Abstract:
A cartridge body is formed with a chamber storing ink and a recessed portion having an ink outlet port from which ink in the chamber flows out. An elastic gasket has a first through hole and is fitted into the recessed portion. A gasket stopper has a second through hole and is fitted into the recessed portion such that the gasket is pressed against an inner face of the recessed portion. A hollowed needle having a hole at a tip end thereof is inserted into the ink outlet port while passing through the first through hole and the second through hole and while enlarging the first through hole in order to supply the ink in the chamber to an ink jet recording head via the hole.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an ink cartridge used as an ink supplying source of an ink jet printer. In further detail, the invention relates to an ink cartridge capable of supplying ink with an ink supplying needle at an ink jet printer side inserted into a needle insertion hole formed on a gasket attached to an ink outlet port when the same ink cartridge is mounted in an ink jet printer. 
   In this type of ink cartridge, for example, as disclosed in Japanese Patent Publication Nos. 2001-113723A and 2002-192739A, an annular projection which protrudes outward from the circumference of a gasket press-fitted to an ink outlet port is formed at the outer circumferential face thereof, and sealing of the gasket is secured. That is, if a gasket is press-fitted to the ink outlet port, the annular projection is forcibly crushed, wherein spacing between the inner circumferential face of the ink outlet port and the outer circumferential face of the gasket is sealed. As a result, air is prevented from invading an ink reservoir in the ink cartridge from outside, passing through the spacing between the outer circumferential face of the gasket and the inner circumferential face of the ink outlet port. Also, air bubbles are prevented from flowing out from the ink reservoir. 
   The gasket attached to the ink outlet port is formed of a rubber material such as silicone rubber, chloroprene rubber, butyl rubber, etc., or a resilient material such as elastomer resin, etc. These rubber materials and elastomer resin deteriorate over time, and plastic deformation thereof becomes worse. Therefore, the sealing property of a gasket is weakened by chronological deterioration, wherein there is an anxiety that, by a force acting on the gasket when attaching and detaching an ink cartridge, air invades inwardly from outside through spacing between the outer circumferential face of the gasket and the inner circumferential face of the ink outlet port, or air bubbles are flown out from inside to outside. Also, where an ink cartridge is stored or where an ink cartridge remains attached in a printer for a long time period, there is a concern that air gradually invades between the outer circumferential face of the gasket and the inner circumferential face of the ink outlet port, so that air bubbles are deposited at the ink outlet port. Accordingly, air bubbles may be supplied to the ink jet head side of an ink jet printer together with ink, resulting in faulty discharge of ink liquid droplets and an inability to discharge, wherein a deterioration in printing quality results. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide an ink cartridge capable of securing an airtight seal between the ink outlet port and a gasket for a long time period. 
   It is also an object of the invention to provide an ink jet printer incorporating such an ink cartridge as an ink supplying source. 
   In order to achieve the above objects, according to the invention, there is provided an ink cartridge, comprising: 
   a cartridge body formed with a first chamber storing ink and a first recessed portion having an ink outlet port from which ink in the first chamber flows out; 
   an elastic first gasket having a first through hole, and the elastic first gasket being fitted into the first recessed portion; and 
   a first gasket stopper having a second through hole and fitted into the first recessed portion such that the first gasket is pressed against an inner face of the first recessed portion. 
   With this configuration, spacing between the gasket and the ink outlet port is kept airtight by the gasket stopper. Therefore, in contrast with an assembly where the seal is kept only by the resilient restoration force of the gasket, the seal in this configuration can be kept airtight even if the gasket chronologically deteriorates, wherein it is possible to prevent air from passing through the spacing. Furthermore, since the gasket stopper is press-fitted directly to the first recessed portion of the cartridge body and retained therein, the gasket stopper is prevented from dropping or falling off while securing the position of the gasket. Accordingly, reliability can be improved. 
   Preferably, the first gasket stopper has a first face brought into contact with a side portion of the inner face of the first recessed portion and a second face brought into contact with the first gasket so as to press the first gasket against a bottom portion of the inner face of the first recessed portion. 
   In this case, when press-fitting the gasket stopper into the first recessed portion, it is possible to manage the amount of insertion thereof. Accordingly, it is possible to manage the airtight seal. 
   Here, it is preferable that the bottom portion of the inner face of the first recessed portion is provided with an annular projection surrounding the ink outlet port. 
   In this case, the projection is cut into the second face of the gasket, whereby the airtight seal between the gasket and the ink outlet port can be secured. 
   Preferably, the first gasket has a projection adapted to be fitted with the first gasket stopper. 
   In this case, the gasket is fitted with the gasket stopper before press-fitting the gasket into the first recessed portion. Accordingly, both members can be simultaneously fitted into the first recessed portion, and the assembling work can be simplified. 
   Alternatively, it is preferable that the first gasket stopper has a first face brought into contact with a first side portion of the inner face of the first recessed portion and a second face brought into contact with an inner face of the first through hole of the first gasket so as to press the first gasket against a second side portion of the inner face of the first recessed portion. 
   Here, it is preferable that an annular protrusion is formed on an outer circumferential face of the first gasket and brought into contact with the second side portion of the inner face of the first recessed portion in order to secure the seal between the gasket and the ink outlet port. 
   Preferably, a first valve body is disposed in the first chamber. Here, a first elastic member urges the first valve body toward the first recessed portion such that the first through hole of the first gasket is closed by the first valve body. 
   Preferably, the cartridge body is formed with a second chamber storing waste ink and a second recessed portion having an ink inlet port from which the waste ink flows in. The ink cartridge further comprises: an elastic second gasket, having a third through hole and fitted into the second recessed portion; and a second gasket stopper, having a fourth through hole and fitted into the second recessed portion such that the second gasket is pressed against an inner face of the second recessed portion. 
   With this configuration, it is possible to securely prevent waste ink from leaking through the ink inlet port. 
   Here, it is preferable that the second gasket stopper has a first face brought into contact with a side portion of the inner face of the second recessed portion and a second face brought into contact with the second gasket so as to press the second gasket against a bottom portion of the inner face of the second recessed portion. 
   It is further preferable that the bottom portion of the inner face of the second recessed portion is provided with an annular projection surrounding the ink outlet port. 
   It is also preferable that the second gasket has a projection adapted to be fitted with the second gasket stopper. 
   Alternatively, it is also preferable that the second gasket stopper has a first face brought into contact with a first side portion of the inner face of the second recessed portion and a second face brought into contact with an inner face of the third through hole of the second gasket so as to press the second gasket against a second side portion of the inner face of the second recessed portion. 
   Here, it is further preferable that an annular protrusion is formed on an outer circumferential face of the second gasket and brought into contact with the second side portion of the inner face of the second recessed portion. 
   It is also preferable that a second valve body is disposed in the second chamber. Here, a second elastic member urges the second valve body toward the second recessed portion such that the third through hole of the second gasket is closed by the second valve body. 
   According to the invention, there is also provided an ink jet printer, comprising:
         an ink jet recording head; and       

   a first hollowed needle, having a first hole at a tip end thereof and adapted to be inserted into the ink outlet port of the above ink cartridge while passing through the first through hole and the second through hole and while enlarging the first through hole in order to supply the ink in the first chamber to the ink jet recording head via the first hole. 
   Preferably, the ink jet printer further comprises a second hollowed needle, having a second hole at a tip end thereof and adapted to be inserted into the ink inlet port of the ink cartridge as set forth in claim  8  while passing through the third through hole and the fourth through hole and while enlarging the third through hole in order to supply the waste ink to the second chamber via the second hole. 
   With the above configurations, since it is possible to securely prevent air from invading the ink cartridge through the spacing between the ink outlet port and the gasket, air bubbles formed by invaded air are prevented from being supplied to the ink jet recording head along with ink, and faulty discharge and an inability to discharge ink droplets are prevented, thereby maintaining printing quality. In addition, it is possible to securely prevent waste ink from leaking through the ink inlet port. 
   According to the invention, there is also provided an ink cartridge, comprising: 
   an ink chamber having a recess portion formed inside a casing and an ink outlet; 
   an elastic gasket fitted into a bottom of the recess portion; 
   a movable cover inserted through a top portion of the recess portion, the movable cover dividing an ink reservoir and an atmospheric communication chamber; and 
   a coil spring urging the movable cover toward the ink reservoir, 
   wherein as ink is filled in the ink reservoir, ink invades a gap between the movable cover and an inner face of the recess portion forming an ink meniscus, wherein the gap is sized such that a strength of the ink meniscus is greater than an ink pulling force acting on the ink outlet. 
   An urging force of the coil spring is preferably less than the strength of the ink meniscus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
       FIG. 1  is a schematic view of an ink jet printer incorporating an ink cartridge according to a first embodiment of the invention; 
       FIG. 2A  is an upper perspective view of the ink cartridge; 
       FIG. 2B  is a lower perspective view of the ink cartridge; 
       FIG. 3  is a perspective view of a disassembled state of the ink cartridge; 
       FIG. 4A  is a top plan view of the ink cartridge; 
       FIG. 4B  is a section view taken along a line IVB-IVB in  FIG. 4A ; 
       FIG. 5A  is an enlarged section view of an ink outlet port in the ink cartridge, showing a state that an ink supplying needle is not inserted into the ink outlet port; 
       FIG. 5B  is an enlarged section view of the ink outlet port, showing a state that an ink supplying needle is inserted into the ink outlet port; and 
       FIG. 6  is an enlarged section view of an ink outlet port in an ink cartridge according to a second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the invention will be described below in detail with reference to the accompanying drawings. 
   As shown in  FIG. 1 , an ink jet printer  1  comprises: a platen  3  for transporting a recording medium  2  in a direction indicated by an arrow Y; an ink jet head  4  whose nozzle face  4   a  is opposed to the platen  3 ; a carriage  5  for causing the ink jet head  4  to reciprocate in directions indicated by arrows X; a cartridge mounting portion  7  capable of mounting an ink cartridge  10  which supplies respective colors of ink to respective ink nozzles of the ink jet head  4 , and a controller  8  configured to drive the respective portions in the ink jet printer  1 . 
   The ink cartridge  10  is provided with four independent ink chambers in which black ink, cyan ink, yellow ink and magenta ink are respectively stored, and a waste ink chamber for collecting waste ink. The cartridge mounting portion  7  is provided with ink supplying needles  7 ( 1 ) through  7 ( 4 ) for taking out ink from respective chambers, and a waste ink supplying needle  7 ( 5 ) for supplying waste ink to the waste ink chamber. When the ink cartridge  10  is mounted in the cartridge mounting portion  7 , an ink supplying channel is formed, which supplies respective colors of ink from the ink cartridge  10  to the jet head  4 . 
   The ink jet printer  1  includes a nozzle cap  9  at a position deviated from the platen  3  in the printing direction X. The nozzle cap  9  is connected with the waste ink supplying needle  7 ( 5 ) via an ink pump  6 . Therefore, if the ink cartridge  10  is mounted in the cartridge mounting portion  7 , a waste ink collecting channel is formed from the nozzle cap  9  to the waste ink chamber in the ink cartridge  10  via the ink supplying needle  7 ( 5 ). If the ink pump  6  is driven with the nozzle cap  9  covered on the nozzle face  4   a  of the ink jet head  4 , it is possible to collect waste ink from the head side into the waste ink chamber. 
   As shown in  FIGS. 2A through 4B , the ink cartridge  10  comprises four ink chambers  12 ( 1 ) through  12 ( 4 ) and one waste ink chamber  13  which are formed in a laterally elongated casing  11 . The casing  11  is composed of a casing body  11   a  and a cover plate  11   b  for sealing a top opening of the casing body  11   a . The cover plate  11   b  is thin, and its rear side is almost flat. Ink outlet ports  14 ( 1 ) through  14 ( 4 ) of the respective ink chambers  12 ( 1 ) through  12 ( 4 ) and a waste ink inlet port  15  for collecting waste ink into the waste ink chamber  13  are formed on the bottom of the casing body  11   a.    
   The casing body  11   a  is provided with cylindrical casings  21  through  25  which are laterally arrayed and top ends thereof are open. Each adjacent casings are connected by a thin vertical plate  26 . The upper end portions of the casings  21  through  25  are connected to a lateral connection plate  27 . A circumferential frame  28  is formed at the outer circumferential edge of the lateral connection plate  27  so as to have a predetermined height. The bottom portions of the cylindrical casings  21  through  25  are connected to each other by a lateral connection plate  29 . The casing body  11   a  is an article molded with plastic injection. 
   The four ink chambers  12 ( 1 ) through  12 ( 4 ) each having a circular cross section and an open top end are formed with the cylindrical casings  21  through  24 . The open top ends of the respective ink chambers  12 ( 1 ) through  12 ( 4 ) are blocked by a partitioning plate  30  made of a material such as plastic, which is mounted inside the circumferential frame  28  of the lateral connection plate  27 . Cylindrical atmospheric communication ports  30   a  passing through the partitioning plate  30  in its thickness direction are formed at points corresponding to the respective ink chambers  12 ( 1 ) through  12 ( 4 ). The open top ends of the outer circumferential plate portion  28  of the casing body  11   a  are blocked by a cover plate  11   b , and a slender space extending in the lateral direction is formed between the partitioning plate  30  and the cover plate  11   b . An L-shaped space extending from the above-described space to the space in the casing  25  is formed to constitute the waste ink chamber  13 . The waste ink chamber  13  is filled with an ink absorbing body  17  such as a foam or felt material. 
   An atmospheric communication port  18  for communicating the waste ink chamber  13  to the atmosphere is formed at the end portion opposite to the end portion opposed to the casing  25  in the cover plate  11   b . The atmospheric communication port  18  is provided with: a recess portion  18   a  having a circular cross section and formed on the outer face of the cover plate  11   b ; a groove  18   b  formed on the outer face of the cover plate  11   b ; a through hole  18   c  piercing through the cover plate  11   b  and communicating with the waste ink chamber  13 ; and a sealing film  18   d . One end portion of the groove  18   b  communicates with the recess portion  18   a  and the other end portion thereof communicates with the through hole  18   c . The sealing film  18   d  is adhered to the outer face of the cover plate  11   b  so as to seal the through hole  18   c  and the groove  18   b  airtight, so that only the recess portion  18   a  is exposed at the outer face of the cover plate  11   b.    
   In the waste ink chamber  13 , empty portions  13   a  having a rectangular cross section and having no ink absorbing body  17  filled therein, are formed at parts where the atmospheric communication ports  30   a  are provided in the partitioning plate  30 . Thereby, the atmospheric communication ports  30   a  are isolated from the ink absorbing body  17  by the corresponding empty portions  13   a . Similarly, an empty portion  13   b  having a rectangular cross section and having no ink absorbing body  17  filled therein is formed at a portion where the through hole  18   c  of the cover plate  11   b  is provided, wherein the through hole  18   c  is isolated from the ink absorbing body  17 . 
   Next, a description follows of the structures of the ink chambers  12 ( 1 ) through  12 ( 4 ). Respective colors of ink, cyan, magenta, yellow and black, are filled in the ink chambers  12 ( 1 ) through  12 ( 4 ). The structures of the respective ink chambers  12 ( 1 ) through  12 ( 4 ) are identical to each other. Therefore, a description follows of the structure of only the ink chamber  12 ( 1 ), and repetitive description of the other ink chambers  12 ( 2 ) through  12 ( 4 ) will be omitted. 
   The ink chamber  12 ( 1 ) is provided with: a circular recess portion  31  formed inside the cylindrical casing  21 ; an ink outlet port  14 ( 1 ) formed at the center portion of the bottom face of the circular recess portion  31 ; a movable cover  32  inserted through the open portion (i.e., a top open portion of the circular recess portion  31 ) of the ink chamber  12 ( 1 ); and a coil spring  33  for urging the movable cover  32  upwards. The movable cover  32  partitions the underside ink reservoir  34 , at which the ink outlet port  14 ( 1 ) is provided, from the atmospheric communication chamber  35  communicating with the waste ink chamber  13  via the atmospheric communication port  30   a . The movable cover  32  is made reciprocal in the vertical direction along the inner circumferential face  31   a  of the circular recess portion  31 . The movable cover  32  is provided with a disk-shaped main body  32   a  and a cylindrical portion  32   b  extending downward from the outer circumferential face of the main body  32   a.    
   As ink is filled in the ink reservoir  34 , ink invades a gap  36  between the movable cover  32  and the inner circumferential face of the circular recess portion  31 , thereby forming an ink meniscus. By setting the gap  36  to an adequate dimension, the strength of the ink meniscus formed in the corresponding gap  36  is made larger than an ink pulling force acting on the ink outlet port  14 ( 1 ), whereby the ink meniscus is prevented from being broken when the ink pulling operation is performed. In the present embodiment, for example, the cylindrical portion  32   b  of the movable cover  32  is formed so that the outer dimension thereof is made smaller by approximately 0.1 mm than the inner dimension of the inner circumferential face  31   a  of the circular recess portion  31 . Therefore, as the movable cover  32  is inserted to be concentric with the circular recess portion  31 , a gap  36  which is 0.05 mm wide is formed to become annular therebetween. 
   Since the inside of the ink reservoir  34  is maintained at a predetermined negative pressure at all times by the coil spring  33  urging the movable cover  32  upward, ink is prevented from leaking outside from the ink reservoir  34  via the ink outlet port  14 ( 1 ) in a state where no ink pulling force acts on the ink outlet port  14 ( 1 ). Further, even if the ink cartridge  10  is inclined sideways or is turned upside down, no ink leaks from the gap  36  between the inner circumferential face  31   a  of the circular recess portion  31  and the movable cover  32  toward the atmospheric communication chamber  35  communicating with the waste ink chamber  13 . 
   The urging force of the coil spring  33  is set so as to become smaller than the strength of the ink meniscus and the ink pulling force acting on the ink outlet port  14 ( 1 ). Therefore, the ink meniscus is prevented from being broken by the urging force of the coil spring  33 , and air bubbles are prevented from invading the ink reservoir  34 . Also, as ink is sucked from the ink outlet port  14 ( 1 ), the movable cover  32  moves toward the ink outlet port  14 ( 1 ) in response to the ink suction force. 
   With reference to  FIGS. 5A and 5B , a description follows of the airtight structure of the ink outlet port  14 ( 1 ). Since the airtight structures of the other ink outlet ports  14 ( 2 ) through  14 ( 4 ) and the waste ink inlet port  15  are the same as that of the ink outlet port  14 ( 1 ), repetitive explanations for those will be omitted. 
   A cylindrical portion  41  is formed at the center of the bottom face of the ink reservoir  34 , which passes through and extends from the bottom plate portion  31   b  of the circular recess portion  31 , and the ink outlet port  14 ( 1 ) is defined by the cylindrical portion  41 . A gasket  42  having an insertion hole  42 A (described later in detail) formed at the center thereof is mounted in the ink outlet port  14 ( 1 ). The gasket  42  is pressed to the ink outlet port side by a gasket stopper  43  from the outside. A valve body  44  is urged from the inside to the gasket  42  by a coil spring  45  at all times, so that the insertion hole  42 A is closed by the valve body  44 . The outside opening (the lower end opening) of the ink outlet port  14 ( 1 ) is sealed by a plastic film  46 , and a filter  47  for eliminating foreign substances is attached to the inside opening (upper end opening) of the ink outlet port  14 ( 1 ). 
   A rectangular positioning frame  7   a  into which the ink outlet port  14 ( 1 ) can be inserted is formed at the cartridge mounting portion  7  at the ink jet printer  1  side. The ink supplying needle  7 ( 1 ) protrudes upwards from the center of the rectangular frame  7   a . A plurality of ink orifices  71  are formed at a tip end portion of the ink supplying needle  7 ( 1 ), and an ink passage  72  is formed inside of the ink supplying needle  7 ( 1 ). 
   As the ink cartridge  10  is mounted at the cartridge mounting portion  7 , the ink supplying needle  7 ( 1 ) breaks through the plastic film  46  and is inserted into the insertion hole  42 A with the gasket  42  widened, thereby pushing up the valve body  44 . As a result, an ink supplying channel is formed from the ink reservoir  34  to the nozzle orifices of the ink jet head  4  in the ink jet printer  1  via the ink supplying needle  7 ( 1 ). If the ink cartridge  10  is removed from the cartridge mounting portion  7 , the valve body  44  is again returned by the pressing force of the coil spring  45  to a state where the valve body  44  is abutted against the gasket  42 , so that the ink outlet port  14 ( 1 ) is returned to a closed state. 
   The lower half portion of the cylindrical portion  41  which forms the ink outlet port  14 ( 1 ) is made into an outer cylindrical portion  51  provided with a circular inner circumferential face  51   a  having a first diameter, and the upper half portion thereof is made into an inner cylindrical portion  52  provided with a circular inner circumferential face  52   a  having a second diameter which is smaller than the first diameter. Therefore, an annular end face  53  is formed at the boundary between the inner circumferential face  51   a  and the inner circumferential face  52   a . An annular projection portion  53   a  is formed along the inner circumferential edge portion on the annular end face  53 . The gasket  42  and the gasket stopper  43  are provided in the outer cylindrical portion  51 , and the valve body  44  and coil spring  45  are provided in the inner cylindrical portion  52 . 
   The gasket  42  is formed of a rubber material such as silicone rubber, chloroprene rubber, butyl rubber, etc., or a resilient material such as an elastomer material, and presents an annular shape provided with an outer circumferential face  42   a  brought into contact with the inner circumferential face  51  a of the outer cylindrical portion  51 . An annular end face  42   b  is continued to the ink reservoir side end of the outer circumferential face  42   a , and an annular valve seat portion  42   c  protruding into the inner cylindrical portion  52  is formed at the inner circumferential edge portion of the annular end face  42   b . The valve body  44  is seated in the annular valve seat portion  42   c . An annular fitting projection  42   d  formed on the other annular end face of the gasket  42 . The inner circumferential face that defines the insertion hole  42 A at the center of the gasket  42  is provided with: a guide face  42   f  for the ink supplying needle, which is widened toward the outside of the insertion hole  42 A; and a circular inner circumferential face  42   g  which is widened by the ink supplying needle  7 ( 1 ) and is brought into contact with the outer circumferential face thereof in a liquid-tight state. 
   The gasket stopper  43  is made of a plastic rigid component and is provided with an outer circumferential face  43   a  which can be inserted into the inner circumferential face  51   a  of the cylindrical portion  41  which defines the ink outlet port  14 ( 1 ). An annular end face  43   b  continued to the ink reservoir side end of the outer circumferential face  43   a  has such a size corresponding to the annular end face  53  at the ink outlet port side. Further, the fitting projection  42   d  of the gasket  42  can be fitted to an inner circumferential face  43   c  of the gasket stopper  43 . 
   The gasket  42  is mounted in a state where it is pressed to the annular end face  53  at the ink outlet port side by the annular end face  43   b  of the gasket stopper  43 . Also, since the annular projection  53   a  is formed at the annular end face  53 , the annular end face  42   b  of the gasket  42  is pressed to the annular end face  53  in a state where the annular projection portion  53   a  is cut into the annular end face  42   b . In other words, the annular end face  42   b  of the gasket  42  is forcibly pressed by the gasket stopper  43  against the annular end face  53  formed with the annular projection portion  53   a . Therefore, even if the gasket  42  deteriorates through a long period of use and is plastically deformed, the airtight seal between the gasket  42  and the ink outlet port  14 ( 1 ) is prevented from being reduced, and air is prevented from invading a small ink chamber  48  formed between the filter  47  and the valve body  44 . In addition, when attaching and detaching the ink cartridge  1 , air is prevented from invading the small ink chamber  48  from outside through the gasket  42  and the ink outlet port  14 ( 1 ) by a force acting on the gasket  42 , and air bubbles are prevented from flowing out from the small ink chamber  48  to the outside. 
   Since the fitting projection  42   d  which can be fitted into the gasket stopper  43  is formed at the annular end face of the gasket  42 , it is possible to simultaneously press-fit both the components  42  and  43  into the insertion hole  42 A after the gasket  42  is fitted into the end of the gasket stopper  43 . Accordingly, the assembly can be simplified in comparison with a case where the respective components are separately press-fitted into the insertion hole  42 A. 
   Therefore, in the ink jet printer  1  employing the above described ink cartridge  10  as an ink supplying source, invasion of air into the ink jet head side due to an insufficient seal between the gasket and the ink outlet port is prevented, so that an inability of ejection or faulty ejection of ink droplets can be avoided. Accordingly, printing quality can be maintained. 
   In a state where ink is filled in the ink reservoir  34  of the ink chamber  12 ( 1 ), as shown in  FIG. 4B , the movable cover  32  is positioned in the vicinity of the upper end position of the circular recess portion  31 , so that the capacity of the atmospheric communication chamber  35  is minimized. 
   Since an ink meniscus is formed in the gap  36  between the movable cover  32  and the inner circumferential face  31   a  of the circular recess portion  31 , the atmospheric communication chamber  35  communicating with the waste ink chamber  13  and the ink reservoir  34  are isolated from each other by the movable cover  32 . Further, since the movable cover  32  is pushed up by the coil spring  33  toward the atmospheric communication chamber  35 , the inside of the ink reservoir  34  is kept in a predetermined negative pressure state. 
   As an ink pulling force brought by the ink jet head  4  side acts on the ink outlet port  14 ( 1 ), the movable cover  32  moves to the ink outlet port  14 ( 1 ) side against the urging force of the coil spring  33 , whereby a predetermined quantity of ink is supplied from the ink outlet port  14 ( 1 ) to the ink jet head  4 . 
   Since the strength of the ink meniscus formed in the gap  36  between the moving movable cover  32  and the inner circumferential face  31   a  of the circular recess portion  31  is larger than the ink pulling force, the ink meniscus is not broken by the ink pulling force. Therefore, air bubbles are prevented from invading the ink reservoir  34  side from the atmospheric communication chamber  35  side through the gap  36 . Additionally, no ink leaks from the ink reservoir  34  side to the atmospheric communication chamber  35  side via the gap  36 . 
   Thus, the inside of the ink reservoir  34  is kept in an adequate negative pressure state, wherein ink can be supplied without mixture of air bubbles therewith and leakage of ink. In the ink end state, as shown in  FIG. 5B , the movable cover  32  falls to the position where it is brought into contact with the bottom face of the circular recess portion  31 , and the capacity of the ink reservoir  34  is minimized. 
     FIG. 6  shows a second embodiment of the invention. The basic configuration of the airtight structure according to the present embodiment is identical to that in the first embodiment. The corresponding parts are given the same reference numerals, and a repetitive description for those will be omitted. 
   The airtight structure of the ink outlet port according to this embodiment is composed of a gasket  420 , which is press-fitted into the ink outlet port  140 , and a gasket stopper  430 . The ink outlet port  140  is basically identical to the ink outlet port  14 ( 1 ) shown in  FIGS. 5A and 5B . However, the annular end face  53  is made into a flat face, and is not provided with the annular projection portion  53   a . The gasket  420  is provided with an insertion hole  42 A at the center thereof, and the outer circumferential portion  421  is press-fitted into the inner circumferential face  51   a  of the ink outlet port  140 . An annular protrusion  422  is formed on the outer circumferential portion  421 . The gasket stopper  430  is made annular as a whole, and is shaped so as to have an L-shaped cross section in which a cylindrical portion  432  extends upwards from the inner circumferential edge portion of an annular bottom plate portion  431 . 
   An outer circumferential face  433  of the annular bottom plate portion  431  is press-fitted into the circular inner circumferential face  51   a  of the ink outlet port  140 . An outer circumferential face  434  of the cylindrical portion  432  is fitted into the inner circumferential face  423 , which defines the insertion hole  42 A of the gasket  420 , and a tapered needle guide face  424  is continued from the inner circumferential face  423 . Also, the outer circumferential face  434  of the cylindrical portion  432  confronts the annular protrusion  422  of the gasket  420  in a press-fitted state. 
   As the gasket  420  is press-fitted into the ink outlet port  140 , the outer circumferential face  421  of the gasket  420  is brought into contact with the inner circumferential face  51   a  in a state where the annular protrusion  422  is crushed. If the gasket stopper  430  is press-fitted into the ink outlet port  140 , the outer circumferential face  434  of the cylindrical portion  432  is fitted inside the gasket  420  where the gasket  420  is forcibly pushed to the inner cylindrical face  51   a.    
   Therefore, in the present embodiment, the outer circumferential face  421 , at which the annular protrusion  422  is formed, in the gasket mounted on the ink outlet port  140  is pushed to the inner circumferential face  51   a  at the ink outlet port side by the gasket stopper  430 , and an airtight seal is secured between the outer circumferential face  421  and the inner circumferential face  51   a . Therefore, even if the gasket  420  deteriorates through a long time period of use and a force operates on the gasket  420  when attaching and detaching an ink cartridge  10 , the airtight seal can be maintained therebetween. 
   In addition, the invention is not limited to the above-described embodiments. It may be subjected to various modifications. For example, although, in the embodiments, a description was given of the ink outlet port using a circular recess portion, a rectangular recess portion may be employed. In this case, if the gasket and the gasket stopper are shaped such that the gasket and the gasket stopper can be fitted into the square recess portion, similar effects can be achieved. 
   Also, it is not necessary that the portion, which contributes to the press-fitting operation, of the outer circumferential face of the gasket stopper may not be the entire circumference, but a part of the outer circumferential face. Further, the assembly may include a plurality of annular projections formed on the outer circumferential face of the gasket.