Abstract:
A writing instrument ( 1 ) is provided with an erasing member ( 2 ) mounted to the rear end section of the writing instrument body ( 3 ) or to the front end section of a cap ( 4 ). The end section has a fitting section ( 14 ) which is disposed on the center axis and a connection section ( 15 ) which connects the end section and the fitting section ( 14 ). The erasing member ( 2 ) has a fitting hole ( 2   c ) which receives both the fitting section ( 14 ) and the connection section ( 15 ). When the erasing member ( 2 ) is mounted in position, a gap space ( 17 ) is formed around the connection section ( 15 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage application of PCT/JP2012/081392, filed Dec. 4, 2012, which claims priority from Japanese patent application nos. JP 2011-270080, filed Dec. 9, 2011 and JP 2012-123324, filed May 30, 2012. 
     TECHNICAL FIELD 
     The present invention relates to a writing instrument which is provided with an erasing member. 
     BACKGROUND ART 
     Known in the art is a writing instrument which is provided with a separate erasing member at a top part of a cap whereby marks which are made by that writing instrument on a paper surface etc. can be erased by the erasing member (for example, PLT 1). 
     Further, PLT 2 describes an attachment structure for attaching a soft member corresponding to an erasing member to the top end part of a body or cap or other tubular member of a writing instrument. According to the attachment structure which is described in PLT 2, a projecting part is provided at the top end part of a tubular member, an attachment hole is provided at the bottom end part of the erasing member, and the projecting part is inserted into the attachment hole for engagement to thereby attach it. 
     CITATION LIST 
     Patent Literature 
     [PLT 1] Japanese Patent Publication No. 2003-200694A 
     [PLT 2] Japanese Patent Publication No. 2009-214515A 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The writing instrument which is described in PLT 1 is predicated on the erasing member being replaced when worn etc., so the cap and the erasing member are not strongly attached. For this reason, when using the erasing member to erase a mark, looseness occurs between the cap and erasing member and stable erasing sometimes is difficult. 
     As opposed to this, according to the attachment structure which is described in PLT 2, while it is possible to strongly attach the erasing member, the contact area between the outer circumferential surface of the projecting part of the tubular member and the inner circumferential surface of the attachment hole of the erasing member increases in accordance with insertion of the projecting part into the attachment hole. That is, therefore, the force countering the frictional resistance which is required when inserting the projecting part into the attachment hole, that is, the press-fitting force, also increases accordingly and insertion of the projecting part firmly deep into the attachment hole is difficult. 
     The present invention has as its object the provision of a writing instrument which is provided with an erasing member which can be easily attached. Further, the present invention has as its object the provision of a writing instrument which is provided with an erasing member which is firmly attached. 
     Means to Solve the Problems 
     In a first aspect of the present invention, there is provided a writing instrument which comprises an erasing member which is attached to a back end part of a writing instrument body or a front end part of a cap, wherein the end part has a fitting part which is arranged on a center axis and a connecting part which connects the end part and the fitting part, the erasing member has a fitting hole which receives the fitting part and the connecting part, and, in a state where the erasing member is attached, a clearance space is formed around the connecting part. 
     That is, in the present aspect, a clearance space is formed around the connecting part. Therefore, even when attaching the erasing member, this clearance space exists. For this reason, the frictional resistance which accompanies attachment of the erasing member is reduced compared with the past, so the advantageous effect is exhibited that the erasing member can be easily attached. Note that, in this Description, in the axial direction of the writing instrument, the writing tip part side is defined as the “front” side, while the side opposite to the writing tip part is defined as the “back” side. Further, in the axial direction of the cap, the open end side where the writing instrument body is inserted is defined as the “back” side, while the opposite side to that is defined as the “front” side. 
     In a second aspect of the present invention, there is provided a writing instrument characterized by further comprising a supporting wall which surrounds part of the erasing member, the side surface of the part of the erasing member is provided with an engagement projecting part, and the engaging projecting part and an inner circumferential surface of the supporting wall abut against each other. 
     That is, in the present aspect, the erasing member is held by the erasing member and supporting wall abutting against each other, so at the time of an erasing operation by the erasing member, stable erasing becomes possible without looseness. That is, strong attachment of the erasing member can be realized. 
     In a third aspect of the present invention, there is provided a writing instrument characterized in that a flat part is provided at the side surface of the part of the erasing member. 
     That is, in the present aspect, when forming the erasing member by injection molding, the flat part can be made the gate position. As a result, even if gate residue is left, since there is a clearance between the surface of the flat part and the inner circumferential surface of the supporting wall, the gate residue can be prevented from contacting the inner circumferential surface and trouble at the time of attachment can be prevented. 
     In a fourth aspect of the present invention, there is provided a writing instrument characterized in that the entrance part of said fitting hole has a tapered shape taper part which becomes narrower the further toward the back. 
     That is in the present aspect, by the entrance part of the fitting hole being made a tapered shape, insertion of the fitting part becomes easy. 
     Effects of the Invention 
     According to the present invention, the advantageous effect is exhibited of providing a writing instrument which is provided with an erasing member which can be easily attached. Furthermore, according to the present invention, the advantageous effect is exhibited of providing a writing instrument which is provided with an erasing member which is strongly attached. Below, the present invention will be able to be understood more sufficiently from the attached figures and the description of the preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view of a writing instrument according to a first embodiment which is provided with an erasing member according to one aspect of the present invention. 
         FIG. 2  is a perspective view of a cap of the writing instrument which is shown in  FIG. 1 . 
         FIG. 3  is a vertical cross-sectional view of the cap which is shown in  FIG. 2 . 
         FIG. 4  is another vertical cross-sectional view of the cap which is shown in  FIG. 2 . 
         FIG. 5  is a perspective view of an erasing member of the writing instrument which is shown in  FIG. 1 . 
         FIG. 6  is another perspective view of the erasing member of the writing instrument  1  which is shown in  FIG. 1 . 
         FIG. 7  is a vertical cross-sectional view of the erasing member which is shown in  FIG. 5 . 
         FIG. 8  is a perspective view of the cap to which the erasing member is attached in the writing instrument which is shown in  FIG. 1 . 
         FIG. 9  is a side view of the cap which is shown in  FIG. 8 . 
         FIG. 10  is a vertical cross-sectional view along the line X-X of  FIG. 9  of the cap which is shown in  FIG. 8 . 
         FIG. 11  is another vertical cross-sectional view of the cap which is shown in  FIG. 8 . 
         FIG. 12  is a horizontal cross-sectional view along the line Y-Y of  FIG. 9  of the cap which is shown in  FIG. 8 . 
         FIG. 13  is a horizontal cross-sectional view along the line Z-Z of  FIG. 9  of the cap which is shown in  FIG. 8 . 
         FIG. 14  is an enlarged cross-sectional view which shows the attachment part of the erasing member and the cap of the writing instrument which is shown in  FIG. 1 . 
         FIG. 15  is a perspective view of a cap of another aspect different from the cap of the writing instrument which is shown in  FIG. 1 . 
         FIG. 16  is a vertical cross-sectional view of the cap which is shown in  FIG. 15 . 
         FIG. 17  is a perspective view of the cap to which is attached an erasing member of another aspect from the erasing member of the writing instrument which is shown in  FIG. 1 . 
         FIG. 18  is a vertical cross-sectional view of the cap which is shown in  FIG. 17 . 
         FIG. 19  is a vertical cross-sectional view of the erasing member which is shown in  FIG. 17 . 
         FIG. 20  is a perspective view of the cap to which is attached an erasing member of still another aspect from the erasing member of the writing instrument which is shown in  FIG. 1 . 
         FIG. 21  is a perspective view of the erasing member which is shown in  FIG. 20 . 
         FIG. 22  is a front view of the erasing member which is shown in  FIG. 20 . 
         FIG. 23  is a perspective view of the cap to which is attached an erasing member of still another aspect from the erasing member of the writing instrument which is shown in  FIG. 1 . 
         FIG. 24  is a perspective view of the erasing member which is shown in  FIG. 23 . 
         FIG. 25  is a front view of the erasing member which is shown in  FIG. 23 . 
         FIG. 26  is a perspective view of the cap to which is attached an erasing member of still further another aspect from the erasing member of the writing instrument which is shown in  FIG. 1 . 
         FIG. 27  is a perspective view of the erasing member which is shown in  FIG. 26 . 
         FIG. 28  is a front view of the erasing member which is shown in  FIG. 26 . 
         FIG. 29  is a perspective view of the cap to which is attached an erasing member of still another aspect from the erasing member of the writing instrument which is shown in  FIG. 1 . 
         FIG. 30  is a perspective view of the erasing member which is shown in  FIG. 29 . 
         FIG. 31  is a front view of the erasing member which is shown in  FIG. 29 . 
         FIG. 32  is a vertical cross-sectional view of a writing instrument according to a second embodiment which is provided with an erasing member according to an aspect of the present invention. 
         FIG. 33  is a perspective view of the cap of the writing instrument which is shown in  FIG. 32 . 
         FIG. 34  is a plan view of the cap which is shown in  FIG. 33 . 
         FIG. 35  is a side view of the cap which is shown in  FIG. 33 . 
         FIG. 36  is a vertical cross-sectional view of the cap which is shown in  FIG. 33 . 
         FIG. 37  is a cross-sectional view along the line S-S of  FIG. 35  of the cap which is shown in  FIG. 33 . 
         FIG. 38  is a view which shows the state of use of the cap to which is attached the erasing member of the writing instrument which is shown in  FIG. 32  at the time of erasure by the cap. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, embodiments of the present invention will be explained in detail while referring to the drawings. Throughout the figures, corresponding elements are assigned common reference signs. 
       FIG. 1  is a vertical cross-sectional view of a writing instrument  1  according to a first embodiment which is provided with an erasing member  2  according to one aspect of the present invention. The writing instrument  1  is a ball pen type of writing instrument which has a writing instrument body  3 , which is provided with a refill  5  and a cylinder  6  which extends in a tubular shape, and a cap  4 . The cylinder  6  has a tubular front cylinder  7  and a back cylinder  8  with a front end part which screws into a back end part of the front cylinder  7 . The front cylinder  7  and back cylinder  8  are formed from a plastic material. For example, in the present aspect, the front cylinder  7  is formed from a polypropylene plastic, while the back cylinder  8  is formed from a polycarbonate plastic. By forming the front cylinder  7  from a material which is softer than the material of the later explained cap  4 , it becomes possible to prevent breakage at the time of fitting. At the front end of the front cylinder  7 , a hole is formed for allowing the writing tip part  11  of the refill  5  to stick out. Note that, in the present Description, in the axial direction of the writing instrument  1 , the writing tip part side is defined as the “front” side, while the side opposite to the writing tip part is defined as the “back” side. Further, in the axial direction of the cap  4 , the opening end side in which the writing instrument body is inserted is defined as the “back” side, while the opposite side to that is defined as the “front” side. 
     The refill  5  has a tubular refill body  9 , coupling member  10 , writing tip part  11 , and refill stopper  12 . The refill body  9  is, for example, formed from a plastic material such as polypropylene or a metal material and is designed to store ink. The coupling member  10  is, for example, formed from polypropylene, polybutylene terephthalate, polyacetal, or other such plastic material or a metal material. Further, in the front end part of the coupling member  10 , the back end part of the writing tip part  11  is fit. The refill  5  is housed inside the cylinder  6 . Part of the writing tip part  11  is exposed through the hole of the above-mentioned front cylinder  7  in the state stored in the cylinder  6 . The writing tip part  11  which forms the writing part holds a ball at its tip. In accordance with rotation of the ball at the time of writing, the ink which is stored at the refill body  9  part is discharged through the inside of the coupling member  10 . At the back end part of the refill body  9 , the refill stopper  12  is press fit. It is attached by fitting by this press fit. 
     The cap  4  has a cap body  4   a , a clip part  4   b , a seal member  13 , and an erasing member  2 . The cap body  4   a  is a tubular member. At its side surface, the clip part  4   b  is integrally provided. The clip part  4   b  is designed to have enough elasticity to enable a document, clothing, or other object to be gripped with the cap body  4   a . Therefore, as the material which forms the cap body  4   a  and clip part  4   b , polycarbonate, acrylonitrile-butadiene-styrene, or other plastic may be mentioned. As explained above, these parts are preferably formed by a material which is harder than the front cylinder  7 . 
     Further, the seal member  13  protects the writing tip part  11  by elastically deforming when engaging with the writing tip part  11  when the cap  4  is attached over the front cylinder  7 . As the material which forms the seal member  13 , isopropylene rubber, butadiene rubber, nitrile rubber, silicone rubber, butyl rubber, ethylene-propylene-diene rubber, styrene-butadiene rubber, fluororubber, and other synthetic rubber etc. may be mentioned. In particular, butyl rubber (IIR) can much better improve the processability and the performance in prevention of evaporation at the tip of the writing part. That is, butyl rubber is not only excellent in processability, but also is particularly excellent in gas tightness (barrier property) among the various types of rubber. For this reason, by forming the seal member by butyl rubber, it is possible to more reliably prevent drying of the writing instrument tip and prevent evaporation of the solvent ingredient in the ink. 
     Next, while referring to  FIG. 2  to  FIG. 4 , the structure of the cap  4  will be explained.  FIG. 2  is a perspective view of the cap  4  of the writing instrument which is shown in  FIG. 1 ,  FIG. 3  is a vertical cross-sectional view of the cap  4  which is shown in  FIG. 2 , and  FIG. 4  is another vertical cross-sectional view of the cap  4  which is shown in  FIG. 2 .  FIG. 4  is a cross-sectional view at a position rotated 90 degrees about the center axis from the cross-sectional view which is shown in  FIG. 3 . 
     At the inside wall of the cap body  4   a  near the open end, an engagement part  4   c  which engages with the front cylinder  7  is provided. At the front end part  4   d  of the cap body  4   a , that is, inside near the top part, three or more ribs  4   e  which extend in the axial direction of the writing instrument  1  are provided at equal intervals in the circumferential direction. In this aspect, the cap body  4   a  has six ribs  4   e . As shown in  FIG. 1 , the seal member  13  is gripped by the ribs  4   e.    
     The ribs  4   e  respectively have equal axial direction lengths, but it is also possible to have only two ribs (long ribs)  4   f  which are arranged facing each other across the center axis extend longer toward the back of the cap  4  compared with the other ribs  4   e . These long ribs  4   f  act as guides at the time of insertion of the seal member  13  when assembling the cap  4  and facilitate insertion. Further, when the cap  4  is formed from a transparent or semitransparent material, one of these long ribs  4   f  may also be arranged at a position corresponding to right below the clip part  4   b  which extends in the long direction. Due to this, the clip part  4   b  and the facing long rib  4   f  will be arranged on substantially the same plane which passes through the center axis of the cap  4  and will give an aesthetic feeling. 
     At the front end part  4   d  of the cap body  4   a , a fitting part  14  which is arranged on the center axis, two connecting parts  15  which connect the end part  4   d  and fitting part  14 , and a supporting wall  16  which is arranged around the fitting part  14  and connecting parts  15  are provided. Further, at the front end part  4   d  of the cap body  4   a , a circular vent opening  4   g  is provided about the center axis, but the vent opening  4   g  may also be omitted. 
     The fitting part  14  has a frustoconical shape which has a back end part which is large in diameter and which becomes smaller in diameter the further to the front end part. The front end face edge  14   a  part of the fitting part  14  is chamfered round. Further, the hack end face edge  14   b  part has a 90 degree or sharp angle corner part  14   c . The shape of the fitting part  14  is not limited to a frustoconical shape and may also be a sphere, column, polygonal prism shape, etc. 
     The connecting parts  15  are two columnar members which extend from the inside wall of the vent opening  4   g  toward the front of the cap  4  and which are arranged symmetrically with respect to the center axis of the cap  4 . The fitting part  14  is supported by the connecting parts  15  so that the disk shaped surface is vertical to the center axis of the cap  4 . Further, the fitting part  14  is supported by the connecting parts  15  at its back end surface near the edge. As clear from  FIG. 3 , the connecting parts  15  do not extend along the center axis but extend slightly at a slant toward the center axis the further to the front. The cap body  4   a  has the vent opening and the two connecting parts  15  are spaced apart, so air can flow from the front end to the back end of the cap body  4   a.    
     In this aspect, the cap body  4   a , fitting part  14 , and connecting parts  15  are integrally formed, but they may also be separately formed. Further, in this aspect, two connecting parts  15  were provided, but providing one or three or more is also possible. If there is a single connecting part  15 , it is connected near the center of the surface which faces the fitting part  14 . Further, if a vent opening  4   g  is not provided at the front end part  4   d  of the cap body  4   a , the connecting part  15  is configured to extend from the front end part  4   d  of the cap body  4   a  toward the front. 
     The supporting wall  16  is a tubular member which is arranged around the fitting part  14  and connecting parts  15 . The outer circumferential surface of the supporting wall  16  is formed on the same plane as the outer circumferential surface of the cap body  4   a . In this aspect, the cap body  4   a  and the supporting wall  16  are integrally formed, but may also be separately formed. The supporting wall  16 , as explained later, has an inner circumferential surface  16   a  into which an insert part  2   a  of the erasing member  2  is fit. 
     Next, while referring to  FIG. 5  to  FIG. 7 , the structure of the erasing member  2  will be explained.  FIG. 5  is a perspective view of the erasing member  2  of the writing instrument  1  which is shown in  FIG. 1 ,  FIG. 6  is another perspective view of the erasing member  2  of the writing instrument  1  which is shown in  FIG. 1 , and  FIG. 7  is a vertical cross-sectional view of the erasing member  2  which is shown in  FIG. 5 . 
     The erasing member  2  has an insert part  2   a  which is inserted into and surrounded by the supporting wall  16  of the cap body  4   a , an erasing part  2   b  which is exposed to the outside in the state where the erasing member  2  is attached to the cap and which is used for rubbing against a paper surface etc., and a fitting hole  2   c  which extends in the axial direction and passes through the insert part  2   a  and the erasing part  2   b . The insert part  2   a  and the erasing part  2   b  may also be integrally formed. As the material which forms the erasing member  2 , silicone rubber, nitrile rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, or other rubber material or a styrene-based elastomer, olefin-based elastomer, polyester-based elastomer, or other thermoplastic elastomer or other such rubbery material, a mixture of two or more types of elastic materials, a mixture of a rubbery material and a plastic, a commercially available eraser, etc. may be mentioned. 
     The insert part  2   a  is a substantially columnar shape which corresponds to the shape of the inner circumferential surface  16   a  of the supporting wall  16  of the cap body  4   a  and has at its side surface in the circumferential direction a ring shaped engagement projecting part  2   d . The engagement projecting part  2   d  abuts against the inner circumferential surface  16   a  of the supporting wall  16  to be held so that the erasing member  2  does not become loose in the state attached to the cap  4 . Note that, instead of the ring-shaped engagement projecting part  2   d , a plurality of projections may also be formed in the circumferential direction. Further, if another means can be used to prevent the erasing member  2  from looseness, the engagement projecting part  2   d  need not be provided. 
     Further, at part of the side surface of the insert part  2   a , a flat part  2   e  may be provided along the axial direction. When forming the erasing member  2  by injection molding, the part of the flat part  2   e  can be made the gate position at the time of molding. Due to this, even if gate residue is left on the flat part  2   e  after molding, since there is a clearance between the surface of the flat part  2   e  and the inner circumferential surface  16  of the supporting wall  16  of the cap body  4   a , gate residue can be prevented from contacting the inner circumferential surface. Further, as explained later, by providing a corresponding projection at the inner circumferential surface  16   a  of the supporting wall  16 , it becomes possible to position the erasing member  2  in a predetermined orientation at the time of attachment and possible to prevent the erasing member  2  from turning after attachment. 
     The erasing part  2   b  has a frustoconical shape which has a back end part which is large in diameter and which becomes smaller in diameter the further to the front end part. The front end face edge part of the erasing part  2   b  is chamfered round. Further, the back end face edge part of the erasing part  2   b  is larger in diameter than the insert part  2   a . Therefore, a step-like flange part  2   f  is formed with the insert part  2   a . When attaching the erasing member  2  to the cap, the back end face of the flange part  2   f  abuts against the front end face  16   b  of the supporting wall  16 . 
     The fitting hole  2   c  extends in the axial direction and passes through the insert part  2   a  and the erasing part  2   b . The fitting hole  2   c  receives the fitting part  14  and connecting parts  15  of the cap  4  when attaching the erasing member  2  to the cap  4 . The fitting hole  2   c  is divided into a back end part into which the fitting part  14  is inserted, that is, an entrance part, then, in order, a taper part  2   g , small diameter part  2   h , and large diameter part  2   i . The taper part  2   q  forms a taper shape which becomes narrower the more from the back end part of the fitting hole  2   c  toward the front, that is, which becomes narrower from the entrance part toward the deep part. The inside diameter of the front end of the taper part  2   g  and the inside diameter of the back end of the small diameter part  2   h  are set substantially equal. The boundary between the small diameter part  2   h  and the large diameter part  2   i  forms a step difference. As explained later, this forms a lock part  2   j  which prevents detachment of the fitting part  14 . Note that, the small diameter part  2   h  may also be eliminated. 
     In this aspect, since the fitting hole  2   c  runs through the erasing member  2 , even if the erasing member  2  detaches from the cap after shipment of the product and is mistakenly swallowed by an infant etc., it will not block the airway so safety can be secured. 
     Next, while referring to  FIG. 8  to  FIG. 14 , the attachment of the erasing member  2  and the cap  4  will be explained.  FIG. 8  is a perspective view of the cap  4  to which the erasing member  2  is attached in the writing instrument  1  which is shown in  FIG. 1 ,  FIG. 9  is a side view of the cap  4  which is shown in  FIG. 8 ,  FIG. 10  is a vertical cross-sectional view along the line X-X of  FIG. 9  of the cap  4  which is shown in  FIG. 8 ,  FIG. 11  is another vertical cross-sectional view of the cap  4  which is shown in  FIG. 8 ,  FIG. 12  is a horizontal cross-sectional view along the line Y-Y of  FIG. 9  of the cap  4  which is shown in  FIG. 8 ,  FIG. 13  is a horizontal cross-sectional view along the line Z-Z of  FIG. 9  of the cap  4  which is shown in  FIG. 8 , and  FIG. 14  is an enlarged cross-sectional view which shows the attachment part of the erasing member  2  and the cap  4  of the writing instrument  1  which is shown in  FIG. 1 .  FIG. 11  is a cross-sectional view at a position rotated 90 degrees about the center axis from the cross-sectional view which is shown in  FIG. 10 . 
     If inserting the erasing member  2  into the supporting wall  16  of the cap body  4   a , the fitting part  14  is inserted into the fitting hole  2   c  of the erasing member  2  and the outer circumferential surface of the insert part  2   a  of the erasing member  2  is guided along the inner circumferential surface of the supporting wall  16 . The fitting part  14  passes the taper part  2   g  and the small diameter part  2   h  of the fitting hole  2   c  to ride over the lock part  2   j . When the back end face of the flange part  2   f  of the erasing member  2  abuts against the front end face  16   b  of the supporting wall  16 , the attachment of the erasing member  2  is completed. 
     The maximum outside diameter of the fitting part  14  is set larger than the minimum inside diameter of the taper part  2   g  of the fitting hole  2   c , that is, the inside diameter of the small diameter part  2   h , and equal to or smaller than the inside diameter of the large diameter part  2   i . Therefore, when the fitting part  14  passes the taper part  2   g  and the small diameter part  2   h  of the fitting hole  2   c , the fitting part  14  or the insert part  2   a  of the erasing member  2  elastically deforms. 
     The front end face edge  14   a  of the fitting part  14  is chamfered round and the entrance part at the time of insertion into the fitting hole  2   c  forms a taper part  2   g , so the fitting part  14  is smoothly inserted into the fitting hole  2   c . Furthermore, during insertion of the fitting part  14  into the fitting hole  2   c , inside the fitting hole  2   c , only the outer circumferential surface  14   d  of the fitting part  14  contacts the inner circumferential surface  2   k  of the fitting hole  2   c  while moving. That is, the press-fitting force which is required for insertion is largely due to the frictional force between the outer circumferential surface  14   d  of the fitting part  14  and the inner circumferential surface  2   k  of the fitting hole  2   c , but the contact area of these is substantially constant, so the press-fitting force which is required during insertion also is substantially constant. Therefore, the erasing member  2  can be easily attached to the cap. 
     Here, the inside diameters of the taper part  2   g  and the small diameter part  2   h  of the fitting hole  2   c  are set so that the two connecting parts  15  are held or abutted against in the state of completion of attachment. That is, the two connecting parts  15 , as explained above, extend slanted toward the center axis the more toward the front, but this slant is set equal to or larger than the slant of the taper part  2   g  of the fitting hole  2   c . Therefore, during attachment of the erasing member  2 , the connecting parts  15  never abut against the inner circumferential surface  2   k  of the fitting hole  2   c . On the other hand, by setting the slants of the two equal, at the time of completion of attachment, the two connecting parts  15  can be made to contact the inner circumferential surface of the taper part  2   g . Due to this, there is no looseness of the erasing member  2  and strong attachment can be realized. 
     As clear from the relationship between the connecting parts  15  and the inner circumferential surface  2   k  of the fitting hole  2   c , insertion so that the above-mentioned contact area becomes substantially constant is realized by the presence of the clearance space  17 , which is formed due to the fitting part  14  being supported by the columnar connecting parts  15 , around the connecting parts  15 . The clearance space  17  is defined by the fitting part  14 , the connecting parts  15 , and the inner circumferential surface  2   k  of the fitting hole  2   c  of the erasing member  2 . Due to the presence of the clearance space  17 , it becomes possible to reduce the frictional resistance during attachment of the erasing member  2  to the cap and enable easy attachment. 
     In the state where attachment is completed, the fitting part  14  is just slightly separated in the axial direction from the step-shaped lock part  2   j  which is provided inside the fitting hole  2   c  of the erasing member  2 . Further, the back end face of the insert part  2   a  of the erasing member  2  as well similarly is separated just slightly in the axial direction from the front end part  4   d  of the cap body  4   a . The engagement projecting part  2   d  which is provided at the side surface of the insert part  2   a  of the erasing member  2  elastically deforms, whereby it engages with the inner circumferential surface  16   a  of the supporting wall  16  and makes it difficult for the erasing member  2  to detach. Furthermore, to make the engagement projecting part  2   d  and the inner circumferential surface  16   a  of the supporting wall  16  engage more reliably, the inner circumferential surface of the supporting wall  16  at the position corresponding to the engagement projecting part  2   d  after completion of attachment may be provided with a recessed part  16   c  of a shape which corresponds to the engagement projecting part. 
     In the state where attachment is completed, the elastic deformation of the fitting part  14  or the insert part  2   a  of the erasing member  2  at the time of attachment is reversed. For this reason, if trying to pull out the erasing member  2  from the cap  4  for the purpose of changing the erasing member  2  etc., the front end face of the lock part  2   j  of the erasing member  2  and the corner part  14   c  of the back end face of the fitting part  14  engage and impair this. Therefore, to pull out the erasing member  2  from the cap  4 , a stronger force must be applied. Due to this, the lock part  2   j  or the corner part  14   c  elastically deforms whereby the fitting is released and the erasing member  2  can be pulled out from the cap  4 . 
     The pullout force which is required for pulling out the erasing member  2  from the cap  4  is preferably designed to be larger than the press-fitting force which is required for attaching the erasing member  2  to the cap  4 . This can be realized by, for example, adjusting the slant or the minimum inside diameter of the taper part  2   g  of the fitting hole  2   c  or by adjusting the maximum outside diameter of the fitting part  14  etc. 
     Note that, the fitting hole  2   c  of the erasing member  2  may be designed to have only the taper part  2   g  and not have the small diameter part  2   h  and the large diameter part  2   i , that is, not have the lock part  2   j . In this case, the fitting part  14  is engaged by the frictional resistance between its outer circumferential surface  14   d  and the inner circumferential surface of the taper part  2   g  of the fitting hole  2   c.    
     Here, the writing instrument  1  according to the aspect of the present invention which was shown in  FIG. 1  uses ink constituted by thermochromic ink. “Thermochromic ink” means ink which has the property of maintaining a predetermined color (first color) at ordinary temperature (for example, 25° C.), changing to another color (second color) if raised to a predetermined temperature (for example, 60° C.), then returning again to the original color (first color) if made to cool to a predetermined temperature (for example, −5° C.). In a writing instrument  1  which uses a thermochromic ink, making the above second color colorless and making a line which is written by the first color (for example, red) rise in temperature to make it colorless is referred to here as “erasure”. Therefore, in the present aspect, the paper surface etc. on which a line is drawn is rubbed by the erasing member  2  to generate heat of friction and thereby change the line to a colorless one, that is, erase it. Note that, only naturally, the above second color may be made any color other than being made colorless. 
     The “erasure” in the present invention means, in addition to the case of use of the above thermochromic ink, absorbing or rubbing off a drawn line, letter, etc. by an eraser or other erasing member  2 . Therefore, the above aspect and following aspects of the present invention can be applied to any writing instrument which uses an erasing member  2  for erasure. 
     Below, a writing instrument according to another aspect of the present invention will be explained. The writing instrument body is similar to the one of the above-mentioned aspect, so explanation of it will be omitted. Only the points which differ from the above aspect will be explained. 
       FIG. 15  is a perspective view of the cap  24  of another aspect different from the cap  4  of the writing instrument which is shown in  FIG. 1 , while  FIG. 16  is a vertical cross-sectional view of the cap  24  which is shown in  FIG. 15 . The cap  24  which is shown in  FIG. 15  and  FIG. 16  differs from the cap  4  which is shown in  FIG. 2  to  FIG. 4  only on the point of having a positioning projection  24   h . The positioning projection  24   h  has a complementary shape to the flat part  2   e  which is provided at the insert part  2   a  of the erasing member  2  in the state where the erasing member  2  is attached to the cap  24 . By the cap  24  having the positioning projection  24   h , it becomes possible to position the erasing member  2  with a predetermined orientation at the time of attachment, and, after attachment, possible to prevent rotation of the erasing member  2 . If the cap  24  is formed from a transparent or semitransparent material, the positioning projection  24   h  is preferably provided at the side with the clip part  4   b  at the inner circumferential surface  16   a  of the supporting wall  16  so as to give rise to an aesthetic feeling in relationship to the alignment with the clip part  4   b.    
       FIG. 17  is a perspective view of the cap  24  to which is attached an erasing member  22  of another aspect from the erasing member  2  of the writing instrument which is shown in  FIG. 1 ,  FIG. 10  is a vertical cross-sectional view of the cap  24  which is shown in  FIG. 17 , and  FIG. 19  is a vertical cross-sectional view of the erasing member  22  which is shown in  FIG. 17 . 
     In this aspect, the cap  24  is the one which is shown in  FIG. 15  and  FIG. 16 . The erasing member  22  differs from the erasing member  2  which is shown in  FIG. 5  to  FIG. 7  only on the point that the fitting hole  22   c  does not run up through the erasing part  22   b . That is, the fitting hole  22   c  is drawn simplified in the drawings, but the insert part  22   a  has at least a taper part, lock part, and large diameter part. The axial direction length of the large diameter part is set to a length for receiving the fitting part  14  and connecting parts  15  of the cap. Note that, as explained above, the fitting hole  22   c  may also be designed having just a taper part. 
     The front end face of the erasing part  22   b  is provided with a recessed part  22   m  of a recessed curved shape. By having the front end face of the erasing part  22   b  be provided with the recessed part  22   m , erasure of fine locations using the edges of the recessed part  22   m  becomes possible. Further, by placing the erasing member  22  at right angle to the paper surface etc. on which a line is drawn and performing an erasing operation, compared with the case where the front end face of the erasing pare is formed into a projecting curved shape, the frictional resistance is reduced and smooth broad range erasure becomes possible. 
       FIG. 20  is a perspective view of the cap  24  to which is attached an erasing member  32  of still another aspect from the erasing member  2  of the writing instrument which is shown in  FIG. 1 ,  FIG. 21  is a perspective view of the erasing member  32  which is shown in  FIG. 20 , and  FIG. 22  is a front view of the erasing member  32  which is shown in  FIG. 20 . 
     In this aspect, the cap  24  is one which is shown in  FIG. 15  and  FIG. 16 . The erasing member  32 , compared with the erasing member  2  which is shown in  FIG. 5  to  FIG. 7 , is the same in the insert part  2   a  and fitting hole  2   c  and only differs in the outer shape of the erasing part  32   b . The erasing part  32   b  has an outer shape which has a horizontal cross-sectional shape which is circular at the back end face, but changes to an elliptical shape with a ratio of the long axis and short axis which gradually becomes larger from the back end face toward the front end face. The length of the long axis of the elliptical shape at the front end face of the erasing part  32   b  is shorter than the diameter of the circle of the back end face of the erasing part  32   b . By making the horizontal cross-sectional shape of the erasing part  32   b  an elliptical shape, at the time of erasure of a line etc., it is possible to make the long axis direction parallel to the paper surface etc. or make the short axis direction parallel to the paper surface etc. or to make it intermediate between them so as to realize different erasure widths, that is, areas which can be rubbed at one time. 
       FIG. 23  is a perspective view of the cap  24  to which is attached an erasing member  42  of still another aspect from the erasing member  2  of the writing instrument which is shown in  FIG. 1 ,  FIG. 24  is a perspective view of the erasing member  42  which is shown in  FIG. 23 , and  FIG. 25  is a front view of the erasing member  42  which is shown in  FIG. 23 . 
     In this aspect, the cap  24  is the one which is shown in  FIG. 15  and  FIG. 16 . The erasing member  42 , compared with the erasing member  2  which is shown in  FIG. 5  to  FIG. 7 , is the same in the insert part  2   a  and fitting hole  2   c  and only differs in the outer shape of the erasing part  42   b . The erasing part  42   b  has a horizontal cross-sectional shape which is circular at the back end face, but is hexagonal at the front end face. It has a shape which gradually changes from a circular shape to a hexagonal shape from the back end face to the front end face. The hexagonal shape of the front end face of the erasing part  42   b  is chamfered round at the corners. Preferably, one side of the hexagonal shape becomes parallel with the flat part  2   e  of the insert part  2   a . By the front end face of the erasing part  2   b  having a hexagonal shape, it becomes possible to utilize the side parts  42   n  and the corner parts  42   o  to erase small locations. Note that, the shape of the front end face of the erasing part  42   b  is not limited to a hexagonal shape and may also be a triangular shape, square shape, or other polygonal shape. 
       FIG. 26  is a perspective view of the cap  24  to which is attached an erasing member  52  of still further another aspect from the erasing member  2  of the writing instrument which is shown in  FIG. 1 ,  FIG. 27  is a perspective view of the erasing member  52  which is shown in  FIG. 26 , and  FIG. 28  is a front view of the erasing member  52  which is shown in  FIG. 26 . 
     In this aspect, the cap  24  is one which is shown in  FIG. 15  and  FIG. 16 . The erasing member  52 , compared with the erasing member  2  which is shown in  FIG. 5  to  FIG. 7 , is the same in the insert part  2   a  and fitting hole  2   c  and only differs in the cuter shape of the erasing part  52   b . The erasing part  52   b , if considering it split into halves in the vertical direction, has a first half  52   p  which has a frustoconical shape and has a second half  52   q  which has a hexagonal frustoconical shape. The first half is positioned at the clip part  4   b  side of the cap  24  by having the flat part  2   c  which is positioned by the positioning projection  24   h  of the cap body  4   a  be provided at the first half  52   p  side of the insert part  2   a.    
     By arranging the first half  52   p  at the clip part  4   b  side of the cap, the hexagonal frustoconical shape surface of the second half  52   q  becomes easier to use. That is, usually, when a user holds the cap  24  to perform an erasing operation, he or she places his or her forefinger and thumb at the outer circumferential surface of the cap body  4   a  while avoiding the clip part  4   b  and places his or her middle finger at part of the outer circumferential surface of the cap body  4   a  at the side opposite to the side with the clip part  4   b  so as to thereby grip the cap  24 . Therefore, in this gripped state, the surface of the hexagonal frustoconical shape of the second half  52   q  faces the paper surface. 
     The first half  52   p  is the same shape as the erasing part  2   b  which is shown from  FIG. 5  to  FIG. 7 . The second half  52   q  is half of a hexagonal frustoconical shape, so has three flat parts  52   r . Therefore, the first half  52   p  part of the erasing part  52   b  can be used for erasure so as to erase a narrow surface. On the other hand, when using the second half  52   q  part of the erasing part  52   b  for erasure, by using the different flat parts  52   r , it becomes possible to erase an area broader than the case of using the first half  52   p . Further, the connecting parts of the flat parts, that is, the peak parts  52   s , or the connecting parts  52   t  of the peak parts and the front end face can be used to erase finer locations. 
       FIG. 29  is a perspective view of the cap  25  to which is attached an erasing member  62  of still another aspect from the erasing member  2  of the writing instrument which is shown in  FIG. 1 ,  FIG. 30  is a perspective view of the erasing member  62  which is shown in  FIG. 29 , and  FIG. 31  is a front view of the erasing member  62  which is shown in  FIG. 29 . 
     In this aspect, the cap  24  is the one which is shown in  FIG. 15  and  FIG. 16 . The erasing member  62 , compared with the erasing member  2  which is shown in  FIG. 5  to  FIG. 7  is the same in the insert part  2   a  and fitting hole  2   c  and only differs in the outer shape of the erasing part  62   b . The erasing part  62   b  is configured as the second half  52   q  part which is shown in  FIG. 26  to  FIG. 28  where the two side surfaces are replaced with the frustoconical shape of the first half  52   p . Therefore, the erasing part  62   b  is comprised of a frustoconical shape part  62   u  and a hexagonal frustoconical shape part  62   v . The frustoconical shape part  62   u  is made to be arranged at the clip part  4   b  side of the cap  24  by having the flat part  2   e  which is positioned by the positioning projection  24   h  of the cap body  4   a  be provided at the frustoconical shape part  62   u  side of the insert part  2   a.    
     By arranging the frustoconical shape part  62   u  at the clip part  4   b  side of the cap  24 , the surface of the hexagonal frustoconical shape part  62   v  becomes easier to use. That is, usually, when the user holds the cap  24  to perform an erasing operation, he or she places his or her forefinger and thumb at the outer circumferential surface of the cap body  4   a  while avoiding the clip part  4   b  and places his or her middle finger at part of the outer circumferential surface of the cap body  4   a  at the side opposite to the side with the clip part  4   b  so as to thereby grip the cap  24 . Therefore, in this gripped state, the surface of the hexagonal frustoconical shape part  62   v  faces the paper surface. 
     By using the frustoconical shape part  62   u  of the erasing part  62   b  for erasure, erasure at a narrow surface becomes possible. On the other hand, when using the hexagonal frustoconical shape part  62   v  of the erasing part  62   b  for erasure, a single surface is used, so erasure of a wider surface than when using the frustoconical shape part  62   u  becomes possible. Further, by using the connecting parts of the surfaces, that is, the peak parts  62   w , or the connecting parts  62   x  of the peak parts  62   w  and the front end face, erasure of finer locations becomes possible. 
     The above aspect of the erasing member of the present invention was one where the erasing member was attached to the front end part of the cap, but it may be similarly applied even at the back end part of the writing instrument body. 
       FIG. 32  is a vertical cross-sectional view of the writing instrument  100  according to the second embodiment which is provided with the erasing member  2  according to one aspect of the present invention. The writing instrument  1  is a ball pen type of writing instrument and has a writing instrument body  3 , which is provided with a refill  5  and a cylinder  6  which extends in a tubular shape, and a cap  104 . The cylinder  6  has a tubular front cylinder  7  and a back cylinder  8  with a front end part which screws into the hack end part of the front cylinder  7 . The writing instrument  100  according to the present embodiment differs from the above-mentioned writing instrument  1  according to the first embodiment only in the outer shape of the cap, in particular the shape of the clip part. Therefore, the following explanation will be given particularly regarding the clip part, while the explanation of the other parts will be omitted. Note that, the cap  104  can, for example, be designed to enable attachment of the erasing member which is attached to the cap  4  which is shown in  FIG. 4 . For example, it can be designed to enable attachment of the erasing member which is attached to the cap  24  which is shown in  FIG. 15 . 
       FIG. 33  is a perspective view of the cap  104  of the writing instrument  100  which is shown in  FIG. 32 ,  FIG. 34  is a plan view of the cap  104  which is shown in  FIG. 33 ,  FIG. 35  is a side view of the cap  104  which is shown in  FIG. 33 ,  FIG. 36  is a vertical cross-sectional view of the cap  104  which is shown in  FIG. 33 , and  FIG. 37  is a cross-sectional view along the line S-S of  FIG. 35  of the cap  104  which is shown in  FIG. 33 . 
     The cap  104  has a cap body  104   a , clip part  104   b , and, in the present embodiment, erasing member  2 . The cap body  104   a  is a tubular member. At its side surface, the clip part  104   b  is provided integrally via a connecting part  104   c . The clip part  104   b  is designed to have elasticity so as to be able to grip a document, clothing, or other object with the cap body  104   a . Therefore, as the material which forms the cap body  104   a  and the clip part  104   b , polycarbonate, acrylonitrile-butadiene-styrene, or other plastic may be mentioned. As explained above, these parts are preferably formed by a material which is harder than the front cylinder  7 . 
     The characterizing feature of the cap  104  is the substantially rectangular shape plate-shaped member where the clip part  104   b  extends over substantially the entire length of the clip body  104   a  in the axial direction. The back end face of the clip part  104   b , as shown in  FIG. 34 , is formed in a curved shape to improve the hand feeling. Further, at the center part of the front end face of the clip part  104   b , a flat surface which is vertical to the center axis, that is, a guide surface  104   d , is formed. The front end face at the two sides of this is formed in a curved shape similar to the back end face. The edges of the clip part  104   b  are chamfered. Note that, the guide surface  104   d  need not be vertical to the center axis. For example, as explained later while referring to  FIG. 38 , it may also be a slanted surface matched with the facing paper surface at the time of erasure. 
     The width W of the clip part  104   b , as clear from the plan view of  FIG. 34 , is substantially the same as the diameter of the tubular cap body  104   a . Therefore, from the viewpoint of the user, the cap body  104   a  is almost completely hidden by the clip part  104   b  and so only the clip part  104   b  and the erasing member  2  are visible. That is, compared with a conventional clip part, for example, the clip part  4   b  of the cap  4  which is shown in  FIG. 2 , the clip part  104   b  of the cap  104  has a wide width and a broad range and smooth surface. Therefore, it is possible to decorate the surface with transfer printing etc. to thereby make the design fancier and improve the appeal to the user. Further, by attaching rubber, an elastomer, or other rubbery material to the surface, an erasing surface which is wider than the erasing member  2  is formed, so it becomes possible to selectively use the areas for erasure. 
     The connecting part  104   c  which connects the cap body  104   a  and the clip part  104   b , as shown in  FIG. 37 , has a T-shaped horizontal cross-sectional shape. For this reason, the strength of the clip part  104   b  with respect to the force in the circumferential direction (up-down force in  FIG. 37 ) is increased. Therefore, at the time of use by the user etc., breakage of the connecting part  104   c  is prevented even when force in the circumferential direction is applied to the clip part  104   b.    
       FIG. 38  is a view which shows the state of use at the time of erasure by the cap  104  to which an erasing member  2  is attached in the writing instrument which is shown in  FIG. 32 . As shown in  FIG. 38 , at the time of erasure, the flat guide surface  104   d  of the clip part  104   b  can be pushed against the paper surface while making the cap  104  slide along the guide surface  104   d  so as to enable a constant width of writing to be erased. At this time, if pressing the guide surface  104   c  of the clip part  104   b  by a ruler or other guide member while making the cap  104  slide, a more stable erasure operation becomes possible and, further, constant width, long range erasure becomes possible. Further, by pressing the guide surface  104   d  of the clip part  104   b  against the paper surface and making the wide width surface of the clip part  104   b  abut against a slanted surface Ja which is provided at the ruler J while sliding the cap  104 , a further stabler erasure operation becomes possible. 
     Further, the shape of the erasing member  2  or the axial direction position of the clip part  104   b  with respect to the cap body  104   a , the shape of the guide surface  104   d , etc. can be adjusted to adjust the angle A which is formed by paper surface and the center axis of the writing instrument  100  at the time of the erasure operation. This angle A is preferably a range of 40 to 80 degrees. 
     In addition to the above-mentioned effect, since the width W of the clip part  104   b  and the diameter of the cap body  104   a  are substantially the same, for example, when turning the wide width flat surface of the clip part  104   b  upward and placing the writing instrument  100  on a desktop etc., the writing instrument  100  turns so that the side surface of the clip part  104   b  contacts the desktop etc. and therefore the writing instrument  100  can be kept in a true horizontal state. Therefore, the effect is exhibited that the cylinder  6  can be easily gripped when picking up the writing instrument  100 . Further, it is possible to prevent the writing instrument  100  from rolling around. 
     Furthermore, by extending the clip part  104   b  up to the center of gravity position of the writing instrument and having the cap  104  have the clip part  104   b  of the above-mentioned structure, for example, when placing the writing instrument  100  on a desktop while arranging the wide width flat surface of the clip part  104   b  down, the back end part of the writing instrument  100  does not contact the desktop and can be kept stable in a floating state. Therefore, when picking up the writing instrument  100 , the effect is exhibited that the cylinder  6  is easy to grip. Further, the clip part  104   b  as a whole is wide in width, so without touching the erasing member  2 , part of the clip part  104   b , for example, the guide surface  104   d , can be pressed to fit the cap  104  with the writing instrument body  3 . When fitting the cap  104 , the fingers do not touch the erasing member  2 , so the surface of the erasing member  2  can be prevented from being contaminated with hand oil etc. 
     Note that, the structure of the clip part  104   b  which was explained in the present embodiment can be applied to attachment to not only the cap, but also the front cylinder and the back cylinder. The present invention was explained in detail based on specific embodiments, but a person skilled in the art could make various changes, corrections, etc. without departing from the claims and concepts of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  writing instrument 
               2  erasing member 
               2   c  fitting hole 
               3  writing instrument body 
               4  cap 
               14  fitting part 
               15  connecting part 
               16  supporting wall 
               17  clearance space