Patent Application
20100282342
1. Field of the Invention
The present invention relates to a liquid supplying member, a negative pressure unit, and a liquid discharging apparatus.
2. Description of the Related Art
In a liquid discharging apparatus such as an ink jet recording apparatus, when bubbles are mixed into a liquid such as ink, the discharge becomes unstable or a discharge amount fluctuates. If bubbles exist in a tank for storing the ink, a flow path for supplying the ink stored in the tank to a liquid discharging head, or the like, the liquid is not smoothly supplied or circulated.
In recent years, the ink jet recording apparatus is also used when an image or characters are recorded onto a sheet of a large size such as A1 format or A0 format.
In the ink jet recording apparatus which consumes a large amount of ink as mentioned above, a main tank and the liquid discharging head (recording head) are connected through the negative pressure unit. The ink in the main tank is supplied to the recording head through the negative pressure unit as necessary and the ink in the recording head is collected to the negative pressure unit.
The negative pressure unit has: a buffer function for temporarily storing the ink which is supplied to the recording head; and a gas/liquid exchanging function for separating the bubbles or foams mixed through the recording head or tube into the ink (liquid) and the gas. A lower space in the negative pressure unit is used mainly to perform the buffer function. An upper space in the negative pressure unit is used mainly to perform the gas/liquid exchanging function.
The gas is often mixed into the recording head in the case of executing a head recovery in order to remove the mist and ink deposited onto the nozzle surface after a predetermined recording was executed. Particularly, when a series of recovering steps due to the ink suction is executed, there is a case where the air is mixed from the nozzle, so that the air remains in the recording head or the tube (ink flow path) or becomes bubbles and flows.
If an air stagnation exists on the nozzle side of a filter on the ejecting side arranged in the recording head, the air passes through the filter and flows to the negative pressure unit side in association with the ink sucking operation by a pump.
If the bubbles remain or are deposited in the ink flow path or the negative pressure unit, the smooth flow of the ink is obstructed and becomes a cause of an increase in drain ink amount at the time of the recovery operation or becomes a cause of occurrence of a trouble in the separation into the liquid and the gas in a gas/liquid exchanging chamber.
An ink tank which has a main ink chamber and a sub-ink chamber and in which the inside of the sub-ink chamber is partitioned to a bubble storage part and an ink storing portion by a partition plate has been disclosed in U.S. Pat. No. 6,848,776. Further, an ink introducing hole to introduce the ink from the bubble storage part to the ink storing portion is formed in the partition plate, and a concave/convex surface is formed on the surface which faces the bubble storage part. In the ink tank having the above structure, the bubbles generated in the bubble storage part are captured by the concave/convex surface and the captured bubbles are coupled and increase in size, so that they are separated from the ink liquid surface and ejected.
However, in the ink tank disclosed in U.S. Pat. No. 6,848,776, shapes and materials of the portions near the ink introducing hole and those of the inner wall of the tank are not the shapes and materials which are effective to separate and eject the bubbles. There is, consequently, a case where the bubbles are deposited in the tank and it becomes difficult to eject them. Therefore, in the case where a portion to be detected (prism) for optically detecting a residual amount of ink in the sub-ink chamber is arranged under the ink introducing hole, there is a possibility that an erroneous detection is caused by the bubbles deposited to the portions near the ink introducing hole or by the grown foams.
It is an object of the invention to provide a liquid supplying member which can prevent deposition of bubbles and foams onto an inner wall of the liquid supplying member and can improve ejecting performance of the bubbles and foams.
Another object of the invention is to provide a liquid supplying member for supplying a liquid to a liquid discharging apparatus, comprising: a filter which is provided at an inlet of the liquid supplying member; and a concave/convex shape which is provided on an inner wall surface of the liquid supplying member and in which a mountain portion and a valley portion are repeated, wherein assuming that an opening diameter of the filter is equal to R (μm), one period f (μm) of a spatial frequency at which the mountain portion and the valley portion of the concave/convex shape are repeated lies within a range from R or more √{square root over (2)}·R or less and a maximum height Ry (μm) of the mountain portion is equal to √2·R/2 or more.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An example of an exemplary embodiment of a liquid supplying member of the invention will be described with reference to the drawings.
As illustrated in
Subsequently, a structure (shape) of the inner wall surface of the liquid supplying member 10 will be described further in detail. Assuming that an opening diameter of the filter 13 is equal to R (μm), the mountain portion 11 and the valley portion 12 are periodically and repetitively formed on the inner wall surface of the liquid supplying member 10 at a spatial frequency in which one period f (μm) lies within a range from R or more to √2·R or less. In other words, a pitch between the centers of the adjacent mountain portions (or valley portions) lies within a range from R (μm) or more to √2·R (μm) or less. Further, a maximum height Ry (μm) of the mountain portion 11 (=maximum depth of the valley portion 12) is equal to √2·R/2 (μm) or more.
The liquid supplying member 10 is molded by using a die. The die is worked by a machining center to which an end mill according to the shape of the inner wall surface of the liquid supplying member 10 mentioned above has been attached. When the die is worked, the working is performed by NC controlling the machining center so that the spatial frequency and the maximum height can be obtained.
The structure (shape) of the inner wall surface of the liquid supplying member 10 may be a structure (shape) illustrated in
The die to obtain the comb-tooth like surface shape as illustrated in
In any of the above cases, whether or not the die surface has a desired shape is evaluated by using a 3-dimensional shape measuring apparatus using an optical method or by a stylus tracing type measuring apparatus. A spatial frequency analysis of a periodic structure is made from data of a measured roughness curve. As a frequency analysis, a power spectrum analyzing method using Fast Fourier transform (FFT) or a correlation function analyzing method can be used. A numerical value of the maximum height Ry (μm) is obtained based on he definition of JIS B 0601-1994.
By the die which was manufactured and evaluated as mentioned above, the liquid supplying member 10 is molded by using an engineering plastics material. The inner wall surface of the liquid supplying member 10 has a concave/convex shape and is worked into a shape having the spatial frequency in the direction parallel with the flowing direction of the liquid or bubbles 14. Specifically speaking, the inner wall surface is worked so as to have the spatial frequency in which one period f (μm) lies within a range from R or more to √2·R or less for the opening diameter of the filter 13 arranged in the liquid supplying member 10 and to obtain the surface shape in which the maximum height Ry (μm) is equal to √2·R/2 or more. The shape of the inner wall surface may be a surface shape of one continuous condition so long as the foregoing conditions are satisfied. It may be a combination of surface shapes of two or more different kinds of conditions as illustrated in
Each of the vertex portion of the mountain portion 11 and the bottom portion of the valley portion 12 illustrated in
The engineering plastics material having good moldability and workability can be used as a material of the liquid supplying member 10. Desirably, polyacetal (POM), polyether ether ketone (PEEK), polyether ketone (PEK), a urea resin, an ethylene-vinylalcohol copolymer resin (EVOH), nylon (NY), polybutylene terephthalate (PBT), or the like which does not have a hydrophobic group on the surface can be properly used. General-use plastics such as polyethylene (PE) can be used.
As for the engineering plastics which do not have a hydrophobic group on the surface, when the bubbles or foams are come into contact with the surface, since the engineering plastics do not have a hydrophobic interaction with a surface active agent which has been impregnated in the liquid such as ink and oriented on the surfaces of the bubbles or foams, the bubbles or foams are chemically difficult to be deposited.
With respect to the shape of the inner wall surface of the molded and worked liquid supplying member 10, a measurement is made in a manner similar to the die surface, a spatial frequency analysis is performed from data of the measured roughness curve, and the shape is evaluated.
Upon verification of the deposition preventing effect of the bubbles in the liquid supplying member 10 and upon evaluation of the ejecting performance of the bubbles, a transparent window is formed in a part of the liquid supplying member 10 so that the inner wall surface can be observed, and an observation evaluation is performed.
Subsequently, an exemplary embodiment of a liquid discharging apparatus of the invention will be described. The liquid discharging apparatus according to the embodiment is an ink jet recording apparatus having the negative pressure unit.
In
A main tank 32 and the recording head 31 are connected through a negative pressure unit 33 arranged on the way of a flow path which couples them. The ink in the main tank 32 is supplied to the recording head 31 through the negative pressure unit 33 as necessary. The ink in the recording head 31 is collected to the negative pressure unit 33.
An enlarged cross sectional view of the negative pressure unit 33 is illustrated in
Referring again to
A head recovery mechanism is provided for the ink jet recording apparatus of the embodiment in order to maintain and stabilize the discharging performance such as discharge amount and impact position precision of the recording head 31.
According to the head recovery mechanism, the ink is sucked by a sucking pump 37 in a state where the nozzle of the recording head 31 has been covered with a cap 36, thereby eliminating clogging of the nozzle. By using a switching valve 38 illustrated in the diagram, the ink sucked by the sucking pump 37 can be collected to the gas/liquid exchanging chamber 33b of the negative pressure unit 33 through a collecting tube 39. By using such an ink path, the ink can be used again and using efficiency of the ink can be improved.
The ink in the recording head 31 is sucked by a circulating pump 41, passes through an ejecting filter 42 provided for the recording head 31, and can be returned to the buffer tank 33a through a circulating tube 43.
The ejecting filter 42 is provided for the recording head 31 in order to prevent the dust from entering the negative pressure unit 33 by the circulating operation of the ink. Therefore, an opening diameter of the ejecting filter 42 is smaller than an inner diameter of the circulating tube 43. An inflow filter 44 is provided to prevent the dust from entering the recording head 31 by the ink supply from the negative pressure unit 33 to the recording head 31. Therefore, an opening diameter of the inflow filter 44 is smaller than dimensions of a nozzle flow path (not shown) formed in the recording head 31.
Subsequently, the gas/liquid exchanging chamber 33b of the negative pressure unit 33 will be described with reference to
The buffer tank 33a and gas/liquid exchanging chamber 33b constructing the negative pressure unit 33 can be molded by using the die in a manner similar to the liquid supplying member 10. Particularly, a concave/convex shape having a spatial frequency similar to that of the inner wall surface of the liquid supplying member 10 is formed on the inner wall surface of the negative pressure unit 33 so as to be parallel with the flowing direction of the ink to which the air has been mixed.
In the gas/liquid exchanging chamber 33b, at the time of the recovery operation of the recording head 31, the ink in which the bubbles have been mixed is returned from the upper portion of the gas/liquid exchanging chamber 33b through the collecting tube 39. At this time, although the bubble generated in the recording head 31 passes through the nozzle and flows to the collecting tube 39 by the continuation of the recovery operation, a size of bubble is determined by the opening diameter of the inflow filter 44 without being influenced by the nozzle diameter.
In the floating chamber 51 in the gas/liquid exchanging chamber 33b, the ink returned through the collecting tube 39 is gas/liquid separated and the gas is ejected from an ejecting flow path 52 in an upper portion of the floating chamber 51. As mentioned above, in the gas/liquid exchanging chamber 33b, the fluid flows in the direction parallel with the inner wall side surface of the gas/liquid exchanging chamber 33b. Therefore, in the gas/liquid exchanging chamber 33b constructing the negative pressure unit 33, the concave/convex shape having the spatial frequency is formed in the direction parallel with the inner wall side surface.
In the gas/liquid exchanging chamber 33b, since the fluid is gas/liquid separated in the floating chamber 51, the ink flows in the direction parallel with the direction which is directed toward an inlet 53 of the floating chamber 51. Therefore, the concave/convex shape having the spatial frequency in the direction parallel with the direction directed toward the inlet 53 of the floating chamber 51 is formed on a bottom surface 54 of the floating chamber 51 on the buffer tank side. That is, assuming that the opening diameter of the filter 44 is set to R (μm), the concave/convex shape which has the spatial frequency in which one period f (μm) lies within a range from R or more to √2·R or less and in which the maximum height Ry (μm) is equal to √2·R/2 or more is formed.
In the buffer tank 33a, the ink in which the bubbles have been mixed is returned from the recording head through the circulating tube 43. At this time, particularly, the bubbles contained in the ink flow to an upper portion in the direction parallel with the inner wall side surface of the buffer tank 33a by a buoyancy. The ink is supplied from the main tank 32 to the buffer tank 33a. In this instance, first, the ink flows to a lower portion in the direction parallel with the inner wall side surface of the buffer tank 33a. When the ink of a predetermined amount is supplied, the flow of the ink stops. As mentioned above, in the buffer tank 33a, the ink flows in the direction parallel with the inner wall side surface in a manner similar to the gas/liquid exchanging chamber 33b. Therefore, also in the buffer tank 33a, the concave/convex shape having the spatial frequency is formed in the direction parallel with the inner wall side surface. That is, assuming that the opening diameter of the filter 42 is set to R (μm), the concave/convex shape which has the spatial frequency in which one period f (μm) lies within a range from R or more to √2·R or less and in which the maximum height Ry (μm) is equal to √2·R/2 or more is formed.
The surface shape of the die to mold the negative pressure unit 33 is evaluated by a method similar to that of the surface shape of the die to mold the liquid supplying member 10. A spatial frequency analysis is performed and the maximum height Ry is obtained also by a method similar to that mentioned above.
The negative pressure unit 33 is molded by using the engineering plastics material by the die which was manufactured and evaluated as mentioned above.
The shape of the inner wall surface of the negative pressure unit 33 may be a surface shape of one continuous condition so long as the foregoing conditions are satisfied. It may be a combination of surface shapes of two or more different kinds of conditions. The shape of the inner wall surface may be a projecting shape.
As a material of the negative pressure unit 33, the engineering plastics material similar to that of the liquid supplying member 10 or a general-use plastics material can be used.
With respect to the shape of the inner wall surface of the negative pressure unit 33, a measurement is made in a manner similar to the die surface, a spatial frequency analysis is performed from data of the measured roughness curve, and the shape is evaluated.
Upon verification of the deposition preventing effect of the bubbles in the negative pressure unit 33 and upon evaluation of the ejecting performance of the bubbles, a transparent window is formed in a part of the negative pressure unit 33 so that the inner wall surface can be observed, and an observation evaluation is performed.
As an Example of the liquid supplying member 10 illustrated in
Any of the trial products is molded by using the die. The surface of the die which was used (surface on which the inner wall surface of the liquid supplying member is formed) is worked by using the machining center to which the end mill has been attached. Polyacetal (POM) is also used as a material of any of the trial products.
In each trial product, the depositing state to the inner wall surface of the bubbles which pass through the filter and are generated is observed. An observation result is shown in Table 1.
An evaluation reference is defined as follows. The trial product in which the deposition of the bubbles to the inner wall surface is hardly observed is shown by ⊚. The trial product in which the depositing state of the bubbles of less than 15% exists in the observation area is shown by ◯. The trial product in which the depositing state of the bubbles in a range from 15% or more to less than 30% exists in the observation area is shown by Δ. The trial product in which the depositing state of the bubbles of 30% or more exists in the observation area is shown by x.
It will be understood from Table 1 that in the trial product in which one period f of the spatial frequency is equal to 15 to 20 (μm) and the maximum height Ry is equal to 15 (μm) or more, the deposition of the bubbles is hardly observed and the good deposition preventing performance of the bubbles and the good ejecting performance are obtained.
In the trial product in which one period f of the spatial frequency is equal to 5 to 15 (μm) and the maximum height Ry is equal to 5 (μm) or more, the deposition of a number of bubbles is observed and a state where the bubbles are mutually coupled and foamed with the elapse of time is observed. Further, also in the trial product in which one period f of the spatial frequency is equal to 25 (μm) or more and the maximum height Ry is equal to 5 (μm) or more, the deposition of a number of bubbles is observed and a state where the bubbles are mutually coupled and foamed with the elapse of time is observed.
As an Example of the negative pressure unit 33 illustrated in
Each trial product is built in the ink jet recording apparatus having the construction illustrated in
In the ink jet recording apparatus in which each trial product has been built, the head recovery operation is executed and the collected ink containing the bubbles is returned to the negative pressure unit (each trial product). Further, when the air existing in the recording head passes through the filter, the bubbles are generated. At this time, although the generated bubbles pass through a pump corresponding to the pump 37 illustrated in
The depositing state of the bubbles to the inner wall surface of each trial product is observed. Thus, in the trial product in which one period f of the spatial frequency of the shape of the inner wall surface is equal to 15 to 20 (μm) and the maximum height Ry is equal to 15 (μm) or more, the deposition of the bubbles is hardly observed and the good deposition preventing performance of the bubbles and the good ejecting performance are obtained.
In the trial product in which one period f of the spatial frequency of the shape is equal to 5 to 15 (μm) and the maximum height Ry is equal to 5 (μm) or more and the trial product in which one period f of the spatial frequency of the shape is equal to 25 (μm) or more and the maximum height Ry is equal to 5 (μm) or more, the deposition of a number of bubbles is observed in the buffer tank and the gas/liquid exchanging chamber. In the gas/liquid exchanging chamber, a state where the bubbles are mutually coupled and foamed with the elapse of time is observed.
According to each embodiment of the invention, the deposition of the bubbles or foams to the inner wall of the liquid supplying member is prevented and the ejecting performance of the bubbles or foams is improved. The increase in drain ink amount in the liquid discharging apparatus and the erroneous operation of the separating mechanism of the gas and liquid are prevented.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-113424, filed May 8, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-113424 | May 2009 | JP | national |
