Patent Publication Number: US-10787022-B2

Title: Writing utensil with pressurizing mechanism

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a writing utensil with a pressurizing mechanism that is designed to increase the flow of ink by pressurizing the inside of a refill. 
     Description of the Related Art 
     As this type of invention, there has conventionally been known a ballpoint pen, such as the one described in Japanese Patent Application Laid-open No. 2005-138356, which has a shaft tube, a refill stored in the shaft tube so as to be movable back and forth, and a knocking member connected at the rear end side of the refill via a pressurizing mechanism, wherein an air layer formed in the refill at the rear end side is pressurized by the pressurizing mechanism by moving the knocking member back and forth. 
     The pressurizing mechanism has a tubular holder (piston) connected to a rear end part of the refill so as to be communicated to the inside of the refill, a valve element (O-ring) attached to an outer peripheral part of the holder, and a bottomed, tubular cylinder covering the holder and the valve element from the rear side, wherein a pressurizing chamber is formed at the rear side of the holder within the cylinder, a ventilation passage is formed on the outer peripheral side of the holder to communicate the pressurizing chamber with the outside air, the valve element is provided in the middle of this ventilation passage, and a front end cylinder part that is reduced in diameter is provided at the rear side of an inner peripheral face of the cylinder. 
     According to this conventional pressurizing mechanism, when the cylinder moves forward relative to the holder, the valve element comes into close contact with the front end cylinder part, thereby sealing the pressurizing chamber, reducing the volume thereof, and consequently pressurizing the inside of a refill. On the other hand, when the cylinder moves backward, a gap is formed around the valve element, and this gap communicates with the ventilation passage and the pressurizing chamber, thereby decompressing the refill. 
     SUMMARY OF THE INVENTION 
     However, according to the prior art, the air flows through the relatively narrow gap formed around the ventilation passage and the valve element, so that as foreign matter and the like happen to clog the ventilation passage and the gap, a malfunction or inhibiting smooth decompression (cancelation of pressurization) is caused, and thereby making ink leakage. 
     In view of these disadvantages, the present invention includes the following constitution. 
     A writing utensil with a pressurizing mechanism that is configured to pressurize an air layer on a rear end side of a refill stored in a shaft tube, wherein the refill is provided with an annular valve element formed along a rear end opening of the refill, and a cylinder that forms, at a rear side of the valve element, a pressurizing chamber communicating with the air layer, by covering the rear end opening and the valve element from the rear side. The cylinder is provided in such a manner that it comes into sliding contact with an outer peripheral part of the valve element and move back and forth. An inner wall face of the cylinder is provided with a ventilating recess communicating with outside air, and an annular non-pressure contact face positioned on a rear side of the ventilating recess. When the cylinder moves forward, the valve element is brought into pressure contact with the non-pressure contact face to seal the pressurizing chamber. When the cylinder moves backward, the valve element is moved forward and separated from the non-pressure contact face such that the ventilating recess communicates with the pressurizing chamber. 
     The constitution of the present invention described above can realize smooth decompression after the pressurization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a full sectional view showing an example of a writing utensil with a pressurizing mechanism according to the present invention; 
         FIG. 2  is an enlarged sectional view showing substantial parts of the writing utensil with the pressurizing mechanism; 
         FIG. 3A  is a half sectional view showing an example of a cylinder and  FIG. 3B  is a full sectional view taken along line a-a of  FIG. 3A ; 
         FIG. 4A  is a half sectional view showing an example of a front-side member of a piston and  FIG. 4B  is a full sectional view taken along line b-b of  FIG. 4A ; 
         FIG. 5A  is a half sectional view showing an example of a rear-side member of the piston and  FIG. 5B  is a diagram of the rear-side member viewed from the front; 
         FIG. 6A ,  FIG. 6B  and  FIG. 6C  are full sectional views showing substantial parts of the writing utensil with the pressurizing mechanism, where  FIG. 6A  shows a state in which a pressurizing chamber communicates with the outside air, FIG. GB shows a state in which the pressurizing chamber is sealed, and  FIG. 6C  shows a state in which the pressurizing chamber is compressed; and 
         FIG. 7  is a full sectional view showing an example of a pressurizing unit. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present embodiment discloses the following features. 
     The first feature is a writing utensil with a pressurizing mechanism that is configured to pressurize an air layer on the rear end side of a refill stored in a shaft tube, the refill is provided with an annular valve element formed along a rear end opening of the refill, and a cylinder that forms, at the rear side of the valve element, a pressurizing chamber communicating with the air layer, by covering the rear end opening and the valve element from the rear side. The cylinder is provided in such a manner that it comes into sliding contact with an outer peripheral part of the valve element and move back and forth. An inner wall face of the cylinder is provided with a ventilating recess communicating with outside air, and an annular non-pressure contact face positioned on the rear side of the ventilating recess. When the cylinder moves forward, the valve element is brought into pressure contact with the non-pressure contact face to seal the pressurizing chamber. When the cylinder moves backward, the valve element is moved forward and separated from the non-pressure contact face such that the ventilating recess communicates with the pressurizing chamber (see  FIGS. 1 to 6C ). 
     According to this constitution, due to the presence of the ventilating recess formed in the inner wall face of the cylinder, a wide ventilation flow path for decompressing the pressurizing chamber can be secured. 
     In the second feature, for the purpose of more effectively securing the ventilation flow path for decompressing the pressurizing chamber, the ventilating recess is a hole passing through a peripheral wall of the cylinder in a radial direction and communicating with the outside air at an outer peripheral side of the cylinder (see  FIG. 2 ). 
     In the third feature, for the purpose of obtaining a specific airtight structure, a tubular piston is fixed at the rear end side of the refill, and the valve element is attached annularly to an outer peripheral part of the piston (see  FIG. 2 ). 
     In the fourth feature, for the purpose of improving the productivity and the like, the outer peripheral part of the piston is provided with an engaging projection protruding radially outward. The piston and the cylinder constitute an integral pressurizing unit by fitting the engaging projection into the ventilating recess so as to move back and forth by a specified distance (see  FIG. 7 ). 
     In the fifth feature, for the purpose of improving the sealability of the pressurizing chamber, an elastic sealing member for sealing a gap between the piston and the refill is provided at the front side of the valve element (see  FIG. 1  and  FIGS. 6A to 6C ). 
     The sixth feature is a retractable writing utensil with a pressurizing mechanism that is configured to move the refill forward against urging force of a refill urging member to cause the refill to protrude from a front end of the shaft tube, wherein the refill is attached to the piston in a detachable manner, and the refill urging member has one end side locked to the shaft tube and has the other end side locked to the piston, thereby urging the piston rearward (see  FIG. 1 ). 
     According to this constitution, it is possible not only to replace the refill promptly without removing the refill urging member, but also to effectively obtain urging force of the refill urging member. 
     Specific Embodiment 
     A specific embodiment of the present invention is now described hereinafter with reference to the drawings. 
     In the following description, the same reference numerals in different diagrams represent substantially the same constitutions; redundant descriptions are omitted accordingly. Furthermore, in the present specification, the term “shaft tube axial direction” means the direction in which the shaft center (centerline) of a shaft tube extends, and the term “shaft tube radial direction” means the direction substantially orthogonal to the shaft tube axial direction. 
     A writing utensil with a pressurizing mechanism  1  is provided with: a shaft tube  10 ; a ballpoint pen refill  20  having an air layer  20   a  at the inner rear end side thereof; a refill urging member  30  urging the refill  20  rearward; a piston  40  having the rear end side of the refill  20  inserted therethrough in a detachable manner so as to receive a rear end part of the refill urging member  30 ; a valve element  45  attached annularly to an outer peripheral part of the piston  40  in such a manner that it follows a rear end opening of the refill  20 ; an elastic sealing member  46  sealing a gap between the piston  40  and the refill  20  at the front side of the valve element  45 ; a cylinder  50  that forms, at the rear side of the valve element  45 , a pressurizing chamber P communicating with the air layer  20   a , by covering the rear end opening of the refill  20  and the valve element  45  from the rear side; a cylinder urging member  55  urging the cylinder  50  rearward with respect to the piston  40 ; and a knocking mechanism  60  for moving the cylinder  50  back and forth by a knocking operation. 
     This writing utensil with the pressurizing mechanism  1  can be, for example, a ballpoint pen having a colored ink in the refill  20  or a correction pen having a correction liquid in the refill  20 . 
     The shaft tube  10  is an elongated tubular member with front and rear end parts thereof opened. In the illustrated example, the shaft tube  10  connects a plurality of cylindrical elements in an axial direction, and a tapered tubular tip opening  11  is detachably connected to front ends of these cylindrical elements. 
     The refill  20  is stored in this shaft tube  10  in such a manner that it moves back and forth. 
     The refill  20  has an elongated cylindrical ink storing tube  21 , a ballpoint pen tip  22  connected to a front end part of the ink storing tube  21 , an ink  23  stored in the front section of the ink storing tube  21 , and a follower  24  stored at the rear side of the ink  23 . The air layer  20   a  is secured at the rear side of the follower  24  in the ink storing tube  21 . 
     The ink  23  may be a colored ink of a ballpoint pen, a whiteout of a correction pen, or the like. 
     The follower  24  is a well-known grease-like liquid, and moves forward as the level of the ink  23  drops as writing progresses. The follower  24  can also be a cylindrical solid. 
     The refill  20  having the foregoing constitution is inserted and detachably fitted into the piston  40  described hereinafter. 
     The refill urging member  30  is a compression coil spring. 
     This refill urging member  30  is attached annularly to the periphery of the refill  20  at the rear side of the center of the entire length of the refill  20 . A front end part of the refill urging member  30  is locked to the shaft tube  10 , and a rear end part of the same is locked to a receiving member  41  of the piston  40 , thereby urging the piston  40  and the refill  20  rearward. 
     The piston  40  is integrally constituted by the receiving member  41  receiving the rear end part of the refill urging member  30 , a piston main body  42  connected to the rear side of the receiving member  41 , and a valve element holding member  43  connected to the rear side of the piston main body  42 . These members constituting the piston  40  can be formed partly or entirely from a single member. 
     The receiving member  41  is formed into a cylinder having a stepped part in an inner wall face thereof, and receives the rear end of the refill urging member  30  by means of this stepped part. 
     As shown in  FIGS. 4A and 4B , the piston main body  42  is formed in a substantially tubular shape, wherein the receiving member  41  is fitted immovably to an inner peripheral face of the piston main body  42  at the front end side, and the valve element holding member  43  is fitted immovably to an inner peripheral face of the piston main body  42  at the rear end side. 
     A flange part  42   a  receiving a front end part of the cylinder urging member  55  protrudes in an annular shape on an outer periphery of the piston main body  42  at the front end side. 
     A plurality of engaging projections  42   b  (two, equally spaced, in the illustrated example), which are fitted into to ventilating recesses  51  of the cylinder  50  in such a manner that it is movable back and forth, are provided at the rear end side of the piston main body  42 . 
     Each of the engaging projections  42   b  protrudes radially outward and has a slant face  42   b   1  in a rear end part thereof. The slant face  42   b   1  rides over the cylinder  50  and is fitted when mounting the cylinder  50  on the rear side of the piston  40 . 
     A tubular section on the rear end side of the piston main body  42  protrudes farther rearward from a rear end part of the ink storing tube  21 , extending the air layer  20   a  in the ink storing tube  21  rearward. 
     As shown in  FIGS. 5A and 5B , the valve element holding member  43  is formed in a substantially tubular shape having the flange part  43   a  at the rear end side thereof and has a valve element attaching part  43   b  at the front side of the flange part  43   a , the valve element attaching part  43   b  having the valve element  45  fitted thereto. The valve element holding member  43  also has a connecting part  43   c  at the front side of the valve element attaching part  43   b , the connecting part  43   c  being fitted and connected to the piston main body  42 . 
     The flange part  43   a  is formed in an annular shape, stretching over the entire circumference of the valve element holding member  43 . A plurality of ventilating grooves  43   a   1  are provided at intervals in a circumferential direction on a front face and/or a rear face of the flange part  43   a . These ventilating grooves  43   a   1  improve the distribution of air in the vicinity of the valve element  45 . As shown in  FIG. 2 , the outer diameter D 2  of the flange part  43   a  is set to be smaller than the outer diameter D 1  of the rear end side of the piston main body  42 , to appropriately secure a ventilation passage at the rear side of the valve element  45 . 
     The valve element attaching part  43   b  is formed into a cylindrical plane, the outer diameter of which is smaller than the inner diameter of the valve element  45 . 
     The valve element holding member  43  having the foregoing constitution is connected integrally to the rear end side of the piston main body  42 . An annular recess  40   a  (see  FIG. 2 ) for fitting the valve element  45  thereto is constituted by the valve element attaching part  43   b , the front face of the flange part  43   a , and a rear end face of the piston main body  42 . 
     The valve element  45  is an O-ring made out of an elastic material such as rubber. 
     As shown in  FIG. 2 , an outer peripheral part of the valve element  45  protrudes radially outward of an outer peripheral face of the piston main body  42  at the rear end side. In other words, the outer diameter of the valve element  45  is larger than the rear end side outer diameter D 1  of the piston main body  42 . 
     The front-rear width of the valve element  45  is set to be narrower than that of the annular recess  40   a  so that the valve element  45  slightly moves back and forth in the annular recess  40   a.    
     According to the illustrated example, the elastic sealing member  46  is an O-ring made out of an elastic material such as rubber. 
     The elastic sealing member  46  is fitted annularly into a stepped part formed in a front-side inner peripheral face of the piston main body  42  (see  FIGS. 6A to 6C ), and elastically deforms between the inner peripheral face of the piston main body  42  and an outer peripheral face of the refill  20 . 
     This constitution can close an air passage extending from the gap between the inner peripheral face of the piston main body  42  and the outer peripheral face of the refill  20  to the outside, improving the airtightness of the pressurizing chamber P. 
     As shown in  FIG. 3A , the cylinder  50  is constituted by a knocking mechanism engaging part  50   a  provided at the rear side and a cylinder main body part  50   b  provided at the front side. 
     The knocking mechanism engaging part  50   a  is formed in the shape of a shaft protruding rearward, wherein a rotor  62  of the knocking mechanism  60  is fitted in a rotatable manner and in such a manner that it is unmovable back and forth, by an annular uneven part formed on an outer peripheral face of the knocking mechanism engaging part  50   a.    
     A cylinder main body part  50   b  is formed in the shape of a bottomed tube that covers the valve element  45  and the piston  40  from the rear side in such a manner that the cylinder main body part  50   b  moves back and forth by having an inner peripheral face thereof in sliding contact with the outer peripheral part of the valve element  45 . 
     A peripheral wall of the cylinder main body part  50   b  is provided with the ventilating recesses  51  communicating with the outside air and an annular non-pressure contact face  52  positioned on the rear side of the ventilating recesses  51 . A front end face of the cylinder main body part  50   b  functions as a receiving face  53  receiving a rear end of the cylinder urging member  55 . 
     The ventilating recesses  51  are each a long hole passing through the peripheral wall of the cylinder main body part  50   b  in the shaft tube radial direction and extending in the shaft tube axial direction. 
     The space inside each ventilating recess  51  communicates with the outside via a gap on an outer periphery of the cylinder main body part  50   b . Specifically, the gap between an outer peripheral face of the cylinder main body part  50   b  and an inner peripheral face of the shaft tube  10 , at the front side thereof, extends forward in a continuous manner through the gaps around the cylinder urging member  55 , the receiving member  41 , the refill urging member  30 , and the refill  20 , and communicates with the outside via a front end opening of the shaft tube  10  (see  FIG. 1 ). Furthermore, the gap, at the rear side thereof, extends rearward in a continuous manner through the gap around the knocking mechanism  60  and communicates with the outside via a rear end opening of the shaft tube  10 . 
     The inner diameter of the section of the cylinder main body part.  50   b  that has the ventilating recesses  51  is set to be larger than the outer diameter of the valve element  45  (see  FIG. 2 ). Therefore, in a case where the valve element  45  is positioned near the ventilating recesses  51  side, an air passage to communicate with the outside air is formed around the valve element  45 . 
     The non-pressure contact face  52  is a tubular inner face positioned at the rear side of the ventilating recesses  51 . The non-pressure contact face  52  is smaller in diameter than the inner diameter of the section of the cylinder main body part  50   b  that has the ventilating recesses  51 , and the inner diameter of the non-pressure contact face  52  is set to be smaller than the maximum diameter of the valve element  45  (see  FIG. 2 ). 
     Therefore, when the cylinder  50  moves forward, the non-pressure contact face  52  is brought into pressure contact with an outer periphery side of the valve element  45 , thereby sealing the pressurizing chamber P formed at the rear side of the valve element  45  (see  FIG. 6B ). 
     The cylinder urging member  55  is a compression coil spring having a weaker urging force than the refill urging member  30 . 
     The cylinder urging member  55  is attached annularly to the outer peripheral part of the piston  40 , and urges the cylinder  50  rearward relative to the piston  40  at a rear half part in the shaft tube  10  by having a front end of the cylinder urging member  55  in abutment with the flange part  42   a  and a rear end of the same in abutment with a front end part of the cylinder  50 . 
     The knocking mechanism  60  is a mechanism that moves the cylinder  50  forward by a specified distance using forward pressing force applied from the outside, to lock the cylinder  50 , and releases this locked state using the forward pressing force applied again. The knocking mechanism  60  can be any well-known mechanism such as the knocking mechanism described in Japanese Patent Application Laid-open No. 2005-138356. 
     The knocking mechanism  60  in the illustrated example has a knocking member  61  protruding rearward from a rear end of the shaft tube  10  and having a cam slant face at a front end part of the knocking member  61 , the rotor  62  that comes into abutment with a front end part of the knocking member  61  and moves back and forth integrally with the knocking member  61 , and a guide groove (not shown) and a cam slant face (not shown) that are formed in the inner peripheral face of the shaft tube  10 . The knocking mechanism  60  rotates the rotor  62  by a specified amount and locks the rotor  62  by moving the knocking member  61  forward by a specified distance, and releases this locked state by moving the knocking member  61  forward again. 
     Next, the characteristic effects of the writing utensil with the pressurizing mechanism  1  having the foregoing constitution are described in detail. 
     In the stored state in which the ballpoint pen tip  22  is placed inside the shaft tube  10  (see  FIG. 1 ), the cylinder  50  is moved backward by the urging force of the cylinder urging member  55  and is in pressure contact with a front end face of the rotor  62 . In this state, as shown in  FIG. 2 , the pressurizing chamber P to communicate with the air layer  20   a  of the refill  20  is secured in the cylinder  50  at the rear side of the piston  40 . This pressurizing chamber P communicates in a front-rear direction in the shaft tube  10  via a gap S 1  around the rear end side of the piston  40 , the spaces inside the ventilating recesses  51 , a gap S 2  around the cylinder  50 , and the like, and further communicates with the outside air via the front and rear end openings of the shaft tube  10 . Thus, in this communication state, the inside of the pressurizing chamber P is at atmospheric pressure. 
     Next, when the cylinder  50  moves forward against the urging force of the cylinder urging member  55  due to forward pressing force applied to the knocking member  61 , the entire circumference of the non-pressure contact face  52  of the cylinder  50  is brought into pressure contact with the valve element  45 , creating a sealed state of the pressurizing chamber P at the rear side of the valve element  45 , as shown in  FIG. 6B . 
     Furthermore, when the knocking member  61  moves forward, the volume of the pressurizing chamber P becomes smaller as shown in  FIG. 6C , compressing the air inside the pressurizing chamber P and the air layer  20   a.    
     When the knocking member  61  moves further forward, a bottom face inside the cylinder main body part  50   b  comes into abutment with the rear end of the piston  40  (precisely, a rear end of the valve element holding member  43 ), integrally moving the cylinder  50 , the piston  40 , the refill  20  and the like forward against the urging force of the refill urging member  30 . As a result, a writing tip part of the ballpoint pen tip  22  protrudes from the front end of the shaft tube  10  and the rotor  62  rotates and then is locked to a locking part (not shown) on the inner peripheral face of the shaft tube  10 . 
     In this protrusion state, the ink  23  and the follower  24  in the refill  20  are pushed forward by the compressed air layer  20   a , increasing the flow of the ink  23  that is ejected from the ballpoint pen tip  22  at the time of writing. 
     Next, when the knocking member  61  moves forward again by the knocking operation, the rotor  62  is removed from the locking part that is not shown, and then moves backward. Consequently, the writing tip part of the ballpoint pen tip  22  is placed inside the shaft tube  10 , the cylinder  50  is moved backward by the urging force of the cylinder urging member  55 , the valve element  45  moves relatively forward to separate from the non-pressure contact face  52 , the ventilating recesses  51  communicates with the pressurizing chamber P, and the inside of the pressurizing chamber P communicates with the outside air (see  FIG. 2  and  FIG. 6A ). 
     At this moment, the air inside the pressurizing chamber P passes through relatively wide space such as the gap S 1  around the flange part  43   a , the ventilating grooves  43   al  on the front face and/or the rear face of the flange part  43   a , and the ventilating recesses  51 . Accordingly, it becomes easy to avoid clogging of foreign matter and the like in the air flow passage. 
     According to the writing utensil with the pressurizing mechanism  1 , the inside of the pressurizing chamber P can be decompressed (cancelation of pressurization) smoothly, preventing ink leakage caused by poor decompression. 
     In addition, since a relatively wide air passage is secured by the ventilating recesses  51 , the size for securing the gap between the piston  40  and the cylinder  50  can be set large, leading to easy part management and productivity improvement. 
     Also, since the refill urging member  30  is provided integrally with the shaft tube  10  away from the refill  20  at the rear half part in the shaft tube  10 , rearward urging force of the refill urging member  30  can be obtained effectively, to reduce the frictional resistance and rubbing noise caused by contraction of the refill urging member  30 . Furthermore, favorable workability is achieved when removing the tip opening  11  to replace the refill  20 , since the refill urging member  30  does not fall off. 
     As shown in  FIG. 7 , the writing utensil with the pressurizing mechanism  1  can also integrally constitute a pressurizing unit A that moves the cylinder  50  back and forth with respect to the piston  40  by a specified distance by means of the engagement between the engaging projections  42   b  and the ventilating recesses  51 . 
     Specifically, the pressurizing unit A shown in  FIG. 7  is integrally constituted by connecting the piston main body  42  to the rear end of the receiving member  41  via the elastic sealing member  46 , connecting the valve element holding member  43  to the rear end side of the piston main body  42 , attaching the cylinder urging member  55  annularly to the rear side of the flange part  42   a  of the piston main body  42 , attaching the valve element  45  annularly to the annular recess  40   a  between the piston main body  42  and the valve element holding member  43 , thereafter attaching the cylinder  50  in such a manner that it covers the piston main body  42 , the valve element  45 , and the valve element holding member  43  from the rear side, and fitting the engaging projections  42   b  into the respective ventilating recess  51 . 
     According to this pressurizing unit A, since the valve element.  45  does not protrude toward the outer peripheral side of the cylinder  50 , foreign matter such as contaminants can be prevented from attaching to the valve element  45 , preventing deterioration of pressurizing performance due to the attachment of the foreign matter. 
     Even when poor assembly occurs where, for example, the cylinder urging member  55  is held between the piston main body  42  and the cylinder  50 , such poor assembly can visually be detected easily before the pressurizing unit A is stored in the shaft tube  10 ; consequently, the defect rate can be reduced. 
     Moreover, the workability of the process of assembling the writing utensil with the pressurizing mechanism  1  is favorable because the integral pressurizing unit A simply needs to be inserted into the shaft tube  10 . 
     In the foregoing embodiment, the ventilating recesses  51  are each configured as a through hole extending in the radial direction. However, each of the ventilating recesses  51  may only need to be formed in a concave shape in an inner peripheral face of the cylinder  50  and communicate with the outside air. In another example, the ventilating recesses  51  can each be a recessed groove that is formed in an inner peripheral face of the cylinder main body part  50   b  but does not pass through a peripheral wall thereof. The ventilating recesses  51  (recessed grooves) according to this aspect may only need to extend forward along the inner peripheral face of the cylinder main body part  50   b  in order to communicate with the outside of the shaft tube  10 . 
     In the foregoing embodiment, the writing utensil with the pressurizing mechanism  1  is constituted as a ballpoint pen or a correction pen but can be applied to writing utensils other than the ones illustrated, such as a marker. 
     In the foregoing embodiment, the valve element  45  is attached at the rear end side of the refill  20  via the piston  40 , which is a particularly preferred constitution, but another constitution is possible in which the valve element  45  is fitted annularly directly the rear end side of the refill  20  without using the piston  40 , and the cylinder  50  is provided therearound. 
     In the foregoing embodiment, the gap between the piston  40  and the refill  20  is closed by the elastic sealing member  46 , which is a particularly preferred constitution, but another constitution is possible in which the gap is closed by an annular projection provided in the inner peripheral face of the piston  40  without using the elastic sealing member  46 , or in which the gap is closed by an adhesive. 
     Although the foregoing embodiment constitutes a retractable writing utensil, another form of writing utensil is possible in which the refill is fixed to the shaft tube in a non-retractable manner and the pressurizing mechanism (the pressurizing unit A or the like) having the constitution described above is provided inside this shaft tube. 
     The present invention is not limited to the foregoing embodiment and can be appropriately modified without changing the gist of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           1  Writing utensil with pressurizing mechanism 
           10  Shaft tube 
           20  Refill 
           20   a  Air layer 
           30  Refill urging member 
           40  Piston 
           40   a  Annular recess 
           42  Piston main body 
           42   b  Engaging projection 
           43  Valve element holding member 
           45  Valve element 
           46  Elastic sealing member 
           50  Cylinder 
           51  Ventilating recess 
           52  Non-pressure contact face 
           55  Cylinder urging member 
           60  Knocking mechanism 
         P Pressurizing chamber