Abstract:
A problem to be solved is to provide a writing implement at low cost that prevents flow of air into an ink tank and prevents writing failure while allowing for productivity. 
     A writing implement refill  10  comprises: an ink tank  20  composed of films  21  storing ink; a joint  30  connected to a tip of the ink tank  20 ; and a writing tip  40  connected to a tip of the joint  30 . An inner circumferential surface of the tip of the ink tank  20  covers an outer circumferential surface of a rear end of the joint  30 . A covering member  50  of a ring shape covers from outside an area where the tip of the ink tank  20  covers the outer circumferential surface of the rear end of the joint  30.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a refill for a writing implement such as a ballpoint pen and a writing implement provided with the refill. 
       BACKGROUND ART 
       [0002]    In the case of a publicly known conventional water-based ballpoint pen including an ink tank filled with low-viscosity ink directly poured therein, air needs to be taken into the ink tank for discharge of the ink during writing. If temperature increases or atmospheric pressure drops rapidly during writing, or if pressure inside the tank increases as a result of temperature increase or drop of atmospheric pressure while a cap is attached and then the cap is removed, the ink may jet out of the tank to soil a sheet of paper being written on or clothes, for example. Hence, action against the jet of ink has been taken by employing a comb-like ink guidance member called a collector or by employing a structure for buffering pressure inside the ink tank. However, these methods increase a number of parts, disadvantageously causing cost increase or complicated assembly process. 
         [0003]    Patent literatures listed below disclose techniques of solving the aforementioned problem. According to these techniques, an ink tank is made of a flexible material and a valve (or a spring) is installed on a writing tip portion, thereby making the ink tank shrink in response to writing. 
         [0004]    Patent Document 1: JP 2000-177290 A. 
         [0005]    Patent Document 2: JP S29-13711 Y. 
         [0006]    Patent Document 3: JP S35-25220 Y. 
       SUMMARY OF INVENTION 
       [0007]    Of the aforementioned conventional techniques, the invention described in Patent Document 1 discloses a writing implement using a laminated film as an ink tank. In this writing implement, however, a writing tip where ink is discharged functions as a valve mechanism. Hence, if an impact is caused by being dropped or writing proceeds particularly with the tip facing upward, air might be mixed into the ink tank. 
         [0008]    In Patent Document 2, a joint between an inner pouch and a mouth piece is tied with a strip of string. Hence, creases occur at a junction of a film and its vicinity so that sufficient attachment strength cannot be assured. As a result, air bubbles may be generated inside an ink tank, causing adverse effect on writing performance to lead to faint writing, for example. 
         [0009]    In Patent Document 3, a neck portion and an inner pouch are joined with a metal ring. Meanwhile, a great deal of power is required for press fitting into a member at a pen tip, making it difficult to realize easy assembly. Additionally, if the pen according to the document is placed in an environment subjected to temperature change such as that from high temperature to low temperature while being used as a writing implement, the low expansion coefficient of the metal ring might reduce joint strength. 
         [0010]    In any case, it has been difficult to ensure sealing performance and strength at a junction between a film part and a writing part such as a pen tip. 
         [0011]    In view of the aforementioned problems, a subject of the present invention is to provide a writing implement of a simple structure that prevents flow of air into an ink tank and prevents writing failure while allowing for productivity. 
         [0012]    (1) First Invention 
         [0013]    In order to solve the aforementioned problem, a first invention of the present invention is a writing implement refill comprising: 
         [0014]    a flexible ink tank storing ink, 
         [0015]    a writing tip connected to a tip of the ink tank, an outer circumferential surface of a rear end of the writing tip being covered with an inner circumferential surface of the tip of the ink tank, and 
         [0016]    a covering member covering over an area where the tip of the ink tank covers the outer circumferential surface of the rear end of the writing tip. 
         [0017]    In the present invention, a “tip” means a side where the writing tip of the writing implement refill exists, and a “rear end” means a side opposite the tip. 
         [0018]    “Flexibility” means formation deformable easily in response to pressing force of a hand. More specifically, using a thin layer (film) made of, for example, synthetic resin to form the ink tank makes the ink tank flexible. 
         [0019]    Regarding the “writing tip,” if the writing implement refill is for a ballpoint pen, for example, a ballpoint pen tip is attached as the writing tip to the tip of the ink tank, for example. If the writing implement refill is for a felt-tip pen, a core made of felt or synthetic fiber is attached as the writing tip to the tip of the ink tank, for example. 
         [0020]    In particular, if the writing tip is for a ballpoint pen, force to press a ball where ink is discharged is applied by a spring and the like in a direction toward the tip in the absence of a writing load. This prevents leakage of the ink from a pen tip even if pressure is applied to the film. 
         [0021]    (2) Second Invention 
         [0022]    In order to solve the aforementioned problem, a second invention of the present invention is a writing implement refill comprising: 
         [0023]    a flexible ink tank storing ink; 
         [0024]    a joint connected to a tip of the ink tank; an outer circumferential surface of a rear end of the joint being covered with an inner circumferential surface of the tip of the ink tank; and 
         [0025]    a writing tip connected to a tip of the joint; and 
         [0026]    covering member covering over an area where the tip of the ink tank covers the outer circumferential surface of the rear end of the joint. 
         [0027]    The “joint” is a member formed so as to distribute ink stored in the ink tank to the writing tip. Specifically, in the present invention, the writing tip is fitted to the ink tank via the joint. 
         [0028]    (3) Third Invention 
         [0029]    In order to solve the aforementioned problem, in addition to the aforementioned characteristics of the second invention, a third invention of the present invention is characterized in that 
         [0030]    the covering member is formed into a ring shape, 
         [0031]    the area where the tip of the ink tank covers the outer circumferential surface of the rear end of the joint is covered with an inner circumferential surface of the covering member, and 
         [0032]    a protruding part is formed on the outer circumferential surface of the rear end of the joint and/or the inner circumferential surface of the covering member, the protruding part protruding toward the other circumferential surface. 
         [0033]    As described above, the outer circumferential surface of the rear end of the joint and the inner circumferential surface of the covering member face each other through a tip portion of the ink tank. The “protruding part” is provided on at least one of these circumferential surfaces. Thus, the protruding part protruding from one of the circumferential surfaces presses the other circumferential surface. As a result, the joint and the covering member fit with each other with greater force. The protruding part may certainly be provided on each of these circumferential surfaces. 
         [0034]    (4) Fourth Invention 
         [0035]    In order to solve the aforementioned problem, in addition to the aforementioned characteristics of the third invention, a fourth invention of the present invention is characterized in that the protruding part is formed on each of the outer circumferential surface of the rear end of the joint and the inner circumferential surface of the covering member, one of the protruding parts functioning to retain the other protruding part. 
         [0036]    Specifically, in addition to the third invention, the protruding part protrudes from each of the circumferential surfaces toward the other circumferential surface. Thus, the joint and the covering member fit with each other with greater force. Additionally, the tip portion of the ink tank is held more reliably between the joint and the covering member while being curved into an S shape formed by these protrusions. 
         [0037]    If the protruding parts on both of the circumferential surfaces are formed as elongated protrusions extending along the outer circumferential surface, one of the protruding parts closer to a rear end also functions to retain a protruding part closer to the tip. If two protruding parts are formed on one of the circumferential surfaces so that one of the two locates in front of the other while one protruding part is formed on the other circumferential surface and between the former two protruding parts, the protruding parts on both the circumferential surfaces function to retain each other. 
         [0038]    (5) Fifth Invention 
         [0039]    In order to solve the aforementioned problem, in addition to the aforementioned characteristics of the first, second or third invention, a fifth invention of the present invention is characterized in that the writing implement refill is entirely made of a plastic material except for ink stored in the writing implement refill. 
         [0040]    The plastic material mentioned herein may be a nonmetallic material that can be incinerated relatively easily represented by a synthetic resin material such as PET, PBT, PE, EVOH, ABS, polypropylene, polycarbonate, polyacetal, or a cyclic olefin resin. The plastic material mentioned herein may also be one formed by adding to such a synthetic resin material a metallic material of a small quantity that generally allows the plastic material to be disposed of as plastic rubbish. As an example, the plastic material mentioned herein may be a material having a surface decorated with metal foil or the like, or a material to which metal powder is mixed. 
         [0041]    Using such a plastic material for forming the writing implement refill allows disposal of the used writing implement refill as plastic rubbish without the need of separately disposing metallic materials, such as a tip. 
         [0042]    (6) Sixth Invention 
         [0043]    In order to solve the aforementioned problem, a sixth invention of the present invention relates to a writing implement comprising the writing implement refill according to the first, second, third or fourth invention, and a shaft tube housing the writing implement refill. 
         [0044]    The “writing implement” is a ballpoint pen or a felt-tip pen, for example. 
         [0045]    The present invention of the aforementioned structure achieves the following effects. 
         [0046]    According to the structure of the first or second invention, the ink tank is composed of the flexible film. Force generated by atmospheric pressure and acting to compress the ink tank is applied to the ink tank swelling with ink filled therein. If the ink flows out of the ink tank, the ink tank contracts by the amount of ink having flown out of the ink tank. Specifically, force acting to push the ink out of the ink tank is applied to the ink in the ink tank. This makes it possible to use up the ink while preventing flow of air into the ink tank while preventing writing failure. Flow of air into the ink tank is also prevented during writing with the writing tip facing upward. Further, since virtually all the air can be eliminated from the ink tank, a structure for buffering pressure inside the ink tank becomes unnecessary. 
         [0047]    According to the structure of the second invention, the area where the tip of the ink tank covers the outer circumferential surface of the rear end of the joint is covered with the inner circumferential surface of the covering member. This covering member functions to prevent leakage of ink due to the tip of the ink tank coming off from the outer circumferential surface of the rear end of the joint. 
         [0048]    Attaching the covering member made of resin realizes a simple structure and favorable assembling performance while providing a strength required for a writing implement. 
         [0049]    According to the structure of the third invention, protrusions are formed on junction surfaces of the joint and the covering member with the ink tank. This reduces a gap around the ink tank to enhance sealing performance and fixation strength without entailing high cost and without involving troublesome work during manufacture. 
         [0050]    According to the structure of the fourth invention, protruding parts are formed both on the joint and the ink tank and the joint and the ink tank are fitted. Further, the joint and the covering member are fitted such that the film is formed into an S shape in cross section. As a result, sealing performance and fixation strength are enhanced further. 
         [0051]    According to the structure of the fifth invention, substantially all of the components are made of a plastic material. Thus, disposal of the writing implement refill does not require separately disposing, for example, a metallic component, allowing reduction of cost for disposal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0052]      FIGS. 1A and 1B  are a side view and a front view, respectively, showing a ballpoint pen refill of a first embodiment of the present invention. 
           [0053]      FIG. 2  is a side sectional view of the ballpoint pen refill of the first embodiment. 
           [0054]      FIG. 3  shows an area I of  FIG. 2  in an enlarged manner. 
           [0055]      FIGS. 4A and 4B  are a front view and a longitudinal sectional view, respectively, showing a ballpoint pen using the ballpoint pen refill of the first embodiment of the present invention. 
           [0056]      FIGS. 5A ,  5 B, and  5 C are a front view, a side view, and a side sectional view, respectively, of a ballpoint pen refill of a second embodiment of the present invention.  FIG. 5D  shows principal part of  FIG. 5C  in an enlarged manner. 
           [0057]      FIGS. 6A ,  6 B, and  6 C are a front view, a side view, and a side sectional view, respectively, of a ballpoint pen refill of a third embodiment of the present invention.  FIG. 6D  shows principal part of  FIG. 6C  in an enlarged manner. 
           [0058]      FIGS. 7A ,  7 B, and  7 C are a front view, a side view, and a side sectional view, respectively, of a ballpoint pen refill of a fourth embodiment of the present invention.  FIG. 7D  shows principal part of  FIG. 7C  in an enlarged manner.  FIG. 7E  shows principal part of  FIG. 7D  in an enlarged manner. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       [0000]    
       
           10  Writing Implement Refill 
           11  Ballpoint pen refill 
           20  Ink tank 
           21  Film 
           22  Ink storage 
           23  Tank coupling part 
           24  Welded part 
           25  Tank port 
           30  Joint 
           31  Joint coupling part 
           32  Flange part 
           33  Diameter shrinking part 
           34  Socket part 
           35  Ink distribution path 
           36  Protruding part 
           40  Writing tip 
           41  Ballpoint pen tip 
           42  Holder 
           43  Writing ball 
           44  Spring 
           45  Rear portion 
           50  Covering member 
           51  Protruding part 
           60  Writing implement 
           61  Ballpoint pen 
           62  Shaft tube 
           63  Air hole 
           64  Tube port 
           65  Mouthpiece 
           66  Tip hole 
       
     
       DESCRIPTION OF EMBODIMENTS 
       [0089]    Embodiments of the present invention are described below by referring to the drawings. 
       (1) First Embodiment 
       [0090]    As shown in  FIG. 1A , a ballpoint pen refill  11  as a writing implement refill  10  of a first embodiment of the present invention includes an ink tank  20  composed of films  21  storing ink, a joint  30  made of synthetic resin connected to a tip of the ink tank  20 , and a ballpoint pen tip  41  connected to a tip of the joint  30 . 
         [0091]    The ink tank  20  is formed by welding the two polyethylene films  21  into a pouch. Specifically, the two polyethylene films  21  are welded at their rear ends and their peripheries at both side ends to form the ink tank  20  such that the resultant ink tank  20  has an opening at its tip. 
         [0092]    As shown in  FIG. 1B , the ink tank  20  includes an ink storage  22  storing ink therein. A welded part  24  where the peripheries of the two films  21  are welded is formed at each of a rear end and both side ends of the ink tank  20 . Specifically, internal space surrounded by parts of the two films  21 , other than the welded part  24  where the films  21  are welded, functions as the ink storage  22 . 
         [0093]    As shown in  FIG. 3 , a joint coupling part  31  of a cylindrical shape is formed at a rear end of the joint  30 . On the other hand, a tank port  25  that can receive the joint coupling part  21  therein opens at the tip of the ink tank  20 . A tip portion of the ink tank  20  functions as a tank coupling part  23  that covers the outer circumferential surface of the joint coupling part  31 . 
         [0094]    As shown in  FIGS. 2 and 3 , the joint  30  has a flange part  32  of a shape that increases stepwise in outer diameter from a tip of the joint coupling part  31 , a diameter shrinking part  33  of a shape that shrinks in outer diameter in a tapered form toward a tip thereof from a tip of the flange part  32 , and a socket part  34  of a cylindrical shape having the same outer diameter as a tip of the diameter shrinking part  33 . As shown in  FIG. 3 , an ink distribution path  35  is formed in the joint  30  that passes through the inside of the joint  30  from the flange part  32  toward the diameter shrinking part  33 . The ink distribution path  35  is provided to distribute ink having flowed into the joint coupling part  31  from the ink tank  20  to the socket part  34 . As shown in  FIG. 2 , a ballpoint pen tip  41  as a writing tip  40  is press fitted in a tip of the socket part  34 . 
         [0095]    As shown in  FIG. 3 , the outer circumferential surface of the rear end of the joint  30  is covered with the inner circumferential surface of the tip of the ink tank  20 . More specifically, the outer circumferential surface of the joint coupling part  31  is covered with the inner circumferential surface of the tank coupling part  23 . 
         [0096]    Specifically, the joint coupling part  31  is inserted in the tank port  25  of the tank coupling part  23  to form abutting contact between a rear end of the flange part  32  and a tip of the tank coupling part  23  while forming contact between the outer circumferential surface of the joint coupling part  31  and the inner circumferential surface of the tank coupling part  23 . 
         [0097]    An area where the tip of the ink tank  20  covers the outer circumferential surface of the rear end of the joint  30  (specifically, an area where the tank coupling part  23  covers the outer circumferential surface of the joint coupling part  31 ) is further covered with a covering member  50  from outside. 
         [0098]    The covering member  50  has a ring shape and made of a polypropylene resin. The covering member  50  is formed such that the inner diameter thereof is substantially the same as the outer diameter of the joint coupling part  31 . 
         [0099]    While the tank coupling part  23  covers the outer circumferential surface of the joint coupling part  31 , the covering member  50  is fitted to the outer circumferential surface of the tank coupling part  23 . This places the tank coupling part  23  between the inner circumferential surface of the covering member  50  and the outer circumferential surface of the joint coupling part  31 , thereby covering the outer circumferential surface of the tank coupling part  23  with the inner circumferential surface of the covering member  50 . 
         [0100]    The ballpoint pen refill  11  is fitted to a shaft tube  62  made of synthetic resin, thereby forming a ballpoint pen  61  as a writing implement  60  shown in  FIG. 4A . As shown in  FIG. 4B , the shaft tube  62  is a hollow columnar shape having a rear end provided with an air hole  63 . A tube port  64  is formed at a tip of the shaft tube  62 . A rear end of the ink tank  20  is inserted through the tube port  64  into the shaft tube  62  to make the flange part  32  of the joint  30  abut on the tube port  64  at a tip edge of the shaft tube  62 . A mouthpiece  65  is screwed to the tip of the shaft tube  62 . The mouthpiece  65  has an outer circumference shrinking in diameter in a tapered form toward a tip thereof. The mouthpiece  65  is formed into a circle in cross section having an inner diameter reduced stepwise from its rear end toward the tip thereof. A tip hole  66  that lets the ballpoint pen tip  41  pass therethrough is formed at the tip of the mouthpiece  65 . While the mouthpiece  65  being screwed, the ballpoint pen tip  41  is caused to pass through the tip hole  66  from the rear end of the mouthpiece  65 . When the tip of the socket  34  abuts on the inner circumferential surface of the mouthpiece  65 , the ballpoint pen tip  41  is secured while a tip portion of the ballpoint pen tip  41  is exposed from the tip hole  66 . When the mouthpiece  65  is screwed to the shaft tube  62 , the joint  30  is held between the inner circumferential surface of the mouthpiece  65  and the tip edge of the shaft tube  62 , thereby fitting the ballpoint pen refill  11  to the shaft tube  62 . 
         [0101]    This embodiment of the aforementioned structure achieves the following effects. 
         [0102]    The ink tank  20  of this embodiment is composed of the flexible films  21 . Force generated by atmospheric pressure and acting to compress the ink tank  20  is applied to the ink tank  20  swelling with ink filled in the ink tank  20 . If the ink flows out of the ink storage  22 , the ink tank  20  contracts by the ink having flown out of the ink tank  20 . Specifically, force acting to push the ink out of the ink storage  22  is applied to the ink in the ink tank  20 . This makes it possible to use up the ink while preventing flow of air into the ink tank  20  while preventing writing failure. Flow of air into the ink tank  20  is also prevented during writing with the ballpoint pen tip  41  facing upward. Further, since almost all the air can be eliminated from the ink tank  20 , a structure for buffering pressure inside the ink tank  20  becomes unnecessary. 
         [0103]    In the first embodiment, the area where the tank coupling part  23  covers the outer circumferential surface of the joint coupling part  31  is covered with the inner circumferential surface of the covering member  50 . The covering member  50  functions to prevent leakage of the ink due to the tank coupling part  23  coming off from the outer circumferential surface of the joint coupling part  31 . 
         [0104]    In this embodiment, the ink tank  20  of an unused ballpoint pen refill  11  swells with ink. Further, force of the films  21  forming the ink tank  20  trying to contract the ink tank  20  is applied as well as atmospheric pressure to the ink tank  20 . As a result, the unused ballpoint pen refill  11  receives greater force acting to push the ink out of the ink storage  22  than the ballpoint pen refill  11  having been used to some extent. Thus, the amount of ink which flows out of the ink storage  22  of the ballpoint pen refill  11  at the start of use is greater than that of the ballpoint pen refill  11  having been used to some extent. 
         [0105]    By the way, as to a conventional ballpoint pen refill, a ballpoint pen tip having been used to some extent achieves more excellent feeling of writing than an unused ballpoint pen tip. In contrast, the ballpoint pen refill  11  of this embodiment allows, as described above, greater amount of ink to flow out of the ink storage  22  at the start of use. Thus, the ballpoint pen tip  41  at the start of use can still achieve excellent feeling of writing. 
         [0106]    In this embodiment, the rear end of the ink tank  20  is thinner than the tip thereof. Further, the welded part  24  is formed at opposite side ends of the ink tank  20 , thereby making it possible to use up the ink while preventing buckling of the ink tank  20 . 
         [0107]    If the joint  30  connected to the tip of the ink tank  20  has a linear expansion coefficient which is the same as, or falls within a range of ±50% of, that of the covering member  50 , change in temperature environment does not change attachment strength. This can ensure long-term storage. 
       (2) Second Embodiment 
       [0108]    As shown in  FIG. 5 , a second embodiment of the present invention does not use the joint  30  of the first embodiment. Specifically, the ballpoint pen tip  41  is fitted directly, without the intervention of the joint  30 , to the ink tank  20  (see  FIGS. 5A to 5C ) of the same structure as that of the first embodiment. 
         [0109]    As shown in  FIG. 5D , the ballpoint pen tip  41  used in this embodiment includes a holder  42  formed by cutting a cylindrical member made of stainless steel and a writing ball  43  made of cemented carbide held at a tip of the holder  42 . The holder  42  has a spring  44  contained therein so as to bias the writing ball  43  toward the tip. 
         [0110]    A rear portion  45  of the holder  42  is cut so as to shrink in diameter. The rear portion  45  is directly covered with the tank coupling part  23  corresponding to a tip portion of the ink tank  20 , and is further covered with the covering member  50  from outside the tank coupling part  23 . 
       (3) Third Embodiment 
       [0111]    As shown in  FIG. 6 , similarly to the second embodiment, the ballpoint pen tip  41  of a third embodiment is fitted directly, without the intervention of the joint  30 , to the ink tank  20  (see  FIGS. 6A to 6C ) of the same structure as that of the first embodiment. In this embodiment, the ballpoint pen tip  41  including the writing ball  43  is entirely made of plastic. 
         [0112]    Specifically, the holder  42  of the ballpoint pen tip  41  is formed by injection molding of a polyacetal material and then by cutting process. The writing ball  43  is made of a mixture of a nylon resin and tungsten powder. The writing ball  43  is pressed to fit through a tip of the holder  42  by elastic deformation. Alternatively, the writing ball  43  is inserted into the tip of the holder  42  and then the circumference of the tip is deformed thermally, thereby holding the writing ball  43  at the tip of the holder  42 . 
         [0113]    As in the second embodiment, the rear portion  45  of the holder  42  is formed so as to shrink in diameter. The rear portion  45  is directly covered with the tank coupling part  23  corresponding to a tip portion of the ink tank  20 , and is further covered with the covering member  50  from outside the tank coupling part  23 . 
       (4) Fourth Embodiment 
       [0114]    In a fourth embodiment, as in the first embodiment, the ballpoint pen tip  41  is fitted through the joint  30  to the ink tank  20  (see  FIGS. 7A to 7C ) of the same structure as that of the first embodiment, as shown in  FIG. 7 . As in the first embodiment, the joint coupling part  31  formed at a rear end of the joint  30  is covered with the tank coupling part  23  corresponding to a tip portion of the ink tank  20 , and the outer circumference of the tank coupling part  23  is further covered with the covering member  50  (see  FIG. 7D ). 
         [0115]    In this embodiment, two elongated protrusions are formed as protruding parts  51  along the inner circumferential surface of the covering member  50 , as shown in  FIG. 7E . Further, one elongated protrusion is formed as a protruding part  36  along the outer circumferential surface of the joint coupling part  31  and in an intermediate position between the two protruding parts  51 . The protruding parts  51 ,  36  and  51  bend the films  21  forming the ink tank  20  into an S shape while the covering member  50  fits the joint coupling part  31 , thereby enhancing fitting force. Each of the protruding parts  51 ,  36  and  51  protrudes from a circumferential surface on which it is formed to press the other circumferential surface. As a result, the joint and the covering member fit each other with greater force. One of the protruding parts  51  of the covering member  50  closer to a rear end functions to retain the protruding part  36  of the joint coupling part  31 . Likewise, the protruding part  36  of the joint coupling part  31  functions to retain one of the protruding parts  51  of the covering member  50  closer to a tip. 
       Examples 
       [0116]    Examples of the present invention are described below by being compared with Comparative Examples. 
         [0117]    In each of Examples 1 to 3 of the present invention, an ink tank composed of films such as that described in the first embodiment was used. In each of Comparative Examples 1 to 3 to be compared with Examples 1 to 3, a conventionally used ink tank composed of a polypropylene tube was used. 
         [0118]    The ink tank of each of Example 1 and Comparative Example 1 was filled with commercially available oil-based ink of a viscosity of 15,000 mPa·sec. The ink tank of each of Example 2 and Comparative Example 2 was filled with commercially available aqueous gel-based ink of a viscosity of 300 mPa·sec. The ink tank of each of Example 3 and Comparative Example 3 was filled with commercially available aqueous gel-based ink of a viscosity of 70 mPa·sec. 
         [0119]    A ballpoint pen tip such as that described in the aforementioned embodiments was fitted to the ink tank of each of Examples and Comparative Examples to form a refill. A ball diameter was 0.7 mm in Example 1 and Comparative Example 1, and 0.5 mm in Example 2, Comparative Example 2, Example 3, and Comparative Example 3. 
         [0120]    The ink tank of each of Examples and Comparative Examples thereby formed was fitted to a shaft tube such as that described in the aforementioned embodiments, and was devoted to a writing test. In the writing test, in each of Examples and Comparative Examples, while being placed on a writing tester in compliance with JIS standards, after a 50-m line being drawn first, the amount of consumed ink while a 100-m line was drawn was measured. 
         [0121]    Table 1 given below shows the properties of the ink tank and the refill of each of Examples and Comparative Examples and a result of the writing test obtained in each of Examples and Comparative Examples. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Examples/ 
                   
                   
                 Ink 
                   
                   
               
               
                 Comparative 
                 Material of 
                   
                 Viscosity 
                 Ball Diameter 
                 Ink Comsumption 
               
               
                 Examples 
                 Ink Tank 
                 Ink Type 
                 (mPa · sec) 
                 (mm) 
                 (mg) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Example 1 
                 film 
                 oil-based 
                 15,000 
                 0.7 
                 20 
               
               
                 Comp. Ex. 1 
                 tube 
                 oil-based 
                 15,000 
                 0.7 
                 21 
               
               
                 Example 2 
                 film 
                 aqueous gel-based 
                 300 
                 0.5 
                 107 
               
               
                 Comp. Ex. 2 
                 tube 
                 aqueous gel-based 
                 300 
                 0.5 
                 111 
               
               
                 Example 3 
                 film 
                 aqueous gel-based 
                 70 
                 0.5 
                 104 
               
               
                 Comp. Ex. 3 
                 tube 
                 aqueous gel-based 
                 70 
                 0.5 
                 100 
               
               
                   
               
             
          
         
       
     
         [0122]    As shown in Table 1, the amount of ink consumption in the ink tank of Example 1 was 20 mg whereas that in the ink tank of Comparative Example 1 was 21 mg, showing that these are substantially the same. 
         [0123]    The amount of ink consumption in the ink tank of Example 2 was 107 mg whereas that in the ink tank of Comparative Example 2 was 111 mg, showing that these are also substantially the same. 
         [0124]    The amount of ink consumption in the ink tank of Example 3 was 104 mg whereas that in the ink tank of Comparative Example 3 was 100 mg, showing that these are still substantially the same. 
         [0125]    As described above, where Examples and Comparative Examples differ only in a material for the ink tanks while other conditions being the same, the ink consumption in the ink tank of each Examples composed of films is as much as that in the ink tank of each Comparative Examples composed of a polypropylene tube. Specifically, the aforementioned results show that the ink tank composed of films is not inferior in terms of the ink consumption to a conventionally used ink tank composed of a polypropylene tube, so that it can provide almost the same feeling of writing. 
       INDUSTRIAL APPLICABILITY 
       [0126]    The present invention is suitably applied for use in writing implements such as ballpoint pens and felt-tip pens, and writing implement refills for such writing implements.