JPH0319068B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an ink drop ejecting device that is incorporated into an inkjet printer or the like and ejects minute ink droplets on demand.

(b) Prior art The inventors of the present invention have
We proposed a new device different from the well-known on-demand ink droplet ejecting device disclosed in No. 53-45698, and filed Japanese Patent Application No. 55-84264 (Japanese Unexamined Patent Publication No. 57-1989) on June 20th.
A patent application has been filed as (No. 8163). The present invention relates to the specific structure of such a new on-demand type ink droplet ejecting device, and first, the ink droplet ejecting device which is the basis of the present invention described in the above patent application specification will be explained.

FIG. 1 is a sectional view showing an ink droplet ejecting device that is the basis of the present invention, in which 1 represents piezoelectric vibration as a pressure changing means that vibrates in response to electrical signals such as sinusoidal, rectangular, and sawtooth waves. 2 is a horn-shaped pressure chamber in which the piezoelectric vibrator 1 forms one side wall of the long diameter end and has a small-diameter opening 3 at an opposing location; 4 closes the opening 3 of the horn-shaped pressure chamber 2; A thin plate 5 such as a resin plate, a metal plate, a rubber sheet, or a film is a propagation medium that fills the pressure chamber 2 closed by the thin plate 4 and propagates the vibration of the piezoelectric vibrator 1 to the thin plate 4. 5 is a colloid of powder in liquids such as water, ink, silicone oil, mercury, viscoelastic substances such as silicone grease, and magnetic fluids that have a high vibration propagation rate and have a damping effect against residual vibrations. Mixed substances can be used as appropriate. Therefore, the thin plate 4 operates as a vibrating section. Reference numeral 6 denotes a front plate which is placed in front of the thin plate 4 with a small gap therebetween and holds an ink layer 7 of a constant thickness in the gap; 8 is a small hole bored in the center of the front plate 6 at a location opposite to the thin plate 4; A small diameter orifice 9 is a capillary tube that supplies ink to the ink layer 7 from the outside.

Next, a specific example of the above-mentioned Japanese Patent Application No. 55-84264 will be described in detail.

A so-called unimorph type piezoelectric element 1 having a diameter D10 mmφ formed by pasting a metal plate to a piezoelectric ceramic plate based on lead zirconate titanate is attached to the long diameter end of a horn-shaped pressure chamber 2, and a propagation medium is placed in the pressure chamber 2. After water was injected in step 5, the opening 3 with a diameter of d2 mmφ was closed with a thin plate 4 made of stainless steel with a thickness of t10 μm. Then, a front plate 6 with an orifice 8 of 50 μm diameter bored in the center is attached with a small gap of 300 μm apart to form an ink layer 7 with a thickness T of 300 μm, and the ink layer 7 is filled with ink as shown in FIG. An ink droplet ejecting device having a shape similar to the above is obtained.

When a sinusoidal electrical signal with a frequency of 20 KHz and an amplitude of 90 V is applied to cause ink droplets to be ejected from this ink droplet ejecting device, ink droplets 20 are ejected from the orifice 8 on demand.

(c) Problems to be Solved by the Invention The present invention provides an ink droplet ejecting device having such a structure in which ink droplets are ejected faithfully to the drive signal.

(d) Means for Solving the Problems The present invention relates a pressure change means to a pressure chamber filled with a propagation medium, and applies pressure changes by the pressure change means to a side wall of the pressure chamber via the propagation medium. In an ink droplet ejecting device, an ink droplet is applied intensively to a small-area vibrating part formed in the vibrating part, and the ink in the ink layer held on the front side of the vibrating part is ejected as ink droplets from an orifice provided at an opposing location. , the vibration diameter and thickness of the vibrating part are 1 to 3, respectively.
mm and 30 to 80 μm.

(e) Effects According to the present invention, ink droplets are ejected only by the vibration of the thin plate that contributes to the ejection of ink droplets, and unnecessary ejection of ink droplets due to residual vibration of the thin plate can be suppressed.

(F) Example First, the inventors of the present invention considered the opening diameter d of the orifice 8 in order to control the diameter of the ink droplet ejected from the orifice 8.

Currently, inkjet printers incorporating various ink droplet ejecting devices are in practical use, and the minimum resolution of characters and figures recorded by such inkjet printers is 6 lines/mm, that is, 6 lines per mm in a 1mm gap.
ink droplets.

On the other hand, since the ink used is water-based due to its viscosity, a material with good water absorption is used as the recording medium, and the diameter of the ink droplet adhering to the recording medium is approximately the diameter of the aperture d of the orifice 8. Enlarge 2-3 times. Therefore, considering that the minimum resolution is 6 lines/mm, the opening d of the orifice 8 is set to 40 to 60 μm.
And so.

Next, in order to eject ink droplets from the orifice 8 with an opening diameter D of 40 to 60 μm, one cycle of a sinusoidal electric signal as shown in FIG. The liquid filled in the pressure chamber 2 is used as a medium to propagate, and the piezoelectric vibrator 1
Vibrations are generated in the thin plate 4 of small diameter, which is placed in a position facing the . Then, the amplitude of about 0.1 μm is amplified to several μm, and piston-like vibration with a high frequency of several +KHz is concentratedly applied to the thin plate 4. in this way,
Since the thin plate 4 intensively receives the pressure increase caused by the piezoelectric vibrator 1, it generates a main vibration 10 contributing to on-demand ejection of ink droplets and a residual vibration 11 as shown in FIG. 2B.

By the way, as mentioned above, the ink droplet ejecting device shown in FIG. 1 supplies power to the piezoelectric vibrator 1 with a sinusoidal electric signal of 20KHz amplitude of 90V to eject ink droplets, but the ink droplets are not ejected. the lowest amplitude value,
In other words, the threshold value is when the ink viscosity is 8 to 12 CPS
It is 80V/20KHz.

Therefore, when the amplitude of this residual vibration 11 exceeds the threshold value (80V), unnecessary ink droplets are ejected.
This will lead to a decline in the quality of recorded images.

Therefore, when the vibration diameter D of the thin metal plate 4 was set to 2 mm, the vibration state was investigated by varying the thickness t of the thin plate 4, and the characteristic results shown in FIG. 3 were obtained. In the figure, the horizontal axis is the thickness t of the thin plate 4, and the vertical axis is the amplitude, where curve A is the main vibration 10 and curve B is the main vibration 10.
represent residual vibrations 11, respectively. That is, the main vibration 10 and the residual vibration 11 are caused by the thickness t of the thin plate 4.
The thinner it is, the more it vibrates due to the pressure amplification effect of the pressure chamber 2, and the more it becomes thicker, the smaller the amplitude is attenuated.

Now, if the minimum amplitude value at which an ink droplet is ejected, ie, the threshold value (80V/20KHz), is set as shown in FIG. 3, when the thickness t becomes 80 μm or more, an ink droplet will not be ejected from the orifice. On the other hand, residual vibration 1
Ink droplet ejection according to No. 1 is no longer performed when the thickness t becomes 30 μm or more. That is, the thickness of the thin plate 4 is
When the vibration is in the range of 30 to 80 μm, ink droplets are ejected from the orifice 8 only by the main vibration 10, and unnecessary ejection of ink droplets caused by the residual vibration 11 can be suppressed.

In addition, the vibration diameter D of the thin plate 4 is ±1 mm from the above 2 mm.
When it was varied within the range of , results were obtained that showed a tendency almost similar to the characteristics shown in FIG.

(G) Effects of the Invention As is clear from the above description, the ink droplet ejecting device of the present invention has an orifice with an opening diameter of 40 to 60 μm, a vibrating section made of a thin metal plate with a thickness of 30 to 80 μm, and a vibration diameter of 1 to 3 mm. Therefore, ink droplets can be faithfully ejected from the orifice in response to the main vibration, and the quality of recorded images can be improved.

[Brief explanation of drawings]

Figure 1 is a sectional view showing the basic structure of the ink droplet ejecting device of the present invention, Figures 2a and b are waveform diagrams showing the relationship between the drive signal and the vibration state, and Figure 3 is the relationship between the thickness of the vibrating part and the amplitude. In the characteristic diagram showing the relationship, 1 is a piezoelectric vibrator;
2 is a pressure chamber, 4 is a thin plate, and 8 is an orifice.

Claims (1)

[Claims] 1. A pressure change means is associated with the long diameter end of a horn-shaped pressure chamber filled with a propagation medium, and the pressure change caused by this pressure change means is applied to a small area formed at the small diameter end of the pressure chamber via the propagation medium. The ink is applied intensively to a vibrating section made of a thin metal plate, and the ink in the ink layer held on the front surface of the vibrating section is ejected as ink droplets from the orifice without the vibrating section coming into contact with an orifice provided at an opposing location. An ink droplet ejecting device characterized in that the opening diameter of the orifice is 40 to 60 μm, and the vibration diameter and thickness of the vibrating portion are 1 to 3 mm and 30 to 80 μm, respectively.