JPH1148469A - Ink jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording head capable of reducing a diameter of ejected ink drops and not having conventional defects such as the ejection unstability of ink drops, the irregularity of the dot positions of the ejected ink drops or the like. SOLUTION: This recording head has a vibration generating part 2 vibrated corresponding to a pixel signal and the leading and 7a coming into contact with ink 8 and is equipped with an elastic member 7 having a cantilevered beam structure making the cross sectional shape of the ink 8 generating bending vibration corresponding to the excitation of the vibration generating part 2 and cut along the surface vertical to the neutral shaft of the bending deformation of the leading part 7a asymmetric to a neutral surface and capillary waves are generated on the surface of the ink 8 to fly the ink 8 to bond the same to a recording medium.

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 recording medium.

[0002]

2. Description of the Related Art A typical method of printing by discharging droplets, particularly ink drops, onto a recording medium is a method using a nozzle. Here, the recording method of the nozzle type includes an on-demand type and a continuous flow type.

The on-demand type is a system in which ink is intermittently ejected from nozzles in accordance with recording information to perform printing, and there are a piezo oscillator type and a thermal type as typical ones. The piezo oscillator type applies a pulse voltage to a piezoelectric element provided in the ink chamber to deform the piezoelectric element, thereby changing the ink liquid pressure in the ink chamber and ejecting an ink drop from a nozzle to print on a recording medium. The dot is recorded in the. In the thermal type, the ink is heated by a heating element provided in the ink chamber, and an ink drop is ejected from a nozzle by a bubble generated thereby,
This is to record dots on a recording medium.

[0004] 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 an ejected ink column into droplets. The recording is performed by selectively charging and deflecting.

Recently, a high resolution such as 600 to 720 dots / inch has been demanded. In order to satisfy such demands, it is necessary to reduce the dot diameter on the recording medium, and in the conventional nozzle-type recording method, it is necessary to reduce the nozzle diameter to reduce the ink drop diameter to be ejected. .

However, when the nozzle diameter is reduced,
Dust and dust, nozzle clogging due to drying of the ink surface in the nozzle, and a change in the ink ejection direction due to these factors are likely to occur, resulting in a defect in the image quality on the recording medium. Therefore, it is difficult to achieve a dot diameter corresponding to the required resolution by reducing the nozzle diameter.

Therefore, as a method of solving such a problem caused by the nozzle, there are several recording methods for performing printing by ejecting ink drops onto a printing target surface using vibration or acoustic waves without using a nozzle. Or has been proposed.

As a first recording method using no nozzle, as disclosed in US Pat. No. 4,308,547, ink generated by vibrating a vibrator is focused on an ink free surface at one point by an acoustic lens. This is a method of discharging a drop. As the acoustic lens, a lens in which the piezoelectric body itself is formed into a lens shape, or a lens using a phase Fresnel lens in which phases are multiplexed as disclosed in Japanese Patent Application Laid-Open No. 3-200199 are used. As for the acoustic lens, the relationship between the shape and the convergence / divergence of the wave is opposite to that of the optical lens, and the convex lens causes the wave to diverge, so it is desirable to use a concave lens.

The diameter of the ink drop is almost equal to the diameter of the longitudinal wave propagating through the ink when the longitudinal wave is focused on the free surface of the ink. Let F be d to 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.

Therefore, for example, when an extremely small ink drop having a drop diameter (converging diameter) d of about 15 μm is to be ejected, if the F value of the lens is 1, the conventional low-viscosity, aqueous ink Is about 1500 m / sec. To cope with this, the driving frequency f of the vibrator must be set to a very high frequency such as about 100 MHz. The F value of the lens is
Since it is practically difficult to make the diameter extremely small due to various problems, generally, when the drop diameter d is made smaller, the vibrator is driven at an extremely high frequency.

As described above, in the first recording method, 100
Since a plurality of vibrators must be driven at a high frequency of about MHz, there is a cost problem that the driving means is generally expensive. In addition, there is a quality problem that the ink viscosity changes due to heat generation and the drop diameter fluctuates, and the ink itself may be dried or solidified in the recording apparatus and the ink cannot be ejected.

As a second recording method which does not use a nozzle, there is a method in which the vibration generated by the vibration generating means is focused on a point on the free surface of the ink by an acoustic horn to discharge an ink drop.

For example, see the above-mentioned US Pat. No. 4,308,547.
In the specification, vibration is focused by an acoustic horn formed on vibration generating means instead of a concave lens, and the vibration is applied to an ink thin film conveyed on a belt in contact with the tip of the acoustic horn. It is shown that an ink drop is ejected. Here, a discharge force is generated at the tip of the acoustic horn.

As a similar technique, Japanese Patent Laid-Open No.
No. 8050 discloses a sound collector 15 as shown in FIG.
Is provided on the piezoelectric body 3. Sound collector 15
Are formed on the vibration generating means 2 including the piezoelectric body 3 and the electrodes 4 and 5 for applying a voltage to the piezoelectric body 3 and the ink 8
Is disposed in the ink reservoir 10 which holds. Sound collector 1
5 has a tapered shape as shown in FIG. In this case, the distortion incident from the bottom of the sound collector 15 is
As it propagates through the inside, the amplitude is amplified, and the large-amplitude wave collected by the sound collector 15 hits the ink 8, and the generated longitudinal wave pushes up the ink free surface 8 a, and the ink drop 9 Is discharged.

However, in US Pat. No. 4,308,547 and JP-A-4-168050, although a sound collector or an acoustic horn is used, the size, driving conditions, vibration mode, etc. are further reduced by a small diameter drop. It is not stated whether or not can be formed.

Regarding the acoustic horn, generally, in the field of acoustics, a sound collector (or acoustic horn) is generated by resonance.
When trying to obtain a discharge force by vibrating the tip of the sound collector with a large amplitude, the length (height) of the sound collector in the vertical cross section must be an integral multiple of half the wavelength of the vibration wave. Are known. For this reason, in the method shown in FIG. 12, when trying to reduce the size of the sound collector 15 in order to produce a high-density recording element, the wavelength of the vibration wave must be shortened.
The driving frequency of the vibration generating means 2 must be increased.

Therefore, in order to manufacture a recording element with a realistic density, several tens of MHs are required as in the first recording method.
It is necessary to drive the vibration generating means at a high frequency of about 100 MHz from z. For this reason, the energy in the ink is greatly attenuated, and the driving circuit becomes expensive. Further, as disclosed in U.S. Pat. No. 4,308,547, it is practically difficult to stably convey an ink thin film with a belt in contact with the tip of an acoustic horn, and the diameter of a discharge drop tends to vary.

As a third recording method without using a nozzle,
There is a so-called electrostatic attraction method using electrostatic force as a discharge force, and a method using vibration to form an ink meniscus (ink protrusion) is known.

For example, Japanese Patent Application Laid-Open No. 62-222853 discloses that a recording needle is made to protrude from the ink surface to apply ultrasonic energy propagating in the axial direction to the recording needle. According to this, ultrasonic flow (acoustic)
Due to the 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 the needle electrode is vibrated at the same time. The scheme is shown. This way,
Ink can be stably formed into particles.

However, in the electrostatic suction method, there is a problem that the diameter of the formed drop varies due to a variation in the thickness of the dielectric of the recording medium due to humidity or a variation in the roughness of the surface of the recording medium. Further, in the electrostatic suction method, a problem arises in that, by discharging a charged ink drop, a dot position variation is increased due to a residual charge of a preceding dot on a recording medium.

[0022]

The conventional methods proposed to reduce the diameter of the ejected ink drop without reducing the diameter of the nozzle have problems of energy efficiency and stability. Japanese Patent Application No. 8-215 filed by the present applicant to solve those problems.
No. 036. However, even the technique according to the application has a problem that fine adjustment of driving conditions is required to stably fly a single ink drop.

An object of the present invention is to reduce the diameter of an ink drop to be ejected, and to reduce the disadvantages of the prior art, such as instability of ejection of the ink drop and variation in the dot position of the ejected ink drop. The object of the present invention is to provide an ink jet recording head having no ink jet recording head. More specifically, an object of the present invention is to prevent ejection failure due to nozzle clogging and drying, to have high energy efficiency, and to be excellent in ink drop flight stability without being affected by the ejection history or adjacent nozzles. That the dot diameter variation on the recording medium is small and the dot position accuracy is good,
An object of the present invention is to provide an ink jet recording head having such characteristics.

[0024]

The object of the present invention is to provide a vibration generating means which vibrates in response to a pixel signal and a tip portion which comes into contact with ink, and which bends and vibrates in response to excitation of the vibration generating means.
Equipped with a cantilevered elastic member that makes the cross-sectional shape of the ink cut at a plane perpendicular to the neutral axis of the bending deformation of the tip part asymmetric with respect to the neutral plane, and generates a capillary wave on the ink surface The ink jet recording head is characterized in that the ink is caused to fly and adhere to the recording medium.

Here, the neutral shaft and the neutral surface will be described with reference to FIGS. 13 to 15 schematically show how the cantilever is bent and deformed. FIG. 13 is a side view of the bent cantilever, and FIG.
4 is a cross-sectional view taken along line NN in FIG. A, and FIG. 15 is a perspective view of a cantilever beam that is being bent and deformed. When the beam is bent and deformed as shown in FIG. 13, a bending stress acts on the cross section of the beam in the vertical direction as shown in FIG.

In the case of the NN cross section in FIG. 13, a tensile strain is generated on the convex surface of the bent beam (the right side of the beam in the figure), and a compressive strain is generated on the concave surface (the left side of the beam in the figure). There is a plane without expansion and contraction in the middle of this. This is called the neutral plane. Then, as shown in FIG. 15, an axis at which the neutral plane and the cross section intersect is called a neutral axis.

Further, the object is to provide an ink jet recording head according to the present invention, wherein the cross-sectional shape of the tip section taken along a plane perpendicular to the neutral axis of bending deformation is asymmetric with respect to the neutral plane of bending deformation. This is achieved even if the configuration is made as described above. Further, the above object is achieved in the ink jet recording head of the present invention, in which the tip has one surface and another surface having different wettabilities from each other. Still further, the above object is achieved even in the ink jet recording head according to the present invention, in which the tip is supplied with ink only to one surface.

Hereinafter, the basic structure and operation principle of the ink jet recording head according to the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing an example of a basic configuration of the ink jet recording head of the present invention. FIG. 2 is an enlarged view near the distal end of the elastic member 7 shown in FIG. The elastic member 7 is connected to the vibration generating section 2 and has a cantilever structure with the connection section as a base end, and at least the vicinity of the tip is in contact with ink. The vibration generating section 2 is excited at a frequency at which the elastic member 7 resonates by bending vibration, and the resonance causes a large amplitude near the tip of the elastic member 7.
The ink thickness in the vibration direction of the bending vibration is formed to be several μm to several hundred μm in the vicinity of the tip of the elastic member 7 due to the effects of the wetting of the ink 8 and the elastic member 7 and the effect of gravity. As a result, the ink 8 is strongly affected by the vibration, and generates a capillary wave on its surface. The action of the capillary wave enables the generation of microdroplets, and the vibration generator 2 can fly a single ink drop by setting its driving conditions to a predetermined value by the external driving unit 12. As shown in FIG. 3, the excitation of the vibration generating unit 2 is intermittently performed every time the number of excitations required for the single ink drop is completed so that the single ink drop is performed in response to one pixel signal. Excitation is demarcated. Note that the excitation pulse required for flying a single ink drop is not limited to a rectangular wave, but may be a sine wave or a triangular wave. As a result, fine droplets are generated without a nozzle, and a high-quality ink jet recording head free from ink clogging can be realized.

The vibration generating section 2 composed of the piezoelectric body 3 and the electrodes 4 and 5 has a characteristic determined by the rigidity of the substrate 1, the thickness and piezoelectric characteristics of the piezoelectric body 3, and the size and rigidity of the connected elastic member 7. Has a resonance frequency fo. The drive frequency of the external drive unit 12 may be any value, but when driven at the resonance frequency fo or a frequency f that is an integral multiple of the resonance frequency fo, the vibration generation unit 2 can be efficiently excited.

The most important piezoelectric body 3 in the vibration generator 2 for bending and vibrating the elastic member 7 may be formed of a piezoelectric substrate or a piezoelectric thin film. Further, the piezoelectric body 3 may be composed of a single layer or a multilayer. Quartz, PZT, barium titanate BaTi
O ₃ , lead niobate PbNb ₂ O ₆ , bismuth germane manut Bi ₁₂ GeO ₂₀ , lithium niobate LiNbO ₃ , lithium tantalate LiTaO _3, etc., a polycrystalline or single crystal, or a piezoelectric thin film such as ZnO or AlN, or A piezoelectric polymer such as polyurea, PVDF (polyvinylidene fluoride) or a copolymer of PVDF, or a composite of an inorganic piezoelectric substance such as PZT and a piezoelectric polymer can be used. Of course, it is necessary to select an optimal piezoelectric material according to the drive frequency set when designing the ink jet recording head. The frequency of the applied alternating current is
If the frequency is between 0 kHz and 1 MHz, 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 must be selected. In any case, it is necessary that the vibration generating portion 2 has stable and sufficient vibration characteristics.

The shape and material of the elastic member 7 are not limited as long as the ink cross section can be formed asymmetrically in the vicinity thereof and a single ink drop can fly by bending vibration of the elastic member 7. If the ink flying is performed with the ink cross-section formed symmetrically, the size and the flying direction of the ink drop become unstable. This is because the ink thin liquid layer is formed symmetrically on the surface of the elastic member, and the ejection of the ink drop varies in a direction other than the intended ejection direction due to bending vibration at the tip of the elastic member. It is considered that a cause of this is that the ink consumption flies at the tip of the elastic member due to the ink drop flying, resulting in unstable ink flow. On the other hand, when the ink cross-sectional shape is asymmetric, the ink consumption at the tip of the elastic member is biased to one surface. It is considered that the flow is stabilized. Therefore, since the location of the capillary wave formed at the tip of the elastic member is limited by the stable ink flow, the ink drop 9 can always be ejected from the same location, and as a result, a single minute ink Drops can be discharged stably.

As described above, it is effective to make the distribution of the thickness of the ink existing near the tip portion of the elastic member non-uniform to stably fly the ink drop. In other words, in other words, as shown in FIG. 2, in the sectional view showing the tip of the elastic member and the ink present on the surface, the sectional shape of the ink is changed to the left side surface of the elastic member. And the right side surface (hereinafter, the expression “the cross-sectional shape of the ink is asymmetric” is used in this specification). Therefore, several examples for asymmetrically forming the cross-sectional shape of the ink in the vicinity of the elastic member will be described with reference to FIGS. First, the elastic member 7
The elastic member 7 preferably has a shape that becomes sharper toward the distal end portion, a thickness that allows bending vibration at the distal end portion, or a material whose bending stiffness is smaller at the distal end portion than at the proximal end portion of the elastic member 7. This is because a displacement of the distal end portion of the elastic member due to bending vibration becomes small at a thick distal end portion, and a very large driving voltage is required to vibrate the distal end portion.

FIG. 4A shows an example in which the cross-sectional shape of the elastic member is asymmetric. In this example, the cross-sectional shape of the elastic member 7 is sharpened toward the tip, but if the cross-sectional shape is asymmetric, the ink cross-sectional shape is inevitably asymmetric. The shape is not particularly limited.

In FIG. 4B, the elastic member 7 is installed so as to be inclined with respect to the surface of the vibration generating section. As a result,
The ink cross section becomes asymmetric. The angle of inclination is not particularly limited as long as the ink cross section can be formed asymmetrically. However, the flight direction of the ink drop also changes depending on the inclination angle, so that it is necessary to consider it when making a device.

In FIG. 4C, the wettability of the surface of the elastic member is changed to make the cross-sectional shape of the ink asymmetric. In order to change the wettability, two or more materials having different wettabilities are applied to the surface of the elastic member. Specifically, it can be realized by applying a different hydrophilic material to the surface, changing the surface roughness of the surface, or making the elastic member of two or more different materials instead of the same material.

In FIG. 4D, the cross section of the ink is made asymmetric by changing the wettability of the surface of the elastic member as in FIG. 4C. is there. On the surface to which the liquid repellent material is applied, it is difficult for the ink 8 to get wet and the ink does not easily flow.
Thus, since the flow for supplying the ink is only on one side, a stable flow of the ink can be realized.

In FIG. 4E, an elastic member 7 is formed on the partition member to supply ink only to one side. In this example, as long as the ink is supplied from only one side of the elastic member 7, the cross-sectional shape of the ink is asymmetric, and the configuration is not necessarily limited to this configuration. Ink is supplied to only one of the elastic member surfaces to form an asymmetric ink cross-sectional shape.

In FIG. 4F, the wettability of the surface of the elastic member 7 which is in contact with the ink, the vibration generating portion, and the surface,
Although the formed ink cross-sectional shape is different, the material, surface wettability, and the like are not particularly limited as long as an asymmetric ink cross-sectional shape is formed.

As the material of the elastic member 7, various resins such as a cyanoacrylate resin, an epoxy resin, and a fluorine resin can be used. In addition, SiO ₂ ,
The elastic member 7 may be formed of various inorganic materials such as SiON, SiN, AlN, and Al ₂ O ₃ . Further, the elastic member 7 may be formed of Al, Fe, Ti, Cr, Au, Mo, TiW, or the like, or various alloys thereof. However, unlike various resins and metals, an inorganic film such as SiO ₂ is used to prevent corrosion during contact with the ink 8.
It is desirable to protect those surfaces. Of course, two or more of the resins, inorganic materials, and metals may be used. Further, if the vibration energy can be efficiently transmitted, the tip and the bottom of the elastic member 7 may be made of different materials.

In the present invention, it is not necessary to use a nozzle to regulate the drop diameter. However, in order to stabilize the ink liquid level and to suppress the drying of the ink, a nozzle having an opening larger than the discharge drop diameter is used. If so, some member may be arranged on a part of the ink surface 8a.

FIGS. 5 and 6 show the results of observation by flash synchronization in order to understand the ink drop ejection phenomenon. FIG. 5 shows a state where the vibration generation unit 2 is stationary.
As shown in (a), the tip 7a of the elastic member 7 protrudes from the ink surface 8a. When a voltage of a burst wave as shown in FIG. 3 is applied to the vibration generator 2 for a short time, FIG.
As shown in (b), it was confirmed that a capillary wave was formed on the side wall 7c due to the bending vibration of the elastic member 7. Then, when the capillary wave is formed, as shown in FIG.
Is discharged. However, when a symmetrical ink sectional shape was formed on the elastic member 7, it was confirmed that the ink drops 9 having different drop diameters fluctuated unstablely in multiple directions as shown in FIG. 6B. This is thought to be because, as described above, the ink consumption flies at the tip of the elastic member due to the ink drop flying, and as a result, the ink flow becomes unstable. Therefore, when the ink cross-sectional shape is symmetric,
It is difficult to stably eject a single minute ink drop.

In the present invention, in which an asymmetric ink sectional shape is formed in the vicinity of the elastic member 7, when the ink sectional shape is asymmetric, the ink consumption at the tip of the elastic member is biased to one surface. It is considered that the ejection direction of the ink drop is stabilized by the bending vibration in the above, and the ink flow by the ink consumption is stabilized. Therefore, since the location of the capillary wave formed at the tip of the elastic member is limited by the stable ink flow, the ink drop 9 can always be ejected from the same location, and as a result, a single fine ink Drops can be discharged stably.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An ink jet recording head according to a first embodiment of the present invention will be described with reference to FIG. FIG. 7 shows a schematic side view of the ink jet recording head according to the present embodiment. The present embodiment is directed to a case where an asymmetric ink cross-sectional shape is formed to cause ink to fly. First, an Ag electrode 4 having a thickness of 1 μm is deposited and patterned on a substrate 1 made of brass having a thickness of 500 μm, and subsequently, PZT (zirconate / lead titanate) having a thickness of 100 μm is formed. After the piezoelectric body 3 is deposited, patterning is performed, and further, an 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 and then patterned to form the vibration generating portion 2. I do.

The piezoelectric body 3 made of PZT is polarized so that when a voltage is applied between the electrodes 4 and 5, the piezoelectric body 3 vibrates in a direction perpendicular to the film surface. The electrode 4 is a common electrode common to the respective vibration generators 2, and the electrode 5 is an address electrode for causing only a specific vibration generator to vibrate.

Further, the vibration generating part 2 composed of the piezoelectric body 3 and the electrodes 4 and 5 is covered with a protective film 6 made of SiO ₂ or the like having a thickness of 1 μm. An elastic member 7 made of a pyramid-shaped cyanoacrylate-based resin having a substantially triangular cross section and having a side of 200 μm and a height of 500 μm is formed.

The elastic member 7 is formed by forming a concave portion in a fluororesin, which has poor wettability with the cyanoacrylate resin and is difficult to adhere to, and is formed into a mold. However, the same applies to the following embodiments, but the method of forming the elastic member 7 is not limited to this, and a processing technique using a lithography technique used in a semiconductor process, a thick film printing technique, or a micro machine. Various forming techniques (such as electric discharge machining and plating techniques) used in the manufacturing process can be used for forming the elastic member 7 made of an inorganic material or a metal material without being limited to the resin.

The same applies to each of the embodiments disclosed below. However, the combination of the vibration generating unit 2 and the elastic member 7 is used for the ejector 11 for ejecting ink drops.
(Broken line in FIG. 7). The distance between the tip 7a of the elastic member 7 and the surface 8a of the ink 8 is 50 μm,
Is put on the ink surface 8a. Then, using an AC power supply (not shown), the vibration
A unique resonance frequency fo determined by the rigidity of the substrate 1
Is applied, or a voltage having a frequency f that is an integral multiple thereof is applied to excite the vibration generating unit 2.

The same applies to other embodiments to be described later, but a voltage is selectively applied to one or more of the plurality of ejectors 11. In this example, a burst wave having an excitation frequency of 198 kHz and a voltage of 40 Vp-p (highest and lowest amplitude) was applied for 100 μsec. As a result, an ink drop 9 having a diameter of 20 μm was stably ejected from the vibration generating section 2 selected by the address electrode 5 in the direction of the arrow in the figure.

When recording was performed by flying the ink drop 9 on recording paper disposed at a distance of 1 mm from the tip of the elastic member 7, continuous printing was performed from the same ejector.
The average dot diameter of 00 dots is 40 μm, and the standard deviation is 1
The root-mean-square of the displacement of the dot center of gravity with respect to the center line of the dots was 3 μm, and the root-mean-square of the relative displacement of the dot positions in the ejector arrangement direction was 3 μm.

On the other hand, as shown in FIG. 6B, by using an ink jet recording head in which the cross section of the ink near the elastic member 7 is symmetrical, the driving conditions are finely adjusted to thereby achieve a single ink drop. It was made to fly and the dots printed on the recording paper were examined. As a result, the average dot diameter of 100 dots continuously printed from the same recording element was 40 μm, the standard deviation was 5 μm, the mean square of the displacement of the dot center of gravity with respect to the center line of the array was 10 μm, and the nozzle arrangement direction was The mean square of the relative displacement of the dot positions is also 10 μm
Met. As described above, it was confirmed from the results of actual printing that, according to the present embodiment, the variation in dot diameter on the recording medium due to the stable flight of the ink drop and the dot position accuracy were good.

FIG. 8 is a schematic view of an ink jet recording head according to a second embodiment of the present invention. Also in the present embodiment, the ink is caused to fly by forming an asymmetric ink cross-sectional shape. The ink jet recording head according to the present embodiment is the same as the first embodiment except for the method of manufacturing the elastic member 7.

The elastic member 7 has a thickness of 15
μm plate-like Al with respect to the vibration generating portion 2 at an elevation angle of about 70 degrees,
It was installed so as to have a height of 500 μm and was bonded with a cyanoacrylate adhesive.

The tip 7a of the elastic member 7 and the surface 8 of the ink 8
The distance to the surface a is set to 50 μm, and the tip 7a of the elastic member 7 is put on the ink surface 8a. Then, by using an AC power source (not shown), a voltage having a frequency f which is the same as the inherent resonance frequency fo determined by the rigidity of the substrate 1 or an integer multiple thereof is applied to the vibration generator 2 from the outside. Generator 2
To excite.

In this example, a burst wave having an excitation frequency of 325 kHz and a voltage of 30 Vp-p (maximum and minimum amplitude) is set to 100
Applied for μs. As a result, from the vibration generating section selected by the address electrode 5, a diameter of 15 μ
m ink drops 9 were ejected in the direction of the arrow in the figure.

Next, it is perpendicular to the vibration generating portion (elevation angle 90
The dots printed on the recording paper were compared between the ink jet recording head having a symmetrical ink cross-sectional shape and the ink jet recording head of the present embodiment by providing an elastic member in (D). As a result, the average of the dot diameters of 100 dots continuously printed from the same recording element was not changed at about 35 μm, but the standard deviation of the dot diameter and the squared average of the displacement of the dot center of gravity with respect to the center line of the array, and the nozzle array The root-mean-square of the relative positional deviation of the dot positions in the directions was several times larger in the inkjet recording head in which the ink cross-sectional shape was formed symmetrically. Table 1 shows specific numerical values.

[0056]

[Table 1]

As described above, from the results of actual printing, it is confirmed that according to the present embodiment, the variation in the dot diameter on the recording medium is small and the dot position accuracy is good due to the stable flight of the ink drop. did.

Next, FIG. 9 shows a schematic view of an ink jet recording head according to a third embodiment of the present invention. Also in the present embodiment, the ink is caused to fly by forming an asymmetric ink cross-sectional shape. The ink jet recording head according to the present embodiment is the same as the first embodiment except for the method of manufacturing the elastic member 7.

As shown in FIG. 4D, the elastic member 7 is coated with a fluororesin on the surface so that the contact angle is a-plane <b.
An asymmetric ink cross-sectional shape was formed on the surface. Next, the height of the elastic member 7 was set to 500 μm, and the distance from the tip 7 a to the surface 8 a of the ink 8 was set to 50 μm. Then, using an AC power supply not shown,
A voltage having a frequency f that is the same as the inherent resonance frequency fo determined by the rigidity of the substrate 1 or an integer multiple thereof is applied to the vibration generator 2 from the outside to excite the vibration generator 2.

In this example, a burst wave having an excitation frequency of 243 kHz and a voltage of 20 Vp-p (maximum and minimum amplitude) is 100
Applied for μs. As a result, an ink drop 9 having a diameter of 20 μm was stably ejected in the direction of the arrow in the figure from the vibration generating section 2 to which the image signal was input.

Next, by making the wettability of the surface of the elastic member the same, the dots printed on the recording paper were compared between the ink jet recording head having a symmetrical ink cross section and the ink jet recording head of the present embodiment. As a result, the dot diameter of 100 dots continuously printed from the same recording element did not change, but the standard deviation of the dot diameter and the root mean square of the displacement of the dot centroid with respect to the center line of the arrangement, and the nozzle arrangement direction The mean square of the relative positional deviation of the dot positions was several times larger in the ink jet recording head in which the symmetrical ink cross-sectional shape was formed with the same wettability on the surface of the elastic member. Table 2 shows specific numerical values.

[0062]

[Table 2]

As described above, from the results of actual printing, it is confirmed that according to the present embodiment, the fluctuation of the dot diameter on the recording medium is small and the positional accuracy of the dots is good due to the stable flight of the ink drop. did.

Next, FIG. 10 shows a schematic view of an ink jet recording head according to a fourth embodiment of the present invention. Also in the present embodiment, the ink is caused to fly by forming an asymmetric ink cross-sectional shape. The ink jet recording head according to the present embodiment is the same as the first embodiment except for the method of manufacturing the elastic member 7.

As the elastic member 7, a cyanoacrylate resin is used. As in the manufacturing method of the first embodiment, a concave mold is used for a fluororesin which has poor wettability with the cyanoacrylate resin and is difficult to adhere to. Thus, the ink was supplied to the elastic member 7 from only one side.

Next, the height of the elastic member 7 is set to 500 μm, and the distance from the tip 7a to the surface 8a of the ink 8 is set to 6 μm.
It was set to 0 μm. Then, by using an AC power source (not shown), a voltage having a frequency f which is the same as the inherent resonance frequency fo determined by the rigidity of the substrate 1 or an integer multiple thereof is applied to the vibration generator 2 from the outside. The generator 2 was excited.

In this example, a burst wave having an excitation frequency of 192 kHz and a voltage of 20 Vp-p (maximum and minimum amplitude) is 90 μm.
Applied for seconds. As a result, an ink drop 9 having a diameter of 15 μm was stably ejected in the direction of the arrow in FIG.

Next, as shown in FIG. 6B, ink is supplied from both sides of the elastic member 7 to record the ink jet recording head having a symmetrical ink cross section and the ink jet recording head of the present embodiment. The dots printed on the paper were compared. As a result, the dot diameter of 100 dots continuously printed from the same recording element did not change, but the standard deviation of the dot diameter and the root mean square of the displacement of the dot centroid with respect to the center line of the arrangement, and the nozzle arrangement direction The mean square of the relative positional deviation of the dot positions was several times larger in the ink jet recording head in which ink was supplied from both sides of the elastic member 7 to form a symmetrical ink cross section. Table 3 shows specific numerical values.

[0069]

[Table 3]

As described above, it was confirmed that the effect of the present invention even in actual printing is that the variation of the dot diameter on the recording medium is small due to the stable flight of the ink drop and that the dot position accuracy is good.

Next, FIG. 11 shows a schematic view of an ink jet recording head according to a fifth embodiment of the present invention. Also in the present embodiment, the ink is caused to fly by forming an asymmetric ink cross-sectional shape. In the ink jet recording head according to this embodiment, the elastic member 7 and the vibration generating unit 2 are the same as those of the third embodiment, but the substrate 1 is separated for each ejector, and the support unit 13 and the concave support unit are separated. 14 were provided.

The support portion 13 was formed by processing a member made of metal, ceramic, or the like, and was adhered to the lower surface of the substrate 1 corresponding to each vibration generating portion 2. Further, a concave support portion 14 is provided on the lower surface of the substrate 1 to support each ejector.

In this example, in order to compare with the case where the vibration generating section 2 is provided on the same substrate in the third embodiment, the burst wave of the excitation frequency, voltage and time under the same conditions as the third embodiment is used. Was applied.

As a result, there was no difference in the stability of the ink drop flying with the ejector alone. However, when ink drops are ejected simultaneously by adjacent ejectors, the configuration in which the vibration generating unit 2 is provided on the same substrate as described in the third embodiment affects the ink drop flying direction. On the other hand, in the present embodiment in which the substrate 1 is separated and supported by the support portion 13, there is almost no effect of the adjacent ejector, and the stable ink drop 9 is stably ejected in the direction of the arrow in the figure. Further, since the vibration generating section 2 was separated for each ejector, each vibration generating section could efficiently and precisely vibrate.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the width W of the surface perpendicular to the vibration direction of the bending vibration in the vicinity of the free end of the free end of the cantilever structure of the elastic member 7 may have a region where the length is approximately W = 2λ. . Here, λ is given by the following equation. λ = {8πσ / (ρfe ² )} ^1/3 × 10 ⁴ (μm) where σ is ink surface tension (mN / m) ρ is ink density (g / cm ³ ) fe is 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 more accurately. .

As described above, according to the present invention, fine droplets can be ejected without using a nozzle, and in particular, a considerably small droplet that satisfies the demand for higher resolution of an image. Can be discharged stably. In particular, the bending vibration of the elastic member having the cantilever structure generates a capillary wave on the ink surface near the tip of the elastic member to make the ink cross-sectional shape near the elastic member asymmetric in the ink jet recording head for flying ink. This makes it possible to stabilize the ink flying phenomenon. In addition, since the liquid can be driven at low frequency and with low power, the energy efficiency is good and the range of physical properties of the usable liquid is widened.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a basic configuration of an inkjet recording head of the present invention.

FIG. 2 is an enlarged view of an elastic member of the ink jet recording head of the present invention and an ink distribution on the surface thereof.

FIG. 3 is a diagram illustrating an image signal and a drive signal applied to the inkjet recording head of the present invention.

FIG. 4 is a diagram showing some examples of a cross-sectional shape of an elastic member of an ink jet recording head of the present invention and a cross-sectional shape of ink formed in the vicinity thereof.

FIG. 5 is a diagram for explaining the operation principle of the ink jet recording head of the present invention.

FIG. 6 is a diagram for explaining the operation principle of the ink jet recording head of the present invention.

FIG. 7 is a schematic diagram illustrating a configuration of the inkjet recording head according to the first embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating a configuration of an inkjet recording head according to a second embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating a configuration of an inkjet recording head according to a third embodiment of the present invention.

FIG. 10 is a schematic diagram illustrating a configuration of an inkjet recording head according to a fourth embodiment of the present invention.

FIG. 11 is a schematic diagram illustrating a configuration of an inkjet recording head according to a fifth embodiment of the present invention.

FIG. 12 is a diagram illustrating an example of a conventional inkjet recording head that does not use nozzles.

FIG. 13 is a diagram illustrating a neutral axis and a neutral surface.

FIG. 14 is a diagram illustrating a neutral axis and a neutral surface.

FIG. 15 is a diagram illustrating a neutral axis and a neutral surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Vibration generation part 3 Piezoelectric body 4, 5 electrode 6 Protective film 7 Elastic member 7a Elastic member tip 7c Elastic member surface 8 Ink 8a Ink surface 9 Ink drop 10 Ink reservoir 11 Ejector 12 External drive part 13 Support part 14 Concave support Part 15 Sound collector

Continued on the front page (72) Inventor Kazuhiro Hayashi 430 Border, Nakai-cho, Ashigarakami-gun, Kanagawa Prefecture Green Tech Nakai Inside Fuji Xerox Co., Ltd.

Claims (4)

[Claims] A vibration generating means for vibrating in response to a pixel signal; and a tip portion which comes into contact with ink, wherein the bending portion vibrates in response to excitation of the vibration generating means, and a neutral axis of bending deformation of the tip portion. An elastic member having a cantilever structure that makes the cross-sectional shape of the ink cut in a plane perpendicular to the surface of the ink asymmetric with respect to a neutral plane; An ink jet recording head characterized by causing the recording head to adhere to a recording medium. 2. The ink jet recording head according to claim 1, wherein a cross-sectional shape of said tip section taken along a plane perpendicular to a neutral axis of said bending deformation is asymmetric with respect to said neutral plane of said bending deformation. An ink jet recording head, comprising: 3. The ink jet recording head according to claim 1, wherein the tip has one surface and another surface having different wettabilities from each other. 4. The ink jet recording head according to claim 1, wherein the ink is supplied to only one surface of the front end portion.