JPS5896565A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To develop steadily and surely ink particles that are constantly of the same dimension and improve the quality of picture images by establishing a frequency that is used for excitation of a nozzle at a value that is a little larger than the fluid resonance frequency of an ink. CONSTITUTION:A piezo-electric element 2 is installed on a nozzle 1. Excitation voltage the frequency of which is set at a frequency that is larger by 4.5-12% than a fluid resonance frequency of the ink 1 is supplied from the excitation source 3 to the piezo-electric element 2 to effect excitation. With this arrangement the pressurized ink 4 supplied to the nozzle 1 is vibrated and the ink 4 is jetted out as ink particles 7 from the tip of the nozzle 1 to charge between charging electrodes 8. Those electrodes 8 are deflected by deflection electrodes 10a and 10b to attach electric charge on a recording body 12 for recording. Setting up the excitation frequency of the nozzle a little higher than the fluid resonance frequency of the ink 4 prevents development of ink particles of small diameter. Ink particles of uniform size can be developed.

Description

[Detailed description of the invention] The present invention relates to an inkjet recording method.

The following inkjet recording method has been applied to Kanji printers and the like.

In FIG. 1, a piezoelectric element 2 is attached to the long nozzle 1.
is attached, and this piezoelectric element is driven by an excitation voltage vf supplied from an excitation source 3.

The frequency of the above excitation voltage V, is the same as the fluid resonance frequency of the ink 1 pumped to the nozzle 1, and by setting the frequency of the excitation voltage V, in this way, the nozzle 1 can be operated efficiently with a small excitation voltage V, Can be driven well.

When the piezoelectric element is excited by the excitation voltage V in this way, the pressurized ink 4 supplied to the nozzle 1 receives vibration,
This vibration is transmitted to the ink column 6 ejected from the nozzle hole 5 formed at the tip of the nozzle l, and ink particles 7 having a diameter of Φ and an interval of λ are separated at the tip of the ink column 6.

The fluid resonance frequency is determined by the nozzle length L1 and the sound velocity of the ink 4, and is generally 100 KH2.
Therefore, the excitation voltage v0 is set to such a high frequency.

Ink particles 7 ejected from the nozzle 1 as described above
are selectively charged in accordance with an information signal, and the charged ink particles fly in an electrostatic field of uniform size, are deflected and adhered to a recording medium placed opposite the nozzle 1. As a result, an image (for example, a Chinese character) corresponding to the information signal is formed on the recording medium.

In this type of apparatus, as shown in FIG. 2(a), ink particles 7 of approximately uniform size are separated from an ink column 6, and accurate charge deflection control is performed to form an image on a recording medium. It is necessary to form it with high quality.

However, in the conventional apparatus described above, as shown in FIGS. 2(b) and 2(C), the large-diameter ink particles 7a and the small-diameter ink particles 7b
In this case, accurate deflection control cannot be performed, resulting in a problem that the quality of the image formed on the recording medium is degraded. That is, in this case, a phenomenon occurs in which the charged small-diameter ink particles 7b with a large specific gravity load do not coalesce, and as a result, the amount of charge (i.e., deflection sensitivity) of the ink particles 7 that should be used for recording decreases.
must change discontinuously, thus making it impossible to perform accurate deflection control.

In view of the above problems, conventionally the excitation voltage is V.

(Japanese Patent Publication No. 52-2779), and set the straight length of the nozzle hole 5 to a predetermined length (Japanese Patent Publication No. 52-2779).
-18625), excite the nozzle 1 using a plurality of excitation sources 3 (Japanese Patent Publication No. 55-27859), or excite the nozzle 1 using multiple excitation sources 3.
Measures were taken such as setting the nozzle length so that the inner I/R 4 would resonate with the fluid at a frequency 7.02 times the excitation voltage.

However, in the past, the fluid resonance of the ink was too strong, causing electrical, mechanical, and fluid distortion, as shown in Figure 2 (
b) Generation of small-diameter ink particles 7b as shown in (C) could not be completely suppressed.

Furthermore, in the conventional method, ink is driven by the ink's fluid resonance frequency, so when the temperature of the ink changes, the physical properties of the ink (surface tension, viscosity, sound velocity, etc.) change, making it possible to separate ink particles of uniform size. This makes it difficult to control the temperature of this waste ink, or it is necessary to accurately detect the ink temperature and adjust the operating point of the nozzle. Therefore, in the past, the apparatus required a configuration for such a control and adjustment mechanism, and there was a problem in that adjustment work for the mechanism was required. However, even with this method, ink particles of uniform size could not be generated sufficiently stably and reliably.

As explained above, in the past, the excitation frequency of the nozzle was matched to the dynamic body resonance frequency of the ink, so if the operating conditions fluctuate or the degree of resonance is too strong, it is necessary to reduce the thickness of the ink droplet to make it stable and reliable. could not be generated.

The present invention has been made in view of the above-mentioned conventional problems,
The purpose is to provide an inkjet recording method that can consistently and reliably generate ink particles of uniform size. In order to achieve the above object, the present invention provides an inkjet recording method in which a nozzle to which pressurized ink is supplied is excited and driven to eject ink particles from the nozzle, and recording is performed using the ink particles. It is characterized in that the nozzle is excited and driven at a frequency slightly higher than the frequency.

Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 3 shows an inkjet recording apparatus to which the present invention is applied, and the same members as in FIG.

The ink particles 7 ejected from the nozzle 1 first reach the charging electrode 8
pass between. An information signal source 9 is connected to the charging electrodes 8, and the ink particles 7 passing between the electrodes 8 are charged in accordance with the information signal supplied from the information signal source 9.

The ink particles 7 charged by the charging electrode 8 then pass between a pair of deflection electrodes 10. A deflection voltage source 11 is connected to one electrode IQH of this charging electrode 10, and the other electrode 10b is grounded. When an ink particle 7 passes between these deflection electrodes 10, the charged ink particle 7 is transferred to the electrode It is deflected toward the recording medium 10a and reaches the recording medium 12, where an image is formed.

Note that the uncharged ink particles 7 travel straight and are captured and recovered by the gutter 13 and reused.

In addition, in this device, it is necessary to increase the flight speed of the ink particles 7 to reduce the turbulence caused by the air during the flight of the ink particles, or to correct various other turbulences, and these measures are taken in the actual device. .

Here, in the embodiment shown in FIG. 3, the nozzle length 11W+the diameter of the nozzle hole 5 30 μm1, the ink pressure 6Kf/crn2,
The ink flow rate was 1 cc/min, and the ink particle diameter Φ was 66 μm, and the distance between each ink particle 7 was λ and 22θ μm.

At this time, the fluid resonance frequency fr of the ink 4 in the nozzle 1
C: Speed of sound in ink 4 n: Since it is determined by an integer greater than or equal to 1, if the speed of sound C is 1600 m/S, the relationship between n and f is as shown in Table 1 below.

Table 1 In this embodiment, the above n is 2, so the fluid resonance frequency f is 109=H2.

As mentioned above, in the past, the excitation frequency F of the nozzle 1 was set equal to the fluid resonance frequency f, but the present invention is characterized in that the nozzle is excited and driven at a frequency slightly higher than the fluid resonance frequency of the ink. Therefore, in this embodiment, the excitation frequency F is set to 118KH2.

The relationship between the excitation frequency F and the excitation voltage V in the above-described embodiment of FIG. 3 is shown in FIG.

Note that the characteristics shown in FIG. 4 were obtained through experiments.

In FIG. 4, the area surrounded by curves 100a and 100b is 20C, the area surrounded by curves 102a and 102b is 5C, and curve 104a.

The area surrounded by 104b shows the temperature range characteristics in which the printer can operate at 45C.

As is clear from Fig. 4, the fluid resonance frequency f1□(1
09KH2), the excitation voltage V is the lowest and the device operates efficiently, but when the nozzle 1 is excited at this frequency, the operating temperature range of the printer changes according to temperature changes and the excitation voltage V is the same.

It is not possible to stably and reliably generate ink particles of uniform size with an amplitude of .

It is understood from FIG. 4 that there is a common region 200 that can operate as a printer over a range of 50 to 35 C in an excitation frequency range higher than the fluid resonance frequency fr2. The present invention has been made focusing on this region 200, and therefore the excitation frequency F is the fluid resonance frequency f72.
The frequency is set to slightly higher than that of the

Furthermore, when the excitation frequency F becomes higher and is set to the formula '-4/2, the generation mode of the ink particles 7 becomes as shown in Fig. 2 (C).
As a result, printing becomes impossible. This is considered to be because the fluid resonance at the excitation frequency f6 actively causes the ink 7 to become particles, making it easier to generate small-diameter ink particles 7b. Therefore, the excitation frequency F cannot be set unnecessarily high.

As described above, the excitation frequency F is set to the fluid resonance frequency f.

It is preferable to set the frequency to a value slightly higher than that.

Furthermore, it has been empirically concluded that it is preferable to set the excitation frequency F to a frequency that exceeds the fluid resonance frequency f by a range of 4.5 to 12 percent.

From this, it is understood that in this embodiment, the setting range of the excitation frequency F is approximately 111 KH2 to 124 KHz.

Note that the range of excitation frequency F that can actually be set is 114KH because the excitation voltage V requires a margin of ±25V or more.
It is preferable to select the range from 2 to 122 KH2 (range indicated by A in FIG. 4). Therefore, in this embodiment, the excitation frequency F is set at 118KH2 located at the center of this excitation frequency range A.

By setting the excitation frequency F as described above, ink particles 7 of uniform size can be generated stably and reliably.

As explained above, according to the present invention, since the excitation frequency of the nozzle is set slightly higher than the fluid resonance frequency of the ink, it is possible to prevent the generation of small diameter ink particles due to resonance distortion. Ink particles of various sizes can be generated stably and reliably. Further, according to the present invention, as is clear from FIG. 4, ink particles of a uniform size can be stably generated regardless of temperature fluctuations.

Furthermore, according to the present invention, since the excitation frequency of the nozzle is set slightly apart from the liquid resonance frequency of the ink,
There is no need to increase the manufacturing precision of the nozzle, and even if operating conditions other than temperature vary, ink particles of uniform size can be generated stably and reliably.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view of the nozzle part, FIG. 2 is an explanatory diagram of the ink droplet generation mode, FIG. 3 is a schematic configuration diagram of an inkjet recording apparatus to which the present invention is applied, and FIG. 4 is an example of the embodiment shown in FIG. FIG. 1... Nozzle, 2... Piezoelectric element, 3... Excitation source,
4... Pressure ink, 5... Nozzle hole, 6... Ink column, 7... A.

Claims (1)

[Claims] 1. In an inkjet recording method in which a nozzle to which pressurized ink is supplied is excited to eject ink particles from the nozzle and recording is performed using the ink particles, An inkjet recording method characterized in that the nozzle is excited and driven at a higher frequency. 2. The inkjet recording method according to claim 1, characterized in that the nozzle is excited and driven at a frequency that exceeds the fluid resonance frequency of the ink by 4.5% to 12%. 3. In the method according to claim 1 or 2, the ink particles ejected from the nozzle are charged in accordance with the information signal, the charged ink particles are deflected by a constant electrostatic field, and the charged ink particles are arranged opposite to the nozzle. An inkjet recording method characterized in that an image is formed by depositing deflected ink particles on a recording medium.