JPS6320709B2 - - Google Patents

Description

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

FIG. 1 shows a new type of inkjet recording head that has already been filed by the present applicant, in which a nozzle plate 2 has air nozzles 1 perforated therein. A wall 3 is disposed parallel to the nozzle plate 2, and ink nozzles 4 are perforated in the wall 3 facing the air nozzles 1. An air flow is sent from the periphery to the air layer 7 created by the nozzle plate 2 and the wall 3, and flows out from the air nozzle 1. The direction of the air flow is
Because it changes rapidly near air nozzle 1,
A rapid change in pressure gradient occurs in the space from the ink nozzle 4 to the air nozzle 1.

On the other hand, a constant pressure is applied to the ink inside the ink nozzle 4, and when the inkjet recording head is not driven, the air pressure near the ink nozzle 4 and the ink pressure inside the ink nozzle 4 are approximately equal. Adjustments are made such that the resulting ink meniscus remains stationary.

The signal source 5 connects the nozzle plate 2 so that a potential difference is generated between the nozzle plate 2 and the ink in the ink nozzle 4.
and an ink supply pipe 6 communicating with the ink nozzle 4
is connected to. When a potential difference is generated between the nozzle plate 2 and the ink in the ink nozzle 4 by the signal source 5, the meniscus generated in the ink nozzle 4 is stretched in the direction of the air nozzle 1 due to the electrostatic force caused by this potential difference. A rapid change in pressure gradient occurs in the space from the ink nozzle 4 to the air nozzle 1, and the degree of this change is larger as the air nozzle 1 is approached. When the ink is stretched beyond a certain length, the ink is torn off by this change in pressure gradient, and the ink drops fly out of the air nozzle 1.

FIG. 2 shows an example of an inkjet recording head that is a multi-layer version of the inkjet recording head shown in FIG.

The ink chamber 19 communicates with a plurality of ink discharge ports 9 and at least one ink supply pipe 10 leading to an ink reservoir. Further, the air flow flowing in from the air supply pipe 11 is made uniform in the air chamber 12, and is ejected from the air discharge ports 14 facing the ink discharge holes 9 through the air layer 13. It is placed in a space where a sudden change in pressure gradient occurs. Air outlet 1
4 are formed in a nozzle plate 18 made of an insulator, and electrodes 15 are independently provided around the holes, and each electrode 15 is electrically connected to an independent signal source 16. The signal source 16 is connected to the ink outlet 9 on the one hand.
The electrode 15 is electrically connected to the ink inside the ink discharge port 9, and has a structure in which a potential difference is generated independently between the electrode 15 and the ink inside the ink discharge port 9.

In this way, the ink nozzles 4 and 9 are moved by electrostatic force.
By changing the shape of the ink meniscus that occurs in
In an inkjet recording head that ejects ink droplets by a sudden change in pressure gradient caused by an air flow, the balance between air pressure and ink pressure is kept constant near the ink nozzle 4 or 9, and the meniscus is stabilized. It becomes extremely important to be in this state. For example, if the ink pressure exceeds the air pressure, the balance of the meniscus will be disrupted, and the ink will protrude from the ink nozzles 4 and 9, causing air in the space from the ink nozzles 4 and 9 to the air nozzles 1 and 14 even without applying a recording signal. Due to the drastic change in the pressure gradient of the airflow, it is torn off and becomes flying droplets. Conversely, if the air pressure exceeds the ink pressure, the meniscus ruptures inside the ink nozzles 4, 9, and air enters the ink chambers 8, 19 from the ink nozzles 4, 9 in the form of bubbles, causing actual damage. Even if a drive signal is applied to the inkjet recording head, the ejection of ink droplets becomes unstable.

In the inkjet recording head shown in FIGS. 1 and 2, when the inkjet recording head is stationary or scans at an extremely slow speed, the state of noniscus is stable and causes almost no problem. However, if an impact is applied to the inkjet recording head or ink supply tube, for example, the ink pressure fluctuations that occur in the ink supply tube or ink chambers 8 and 19 will cause the meniscus to collapse and cause unnecessary ink ejection or Air bubble ink chambers 8, 19
An unstable situation may occur due to contamination within the country.

Shocks to the inkjet recording head and the inkhead supply tube occur particularly when the inkjet recording head is scanned at high speeds. Recently, particularly high-speed recording has been required, and the scanning speed of inkjet recording heads has also become faster, such as in flat-plane scanning printers. It's becoming a problem.

The present invention has been made in view of the above-mentioned problems, and when the inkjet recording head is scanned at high speed, the ink in the ink supply tube connected to the inkjet recording head is caused to oscillate. An object of the present invention is to provide an inkjet recording head having a function of blocking pressure fluctuations before they are propagated to an ink chamber within the inkjet recording head.

Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 3 shows an embodiment of an inkjet recording head 30 of the present invention. Ink chambers 2 are provided on the extensions of the two ink supply pipes 6 and 6'.
2, 22', and an orifice plate 23, which has a pair of orifices 25, 25'.
23', forming a thin liquid supply layer 24 between them. Before and after the liquid supply layer 24, there are ink chambers 21 and 2 that are connected to each other through a source other than the liquid supply layer 24.
1' is formed, and a nozzle plate 20 having nozzles 4 is provided in front of the ink chamber 21. A screw 26 is provided at the rear of the ink chamber 21' in order to facilitate the filling of ink into the ink chambers 21, 21' and to remove air bubbles that may cause unstable ejection. 27 is an O-ring.

Ink chambers 22, 22', 21, 2 are supplied from an ink reservoir (not shown) through ink supply pipes 6, 6'.
1' and the liquid supply layer 24 with ink,
Adjust the screws 26 to open the ink chambers 22, 22', 21,
21' and the air bubbles in the liquid supply layer 24 are removed.
In this state, a constant pressure is applied to the ink within the ink nozzle 4.

On the other hand, an air flow is introduced from the air supply pipe 11 and discharged from the air nozzle 1 through the air chamber 12 and the air layer 7. At this time, since the flow direction of the air flow changes rapidly near the air nozzle 1, a sudden change in pressure gradient occurs in the space from the ink nozzle 4 to the air nozzle 1. When the inkjet recording head is not driven, the pressure applied to the ink within the ink nozzle 4 and the air pressure near the ink nozzle 4 are balanced, and the ink meniscus generated in the ink nozzle 4 is kept stationary.

When an electrical signal to be recorded is applied from the signal source 5 between the ink and the nozzle plate 2, the meniscus of the ink in the ink nozzle 4 is extended in the direction of the air nozzle 1 in response to this electrical signal, and an electric signal is generated in this space. The ink is torn off by the sudden pressure gradient and flies out of the air nozzle 1 as ink droplets.

In the configuration shown in FIG. 3, it is possible to prevent or alleviate ink pressure fluctuations that cause the meniscus in the nozzle 4 to become unbalanced. This is due to the following three reasons.

(1) Since the ink jet recording head of this embodiment has two ink supply pipes 6 and 6', the ink supply pipe system is as shown in FIG. 4, for example. In this case, two ink supply tubes 6, 6' form a loop, and on the opposite side of the inkjet recording head 30, they become one and are connected to an ink reservoir. Inkjet recording head 3
0 scans in the order of a, b, and c in FIG. 4. That is, the ink supply pipe section 60 from the ink reservoir
The inkjet recording head 30 scans left and right at high speed centering on . In the state shown in FIGS. 4b and 4c where the direction of movement is reversed, inertial force is generated in the ink within the ink supply pipes 6 and 6', and the ink supply pipes 6 and 6'
A flow relative to the current occurs. This flow is converted into pressure fluctuations and becomes a major factor in disrupting the balance of the meniscus. However, by providing the orifice 25 as shown in Fig. 3, the cross-sectional area is rapidly narrowed down, so the orifice 25
The ink flow rate within 5 is greatly increased. Assuming that Bernoulli's equation holds true in the ink supply pipes 6 and 6' and near the orifice 25, the total pressure = dynamic pressure + static pressure, so the dynamic pressure increases by the amount that the ink flow rate increases in the orifice 25. Therefore, the static pressure will decrease by that amount. The thin ink supply layer 24 applies almost only static pressure to the ink chambers 21 and 2.
1', pressure fluctuations can be suppressed by this reduced static pressure. When an ordinary inkjet recording head, which generally does not have the structure shown in Fig. 3, is scanned as shown in Fig. 4,
However, as mentioned above, in this embodiment, the pressure fluctuations work to reduce on the side, so in some cases, the effect may be too strong and cause pressure fluctuation on the side. be. Since this depends on the diameter of the orifice 25 and the thickness of the ink supply layer 24, it is necessary to select these appropriately. The diameter of the orifice 25 and the thickness of the ink supply layer 24 vary depending on the size of the inkjet recording head, the length of the ink supply tube, etc., but are approximately 100 to 300 μm and 20 to 150 μm, respectively.
m is the actual effective range.

(2) Next, pressure loss due to resistance in the orifices 25, 25' and the ink supply layer 24 is effective in preventing and mitigating ink pressure fluctuations. This is different from case (1), in which the pressure fluctuation acts in the direction of zero on both sides, and is ideal for operation, but the diameter of the orifices 25, 25' and the ink supply layer If the thickness is reduced, the amount of ink supplied will be insufficient, so it is necessary to select an appropriate value while also considering the relationship with (1).

(3) The third cause is orifice 25,2
Ink chambers 22, 22', 21, and 21' are provided before entering the ink supply layer 5' and after leaving the ink supply layer 21, and act as dampers to absorb pressure fluctuations. Unlike gas, the fluid being handled here is a liquid, so it is not as effective as gas. However, for example, if the ink nozzle plate 20 is made of thin metal (approximately 20 to 30 μm), pressure fluctuations can be absorbed by the flexure of the ink nozzle plate 20. Easy and effective.

For the three reasons explained above, the balance of the meniscus in the nozzle 4 is maintained stably. The air flow flows from the air supply pipe 11 through the air chamber 12 provided around the ink nozzle plate 20 and from the air layer 7 toward the air nozzle 1 , and is sharply bent near the air nozzle 1 . is being released into the atmosphere. Therefore, a sudden change in pressure gradient occurs in the space from the ink nozzle 4 to the air nozzle 1, and this is caused by the electrostatic force generated by the potential difference between the nozzle plate 2 and the ink inside the ink nozzle 4. The stretched meniscus is torn off from the air nozzle 1, and is made to fly as ink droplets from the air nozzle 1.

The higher the speed of the air flowing out from the air nozzle 1, the greater the pressure gradient that occurs in the space from the ink nozzle 4 to the air nozzle 1. Transporting the ink droplets onto the surface of the recording paper. Therefore, the frequency characteristics are improved and the recording speed is increased, but because the air flow velocity is high, when ink droplets fly and adhere to the surface of the recording paper, they scatter around the periphery, making it difficult to form beautiful dots. Furthermore, if the balance of the meniscus in the ink nozzle 4 is even slightly disturbed, the ink will fly, making it even more necessary to keep the balance of the meniscus stable. Therefore, it is important to adjust the air pressure to obtain an appropriate flow rate. In the case of the inkjet recording head of the present invention, good results were obtained when the air flow velocity in the air nozzle 1 was in the range of 30 m/s to 200 m/s.

As described above, the present invention causes an air flow to be ejected from an air nozzle with a sharp bend, and is placed in a space facing the air nozzle opening in a space having a sudden change in pressure gradient caused by the bend in the air flow. An ink nozzle with an opening is provided, and an electric field is applied between the air nozzle and the ink in the ink nozzle to cause a change in the shape of the ink meniscus formed in the ink nozzle.The change in pressure gradient generated at the tip of the meniscus causes the ink liquid to change. Two ink supply tubes are connected to an inkjet recording head that stops ejecting droplets, and an ink supply layer is formed by an orifice plate having an orifice inside the head as an extension of the two ink supply tubes. This is an inkjet recording head in which the other ends of the supply tubes are connected to an ink reservoir through each or a single tube, and has the effect of preventing or mitigating ink pressure fluctuations and keeping the meniscus formed by the ink nozzles stable. be.

It goes without saying that the present invention is effective not only in monoheads as in the above embodiment but also in multiheads, and is also effective in other heads where the stability of the meniscus of the ink nozzle is important.

[Brief explanation of the drawing]

1 and 2a are sectional views of an inkjet recording head according to an earlier application of the present applicant, FIG. 2b is a front view thereof, and FIG. 3 is a sectional view of an inkjet recording head according to an embodiment of the present invention. Figure, 4th
Figures a, b, and c are cross-sectional views showing an example of the configuration of a piping system when the inkjet recording head of the present invention is used. 1...Air nozzle, 2...Air nozzle plate, 4...
...Ink nozzle, 6, 6'...Ink supply pipe, 7
...Air layer, 21, 21', 22, 22'...Ink chamber, 11...Air supply pipe, 12...Air chamber, 2
0... Ink nozzle plate, 23, 23'... Orifice plate, 24... Ink supply pipe, 25, 25'...
...Orifice, 26...screw, 27...O-ring.

Claims (1)

[Scope of Claims] 1. An air discharge port is installed coaxially with the ink discharge port and opposite to the ink discharge port, and air flow is sent out from the air discharge port while creating a sharp bend in the gap between the ink discharge port and the air discharge port. a first means for forming a space in which the pressure gradient changes such that the air pressure decreases in the direction from the ink discharge port to the air discharge port;
A potential difference is selectively generated between the member in which the air discharge port is formed and the ink in the ink discharge port in accordance with a signal, and the meniscus of the ink generated in the ink discharge port is stretched by the attractive force caused by this potential difference. and a second means for ejecting the ink in the ink ejection port outward through the air ejection port by applying an accelerating force of the air flow generated in the space where the pressure gradient changes by the first means, and a second means facing each other. Arranged 2
an ink supply layer formed between the two plates and communicating with the ink ejection opening; and an orifice bored in each of the two plates in parallel to the scanning direction of the head; one end communicating with the orifice. An inkjet recording head characterized in that it has two ink supply tubes. 2. The inkjet recording head according to claim 1, wherein an ink chamber is formed between the ink supply pipe and the orifice and between the ink supply layer and the ink discharge port.