JP3450703B2 - Ink jet recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an ink jet recording apparatus for recording an image by forming liquid ink into droplets and flying them onto a recording medium. The present invention relates to an ink jet recording apparatus that ejects ink droplets by sound pressure of an ultrasonic beam radiated by a piezoelectric element and flies over a recording medium. 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 on a 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. A number of ink jet printer systems have been devised up to now. 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 Japanese Patent Application Laid-Open No. 53-1213.
No. 8) is a typical example. However, since these ink jet printers are of the type in which ink is ejected from the tip of a nozzle, local concentration of the ink occurs due to evaporation or volatilization of a solvent in the ink, and there is a problem that the nozzle is clogged. . Furthermore, it is difficult for these ink jet printers to reduce the diameter of the ink droplet to be ejected (diameter of 20 μm or less), and it is difficult to increase the resolution. In order to overcome these drawbacks, a method has been proposed in which ink is ejected from an ink liquid surface by using the sound pressure of an ultrasonic beam generated by a piezoelectric element constituted as a thin film piezoelectric layer (for example, see, for example, Japanese Patent Application Laid-Open No. H11-157,979). IBM TDB, Vo
l. 16, No. 4,1168 (1973-10),
U.S. Pat. No. 4,308,547, JP-A-63-166
548, JP-A-63-166548, JP-A-63-31157, JP-A-2-184443
Reference). However, these conventional inkjet recording apparatuses using piezoelectric elements have a problem that the image recording speed cannot be improved. Accordingly, the present inventors have made Japanese Patent Application No. Hei 6-238.
Japanese Patent Application Laid-open No. 102-102 and others, a linear electronic scanning type ink jet system in which a plurality of element groups of a piezoelectric element array formed by a plurality of individual electrodes are sequentially moved by switching electronic switches to increase a printing speed. A recording device is proposed. This type of recording apparatus can achieve a high recording speed. However, the present inventors have found that the ink droplets may not fly depending on the wave number of the burst signal for driving the piezoelectric element, or that a plurality of ink droplets may fly at the same time differently than expected. . As described above, an ink jet recording apparatus using ultrasonic waves can achieve high image quality without nozzle clogging, and further increases the recording speed according to the linear electronic scanning method. However, there is a problem that, depending on the piezoelectric element drive signal, the ink droplet may not fly or a predetermined number or more of the ink droplets may fly at the same time. An object of the present invention is to solve such a problem. Ink jet recording in which one drop of ink can be stably ejected by setting the wave number of a burst signal for driving a piezoelectric element within a predetermined range. It is an object to provide a device. SUMMARY OF THE INVENTION The object of the present invention is to provide an ink liquid holding chamber for holding an ink liquid and a burst of a peak value V [Vpp] at a wave number N acoustically connected to the ink liquid. Ultrasonic wave generating means including a piezoelectric element driven by applying a signal voltage, and ultrasonic wave focusing means for focusing the ultrasonic wave generated from the ultrasonic wave generating means near the surface of the ink liquid The diameter of the ultrasonic generating means in the main scanning direction (as defined below) is Ds, the diameter in the sub-scanning direction (as defined below) is Df, the focal length is Fp, and the ink liquid is The wavelength of the ultrasonic wave inside is λ [μ
m], and the amount of ultrasonic attenuation between the ultrasonic radiation surface and the ink liquid surface is a [dB], and {(Fp / Ds) × (Fp / Df)}
^{When 1/2} is Fr, the wave number N is expressed by the following two formulas: 4Fr · λ <N <200Fr · λ (1) and 2 × 10 ⁴ / (10 ^{−a / 10} .V ² ) <N <1 × 10 ⁶ /
(10− ^{a / 10} · V ² ) An ink jet recording apparatus characterized by simultaneously satisfying (2) . In the present invention, when the ultrasonic wave generating means includes a plurality of piezoelectric elements arranged in an array, the main scanning direction refers to the arrangement direction of the plurality of piezoelectric elements. When it is composed of one piezoelectric element, it corresponds to a direction orthogonal to the paper feed direction of the recording paper. The sub-scanning direction corresponds to a direction orthogonal to the main scanning direction. In the present invention, the aperture in the main scanning direction of the ultrasonic wave generating means means that when the ultrasonic wave generating means includes a plurality of piezoelectric elements arranged in an array, a part thereof is driven simultaneously. Pressure at both ends of element group in main scanning direction
It refers to the distance between the outermost ends of the electric elements, and when the ultrasonic wave generating means comprises a single piezoelectric element, it refers to the length in the main scanning direction. In the present invention, the diameter of the ultrasonic wave generating means in the sub-scanning direction is the length of the piezoelectric element in the sub-scanning direction when the ultrasonic wave generating means includes a plurality of piezoelectric elements arranged in an array. In other words, it generally corresponds to the diameter of the ultrasonic focusing means. When the ultrasonic wave generating means is formed of a single piezoelectric element, it refers to the length in the sub-scanning direction, and usually coincides with the diameter in the main scanning direction. Further, the focal length refers to a distance from the ultrasonic wave emitting surface, for example, specifically, corresponds to a distance from the surface of the ultrasonic converging lens. Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a perspective view showing an ink jet recording apparatus according to one embodiment of the present invention. In the recording apparatus shown in FIG. 1, a long flat plate-like piezoelectric body 12 constituting an ultrasonic wave generating means is provided on a support substrate (backing member) 11. Piezoelectric body 1
2 is made of a material capable of generating an ultrasonic wave by a predetermined burst wave voltage driving signal applied thereto, but actually, for example, the dielectric material is changed according to the frequency of the ultrasonic wave and the size of the piezoelectric element. It is determined in consideration of the rate, frequency constant, workability, manufacturing method (such as growth method), and the like. Specifically, the piezoelectric body 12
Are lead zircon / titanate (PZT) and lead titanate (P
T) or the like, formed of 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. Can be. A plurality of stripe-shaped individual electrodes 13 are arranged on the lower surface of the piezoelectric body 12 so as to be separated from each other in the longitudinal direction of the piezoelectric body 12. The piezoelectric body 12 is connected to these individual electrodes 1
3 functionally divides into a plurality of piezoelectric elements. On the other hand, on the upper surface of the piezoelectric body 12, a common electrode 14 formed integrally therewith is formed. These electrodes 13 and 1
No. 4 is usually formed as a thin film from a metal material such as Ti, Ni, Al, Cu, or Au by vapor deposition or sputtering.
Alternatively, the electrodes 13 and 14 can also be formed by printing a mixture of glass frit in a silver paste or the like in a predetermined shape by a screen printing method and baking it. A piezoelectric body 12 is provided at one end of the support substrate 11.
A plurality of array electrodes 21 are formed at the same interval as the individual electrodes 13 formed on the lower surface of the piezoelectric substrate 12. Each array electrode 21 on the support substrate 11 and each individual electrode 13 formed on the lower surface of the piezoelectric body 12 , Are aligned and crimped via a conductive adhesive (not shown), and are electrically connected. The array electrode 21 on the support substrate 11 is connected to each drive circuit 22 disposed in an end region of the support substrate 11 by a bonding wire (not shown), and is formed on the upper surface of the piezoelectric body 12. The common electrode 14 is also connected to the drive circuit 22 by a wiring (not shown). A one-dimensional Fresnel lens 15 as an acoustic lens is provided on the piezoelectric body 12 via the common electrode 14. The Fresnel lens 15 is formed by forming grooves at a predetermined pitch based on Fresnel's ring zone theory. These grooves extend in the arrangement direction (main scanning direction) of the piezoelectric elements divided by the individual electrodes 13, respectively.
They are formed parallel to each other. Incidentally, it is desirable to form an acoustic matching layer in order to perform acoustic matching between the piezoelectric element and the ink liquid 17. The acoustic impedance of the acoustic matching layer is the acoustic impedance Zp of the piezoelectric element and the ink Z
Use the one close to the square root of the product with i. As such a matching material, an epoxy resin, a polyimide, a material mixed with a fiber or the like for changing the acoustic impedance, a mixture with a powder such as an alumina powder or a tungsten, or the like is used. Further, a silicon dioxide film or the like may be formed by a sputtering method, a CVD method, or the like.
In the example shown in FIG. 1, since the Fresnel lens 15 also serves as the acoustic matching layer, the Fresnel lens 15 is formed of such an acoustic matching material. The thickness t _m of the acoustic matching layer is calculated by the following formula: t _m = (2n + 1) λ _m /
4 (where n is an integer of 0 or more, lambda _m the ultrasonic wavelength in the acoustic matching layer which is determined by the ultrasound frequency) is preferably satisfied. In practice, thicknesses within ± 20% of this calculated value are acceptable. When the Fresnel lens 15 also functions as an acoustic matching layer as shown in FIG.
Formula: 1 / (1 / λ _ink −1 / λ _m ) = (2n + 1) λ _m
/ 2 (where λ _ink is the wavelength of the ultrasonic wave in the ink liquid)
Is preferably satisfied. Referring again to FIG. 1, an ink liquid 17 is stored on the support substrate 11 in contact with the Fresnel lens 15.
An ink liquid holding chamber 16 for holding is provided. The ink liquid holding chamber 16 has a slit 16a formed on the upper surface thereof. The ink droplet flies from the ink liquid 17 through the slit 16a. In order to operate the ink jet recording apparatus described with reference to FIG. 1, some of the plurality of piezoelectric elements divided into an array by the individual electrodes 13 are simultaneously driven (at this time, simultaneous driving is performed). A plurality of elements are referred to as a simultaneous driving element group), and ultrasonic waves are generated while scanning the simultaneous driving element group in the main scanning direction while shifting each element, for example. The ultrasonic waves generated from the group of simultaneous driving elements are focused near the ink surface in the main scanning direction. Then, the focusing of the ultrasonic waves in the sub-scanning direction is performed by the Fresnel lens 15, and the ink droplets are made to fly one by one through the slit 16a. The simultaneous driving element group may be provided at a plurality of places instead of one place. Multiple simultaneous drive element groups
If provided, it goes without saying that the
The expressions (1) and (2) should be satisfied at the same time.
You. The present inventors have made various evaluations, such as printing quality and printing speed, using a prototype ink jet recording apparatus. As a result, the drive voltage applied to the piezoelectric element cannot be made too high due to the limitation of the withstand voltage of the recording apparatus in consideration of power consumption and practical price, and the wave number of the burst signal is required for the ink droplet to fly. It has been found that the peak value of N and its driving voltage has a great effect. In addition, the number of simultaneously driven elements cannot be set in a wide range, and several combinations exist when the drive frequency and the drive voltage are determined. As shown in FIG. 2, a burst signal applied to drive the piezoelectric element may be a sine wave (FIG. 2A), a short wave (FIG. 2B), or a sawtooth wave. it can. Further, the polarity may be applied to both the positive electrode side and the negative electrode side as shown in FIG. 2A, or may be applied only to the positive electrode side as shown in FIG. 2B. The present inventors have determined that the optimal range of the wave number N of the burst signal is, in particular, the F number of the piezoelectric element in both the forward and sub scanning directions (ie, the ratio of the focal length to the aperture in the main scanning direction (Fs) and the sub scanning). Of the focal length to the aperture in the direction (F
f), the wavelength of the ultrasonic wave in the ink liquid (λ [μm]),
The peak value (V (Vpp)) of the driving voltage of the piezoelectric element and the amount of ultrasonic attenuation (a [d) between the ink liquid surface and the ultrasonic radiation surface
B]). Further, as a result of examining these parameters, the wave number N of the burst signal is expressed by the following two equations: 4Fr · λ <N <200Fr · λ (1) and 2 × 10 ⁴ / (10 ^{−a / 10} · V ² ) <N <1 × 10 ⁶ / (10 ^{−a / 10} · V ² ) (2) (where Fr is the square root of the product of Ff and Fs) at the same time, the ink droplet is stably formed. Was found to fly. When N is smaller than 4Fr.lambda. In the above equation, the growth of the meniscus on the ink surface may be insufficient and the ink droplet may not fly. On the other hand, N is 200 Fr
If the value is larger than λ, the meniscus may become abnormally high, or two or more ink droplets may fly at the same time. When N is smaller than 2 × 10 ⁴ / (10 ^{−a / 10} · V ² ), the ink droplets may not fly, while N is 1 × 10 ⁶ / (10 ^{-a / 10} · V 2). ^If it is larger than ² ), two or more ink droplets may fly. Equation (2) is given by {2 × 10 ⁴ / (10 ^{−a / 10 .N} )} ^1/2 <V <{1 × 10 ⁶ / (10 ^{−a / 10 .N} )} ^{1 / 2} ... (3) and can be deformed, the equation (3), the one that defines the range of V of when the N is constant. In FIG. 1, the ultrasonic focusing means in the sub-scanning direction has a concave surface as shown in FIGS. 3 and 4 in addition to a Fresnel lens which forms grooves of a predetermined width at a predetermined pitch based on the Fresnel zone theory. A lens may be formed. That is, FIG. 3 shows that the common electrode 14
An ordinary concave acoustic lens 31 is provided instead of a Fresnel lens as an acoustic lens, and an acoustic matching layer 32 formed of the acoustic matching material described for the Fresnel lens 15 is provided thereon. FIG. 5 shows a structure in which the supporting substrate 11 itself is formed in a concave shape and the individual electrodes 13, the piezoelectric body 12, the common electrode 14, and the acoustic matching layer 32 are provided along the concave shape. In this case, the acoustic matching layer 32 forming the concave surface also functions as an acoustic lens. Example 1 In this example, an ink jet recording apparatus having the structure shown in FIG. 1 was manufactured. The piezoelectric body 12 has a relative dielectric constant of 20.
0 lead titanate-based ceramic, frequency 50MHZ
z (thickness: 50 μm). Both sides of the piezoelectric body 12 have T
An i / Au laminated electrode was formed by sputtering so that the thicknesses of Ti and Au were 0.05 μm and 0.5 μm, respectively, and polarization treatment was performed by applying an electric field of 2 kV / mm. Thereafter, one Ti / Au laminated electrode was etched to form an individual electrode 13, and the width of one element was 65 μm, and the electrode interval was 20 μm (the arrangement pitch of the individual electrodes was 85 μm). This piezoelectric element array was bonded to a support substrate 11 made of glass provided with an array electrode 21 and a drive circuit 22 with an epoxy resin. Thereafter, the piezoelectric body 12 is polished so as to have a thickness of 50 μm, and then the Ti / Au common electrode 14 is sputtered to reduce the thickness of each of Ti and Au to 0 so that the effective aperture Df in the sub-scanning direction becomes 2 mm. It was formed to 0.05 μm and 0.5 μm. The lead out of the common electrode 14 was connected to the wiring pattern formed on the support substrate at both ends in the main scanning direction to establish conduction. As a material of the acoustic matching layer and the acoustic lens, a mixture of epoxy resin and alumina powder was used. First, the mixing ratio was adjusted so that the sound speed was around 3 × 10 ³ m / s (seconds), and a density of 2.20 × 10 ³ kg / m ³ and a sound speed of 2.95 × 10 ³ m / s were obtained. This was applied and cured on the surface of the common electrode 14 and polished to a thickness of 45 μm. Thereafter, a plurality of grooves having a half wavelength (about 30 μm, in this case, one wavelength is about 60 μm) are formed parallel to each other in the main scanning direction so that the focal length becomes 2.7 mm. Was formed. Then, as shown in FIG. 1, the ink liquid holding chamber 16 is provided so that the distance between the ultrasonic wave emitting surface and the ink liquid surface is approximately 2.7 mm, the ink liquid 17 is filled, and a drive circuit is further configured. Thus, an ink jet recording apparatus was completed. A printing experiment was performed using this ink jet recording apparatus. First, assuming that the number of simultaneous driving elements is 16, and the phases of signals given to these simultaneous driving elements are represented by 0 and π (0 and π are opposite phases), “π0π0ππ0000π
π0π0π ”. In this case, the aperture Ds in the main scanning direction
Is 85 μm × 16 = 1.36 mm. The burst signal is a sine burst shown in FIG. 2A, and the driving voltage can be controlled within a range of 30 Vpp or less. As described above, the distance between the ultrasonic radiation surface and the ink liquid surface was approximately 2.7 mm, and the ultrasonic attenuation in the ink liquid 17 at a frequency of 50 MHz was 2.3 dB. First, N is set to 1000 so as to satisfy the expression (1).
And Thus, the range of V is 5.8 to 40 Vpp (from equation (3)). Repetition cycle 500μ at 30Vpp
s for 1 second (2000 dots)
It was confirmed that the droplets fly 0% one drop at a time. But 5Vp
When driven at p, only about 1800 dots of flight could be confirmed. As described above, a drive voltage exceeding 30 Vpp could not be applied. Next, N is set to 4000 so as to satisfy the expression (1).
And The range of V is 2.9 to 20 Vpp ((3)
From the formula). When 10 Vpp was applied, 100% of the droplet flies one drop at a time, but at 2 Vpp, only about 1700 dots fly. Further, when 30 Vpp was applied, two or more drops could fly, and the reproducibility was not sufficient, resulting in instability. Next, N is set to 10 so as not to satisfy the expression (1).
000. In this case, the range of V satisfying the expression (2) is 1.8 to 13 Vpp (from the expression (3)). However, even at a voltage in this range, there was no voltage at which one droplet stably flies. Observation of the meniscus with a high-speed camera revealed that the height of the meniscus was higher than that of the example in which one drop of 100% was flying. There was no. As a result, recording dots could not be obtained stably. Embodiment 2 In this embodiment, an ink jet recording apparatus having the same structure as that of Embodiment 1 but having different specifications was manufactured, and a flying experiment was performed. The piezoelectric element and the driving frequency were the same as in the first embodiment.
However, in the present embodiment, the width of one element is set to 30 μm, and the electrode interval is set to 13 μm (the arrangement pitch of the individual electrodes is 43 μm), which is about の of that of the first embodiment. This piezoelectric element array was bonded to a support substrate 11 made of glass as in Example 1 with an epoxy resin. The effective aperture was 1.8 mm, and the common electrode and the acoustic lens / acoustic matching layer were formed of the same material and the same process as in Example 1. Thereafter, a groove having a depth of about 30 μm was formed in the main scanning direction so that the focal length became 0.8 mm, and a Fresnel lens was manufactured. Thereafter, an ink jet recording apparatus was completed in the same manner as in Example 1.
The ultrasonic attenuation at a distance of 0.8 mm at 50 MHz in the ink liquid was 0.7 dB. As driving conditions, N is set so as to satisfy equation (1).
Was set to 500. Thereby, the range of V is 6.9-49V.
pp (from equation (3)). When printing (2,000 dots) was performed at 25 Vpp at a repetition cycle of 500 μs for 1 second, it was confirmed that 100% of the ink droplets flies one by one. However, when the device was driven at 5 Vpp, only a flight of about 1700 dots could be confirmed. As the next driving condition, N was set to 2000 so as to satisfy the expression (1). V ranges from 3.4 to 24 Vpp
(From equation (3)). When 20 Vpp was applied, 100% of each droplet flies, but at 3 Vpp, about 18 drops.
00 dots did not fly. Next, N is set to 50 so as not to satisfy the expression (1).
00. In this case, the range of V that satisfies the expression (2) is 2.2 to 15 Vpp (from the expression (3)). However, even at a voltage in this range, there was no voltage at which one droplet stably flies. Observation of the meniscus with a high-speed camera revealed that the height of the meniscus was unstable and higher than that of the example in which one drop of the meniscus flew 100%. As a result, it can be said that stable recording dots could not be obtained. Note that the same result as above was also confirmed when the concave lens shown in FIG. 3 or FIG. 4 was used. As described above, according to the present invention, the F number in both the main scanning direction and the sub-scanning direction as parameters for determining the optimum range of the wave number N of the burst signal, Equations (1) and (2) are expressed between the wavelength (λ) of the ultrasonic wave, the peak value (V) of the drive voltage, and the ultrasonic attenuation (a) between the ink liquid surface and the ultrasonic radiation surface. Are simultaneously satisfied, it is possible to provide an ink jet recording apparatus in which one ink droplet stably flies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an example of an ink jet recording apparatus according to the present invention. FIG. 2 is a waveform diagram of a drive signal for driving the ink jet recording apparatus of the present invention. FIG. 3 is a cross-sectional view for explaining another example of the ink jet recording apparatus according to the present invention. FIG. 4 is a sectional view for explaining still another example of the ink jet recording apparatus according to the present invention. DESCRIPTION OF SYMBOLS 11 ... Support substrate 12 ... Piezoelectric 13 ... Individual electrode 14 ... Common electrode 15 ... Ultrasonic focusing means (Fresnel lens) 16 ... Ink liquid holding chamber 16a ... Slit 17 ... Ink liquid 21 ... Array electrode 22 ... Drive circuit 31 ... concave acoustic lens 32 ... acoustic matching layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeo Miki 70, Yanagimachi, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Yanagicho Plant (56) References JP-A-9-254377 (JP, A) JP-A-9 −290504 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/01-2/015 B41J 2/045 B41J 2/055

Claims (1)

(57) Claims 1. An ink liquid holding chamber for holding an ink liquid, and a burst signal voltage acoustically connected to the ink liquid and having a wave number N and a peak value V [Vpp]. An ultrasonic wave generating means driven by applying an ultrasonic wave, and an ultrasonic wave focusing means for focusing an ultrasonic wave generated from the ultrasonic wave generating means near a liquid surface of the ink liquid. The generating means includes a plurality of piezoelectric elements arranged in an array in one direction, and a group of piezoelectric elements including some of the piezoelectric elements are simultaneously driven, or a single piezoelectric element is used. And the wave number N is expressed by the following two equations (1) and
And an ink jet recording apparatus that satisfies the formula (2) at the same time. 4Fr · λ <N <200Fr · λ (1) 2 × 10 ⁴ / (10 ^{−a / 10} .V ² ) <N <1 × 10 ⁶ /
In ^{(10 -a / 10 · V 2} ) ... (2) ( the above formulas, Fr is, {(Fp / Ds) × (Fp / Df)} 1/2 der
Ri, Fp represents the focal length, lambda represents the ultrasonic wave in the ink liquid in [[mu] m], Ds, the ultrasonic wave generating means is arranged in said array
When the device includes a plurality of piezoelectric elements,
The piezoelectric elements located at both ends in the main scanning direction of the dynamic piezoelectric element group
The distance between the outermost ends of each
When the means comprises the single piezoelectric element, the piezoelectric element
Represents the length in the main scanning direction, and Df represents the length of the piezoelectric element constituting the ultrasonic wave generating means.
Represents the length in the scanning direction, a is the amount of ultrasonic attenuation between the ultrasonic radiation surface and the ink liquid surface
[Indicating [dB]) .