JPH0255143A - inkjet recording device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet recording apparatus, and more particularly, to a head section in an inkjet recording apparatus.

BACKGROUND OF THE INVENTION Hitherto, various configurations of inkjet recording apparatuses that eject ink droplets by applying voltage pulses have been known, but each of them has various problems. For example, the method described in Japanese Patent Application Laid-Open No. 58-36462 uses conductive ink, but the voltage pulse is 300
Because the voltage is as high as 0V, the shame circuit is expensive, especially
There is a problem when using multiple heads.

In addition, the method described in Japanese Patent Publication No. 62-9430 has an explanation that the distance between the electrodes is equivalent to the nozzle diameter (several tens of μm or more), and that a voltage pulse higher than the discharge breakdown voltage of that distance is applied. However, it has the disadvantages that insulating ink must be used and high voltage is required.

Further, in the device described in U.S. Pat. No. 3,179,042, a liquid chamber tank is provided near the head, the ink is heated in the tank, and the ink is preheated to have certain characteristics. Ink is sent to the head through a flow path, and then passes through opposing electrodes to ionize, vaporize, etc. the ink between the electrodes, thereby generating a sudden force and ejecting the ink. . However, this method requires additional equipment such as the provision of a preheating section, resulting in high costs, and, like the above-mentioned prior art, has the disadvantage of requiring a high driving voltage.

FIG. 1 is a diagram for explaining an example of an inkjet recording device to which the present invention is applied, and is also a diagram for explaining an example of an inkjet recording device previously proposed by the applicant. FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line B-B in FIG. 2 is the injection opening.

3 is the first electrode (recording electrode), 4 is the second electrode (common electrode)
, 5 is a connection lead for the first electrode 3, 6 is an ink supply channel,
7 is a common liquid chamber, and the first electrode 3 is arranged corresponding to each injection opening 2, and is connected to an electric circuit (not shown) so that voltage pulses can be applied to each of them individually. The second electrode 4 is arranged as one common conductor for all injection openings 2 and is connected to the other side of the electrical circuit. The ink is
The ink is supplied to the common liquid chamber 7 from an ink tank or the like (not shown), passes through each recording ink supply channel 6, and is supplied to the ejection opening 2. The picture electrodes 3 and 4 are preferably made of a material such as platinum, which is chemically stable, has excellent heat resistance, has a high melting point and high thermal conductivity, and has good wear resistance.

Note that the other head materials (illustrated parts) are insulating materials.

In the above configuration, when ink is supplied and a voltage pulse is applied between the recording electrode 3 and the common electrode 4, electrical energy is released between both electrodes, thereby vaporizing the ink and growing bubbles. .

That is, by applying a voltage pulse, bubbles are generated and grown, pressure increases at the ejection opening 2, and ink is ejected from the ejection opening 2.

Now, when the pulse voltage shown in FIG. 4(a) is applied between the first electrode 3 and the second electrode 4, a current having the waveform shown in FIG. 4(b) flows.

FIG. 5 is a diagram for explaining the current waveform shown in FIG. 4(b) in relation to the generation and growth of bubbles.
When a negative voltage is applied to the electrode 3 and a positive voltage is applied to the second electrode 4, small bubbles 9 are generated on the first electrode 3 due to hydrogen generation due to electrolysis and heat generation due to I''R loss (Fig. 5 (a) )).

Hydrogen bubbles (including vaporization of ink due to heat generation depending on the conditions) grow to cover the surface of the first electrode 3, and the current supply is stopped (FIG. 5(b)). At this time, the current changes from ■ to ■ in FIG. 4(b). Hydrogen bubbles 9 and ink 8
The interface 10 has the same potential as the second electrode 4, the electric field strength between the interface 10 and the first electrode 3 increases, and a discharge 11 occurs within the hydrogen bubble 9 (FIG. 5(C)). The current waveform at this time is shown by ■ in FIG. 4(b).

Due to the heat generated during the discharge, the electric field strength decreases due to the expansion of the hydrogen bubbles 9 and the bubbles caused by the vaporization of the ink 8, and the discharge stops (Fig. 5(d)).The current at this time is as shown in Fig. 4. (
b) becomes ■. At this time, the pressure within the flow path increases due to the rapid expansion of the bubbles, and ink is ejected from the ejection opening 2.

Although not shown, it is also possible to provide the first electrode 3 near the ejection opening 2 and eject the ink by causing the bubbles 9 to burst through discharge. Note that the form of the multi-nozzle head is not limited to the above-mentioned nozzle type, but may also be a slit opening as shown in FIG. In addition, the seventh
The figure is a cross-sectional view taken along the line A-A in FIG. 6. In FIGS. The same reference numerals will be given, and the description thereof will be omitted.

Further, the second electrode does not necessarily have to be provided in the nozzle section, but can also be provided near the ink supply port 16 from the internal ink tank of the nozzle section, as shown in FIG.

However, in the above-mentioned inkjet recording device, the positional accuracy of the ejected ink on the recording medium affects the image quality, and one of the factors that changes the position is the discharge from the rising (falling) of the voltage pulse. There is a variation in the time t until the start of . This fluctuation becomes larger as the time t becomes longer, so it is effective to apply a high voltage pulse, but this increases the cost and is not a good idea.

■---Five inventions were made in view of the above-mentioned circumstances.
In particular, the inkjet uses an electrolytic discharge method that allows for lower voltage than the conventional discharge methods mentioned above, which reduces the delay in the start of discharge relative to the recording signal, thereby improving printing position accuracy and image quality. It was created for the purpose of providing a recording device.

In order to achieve the above object, the present invention includes a discharge port for discharging a liquid, a liquid chamber communicating with the discharge port, a pair of electrodes provided in the liquid chamber, and a discharge port for discharging a liquid. a voltage applying means for applying a first voltage between a pair of electrodes to generate bubbles in the liquid in the liquid chamber by electrolysis, and a second voltage to change the volume of the bubbles by electric discharge. It is characterized by this. Hereinafter, the present invention will be explained based on examples.

As described above, in the electrolytic discharge type inkjet recording device previously proposed by the present applicant, the pressure in the flow path increases due to the rapid expansion of bubbles, and ink is ejected from the ejection opening 2. At this time, the positional accuracy of the ejected ink on the recording medium affects the image quality, and one of the factors that changes the position is the time from the rise (fall) of the voltage pulse to the start of discharge. There are fluctuations in the time. Since this fluctuation becomes larger as the time t becomes longer, it is effective to apply a high voltage pulse, but this increases the cost and is not a good idea. Therefore, in the present invention, the electrolysis step (1) is performed before applying a voltage pulse (for discharging) to shorten the time t.

Figures 9(a) and (b) show the first 'it h
The waveform of the voltage applied between 3 and the second electrode 4, Fig. 9 (
c) shows the current waveform flowing between both electrodes at this time, and as shown in the figure, a voltage pulse VP2 for electrolysis is applied just before a voltage pulse Vp□ for discharge. Although FIG. 1 shows one pulse, there may be a plurality of pulses. However, although VPz is a potential sufficient to cause electrolysis, it must be sufficiently lower than the discharge starting potential.

10 is a diagram showing the potential applied to the first electrode 3 and the potential applied to the second electrode 4 in order to apply the voltage shown in FIG. 9(a), and FIG. This is a diagram showing the potential applied to the first electrode 3 and the potential applied to the second electrode 4 in order to apply the voltage shown in Figure (b), and in both diagrams, (a) is the voltage applied to the first electrode 3. (b) shows the potential applied to the second electrode 4. However, these are examples of generating hydrogen bubbles (low discharge starting voltage) in the first electrode 3, and the intended purpose of the present invention can be achieved even if other potentials are applied.

FIGS. 12(a) and 12(b) show the first electrode 3 and the second electrode, respectively.
The waveform of the voltage applied between the electrode 4 and FIG. 12(c) shows the waveform of the current flowing between the two electrodes at this time. Then,
In this embodiment, a constant voltage is constantly applied for electrolysis, and since the time between discharge pulses can be used effectively, Vp'2 can be at a lower potential than V P z.

FIG. 13 is a diagram showing the potential applied to the first electrode 3 and the potential applied to the second electrode 4 in order to apply the voltage shown in FIG. 12(a), and FIG. This is a diagram showing the potential applied to the first electrode 3 and the potential applied to the second electrode 4 in order to apply the voltage shown in b), in which (,) is the potential applied to the first electrode 3, (b) ) indicates the potential applied to the second electrode 4. Therefore, in the case of Figure 14, -Vp□=-V
p+V P 2', and it is possible to lower the potential applied to the first electrode 3.

FIGS. 15(a) and 15(b) show the first electrode 3 and the second electrode, respectively.
This shows another method of applying a potential difference between the two electrodes, but there are many other possible methods of applying a potential difference between both electrodes.

As is clear from the above explanation, according to the present invention, a potential difference that is higher than the decomposition voltage for generating bubbles by electrolysis and lower than the discharge starting voltage of the generated gas is lower than the voltage for discharging. By first applying it between both electrodes, discharge can start immediately after the voltage pulse (Vp) rises, and the ink can be jetted. This reduces fluctuations in the jetting timing relative to the recording signal, and reduces the amount of ink on the recording medium. It is possible to improve the positional accuracy, that is, to improve the image quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an example of an inkjet recording device to which the present invention is applied, and also a part of an inkjet head for explaining an example of an inkjet recording device previously proposed by the applicant. A cutaway perspective view of
Figure 2 is a sectional view taken along the line A-A in Figure 1, Figure 3 is a sectional view taken along the line B-B in Figure 1, Figure 4 is a voltage and current waveform diagram between the electrodes, and Figure 5 is a diagram of the voltage and current waveforms between the electrodes. , an explanatory diagram of the bubble generation process, FIG. 6 is a cutaway perspective view showing another example, and FIG. 7 is a diagram showing A- in FIG. 6.
8 is a sectional view taken along line A, and FIG. 9 is a diagram showing a modified example of the electrode section.
The figure shows a waveform diagram of the voltage applied according to the present invention applied between the first electrode and the second electrode, and a waveform diagram of the current flowing between both electrodes. Figure 10 shows the voltage shown in Figure 9 (,) applied FIG. 11 is a diagram showing an example of applying the voltage shown in FIG. 9(b), and FIG. 12 is another example of the applied voltage applied between both electrodes. A voltage waveform diagram showing
The current waveform diagram flowing between both electrodes, Figure 13, is similar to Figure 12 (
Figure 1 shows an example of applying the voltage shown in , ).
Figure 4 shows an example of applying the voltage shown in Figure 12(b), and Figures 15(a) and (b) show other examples of the voltage applied between the two electrodes. It is a voltage waveform diagram shown. DESCRIPTION OF SYMBOLS 1...Multi-nozzle recording head base, 2...Ejection opening, 3...First electrode, 4...Second electrode, 5...Connection lead, 6...Ink supply channel, 7 ...Common liquid chamber. Ivy 1 Figure 4 Figure 5 Figure 2? Figure 3 Figure 8 Figure Figure Figure Figure Figure District Figure Figure (b)

Claims (1)

[Claims] 1. A discharge port for discharging liquid, a liquid chamber communicating with the discharge port, a pair of electrodes provided within the liquid chamber, and bubbles caused by electrolysis in the liquid in the liquid chamber between the pair of electrodes. 1. An inkjet recording apparatus comprising: a voltage applying means for applying a first voltage for generating the bubble and a second voltage for changing the volume of the bubble by discharge.