JPH04294150A - Ink-jet head - Google Patents

Abstract

PURPOSE:To realize a ink-jet head enabling density modulation at a dot unit and enabling recording in high density at low cost by selectively changing ink jet mists by both acoustic energy and Coulomb force. CONSTITUTION:Ink discharge openings 7 at intervals of severl dozen mum are formed at the end section of a piezoelectric body substrate 1. Ink 12 is charged by applying voltage between a conductive layer 9 brought into contact with ink 12 in the discharge openings and a platen 10, and ink receives force in the direction of the platen 10 by Coulumn force. A driving signal having constant frequency is inoutted between a driving electrode 2 and a common electrode 3 under the state, thus changing ink into mists and discharging mists, then obtaining a record on recording paper. A record having desired density can be acquired by controlling a time when the driving signal is inputted. Since ink receives force by Coulumn force, the voltage amplitude of the driving signal inputted to the driving electrode can be made lower than conventional devices.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording head for a printing apparatus, and more particularly to an inkjet head for selectively ejecting liquid ink to print on a recording medium.

0002

2. Description of the Related Art FIG. 8(a) is a sectional view of a conventional inkjet recording apparatus, and FIG. 8(b) is a perspective view thereof. In this type of inkjet head, a rectangular drive electrode 102 is formed on one side of a piezoelectric substrate 101, and a single common electrode 103 is formed at the end of the other side, and a specific drive electrode is formed on any drive electrode. By inputting a drive signal having a frequency, the piezoelectric substrate near the ink ejection port 107 is vibrated. As a result, the ink 106 in the ink ejection port 107 is made into a mist and is ejected in the A direction to obtain a record. Since this type of inkjet head is capable of continuously ejecting ink in the form of a mist, it is possible to obtain a print of any density by controlling the print time. Therefore, the head is suitable for recording images that include density data. Furthermore, since the electrode pattern is simple and most of the steps can be formed using photolithography, it has the advantage that a large head can be realized at low cost.

0003

SUMMARY OF THE INVENTION In the above-described ink jet head, as the density of the drive electrodes is increased in order to increase the recording density, the area per element becomes narrower. Therefore, it is necessary to increase the amplitude of the voltage for ejecting ink. Therefore, if the density is too high, the driving voltage becomes too high, making it extremely difficult to manufacture the driving circuit at low cost. As a result, there has been a problem in that it is difficult to manufacture high-density inkjet heads at low cost.

0004

[Means for Solving the Problems] The inkjet head of the present invention includes a piezoelectric substrate having a rectangular drive electrode formed on one surface and a common electrode formed at the end of the other surface;
a slit member parallel to the piezoelectric substrate and positioned so as to form an ink discharge port between the piezoelectric substrate; an ink supply means for supplying ink to the ink discharge port; and a slit member located between the drive electrode and the common electrode. A drive circuit is provided that generates a signal to vibrate the piezoelectric substrate by periodically varying the electric field between the two, and the vibration mode (vibration mode) in which the vibration of the piezoelectric substrate has a maximum amplitude at the end where the common electrode is formed is provided. The inkjet head is configured to be an inkjet head (thickness edge mode), characterized by comprising a conductive layer that is in contact with the ink and can generate an electric field between it and the platen.

[0005]

Embodiment FIG. 1 is an explanatory diagram showing the entire inkjet head according to an embodiment of the present invention, FIG. 2 is a perspective view of a resonant member 20 of the inkjet head, FIG. 3 is a sectional view of the resonant member 20, and FIG. Ink supply member 3 of inkjet head
0, FIG. 5 is a perspective view of the resonance member 20 and the ink supply member 30.
FIG. Embodiments of the present invention will be described below using these drawings.

The resonant member 20 includes a piezoelectric substrate 1, a drive electrode 2 formed on the surface thereof, a common electrode 3, and an insulating layer 11. A rectangular drive electrode 2 is formed on one surface of the piezoelectric substrate 1, and a single common electrode 3 is formed on the end of the other surface. The drive electrode 2 and the common electrode 3 are connected to a drive circuit, and a signal having a constant amplitude and frequency can be input to any drive electrode 2. An insulating layer 11 is formed on the surface of the drive electrode 2 to prevent electrical contact between the ink 12 and the drive electrode 2.

In FIG. 2, the end surface B of the drive electrode 2 is depicted as coming out from the insulating layer 11 in order to make the structure easier to see, but in reality, the end surface B of the drive electrode 2 also extends from the insulating layer 11 as shown in FIG. 1
Must be covered by 1.

In this embodiment, PZT ceramics (Nepec N21 manufactured by Tokin Co., Ltd.) with a thickness of 600 μm is used as the piezoelectric substrate 1. Then, nichrome (NiCr) was applied to both sides of the PZT ceramics by sputtering.
) - After forming two metal layers of gold (Au), the drive electrode 2 and the common electrode 3 were patterned by a photolithography process. Furthermore, SiO2 was formed as an insulating layer on the drive electrode 2 by the CVD method. In reality, since the drive electrode 2 is thin, at 1 μm or less, the end portion B of the drive electrode 2 is covered with an insulating layer of SiO2 as shown in FIG. The width of drive electrode 2 is 150μ
m, the width of the common electrode 3 is 300 μm, the interval between the drive electrodes 2 is 254 μm, and the number of drive electrodes 2 is 40.

As shown in FIG. 4, the ink supply member 30 is composed of a slit member 4, a gap member 5 having a constant thickness formed at the end of the slit member 4, and a conductive layer 9. The conductive layer 9 can generate an electric field between it and the platen 10 by applying a voltage.

The resonance member 20 and the ink supply member 30 are shown in FIG.
The gap member 5 and the insulating layer 11 are bonded together so that the drive electrode 2 is located between the gap members 5 as shown in FIG. As a result, an ink chamber 6 and an ink discharge port 7, which is an ink discharge section, are formed between the resonance member 20 and the ink supply member 30. Length of cross section of ink discharge port 7 (piezoelectric substrate 1 and slit member 4
) is narrower than the cross-sectional length of the ink chamber 6. The cross-sectional length of the ink discharge port 7 determined by the thickness of the gap member 5 is 30 μm or less. If the length of this cross section is longer than 30 μm, it becomes impossible to stably eject ink into a mist form.

An ink supply port 8 is formed in the slit member 4, so that necessary ink can be supplied from an ink tank (not shown) at any time.

In this embodiment, the slit member 4 has a diameter of 1 mm.
After forming an ink chamber 6 by dicing using thick Pyrex glass, a thin nichrome film was formed by sputtering, and this was used as a conductive layer 9. Furthermore, a 10 μm thick aluminum thin film was formed by sputtering, and the gap member 5 was formed by etching this aluminum thin film using a photolithography process. The width of the gap member 5 is 100
The thickness is 10 μm.

FIG. 6 shows the operation of the present invention configured as described above.
, will be explained using FIG.

For the purpose of explanation, the ink discharge ports 7 are drawn in a large size.

FIG. 6(a) shows a state in which the resonant member is not vibrating. Voltages with different polarities are applied to each of the conductive layer 9 and the platen 10 to generate an electric field therebetween. Figure 6
Although the conductive layer 9 has a positive polarity and the platen 10 has a negative polarity, the reverse polarity may be used. At this time, the ink discharge port 7
Since the conductive layer 9 and the ink 12 are in contact with each other, if the ink has slight conductivity, charges 13 (positive charges) move from the conductive layer 9 to the ink 12 to the ink surface. As a result, the charged ink 12 receives a force in the direction of the platen 10 due to the Coulomb force between it and the platen 10. While the voltage applied to the conductive layer 9 is set within a range in which ink is not ejected from the ink ejection port 7, driving is performed by inputting a signal having a specific frequency that vibrates the end of the resonant member to the drive electrode of the resonant member 20. The end of the resonant member near the driven electrode vibrates to generate thickness edge mode vibration.

FIG. 7 shows the thickness edge mode vibration. Figure 7
is a diagram showing a cross section of the piezoelectric substrate 1 vibrating in the thickness edge mode, and the broken line indicates the state at a certain moment when the piezoelectric substrate 1 is vibrating in the thickness edge mode. When observing the vibration mode, the thickness edge mode is a vibration in which the corners of the piezoelectric substrate 1 often sway as shown in FIG. 7, and the center line 5 of the cross section
This is a vibration mode in which the displacement is symmetrical with respect to 5. In this example, the frequency of the signal input to the drive electrode 2 is 2.2M.
A thickness edge mode vibration mode can be generated in the piezoelectric substrate at Hz.

FIG. 6(b) shows a state in which the ink is vibrating. This vibration is transmitted to the ink 12 through the insulating layer 11, and the ink near the driven drive electrode 2 vibrates. When the ink vibrates, the charge 13 moves to the tip of the ink surface wave closest to the platen 10 due to Coulomb force, so the charge at the tip of the surface wave increases, and this portion receives a force greater than the Coulomb force, causing the platen 10 to move. The ink particles 14 fly out in the direction and adhere to the recording paper 15, so that a record can be obtained. Therefore, by inputting a drive signal to any drive electrode, ink particles 14 can be ejected from that location and recorded at any location on the recording paper.

Another embodiment of the present invention involves varying the voltage applied to conductive layer 9 (or platen 10).

By varying the voltage applied to the conductive layer 9, the electric field between the conductive layer 9 and the platen 10 is varied, and the ink particles 14 are more likely to be ejected at the moment when the electric field is high. It is possible to further lower the drive voltage input to the This effect can be obtained even if the fluctuation is not periodic, but if the frequency of the fluctuation is close to the frequency of the signal input to the drive electrode 2, the surface wave due to the electric field fluctuation and the resonant member 2
Surface waves due to zero vibrations are synthesized and the peak value of the surface waves tends to increase, and the above-mentioned effects also overlap, making it possible to eject ink particles with lower energy.

However, if the period of voltage fluctuation is not sufficiently fast compared to the time to record one dot, it will cause a decrease in the reproducibility of recorded dots.

In the case of the head of the present invention, ink particles can be generated by both the acoustic energy of the resonant member 20 and the Coulomb force due to electric charge, so the acoustic energy of the resonant member is at a lower level than in conventional inkjet heads. Even when the density of the drive electrodes 2 is increased, the amplitude of the voltage of the signal input to the drive electrodes 2 can be reduced. Therefore, the drive circuit can be manufactured at low cost, and a high-density inkjet head can be manufactured at low cost.

[0022]

[Effects of the Invention] According to the present invention, an ink discharge port is formed between the piezoelectric substrate and the slit member, and a voltage is applied between the platen and the conductive layer that is in contact with the ink within the ink discharge port. As a result, the ink is charged and receives a force toward the platen due to Coulomb force. By causing the piezoelectric substrate to vibrate resonantly in the thickness edge mode in this state, ink can be ejected in the form of a mist with a voltage with a lower amplitude than that of conventional inkjet heads, making it possible to manufacture high-density heads at low cost. .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an entire inkjet head according to an embodiment of the present invention.

FIG. 2 is a perspective view of a resonant member of an inkjet head according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a resonant member of an inkjet head according to an embodiment of the present invention.

FIG. 4 is a perspective view of an ink supply member of an inkjet head according to an embodiment of the present invention.

FIG. 5 is an assembly diagram of a resonance member and an ink supply member of an inkjet head according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating the operation of the inkjet head according to the embodiment of the present invention.

FIG. 7 is a diagram showing a vibration form of a piezoelectric substrate of an inkjet head according to an embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a conventional inkjet head.

[Explanation of symbols]

1...piezoelectric substrate 2... Drive electrode 3...Common electrode 4...Slit member 5... Gap member 6... Ink chamber 7...Ink discharge port 8...Ink supply port 9... Conductive layer 10...Platen 11...Insulating layer 12...Ink 14... Ink particles 15...recording paper 20... Resonant member 30... Ink supply member

Claims (1)

[Claims] 1. A piezoelectric substrate having a rectangular drive electrode formed on one surface and a common electrode formed at the end of the other surface, a piezoelectric substrate parallel to the piezoelectric substrate; a slit member positioned so as to form an ink ejection port therebetween;
The piezoelectric substrate includes an ink supply means for supplying ink to the ink ejection port, and a drive circuit that periodically varies an electric field between the drive electrode and the common electrode to generate a signal that vibrates the piezoelectric substrate. In an inkjet head configured such that the vibration is in a vibration mode (thickness edge mode) in which the amplitude is maximum at the end where the common electrode is formed, the conductive head is in contact with the ink and can generate an electric field between it and the platen. An inkjet head characterized by having layers.