Patent Publication Number: US-7588383-B2

Title: Mechanical pencil

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a mechanical pencil provided with a slider. 
   2. Background Art 
   Mechanical pencils adapted to advance a lead by a knocking operation are conventionally used. In using such mechanical pencils, a lead is advanced and exposed from its distal end by an appropriate length and the lead is further advanced by a knocking operation when the lead has become short by the use. 
   The known mechanical pencils are disclosed in the patent documents 1 and 2, the mechanical pencils each being provided with a slider having a lead guide at a distal end of the mechanical pencil, which guide is forced to slide to feed the lead in response to a remaining length of the lead so as to keep on being used. 
   Such mechanical pencils as disclosed in the patent documents each arrange the slider within a head section thereof. The slider is movable back and forth and includes an inner friction part to friction with a lead and an outer friction part to friction with an inner surface of the head section. 
   A tubular lead guide is fixed to a distal end of the slider and communicates with the inner friction part of the slider. In advancement of a lead toward the distal end by a knocking operation, the slider moves toward a distal side from a proximal side due to a frictional resistance between the lead and the inner friction part of the slider. In writing, the lead guide appropriately moves in response to a remaining length of the lead, so as to expose the lead by an appropriate length. 
   A chuck having a chuck portion is moved forward and backward with a collar (also called “a chuck ring”) for fastening the chuck by a knocking operation. The collar is disengaged from the chuck at a position during forwardly moving and the lead is advanced to the position. When the chuck portion is moved backward, the frictional resistance of the slider prevents the lead from being retracted with the collar disengaged, so that the lead is advanced by a predetermined length. 
   Patent document 1: JP 3-47907 Y 
   Patent document 2: JP 2560818 Y 
   DISCLOSURE OF THE INVENTION 
   Problems to be Solved by the Invention 
   Mechanical pencils having such a slider need to make a frictional resistance between the inner friction part and a lead within an appropriate range. 
   Too small frictional resistance at the inner friction part might result in an insufficient advancement of a lead because of slip of the lead at the inner friction part that causes retraction of the lead in taking back of a knocking operation. 
   On the other hand, the frictional resistance at the inner friction part cannot be made too large because of the following reason. 
   The chuck portion holds a lead just before completion of taking back of a knocking operation, thereby slightly retracting the lead. At this time, it is desired not to move the slider with retraction of the lead. That is why the frictional resistance at the inner friction part of the slider is necessary to be smaller than that at the outer friction part of the slider so as to make the lead to slip at the inner friction part. 
   Further, in writing, it is necessary to make the lead guide movable appropriately in response to a length of a lead. That is why the frictional resistance at the outer friction part cannot be above a certain level. 
   Therefore, in order to satisfy the both, it is necessary to make the frictional resistance at the inner friction part smaller than a predetermined value and not more than that value. 
   In this way, the frictional resistance at the inner friction part should be in a predetermined range. The frictional resistance between the inner friction part and a lead depends on a contacting area, an inner diameter, a material, and so on of the inner friction part. However, variation of an inner diameter caused in manufacturing of a component might be out of the above-mentioned range, resulting in being unable to carry out an assured knocking operation. 
   Accordingly, it is an object of the present invention to provide a mechanical pencil adapted to carry out an assured knocking operation, dispensing with a complicated structure. 
   Means to Solve the Problem 
   A first form of the invention for achieving the object described above is a mechanical pencil including a main body of a tubular shape and having a length direction and a distal end and a proximal end in the length direction, an advancing mechanism arranged within the main body, and a slider arranged within the main body, wherein the advancing mechanism includes a chuck adapted to hold a lead, a collar for fastening the chuck and disposed outside of the chuck, and a biasing member for biasing the chuck toward the proximal end, the chuck being movable in the length direction by a knocking operation in such a manner as being moved forward to an advanced position by an external operation and moved backward to a retracted position by means of the biasing member on condition that the external operation is released with the chuck at the advanced position, the chuck being engaged with the collar so as to hold the lead on condition of being at the retracted position, and being disengaged from the collar so as to release the lead on condition of being at the advanced position, wherein the slider, including a lead guide and a lead friction member, is positioned at a distal side of the chuck so as to be movable in the length direction, the lead friction member being made of thermoplastic elastomer, and wherein the knocking operation renders the chuck to be advanced holding the lead so as to extend the lead to a predetermined position, to release the lead at the position, and to be retracted with maintaining the position of the lead by friction between the lead and the lead friction member, consequently advancing the lead to a distal end of the lead guide. 
   The first form has an advancing mechanism adapted to render a chuck to be in a holding condition and a releasing condition and a slider being slidable relative to a main body, and is adapted to advance a lead and to make a positional adjustment of a lead guide of the slider. The slider has a lead friction member to contact with a lead, the member being precisely molded because being made of thermoplastic elastomer, thereby reducing variation in manufacturing and reducing fluctuation of knocking operations in using. 
   A second form of the invention is the mechanical pencil as set forth above, wherein the slider further includes a sliding main body of a tubular shape, into which the lead friction member is inserted. 
   In the second form, the lead friction member is inserted into a tubular sliding main body, so as to ensure fixation of the lead friction member. 
   A third form of the invention is the mechanical pencil in any of the forms noted above, the lead friction member having an inner diameter smaller than an outer diameter of a lead to be used. 
   In the third form, the lead friction member has an inner diameter smaller than an outer diameter of a lead to be used, so as to ensure contact of the member with the lead. 
   A fourth form of the invention is the mechanical pencil according to any of the above forms, wherein the slider is adapted to move in the length direction maintaining contact with the main body and has an outer friction part in contact with the main body and an inner friction part to be in contact with a lead, the inner friction part being formed on the lead friction member, and the inner and the outer friction parts each having a frictional resistance so that the frictional resistance of the inner friction part is smaller than that of the outer friction part. 
   In the fourth form, the slider has an outer friction part in contact with the main body and an inner friction part to be in contact with a lead, a frictional resistance of the inner friction part being smaller than that of the outer friction part, thereby stabilizing movement of the slider. 
   A fifth form of the invention is the mechanical pencil according to any of the above forms, being adapted to push and advance the slider by advancing the chuck. 
   In the fifth form, the chuck pushes and advances the slider, thereby ensuring advancement of the slider in using. 
   Advantageous Effect of the Invention 
   The mechanical pencil using the slider of the present invention enables an assured knocking operation, dispensing with a complicated structure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  show a mechanical pencil in an embodiment of the present invention,  FIG. 1A  being a front view thereof, and  FIG. 1B  being a cross section taken along the line A-A in  FIG. 1A ; 
       FIG. 2  is a partly-broken cross section on an enlarged scale of a vicinity of a distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of an end cone and a slider; 
       FIG. 4  is a cross section of the slider; 
       FIG. 5  is a partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 6  is another partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 7  is a further partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 8  is a further partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 9  is a further partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 10  is a further partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; 
       FIG. 11  is a further partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 ; and 
       FIG. 12  is a further partial cross section on an enlarged scale of the vicinity of the distal end of the mechanical pencil in  FIG. 1 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   A mechanical pencil  1  of the present invention is shown in  FIGS. 1A and 1B  and is adapted to advance a lead  90  by a knocking operation and to expose the lead  90  from its distal end, thereby writing down with the exposed lead  90 . 
   The mechanical pencil  1 , as shown in  FIGS. 1B and 2 , includes a main body  12 , a slider  13 , and an advancing mechanism  14 . 
   The main body  12  has an outer barrel  20  and an end cone  24 . The main body  12  is of a tubular shape as a whole with an opening  12   a  at its proximal end and another opening  12   b  at its distal end. A knocking member  45  of the advancing mechanism  14  is arranged at the opening  12   a , whereas a lead guide  32  of the slider  13  is arranged at the opening  12   b.    
   The outer barrel  20  is of a tubular shape and is a portion to be gripped when writing. Members such as an inner barrel  40  of the advancing mechanism  14  are disposed within the outer barrel  20 . 
   Further, the outer barrel  20  is roughly composed of a front barrel  20   a , a rear barrel  20   b , and a grip  23 , integrally arranged with a proximal end of the front barrel  20   a  inserted into a distal end of the rear barrel  20   b  and with the grip  23  attached around outside of the front barrel  20   a.    
   The rear barrel  20   b  has a clip  22 , which is adapted to fix the mechanical pencil  1  to a desired portion such as a pocket by interposing the portion between inside of the clip  22  and the rear barrel  20   b , so as to protect the mechanical pencil  1  from being lost. 
   The front barrel  20   a  has at an outer surface of its distal end a threaded portion  25 , which is engaged with a threaded portion  50   d  formed on an inner surface of a proximal end of the end cone  24 , so that the cone  24  is detachably fixed to the front barrel  20   a.    
   As shown in  FIG. 5 , the front barrel  20   a  further has adjacent to its distal end a diameter-enlarged bore  58 . The diameter-enlarged bore  58  is provided with a step  58   a  at its proximal end. The diameter-enlarged bore  58  arranges therein a protrusion  43   b  of a chuck  43  and a flange  44   a  of a chuck ring (a collar for fastening the chuck)  44 , so that the protrusion  43   b  and the flange  44   a  are prevented from moving backward (toward the proximal end) of the step  58   a  even when the knocking member  45  is not pushed. 
   The end cone  24  has a conical shape, and as shown in  FIGS. 2 and 3 , has therewithin a cavity  50 , in which the slider  13  described below is placed. 
   The cavity  50  within the end cone  24  is divided into four portions: a distal portion  50   a  adjacent to an opening, a rib portion  50   b , a front-barrel insertion portion  50   c , and the threaded portion  50   d  in the order from a distal end of the cone  24 . 
   The distal portion  50   a  is a substantially columnar cavity, having the opening  12   b  at its distal end. The distal portion  50   a  has an inner diameter substantially equal to an outer diameter of the lead guide  32  of the slider  13 . 
   The rib portion  50   b  is, as shown in  FIG. 3 , a cavity with six ribs  51  protruding inward thereof. The ribs  51  have end faces  51   a  contacting with a protrusion  30   a  of a sliding main body  30 . 
   The front-barrel insertion portion  50   c  is a substantially columnar cavity, into which a distal portion of the front barrel  20   a  is inserted. The threaded portion  50   d  is a female thread to be engaged with the threaded portion  25  of the front barrel  20   a  so as to fix the end cone  24  to the front barrel  20   a.    
   The advancing mechanism  14  includes the inner barrel  40 , a guiding tube  41 , a biasing member  42 , the chuck  43 , the chuck ring (collar for fastening the chuck)  44 , and the knocking member  45 . 
   The inner barrel  40  has a tubular shape and is located within the outer barrel  20  of the main body  12 . The inner barrel  40 , in which leads  90  for use in the mechanical pencil  1  are stored, transmits force from the knocking member  45  on a knocking operation. 
   As shown in  FIG. 1B , the inner barrel  40  further has the guiding tube  41  therewithin. The guiding tube  41  has a tubular shape and has a tapered opening at its proximal end such that its diameter increases toward the proximal end. The guiding tube  41  is located adjacent to a distal end of the inner barrel  40  and is adapted to supply a lead  90  within the inner barrel  40  to the chuck  43 . 
   The biasing member  42  is specifically a coil spring and is adapted to bias the inner barrel  40  and the chuck  43  toward the proximal end thereof. 
   The knocking member  45  has a cap-like shape and is located at a proximal end of the outer barrel  20  and the inner barrel  40 . The knocking member  45  is detachable and attached so that a shell  45   a  of the knocking member  45  is inserted into between the outer barrel  20  and the inner barrel  40 , i.e., inside of the outer barrel  20  and outside of the inner barrel  40 . 
   Herein, an eraser  92  of a columnar shape can be arranged within the knocking member  45 . The eraser  92  is fitted into inside of the proximal end of the inner barrel  40 . In this case, the eraser  92  is removed so as to supply additional leads  90 . 
   The knocking member  45  is exposed outside when being attached. The knocking member  45 , functioning as an operating part in the present embodiment, is pushed from its proximal end so as to advance the lead  90 . The knocking member  45  is removed so as to supply leads  90  into the inner barrel  40 . 
   The chuck  43  has therein a cavity adapted to pass the lead  90  therethrough and is provided with a chuck portion  43   a  adapted to hold the lead  90 . As shown in  FIG. 5 , the chuck  43  is moved forward (toward the distal end) with holding the lead  90 , thereby advancing the lead  90 . 
   The chuck portion  43   a , normally opening outward, makes a holding by means of the chuck ring  44 . The chuck portion  43   a  has an outer periphery tapered with its diameter increasing toward its distal end in holding the lead  90 , forming the protrusion  43   b  at the distal end. 
   The chuck ring  44  is a trumpet-shaped tube having a diameter increasing toward its distal end, having the flange  44   a  protruding outward at the distal end. The chuck ring  44  is located outside the chuck part  43   a  for holding the chuck part  43   a  from outside, releasing holding of the chuck part  43   a  when the chuck ring  44  is moved backward. 
   The protrusion  43   b  of the chuck part  43   a  prevents the chuck ring  44  from getting out toward the distal end. Further, the chuck ring  44  has the flange  44   a  having an outer width larger than an inner gap between the ribs  51 , so as to get stuck on the ribs  51  and to be prevented from moving past toward the rib portion  50   b  of the end cone  24 . 
   The front barrel  20   a  and the rear barrel  20   b  of the outer barrel  20 , the clip  22 , the end cone  24 , and the knocking member  45  are made of resin plastic, having an appropriate stiffness so as to be undeformable in writing or advancing a lead. The grip  23  is made of a material having a high frictional resistance, thereby avoiding slipping in writing. 
   The slider  13 , as shown in  FIGS. 3 and 4 , includes the sliding main body  30 , a lead friction member  31 , and the lead guide  32 . The slider  13  defines therein a throughhole so as to pass the lead  90  therethrough. The slider  13  is located within the end cone  24 , i.e., adjacent to a distal end of the mechanical pencil  1 , being adapted to guide the lead  90  to the distal end by means of the lead guide  32  in using the pencil  1 . 
   The sliding main body  30 , as shown in  FIGS. 3 and 4 , has a tubular shape with a small diameter part  55  at its distal end and a large diameter part  56  at its proximal end. The large diameter part  56  includes the protrusion  30   a  with three slots  30   b , the protrusion  30   a  protruding outward. 
   The sliding main body  30  defines a stepped throughhole extending in a length direction (direction from the distal end to the proximal end), with an opening  53  at its distal end and another opening  54  at its proximal end. 
   The small diameter part  55  has an outer diameter equal to or smaller than the inner diameter of the distal portion  50   a  of the end cone  24  and the large diameter part  56  has an outer diameter equal to or smaller than the inner gap of the ribs  51  of the rib parts  50   b  of the end cone  24 , so that the sliding main body  30  is insertable into the end cone  24 . Further, though an outer width of the protrusion  30   a  of the large diameter part  56  is larger than the inner gap of the ribs  51 , the slots  30   b  allow the part  56  to be inwardly bent, so that an outer surface of the protrusion  30   a  is brought into contact with the end faces  51   a  of the ribs  51 , with a proximal portion of the large diameter part  56  being inwardly bent, when the sliding main body  30  is inserted into the end cone  24 . 
   The lead friction member  31  is inserted into the large diameter part  56 . The large diameter part  56  has the step  67  therewithin, with which a tapered portion  65  on an outer side of the lead friction member  31  is brought into contact when the lead friction member  31  is inserted into the large diameter part  56 , so that the tapered portion  65  is deformed within the throughhole. 
   The lead friction member  31  is of a tubular shape and defines a throughhole  66  therewithin. The lead friction member  31  has a columnar shape with the tapered portion  65  tapering toward its distal end, and has therewithin a small opening  59  at its distal end with a tapered portion  60  at its proximal end. The small opening  59  has an inner diameter equal to or slightly smaller than an outer diameter of the lead  90  to be used. The tapered portion  60  has a diameter increasing toward its proximal end. 
   The lead friction member  31  has an outer diameter at its proximal side equal to or slightly larger than an inner diameter of the large diameter part  56  of the sliding main body  30 . The lead friction member  31  is inserted into the large diameter part  56  so that an outer surface of the lead friction member  31  has a close contact with an inner surface of the large diameter part  56 , so as to be resistant to disengagement in using the mechanical pencil  1 . 
   The lead friction member  31  is made of thermoplastic elastomer. A thermoplastic elastomer is generally a material consisting mainly of both a flexible component (soft segment) having rubber elasticity and a molecule restricting component (hard segment). The hard segment aggregates to form a domain, which expresses rubber elasticity similar to that of a crosslinked rubber around normal temperature, and which fuses at high temperature to be plastically deformed similarly to plastics, thereby freely flowing. Thus, the lead friction member  31  can be molded by plasticization as well as thermoplastic resin. 
   That reduces size variation in molding, in comparison with crosslinked rubber. Further, elasticity relatively stabilizes a friction between the lead friction member  31  and the lead  90 . 
   Further, the lead friction member  31 , which is made of thermoplastic elastomer, has such advantages as follows, in comparison with the use of crosslinked rubber. 
   Two-color molding (or coinjection molding) for the sliding main body  30  and the lead friction member  31  can be achieved, and in this case, the lead friction member  31  is certainly fixed to the sliding main body  30  and restrained from being detached. Further, the lead friction member  31  can be colored, having an attractive design. Still further, the lead friction member  31  can be molded with blending antibacterial agent thereinto, being sanitized. 
   Thermoplastic elastomer for use in the lead friction member  31  is selected from a styrene elastomer, an olefin elastomer, a urethane elastomer, an ester elastomer, and an amide elastomer, and especially a styrene elastomer and an olefin elastomer are preferable. 
   Specifically, Olefin Elastomer 3782 (JIS A hardness of 63) manufactured by Sumitomo Chemical Co., Ltd. or Styrene Elastomer T-436 (JIS A hardness of 70) manufactured by Asahi Chemical Industries Co., Ltd. can be used. 
   The lead guide  32 , as shown in  FIGS. 3 and 4 , is of a tubular shape and divided into three parts: a tapered part  32   a , a large diameter part  32   b , and a small diameter part  32   c  in the order from its distal end. Further, the lead guide  32  has therewithin a throughhole  57  having an inner diameter slightly larger than the outer diameter of the lead  90 . 
   The tapered part  32   a  tapers toward its distal end and has a truncated cone shape. The large diameter portion  32   b  has an outer diameter substantially equal to the diameter of the large diameter part  56  of the sliding main body  30 , being movable within the distal portion  50   a  of the end cone  24 . The small diameter part  32   c  has an outer diameter substantially equal to the inner diameter of the small diameter part  55  of the sliding main body  30 , being insertable into the sliding main body  30  through the opening  53 . 
   The sliding main body  30  in which the lead friction member  31  and the lead guide  32  are fitted (i.e., the slider  13 ) is put into the end cone  24 . Further, the members including the inner barrel  40 , the guiding tube  41 , the biasing member  42 , the chuck  43 , and the chuck ring  44  are put into the outer barrel  20 . Thereupon, the end cone  24  is fitted to the outer barrel  20 , to which the knocking member  45  is attached, and whereby the mechanical pencil  1  is manufactured. 
   The above-mentioned members are arranged in the outer barrel  20 , before having the front barrel  20   a  and the rear barrel  20   b  brought together. Thereafter, the front and the rear barrels  20   a  and  20   b  are integrally arranged. 
   The slider  13  arranged in the end cone  24  has friction with the end cone  24  at its outer surface and with the lead  90  at its inner surface when sliding. In the mechanical pencil  1  of the present embodiment, the protrusion  30   a  having friction with the end cone  24  works as an outer friction part, whereas the small opening  59  having friction with the lead  90  works as an inner friction part. 
   A frictional resistance between the lead  90  and the small opening  59  (inner friction part) where the lead friction member  31  contacts with the lead  90  is smaller than that between the ribs  51  and the protrusion  30   a  (outer friction part) where the main body  12  contacts with the slider  13 . 
   As described above, the inner diameter of the small opening  59  is equal to or slightly smaller than the outer diameter of the lead  90 . In the lead friction member  31  of the present embodiment, the small opening  59  has an inner diameter 0.05 mm smaller than the outer diameter of the lead  90 . Specifically, in the case of a lead  90  having an outer diameter of 0.5 mm, the small opening  59  has an inner diameter of 0.45 mm, and in the case of a lead  90  having an outer diameter of 0.7 mm, the small opening  59  has an inner diameter of 0.65 mm. The small opening  59  of the lead friction member  31  of the present embodiment has a length of 0.5 mm. 
   The lead friction member  31  molded by thermoplastic elastomer and having the small opening  59  with the inner diameter smaller than the outer diameter of the lead  90  has high dimensional precision and elasticity, thereby ensuring friction with the lead  90  at the small opening  59  and keeping a frictional resistance with the lead  90  within a reasonable range. 
   Specifically, a slightly smaller diameter of the small opening  59  than the lead  90  ensures friction and increases a frictional resistance with the lead  90 . Further, the use of thermoplastic elastomer, which is an elastic body, as a material of the lead friction member  31  stabilizes friction at the inner friction part even if the outer diameter of the lead  90  or the inner diameter of the small opening  59  varies slightly. Further, dimension variation in molding of thermoplastic elastomer is smaller than other materials such as rubber, so that friction is made more stable. Thereby, the mechanical pencil  1  adapted to allow a stable knocking operation is certainly manufactured. 
   Now, how to use the mechanical pencil  1  of the present embodiment 1 will be described below. 
   First, the knocking member  45  is detached to fill the inner barrel  40  with a lead  90 , and the knocking member  45  is attached again. When a distal side of the pencil  1  is made downward-facing, as shown in  FIG. 6 , the lead  90  passes through the guiding tube  41  and a tip  90   a  of the lead  90  comes just before the chuck portion  43   a  of the chuck  43 . 
   Before pushing of the knocking member  45 , the chuck  43  is biased toward its proximal end, but the flange  44   a  of the chuck ring  44  has contact with the step  58   a  of the front barrel  20   a . Thus, the chuck ring  44  is located adjacent to a distal end of the chuck  43 , so that the chuck portion  43   a  is in a holding condition. Therefore, the lead  90  is not advanced beyond the chuck portion  43   a , being located at a proximal side of the chuck portion  43   a.    
   Pushing of the knocking member  45  toward the distal end advances the chuck  43  and the chuck ring  44  relative to the main body  12 , but the flange  44   a  of the chuck ring  44  is stuck in the ribs  51  at a position during being advanced. Thereupon, as shown in  FIG. 7 , the chuck ring  44  comes to be located at a proximal side of the chuck  43 , thereby allowing the chuck portion  43   a  to release the holding condition and to be placed in a releasing condition. 
   Then, the lead  90  is advanced toward the distal end due to gravity force and the tip  90   a  of the lead  90  is moved to a vicinity of the tapered portion  60  of the lead friction member  31  of the slider  13 . 
   Further, the protrusion  43   b  located at the distal end of the chuck  43  pushes the proximal end of the sliding main body  30 , so that the slider  13  is advanced with the chuck  43  being advanced. 
   When the knocking member  45  is stopped being pushed, as shown in  FIG. 8 , the chuck  43  is retracted relative to the main body  12  due to a biasing force by the biasing member  42 , and the chuck ring  44  is also retracted because of retraction of the chuck  43 , so that the chuck  43  maintains its releasing condition. 
   Further retraction of the chuck  43 , as shown in  FIG. 9 , makes the flange  44   a  of the chuck ring  44  to be brought into contact with the step  58   a , so that the chuck  43  and the chuck ring  44  revert to the previous condition before pushing of the knocking member  45 . That is, the chuck ring  44  pinches the chuck portion  43   a  to revert in a holding condition. The holding condition starts just before completion of retraction, and whereby the lead  90  is slightly retracted. 
   Another pushing of the knocking member  45  toward the distal end advances again the chuck  43 , and as shown in  FIG. 10 , the lead  90  is advanced. Thereupon, the tip  90   a  of the lead  90  proceeds into the small opening  59 . Further, the chuck  43  is advanced in a releasing condition, but the lead  90  is not advanced, so as to be in a state shown in  FIG. 11 . 
   When the knocking member  45  is stopped being pushed, the chuck  43  is retracted relative to the main body  12  due to the biasing force by the biasing member  42 , but the lead  90  is not retracted because the chuck  43  maintains its releasing condition. 
   The chuck ring  44  is retracted by retraction of the chuck  43  ( FIG. 12 ). During this retraction, maintenance of the releasing condition prevents the lead  90  from relative movement due to a frictional resistance with the small opening  59  (inner friction part), thereby maintaining the position of the lead  90  due to the frictional resistance between the small opening  59  and the lead  90 . 
   The slider  13  is slidable relative to the main body  12 , but a frictional resistance between the ribs  51  and the protrusion  30   a  (outer friction part), where the slider  13  has contact with the main body  12 , is higher than a frictional resistance between the lead  90  and the small opening  59  (inner friction part), where the lead friction member  31  has contact with the lead  90 , so that the slider  13  is prevented from being moved. 
   And then, the chuck  43  and the chuck ring  44  revert again to the previous condition before pushing of the knocking member  45 . 
   In this way, one knocking operation in which the knocking member  45  is pushed toward the distal end and reverts to the previous condition advances the lead  90  by a length in which the chuck ring  44  is moved, i.e., a length similar to that in a length direction of the diameter-enlarged bore  58  of the front barrel  20   a.    
   Users can advance the lead  90  of a necessary length to extrude the tip  90   a  of the lead  90 , so as to use for writing. 
   During writing, the lead  90  is worn away and the tip  90   a  recedes. In this case, the lead guide  32  touches an object on which the writing is performed and the slider  13  is made retracted, thereby maintaining the tip  90   a  by an appropriate length. 
   After the use of the mechanical pencil  1 , in the same manner as in ordinary ones, the knocking member  45  is pushed to force the slider  13  to be pressed onto the object, whereupon the knocking member  45  is stopped being pushed, so that the lead  90  and the slider  13  are put into the end cone  24 . 
   As described above, the mechanical pencil  1  of the present embodiment uses the lead friction member  31  made of thermoplastic elastomer, thereby stabilizing a frictional resistance at the inner friction part. That enables an assured knocking operation, dispensing with a complicated structure.