JPS62231762A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To obtain the multi nozzle head type ink jet recorder having uniform characteristic, by a method wherein the discharge openings at the both ends of air discharge openings arranged on one straight line are so constructed as to be not concerned in discharge of ink. CONSTITUTION:Electrodes 14-a and 14-b are formed on the inside surfaces of the other air opening exception the air discharge openings at both ends among air discharge openings 13-0, 13-a, and 13-b. The ink discharge opening 13-3 is not opposed to an ink slit 17 and the other air discharge openings 13-a and 13-b excepting the discharge opening 13-b are opposed to the ink slit 17 so as to form the meniscus of ink on the central axes thereof. If a potential difference is applied between the electrode and the ink, the meniscus of the ink is elongated in the direction of the air discharge openings 13-a and 13-b and ink liquid drops are selectively discharged by the action of air flow. Though the distribution of air pressure near the discharge opening 13-0 differs from those of other discharge openings, the pressure distribution of air generated near the discharge openings 13-a and 13-b becomes uniform by the presence of the discharge opening 13-0.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel inkjet recording device that utilizes a pressure gradient generated by air flow and an electric field force.

Figure WJ1 is a sectional view showing an example of an inkjet recording head that is the basis of the present invention, which is related to an earlier application filed by the present applicant. In the same figure, an air discharge port 1 is perforated in the acid-conducting nozzle plate 2, and a wall 3 is disposed parallel to the nozzle plate 2. An ink ejection port is perforated on the top. Nozzle plate 2 and wall 3
An air flow is sent from the surrounding area to the air layer created by this, and it flows out from the air discharge port 1. The direction of the air flow changes rapidly near the air outlet 1, so in the space from the ink outlet 4 to the air outlet 1, there is a flow direction from the ink outlet 4 toward the air outlet 1. A sudden pressure gradient change occurs such that the pressure decreases.

On the other hand, a constant pressure is applied to the ink inside the ink ejection port 4, and when the inkjet recording head is not driven, the air pressure of the ink ejection port 4 and the ink ejection port 4 are applied.
The ink pressure within the ink discharge port 4 is adjusted so that the ink meniscus generated at the ink ejection port 4 remains stationary.

The signal source 5 is electrically connected to an ink supply pipe 6 communicating with the nozzle plate 2 and the ink discharge ports 4 so that a potential difference is generated between the nozzle plate 2 and the ink within the ink discharge ports 4. When the signal source 5 generates a potential difference between the nozzle plate 2 and the ink in the ink discharge port 4 according to the signal, the meniscus generated in the ink discharge port 4 is stretched in the direction of the air discharge port 1 due to the electric field force caused by the potential difference. . A rapid change in pressure gradient occurs in the space from the ink discharge port 4 to the air discharge port 1, and the degree of change is greater as it approaches the air discharge port 1. When the ink meniscus is stretched beyond a certain length, it is torn off by a change in pressure gradient and flies as ink droplets through the air discharge port 1 along with the air flow.

As explained above, the inkjet recording head shown in FIG. 1 changes the shape of the ink meniscus generated at the ink ejection port 4 by electric field force, and the ink droplet is It discharges.

In addition, Figure 2 (B) is an example in which the inkjet recording shown in Figure 1 is changed to a so-called multi-nozzle having multiple ink ejection ports. FIG. 2(B) shows a sectional view taken along a-a' plane.

The ink chamber 7 communicates with a plurality of ink discharge ports 8 and at least one ink supply path 9 leading to an ink reservoir (not shown). Further, the air flow flowing in from the air supply path 10 is made uniform in the air chamber 11, and is ejected from the air discharge ports 13 facing the ink discharge ports 8 through the air layer 12. It is placed in a space where a sudden change in pressure gradient occurs. Electrodes 14 are provided independently around the air outlet 13, each electrode 14 is connected to a signal source 15, and a potential difference is independently applied between the electrode 14 and the ink within the ink outlet 8. It has a structure that allows Note that the body 16 is made of a material with a high dielectric constant and low electrical conductivity.

In the multi-nozzle head shown in FIGS. 1 and 2, particularly in FIG. 2, there is difficulty in aligning the air outlet 13 and the ink outlet 8. The ink discharge port 8 and the air discharge port 13 are installed facing each other, but their positions need to be as concentric as possible, so that the streamlines of the air flow and the lines of electric force of the electric field near the ink discharge port 8 are It is desirable that it be rotationally symmetrical with respect to the center line of the ink ejection port 8. If the positional misalignment between the ink ejection port 8 and the air ejection port 13 is large, the ink droplet may be bent in the flight direction, causing deterioration of the recorded image quality. Discharge port 1
3, and may become unrecordable.

Generally speaking, the shape of the nozzle for ink and air discharge ports needs to be clean and free of cracks and sag, so they are drilled separately and then assembled after being finished. In this case, the positional accuracy of the ink discharge port and the air discharge port becomes a problem. Particularly in a multi-nozzle head as shown in FIG. 2, it is difficult to align the ink discharge ports 8 and the air discharge ports 13. In other words, in a multi-nozzle head, it is necessary to align multiple nozzles, so it is necessary to improve the accuracy of the nozzle spacing of the ink discharge port and air discharge port, the linearity of the nozzle arrangement, etc. Skill in the assembly process is required.

3(A), (Bl shows the configuration of another multi-nozzle head, and is an inkjet head having a configuration in which the nozzle alignment described above is easy.

3(B) are the ink ejection openings 80 in FIG. 2(B) replaced with ink slits 17, respectively.

The slit width of the ink slit 17 is selected to be approximately the same as the diameter of the ink discharge port 8 in FIG. 2, and communicates with the ink chamber 7 which plays the same role as in FIG. Since the air supply system, electrodes, etc. are almost the same as those in FIG. 2, their explanations will be omitted.

FIGS. 4(3) and 4(B) are enlarged views of the air discharge port 13 and ink slit 17 in FIGS. 3(b) and 4(b), respectively. The air flow sent from the air chamber 11 passes through the air layer 12 and flows out from the air outlet 13.If the streamline 18 of the air flow is illustrated in more detail,
It takes the form shown in the figure. Style #i! 18, at the center of the ink slit 17 and on the interface with the air layer 12 (fourth
Considering the air flow velocity on the straight line AlA2 in the figure, B, B
At point 2, the air flow velocity is zero in any direction, and increases as it approaches the air outlet 13. On the other hand, Al.

At points A2 and A3, all of the airflow flowing toward the air outlet 13 is bent in the right angle direction, so the upstream velocity actually becomes zero.

However, from the point A11A2 1A3, air outlet 1
At the position shifted to the third side, a flow velocity exists in the direction of the center line of the air discharge port 13.

Next, let's talk about air pressure. B1. Since the air flow velocity is almost O near point B2, the air pressure is approximately equal to the pressure in the air chamber 11 described above. That is, there is almost no pressure loss due to air flow velocity and pressure drop due to energy conversion. On the other hand, At lA2 1A3
At the points AH, A2, and IA, the air flow velocity at the three points is O. However, around these points, there is an air flow with a sharp bend, so that the air flow velocity from the air chamber 11 to A1. A
2. Due to the pressure loss up to point A3, the air chamber 11
The pressure is lower than the air pressure.

Therefore, AI lA2 IA3 points and B in Figure 4
There is an air pressure difference between the two points 1yB, and A1.

It can be seen that the air pressure is lower at points A2 and A3. Although such a pressure difference differs depending on the size and structure, it has been found that it is greatly influenced by the thickness of the air layer 12.
It has been confirmed that the air pressure at the AI IA 2A 3 point decreases rapidly when the pressure becomes less than m.

On the other hand, a constant pressure is applied to the ink in the ink chamber 7, and the pressure of the ink in the ink slit 17 is also equal to the ink pressure in the ink chamber 7. Now, if the ink pressure is set to the pressure at point AI r A2 IA3 in FIG.
+ It is thought that it becomes a plane at point A3. However, +3. , at point B2, A4, A2
, Since the air pressure is higher than point A3, the ink meniscus 19 is pushed toward the ink chamber 7 and becomes a concave meniscus. That is, the difference between the air pressure and the ink pressure at point B1.82 is balanced by the surface tension acting on the meniscus 19 generated in the ink slit 17.

By setting the pressure in the ink chamber 11 to an appropriate value, it is also possible to create a meniscus that is convex at point AI + A2+ A3 and concave at point J+B2, as shown in FIG.

As explained above, the ink ejection port 8 is connected to the ink slit 1.
7 and by appropriately adjusting the balance between the ink pressure and the air pressure, it is possible to cause the ink meniscus 19 generated in the ink chamber 7 ) 17 to have irregularities at intervals of the air discharge ports 13 .

When a potential difference is established between the meniscus 19 and the electrode 14 in this state, the force acting on the meniscus 19 is inversely proportional to the square of the distance from the electrode, so that A1°A2. It is a dog at point A3, and small at points Bl and B2. Moreover, since the air flow flows from the surroundings toward the air outlet 13, the ink meniscus 19 stretched by the electric field force is limited to the air outlet 13 where the electrode 14 with a potential difference is located.

In this way, ink spools with a common ink ejection port,
Even in the case where the air outlet 17 is adopted, if the air outlet 13 and the 'electrode 14 are each independent, it is possible to stop the ejection of ink droplets from each air outlet 13 independently.

In the multi-nozzle head shown in FIG. 3, since the ink ejection ports are the ink slits 17,
It is easy to manufacture as there is no need to drill holes one by one.
Furthermore, as far as alignment with the air outlet 13 is concerned, as long as the linearity of the ink slit 17 and the air outlet 13 is good, the complexity in the assembly process can be greatly reduced. As described above, the multi-nozzle head shown in FIG. 3 can provide an inkjet recording apparatus with a simpler structure and lower cost than the multi-nozzle head with the structure shown in FIG. Note that the groove-shaped ink ejection orifice can be applied not only to a multi-nozzle head as shown in FIG. 3, but also to an inkjet head with a single air ejection port or an electrode.

Next, the air outlet 13 in the multi-nozzle head shown in FIG. 3 will be described in detail.

FIG. 5 is an enlarged cross-sectional view of the end (the right end in the figure) of the ink discharge port 17 and the air discharge port 13 in FIG. 3. As is clear from the figure, the ink meniscus 19 generated near the air outlet 13-1 located at the end may have a different shape from other air outlets, for example, the air outlet 13-2. One of the reasons for this is the way the air flows. For example, at the air outlet 13-2, the air flows from both sides of the ink slit 17, and near the air outlet 13-2, the air flows from the surroundings. On the other hand, at the air outlet 13-1, the air flow also flows in from the edge 21 side of the plate forming the ink slit, and at the air outlet 13-1, the air flows into the other air outlets. This is because the air pressure distribution may be different in comparison.

Such differences in air pressure distribution between multiple air ejection ports are not limited to multi-nozzle heads with slit-shaped ink ejection ports shown in FIG. The multi-nozzle head with ejection ports also has an influence, and the variations in the ink meniscus shape that occur corresponding to each air ejection port lead to variations in the amount of ink ejection and the responsiveness of ink ejection. The problem was that it appeared.

However, when the ink ejection opening has a slit-like shape, the holding force of the ink meniscus due to surface tension is weaker than when the ink ejection opening is circular, so it can be said that it is greatly affected by variations in air pressure distribution.

The present invention has been made to eliminate such drawbacks, and will be described in detail below with reference to the drawings.

FIG. 6 shows an embodiment in which the present invention is applied to the inkjet recording head shown in FIG. The nozzle plate 22 is formed with a plurality of air discharge ports 13-0.13-a, 13-b, . . . arranged in a straight line. These air discharge ports 13-0, 1
3-a, 13-b, . . . except for the air outlet ports at both ends (only one end 13-0 is shown in the figure). Electrodes 14-a, 14b+, . . . are formed on the inner surface thereof. Reference numeral 23 denotes an ink ejection port member having an ink slit 17 formed therein as an ink ejection port, and is arranged opposite to the nozzle plate 22 . In this case, the air outlet 13-0 does not face the ink slit 7, and the air outlet 13-a, 13
-b, . . ., air discharge ports 13-0 at both ends
Other air discharge ports 13-a, 13-b, ・
... are arranged opposite to the ink slit 17 so that an ink meniscus is formed on the center 1 of the ink slit 17. An air flow is sent from an air supply source (not shown) to the gap formed between the nozzle plate 22 and the ink ejection port member 23, and this air flow is applied to each of the air ejection ports 13-0 and 13-a.
, L 3-b , . . . causes a sharp bend and flows outward.

On the other hand, as described above, when the pressure of the ink chamber is set to an appropriate value, each air discharge port 13-a, 13-b.

It is possible to make the ink meniscus 19 convex at positions corresponding to . . . and concave at other parts.

In this state, the electrodes 14-a, 14-b,...
When a potential difference according to a signal is applied between the ink and the ink, the meniscus 19 of the ink moves to the air discharge ports 13-a and 13-b.

The air flow acts on the air discharge ports 13-a, +13-b,...
Ink droplets are ejected more selectively.

The air discharge ports 13-a, 13-b, . . . are formed with electrodes 14a, 1, 1k)+, and are opposed to the ink slit 17, so that the ink Although it is involved in the ejection of ink droplets, the air ejection port 13-0 does not have an electrode formed thereon and is spaced apart from the ink slit 17, so it does not participate in the ejection of ink droplets.

Air discharge ports 13-a, 13 involved in the discharge of ink droplets
-b, . . ., the rightmost air outlet 13-a is arranged at a position away from the right end 20 of the ink slit, and the distance between the ink slit end 20 and the air outlet 13-a is set to 2 of the air outlet diameter. The influence of ink slits and edges 20 can be sufficiently removed by setting the distance to be at least twice as long as the distance between the air discharge ports.

On the other hand, the electric air discharger 13, which is not involved in the discharge of ink droplets,
The distribution of air pressure near -0 may be different from that of other air outlets, but due to the presence of the air outlet 13-0, the air outlet 13-a actually participates in ejecting ink.
13-b, the pressure distribution of the air at the air discharge port near the air outlet becomes uniform, and the shape of the meniscus of the ink produced correspondingly can be made uniform.

Although the above explanation relates only to the right end of the ink slit, the same can be said to the left end. Note that the ink ejection port is not limited to the slit-shaped one.
The present invention is also applicable to the case of the circular ink ejection port array shown in the figure.

As described above, in the present invention, a plate member having a plurality of air discharge ports arranged in a straight line and a member having an ink discharge port are disposed facing each other, and the plate member and the ink discharge port are arranged opposite to each other. An inkjet recording system in which an air flow is sent into a gap created by a member having an outlet, and the air is caused to flow out of the air outlet while causing a sharp bend, and ink is ejected in a circle around the ink outlet in response to a drive signal. In this case, the air discharge ports at both ends of the air discharge ports arranged in a straight line are configured so as not to participate in the ejection of ink, and the air pressure distribution at both ends is different from that in the vicinity of the air discharge ports. Because it does not use ink ejection/stop, and uses only the air ejection port with uniform pressure distribution at the air ejection port in the middle, the shape of the ink meniscus that occurs at the ink ejection port can be made uniform, resulting in uniform characteristics. A multi-nozzle head type inkjet recording device can be realized.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional side view showing an inkjet recording head according to the applicant's earlier application, FIG. 2 (B) shows the inkjet recording head in FIG. front view and a-a
A line sectional view, FIG. 3, (B) is a front view showing the structure of an inkjet recording device related to another application of the present applicant, and a sectional view taken along a-a line, FIGS. 4 (A) and (B). are an enlarged front view and an enlarged sectional side view of the main parts in the configuration shown in FIG.
FIG. 5 is an enlarged cross-sectional side view of other parts of the structure shown in FIG. 3, and FIG. 6 is a cross-sectional side view of essential parts in an embodiment of the inkjet recording apparatus according to the present invention. ■... Air discharge port, 22... Nozzle plate, 3.
... Wall, 4... - Ink ejection port, 5... Signal, 6... Ink supply pipe, 7... Ink chamber, 8... Ink ejection port, 9... Ink supply path, 10... Air supply path, 11... Air chamber, 12... Air layer, 13... Air discharge Exit, 14... Electrode, 15... Signal source, 16... Body, 17... Ink slit, 19... Ink meniscus, 23・・・・・・
Ink ejection port member. Name of agent: Patent attorney Toshio Nakao and 1 other person @1
Figure Wg2CiU “August La. :A) (Bunman
3 Figure IAI tel-
a. 1F! Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A plate-shaped body having a plurality of air discharge ports arranged in a straight line and a member having ink discharge ports are arranged facing each other,
An ink discharge port is installed such that an ink meniscus is formed on a central axis of the air discharge ports excluding both ends of the plurality of air discharge ports, and a gap portion between the plate-shaped body and the member having the ink discharge port. a first means for sending an air flow to the air outlet and causing the air to flow out from the air outlet while causing a sharp bend;
and second means for transporting the ink within the ink discharge port in the direction of the air discharge port in response to a signal and ejecting the ink outward through the air discharge port, wherein the air discharge ports at both ends of the plurality of air discharge ports are configured to An inkjet recording device characterized in that it does not involve ejection.