JP2708519B2 - Inkjet recording head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording head, and more particularly, to an ink jet recording head that generates bubbles in ink by thermal energy and discharges ink by a change in the state of the bubbles.

[Prior Art] In an ink jet recording head of this type, an ink liquid path provided with a discharge heater for generating thermal energy is provided adjacent to a common liquid chamber for supplying ink to a rear end thereof. Was. In this configuration, if the ink ejection for recording is repeated, the dissolved gas in the ink generated due to the change in the state of the bubbles remains in the ink even after the ink is ejected, and cannot be redissolved in the ink and becomes fine bubbles. It is left in the ink liquid path. This is pushed out to the rear common liquid chamber and stays in the common liquid chamber, and the fine bubbles that are sent out one after another gather gradually and become large. Thereafter, when the size of the air bubbles increases until the common liquid chamber is closed, the air bubbles move in the direction of the ink liquid path according to the flow of the ink, and the air bubbles that enter the ink liquid path enter and stop the flow of the ink.

Details of this principle will be described with reference to FIGS. 11 (A) and (B). As shown in FIG. 11 (A), in the above-described recording head, thermal energy is applied to the ink, and expansion / contraction of the discharge bubble 1 is performed by vaporization / condensation of the ink, and this is used as the discharge energy. . At this time, dissolved gases and the like contained in the ink are also vaporized at the same time, but these dissolved gases cannot be redissolved at a high speed following the shrinkage of the bubbles 1, and thus are left as fine bubbles 2 in the ink liquid path.

Among the remaining bubbles 2, the bubbles 2 existing behind the heater 51 move toward the common liquid chamber 7 by a compression wave generated at the time of the next bubbling. In such a case, when the bubble 2 is in the ink liquid path 6, it moves at high speed because the cross-sectional area in the ink liquid path is small, but when the bubble reaches the common liquid chamber 7, the cross-sectional area of the common liquid chamber becomes The speed drops rapidly because it is larger than that of the fluid path. Therefore, fine bubbles 2
Stay inside the common liquid chamber 7.

Bubbles that move and accumulate one after another as ink is ejected for printing coalesce and gradually increase in size as bubbles 3 in the common liquid chamber. When the size of the coalesced bubbles 3 is increased, the ratio of the surface area to the volume is reduced, so that the time required for dissolution increases extremely.

Further, as the size increases as shown in FIG. 11 (B),
The bubble 3 blocks the cross-sectional direction of the common liquid chamber 7, thereby blocking the supply of ink to each ink liquid path 6. That is, when the bubbles 3 grow to this extent, the bubbles 3
To stop the ink ejection.

Further, even if the bubbles 3 do not completely block the direction of the cross-sectional area of the common liquid chamber 7, the ink flow is prevented. In such a case, when the ejection duty becomes high and a large ink supply speed to the ink flow path is required, the probability of non-ejection increases.

Conventionally, when such non-ejection occurs, a method of sucking ink from the ejection port by a recovery pump provided in the ink jet printer body and thereby sucking the bubbles 3 out of the ink flow path to perform ejection recovery has been proposed. Has been taken.

[Problems to be Solved by the Invention] By the way, in recent years, when the ink of a certain amount of ink is integrally used up to increase the maintainability of the user or to reduce the cost of the recording head, the recording head is also replaced. Disposable ink jet recording heads are attracting attention.

In the case of this type of print head, about 200c from the viewpoint of carriage size, body size, running cost, etc.
The recording head is equipped with an ink amount of c or less. Therefore, the ejection recovery system of the printer is greatly simplified unless the ejection failure caused by the accumulation of bubbles in the common liquid chamber occurs until the ejection of the ink amount is completed.

Further, the present invention is not limited to the disposable type ink jet recording head, and the ejection recovery system and the operation thereof can be simplified if the ejection failure does not occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a method in which a residual gas in an ink liquid path generated by deposition of a dissolved gas in an ink by thermal energy grows. It is an object of the present invention to provide an ink jet recording head that can prevent a passage or a liquid chamber from being blocked and always supply good ink.

[Means for Solving the Problems] In the present invention, for this purpose, a discharge port for discharging ink and a thermal energy generating element which communicates with the discharge port and generates heat energy used for discharging ink are arranged. An ink passage provided, a common liquid chamber provided for supplying ink to the ink passage along with ink ejection, and a supply of ink to the common liquid chamber disposed behind the ink passage. The common liquid chamber has a cross-sectional area larger than the cross-sectional area of the ink liquid path, and has a cross-sectional area smaller than the cross-sectional area of the common liquid chamber. An inkjet recording head communicating with the
A bubble trap is provided on at least one of the walls of the bubble elimination chamber and the common liquid chamber.

[Operation] According to the above configuration, in addition to the cross-sectional area of the bubble elimination chamber being smaller than the cross-sectional area of the common liquid chamber, the bubble elimination chamber provided between the common liquid chamber or the common liquid chamber and the ink liquid path. Since the bubble trap portion is provided on any of the walls, the minute bubbles once removed from the ink liquid path to the bubble elimination chamber or the common liquid chamber side are retained in the trap section, and the backflow to the ink liquid path side is prevented. . As a result, the bubbles are gradually eliminated toward the common liquid chamber, where they grow and stay.

Examples Hereinafter, the present invention will be described in detail with reference to the drawings.

Before describing the embodiments, the principle of the present invention will be described with reference to FIGS. 1 (A) and 1 (B).

As is clear from FIG. 1A, the fine bubbles 2 generated each time ink is ejected move toward the common liquid chamber every time ink is ejected. Thereafter, the fine bubbles 2 reach the bubble elimination chamber 10 according to the present invention, but since the cross-sectional area of the bubble elimination chamber 10 does not increase so rapidly with respect to the ink liquid path 6 as the common liquid chamber 7 does, The bubble moving speed in the exclusion chamber 10 does not decrease so much, and the speed for moving the bubbles is secured.

As a result, the fine bubbles are slightly merged into residual bubbles 2A and move toward the common liquid chamber. In the common liquid chamber 7, the bubbles 2A further coalesce and grow into accumulated bubbles 3A.

However, as shown in FIG. 1B, even if the accumulated bubbles 3A are pushed forward during ink supply, the bubbles 3A are prevented from moving in the ink liquid path direction due to the presence of the bubble elimination chamber 10. Since there is no sharp change in the cross-sectional area between the cross-sectional area of the common liquid chamber and the cross-sectional area of the ink liquid path as in the related art, the flow rate at the time of ink supply generated at the boundary does not increase and bubbles
3A cannot enter forward from the exclusion chamber 10. Further, in this case, as shown in FIG. 1 (B), the bubble exclusion chamber 10 secures communication with the common liquid chamber 7 in the lateral direction, so that the exclusion chamber 10
The ink can be supplied to the ink liquid path 6 through the above-mentioned configuration, thereby avoiding a problem that the ejection is stopped.

And if the recording head is of a disposable type,
If the common liquid chamber 7 is sufficiently large with respect to the amount of ink to be ejected, the above-described non-ejection does not occur while the ink in the ink cartridge is used up, and the recovery system of the printer can be simplified. Become.

FIG. 2 shows an ink jet recording head according to one embodiment of the present invention, which is a disposable one in which an ink tank is integrated.

As shown in FIG. 1, the ink jet recording head shown in FIG. 1 has a top plate integrally formed with a concave portion (hereinafter, a groove) for forming an ink liquid path, a bubble elimination chamber, and a common liquid chamber, and a discharge energy. (Hereinafter referred to as "heater board") formed by forming an electrothermal transducer (hereinafter referred to as "discharge heater") to generate electric discharge and Al wiring for supplying an electric signal to this substrate on a Si substrate by film forming technology The recording head main body (not shown) is formed by performing the above operation, and only the discharge port 8 is shown in FIG.

In the figure, reference numeral 600 denotes a sub ink tank disposed adjacent to the recording head main body.
And the body is supported by lids 300 and 800.
Further, reference numeral 1000 denotes a cartridge main body, and 1100 denotes a lid member of the cartridge main body. An ink tank is built in the cartridge body, and supplies ink to the sub ink tank 600 as appropriate. Hereinafter, an embodiment using the configuration shown in FIG. 1 will be described.

In FIG. 1, a heating element 51 (discharge heater) formed in advance as a thin film is provided on a substrate 5 formed of Si, glass, ceramics or the like. On this substrate (heater board) 5, a mold top plate 4 having a concave portion for forming an ink liquid path 6, a common liquid chamber 7, and a gas exclusion chamber 10 is bonded in advance. The top plate 4 is made of a resin such as PS, PSF, PES, modified PPO, ABS, POM, PPS, and the like. The heater board 5 is installed on a base plate (not shown) provided with a PCB or the like, and forms a recording head body. The wiring and the wiring provided on the heater board 5
Electrical connection is made by Al wire bonding. The recording head body thus configured is attached to an ink tank in which ink is retained in an absorber such as urethane foam, and a communication port is provided between the tank and the head body to supply ink from the absorber. It is a disposable type ink jet recording head as shown in FIG.

As the heater board 5, a substrate provided with a functional element of a diode in advance to reduce the number of wiring outlets and driven in a matrix was used.

The design values of the ink liquid path 6 are as follows: the discharge port is a circular hole having a diameter of 32 μm, the height of the ink liquid path 6 is 40 μm, and the ink liquid path length is 400 μm.
μm, the height and length of the bubble elimination chamber 10 are 80 μm and 200 μm.
μm, the height of the common liquid chamber 7 was 500 μm, and its length was 2 mm.

The recording head has 64 ejection ports, and has a recording density
Characters were recorded at 360 dpi and a driving frequency of 4 KHz to evaluate the examples.

As a result, the recording head without the bubble elimination chamber 10 did not discharge at a discharge amount of 2 × 10 ⁷ pulses / head, but the recording head with the bubble elimination chamber of the present example had 6 × 10 ⁸ pulses / head. Non-discharge was performed at about 30 times the discharge amount, and it was possible to perform more printing than before.

In general, in normal printing, an ink liquid path to be ejected and an ink liquid path to not be ejected are mixed depending on a recording signal. In such a case, a phenomenon may occur in which fine bubbles flow backward between a portion where ejection is continuously performed and a portion where ejection is not performed. In order to prevent such a phenomenon, the following other embodiments are proposed.

FIG. 3 is a sectional view of a recording head body showing another embodiment of the present invention.

It is desirable that the bubble elimination chamber 10 has a structure in which the bubbles are easily pushed backward as much as possible and the bubbles in the common liquid chamber 7 are hard to enter. Therefore, in this example, the upper wall 10A of the bubble elimination chamber 10 has a wavy structure, and the shape is such that bubbles transmitted on the wall surface do not easily flow backward and are easy to push out.

FIG. 4 is a cross-sectional view of a recording head body according to another embodiment of the present invention. As in the embodiment of FIG. Toward the height of the bubble elimination chamber, the upper wall 10
Form B This makes it difficult for the air bubbles flowing on the wall surface to flow backward once the air bubbles are pushed rearward, so that the air bubbles can be easily eliminated rearward.

FIG. 5 is a sectional view of a recording head body showing another embodiment of the present invention.

As shown in FIG.
By providing a bubble trap 7A on the upper wall of the common liquid chamber 10 in order to prevent the backflow as much as possible, the bubbles are retained, and the bubbles are prevented from being pulled in the ink liquid path direction.

As a method of forming the trap portion 7A, a water repellent is applied to a part of the upper wall of the common liquid chamber 7 or the surface is roughened by chemical etching to form a surface where air bubbles can be easily trapped. I do.

By the way, in forming the bubble elimination chamber as described above,
When a resin film is laminated and a space plate 20 for forming a bubble elimination chamber is provided on the ink liquid path where the ink liquid path is formed (see FIG. 7), it is very easy to form. However, over a long period of use, the adhesion force of the space plate 20 forming the bubble elimination chamber to the top plate 4 is reduced, and as shown in FIG. The recording quality is impaired.

Therefore, in the embodiment of the present invention, for example, as shown in FIG. 1, the bubble elimination chamber and the ink liquid path are integrally formed by molding.

7A and 7B are a side sectional view and a lower sectional view, respectively, of a recording head main body showing another embodiment of the present invention.

This example shows a case where the present invention is applied to a so-called multi-nozzle type recording head in which a plurality of discharge ports are arranged,
Is provided with a groove 21 at a part thereof to secure ink flow paths at several places. The grooves 21 ensure the flow of ink evenly in all ink liquid paths, and even when bubbles grow large, ink required for ejection is sufficiently supplied to each ink liquid path.

Furthermore, if this embodiment is applied to a full multi-type recording head having ejection openings such as thousands of orifices, ejection can be continued for a long time without locally causing ejection failure.

8A and 8B are a side sectional view and a lower sectional view, respectively, of a recording head body showing another embodiment of the present invention.

As described above, the bubble elimination chamber 10 is provided in each ink liquid passage 6.
Are arranged in the longitudinal direction corresponding to the arrangement, and have a structure in which fine bubbles generated in the ink liquid path at the time of ink ejection are pushed backward, but also serve as an ink supply source at the time of ink refilling. Therefore, as shown in FIG. 8, at least the ink injection port 41 is connected to the bubble elimination chamber 10.
A groove 101 for supplying ink at the same height as the bubble elimination chamber 10 is provided on the side wall of the common liquid chamber 7, and the effect of the present embodiment can be further obtained.

That is, the bubbles removed from the bubble removing chamber 10 gradually grow in the bubble chamber in the common liquid chamber 7.
Since the height of the liquid chamber 7 is different from that of the liquid chamber 7, the liquid cannot enter the space 101, and a supply path for supplying ink is always secured. This allows
The time required for non-ejection becomes longer.

Also, for example, at the time of pumping for recovery, since the fluid resistance in the liquid chamber 7 is low, bubbles can be easily taken out.

Further, as shown in FIG. 8, the same effect can be obtained even if the ink supply groove 101 is provided all around the liquid chamber 7.

FIG. 9 is a side sectional view for explaining the dimensional relationship of each part of the recording head main body described above.

The bubble elimination chamber 10 needs to be set to an optimal shape so as to eliminate the fine bubbles generated in the ink liquid path 6 to the rear common liquid chamber 7 every time ejection is performed.

First, the ink liquid passage, the expansion of the bubble for ink discharge begins, to the common liquid chamber direction and the discharge direction about the disposed position of the ejection heater 51, at a speed V ₁ by volume rapid change in bubble Fluid movement occurs. The V ₁ was reaches the bubble elimination chamber, changes in the speed V ₂ is reduced by an increase in cross-sectional area. The V ₁ and V ₂ is, S ₁ the ink passage cross-sectional area, the bubble elimination chamber cross-sectional area than the S ₂ Then successive _{formula, V 1 × S 1 = V} 2 × S 2 (1) , and the where for multi-nozzle, S ₁ and for the ratio of S ₂ that is proportional to approximately the ink liquid passage and the height h ₁ and the bubble elimination chamber height _{h 2, V 1 × h 1} ≒ V 2 × h 2 (2) Becomes

At this speed V ₂ , the fine bubbles move through the bubble elimination chamber 10 and reach the common liquid chamber 7. Time when this V ₂ works effectively
t ₂ is the time to discharge air bubbles disappear occurs, then gradually starts refilling the ink path direction. During this time, the air bubbles must move by the speed V _{2 for} a length l ₂ or more of the air bubble elimination chamber 10. Therefore, l ₂ <V ₂ × t ₂ (3) must be satisfied. From equation (2), equation (3) is Furthermore, since the case of the ejection system of the present example, t ₂ is about 50 [mu] s, the ink liquid path velocity V ₁ of about 10 m / s, Is desirable.

Also, even if the fine bubbles stay in the middle of the exclusion chamber 10, the refilling liquid passage speed V ₁ ′ is considerably slow at about 0.4 m / s, and the rearward flow is repeated in two or several times of repeated foaming. Rejected into the liquid chamber.

Furthermore, if the height h ₃ of the rear common liquid chamber 7 is set to be sufficiently large with respect to h ₁ and h ₂ , the flow velocity in the liquid chamber 7 will be extremely small, and the eliminated bubbles will become Combined with the air bubbles coming from, it gradually increases without affecting the ejection.

The recording head body described above can be obtained in the form of a cartridge as shown in FIG. 2, and further, using this, an ink jet printer as shown in FIG.
An ink jet printer using a disposable cartridge can be configured.

In FIG. 10, reference numeral 80 denotes the cartridge shown in FIG. 2. The cartridge 80 is fixed on the carriage 15 by a pressing member 81.
Can be reciprocated in the longitudinal direction along. The positioning with respect to the carriage 15 can be performed by, for example, a hole provided in the lid 300, a dowel provided on the carriage 15 side, or the like. Further, for electrical connection, a connector on the carriage 15 may be connected to a connection pad provided on the wiring board.

The ink discharged by the recording head reaches the recording medium 18 whose recording surface is regulated by the platen 19 at a minute interval from the recording head, and forms an image on the recording medium 18.

An ejection signal corresponding to image data is supplied to the recording head from a suitable data supply source via a cable 16 and a terminal connected thereto. One or more (two in the figure) cartridges 80 can be provided depending on the ink color and the like to be used.

In FIG. 10, reference numeral 17 denotes a carriage 15
A carriage motor for scanning along 21 and a wire 22 for transmitting the driving force of the motor 17 to the carriage 15. Reference numeral 20 denotes a recording medium connected to a platen roller 19.
Is a feed motor for transporting the paper.

[Effects of the Invention] As is apparent from the above description, according to the present invention, in addition to the cross-sectional area of the bubble elimination chamber being smaller than the cross-sectional area of the common liquid chamber, the common liquid chamber or the common liquid chamber and the ink liquid Since the bubble trap portion is provided on any wall of the bubble elimination chamber provided between the paths, the microbubbles once removed from the ink liquid path to the bubble elimination chamber or the common liquid chamber side are held in the trap portion, Backflow to the ink liquid path side is prevented.
As a result, the bubbles are gradually eliminated toward the common liquid chamber, where they grow and stay.

As a result, the accumulated bubbles formed by the coalescence of the fine bubbles accumulate in the common liquid chamber and can prevent the ink supply path to the ink liquid path from being blocked.

In addition, continuous discharge increases the amount of accumulated bubbles, thereby increasing the time required for non-discharge, as compared with the related art, and has advantages such as simplification of the discharge recovery system.

Further, it is possible to obtain a recording head in which the above-mentioned non-ejection is prevented while a predetermined amount of ink, for example, the amount of ink stored in an ink tank integrated with the disposable recording head is used up.

[Brief description of the drawings]

FIGS. 1A and 1B show an embodiment of the present invention,
FIG. 2 is a side sectional view and a lower sectional view of an ink jet recording head body for explaining the principle of the present invention. FIG. 2 is a perspective view of a recording head cartridge according to an embodiment of the present invention. 6 (A) and 6 (B) are side sectional views of a recording head body showing another embodiment of the present invention. FIGS. 6 (A) and 6 (B) show problems when the bubble elimination chamber of this embodiment is formed separately from the ink liquid passage. FIGS. 7A and 7B are side and bottom sectional views, respectively, of a recording head body showing another embodiment of the present invention, and FIG. 8A. And (B) are a side sectional view and a lower sectional view of a recording head body showing still another embodiment of the present invention, respectively, and FIG. 9 is a view for explaining a dimensional relationship of each part of the recording head body showing an embodiment of the present invention. FIG. 10 is a side sectional view of an embodiment of the present invention. Perspective view showing an example of mounting an ink jet recording apparatus head, FIG. 11 (A) and (B) is a side sectional view showing a conventional example of the respective ink jet recording heads. 1 ... discharge bubbles, 2 ... fine bubbles, 2A ... residual bubbles, 3A ... accumulated bubbles, 4 ... top plate, 5 ... substrate (heater board), 6 ...
Ink liquid path, 7: common liquid chamber, 7A: bubble trap section, 8 ...
Discharge port (orifice), 10: bubble elimination chamber, 10A: corrugated upper wall, 10B: multi-stage upper wall, 21: groove, 51: electrothermal converter (discharge heater), 101: ink supply groove.

Continuation of front page (56) References JP-A-57-87962 (JP, A) JP-A-58-187368 (JP, A) JP-A-1-308645 (JP, A)

Claims (6)

(57) [Claims] An ink discharge passage provided with a discharge port for ink discharge, a thermal energy generating element communicating with the discharge port and generating thermal energy used for ink discharge, and A common liquid chamber provided for supplying ink to the ink liquid path with the ink liquid path, and an ink supply port for supplying ink to the common liquid chamber, The common liquid chamber is an ink jet recording head that is larger than a cross-sectional area of the ink liquid path, and communicates with the ink liquid path through a bubble elimination chamber having a cross-sectional area smaller than the cross-sectional area of the common liquid chamber, An ink jet recording head having a bubble trap portion on at least one of the walls of the bubble elimination chamber and the common liquid chamber. 2. An ink jet recording head according to claim 1, wherein said bubble trap portion is a portion where a water repellent is applied to said wall. 3. The ink jet recording head according to claim 1, wherein said bubble trap portion is a portion whose surface is roughened by chemical etching of said wall. 4. The ink jet recording head according to claim 1, wherein said bubble trap portion has a wavy structure. 5. The ink jet recording head according to claim 1, wherein said bubble trap portion is a plurality of grooves. 6. The ink jet recording head according to claim 1, wherein the ink liquid path, the bubble elimination chamber, and the common liquid chamber are integrally formed in one member.