JPH1120163A - Ink-jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge minute liquid drops without using a nozzle by providing an elastic member which has a vibration generation part vibrating in response to pixel signals and projecting parts formed at a predetermined distance, and vibrates correspondingly to the vibration of the vibration generation part, and generating capillary waves by the vibration of the elastic member. SOLUTION: An elastic member 1 has projecting parts bonded so that a common part is held by a substrate and formed sharp at leading ends to conform to a pitch whereby ink drops are discharged. A plurality of vibration generation parts 4a-4c are formed at positions corresponding to the projecting parts of the elastic member 1. When an alternation voltage is applied to the vibration generation part 4 from an external driving mechanism thereby driving the vibration generation part 4, the elastic member 1 connected to the substrate vibrates. In consequence, the projecting parts of the elastic member bend and vibrate, and leading end parts of the projecting parts vibrate greatly right and left, with generating capillary waves at an ink surface. Crests of the capillary waves are torn when an amplitude of the leading end parts is made large enough, thus forming and flying ink drops.

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 head for performing printing by discharging droplets such as ink drops on a surface to be printed.

[0002]

2. Description of the Related Art A typical example of an ink jet recording system for performing printing by discharging droplets such as ink drops on a surface to be printed is a system using a nozzle. Nozzle-type recording methods include an on-demand type and a continuous flow type.

The on-demand type is a system in which printing is performed by intermittently ejecting ink from nozzles in accordance with recording information. Representative examples of the on-demand type include a piezo oscillator type and a thermal type. The piezo vibrator type applies a pulse voltage to a piezoelectric element attached to the ink chamber to deform the piezoelectric element, thereby changing the ink liquid pressure in the ink chamber and discharging ink drops from nozzles to form dots on recording paper. It is to be recorded. In the thermal type, ink is heated by a heating element provided in an ink chamber, and ink droplets are ejected from nozzles by bubbles generated thereby to record dots on recording paper.

On the other hand, in the continuous flow type, ink is continuously ejected from a nozzle by applying pressure to the ink, and at the same time, a vibration is applied by a piezo vibrator or the like to form a droplet of the ejected ink,
Recording is performed by selectively charging and deflecting droplets.

In each of these methods, the diameter of the ink drop is determined mainly by the diameter of the nozzle. When the nozzle diameter is reduced, the nozzle may be clogged due to dust and dirt or the drying of the ink surface of the nozzle portion, and the ink discharge direction may change due to the adhesion of the ink residue to the nozzle circumference. Occurs.

[0006] On the other hand, there have been proposed some recording systems for performing printing by ejecting ink drops onto a printing surface without using a nozzle.

[0007] US Pat. No. 4,308,547 discloses a method in which a concavely curved spherical piezoelectric shell is arranged in ink and a voltage is applied to the piezoelectric shell via an electrode. In this method, longitudinal waves radiated into the ink from the piezoelectric shell are collected at one point on the free ink surface, and ink drops are ejected from the free ink surface.

In Japanese Patent Publication No. 6-45233, a concave portion having a spherical shape is provided on a substrate such as glass, which is used as an acoustic lens. A piezoelectric member is provided on the back surface of the substrate, and a voltage is applied to the piezoelectric member. A method of forming a vibrator made of electrodes and disposing the vibrator in ink is shown.

Further, Japanese Patent Application Laid-Open No. 3-200199 discloses that instead of a concave lens, a thin-plate flat phase Fresnel lens which can be sharply focused at a lower cost is provided on a substrate.

As another example of a recording method that does not use a nozzle, there is a so-called electrostatic suction method that uses an electrostatic force as a discharge force. As an example of the electrostatic suction method, a method using vibration to form an ink meniscus (ink protrusion) is known.

For example, Japanese Patent Application Laid-Open No. 62-222853 discloses a method in which a recording needle is projected from the ink surface to apply ultrasonic energy propagating in the axial direction to the recording needle. According to this, ultrasonic flow (acousti)
Due to the c-streaming phenomenon, the ink in contact with the recording needle moves toward the tip of the recording needle, and a convex ink meniscus is formed at the tip of the recording needle. In this state, an electrostatic field is applied between the recording needle and the back electrode to tear off the ink, and an ink drop lands on a recording medium disposed between the recording needle and the back electrode. According to this method, since an ink meniscus is formed at the tip of the recording needle, a smaller ink drop can be formed as compared with the conventional electrostatic suction method.

Japanese Patent Application Laid-Open No. 56-28867 also discloses an electrostatic attraction in which an image signal is applied to a needle electrode while an electrostatic field is applied between the needle electrode and the back electrode, and at the same time, the needle electrode is vibrated. The scheme is shown.

[0013]

In a system in which longitudinal waves are focused on the free ink surface and ink drops are ejected from the free ink surface, the diameter of the ink drop is substantially equal to the focused diameter of the longitudinal waves. Here, the ink drop diameter or the focusing diameter d of the longitudinal wave is represented by f: the driving frequency of the vibrator and F: the F value of the lens.
Then, approximately d = F / f. When the wavelength of the longitudinal wave propagating in the ink is λ and the propagation speed is v, there is a relation v = f · λ between these and the driving frequency f of the vibrator.

For example, when it is desired to eject a very small ink drop having an ink drop diameter d of about 15 μm, assuming that the F value of the lens is 1, the longitudinal wave propagation velocity v
Using a conventional low-viscosity, water-based ink of about 1500 m / sec, the driving frequency f required for driving the vibrator is about 1
This is a very high value of 00 MHz. Since it is practically difficult to make the F value of the lens significantly smaller than the above assumed value due to various problems, generally, when trying to reduce the ink drop diameter d, the vibrator is required to be driven at an extremely high frequency. You have to drive.

As described above, in the method in which longitudinal waves are focused on the free ink surface and ink drops are ejected from the free ink surface, a plurality of vibrators must be driven at a high frequency of about 100 MHz. This raises the cost problem of being expensive. In addition, there is a problem that the ink viscosity changes due to the heat generated by the absorption and the drop diameter fluctuates, and the ink itself is dried or solidified in the recording element, so that the ink cannot be ejected.

On the other hand, the electrostatic suction method has a drawback that the diameter of the formed drop is apt to fluctuate due to fluctuations in the thickness of the dielectric material of the recording medium due to humidity or variations in the surface roughness of the recording medium.

An object of the present invention is to provide an ink jet recording head capable of discharging fine liquid droplets by using a low-frequency low-voltage driving method which does not use a nozzle and does not easily generate heat. .

[0018]

SUMMARY OF THE INVENTION The object of the present invention is to provide a vibration generating section which vibrates in response to a pixel signal, and a projection formed at a predetermined interval. An ink jet recording head is provided, comprising: a vibrating elastic member; generating a capillary wave on the surface of the ink by vibrating the elastic member; and causing the ink to fly and adhere to a recording medium. In the ink jet recording head of the present invention, it is desirable that the bending stiffness of the distal end of the projection is smaller than the bending stiffness of the base end of the projection.

The elastic member has protrusions at predetermined intervals, and a portion corresponding to the protrusion is connected to the vibration generator. At least the vicinity of the tip of the protrusion of the elastic member is in contact with the ink. When the vibration generator excites the elastic member at a frequency at which the protrusion of the elastic member resonates with bending vibration,
The vicinity of the tip of the protrusion of the elastic member vibrates with a large amplitude due to resonance. The ink liquid thickness in the vibration direction of the bending vibration that is in contact with the protrusion is near the tip of the protrusion of the elastic member.
The thickness is several μm to several hundred μm due to the effects of ink and the wetting of the protrusions and the effect of gravity. As a result, the ink is strongly affected by the vibration, and a capillary wave is generated on the surface of the ink. By the action of the capillary wave, it is possible to generate fine droplets.
By setting the driving condition of the vibration generating unit to a predetermined value, it is possible to fly for each ink droplet. The excitation of the vibration generating section intermittently separates the excitation every time the number of excitations required for the flight of one ink droplet is completed so as to realize the flight of one ink droplet according to one pixel signal. Accordingly, a recording head capable of producing high image quality without ink clogging without generating nozzles without ink nozzles can be realized.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An ink jet recording head according to one embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a side view showing the basic structure of the ink jet recording head according to the present embodiment. As the elastic member 1, nickel having a thickness of about 7 μm formed by electroforming was used. The elastic member 1 is adhered so as to be sandwiched between the ceramic substrates 2a and 2b having a thickness of about 100 μm, and at least a part of the tip is buried in the ink 3. The vibration generator 4 includes a piezoelectric ceramic thin film 5 made of lead zirconate titanate (PZT) and an electrode 6 for applying a voltage to the piezoelectric ceramic thin film 5.
a, 6b, which are bonded to the surfaces of the ceramic substrates 2a, 2b opposite to the surface on the ink 3 side at positions corresponding to the elastic members 1. The piezoelectric ceramic thin film 5 made of PZT has been subjected to polarization processing, and vibrates in a direction perpendicular to the surfaces of the ceramic substrates 2a and 2b when a voltage is applied between the electrodes 6a and 6b. The electrodes 6a and 6b are 0.05
It consists of two layers of chrome with a thickness of μm and gold with a thickness of 1 μm. The ink chamber 7 is formed by ink chamber walls 8a and 8b made of a ceramic material and a top plate 9. Ink 3
Is supplied from an ink tank (not shown) to the ink chamber 7 through an ink supply path 10. At this time, the tip of the elastic member 1 is wetted by the ink 3. The ink droplet ejection port 11 is formed by the ink chamber wall 8a and the top plate 9.

Ceramic substrates 2a, 2b, ink chamber wall 8
a, 8b, the top plate 9, and the partition 12 are desirably made of the same ceramic material.
Alternatively, it can be manufactured by any of the methods of individually forming and then bonding. A plastic substrate may be used instead of the ceramic substrate.

The material of the elastic member 1 may be formed of various metallic materials or alloys thereof. The elastic member 1 may be made of a resin material such as polyimide instead of a metal material. Further, the elastic member 1 may be formed of various inorganic materials such as SiO ₂ and Al ₂ O ₃ .

The piezoelectric ceramic thin film 5 is made of barium titanate BaTiO ₃ or lead niobate PbNb ₂ O in addition to PZT.
₆ , polycrystalline or single crystal such as lithium niobate LiNbO ₃ and lithium tantalate LiTaO ₃ , or ZnO
A piezoelectric thin film material such as AlN or AlN may be used.

FIG. 2 is a front view showing the basic configuration of the ink jet recording head according to the present embodiment. For easy understanding, illustration of the ink chamber walls 8a and 8b described with reference to FIG. 1 is omitted.

The elastic member 1 has a projection 1a corresponding to the pitch at which ink droplets are ejected. The tip of the protruding portion 1a is formed in a sharp shape. The plurality of vibration generating parts 4a, 4b, 4c are respectively provided with protrusions 1a,
It is formed at a position corresponding to 1b and 1c. Each of the vibration generating parts 4a, 4b, 4c is formed by sandwiching the integral piezoelectric ceramic thin film 5 between the electrodes 6a and 6b. Between the protrusions 1a, 1b, 1c of the elastic member 1, a partition 12 connecting the top plate 9 and the ceramic substrates 2a, 2b is arranged. In addition, the vibration generating units 4a, 4
Between b and 4c, it is fixed to the support substrate 13 made of an aluminum plate so that the vibration generated in one vibration generating unit does not excite the elastic member on the other vibration generating unit.

The elastic member 1 has a width W (see FIG. 2) perpendicular to the vibration direction of the bending vibration near the free end of the free end of the cantilever structure of the elastic member 1 having a length of approximately 2λ. It has an area which becomes Here, λ is given by the following equation 1. λ = {8πσ / (ρfe ² )} ^1/3 × 10 ⁴ (μm) Expression 1 where σ is the ink surface tension (mN / m) and ρ is the ink density (g / cm ³ ) fe Is the excitation frequency (Hz). By doing so, it is possible to generate two peaks of the capillary wave in the width W, and thereafter, one peak of the ink ridge is formed, and this is separated at the next moment, so that one ink droplet can fly accurately.

FIG. 3 shows the entire shape of the elastic member 1. The elastic member 1 includes a protruding portion 21, a tip portion 22 of the protruding portion from which ink droplets are ejected, and a common portion 23 corresponding to the thickness of the ceramic substrate. It is possible to form only the protrusions 21 individually and assemble them into the configuration as shown in FIGS. However, since the thickness and the size of the elastic member are small, it is very difficult to assemble the individual protrusions 21 with high precision. Therefore, as shown in FIG. 3, it is much better to form them as an integral unit in terms of simplicity of the assembling method and assembling accuracy. As an actual forming method, in addition to the above-described electroforming, a forming method according to a material to be used, such as laser processing, electric discharge processing, and plastic molding, can be used.

The same applies to the vibration generator 4. Even if the piezoelectric ceramic thin films are not integrally formed, similar functions can be provided by forming them individually and forming electrodes individually. However, it is much better to form them integrally as shown in FIG. 2 in terms of simplicity of the assembling method and assembling accuracy.

Next, the operation of the ink jet recording head of this embodiment will be described with reference to FIG. FIG. 4 is a side view showing the state of the protrusion 21 of the elastic member 1 when the vibration is generated by the vibration generator 4. The vibration generator 4 has a resonance frequency fo determined by the rigidity of the ceramic substrates 2a and 2b, the thickness of the piezoelectric ceramic thin film 5, and the piezoelectric characteristics. An external voltage is applied from the external drive mechanism 14 to the vibration generator 4 at fo or an integer multiple of the frequency f to excite the vibration generator 4. The driving frequency may be any value. However, when the driving is performed at the resonance frequency fo or a frequency f that is an integral multiple of the resonance frequency fo, the vibration is efficiently performed.

The vibration generated by the vibration generating section 4 causes the elastic member 1 connected to the ceramic substrates 2a and 2b to vibrate. As a result, the protrusion 21 of the elastic member
Bending vibration as shown in Fig. 4 Projection 21 of elastic member 1
Also has a unique resonance frequency fe determined by the rigidity and size of the elastic member, the manner of contact with the ink, and the like. Resonance frequency fe
Is the resonance frequency of only the protruding portion without considering the common portion 23 of the elastic member shown in FIG. Since the common portion 23 of the elastic member is bonded so as to be sandwiched between the ceramic substrates 2a and 2b, there is almost no need to consider it. By determining the rigidity of the elastic member, the size of the protruding portion, the manner of contact with the ink, and the like, such that the unique resonance frequency fe or a value of an integral multiple thereof matches the drive frequency for exciting the vibration generating section 4. The elastic member 1 can be efficiently bent and vibrated. In the present embodiment, referring to FIG. 2, the protrusion of the elastic member has a width a = 300 μm and a height b = 260 in the ink chamber.
μm.

FIG. 5 shows the structure of the external drive mechanism 14 to the vibration generator 4.
5 shows an alternating voltage waveform applied to the. In the present embodiment, a sinusoidal alternating voltage of 192 kHz and 40 Vp-p (maximum / lowest amplitude) was applied to the vibration generating section as a burst wave for only 52 μsec to excite. Therefore,
This means that a 192 kHz sinusoidal alternating voltage was applied for 10 bursts. Although the waveform shown in FIG. 5 is a sine wave, it can be driven by a rectangular wave or a triangular wave.

FIG. 6 is an enlarged view of the side surface of the distal end of the protrusion 21 of the elastic member 1 that is bending and vibrating. When the protrusion 21 of the elastic member performs bending vibration as shown in FIG. 4, the tip of the protrusion 21 of the elastic member vibrates largely right and left as indicated by a dashed arrow. When the distance t (hereinafter referred to as ink liquid thickness) from the surface perpendicular to the vibration direction of the tip to the surface of the ink 3 is set to several μm to several hundred μm, a capillary wave is generated on the ink surface. The ink 3 has a viscosity of 2 m, for example.
Pa · s black aqueous ink. The ink liquid thickness t can be changed by controlling the shape of the tip 21 of the protrusion of the elastic member, the ink height, the wettability of the tip with ink, and the like.

By making the amplitude of the tip 21 sufficiently large, the wave front of the capillary wave is torn off and fly as an ink droplet 15. In the present embodiment, the diameter of the ink droplet 15 was approximately 20 μm. The voltage value V of the alternating voltage applied to the vibration generating unit 4 and the number of burst waves are determined by several conditions such as the viscosity of the ink used and the thickness of the ink liquid. If these conditions deviate from appropriate values, problems such as ejection of a plurality of ink droplets or non-ejection of ink droplets occur.

The direction in which the ink droplet 15 flies is substantially equal to the direction in which the tip vibrates. In the present embodiment, since the ink is caused to fly only in one direction (rightward) with respect to the tip, the generation of the capillary wave is suppressed by increasing the thickness of the ink liquid on the non-flying side (left side). As a method of increasing the thickness of the ink liquid on one side, the wettability of the ink in the ink chamber wall 8b shown in FIG. 1 may be controlled, or a member for determining the height of the ink may be provided. As another method for causing the ink droplet 15 to fly only in one direction, a configuration in which no ink is supplied to the tip of the elastic member in the direction in which the ink droplet 15 does not fly can also be used. In order to limit the region where the capillary wave is generated, the shape of the distal end portion 21 of the elastic member is sharpened as shown in FIG. 3 so that ink droplets are ejected from only one capillary wave.

As shown in FIG. 5, the application of the alternating voltage is stopped after the ink droplet is ejected. After a lapse of a predetermined time, the alternating voltage is applied again to eject the next ink droplet. High-speed printing is possible by shortening the time interval T for ejecting ink droplets. In this embodiment, the interval at which ink droplets can be ejected is about 10 kHz.

Next, FIG. 7 shows an example of an array head which is a main part of a recording mechanism provided with the ink jet recording head of the present embodiment. FIG. 7 is a perspective view of the array head of the present embodiment. In FIG. 7, the array head 17
Has four inkjet recording heads 17a to 17d vertically stacked in the figure, and ink supply units 16a to 16d attached to the back of the inkjet recording heads 17a to 17d. Between the inkjet recording heads 17a to 17d and the ink supply 16a
The support substrate 13 described above is provided between 16d. These ink jet recording heads 17a to 17d
Are supplied with black, yellow, magenta, and cyan inks, which are stored one by one in the ink supply units 16a to 16d, respectively, and discharge predetermined ink droplets based on the operation described in the present embodiment. A predetermined color ink is ejected from the outlet 11.

FIG. 8 shows an example of a recording mechanism provided with the ink jet recording head of the present embodiment. In the recording mechanism of this embodiment, the array head 17 shown in FIG. 7 is fixed to the carriage 18 and connected to the ink cartridge 19. The ink cartridge 19 holds four color inks of black, yellow, magenta, and cyan. The carriage 18 reciprocates while being guided by the guide 20. The printing paper 31 is wound around a roller 32, and the rotation of the roller 32 and the movement of the carriage cause the printing paper 31 to rotate.
An image is printed over the entire surface of the printing paper 31.

[0039]

According to the present invention, fine ink droplets can be ejected without using a nozzle, so that a demand for higher resolution of an image can be satisfied without causing a problem such as nozzle clogging. Can be. Since the present invention utilizes a capillary wave, it can be driven at a low frequency, and can be driven with low power because a piezoelectric material is used. Therefore, the present invention is energy efficient, and the range of physical properties of the ink that can be used in the present invention is wide. Further, since the constituent parts are integrally formed and assembled, a highly accurate inkjet recording head can be manufactured at a low cost by a simple assembling method.

[Brief description of the drawings]

FIG. 1 is a side view of an ink jet recording head according to an embodiment of the present invention.

FIG. 2 is a front view of the ink jet recording head according to the embodiment of the present invention.

FIG. 3 is a view showing the entire shape of an elastic member of the ink jet recording head according to the embodiment of the present invention.

FIG. 4 is a side view showing a state of a protrusion of the elastic member when the elastic member is vibrated by the vibration generating unit of the ink jet recording head according to one embodiment of the present invention.

FIG. 5 is a diagram showing an alternating voltage waveform applied from an external drive mechanism to a vibration generating unit of the inkjet recording head according to one embodiment of the present invention.

FIG. 6 is an enlarged view of a side surface when a protrusion of an elastic member of the inkjet recording head according to the embodiment of the present invention is bending vibrating.

FIG. 7 is a diagram showing an example of an array head of a recording mechanism provided with an inkjet recording head according to an embodiment of the present invention.

FIG. 8 is a diagram showing an example of a recording mechanism provided with an ink jet recording head according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Elastic member 2 Substrate 3 Ink 4 Vibration generation part 5 Piezoelectric ceramic thin film 6 Electrode 7 Ink chamber 8 Ink chamber wall 9 Top plate 10 Ink supply path 11 Ink droplet ejection port 12 Partition wall 13 Support substrate 14 External drive mechanism 15 Ink droplet 16 Ink Supply section 17 Array head 18 Carriage 19 Ink cartridge 20 Guide 21 Projection section 22 Tip section 23 Common section 31 Printing paper 32 Roller

Claims (3)

[Claims] A vibration generating means for vibrating in response to a pixel signal; and an elastic member integrally formed with a plurality of protrusions which bend and vibrate in response to excitation of the vibration generation means. An ink jet recording head, wherein a capillary wave is generated on the surface of the ink by any of the vibrations described above, and the ink is caused to fly and adhere to a recording medium. 2. The ink jet recording head according to claim 1, wherein the tip of the projecting portion has a smaller bending stiffness than the base end of the projecting portion. 3. The ink jet recording head according to claim 1, wherein said vibration generating means includes a plurality of electrodes corresponding to each of said plurality of projections formed on one piezoelectric material. Inkjet recording head.