Abstract:
A retractable writing instrument that substantially prevents writing fluid from evaporating through the tip when the tip is in a retracted position to eliminate the need for a cap. Within the writing instrument is an enclosure member that has a vapor chamber. In the retracted position, the tip of the writing instrument is within the vapor chamber to substantially seal the tip from ambient air so that writing fluid does not evaporate through the tip. The enclosure member has a lip that opens to allow the tip to move forward and extend from the writing instrument so that writing fluid can be delivered to the writing surface for writing. When the tip is moved back into the retracted position the lip closes to substantially seal the tip from the ambient air. An external compression force may be applied to the lip to assist in sealing the lip. The enclosure member may be made of a material that is durable so that the lip does not wear out after many cycles of moving the tip between the retracted and protracted positions, such as silicone, butyl rubber, and thermoplastic vulcanizate (TPV) material including butyl rubber cross-linked with polypropylene.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application claims the benefit of three Provisional Patent Applications: (1) Ser. No. 60/373,497, filed Apr. 17, 2002; (2) Ser. No. 60/386,173, filed Jun. 4, 2002; and (3) Ser. No. 60/426,917, filed Nov. 15, 2002, all entitled “Self-Sealing Retractable Writing Instrument,” which are all incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   This invention relates to writing instruments, and more particularly to writing instruments that dispense volatile inks, such as felt tip markers and the like. 
   DESCRIPTION OF RELATED ART 
   This invention relates to ink impregnated marking and writing instruments, commonly known as “markers.” The term “markers” as used herein generally includes all such writing instruments where ink may have a tendency to evaporate from its tip. Some examples of markers include, but not limited to, felt-tipped pens, dry erase, permanent and non-permanent markers, and children&#39;s markers. Markers have at least one end with a writing tip for writing onto a surface. The writing tip is also referred to as a nib. The ink formulations typically comprise dye and solvent in which the dye is dissolved. These ink solvents are typically volatile, being prone to evaporation when exposed to ambient air. If a sufficient amount of the ink solvent evaporates from the writing tip of the marker, the writing tip dries out, and the performance of the marker substantially degrades. 
   The problem with ink evaporating from the tip is solved by placing a cap over the tip when the marker is not in use. One of the problems with the cap is that the cap is often not put back on the tip after its use because users sometimes forget to put the cap back on or it is misplaced, and without the cap, the tip dries out to shorten the life of the marker. 
   To overcome the problem of having a cap for the marker, some markers are designed with a self-sealing cap integrated into the maker housing. These markers have their own problems in that the self-sealing cap designs are complex and do not work very well. One of the problems is that the writing tip is typically isolated in a relatively large air chamber when the writing instrument is not in use. With a large air chamber, a large amount of ink can still evaporate into the air chamber. Another problem is that as the tip moves in and out of the self-sealing cap there is friction between the self-sealing cap and the tip that can cause the self-sealing cap to deteriorate over time. In addition, the assembly of self-sealing caps is complex so that they may be unsuitable for high volume manufacturing processes. Therefore, there is a need for an improved self-sealing writing instrument. 
   SUMMARY OF THE INVENTION 
   This invention provides a retractable writing instrument that substantially prevents writing fluid from evaporating through the tip when the tip is in a retracted position. The retractable writing instrument includes a front barrel with a front opening to allow the tip to move in and out of the opening. Adjacent to the front opening and within the front barrel is an enclosure member that substantially seals the tip from outside air when the tip is in a retracted position. The writing instrument also includes a back barrel with a back opening. Disposed within the back opening is a plunger that is adapted to move back and forth axially. When the plunger is activated by clicking on it, for example, the tip may be moved in and out of the enclosure member and front opening. Writing fluid is stored in a feeder. A nib is between the feeder and the tip to convey the writing fluid in the feeder to the tip. The nib may be unitary with the tip or may be a separate component. At least a portion of the feeder may extend into the back opening and into the plunger to lengthen the size of the feeder to store more writing fluid. 
   The enclosure member includes a first end and a second end, where the first end is adapted to open to allow the tip to extend through the first end. To open, the first end may have a lip with a slit. To further assist in substantially sealing the lip in the retracted position, a clip may be provided to add compression force to the lip. The second end may have an inner configuration adapted to substantially seal the second end of the enclosure member yet allow the tip to move axially in and out when activated by the plunger. In the retracted position, the tip is between the first and second ends to substantially seal the tip from the ambient air, thereby eliminating the need for a cap. 
   The enclosure member may be made of a material that is durable so that the lip does not wear out after many cycles of moving the tip in and out of the enclosure member. The material should be also impermeable vapor to seal the tip from the ambient air. In this regard, the enclosure member may be made of thermoplastic vulcanizate (TPV) material including butyl rubber cross-linked with polypropylene. 
   Other systems, methods, features, and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
       FIG. 1  illustrates a side view of a writing instrument with the tip in a protracted position. 
       FIG. 2  illustrates a side view of the writing instrument with the tip in a retracted position. 
       FIG. 3  illustrates a writing instrument that is disassembled. 
       FIG. 4  is a cross-sectional view of the writing instrument in a retracted position. 
       FIG. 5  is a cross-sectional view of the writing instrument in a protracted position. 
       FIG. 6  is a front perspective view of an enclosure member. 
       FIG. 7  is a rear perspective view of the enclosure member. 
       FIG. 8  is a cross-sectional view of the writing side of the writing instrument. 
       FIG. 9  is cross-sectional view of an alternative writing side of a writing instrument. 
       FIG. 10  is a front perspective view of a clip. 
       FIG. 11  is a rear perspective view of the clip. 
       FIG. 12  is a perspective view of an alternative clip and enclosure member combination. 
       FIG. 13  is a rear perspective view of the enclosure member of  FIG. 12 . 
       FIG. 14  is another perspective view of the clip of  FIG. 12 . 
       FIG. 15  is a perspective view of another clip and enclosure combination in a retracted position. 
       FIG. 16  is another perspective view of the clip and enclosure combination of  FIG. 15  transitioning from the retracted position to the protracted position. 
       FIG. 17  is another perspective view of the clip and enclosure combination of  FIG. 15  in the protracted position. 
       FIG. 18  is a perspective view of an alternative writing instrument that is disassembled. 
       FIG. 19  is a cross-sectional view of a cartridge with an elongated portion. 
       FIG. 20  is a front view of the opening in the elongated portion of  FIG. 19 . 
       FIG. 21  is a side view of the tip and nib. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a writing instrument  100  in a protracted position. The writing instrument  100  has a housing  101  comprised of a first barrel  104  and a second barrel  108 . In the protracted position, a tip  102  of the writing instrument  100  extends from the first barrel  104 . The first barrel  104  has a first opening  106  at the front side to allow the tip  102  to move between the protracted position and the retracted position. The second barrel  108  has a second opening  110  at the back end to allow a plunger  112  to extend between the protracted position and the retracted position. In the protracted position, the plunger  112  is pressed down relative to the second barrel  108 , which causes the tip  102  to extend through the first opening  106  and extend from the first barrel  104 . A support member  115  may wrap around the side of the tip  102  in order to guide the tip  102  through the first opening  106 . The first barrel  104  may reduce the diameter of the housing towards the tip  102  to form the first opening  106 . 
     FIG. 2  illustrates the writing instrument  100  in a retracted position where the tip  102  is inside the first barrel  104 . In the retracted position, the plunger  112  further extends from the second barrel  108  that causes the tip  102  to retract into the first barrel  104  by moving back into the first opening  106 . As such, activating the plunger  112  between the retracted and protracted positions causes the tip  102  to move correspondingly between the retracted and protracted positions as well. The housing  101  may be made of a unitary member as well, where the internal mechanism for the writing instrument  100  are inserted into the housing  101  through the second opening  110 , or through any other alternative mechanism known to one skilled in the art. 
     FIG. 3  is an exploded view of the interior mechanism of the writing instrument  100 . The writing instrument  100  includes an enclosure member  300  adapted to fit within the first barrel  104  adjacent to the first opening  106 . The enclosure member  300  has a first end  302  and a second end  304  forming a vapor chamber within the enclosure member  300 . The vapor chamber is configured to receive the tip  102  to substantially seal the tip  102  from the ambient air. In the protracted position, the first end  302  of the enclosure member  300  opens to allow the tip  102  to extend through the first opening  106 . In the retracted position, the first end  302  closes to substantially seal the tip from the ambient air. The tip  102  may be coupled to a nib  308  along the longitudinal axis  310 . The tip  102  may be a separate component from the nib  308  or a unitary piece. 
   The writing instrument  100  may include a clip  301  to aid in closing the first end  302  of the enclosure member  300 . The clip  300  may be preloaded to apply compressive force on the first end  302 . The enclosure member  300  may be configured so that the clip  301  may couple to the enclosure member  300  on its outer surface. In this way, the clip  301  may be disposed between the enclosing member  300  and the first barrel  104  and encircle the circumference of the second end  304  of the enclosing member  300 . In addition, the second end  304  of the enclosure member  300  may have cutouts for the clip  301  so that the outer circumference of the enclosure member and the clip may combine to form the surface that contacts the inner wall of the housing  101 . 
   The writing instrument  100  may also include a first cartridge  312  adapted to couple to a second cartridge  314 . The first and second cartridges  312  and  314  are adapted to enclose a feeder  316 . The feeder  316  is adapted to store writing fluid that conveys through the nib  308  and then to the tip  102 . The capillary relationship among the feeder  316 , nib  308 , and tip  102  causes the writing fluid to convey from the feeder  316  to the tip  102 . The first cartridge  312  may have an elongated portion  318  with an opening  320  adapted to receive and seal the nib  308  or tip  102 . This allows the back tip  322  of the nib  308  to make contact with the feeder  316  to convey the writing fluid to the tip  102 . The first cartridge  312  has a back flange  327  adapted to associate with a second cartridge member  314 . The back flange  327  may have at least one tab  324  that is adapted to associate with a corresponding channel formed in the second barrel  108  so that the first cartridge  312  moves between the retracted and protracted positions without rotating. This may be done to ensure that the first cartridge moves along the axial direction  310  consistently. The elongate portion  318  of the first cartridge  312  may be inserted into the resisting member  326  such that the resisting member  326  is positioned between the second end  304  of the enclosing member  300  and the edge  325  of the first cartridge  312 . 
   The writing instrument  100  may include a gear  328  that works with the plunger  112  and the second barrel  108  to lock the plunger  112  in the retracted position or the protracted position. The gear  328  is hollow to allow the back end of the second cartridge  314  to pass through the gear  328 . The plunger  112  has a bore  114  that is adapted to receive at least a portion of the feeder  316  held within the second cartridge  314 . Incorporating the feeder  316  inside the plunger  112  extends the length of the feeder  316  to store more writing fluid. 
     FIG. 4  illustrates the cross-sectional view of the writing instrument  100  in a retracted position. In the retracted position, the tip  102  is within the vapor chamber  306  with the first end  302  forming a seal from ambient air, and the second end  304  substantially forms a seal around the elongated portion  318  so that the tip  102  extending from the opening  320  is within the vapor chamber  306  and substantially sealed from the ambient air. The back tip  322  makes contact with the feeder  316  so that the writing fluid stored in the feeder  316  conveys through the nib  308  and to the tip  102 . In the retracted position, as the writing fluid evaporates from the tip  102 , the vapor is substantially sealed within the vapor chamber  306 . The volume in the vapor chamber  306  may be minimized to limit the evaporation of the writing fluid. 
     FIG. 5  illustrates the writing instrument  100  in a protracted position. To write, the plunger  112  is activated or pushed towards the second barrel  108 . This causes the first and second cartridges  312  and  314 , the nib  308 , and the tip  102  to move forward towards the first opening  106 . The resisting member  326  resists against the pushing force until the gear  328  engages to lock the plunger  112  in the protracted position. As the tip  102  pushes against the first end  302 , the first end  302  opens to allow the tip  102  to pass through and extend through the first opening  106 . Once the tip  102  is in a protracted position, it is ready for writing onto a writing surface. 
   In the protracted position, the elongated portion  318  of the first cartridge  312  may extend from the first opening  106  along with the tip  102 . The elongated portion  318  may assist in guiding the tip through the first end  302  of the enclosure member  300  and the first opening  106 . The elongated portion  318  may have a vent  307  for allowing air into the feeder  316  when the writing instrument  100  is in use. The vent  307  may be a passage formed in the wall of the elongated portion  318 , or formed between the inner wall of the elongated portion  318  and the nib  308 . With the later formation of the vent  307 , the size and configuration of the vent  307  may be varied by altering the outer wall configuration of the nib  308 . The vent or passage may be also formed within the feeder with a certain pore size to allow air to pass to the feeder. 
   The elongated portion  318  may be configured so that it resides within the resisting member  326 . As illustrated in  FIG. 4 , in the retracted position, the resisting member  326  is in an uncompressed state. As illustrated in  FIG. 5 , in the protracted position, the resisting member  326  is in a compression state. As the plunger  112  is activated between the retracted and protracted positions, the resisting member  326  exerts expansive force between the second end  304  of the enclosure member  300  and the edge  325  of the first cartridge  312  to cause the tip  102  to move in and out of the enclosure member  300 . The plunger  112  and resisting member  326  described above may be employed in a variety of ways. For example, twist cam mechanisms and latching push button mechanisms may be used, or any other return mechanisms known to one skilled in the art. 
     FIGS. 6 and 7  illustrate perspective views of the first end  302  and the second end  304  of the enclosure member  300 . The first and second ends  302  and  304  may be integral or formed from separate pieces of elastomeric material. The first end  302  has a lip  600  with a slit  602  that opens and closes as the tip  102  moves in and out of the enclosure member  300 . The elongated portion  318  may guide the tip  102  through the lip  600  as it moves through the lip  600 . In the retracted position, the lip  600  substantially seals the ambient air from the vapor chamber  306  as shown in  FIG. 7 . 
   The second end  304  may have an outer configuration  700  in the form of a ring. The outer configuration may have an outer diameter sized to fit within the inner wall of the housing  101 , or in the first barrel portion  104 . The size of the diameter may vary so that the second end may seal around the inner wall of the housing  101 , or a gap may be formed between the second end and the housing. The second end  304  may have an inner configuration  702  sized to allow the elongated portion  318  to slide forward and backwards along the longitudinal direction. The inner configuration  702  may be also sized so that it forms a substantially airtight seal around the elongated portion  318  as it slides along the longitudinal direction. This allows the vapor chamber  306  to be formed within the enclosure member  300  that is substantially sealed from the ambient air when the lip  600  is closed. In addition, the vent  307  may be formed near the tip  102  so that the enclosure member  300  may substantially seal the vent and the tip when the writing instrument  110  is in a retracted position. 
   The enclosure member  300  may be configured to minimize the size of the vapor chamber  306 . This may be accomplished by tapering the thickness of the second wall  704  from the outer configuration  700  towards the inner configuration  702 . The tapering second wall  704  may conform to provide the inner configuration that serves to guide and seal around the elongated portion  318  to minimize the space in the vapor chamber  306 . 
   The inner configuration  702  may be configured to minimize the resistance on the elongated portion  318  as it slides back and forth. The inner configuration may have one or more edges  706  and  708  separated by a depression, reducing the thickness of the second wall  704  with every depression. Reducing the wall thickness with the edges  706  and  708  reduces the friction between the inner configuration  702  and the elongated portion  318 . 
     FIG. 6  illustrates the front perspective view of the enclosure member  300 . From the second end  304 , the enclosure member  300  may be configured to taper down towards the lip  600 . This may be done to minimize the space within the vapor chamber  306 . The tapering may be done so that the inner wall of the enclosure member  300  substantially conforms to the shape of the tip  102  and the elongated portion  318  without touching when the writing instrument is in a retracted position. The enclosure member tapers to form the lip  600  having a slit like opening  602  that opens to allow the tip  102  to protrude out. 
     FIG. 8  illustrates a cross-sectional view around the first barrel  104  along with its internal mechanisms including a clip  301  over the enclosure member  300 . As the elongated portion  318  moves towards the protruding position, the open end  800  of the elongated portion  318  may first engage with the inner wall  802  of the enclosure member  300  to open the lip  600  so that the tip  102  may freely extend through the lip  600 . This way, the integrity and shape of the tip  102  may be maintained. The open end  800  may have a bulging configuration to further assist .in pushing the lip  600  open as it engages with the inner wall  802 . The first barrel  104  may also have slots  804  formed along a portion around the first barrel  104  to allow the clip  301  to open without being restrained by the inner wall of the first barrel  104 . The slots  804  may be formed near the edge  806  of the clip  301  that extends out the most as the clip opens. This allows first barrel  104  to have a nominal outer configuration or minimize the diameter of the housing  101 . 
     FIG. 9  is another cross-sectional view around the first barrel  104  where the writing instrument is in a retracted position. Here, the tip  102  extends further from the open end  900  of the elongated portion  318  so that the tip  102  may engage with the inner wall  802  of the enclosure member  300  first to open the lip  600 . As the tip  102  extends further towards the protracted position, the open end  900  of the elongated portion  318  engages with the lip  600  to keep the lip opened. Note that in the retracted position, the lip  600  and the inner configuration  702  of the second end  304  substantially seal the tip  102  from the ambient air in a small space to minimize evaporation of the ink. That is, the vapor chamber  306  may be configured to seal the tip  102  with minimal volume. This may be done by providing the second end  304  adjacent to the end of the tip  102  and providing the first end adjacent to the front end of the tip  102 . In addition, the second end  304  tapers towards the inner configuration  702  to provide as much distance as possible between the first end and the second end with minimal volume. The inner wall  802  may taper from the second end  304  to the first end  302  to form the lip  600  to minimize the volume of the vapor chamber  306  as well.  FIG. 9  also illustrates divots  902  formed within the inner wall  904  of the first barrel  104  to allow the clip  301  to expand without being constrained by the inner wall of the first barrel  104 . 
   The enclosure member  300  may be made of one piece as described above, or from a number of pieces. For example, the outer configuration  700  of the second end  304  may be coupled to the inner wall of the housing, and the first end  302  with the lip  600  may be coupled to the housing closer to the first opening  106 , where the space between the first and second ends form the vapor chamber. 
     FIGS. 10 and 11  illustrate the front and rear perspective views of the clip  301 , respectively. The clip  301  may include a support rim  1000 , and two bias arms  1002 . The support rim  1000  is configured to receive the second end  304  of the enclosure member  300 . The bias arms  1002  are configured to taper towards the pinch end  1004  and house the enclosure member  300  as illustrated in  FIGS. 8 and 9 . The pinch end  1004  is placed over the lip  600  of the enclosure member  300  to apply compression force over the lip  600  to assist in sealing the lip  600 . The bias arms  1002  may be formed from a material that is resistant to fatigue and the development of positional memory (e.g., spring steel.) The bias arms  1002  may be configured so that when it is compressing over the lip  600  in the retracted position, it may apply sufficient compression force to assist in substantially sealing the lip  600 . As the elongated portion  318  engages with the inner wall of the enclosure member  300  to open the lip  600 , the bias arms  1002  may release, at least, partially the compression force on the lip  600  to minimize the friction between the lip  600  and the elongated portion  318  as it moves towards the protracted position. 
     FIG. 12  illustrates a perspective view of another enclosure member  1200  having a first end  1202  with a lip  1206  and a second end  1204 . The enclosure member  1200  may have cavities  1208 , one on each side of the enclosure member  1200 , adapted to receive a clip  1400  on each side as illustrated in  FIG. 14 , as discussed in more detail below. 
     FIG. 13  illustrates the perspective view of the second end  1204  of the enclosure member  1200 . The second end  1204  has an inner configuration  1300  adapted to receive the elongated portion  318  with the nib  308  inside. As the tip  102  moves between the retracted and protracted positions, the elongated portion  318  correspondingly moves axially relative to the inner configuration  1300 . The inner configuration  1300  substantially seals around the elongated portion  318  during this axial movement. The inner configuration  1300  may have an edge  1302  beveled to minimize the friction between the second end  1204  and the elongated portion  318 . Alternatively, the inner configuration  1300  may have a rounded edge to minimize the friction with the elongated portion  318 . In addition, within the inner wall of the first barrel  104  there may be channels that are aligned to associate with the cavities  1208  so that the enclosure member is properly aligned in relation to the first barrel during the assembly of the writing instrument. 
     FIG. 14  illustrates the clip  1400  for the enclosure member  1200 . The clip  1400  may be placed over the enclosure member  1200  so that the bias arms  1406  fit into the cavities  1208  formed in the enclosure member  1200 . The clip  1400  has a pinch end  1402  adapted to compress the lip  1202  and the back support end  1404  on the opposite side to support the second end  1204  so that the enclosure member substantially maintains its shape as the tip moves between the retracted and protracted positions. That is, the clip  1400  may act as a back bone so that the enclosure member  1200  substantially maintains its shape as the elongated portion  318  moves back and forth along the inner configuration  1300  and the lip  1206 . The width of the pinch end  1402  may cover at least the width of the slit  1206  in  FIG. 12  to substantially seal the vapor formed in the vapor chamber of the enclosure member  1200  from escaping through the slit. The clip  1400  may have bias arms  1406  that are configured to provide sufficient compression force to the lip  1206  in the retracted position, but relieve at least a portion of its compression force when the tip  102  or the open end of the elongated portion  318  engages with the inner wall  802  of the enclosure member  1200 . This way, the friction between the elongated portion  318  and the inner configuration  702  may be minimized so that less force is required to activate the plunger  112 . 
     FIG. 15  illustrates an enclosure member  1500  having a clip member  1502  that is integrated into the enclosure member  1500 . The clip  1502  may be formed from two separate pieces integrated into the second end  1504  of the enclosing member  1500 . Each piece may have a “U” shape configuration. The clip  1502  may have a pinch end  1506  that substantially seals the lip  1508  of the enclosure member  1500  in the retracted position. 
     FIG. 16  illustrates the tip  102  engaging with the lip  1508  to open the lip  1508 . As the tip  102  further extends towards the protracted position as illustrated in  FIG. 17 , the elongated portion  318  engages with the lip  1508  and keeps the lip  1508  open. 
     FIG. 18  illustrates a disassembled perspective view of an alternative writing instrument  1800 . In this example, the writing instrument  1800  includes a plunger  1802 , feeder  1804 , the writing tip  1806 , the cartridge  1808  with an elongated portion  1809 , resisting member  1810 , the enclosure member  1812 , the clip  1814 , and the housing  1816 . For assembly, the writing tip  1806  may be inserted into the cartridge  1808  followed by the feeder  1804  and the plunger  1802 , which seals the back end of the cartridge  1808 . The enclosure member  1812  and the clip  1814  may be assembled as discussed above, and may be disposed into the housing  1816 . The resisting member  1810  may be then inserted into the housing  1816  followed by the cartridge  1808 . Alternatively, bias arms  1002  may be coupled to the first barrel portion of the housing to engage with the lip of the enclosure member to assist in sealing the lip. In addition, the internal mechanism described above may be manufactured in various sizes appropriate for different diameters of the writing instrument or other non-writing devices for applying volatile liquids such as cosmetics, paint, and the like. 
     FIG. 19  illustrates an enlarged cross-sectional view of the first cartridge  312 . The leading section  1900  of the elongated portion  318  may have three sections, a first leading section  1902 , a second leading section  1904 , and a third leading section  1906 , where the second leading section  1904  is between the first and third leading sections  1902  and  1906 . In the retracted position, the first leading section  1902  is within the vapor chamber  306 , the second leading section  1904  substantially forms a seal with the second end  304 , and the third leading section  1906  is on the rear side of the second end  304 . The first leading section  1902  tapers downward towards the opening  320  along the longitudinal axis to make it easier for the first leading section  1902  to pass through the slit like opening in the lip of the enclosure member. The second leading section  1904  is substantially flat along the longitudinal axis to form a seal with the inner configuration of the second end  304  in the retracted position. The circumference around the second leading section  1904  may be about the same or slightly greater than the size of the inner configuration  702  and  1300  in the second end  304  to form a seal. The third leading section  1906  tapers upward towards the opening  320  along the longitudinal axis so that as the third leading section  1906  is pushed into the second end  304 , the circumference around the third leading section  1906  is reduced to minimize the friction between the third leading section  1906  and the second end  304 . This in turn minimizes the wear along the inner configuration of the second end  304 . 
     FIG. 19  also illustrates that the third leading section  1906  may have a recess area  1908  formed behind the second end  302  of the enclosure member  300  in the retracted position to control the release of vapor formed within the vapor chamber  306 . In the retracted position, vapor may form within the vapor chamber  306  as writing fluid evaporates through the tip  102 . As the tip  102  moves from the retracted position to the protracted position, the recess area  1908  formed in the elongated portion  318  slides into the second end  304  forming a gap between the third leading section  1906  and the inner configuration. The gap may be formed on the second end  304  before the tip  102  passes through the first end  302 . As such, any vapor inside the vapor chamber  306  is released through the gap on the back side or second end  304  rather than through the slit in the lip on the front end or first end  302  of the enclosure member  300 . This eliminates the potential problem of releasing vapor through the first opening  106  of the writing instrument  100 , which can spray ink spots onto the writing surface. 
     FIG. 20  illustrates a front view of the opening  320  formed along the first leading section  1902 . Within the opening  320  there may be at least one tooth  2000  adapted to engage with the nib  308  to hold the tip  102  in a predetermined position. 
     FIG. 21  shows an enlarged view of the tip  102  and the nib  308 . The tip  102  may have an edge  2100  with a pitch angle to allow the tip  102  to penetrate through the slit  602  in the lip  600  more easily. The tooth  2000  inside the opening  320  may hold the tip  102  so that the edge  2100  of the tip  102  may be aligned relative to the orientation of the slit  602  on the lip  600 . With the enclosure member  300  and the edge  2100  aligned and held in a predetermined position, the tip  102  may cycle in and out of the slit  602  without damaging the slit  602 . This also ensures that the edge  2100  of the tip  102  protracts consistently in relation to the first and second barrels. That is, the edge of the tip  102  is substantially prevented from rotating in relation to the first and second barrels. In embodiments where the writing instrument  100  has a side clip on the second barrel or an asymmetrically shaped outer configuration, having the tip  102  protract consistently allows a user to hold the writing instrument as intended as well. 
   The enclosure member  300  may be made of a material that is durable and flexible so that the slit  602  does not wear out after many cycles of the tip  102  moving in and out of the slit  602 . The material may have low permeability to vapor and air to seal the tip  102  from the outside air. The material may be also soft enough to provide a better seal around the imperfections in the slit and the inner configuration. In this regard, the material may have a shore hardness of about 30 to about 80, and in particular in the range of about 50 to 65. The enclosure member may be formed from a variety of materials such as silicon, butyl-rubber, and thermoplastic elastomer with thermoplastic rubber that has low-permeability to vapor. A variety of methods may be used to form the enclosure member using silicone such as injection molding, blow molding, extrusion molding, and other methods known to one skilled in the art. For alcohol-based writing fluid with higher evaporation rate, butyl rubber may be compression molded or other methods known to one skilled in the art may be used to form the enclosure member. Alternatively, the enclosure member may be formed from thermoplastic elastomer with thermoplastic rubber that has low-permeability to vapor. Such a material is manufactured by Advance Elastomer Systems, L. P. 388 South Main Street, Akron, Ohio 44311, under the name of Trefsin® that can be formed into the enclosure member  300  using a variety of methods, such as injection molding, blow molding, and extrusion molding. 
   Although the invention has been described with specific reference to certain exemplary embodiments, other advantages, and modifications and variations of the invention, including adaptation or incorporation of the inventive seal into writing instruments of different sizes and configurations, are all within the scope of the invention as defined by the claims and equivalents thereof.