JP3740791B2 - Droplet forming apparatus and image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a droplet forming apparatus and an image forming method that atomize a liquid and fly as droplets, and more particularly to a recording apparatus and an image forming apparatus that perform printing by discharging droplets such as ink drops onto a printing surface.
[0002]
[Prior art]
The droplet forming device is applied to various applications such as humidifiers and medical suction devices. As a typical application example, ink containing a colorant is used as a liquid, and it is made to fly to the surface to be printed. A recording device that performs printing may be used.
[0003]
As a recording method for causing a droplet to fly, there is a method using a nozzle. Recording methods using this nozzle are roughly classified into an on-demand type and a continuous flow type.
[0004]
The on-demand type is a method in which printing is performed by intermittently ejecting ink from nozzles corresponding to recorded information, and representative examples include a piezo vibrator type and a thermal type. The piezoelectric vibrator type applies a pulse voltage to a piezoelectric element attached to the ink chamber, and deforms the piezoelectric element to change the ink hydraulic pressure in the ink chamber, thereby ejecting ink droplets from the nozzles, In this case, dots are 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.
In the continuous flow type, pressure is applied to ink and ink is ejected continuously from the nozzles, and at the same time, vibration is applied by a piezo vibrator or the like to form protruding ink columns into droplets that are selective to the droplets. Recording is performed by charging and deflecting.
[0005]
In any of these methods, the ink droplet diameter is mainly determined by the nozzle diameter. When the nozzle diameter is reduced, problems such as nozzle clogging due to dust or dust, nozzle clogging due to drying of the ink surface in the nozzle portion, and changes in the ink ejection direction due to adhesion of ink residue to the nozzle circumferential portion occur. .
[0006]
On the other hand, several recording systems have been proposed in which printing is performed by ejecting ink droplets onto a printing surface without using a nozzle.
For example, as shown in U.S. Pat. No. 4,308,547, there is known a technique in which a concavely curved spherical shell is disposed in ink and a voltage is applied to the piezoelectric shell via an electrode. It has been. In this method, longitudinal waves radiated into the ink from the piezoelectric shell are collected at one point on the ink free surface, and droplets are ejected from the ink free surface.
In addition, as disclosed in Japanese Examined Patent Publication No. 6-45233, a spherical concave portion is provided on a substrate such as glass, and this is used as an acoustic lens, a piezoelectric body is applied to the back surface of the substrate, and a voltage is applied to the piezoelectric body. It is known to form a vibrator composed of electrodes for the purpose of arranging the vibrator in ink.
Further, JP-A-3-2001199 discloses that a thin-film flat-plate phase Fresnel lens is provided on a substrate instead of a concave lens as a lens that is cheaper and can be focused more sharply.
[0007]
Furthermore, as another example in which the nozzle is not used, there is a so-called electrostatic attraction method that uses electrostatic force as an ejection force, and a device that uses vibration to form an ink meniscus (ink bulge) is known. .
For example, Japanese Patent Application Laid-Open No. 62-222853 discloses that a recording needle is projected from the ink surface and is given ultrasonic energy propagating in the axial direction. According to this, due to the ultrasonic 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 ink droplets are landed on the 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, it is said that smaller ink droplets can be formed compared to the conventional electrostatic attraction method.
Japanese Patent Application Laid-Open No. 56-28867 also discloses an electrostatic attraction method in which an image signal is applied to the 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. It is shown.
[0008]
[Problems to be solved by the invention]
Among the methods that do not use the nozzle, in the method in which longitudinal waves are focused on the ink free surface and droplets are ejected from the ink free surface, the droplet diameter is approximately equal to the focused diameter of the longitudinal wave, and the focusing diameter d Is d to F / f, where f is the driving frequency of the vibrator and F is the F value of the lens. If the wavelength of the longitudinal wave propagating in the ink is λ and the propagation speed is v, there is a relationship of v = f · λ between these and the drive frequency f of the vibrator.
Therefore, for example, when an extremely small ink droplet having a droplet diameter (focusing diameter) d of about 15 μm is to be ejected, if the F value of the lens is 1, the conventional low viscosity / water-based ink Since the propagation velocity v of the longitudinal wave is approximately 1500 m / second, the drive frequency f of the vibrator must be set to a very high frequency such as approximately 100 MHz. Since it is practically difficult to reduce the F value of the lens due to various problems, it is generally necessary to drive the vibrator at a higher frequency when the droplet diameter d is made smaller.
Therefore, since a plurality of vibrators must be driven at a high frequency of about 100 MHz, there is a problem in cost that the driving means is generally expensive, and the ink viscosity changes due to heat generation due to absorption, resulting in a drop diameter. This causes a serious problem that the ink cannot be ejected due to fluctuations or drying and solidification of the ink itself in the recording element.
[0009]
On the other hand, the electrostatic attraction method has a disadvantage that the diameter of the formed droplets is likely to fluctuate due to variations in the dielectric thickness of the recording medium due to humidity or the like, variations in the surface roughness of the recording medium, and the like.
[0010]
Therefore, the present invention has been made for the purpose of solving the above-mentioned problems in the method using no nozzle. That is, the present invention provides a droplet forming apparatus and an image recording method that are capable of efficiently discharging minute droplets by a method that does not use a nozzle, and that are excellent in droplet uniformity and directionality.
[0011]
[Means for Solving the Problems]
The droplet forming apparatus of the present invention has a single vibration generating means and a vibration transmitting means, and the liquid is brought into contact with the vibration transmitting means to cause the liquid near the tip to fly. The elastic member having a concavo-convex structure composed of a plurality of sharp end portions and one or more concave portions at the tip, formed on the single vibration generating means, and vibrating the liquid surface with the vibration Transmission Located between the tip and bottom of the means, front Recording Movement Transmission It is characterized by causing droplets to fly by means.
[0012]
The droplet forming apparatus of the present invention is preferably used for image formation. In this case, the image forming droplet forming apparatus includes a plurality of vibration generating means and a plurality of vibrations corresponding to each of the vibration generating means. It has a transmission means, the liquid is brought into contact with the vibration transmission means and the liquid in the vicinity of the tip is caused to fly, and the vibration transmission means has a concavo-convex structure consisting of two sharp end portions and one concave portion at the tip. It is made of an elastic member and is formed on a corresponding single vibration generating means, and the liquid level of the liquid is Transmission Located between the tip and bottom of the means, front Recording Movement Transmission A droplet is caused to fly from each of the means.
[0013]
Further, the image forming method of the present invention generates vibration from the vibration generating means based on the image information and transmits the vibration to the tip of the vibration transmitting means, and the droplets fly from the vicinity of the tip of the vibration transmitting means by the transmitted vibration. The vibration transmitting means is formed on a single vibration generating means, and has a concavo-convex structure consisting of two sharp end portions and one concave portion at the tip. The liquid surface of the liquid is made of the elastic member having the vibration. Transmission In the position between the tip and bottom of the means Recording Movement Transmission It is characterized by causing droplets to fly by means.
[0014]
More specifically, the droplet forming apparatus of the present invention has vibration generating means and a plate-like elastic member having a cantilever structure, and the elastic member is resonated by bending vibration by excitation of the vibration generating means. And the liquid in the vicinity of the tip of the elastic member flies by the bending vibration, and the free end of the elastic member of the cantilever structure is composed of a plurality of sharp end portions and one or more concave portions. Has an uneven structure.
[0015]
Another aspect of the droplet forming apparatus of the present invention is an image forming apparatus having a plurality of vibration generating means arranged at a predetermined interval and a plurality of cantilever structures respectively corresponding to the vibration generating means. A plate-like elastic member, and the vibration generating means intermittently excites according to an image signal, resonates the elastic member by bending vibration by the excitation, and near the tip of the elastic member by the bending vibration. The elastic member free end of the cantilever structure has a concavo-convex structure including two sharp end portions and one concave portion.
[0016]
In the droplet forming apparatus of the present invention, the liquid has a surface tension of σ (mN / m) and a density of ρ (g / cm ^Three ), When the vibration frequency near the tip of the elastic member is f (Hz), the distance between the adjacent sharp edges at the sharp edges, that is, the width of the recess is approximately {(8πσ / ρf ² ) ^1/3 } / 2 (cm) or more.
[0017]
Further, the surface tension of the liquid is σ (mN / m), and the density is ρ (g / cm ^Three ), Where the vibration frequency near the tip of the elastic member is f (Hz) and the natural number is n, the distance between adjacent sharp edges at the sharp edges is approximately {(8πσ / ρf ² ) ^1/3 -It is preferable that it is n} / 2 (cm).
[0018]
Further, the surface tension of the liquid is σ (mN / m), and the density is ρ (g / cm ^Three ), When the vibration frequency in the vicinity of the tip of the elastic member is f (Hz), the maximum width of at least one of the plurality of sharp ends is {(8πσ / ρf ² ) ^1/3 } / 2 (cm) or less is preferable.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an application of the droplet flying phenomenon found by the inventors as a result of experimental considerations to a droplet forming apparatus. Before describing the present invention with each specific embodiment, the basic configuration and operating principle of the present invention will be described.
[0020]
1A and 1B show an example of a basic configuration of the present invention, in which FIG. 1A is a front view of a main part of a droplet forming apparatus, and FIG. The droplet forming apparatus of this example is provided with a vibrator 2 on a substrate 1 as vibration generating means, and a plate-like elastic member 7 is formed on the vibrator 2 as vibration transmitting means. . The elastic member 7 has a cantilever structure whose base end is a connection portion with the vibration generating means, and the tip thereof has two sharp end portions 7a and 7a and one concave portion 7b. The liquid 8 is brought into contact as a thin liquid layer at least near the tip of the cantilever structure. In the configuration of this example, the liquid surface 8a is filled so as to be positioned between the distal end and the bottom surface (base end portion) of the elastic member 7, and due to the wettability of the liquid 8 and the elastic member 7 and the effect of gravity, FIG. The liquid thickness 8b on the side of the elastic member in (B) is in the range of several μm to several hundred μm. Here, since the liquid only needs to be in contact with at least a part of the elastic member in the vicinity of the tip, it is possible to change the liquid supply to only one surface of the plate-like elastic member.
[0021]
The vibrator 2 is formed of a piezoelectric body 3 and electrodes 4 and 5 for applying a voltage to the piezoelectric body 3, and the electrodes 4 and 5 are connected to the driving means 9. In order to insulate the vibrator 2 and the liquid 8 from each other, SiO ₂ It is the structure covered with the protective layer 6 which consists of these. In this example, the vibrator 2 is formed on the substrate 1, but it can also be produced on the opposite side of the surface on which the elastic member 7 exists. In this case, the elastic member 7 is directly connected to the substrate 1. Further, the substrate 1 may be an elastically deformable member, which is an effective means because it can be deflected by the monomorph effect with the vibrator 2 to amplify the vibration amplitude. Further, if the vibrator can be carried by itself as the vibration generating means, a configuration using no substrate is possible.
[0022]
As the piezoelectric body 3, crystal, zirconate / lead titanate (PZT), barium titanate BaTiO _Three , Lead niobate PbNb ₂ O ₆ Bismuth germanate Bi ₁₂ GeO ₂₀ Lithium niobate LiNbO _Three Or lithium tantalate LiTaO _Three Polycrystals and single crystals such as, piezoelectric thin films such as ZnO or AlN, piezoelectric polymers such as polyurea, PVDF (polyvinylidene fluoride) or vinylidene fluoride copolymers, and inorganic piezoelectric materials such as PZT and piezoelectrics A complex with a functional polymer can be used. Of course, an optimum piezoelectric material must be selected according to the drive frequency set when designing the device. If the frequency of the alternating current applied is between several tens of kHz to 1 MHz, a ceramic such as PZT may be used. However, when driving at a higher frequency, a piezoelectric thin film corresponding to a high frequency such as ZnO is selected. There must be. In any case, the vibrator 2 needs to have vibration characteristics that allow stable and sufficient vibration. The piezoelectric body 3 may be formed of a piezoelectric substrate, a piezoelectric thin film, a single layer, or a multilayer.
[0023]
In the above case, the vibrator 2 is formed using a piezoelectric element, but is not limited to the case where a piezoelectric element is used. The elastic member of the present invention such as various electrostrictive elements, magnetostrictive elements, mechanical actuators, etc. Any device that can excite 7 can be used.
[0024]
The plate-like elastic member 7 is a member that resonates by bending vibration in the direction indicated by the arrow c in FIG. In this example, the plate-like elastic member 7 having a constant thickness is used, but the thickness may have a distribution. Preferably, a structure in which the distal end portion has a smaller bending stiffness expressed by (second moment of cross section) × (Young's modulus) of the elastic member than the proximal end portion is used. The above-mentioned second moment of section is a second moment of section related to the bending direction of the bending vibration. In order to reduce the moment, the distal end portion has a smaller width in the bending vibration direction than the base end portion. It is sufficient if the width of the vibration in the direction perpendicular to the vibration direction is small. Similarly, regarding the Young's modulus, the distal end portion may be smaller than the proximal end portion. In this way, by making (second moment of section) × (Young's modulus) smaller at the tip than at the base, the amplitude of bending vibration can be obtained more efficiently near the tip of the elastic member. In the above case, the plate-like elastic member is arranged substantially perpendicular to the vibration surface of the vibrator. However, the present invention is not limited to this, and changes such as forming an elastic member parallel to the vibration surface of the vibrator Is also possible.
[0025]
FIG. 2 shows a typical shape of the tip of the elastic member. As shown in FIGS. 2 (A) and 2 (B), the sharp end portion means a protrusion having a tip section sectional area b equal to or smaller than the bottom section area a of the protrusion. And the recessed part 7b is formed in the front-end | tip part of the elastic member 7 by the two sharp end parts 7a and 7a.
[0026]
As the material of the elastic member 7, various resins such as polyimide, cyanoacrylate resin, epoxy resin, and fluorine resin can be used. The elastic member is made of SiO. ₂ , SiON, SiN, AlN, Al ₂ O _Three You may form with various inorganic materials, such as. The elastic member may be formed of Al, Fe, Ti, Cr, Au, Mo, TiW, or the like, or an alloy thereof. However, unlike various resins and metals, SiO2 is used to prevent corrosion during contact with the liquid 8. ₂ It is desirable to protect their surfaces with an inorganic film such as. Of course, two or more materials among resin, inorganic material, and metal may be used. If the vibration energy can be efficiently propagated, the distal end portion and the proximal end portion of the elastic member 7 may be made of different materials.
[0027]
Next, the operation principle of the present invention will be described.
When an AC signal is applied to the vibrator 2 by the driving means 9, the vibrator 2 is excited by the frequency of the AC signal. The elastic member 7 resonates with the vibration of the vibrator 2, and the vicinity of the tip of the elastic member 7 has a large amplitude (c in FIG. 1B). The liquid thickness in the bending vibration direction is several μm to several hundred μm in the vicinity of the tip of the elastic member 7 due to the wetness of the liquid 8 and the elastic member 7 and the effect of gravity. The droplets fly under the strong action of.
[0028]
When an AC signal is applied continuously, continuous ink columns continue to be ejected, and minute droplets are ejected when the wave is a burst wave. Here, the burst wave is one in which an alternating voltage composed of one to a plurality of waves is intermittently generated with a constant frequency. As an example, the waveform when the number of bursts is 3 is shown in FIG. Show. In the case of a burst wave, an AC voltage can be applied to the vibrator 2 for a short time while maintaining the same frequency as the resonance frequency of the elastic member 7 or an integer multiple thereof. Therefore, the vibrator 2 is driven with a burst wave. However, the burst wave is not limited to a sine wave but may be a square wave or a triangular wave.
[0029]
In order to understand the above-mentioned flight state, the light emission of the strobe was observed in synchronization with the burst wave repetition period. The time-dependent change in the flight state can be achieved by shifting the light emission timing. As a result, first, when bending vibration of the elastic member 7 acts on the liquid 8, a capillary wave is generated on the surface of the liquid. Furthermore, the capillary wave is amplified and grown with the passage of time, and it is observed that the micro droplets fly from the wave front.
[0030]
A typical flight state is shown in FIG. FIG. 4A is a front view of the distal end portion of the elastic member, and FIG. 4B is a side view thereof. As shown in FIG. 4A, the capillary wave is most strongly amplified in the concave portion 7b between the sharp end portions 7a and 7a, and it is easy to limit the droplet flight position at the tip of the elastic member by adjusting the burst wave condition. . Further, a typical flight direction of the droplet 10 is indicated by d in FIG. 4, and it was found that in addition to the force in the bending vibration direction e of the elastic member 7, a force due to flow acts in the flow direction f. Although the cause of the flow is not clear, the pressure direction of the vibration applied to the liquid 8 and the direction of the force with which the surface tension restores the deformation of the liquid deviates, so that the component parallel to the flow direction f as shown in FIG. It is estimated that the power of
[0031]
For comparison, when observed using a plate-like elastic member that does not have a plurality of sharp edges, a large number of capillary waves are generated on the elastic member surface, making the droplet flight position and flight direction stable. Could not be controlled.
[0032]
FIG. 5 is a diagram showing the flying state of the droplet when the flying condition is changed. If the condition of the burst wave repetition frequency is constant and the condition is changed in such a manner that the thickness of the liquid contacting the elastic member 7 is reduced and the number of bursts is reduced, the droplet 10 becomes d1 in FIG. If the liquid thickness is increased and the number of bursts is increased, the flight direction tends to approach the flight direction indicated by d2 in FIG. 5B. This is presumably because the magnitude and ratio of the force in the directions e and f in FIG. 4 are changed. Furthermore, under the conditions shown in FIG. 5B, droplet flying having a diameter depending on the width of the recess, that is, the distance between the sharp edges, is observed instead of the wavelength of the capillary wave. Since the capillary wave is a surface wave having a surface tension as a restoring force, it is considered that the force of the component perpendicular to the liquid surface basically contributes to the generation and growth of the capillary wave. Under the conditions of FIG. 5B, the force component due to the flow is very large compared to the force contributing to capillary wave generation, so it is considered that the above-described flight form has been achieved. In any case, if the flight conditions are determined, the uniformity of the droplet diameter and the stability of the flight direction are very good, and various designs are possible depending on the intended use.
[0033]
Generally, the wavelength of the capillary wave is such that the surface tension of the liquid 8 is σ (mN / m) and the density is ρ (g / cm ^Three ), When the excitation frequency is f (Hz), (8πσ / ρf ² ) ^1/3 (Cm) is known. Therefore, the width of the recess that defines the amplification region of the capillary wave, that is, the distance between the sharp edges (g in FIG. 2) is the minimum half wavelength {(8πσ / ρf) that the capillary wave can amplify. ² ) ^1/3 } / 2 (cm) is desirable. Furthermore, the capillary wave can be generated as a standing wave in a limited region by setting the distance between the sharp edges (g in FIG. 2) to be an integral multiple of a half wavelength. Thereby, it is possible to efficiently amplify the capillary wave. Further, it is desirable that the maximum width (h in FIG. 2) of the sharp end is not more than a half wavelength of the capillary wave. Accordingly, it is possible to more surely realize the suppression of the generation of capillary waves on the sharp end face and the limitation of the capillary wave amplification region between the concave portions, that is, the sharp end portions.
[0034]
【Example】
Hereinafter, based on an Example, this invention is demonstrated concretely.
Example 1
6A and 6B are diagrams showing the main part of an embodiment of the droplet forming apparatus of the present invention, wherein FIG. 6A is a front view and FIG. 6B is a side view. In this example, an Ag electrode 4 having a thickness of 1 μm was deposited on a substrate 1 made of brass having a thickness of 200 μm, and then patterned. Subsequently, after depositing a piezoelectric body 3 made of PZT (zirconic acid / lead titanate) having a thickness of 100 μm, patterning is performed, and further, 2 of Cr having a thickness of 0.05 μm and Au having a thickness of 1 μm. After depositing the electrode 5 composed of layers, the vibrator was formed by patterning.
A piezoelectric body 3 made of PZT is used as a constituent element of the vibrator 2 so as to vibrate in a direction perpendicular to the film surface when a voltage is applied between the electrodes by polarization treatment. Furthermore, the vibrator 2 composed of the piezoelectric body 3 and the electrodes 4 and 5 is made of SiO 2 having a thickness of 1 μm. ₂ Then, a stainless steel foil having a thickness of 7 μm was bent into an “L” shape as the elastic member 7 on the vibrator 2 and bonded as shown in FIG.
The front shape of the elastic member is processed by a YAG laser and has a plurality of sharp end portions 7a and a plurality of concave portions 7b as shown in FIG. However, the same applies to the following embodiments, but the method of forming the elastic member is not limited to this, and is not limited to the processing technique using the lithography technique used in the semiconductor process, the thick film printing technique, or the micromachine manufacturing process. Various forming techniques (anisotropic etching, excimer laser processing, electric discharge processing, plating technique, etc.) that are used can be used to form elastic members made of various metal materials, inorganic materials, organic materials such as resins, and the like.
[0035]
In this example, water was used as the liquid 8 to be caused to fly. The liquid surface 8a was filled so as to be positioned between the tip and bottom surfaces of the elastic member 7, and an AC signal was applied to the vibrator from the outside using the driving means 9 to excite the vibrator. The frequency of the AC signal is most preferably the same as the natural frequency of the vibrator 2 and the elastic member 7 in terms of efficiency. In this embodiment, the AC signal is designed to resonate at 192 kHz. Specifically, since the front width of the elastic member 7 is 600 μm, the maximum height is 520 μm, and the wavelength of the capillary wave at 192 kHz of water is about 30 μm, the sharp end distance is 45 μm, which is three times the half wavelength. The sharp end width was set to 12 μm.
[0036]
As a burst wave condition, 192 kHz, 10 V _PP 20 cycles of AC waves were repeatedly applied at a cycle of 1 kHz. As a result, it was confirmed by flight observation using a strobe that the droplets 10 flew between the sharp end portions at every repetition cycle, the diameter was uniform as 15 μm, and the direction stability was excellent. .
[0037]
According to this embodiment, uniform fine droplets can be ejected with good directivity and the number of droplets can be controlled, so that it can be used as a droplet forming apparatus suitable for spraying medical drugs. In the above case, a plurality of elastic members may be provided with respect to the vibrator, or a plurality of elastic members may be provided with respect to the plurality of produced elastic members.
[0038]
FIG. 7 shows a representative example of the shape of the tip of an elastic member that can be used in the droplet forming apparatus of the present invention in the same manner as in the above embodiment. (A) is a front view, (B) is a side view, and all combinations of (A) and (B) are possible. Thus, the elastic member shape can be variously changed without departing from the requirements of the present invention.
[0039]
Example 2
FIG. 8 shows the main part of an embodiment of an image forming apparatus to which the droplet forming apparatus of the present invention is applied. (A) is a front view, (B) is a side view. In this embodiment, an Ag electrode 4 having a thickness of 1 μm is deposited on a substrate 1 made of brass having a thickness of 200 μm, followed by patterning, followed by PZT (zirconic acid / titanic acid having a thickness of 100 μm). After the piezoelectric body 3 made of lead is deposited, patterning is performed, and further, the electrode 5 composed of two layers of Cr having a thickness of 0.05 μm and Au having a thickness of 1 μm is deposited, followed by patterning and vibration. Formed a child.
The piezoelectric body 3 made of PZT is polarized as a constituent element of the vibrator 2 so as to vibrate in a direction perpendicular to the film surface when a voltage is applied between the electrodes. Furthermore, the vibrator 2 composed of the piezoelectric body 3 and the electrodes 4 and 5 is made of SiO 2 having a thickness of 1 μm. ₂ Then, the elastic layer 7 made of stainless steel was formed on the vibrator 2. The front shape of the elastic member had two sharp end portions and one concave portion as shown in FIG. With respect to the design value 192 kHz of the resonance frequency, the elastic member 7 has a maximum front width of 600 μm and a maximum height of 520 μm. Further, in this embodiment, since the aqueous black ink is used as the liquid 8, and the wavelength of the capillary wave of the aqueous black ink is about 30 μm, the sharp end distance is sharpened to 45 μm, which is three times the half wavelength. The maximum width of the end portion was set to 12 μm.
[0040]
In this embodiment, the combination of the vibrator 2 and the elastic member 7 constitutes an ejector for discharging ink droplets. Further, as shown in FIG. 8B, the liquid level before and after the elastic member is changed so that the droplet 10 flies only in one direction. Here, means for realizing flight in one direction is not limited to the above case, and it is also possible to make the protrusion side surface shape asymmetric. The electrode 4 may be configured as a common electrode common to a plurality of ejectors, and the electrode 5 may be configured as an address electrode that drives only a specific ejector. Accordingly, it is possible to record the visualization information by driving a specific ejector in accordance with the image signal to eject ink droplets and attaching them to the printing surface.
[0041]
FIG. 9 shows a main part of an example of an image forming apparatus to which the droplet forming apparatus of the present invention is applied. In the image forming apparatus of this example, the recording element 11 having the above-described ejector is fixed to the carriage 12. The carriage 12 is guided by the guide 13 and reciprocates in the paper width direction of the printing paper 14, and the printing paper 14 is fed along the guides 16 and 17 by the rotation of the feed roller 15. An image is printed.
[0042]
As shown in FIG. 10, the recording element 11 includes ejectors 19 each composed of a vibrator and an elastic member arranged in a plover shape on a substrate, so that even if the vibrator and the elastic member are relatively large, High density printing is possible.
[0043]
The example shown in FIG. 10 is an example of so-called matrix drive, and the leads A1 to A5 are leads of one electrode, and are connected to the respective ejectors 19 in the vertical direction, and the leads B1 to B6 are connected to the other. It is an electrode lead and is connected to each ejector 19 in the lateral direction. A voltage is applied between any one of the leads A1 to A5 and any one of the leads B1 to B6, whereby one ejector is selected and excited.
[0044]
In the image forming apparatus shown in FIG. 9, the feeding speed of the carriage 12 and the arrangement interval of the vibrators in the recording element 11 correspond to 600 dpi (dots / inch).
The recording element 11 includes four recording element units corresponding to four colors of black, yellow, magenta, and cyan, and is connected to the ink supply unit 18. The ink supply unit 18 has a structure in which inks of four colors of black, yellow, magenta, and cyan are held inside.
The ink of each color held in the ink supply unit 18 is supplied to the recording element unit of each color of the recording element. When a voltage is applied to the vibrator corresponding to the image signal, ink droplets are ejected from the ink surface on the selected vibrator, and an image is formed. Although not shown, an electrical signal to the recording element 11 is sent from the outside via the carriage 12.
[0045]
As burst wave conditions, 192 kHz, 30 V _PP Five cycles of alternating waves were applied at a repetition rate of 1 kHz. Accordingly, it is possible to selectively fly one droplet from the concave portion between each sharp end portion every repetition cycle, the diameter thereof is uniform at 16 μm, and excellent directional stability. It was confirmed by flight observation using
The dots formed on the printing paper 14 after printing were uniform dots arranged in a circle with a diameter of approximately 30 μm, which is approximately twice the diameter of the ejected ink droplet. Even when printing was continued, the dot diameter did not fluctuate and ink was not discharged.
[0046]
Since the image forming apparatus of this embodiment has the recording element 11 equipped with the droplet forming apparatus of the present invention, it is possible to stably form minute dots corresponding to a high resolution on the printing paper 14, and high-quality printing is possible. Met.
[0047]
FIG. 11 shows a representative example of the shape of the elastic member that can be used in the image forming apparatus shown in FIG. (A) is a front view, (B) is a side view, and all combinations of (A) and (B) can be used. As described above, the shape of the elastic member can be variously changed without departing from the requirements of the present invention.
[0048]
【The invention's effect】
As described above, the droplet forming apparatus of the present invention can efficiently eject minute droplets without using a nozzle, and is excellent in droplet uniformity and directionality. That is, by bending vibration of a plate-like elastic member having a cantilever structure, a capillary wave can be generated on the liquid surface near the tip of the elastic member, and the liquid can fly, and the tip of the elastic member has a plurality of tips. By providing the concavo-convex structure including the sharp end portion and one or more concave portions, there is an effect that the amplification region of the capillary wave is limited to the concave portions between the plural sharp end portions. Due to this effect, the uniformity of the diameter of the droplets to fly and the flying directionality can be improved, and it is possible to drive with low frequency and low power. Therefore, the droplet forming apparatus of the present invention is suitable for use in various applications, particularly in an image forming apparatus, and can form a recorded image with excellent image quality by an image recording method using the apparatus. .
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a basic configuration of a droplet forming apparatus of the present invention.
FIG. 2 is a perspective view showing a representative elastic member tip in the droplet forming apparatus of the present invention.
FIG. 3 is a diagram showing a typical burst wave of a drive signal used in the present invention.
FIG. 4 is an explanatory diagram showing a typical flight state in the basic configuration of the droplet forming apparatus of the present invention.
FIG. 5 is an explanatory diagram showing a flying state when a flying condition is changed in the basic configuration of the droplet forming apparatus of the present invention.
FIG. 6 is a diagram showing a main part of an embodiment of the droplet forming apparatus of the present invention.
FIG. 7 is a diagram showing a representative example of an elastic member shape applicable to the droplet forming apparatus of the present invention.
FIG. 8 is a diagram showing a main part of an embodiment of a recording element to which the droplet forming apparatus of the present invention is applied.
FIG. 9 is a perspective view of an embodiment of an image forming apparatus to which the droplet forming apparatus of the present invention is applied.
FIG. 10 is a diagram illustrating a driving method of an image forming apparatus to which the droplet forming apparatus of the present invention is applied.
FIG. 11 is a diagram showing a representative example of an elastic member shape applicable to an image forming apparatus to which the droplet forming apparatus of the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Vibrator, 3 ... Piezoelectric body, 4,5 ... Electrode, 6 ... Protective layer, 7 ... Elastic member, 7a ... Sharp-end part, 7b ... Recessed part, 8 ... Liquid, 8a ... Liquid surface, 8b ... Liquid thickness, 9 ... Driving means, 10 ... Droplet, 11 ... Recording element, 12 ... Carriage, 13 ... Guide, 14 ... Printing paper, 15 ... Feed roller, 16, 17 ... Guide, 18 ... Ink supply section, 19 DESCRIPTION OF SYMBOLS ... Ejector, a ... Cross-sectional area of bottom part of protrusion part, b ... Cross-sectional area of front-end | tip part of protrusion part, c ... Arrow which shows the bending vibration direction of an elastic member, d ... Flying direction of a droplet, e ... Bending vibration direction of an elastic member F: Flow direction, g: Distance between sharp edges, h: Maximum width of sharp edges.

Claims (3)

In a droplet forming apparatus that includes a vibration generating unit and a vibration transmitting unit, and the liquid is brought into contact with the vibration transmitting unit to fly the liquid in the vicinity of the tip, the vibration transmitting unit includes a plurality of sharp end portions and one or more at the tip. Is formed of an elastic member having a concavo-convex structure composed of a concave portion of the above, and is formed on a single vibration generating means, and the liquid level of the liquid is positioned between the tip and bottom surfaces of the vibration transmitting means, droplet forming apparatus characterized by jetting liquid droplets from front Kifu kinematic transmission means. In an image forming droplet forming apparatus that has a plurality of vibration generating means and a plurality of vibration transmitting means corresponding to each of the vibration generating means, and in which liquid is brought into contact with the vibration transmitting means and the liquid in the vicinity of the tip is caused to fly. The vibration transmitting means is composed of an elastic member having a concavo-convex structure consisting of two sharp end portions and one concave portion at the tip, each formed on a corresponding single vibration generating means, and the liquid level is located between the tip and the bottom surface of the vibration transmitting means, the image forming liquid droplet forming apparatus characterized by jetting liquid droplets from the respective front Kifu dynamic transmission means. Image formation in which vibration is generated from the vibration generating means based on image information and transmitted to the tip of the vibration transmitting means, and droplets are ejected from the vicinity of the tip of the vibration transmitting means by the transmitted vibration and recorded on a recording medium. In the method, the vibration transmitting means is formed on a single vibration generating means, and is composed of an elastic member having a concavo-convex structure including two sharp end portions and one concave portion at the tip, in a state where the surface is located between the tip and the bottom surface of the vibration transmitting means, the image forming method characterized by jetting liquid droplets from front Kifu kinematic transmission means.

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