Patent Publication Number: US-6220774-B1

Title: Ballpoint tip for ballpoint liquid container

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ballpoint tip for a ballpoint liquid container, such as a ballpoint refill using a ball as a writing medium. 
     2. Description of the Related Art 
     Most factors that determine the performance of a ballpoint liquid container for a ballpoint pen or the like are dependent on the accuracy of a ballpoint tip. A 0.7 mm diameter ball needs to rotate 44.5 full turns for drawing a line of only 10 cm, and a 0.5 mm diameter ball needs to rotate as many as 63.7 full turns for the same purpose at a very high rotating speed. Therefore, it is a very important problem with the ballpoint tip of this kind to prevent the abrasion of the ball friction necessarily caused by the high-speed rotation of the ball and the corrosional deterioration of the ball caused by static electricity generated by the high-speed rotation of the ball that occur as a logical consequence of the high-speed rotation of the ball, and to maintain the ability of the ball. If the ballpoint tip has problems in construction and accuracy, there is the possibility that “seepage” or “blotting” of the ink occurs. 
     A liquid applying implement disclosed in Japanese Utility Model provisional Publication No. Hei 5-76568 is an example of a ballpoint tip for a liquid container, such as a ballpoint refill of this kind. Referring now to FIG. 1, the liquid applying implement has a highly flexible liquid tank  14 , and a ballpoint tip  12  provided with a ball  11  and connected to the liquid tank  14  by a connecting member  13  and a press-fit cylindrical member  17 . The tank  14  contains a film-forming liquid of a high viscosity. The ball  11  is held for rotation in a forward end part of a body member of the ballpoint tip  12  so as to be partly exposed. A movable pin  15  having a small mass is placed in the body member of the ballpoint tip  12 , and a spring  16  is compressed in the body member so as to push the movable pin  15  forward to press the ball  11  against the inner surface of the forward end part of the body member. 
     These prior art techniques applied to control a liquid, such as a gel employed in a gel ballpoint pen or a covering liquid use a ball pressing means including the movable pin formed by molding a resin, and a coil spring. These parts are difficult to assemble, springs have tendency to become tangled with each other when the pitches of the coils is greater than twice the diameter of the spring wire, and hence an automatic assembling machine cannot be used for assembling those parts, and the gel ballpoint pens or the like cannot be mass-produced. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the foregoing problems in the prior art, and to enable an automatic assembling machine to handle coil springs in assembling ballpoint tips by using a coil spring capable of serving as both a spring for indirectly pressing the ball and a ball pressing member in contact with the ball, forming the coil spring so that gaps between the coils of the coil spring in an unloaded state is smaller than the diameter of a spring wire forming the coil spring to prevent entangling coil springs with each other, and coiling the spring wire in end coils to form an end part of the coil spring to be held in a caulked back end part of the body member of a ballpoint tip in an outside diameter greater than that of effective coils of the coil spring so that coil springs can be suspended in the same position. 
     Another object of the present invention is to provide a push-button type or a cap type ballpoint liquid container containing an ink having a viscosity in the range of a low viscosity of 3.5 cps to a high viscosity of 5,000 cps at 20° C., including a ballpoint tip having a body member, a ball held in a tip part of the body member, and a spring disposed behind the ball and having a large base end held in a back end part of the body member by caulking the back end part of the body member. The ball is pressed against the inner surface of the tip part of the body member by the spring so as to close the open tip of the body member to prevent the leakage of the ink from the tip of the ballpoint tip while the ballpoint liquid container is not in use or being carried and to prevent the ink around the ball from drying up. 
     With the foregoing objects in view, the present invention provides a ball point tip for a ballpoint liquid container including a tubular body member, a ball rotatably held in a tip part of the tubular body member, and a coil spring formed by coiling a spring wire, inserted in the tubular body member and capable of being strained by a pressure applied to the ball; in which the coil spring has a straight forward end part formed by linearly extending the spring wire and a base end formed by coiling the spring wire in end coils of an outside diameter greater than that of effective coils of the coil spring, the coil spring is extended in the tubular body member with the straight forward end part thereof extended through a liquid passage and pressed against the ball and with the base end thereof held by a back end part of the body member by caulking the back end part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a fragmentary longitudinal sectional view of ballpoint liquid container provided with a prior art ball point tip. 
     FIG. 2 is longitudinal sectional view of a ballpoint tip in a preferred embodiment according to the present invention for a ballpoint liquid container; 
     FIG. 3 is an enlarged, fragmentary longitudinal sectional view of a forward end part of the ballpoint tip shown in FIG. 2, in which a coil spring is removed; 
     FIG. 4 is a cross sectional view taken on line A—A in FIG. 3; 
     FIG. 5 is an end view taken in FIG. 3, in which a ball is removed; 
     FIG. 6 is a longitudinal sectional view showing a state in which the ballpoint tip is provided with a ballpoint refill shown in FIG. 2; 
     FIG. 7 is a longitudinal sectional view of a ballpoint pen formed by inserting the ballpoint refill shown in FIG. 6 in a barrel; and 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2 showing a ballpoint tip  1  in a preferred embodiment according to the present invention for a ballpoint liquid container, the ballpoint tip  1  includes a body member  2 , a ball  3  and a coil spring  4 . The body member  2  of the ballpoint tip  1  has a forward end part  2   a . The body member  2  has a back end part  2   b  having a reduced wall thickness demarcated by a shoulder  2   c  from a middle part of the body member  2 . 
     The inside diameter of the forward end part  2   a  is decreased stepwise toward the tip so as to form a first shoulder  2   d , a second shoulder  2   e  and a third shoulder  2   f . An ink passage  2   g  is formed between the third shoulder  2   f  and the tip of the body member  2 . 
     Referring to FIG. 3 showing a forward end part of the ballpoint tip  1  shown in FIG. 2 in an enlarged, fragmentary longitudinal sectional view, the ball  3  is held for rotation in the forward end part  2   a  of the body member  2  by caulking a tip part  2   i  of the forward end part  2   a . The ball  3  is formed of a hard material containing 96% tungsten carbide and 4% cobalt. 
     Referring to FIGS. 4 and 5, the ink passage  2   g  is formed in the tip part of the forward end part  2   a  of the body member  2 . The tip part of the forward end part  2   a  has a ball holding part  2   h (FIG. 2) extending in front of the ink passage  2   g . The ball  3  is held loosely for rotation in the ball holding part  2   h.    
     The coil spring  4  is inserted in the body member  2  through the open back end of the body member  2 . As shown in FIG. 2, a forward end part of a spring wire forming the coil spring  4  is extended linearly to form a straight part  4   a . When the coil spring  4  is inserted in the body member  2 , the straight part  4   a  of the coil spring  4  extends through the ink passage  2   a , the tip of the straight part  4   a  comes into contact with the ball  3 , and the coil spring  4  presses the ball  3  against the inner surface of the tip part of the forward end part  2   a  so that the ball  3  is partly exposed. In an optimum state, a part of the ball  3  corresponding to 35%-40% of the diameter of the ball  3  is exposed. 
     The spring wire is wound in end coils of an increased diameter to form a large back end  4   b . A back end part  2   j  of the body member  2  is caulked to hold the large back end  4   b  therein. Although the ball  3  is held loosely in the forward end part  2   a , the ball  3  is unable to fall off the caulked tip part  2   i  of the forward end part  2   a.    
     As obvious from FIGS. 4 and 5, the ink passage  2   g  has a plurality of radial grooves  2   gg  to enable the ink to flow smoothly through the ink passage  2   g.    
     Since the end surface of the straight part  4   a  of the coil spring  4  is flat while the surface of the ball  3  is spherical, the ball  3  is in point-contact with the end surface of the straight part  4   a  of the coil spring  4 . Since the ball is pressed forward by the spring  4  so as to be in perfectly close contact with the inner surface of the tip part  2   i , the ball  3  does not permit the leakage of the ink when the ballpoint tip  1  is attached to a liquid container to form a ballpoint refill. 
     The coil spring  4  has the large back end  4   b  of an outside diameter greater than that of the effective coils of the coil spring  4  and a step portion  4   c  between the effective coils of the coil spring  4  and the large back end  4   b . The back end part  2   j  of the body member  2  corresponding to the large back end  4   b  of the coil spring is caulked to hold the large back end  4   b  of the coil spring  4  therein. Since the outside diameter of the large back end  4   b  is nearly equal to the inside diameter of the back end part  2   j , the coil spring  4  can be firmly held in the body member  2  by slightly caulking the back end part  2   j  of the body member  2 . 
     It is an important feature of the present invention that the gaps between the coils of the coil spring  4  in an unloaded state are smaller than the diameter of the spring wire forming the coil spring  4 . More concretely, the diameter of the spring wire forming the coil spring  4  is in the range of 0.1 to 0.2 mm, and the pitches of the coils of the coil spring  4  is in the range of 1.5 to 1.9 times the diameter of the spring wire. The coil spring is held behind the ball  3  in the body member  2  by holding its large back end  4   b  by the caulked back end part  2   j  of the body member. Since the coil spring  4  has the large back end  4   b  of the outside diameter greater than that of the effective coils of the coil spring  4 , coils springs  4  can be automatically arranged in the same direction. 
     FIG. 6 is a longitudinal sectional view of a ballpoint refill provided with the ballpoint tip  1 . The ballpoint refill has a liquid container  5  containing a gel ink. The ballpoint tip  1  is pressed in a reduced forward part  5   a  of the liquid container  5 . 
     The liquid container  5  has an open back end. An end plug  6  provided with a vent hole  6   a  is fitted in the back end part of the liquid container  5 . A reverse flow preventing member  7  made of polybutylene or the like is inserted in the liquid container  5  so as to be in contact with the back end surface of the ink filled in the liquid container  5  to prevent the reverse flow of the ink. As the ink is consumed, the back end surface of the ink moves forward and the reverse flow preventing member  7  moves forward together with the back end surface of the ink to prevent the reverse flow of the ink. 
     FIG. 7 is a longitudinal sectional view of a push-button ballpoint pen formed by inserting the ballpoint refill shown in FIG. 6 in a barrel  8 . As shown in FIG. 7, the ballpoint refill is urged backward by a return spring  9  compressed between a shoulder  8   a  formed in the inner circumference of a forward end part of the barrel  8  and a shoulder  5   b  provided at the liquid container  5 . 
     When using the ballpoint pen, a push-button  11  is pressed to advance the ballpoint refill against the resilience of the return spring  9 . Then the forward end part of the ballpoint tip  3  projects from the open forward end of the barrel  8 . In this state, a stopping projection  10   a  formed in the back surface of a clip  10  engages with a stopping projection  8   b  formed on the outer surface of the barrel  8  to hold the ballpoint refill in a writing state. 
     When retracting the ballpoint refill into the barrel  8 , a back end part of the clip  10  is depressed or a front end part of the clip  10  is separated from the barrel  8 . Consequently, the stopping projection  10   a  is disengaged from the stopping projection  8   b  of the push-button  11  and the ballpoint refill is returned to its original position by the return spring  9 , and the tip of the ballpoint chip  1  is retracted into the barrel  8 . 
     When assembling ballpoint tips similar to the foregoing ballpoint tips  1  for the ballpoint liquid container, a plurality of body members  2  each having a caulked tip part  2   i  holding a ball  3  are set in a vertical position on a turntable, the turntable is turned to set the body members  2  successively at a spring feed position, coil springs  4  suspended in a vertical position with their large end part  4   b  on the upper side are inserted in the body members  2  successively at the spring feed position, and the back end parts  2   j  of the body members are caulked successively to complete ballpoint tips  1 . Thus the ball point tips  1  can be easily automatically assembled. 
     As apparent from the foregoing description, the ballpoint tip according to the present invention is provided with the coil spring  4  serving as both the spring  16  for indirectly pressing the ball  11 , and the movable pin  15  in contact with the ball  11  of the prior art ballpoint tip  12 , the coil spring is formed so that gaps between the coils of the coil spring in an unloaded state is smaller than the diameter of the spring wire forming the coil spring to prevent entangling coil springs with each other, and the spring wire is coiled in end coils to form the end part of the coil spring to be held in the caulked back end part of the body member of the ballpoint tip in an outside diameter greater than that of effective coils of the coil spring so that coil springs can be suspended in the same position to enable the use of an automatic assembling machine for assembling ballpoint tip for mass production. 
     According to the present invention, in the push-button type or a cap type ballpoint writing implement using an ink having a viscosity in the range of a low viscosity of 3.5 Cps to a high viscosity of 5,000 Cps at 20° C., the coil spring is held in the body member by caulking the back end part of the body member so as to press the ball against the inner surface of the tip part of the forward end part of the body member, so that the leakage of the ink while the writing implement is not in use can be prevented and the ink around the ball is prevented from drying up. 
     Although the invention has been described in its preferred form with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof.