Abstract:
A liquid ejection apparatus includes a liquid ejection head that ejects a liquid and a switching device. The switching device includes a first ON-OFF valve that selectively opens and closes a first supply passage at a position upstream from the joining point, and a second ON-OFF valve that selectively opens and closes a second supply passage at a position upstream from the joining point. When the first ON-OFF valve is open and the second ON-OFF valve is closed, the liquid guide portion divides the first liquid into a first liquid flow proceeding from the first supply passage directly to the head supply passage and a second liquid flow flowing from the first supply passage into the head supply passage after passing the vicinity of the second ON-OFF valve in the second supply passage. When the first ON-OFF valve is closed and the second ON-OFF valve is open, the liquid guide portion divides the second liquid into a third liquid flow proceeding from the second supply passage directly to the head supply passage and a fourth liquid flow flowing from the second supply passage into the head supply passage after passing the vicinity of the first ON-OFF valve in the first supply passage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-315319 filed on Nov. 22, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a liquid ejection apparatus such as an inkjet type printer. 
         [0004]    2. Related Art 
         [0005]    Typically, an inkjet type printer (hereinafter, referred to as a printer) is broadly known as a liquid ejection apparatus that ejects liquid onto a target. In the printer, ink (the liquid) is supplied from an ink cartridge retaining the ink to a recording head (a liquid ejection head), which ejects the ink. The recording head ejects the ink through a nozzle defined in a nozzle forming surface of the recording head onto a sheet of recording paper, or the target, thus subjecting the sheet of paper to printing. If the ink cartridge is arranged at a position spaced from the recording head, as in some printers, the ink is supplied from the ink cartridge to the recording head through a tube routed in the printer. 
         [0006]    To change the ink to be ejected from the nozzle of the recording head to a different type of ink, supply of the ink from the currently used ink cartridge to the recording head is suspended. In this state, the ink is drained from the tube through the nozzle of the recording head. The different type of ink is then supplied from a corresponding ink cartridge, which retains this type of ink, to the recording head through the tube. 
         [0007]    However, such drainage of the ink in switching of the types of the ink wastefully increases consumption of the ink. To solve this problem, Japanese Laid-Open Patent Publication No. 2006-175626 proposes a printer having a switching device that is connected to tubes extending from respective ink cartridges and arranged in the vicinity of a recording head. 
         [0008]    In the printer of Japanese Laid-Open Patent Publication No. 2006-175626, the types of ink supplied to the recording head is switched between a first type of ink (first liquid) and a second type of ink (second liquid) in the switching device. Specifically, in the switching device, the downstream end of a first passage (a first supply passage) that supplies the first type of ink and the downstream end of a second passage (a second supply passage) that supplies the second type of ink are joined together. A head supply passage through which the ink is supplied to the recording head is provided between the joining point and the recording head. The switching device accommodates a first diaphragm (a first ON-OFF valve), which selectively opens and closes the first passage, and a second diaphragm (a second ON-OFF valve), which selectively opens and closes the second passage. Supply of the ink is thus switched between the first type of ink and the second type of ink by closing one of the diaphragms and opening the other. 
         [0009]    To supply the first type of ink to the recording head, the switching device opens the first diaphragm and closes the second diaphragm. Contrastingly, to supply the second type of ink to the recording head, the switching device opens the second diaphragm and closes the first diaphragm. 
         [0010]    When the first diaphragm is open and the second diaphragm is closed in the above-described printer, the portion of the second passage between the joining point of the first and second passages and the second diaphragm forms a “dead end” portion. Similarly, when the second diaphragm is open and the first diaphragm is closed in the printer, the portion of the second passage between the joining point of the first and second passages and the first diaphragm forms a “dead end” portion. 
         [0011]    Thus, when the first type of ink is supplied to the recording head, some of the ink is led from the first passage into the dead end portion of the second passage via the joining point and retained in the dead end portion. When the second type of ink is supplied to the recording head, some of the ink is sent from the second passage into the dead end portion of the first passage via the joining point and retained in the dead end portion. 
         [0012]    The properties of the ink retained in the dead end portions deteriorate as the time elapses and the ink with the deteriorated properties gradually diffuses from the dead end portion and flows into the head supply passage. This adversely influences the properties of the ink to be ejected from the nozzle of the recording head. 
       SUMMARY 
       [0013]    Accordingly, it is an objective of the present invention to provide a liquid ejection apparatus that prevents ink from being retained in a switching device that switches types of liquid to be supplied to a liquid ejection head. 
         [0014]    To achieve the above object and in accordance with a first aspect of the present invention, a liquid ejection apparatus including a liquid ejection head that ejects a liquid and a switching device is provided. The switching device selectively switches types of the liquid supplied to the liquid ejection head between a first liquid and a second liquid different from the first liquid. The switching device includes a first supply passage through which the first liquid flows, a second supply passage through which the second liquid flows, a head supply passage, a first ON-OFF valve, a second ON-OFF valve, and a liquid guide portion. The head supply passage extends from a joining point between a downstream end of the first supply passage and a downstream end of the second supply passage to the liquid ejection head. The first ON-OFF valve selectively opens and closes the first supply passage at a position upstream from the joining point. The second ON-OFF valve selectively opens and closes the second supply passage at a position upstream from the joining point. The a liquid guide portion is formed in the first and second supply passages at a position between the first ON-OFF valve and the second ON-OFF valve. When the first ON-OFF valve is open and the second ON-OFF valve is closed, the liquid guide portion divides the first liquid into a first liquid flow proceeding from the first supply passage directly to the head supply passage and a second liquid flow flowing from the first supply passage into the head supply passage after passing the vicinity of the second ON-OFF valve in the second supply passage. When the first ON-OFF valve is closed and the second ON-OFF valve is open, the liquid guide portion divides the second liquid into a third liquid flow proceeding from the second supply passage directly to the head supply passage and a fourth liquid flow flowing from the second supply passage into the head supply passage after passing the vicinity of the first ON-OFF valve in the first supply passage. 
         [0015]    In accordance with a second aspect of the present invention, a liquid ejection apparatus including a liquid ejection head that ejects a liquid and a switching device is provided. The switching device selectively switches types of the liquid supplied to the liquid ejection head between a first liquid and a second liquid different from the first liquid. The switching device includes a first supply passage through which the first liquid flows, a second supply passage through which the second liquid flows, a head supply passage, a first ON-OFF valve, a second ON-OFF valve, and a liquid guide portion. The first supply passage and the second supply passage extend along a common imaginary line and are joined together at the downstream ends of the first and second supply passages. The head supply passage extends from the joining point between the first supply passage and the second supply passage to the liquid ejection head. The first ON-OFF valve selectively opens and closes the first supply passage at a position upstream from the joining point. The second ON-OFF valve selectively opens and closes the second supply passage at a position upstream from the joining point. The liquid guide portion projects from a wall surface defining the first and second supply passages and extends linearly and continuously along both of the first and second supply passages. 
         [0016]    Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
           [0018]      FIG. 1  is a plan view schematically showing an inkjet type printer according to an embodiment of the present invention; 
           [0019]      FIG. 2  is a front view schematically showing a carriage of the printer shown in  FIG. 1 ; 
           [0020]      FIG. 3  is an exploded perspective view showing a switching device of the printer shown in  FIG. 1 ; 
           [0021]      FIG. 4  is a perspective view showing a main portion of the switching device shown in  FIG. 3 ; 
           [0022]      FIG. 5  is an enlarged cross-sectional view showing a main portion of a joint portion of the switching device shown in  FIG. 3 ; 
           [0023]      FIG. 6  is a plan view showing the switching device shown in  FIG. 3 ; 
           [0024]      FIG. 7  is a cross-sectional view showing a main portion of the switching device shown in  FIG. 3 ; 
           [0025]      FIG. 8  is a perspective view showing transmission members of the switching device shown in  FIG. 3 ; 
           [0026]      FIG. 9  is a view showing the switching device shown in  FIG. 3  in a state in which a first ON-OFF valve is open and a second ON-OFF valve is closed; and 
           [0027]      FIG. 10  is a view showing the switching device shown in  FIG. 3  in a state in which the first ON-OFF valve is closed and the second ON-OFF valve is open. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0028]    A first embodiment of the present invention will now be described with reference to the drawings. The “front-and-rear direction”, the “left-and-right direction”, and the “up-and-down direction” herein correspond to the directions indicated by the corresponding arrows in the attached drawings. 
         [0029]    As shown in  FIG. 1 , an inkjet type printer  11 , or a liquid ejection apparatus, includes a body frame  12  having a rectangular form as viewed from above. A platen  13 , which extends in the left-and-right direction coinciding with the main scanning direction, is provided in the body frame  12 . A non-illustrated paper feeder mechanism sends a sheet of recording paper, or a target, along the platen  13  and in the front-and-rear direction coinciding with the sub scanning direction. A bar-like guide shaft  14 , which extends parallel with the longitudinal direction of the platen  13  at a position above the platen  13 , is arranged in the body frame  12 . 
         [0030]    The guide shaft  14  supports a carriage  15  in such a manner as to allow the carriage  15  to reciprocate in the axial direction of the guide shaft  14 . The carriage  15  is connected to a carriage motor  17  mounted in a rear wall of the body frame  12  through an endless timing belt  16 , which is wound around a pair of pulleys  16   a  provided in an inner surface of the rear wall. The carriage  15  is driven by the carriage motor  17  to reciprocate along the axial direction of the guide shaft  14 . 
         [0031]    With reference to  FIGS. 1 and 2 , a recording head  18 , or a liquid ejection head, is mounted on the surface of the carriage  15  opposed to the platen  13 . The carriage  15  accommodates valve units  19   a ,  19   b ,  19   c ,  19   d , which temporarily retain ink as liquid and supply the ink to the recording head  18 . In the first embodiment, four valve units, which are first valve unit  19   a , a second valve unit  19   b , a third valve unit  19   c , and a fourth valve unit  19   d , are provided. A plurality of (in the first embodiment, three) nozzles  20   a ,  20   b ,  20   c  are defined in the lower surface of the recording head  18 . Droplets of the ink are thus ejected from the nozzles  20   a  to  20   c  onto the recording paper sheet (not shown), which has been fed onto the platen  13 , thus subjecting the recording paper sheet to printing. 
         [0032]    A cartridge holder  21  is arranged at the right end in the body frame  12 . Ink cartridges  22   a ,  22   b ,  22   c ,  22   d , which retain different types of ink, are removably mounted in the cartridge holder  21 . In the first embodiment, four ink cartridges, which are a first ink cartridge  22   a , a second ink cartridge  22   b , a third ink cartridge  22   c , and a fourth ink cartridge  22   d , are provided. Each of the ink cartridges  22   a  to  22   d  is connected to the corresponding one of the valve units  19   a  to  19   d  mounted in the carriage  15  through a corresponding one of ink supply tubes  24   a ,  24   b ,  24   c ,  24   d . When the ink cartridges  22   a  to  22   d  are installed in the cartridge holder  21 , the ink cartridges  22   a  to  22   d  are connected to the corresponding valve units  19   a  to  19   d  through the associated ink supply tubes  24   a  to  24   d.    
         [0033]    The first ink cartridge  22   a  receives photo black ink, or first liquid, and the second ink cartridge  22   b  receives matte black ink, or second liquid. Thus, the first valve unit  19   a  temporarily retains the photo black ink and the second valve unit  19   b  temporarily retains the matte black ink. 
         [0034]    The photo black ink is suitable for printing on glossy paper and the matte black ink is suitable for printing on matte paper. As shown in  FIG. 2 , a switching device  25  is arranged between the valve units  19   a ,  19   b  of the carriage  15  and the recording head  18 . The switching device  25  switches the ink supplied from the valve units  19   a ,  19   b  to the recording head  18  between the photo black ink and the matte black ink. 
         [0035]    The switching device  25  switches the ink ejected from the nozzle row  20   a  of the recording head  18  between the photo black ink and the matte black ink depending on whether glossy paper or matte paper is used. 
         [0036]    With reference to  FIG. 1 , a home position of the carriage  15  is defined at a position close to the right end in the body frame  12 . A maintenance unit  26 , which performs cleaning on the recording head  18 , is provided at the home position. The maintenance unit  26  includes a cap  27 , which air-tightly seals the nozzles  20   a  to  20   c  of the recording head  18  and receives the ink that has been ejected from the nozzles  20   a  to  20   c  through flushing. 
         [0037]    The switching device  25  will hereafter be explained in detail. 
         [0038]    As shown in  FIGS. 3 to 5 , the switching device  25  includes a body  30  having a symmetric block-like shape and a pair of connection pipes, or a first connection pipe  31  and a second connection pipe  32 . The first and second connection pipes  31 ,  32  are provided on the upper surface of the body  30  and spaced from each other at a predetermined interval. The first connection pipe  31  is connected to the first valve unit  19   a  and the second connection pipe  32  is connected to the second valve unit  19   b . The switching device  25  has a first valve body receiving portion  33  having a cylindrical shape and a bottom with an opening faced leftward and a second valve body receiving portion  34  having a cylindrical shape and a bottom with an opening faced rightward. The first valve body receiving portion  33  is arranged forward from the first connection pipe  31  and the second valve body receiving portion  34  is provided forward from the second connection pipe  32 . 
         [0039]    A joint portion  35  is formed between the first valve body receiving portion  33  and the second valve body receiving portion  34 . A joint passage  36 , which extends linearly along the left-and-right direction, is defined in the joint portion  35 . The first and second valve body receiving portions  33 ,  34  communicate with each other at their centers through the joint passage  36 . In other words, the joint passage  36  has openings at the centers of the first and second valve body receiving portions  33 ,  34 . 
         [0040]    A first communication groove  37 , through which the first connection pipe  31  communicates with the interior of the first valve body receiving portion  33 , is defined in the body  30 . The first communication groove  37  has a proximal end connected to the first connection pipe  31 . The first communication groove  37  extends from its proximal end sequentially on the left surface of the body  30 , an inner circumferential surface  33   a  of the first valve body receiving portion  33 , and an inner bottom surface  33   b  of the first valve body receiving portion  33 , in this order. The first communication groove  37  extends around the opening of the joint passage  36  on the inner bottom surface  33   b  from above and reaches a position diagonally downward and forward from the opening of the joint passage  36 . An annular first projection  33   c  projects from the inner bottom surface  33   b  of the first valve body receiving portion  33  and encompasses the opening of the joint passage  36 . 
         [0041]    Like the first communication groove  37 , a second communication groove  38 , through which the second connection pipe  32  communicates with the interior of the second valve body receiving portion  34 , is defined in the body  30 . The second communication groove  38  has a proximal end connected to the second connection pipe  32 . The second communication groove  38  extends from its proximal end sequentially on the right surface of the body  30 , an inner circumferential surface  34   a  of the second valve body receiving portion  34 , and an inner bottom surface  34   b  of the second valve body receiving portion  34 , in this order. The second communication groove  38  extends around the opening of the joint passage  36  on the inner bottom surface  34   b  from above and reaches a position diagonally downward and forward from the opening of the joint passage  36 . An annular second projection  34   c  projects from the inner bottom surface  34   b  of the second valve body receiving portion  34  and encompasses the opening of the joint passage  36 . 
         [0042]    As illustrated in  FIG. 6 , a groove  40  extending in the front-and-rear direction is defined in the upper surface of the joint portion  35 . With reference to  FIGS. 5 and 6 , a first through hole  39  connecting the joint passage  36  to the front end of the groove  40 , is defined at a forward position at the center of the joint passage  36  in the left-and-right direction. A second through hole  41  communicating with the recording head  18  (see  FIG. 2 ) is defined at the rear end of the groove  40 . A non-illustrated seal member, which seals the opening of the groove  40 , is arranged on the upper surface of the joint portion  35 . In the first embodiment, the first through hole  39 , the groove  40 , and the second through hole  41  form a head supply passage. 
         [0043]    As illustrated in  FIG. 5 , a first joint line  44  is defined by the portion of the joint passage  36  extending leftward from the center in the left-and-right direction. A second joint line  45  is defined by the portion of the joint passage  36  extending rightward from the center. The center of the joint passage  36  forms a joining point G between the first joint line  44  and the second joint line  45 . The first joint line  44 , the second joint line  45 , and the first through hole  39  communicate with one another at the joining point G. 
         [0044]    Large diameter portions  36   a , the diameters of which are greater than the diameter of the central portion of the joint passage  36 , are provided at both ends of the joint passage  36 , which are the left end of the first joint line  44  and the right end of the second joint line  45 . A block-like ink guide portion (a liquid guide portion)  42  projects from the lower wall of the joint passage  36  and linearly extends along the joint passage  36  continuously from the first joint line  44  to the second joint line  45 . The width of the ink guide portion  42 , or the dimension of the ink guide portion  42  in a direction perpendicular to the longitudinal direction of the ink guide portion  42 , becomes smaller toward the top of the ink guide portion  42 . Both ends of the ink guide portion  42  reach the interiors of the corresponding large diameter portions  36   a  of the joint passage  36 . 
         [0045]    An interference suppressing portion  43  is provided in the ink guide portion  42  at the position corresponding to the first through hole  39 . The interference suppressing portion  43  extends from a front surface of a central portion of the ink guide portion  42  toward the first through hole  39 . The left portion and the right portion of the ink guide portion  42  are symmetrical with respect to the interference suppressing portion  43 . In other words, the portions of the ink guide portion  42  divided by a plane extending perpendicular to the longitudinal direction of the ink guide portion  42  and including the interference suppressing portion  43  form mirror images in shape. 
         [0046]    As shown in  FIG. 7 , substantially columnar transmission members  46  are received in the first joint line  44  and the second joint line  45  in such a manner that the transmission members  46  are slidable in the left-and-right direction. With reference to  FIG. 8 , each of the transmission members  46  has a columnar small diameter portion  46   a  and a large diameter portion  46   b  the diameter of which is greater than the diameter of the small diameter portion  46   a . A cutout  46   c  is provided in the large diameter portion  46   b  in such a manner as to cover the angular range of 90 degrees. The diameter of the cutout  46   c  is equal to the diameter of the small diameter portion  46   a.    
         [0047]    With reference to  FIGS. 3 and 7 , one of the two transmission members  46  is passed through the first joint line  44  from the side corresponding to the small diameter portion  46   a  and the other transmission member  46  is passed through the second joint line  45  from the side corresponding to the small diameter portion  46   a . In this manner, each of the transmission members  46  is accommodated in the corresponding one of the joint lines  44 ,  45 . In this case, the cutout  46   c  of each transmission member  46  faces downward and the large diameter portion  46   b  of the transmission member  46  is received in the corresponding large diameter portion  36   a  of the joint passage  36 . The end surfaces of the small diameter portions  46   a  of the transmission members  46  contact each other at the center of the joint passage  36  in the left-and-right direction. The sum of the longitudinal dimensions of the two transmission members  46  is slightly greater than the longitudinal dimension of the joint passage  36  in the left-and-right direction. 
         [0048]    A first disk-like flexible ON-OFF valve  47  is loosely arranged in the first valve body receiving portion  33  and a second ON-OFF valve  48  shaped and configured identically with the first ON-OFF valve  47  are loosely received in the second valve body receiving portion  34 . A first circular recess  47   a  is defined in the outer central portion of the first ON-OFF valve  47  and a second circular recess  48   a  is provided in the outer central portion of the second ON-OFF valve  48 . A first disk-like rigid link member  49  is loosely received in the first recess  47   a  and a second disk-like rigid link member  50  is loosely accommodated in the second recess  48   a.    
         [0049]    The first recess  47   a  and the second recess  48   a  are shaped identically with each other and the first link member  49  and the second link member  50  are shaped identically with each other. A flexible film (not shown) is secured to the left surface of the body  30  in such a manner as to seal the opening of the first valve body receiving portion  33  and the opening of the first communication groove  37 . Another flexible film (not shown) is secured to the right surface of the body  30  in such a manner as to seal the opening of the second valve body receiving portion  34  and the opening of the second communication groove  38 . 
         [0050]    Operation of the switching device  25  will hereafter be explained. 
         [0051]      FIGS. 9 and 10  are cross-sectional views each showing the body  30  with the joint portion  35  viewed from below. 
         [0052]    To switch types of the ink supplied to the recording head  18  from matte black ink to photo black ink, the second ON-OFF valve  48  is first pressed leftward through the second link member  50 . This causes close contact between the second ON-OFF valve  48  and the second projection  34   c , as illustrated in  FIG. 9 , and the first ON-OFF valve  47  is pressed leftward through the two transmission members  46 . The first ON-OFF valve  47  is thus separated from the first projection  33   c . In this state, the first communication groove  37  and the first joint line  44  communicate with each other through the first receiving portion  33  and the second communication groove  38  and the second joint line  45  are disconnected from each other. In other words, the first ON-OFF valve  47  is maintained open and the second ON-OFF valve  48  is held closed. 
         [0053]    Subsequently, flushing is performed so that the matte black ink, which is the ink that has been previously used, is drained from the nozzle row  20   a  of the recording head  18  into the cap  27 . This causes the photo black ink to flow from the first communication groove  37  into the first joint line  44  through the first receiving portion  33 . In such flushing, the ink is discharged exclusively from the nozzle row  20   a.    
         [0054]    After having flowed into the first joint line  44 , the photo black ink is divided into a first ink flow A indicated by arrow A in  FIG. 9  and a second ink flow B indicated by arrow B in the drawing. The first ink flow A proceeds in the space forward from the ink guide portion  42  in the first joint line  44  and reaches the first through hole  39 . The second ink flow B passes through the space rearward from the ink guide portion  42  in the first and second joint lines  44 ,  45 , the vicinity of the second ON-OFF valve  48 , and the space forward from the ink guide portion  42  in the second joint line  45  and reaches the first through hole  39 . These flows of the photo black ink in the second joint line  45  suppress retaining of the photo black ink in the joint passage  36  as a whole. As a result, the matte black ink, the ink that has been previously used, is prevented from being retained in the second joint line  45  after the matte black ink is switched to the photo black ink. 
         [0055]    The interference suppressing portion  43  suppresses interference between the first ink flow A and the second ink flow B. The first ink flow A and the second ink flow B are thus allowed to smoothly flow into the first through hole  39  without stopping. 
         [0056]    Contrastingly, to switch the types of the ink supplied to the recording head  18  from the photo black ink to the matte black ink, the first ON-OFF valve  47  is pressed rightward through the first link member  49 . This causes close contact between the first ON-OFF valve  47  and the first projection  33   c , as illustrated in  FIG. 10 , and the second ON-OFF valve  48  is pressed rightward through the two transmission members  46 . The second ON-OFF valve  48  is thus separated from the second projection  34   c . In this state, the second communication groove  38  and the second joint line  45  communicate with each other through the second receiving portion  34 , and the first communication groove  37  and the first joint line  44  are disconnected from each other. In other words, the first ON-OFF valve  47  is closed and the second ON-OFF valve  48  is held open. 
         [0057]    Subsequently, the photo black ink, the ink that has been previously used, is drained from the nozzle row  20   a  of the recording head  18  into the cap  27  through flushing. This causes the matte black ink to flow from the second communication groove  38  into the second joint line  45  through the second receiving portion  34 . In flushing, the ink is discharged exclusively from the nozzle row  20   a.    
         [0058]    After having flowed into the second joint line  45 , the matte black ink is divided into a third ink flow C indicated by arrow C in  FIG. 10  and a fourth ink flow D indicated by arrow D in the drawing. The third ink flow C proceeds in the space forward from the ink guide portion  42  in the second joint line  45  and reaches the first through hole  39 . The fourth ink flow D passes through the space rearward from the ink guide portion  42  in the first and second joint lines  44 ,  45 , the vicinity of the first ON-OFF valve  47 , and a front space in the first joint line  44 , and reaches the first through hole  39 . These flows of the matte black ink in the first joint line  44  suppress retaining of the matte black ink in the joint passage  36  as a whole. As a result, the photo black ink, the ink that has been previously used, is prevented from being retained in the first joint line  44  after the photo black ink is switched to the matte black ink. 
         [0059]    The interference suppressing portion  43  suppresses interference between the third ink flow C and the fourth ink flow D. The third ink flow C and the fourth ink flow D are thus allowed to smoothly flow into the first through hole  39  without stopping. 
         [0060]    As has been described, in switching between the photo black ink and the matte black ink, the previously used ink is prevented from being retained in the joint passage  36  of the switching device  25 . The photo black ink and the matte black ink are thus prevented from being mixed together. This suppresses lowering of printing quality after switching of ink types. 
         [0061]    The illustrated embodiment has the following advantages. 
         [0062]    When the first ON-OFF valve  47  is open and the second ON-OFF valve  48  is closed, the ink guide portion  42  causes some of the photo black ink to flow into the first through hole  39  via the second joint line  45 . When the second ON-OFF valve  48  is open and the first ON-OFF valve  47  is closed, the ink guide portion  42  causes some of the matte black ink to flow into the first through hole  39  via the first joint line  44 . This suppresses retaining of the photo black ink or the matte black ink in the joint passage  36 . In other words, in switching between the photo black ink and the matte black ink, the previously used ink is prevented from being retained in the joint passage  36  after the ink is switched to the other type. This suppresses mixing of the currently used ink, which is the photo black ink or the matte black ink, with the other ink. As a result, printing quality is maintained regardless of switching of the ink types. 
         [0063]    The width of the ink guide portion  42  becomes smaller toward the top. This decreases the volume of the space occupied by the ink guide portion  42  in the joint passage  36 , increasing the volume of the joint passage  36  in the switching device  25 . 
         [0064]    The ink guide portion  42  has the interference suppressing portion  43  projecting into the first through hole  39 . This suppresses interference between the first ink flow A and the second ink flow B when the photo black ink flows in the joint passage  36  after the matte black ink has been switched to the photo black ink. The first ink flow A and the second ink flow B are thus allowed to smoothly flow into the first through hole  39 . Likewise, the interference suppressing portion  43  suppresses interference between the third ink flow C and the fourth ink flow D when the matte black ink flows in the joint passage  36  after the photo black ink has been switched to the matte black ink. The third ink flow C and the fourth ink flow D are thus allowed to smoothly flow into the first through hole  39 . 
         [0065]    The ink guide portion  42  is configured by the two portions that are laterally symmetrical with respect to the interference suppressing portion  43 , which is located at the longitudinal center of the ink guide portion  42 . Thus, interference between the first ink flow A and the second ink flow B and interference between the third ink flow C and the fourth ink flow D are suppressed to the equal extents. 
         [0066]    Switching between the matte black ink and the photo black ink is brought about through flushing in which the ink is discharged solely from the nozzle row  20   a . Thus, in switching of the inks, types of ink other than the matte black ink and the photo black ink are prevented from being consumed. If the cap  27  is an integral type that covers the nozzle rows  20   a  to  20   c  as a whole and switching between the matte black ink and the photo black ink is carried out through cleaning, the types of ink other than the matte and photo black inks are wastefully consumed. 
         [0067]    The illustrated embodiment may be modified in the following forms. 
         [0068]    The interference suppressing portion  43  does not necessarily have to be arranged at the longitudinal center of the ink guide portion  42 . Specifically, the interference suppressing portion  43  may be provided at a position rightward or leftward from the longitudinal center of the ink guide portion  42 . 
         [0069]    The interference suppressing portion  43  may be formed in a thin plate-like shape. 
         [0070]    The interference suppressing portion  43  does not necessarily have to extend toward the first through hole  39 . 
         [0071]    The interference suppressing portion  43  may be omitted. 
         [0072]    The interference suppressing portion  43  may be formed separately from the ink guide portion  42 . 
         [0073]    The width of the ink guide portion  42  does not necessarily have to become smaller toward the top. 
         [0074]    The ink guide portion  42  may be formed either integrally with or independently from the lower wall of the joint passage  36 . 
         [0075]    In the illustrated embodiment, the switching device  25  switches between the matte black ink and the photo black ink. However, such switching may be carried out between a dark tone and a light tone of the same color of ink such as cyan ink and light cyan ink or magenta ink and light magenta ink. 
         [0076]    The switching device  25  may be configured in such a manner that the first joint line  44  and the second joint line  45  are connected together to form a V shape or a U shape. In other words, the switching device  25  may be provided in such a manner that the joint passage  36  is V-shaped or U-shaped. In this case, the shape of each transmission member  46  must be changed in correspondence with the shape of the joint passage  36 . 
         [0077]    The liquid ejection apparatus is not restricted to the inkjet type printer but may be a type that ejects a different type of liquid. That is, the liquid ejection apparatus may be, for example, a liquid ejection apparatus that ejects liquid such as electrode material or color material used in the manufacture of liquid crystal displays, EL displays, and surface light emitting displays, or a liquid ejection apparatus that ejects bioorganic matter used in the manufacture of biochips or a sample ejection apparatus such as a precision pipette.