JPH0343985B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an inkjet recording device used in color printers, facsimile machines, and the like.

Structure of the Prior Art and its Problems FIG. 1 is a sectional view of an on-demand type ink jet head disclosed in Japanese Patent Publication No. 53-45698. In this ink jet head, the ratio of the diameter of the ink ejection port 2 to the coupling passage 3 and the ratio of the diameter of the ink ejection port 2 to the thickness of the second ink chamber 4 are 1/1/1, respectively.
It is specified that it is 4-4. That is, if the diameter of the ink discharge port 2 is 40 μm, the diameter of the coupling passage 3 and the thickness of the second ink chamber 4 are each 10 to 160 μm.
becomes.

When the diameter of the coupling passage 3 is within the above range, the vibration applied to the ink supply system (not shown), that is, the pressure fluctuation of the ink in the ink supply pipe caused by scanning the head carriage, is caused by the cylindrical scanning. The scanning speed is several
mm/sec or less, the holding force P of the ink meniscus at the ink ejection port 2 has sufficient margin, and air suction does not occur. Since no air bubbles are sucked into the head, the head operates stably.

Incidentally, the meniscus holding force P at the ink ejection port 2 can be expressed as P=2Tcosθ/r·g×10 ⁻³ (Kg/cm ² ). However, T is the surface tension of the ink, cos θ is the contact angle, r is the radius of the ink discharge port 2, and g is the acceleration of gravity. In addition, with normal water-based ink, if the diameter of the ink ejection port 2 is 40 μm, the meniscus retention force P
shows a value of approximately 0.04 to 0.045 Kg/cm ² , and when a pressure fluctuation exceeding the meniscus holding force occurs, air is sucked in from the ink ejection port 2 or, conversely, ink is ejected.

However, in the plane scanning method in which the head carriage is scanned left and right at high speed, the ink supply pipe is also swung left and right as the head moves, causing large force fluctuations within the ink pipe. For this reason,
The range of scanning speeds in which the ink meniscus at the ejection port 2 can withstand the pressure fluctuations is very narrow, up to several tens of cm/second at most.

However, with the passage of time, there has been a demand for higher speeds in plane scanning methods, and the scanning speed has also increased to 1.5
The speed has reached m/s. In order to achieve such a high scanning speed, for example,
It is necessary to use the fluid element disclosed in Japanese Patent No. 176170 for alleviating pressure fluctuations.

However, even if the above-mentioned fluidic elements are used together,
In the operating environment, for example, when operating in an atmosphere of 40°C or higher, the physical properties of the ink, piping dimensions, hardness, etc. change significantly, and the reduction in the meniscus retention force and the reduction in the performance of the fluidic element combine to make it easier for air bubbles to be inhaled. , recording may become impossible or unstable. The reason for this is that the ink pressure fluctuations in the ink supply pipe cannot be fully absorbed by the fluid element, and the meniscus of the ink discharge port 2 is torn, and the air bubbles sucked into the second ink chamber 4 are sucked into the first ink chamber 5. It happens. Normally, the diameter of the bubbles inhaled during recording operation is usually less than several hundred μm.
As shown in Fig. 2, since the distance between the ink ejection port nozzle 2 and the coupling passage 3 is close, 10 to 160 μm, the inhaled air bubbles 7 block the coupling passage 3, and when the head is driven. These air bubbles 7 are sucked into the first ink chamber 5 from the coupling passage 3 instead of ink, causing head malfunction.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an inkjet recording device which improves the above-mentioned drawbacks and is capable of stable recording over a wide temperature range without air bubbles being sucked into the first ink chamber.

Structure of the Invention The present invention provides an on-demand inkjet having a two-chamber structure, in which a first pressure chamber and a second pressure chamber are connected to each other so as to be openable and closable in accordance with the pressure generated and changed in response to a predetermined signal. The connecting means has an ink inflow passage and a connecting passage that always connects the first and second pressure chambers regardless of pressure, and a connecting means that connects the first and second ink chambers. The ink jet recording apparatus is configured such that the ink inflow passage is closed when ink is ejected and is opened when ink is not ejected.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which the ink discharge port 2
This is an embodiment in which an air nozzle 9 having an opening is provided opposite to the inkjet head and is applied to an ink jet head that also uses an air flow. In the present invention, it is not necessarily necessary to provide the air nozzle 9 and eject an air stream from the air nozzle 9, but in actual inkjet recording, it is preferable to use the air stream in combination.

In FIG. 3, the ink chamber is divided into a first ink chamber 5 and a second ink chamber 4, and the first ink chamber 5 is adjacent to a pressure raising device consisting of a piezo vibrator 61 and a metal diaphragm 62.
The first ink chamber 5 and the second ink chamber 4 are partitioned by a flexible plate wall 11 and connected by a connecting passage 3 provided in the plate wall 11. The plate wall 11 further has an ink inflow passage 14 formed therein. This ink inflow passage 14 is normally blocked by an auxiliary member 15. First ink chamber 5 and second ink chamber 4
An opening for filling ink is provided above, and is closed with screws 13 and 12 after filling with ink. The second ink chamber 4 is supplied with ink from an ink reservoir (not shown) via an ink supply pipe 8. 10
An air supply pipe discharges an air stream from an air nozzle 9, and in response to an electric signal applied to a pressure raising device 6, ink droplets discharged from an ink discharge port 2 fly at high speed.

The plate wall 11 functions as a diaphragm-type check valve when the head is operated, and prevents air bubbles from being sucked in from the coupling passage 3. That is, this diaphragm type check valve opens only when ink is supplied to the first ink chamber 5, and closes when ink is pressurized and discharged.

The check valve is deflected toward the second ink chamber 4 when the ink is pressurized, and air bubbles accumulated in front of the coupling passage 3 can be discharged to the outside together with the ink.

Furthermore, the pressure wave from the coupling passage 3 and the pressure increase in the second ink chamber 4 due to the deflection of the diaphragm combine to efficiently discharge ink from the second ink chamber 4.

To explain this a little more concretely,
4a to 4d are the ink ejection ports 2 in FIG.
This is an enlarged cross-sectional view showing changes in the operating state in the vicinity, and FIG. a shows a state in which air bubbles 7 sucked in from the ink discharge port 2 remain in the second ink chamber 4. Figure b shows a state in which an electric signal is applied to the piezoelectric vibrator 61 in Figure 3, and the volume increases in the first ink chamber 5, resulting in negative pressure inside the first ink chamber 5, which is made of a thin plate. The plate wall 11 is bent toward the first ink chamber 5,
At the same time, the ink in the second ink chamber 4 is transferred to the plate wall 1.
The ink flows into the first ink chamber 5 from the inlet passage 14 and the coupling passage 3 provided in the ink chamber 1 . In this case, even if there is a bubble 7 in front of the coupling passage 3, if the diameter of the coupling passage 3 is less than 1/4 of the diameter of the ink discharge port 2, the meniscus retention force in the coupling passage 3 will be Approximately 0.16 to 0.22, which is four times the meniscus retention force of
Kg/ ^cm2 , and if the inflow resistance of the inflow passage 14 is designed to be sufficiently smaller than the meniscus retention force in the coupling passage 3, air bubbles will not be sucked into the first ink chamber 5 from the coupling passage 3, and the ink is the inflow passage 14
The ink is then supplied to the first ink chamber 5. Next, the piezo vibrator 6 is bent toward the first ink chamber 5, and the first
When the volume decreases in the ink chamber 5, as shown in Fig. 4c and d.
As shown in , the ink in the first ink chamber 5 is pressurized, and the plate wall 11 made of a thin plate
At the same time, the inflow passage 14 provided in the plate wall 11 is partially blocked by the auxiliary member 15 constituting the first ink chamber 5, and the ink pressure is effectively transmitted to the plate wall 11 and the coupling passage 3. . Then, due to the combination of the high-speed ink flow flowing out from the coupling passage 3 and the pressure rise in the second ink chamber 4 caused by the deflection of the plate wall 11, the bubbles 7 stagnant near the coupling passage 3 become ink droplets. Together with this, the ink is ejected from the ink ejection port 2 and the normal state is restored.

FIG. 5 shows a specific embodiment of the present invention, in which figure a is a sectional view of the vicinity of the nozzle, and figure b is a view taken in the direction of arrow A. In FIG. 5, an annular joint 17 of a plate wall 11 and an auxiliary member 15, which are made to a predetermined size by etching or electroforming, is joined.
In this case, a bonding method such as diffusion bonding that leaves almost no gap in the non-bonded portion is used.

Showing the dimensions in this example, D is 2 to 5
mmφ, d is 1 to 3 mmφ, width of inflow passage 14 is 0.05
The thickness of the plate wall 11 is 0.02 to 0.2 mm.
Note that the number and width of the bridges 18 forming the inflow passage 14 in the figure are not limited to those in this figure, and may vary depending on the thickness of the plate wall 11, the spring constant, the dimensions of D and d, etc. It is selected as appropriate.

Effects of the Invention As described above, the present invention provides an inlet passage which functions only when ink is supplied to the first ink chamber, in addition to the coupling passage, in the plate wall forming the coupling passage of the ink jet head. As a result, air bubbles sucked from the ink discharge port are less likely to be sucked into the first ink chamber from the coupling passage, and by operating the piezo vibrator, air bubbles sucked into the second ink chamber are also prevented from being sucked into the ink chamber from the ink discharge port. The inkjet recording device is ejected together with the inkjet droplets and is always stable.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional inkjet head, FIG. 2 is an enlarged sectional view of the vicinity of the nozzle showing the state in which air bubbles are sucked in in FIG. 1, and FIG. 3 is an embodiment of the inkjet head according to the present invention. 4A to 4D are sectional views of the vicinity of the nozzle showing the operating state of the ink jet head in FIG. 3, and FIGS. 5A and 5B are structural views of the plate wall in one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Ink jet head, 2... Ink discharge port, 3... Connection passage, 4... Second ink chamber, 5
...First ink chamber, 6...Pressure increase device, 7...
Air bubble, 8... Ink supply passage, 9... Air nozzle, 10... Air inflow passage, 11... Plate wall, 1
2, 13... Ink filling screw, 14... Inflow passage, 15... Auxiliary member, 16... Head body,
17... Annular joint, 18... Board wall bridge,
61... Piezo vibrator, 62... Metal diaphragm.

Claims (1)

[Scope of Claims] 1. Pressure generating means for ejecting ink from an ink ejection port by generating a change in pressure in response to a predetermined signal, and a first ink chamber connected to the pressure generating means. an ink supply passage connected to an ink supply source and a second ink chamber communicating with the ink discharge port; and a second ink chamber communicating with the ink discharge port and the first and second ink chambers in response to the pressure generated and changed in response to the predetermined signal. The first and second ink chambers are connected by an ink inflow passage that connects the pressure chambers so as to be openable and closable, and a connection passage that constantly connects the first and second pressure chambers regardless of the pressure. An inkjet recording apparatus comprising: a coupling means, wherein an ink inflow passage of the coupling means is closed when ink is ejected and is opened when ink is not ejected. 2. The coupling means includes a moving member at least partially movable in a predetermined direction, and by the movement of the moving member, the ink inflow passage of the coupling means is closed when ink is ejected and opened when ink is not ejected. An inkjet recording apparatus according to claim 1, characterized in that: 3. The predetermined moving direction of the moving member substantially coincides with the connecting direction connecting the first and second ink chambers, and when ink is ejected, the moving member moves toward the second ink chamber, thereby opening the ink inflow passage. 3. The ink jet recording apparatus according to claim 2, wherein when the inkjet ink is closed and the ink is not ejected, the moving member moves toward the first ink chamber to open the ink inflow passage. 4. The coupling means further includes an auxiliary member, and the moving member is a movable plate member extending in a direction substantially perpendicular to the coupling direction connecting the first and second ink chambers, and is connected to the ink inflow passage. The coupling passage is provided in the movable member and extends substantially in the coupling direction, and when ink is ejected, the movable member moves toward the second ink chamber and comes into contact with the auxiliary member, thereby closing the ink inflow passage and preventing ink from flowing. 4. The inkjet recording apparatus according to claim 3, wherein during ejection, the moving member moves toward the first ink chamber and is released from contact with the auxiliary member to open an ink inflow passage. 5. The inkjet recording device according to claim 4, wherein the coupling passage is provided approximately coaxially with the ink discharge port. 6 The diameter of the coupling passage is 1/4 of the diameter of the ink discharge port.
Claim 1 characterized in that it is less than or equal to
The inkjet recording device according to any one of items 1 to 5.