JP3427608B2 - Ink jet recording device - 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 apparatus that uses vibration to eject ink.

[0002]

2. Description of the Related Art Conventionally, there is a so-called on-demand type ink jet recording system in which ink droplets are ejected from a nozzle as needed to perform printing, and typical systems include a piezo vibrator type and a thermal type. The piezoelectric vibrator type applies a pulse voltage to the piezoelectric element attached to the ink chamber to deform the piezoelectric element to change the ink liquid pressure in the ink chamber and eject ink droplets from the nozzle to form dots on the recording paper. To record. The thermal type is
The ink is heated by the heating means provided in the ink chamber, and the ink droplets are ejected from the nozzles by the bubbles generated thereby to record dots on the recording paper.

In these ink jet technologies, the resolution has hitherto been about 300 dpi, but recently, the resolution has been increased from 600 to 720 dpi. Along with this, it is necessary to reduce the dot diameter to be printed according to the resolution in order to effectively bring out the effect of the higher resolution. As a method of reducing the dot diameter in the conventional method, there is a method of reducing the nozzle diameter. However, when the nozzle diameter is reduced, the nozzle is likely to be clogged due to dust or the drying of the ink surface in the nozzle, and the change in the ink ejection direction due to the adhesion of the residue to the circumferential portion of the nozzle is likely to occur. Therefore, the image quality on the recording paper is defective,
There was a problem that the nozzle diameter necessary for printing the dot diameter corresponding to the original resolution could not be adopted.

On the other hand, in recent years, an ink jet recording system using surface acoustic waves has been proposed. For example, Japanese Patent Laid-Open No. 54-10731 discloses a structure in which a surface acoustic wave is formed by an interdigital electrode provided in a liquid chamber, and the leaky Rayleigh wave causes the ink to vibrate to eject an ink droplet from a slit or a nozzle. Have been described. Further, in Japanese Unexamined Patent Publication No. 62-66943, an interdigital electrode is formed concentrically at the bottom of the liquid chamber, a leaky Rayleigh wave is formed in the ink in a cone shape, and an ink surface is provided near the focal point. A method has been proposed in which the vibration energy propagated in the ink is concentrated on the ink surface and the ink droplets are ejected.

In these methods, since the size of the ink droplets formed is not directly affected by the nozzle diameter, it is not necessary to make the ink ejection port small, and there is essentially no problem with the slit shape. . However, since the interdigital electrodes that generate surface acoustic waves are arranged in the ink, high-frequency vibration causes the electrode material to react with the components in the ink to elute the electrodes, and the ink components may adhere to the electrodes. The problem occurs. Further, there is a problem that the leaky Rayleigh wave is attenuated when propagating in the ink, resulting in low energy efficiency.

To address these problems, a new ink jet recording system using surface acoustic waves has been proposed. The device described in JP-A-2-269058 is an example. FIG. 11 is a diagram illustrating the principle of a conventional ink jet recording method using surface acoustic waves. In the figure, 41 is the surface of the piezoelectric substrate, 42 is the interdigital electrode, 43 is the piezoelectric substrate, 44
Is ink, 45 is a droplet, and 46 is a high frequency power source. Interdigital electrodes 42 are formed on the surface 41 of the piezoelectric substrate. A high-frequency voltage is applied from the high-frequency power source 46 to the interdigital electrode 42, and the ink 44 is placed on the propagation path of the generated surface acoustic wave. Then, the surface acoustic wave comes into contact with the ink 44, and vibration energy leaks to the ink 44 (a leaky Rayleigh wave is generated). As a result, a part of the ink 44 drops 45.
And fly. In this method, the interdigital electrodes 4
2 does not come into direct contact with the ink 44, and since it is not necessary to form a small nozzle, there is no problem with reliability as in the above-described method.

However, in this structure, since the parallel interdigital electrodes are used as the electrodes, the surface acoustic waves easily propagate in multiple directions, resulting in poor energy efficiency and a cause of crosstalk. The direction and size of the droplets formed are extremely unstable as compared with the above-mentioned conventional example. In order to increase the directivity of surface acoustic wave propagation,
The width d of the interdigital electrodes needs to be at least 10 times the wavelength λ or more. Further, since the diameter of the droplet depends on the width d of the interdigital electrode, it is necessary to shorten the wavelength λ in order to form a droplet having a small diameter. However, shortening the wavelength λ raises the oscillation frequency and requires an expensive power source, so there is a problem that the oscillation frequency cannot be increased unnecessarily.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides an ink jet recording apparatus capable of efficiently ejecting an ink droplet having a small diameter without requiring a minute nozzle. It is intended.

[0009]

According to a first aspect of the present invention, there is provided an ink jet recording apparatus, wherein a nozzle portion, which is an end portion of a vibrating substrate on which an opening is provided and a nozzle is formed, is moved up or down to vibrate. A vibration generating unit configured to generate a longitudinal wave by vibrating the vibration generating unit so that a standing wave is generated near the surface of the liquid ink held in the nozzle toward the center of the nozzle. Then, the liquid droplets are caused to fly from the surface of the liquid ink in the central portion.

According to a second aspect of the present invention, in the ink jet recording apparatus according to the first aspect, the vibration generating means is composed of a piezoelectric member or a plurality of piezoelectric members. is there.

According to a third aspect of the present invention, in the ink jet recording apparatus according to the first or second aspect, the vibration generating means are arranged in a line.

According to a fourth aspect of the invention, in the ink jet recording apparatus according to the first or second aspect, the vibration generating means are arranged in a matrix, and the vibration generating means arranged in each row or column are arranged in a column or row direction. It is characterized by being placed in different positions.

[0013]

[0014]

[0015]

[0016]

[0017]

1 is a sectional view showing a first reference example of an ink jet recording apparatus of the present invention, and FIG. 2 is a plan view of the same. In the figure, 1 is a nozzle, 2 is a vibrating member, and 3 is ink. FIG. 2 is a view of FIG. 1 viewed from the direction A.
The nozzle 1 has a cylindrical shape, and the ink 3 is supplied to the inside thereof. The vibrating member 2 is provided near the liquid surface of the ink 3 supplied to the nozzle 1.

The vibrating member 2 is made of a material that causes mechanical strain by an electric field, and for example, a piezoelectric material such as barium titanate, lithium niobate, lead zirconate titanate, or zinc oxide is used. The vibrating member 2 is deformed so as to contract or expand in the direction perpendicular to the surface of the nozzle 1. Here, the vibrating member 2 uses an integral cylindrical piezoelectric material and is arranged on the circumference of the nozzle 1. Not limited to this,
It is also possible to divide into a number of members and dispose a plurality of arc-shaped vibrating members on the entire circumference of the nozzle 1, or intermittently dispose on the circumference of the nozzle 1. Further, the cross-sectional shape of the nozzle 1 is not limited to a circle, but may be various shapes such as a regular n-sided shape, and the vibrating member may be arranged so that the longitudinal waves generated by the vibrating member are concentrated at one point. .

Although only the nozzle 1 is shown here, the nozzle 1 is directly connected to an ink supply mechanism (not shown) for supplying the ink 3, or an ink (not shown) for temporarily storing the supplied ink. It can be configured to be connected to the chamber. In addition, the length of the nozzle 1 may be equal to or longer than the length at which the liquid surface of the ink 3 can be position-controlled in the nozzle 1.

FIG. 3 is a plan view for explaining the operating principle of the first reference example of the ink jet recording apparatus of the present invention, and FIG. 4 is a sectional view of the same. An electric field is applied to the vibrating member 2,
As shown in FIG. 3, when vibrating at a frequency perpendicular to the wall surface of the nozzle 1, a longitudinal wave is generated below the liquid surface of the ink 3 toward the center of the cylinder. Since these longitudinal waves are concentrically gathered from the entire wall surface of the nozzle 1 at the center, the vibration energy applied from the nozzle wall surface is concentrated at the center of the cylinder. Therefore, when sufficient vibration intensity is applied at a certain frequency, droplets are ejected from the surface of the ink near the center of the cylindrical nozzle 1 as shown in FIG. Recording can be performed by attaching the droplets to the recording medium.

As a specific example, the vibrating member 2 has a frequency of 60 MHz.
By applying the vibration of, a droplet having a diameter of about 50 μm was generated. Also, when the vibrating member 2 is divided into a plurality of arc-shaped vibrating members, the ink 3 can be ejected from the central portion of the cylindrical nozzle 1 by adjusting the vibrating phases.

Next, a second reference example of the ink jet recording apparatus of the present invention will be described. The structure of the nozzle in this second reference example is almost the same as that of the above-mentioned first reference example shown in FIGS. 1 and 2. In this embodiment, the vibrating member 2 vibrates in the axial direction of the nozzle 1.

5 and 6 are cross-sectional views for explaining the principle of the second reference example of the ink jet recording apparatus of the present invention. When the vibrating member 2 is vibrated at a certain frequency in the axial direction of the nozzle 1, a standing wave for one wavelength is generated as shown in FIG. When the frequency of the vibrating member 2 is increased, a standing wave of two wavelengths is generated at a certain frequency as shown in FIG. 5 (B). Similarly, when the frequency of the vibrating member 2 is increased, a standing wave of n wavelength (n is an integer) is generated in the cylindrical nozzle at a certain frequency. On the other hand, the vibration intensity (amplitude) of the cylindrical vibration member
As shown in FIG. 6 (A) to (C), the amplitude of the standing wave increases, and when the vibration reaches a certain intensity, as shown in FIG. The wave front at the center of the large cylinder breaks and small droplets fly. Recording can be performed by attaching the droplets to the recording medium.

As a specific example, an integral cylindrical vibrating member 2 is attached near the tip of a cylindrical nozzle 1 having a diameter of 200 μm, in which a surface tension of 0.040 N / m and a density of 105 are set.
The experiment was carried out while holding 0 kg / m ³ of ink. The frequency at which the standing wave appears is determined by the principle shown below. Since the vibration is transmitted on the ink surface and is generated in the nozzle of 200 μm, the wavelength of the wave to be handled is 200 μm.
It is as follows.

It is the surface tension that governs the progression of this wave. Therefore, when the liquid surface tension is σ (mN / m), the liquid density is ρ (g / cm3), and the wavelength is λ (μm), the traveling velocity v of the surface tension wave (transverse wave) is v = (2πσ / ρλ ) ^1/2 ... (1) can be represented. On the other hand, the frequency f _k of the wave is given by the traveling speed and the wavelength as follows. f _k = v / λ ... (2) From formulas (1) and (2), λ = {2πσ / (ρf _k ² )} ^1/3 (3). Further, when the transmission frequency and fe (Hz), since it is _{f k = f e / 2 ···} (4), (3) equation (4) from equation _{λ = {8πσ / (ρf e} 2) } ^1/3 ... (5) (5) than, and _{f e = (8πσ / ρ)} 1/2 λ -3/2 ··· (6).

As in the above specific example, σ = 0.040N
/ M, ρ = 1050 kg / m ₃ ink is used,
When calculated by substituting these values into equation (6), and ^{_{f e = 0.031λ -3/2 ··· (7}} ). On the other hand, the wavelength of the wave generated in the cylinder is given by λ = D / n (8) where D is the diameter of the cylinder. However, n is the wave number of the wave generated in the cylinder and is an integer. From equations (7) and (8), f _e = 0.031 (D / n) ^−3/2 (9) In the specific example, since a nozzle of D = 200 μm was used, it is determined that _fe = 10960n ^3/2 (10).

FIG. 7 is a graph for explaining the relationship between the number of wave fronts generated in the cylindrical nozzle and the applied frequency in the second reference example of the ink jet recording apparatus of the present invention.
As described above, σ = 0.040 for the 200 μm diameter nozzle.
When the ink of N / m, ρ = 1050 kg / m ³ is filled and vibration is applied, the relationship between the wave number of the wave generated in the nozzle and the frequency is as shown in FIG. 7. For example, by applying a vibration of 88 kHz from the vibrating member 2, it is found from FIG. 7 that the wave front number of the wave generated in the cylinder is four. That is, by giving a vibration of 88 kHz from the vibrating member 2, as shown in FIG.
A wavelength component can be generated on the surface of the ink in the nozzle 1. When the voltage applied to the vibrating member 2 reaches a certain value, ink droplets start flying from the center of the nozzle 1, as shown in FIG. At this time, the particle diameter of the ink droplet was about 20 μm.

The second reference example can also be constructed by using a plurality of vibrating members. In that case, ink droplets can be similarly ejected from the center of the nozzle 1 by matching the phases of vibration of the plurality of vibrating members.

In the second reference example, the ink 3 is vibrated by the vibrating member 2 as described above, but the present invention is not limited to this. The vibrating member 2 vibrates the nozzle 1 and the vibration vibrates the ink 3. It is also possible. Figure 8
FIG. 9 is an explanatory diagram of an embodiment of a recording apparatus of the present invention, which is a modification of the second reference example. In the figure, 11 and 12 are substrates. In this embodiment, two substrates 11 and 12 having different characteristics are bonded to each other and an opening is provided to form a cylindrical nozzle 1.
Is formed. The lower surface of the substrate 12 can form a part of the ink chamber, and the ink is filled up to the nozzle 1.

In this structure, the two substrates 11 and 12 are
By contracting or expanding one of the substrates around the nozzle 1, the two substrates 11 and 12 are bent, and the end portion of the nozzle 1 moves upward or downward.
This principle is the same as the operation principle when heating a bimetal in which two kinds of metals having different coefficients of thermal expansion are joined. By repeating this operation, the ink 3 can be vibrated. The vibrating member 2 includes the substrates 11 and 1
It may be configured according to the physical characteristics of No. 2, and for example, when a piezoelectric substrate is used as the substrate 11 or 12, it can be configured by means for giving an electric signal to the piezoelectric substrate. In addition, for example, if the substrates 11 and 12 are made of a bimetal or a shape memory alloy and the like and high-speed bending and restoring operations are possible, the vibrating member 2 may be constituted by a heating means or the like.

FIG. 9 is an explanatory diagram of a configuration example in which a plurality of nozzles are arranged. In the figure, 21 is a substrate, 22 is an ink chamber, 2
Reference numeral 3 is an ink supply pipe. Although each of the above-described examples shows only one nozzle, a plurality of nozzles may be arranged. In the example shown in FIG. 9, the nozzles 1 are arranged in a matrix.

The substrate 21 has openings for forming the nozzles 1 formed in a matrix. The opening can be formed by, for example, a laser. At this time, a CO ₂ laser having a good throughput is preferred when cost is important, and an excimer laser is preferred when heat damage and cracks are taken into consideration. Drilling or punching can be used to further reduce the cost.

In the example shown in FIG. 9A, the nozzle 1 is
The nozzles are arranged in a straight line in the lateral direction, and the other nozzles are arranged while being slightly shifted in the lateral direction so that the other nozzles are not arranged in the direction orthogonal to the arrangement direction. By performing recording while relatively moving the recording head and the recording medium having such an arrangement in the vertical direction, it is possible to perform recording with a recording density higher than the arrangement interval of the nozzles 1 in the horizontal direction.

Each nozzle 1 is provided with a vibrating member 2. In order to supply electric energy to the vibrating member 2, as shown in FIG. 9A, vertical leads A1 to A5 and horizontal leads B1 to B6 are arranged. Here, by selecting any one of the leads A1 to 5 and one of the other leads B1 to 6 to supply electric energy, the vibrating member 2 corresponding to one nozzle 1 selectively operates. , It becomes possible to excite. An image can be recorded on the recording medium by controlling the selection operation, the operation timing, and the relative movement with respect to the recording medium according to the image data.

Further, in each nozzle 1, it is necessary to prepare for the next flight of ink by ejecting the ink and then supplying the ejected ink. Therefore, in this example, as shown in FIG.
Can be provided to store the ink and to supply the ink from the ink tank (not shown) to the ink chamber 22 at a constant pressure via the ink supply pipe 23. As a result, it is possible to always keep the position of the ink surface in the nozzle 1 constant, and to align the dots to be printed while keeping the distance to the recording medium constant, so that it is possible to perform high quality printing.

FIG. 10 is a plan view showing an example in which a plurality of nozzles are formed by slits. In the figure, 31 is a slit. In the example shown in FIG. 9, each nozzle is formed by an opening, but as shown in FIG. 10, it may be formed as a slit 31 common to a plurality of nozzles. In the example shown in FIG. 10, slits 31 are provided in the lateral direction, and arcuate vibration members are arranged on both sides of the positions on the slits 31 corresponding to the nozzles. By setting the centers of the circular arcs of the vibrating members arranged on both sides to the same position, the ink droplets fly from the central portions of the circular arcs. This arcuate vibration member may be provided on only one side.

Although the matrix arrangement is shown in FIGS. 9 and 10, the arrangement is not limited to this, and a structure having only one line is also possible.

[0038]

As is apparent from the above description, according to the present invention, the vibration energy is applied to the vicinity of the surface of the liquid ink to propagate and concentrate the vibration energy.
Since the energy efficiency is high and the vibration energy can be concentrated in a minute area, there is an effect that small droplets can be accurately ejected in the direction perpendicular to the surface of the liquid ink.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first reference example of an inkjet recording apparatus of the present invention.

FIG. 2 is a plan view showing a first reference example of the inkjet recording apparatus of the present invention.

FIG. 3 is a plan view for explaining the operation principle of the inkjet recording apparatus of the present invention in a first reference example.

FIG. 4 is a cross-sectional view illustrating the operation principle of the first reference example of the inkjet recording apparatus of the present invention.

FIG. 5 is a cross-sectional view illustrating the number of wave crests generated in a second reference example of the inkjet recording apparatus of the present invention.

FIG. 6 is a cross-sectional view illustrating a wave height generated in a second reference example of the inkjet recording apparatus of the present invention.

FIG. 7 is a graph for explaining the relationship between the number of wave fronts generated in the cylindrical nozzle and the frequency to be applied in the second reference example of the inkjet recording apparatus of the present invention.

FIG. 8 is an explanatory diagram of an embodiment of an inkjet recording apparatus of the present invention.

FIG. 9 is an explanatory diagram of a configuration example in which a plurality of nozzles are arranged.

FIG. 10 is a plan view showing an example in which a plurality of nozzles are formed by slits.

FIG. 11 is a principle explanatory diagram of an ink jet recording method using a conventional surface acoustic wave.

[Explanation of symbols]

1 ... Nozzle, 2 ... Vibration member, 3 ... Ink, 11, 12,
21 ... Substrate, 22 ... Ink chamber, 23 ... Ink supply pipe, 3
1 ... slit.

Front page continued (72) Inventor Keizo Abe, 430 Nakai-cho, Ashigagamigami-gun, Kanagawa Green Tech Nakakai Fuji Xerox Co., Ltd. ) References JP-A-2-225048 (JP, A) JP-A-5-57891 (JP, A) JP-A-4-290750 (JP, A) JP-A-55-19523 (JP, A) JP-A-5-19523 (JP, A) 2-55139 (JP, A) JP-A-62-251153 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/015 B41J 2/01

Claims (4)

(57) [Claims] 1. A liquid held by the nozzle, comprising vibration generating means for moving a nozzle portion, which is an end portion of a vibrating substrate having an opening to form a nozzle, up or down to vibrate. To vibrate the vibration generating means to generate a longitudinal wave so that a standing wave is generated in the vicinity of the surface of the ink toward the center of the nozzle, and to cause a droplet to fly from the surface of the liquid ink in the center. An inkjet recording device characterized by the above. 2. The ink jet recording apparatus according to claim 1, wherein the vibration generating unit includes a piezoelectric member or a plurality of piezoelectric members. 3. The ink jet recording apparatus according to claim 1, wherein the vibration generating means are arranged in a line. 4. The vibration generating means is arranged in a matrix, and the vibration generating means arranged in each row or column are arranged at different positions in the column or row direction. Inkjet recording device.