JPS583874A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To obtain a stable printing head by making the resonant frequency at a low temperature coincident with the frequency to be used in an inkjet recorder, thereby minimizing variation of droplet characteristics with temperature change. CONSTITUTION:The printing head in an inkjet recorder is to cut an ink column injecting from a nozzle by oscillating a vibration element of deform a liquid chamber thereby generating pressure waves in the ink. In the printing head, the sonic speed in the liquid increases as the temperature rises so that resonant frequency increases with the temperature. The length of the liquid chamber is so determined that the resonant frequency coincides with the used frequency at the lowest ambient temperature such as 5 deg.C to create a resonant state. The printing head constructed as above deviates from the resonant frequency and so becomes inefficient at higher temperatures, for example, 25 deg.C. However, this is compensated for by some increase in efficiency becuase of lower viscosity at high temperatures. Thus, the relative efficiency is kept stable, enabling a stable injection over wider temperature ranges.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an inkjet recording apparatus that avoids the following.

Generally, a charge deflection type inkjet recording apparatus is constructed as shown in FIG. In FIG. 1, 1 is a printing head, 2 is a charging electrode, 3 is a deflection electrode, 4 is printing paper, 5 is a gutter, 6 is an ink reservoir, 7 is a pressure pump, 8 is a filter, 9 is pulp, 11 is a piezoelectric vibrator, 12 is an excitation power source, 13 is a charge control unit, and 14 is a deflection power source.The ink pressurized by the pressure pump 7 passes through the filter 8 and pulp 9 to the nozzle 1 of the printing head 1 At that time, the piezoelectric vibrator 1l in the printing head 1 is excited by an excitation signal from an excitation power source 12, thereby regularly turning the ink into particles. This jetted ink column 10
When the ink droplets are formed into droplets 10', they are selectively charged by sending a signal from the charge controller 13 to the charging electrode 2, and the charged ink droplets are sent to the deflection power source 14. The ink droplets are deflected by the voltage sent to the deflection electrode 3 and printed on the printing paper 4, and uncharged ink droplets travel straight and are captured and collected by the gutter 5.

In terms of the performance of an inkjet recording apparatus configured in this manner, it is important to stabilize the state of ink jetting, and stability against temperature changes is a particularly important factor. In other words, the physical properties of the ink jet used for the ink jet change with temperature, and the excitation efficiency of the nozzles of the printing head changes with temperature, so the filter conditions for creating ink particles change with temperature. This has the disadvantage that the recording quality deteriorates further and the recording becomes unstable.

In order to overcome this drawback, an inkjet recording device is known that expands the stable region by changing the excitation waveform in accordance with changes in temperature (% 1978-578
(Refer to Publication No. 38), the disadvantages were that the effect was low and the cost was high.

There is also an inkjet recording device that warms the ink and keeps it at a constant temperature so that it is not affected by changes in the temperature of the outside air (see Japanese Patent Publication No. 53-'42619).
However, the disadvantage is that it takes time to heat the ink to a certain temperature, resulting in high costs.

Furthermore, there are also known inkjet printing devices that detect temperature and change the excitation voltage depending on the change in temperature (see Japanese Patent Application Laid-Open No. 53-98826). There was a point to control the voltage.

The present invention is characterized by matching the resonant frequency at low temperatures and the operating frequency in order to eliminate the above-mentioned drawbacks of the conventional and conventional examples. An object of the present invention is to provide an inkjet printing device that avoids the above problems and obtains a stable printing head. Hereinafter, the present invention will be explained in detail with reference to the drawings.

First, in the inkjet recording apparatus shown in FIG. 1, there are various types of printing heads depending on the shape and handle of the piezoelectric vibrator. Namely, there are known types such as the diaphragm type in which a piezoelectric voice is installed behind the liquid chamber communicating with the nozzle, the Langevin type in which a piezoelectric vibrator is installed on the wall of the liquid chamber, and the pipe type in which the piezoelectric vibrator is shaped like a pipe. However, both of them excite a vibrator to deform the liquid chamber, generate pressure waves in the ink,
Cut the column of ink ejected from the nozzle.

In such a printing head, when we investigated the temperature characteristics of a diaphragm type printing head with an excitation frequency of 32 KHz, we found that the area without satellites has a temperature and piezoelectric vibrator effect, as shown by 8 in Figure 2. It is determined by the applied voltage of 15
This printing head could not be used at temperatures below .degree.

Here, the governing equation for the pressure in the liquid chamber of the printing head is as follows: boundary change, C is the sound velocity in the liquid), and the resonance frequency is governed by the sound velocity C in the liquid.

That is, since the speed of sound C in a liquid increases as the temperature increases, as shown by curve A in FIG. 3, the resonance frequency also increases as the temperature increases. Since this resonant frequency is determined by the length of the liquid chamber of the print head, the resonant frequency can be arbitrarily changed by changing the length l of this liquid chamber.

Here, if the length l of the liquid chamber is determined so that the resonant frequency and the operating frequency match when the operating environment temperature condition is the lowest, for example, if the length l of the liquid chamber is set to l=7.5-, Fourth
As shown by A in the figure, a resonance state occurs at 132KH2 at 5°C. When a printing head configured in this way is heated to a high temperature, for example 25°C, as shown in B in Fig. 4, it deviates from the resonant frequency and the efficiency deteriorates, but in general, the viscosity of the print head becomes low. This offsets the increase in efficiency, so efficiency remains relatively unchanged and remains constant. As a result, there is no need to add any temperature countermeasure functions, the operating temperature range is widened, and injection is stabilized.

As explained above, according to the present invention, the resonant frequency at low temperatures and the operating frequency are matched by changing the length of the liquid chamber of the printing head, so that the particle formation characteristics do not change even when the temperature changes. First, since there is no need to add any function to deal with temperature changes, there are advantages in that the cost does not increase, the temperature range is widened, and the injection is stable.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an inkjet recording apparatus, and FIG.
The figure shows the satellite-free region with respect to changes in excitation voltage and ambient temperature, Figure 3 shows the relationship between sound speed and temperature, and Figure 4 shows the relationship between excitation voltage and resonant frequency. This is a diagram. l...Printing head, 2...Charging electrode, 3...Deflection electrode, 4...Printing paper, 5...Gutter, 6...Ink reservoir, 7...Pressure pump , 8... Pulp, 11.
. . . pressure, electric vibrator, 12 . . . excitation section, 13 . . . charge control section, 14 . . . deflection power supply. Patent applicant Rico Co., Ltd. −

Claims (1)

[Claims] A piezoelectric vibrator is provided in the liquid chamber of the printing head, and ink is ejected from the nozzle of the printing head, and when the ink becomes an ink droplet, a charging electrode turns the ink droplet into a charged current or an uncharged droplet. Accordingly, in an inkjet recording device that prints characters or figures on printing paper by deflecting or undeflecting the charged current or uncharged droplets, the resonant frequency at low temperature and the operating frequency are made to match. Inkjet recording device.