JPH0365796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an inkjet printer that jets minute ink droplets toward a printing medium and prints a desired image by the adhesion of the ink droplets.

(b) Prior Art It is widely known that the biggest drawback of ink droplet ejecting devices is that the orifice through which ink droplets are ejected is clogged, and various proposals have been made to prevent such clogging. ing.

FIGS. 2 and 3 are cross-sectional views for explaining a clogging prevention method for which the applicant has already applied for a patent and published the application as Japanese Patent Application Laid-open No. 14757/1983. In both figures, 1 is an on-demand type ink droplet ejecting device, and the ink droplet ejecting device 1 includes:
a piezoelectric diaphragm 2 that vibrates in a curved manner in response to an image signal;
A horn-shaped pressure chamber 3 in which the piezoelectric diaphragm 2 is disposed in the opening on the long diameter side, a thin plate-shaped vibrator 4 provided on the short diameter side of the pressure chamber 3 so as to be able to freely vibrate, and a front surface of the vibrator 4. an ink chamber 5 for holding ink; a front plate 6 facing the vibrator 4 with the ink chamber 5 in between;
A first orifice 7 with a minute diameter is bored at a location opposite to the vibration center of the vibrator 4 in the front plate 6, and a thin air layer 8a provided in front of the first orifice 7. and an air layer 8 consisting of an air straightening layer 8b, and a first orifice 7 which is opened from the thin air layer 8a of the air layer 8 and through which the ink droplets 9 jetted from the first orifice 7 pass. The second orifice 10 has a larger opening diameter that is more than twice as large.
It is equipped with. Reference numeral 11 denotes an ink tank for supplying ink to the ink chamber 5 of the ink droplet ejecting device 1, and several hundred cc of ink is stored in a bag made of polymer film or the like with low air permeability. 12 is an ink supply pipe that connects the ink tank 11 and the ink chamber 5; 13 is an ink coupler inserted in the middle of the ink supply pipe 12; The supply pipe 12 is freely attachable, and ink can be replenished by replacing each ink tank 11. 14 is the air layer 8 and the ink tank 11 of the ink droplet ejecting device 1;
A thin air layer 8a is provided between the air pump 14, the ink droplet ejecting device 1, and the thin air layer 8a of the air layer 8. An annular air rectifying layer 8b that rectifies the air flow 16 supplied from the periphery thereof, and a valve device 17 provided in the air supply pipe 15 and consisting of, for example, a three-way electromagnetic valve are respectively disposed. The valve device 17 brings the air pump 14 and the thin air layer 8a into communication during a printing operation, and sets the two in a disconnected state during a non-printing operation. A recording medium 18 is placed at a short distance in front of the second orifice 10 of the ink droplet ejecting device 1 during the printing operation in FIG. 2, and is wound around a rotating drum 19 and main scanned in the rotation direction. Ru.

FIG. 3 shows a device for filling the thin air layer 8a of the ink droplet ejecting device 1 with ink during a non-printing operation. That is, the second orifice 10 is covered with a lid 20 made of an elastic material such as rubber, and the valve device 17 cuts off communication between the air pump 14 and the air layer 8 and opens the air layer 8. When the air pump 14 is operated to pressurize the ink in the ink tank 11, the pressure of the ink in the ink chamber 5 of the ink droplet ejecting device 1 also increases, and the ink that was in an equilibrium state in the first orifice 7 finally rises. flows out from the high-pressure ink chamber 5 into the air layer 8.
When an electric signal is applied to the piezoelectric diaphragm 2 to make the vibrator 4 continuously vibrate in a curved manner to assist the ink to flow out, the balance of the ink immediately collapses and the ink flows from the first orifice 7 into the air layer 8. start. Once the ink starts to flow, even if the application of the electric signal to the piezoelectric diaphragm 2 is stopped, the pressure in the air layer 8 (air pressure) is lower than the ink pressure in the ink chamber 5, so the ink supply continues. . In this way, the first orifice 7 is covered with ink supplied into the air space 8. This ink supply is controlled by suitable detection means, for example by detecting the resistance value between the body 22 of the ink drop ejector 1 and the detection electrode 23 in the insulated air supply tube 15. That is, when the ink rises in the air supply pipe 15 and immerses the detection electrode 23, the body 22 and the detection electrode 23
The resistance value between them is drastically reduced by the ink, and the end of ink filling is detected.

Further, if the vibration of the piezoelectric diaphragm 2 is continued until the filling is completed, the filling of the ink is not only done quickly but also completely, so this method is usually adopted. When the detection means detects that the air layer 8 has been filled with ink, the air pump 14 stops operating and the pressure in the ink tank 11 gradually decreases. On the other hand, the air layer 8 is in communication with the outside air via the air supply pipe 15, and when the pressure of the ink tank 11 decreases as described above in this state, the ink supplied and filled into the air layer 8 is transferred to the ink tank 11. The valve device 17 is closed in order to allow the flow to flow backwards. Therefore, the system of the air layer 8 and the air supply pipe 15 is closed, and the backflow of ink is prevented by the so-called Torricelli principle.

As a result, the ink droplet ejecting device 1 is in a state where the air layer 8 is filled with ink in the home position indicated by (HP) in FIG. 4 during non-printing operation, and the first orifice 7 is Since it is covered with ink, clogging mainly caused by drying and adhesion of dust is prevented.

In this way, ink is supplied into the air layer 8 at the home position (HP) and the ink is supplied to the first orifice 7.
Ink droplet ejecting device 1 where clogging was prevented
is moved to the standby position (SP) and faces the gutter 21 prior to the printing operation. In this state, operate the valve device 17 to connect the air pump 14 and the air layer 8.
At the same time, the air pump 14 is operated. Then, the ink filled in the air layer 8 flows into the air flow 16 as shown by the arrow in FIG.
The liquid is pressurized from the outer circumferential direction by the cylinder, and is discharged from the second orifice 10 which is opened at the center.
This discharged ink is captured by the gutter 21 disposed opposite to each other. When the ejection operation is completed, the air flow 16 is stopped, the ink is balanced in the first orifice 7, and the ink droplet ejecting device 1 is in a standby state.

According to this structure, during non-printing operation, the air layer 8 of the ink droplet ejecting device 1 is filled with the first orifice 7.
Although the ink that prevents clogging is retained by the principle of trituration due to the blockage of the valve device 17, the ink backflow phenomenon occurs due to the expansion of the air in the air supply pipe 15 which is in the closed state. It was confirmed that there is.

(C) Problems to be Solved by the Invention That is, the ink filled in the air layer 8 is discharged into the gutter 21 prior to the printing operation without contributing to the actual printing as described above. Therefore, although the filling amount is extremely small, for example, 0.1 cc or less, the air volume trapped in the air supply pipe 15 from the valve device 17 to the air layer 8 is several cc to several tens of cc. .c., a temperature rise of about 10℃ occurs with respect to this air capacity, and if we ignore resistance to ink backflow, logically all of the ink of 0.1cc or less will flow back through the first orifice. 7 will be exposed to the atmosphere.

Note that the exposure of the first orifice 7 due to the backflow of the ink is based on the air volume when the air volume is 3 c.c., the volumetric expansion coefficient of air is approximately 3.7×10 ^-3 deg ^-1 , and the temperature rise is 10°C. When we calculated the increase in capacity, it was 0.11cc, and this increase is 0.1cc, which is the filling amount of air layer 8.
Based on exceeding the following:

The present invention has been made in view of the above, and its purpose is to eliminate the expansion of the air in the ink filled in the air layer to cover the first orifice during non-printing operations. The purpose is to prevent backflow.

(d) Means for Solving the Problems The inkjet printer of the present invention is equipped with an ink droplet ejecting device that fills the air layer with an anti-clogging liquid to prevent clogging of the first orifice during non-printing operations. The air flow supply system that connects the air flow generation source that generates the air flow supplied to the air layer and the ink droplet ejecting device is provided with an opening means that is constantly open to the atmosphere, and the ink tank and the ink The present invention is characterized in that the ink supply system connected to the droplet ejecting device is provided with a valve device that sets the ink supply system to a cutoff state during non-printing operations.

(E) Effect According to the present invention, the air in the air flow supply system that has expanded in volume and increased due to the rise in environmental temperature during non-printing operation can be caused to leak from the opening means, and the air pressure in the air flow supply system can be almost reduced. In addition to being able to maintain a constant amount of ink, backflow of ink can be reliably prevented by a valve device that sets the ink supply system to a cutoff state.

(F) Embodiment FIG. 1 shows the inkjet printer of the present invention during non-printing operation, and the same parts as those of the conventional printer are given the same numbers and the explanation thereof will be omitted. That is, the difference is that the air supply pipe 15 of the air flow supply system from the air pump 14 acting as an air flow generation source to the air tank 8 of the ink droplet ejecting device 1 is
A small diameter opening 22 is provided as an opening means for constantly opening the inside to the atmosphere. The microscopic diameter of the opening 22 is, for example, about 10 times or less than the second orifice 10, and more preferably 1 time or less.

Then, such a minute diameter opening 22 is connected to the air supply pipe 1.
Conventionally, in order to open the inside of the air supply pipe 15 only when the air layer 8 is filled with ink, two-way solenoid valves are combined to form a three-way valve. Valve device 17
can be formed by one two-way solenoid valve. That is, even if the valve device 17 consisting of one two-way solenoid valve is in the closed state during the ink filling operation,
The air supply pipe 15 is in an open state through the aperture 22, and the air inside the air supply pipe 15 accompanying ink filling is exhausted from the aperture 22. Therefore, ink filling can be performed without adopting a three-way valve configuration. The operation is executed without any problem.

When the surrounding environmental temperature rises and the air stagnant in the air supply pipe 15 expands during the non-printing operation shown in FIG. The small diameter opening 22 provided between the device 17 and the ink droplet ejecting device 1
Leak sequentially from Therefore, the air pressure within the air supply pipe 15 does not increase as the temperature rises, but only exhibits a substantially constant value, and the ink filled in the air layer 8 does not flow back.

Incidentally, in the conventional example, the ink filled in the air layer 8 was held by the principle of trichrye by air-tightly closing the air supply pipe 15 as in the above-mentioned example, but in this embodiment, the ink filled in the air layer 8 Supply pipe 15
Since it is always in an open state, it cannot be held according to the Toritietsuri principle. Therefore, in this embodiment, the thickness of the air layer 8 is set to be extremely thin, and the ink is retained by capillary action.

In order to more reliably prevent backflow of ink, a valve device 23 consisting of a normally closed two-way valve or the like is inserted in the middle of the ink supply pipe 12, and the ink supply pipe 12 is shut off during non-printing operations. It is set.

In this way, the air supply pipe 15 is always open due to the presence of the minute openings 22, and although it is possible to prevent the filled ink from flowing back due to air expansion during non-printing operations, However, the air flow 16 starting from the air pump 14 and being supplied to the air layer 8 of the ink droplet ejecting device 1 inevitably leaks through the minute openings 22 . Therefore, the air pressure of the air flow 16 departing from the air pump 14 during the printing operation is set to be higher than that of the conventional example, taking into account the reduction in pressure due to leakage from the apertures 22.

(G) Effects of the Invention As is clear from the above description, the present invention is provided with an opening means for constantly opening the inside of the air flow supply system to the atmosphere, so that volume expansion due to an increase in environmental temperature during non-printing operation is prevented. The increased air in the air flow supply system can be leaked out from the opening means, and the air pressure in the air flow supply system connected to the air layer filled with the anti-clogging liquid of the ink droplet ejecting device can be maintained almost constant. In addition, backflow of ink can be reliably prevented by a valve device that sets the ink supply system to a cutoff state. Therefore, the anti-clogging liquid in the air layer is filled and held within the predetermined air layer, and the intended purpose is achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention during non-imprinting operation, FIGS. 2 to 5 show a conventional example, FIG. 2 is a sectional view showing during printing operation, and FIG. 3 4 is a sectional view showing the ink filling operation, FIG. 4 is a schematic diagram showing the operation positions of the ink droplet ejecting device, and FIG. 5 is a sectional view showing the ink discharging operation. DESCRIPTION OF SYMBOLS 1... Ink droplet ejecting device, 7... First orifice, 8... Air layer, 10... Second orifice, 14... Air pump, 15... Air supply pipe,
17... Valve device, 22... Hole opening, 23... Valve device.

Claims (1)

[Claims] 1 It has first and second orifices arranged coaxially with an air layer in between, and the ink droplets ejected from the first orifice during the printing operation are transferred from the outer periphery of the air layer to the second orifice. The ink is ejected from the second orifice through an air flow supplied toward the ink, and during non-printing operations, the air layer is filled with an anti-clogging liquid to prevent clogging of the first orifice. In an inkjet printer equipped with a droplet jetting device, an airflow supply system that connects an airflow source that generates an airflow to be supplied to the air layer and the ink droplet jetting device has an air flow supply system that connects the inside of the inkjet printer to the atmosphere. An ink cartridge characterized in that an opening means that is always open is provided, and an ink supply system that connects an ink tank and an ink droplet ejecting device is provided with a valve device that sets the ink supply system to a cutoff state during non-printing operations. et printer.