Abstract:
To solve the problem of a liquid supply unit of the related art in that liquid supply may become difficult. 
     The invention provides a tank capable of supplying a liquid to a liquid ejection head, the tank including: a liquid containing portion capable of containing the liquid; and an atmospheric air introducing portion constituting an atmospheric air flow channel capable of introducing atmospheric air into the liquid containing portion, wherein the atmospheric air introducing portion includes a buffer chamber capable of containing the atmospheric air, a liquid retaining member is housed in the buffer chamber, and in a state in which the liquid retaining member is housed in the buffer chamber, a gap that allows the atmospheric air to move between a first communication port and a second communication port of the atmospheric air flow channel is provided within the buffer chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The entire disclosure of Japanese Patent Application No. 2015-055789, filed Mar. 19, 2015 is expressly incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a liquid supply unit and the like. 
         [0004]    2. Related Art 
         [0005]    An inkjet printer has long been known as an example of a liquid ejection apparatus. The inkjet printer can perform printing onto a print medium such as print paper by discharging ink, which is an example of a liquid, from an ejection head to the print medium. It has long been known that the inkjet printer is configured to supply ink stored in a tank, which is an example of a liquid supply unit, to the ejection head. The tank is provided with an ink injection inlet. The user can load ink into the tank from the ink injection inlet. It has long been known that the tank has a configuration in which a liquid containing chamber in which ink is contained and an air containing chamber into which atmospheric air is introduced communicate with each other by a communication portion (see, for example, JP-A-2012-20495). The configuration in which the liquid supply unit is attached to the liquid ejection apparatus is referred to as a liquid ejection system. 
         [0006]    In the tank disclosed in JP-A-2012-20495 mentioned above, for example, even if the ink contained in the liquid containing chamber flows out to the air containing chamber side via the communication portion, the ink that has flowed into the air containing chamber can be stored in the air containing chamber. For this reason, with this tank, leakage of the ink contained in the liquid containing chamber to the outside via an atmospheric air opening is easily suppressed. However, if the orientation of the inkjet printer is changed with the ink having flowed into the air containing chamber from the liquid containing chamber, the ink contained in the air containing chamber may flow to the outside of the tank via the atmospheric air opening. To address this, it is considered effective to house a liquid retaining member in the air containing chamber. The liquid retaining member is a member having a high level of ability to absorb and retain a liquid such as ink. The material of the liquid retaining member can be, for example, sponge, sea sponge or the like. By housing the liquid retaining member in the air containing chamber, the ink that has flowed into the air containing chamber from the liquid containing chamber can be retained by the liquid retaining member, and thus the ink is likely to remain in the air containing chamber. However, if the ink that has flowed into the air containing chamber is absorbed by the liquid retaining member, a flow of the atmospheric air may be blocked by the liquid retaining member. In other words, if the ink that has flowed into the air containing chamber is absorbed by the liquid retaining member, entry of the atmospheric air into the liquid containing chamber from the atmospheric air opening may be blocked. If the entry of the atmospheric air into the liquid containing chamber is blocked, along with printing onto a print medium, or in other words, along with consumption of the ink contained in liquid containing chamber, the pressure within the liquid containing chamber becomes lower than the atmospheric pressure. If such a situation occurs, it becomes difficult to supply ink from the tank to the ejection head. In other words, the liquid supply unit of the related art is problematic in that liquid supply may become difficult. 
       SUMMARY 
       [0007]    The invention can solve at least the problem described above, and may be implemented as embodiments or application examples described below. 
       APPLICATION EXAMPLE 1 
       [0008]    A tank capable of supplying a liquid to a liquid ejection head, the tank including: a liquid containing portion capable of containing the liquid; and an atmospheric air introducing portion constituting an atmospheric air flow channel capable of introducing atmospheric air into the liquid containing portion, wherein the atmospheric air introducing portion includes a buffer chamber capable of containing the atmospheric air, the buffer chamber is provided with a first communication port located at a position on the liquid containing portion side in the atmospheric air flow channel and a second communication port located at a position on a side opposite to the liquid containing portion in the atmospheric air flow channel, a liquid retaining member is housed in the buffer chamber, and in a state in which the liquid retaining member is housed in the buffer chamber, a gap that allows the atmospheric air to move between the first communication port and the second communication port is provided within the buffer chamber. 
         [0009]    In the tank according to this application example, because the gap that allows the atmospheric air to move between the first communication port and the second communication port is formed within the buffer chamber, even if the liquid permeates into the liquid retaining member in the buffer chamber and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. 
       APPLICATION EXAMPLE 2 
       [0010]    The tank according to the above-described application example, wherein the gap is provided between the liquid retaining member and an inner wall constituting the buffer chamber. 
         [0011]    In the tank according to this application example, the gap is provided between the liquid retaining member and the inner wall constituting the buffer chamber, and thus the atmospheric air can easily move between the first communication port and the second communication port. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. 
       APPLICATION EXAMPLE 3 
       [0012]    The tank according to the above-described application example, wherein a dimension in a vertical direction of the liquid retaining member is smaller than a dimension in the vertical direction of the buffer chamber, and a dimension in a horizontal direction of the liquid retaining member is smaller than a dimension in the horizontal direction of the buffer chamber, the horizontal direction being perpendicular to the vertical direction. 
         [0013]    In the tank according to this application example, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, by reducing the dimensions of the liquid retaining member, the cost for the liquid retaining member can be reduced. 
       APPLICATION EXAMPLE 4 
       [0014]    The tank according to the above-described application example, including a protrusion protruding from an inner wall of the buffer chamber toward the liquid retaining member. 
         [0015]    In the tank according to this application example, with the protrusion protruding from the inner wall of the buffer chamber toward the liquid retaining member, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, even if there are variations in the dimensions of the liquid retaining member, the gap can be ensured by the protrusion, and thus the reduction in the pressure of the liquid containing portion can be further suppressed. 
       APPLICATION EXAMPLE 5 
       [0016]    The tank according to the above-described application example, including: a first protrusion protruding in a vertical direction from an inner wall of the buffer chamber toward the liquid retaining member; and a second protrusion protruding in a horizontal direction, which is perpendicular to the vertical direction, from the inner wall of the buffer chamber toward the liquid retaining member. 
         [0017]    In the tank according to this application example, with the first protrusion and the second protrusion protruding from the inner wall of the buffer chamber toward the liquid retaining member, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, even if there are variations in the dimensions of the liquid retaining member, the gap can be ensured by the protrusions, and thus the reduction in the pressure of the liquid containing portion can be further suppressed. 
       APPLICATION EXAMPLE 6 
       [0018]    The tank according to the above-described application example, including a protrusion protruding from the liquid retaining member toward an inner wall of the buffer chamber. 
         [0019]    In the tank according to this application example, with the protrusion protruding from the liquid retaining member toward the inner wall of the buffer chamber, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. For example, in a configuration in which the inner wall of the buffer chamber and the liquid retaining member are in face contact with each other, the attraction force between the inner wall and the liquid retaining member into which the liquid has permeated increases, and it is considered that the liquid retaining member is fixed. At this time, if the liquid retaining member is fixed while covering the first communication port, it is difficult for the atmospheric air to move between the first communication port and the second communication port. As a result, it is considered that the pressure in the liquid containing portion is likely to decrease. In contrast, in the tank of this application example, with the protrusion protruding from the liquid retaining member toward the inner wall of the buffer chamber, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. Accordingly, the reduction in the pressure of the liquid containing portion can be further suppressed. 
       APPLICATION EXAMPLE 7 
       [0020]    The tank according to the above-described application example, including: a first protrusion protruding in a vertical direction from the liquid retaining member toward an inner wall of the buffer chamber; and a second protrusion protruding in a horizontal direction, which is perpendicular to the vertical direction, from the liquid retaining member toward the inner wall of the buffer chamber. 
         [0021]    In the tank according to this application example, with the first protrusion and the second protrusion protruding from the liquid retaining member toward the inner wall of the buffer chamber, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. For example, in a configuration in which the inner wall of the buffer chamber and the liquid retaining member are in face contact with each other, the attraction force between the inner wall and the liquid retaining member into which the liquid has permeated increases, and it is considered that the liquid retaining member is fixed. At this time, if the liquid retaining member is fixed while covering the first communication port, it is difficult for the atmospheric air to move between the first communication port and the second communication port. As a result, it is considered that the pressure in the liquid containing portion is likely to decrease. In contrast, in the tank of this application example, with the protrusions protruding from the liquid retaining member toward the inner wall of the buffer chamber, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. Accordingly, the reduction in the pressure of the liquid containing portion can be further suppressed. 
       APPLICATION EXAMPLE 8 
       [0022]    The tank according to the above-described application example, including a support member located in the gap between an inner wall of the buffer chamber and the liquid retaining member. 
         [0023]    In the tank according to this application example, with the support member located in the gap between the inner wall of the buffer chamber and the liquid retaining member, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. For example, in a configuration in which the inner wall of the buffer chamber and the liquid retaining member are in face contact with each other, the attraction force between the inner wall and the liquid retaining member into which the liquid has permeated increases, and it is considered that the liquid retaining member is fixed. At this time, if the liquid retaining member is fixed while covering the first communication port, it is difficult for the atmospheric air to move between the first communication port and the second communication port. As a result, it is considered that the pressure in the liquid containing portion is likely to decrease. In contrast, in the tank of this application example, with the support member located in the gap between the inner wall of the buffer chamber and the liquid retaining member, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. Accordingly, the reduction in the pressure of the liquid containing portion can be further suppressed. 
       APPLICATION EXAMPLE 9 
       [0024]    The tank according to the above-described application example, including a first support member located in a gap in a vertical direction between an inner wall of the buffer chamber and the liquid retaining member; and a second support member located in a gap in a horizontal direction between the inner wall of the buffer chamber and the liquid retaining member, the horizontal direction being perpendicular to the vertical direction. 
         [0025]    In the tank according to this application example, with the first support member and the second support member located in the gap between the inner wall of the buffer chamber and the liquid retaining member, a gap that allows the atmospheric air to move between the first communication port and the second communication port can be formed within the buffer chamber. For this reason, even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the reduction in the pressure of the liquid containing portion can be suppressed, and thus the liquid can be easily supplied to the liquid ejection head from the tank. Furthermore, in the tank according to this application example, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. For example, in a configuration in which the inner wall of the buffer chamber and the liquid retaining member are in face contact with each other, the attraction force between the inner wall and the liquid retaining member into which the liquid has permeated increases, and it is considered that the liquid retaining member is fixed. At this time, if the liquid retaining member is fixed while covering the first communication port, it is difficult for the atmospheric air to move between the first communication port and the second communication port. As a result, it is considered that the pressure in the liquid containing portion is likely to decrease. In contrast, in the tank of this application example, with the first support member and the second support member located in the gap between the inner wall of the buffer chamber and the liquid retaining member, the face contact between the inner wall of the buffer chamber and the liquid retaining member can be easily avoided. Accordingly, the reduction in the pressure of the liquid containing portion can be further suppressed. 
       APPLICATION EXAMPLE 10 
       [0026]    The tank according to the above-described application example, wherein the liquid retaining member includes a plurality of plate-like members and a binding member that bundles the plurality of plate-like members. 
         [0027]    In the tank according to this application example, the liquid retaining member has a configuration in which a plurality of plate-like members are bundled by a binding member. In the tank according to this application example, the liquid retaining member can be configured to fit into buffer chambers of various sizes by adjusting the number of plate-like members bundled. With this configuration, the plate-like members can be used commonly in buffer chambers of various sizes. As a result, the cost for the liquid retaining member can be easily reduced. 
       APPLICATION EXAMPLE 11 
       [0028]    The tank according to the above-described application example, further including: a liquid injection portion capable of injecting the liquid into the liquid containing portion; and a cap member that is detachably attached to the liquid injection portion. 
         [0029]    In the tank according to this application example, a gap that allows the atmospheric air to move between the first communication port and the second communication port is provided within the buffer chamber, and thus even if the liquid contained in the buffer chamber permeates into the liquid retaining member and the gap of the liquid retaining member is closed by the liquid, the atmospheric air easily flows into the liquid containing portion from the atmospheric air introducing portion. As a result, the change in the pressure of the liquid containing portion can be suppressed. Here, for example, if the pressure within the liquid containing chamber increases to a level higher than the atmospheric pressure, with a flow of the atmospheric air into the liquid containing chamber being blocked, the cap member attached to the liquid injection portion may be detached therefrom. To address this, in the tank of this application example, the gap that allows the atmospheric air to move between the first communication port and the second communication port is provided within the buffer chamber, and thus the atmospheric air can easily flow out of the tank from the liquid containing portion. As a result, in the tank according to this application example, it is possible to use a detachable cap member. 
       APPLICATION EXAMPLE 12 
       [0030]    The tank according to the above-described application example, wherein the buffer chamber includes a first atmospheric air introducing inlet formed at an intersection with the liquid containing portion and a second atmospheric air introducing inlet that is open toward outside of the tank, and the first communication port is the first atmospheric air introducing inlet, and the second communication port is the second atmospheric air introducing inlet. 
       APPLICATION EXAMPLE 13 
       [0031]    The tank according to the above-described application example, wherein the atmospheric air introducing portion further includes a first atmospheric air communication path that communicates between the buffer chamber and the liquid containing portion, the first atmospheric air communication path includes a first atmospheric air introducing inlet formed at an intersection with the liquid containing portion, and the first communication port is an area where the buffer chamber is connected to the first atmospheric air communication path. 
         [0032]    Because the tank according to this application example is provided with the first atmospheric air communication path, it is possible to make it difficult for the liquid to leak to the outside from the atmospheric air introducing portion. 
       APPLICATION EXAMPLE 14 
       [0033]    The tank according to the above-described application example, wherein the atmospheric air introducing portion further includes a second atmospheric air communication path that communicates between the buffer chamber and outside of the tank, the second atmospheric air communication path includes a second atmospheric air introducing inlet that is open toward the outside of the tank, and the second communication port is an area where the buffer chamber is connected to the second atmospheric air communication path. 
         [0034]    Because the tank according to this application example is provided with the second atmospheric air communication path, it is possible to make it difficult for the liquid to leak to the outside from the atmospheric air introducing portion. 
       APPLICATION EXAMPLE 15 
       [0035]    The tank according to the above-described application example, wherein when it is assumed that the buffer chamber is a first buffer chamber, the second atmospheric air communication path includes a second buffer chamber that is smaller than the first buffer chamber, the second buffer chamber is located further upstream of the atmospheric air flow channel than the first buffer chamber, when it is assumed that the liquid retaining member is a first liquid retaining member, a second liquid retaining member that is smaller than the first liquid retaining member is housed in the second buffer chamber, and in a state in which the second liquid retaining member is housed in the second buffer chamber, a gap that allows the atmospheric air to move between the outside and the first buffer chamber is provided within the second buffer chamber. 
         [0036]    Because the tank according to this application example is provided with the second buffer chamber, it is possible to make it difficult for the liquid to leak to the outside from the atmospheric air introducing portion. 
       APPLICATION EXAMPLE 16 
       [0037]    A tank unit including: the tank according to the above-described application example; and a case that houses the tank. 
         [0038]    In the tank unit according to this application example, the tank can be protected by the case. 
       APPLICATION EXAMPLE 17 
       [0039]    A liquid ejection system including: the tank unit according to the above-described application example; a tube connected to the tank unit; and a liquid ejection apparatus connected to the tank unit via the tube, wherein when it is assumed that the case is a first case, the liquid ejection apparatus includes the liquid ejection head and a second case that houses the liquid ejection head. 
         [0040]    In the liquid ejection system according to this application example, the tank can be protected by the first case, and the liquid ejection head can be protected by the second case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0042]      FIG. 1  is a perspective view showing main constituent elements of a liquid ejection system according to an embodiment of the invention. 
           [0043]      FIG. 2  is a perspective view showing another example of the main constituent elements of the liquid ejection system of the embodiment. 
           [0044]      FIG. 3  is an exploded perspective view showing a tank according to Example 1. 
           [0045]      FIG. 4  is a side view of the tank according to Example 1 as viewed from a sheet member side. 
           [0046]      FIG. 5  is a side view of the tank according to Example 1 as viewed from a sheet member side. 
           [0047]      FIG. 6  is an exploded perspective view showing a tank according to Example 2. 
           [0048]      FIG. 7  is an exploded perspective view showing a tank according to Example 3. 
           [0049]      FIG. 8  is an exploded perspective view showing a tank according to Example 4. 
           [0050]      FIG. 9  is a side view of a tank according to Example 5 as viewed from a sheet member side. 
           [0051]      FIG. 10  is a side view of a tank according to Example 6 as viewed from a sheet member side. 
           [0052]      FIG. 11  is a side view of a tank according to Example 7 as viewed from a sheet member side. 
           [0053]      FIG. 12  is an exploded perspective view showing a tank according to Example 8. 
           [0054]      FIG. 13  is a perspective view showing a case according to Example 8. 
           [0055]      FIG. 14  is a side view of the tank according to Example 8 as viewed from a sheet member side. 
           [0056]      FIG. 15  is an exploded perspective view showing a tank according to Example 9. 
           [0057]      FIG. 16  is an exploded perspective view showing a tank according to Example 10. 
           [0058]      FIG. 17  is an exploded perspective view showing a first liquid retaining member according to Example 10. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0059]    An embodiment will be described with reference to the drawings by taking a liquid ejection system as an example. In the diagrams, in order to show constituent elements so as to be recognizable, the constituent elements and members may be scaled differently. 
         [0060]    A liquid ejection system  1  according to the present embodiment includes, as shown in  FIG. 1 , a printer  3 , which is an example of a liquid ejection apparatus, and an ink supply apparatus  4 , which is an example of a liquid supply apparatus. The printer  3  includes a recording portion  6  and a control portion  9 . In  FIG. 1 , X, Y and Z axes, which are mutually perpendicular coordinate axes, are shown. In the diagrams mentioned hereinafter, the X, Y and Z axes are shown as appropriate. In the present embodiment, a state in which the liquid ejection system  1  is disposed on a horizontal plane (XY plane) defined by the X axis and the Y axis is the in-use state of the liquid ejection system  1 . The Z axis is an axis perpendicular to the horizontal plane. In the in-use state of the liquid ejection system  1 , the Z axis direction is the vertically upward direction. Also, in the in-use state of the liquid ejection system  1 , in  FIG. 1 , −Z axis direction is the vertically downward direction. In each of the X, Y and Z axes, the direction of the arrow indicates the positive (+) direction, and a direction opposite to the direction of the arrow indicates the negative (−) direction. 
         [0061]    In the printer  3 , the recording portion  6  and the control portion  9  are housed in a housing  11 . The recording portion  6  performs recording on a recording medium P conveyed in the Y axis direction by a conveyance apparatus (not shown) by using ink, which is an example of liquid. The unshown conveyance apparatus intermittently conveys the recording medium P such as recording paper in the Y axis direction. The recording portion  6  is configured so as to be capable of reciprocal movement along the X axis by a moving apparatus (not shown). The ink supply apparatus  4  supplies ink to the recording portion  6 . The control portion  9  controls driving of the above-described constituent elements. In the liquid ejection system  1 , at least a part of the ink supply apparatus  4  protrudes to the outside of the housing  11 . The recording portion  6  is housed in the housing  11 , which is an example of a second case. With this configuration, the recording portion  6  can be protected by the housing  11 . 
         [0062]    The direction along the X axis is not limited to the direction completely parallel to the X axis, and encompasses directions inclined due to error, tolerance or the like excluding the direction perpendicular to the X axis. Likewise, the direction along the Y axis is not limited to the direction completely parallel to the Y axis, and encompasses directions inclined due to error, tolerance or the like excluding the direction perpendicular to the Y axis. The direction along the Z axis is not limited to the direction completely parallel to the Z axis, and encompasses directions inclined due to error, tolerance or the like excluding the direction perpendicular to the Z axis. In other words, the direction along an arbitrary axis or plane is not limited to the direction completely parallel to the arbitrary axis or plane, and encompasses directions inclined due to error, tolerance or the like excluding the direction perpendicular to the arbitrary axis or plane. 
         [0063]    The recording portion  6  includes a carriage  17  and a recording head  19 . The recording head  19  is an example of a liquid ejection head, and performs recording on the recording medium P by discharging ink in the form of ink droplets. The carriage  17  includes the recording head  19  mounted thereon. The recording head  19  is electrically connected to the control portion  9 . The discharge of ink droplets from the recording head  19  is controlled by the control portion  9 . 
         [0064]    As shown in  FIG. 1 , the ink supply apparatus  4 , which is an example of a tank unit, includes a tank  31 , which is an example of a liquid supply unit. In the present embodiment, the ink supply apparatus  4  includes a plurality of (four in the present embodiment) tanks  31 . The plurality of tanks  31  protrude to the outside of the housing  11  of the printer  3 . The plurality of tanks  31  are housed in a housing  32 . With this configuration, the tanks  31  can be protected by the housing  32 . The housing  32 , which is an example of a first case, protrudes from the housing  11 . 
         [0065]    The housing  32  and the housing  11  may be provided as separate units or integrated as a single unit. If the housing  32  and the housing  11  are integrated as a single unit, it can be said that the plurality of tanks  31  are housed together with the recording head  19  and ink supply tubes  34  in the housing  11 , as shown in  FIG. 2 . 
         [0066]    Each tank  31  contains an ink, which is an example of a liquid. The tank  31  is provided with a liquid injection portion  33 . With the tank  31 , an ink can be injected into the tank  31  via the liquid injection portion  33  from the outside of the tank  31 . The operator can access the liquid injection portion  33  of the tank  31  from the outside of the housing  32 . Also, the liquid injection portion  33  is sealed by a lid (not shown). When an ink is injected into the tank  31 , the liquid injection portion  33  is opened by detaching the lid before injection of the ink. 
         [0067]    An ink supply tube  34  is connected to each tank  31 . The ink contained in the tank  31  is supplied from the ink supply apparatus  4  to the recording head  19  via the ink supply tube  34 . Then, the ink supplied to the recording head  19  is discharged in the form of ink droplets from a nozzle (not shown) directed toward the recording medium P side. In the above-described example, the printer  3  and the ink supply apparatus  4  are described as separate constituent elements, but the ink supply apparatus  4  may be included in the configuration of the printer  3 . 
         [0068]    In the liquid ejection system  1  having the above-described configuration, the recording medium P is conveyed in the Y axis direction, and the carriage  17  is reciprocally moved along the X axis, and at the same time, the recording head  19  is caused to discharge ink droplets at predetermined positions, whereby recording is performed on the recording medium P. These operations are controlled by the control portion  9 . 
         [0069]    The ink is not limited to either water-based ink or oil-based ink. As the water-based ink, any of those having a configuration in which a solute such as a dye is dissolved in an aqueous solvent and those having a configuration in which a dispersoid such as a pigment is dispersed in an aqueous dispersion medium may be used. As the oil-based ink, any of those having a configuration in which a solute such as a dye is dissolved in an oil-based solvent and those having a configuration in which a dispersoid such as a pigment is dispersed in an oil-based dispersion medium may be used. 
         [0070]    Various examples of the tank  31  will be described. In the following description, in order to identify a tank  31  of each example, a different alphabet is attached to the reference numeral of the tank  31  of each example. 
       EXAMPLE 1 
       [0071]    A tank  31 A according to Example 1 will be described. As shown in  FIG. 3 , the tank  31 A includes a case  61 A, which is an example of a tank body, a sheet member  62  and a liquid retaining member  63 . The case  61 A is made of, for example, synthetic resin such as nylon or polypropylene. Also, the sheet member  62  is formed in a film by using synthetic resin (for example, nylon, polypropylene or the like), and has flexibility. In the present embodiment, the sheet member  62  is light-transmissive. 
         [0072]    The liquid retaining member  63  has a property that absorbs a liquid and retaining the absorbed liquid. As the material of the liquid retaining member  63 , for example, various materials such as foam, felt and non-woven fabric can be used. 
         [0073]    The case  61 A includes a hollow  64  and a hollow  65 . The liquid retaining member  63  is housed in the hollow  65 . The case  61 A is provided with a bonding portion  66 . In  FIG. 3 , for the sake of clarity of the configuration, the bonding portion  66  is indicated by hatching. The sheet member  62  is bonded to the bonding portion  66  of the case  61 A, with the liquid retaining member  63  being housed in the hollow  65 . In the present embodiment, the case  61 A and the sheet member  62  are bonded by welding. As a result of the sheet member  62  being bonded to the case  61 A, the hollow  64  and the hollow  65  are closed by the sheet member  62 . A space formed by the hollow  64  and the sheet member  62  will be referred to as “liquid containing portion  67 ” (described later). Likewise, a space formed by the hollow  65  and the sheet member  62  will be referred to as “buffer chamber  68 ” (described later). Accordingly, the liquid retaining member  63  is housed in the buffer chamber  68 . 
         [0074]    As shown in  FIG. 3 , the case  61 A includes a first wall  81 , a second wall  82 , a third wall  83 , a fourth wall  84 , a fifth wall  85 , a sixth wall  86  and a seventh wall  87 . The hollow  64  is located in the −Z axis direction of the fifth wall  85 . The hollow  65  is located in the Z axis direction of the fifth wall  85 . The hollow  64  and the hollow  65  are stacked along the Z axis with the fifth wall  85  interposed therebetween. The first wall  81  of the hollow  64  and the first wall  81  of the hollow  65  are the same wall. In other words, the hollow  64  and the hollow  65  share the first wall  81 . 
         [0075]    The hollow  64  is surrounded by the second wall  82 , the third wall  83 , the fourth wall  84  and the fifth wall  85  when the first wall  81  is viewed planarly in the Y axis direction. Likewise, the hollow  65  is surrounded by the second wall  82 , the fifth wall  85 , the sixth wall  86  and the seventh wall  87  when the first wall  81  is viewed planarly in the Y axis direction. The second wall  82  of the hollow  64  and the second wall  82  of the hollow  65  are the same wall. In other words, the hollow  64  and the hollow  65  share the second wall  82 . Likewise, the fifth wall  85  of the hollow  64  and the fifth wall  85  of the hollow  65  are the same wall. In other words, the hollow  64  and the hollow  65  share the fifth wall  85 . 
         [0076]    The second to seventh walls  82  to  87  intersect with the first wall  81 . The second wall  82  and the third wall  83  are provided at facing positions along the X axis with the first wall  81  interposed therebetween. The second wall  82  and the sixth wall  86  are provided at facing positions along the X axis with the first wall  81  interposed therebetween. The fourth wall  84  and the fifth wall  85  are provided at facing positions along the Z axis with the first wall  81  interposed therebetween. The fifth wall  85  and the seventh wall  87  are provided at facing positions along the Z axis with the first wall  81  interposed therebetween. The second wall  82  intersects with the fourth wall  84 , the fifth wall  85  and the seventh wall  87 . The third wall  83  intersects with the fourth wall  84  and the fifth wall  85 . The sixth wall  86  intersects with the fifth wall  85  and the seventh wall  87 . 
         [0077]    The second wall  82 , the third wall  83 , the fourth wall  84  and the fifth wall  85  protrude in the −Y axis direction from the first wall  81 . With this configuration, the hollow  64  is constituted by, with the first wall  81  being defined as the main wall, the second wall  82 , the third wall  83 , the fourth wall  84  and the fifth wall  85  that extend in the −Y axis direction from the main wall. The hollow  64  is configured so as to form a recess extending toward the Y axis direction. The hollow  64  is open toward the −Y axis direction, or in other words, toward the sheet member  62  side. To rephrase it, the hollow  64  is provided so as to form a recess extending toward the Y axis direction, or in other words, a direction opposite to the sheet member  62 . As a result of the sheet member  62  being bonded to the case  61 A, the hollow  64  is closed by the sheet member  62 , and thereby the liquid containing portion  67  is formed. 
         [0078]    The sixth wall  86  and the seventh wall  87  protrude in the −Y axis direction from the first wall  81 . With this configuration, the hollow  65  is constituted by, with the first wall  81  being defined as the main wall, the second wall  82 , the fifth wall  85 , the sixth wall  86  and the seventh wall  87  that extend in the −Y axis direction from the main wall. The hollow  65  is configured so as to form a recess extending toward the Y axis direction. The hollow  65  is open toward the −Y axis direction, or in other words, toward the sheet member  62  side. To rephrase it, the hollow  65  is provided so as to form a recess extending toward the Y axis direction, or in other words, a direction opposite to the sheet member  62 . As a result of the sheet member  62  being bonded to the case  61 A, the hollow  65  is closed by the sheet member  62 , and the buffer chamber  68  is formed. The first to seventh walls  81  to  87  are not limited to flat walls, and may have irregularities. Also, the extent to which the second to seventh walls  82  to  87  protrude from the first wall  81  is set to be the same. 
         [0079]    The sixth wall  86  and the third wall  83  have a step in the X axis direction. The third wall  83  is located at a position farther toward the X axis direction than the sixth wall  86 . When the first wall  81  is viewed planarly from the sheet member  62  side, the liquid injection portion  33  is present between the third wall  83  and the sixth wall  86 . The liquid injection portion  33  is provided on the fifth wall  85 . The seventh wall  87  is provided with an introducing path  91 . The introducing path  91  extends into the hollow  65 . Atmospheric air is introduced into the buffer chamber  68  via the introducing path  91 . 
         [0080]    Also, a notch  92  is formed in an area of the fifth wall  85  in which the hollow  65  and the hollow  64  intersect with each other. The area of the fifth wall  85  in which the hollow  65  and the hollow  64  intersect with each other is an area of the fifth wall  85  in which the hollow  65  and the hollow  64  are overlaid in the Z axis. The notch  92  is formed in an end portion in the −Y axis direction of the fifth wall  85 . The notch  92  is formed so as to form a recess extending toward the Y axis direction from the end portion in the −Y axis direction of the fifth wall  85 . Accordingly, when the sheet member  62  is bonded to the case  61 A, the hollow  64  and the hollow  65  communicate with each other via the notch  92 . A space formed by the notch  92  and the sheet member  62  constitutes at least a part of a first atmospheric air communication portion  102  (described later). 
         [0081]    A hollow  93  is provided within the hollow  64 . The hollow  93  is provided so as to form a recess extending toward a direction opposite to the fifth wall  85  from the fourth wall  84 , or in other words, toward the −Z axis direction from the fourth wall  84 . In the hollow  93 , a supply inlet  95  is provided on a wall  94  confronting with the third wall  83  and the second wall  82 . Accordingly, when the first wall  81  is viewed planarly in the Y axis direction, the supply inlet  95  is present between the third wall  83  and the second wall  82 . The liquid injection portion  33  and the supply inlet  95  each communicate between the outside of the case  61 A and the inside of the hollow  64 . The supply inlet  95  protrudes in the −X axis direction from the wall  94 . 
         [0082]    As shown in  FIG. 3 , the sheet member  62  confronts with the first wall  81  with the second to seventh walls  82  to  87  interposed therebetween in the Y axis direction. As viewed planarly in the Y axis direction, the sheet member  62  has a size enough to cover the hollow  64 , the hollow  65  and the hollow  93 . The sheet member  62  is welded to the bonding portion  66 , with a gap between the sheet member  62  and the first wall  81 . As a result, the hollow  64 , the hollow  65  and the hollow  93  are sealed by the sheet member  62 . For this reason, the sheet member  62  can also be regarded as the lid for the case  61 A. 
         [0083]    As shown in  FIG. 4 , the tank  31 A includes the liquid containing portion  67  and an atmospheric air introducing portion  101 . The atmospheric air introducing portion  101  includes the first atmospheric air communication portion  102 , the buffer chamber  68  and a second atmospheric air communication portion  103 . The first atmospheric air communication portion  102  is an example of a first atmospheric air communication path. The second atmospheric air communication portion  103  is an example of a second atmospheric air communication path. The atmospheric air introducing portion  101  is an atmospheric air flow channel between the outside of the tank  31 A and the inside of the liquid containing portion  67 . In  FIG. 4 , in order to clearly indicate the configuration of the second atmospheric air communication portion  103 , a partial cross-section of the tank  31 A is shown. Also, in  FIG. 4 , in order to clearly show the configuration, the liquid retaining member  63  is not illustrated. 
         [0084]    The atmospheric air introducing portion  101  communicates with the outside of the tank  31 A in the second atmospheric air communication portion  103 . Also, the atmospheric air introducing portion  101  communicates with the inside of the liquid containing portion  67  in the first atmospheric air communication portion  102 . The liquid containing portion  67  communicates with the outside of the tank  31 A via the first atmospheric air communication portion  102 , the buffer chamber  68  and the second atmospheric air communication portion  103 . To rephrase it, the liquid containing portion  67  is open to the atmospheric air via the first atmospheric air communication portion  102 , the buffer chamber  68  and the second atmospheric air communication portion  103 . 
         [0085]    The first atmospheric air communication portion  102  is an atmospheric air flow channel between a first atmospheric air introducing inlet  104  and a first communication port  105 . In this example, the first atmospheric air communication portion  102  is formed as the notch  92  formed in the fifth wall  85 . Accordingly, in this example, the path length of the first atmospheric air communication portion  102  is equal to the thickness dimension of the fifth wall  85 . The first atmospheric air introducing inlet  104  is defined as an opening formed in an intersection where the inner wall of the liquid containing portion  67  and the first atmospheric air communication portion  102  intersect. To rephrase it, the first atmospheric air introducing inlet  104  is an area where the first atmospheric air communication portion  102  is connected to the liquid containing portion  67 . Likewise, the first communication port  105  is defined as an opening formed in an intersection where the inner wall of the buffer chamber  68  and the first atmospheric air communication portion  102  intersect. To rephrase it, the first communication port  105  is an area where the first atmospheric air communication portion  102  is connected to the buffer chamber  68 . 
         [0086]    In this example, the first atmospheric air communication portion  102  is configured as the notch  92  formed in the fifth wall  85 , and the path length of the first atmospheric air communication portion  102  is equal to the thickness dimension of the fifth wall  85 , and thus the first atmospheric air introducing inlet  104  and the first communication port  105  can be regarded as the same. In other words, in this example, the first communication port  105  can also be regarded as the first atmospheric air introducing inlet  104 . 
         [0087]    The second atmospheric air communication portion  103  is an atmospheric air flow channel between a second atmospheric air introducing inlet  106  and a second communication port  107 . In this example, the second atmospheric air communication portion  103  is configured to include the introducing path  91  formed on the seventh wall  87  and the thickness of the seventh wall  87 . Accordingly, in this example, the path length of the second atmospheric air communication portion  103  is equal to a length obtained by addition of the path length of the introducing path  91  and the thickness dimension of the seventh wall  87 . The second atmospheric air introducing inlet  106  is defined as an opening that is open toward the outside of the tank in the second atmospheric air communication portion  103 . Likewise, the second communication port  107  is defined as an opening formed at an intersection where the inner wall of the buffer chamber  68  and the second atmospheric air communication portion  103  intersect. To rephrase it, the second communication port  107  is an area where the second atmospheric air communication portion  103  is connected to the buffer chamber  68 . 
         [0088]    In this example, the introducing path  91  is provided, but it is also possible to use a configuration that does not include the introducing path  91 . In the tank  31 A without the introducing path  91 , the path length of the second atmospheric air communication portion  103  is equal to the thickness dimension of the seventh wall  87 , and thus the second atmospheric air introducing inlet  106  and the second communication port  107  can be regarded as the same. In other words, in the tank  31 A without the introducing path  91 , the second communication port  107  can also be regarded as the second atmospheric air introducing inlet  106 . 
         [0089]    The liquid retaining member  63  has, as shown in  FIG. 5 , a shape smaller than the hollow  65  of the case  61 A as viewed planarly in the Y axis direction. In this example, the Z axis dimension (vertical direction) of the liquid retaining member  63  is smaller than the Z axis dimension of the buffer chamber  68 . Also, the X axis dimension (horizontal direction) of the liquid retaining member  63  is smaller than the X axis dimension of the buffer chamber  68 . Accordingly, within the buffer chamber  68 , a gap  111  is formed between the inner wall of the buffer chamber  68  and the liquid retaining member  63 . 
         [0090]    The gap  111  is provided between the contour surface of the liquid retaining member  63  and the inner wall of the buffer chamber  68 . The gap  111  connects between the first communication port  105  and the second communication port  107 . In other words, a passage extending from the first communication port  105  through the gap  111  and to the second communication port  107  can be formed. Accordingly, atmospheric air can move between the first communication port  105  and the second communication port  107  through the gap  111  between the contour surface of the liquid retaining member  63  and the inner wall of the buffer chamber  68 . 
         [0091]    In this example, the liquid retaining member  63  has a shape smaller than the hollow  65  of the case  61 A. With this configuration, the gap  111  is provided. However, the method of providing the gap  111  is not limited thereto. As the method of providing the gap  111 , for example, it is possible to use a method in which the gap  111  is provided by forming a groove, a through hole, a notch or the like in the liquid retaining member  63 . With this method, it is possible to provide the gap  111  even when the shape of the liquid retaining member  63  is set to have the same shape as the hollow  65  of the case  61 A or a shape larger than the hollow  65  of the case  61 A. 
         [0092]    In the tank  31 A, as shown in  FIG. 5  illustrating a side view of the tank  31 A as viewed from the sheet member  62  side, the liquid containing portion  67  contains ink  112 . In  FIG. 5 , for the sake of clarity of the configuration, the sheet member  62  is not illustrated, and the bonding portion  66  is indicated by hatching. The ink  112  contained in the liquid containing portion  67  is supplied to the recording head  19  via the supply inlet  95 . In the present embodiment, in a state in which the liquid ejection system  1  is used to perform printing, the ink supply tube  34  is connected to the supply inlet  95 , and a cap  113  is attached to the liquid injection portion  33 . The cap  113  is an example of a cap member, and is configured to be detachable. 
         [0093]    The ink  112  contained in the liquid containing portion  67  is sent to the recording head  19  side along with printing by the recording head  19 . Accordingly, along with printing by the recording head  19 , the pressure within the liquid containing portion  67  becomes lower than the atmospheric pressure. When the pressure within the liquid containing portion  67  becomes lower than the atmospheric pressure, the atmospheric air in the buffer chamber  68  is sent to the inside of the liquid containing portion  67  through the first atmospheric air communication portion  102 . As a result, the pressure within the liquid containing portion  67  is easily maintained at the atmospheric pressure. Atmospheric air flows into the buffer chamber  68  from the second atmospheric air introducing inlet  106  by passing through the second atmospheric air communication portion  103  and the second communication port  107  in this order. With the above-described configuration, the ink  112  contained in the tank  31 A is supplied to the recording head  19 . When the ink  112  contained in the liquid containing portion  67  of the tank  31 A is consumed and the remaining amount of the ink  112  becomes low, the operator can load new ink from the liquid injection portion  33  into the liquid containing portion  67 . At this time, the operator injects new ink by detaching the cap  113  from the liquid injection portion  33 . 
         [0094]    In the tank  31 A, even when the orientation of the tank  31 A is changed such as, for example, when the liquid ejection system  1  is transported, to cause the ink contained in the liquid containing portion  67  to flow into the atmospheric air introducing portion  101 , the ink is likely to remain in the buffer chamber  68 . Accordingly, with the tank  31 A, the risk of leakage of the ink contained in the liquid containing portion  67  from the second atmospheric air introducing inlet  106  to the outside of the tank  31 A can be reduced. 
         [0095]    Furthermore, in the tank  31 A, the liquid retaining member  63  is housed in the buffer chamber  68 , and thus the ink that has flowed into the buffer chamber  68  from the liquid containing portion  67  is likely to be retained by the liquid retaining member  63 . Accordingly, even if the ink contained in the liquid containing portion  67  flows into the atmospheric air introducing portion  101 , the ink is more likely to remain in the buffer chamber  68 . 
         [0096]    At this time, if the ink permeates into the liquid retaining member  63 , the air permeability of the liquid retaining member  63  becomes extremely low. This is because when a liquid permeates into the liquid retaining member  63 , a meniscus is formed by the permeated liquid in the liquid retaining member  63 , which makes it difficult for a gas to move. Accordingly, in a state in which the ink has permeated into the liquid retaining member  63 , for example, if the gap  111  is not provided in the buffer chamber  68 , the airtightness of the liquid containing portion  67  becomes extremely high. If printing is performed by the recording head  19  in this state, a negative pressure state in which the pressure within the liquid containing portion  67  is lower than the atmospheric pressure is likely to persist. In other words, the pressure within the liquid containing portion  67  is unlikely to return from a negative pressure to the atmospheric pressure. If the negative pressure state in the liquid containing portion  67  persists, the ink is unlikely to be supplied to the recording head  19 , which is likely to cause a deterioration in the quality of printing. 
         [0097]    When the airtightness of the liquid containing portion  67  becomes very high with the ink having permeated into the liquid retaining member  63 , and, for example, the pressure within the liquid containing portion  67  increases to a level higher than the atmospheric pressure, the cap  113  is likely to be detached from the liquid injection portion  33 . As a result, the ink contained in the liquid containing portion  67  may leak out of the tank  31 A from the liquid injection portion  33 . 
         [0098]    To address the above-described problems, in the tank  31 A of this example, the gap  111  is provided within the buffer chamber  68 , and thus even in a state in which the ink has permeated into the liquid retaining member  63 , atmospheric air can move between the first communication port  105  and the second communication port  107 . With this configuration, pressure fluctuations within the liquid containing portion  67  can be reduced. Accordingly, even if the pressure within the liquid containing portion  67  becomes lower than the atmospheric pressure due to printing by the recording head  19 , the pressure within the liquid containing portion  67  easily returns to the atmospheric pressure. As a result, it is easy to maintain ink supply to the recording head  19 , and thus the quality of printing can be easily maintained at a high level. Also, even if the pressure within the liquid containing portion  67  becomes higher than the atmospheric pressure, the atmospheric air contained in the liquid containing portion  67  can easily flow out of the tank  31 A from the atmospheric air introducing portion  101 , the pressure within the liquid containing portion  67  easily returns to the atmospheric pressure. Thus, the risk that the cap  113  is detached from the liquid injection portion  33  is easily suppressed. As a result, it is possible to use a detachable cap  113 . 
       EXAMPLE 2 
       [0099]    A tank  31 B of Example 2 includes a liquid retaining member  121  as shown in  FIG. 6 . The tank  31 B of Example 2 has a configuration in which the liquid retaining member  63  of the tank  31 A of Example 1 is replaced by the liquid retaining member  121 . Other than this point, the tank  31 B of Example 2 has the same configuration as that of the tank  31 A of Example 1. For this reason, hereinafter, constituent elements similar to those of Example 1 will be given the same reference numerals as those used in Example 1 and a detailed description thereof is omitted here. 
         [0100]    The liquid retaining member  121  has a plurality of protrusions  122  provided thereto. The plurality of protrusions  122  protrude from the liquid retaining member  121  toward the inner wall of the buffer chamber  68 . A gap  111  is provided by the plurality of protrusions  122  within the buffer chamber  68 . The plurality of protrusions  122  include first protrusions  122 A protruding along the Z axis (protruding in the vertical direction) and second protrusions  122 B protruding along the X axis (protruding in the horizontal direction). In Example 2 as well, the same effects as those of Example 1 can be obtained. In this example, a plurality of first protrusions  122 A and a plurality of second protrusions  122 B are provided, but the number of first protrusions  122 A and the number of second protrusions  122 B may be one. The second protrusions  122 B may protrude along the Y axis. 
         [0101]    Furthermore, in Example 2, a face contact between the inner wall of the buffer chamber  68  and the liquid retaining member  121  can be easily avoided. For example, in a configuration in which the inner wall of the buffer chamber  68  and the liquid retaining member  121  are in face contact with each other, the attraction force between the inner wall and the liquid retaining member  121  into which the liquid has permeated increases, and it is considered that the liquid retaining member  121  is fixed within the buffer chamber  68 . At this time, if the liquid retaining member  121  is fixed while covering the first communication port  105 , it is difficult for the atmospheric air to move between the first communication port  105  and the second communication port  107 . As a result, the pressure within the liquid containing portion  67  is likely to fluctuate significantly. To address this, in the tank  31 B of Example 2, due to the presence of the plurality of protrusions  122 , the face contact between the inner wall of the buffer chamber  68  and the liquid retaining member  121  can be easily avoided, and thus fluctuations in the pressure within the liquid containing portion  67  can be further reduced. 
       EXAMPLE 3 
       [0102]    A tank  31 C of Example 3 includes a case  61 B as shown in  FIG. 7 . The tank  31 C of Example 3 has a configuration in which the case  61 A of the tank  31 A of Example 1 is replaced by the case  61 B. Other than this point, the tank  31 C of Example 3 has the same configuration as that of the tank  31 A of Example 1. For this reason, hereinafter, constituent elements similar to those of Example 1 will be given the same reference numerals as those used in Example 1 and a detailed description thereof is omitted here. 
         [0103]    The case  61 B has a plurality of protrusions  123  provided thereto. In this example, the plurality of protrusions  123  are configured as ribs formed on the case  61 B. The plurality of protrusions  123  protrude from the inner wall of the buffer chamber  68  toward the liquid retaining member  63 . A gap  111  is provided by the plurality of protrusions  123  within the buffer chamber  68 . The plurality of protrusions  123  include first protrusions  123 A protruding along the Z axis (protruding in the vertical direction) and second protrusions  123 B protruding along the X axis (protruding in the horizontal direction). In Example 3 as well, the same effects as those of Examples 1 and 2 can be obtained. In this example, a plurality of first protrusions  123 A and a plurality of second protrusions  123 B are provided, but the number of first protrusions  123 A and the number of second protrusions  123 B may be one. The second protrusions  123 B may protrude along the Y axis from the inner wall of the buffer chamber  68 . 
         [0104]    Furthermore, in Example 3, even if there are variations in the dimensions of the liquid retaining member  63 , the gap  111  can be ensured by the plurality of protrusions  123 . With this configuration, fluctuations in the pressure within the liquid containing portion  67  can be further reduced. 
       EXAMPLE 4 
       [0105]    In Example 3, the plurality of protrusions  123  are configured as ribs formed on the case  61 B. However, the configuration of the plurality of protrusions  123  is not limited thereto. As shown in  FIG. 8 , as the plurality of protrusions  123 , it is possible to use spacers  124  provided on the inner wall of the hollow  65 . An example in which the plurality of protrusions  123  are formed by the spacers  124  will be described as Example 4. The spacers  124  are an example of a support member. The spacers  124  are located in a gap  111  between the inner wall of the buffer chamber  68  and the liquid retaining member  63 . 
         [0106]    As shown in  FIG. 8 , the tank  31 D of Example 4 includes a case  61 C. The tank  31 D of Example 4 has a configuration in which the case  61 A of the tank  31 A of Example 1 is replaced by the case  61 C. Other than this point, the tank  31 D of Example 4 has the same configuration as that of the tank  31 A of Example 1. For this reason, hereinafter, constituent elements similar to those of Example 1 will be given the same reference numerals as those used in Example 1 and a detailed description thereof is omitted here. 
         [0107]    In this example, the plurality of protrusions  123  are provided by ball-like spacers  124  bonded to the inner wall of the hollow  65 . The plurality of spacers  124  include first spacers  124 A that are located in the gap  111  extending along the Z axis (the vertical direction) between the inner wall of the buffer chamber  68  and the liquid retaining member  63  and second spacers  124 B that are located in the gap  111  extending along the X axis (the horizontal direction) between the inner wall of the buffer chamber  68  and the liquid retaining member  63 . In Example 4 as well, the same effects as those of Examples 1 to 3 can be obtained. As the method for bonding the spacers  124  to the inner wall of the hollow  65 , various methods can be used such as adhesive bonding, welding and the like. 
       EXAMPLE 5 
       [0108]    In a tank  31 E of Example 5, as shown in  FIG. 9 , an atmospheric air chamber  125  and a communication path  126  are provided between the introducing path  91  and the buffer chamber  68 . In other words, in this example, the second atmospheric air communication portion  103  includes the introducing path  91 , the atmospheric air chamber  125  and the communication path  126 . In the tank  31 E of Example 5, the atmospheric air introducing portion  101  has a configuration that is different from that of Examples 1 to 4. Other than this point, the tank  31 E of Example 5 has the same configuration as that of the tanks  31  of Examples 1 to 4. For this reason, hereinafter, constituent elements similar to those of Examples 1 to 4 will be given the same reference numerals as those used in Examples 1 to 4 and a detailed description thereof is omitted here. 
         [0109]    The configuration in which the atmospheric air chamber  125  and the communication path  126  are provided between the introducing path  91  and the buffer chamber  68  is applicable to each of Examples 1 to 4. In other words, it is possible to use a configuration in which the protrusions  123  ( FIG. 7 ) or the spacers  124  ( FIG. 8 ) are provided to the buffer chamber  68  of the tank  31 E. 
         [0110]    The atmospheric air chamber  125  is provided between the introducing path  91  and the buffer chamber  68 . In the path of the atmospheric air flow channel through which the atmospheric air outside of the tank  31  flows from the second atmospheric air introducing inlet  106  into the liquid containing portion  67 , the atmospheric air chamber  125  is located upstream of the buffer chamber  68 . The communication path  126  is provided between the atmospheric air chamber  125  and the buffer chamber  68 . In the path of the atmospheric air flow channel, the communication path  126  is located at a position that is downstream of the atmospheric air chamber  125  and upstream of the buffer chamber  68 . The communication path  126  communicates between the atmospheric air chamber  125  and the buffer chamber  68 . The communication path  126  is meandered. The atmospheric air chamber  125  is meandered via the communication path  126  and communicates with the buffer chamber  68 . As the configuration of the communication path  126 , it is possible to use a configuration in which the communication path  126  is not meandered. 
         [0111]    In Example 5 as well, the same effects as those of Examples 1 to 4 can be obtained. Furthermore, in Example 5, the communication path  126  and the atmospheric air chamber  125  are provided upstream of the buffer chamber  68 , and thus the risk of leakage of the ink contained in the liquid containing portion  67  from the second atmospheric air introducing inlet  106  to the outside of the tank  31  can be further reduced. 
       EXAMPLE 6 
       [0112]    In a tank  31 F of Example 6, as shown in  FIG. 10 , a communication path  127  is provided between the buffer chamber  68  and the liquid containing portion  67 . In other words, in this example, the first atmospheric air communication portion  102  includes the communication path  127 . In the tank  31 F of Example 6, the atmospheric air introducing portion  101  has a configuration different from that of Examples 1 to 5. Other than this point, the tank  31 F of Example 6 has the same configuration as that of the tank  31  of Examples 1 to 5. For this reason, hereinafter, constituent elements similar to those of Examples 1 to 5 will be given the same reference numerals as those used in Examples 1 to 5 and a detailed description thereof is omitted here. 
         [0113]    The configuration in which the communication path  127  is provided between the buffer chamber  68  and the liquid containing portion  67  is applicable to each of Examples 1 to 5. In other words, it is possible to use a configuration in which the protrusions  123  ( FIG. 7 ) or the spacers  124  ( FIG. 8 ) are provided to the buffer chamber  68  of the tank  31 F. 
         [0114]    The communication path  127  is provided between the buffer chamber  68  and the liquid containing portion  67 . In the path of the atmospheric air flow channel through which the atmospheric air outside of the tank  31  flows from the second atmospheric air introducing inlet  106  into the liquid containing portion  67 , the communication path  127  is located downstream of the buffer chamber  68 . The communication path  127  communicates between the buffer chamber  68  and the liquid containing portion  67 . The communication path  127  is meandered. The buffer chamber  68  is meandered via the communication path  127  and communicates with the liquid containing portion  67 . As the configuration of the communication path  127 , it is possible to use a configuration in which the communication path  127  is not meandered. 
         [0115]    In Example 6 as well, the same effects as those of Examples 1 to 5 can be obtained. Furthermore, in Example 6, the communication path  127  is provided downstream of the buffer chamber  68 , and thus the risk of leakage of the ink contained in the liquid containing portion  67  from the second atmospheric air introducing inlet  106  to the outside of the tank  31  can be further reduced. 
       EXAMPLE 7 
       [0116]    In a tank  31 G of Example 7, as shown in  FIG. 11 , an atmospheric air chamber  125  and a communication path  126  are provided between the introducing path  91  and the buffer chamber  68 , and a communication path  127  is provided between the buffer chamber  68  and the liquid containing portion  67 . In other words, in this example, the second atmospheric air communication portion  103  includes the introducing path  91 , the atmospheric air chamber  125  and the communication path  126 , and the first atmospheric air communication portion  102  includes the communication path  127 . In the tank  31 G of Example 7, the atmospheric air introducing portion  101  has a configuration different from that of Examples 1 to 6. Other than this point, the tank  31 G of Example 7 has the same configuration as that of the tank  31  of Examples 1 to 6. For this reason, hereinafter, constituent elements similar to those of Examples 1 to 6 will be given the same reference numerals as those used in Examples 1 to 6 and a detailed description thereof is omitted here. 
         [0117]    The configuration in which the atmospheric air chamber  125  and the communication path  126  are provided between the introducing path  91  and the buffer chamber  68  and the communication path  127  is provided between the buffer chamber  68  and the liquid containing portion  67  is applicable to each of Examples 1 to 6. In other words, it is possible to use a configuration in which the protrusions  123  ( FIG. 7 ) or the spacers  124  ( FIG. 8 ) are provided to the buffer chamber  68  of the tank  31 G. 
         [0118]    In Example 7 as well, the same effects as those of Examples 1 to 6 can be obtained. Furthermore, in Example 7, the communication path  126  and the atmospheric air chamber  125  are provided upstream of the buffer chamber  68  and the communication path  127  is provided downstream of the buffer chamber  68 , and thus the risk of leakage of the ink contained in the liquid containing portion  67  from the second atmospheric air introducing inlet  106  to the outside of the tank  31  can be further reduced. 
       EXAMPLE 8 
       [0119]    A tank  31 H of Example 8 includes, as shown in  FIG. 12 , a case  61 D, a sheet member  62 , a first liquid retaining member  131 A and a second liquid retaining member  132 . Of the constituent elements of Example 8, those having the same functions as the constituent elements of Examples 1 to  7  will be given the same reference numerals as those of Examples 1 to 7, and a detailed description is omitted. 
         [0120]    The case  61 D includes an eighth wall  88  and a ninth wall  89 . The first to seventh walls  81  to  87  of the case  61 D have the same functions as the first to seventh walls  81  to  87  of Examples 1 to 7. The eighth wall  88  is provided between the fifth wall  85  and the seventh wall  87 . The eighth wall  88  extends along the XY plane and is located opposite to the fifth wall  85  and to the seventh wall  87 . The ninth wall  89  is provided between the sixth wall  86  and the second wall  82 . The ninth wall  89  extends along the YZ plane and is located opposite to the second wall  82  and to the sixth wall  86 . Also, a partition wall  133  extending along the YZ plane is provided between the sixth wall  86  and the ninth wall  89 . The partition wall  133  is located opposite to the sixth wall  86  and to the ninth wall  89 . 
         [0121]    The eighth wall  88 , the ninth wall  89  and the partition wall  133  protrude in the −Y axis direction from the first wall  81 . As a result, a hollow  134  is constituted by, with the first wall  81  being defined as the main wall, the sixth wall  86 , the seventh wall  87 , the eighth wall  88  and the partition wall  133  that extend in the −Y axis direction from the main wall. The hollow  134  is configured so as to form a recess extending toward the Y axis direction. As a result of the sheet member  62  being bonded to the case  61 D, the hollow  134  is closed by the sheet member  62 , and thereby a first buffer chamber  135  is formed. Then, the first liquid retaining member  131 A is housed in the first buffer chamber  135 . 
         [0122]    Also, a hollow  136  is constituted by, with the first wall  81  defined as the main wall, the seventh wall  87 , the eighth wall  88 , the ninth wall  89  and the partition wall  133  that extend in the −Y axis direction from the main wall. The hollow  136  is configured so as to form a recess extending toward the Y axis direction. As a result of the sheet member  62  being bonded to the case  61 D, the hollow  136  is closed by the sheet member  62  and thereby a second buffer chamber  137  is formed. Then, the second liquid retaining member  132  is housed in the second buffer chamber  137 . As the material for the first liquid retaining member  131 A and the second liquid retaining member  132 , the same material as that of the liquid retaining member  63  of Example 1 can be used. Also, the first liquid retaining member  131 A and the second liquid retaining member  132  have the same function as the liquid retaining member  63 . 
         [0123]    The volume of the first buffer chamber  135  is larger than that of the second buffer chamber  137 . For this reason, the volume of the first liquid retaining member  131 A is larger than that of the second liquid retaining member  132 . The first buffer chamber  135  and the second buffer chamber  137  have the same function as the buffer chamber  68  of Example 1. In the path of the atmospheric air flow channel through which the atmospheric air outside of the tank  31  flows from the second atmospheric air introducing inlet  106  (not shown in  FIG. 12 ) into the liquid containing portion  67 , the atmospheric air chamber  125  is located upstream of the first buffer chamber  135  and the second buffer chamber  137 . 
         [0124]    In this example, as shown in  FIG. 13 , an introducing path  91  is provided on the ninth wall  89 . The introducing path  91  protrudes in the −X axis direction from the ninth wall  89 . The introducing path  91  communicates with the second buffer chamber  137  by penetrating through the ninth wall  89 . A communication portion  138  is provided between the partition wall  133  and the eighth wall  88 . In this example, the communication portion  138  is configured as a gap provided between the partition wall  133  and the eighth wall  88 . The first buffer chamber  135  and the second buffer chamber  137  communicate with each other via the communication portion  138 . 
         [0125]    In this example, a communication path  139  is present between the first buffer chamber  135  and the liquid containing portion  67 . The communication path  139  is provided between the first buffer chamber  135  and the liquid containing portion  67 . In the path of the atmospheric air flow channel through which the atmospheric air outside of the tank  31  flows from the second atmospheric air introducing inlet  106  into the liquid containing portion  67 , the communication path  139  is located downstream of the first buffer chamber  135 . The communication path  139  communicates between the first buffer chamber  135  and the liquid containing portion  67 . The communication path  139  is meandered. The first buffer chamber  135  is meandered via the communication path  139  and communicates with the liquid containing portion  67 . Accordingly, the atmospheric air outside of the tank  31  can enter from the second atmospheric air introducing inlet  106 , pass through the second buffer chamber  137 , the first buffer chamber  135  and the communication path  139  in this order, and flow into the liquid containing portion  67  through the first atmospheric air introducing inlet  104 . As the configuration of the communication path  139 , it is possible to use a configuration in which the communication path  139  is not meandered. 
         [0126]    As shown in  FIG. 14 , the first liquid retaining member  131 A has a shape smaller than the hollow  134  of the case  61 D, as viewed planarly in the Y axis direction. In this example, the Z axis dimension (vertical direction) of the first liquid retaining member  131 A is smaller than the Z axis dimension of the first buffer chamber  135 . Also, the X axis dimension (horizontal direction) of the first liquid retaining member  131 A is smaller than the X axis dimension of the first buffer chamber  135 . Accordingly, within the first buffer chamber  135 , a gap  111  is provided between the inner wall of the first buffer chamber  135  and the first liquid retaining member  131 A. 
         [0127]    The second liquid retaining member  132  has a shape smaller than the hollow  136  of the case  61 D, as viewed planarly in the Y axis direction. In this example, the Z axis dimension (vertical direction) of the second liquid retaining member  132  is smaller than the Z axis dimension of the second buffer chamber  137 . Also, the X axis dimension (horizontal direction) of the second liquid retaining member  132  is smaller than the X axis dimension of the second buffer chamber  137 . Accordingly, within the second buffer chamber  137 , a gap  111  is provided between the inner wall of the second buffer chamber  137  and the second liquid retaining member  132 . 
         [0128]    The method of providing the gap  111  is not limited to those described above. As the method of providing the gap  111 , it is possible to, for example, use a method in which the gap  111  is provided by forming a groove, a through hole, a notch or the like in the first liquid retaining member  131 A or the second liquid retaining member  132 . With this method, the gap  111  can be provided even when the shape of the first liquid retaining member  131 A is set to be the same as that of the hollow  134  of the case  61 D or larger than that of the hollow  134  of the case  61 D. Also, with this method, the gap  111  can also be provided even when the shape of the second liquid retaining member  132  is set to be the same as that of the hollow  136  of the case  61 D or larger than that of the hollow  136  of the case  61 D. 
         [0129]    The gap  111  has the same function as the gap  111  of Examples 1 to 7. In Example 8 as well, the same effects as those of Examples 1 to 7 can be obtained. 
       EXAMPLE 9 
       [0130]    In a tank  31 J of Example 9, as shown in  FIG. 15 , the first liquid retaining member  131 A is constituted by a plurality of members  141  (three members  141  in the example shown in  FIG. 15 ). Other than this point, the tank  31 J has the same configuration as that of the tank  31 H of Example 8. For this reason, hereinafter, constituent elements similar to those of Example 8 will be given the same reference numerals as those used in Example 8 and a detailed description thereof is omitted here. 
         [0131]    A member  141  has a plate-like outer shape. The member  141  is an example of a plate-like member. A plurality of members  141  are brought together in a bundle to constitute the first liquid retaining member  131 A. It is also possible to use a configuration in which a plurality of members  141  are separately housed in the first buffer chamber  135 . As the method for bringing the plurality of members  141  together in a bundle, various methods can be used such as for example, a method in which the plurality of members  141  are bundled by bonding them together, or by using a binding member. 
         [0132]    In Example 9 as well, the same effects as those of Example 8 can be obtained. Also, in Example 9, the first liquid retaining member  131 A that can fit into the first buffer chamber  135  of a different size is easily configured by adjusting the number of members  141  constituting the first liquid retaining member  131 A. With this configuration, the members  141  can be used commonly in first liquid retaining members  131 A of various sizes. As a result, the cost for the first liquid retaining member  131 A can be easily reduced. 
         [0133]    In this example, the size of the members  141  is set to be equal to that of the second liquid retaining member  132 . In other words, the second liquid retaining member  132  is constituted by one member  141 . With this configuration, the members  141  can be used commonly in the first buffer chamber  135  and the second buffer chamber  137 . As a result, the cost for the first liquid retaining member  131 A and the second liquid retaining member  132  can be easily reduced. 
       EXAMPLE 10 
       [0134]    As shown in  FIG. 16 , a tank  31 K of Example 10 includes a first liquid retaining member  131 B. The tank  31 K has a configuration in which the first liquid retaining member  131 A of the tank  31 J of Example 9 is replaced by the first liquid retaining member  131 B. Other than this point, the tank  31 K of Example 10 has the same configuration as that of the tank  31 J of Example 9. For this reason, hereinafter, constituent elements similar to those of Example 9 will be given the same reference numerals as those used in Example 9 and a detailed description thereof is omitted here. 
         [0135]    The first liquid retaining member  131 B includes, as shown in  FIG. 17 , a plurality of members  141  and a clip  142 . The members  141  are similar to the members  141  of Example 9, and thus a detailed description is omitted here. In the first liquid retaining member  131 B of this example, the plurality of members  141  are bundled by the clip  142 , which is an example of the binding member. Grooves  143  are formed in the members  141 . In the members  141 , the grooves  143  are formed in the surface facing toward the Z axis direction and in the surface facing toward the −Z axis direction. Hereinafter, the groove  143  formed in the surface facing toward the Z axis direction of the members  141  will also be referred to as “groove  143 A”. Likewise, the groove  143  formed in the surface facing toward the −Z axis direction of the members  141  will also be referred to as “groove  143 B”. 
         [0136]    The clip  142  includes a pair of arm portions  144  and a connection portion  145 . The pair of arm portions  144  each extend along the XY plane. The pair of arm portions  144  are located opposite to each other along the Z axis with a gap therebetween. Hereinafter, one of the pair of arm portions  144  that is located in the Z axis direction will also be referred to as “arm portion  144 A”. Likewise, the other one of the pair of arm portions  144  that is located in the −Z axis direction will also be referred to as “arm portion  144 B”. Each of the pair of arm portions  144  has a claw portion  146  provided at one end thereof in the −Y axis direction. In the pair of arm portions  144 , the claw portions  146  are provided on the surfaces that are located opposite to each other. The claw portion  146  of the arm portion  144 A protrudes in the −Z axis direction. The claw portion  146  of the arm portion  144 B protrudes in the Z axis direction. 
         [0137]    Also, in each of the pair of arm portions  144 , claw portions  147  are respectively provided at one end thereof in the X axis direction and the other end thereof in the −X axis direction. In the pair of arm portions  144 , the claw portions  147  are provided on the surfaces that are located opposite to each other. The claw portions  147  of the arm portion  144 A protrude in the −Z axis direction. The claw portions  147  of the arm portion  144 B protrude in the Z axis direction. 
         [0138]    The connection portion  145  is provided between the pair of arm portions  144 . The connection portion  145  is provided at the other end, which is opposite to the one end at which the claw portions  146  of the pair of arm portions  144  are provided. The connection portion  145  extends along the XZ plane. The pair of arm portions  144  protrude farther than the connection portion  145  in the Y axis direction. 
         [0139]    The plurality of members  141  are sandwiched between the arm portion  144 A and the arm portion  144 B. At this time, the claw portion  146  of the arm portion  144 A is inserted into the groove  143 A of the members  141 , and the claw portion  146  of the arm portion  144 B is inserted into the groove  143 B of the members  141 . With this configuration, it is possible to prevent the members  141  from being detached in the −Y axis direction from the clip  142 . 
         [0140]    The claw portions  147  are located on the outer sides of the width, which is along the X axis, of the plurality of members  141 . For this reason, the claw portions  147  can prevent, when the plurality of members  141  are sandwiched between the arm portion  144 A and the arm portion  144 B, the plurality of members  141  from being detached in the X axis direction and the −X axis direction. 
         [0141]    As shown in  FIG. 16 , the first liquid retaining member  131 B having the above-described configuration is housed in the hollow  134  of the case  61 D from the connection portion  145  side. At this time, as described above, in the first liquid retaining member  131 B, the pair of arm portions  144  protrude farther than the connection portion  145  in the Y axis direction, and thus a gap  111  is provided between the connection portion  145  and the first wall  81 , which is the bottom of the hollow  134 . With this configuration, in Example 10 as well, the same effects as those of Examples 8 and 9 can be obtained. Furthermore, in Example 10, the plurality of members  141  are bundled by the clip  142 , and thus troublesome tasks of handling the first liquid retaining member  131 B can be reduced. 
       EXAMPLE 11 
       [0142]    In a tank  31 L of Example 11 (not shown), the plurality of protrusions  122  of Example 2 ( FIG. 6 ) are provided to the first liquid retaining member  131 A of Example 8. Other than this point, the tank  31 L of Example 11 has the same configuration as that of the tank  31 H of Example 8. For this reason, hereinafter, constituent elements similar to those of Example 8 will be given the same reference numerals as those used in Example 8 and a detailed description thereof is omitted here. 
         [0143]    In Example 11 as well, as in Example 8, a gap  111  can be provided by the plurality of protrusions  122  within the first buffer chamber  135 . Also, in Example 11 as well, as in Example 2, the face contact between the inner wall of the first buffer chamber  135  and the first liquid retaining member  131 A can be easily avoided. 
       EXAMPLE 12 
       [0144]    In Examples 8 and 9, it is possible to use a configuration in which the protrusions  123  ( FIG. 7 ) of Example 3 or the spacers  124  ( FIG. 8 ) of Example 4 are provided to the first buffer chamber  135  and the second buffer chamber  137 . A tank  31 M (not shown) in which the protrusions  123  ( FIG. 7 ) of Example 3 or the spacers  124  ( FIG. 8 ) of Example 4 are provided to the first buffer chamber  135  and the second buffer chamber  137  will be referred to as Example 12. In Example 12 as well, the same effects as those of Example 8 or 9 can be obtained. 
         [0145]    In the embodiments described above, the liquid ejection apparatus may be a liquid ejection apparatus that consumes a liquid other than ink by ejecting, discharging or applying the liquid. The liquid discharged from the liquid ejection apparatus in the form of micro-droplets can be in the shape of granules, teardrops or long strings. Also, the liquid as used herein can be any material, as long as it can be consumed by the liquid ejection apparatus. As the liquid, for example, a substance in a liquid phase can be used, and examples include liquids having a high or low viscosity and fluids such as sol, gel water, other inorganic solvents, organic solvents, solutions, liquid resins and liquid metals (metal melts). The liquid also encompasses not only a liquid which is one of the states of a substance, but also a liquid in which functional material particles made of a solid such as a pigment or metal particles are dissolved, dispersed or mixed in a solvent, and the like. Typical examples of the liquid include, in addition to the ink described in the embodiments above, a liquid crystal, and the like. The ink as used herein encompasses commonly used water-based ink, oil-based ink and various liquid compositions such as gel ink and hot melt ink. Specific examples of the liquid ejection apparatus include liquid ejection apparatuses that eject a liquid containing a material such as an electrode material or a coloring material being dispersed or dissolved therein, which is used to manufacture a liquid crystal display, an EL (electroluminescent) display, a surface-emitting display or a color filter. It is also possible to use, for example, a liquid ejection apparatus that ejects a biological organic substance used to manufacture biochips, a liquid ejection apparatus that ejects a sample liquid and is used as a precision pipette, a textile printing apparatus, and a micro-dispenser. Furthermore, it is also possible to use a liquid ejection apparatus that ejects a lubricating oil to a precision instrument such as a clock or a camera with a pin-point accuracy, and a liquid ejection apparatus that ejects a transparent resin solution such as UV curable resin onto a substrate so as to form a micro hemispherical lens (optical lens) or the like for use in an optical communication device or the like. It is also possible to use a liquid ejection apparatus that ejects an acidic or alkaline etching solution so as to etch a substrate or the like. 
         [0146]    It should be noted that the invention is not limited to the embodiment and examples described above, and can be implemented by various configurations within a range that does not depart from the spirit and scope of the invention. For example, the technical features described in the embodiments and examples corresponding to the technical features of respective embodiments described in the summary section can be replaced or combined as appropriate in order to solve some or all of the above-described problems or achieve some or all of the above-described effects. Also, a technical feature that is not described as essential in the specification may be removed as appropriate.