JP3422230B2 - Inkjet recording head - Google Patents

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 that prints by depositing ink drops on a recording medium.

[0002]

2. Description of the Related Art In recent years, as one of recording devices capable of easily forming fine dots to obtain high image quality, so-called on-demand type ink-jet printers that eject ink droplets from nozzles as necessary to print. Ink jet recording methods are known. Typical methods of the on-demand type ink jet recording method include a piezoelectric vibrator method and a thermal method.

In the piezoelectric vibrator method, a pulse voltage is applied to a piezoelectric element provided in an ink chamber leading to a nozzle to deform the piezoelectric element to change the ink liquid pressure in the ink chamber, thereby causing an ink drop from the nozzle. Is a method of recording dots on a recording paper by ejecting. In the thermal system, ink is heated by a heating mechanism provided in the ink chamber, ink droplets are ejected from nozzles by bubbles generated by the heating, and dots are recorded on recording paper.

Conventionally, these ink jet recording systems have a resolution of about 300 dots / inch, but in recent years, the resolution has been increased to 600 to 720 dots / inch, and further higher resolution is desired. ing. In order to realize such high resolution, it is necessary to reduce the dot diameter to be recorded according to the resolution.

However, in these recording methods, the drop diameter of the ejected ink is determined by the nozzle diameter. Therefore, if the nozzle diameter is reduced in order to reduce the ink drop diameter, nozzle clogging due to dust or dust, and nozzle inside Nozzle clogging due to drying of the ink surface and change in the ink ejection direction due to the deposition of ink residue on the circumference of the nozzle are likely to occur, causing defects in the image quality on recording paper. Therefore, there is a problem that the nozzle diameter cannot be reduced to the extent necessary to make the dot diameter correspond to the required resolution.

Therefore, as a method of solving the problem caused by such a nozzle, there is a recording method in which the ink is ejected onto the surface to be printed by using vibration or acoustic waves without using the nozzle to perform printing. Several have been proposed.

As a first recording method which does not use a nozzle, as disclosed in US Pat. No. 4,308,547, the vibration generated by a vibrator is focused on a point on the ink free surface by an acoustic lens, and the ink is discharged. Discharge the drop. As the acoustic lens, the piezoelectric body itself is formed into a lens shape, or as disclosed in Japanese Patent Application Laid-Open No. 3-200199, a phase Fresnel lens for superimposing phases is used, or a concave shape is used. I use things. However, if the drop diameter to be ejected is reduced by these methods, the vibrator is generally driven at a higher frequency. For example, in order to eject an ink having a drop diameter of 15 μm, it is necessary to drive a plurality of vibrators at a high frequency of around 100 MHz, which causes a cost problem that a driving mechanism is generally expensive, and heat generation causes ink to be generated. There is a serious problem that the viscosity may change to change the drop diameter, or the ink itself may be dried or solidified in the recording element to make it impossible to eject the ink.

As a second recording method which does not use nozzles,
There is a so-called electrostatic attraction method that uses an electrostatic force as the ejection force, and a method that uses vibration to form the ink meniscus (ink protrusion) is known.

For example, Japanese Unexamined Patent Publication (Kokai) No. 62-222853 discloses that a recording needle is projected from the ink surface and ultrasonic energy propagating in the axial direction is applied 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 that state, an electrostatic field is applied between the recording needle and the back electrode to tear off the ink, and an ink drop is landed on the recording medium arranged between the recording needle and the back electrode. According to this method, an ink meniscus is formed at the tip of the recording needle, so that a smaller ink drop can be formed as compared with the conventional electrostatic suction method.

Further, in Japanese Patent Application Laid-Open No. 56-28867, an electrostatic signal for vibrating the needle electrode at the same time as applying an image signal to the needle electrode in a state where an electrostatic field is applied between the needle electrode and the back electrode. The suction method is shown. By doing so, the ink can be stably made into particles.

However, the electrostatic attraction method has a problem in that the formed drop diameter fluctuates due to fluctuations in the thickness of the dielectric of the recording medium due to humidity and the like, and variations in the roughness of the surface of the recording medium. Further, variations in the drop diameter also cause variations in dot position on the recording medium.

As described above, the prior art which does not use a nozzle has a problem that it requires a large amount of energy and is unstable to environmental changes.

Further, in the conventional technique, in order to obtain a high-quality image, in order to print using a recording element having a small dot diameter, it is necessary to arrange the recording elements at a high density.

This will be described with reference to FIG. To enable high-quality printing, it is necessary to be able to reproduce gradations.
As shown in, gradation reproduction is obtained by changing the number of dots of the same diameter printed in the matrix of the minimum pixels. As described above, in the conventional technique that can only print in binary, a plurality of dots must be formed by using the recording element 20 having a small nozzle diameter so that a dot diameter smaller than the minimum pixel area can be printed. However, in order to form a plurality of dots in the minimum pixel, it is necessary to narrow the nozzle interval and arrange them at a high density. If this is not possible, it is necessary to devise a nozzle interval such as a staggered arrangement. As the recording elements 20 are arranged in a high density in this manner, the yield is low due to the high density, and the crosstalk between adjacent parts also becomes a problem, which causes the problem of deterioration of image quality. In addition, if the nozzles are designed to be spaced apart from each other such as a staggered arrangement, a new problem arises in that the device becomes large.

Further, if the number of recording elements remains the same,
To print the pattern of FIG. 11A, printing cannot be completed at time T1, and it is necessary to print until time T3 after moving the recording element or the recording medium. That is,
Since the dot diameter to be printed is small, it takes three times or more time as compared with the method in which the minimum pixel unit is printed with one dot. Although there is an improvement in which the number of recording elements is increased to compensate for this, on the other hand, there are problems such as high cost.

On the other hand, as shown in FIG. 11B, one recording element 2 is formed for each minimum pixel unit that forms an output image.
There is a method in which only the area corresponding to 1 is made to fly and the ink drops 22 having different sizes are ejected from the recording element 21 to make the area of the dot variable to obtain gradation reproduction. By using this method, high density printing of the recording elements can be avoided and printing can be performed at high speed. That is, in the example of FIG. 11, it was necessary to print a maximum of 9 dots to print the smallest pixel in the prior art, but this method requires only one ink drop flight, so printing is completed at time T1. .
Further, since the distance between the adjacent recording elements can be separated by the minimum pixel unit, it is possible to provide a high-speed, high-reliability and low-cost recording technique.

By the way, as a recording technique for ejecting an ink drop having a different size from one recording pixel, there are many examples in which a technique used for an atomizer is applied. For example, in Japanese Unexamined Patent Publication (Kokai) No. 5-184993, a cantilever is provided on each of both vibrating surfaces of a piezoelectric body, and droplets fly by changing the diameter of a perforated hole formed at the tip of the cantilever. An atomizer of varying size is disclosed. Further, Japanese Patent Laid-Open No. 5-277413 discloses a technique in which a droplet is enlarged by increasing the repetition frequency of a burst wave to be driven by an atomizer including a piezoelectric body and a porous plate in contact with the piezoelectric body.

As a printing device which changes the size of a droplet by applying the technique of such an atomizer, Japanese Patent Laid-Open No. 2-141250.
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a technique of increasing the driving frequency to reduce the fog diameter to spread the fog and increase the dot diameter. However, with this method, the density of dots due to the spread of fog is low and the contrast of the image quality is lowered, so high image quality is difficult, and even if the driving frequency is lowered, many ink droplets fly and it is difficult to form a small dot diameter. Is. That is, even if the structure of the atomizer is used as it is in the recording apparatus as in this example, an infinite number of ink droplets are generated in a mist state, and it is difficult to control the number of drops and the direction in which the drops fly.
It is difficult to use for a recording technique for printing by controlling small ink drops one by one.

Another technique for changing the diameter of the ink drop is that the vibration generated by the vibrator disclosed in the above-mentioned US Pat. No. 4,308,547 is converged by an acoustic lens and focused on one point on the ink free surface. There are recording devices for ejecting ink drops and recording devices of electrostatic attraction type, but as described above, they each have the drawbacks of requiring high energy and poor environmental stability.

Therefore, it is easy to think of a recording apparatus in which a plurality of recording elements having different ejection sizes are assigned to one pixel, but the array density of the recording elements is further increased, the yield is deteriorated, and the image quality due to crosstalk is increased. There are drawbacks such as deterioration of the device and complication of driving switching.

[0021]

SUMMARY OF THE INVENTION An object of the present invention is to reduce defects such as deterioration of image quality and reliability due to clogging, and
It is an object of the present invention to provide an inkjet recording head that solves the drawbacks such as deterioration of image quality and recording speed due to high density. Another object of the present invention is to provide an inkjet recording head capable of achieving high image quality, high speed, small size, energy saving, and cost reduction.

[0022]

The above object is to provide a vibration generating means that vibrates in response to a pixel signal and a cantilever structure that bends and vibrates in accordance with any of a plurality of excitation frequencies generated by the vibration generating means. And an elastic member for generating a capillary wave on the surface of the ink corresponding to the excitation frequency to cause the ink to fly with different drop diameters and adhere to the recording medium. be able to.

Here, the elastic member may be driven at any of two or more different effective resonance frequencies.
Further, the elastic member may have a plurality of cantilever structures having different effective resonance frequencies.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the basic structure of an ink jet recording head according to a first embodiment of the present invention. FIG. 1A is a front view of the ink jet recording head according to this embodiment, and FIG. 1B is a side view of the same. Further, FIG. 1C is a side view in the vicinity of the tip of the elastic member 7 in which the block c shown by the broken line in FIG. 1B is enlarged, and shows the operation of ink ejection. The ink jet recording head according to the present embodiment includes a substrate 1 and a vibrator 2.
The vibration generating mechanism, the external driving mechanism 12, and the elastic member 7 are included. The vibrator 2 has a shape in which the piezoelectric body 3 is sandwiched between two electrodes 4 and 5.

In this example, the elastic member 7 is connected to the vibration generating mechanism in which the vibrator 2 is formed on the substrate 1, and the ink 8 is loaded so that the elastic member 7 contacts the vibration generating mechanism. The elastic member 7 is driven to be excited by the frequency 12 at which the elastic member 7 resonates due to bending vibration. As the vibration generating mechanism, the substrate 1 may not be used as long as the vibrator 2 can be carried.

Next, the basic operation of the ink jet recording apparatus according to this embodiment will be described. One end of the elastic member 7 is connected to the vibration generating mechanism and the other end constitutes a cantilever beam, and the other end is a cantilever, and the elastic member 7 is filled with the ink 8 in contact therewith. A signal generated by the external drive mechanism 12 is converted into mechanical vibration by the vibrator 2 by the vibration generating mechanism, and the vibration energy is transmitted to the elastic member 7. Due to this vibration energy, the elastic member 7 causes bending vibration,
Since the external drive mechanism 12 is excited and driven at a frequency at which the elastic member 7 resonates with bending vibration, this resonance causes a large amplitude in the vicinity of the tip of the elastic member. On the other hand, as shown in FIG. 1C, the ink 8 in contact with the elastic member 7
The ink thickness in the vibration direction of the bending vibration is formed to be several μm to several hundreds μm in the vicinity of the tip of the elastic member 7 due to the wetting of the ink 8 and the elastic member 7 and the effect of gravity. And a capillary wave is generated on the ink surface 8a. Due to the action of this capillary wave, it is possible to generate minute droplets, and the vibration generating mechanism can fly one ink droplet 9 by setting its driving condition to a predetermined value.

In the elastic member 7, the width W (see FIG. 1A) of the surface perpendicular to the vibration direction of the bending vibration in the vicinity of the free end of the cantilever structure of the elastic member 7 is almost the same. Two
It has a region with a length of λ. However, λ is given by the following Expression 1. λ = {8πσ / (ρfe ² )} ^1/3 × 10 ⁴ (μm) Equation 1 where σ is the ink surface tension (mN / m) ρ is the ink density (g / cm ³ ) fe Is the excitation frequency (Hz). By doing so, it is possible to generate two ridges of the capillary wave in the width W, and then one ridge of the ink ridge is formed and separated at the next moment so that one ink drop can be accurately ejected.

FIG. 2 shows a pattern of voltage applied to the electrodes 4 and 5 for exciting the vibration generating mechanism. The excitation of the vibration generating mechanism is such that the excitation is intermittently divided every time the number of excitations required for the flight of one ink droplet is completed so that the flight of one ink droplet is realized according to one pixel signal. With these, minute droplets are generated without nozzles, and recording can be performed without ink clogging.

In order to drop the ink 8 and fly it from the elastic member 7 as described above, the drive frequency applied by the external drive mechanism 12 must be equal to or very close to the resonance frequency of the elastic member 7. Depending on the physical properties of the ink 8 and the relationship between the ink 8 and the elastic member 7, the resonance frequency of the elastic member 7 including the ink 8 may often deviate from the resonance frequency of the elastic member 7 only. Instead, it is better to use a resonance frequency including the ink 8 in contact with the elastic member 7. Such a resonance frequency will be referred to as an effective resonance frequency here. Also,
Depending on the system, it may be more preferable to use the resonance frequency in the system including the vibration generating mechanism such as the substrate 1 and the vibrator 2 as the effective resonance frequency.

FIG. 3 shows an example of a recording apparatus incorporating a plurality of ink jet recording heads according to the first embodiment of the present invention. The elastic members 71, 72, 73 are each composed of a single protrusion having two or more effective drop resonance frequencies. The driving frequency fA is the elastic members 71, 72,
It is one of the effective resonance frequencies of 73, and the ink 8 has an ink drop 9a having a certain drop diameter due to this frequency.
Fly in. The drive frequency fB different from the drive frequency 1 is also the effective resonance frequency of the elastic member 7, and the frequency causes the recording member to fly with the drop 9b smaller than the drop diameter when the drive frequency 1 is applied.

With such a configuration, in the portion where the density of the image information to be printed is high, the external driving mechanism 12 sends the driving frequency fA to the vibration generating mechanism, so that the elastic member 7 causes the large ink drop 9a to fly, and The external driving mechanism 12 sends a driving frequency fB higher than the driving frequency fA to the vibration generating mechanism in the portion where the density is low due to the image information to be printed, so that the elastic member 7 can fly the small ink drop 9b, and the dot It is possible to obtain a high-quality image by gradation reproduction by area gradation.

Further, by adopting such a configuration,
For example, when printing as shown in FIG.
Compared with a printing method that can only print values, the number of recording elements is small, and printing can be performed at one time at time T1, so the printing time can be shortened. Therefore, a high-quality and high-speed recording device can be provided at low cost.

The materials and specific examples of each component will be described below. The material used for the substrate 1 is brass, copper, N
Various metals such as i and stainless steel can be used. That is, as long as the rigidity is high and the vibration can be transmitted to the elastic member 7, ceramic may be used when metal is not used, or a combination thereof may be used.

The most important piezoelectric body 3 of the vibrator 2 may be a piezoelectric substrate or a piezoelectric thin film. The piezoelectric body may be composed of a single layer or multiple layers.
As the piezoelectric body 3, quartz, PZT, barium titanate B
aTiO ₃ , lead niobate PbNb ₂ O ₆ , bismuth germanate Bi ₁₂ GeO ₂₀ , lithium niobate LiNb
Polycrystalline or single crystalline materials such as O ₃ and lithium tantalate LiTaO ₃ , piezoelectric thin films such as ZnO and AlN, polyurea, PVDF (polyvinylidene fluoride) and PV
A piezoelectric polymer such as a DF copolymer or a composite of an inorganic piezoelectric substance such as PZT and a piezoelectric polymer can be used. Of course, the optimum piezoelectric material must be selected according to the drive frequency set when designing the inkjet recording head. A ceramic such as PZT may be used as long as the frequency of the applied alternating current is between several tens of kHz and 1 MHz, but when driving at a higher frequency, a piezoelectric thin film such as ZnO that supports high frequencies must be selected. I have to. In any case, it is necessary to have a vibration characteristic that allows stable and sufficient vibration to be applied to the vibrator 2. The elastic member 7 may be formed of the piezoelectric material itself that forms the vibrator 2. Also,
When the vibrator 2 may come into contact with the ink 8 and cause a short circuit, an insulating protective film 10 made of various insulating materials may be attached.

A signal applied to the vibrator 2 from the external drive mechanism 12 to vibrate the vibrator 2 is a waveform in which at least one waveform having an effective resonance frequency as one cycle is continuous as shown in FIG. A burst wave that has signals and is applied intermittently at the cycle of the printing frequency is used. However, the burst wave is not limited to the illustrated rectangular wave and may be a sine wave or a triangular wave.

As the material of the elastic member 7, various resins such as cyanoacrylate resin, epoxy resin, and fluorine resin can be used. In addition, SiO ₂ , S
The elastic member 7 may be formed of various inorganic materials such as iON, SiN, AlN, and Al ₂ O ₃ . Further, the elastic body 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, it is desirable to protect their surface with an inorganic film such as SiO ₂ so as not to corrode during contact with the ink 8. Of course, two or more materials may be used among resins, inorganic materials and metals. Further, if the vibration energy can be efficiently propagated, the tip and bottom of the elastic member 7 may be made of different materials.

Further, in the ink jet recording head according to the present embodiment, in order to stably eject a single minute ink drop, the shape of the elastic member 7, the tip 7a of the elastic member 7 and the ink surface 8a are formed. Relative positional relationship is important. These are shown in detail below.

The shape of the elastic member 7 will be described with reference to FIG. FIGS. 4A to 4G are examples of cross-sectional shapes when viewed from the side, which are suitable as the elastic member. FIG. 4 (h) is a perspective view showing a suitable elastic member. In the elastic member 7, it is preferable that the bending stiffness of the tip portion including the tip 7a is smaller than that of the fixed end portion (base end portion).
As a result, the bending vibration amplitude can be obtained more efficiently near the tip of the elastic member 7. The bending stiffness is represented by (second moment of area) × (Young's modulus) of the elastic member 7. Therefore, on the basis of FIG. 4A in which the width in the amplitude direction where bending vibration occurs is uniform from the base end to the tip, in order to reduce the bending stiffness of the tip from the base, FIG.
As in (b), (c), (e), (f), (g), and (h), the bending of the distal end portion is larger than the width in the amplitude direction in which bending vibration of the proximal end portion of the elastic member 7 occurs. Decrease the width in the amplitude direction in which vibration occurs, or make the width in the direction perpendicular to the amplitude direction in which bending vibration occurs at the tip end smaller than the width in the direction perpendicular to the amplitude direction in which bending vibration occurs at the base end. Is desirable. Similarly, this can be achieved by using a material that is softer than the material used for the base end of the elastic member 7 for the tip.

Further, it is preferable that the tip of the elastic member 7 is formed in a sharp shape in a direction perpendicular to the amplitude direction in which bending vibration occurs. As a result, it is possible to limit the region where the capillary wave is generated, and it is possible to more stably eject one drop. Further, the elastic member 7 is, as shown in FIGS. 4 (d), (e), (f), (g) and (h),
The proximal end portion side and the distal end 7a of the elastic member 7 may be made of different members or different materials. As a result, in forming the bending stiffness to a predetermined value or forming the sharpened tip 7a with high accuracy, the degree of freedom in design can be expanded and the selection range of the manufacturing method can be expanded. As a result, it becomes possible to manufacture a device with higher precision at a lower price.

Further, as shown in FIG. 4 (g), the elastic member 7 may have a tip 7a composed of a plurality of members 7b and 7c. The members 7b and 7c are formed so as to have different resonance frequencies, and by switching the driving frequency, it is possible to eject drops of different sizes. In this case, as shown in FIG. 4 (h), the tips 7b, 7
The c may be arranged in one row in the depth direction of the elastic member 7.

The relative positional relationship between the elastic member 7 and the ink surface 8a is shown in FIG. 5 when a capillary wave is generated on the ink surface 8a to eject a single minute ink drop according to this embodiment. As shown in a), at least the ink thickness of the elastic member 7 in the vibration direction of the bending vibration is several μm due to the wetting of the ink 8 and the elastic member 7 and the effect of gravity.
The ink 8 is applied to the elastic member 7 so that
It is important to place them in. Because Figure 5
When the elastic member 7 is embedded in the ink 8 as shown in (b) and (c), the liquid thickness becomes too thick and it becomes difficult to generate a capillary wave. In addition, if the energy that can be ejected is applied, the amount of ink is excessively supplied, which causes a large drop, which is not desirable.

The fact that the surface of the elastic member 7 has a proper wetting property with the ink is also important for forming a stable capillary wave and ejecting a stable ink drop. If the surface of the elastic member 7 does not easily get wet with ink,
This is because it may be difficult to supply the ink to the tip 7a depending on the supply method. Regarding the wettability with the ink, the surface state of the elastic member 7 may be controlled so as to correspond to the ink, or the physical properties of the ink may be controlled according to the surface of the elastic member 7.

Further, in the configuration examples shown in FIGS. 1 and 3, the ink is filled and the ink surface is formed on both sides of the elastic member 7. However, the present invention is not limited to this, and the elastic member as shown in FIG. 6A is used. The filling of the ink 8 and the surface of the ink 8 may be formed on only one side of 7.

Further, as shown in FIGS. 6 (b), 6 (c) and 6 (d), it may be tilted at an angle orthogonal to the direction in which gravity acts, or at an arbitrary angle. ), The elastic member 7 may be connected to the surface of the vibrator 2 at an angle other than perpendicular.

Further, in this embodiment, it is not necessary to use a nozzle for defining the drop diameter, but in order to stabilize the ink liquid surface and suppress the drying of the ink,
Some member may be disposed on a part of the ink surface 8a as long as it has an opening larger than the ejection drop diameter.

In the present embodiment, it is important to select the material, physical properties and size of the elastic member 7 so as to have at least two effective resonance frequencies within the actually used driving frequency range.

Here, the drive frequency range actually used is
Depending on the specifications of the inkjet recording head and the performance of the vibrator, the lower limit of the drive frequency is determined by the length of the burst wave of the drop flight and the print frequency which is the interval of the drop flight, and the upper limit is the resonance frequency of the vibrator 2, the performance limit, and the drive frequency. Is determined in consideration of energy loss and the like which become large at high frequencies.

In order to bring the resonance frequency of the elastic member 7 itself to a desired value within the driving frequency range, an appropriate material, size and shape are selected. That is, the elastic modulus, the second moment of area, the density, the length, the width, the thickness of the beam, the desired resonance frequency for a plurality of different orders i,
Adjust the shape. Of course, when the effective resonance frequency deviates from the resonance frequency by filling the ink 8, it is important to make it so as to match the effective resonance frequency.

In this example, a ceramic piezoelectric element is used for the vibrator 2. The piezoelectric element used is 20 Hz to 500
KHz has a practical frequency range with little energy loss. In this practical frequency range, the vibrator 2 is
90.5kHz, 162.3kHz, 195.6kHz
z, 302.0 kHz, 440.3 kHz, 540.8
Measurements have shown to have a resonant frequency at kHz.

SUS 1052 having a thickness of 7 μm is formed on the elastic member.
As a result of measuring the effective resonance frequency including the ink 8 using a foil molded to a size of μm × 486 μm, 5.2 kHz, 2
4.1kHz, 32.6kHz, 77.8kHz, 9
0.5 kHz, 147.3 kHz, 162.3 kHz,
182.1 kHz, 195.6 kHz, 215.5 kHz
z, 240.2 kHz, 295.3 kHz, 302.0
kHz, 309.2 kHz, 340.0 kHz, 40
It was found that the resonant frequencies were 6.2 kHz and 442.2 kHz.

Therefore, the resonance frequency of the vibrator 2 and the ink 8
90.5kHz, 162.3kHz, 195.6kHz in which the effective resonance frequencies of the elastic member 7 including
z, the place printed using the frequency of 302.0 kHz,
103μm, 82μm, 43μ on the recording medium, respectively
It was possible to print with different sizes of m and 21 μm.

As described above, by using the driving frequency, it is possible to fly drops of different sizes, gradation expression becomes possible, and the conventional ink jet recording head which can fly only one kind of drop size. In comparison, it is possible to provide a high-quality image with excellent gradation reproducibility.

Next, an ink jet recording head according to a second embodiment of the present invention will be described with reference to FIG. First
The same components as those of the inkjet recording head according to the embodiment are shown by the same reference numerals. In this embodiment, at least two or more elastic members are assigned to form one pixel. The elastic members are driven at driving frequencies having different effective resonance frequencies, and the formed drop diameters are also different. In a portion where the image information to be printed has a high density, the external driving mechanism 12 sends the driving frequency fa to the vibration generating mechanism so that the elastic member 7a causes the large ink drop 9a to fly and the image information to be printed causes the density to be low. In part, the external drive mechanism 12 sends the drive frequency fb to the vibration generating mechanism, whereby the elastic member 7
The elastic member 7b different from a can fly a small ink drop 9b, and a high quality image can be obtained by gradation reproduction by dot area gradation.

Also in this embodiment, the same material as in the previous example can be used for the vibration generating mechanism and the elastic members 7a and 7b. The feature of this example is that different elastic members are assigned to one pixel which is the minimum unit that constitutes an image. That is, the different elastic members 7a and 7b arranged on the substrate 1 have different effective resonance frequencies fa and fb, respectively. When a drive frequency equal to the effective resonance frequency fa is given, the elastic member 7a can fly a drop of a certain size. Further, when a drive frequency equal to the effective resonance frequency fb is given, the elastic member 7b can fly drops of different sizes. Therefore, as described in the previous example, it is possible to print with a smaller number of recording elements and a shorter recording time as compared with the conventional print recording apparatus.

Further, in the example in which one elastic member is formed as described above, in order to give the next driving frequency after giving one driving frequency to eject different ink drops. It is necessary to wait until the residual vibration of the elastic member subsides. However, since this embodiment has a plurality of different elastic members, after discharging from one elastic member,
Another elastic member may be used. Therefore, the drive frequency can be immediately applied, and as a result, the printing speed can be increased.

The elastic members of this embodiment are made of materials, sizes, shapes, that is, elastic moduli, second moments of area, densities, beam lengths, widths, thicknesses, shapes, or combinations thereof. It can be realized by making them different.

At this time, each elastic member has a resonance frequency of each order, but in a plurality of elastic members, at least one set of elastic members has a common resonance frequency, and the resonance frequency is the same. Even if it is the resonance frequency that actually drives one elastic member, the same resonance frequency may be shared as long as the drive resonance frequency is applied and ink does not fly from other elastic members. . However, to reduce crosstalk,
It is desirable that none of the effective resonance frequencies of one elastic member is equal to the effective resonance frequencies of the remaining elastic members. Furthermore, if different effective resonance frequencies are in an integral multiple relationship, resonance is likely to occur.Therefore, among the effective resonance frequencies of one elastic member, the effective resonance frequency of the remaining elastic member becomes a frequency that is an integer multiple of any one frequency. It is more desirable that the are not equal.

The example shown in FIG. 7 shows an example of two kinds of elastic members 7a and 7b corresponding to one pixel, but if the above-mentioned conditions are satisfied, not only two kinds as shown in FIG. Combinations of more than one type may be used. Also, each elastic member 7
4 can be all the shapes shown in FIG. 4 as shown in the previous example. Further, in the example shown in FIG. 7, the two types of elastic members 7a and 7b corresponding to one pixel are adjacent to each other, but they may be installed separately if they are assigned to one pixel.

The two main embodiments have been described above.
Of course, a combination of these two embodiments may be used. That is, a plurality of types of elastic members having different effective resonance frequencies are provided corresponding to one pixel, and each of the elastic members can eject ink drops of different sizes at different effective resonance frequencies. With a configuration that allows
Since the size of the ink drop can be varied more widely, higher gradation printing can be performed.

Next, a recording apparatus incorporating the ink jet recording head according to the above two embodiments will be described. FIG. 9 is a diagram showing an example of a recording device 33 using a single protrusion that ejects drops of different sizes at different resonance frequencies.

In this example, after the Ag electrode 4 having a thickness of 1 μm is deposited on the substrate 1 made of brass having a thickness of 500 μm,
Patterned, then 100 μm thick PZT
After depositing the piezoelectric ceramic thin film 3 made of (zirconic acid / lead titanate), patterning is performed, and further, 0.05 μm
After depositing an electrode 5 consisting of two layers of Cr having a thickness of m and Au having a thickness of 1 μm, patterning is performed to form the vibrator 2.

The piezoelectric ceramic thin film 3 made of PZT is
When polarization is applied and a voltage is applied between the electrodes 4 and 5,
It vibrates in the direction perpendicular to the film surface. Electrode 4
Is a common electrode common to each transducer 2, and the electrode 5
Is an address electrode for vibrating only a specific vibrator.

Further, the vibrator 2 composed of the piezoelectric ceramic thin film 3 and the electrodes 4 and 5 was covered with a protective film 10 composed of SiO _{2 having} a thickness of 1 μm. As a result of measuring the piezoelectric ceramic thin film including the created substrate with an impedance analyzer, 20 Hz to 500 KHz has a practical frequency range with little energy loss, and 90.5 kHz, 162.3 kHz, 195.
6 kHz, 302.0 kHz, 440.3 kHz, 54
It was found to have a resonant frequency of 0.8 kHz.

Subsequently, a SUS having a thickness of 7 μm is formed as an elastic member 7 on each vibrator 2 in a height of 1052 μm × width of 486.
It was laser-cut into a triangular shape of μm and set using an epoxy adhesive. The manufactured ink jet recording head is fixed in the housing 100 by the support portion 21, and the signal connection connector 103 and the vibrator 2 are electrically connected.
An ink chamber constituent member 28 is attached to the ink ejection side surface of the housing 100.

The ink supply chamber 6 is provided below the housing 100, and the ink supplied from the ink supply port 104 is
It is supplied from the ink supply chamber 6 to the ink chamber side via the filter 102. Then, pressure was applied from the ink supply port 104 using a pressure supply mechanism (not shown) so that the thickness of the ink 8 for wetting the tip 7a of the elastic member 7 would be 50 μm.

Here, the effective resonance frequency of the elastic member 7 containing the ink 8 was measured by an impedance analyzer. Then, the elastic member 7 has a frequency of 5.2 kHz, 24.1 kHz.
z, 32.6 kHz, 77.8 kHz, 90.5 kHz
z, 147.3 kHz, 162.3 kHz, 182.1
kHz, 195.6 kHz, 215.5 kHz, 24
0.2 kHz, 295.3 kHz, 302.0 kHz,
309.2 kHz, 340.0 kHz, 406.2 kHz
It was found to have an effective resonant frequency of z, 442.2 kHz.

Therefore, by using the external drive mechanism 12, the resonance frequency of the vibrator 2 including the substrate 1 and the effective resonance frequency of the elastic member 7 including the ink 8 are equal to each other 90.5 k.
When a burst wave having a frequency of Hz and repeating this wave 5 times is applied to the vibrator 2, the ink 8 is ejected as a drop from the elastic member 7 and has a diameter of 1 on the recording medium 36.
A dot of 03 μm was formed. Next, when a burst wave having a frequency of 162.3 kHz which is also a common frequency and this wave is repeated 5 times is applied to the vibrator 2,
The ink 8 was discharged as drops from the elastic member 7 to form dots having a diameter of 82 μm on the recording medium 36. Similarly, when printed using the frequencies of 195.6 kHz and 302.0 kHz, 43 μm on the recording medium 36,
It was possible to print dots having different sizes of 21 μm.

Therefore, the density is divided into four levels according to the image information, a burst wave of 90.5 kHz is generated at the highest density, and 162.3 kHz and 1 as the lightness decreases.
Programming the external drive mechanism 12 to generate a burst wave of 95.6 kHz, 302.0 kHz,
When actually printed, it was possible to obtain a high-quality printed image with rich gradation reproducibility as compared with the conventional binary printed image with one driving frequency.

Further, when compared with an ink jet recording head having the same number of recording elements and capable of printing with the same resolution and capable of printing only a dot diameter of 20 μm on a recording medium,
Printing speed is 2-3 times faster. This is significantly different in the ink jet recording head of the present embodiment, which can form a dot diameter of 103 μm with one discharge, as compared with a conventional apparatus that can print only a dot diameter of 20 μm, which is necessary for printing a high density area. Because it will be less.

Further, in this example, since the nozzles are not arranged on the ink surface, it is possible to eject the microdrops stably without needing to fix the ink in and around the nozzles. Further, since the driving frequency is low, there is no heat generation, and there is no problem such as viscosity change or solidification of the ink 8. Similar results were obtained in the following examples, but similar results were obtained when the elastic member 7 had a plate-shaped or needle-shaped tip instead of the sharpened shape.

FIG. 10 shows another example of a recording apparatus incorporating the ink jet recording head according to the embodiment of the present invention. In this example, a substrate 1 made of brass having a thickness of 500 μm is deposited with a Ag electrode 4 having a thickness of 1 μm and then patterned, and then, a PZT (lead zirconate titanate zirconate) layer having a thickness of 100 μm is formed. The piezoelectric ceramic thin film 3 is deposited and then patterned, and the electrode 5 composed of two layers of 0.05 μm thick Cr and 1 μm Au is deposited and patterned to form the vibrator 2. Form.

The piezoelectric ceramic thin film 3 made of PZT is
When polarization is applied and a voltage is applied between the electrodes 4 and 5,
It vibrates in the direction perpendicular to the film surface. Electrode 4
Is a common electrode common to each transducer 2, and the electrode 5
Is an address electrode for vibrating only a specific vibrator.

Further, the vibrator 2 composed of the piezoelectric ceramic thin film 3 and the electrodes 4 and 5 was covered with a protective film 6 composed of SiO _{2 having} a thickness of 1 μm. As a result of measuring the piezoelectric ceramic thin film including the created substrate with an impedance analyzer, 20 Hz to 300 KHz has a practical frequency range with little energy loss, and 90.5 kHz, 163.3 kHz, 195.6 are included in the driving frequency range.
It was found to have resonant frequencies of 20 kHz and 207.3 kHz.

The elastic member 7a made of cyanoacrylate resin and having a thickness of 7 μm, a width of 486 μm and a height of 1052 μm and an elastic member 7b having a thickness of 7 μm, a width of 486 μm and a height of 1152 μm are adjacent to each other. Installed on top.

The elastic member 7 is formed by forming a concave portion in a fluororesin, which has poor wettability with a cyanoacrylate resin and is difficult to adhere to, and uses this as a mold. However, the method for forming the elastic member 7 is not limited to this, and a processing technique using the lithography technique used in the semiconductor process,
The thick film printing technique or various forming techniques (such as electric discharge machining and plating technique) used in the manufacturing process of the micromachine are not limited to the resin, but when forming the elastic member 7 made of an inorganic material or a metal material. Can be used.

The effective resonance frequencies of the elastic member 7a thus created are 147.1 kHz and 163.3 kHz.
z, 181.8 kHz, 215.5 kHz, 240.0
It was kHz. Similarly, the effective resonance frequencies of the elastic member 7b are 129.1 kHz, 147.5 kHz, 16
The frequencies were 5.3 kHz, 205.6 kHz and 207.3 kHz.

From among these, the elastic member 7a has an effective resonance frequency of 163.3 kHz and the elastic member 7b has an effective resonance frequency of 167.3 kHz, which is the same as one of the resonance frequencies of the oscillator 2 including the substrate 1 and is different from each other. When selected as each drive frequency and actually applied, drive frequency 16
At 3.3 kHz, an ink drop flies from the elastic member 7a to form a dot of 60 μm on the recording medium 36, and at a driving frequency of 207.3 kHz, an ink drop flies from the elastic member 7b and 20 μm on the recording medium 36. Of dots could be formed.

Therefore, the external drive mechanism 12 is programmed so as to generate a burst wave of 163.3 kHz in the high density area of the image information and a 207.3 kHz burst wave in the low density area of the image information. When printed, we were able to create high-quality printed samples with rich gradation reproduction. In addition, it was possible to print at a higher speed than the conventional ink jet recording head.

[0079]

According to the present invention, since dots of different sizes can be easily ejected for one pixel, gradation reproducibility is excellent, and compared with other techniques that perform binary recording. In addition, it is inexpensive, can be made compact, and can be printed at high speed.

[Brief description of drawings]

FIG. 1 is a diagram showing an inkjet recording head according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a signal waveform for driving the inkjet recording head of the present invention.

FIG. 3 is a diagram showing an example of a recording apparatus incorporating the inkjet recording head according to the first embodiment of the invention.

FIG. 4 is a diagram showing an elastic member of the inkjet recording head of the present invention.

FIG. 5 is a diagram showing a relationship between an elastic member and an ink liquid surface of the inkjet recording head of the present invention.

FIG. 6 is a diagram showing the relationship between the elastic member of the inkjet recording head of the present invention and the distribution of ink.

FIG. 7 is a diagram showing an inkjet recording head according to a second embodiment of the present invention.

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

FIG. 9 is a diagram showing a recording apparatus incorporating the inkjet recording head of the present invention.

FIG. 10 is a diagram showing a recording apparatus incorporating the inkjet recording head of the present invention.

FIG. 11 is a schematic diagram for comparing printing of the present invention and a conventional example.

[Explanation of symbols]

1 substrate 2 oscillators 3 Piezoelectric body 4, 5 electrodes 7 Elastic member 8 ink 9 ink drop 10 Insulation protection film 12 External drive mechanism 22 ink drop 28 buffer walls 33 inkjet recording head 36 Recorded material 71, 72, 73 Elastic member

Continuation of front page (56) Reference JP-A-6-106723 (JP, A) JP-A-5-57892 (JP, A) JP-A-10-34916 (JP, A) JP-A-11-34327 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/015 B41J 2/045 B41J 2/055

Claims (3)

(57) [Claims] 1. A vibration-generating unit that vibrates in response to a pixel signal, and a cantilever structure that bends and vibrates in accordance with any of a plurality of excitation frequencies generated by the vibration-generating unit. Correspondingly, an ink jet recording head is provided with an elastic member for generating a capillary wave on the surface of the ink to cause the ink to fly with different drop diameters and adhere to the recording medium. 2. The ink jet recording head according to claim 1, wherein the elastic member is driven at any one of two or more different effective resonance frequencies. 3. The ink jet recording head according to claim 2, wherein the elastic member has a plurality of cantilever structures having different effective resonance frequencies.