JPS6248586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new inkjet recording method that utilizes pressure gradients created by airflow.

FIG. 1 is an example for explaining the principle of a configuration in which a pressure gradient is generated by an air flow. Air discharge ports 1 are perforated in the nozzle plate 2, and a wall 3 is arranged parallel to the nozzle plate 2.
An air flow 5 flows from the periphery in the direction of the air outlet 1 into the air layer 4 formed by the nozzle plate 2 and the wall 3.
In the configuration shown in FIG. 1, the streamlines 5 of the air flow are sharply bent near the air outlet 1, so that the constant pressure lines 6 generated by the air flow 5 are also bent near the air outlet 1, as shown by dotted lines. There is a sudden change.

The configuration as shown in FIG. When the air flow 5 is sent from the surroundings toward the slit 1 as a discharge port, or when the air flow 5 is sent from the top and bottom of the figure in a shape where the nozzle 1 is bored in a tube 6 as shown in FIG. Although not shown in the drawings, if the airflow is sent from three or more directions instead of from two directions as shown in FIG.

Although different from the configuration shown in FIG. 1, even in a configuration in which the air flow 5 is sent from only one direction of the pipe 6 as shown in FIG. 5, a sudden change in the constant pressure line can be caused near the nozzle 1. .

However, when comparing the configurations shown in FIGS. 2 to 5, the configuration shown in FIG. 2 shows a large change in the air flow velocity near the nozzle, and a significant change in the constant pressure line. Therefore, assuming the configuration shown in FIG. 2, FIG. 1 will be explained in more detail.

The pressure on the x-axis in FIG. 1 is illustrated in FIG. 6. That is, the air pressure is highest at point O, gradually decreases as it approaches point B, decreases linearly from a point slightly past point B, and decreases to almost atmospheric pressure at point A.

Figure 7 shows the differentiation of the characteristics in Figure 6, and x
It shows the pressure gradient on the axis, that is, the degree of change in pressure. The pressure gradient is almost close to O at point O, but increases rapidly as it approaches point B,
It becomes constant from a point slightly past the point.

In a fluid space where the pressure is changing, the fluid flows from the area with higher pressure to the area with lower pressure. When another fluid called ink is placed in such a space, an accelerating force acts on the ink as well, causing it to flow from the higher pressure side to the lower pressure side. This acceleration force is dependent on the degree of pressure drop,
That is, it is proportional to the pressure gradient.

Near point O, the pressure gradient is almost O, so there is no pressure change in the x direction, and no acceleration force due to the air flow acts in the x direction. However, as the point B approaches, the air pressure rapidly decreases (the pressure gradient increases) and an accelerating force due to the air flow begins to act in the x direction. Further, after passing point B, the air pressure decreases at a constant rate (the pressure gradient becomes a constant value)
However, since the rate of decrease is the maximum, the maximum accelerating force acts within this space.

The present invention utilizes such a rapid change in pressure gradient to stop the ejection of ink droplets, but the change in pressure gradient that occurs in FIG. It varies depending on the thickness of the air layer 4 (length of the OB), etc., and by setting these appropriately, a more rapid change in the pressure gradient occurs.

On the other hand, in the configuration shown in FIG. 1, the direction of the airflow 5 is bent at a right angle, but in some cases, the direction of the airflow 5 is bent at an acute angle as shown in FIG. May be bent at an obtuse angle. 1st
FIG. 10 shows the influence that the difference in the bending angle θ of the air flow 5 as shown in FIGS. 1, 8, and 9 has on the pressure gradient. In Fig. 10, when the bending angle θ of the airflow is a right angle, the curve 7 is, when the bending angle θ is an acute angle, the curve 8 is, and when the bending angle θ is an obtuse angle, it is the curve 9. Changes in pressure gradient tend to be rapid. Furthermore, although this is not possible in actual construction, if the bending angle θ of the airflow is 180°, the pressure gradient will be constant and will be represented by a straight line 10. Therefore, in order to cause a rapid change in pressure gradient, the smaller the bending angle θ of the air flow 5 as shown in FIG. 8, the better.

Hereinafter, a detailed explanation will be given of a specific embodiment of the present invention that utilizes a sudden change in pressure gradient.

FIG. 11 shows an embodiment of the present invention. An ink chamber 17 having an ink discharge port 16 is connected to an ink reservoir via an ink supply path 18, and the ink chamber 17 is filled with ink.

An air discharge port 13 is perforated in the diaphragm 11 and the electrostrictive element 12 opposite to the ink discharge port 16,
The air flow sent from the air supply path 20 flows into the air chamber 14.
and an air layer 19 formed by the nozzle plate 15 having the ink ejection ports 16 and the diaphragm 11,
The air is discharged from the air outlet 13. The diaphragm 11 and the electrostrictive element 12 are coupled, and when an electric signal 21 is applied, the electrostrictive element 12 bends due to the vibrational force generated in the electrostrictive element 12. ) changes.

FIG. 12 is an enlarged view of the ink discharge port 16 and air discharge port 13 portion. The air outlet 131 is shown in a state in which the electrical signal 21 is not applied, and the air outlet 132 is shown in a state in which the electrical signal 21 is applied. That is, the outlet, point A, and inlet point B of the air discharge port 13 are moved to point A' and point B', respectively, by applying an electric signal. An estimated diagram of the pressure gradient on the center line of the ink discharge port 16 and the air discharge port 13 at this time is shown in FIG. That is, when the electrical signal 21 is not applied, the pressure gradient is expressed as a curve 22, and when the electrical signal 21 is applied, the pressure gradient is expressed as a curve 23. As can be seen from FIG. 13, the pressure gradient curve tends to shift to the right by AA' by applying the electric signal 21, and the pressure gradient at the exit of the ink discharge port 16, point O, increases. do.

In FIG. 11, a certain pressure is applied to the ink chamber 17, and if the electric signal 21 is not applied, the meniscus formed at the exit point O of the ink discharge port 16 will not collapse and be drawn in. Also, the liquid must be balanced so that the meniscus does not break off and become droplets due to the pressure gradient. The balance method will be described later.
When the electric signal 21 is applied, the pressure gradient at the outlet O point of the ink discharge port 16 increases as shown in FIG. When the pressure gradient generated at the ink discharge port 16 exceeds a certain value, that is, a value exceeding the holding force due to the surface tension of the ink (ΔP _l in FIG. 13), the meniscus is torn off and the ink droplets form into air discharge ports. Discharge from 13.

The amount of displacement at which an ink droplet can be ejected varies depending on the shapes and dimensions of the ink ejection port 16, the air ejection port 13, the air layer 19, the air flow velocity, the physical properties of the ink, etc. diameter of approximately 60μ
m, diameter of air outlet 13 approximately 150 μm, air layer 19
It has been found that when the thickness of the ink droplet is approximately 30 μm, the air flow rate is approximately 80 m/s, and the surface tension of the ink is approximately 40 dyn/cm, a displacement of several μm is sufficient to eject and stop ink droplets. .

FIG. 14 shows a specific example of an apparatus employing the configuration shown in FIG. 11. An ink jet head 57 is disposed facing the recording material 62, the ink chamber 17 of the ink jet head 57 is connected to an ink reservoir 58, and the air chamber 14 is connected to an air supply source 59. The air flow from the air supply source 59 is sent to the air chamber 14 and is also sent to the ink reservoir 58 via the pressure regulating valve 60, thereby applying a constant pressure to the ink chamber 17. The pressure applied to the ink chamber 17 can be adjusted by a pressure regulating valve 60 or a pressure regulating valve 61.
maintain balance by controlling the shape of the meniscus that is formed.

Based on the principle explained in detail above, ink droplets can be ejected and stopped by the configuration shown in FIG. Since the ink droplets are ejected and stopped by changing the interval between the ejection ports 13, the speed of ejection and stopping is determined only by the mechanical vibration ability, so high speed is possible. Since the air flow can be used in the laminar range, the flying droplets are stable and in a straight line, making it possible to record high-resolution images. Since the flying speed of the ink droplets is high, there is little delay in recording time, and there is little influence from changes in the distance to the recording medium. Since the amount of ink droplets ejected changes depending on the magnitude of the change in the distance between the ink ejection ports 16 and the air ejection ports 13, there are many advantages such as the ability to obtain recorded images with high gradation.

In the configuration shown in FIG. 11, the air outlet 13 is bored through the diaphragm 11 and the electrostrictive element 12, but the diameter of the hole in the electrostrictive element 12 may be made larger. Further, in the configuration shown in FIG. 11, the electrostrictive element 12 is used as the drive source, but the distance between the air discharge port 13 and the ink discharge port 16 may be changed by other driving methods. For example, a method using magnetic force is also effective. In addition, in FIG. 11, only the air outlet 13 is displaced, but it is also possible to displace the ink outlet 16 or the air outlet 13 and the ink outlet 1.
It is also possible to change the size of the air layer 19 by displacing both 6.

Note that the pressure gradient can also be changed by changing the hole diameter of the air discharge port 13 instead of the air layer 19;
Practical configuration is difficult and not common.

Next, another embodiment based on the principle explained in FIG. 1 will be explained. FIG. 15 shows another embodiment of the invention in which the nozzle tube 28 is installed in line with the air outlet 30 and with the ink outlet 31 within the pressure gradient detailed in FIG. has been done. The nozzle tube 28 is made of a permanent magnet and is supported by the support plate 24. A coil 26 is installed around the nozzle tube 28, and by passing a current through the coil 26, the nozzle tube 28 is displaced in the axial direction. 25 is an ink supply path, 27 is an air supply path, and 32 is an air chamber.

FIG. 16 is an enlarged view of the air outlet 30 and ink outlet 31 in FIG. 15. coil 2
The tip of the ink ejection port 31 is designed to be located at point C when no current is passed through the ink discharge port 6, and to be located at point C' when a certain current is passed through the ink discharge port 31.
FIG. 17 shows the relationship between the tip position of the ink discharge port 31 and the pressure gradient in the air layer 29 and the air discharge port 30.

In Fig. 17, the vertical axis shows the pressure gradient (dp/dx), the horizontal axis shows the position on the x-axis in Fig. 16, and x
The pressure gradient on the axis is shown. As can be seen from FIG. 15, by applying current to the coil 26, the tip of the ink discharge port 31 moves from point C to point C', and the pressure gradient generated at the tip changes from ΔP _p to Δ
Changes to P _a . A certain pressure is applied to the ink in the nozzle pipe 28 via the ink supply path 25, and when no current is applied to the coil 26, the ink meniscus generated at the tip of the ink discharge port 31 is drawn in. The ink droplets are balanced so that they do not break and become flying ink droplets. This specific method can be implemented as shown in FIG. Therefore, the pressure gradient ΔP _l at which the flying ink droplets occur has a value slightly larger than ΔP _p . When current is applied to the coil 26, the pressure gradient increases to ΔP _a , causing the ink droplets to break off and fly. Once the ink droplet has started flying, it approaches point A and moves to a place where the pressure gradient is higher and higher, so that it is further accelerated and flies.

The inkjet recording apparatus having the configuration shown in FIG. 15 has the same advantages as the configuration shown in FIG.
The shapes and dimensions of the 15th
In the figure, since the tip of the ink ejection port 31 can be placed at any position in the air layer 29 (however, on the axis of the nozzle tube 28), the tip of the ink ejection port 31 can be placed at a position where the pressure gradient changes particularly. It is possible to eject and stop ink droplets with a very small amount of displacement.

In the configuration shown in FIG. 15, the coil 26 is used as a drive source.
However, it is of course possible to displace the nozzle tube 28 in other ways. FIG. 18 shows an example in which an electrostrictive element 33 is used as a drive source. The electrostrictive element 33 is coupled to the support 24, and when an electric signal is applied, it bends together with the support 24 and displaces the nozzle tube 28. The other parts are the same as those in FIG. 15, and their explanation will be omitted.

FIG. 19 shows still another embodiment in which the ink discharge ports are displaced, and an ink supply path 38 leading to an ink reservoir (not shown) is connected to one side.
On the other hand, an ink chamber 37 having a guide hole 35 containing a nozzle pipe 36 is provided. Nozzle pipe 36
is moved in the axial direction by a coil 34 provided around it, and the ink discharge port 39 is displaced. The ink ejection port 39 is arranged within the pressure gradient caused by the air flow in the air layer 29, as described in FIG. You can fly it further.

The nozzle pipe 36 is only held by the guide hole 35 with a very narrow gap.
Moreover, since the gap is filled with ink due to surface tension, smooth axial movement is possible. Further, the configuration shown in FIG. 19 has the advantage that a large displacement can be obtained with a small current by using an ink with a high dielectric constant, for example, a water-based ink.

In FIG. 20, a displacement needle 40 is housed in a guide hole 42 instead of the nozzle pipe 36 in FIG. 19. The other parts are the same as those in FIG. 19, and their explanation will be omitted. Similar to the nozzle pipe 36 in FIG. 19, the displacement needle 40 is inserted into the guide hole 42 while maintaining a very narrow gap.
Since the ink is stored in the ink, the gap is always filled with ink due to surface tension. Furthermore, since the displacement needle 40 is made of a material that is easily wetted with ink, a thin ink meniscus is formed at the tip 41. Therefore, according to the same principle as shown in FIG. 19, the pressure gradient generated in the ink meniscus can be changed, so that ink droplets can be ejected and stopped. Compared to FIG. 19, FIG. 20 does not require nozzle processing of the nozzle pipe 36, so it can be easily assembled.

Next, still another embodiment will be explained. 21 is the same as in FIG. 19 or 20, with the nozzle tube 35 or the displacement needle 40 removed, but the guide hole 43 is filled with magnetic ink and the coil 44 is shown in FIG. By applying a magnetic field to the ink by applying an electric current, a force acts on the ink itself, causing fluctuations in the meniscus generated at the ink ejection port 45. Since this meniscus is located in a space where there is a rapid change in pressure gradient, as in the embodiment shown in FIG. 20, ink droplets are ejected and stopped depending on the movement of the meniscus. Other parts are first
This is the same as FIG. 9 and FIG. 20, and the explanation will be omitted.

FIG. 22 shows a multiplication of the configuration shown in FIG. 19. The ink chamber 50 has an ink supply path 51 leading to at least one ink reservoir and a plurality of guide holes 47.
Each has a built-in nozzle pipe 48,
An axial displacement occurs due to the surrounding coil 46. Further, the air flow flowing in from the air supply path 56 is made uniform in the air chamber 54, and is ejected from the air discharge ports 52 facing the guide holes 47 through the air layer 53.
The ink discharge port 55 at the tip of the nozzle pipe 48 is arranged in a space where a rapid change in pressure gradient occurs. The sealing material 49 is provided to eliminate mutual interference between the respective ink ejection ports 55. In the configuration shown in FIG. 22, ink droplets are ejected and stopped according to the same principle as in FIG. 19, but
Since the plurality of ink ejection ports 55 can independently eject and stop ink droplets, images can be formed using ink droplets at a very high speed. Note that FIG. 22 is a multiplication of the configuration of FIG. 19, but for example,
Similarly, the configurations shown in FIGS. 15, 18, 20, 21, etc. can be multiplied.

As explained in detail above, the present invention causes the air flow to be sharply bent from the air outlet,
The pressure gradient that occurs in the meniscus of liquid that is formed at the ink ejection port by arranging the ink ejection port opposite to the air ejection port in a space where there is a sudden change in pressure gradient caused by the bending of the air flow. In other words, the ejection and stopping of ink droplets is controlled by changing the acceleration force of the air flow.

Note that various means can be considered for causing the above-mentioned bending of the air flow, as shown in FIGS. 2 to 8, and methods for changing the pressure gradient generated in the liquid meniscus include: Figures 11 and 15
18, 19, 20, and 21, (i) a method of changing the interval between walls having air discharge ports and ink discharge ports; method of displacing a nozzle tube with an outlet;
(iii) Various methods are possible, such as a method of displacing the meniscus of the liquid formed at the ink ejection port.

In the inkjet recording method with such a configuration, there is no need to control air flow, and ink droplets are ejected and stopped only by mechanical or electrical control, so high speeds are possible.

Furthermore, since the air flow can be used in a laminar flow range, the flying droplets are stable and in a straight line, resulting in good resolution.

Furthermore, since the flying speed of the ink droplets is high, there is little delay in recording time, and there is little influence from changes in the distance from the recording medium. Furthermore, since the amount of ink droplets ejected can be controlled by varying the magnitude of the pressure gradient, a recorded image with high gradation can be obtained. Further, there are many advantages such as relatively easy multiplication, and an extremely high-performance inkjet recording device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the operating principle of the present invention, FIGS. 2 to 5 a are front views showing a configuration example of an air discharge system for implementing the operating principle of FIG. 1, and FIG. 5 b is a sectional view of the same;
6 and 7 are explanatory diagrams of pressure and pressure gradient for explaining the operation of FIG. 1, FIGS. 8 and 9 are sectional views showing still other configuration examples of the air discharge system, and FIG. 10 11 is a cross-sectional side view showing the first embodiment of the inkjet recording apparatus according to the method of the present invention, and FIGS. 12 is an explanatory diagram of the operation of the apparatus of FIG. 12, FIG. 14 is an explanatory diagram of the ink supply system and air supply system of the apparatus of FIG. 11, and FIG. 15 is a second embodiment of the inkjet recording apparatus according to the method of the present invention. Cross-sectional side view showing an example, Figure 16 and Figure 1
Figure 7 is an explanatory diagram of the operation of the device in Figure 15, and Figures 18-
FIG. 21 is a cross-sectional side view showing yet another embodiment of an inkjet recording device according to the method of the present invention, and FIG. 22 is a cross-sectional side view of an embodiment in which the inkjet recording device according to the method of the present invention is made into a multi-nozzle. be. 1... Air discharge port, 2... Nozzle plate, 3... Wall, 4...
Air layer, 5... Stream line, 6... Equal pressure line, 11... Vibration plate, 12... Electrostrictive element, 13... Air discharge port, 14...
Air chamber, 15... nozzle plate, 16... ink discharge port,
17... Ink chamber, 18... Ink supply path, 19... Air layer, 20... Air supply path, 21... Electric signal, 2
2, 23...Curve, 24...Support plate, 25...Ink supply path, 26...Coil, 27...Air supply path, 28...
Nozzle pipe, 29... Air layer, 30... Air discharge port, 3
DESCRIPTION OF SYMBOLS 1... Ink discharge port, 32... Air chamber, 33... Electrostrictive element, 34... Coil, 35... Guide hole, 36... Nozzle pipe, 37... Ink chamber, 38... Ink supply path, 3
9... Ink discharge port, 40... Displacement needle, 42... Guide hole, 43... Guide hole, 44... Coil, 45... Ink discharge port, 46... Coil, 47... Guide hole, 48
... nozzle pipe, 49 ... sealing material, 50 ... ink chamber,
51... Ink supply path, 52... Air discharge port, 53...
Air layer, 54...Air chamber, 55...Ink discharge port, 5
6... Air supply path, 57... Ink jet head,
58... Ink reservoir, 59... Air supply system, 60,6
1...Pressure regulating valve.

Claims (1)

[Claims] 1. An air outlet is installed coaxially with an ink outlet and facing each other, and the air flow is directed from the air outlet while creating a sharp bend in the gap between the ink outlet and the air outlet. A space is created in which the pressure gradient of the air decreases in the direction from the ink discharge port to the air discharge port, and the ink meniscus formed in the ink discharge port is connected to the air discharge port. The distance is selectively reduced in accordance with the signal to increase the acceleration force of the air flow acting on the meniscus of the ink by the space where the pressure gradient changes, and the ink liquid is discharged outward through the air discharge port. An inkjet recording method characterized by ejecting inkjet. 2. The inkjet recording method according to claim 1, wherein the distance between the ink ejection port and the air ejection port is changed to be smaller in accordance with a signal to increase the acceleration force of the air flow acting on the ink meniscus. 3. The air outlet is formed in a plate made of a diaphragm and an electrostrictive element, and the plate is bent in response to an electric signal to change the distance between the ink outlet and the air outlet. The inkjet recording method according to item 2. 4. Ink jet recording according to claim 1, in which the ink meniscus formed at the ink ejection port is moved in the direction of the air ejection port in response to a signal to increase the acceleration force of the air flow acting on the ink meniscus. Method. 5. The inkjet recording method according to claim 4, characterized in that a nozzle pipe having an ink discharge port is moved in the direction of the air discharge port. 6. The inkjet recording method according to claim 4, wherein a meniscus of ink formed in the inkjet orifice is raised by movement of a displacement needle inserted into the inkjet orifice. 7. The inkjet recording method according to claim 4, characterized in that a magnetic ink is used as the ink, and a magnetic field is applied to the ink to raise a meniscus of the ink formed at the ink ejection port.