Patent Document

BACKGROUND OF THE INVENTION 
     The present invention relates to a ballpoint pen tip, and also a ball point pen using the same. In detail, the invention relates to a ballpoint pen tip of such a type in which a ball receiving seat is formed by inwardly pressing and deforming a side wall in the vicinity of a front end portion of a metallic pipe body. 
     In the ballpoint pen tip of this type, conventionally, U.S. Pat. No. 5,899,625 and U.S. Pat. No. 5,904,432 disclosed a ballpoint pen tip in which a ratio (A/T) of an outer diameter A of a ball to a thickness T of a pipe is set to be 5.8 or less, and furthermore, a ratio (D/T) of a depth D of a concave portion to the thickness T of the pipe is set to be 2.0 or less in order to enhance a strength of a ball receiving seat, for example. 
     Although the conventional ballpoint pen tip having a comparatively small size (for example, 0.3 mm, 0.4 mm or 0.5 mm) is effective in enhancing the strength of the ball receiving seat, the ballpoint pen tip having a large size (for example, 1.0 mm or more) is not preferable in respect of manufacture because the quantity of projection (that is, the quantity of inward pressing and deformation) of an inwardly projecting portion for forming the ball receiving seat is more increased when the outer diameter of the ball is made greater so that a pressing force might be increased during the pressing and deformation and a front end portion of a tool such as a punch for the pressing and deformation might be damaged. On the other hand, even if the thickness of the pipe is simply set to be small in order to easily carry out the pressing and deformation, the thickness of the ball receiving seat itself is reduced so that the strength of the ball receiving seat is lowered. 
     In the ballpoint pen tip of this type (that is, a ballpoint pen tip of such a type as to form the ball receiving seat through the pressing and deformation), moreover, as the outer diameter of the ball is increased, the size of an ink flowing gap in a central portion of the ball receiving seat tends to be enlarged. Consequently, the capillary force of the ink flowing gap in the central portion is remarkably reduced as compared with that in the ink flowing gap between adjacent inwardly projecting portions. Therefore, it is impossible to rapidly supply ink to the whole ball having a large size so that a blur in handwriting or a break in handwriting might be caused. 
     In the conventional ballpoint pen tip, furthermore, a spew is easily generated on the outer peripheral edge of a rear end thereof. When the rear end of the ballpoint pen tip is to be pressed and fastened into a fitting hole formed in the front end portion of the penholder or the connecting member, consequently, the outer peripheral edge of the rear end of the ballpoint pen tip (a portion in which the spew is generated easily) bites at the inner face of the fitting hole so that the ballpoint pen tip might be hindered from being pressed and fitted smoothly or pressing and fitting failures might be caused, for example, the inner face of the fitting hole might be damaged. In particular, in the case of the ballpoint pen tip including a ball having a large size, it is necessary to apply a great pressing force depending on a large outer diameter of the pipe. In addition, when the biting at the outer peripheral edge of the rear end is caused, a much greater pressing force is required and the pressing and fitting operations are hard to carry out. Thus, there is a high possibility that the pressing and fitting failures might be caused. 
     SUMMARY OF THE INVENTION 
     In order to solve the conventional problems, it is an object of the invention to provide a ballpoint pen tip capable of obtaining a ball receiving seat having easiness of pressing and deformation, a sufficient ink fluidity, a smooth rotation of a ball and a sufficient strength and capable of being smoothly pressed and fitted in a fitting hole even if the ball having a large size is employed. 
     A ballpoint pen tip, according to the invention, rotatably holds a ball at its front end portion. The ball is held by a plurality of inwardly projecting portions for a ball receiving seat which is formed by inwardly pressing and deforming a neighborhood of a front end portion of a metallic pipe body  2  and a front end edge portion which is formed by inwardly pressing and deforming the front end portion of the pipe body. In the ballpoint pen tip according to the present invention, a relation of A/T&gt;5.8 is satisfied, where A is an outer diameter of the ball and T is a thickness of the pipe body. 
     The value of the ratio (A/T) of the outer diameter A of the ball to the thickness T of the pipe body  2  is greater than 5.8 (that is, “A/T&gt;5.8”). Therefore, even if the ball  5  having a large size is employed, pressing and deformation for forming the ball receiving seat can be carried out easily. The reason is as follows. Supposing that the value of A/T is equal to or smaller than 5.8 (that is, “A/T≦5.8”), the thickness T of the pipe body  2  is comparatively increased and a great pressing force is required for forming the ball receiving seat even if a strength of the ball receiving seat can be enhanced. Consequently, there is a possibility that the front end portion of a tool (for example, a punch) for pressing and deformation might be damaged and it is hard to carry out manufacture through the pressing and deformation. 
     Furthermore, it is preferable that the value of A/T according to the present invention is made smaller than 10.0 (that is, “A/T&lt;10.0”). Consequently, it is possible to obtain a ball receiving seat having a sufficient strength. The reason is as follows. If the value of A/T is equal to or greater than 10.0 (that is, “A/T≧10.0”), the thickness T of the pipe body  2  to the outer diameter A of the ball is reduced too much so that the strength of the ball receiving seat is reduced remarkably. Consequently, there is a possibility that a smooth and stable rotation of the ball  5  cannot be obtained for a long period of time. 
     Accordingly, the ballpoint pen tip  1  according to the invention satisfies a relation of “5.8&lt;A/T&lt;10.0”. Consequently, even if the ball  5  having a large size is employed, it is possible to easily carry out the pressing and deformation for forming the ball receiving seat. In addition, it is possible to set such a proper thickness T that the strength of the ball receiving seat is not reduced. 
     In the ballpoint pen tip  1  according to the present invention, moreover, it is advantageous that a relation of “D/T&gt;2.0” should be satisfied, where D is a depth of a concave portion  32  which is formed at an outside of the inwardly projecting portions  3 . 
     The value of the ratio (D/T) of the depth D of the concave portion  32  to the thickness T of the pipe body  2  is greater than 2.0 (that is, “D/T&gt;2.0”). Therefore, even if the ball  5  having a large size is employed, a sufficient ink fluidity can be obtained without causing a blur in handwriting or a break in handwriting. In addition, the ball  5  can be stabilized and supported sufficiently so that a smooth rotation of the ball  5  can be obtained. 
     The reason is as follows. If the value of D/T is equal to or smaller than 2.0 (that is, “D/T≦2.0”), the depth D of the concave portion  32  to the thickness T of the pipe body  2  is reduced too much (that is, the quantity of projection of the inwardly projecting portion  3  is reduced too much). In particular, if the ball  5  has a large size, the capillary force of an ink discharging gap  31  in the central portion of the ball receiving seat becomes remarkably smaller than the capillary force of the ink discharging gap  31  (a radial groove) between the adjacent inwardly projecting portions  3 . Consequently, the quantity of an ink to be supplied to the ball  5  is lacked so that a blur in handwriting or a break in handwriting is caused. Moreover, if “D/T≦2.0” is obtained, the size of the ball receiving seat itself is reduced so that the ball  5  cannot be supported stably. Thus, there is a possibility that the smooth rotation of the ball  5  might not be obtained. 
     Furthermore, it is advantageous that the value of D/T according to the present invention should be set to be smaller than 4.0 (that is, “D/T&lt;4.0”. Consequently, it is possible to easily carry out pressing and deformation, and furthermore, it is possible to obtain a ball receiving seat having a sufficient strength. The reason is as follows. If the value of D/T is equal to or greater than 4.0 (that is, “D/T≧4.0”), the depth D of the concave portion  32  to the thickness T of the pipe body  2  (that is, the quantity of projection of the inwardly projecting portion  3 ) is increased too much so that the pressing force is increased during the formation of the concave portion  32 . Therefore, there is a possibility that a front end portion of a tool such as a punch might be damaged. In this case, moreover, the thickness of the inwardly projecting portion  3  becomes remarkably smaller, through pressing and plastic deformation, than the thickness T of a portion of the pipe body  2  which is subjected to neither the pressing nor the plastic deformation. Therefore, there is a possibility that the strength of the ball receiving seat might be lacked. 
     Accordingly, the ballpoint pen tip  1  according to the invention satisfies a relation of “2.0&lt;D/T&lt;4.0”. Consequently, the thickness T of the pipe body  2  can be set more properly. Even if the ball  5  having a large size is employed, it is possible to avoid a blur in handwriting or a break in handwriting. In addition, it is possible to form a ball receiving seat through easy pressing and deformation without reducing the strength of the ball receiving seat. 
     The ballpoint pen tip  1  according to the invention mentioned above is more effective in the case in which a ball having a large size is employed. More specifically, it is preferable that the outer diameter A of the ball  5  should be set in the range of 0.7 mm to 1.6 mm . In particular, when the outer diameter A of the ball is set in the range of 0.7 mm to 1.6 mm (more preferably, in the range of 1.0 mm to 1.6 mm), functions and effects according to the invention mentioned above can be produced effectively. Consequently, it is possible to obtain a ball receiving seat having easiness of pressing and deformation, a sufficient ink fluidity, a smooth rotation of the ball and a sufficient strength. 
     In the ballpoint pen tip  1  according to the present invention, the inwardly projecting portions  3  may be provided in three places, preferably, four places or more. 
     When the inwardly projecting portions  3  are provided in four places or more, the ball receiving seat can be supported more stably than the case in which the inwardly projecting portion  3  is provided in three portions. Furthermore, in the case in which the number of ink discharging gaps  31  to be provided between the inwardly projecting portions  3  is not three but four or more, an ink can be caused to spread more rapidly over the whole surface of the ball  5  having a large surface area and a large size. Thus, it is possible to obtain a sufficient ink fluidity without causing a blur in handwriting or a break in handwriting. In particular, it is preferable that the number of inwardly projecting portions  3  should be four in that a sufficient ink fluidity can be satisfied and manufacture can be carried out easily. 
     In the ballpoint pen tip  1  according to the present invention, it is preferable that a curved surface portion  6  should be provided on an outer peripheral edge of a rear end of the pipe body  2 . 
     Consequently, when the ballpoint pen tip  1  is to be pressed into a penholder and a fitting hole of a connecting member, the curved surface portion  6  and the inner face of the fitting hole slide smoothly and there is no possibility that the outer peripheral edge of the rear end of the pipe body  2  might bite at the inner face of the fitting hole to inhibit smooth pressing and fitting in the fitting hole or to generate pressing and fitting failures, for example, to damage the inner face of the fitting hole differently from the conventional art. 
     Examples of the shape of the pipe body  2  according to the invention include a right cylinder, a taper cylinder and a stepped cylinder having a small diameter portion and a large diameter portion. 
     The thickness T of the pipe body  2  according to the invention represents a thickness of a front end portion of the pipe body  2  in a part to which the pressing and deformation is not applied (that is, a thickness in the vicinity of the inwardly projecting portion  3 ) and does not represent thicknesses of the inwardly projecting portion  3  and the front end edge portion  4  which are reduced through the pressing and deformation. Moreover, the thickness T of the pipe body  2  can represent a mean thickness of the front end portion of the pipe body  2  in which the inwardly projecting portion  3  has not been formed. 
     The depth D of the concave portion  32  according to the invention represents a distance in a radial direction from an outer peripheral surface of the pipe body  2  of the concave portion  32  which has not been formed to the bottom most part of the concave portion  32  which has been formed (that is, the quantity of pressing and deformation in a radial direction of a side wall of the pipe body  2 ). Moreover, the concave portion  32  is provided in a plurality of places on the outer peripheral surface of the pipe body  2 , and the depth D of the concave portion  32  is set to be equal. Furthermore, while the shape of the concave portion  32  may be any of a conical surface, a spherical surface and a prism, the shape of the conical surface is preferable in that the thickness can be changed uniformly and manufacture can be carried out easily. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view showing an embodiment of the invention; 
     FIG. 2 is an enlarged sectional view showing a main part of FIG. 1; 
     FIG. 3 is an enlarged sectional view taken along the line P—P in FIG. 2; 
     FIG. 4 is a longitudinal sectional view showing a first application example according to the invention; 
     FIG. 5 is a longitudinal sectional view showing a second application example according to the invention; and 
     FIG. 6 is a longitudinal sectional view showing a third application example according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the invention will be described with reference to the drawings. 
     FIGS. 1 to  3  show the embodiment of the invention. 
     In a ballpoint pen tip  1  according to the embodiment, a side wall in the vicinity of the front end portion of a right cylindrical pipe body  2  formed of a metal (for example, austenite based stainless steel such as SUS304, SUS305 or SUS321) is pressed and deformed to provide four inwardly projecting portions  3  at regular intervals in a circumferential direction, thereby forming a ball receiving seat. Furthermore, the front end portion of the pipe body  2  is provided with a tapered front end edge portion  4  which is inwardly deformed, and a ball  5  is rotatably held by the inwardly projecting portion  3  (ball receiving seat) and the front end edge portion  4 . 
     The metallic pipe body  2  is a straight cylinder and has a longitudinal dimension of 6.2 mm and an inner diameter set to be larger, by approximately 0.03 mm to 0.05 mm, than an outer diameter A of the ball  5  to be employed. Moreover, a convex curved surface portion  6  which is rounded through barrel polishing is formed on the outer peripheral edge of the rear end of the pipe body  2 . Consequently, a spew is not generated on the outer peripheral edge of the rear end of the pipe body  2  and the biting of the outer peripheral edge of the rear end of the pipe body  2  and the inner faces of fitting holes  61   a ,  71   a  and  81   a  is avoided when the rear portion of the pipe body  2  is pressed into the fitting holes  61   a ,  71   a  and  81   a  as shown in FIGS. 4 to  6 . Thus, pressing and fitting can be carried out smoothly. Moreover, it is preferable that the curved surface portion  6  should have a radius of curvature of approximately 0.03 mm to 0.10 mm because the biting at the inner faces of the fitting holes  61   a ,  71   a  and  81   a  can be prevented sufficiently and manufacture can easily be carried out. 
     Moreover, it is preferable that the outer diameter of the rear end of the metallic pipe body  2  should be greater than 1.0 mm. If the outer diameter of the rear end of the pipe body  2  to be pressed into the fitting holes  61   a ,  71   a  and  81   a  is greater than 1.0 mm, a great pressing force is required. Therefore, if the outer peripheral edge of the rear end of the pipe body  2  bites at the inner faces of the fitting holes  61   a ,  71   a  and  81   a , there is a high possibility that the inner faces of the fitting holes  61   a ,  71   a  and  81   a  might be damaged considerably and pressing failures might be caused. However, since the curved surface portion  6  is provided on the outer peripheral edge of the rear end of the pipe body  2 , it is possible to obtain a ballpoint pen tip comprising a ball having a large diameter which suppresses the pressing failures. 
     Moreover, it is preferable that the apexes of the inwardly projecting portions  3  in the four places should not come in contact with each other and a ratio (B/T) of a diameter B of a virtual inscribing circle contacting the apexes to a thickness T of the pipe body  2  should be set in the range of 1.8 to 3.0. Consequently, it is possible to obtain a ball receiving seat having easiness of pressing and deformation and a sufficient strength. 
     Furthermore, a cross-shaped ink discharging gap  31  is formed between the inwardly projecting portions  3  in the four places. When a sectional area in a radial direction of the ink discharging gap  31  (that is, a cross-shaped groove) is represented by S 1  (a slant-line portion shown in a dotted line of FIG. 3) and a sectional area in a radial direction of an inner hole portion of a ball holding portion of the pipe body  2  which has an inner diameter slightly greater than the outer diameter A of the ball is represented by S 2 , it is preferable that a ratio (S 1 /S 2 ) of the Si to the S 2  should be set in the range of 0.10 to 0.39. If the S 1 /S 2  satisfies the range, the pressing and deformation can easily be carried out and a sufficient ink fluidity can be obtained. 
     Table 1 shows a value of A/T and a value of D/T which are obtained by a calculation based on a thickness T of the pipe body  2 , a depth D of a concave portion  32  and the values of A, D and T in the case in which five kinds of balls  5  (more specifically, 0.7 mm, 1.0 mm, 1.2 mm, 1.4 mm and 1.6 mm) are applied to the ballpoint pen tip  1  shown in FIGS. 1 to  3 . 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 A [mm] 
                 D [mm] 
                 T [mm] 
                 A/T 
                 D/T 
               
               
                   
               
             
             
               
                 0.7 
                 0.240 
                 0.115 
                 6.09 
                 2.09 
               
               
                 1.0 
                 0.370 
                 0.135 
                 7.41 
                 2.74 
               
               
                 1.2 
                 0.420 
                 0.195 
                 6.15 
                 2.15 
               
               
                 1.4 
                 0.500 
                 0.195 
                 7.18 
                 2.56 
               
               
                 1.6 
                 0.550 
                 0.195 
                 8.21 
                 2.82 
               
               
                   
               
             
          
         
       
     
     FIG. 4 shows a first application example of the ballpoint pen tip  1  according to the invention. A ballpoint pen  6  (a so-called aqueous gel ink ballpoint pen or an oil ballpoint pen) is obtained by pressing and fastening the ballpoint pen tip  1  according to the invention shown in FIGS. 1 to  3  into the fitting hole  61   a  of the front end portion of a cylindrical connecting member  61  formed of synthetic resin (for example, polyacetal, polypropylene or polyethylene) and by pressing and fastening the connecting member  61  into an opening on the front end portion of an ink reservoir  62  formed of an extrusion molded body made of synthetic resin (for example, polypropylene or polyethylene). 
     An ink  63  (an aqueous ink having a shear thinning viscosity or an oil ink having a viscosity of 1000 mPa·s to 1000 mPa·s at 20° C.) is accommodated in the ink reservoir  62  and a follower  64  (for example, a greasy substance) which moves forward with the consumption of the ink  63  is accommodated in the rear end of the ink  63 . 
     Second Application Example 
     FIG. 5 shows a second application example of the ballpoint pen tip  1  according to the invention. 
     A ballpoint pen  7  (a so-called direct liquid type ballpoint pen), according to one example of the present invention, comprises a connecting member  71  made of synthetic resin (for example, polyacetal, polypropylene or polyethylene) which is formed by pressing and fastening the ballpoint pen tip  1  according to the invention shown in FIGS. 1 to  3  into the fitting hole  71   a  on the front end portion, an ink holding member  73  having the connecting member  71  fastened to a front end portion, and a penholder  72  attaching the ink holding member  73  to a front end portion and having an ink tank  72   a  for accommodating an ink which is formed in a rear portion. 
     The ink holding member  73  serves to temporarily hold an excess ink depending on a change in an internal pressure of the ink tank  72   a  and is provided with a plurality of comb teeth  73   b  forming a large number of ink holding grooves  73   a  on a peripheral surface, a slit-shaped ink groove  73   c  penetrating through the comb teeth  73   b  in an axial direction and communicating with the ink holding grooves  73   a , an air exchange concave groove  73   d  provided on the comb teeth  73   b  in an opposite position to the slit-shaped ink groove  73   c , and a center hole  73   e  penetrating through an axial core which are formed integrally of synthetic resin (for example, ABS resin). 
     An ink guiding member  74  formed of an extrusion molded body made of synthetic resin is inserted and fixed into the center hole  73   e . An outer or inner peripheral surface of the ink guiding member  74  is provided with an ink introducing path having a capillary force which is extended in an axial direction. Moreover, an ink relaying member  75  formed of a porous material body or a fiber worked body to which the front end portion of the ink guiding member  74  is connected to be stick-shaped is accommodated in the rear portion of the connecting member  71 . Furthermore, the inside of a pipe body  2  of the ballpoint pen tip  1  is provided with a bar-shaped body  76  made of synthetic resin which has a rear end connected to the front end portion of the ink relaying member  75  and a front end portion connected to an ink discharging gap  31  of a ball receiving seat. A clearance having a capillary force is formed between the bar-shaped body  76  and the inner peripheral surface of the pipe body  2  so that the ink is smoothly guided to the back of a ball  5 . Moreover, it is also effective that a slit having a capillary force for introducing the ink is provided on the outer peripheral surface of the bar-shaped body  76 . 
     Third Application Example 
     FIG. 6 shows a third application example of the ballpoint pen tip  1  according to the invention. 
     A ballpoint pen  8  (so-called inner cotton type ballpoint pen), according to other example of the present invention, comprises a connecting member  81  made of synthetic resin (for example, polyacetal, polypropylene or polyethylene) having a fitting hole  81   a  on a front end portion into which the ballpoint pen tip  1  according to the invention shown in FIGS. 1 to  3  is pressed and fixed, and a penholder  82  provided with a front end opening to which the connecting member  81  is fastened and accommodating an ink impregnation body  83  formed of a porous material body or a fiber worked body therein. The ink impregnation body  83  is impregnated with the ink and is held and fixed by an attaching rib  82   a  provided on an inner wall of the penholder  82  and a tail plug  82   b  fitted in an opening formed on the rear end of the penholder  82 . 
     Moreover, an ink relaying member  84  formed of a porous material body or a fiber worked body which is connected to the ink impregnation body  83  is attached to the rear portion of the connecting member  81 . Furthermore, the inside of the pipe body  2  of the ballpoint pen tip  1  is provided with a bar-shaped member  85  (for example, an extrusion molded body made of synthetic resin or a fiber collected worked body) having a rear end connected to the front end portion of the ink relaying member  84  and a front end portion connected to an ink discharging gap  31  of a ball receiving seat. Moreover, an air hole  82   c  for communicating the inside of the penholder  82  with the outside is provided in the front of the penholder  82 . 
     While there has been described in connection with the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the invention. 
     According to the first aspect of the invention, even if a ball having a large size is employed, the pressing and deformation for forming the ball receiving seat can easily be carried out. 
     According to the second aspect of the invention, even if a ball having a large size is employed, a sufficient ink fluidity can be obtained without causing a blur in handwriting or a break in handwriting, and the ball can be sufficiently stabilized and supported to obtain a smooth rotation thereof. 
     According to the third aspect of the invention, it is possible to obtain a ballpoint pen tip including a ball having a specifically large size which comprises a ball receiving seat capable of obtaining easiness of pressing and deformation, a sufficient ink fluidity and a smooth rotation of the ball. 
     According to the fourth aspect of the invention, the ink can be caused to rapidly spread over the whole surface of the ball having a large surface area and a large size. Consequently, it is possible to obtain a sufficient ink fluidity without causing a blur in handwriting or a break in handwriting. 
     According to the fifth aspect of the invention, the ballpoint pen tip can be smoothly pressed and fitted into the penholder and the fitting hole of the connecting member. Thus, it is possible to prevent pressing and fitting failures from being generated.

Technology Category: b