JPH0752405A - Ink supply device - Google Patents

Abstract

PURPOSE:To stabilize the ink-supply performance, to suppress the influence from the change of an environment and to enhance the ink-containing efficiency. CONSTITUTION:In an ink tank 2, a main ink chamber 4 and a sub ink chamber 6 wherein an absorption member 9 is disposed are adjacent with each other and an air communication hole 8 is provided in an upper section of the sub ink chamber 6. The absorption member 9 keeps the ink pressure at a constant level by its capillary force. First, an ink in the sub ink chamber 6 is used in accordance with the ink consumption. In the case where a prescribed amount of ink has been used, an air passes through the inside of the absorption member 9 and becomes bubbles when passing through a meniscus forming section 10 to move into the main ink chamber 4. An ink pressure is maintained at a constant level by a surface tension in the meniscus forming section 10. Even when an amount of the residual ink is reduced, the meniscus forming section 10 is in a wettable condition because of an ink conduction section 11 so that the ink pressure is constantly maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink supply device for supplying ink to a recording head in an ink jet recording device.

[0002]

2. Description of the Related Art Conventionally, as an ink supply mechanism used in an ink jet recording apparatus, as described in, for example, Japanese Patent Laid-Open No. 63-87242, the entire area inside an ink tank connected to a recording head. It is known that an ink absorber is loaded in the ink absorber, the ink is impregnated and held in advance in the ink absorber, and the ink in the ink absorber is supplied to the recording head. As the ink absorber, a sponge which is a porous material or a felt which is a fibrous material is used. In such an ink supply mechanism, about 4 times the volume in the ink tank is used.
Only 0% to 60% of the ink amount can be used, and the use efficiency is low. Therefore, when trying to extend the service life of the ink tank, the size of the ink tank inevitably becomes large, and there is a problem that the request for downsizing cannot be met.

Further, in the above-mentioned conventional ink supply mechanism,
Since the ink is held by the capillary force of the ink absorber, an appropriate negative pressure is generated for the print head. Therefore, as the amount of ink held in the ink absorber decreases as the ink is consumed, the negative pressure acting on the ink impregnated in the ink absorber gradually increases due to the decrease in the ink head pressure, and There is a problem that the ink supply is interrupted. When this phenomenon progresses and the negative pressure applied to the ink exceeds a certain value, air bubbles flow back from the print nozzle of the print head, and the ink is ejected without ink being supplied to the print head. There is a problem that a defect causes a defect in a recorded image, resulting in deterioration of image quality. This phenomenon also reduces the ink use efficiency.

In order to solve such a problem, for example,
Japanese Patent Publication No. 59-500609, Japanese Patent Laid-Open No. 1-1485.
In the ink supply device described in Japanese Patent Application Laid-Open No. 59-180357 and Japanese Patent Application Laid-Open No. 3-180357, only a closed ink tank is filled with ink, and a capillary tube whose one end is open to the atmosphere is connected or connected. , Those with small holes have been proposed. According to this ink supply device, when the negative pressure in the ink tank increases as the ink in the ink tank is consumed, air is introduced into the ink tank through the capillaries and small holes, and the negative pressure value in the ink tank is increased. Is kept almost constant, and the ink in the ink tank can be stably supplied to the recording head.

When the surrounding environment changes and, for example, the air in the upper space inside the ink tank expands, the ink inside the ink tank flows back through the capillaries. Therefore, in one example of the ink supply device described in JP-A-59-500609 and the ink supply device described in JP-A-1-148559, the atmosphere is provided only through a capillary tube. Since the ink tank is communicated with the ink tank, there is a possibility that the backflowing ink may be ejected, which is a problem. It is conceivable to lengthen the capillary tube, but the structure becomes complicated.

An example of another ink supply device described in JP-A-1-148559 and JP-A-3-1803.
The ink supply device described in Japanese Patent Publication No. 57, etc. has a small chamber, and when the air in the upper space in the ink tank expands, the ink in the ink tank temporarily evacuates to the small chamber side. As a result, the pressure in the ink tank is reduced, and the situation in which the ink leaks from the recording head and the ink leaks from the capillaries or small holes communicating with the atmosphere is effectively prevented.

However, in the ink supply device having such a small chamber, the small chamber is arranged below the main ink chamber. Therefore, in order to mitigate the pressure fluctuation inside the ink tank, when the ink that has moved from the main ink chamber to the small chamber returns to the main ink chamber again, it is necessary to overcome the capillary force and move it against the direction of gravity. There is. Therefore, the ink in the small chamber cannot be completely transferred to the main ink chamber and remains in the small chamber. That is, the volumetric efficiency is reduced by the amount of the remaining ink.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and stabilizes the ink supply performance.
Another object of the present invention is to provide an ink supply device that realizes suppression of the influence of changes in the surrounding environment and that improves the ink storage efficiency.

[0009]

According to the present invention, there is provided an ink supply device which is connected to an ink jet head and supplies ink to the ink jet head, and a main ink storage chamber which is connected to the ink jet head and stores the ink. A sub ink storage chamber which is disposed adjacent to the side of the ink storage chamber and communicates with the main ink storage chamber through a communication hole in a lower space and an air communication port is opened on the upper side, and the sub ink storage chamber. An ink absorbing member that is disposed inside and is disposed so as to be in close contact with the inner wall of the sub ink containing chamber at least laterally, and a meniscus forming portion that is provided so as to cover the communication hole of the sub ink containing chamber. It is a feature. The meniscus forming portion can be formed of a mesh body or a porous body.

Further, an ink guiding portion is provided which is in contact with a lower surface of the meniscus forming portion and extends into a lower space communicating with the main ink containing chamber. The ink guiding portion may be configured such that one end thereof contacts the meniscus forming portion and the other end thereof contacts a bottom portion of a lower space communicating with the main ink storage chamber. In addition, the ink guide portion has a smaller cross section than the communication hole, and a region that is not in contact with the ink guide portion is formed in the meniscus forming portion.

Further, a filter having a higher filtering accuracy than the meniscus forming portion can be arranged between the main ink containing chamber and the ink jet head.

[0012]

According to the present invention, the main ink storage chamber and the sub ink storage chamber are provided, and the ink absorbing member is inserted into the sub ink storage chamber. The pressure can be controlled, and the negative pressure applied to the inkjet head can be maintained within a desired range.

The ink absorbing member in the sub ink containing chamber can absorb ink up to the holding capacity limit of the absorbing member by the capillary phenomenon in the initial stage, and functions as an ink chamber. Since the atmosphere communication port is located at the upper portion and communicates with the main ink storage chamber in the lower space of the ink absorbing member that is inserted in close contact with the sub ink storage chamber, the negative pressure generated by the ink consumption in the recording head causes Ink in the sub ink storage chamber moves to the main ink storage chamber. When the ink in the sub ink storage chamber is almost exhausted, air bubbles are generated from the meniscus forming portion, and the air bubbles are supplied to the main ink storage chamber through the lower space, thereby increasing the negative pressure in the main ink storage chamber. suppress. As a result, an appropriate negative pressure is always generated in the recording head, and good printing can be compensated.

Further, when the ambient environment changes and the pressure in the main ink containing chamber rises, the pressure in the main ink containing chamber can be kept substantially constant by the ink flowing into the sub ink containing chamber. Even in such a case, the ink that has flowed into the sub ink containing chamber moves to the main ink containing chamber due to the pressure drop due to the consumption of the ink, so that the amount of ink remaining in the sub ink containing chamber can be reduced.
Volumetric efficiency can be increased.

By forming the meniscus forming portion with a mesh-like body or a porous body, it is possible to form an ink meniscus in the meshes or the holes of the porous body, and the surface tension causes atmospheric pressure. It is possible to generate bubbles at a desired differential pressure between and to maintain the main ink storage chamber at a substantially constant negative pressure.

Even if both surfaces of the meniscus forming portion come into contact with the air layer due to bubbles or the like generated in the meniscus forming portion, ink is sucked up by the ink guiding portion and supplied to the meniscus forming portion. Due to the surface tension of the ink in the meniscus forming portion, the negative pressure in the main ink storage chamber can be kept substantially constant. Further, even when the amount of ink is reduced and the liquid surface is lower than the meniscus forming portion, the meniscus forming portion can be kept wet with the ink, and the residual amount of ink can be reduced.

The ink guiding portion is configured such that one end thereof contacts the meniscus forming portion and the other end thereof contacts the bottom portion of the lower space communicating with the main ink containing chamber, whereby the ink is slightly left. However, since the ink is supplied to the meniscus forming part by the ink guiding part and the pressure in the main ink storage chamber is kept substantially constant by the meniscus forming part, the ink can be used up and the ink utilization efficiency is further improved. Can be made.

Further, the ink guide portion is formed to have a smaller cross section than the communication hole, and a region which is not in contact with the ink guide portion is formed in the meniscus forming portion,
Bubbles can be generated in this region, and the generated bubbles can be smoothly moved to the lower space.

Further, by disposing a filter having a filtration accuracy higher than that of the meniscus forming portion between the main ink storage chamber and the ink jet head, the absorbing member and the meniscus forming portion when the ambient environment changes,
It is possible to promote the adjustment of the pressure by the ink guide portion and the like, and prevent the outflow of ink from the inkjet head.

[0020]

1 is a sectional view showing an embodiment of an ink supply apparatus of the present invention, and FIG. 2 is an enlarged view of a lower portion of a sub ink chamber. In the figure, 1 is an inkjet head, 2 is an ink tank, 3 is ink, 4 is a main ink chamber, 5 is a communication passage, 6 is a sub-ink chamber, 7 is a communication hole, 8 is an atmosphere communication hole, 9 is an absorbing member, Reference numeral 10 is a meniscus forming portion, 11 is an ink guiding portion, 1
2 is a supply path. In this embodiment, the inkjet head 1 and the ink tank 2 are integrally formed. A heat sink (not shown) to which the head itself is attached, a printed wiring board (not shown) that supplies an electric signal to the inkjet head 1, and the like are present around the inkjet head 1. A large number of nozzles (not shown) are formed at high density in the inkjet head 1. For example, 128 nozzles can be formed with a density of 300 spi. Each nozzle is provided with a heating element (not shown) for generating bubbles by energization and ejecting ink droplets. In FIG. 1, ink droplets are ejected downward.

Inside the ink tank 2, the main ink chamber 4
And the sub ink chamber 6. The housing of the ink tank 2 has rigidity and is capable of holding ink for a long period of time, so a material having good ink resistance is selected. Main ink chamber 4
Contains ink only. Ink is supplied from the main ink chamber 4 to the inkjet head 1 through the supply path 12.

A communication hole 7 is provided in the lower portion of the sub ink chamber 6, and communicates with the main ink chamber 4 via a communication passage 5. The cross-sectional shape of the communication hole 7 can be various shapes such as a circle, an ellipse, a polygon, a star, a cross, and a slit shape. The upper wall of the communication passage 5 may be flat, but as shown in the drawing, the communication hole 7 is formed by being inclined so as to gradually increase toward the main ink chamber 4.
It is possible to smoothly move the generated bubbles to the main ink chamber 4. An absorbing member 9 is arranged inside the sub ink chamber 6. As the material of the absorbing member 9, a fibrous material having a two-dimensional structure, a porous material having a three-dimensional structure,
It is possible to use a felt and a non-woven fabric material obtained by spinning a fibrous material into a three-dimensional shape. Specifically, for example,
A batting material obtained by bundling polyester fibers in one direction can be used. As this batting material, for example, a polyester felt having a density (= weight / volume) of 800 g / m ³ can be used. The volume density is 5% to 15%.
It is possible to use a material having a value in this range, and it is desirable to use a material having such a value from the viewpoint of fluid resistance and capillary force. The composition of the material is not limited to polyester fiber, and as long as the material has an appropriate capillary force and is ink resistant, for example, a porous member such as polyurethane or melamine foam, one-dimensional, A two-dimensional fiber structure or the like can also be used.

At the upper part of the sub ink chamber 6, an atmosphere communicating hole 8 is provided which is capable of communicating with the absorbing member 9 to the atmosphere. In this embodiment, the diameter of the atmosphere communicating hole 8 is set to be larger than the hole of the absorbing member 9 or the gap between the fibers. Absorbing member 9
Is open to the atmosphere and communicates with the atmosphere above it.
The ink in the absorbing member 9 is pushed by the atmospheric pressure and is drawn out from below the absorbing member 9 to the main ink chamber side by the negative pressure, so that the ink in the absorbing member 9 can be used efficiently. At this time, the negative pressure in the main ink chamber 4 is kept constant by the capillary force of the absorbing member 9. It is also possible to provide a sheet in the atmosphere communicating hole 8 that does not allow ink to pass therethrough and allows air to pass therethrough so that the ink does not fly out from the atmosphere communicating hole 8. Alternatively, the air communication hole 8 may be formed by arranging a large number of fine holes through which the ink does not flow out. The periphery of the absorbing member 9 is inserted so as to be in close contact with the inner wall of the sub ink chamber 6. The purpose of this is to prevent the air introduced from the atmosphere communication hole 8 from entering along the inner wall of the sub ink chamber 6.

The meniscus forming portion 10 is arranged so as to cover the communicating hole 7 and to contact the bottom portion of the absorbing member 9. For example, the absorbent member 9 may be installed so as to project from the bottom surface of the absorbent member 9 by several millimeters. In that case, the absorbent member 9 is pressed against the meniscus forming portion 10, and the surface of the meniscus forming portion 10 is immersed in the absorbent member 9. In this state, a better fluid bond can be obtained. Meniscus forming part 1
For 0, a mesh-like body such as a wire net or a resin net, or a porous body can be used. As a specific example of the mesh body, a metal mesh filter, a metal fiber, for example, a thin wire of SUS made into a felt shape, and a filter using a material obtained by compression sintering as a base material, an electroforming metal filter, etc. are used. be able to. Further, it is possible to use a filter which is a knitted resin fiber, or a filter having a fine hole diameter obtained by laser beam processing, electron beam processing, or the like. The meniscus forming portion 10 can be configured to be heat-sealed to the absorbing member 9.

When the ink is absorbed in the absorbing member 9, the ink passes through the meniscus forming portion 10 and moves to the main ink chamber 4. The meniscus forming unit 10 prevents unnecessary air from entering the main ink chamber 4 even when the absorbing member 9 runs out of ink. When more ink is consumed,
The air that has entered from the atmosphere communication hole 8 passes through the absorbing member 9, and the negative pressure in the main ink chamber 4 increases, so that the ink liquid that is spread over the eyes of the meniscus forming portion 10 that is in close contact with the absorbing member 9 It pushes the surface, overcomes the surface tension, passes through it, and becomes a bubble. The generated bubbles pass through the communication hole 7 and move to the main ink chamber 4. The pressure at which bubbles are generated (bubble point pressure) depends on the filtration accuracy of the meniscus forming portion 10, but by optimizing this filtration accuracy, the negative pressure in the main ink chamber 4, that is, the inkjet head 1 The ink supply pressure to the ink can be kept constant. As the filtering accuracy of the meniscus forming portion 10, for example, a filtering accuracy of about 70 μm can be used. Meniscus forming part 1
0 also has a function of removing dust and the like that is larger than the filtering accuracy.

FIG. 3 is an explanatory view of an example of a mesh body that can be used in the meniscus forming portion 10. When a wire net is used as the meniscus forming portion 10, there are various methods for weaving the wire net. In Figure 3, Tatami Twill (Twill)
1 shows the weave of a wire mesh of ed Dutch Weave). The tatami twill weave uses thick vertical lines, the horizontal lines are adjacent to each other, and they are woven so as to get over two vertical lines. Figure 3
As shown in (A), when viewed from the front, the horizontal lines are in contact with each other, and therefore cannot be seen through. However, when viewed diagonally,
As shown in FIG. 3 (C), a triangle opening is formed by a horizontal line running diagonally from the back to the front or from the front to the back, a horizontal line extending adjacent to the horizontal line, and a vertical line. Ink passes through the triangular openings, and bubbles are generated in this portion. As described above, the tatami twill wire mesh can be finely woven, has even mesh, and can generate uniform bubbles. Further, it has a feature that it has a higher mechanical strength and is stronger than other wire nets having the same filtration accuracy. Usually, such a wire mesh is usually used for filtration, but in the present invention, in addition to filtration, it also has a function of adjusting the pressure due to generation of bubbles as described above.

FIG. 4 is an explanatory view of the characteristics of a Twill twill weave wire mesh. In the figure, the tatami twill wire mesh shown by A has a filtration particle size of 1
The liquid resistance average difference is 10.3 × 1.
The pressure loss is 0 ⁴ g / cm ⁴ s and the pressure loss is about 4.2 cmH ₂ O. Further, in the Tatami-woven wire mesh shown by B, the filter particle size is about 5 μm, and the average liquid resistance difference is 56.1 × 1.
The pressure loss is 0 ⁴ g / cm ⁴ s and the pressure loss is about 23.1 cmH ₂ O. As described above, since the liquid resistance and the pressure loss change depending on the roughness of the mesh of the wire mesh used, it is possible to use an optimal wire mesh in consideration of the ink pressure applied to the head.

Returning to FIGS. 1 and 2, the ink guiding portion 11 is
It is in contact with the meniscus forming portion 10 and extends downward through the communication hole 7. When air bubbles are accumulated on the lower surface of the meniscus forming portion 10 and an air layer is formed, or when the ink in the main ink chamber 4 is reduced and the liquid level of the ink is smaller than the diameter of the communication passage 5, the meniscus is formed. Both sides of the part 10 will be exposed to air. However, since the pressure inside the main ink chamber 4 needs to be maintained at a negative pressure, it is necessary to form the ink liquid surface in the meniscus forming portion 10 even in such a case. Therefore, the ink guiding portion 11 sucks the ink from the bottom of the communication passage 5 and supplies the ink to the meniscus forming portion 10, thereby keeping the meniscus forming portion 10 in a wet state and keeping the negative pressure in the main ink chamber 4. You can By extending the lower surface of the ink guide portion 11 to the bottom of the communication hole 7, that is, the bottom of the communication passage 5, the best state can be maintained until the ink is used up. The ink guide portion 11 is made of a material capable of raising the ink to the meniscus forming portion 10 by a capillary force. For example, a batting material obtained by bundling polyester fibers in one direction, a porous member such as polyurethane or melamine foam, A two-dimensional, three-dimensional fiber structure or the like can be used. The shape is arbitrary and may be a slit shape, a rectangular parallelepiped, a prism such as a triangular prism, a cylindrical shape, or an elliptic cylinder.
Further, as shown in FIG. 2, by making the cross-sectional dimension of the ink guiding portion 11 smaller than the opening dimension of the meniscus forming portion 10, a gap A is provided around the ink guiding portion 11. Thereby, it is possible to easily move the bubbles generated in the meniscus forming portion 10 to the main ink chamber 4.
It is desirable that the gap A has a width of 0.5 mm or more. The ink guiding portion 11 may be directly attached to the meniscus forming portion 10 or may be fixed to the side wall of the communication hole 7 by a rib.

The volumetric efficiency of the ink supply device having such a configuration will be described. In this embodiment, the volume ratio between the main ink chamber 4 and the sub ink chamber 6 is set to 1: 1 and the main ink chamber 4 is filled with 100% ink in the initial state inside the ink tank 2. On the other hand, the inside of the sub ink chamber 6 is filled with an amount of ink that can be impregnated with the absorbing member 9. As a material of the ink absorbing member 9, for example, a batting material obtained by bundling polyester fibers in one direction can be used. When this material is used, the ink retaining efficiency (= ink filling amount / total ink chamber volume) is about 80%. The ink use efficiency of the sub ink chamber 6 (= suppliable ink amount / ink filling amount) is about 70%. On the other hand, the ink retaining efficiency in the main ink chamber 4 (= ink filling amount / ink absorbing member volume)
Is about 100%, and the ink use efficiency (suppliable ink amount / ink filling amount) is also about 100%. Therefore, the volume efficiency of the ink tank 2 (= suppliable ink amount / total ink chamber volume) is about 78%. As described above, the ink supply device of the present invention has very good ink use efficiency.

The sizes of the main ink chamber and the sub ink chamber do not have to be the volume ratio of 1: 1 as described above, and the size may be determined based on the ink amount and the like. At this time, as described later, the air layer formed above the main ink chamber 4 is
If it expands due to a rise in temperature or a drop in atmospheric pressure,
Since the amount of ink required to maintain the negative pressure in the main ink chamber 4 is stored in the absorbing member 9 in the sub ink chamber 6, the volume of the absorbing member 9 is set in consideration of the amount of ink stored at this time. There is a need.

As for the positional relationship between the main ink chamber and the sub ink chamber, as shown in FIG. 1, in addition to the shape such that the ink tank is divided into two, two or three sub ink chambers are mainly used. The shape may be such that the ink chamber is surrounded, or the sub ink chamber may be arranged on the island in the main ink chamber. In these configurations, by forming all or part of the side surface of the ink tank with a transparent body, it is possible to check the liquid surface in the main ink chamber from any direction. The confirmation method is
It is possible to use a method such as visual recognition or an optical sensor.

The operation of the ink supply device of the present invention will be described. The above-mentioned state shown in FIG. 1 shows the state when ink is filled. In this state, the ink tank 2 has about 80% of the inner volume of the absorbing member 9 and 100% of the inner volume of the main ink chamber 4.
% Is filled with ink. Inkjet head 1
The ink pressure in can be, for example, −20 mmH ₂ O. This ink pressure is realized by the capillary force of the absorbing member 9 and holds the ink. As a state at the start of use, it is desirable to fill the ink in the ink tank 2 as much as possible from the viewpoint of ink use efficiency. However, in order to generate a negative pressure by the capillary force of the absorbing member 9, the absorbing member is Some amount of unfilled ink is required. Before use, a confidential seal can be attached to the nozzle portion of the inkjet head 1 and the atmosphere communication hole 8. It is packaged in this state.

When printing starts, the ink jet head 1
Ink is consumed in, and ink is replenished to the inkjet head 1 from the main ink chamber 4 via the supply path 12 by the amount of consumed ink. Accordingly, while the absorbing member 9 holds the ink, the ink in the absorbing member 9 moves to the main ink chamber 4 through the communication passage 5, and the air gradually flows from the atmosphere communicating hole 8 into the absorbing member 9. It spreads inside.

FIG. 5 is an explanatory diagram of a process of ink consumption. FIG. 5A shows a state in which the ink has been consumed and the air has reached the meniscus forming portion 10. Until this state is reached, the meniscus forming unit 10 prevents air from entering the main ink chamber 4. Therefore, the absorbing member 9
It is possible to reduce the amount of remaining ink inside. At this point, a meniscus where the ink and the air are in contact with each other is formed on the meniscus forming portion 10. Even when air is in contact with the upper surface of the meniscus forming portion 10, since the filtration accuracy of the meniscus forming portion 10 is smaller than that of the absorbing member 9, the air continues to move while being trapped on the meniscus forming portion 10.

As the ink is further consumed, the negative pressure gradually increases from the decrease in the ink head pressure, and a certain negative pressure value (the bubble point of the filter and the ink determined by the filtration accuracy of the meniscus forming portion 10) is increased. When (pressure) is applied to the meniscus formation portion 10, air is generated as fine bubbles through the meniscus of the ink formed on the meniscus formation portion 10. The generated small bubbles are combined with the adjacent small bubbles and subsequent bubbles,
The air bubbles move into the main ink chamber 4 through the communication passage 5 while forming large air bubbles. At this time, since the upper wall of the communication passage 5 is formed obliquely toward the main ink chamber 4, the bubbles smoothly move in the communication passage 5 and reach the main ink chamber 4. The pressure at the time of bubble generation (bubble point pressure) depends on the filtering accuracy of the meniscus forming portion 10, but by optimizing this filtering accuracy, the ink supply pressure to the inkjet head 1 thereafter is kept constant. be able to. The bubbles that have moved to the main ink chamber 4 will be accumulated in the upper part of the main ink chamber 4. This state is shown in FIG.

The bubble generation process in the meniscus forming portion 10 at this time will be described. FIG. 6 is an explanatory diagram of a process of generating bubbles in a Tatami-woven cloth. As an example, a case where a tatami twill wire mesh shown in FIG. 3 is used as the meniscus forming portion 10 will be described. As shown in FIG. 3C, the tatami twill wire mesh has triangular openings. When this portion is wet with ink, an ink film is formed due to the surface tension of the ink. While the pressures on both sides of the wire net are balanced, the ink film is flat, as shown in FIG. In FIG. 4, when the pressure on the front surface side of the wire mesh decreases, the air on the back surface of the wire mesh pushes the ink film due to the pressure difference, and becomes convex as shown in FIG. 4B. If the pressure on the surface side of the wire mesh further decreases, the
As shown in FIG. 4C, the convex portion protrudes, and finally, as shown in FIG. At this point, the pressure in the ink rises by the volume of the bubbles and the drop in the pressure on the surface side of the wire netting is canceled out, so that the ink film becomes flat. The air bubbles separated in the ink merge with the air bubbles similarly generated from the nearby eyes, and become large air bubbles while moving to the main ink chamber 4.

Returning to FIG. 5, when the ink is further consumed, the liquid level of the ink does not fill the communication passage 5. This state is shown in FIG. In this state, both surfaces of the meniscus forming portion 10 are exposed to air. But,
Since the ink guiding portion 11 is immersed in the ink, the ink is raised to the meniscus forming portion 10 by the capillary phenomenon of the ink guiding portion 11, and the meniscus forming portion 10 is kept wet. Therefore, in the meniscus forming portion 10,
The ink film is continuously formed, and the operation of maintaining the pressure in the main ink chamber 4 due to the generation of bubbles effectively operates. From this state,
The ink supply pressure to the inkjet head 1 is kept constant until the ink in the main ink chamber 4 is completely exhausted. Therefore, a highly efficient ink supply device can be realized.

As described above, since the meniscus forming portion 10 is constantly immersed in the ink, the meniscus of the ink formed on the meniscus forming portion 10 is destroyed until the ink is exhausted after the generation of bubbles. However, the negative pressure in the main ink chamber 4 is kept substantially constant.

FIG. 7 is an explanatory diagram showing the relationship between the ink amount and the ink pressure in the ink jet head. Fluctuations in the ink pressure in the inkjet head will affect the ejection characteristics of the ink from the nozzles. In FIG. 7, changes in the ink static pressure and the ink dynamic pressure in the inkjet head with respect to the ink amount measured using the ink supply device of the embodiment of the present invention shown in FIG. 1 are shown by thick lines and thick dotted lines. The ink static pressure is the pressure when printing is not performed. This pressure is the pressure generated by the capillary force of the absorbing member or the meniscus forming portion,
It is generated by the head pressure from the ink surface. Further, the ink dynamic pressure can be considered to be the sum of the ink static pressure and the pressure loss generated by the ink flow rate and the fluid resistance of the flow path system. The measurement of ink dynamic pressure in the figure is for solid printing.

Further, FIG. 7 shows the same size as the ink supply device of the embodiment of the present invention used for measurement, using an ink tank in which a conventional ink absorber is loaded in the entire internal volume,
It measured similarly. The fluctuations of the ink static pressure and the ink dynamic pressure with respect to the ink amount at this time are shown by thin lines and thin dotted lines for comparison.

Referring to FIG. 7, the pressure loss generated by the fluid resistance of the flow path system, that is, the difference between the solid line and the broken line is not significantly different, but the ink static pressure is considerably different. There is. First, in the embodiment of the present invention, the initial filling amount of ink is larger because the ink tank can be filled with more ink.

In the conventional ink tank, the static ink pressure rises almost in proportion to the decrease in the remaining ink amount. This is because the head pressure of ink from the head surface is reduced. However, in the case of the embodiment of the present invention, although the ink static pressure rises with a similar inclination at the beginning, when the ink is consumed from the absorbing member and air bubbles are generated from the meniscus forming portion. , The static ink pressure becomes constant. The ink pressure at this time is considered to be expressed by the following equation. Phead = Pair-4γ cos θ / D + ρ · g · h2 where Phead is the pressure in the inkjet head,
Pair is the atmospheric pressure, γ is the interfacial tension between the ink and the meniscus forming portion, θ is the wetting angle, D is the void diameter of the meniscus forming portion,
ρ is the density of the ink, g is the gravitational acceleration, and h2 is the height from the ink surface of the meniscus forming portion to the inkjet head. Items 1 and 2 of this equation are determined by the atmospheric pressure and the meniscus forming portion. The head pressure of the ink of the three items from the head surface also has a constant value because the height h2 is constant, so the ink static pressure is also constant. As a result, the ink dynamic pressure, which is the sum of the pressure loss and the ink static pressure generated by the flow rate of ink and the fluid resistance of the flow path system, becomes constant, and an efficient ink supply device with a large amount of usable ink is realized. ing.

In this example, when the negative pressure value in the ink jet head exceeds 125 mmH ₂ O, the refilling of the ink is hindered and the amount of ink droplets ejected from the nozzle is reduced, which causes a print image quality called blur. It is known to cause a decline. From this, in the embodiment of the present invention, the ink pressure is kept in an appropriate range with respect to the change in the remaining ink amount, and good printing can be performed until the ink is used up.

By the way, there are cases in which the surrounding environment changes, such as changes in the outside air pressure and changes in the outside temperature. First, when the main ink chamber is full of ink and the ink is being supplied from the sub ink chamber, the atmospheric pressure received by the absorbing member from the atmosphere communication hole and the atmospheric pressure received by the tip of the nozzle of the inkjet head are Since it is the same, even if the atmospheric pressure changes, the pressure balance is not lost and the influence is small.

Next, consider the case where an air layer is formed in the main ink chamber. 8 and 9 are explanatory views of the state inside the ink tank due to changes in the surrounding environment. 1 in the figure
3 is an air layer. When the outside air pressure drops or the outside air temperature rises, the air layer 13 above the main ink chamber 4
Since the volume of the ink is expanded, the negative pressure value in the main ink chamber 4 tends to be relatively small. Therefore, as shown in FIG. 8, the ink in the main ink chamber 4 passes through the communication hole 7, the meniscus forming portion 10, and is absorbed by the absorbing member 9 in the sub ink chamber 6. As a result, the pressure difference between the pressure in the main ink chamber 4 and the atmospheric pressure is maintained, and the ink does not leak.

When the outside air pressure rises or the outside air temperature falls, the air layer 13 above the main ink chamber 4 contracts, so that the negative pressure value in the main ink chamber 4 is relatively large. Trying to become. In this case, as shown in FIG. 9, in the same manner as when the ink is consumed, the atmosphere communicating hole 8 passes through the absorbing member 9, the meniscus forming portion 10, and the communicating hole 7
The air is introduced into the main ink chamber 4 via the so that the differential pressure inside the main ink chamber 4 is kept constant. Further, when the ink is present in the sub ink chamber 6, the ink is moved into the main ink chamber 4, and the negative pressure in the main ink chamber 4 is maintained. In either case, no ink leaks.

FIG. 10 is an explanatory diagram of the relationship between atmospheric pressure and ink static pressure. The ink supply device shown in FIG. 1 is installed in a decompression chamber and the ambient pressure is 0.02 atm / hour.
It was carried out by gradually decreasing it at the fluctuation speed. Figure 10
Indicates the change in the ink negative pressure value generated in the inkjet head 1 at this time. However, the remaining amount of ink in the ink tank 2 was 40% of the inner volume of the ink tank 2, and the air layer 13 was formed in the main ink chamber 4 to be about half the inner volume of the main ink chamber 4. This air layer is generated by the movement of air into the ink chamber through the meniscus forming portion, as described with reference to FIG.

The ink negative pressure value of the ink jet head before depressurization, that is, when the atmospheric pressure is 1 atm, is a negative pressure of 60 mmH ₂ O. When the ambient atmospheric pressure is gradually decreased, the negative pressure value inside the ink tank becomes relatively smaller. At this time, as described above, since the pressure of the air layer 13 in the main ink chamber 4 relatively increases and expands, the ink flows through the ink guiding portion 11 provided below the meniscus forming portion 10. The ink starts moving from the main ink chamber 4 into the sub ink chamber 6, and the moved ink is absorbed by the absorbing member 9. By supplying the ink to the absorbing member 9 again, the interfacial tension with the ink is
It will be determined by the inter-fiber void diameter of the absorbent member 9.
At this time, it is considered that an ink negative pressure value corresponding to the ink amount in the sub ink chamber 6 acts on the inkjet head 1 according to the ink static pressure curve before the start of bubble generation shown in FIG.

In FIG. 10, ink is moved from the main ink chamber 4 to the sub ink chamber 6 until the atmospheric pressure reaches 0.8 atm, so that the ink jet head 1 has a negative pressure value of 20 mmH ₂ O or more. Is kept at. When the atmospheric pressure falls below this, the amount of ink that has moved to the sub ink chamber 6 exceeds the amount that the absorbing member 9 can hold the negative pressure, and the negative pressure cannot be held, so that the negative pressure value of the inkjet head 1 suddenly increases. And the ink leakage occurs. At this time, by increasing the ink holding capacity of the absorbing member 9, it is possible to further reduce the atmospheric pressure at which ink leakage occurs. In this way, by changing the volume ratio of the main ink chamber 4 and the absorbing member 9 in the sub ink chamber 6, the resistance to the fluctuation of the atmospheric pressure and the fluctuation of the ambient temperature changes.

In the above description of the volume efficiency, the volume ratio between the main ink chamber 4 and the sub ink chamber 6 is 1: 1. Further, the ink retaining efficiency of the absorbing member 9 in the sub ink chamber 6 is not 100% but is, for example, about 80%. Therefore, considering the volumetric efficiency of the ink supply device, the volume of the absorbing member 9 should be small. However, in consideration of the fluctuation of the atmospheric pressure described above, the larger the volume of the absorbing member 9, the higher the ability to absorb the fluctuation of the atmospheric pressure. Therefore, it is necessary to determine the volumes of the main ink chamber 4 and the absorbing member 9 from the viewpoints of both the ink use efficiency and the resistance to fluctuations in the atmospheric pressure and the ambient temperature.

The volume ratio between the main ink chamber 4 and the sub ink chamber 6 is
Try to make a trial calculation under certain conditions. Here, consider a case where the atmospheric pressure decreases and a case where the ambient temperature rises. In the opposite case, there is no problem because the air layer 13 in the main ink chamber 4 contracts and the negative pressure is maintained in the same manner as when the normal ink is consumed. In the following description, the fluctuation of the atmospheric pressure is within 0.15 atm, and the fluctuation of the temperature is between 25 ° C and 70 ° C.
And In addition, the volume of the main ink chamber 4 is X, and the sub ink chamber 6 is
The volume of the absorbing member 9 therein is Y.

It is assumed that the static pressure in the initial state is 50 mmH ₂ O in the ink jet head 1. Also, 1
Atmospheric pressure = 10332 mmH ₂ O. If an ink leak occurs when the static pressure of the inkjet head 1 becomes negative, the change amount of the atmospheric pressure until the ink leak occurs is spent to alleviate the initial negative pressure. Is 0.15-0.005 = 0.145 (atmospheric pressure). The change after this can be considered to be a constant pressure volume change, and P · V = nRT = const. (However,
It is assumed that P is the atmospheric pressure, V is the volume, R is the gas constant, and T is the absolute temperature), and the ink leak amount is considered to correspond to this volume change. Here, if the volume after change is V ′ and the change is ΔV ′, then V ′ = 1.145V ΔV ′ = 0.145V.

Also, the temperature change (from 25 ° C. (T) to 70
Since ℃ (T ') also contributes to the volume expansion, if the changed volume is V "and the changed amount is ΔV", then V "= (T' / T) V = (343/298) V = 1.1
5V ΔV ″ = 0.15V. Here, since the change amount of the vapor pressure of the ink also contributes to the volume expansion, the changed volume is V ″ ′ and the change amount is Δ.
If V ″ ′, ΔV ′ ″ = (0.31-0.03) V = 0.28V.

Letting ΔV ″ ”be the volume change considering the influence of atmospheric pressure change, temperature change, and vapor pressure change, ΔV ″ ″ = ΔV ′ + ΔV ″ + ΔV ″ ′ = 0 .145V
+ 0.15V + 0.28V = 0.575V. From this, the volume expansion is 0.575 · X.

When the total volume of the main ink chamber 4 and the absorbing member 9 is 1, X + Y = 1. Assuming that the actual use efficiency of the absorbing member 9 is 56%,
In order to absorb the volume expansion, the following two relationships need to be established. 0.56Y ≧ 0.575X Y ≧ 1.03X (substantially, = X) When this relational expression is substantially satisfied and the volume X of the main ink chamber 4 is increased as much as possible, the volume ratio between the main ink chamber 4 and the absorbing member 9 becomes , 50%: 50%. At this time, the ink water retention efficiency H, the usage efficiency S, and the actual usage efficiency J are H = 50 + 50 × 0.8 = 90 (%) S = 50 + 50 × 0.7 = 85 (%) J = S × H = 0. It is 9 * 0.85 = 77 (%).

In the above calculation, the allowable atmospheric pressure fluctuation is 0.15 atmospheric pressure and the temperature fluctuation is 25 ° C. to 70 ° C. However, when changing these allowable values, the main ink chamber 4 and the absorbing member are changed. The volume ratio of 9 varies. Further, in the above calculation, assumptions are made for various conditions such as the water retention capacity of the absorbing member 9, the static pressure in the inkjet head 1, the ink vapor pressure, etc. Therefore, based on these various conditions, the main ink chamber 4 and the volume ratio of the absorbing member 9 may be determined.

FIG. 11 is a sectional view showing another embodiment of the ink supply device of the invention. In the figure, the same parts as those in FIG. 14 is a filter,
Reference numeral 15 is a buffer member. This embodiment is almost the same as the embodiment shown in FIG. 1, but a filter 14 and a buffer member 15 are inserted between the main ink chamber 4 and the supply passage 12. The filter 14 is arranged below the cushioning member 20. As a result, filtration can be performed at the end of the supply path 12 connected to the inkjet head 1, and dust and foreign matter can be reliably removed. The filter 14 is reliably adhered to the upper portion of the supply path 12 by ultrasonic fusion, heat fusion, or the like. As the material of the filter 14,
A mesh with a filter particle size of 5 μm to 50 μm,
Alternatively, it is possible to use a filter in which a fine SUS wire is made into a felt shape and further compressed and sintered is used as a base material. The filtration particle size is determined to trap foreign matter having a size larger than the diameter of the ink flow path in the inkjet head.

The relationship between the filtering precisions of the meniscus forming portion 10 and the filter 14 is determined so that the meniscus forming portion 10 is rougher. For example, the filtration accuracy of the meniscus forming portion 10 is 70 μm, and the filtration accuracy of the filter 14 is 20 μm.
It can be μm. It is conceivable that when the ink supply device is left sideways or the like, if the ink remaining amount is small, the ink does not contact the meniscus forming portion 10 and the filter 14. In this state, the outside temperature rises,
Alternatively, when the atmospheric pressure decreases and the negative pressure in the main ink chamber becomes relatively small, the ink does not move to the absorbing member 9, and the internal pressure in the main ink chamber becomes considerably high. Here, the capillary force generated by the meniscus in the meniscus forming unit 10 is more
Alternatively, by making the force smaller than the capillary force generated by the meniscus formed in the nozzle of the inkjet head 1, the expanded air destroys the meniscus of the meniscus forming portion 10, and the air moves to the sub ink chamber 6. ,
No ink leaks from the printhead nozzles. It should be noted that the filter 14 also has a part of the effect that the inkjet head 1 is not subjected to excessive pressure fluctuation due to vibration, shock, or acceleration.

The buffer member 15 is made of, for example, a batting material in which polyester fibers similar to those of the absorbing member 9 are bundled in one direction. The cushioning member 15 is preferably arranged immediately before the mouth of the supply passage 12, and prevents vibrations and impacts, pressure fluctuations due to acceleration, and air bubble mixing from the nozzle side of the inkjet head 1.

FIG. 12 is a schematic configuration diagram of an ink jet recording unit using the ink supply device of the present invention. In the figure, 21 is an inkjet recording unit, 22 is an ink tank, 23 is a heat dissipation plate, 24 is a flow path forming member, 25 is a substrate, 26 is an inkjet head, 27 is a wiring pad,
28 is an auxiliary ink chamber, 29 is an air communication hole, 30 is an absorbing member, 31 is an ink guiding portion, 32 is a main ink chamber, and 33 is a meniscus forming portion.

The ink jet recording unit 21 includes an ink tank 22, a heat dissipation plate 23, a flow path forming member 24, and a substrate 2.
5, the inkjet head 26, the wiring pad 27 and the like. The ink tank 22 includes a sub ink chamber 28, an atmosphere communication hole 29, an absorbing member 30, an ink guiding portion 31, a main ink chamber 32, and a meniscus forming portion 33. The inkjet head 26 and the substrate 2 are placed on the heat sink 23.
5 are arranged and electrically connected by wire bonding or the like. Electric signals are received from the recording apparatus main body (not shown) via the wiring pads 27 on the substrate 25. A drive circuit and the like are arranged on the substrate 25, and the heating elements provided in the inkjet head 26 are controlled to eject ink from the nozzles. On the other hand, the ink supply from the ink tank 22 is as described above.
The ink supplied from the ink tank 22 is sent to the inkjet head 26 via the ink supply path formed by the flow path forming member 24, and is ejected from the nozzle to perform printing.

The ink jet recording unit 21 shown in FIG. 12 has an ink tank and an ink jet head integrally formed, and by using the ink supply device of the present invention, a compact recording unit having a high ink utilization rate is constituted. It is possible to do. With such a configuration, the inkjet recording unit 21 is configured to be detachably attached to the recording apparatus main body. Therefore, when the ink runs out, the inkjet head must be replaced, but since the usable ink amount can be increased more than before, it is possible to extend the replacement interval, reduce the cost, and reduce the amount of waste. Can be planned. Of course, the ink tank portion may be separately configured and replaceable.

[0063]

As is apparent from the above description, according to the present invention, there is a main ink chamber for storing ink in the ink tank, a sub ink chamber containing an absorbing member, and
By having a meniscus forming portion and an ink guiding portion, air is introduced into the main ink chamber in response to a pressure drop in the ink chamber that occurs with the consumption of ink by printing.
It is possible to keep the fluctuation of the ink pressure acting on the inkjet head within an appropriate value range and always obtain a good image quality. In addition, the ink in the sub ink chamber can be used up, and even when the amount of ink in the main ink chamber becomes very small, printing can be performed without causing pressure fluctuations in the main ink chamber. It is possible to improve efficiency. Further, even if there is a pressure change in the main ink chamber caused by a change in the surrounding environment, there is no ink leakage, and since an appropriate pressure can be maintained, good printing can be achieved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an ink supply device of the present invention.

FIG. 2 is an enlarged view of a lower portion of the sub ink chamber.

FIG. 3 is an explanatory diagram of an example of a mesh body that can be used in the meniscus forming portion 10.

FIG. 4 is an explanatory diagram of characteristics of a tatami twill wire mesh.

FIG. 5 is an explanatory diagram of a process of ink consumption.

FIG. 6 is an explanatory diagram of a process of generating air bubbles in a tatami twill wire mesh.

FIG. 7 is an explanatory diagram of a relationship of ink pressure in an inkjet head with respect to an ink amount.

FIG. 8 is an explanatory diagram of a state inside the ink tank due to a change in surrounding environment.

FIG. 9 is an explanatory diagram of a state inside the ink tank due to another change in the surrounding environment.

FIG. 10 is an explanatory diagram of a relationship between atmospheric pressure and ink static pressure.

FIG. 11 is a sectional view showing another embodiment of the ink supply device of the invention.

FIG. 12 is a schematic configuration diagram of an inkjet recording unit using the ink supply device of the present invention.

[Explanation of symbols]

1 inkjet head, 2 ink tanks, 3 inks, 4 main ink chambers, 5 communication passages, 6 sub ink chambers,
7 communication hole, 8 atmosphere communication hole, 9 absorbing member, 10 meniscus forming part, 11 ink guiding part, 12 supply path,
13 air layer, 14 filter, 15 cushioning member, 21
Inkjet recording unit, 22 ink tank, 2
3 heat sink, 24 flow path forming member, 25 substrate, 26
Inkjet head, 27 wiring pad, 28 sub-ink chamber, 29 atmosphere communication hole, 30 absorbing member, 31 ink guiding part, 32 main ink chamber, 33 meniscus forming part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiko Fujimura 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (7)

[Claims] 1. An ink supply device which is connected to an inkjet head and supplies ink to the inkjet head, and a main ink storage chamber which communicates with the inkjet head and stores the ink, and adjacent to a side of the main ink storage chamber. And a sub-ink storage chamber which is communicated with the main ink storage chamber in the lower space through a communication hole and has an atmosphere communication port opened on the upper side, and at least laterally disposed inside the sub-ink storage chamber. And an ink absorbing member arranged so as to be in close contact with the inner wall of the sub ink containing chamber, and a meniscus forming portion provided so as to cover the communication hole of the sub ink containing chamber. 2. The ink supply device according to claim 1, wherein the meniscus forming portion is formed of a mesh body. 3. The ink supply device according to claim 1, wherein the meniscus forming portion is made of a porous material. 4. The ink according to claim 1, further comprising an ink guide portion which is in contact with a lower surface of the meniscus forming portion and extends into a lower space communicating with the main ink storage chamber. Supply device. 5. The ink guide portion has one end in contact with the meniscus forming portion and the other end in contact with a bottom portion of a lower space communicating with the main ink storage chamber. Ink supply device described. 6. The ink according to claim 4, wherein the ink guide portion has a cross section smaller than that of the communication hole, and forms a region in the meniscus forming portion that is not in contact with the ink guide portion. Supply device. 7. The ink supply device according to claim 1, wherein a filter having a higher filtration accuracy than the meniscus forming portion is arranged between the main ink storage chamber and the inkjet head. .