element acoustically connected to the ink liquid, a driving means for driving the piezoelectric element, and the ultrasonic wave generating means. In an ink jet recording apparatus having an ultrasonic focusing means formed on the ultrasonic focusing means for focusing the ultrasonic waves generated from the ultrasonic generating means in the vicinity of the liquid surface of the ink liquid, the ultrasonic focusing means is a Fresnel ring zone. The Fresnel lens has a groove formed on the basis of theory, and the Fresnel lens has a concave curved surface with a curvature R of 2 μm <R <d at the bottom, where d is the depth of the groove. Characteristic inkjet recording device. Wherein said ultrasonic wave generating means, according to claim 1 Symbol mounting of the ink jet recording apparatus characterized in that it is a piezoelectric element array in which a piezoelectric element in the main scanning direction.