JPH0538809A - Ink jet head - Google Patents

Abstract

PURPOSE:To carry out the driving by a low voltage for an ink jet head for which an ink mist stream is utilized. CONSTITUTION:The subject ink jet head is equipped with a piezoelectric substrate 1, a pair of electrodes 2 which are arranged on the front and rear surfaces of the piezoelectric substrate 1, a nozzle plate which is arranged in parallel with the piezoelectric substrate 1, and an ink which is held in a gap between the piezoelectric substrate 1 and the nozzle plate 4; and an acoustic lens 6 is provided between the piezoelectric substrate 1 and the nozzle plate 4 in order to discharge the ink 7 as an ink mist 8 from a nozzle 5 of the nozzle plate 4.

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 non-impact recording apparatus, and more particularly to an ink jet head for selectively ejecting liquid ink to record on a recording medium.

[0002]

2. Description of the Related Art A recording device using an ink jet head, particularly a recording device using an on-demand type ink jet head, is a promising recording device because of its features such as high-speed printing, low noise, low running cost and high printing quality. Has been attracting attention in recent years.

At present, as an on-demand type ink jet head, a piezoelectric body is used to deform an ink cavity and ink is ejected from a nozzle provided in each ink cavity, or a nozzle and a piezoelectric substrate are used. There is a method in which the ink is filled in the space and the ink is ejected from the nozzle by the deformation of the piezoelectric body, or a method in which the ink in the ink cavity is vaporized by the heating element and the pressure causes the ink to be ejected from the nozzle.

[0004]

In the ink jet head of the printing apparatus as described above, the size of the ink particles to be ejected is constant, so that data including density information such as image information such as photographs and pictures is used. In order to express it on the recording medium, it is necessary to express it by an area gradation method such as a dither method.
Therefore, one data must be expressed by a plurality of ink particles, which causes a problem that the printing speed becomes slow and the resolution decreases when the gradation is improved.

In order to solve the drawbacks of the conventional ink jet head, we have developed a new ink jet head utilizing an ink mist flow as shown in FIG. Since this new ink jet head ejects the ink in the form of mist, gradation can be expressed by controlling the amount of mist, so that the above-mentioned problem can be almost solved. However, in this method, since the drive voltage for ejecting mist is relatively high, the cost of the drive element is inevitably increased. Therefore, the inkjet head of the present invention solves such a problem, and the purpose thereof is to reduce the driving voltage of the inkjet head using the ink mist flow.

[0006]

An ink jet head of the present invention comprises a piezoelectric substrate, at least one pair of electrodes arranged on the front and back surfaces of the piezoelectric substrate, and the resonance of the piezoelectric substrate between the electrodes. A driving unit that selectively applies a voltage that changes in a cycle equal to the frequency; a nozzle plate arranged in parallel with the piezoelectric substrate; and ink held in a gap between the piezoelectric substrate and the nozzle plate, In an inkjet head that ejects the ink as ink mist from nozzles of a nozzle plate, an acoustic lens is provided between the piezoelectric substrate and the ink.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an ink jet head according to an embodiment of the present invention. Reference numeral 1 is a piezoelectric substrate, and 23 is an electrode for driving the piezoelectric substrate 1. As the piezoelectric substrate, a material having a piezoelectric effect, PZT, PVDF, quartz,
Lithium niobate or the like can be used. In this embodiment, PZT ceramics (Nepec N21 manufactured by Tokin Co., Ltd.) having a thickness of 1 mm is used as the piezoelectric substrate 1. Then, two metal layers of nichrome (NiCr) -gold (Au) were formed on both surfaces of the PZT ceramics by sputtering, and then the drive electrode 2 and the common electrode 3 were patterned by a photolithography process. Each electrode is connected to a driving circuit (not shown), and a voltage amplitude having a frequency equal to the resonance frequency determined by the thickness d of the piezoelectric substrate 1 is applied between the electrodes to resonate the piezoelectric substrate. , Ultrasonic waves 9 are generated in the ink 7. 4 is a nozzle plate, which is a nozzle 5 for ejecting the ink mist 8.
Are formed.

The ultrasonic waves in the ink 7 propagate in the ink and generate a surface wave on the ink surface in the nozzle 5. When the surface wave becomes larger than a certain amplitude and becomes large, it is ejected from the nozzle 5 as the ink mist 8. The size of the ink mist 8 is related to the frequency of the voltage amplitude applied to the piezoelectric substrate 1, and the higher the frequency, the smaller the size of the ink mist 8. In this embodiment, the frequency is about 2.2 MHz, and the size of the ink mist is 3 μm-
Although it was 10 μm, the size of the ink mist can be changed by changing the frequency according to the purpose.

An acoustic lens 6 has a function of refracting the ultrasonic wave generated from the piezoelectric substrate so that the ultrasonic wave is concentrated near the nozzle 5. Since the acoustic lens has a higher speed of sound in the solid than the speed of sound in the liquid ink, unlike the optical lens, the concave lens as shown in the figure can concentrate the ultrasonic waves. As a result, conventionally, only ultrasonic energy generated by the piezoelectric body having the same area as the nozzle area can be used, but ultrasonic energy generated by the piezoelectric body having a larger area than the nozzle area can be used, and the piezoelectric substrate The drive voltage could be drastically reduced. As the material of the acoustic lens, it is desirable to use a material having a large mechanical quality factor Q in order to reduce the internal loss of ultrasonic waves.

FIG. 2 is a diagram showing a circuit configuration for changing the recording time. 2.2MHz generated by the oscillator
The basic signal of is amplified by the amplifier 60. The drive signal is logically ANDed with the recording data generated by the data generation unit and sequentially stored in the shift register 65 ... Group and the pulse of the write control unit to form the vibrator 62 (piezoelectric substrate 1, drive electrode 2). , The common electrode 3).

FIG. 3 is a diagram showing the results of measuring the relationship between recording time and print density using the ink jet head of this embodiment. The print density changes smoothly as the recording time increases. Through further detailed experiments, it was found that the number of expression gradations that can be practically used is 256 gradations or more. Therefore, by using the ink jet head of the present invention, it is possible to modulate the density of the printed dots in 1-dot units by changing the recording time. Therefore, it is possible to record information including gradation information such as image information without lowering the resolution.

4 and 5 are perspective views showing other examples of the acoustic lens of the ink jet head of the present invention. The shaded portion is the cross-sectional shape.

Unlike the acoustic lens shown in FIG. 1, the one shown in FIG. 4A does not have a curved portion in its cross-sectional shape. With this shape, the area of the focal point of ultrasonic waves is larger than that in FIG. 1, and the effect as an acoustic lens is less than that in FIG. FIG. 4B is a device for bringing the effect of FIG. 4A closer to that of FIG. 1, which is a method well known as a Fresnel lens of an optical lens. The type shown in FIG. 5 is a type that is completely non-curved. These are types in which ultrasonic waves are focused only in one direction, and the efficiency as an acoustic lens is worse than that of the type shown in FIG. 4, but in the case of a line head in which nozzles are formed in line, 1 and 4
It has the advantage of being much easier to form than the type shown in.

FIG. 6 shows an embodiment in which the ink jet head of the present invention is constructed as a line head.

A 1 mm-thick PZT substrate was used as the piezoelectric substrate 1, and the drive electrode 2 and the common electrode 3 were patterned thereon by the photolithography method. A supply port 10 that is a hole or a slit is formed in the center of the piezoelectric substrate to supply ink to the nozzle from the outside. Further, the acoustic lens 6 was adhered onto the piezoelectric substrate, and the nozzle plate 4 was adhered onto the acoustic lens 6, thereby producing a line-shaped inkjet head. As the acoustic lens type, the type shown in FIG. 5A was used. The nozzles are formed on two lines l1 and l2 as shown in the figure, and the pitch d between nozzles on different lines is p = 2 * d with respect to the pitch p between nozzles on each line. The nozzles of the nozzles l1 and l2 are formed so as to have a relationship, and the resolution is twice the nozzle pitch p on the recording paper by adjusting the printing timings of the nozzles of the l1 and l2 so that the recording images are on the same line on the recording paper. Therefore, high resolution recording can be easily achieved.

[0017]

According to the present invention, in the ink jet head for ejecting the ink held in the gap between the piezoelectric substrate and the nozzle plate as the ink mist from the nozzle, the acoustic lens is provided between the piezoelectric substrate and the ink. As a result, it is possible to utilize the vibration of the piezoelectric substrate having a larger area than that of the conventional one, and thus it is possible to reduce the voltage for driving the piezoelectric substrate.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a cross-sectional view of an inkjet head according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a circuit configuration for driving the inkjet head according to the embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the recording time and the print density of the inkjet head of the embodiment of the present invention.

FIG. 4 is a diagram showing a second embodiment of the acoustic lens of the inkjet head according to the embodiment of the present invention.

FIG. 5 is a diagram showing a third example of the acoustic lens of the inkjet head according to the example of the present invention.

FIG. 6 is a diagram showing an inkjet head of another embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a conventional inkjet head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2 ... Drive electrode 3 ... Common electrode 4 ... Nozzle plate 5 ... Nozzle 6 ... Acoustic lens 7 ... Ink 8 ... Ink mist 9 ....・ Ultrasonic 10 ・ ・ ・ Supply port

Claims (1)

[Claims] 1. A piezoelectric substrate, at least one pair of electrodes arranged on the front and back surfaces of the piezoelectric substrate, and a voltage between the electrodes that changes at a period equal to the resonance frequency of the piezoelectric substrate. Drive means for applying to the piezoelectric substrate, a nozzle plate arranged in parallel with the piezoelectric substrate, and ink held in the gap between the piezoelectric substrate and the nozzle plate, the ink as an ink mist from the nozzle of the nozzle plate. An inkjet head for discharging, comprising an acoustic lens provided between the piezoelectric substrate and ink.