JPH0211429B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink droplet ejecting device that ejects minute ink droplets.

Among ink droplet ejecting devices that eject ink droplets, the on-demand type, which ejects ink droplets when needed, has the following advantages: (1) No unnecessary ink processing, (2) Extremely easy colorization, and (3) Ink droplet ejection. It has the excellent features of variable droplet diameter and the ability to express light and shade, and has been put into practical use in a variety of ways.

Figures 1 and 2 show the well-known ink droplet ejecting device that has been put into practical use. Figure 1 shows a so-called single-cavity type ink droplet ejecting device that has one ink chamber 1 filled with ink. A detailed explanation is given in Special Publication No. 53-12138. FIG. 2 shows a double cavity type ink drop ejecting device in which the ink chamber 1 is divided into an inner chamber 1a and an outer chamber 1b, which is disclosed in Japanese Patent Publication No. 53-45698. What these both have in common is that the piezoelectric vibrator 2 responds to an electrical signal.
vibrates in a curved manner, and the pressure inside the ink chamber 1 rises due to the vibration, causing the ink column 4 to protrude from the orifice 3, and the ink column 4 becomes an ink droplet 5 due to its own kinetic energy and surface tension. The present invention is based on an on-demand ejection mechanism of ink droplets 5 that fly toward a recording medium (not shown) disposed opposite to each other.

The present invention is a new jetting device belonging to such on-demand type ink droplet jetting devices.
Patent Application No. 1984-84264 filed on the 20th (Japanese Unexamined Patent Publication No. 57
8163), first, the ink droplet ejecting device which is the basis of the present invention described in the above patent specification will be explained.

FIG. 3 is a sectional view showing the ink droplet ejecting device which is the basis of the present invention, and 10 is a piezoelectric vibrator as a pressure changing means that vibrates in response to an electric signal such as a sine wave, a rectangular wave, or a sawtooth wave; 11 is a horn-shaped pressure chamber in which the piezoelectric vibrator 10 forms one side wall of the long diameter end and has a small-diameter opening 12 at an opposing location; 13 is a resin plate that closes the opening 12 of the horn-shaped pressure chamber 11; , metal plates, rubber sheets, thin plates such as films,
14 is a pressure chamber 11 closed by the thin plate 13;
A propagation medium that satisfies the above conditions and propagates the vibrations of the piezoelectric vibrator 10 to the thin plate 13, and the propagation medium 14 is a liquid such as water, ink, silicone oil, or mercury that has a high vibration propagation rate and has a damping effect on residual vibrations. , viscoelastic substances such as silicone grease, and liquids such as magnetic fluids mixed with powder in colloidal form are used as appropriate. Therefore, the thin plate 13 operates as a vibrating section. Reference numeral 15 denotes a front plate which is placed in front of the thin plate 13 with a small gap therebetween and holds an ink layer 16 of a constant thickness in the gap; 17 is a front plate 16;
A small-diameter orifice 18 is bored at a location facing the thin plate 13 in the approximate center thereof, and is a capillary tube for supplying ink to the ink layer 16 from the outside.

Piezoelectric vibrator 10 of an ink droplet ejecting device having such a structure
When an electric signal is supplied to the piezoelectric vibrator 10 , the piezoelectric vibrator 10 vibrates in a curved manner and bends toward the pressure chamber 11 .
Increase the pressure inside 1. This pressure increase reaches the small-area thin plate 13 through the propagation medium 14 while being amplified due to the horn-like shape, causing the thin plate 13 to be rapidly displaced toward the ink layer 16 side.
Therefore, due to this sudden displacement of the thin plate 13, the ink in the ink layer 16 protrudes from the orifice 17 bored at the opposing location and is ejected as ink droplets. Next, when the piezoelectric vibrator 10 curves in the opposite direction, the pressure chamber 11
The pressure inside decreases, the thin plate 13 returns to its flat state, and ink is replenished from the capillary tube 18 to the ink layer 16.

In this way, ink droplets are ejected and ink is replenished by the vibration of the thin plate 13, and it is very important to vibrate the thin plate 13 faithfully in response to electrical signals.

On the other hand, the filling of the propagation medium 14 into the pressure chamber 11 is carried out through the pores communicating with the pressure chamber 11, as shown in FIG.
The pressure chamber 11 is filled with the propagation medium 14 while the air inside the pressure chamber 11 is evacuated through the pore 19, and then the pressure chamber 11 is closed with a screw-type sealing stopper 20. According to this method, the sealing stopper 20
An elastic packing 21 such as an O-ring is inserted between the seat and the pore 19 to close the pore 19 watertightly.

However, if the screwing amount of the sealing stopper 20 is increased in order to improve the sealing degree of the sealing stopper 20, the pressure of the propagation medium 14 in the pore 19 will increase, pressurizing the propagation medium 14 in the pressure chamber 11, and the As shown in Figure 4, the thin plate 13
There is a risk that it may bend. There is a risk that the thin plate 13 may be bent due to the propagation medium 14 inside the sealed pressure chamber 11.
It also occurs during thermal expansion and contraction. When the thin plate 13 is bent in this manner, the thin plate 13 cannot vibrate faithfully even when subjected to pressure changes caused by the piezoelectric vibrator 11, and cannot eject ink droplets on demand.

Furthermore, if the pressure chamber 11 is sealed, the propagation medium 14 filled inside may deteriorate over time, and there is a possibility that desired ink droplets may not be ejected.

The ink droplet ejecting device of the present invention has been developed in view of this point, and will be described in detail below with reference to FIG. 5 and subsequent figures.

FIG. 5 is a cross-sectional view showing the device of the present invention, with 1
0 to 21 are piezoelectric vibrators or elastic packings as in FIGS. 3 and 4, but the difference is that the thin plate 13 that controls the vibrating part has an opening area that is large enough not to affect the vibration of the thin plate 13. A communication passage 2 having
It is located where 2 was formed. That is, the pressure chamber 11 is constantly in communication with the ink layer 16 via the communication passage 22. Furthermore, since the pressure chamber 11 and the ink layer 16 are in communication, ink is used as the propagation medium 14' filled in the pressure chamber 11.

In this way, the pressure chamber 11 of the ink droplet ejecting device having the communication passage 22 in the thin plate 13 is filled with the propagation medium 14' made of ink by immersing it in the ink with the pressure chamber 11 open as in the conventional method. The air in the pressure chamber 11 is replaced with the propagation medium 14 through the pores 19. At this time, although not shown, the ink layer 16 is also filled with ink of the same quality as the propagation medium 14' through the pores. Then, a sealing plug 20 with an elastic packing 21 inserted therein is screwed into the pore 19 communicating with the pressure chamber 11. Furthermore, a sealing plug 2 is provided to close this pore 19 watertightly.
When the screwing amount of 0 is increased, the pressure of the propagation medium 14' in the pore 19 increases and pressurizes the propagation medium 14' in the pressure chamber 11. This pressure is applied to the thin plate 1 of the vibrating part.
3 and temporarily bends the thin plate 13. However, the pressure increase in the propagation medium 14 that is bending the thin plate 13 causes the ink layer 1 to move from the communication passage 22 to the ink layer 16 side.
Leakage occurs until the ink pressure in the ink inside the thin plate 6 and the ink pressure in the propagation medium 14' become the same, and the thin plate 13 gradually becomes flat. In other words, the pressure increase generated by watertightly closing the pores 19 pressurizes the propagation medium 14 in the pressure chamber 11, and although the thin plate 13 is once bent, the communication passage formed in the thin plate 13 22 leaks from the thin plate 13 when ink droplets are not ejected.
is held in a flat state. Therefore, the thin plate 13, which assumes a flat plate state during non-injection, faithfully responds to the vibrations of the piezoelectric vibrator 10.

Incidentally, the shape of the communication passage 22 may be a single communication hole as shown in FIGS. The pressure change in the propagation medium 14'
Any shape may be used as long as the thin plate 13 vibrates when applied to the thin plate 14 via the ink droplet and the ink droplet is ejected. According to experiments conducted by the present inventors, a single passage 22 in the shape of a single continuous hole with an opening diameter of 30 μm as shown in FIG. An ink layer 16 with a thickness of 200 μm is held, and an orifice 17 with an opening diameter of 50 μm is placed in front of the ink layer 16, and a piezoelectric vibrator 10 with a diameter of 10 mm is placed at 20K.
When vibrated at about Hz, the above orifice 1
On-demand ink drop ejection with a resolution of 7 to 6 drops/mm is obtained. Also, only the communication passage 22
It has been confirmed that ink droplets can be ejected on demand even when conducting experiments with the diameter of 70 μm and other conditions being the same.

As is clear from the above description, the present invention is directed to filling a pressure chamber with ink, using the ink as a propagation medium, and applying the pressure change of the pressure change means intensively to a small-area vibrating part to maintain an ink layer on the front surface. In an ink droplet ejecting device that ejects ink droplets from a pressure chamber, a communication passage having an opening area that does not affect the vibration of the vibrating portion is formed in the vibrating portion to communicate the pressure chamber and the ink layer. Therefore, the abnormal pressure increase that occurs when filling the pressure chamber with ink can be leaked to the ink layer side through the communication passage,
During non-ejection, the ink pressures in the pressure chamber and the ink layer are the same, making it possible to avoid bending and deformation of the vibrating portion due to the pressure increase. Therefore, the vibrating section can constantly and faithfully respond to pressure changes of the pressure changing means and eject ink droplets on demand over time.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing a conventional on-demand ink droplet ejecting device, and FIGS.
5 is a sectional view showing the basic structure of the inventive device, FIG. 5 is a sectional view showing the ink droplet ejecting device of the invention, and FIGS. 6a and 6b are enlarged front views showing essential parts of the invention. 10...piezoelectric vibrator, 11...pressure chamber, 13...
... Thin plate, 16 ... Ink layer, 17 ... Orifice, 22 ... Communication passage.

Claims (1)

[Claims] 1 A pressure change means is associated with a pressure chamber filled with ink, and the pressure change caused by the pressure change means is concentrated through the ink to a small-area vibrating part formed on a part of the side wall of the pressure chamber. In an ink droplet ejecting device that applies a voltage to the ink layer held on the front surface of the vibrating section and ejects the ink as ink droplets, the vibrating section has an aperture area that does not affect the vibration of the vibrating section. An ink droplet ejecting device characterized in that a communication passage is formed to communicate a pressure chamber and an ink layer, and the ink pressure in the pressure chamber and the ink layer is the same when not ejecting.