JPS6052353A - Inkjet recording method and its apparatus - Google Patents

Abstract

PURPOSE:To enable the jetting of fine ink drips by forming an air current toward a recording paper in the perimeter of a nozzle orifice with a thin wall so that the viscosity resistance due to the air current works on an ink extruded from the nozzle orifice under a pressure along the direction of the air current. CONSTITUTION:An orifice 110 of a nozzle 102 is formed extremely thin so as not to exceed 1.5 in the ratio of the outer diameter to the inner diameter of an orifice section and air current flows evenly without generating a large turbulence in the perimeter of the orifice 110 and an ink meniscus 113. As a result, the extrusion of the ink meniscus 113 can be always done stably by a pulse pressure to form a stable ink drip. Since the ink meniscus 113 being extruded receives a force in the direction of being torn from the orifice 110 by a viscosity resistance due to the ambient air current, it flies in ink drips on the air current even when it has not a kinetic energy enough to separate from the orifice 110.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called on-demand type inkjet recording method and apparatus, and more particularly to an inkjet recording method and apparatus using an air stream as an auxiliary means for ink jetting.

Conventionally, in order to obtain a clear image during inkjet recording, an inkjet recording device has been disclosed in Japanese Patent Laid-Open No. 109738/1983, which uses an air flow as an auxiliary means to increase the flying speed of ink droplets immediately after the ink droplets are ejected. It was returned. That is, as shown in FIG. 1, a second nozzle 12 having an opening is provided opposite to the first nozzle 11 for ejecting ink, so that an air flow 13 flows out from the second nozzle. The ejected ink droplets ride on this air flow and are greatly increased in speed. However, in this conventional technology,
It was necessary that the ink droplets first be driven into the interior 14 of the second nozzle where an air stream was formed. In order to shoot ink droplets, a pulsed pressure is applied to the ink using an electromechanical transducer such as a piezoelectric element, but this pulsed pressure is small and the ink pushed out from the first nozzle 11 is If the ink droplet did not reach the interior 14 of the second nozzle, stable ink droplets could not be formed due to the influence of the complicated movement of the air flow between the two nozzles. Therefore, there is a limit to the ability to create small volume ink droplets by reducing the pulse pressure. Further, in the conventional example described above, the air flowing through the passage 15 between the two nozzles is rapidly accelerated inside the second nozzle 12, so that the fourth The ink meniscus 16 in the nozzle was subjected to a force that pushed it back into the nozzle as indicated by an arrow 17. As a result, air entered the ink, making it impossible to eject the ink even if pulse pressure was applied.

In order to prevent such a situation, when using an air flow, it is necessary to apply a certain pressure to the ink so that the ink meniscus 16 is stably located inside the first nozzle 11.

Another conventional example of using airflow during ink jetting is a method published in Japanese Patent Laid-Open No. 57-182448, which aims to prevent dust from recording paper from adhering to the nozzle orifice of an inkjet head. It is shown. That is, as shown in FIG. 2, an air supply pipe 19 is attached to the outside of the piezoelectric element 18 constituting the inkjet head, and air is blown from the tip of the head toward the recording paper.

In this prior art, as in the previous conventional example, it is possible to increase the flying speed of the ink droplets by using airflow as an auxiliary means after the ink droplets are ejected. However, in this prior art example, the opening of the pipe 19 is larger than in the prior art example shown in FIG. 1, and therefore a large amount of air needs to be replenished in order to form a sufficiently high-speed air flow. As a result, a large pump was required, resulting in problems such as increased equipment cost and increased noise. Furthermore, as shown in Figure 2, when a high-speed airflow flows through the head tip, the nozzle orifice 2
An airflow vortex 21 is generated in front of the airflow, creating turbulent flow.

This turbulence caused the flight direction and speed of the ink droplets to become unstable, and when the volume of the ink droplets was reduced, problems with bales that made it difficult to eject the ink droplets frequently occurred. Therefore, in order to achieve stable ink droplet splashing, it was necessary to increase the ejection energy and eject the ejected droplets to a portion 22 away from the nozzle where turbulence does not occur, but this reduces the ink volume. It was difficult if I tried to do so.

An object of the present invention is to provide a new inkjet recording method and apparatus that improves the drawbacks of the prior art described above.

According to this invention, in an inkjet recording method in which recording is performed by applying pulse pressure to ink using an electromechanical conversion means and ejecting ink droplets from a nozzle orifice toward recording paper, the ratio of the outer diameter to the inner diameter is 1. An air flow in the direction toward the recording paper is formed around a nozzle orifice with a thin wall thickness not exceeding .5, and the ink pushed out from the nozzle orifice by the pulse pressure is directed in the direction of the air flow. There is obtained an inkjet recording method characterized in that the extruded ink is torn off through the nozzle orifice to form ink droplets by applying viscous resistance due to the air flow along the nozzle orifice.

Further, according to the present invention, there is provided a nozzle in which the wall thickness of the orifice portion is formed to be thin so that the ratio of the outer diameter to the inner diameter of the orifice portion does not exceed 1.5, and pressurized anaerobic gas introduced into the vicinity of the nozzle is recorded. An inkjet recording apparatus characterized in that the inkjet recording apparatus has a guide passage for causing the pressurized air to flow out toward the paper, and the orifice part is disposed within the guide passage so that the pressurized air flows out from around the orifice part. can get.

The present invention will be described in detail below with reference to the drawings.

Referring to FIG. 3, one embodiment of the inkjet recording apparatus according to the present invention includes a cylindrical piezoelectric element 101, a nozzle 102 fixed to one end of the piezoelectric element, and 1. It has an ink jet radiator 104 fixed to the other end of the piezoelectric element and composed of a supply passage 103 that introduces ink from an external tank, and further directs pressurized air guided near the nozzle 102 toward the recording paper. Guide passage 105 for draining water
It has an air flow forming means 106 having a. The air flow forming means 106 includes plate members 107a, 107b, and 107.
Air pressurized by an external pump is guided to the vicinity of the nozzle 102 through the introduction passage 108.

An enlarged view of the vicinity of the nozzle 109 is shown in FIG. That is, the orifice IIO of the nozzle 102 is formed to have an extremely thin wall thickness, and the air flow guide passage 10
It is arranged so that it is located inside 5. The pressurized air guided near the nozzle is rapidly accelerated at the entrance 111 of the guide passage 105, and then becomes a uniform air flow toward the recording paper in the guide passage 105. Due to the rapid acceleration of the air in the passageway 111, a large pressure difference occurs in the passageway 111 due to the inertial effect, and most of the pressure of the pressurized air guided near the nozzle is caused by the pressure difference in the passageway 111. is formed. Around the orifice 110 inside the guide passage 105, the velocity of the air flow is #1 uniform, so the generation of pressure due to the inertial effect can be almost ignored, but the generation of pressure due to the viscous effect of the air is observed. However, this pressure due to the viscous effect is negligibly small compared to the pressure due to the inertial effect at the passage entrance 111. Furthermore, the vicinity 112 of the exit of the guide passage 105
In this case, the cross section of the passage is widened due to the absence of the nozzle orifice 110, and the high-speed air flow flowing around the orifice 110 is slightly decelerated near the outlet 112. For this reason, pressure is generated near the outlet 112 due to the inertial effect, but it is in the opposite direction to the pressure due to the viscous effect around the orifice 110 described above, and by canceling both of them, the air pressure around the orifice is reduced to #1y atmospheric pressure. It was experimentally confirmed that it can be equivalent to . It goes without saying that this offset effect changes depending on the position of the orifice 110 in the guide passage 105, but by arranging the orifice 110 at a position of 14 to V4 of the length of the guide passage 105, the above-mentioned offset effect can be sufficiently achieved. It turns out that it can be obtained. As a result, the ink meniscus inside the orifice is not pushed inward or pulled out to the outside, and the ink meniscus inside the orifice stays inside the orifice. It becomes possible to be positioned stably.

Therefore, unlike the prior art disclosed in JP-A-51-109733, a device mechanism for pressurizing ink through an ink tank is not required, making it possible to realize a simple and low-cost device.

Further, as shown in FIG. 4, the nozzle orifice 11
Since the wall thickness of 0 is extremely thin, even when pulse pressure acts on the ink and the ink meniscus 113 is pushed out of the orifice as shown in the same figure, the area around the air flow orifice and around the ink meniscus 1 It becomes possible for the water to flow uniformly without causing any major turbulence. As a result, the extrusion of the inktans 113 can be carried out stably at all times, and as mentioned above in JP-A-57-1
Formation of ink droplets is much more stable than in the conventional example of 82448. In addition, the extruded ink meniscus receives a force in the direction of tearing it off from the orifice due to the viscous resistance of the surrounding air flow, so if the extruded ink meniscus itself does not have enough kinetic energy to separate from the orifice. However, it becomes possible for the ink to turn into ink droplets and fly on the air current. It is preferred that the wall thickness of the orifice be as thin as possible, whereas from a production technology standpoint it is preferred that the wall thickness of the orifice be thick.

As a result of measuring the ink jetting characteristics by varying the wall thickness of the orifice, it was experimentally confirmed that, for example, for a nozzle orifice with an inner diameter of 50 μφ, stable ink jetting is possible up to an outer diameter of approximately 75 μφ. .

It was also found that the allowable range of the outer diameter when changing the inner diameter changes in proportion to the inner diameter, and good ink jetting is possible as long as the ratio of the outer diameter to the inner diameter does not exceed 1.5. This was confirmed. As a result, due to the viscous resistance effect of the extruded ink meniscus, it is possible to eject extremely small ink droplets that are impossible to eject using conventional techniques. It is now possible to record halftones.

[Brief explanation of drawings]

1 and 2 are schematic sectional views for explaining an inkjet recording apparatus according to the prior art, and FIGS. 3 and 4 are schematic sectional views for explaining an inkjet recording apparatus and method according to the present invention. Schematic cross-sectional view of the configuration, 11...first nozzle, 12, respectively.
...Second nozzle. 13... Air flow, 14... Inside the second nozzle. 15... Passage between the first and second nozzles. 16... Ink meniscus, 17...
arrow. 18...Piezoelectric element, 19...Air supply pipe. 20... Nozzle orifice, 21...
Vortex of airflow, 22...A part of the airflow away from the nozzle where there is no turbulence. 101... Cylindrical piezoelectric element, 102...
nozzle. 103... Ink supply passage, 104...
・=Inkjet bed, 105...Guidance passage. 106...Air flow forming means tio'ya,
107b, and 107C... plate-shaped portion *4',
108...Air introduction passage. 109...Near the nozzle, 110...
Orifice. 111...Near the entrance of the guide passage. 112...Near the exit of the guide passage. 113... Indicates an extruded ink meniscus. Figure 1 Figure 2 Figure 3 Figure 04 @Figure 4

Claims (1)

[Claims] 1. In an inkjet recording method in which recording is performed by applying pulse pressure to ink using an electromechanical transducer and injecting ink droplets from a nozzle orifice toward recording paper, the ratio of the outer diameter to the inner diameter An air flow in the direction toward the recording paper is formed around a nozzle orifice with a thin wall thickness such that the wall thickness does not exceed 1.5, and the air flow is directed toward the recording paper by the pulse pressure. An ink jet recording method characterized in that the extruded ink is torn off through the nozzle orifice by applying viscous resistance due to the air flow along the direction to form ink droplets. 2. In an inkjet recording apparatus that performs recording by applying pulse pressure to ink using electromechanical conversion means and ejecting ink droplets from a nozzle orifice toward recording paper, the ratio of the outer diameter to the inner diameter of the orifice portion is 1. a nozzle in which the wall thickness of the orifice portion is formed to be thin so as not to exceed 5, and a guide passage through which the pressurized air guided near the nozzle flows out toward the recording paper, and An inkjet recording apparatus characterized in that the orifice portion is disposed in the guide passage (C) so that air flows out from around the orifice portion.