JPH1191095A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance ink droplet flight efficiency and to increase a recording speed in an ink jet recording apparatus emitting ink droplets by the radiation pressure of ultrasonic waves to record an image. SOLUTION: An ink jet recording apparatus has an ink liquid holding chamber 19, an ultrasonic generation means consisting of a piezoelectric member 12 and piezoelectric elements constituted of a pair of counter electrodes 13, 14 respectively formed on the opposed surfaces of the piezoelectric member 12, a drive means 16 for driving the piezoelectric elements and an ultrasonic generation means containing an ultrasonic converging lens member 18 converging ultrasonic waves generated from the ultrasonic generation means to the vicinity of the liquid surface of an ink liquid. The electrodes 14 are present within a piezoelectric member surface region wherein the respective ends thereof in a sub-scanning direction are less than the length corresponding to the thickness of the piezoelectric elements from the respective ends of the electrodes 3 and first and second sound insulating members 21a, 21b insulating ultrasonic waves are respectively provided in the regions corresponding to the respective end parts of the electrodes 14.

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 ink droplets into droplets and flying them onto a recording medium. The present invention relates to an ink jet recording apparatus that ejects droplets to fly on a recording medium.

[0002]

2. Description of the Related Art An apparatus for forming an image point and recording an image by forming an ink droplet into droplets and flying on a recording medium has been put to practical use as an ink jet printer.
This ink-jet printer has the advantages that it has less noise than other recording methods and does not require processing such as development and fixing, and has thus attracted attention as a plain paper recording technique. Many ink jet printer systems have been proposed up to now. In particular, the pressure of steam generated by the heat of the heating element disclosed in Japanese Patent Publication No. 56-9429 and Japanese Patent Publication No. 61-59911 is disclosed. Representative methods include a method of flying ink droplets and a method of flying ink droplets by a pressure pulse due to displacement of a piezoelectric body disclosed in Japanese Patent Publication No. 53-12138.

[0003] However, in these systems, local concentration of the ink tends to occur locally due to evaporation and volatilization of the solvent.
Because the individual nozzle corresponding to each resolution is thin,
There is a problem that the nozzle is easily clogged. In particular, in the method using the pressure of the vapor, the adhesion of insoluble matter caused by a thermal or chemical reaction with the ink or the like, and in the method using the pressure due to the displacement of the piezoelectric body, complicated methods in the ink flow path or the like are used. The structure makes it easier to induce clogging. Serial scanning heads using tens to hundreds of tens of nozzles can reduce the frequency of clogging, but line scanning heads that require thousands of nozzles have a stochastic probability. Clogging occurs at a very high frequency, which is a major problem in terms of reliability. Further, these systems have a disadvantage that they are not suitable for improving the resolution.

In order to overcome these drawbacks, there has been proposed a system using ultrasonic waves in which ink droplets fly from an ink liquid surface using the pressure of an ultrasonic beam generated from a thin-film piezoelectric material (IBM). TDB, vol.
No. 4,1168 (1973-10), JP-A-63
JP-A-162253, JP-A-63-166548,
JP-A-63-212157, JP-A-2-1844
43, etc.). Since this method is a so-called nozzleless method that does not require a nozzle for each individual dot or a partition wall between ink flow paths, there is no problem of clogging and recovery from it, which was a major obstacle in forming a line head. . In addition, this method can stably fly an ink droplet having a very small diameter, and is therefore suitable for high resolution. However, the method using these ultrasonic waves has a problem that the flying efficiency of the ink droplets is low, so that the image recording speed cannot be improved.

Further, in a typical head structure of a conventional ultrasonic type ink jet recording apparatus, an acoustic lens, particularly a Fresnel lens, which constitutes an ultrasonic focusing means has a support for an ink liquid holding chamber for containing and holding an ink liquid. Since it also functions as a member, it is sufficiently thicker than the piezoelectric body in terms of imparting mechanical strength, and has the same thickness or more than the depth of the ink liquid. In such a structure, the ultrasonic waves radiated from the piezoelectric element cause large attenuation and scattering when propagating inside the Fresnel lens due to the thick Fresnel lens, and the ultrasonic waves are efficiently radiated into the ink liquid. It is difficult. In particular, when high-frequency ultrasonic waves are radiated to fly small-diameter ink droplets, the effects of attenuation and scattering of ultrasonic waves in the Fresnel lens are extremely large.

Another problem is that ultrasonic waves are irradiated into the ink liquid from portions other than the effective lens portion due to irregular reflection generated inside the Fresnel lens. In order to solve this, a portion other than the effective lens portion of the Fresnel lens is covered with a side wall of an ink chamber or the like so as not to come into direct contact with the ink liquid. However, if a certain obstacle such as an ink chamber is provided near the effective lens portion in this way, the ultrasonic waves radiated into the ink liquid are strongly reflected at the interface between the ink liquid and the obstacle, and other ultrasonic waves are emitted. Interfere with each other and the focusing is disturbed.

As described above, in the conventional system and structure,
It is difficult to make ink droplets fly efficiently, and therefore, it is necessary to apply an extra voltage to the piezoelectric element, and it is necessary to lengthen the voltage application time. As a result, power consumption is increased, and the image recording speed cannot be increased.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem by improving the flying efficiency of ink droplets with low power consumption while using ultrasonic waves, thereby driving the piezoelectric element. It is an object of the present invention to shorten the time from when the ink droplet flies to the ink droplet and to increase the recording speed.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention firstly provides an ink liquid holding chamber for holding an ink liquid, a piezoelectric body and a piezoelectric body which is opposed to both surfaces of the piezoelectric body. An ultrasonic wave generating means including a plurality of piezoelectric elements formed of a pair of first and second electrodes and acoustically connected to the ink liquid; a driving means for driving the ultrasonic wave generating means; An ultrasonic focusing means including an ultrasonic focusing lens member formed on a sound wave generating means and focusing an ultrasonic wave generated by the ultrasonic wave generating means near a liquid surface of the ink liquid;
Of the pair of electrodes, the first electrode has a piezoelectric element whose end in a direction orthogonal to the arrangement direction of the piezoelectric elements has a length equal to or less than a length corresponding to the thickness of the piezoelectric element from each corresponding end of the second electrode. First and second sound insulating members for shielding ultrasonic waves are provided in regions corresponding to the respective ends of the second electrode in a direction orthogonal to the arrangement direction of the piezoelectric elements, which are present in the body surface region. An ink jet recording apparatus is provided.

According to the present invention, secondly, there are provided an ink liquid holding chamber for holding an ink liquid, and a plurality of piezoelectric members each comprising a piezoelectric member and a pair of first and second electrodes disposed opposite to both surfaces of the piezoelectric member. Including a piezoelectric element, ultrasonic generating means acoustically connected to the ink liquid, driving means for driving the ultrasonic generating means, formed on the ultrasonic generating means,
An ink jet recording apparatus comprising: an ultrasonic focusing means including an ultrasonic focusing lens member that focuses an ultrasonic wave generated from the ultrasonic wave generating means near a liquid surface of the ink liquid; The first electrode has a structure in which each end in a direction orthogonal to the direction in which the piezoelectric elements are arranged is present in a piezoelectric body surface region exceeding a length corresponding to the thickness of the piezoelectric element from a corresponding end of the second electrode. An ink jet recording apparatus is provided. In this case, the effective lens aperture W _L of the ultrasound focusing lens member, the thickness T of the piezoelectric
_P and the overlap width W of the pair of counter electrodes in the sub-scanning direction
_E is preferably satisfy the relationship represented by the following formula _{W L ≧ W E + 2T P} (1).

In the present invention, the ultrasonic focusing lens member preferably includes a Fresnel lens. In the present invention, it is preferable that the ultrasonic focusing lens member also has a function as an acoustic matching layer.

The present inventors have found that an ink jet recording apparatus which discharges ink droplets from the ink liquid surface by the radiation pressure of an ultrasonic beam and flies over a recording medium to record an image cannot be achieved by a conventional method. In order to increase the recording speed and increase the resolution, a plurality of piezoelectric elements are arranged at predetermined intervals, and some of the piezoelectric elements (drive elements)
And a driving means (linear electronic scanning means) for converging an ultrasonic beam near the ink liquid surface to fly an ink droplet by moving the driving element group in a predetermined direction by applying a predetermined phase difference to the ink. An inkjet recording device has been proposed.

Further, in order to suppress a decrease in flying efficiency due to attenuation and scattering of ultrasonic waves in the lens caused by a thick acoustic lens in the above-mentioned conventional ink jet recording apparatus, its supporting function is separated from the acoustic lens. Thus, a structure has been proposed in which a support member is provided on the back surface of a piezoelectric element separately from an acoustic lens. In this case, since the acoustic lens, particularly the Fresnel lens, does not need to have a function as a supporting member, the thickness thereof may be the minimum necessary for focusing the ultrasonic wave, and the thickness is equivalent to the thickness of the piezoelectric body. It is sufficient that the thickness is sufficiently smaller than the depth. As a result, attenuation and scattering of ultrasonic waves in the acoustic lens can be reduced to a negligible level, so that the flying efficiency of ink droplets can be improved, and the recording speed can be increased. When the ultrasonic focusing means is composed of a Fresnel lens, the thickness of the unevenness is set to (2n + 1) of the wavelength of the ultrasonic wave in the Fresnel lens.
/ 4 times (n is an integer of 0 or more)
In addition, by using a material having an acoustic impedance value close to the square root of the product of the acoustic impedance of the piezoelectric body and that of the ink liquid as the Fresnel lens material, the Fresnel lens can also have a function as an acoustic matching layer. Thereby, the reflection of the ultrasonic wave at the interface is reduced, and the flying efficiency can be further improved.

However, in a conventional structure in which a counter electrode is formed on the piezoelectric body over the entire width thereof and an ultrasonic focusing lens member having an effective lens diameter of the same width as the piezoelectric body is formed thereon, the piezoelectric body is It has been found that when processed into a predetermined shape, characteristic deterioration is likely to occur due to depolarization or the like near the cut portion of the piezoelectric body. In addition, it has been found that such a structure easily causes a short circuit between the opposing electrode positions at the ends of the piezoelectric body.

The inventors of the present invention have conducted intensive studies on the influence of the width of the counter electrode on the width of the piezoelectric body and the effective lens aperture of the ultrasonic focusing lens member. The first electrode has a length equal to or less than the length corresponding to the thickness of the piezoelectric element from each corresponding end of the other electrode (second electrode) in a direction (sub-scanning direction) orthogonal to the arrangement direction of the piezoelectric elements. Are provided so as to be present in the surface area of the piezoelectric body, and the first and second areas for shielding ultrasonic waves are provided in areas corresponding to respective ends of the second electrode in the sub-scanning direction.
Of the ink droplets caused by depolarization or the like, for example, strong side lobes are generated at locations other than the main beam position (focal position) and obstruction of ultrasonic focusing. It has been found that a reduction in flight efficiency can be prevented. In this case, the first electrode can be formed shorter than the second electrode, or can be formed to have the same length as the second electrode.

Further, the present inventors have proposed a method in which the first electrode has a piezoelectric surface whose end in the sub-scanning direction exceeds a length corresponding to the thickness of the piezoelectric element from each corresponding end of the second electrode. It has been found that the property deterioration caused by the depolarization or the like can be prevented by providing the element in the region.
In this case, the effective lens aperture W _L of the ultrasound focusing lens member, and the thickness T _P of the piezoelectric body, the overlapping width W _E of a pair of opposed electrodes, the following formula _{(1): W L ≧ W} E + 2T P It has been further found that satisfying the relationship shown in (1) not only can prevent the occurrence of the side lobe, but also can suppress the occurrence of a short circuit between the opposing electrodes at the end of the piezoelectric body. In this case, the width of the ultrasonic focusing lens member can be equal to the width of its effective lens area, and furthermore,
It can be equal to the width of the piezoelectric body.

When the ultrasonic focusing lens is a Fresnel lens, the position of each groove from the center is determined by the following equation (2) or (3) as known in the art.
Is formed at a position corresponding to the radius r (a) of the Fresnel ring zone represented by

[0018] r (a) = [(2a -1) λ i / 2 × {F + (2a-1) λ i / 8}] 1/2 (2) r (a) = (aλ i F) 1 / ² (3) In equations (2) and (3), λ _i is the wavelength of the ultrasonic wave in the ink liquid, F is the focal length (depth of the ink liquid), a
Is an integer of 1 or more.

In the present invention, when the ultrasonic focusing lens is a Fresnel lens, the effective lens aperture is a radius r defined by the above equation (2) or (3) corresponding to the number n of the formed grooves. (N) is equivalent to twice.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same parts are denoted by the same reference numerals. FIG. 1 is a perspective view of a recording head unit of an ink jet recording apparatus according to one embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a region including a piezoelectric element and an ultrasonic focusing lens member in a head portion of the ink jet recording apparatus shown in FIG.

The head portion of the ink jet recording apparatus shown in FIGS. 1 and 2 has a flat piezoelectric member 12 constituting an ultrasonic wave generating means on a support member 11. The piezoelectric body 12 is made of lead titanate (P
T), ceramic materials such as zircon / lead titanate (PZT), polymer materials such as a copolymer of vinylidene fluoride and ethylene trifluoride, single crystal materials such as lithium niobate,
It can be formed of a piezoelectric semiconductor material such as zinc oxide. Further, the support member 11 can be formed of a material such as glass.

On the lower surface of the piezoelectric body 12, a plurality of individual electrodes 13 separated from each other are formed. The piezoelectric body 12 is functionally divided into a plurality of piezoelectric elements by the individual electrodes 13. On the other hand, on the upper surface of the piezoelectric body 12,
An integral common electrode 14 is formed. These electrodes 13
And 14 are titanium, nickel, aluminum, copper,
A metal material such as gold can be formed as a thin film by vapor deposition or sputtering. Alternatively, these electrodes 13 and 1
4 can also be formed by printing a glass frit mixed with a silver paste by a screen printing method and baking it. The individual electrode 13 and a portion corresponding to the common electrode 14 constitute each counter electrode.

On one end side of the support member 11, at the same interval as the individual electrodes 13 formed on the lower surface of the piezoelectric body 12,
A plurality of array electrodes 15 are formed, and each array electrode 15 on the support member 11 and each individual electrode 13 on the lower surface of the piezoelectric body 12 are aligned and pressure-bonded via a conductive adhesive, and It is connected to the. The array electrode 15 on the support member 11 is connected to a drive circuit 16 disposed on an end of the support member 11 by a bonding wire 17, and the common electrode 14 formed on the upper surface of the piezoelectric body 12 is also , Driving circuit 16.

An ultrasonic focusing acoustic lens member 18 is provided so as to cover the entire surface of the piezoelectric body 12 with the common electrode 14 interposed therebetween. The lens member 18 has a plurality of grooves (four grooves 1 in FIGS. 1 and 2) at a predetermined pitch based on Fresnel's ring theory at a symmetrical position from the center thereof.
8a to 18d, 18a and 18b, 18c and 18d
Are formed symmetrically), but are formed in parallel with the arrangement direction of the piezoelectric elements divided by the individual electrodes 13 (corresponding to the main scanning direction). The depth of each groove is set to (2 m) of the wavelength of the ultrasonic wave in the lens member 18 so that the phase of the ultrasonic wave emitted from the top and bottom surfaces of the groove is shifted by a half wavelength.
+1) / 4 (m is an integer of 0 or more). The groove is formed in parallel with the arrangement direction (corresponding to the main scanning direction) of the piezoelectric elements divided by the individual electrodes.

In the present invention, it is preferable that the Fresnel lens member 18 also functions as an acoustic matching layer for acoustic matching between the piezoelectric element and the ink liquid. For this purpose, the square root of the product of the Fresnel lens member acoustic impedance Z _m and the acoustic impedance Z _i of the acoustic impedance Z _p and the ink liquid of the piezoelectric body (Z _m =
(Z _p × Z _i) is preferably formed of a material having a value close to ^1/2). Examples of such a material include a polymer material such as an epoxy resin and a polyimide, or a mixture of the polymer material with a fiber or a powder such as alumina or tungsten for adjusting acoustic impedance.

On the supporting member 11, the piezoelectric element 1
2. An ink liquid holding chamber 19 for storing a Fresnel lens member 18 and an ink liquid 20 is provided. In the ink liquid holding chamber 19, a side wall surrounding the ink liquid 20 is inclined so as to meet upward from both ends of the Fresnel lens, and the upper part thereof is opened by forming a slit 19a.

As shown best in FIG. 2, the individual electrode 13 formed on the lower surface of the piezoelectric body 12 has a length W1 equal to the width of the piezoelectric body 12. However, in the illustrated example, the common electrode 14 formed on the upper surface of the piezoelectric body 12 is shorter than the piezoelectric body 12 (length W2), and is formed only in the central region excluding both ends of the piezoelectric body 12. I have. Therefore, the portion of the piezoelectric body 12 that functions as each piezoelectric element is only a region corresponding to the common electrode 14. In this case, the lengths W3 and W4 of the end surface regions of the piezoelectric body exposed by the common electrode 14 are set to be equal to or less than the length corresponding to the thickness of the piezoelectric body 12. In regions corresponding to both ends of the individual electrode, sound insulation members 21a and 21b for shielding ultrasonic waves are provided, respectively. FIG.
In the example shown in FIG. 2, the sound insulation members 21a and 21b not only cover the above-mentioned exposed region of the piezoelectric body 12, but are provided over the end of the common electrode 14. Such sound insulation members 21a and 21b are made of a material different from the lens member 18 and can be made of a material capable of shielding ultrasonic waves radiated from the piezoelectric body 12, for example, a silicone resin.

By adopting such a structure, it is possible to shield the ultrasonic wave which can be oscillated from the piezoelectric portion corresponding to the periphery of the common electrode 14, so that the generation of the side lobe is suppressed and the efficient ink liquid is formed. Droplets can be made to fly. In addition, since the length of the piezoelectric body region where the sound insulation members 21a and 21b are provided is equal to or less than the thickness of the piezoelectric body 12, the lens member 18 can be provided widely, and further effective use of ultrasonic waves is achieved. You can also. Further, since the region of the piezoelectric body 12 beyond the common electrode 14 is covered with the sound insulating members 21a and 21b, a short circuit between the common electrode 14 and the individual electrode 13 is also prevented.

Next, an example of a method of focusing ultrasonic waves and a method of driving a piezoelectric element in the above-described ink jet recording apparatus will be described. The method of focusing ultrasonic waves in the arrangement direction (main scanning direction) of the piezoelectric elements 11 is based on a partial piezoelectric element group (simultaneous driving element group) of the piezoelectric elements composed of the piezoelectric bodies 12 operated by the individual electrodes 13 in an individual array. , A predetermined delay time is set for them, and they are simultaneously driven. At that time, the phase of the ultrasonic wave radiated from each piezoelectric element is controlled, and the intensity of the ultrasonic wave becomes locally strong near the ink liquid level. , That is, to focus. Specifically, the delay time at the center of the simultaneous driving element group is the longest, and the delay time is gradually reduced toward the outside. On the other hand, a method of focusing ultrasonic waves in a direction perpendicular to the arrangement direction of the arrayed piezoelectric elements (in the present invention, referred to as a sub-scanning direction) is performed by an acoustic lens, here, a Fresnel lens 18. By focusing the ultrasonic waves from two directions,
Ink droplets are ejected and fly from any position on the ink surface with ultrasonic pressure. The flying position of the ink droplet can be changed by electronically scanning the piezoelectric elements that are driven simultaneously. Further, by providing a plurality of the simultaneous driving element groups among the piezoelectric elements arranged in an array, a plurality of ink droplets can be caused to fly at the same time.

The other is based on the Fresnel zone theory,
The number of simultaneously driven elements is divided into two groups, and the timing of driving one is shifted by π in phase with respect to the other. This is called Fresnel driving.

If the degree of convergence of ultrasonic waves in the sub-scanning direction is high, only a plurality of elements are simultaneously driven in the main scanning direction.
Even if the ink droplets fly without giving a delay time to converge, there is no need to give a delay time.

FIG. 3 shows a second embodiment of the present invention, and is different from FIGS. 1 and 2 except that the lens member 18 is formed beyond the common electrode 14 at both ends. FIG. 3 is a perspective view of a head unit similar to the head unit of the illustrated inkjet recording apparatus. Also in this case, the sound insulation members 21a and 21a
1b is provided.

FIG. 4 shows a head similar to the head of the ink jet recording apparatus shown in FIGS. 1 and 2, except that the common electrode 14 is formed with a width equal to the length of the individual electrode 13. In this case, the sound insulating members 21a, 21b
Are formed so as to cover at least the end of the common electrode 14. As described above, by forming the common electrode 14 with a width equal to the length of the individual electrode 13, the oscillation region of the ultrasonic wave can be expanded.

It should be noted that, in FIGS.
At least one of the ink liquid holding chambers 1a and 21b.
It is also possible to use a side wall surrounding the 9 ink liquid 20. FIG. 5 shows that the sound insulation members 21 a and 21 b are connected to the lens member 18.
1 and 2 except that the thickness is set to a thickness larger than the wavelength of the ultrasonic wave (for example, a thickness larger than 60 μm). 3 shows a head unit similar to the head unit of the apparatus.

In the embodiment shown in FIG. 5, the lens member having the arrangement shown in FIG. 3 may be formed to extend beyond the common electrode at both ends. FIG. 6 shows the sound insulating member 21.
5 shows a head unit similar to the head unit of the ink jet recording apparatus shown in FIG. 4, except that a and 21b are formed in the form shown in FIG.

FIG. 7 shows that the sound insulation members 21a and 21b are roughened on the surface of the lens member (reference numerals 211a and 211a, respectively).
11b), and shows a head unit similar to the head unit of the ink jet recording apparatus shown in FIGS.

In the embodiment shown in FIG. 7, the lens member having the arrangement shown in FIG. 3 may be formed to extend beyond the common electrode at both ends. FIG. 8 shows the sound insulating member 21.
The surfaces of the lens members a and 21b are roughened as in the case of FIG. 7 (represented by reference numerals 211a and 211b, respectively).
Except for the configuration, a head unit similar to the head unit of the ink jet recording apparatus shown in FIG. 4 is shown.

FIGS. 9 and 10 show an ink jet recording apparatus according to still another embodiment of the present invention.
FIG. 10 is an enlarged sectional view showing a region including a piezoelectric element and an ultrasonic focusing lens member of the ink jet recording apparatus shown in FIG. 1 and FIG. 2,
The same reference numerals are used, and the details are the same as those described with reference to FIGS.

In this recording apparatus, as best shown in FIG. 10, the length WE of the common electrode 14 is shorter than the length W1 of the individual electrode 13, and the piezoelectric material exposed by the common electrode The lengths W3 'and W4' of the twelve end surface regions have a length longer than the length corresponding to the thickness of the piezoelectric body. In this case, the same effects as those of the ink jet recording apparatus described with reference to FIGS. 1 to 8 can be obtained without providing a sound insulating member.

Further, in the examples shown in FIGS. 9 and 10,
In addition to the grooves 18a to 18d, grooves 18e to 18j are formed in both end regions beyond the common electrode 14 on the lens member 18 of the individual electrode based on Fresnel's ring theory. The width of the area 18 _eff (effective lens diameter) is set to be larger than the overlapping width of the individual electrode 13 and the common electrode 14 in the sub-scanning direction (in this case, the width of the common electrode 14 in the sub-scanning direction) by a predetermined degree. I have.

More specifically, as shown in FIG. 10, individual electrodes 13 and 14 are formed on the piezoelectric body 12 as described with reference to FIGS. 1 and 2, and the lens member 18 is also formed as shown in FIGS. However, as the Fresnel lens groove is formed beyond the area of the common electrode 14 as described above, the effective lens aperture W of the lens member 18 is increased.
_L is greater than the width W _E of the common electrode 14 in the sub-scanning direction. In this case, it has been found that it is important that the degree to which the effective lens diameter becomes large is also defined by the thickness T _P of the piezoelectric body 12. That is, the effective lens aperture W _E is the formula (1): W _L ≧ W preferably satisfies the relationship represented by _E + 2T _P.

This relationship applies to the case where the Fresnel lens is formed with an effective aperture larger than the overlapping width in the sub-scanning direction of the opposing electrodes formed on both surfaces of the piezoelectric body, in other words, the effective lens area formed on the lens member. However, when the width is formed to be larger than the overlap width of the counter electrode, it can be said that the size should be increased.

When the effective lens aperture has such a relationship, prevention of short-circuit and suppression of side lobe generation as described with reference to FIGS. 1 and 2 are more effectively achieved. FIG. 11 shows that the lens member 18 is formed to be larger than the width of the common electrode 14 in the sub-scanning direction but smaller than the width of the piezoelectric body 12 in the sub-scanning direction, so that the number of Fresnel lens grooves is reduced. FIG. 11 is a schematic cross-sectional view showing a head unit similar to the head unit of the inkjet recording apparatus shown in FIGS. 9 and 10. Also in this case, the same effects as those shown in FIGS. 3 and 4 can be obtained.

Although the embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to these embodiments. For example, the case where the length (width) of the individual electrode 13 is the same as the width of the piezoelectric body 12 in the sub-scanning direction and the width of the common electrode 14 is smaller than the width of the piezoelectric body 12 in the sub-scanning direction has been described. It goes without saying that the same effect can be obtained even if the width relationship between the individual electrode 13 and the common electrode 14 is reversed.

[0045]

The present invention will be further described below with reference to examples. Examples 1 and 2 In this example, an ink jet recording apparatus having the structure shown in FIGS. 9 and 10 was manufactured.

As the piezoelectric body 12, a lead titanate-based piezoelectric ceramic having a thickness of about 0.5 mm and a relative dielectric constant of 200 was used. Ti / A is formed on both surfaces of the piezoelectric body by sputtering.
u electrode layers each having a thickness of 0.05 μm, and a thickness of 0.05 μm.
The piezoelectric body 12 was formed so as to have a thickness of 2 μm, and an electric field of 3 kV / mm was applied to perform polarization processing of the piezoelectric body 12. Then, the piezoelectric body 1
The electrode layer on one of the two surfaces was patterned by etching to form the individual electrodes 13 so that the width of one piezoelectric element was 60 μm and the interval between the individual electrodes was 25 μm (the arrangement pitch of the individual electrodes was 85 μm). . The width of the piezoelectric body 12 in the sub-scanning direction was 5 mm.

On the other hand, Ti / A
The array electrode 15 of u was formed. Next, in a state where the individual electrodes 13 on the piezoelectric body 11 and the array electrodes 15 on the support member 11 were aligned, they were bonded with a conductive epoxy resin, and pressure was applied so that both electrodes were conducted.

Next, after the piezoelectric body was polished to a thickness of 50 μm, a common electrode 14 made of aluminum was formed to a thickness of 0.3 μm by sputtering. At this time, the length of the electrode in the sub-scanning direction was 2.0 mm.

Next, in order to produce a Fresnel lens 18 also serving as an acoustic matching layer, a mixture of an epoxy resin and an alumina powder is blended at a ratio such that the sound speed becomes about 3 × 10 ³ m / s, and a density of 2 .20 × 10 ³ kg / m ³ ,
A mixture having a sound speed of 2.95 × 10 ³ m / s was obtained. This is applied on the upper surface of the common electrode 14 and cured to have a thickness of 45 μm.
It was polished to become. Thereafter, a groove having a depth of 1/2 wavelength (about 30 μm) was formed in parallel with the main scanning direction so that the focal length became 2.5 mm, thereby forming the Fresnel lens 18.
The width of the groove forming region (lens diameter) is 2.1 mm which is 0.1 mm wider than the common electrode width (corresponding to the overlapping width of the counter electrode) of 2.0 mm (Example 1), and 0.2 mm wider. 0.2 mm (Example 2). Then, an ink liquid holding chamber 19 is provided so that the distance between the ultrasonic wave emitting surface and the ink liquid surface is approximately 2.5 mm, the ink liquid is filled, and a drive circuit 16 is installed to provide two types of ink jet inks of the present invention. The recording device was completed.

Comparative Examples 1-2 The lens diameter was 2.0 mm (same as the width of the piezoelectric body:
Two types of ink jet recording apparatuses were produced in the same manner as in Example 1 except that the thickness was set to Comparative Example 1) or 2.05 mm (Comparative Example 2).

The samples 4 prepared in Examples 1 and 2 and Comparative Examples 1 and 2
A flying experiment of ink droplets was performed using two recording devices. In the flying experiment of the ink droplet, the driving frequency (50 MHz) and the driving voltage (20 V) were set to be the same, and the application time of the driving burst signal at that time was used as the evaluation standard of the flying efficiency. FIG. 12 shows the minimum burst application time required to obtain a stable flight of the ink droplet. In FIG. 12, point a
Represents the result of Example 1, point b represents the result of Example 2, and point c represents the result of Example 2.
Indicates the result of Comparative Example 1, and point d indicates the result of Comparative Example 2.

As shown in FIG. 12, when the width of the effective lens area is made larger than the overlap width of the counter electrode, by satisfying the relationship of the above equation (1) (Examples 1 and 2), It can be seen that stable ink droplet flight can be achieved with a shorter burst application time than in the case of Comparative Example 2, and almost constant ink droplet flight can be achieved with high efficiency. When the overlap width of the counter electrode and the width of the effective lens area are the same (Comparative Example 1), when the width of the effective lens area is larger than the overlap width of the counter electrode (Examples 1 and 2 and Comparative Example 2). It can also be seen that the flying efficiency of ink droplets is much lower than that.

[0053]

As described above, according to the present invention, it is possible to suppress the generation of a sound wave that interferes with the focusing of ultrasonic waves, and to make ink droplets fly more effectively. The present invention provides an ink jet recording apparatus capable of achieving low power consumption and low power consumption. In the ink jet recording apparatus of the present invention, a short circuit between the opposing electrodes can be prevented.

[Brief description of the drawings]

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

FIG. 2 is an enlarged schematic cross-sectional view of a region including a piezoelectric body and an ultrasonic focusing lens member of a head unit of the ink jet recording apparatus shown in FIG.

FIG. 3 is a perspective view of a head section of another ink jet recording apparatus according to the present invention.

FIG. 4 is a perspective view of a head section of another inkjet recording apparatus according to the present invention.

FIG. 5 is a perspective view of a head section of another inkjet recording apparatus according to the present invention.

FIG. 6 is a perspective view of a head section of another inkjet recording apparatus according to the present invention.

FIG. 7 is a perspective view of a head section of another inkjet recording apparatus according to the present invention.

FIG. 8 is a perspective view of a head section of another inkjet recording apparatus according to the present invention.

FIG. 9 is a perspective view of a head section of still another inkjet recording apparatus according to the present invention.

10 is an enlarged schematic cross-sectional view of a region including a piezoelectric body and an ultrasonic focusing lens member of a head portion of the ink jet recording apparatus shown in FIG.

FIG. 11 is a schematic cross-sectional view of a head section of still another inkjet recording apparatus according to the present invention.

FIG. 12 is a graph showing the results of Examples according to the present invention together with the results of Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Support member 12 ... Piezoelectric element 13 ... Individual electrode 14 ... Common electrode 15 ... Array electrode 16 ... Drive circuit 18 ... Ultrasonic focusing lens member 19 ... Ink liquid holding chamber 19a ... Slit 20 ... Ink liquid

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenichi Mori 1st Toshiba R & D Center, Komukai, Kawasaki City, Kanagawa Prefecture (72) Inventor Hitoshi Yagi Komukai Toshiba, Saiwai District, Kawasaki City, Kanagawa Prefecture No. 1 Town, Toshiba R & D Center (72) Inventor Noriko Yamamoto No. 1, Komukai Toshiba Town, Koyuki-ku, Kawasaki, Kanagawa Prefecture, Japan Toshiba R & D Center

Claims (8)

[Claims] An ink liquid holding chamber for holding an ink liquid, and a plurality of piezoelectric elements each comprising a piezoelectric body and a pair of first and second electrodes disposed opposite to both surfaces of the piezoelectric body, Ultrasonic wave generation means acoustically connected to the ink liquid, Driving means for driving the ultrasonic wave generation means, Ultrasonic waves formed on the ultrasonic wave generation means and generated by the ultrasonic wave generation means An ink jet recording apparatus comprising: an ultrasonic focusing unit including an ultrasonic focusing lens member that focuses the ink liquid in the vicinity of the liquid surface; wherein the first electrode of the pair of electrodes is orthogonal to the direction in which the piezoelectric elements are arranged. Each end in the direction in which the piezoelectric element is present is located in a piezoelectric body surface area not more than the length corresponding to the thickness of the piezoelectric element from each corresponding end of the second electrode, and the second end in a direction orthogonal to the arrangement direction of the piezoelectric elements. electrode Wherein the area corresponding to each end, an ink jet recording apparatus characterized by first and second sound insulating member for shielding the ultrasonic wave, respectively. 2. The ink jet recording apparatus according to claim 1, wherein the first electrode has a shorter length than the second electrode in a direction orthogonal to an arrangement direction of the piezoelectric elements. 3. An ink jet recording apparatus according to claim 1, wherein an effective lens diameter of said lens member is shorter than said first electrode in a direction orthogonal to an arrangement direction of said piezoelectric elements. . 4. The ink jet recording apparatus according to claim 3, wherein said first and second sound insulation members also cover each end of said first electrode. 5. An ink jet recording apparatus according to claim 1, wherein said first electrode has a length substantially equal to said second electrode in a direction orthogonal to an arrangement direction of said piezoelectric elements. apparatus. 6. The ink jet recording apparatus according to claim 5, wherein said first and second sound insulation members are provided on said first electrode. 7. An ink liquid holding chamber for holding an ink liquid, and a plurality of piezoelectric elements each including a piezoelectric body and a pair of first and second electrodes disposed opposite to both surfaces of the piezoelectric body, Ultrasonic wave generation means acoustically connected to the ink liquid, Driving means for driving the ultrasonic wave generation means, Ultrasonic waves formed on the ultrasonic wave generation means and generated by the ultrasonic wave generation means An ink jet recording apparatus comprising: an ultrasonic focusing unit including an ultrasonic focusing lens member that focuses the ink liquid in the vicinity of the liquid surface; wherein the first electrode of the pair of electrodes is orthogonal to the direction in which the piezoelectric elements are arranged. An ink jet recording apparatus characterized in that each end in the direction in which the surface of the piezoelectric element extends from a corresponding end of the second electrode exceeds a length corresponding to the thickness of the piezoelectric element. And wherein said effective lens aperture W of the ultrasound focusing lens member _L, a thickness T _P of the piezoelectric body, said pair of electrodes of the overlapping width W _E in the direction orthogonal to the array direction of the piezoelectric element , the following equation _{W L ≧ W E + 2T P} (1) ink jet recording apparatus according to claim 7, characterized by satisfying the relationship represented by.