JPH01285356A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To prevent an unsatisfactory ink discharge when nozzles are unused for a long time and to enable a high-speed recording at a high drive frequency, by providing ink discharge nozzles, an ink liquid chamber connecting to the nozzles, and a holding means holding a bubble in a part of the ink liquid chamber. CONSTITUTION:During an ink loading operation or an ink discharge recovery operation, an ink is loaded or supplied from spare tank 107 to nozzles 105 through an ink supply tube 106 and a relay liquid chamber 104. At this time, an operation suitable for holding a bubble 502 in a bubble holding chamber 501 provided in a part of the relay liquid chamber 104 is carried out. Since the bubble stagnating chamber 501 is so constructed that the open area of an inlet is smaller than the area of the center part thereof and an outlet is not provided, the chamber 501 can always hold the bubble 502. In addition, because the bubble holding chamber 501 is positioned so as not to prevent an ink flow, the bubble 502 existing in the bubble stagnating chamber 501 helps a rapid refilling. Therefore, a high-speed and stable ink discharge is enabled, and a high-quality recording image is made available.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an inkjet recording head that records images and the like by depositing ink droplets ejected and flown from ink ejection ports onto a recording medium such as paper.

[Prior Art] Conventionally, a liquid jet recording method (inkjet recording method) is known in which recording is performed by ejecting and flying ink. This method allows high-speed recording, low noise, high recording quality, and easy color image recording.
It also has the excellent feature of being able to record on plain paper.

An inkjet recording device used in such an inkjet recording method generally includes an ink ejection opening (orifice) for ejecting ink as flying droplets;
An inkjet recording head comprising an ink flow path (nozzle) communicating with the orifice and an ejection energy generating means provided in a part of the nozzle for applying ejection energy to the ink in the nozzle to form flying droplets. ing.

Printing by the print head is performed by driving the ejection energy generating means to supply ejection energy to the ink in the nozzles, ejecting the ink as flying droplets from the orifice, and making the droplets adhere to the print medium.

The ink used for recording with such an inkjet recording device generally consists of a solute component such as a pigment or dye, and mainly water, or water and a water-soluble organic solvent or a non-aqueous solvent to dissolve or disperse the solute component. and a solvent component consisting of a solvent.

FIG. 2 is a sectional view showing the configuration of a conventional example of a recording head and an ink supply system in an inkjet recording apparatus.

In FIG. 2, 101 indicates a recording head, and the recording head 101 has a plurality of orifices (ink ejection ports) 103, a plurality of nozzles (ink flow paths) 105 consecutively provided in each of the orifices 103, and each of the nozzles 105. It is composed of a communicating relay liquid chamber 104. In addition, a discharge energy generating body 1 such as a heating resistor is disposed inside the nozzle 105.
02 is installed. The ejection energy generator 102 generates air bubbles in the nozzle 105 by driving pulses based on recording information, and ink droplets are ejected from the orifice 103 as the air bubbles expand and contract.

Further, 106 indicates an ink supply pipe, and 107 indicates a reserve tank. The ink supply pipe 106 communicates the relay liquid chamber 104 with the reserve tank 107, so that ink is supplied from the reserve tank 107 to the relay liquid chamber 104.

The pressure caused by the bubbles generated in the ejection energy generator 102 is applied to the orifice 103 direction and the relay liquid chamber 10 via the ink.
It is transmitted in four directions. The pressure transmitted in the direction of the orifice 103 pushes the ink in the nozzle 105 out of the orifice 103 to form flying ink droplets, and the flying ink droplets adhere to the recording surface to perform recording. When the flying ink droplets leave the recording nozzle, depending on the ejection amount of the flying ink droplets,
The ink in the nozzle 105 compresses and pulls the meniscus, causing the meniscus at the orifice to retreat;
After a certain period of time, the meniscus returns to its initial state before ejection due to the surface tension of the ink from the point at which the retraction reaches its maximum (this process of return is called refilling). By repeating this mechanism, inkjet recording always maintains stable ejection, making it possible to record high-quality images.

[Problems to be Solved by the Invention] However, if ejection continues with the refill incomplete, the meniscus will not completely return to its initial state, and the amount of ink in the ejection direction will decrease, causing dots on the recording paper. As the diameter becomes smaller and the ejection speed becomes unstable, the adhesion position of the ink droplets on the recording paper varies, resulting in problems such as extremely deteriorating image quality.

Particularly in an inkjet recording apparatus equipped with a large number of nozzles, as shown in FIG. 3(A), pressure is generated by expanding air bubbles 108 in a large number of nozzles simultaneously or with a slight time difference for ejection. When this happens, the total amount of pressure that pushes the ink toward the rear relay liquid chamber 104 increases, and as a result, a force that moves the ink in the opposite direction to the ejection direction acts.

Next, when the meniscus 109 retreats and refilling starts as shown in FIG. 3(B), it is necessary to move the rear ink rapidly and in large quantities in the ejection direction in conjunction with the refilling. However, in order to move a large amount of ink instantly at the start of recording, a force is required to overcome the inertial force of this large amount of ink. Especially when there are many nozzles, the total pressure generated by the ejection energy generator 102 is large. As a result, the amount pushed backwards and therefore the amount returned by refilling increases, and the influence of inertia increases.

As a result, when the meniscus 109 returns to its initial state, the return time is delayed, and ejection is repeated before the meniscus 109 completely returns to its initial state as described above, resulting in a phenomenon in which image quality is extremely degraded. bring.

FIG. 4(^) is a diagram for explaining the behavior of the meniscus mentioned above, and FIG. 4(B) is a top view of the nozzle for explaining the retreat of the meniscus in the orifice and the amount of the retreat. .

In FIG. 4(A), the horizontal axis indicates time t, and the vertical axis indicates the meniscus retreat amount a. Further, in FIG. 4(B), the length indicated by 1 defines the amount of retreat of the meniscus 109.

In FIG. 4(A), meniscus regression curves are shown separately for the case of one nozzle discharge and the case of all nozzle discharge. In the case of one discharge, the time t when the drive pulse is applied. The meniscus 109 rapidly retreats from time to' when a predetermined time has elapsed due to ink ejection, etc., and reaches its maximum value at times t and l. Thereafter, the meniscus 109 gradually returns to its initial state due to the restoring force due to the surface tension of the meniscus, and at time t, the meniscus 109 completely returns to complete the filling.

When multiple tubes are discharged, the maximum value of the retreat amount reached at t21 is smaller than when one tube is discharged, and the refill speed is also lower.

This is because as the number of ejected ink increases, the total pressure behind the nozzles increases, but the amount of pressure absorbed because it is instantly absorbed in the liquid chamber 104 also increases, and the amount of ink only in the liquid chamber 104 is compressed Since the pressure that can be absorbed is limited, the amount of compression of the ink becomes small, and therefore the amount of retreat l of the meniscus 109 decreases. Also, the amount that cannot be compensated for by the compression of the ink in the liquid chamber 104 becomes a force that moves the ink backward.
This force is in the opposite direction to the force that pulls the ink due to the surface tension of the meniscus 109. Therefore, the refill speed is also extremely slow at the beginning.

Even if the above phenomenon occurs, if the drive frequency is such that the next drive pulse is generated after time t2, no deterioration in image quality will be observed. In this case, the meniscus retreat amount l before time t2, especially at time t3 when the repetitive drive pulse is generated.
It is recognized that image quality deteriorates when the thickness is 30 μm or more.

As a result, refill delay becomes an important problem during high frequency drive, that is, high speed recording.

U.S. Patent 4, which solves the above problems,
578,687, providing an atmosphere opening section,
Some inks absorb pressure, but in this case, non-discharge, defective printing, etc. occur due to thickening of the ink due to ink evaporation from the atmosphere-opening part and sticking of the ink to the nozzle.

Furthermore, there is a drawback that the device for preventing air bubbles from getting into the liquid chamber due to vibrations and the like, and the device for preventing dust from getting into the liquid chamber is complicated.

Therefore, the purpose of the present invention is to solve the above-mentioned conventional problems,
It is an object of the present invention to provide an inkjet recording head that is unlikely to cause ink ejection failure even when nozzles are not used for a long period of time, and is capable of high-speed recording using a high driving frequency.

[Means for Solving the Problems] To this end, the present invention includes a nozzle for discharging ink, an ink chamber communicating with the nozzle, and a retention means for retaining air bubbles in a part of the ink chamber. It is characterized by

[Function J] According to the above configuration, it is possible to retain air bubbles in the ink liquid chamber, and the air bubbles contract or expand according to the ink pressure in the ink liquid chamber by volume conversion of the pressure. The ejection pressure generated is absorbed in the ink chamber by the contraction of air bubbles. Further, pressure for returning the meniscus to its initial state is applied to the ink by the expansion of the bubbles.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

Before explaining the present invention in detail, the principle of the present invention is explained in Fig. 5 (A
) and (B).

5A and 5B are cross-sectional views of a recording head similar to that described above in FIG. This shows a state in which air bubbles 401 remain in a portion where the flow of ink related to other ink ejections cannot be prevented.

When multiple nozzles 105 generate pressure for discharge by expanding bubbles 108 in multiple nozzles 105 simultaneously or with a slight time difference, the pressure for discharge is generated.
), a pressure is generated that pushes the ink toward the relay liquid chamber 104 at the rear, but at this time, the air bubbles 401 undergo volume conversion of the pressure, contract, and absorb the pressure that pushes the ink.

Next, as shown in FIG. 5(8), when refilling is started, it is necessary to rapidly move the entire ink behind the nozzle 105, and the driving force for this is the surface tension of the meniscus 109. At this time, the bubble 401 performs a volume conversion of pressure and expands, contrary to the case shown in FIG. 4(A), and serves to help the surface tension of the meniscus 109. As a result, the inertia of the ink can be overcome and refilling can be performed quickly.

However, it is difficult to keep the bubbles 401 in the relay liquid chamber 104 of the recording head 101 in the same state all the time. Therefore, the present invention is designed so that air bubbles always remain in the relay liquid chamber 104 without providing any particularly complicated tS operation or mechanism, and FIGS. 1(A) and 1(B) are examples thereof. .

FIGS. 1(^) and 1(B) are cross-sectional views of recording heads showing two embodiments of the present invention.

In FIG. 1(A), during an ink filling operation or an ink discharge recovery operation, ink flows from a reserve tank 107 through an ink supply pipe 106, passes through a relay liquid chamber 104, and enters a nozzle 105.
filled or supplied. At this time, an appropriate operation is performed so that the bubbles 502 are retained in a bubble retention chamber 501 disposed in a part of the relay liquid chamber 104. The bubble retention chamber 501 has a structure in which the inlet passage is narrower than the area of the center and has no outlet passage, so it is possible to retain the bubbles 502 at all times. The bubbles 50 existing in the bubble retention chamber 501 are located in a position where it is impossible to prevent
2 helps to speed up refills as per the above theory.

FIG. 1(B) is a sectional view of a recording head showing another embodiment of the present invention, in which instead of providing a bubble retention chamber 501 in the relay liquid chamber 104, a wall 503 having a cylindrical side surface shape is used to ink. They are installed at two locations where ink flow during ejection cannot be prevented. Similar to the bubble retention chamber 501, the wall 503 has a structure in which the entrance path is narrower than the area of the center and has no exit path.

[Effects of the Invention] As is clear from the above description, it is possible to retain air bubbles in the ink liquid chamber, and the air bubbles contract or expand according to the ink pressure in the ink liquid chamber by volume conversion of the pressure. As a result, the ejection pressure generated in the nozzle is absorbed in the ink chamber by the contraction of the bubbles. Further, pressure for returning the meniscus to its initial state is applied to the ink by the expansion of the bubbles.

As a result, the ink inside the nozzle is quickly filled, making it possible to eject ink stably at high speed, and to obtain a high-quality recorded image.

Furthermore, since a complicated structure for bubble retention is not required and there is no need for communication with the atmosphere, a recording head with a simple structure has the effect of making ink ejection failures due to ink thickening less likely to occur.

[Brief explanation of the drawing]

1A and 1B are cross-sectional views of a recording head showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the configuration of a conventional example of a recording head and an ink supply system, and FIG. The figure is a cross-sectional view for explaining the operation of a conventional example of a recording head, Figure 4 (^) is a line diagram showing the behavior of the meniscus,
B) is a sectional view of the nozzle for explaining the behavior of the meniscus shown in FIG. 4(A), and FIG. 5 is a sectional view of the recording head for explaining the present invention in detail. 101... Recording head, 102... Ejection energy generator, 103... Orifice, 104... Relay liquid chamber, 105... Nozzle, 106... Ink supply pipe, 107... Spare tank , 108 , 401 , 502... bubble, 109...
meniscus, 501... air bubble retention chamber, 503... wall. (A) Figure 1 Figure 2 108 ki 5 and ('A) Figure 3 tato j; t'x ty
tt de 2(A)

Claims (1)

[Claims] 1) An inkjet recording comprising: a nozzle for discharging ink; an ink chamber communicating with the nozzle; and a retention means for retaining air bubbles in a part of the ink chamber. head. 2) The inkjet recording head according to claim 1, wherein the retention means has the form of a bubble retention chamber communicating with the ink liquid chamber, and the communication portion is narrower than the inside of the bubble retention chamber. Inkjet recording head.