Ballpoint pen tip, manufacturing method therefor, and ballpoint pen using the same

A ballpoint pen tip including a metallic pipe having a plurality of inwardly projecting portions at a neighborhood of a front end portion of the pipe at regular intervals, and a front end edge portion at a front end of the pipe, and a ball rotatably held between the front end edge portion and the plurality of inwardly projecting portions, wherein the pipe satisfies a relation of A/T.ltoreq.5.8 where A is an outer diameter of the ball and T is a thickness 10 of the pipe, and also the relation of B/T.ltoreq.2.3 where B is a diameter of a virtual inscribing circle contacting a top of the plurality of inwardly projecting portions and T is the same as above.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a ballpoint pen tip, manufacturing method 
therefor and ballpoint pen using it. More specifically, the present 
invention relates to a ballpoint pen tip rotatably holding a ball at the 
front end thereof by a plurality of inwardly projecting portions for a 
ball receiving seat which is formed by inwardly compressing and deforming 
the periphery of a neighborhood of the front end of a metallic pipe and a 
front end edge portion which is formed by inwardly compressing and 
deforming the front end of the pipe, a manufacturing method and a 
ballpoint pen using it. 
2. Description of the Related Art 
U.S. Pat. No. 4,457,644 discloses a conventional ballpoint pen tip 
rotatably holding a ball at the front end thereof by a plurality of 
inwardly projecting portions for a ball receiving seat which is formed by 
inwardly compressing and deforming the periphery of the neighborhood of 
the front end of a metallic pipe and a front end edge portion which is 
formed by inwardly compressing and deforming the front end of the pipe. 
However, this conventional ballpoint pen tip does not take into account the 
thickness of the metallic pipe. Namely, the thickness of the pipe with 
respect to the ball size is set to be relatively thin so that the side of 
the metallic pipe can be easily compressed and deformed. Accordingly, a 
ball receiving seat does not have a sufficient strength due to the 
thinness of the inwardly projecting portion. During writing, since the 
ball receiving seat can not support the ball when a strong writing force 
is applied, it may be spread outwardly by the ball. Therefore, the ball 
bites at the ball receiving portion, thereby preventing its smooth 
rotation, and the ball gradually falls into the pipe, thereby losing a 
stable and smooth writing feeling. The smaller the ball size is, the more 
this phenomenon occurs. 
Further, the top portion of the inwardly projecting portion of the 
conventional ballpoint pen tip has a relatively small radius of curvature. 
Accordingly, the surface of the top portion of the inwardly projecting 
portion is easily cracked by the compressing and deforming. Therefore, the 
cracking gives a user an unpleasant feeling with the ball rotation during 
writing. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a ballpoint pen tip 
having a strong ball receiving seat, and giving a user a smooth writing 
feeling for a long time without cracking the ball receiving seat, and a 
ballpoint pen using it. 
A ballpoint pen tip of the present invention is comprised of a metallic 
pipe having a plurality of inwardly projecting portions for a ball 
receiving seat which are formed by inwardly deforming a neighborhood of a 
front end portion of the pipe at regular intervals, and a front end edge 
portion which is formed by inwardly deforming a front end of the pipe; and 
a ball which is rotatably held between the front end edge portion and the 
plurality of inwardly projecting portions; wherein the pipe satisfies a 
relation of A/T.ltoreq.5.8 where A is an outer diameter of the ball and T 
is a thickness of the pipe. 
Accordingly, such a ballpoint pen tip satisfies the above relation, namely, 
that ratio is smaller than that of the conventional ballpoint pen tip, so 
as to obtain the ball receiving seat having sufficient strength 
corresponding to the size of the ball. Therefore, the smooth and stable 
writing can be maintained for a long time. In addition, the value of A/T 
is preferably equal to or more than 2.5. If it is less than 2.5, the 
thickness of the pipe is much thicker than the outer diameter of the ball, 
such that it is difficult to deform the pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1, 2 and 3 show a ballpoint pen tip 1 of the present invention having 
three inwardly projecting portions 3. 
FIGS. 4 and 5 shows the ballpoint pen tip 1 of the present invention having 
four inwardly projecting portions 3. Table 1 shows sizes of respective 
portions on which symbols are put down in these drawings. As shown in 
table I, five balls 5 having an outer diameter A of 0.3 mm, 0.4 mm, 0.5 
mm, 0.7 mm and 1.0 mm respectively are used in this embodiment, and 
further, suitable ranges for the respective ball diameter of a pipe 
thickness T and a diameter B of a virtual inscribing circle inscribing at 
a top point of the inwardly projecting portion 3 are indicated. Here, the 
pipe thickness T is not a thickness of the inwardly projecting portion 3 
or a front end edge portion 4 where its thickness is changed by 
compressing and deforming, but is that of a front end portion of a pipe 2 
(that of a neighborhood of the inwardly projection portion 3) where is not 
compressed and deformed, or an average thickness of the front end portion 
of the pipe 2 before forming the inwardly projecting portion 3. 
TABLE I 
______________________________________ 
A (mm) T (mm) A/T B (mm) B/T 
______________________________________ 
0.3 0.08-0.10 
3.0-3.8 0.11-0.15 
1.1-1.9 
0.4 0.10-0.12 
3.3-4.0 0.12-0.16 
1.0-1.6 
0.5 0.13-0.15 
3.3-3.9 0.14-0.18 
0.9-1.2 
0.7 0.12-0.14 
5.0-5.8 0.23-0.27 
1.6-2.3 
1.0 0.18-0.21 
4.8-5.5 0.27-0.31 
1.3-1.7 
______________________________________ 
An ultra hard alloy, stainless steel, ruby, ceramic or the like is suitable 
for a material of the ball 5. A suitable material for the pipe 2 is 
stainless steel, and further austenitic stainless steel (e.g. SUS304, 
SUS305, SUS321 or the like) is more preferable. Too hard a surface of the 
stainless steel causes the pipe to crack during the compressing and 
deforming. On the other hand, if it is too soft, the pipe 2 is easily bent 
during writing. Accordingly, Vickers hardness of the surface of the pipe 2 
is set in the range of 150 to 300, preferably, 200 to 240. 
An inner diameter of the pipe 2 is set to be 0.01 to 0.05 mm larger than 
the outer diameter A of the ball. More specifically, if the outer diameter 
A of the ball is equal to or less than 0.55 mm, the inner diameter of the 
pipe 2 is approximately 0.01 to 0.03 mm larger than the outer diameter A 
of the ball. Further, if the outer diameter A of the ball is larger than 
0.55 mm, the inner diameter of the pipe 2 is approximately 0.02 to 0.05 mm 
larger than the outer diameter A of the ball. 
A method for manufacturing the ball pen tip 1 of the present invention will 
be described as follows. 
As shown in FIG. 13, under a condition where a core stick is inserted into 
the metallic pipe 102 having a longitudinal length of 12 mm and a 
substantially uniform thickness, the side wall of the metallic pipe 102 is 
plastically deformed so as to be divided into two equal parts by a 
rotating blade 103 having an included angle of Z'=130.degree.. Owing to 
the included angle of the rotating blade 103, a circular-cone-shaped taper 
surface 41 having a Z angle of 50.degree. at the end portion of the each 
pipe 2 as shown in FIG. 1. The Z angle is preferable in the range of 
45.degree. to 75.degree.. The included angle of the rotating blade for 
manufacturing it is set to an angle of (180-Z).degree.. 
Next, as shown in FIG. 14A, a steepled guide pin 105 having a steeple angle 
(Y=98.degree.) which is fixed to a collet chuck 104 is inserted into an 
opening 106 in the side of the taper surface of the pipe 2 having a 
longitudinal length of about 6 mm so that a guide pin base 105' is 
attached to the end of the pipe 2. Then, as show in FIG. 14B, the front 
end portion of the pipe 2 is put between and compressed by the guide pin 
105 and a punch 107 having a steeple angle (X=82.degree.) and a radius of 
curvature R less than 0.03 mm so that the punch 107 compresses to deform 
the front end portion inwardly (vertical to an axis line) at regular 
intervals in three or four directions to form the inwardly projecting 
portions 3. At this time, as shown in FIG. 1, a coned concave portion 32 
(angle X: 82.degree.) is formed at the outside of the inwardly projecting 
portion 3 and a ball receiving seat 31 having a coned concave portion 
(angle Y: 98.degree.) is formed at an convex portion in the inside of the 
inwardly projecting portion 3. 
Finally, as shown in FIG. 14C, the ball 5 is accommodated in the front of 
the ball receiving seats 31, and the front end edge portion 4 of the pipe 
2 is compressed and deformed inwardly by a crimping jig 108 including a 
coned concave surface having an inclined angle of substantially 90.degree. 
so as to obtain the ballpoint pen tip 1 rotatably holding the ball 5. 
In addition, in the above manufacturing method, the ratio of the diameter A 
of the ball to the thickness T of the pipe T (A/T) is equal to or less 
than 5.8 (preferably, in the range of 2.5 to 5.8), and/or that of the 
diameter B of a virtual inscribing circle inscribing at a top point of the 
inwardly projecting portion 3 to the thickness T of the pipe (B/T) is 
equal to or less than 2.3 (preferably, in the range of 0.5 to 2.3). 
Accordingly, the ball receiving seat 31 and the front end edge portion 4 
having a sufficient strength against the deformation by writing force can 
be formed easily. 
Especially, if the number of the inwardly projecting portion 3 is three and 
the outer diameter A of the ball is equal to or less than 0.55 mm 
(specifically, in the range of 0.25 mm to 0.55 mm, preferably, in the 
range of 0.25 mm to 0.45 mm), the thickness T of the pipe is preferable to 
satisfy the relations of 2.5.ltoreq.A/T.ltoreq.4.5 and 
0.5.ltoreq.B/T.ltoreq.2.0. On the other hand, if the number of the 
inwardly projecting portio 3 is four and the outer diameter A of the ball 
is more than 0.55 mm (specifically, in the range of 0.55 to 1.2 mm, 
preferably, in the range of 0.6 to 1.1 mm), the thickness T of the pipe is 
preferable to satisfy the relations of 4.5.ltoreq.A/T.ltoreq.5.8 and 
1.0.ltoreq.B/T.ltoreq.2.3. 
Owing to the thickness of the pipe in the above range, the thickness T of 
the pipe is not too large compared with the outer diameter A of the ball 
and the diameter B of the virtual inscribing circle, so that a large 
compressing is not necessary force. Therefore, the ball 5 is not damaged 
when forming the front end edge portion 4, and the ball receiving seat 31 
can be easily formed without damaging the top end of the punch 107 when 
forming the concave portion 32. Further, the thickness T of the pipe is 
not too small compared to the outer diameter A of the ball and the 
diameter B of the virtual inscribing circle, thereby forming the ball 
receiving seat 31 and the front end edge portion 4 having a sufficient 
strength. 
The taper angle S of the front end of the front end edge portion (the taper 
angle of a front end reduced diameter portion) is set to substantially 
90.degree. (specifically, in the range of 85.degree. to 115.degree.). In 
addition, the taper angle is preferable to be an angle of (Z+40).degree.. 
Moreover, even if a ballpoint pen is inclined with respect to a written 
surface during writing, the exposure quantity of the ball 5 from the front 
end of the pipe 2 is in the range of 25% to 35% of the diameter A of the 
ball (preferably, in the range of 28% to 33% of the diameter A) in order 
to maintain the contact between the written surface and the ball 5 as much 
as possible. 
The angle Y of the ball receiving seat 31 is set to be in the range of 
80.degree. to 140.degree., preferably in the range of 90.degree. to 
110.degree., more preferably, in the range of 97.degree. to 99.degree.. 
The reason of this setting is that: if the angle Y is larger than 
140.degree., the top portion of the inwardly projecting portion 31 is 
cracked, thereby obtaining no smooth rotation of the ball 5, and if the 
angle Y is smaller than 80.degree., the ball 5 may bite at the ball 
receiving seat 31 during writing, thereby preventing the smooth rotation 
of the ball 5. 
On the other hand, the angle X of the concave portion 32 of the inwardly 
projecting portion 3 is set to be in the range of 40.degree. to 
100.degree., preferably in the range of 70.degree. to 90.degree., more 
preferably 80.degree. to 85.degree.. The reason of this setting is that: 
if the angle is smaller than 40.degree., the surface of the top portion of 
the inwardly projecting portion 3 is cracked, and if the angle is larger 
than 100.degree., the angle Y of the ball receiving seat 31 is made small 
so that the ball 5 may bite at the ball receiving seat 31 during writing. 
Namely, similar to the angle Y, if the angle X is outside the above range, 
the smooth rotation of the ball is prevented. 
The angles X and Y are set so that the sum of the angles X and Y is 
substantially equal to 180.degree., preferably in the range of 178.degree. 
to 182.degree.. Accordingly, the ball receiving seat 31 having a uniformly 
compressed and deformed state can be obtained. 
The concave depth d (the maximum value of the deformation) in the thickness 
direction of the ball receiving seat 31 is set to be in the range of 0 to 
0.05 mm, preferably in the range of 0.01 mm to 0.05 mm, more preferably in 
the range of 0.01 to 0.03 mm. The linear contact quantity between the ball 
5 and the ball receiving seat 31 is adjusted by the concave depth d. 
Namely, if the linear contact quantity is too large, the ink is 
insufficient to write so as to prevent the smooth rotation of the ball. 
Further, if the linear contact quantity is too small, the ball receiving 
portion 31 is severely worn away and the ball 5 gradually falls into the 
pipe 2, thereby preventing the smooth rotation of the ball due to the 
friction between the written surface and the front end of the pipe 2. 
The maximum depth D of the concave portion 32 is set to be in the range of 
0.1 mm to 0.4 mm, preferably in the range of 0.13 mm to 0.25 mm. Taking 
account of the strength of the ball receiving seat 31 to be formed, the 
maximum depth D of the concave portion 32 is in the range of one to two 
times as thick as the thickness T of the pipe. If the maximum depth D is 
extremely large, the thickness of the inwardly projecting portion 3 to be 
formed is much thinner than the thickness T of the pipe, thereby lowering 
the length of the ball receiving seat 31. 
The top portion of the inwardly projecting portion has a substantially 
spherical surface shape. A radius of curvature of the top portion is set 
to be in the range of 0.2 to 0.5 times as long as the outer diameter A of 
the ball. Accordingly, the top portion of the inwardly projecting portion 
3 within the above range is free from the cracking due to the compressing 
and deforming. 
Gaps 33 are provided between respective inwardly projecting portions 3. The 
size C of the gap 33 is set to be in the range of 0.01 mm to 0.12 mm, 
preferably in the range of 0.06 mm to 0.10 mm in which the gap has an 
appropriate capillary force. Consequently, owing to the capillary function 
of the gaps 33, the ink of the appropriate quantity corresponding to the 
consumption speed thereof is supplied to the ball 5 so that the ink always 
exists between the ball 5 and the ball receiving seat 31 to allow the 
smooth writing without broken handwriting. Further, even if the front of 
the pen is turned upward, the drop back of the ink due to the gravity can 
be prevented so that the ink is always attached to the back of the ball 5. 
Further, if the outer diameter A of the ball is equal to or smaller than 
0.55 mm, three inwardly projecting portions 3 are preferably provided at 
regular intervals. If it is larger than 0.55 mm, four inwardly projection 
portions 3 are preferably provided at regular intervals. The reason for 
this setting is that the size of the gaps 33 provided between respective 
inwardly projecting portions 3 have to be set in the range (namely, 0.01 
mm to 0.12 mm) in which the capillary force can act with respect to any 
ball size. If the outer diameter A of the ball is larger than 0.55 mm and 
the number of inwardly projecting portion 3 is not four but three, the 
maximum depth D of the concave portion 32 have to be even deeper than that 
of the concave portion 32 of the ballpoint pen tip 1 having four inwardly 
projecting portion. Consequently, the ball receiving seat 31 is extremely 
thin, thereby lowering its strength. 
FIGS. 6 to 12 show ballpoint pens to which the ballpoint pen tip 1 of the 
present invention is applied. 
FIG. 6 shows a first embodiment of the ballpoint pen or a ballpoint pen 
refill of the present invention. The ballpoint pen is produced in such a 
manner that: the ballpoint pen tip 1 of the present invention is fixed to 
the front end of a tube-shaped joint member 8 made of synthetic resin 
(e.g. polyacetal, polypropylene, polyethylene or the like) by force 
fitting; and the joint member 8 is fixed to the front end of a transparent 
or semi-transparent ink reservoir 6 formed by an extrusion molded body 
made of synthetic resin (e.g. polypropylene, polyethylene or the like) by 
force fitting. In addition, the outer periphery of the intermediate 
portion of the joint member 8 is provided with a flange 82 which attaches 
to the top end opening edge of the ink reservoir 6. 
A shear thinning aqueous ink 61 (viscosity: 10 to 150 mPa.cndot.s at 
20.degree. C. and share rate of 384 sec.sup.-1) and a viscoelastic ink 
follower are stored in the ink reservoir 6. Here, the ballpoint pen tip 
having three inwardly projecting portions 3 and the outer diameter A of 
the ballpoint pen 1 in the range of 0.25 mm to 0.55 mm, preferably in the 
range of 0.25 mm to 0.45 mm, is used so as to obtain a thin handwriting 
width suitable for writing on a pocket notebook or the like. On the other 
hand, the ballpoint pen tip having four inwardly projecting portions and 
the outer diameter A of the ballpoint pen 1 in the range of 0.55 mm to 1.2 
mm is used so as to obtain a thick handwriting width suitable for writing 
a signature or the like. 
A cylindrical ink introduce control path 21 is formed in the ballpoint pen 
tip 1 in the rear of the ball 5. Further, an inner hole 81 having a 
taper-shaped inner surface for communicating the ink introduce control 
path 21 with the ink reservoir 6 is formed in the joint member 8. 
FIG. 7 shows a second embodiment of the ballpoint pen of the present 
invention. 
A backflow prevention mechanism is provided in the inner hole 81 of the 
joint member 8. Consequently, the backflow of the ink 61 can be prevented 
even when the front of the ballpoint pen is turned upward or the ballpoint 
pen is impacted, such as if it is dropped on the floor. 
The backflow prevention mechanism includes a valve ball 811 stored in the 
inner hole 81 movable forward and backward, a regulating wall 812 
attaching to the valve ball 811 moved forward and ensuring the ink flow, 
and a valve seat 813 closely attaching to the valve ball 811 moved 
backward. The valve ball 811 is a metallic ball having an outer diameter 
slightly smaller than the inner diameter of the inner hole 81. The 
regulating wall 812 is an attaching wall having a notch or a groove which 
is integrally formed with the inner wall of the inner hole 81. The valve 
seat 813 is a tube-shaped body made of metal or synthetic resin which is 
fixed to the inner periphery wall of the inner hole 81 by force fitting. 
Remaining elements are similar to the first embodiment. 
FIGS. 8 and 9 show a third embodiment of the ballpoint pen of the present 
invention. 
These drawings show a ballpoint pen in which the ballpoint pen refill is 
accommodated in a penholder 7. The structure of the ballpoint pen refill 
is substantially similar to that of the ballpoint pen shown in FIG. 6 in 
which the ballpoint pen tip 1 is connected with the ink reservoir 6 by the 
joint member 8. The penholder 7 is made of a transparent or 
semi-transparent synthetic resin. A tapering front body 71 is engaged with 
the front end of the penholder 7. A tail plug 72 made of synthetic resin 
painted with substantially the same color as the ink is engaged with the 
rear end of the penholder 7. A convex portion 721 is formed at the front 
end of the tail plug 72 so as to compressedly attach the rear end of the 
ink reservoir 6. The front end of the ballpoint pen tip 1 projects outward 
from a front end hole 711 of the front body 71. 
The inside of the ink reservoir 6 is filled with a medium viscosity ink 61. 
The medium viscosity ink 61 is an aqueous ink having the viscosity in the 
range of 10 to 150 mPa.cndot.s, preferably in the range of 30 to 100 
mPa.cndot.s, at 20.degree. C. and the shear rate of 384 sec.sup.-1, or an 
oil ink having the viscosity in the range of 1000 to 10000 mPa.cndot.s, 
preferably in the range of 1500 to 9000 mPa.cndot.s. 
An ink follower 62 (e.g. a greasy viscoelastic ink follower, a solid 
stopper having a piston-shape made of an elastic member or the like) 
moving forward with the consumption of the ink is stored in the ink 
reservoir 6 at the rear of the ink. The ink reservoir 6 and the penholder 
7 are made of transparent or semi-transparent synthetic resin so as to 
easily confirm the consumption state of the ink from the outside. 
FIG. 9 is an enlarged view of the main portion of FIG. 8. The joint member 
8 is a tube-shaped body made of synthetic resin (e.g. polyacetal, 
polypropylene, polyethylene or the like) molded by the injection molding. 
The flange 82 is integrally provided on the outer periphery of the joint 
member 8. A mounting tube portion 83 is provided at the rear of the flange 
82, which is compressedly inserted into the front end opening portion of 
the ink reservoir 6. In addition, a supporting tube portion 84 is provided 
at the front of the flange 82, which is compressedly attached to the inner 
wall of the front end hole 711. Further, the ballpoint pen tip 1 is fixed 
to the front end of the joint member 8. Still further, a metallic cover 
member 85 is engaged with the outer periphery of the fixing portion. The 
swinging or falling of the ballpoint pen tip during writing can be 
prevented by the cover member 85. 
The front end of the flange 82 is compressedly attached to a tapering inner 
surface 712 of the front body 71. The rear end of the flange 82 is closely 
attached to the top end edge of the ink reservoir 6 so as to still prevent 
the leak of the ink as well as attached to the front end edge of the 
penholder 7. That is, the flange 82 is put between the tapering inner 
surface 712 of the front body 71 and the front end edge of the penholder 7 
and held by them. 
The inner hole 81 having the tapering inner surface whose diameter is 
reduced from the rear portion to the front portion is provided in the 
inside of the joint member 8. The inner hole 81 is communicated with the 
hollow and straight ink introduce control path 21 in the ballpoint pen tip 
1. 
The ink introduce control path 21 at the rear of the inwardly projecting 
portion 3 of the ballpoint pen tip 1 is set in accordance with the 
longitudinal size and the inner diameter of the metallic pipe 2 to be 
applied. Although the preferable length of the pipe 2 is in the range of 3 
mm to 10 mm, it is set to about 6 mm in this embodiment. The inner 
diameter E of the pipe is set to be 0.01 mm to 0.05 mm larger than the 
outer diameter A of the ball. More specifically, if the outer diameter A 
of the ball is smaller than 0.55 mm, the inner diameter E is preferably 
set to be 0.01 mm to 0.03 mm larger than the outer diameter A of the ball. 
On the other hand, if the outer diameter A of the ball is larger than 0.55 
mm, the inner diameter E is preferably set to be 0.02 mm to 0.05 mm larger 
than the outer diameter A of the ball. When these diameters are set within 
the above ranges respectively, the ink introduce control path 21 prevents 
the excess flowing of the ink and works to fulfil its sufficient function 
to prevent a break in handwriting due to the insufficient ink. 
Here, it is preferable to use the medium viscosity ink 61 being an aqueous 
ink having the viscosity in the range of 10 to 150 mPa.cndot.s at 
20.degree. C. and the shear rate of 384 sec.sup.-1. 
In the ballpoint pen to which the above shear thinning aqueous ink 61 is 
applied, the ink 61 stored in the ink reservoir 6 is introduced to the ink 
introduce control path 21 via the inner hole 81 of the joint member 8. The 
ink is maintained to be in the medium viscosity state (gel state) in the 
ink introduce control path 21. On the other hand, the viscosity of the ink 
61 positioned at the neighborhood of the front end of the ink introduce 
control path 21 is decreased by the shearing stress due to the rotation of 
the ball 5 during writing so that the ink 61 is discharged with fitting to 
the ball 5. The ink introduce control path 21 acts for adjusting the ink 
discharging quantity, namely, it adjusts the ink discharging quantity to 
be in an appropriate range for writing without the excess or insufficient 
ink flow. 
Further, in the ballpoint pen to which the above shear thinning aqueous ink 
61 is applied, the gaps 33 having the capillary force formed between 
respective inwardly projecting portions 3 is provided at the back of the 
ball 5. The size C of the gap is in the range of 0.01 mm to 0.12 mm, 
preferably in the range of 0.06 to 0.1 mm. Owing to the capillary force of 
the gaps 33, the appropriate ink corresponding to its consumption speed 
can be supplied from the ink introduce control path 21 to the back of the 
ball 5. The cooperation function of the ink introduce control path 21 and 
the gaps 33 cause a discharge of the appropriate amount of ink without 
breaks. Further, even if the ballpoint pen is turned upward, such a 
cooperation function prevents the backflow of the ink 61 due to the 
gravity so that the ink 61 is always attached to the back of the ball 5. 
Preferably, the ink introduce control path 21 has a thin inner diameter. 
Accordingly, the outer diameter A of the ball has to be smaller than 0.55 
mm, preferably smaller than 0.45 mm (e.g. 0.3 mm, 0.4 mm or the like). 
In the ballpoint pen to which the above shear thinning aqueous ink 61 is 
applied, it is preferable to form the ball receiving seat 31 having the 
coned concave portion at the front of the inwardly projecting portion 3. 
The ball receiving seat 31 contacts linearly with the ball 5. Therefore, 
the ballpoint pen tip of the present invention has no disadvantages such 
as the insufficiency of the ink or the friction of the ball receiving seat 
31 which is caused by the conventional contact in a plane or point. 
Therefore, sufficient ink is always supplied between the ball receiving 
seat 31 and the ball 5 during writing. Namely, the sufficient ink contacts 
the back of the ball 5 so as to apply the appropriate shearing stress to 
the ink 61. As a result of this, it is possible to write smoothly with the 
ballpoint pen of the present invention, without handwriting breaks. 
Further, the above described ballpoint pen with the viscosity of the medium 
viscosity ink in the range of 10 to 150 mPa.cndot.s, preferably in the 
range of 30 to 100 mPa.cndot.s, at 20.degree. C. and the shear rate of 384 
sec.sup.-1 allows the writer to smoothly and appropriately discharge the 
ink. If the viscosity of the medium viscosity ink is smaller than the 
above range, it is difficult for the ink 61 to be held in the ballpoint 
pen tip (especially, in the ink introduce control path 21), thereby 
causing the dropping of the ink. On the other hand, if it is larger than 
the above range, the ink 61 does not smoothly flow in the ballpoint pen 
tip 1, thereby causing the handwriting break. 
FIG. 10 shows a fourth embodiment of the ballpoint pen of the present 
invention, which is an application example of the first embodiment (FIG. 
6). 
This drawing shows the ballpoint pen or ballpoint pen refill in which the 
ballpoint pen tip 1 of the present invention is fixed to the front end of 
the joint member 8 made of synthetic resin (e.g. polyacetal, polypropylene 
or the like), and the joint member 8 is compressedly inserted into the 
front end of the ink reservoir 6 made of synthetic resin (e.g. 
polypropylene, polyethylene or the like) molded by an injection or an 
extrusion molding. The ink reservoir 6 is filled with the oil ink 61 
having a low or medium viscosity in the range of 1000 to 10000 
mPa.cndot.s, at 20.degree. C., preferably in the range of 1500 to 9000 
mPa.cndot.s, and stores the greasy ink follower 62 which moves forward 
with the ink consumption. 
The ballpoint pen tip 1 includes the metallic pipe 2 having a rear portion 
(outer diameter: 0.65 mm, inner diameter: 0.42 mm) and a front end small 
diameter portion 22 (outer diameter: 0.5 mm, inner diameter: 0.32 mm). The 
ball 5 having the outer diameter of 0.3 mm is rotatably held at the front 
end of the ballpoint pen tip 1. The longitudinal length of the front end 
small diameter portion 22 is set to be one to three times as long as the 
outer diameter A of the ball. The shape of the ink introduce control path 
21 corresponds to the pipe 2. In addition to this shape, that of the ink 
introduce control path 21 may have a tapering shape in which the diameter 
is reduced toward the front end. The shape of the ink introduce control 
path 21 must be suitable for the viscosity (fluidity) of the ink. 
Accordingly, the ink discharge quantity without the excess flow of ink and 
the handwriting break can be surely adjusted. Here, the thickness T of the 
pipe is the thickness of the front end small diameter portion 22. 
The inner hole 81 of the joint member 8 is provided with the backflow 
prevention mechanism. Consequently, the ink 61 can be surely prevented 
from backflowing when the top of the ballpoint pen is turned upward or the 
ballpoint pen is falls on the floor to cause a shock to the pen. 
The backflow prevention mechanism includes the valve ball 811 movable 
forward and backward stored in the inner hole 81, the regulating wall 812 
attaching to the valve ball 811 moved forward and ensuring the ink flow, 
and the valve seat 813 closely attached to the valve ball 811 moved 
backward. The valve ball 811 is a metallic ball having the outer diameter 
slightly smaller than the inner diameter of the inner hole 81. The 
regulating wall 812 has four ribs which are integrally formed with the 
inner wall of the inner hole 81. The valve seat 813 is an annular body 
made of synthetic resin or metal having the coned concave surface, and is 
fixed in the inner hole 81 by force fitting. 
FIG. 11 shows a fifth embodiment of the ballpoint pen of the present 
invention. 
A direct liquid type aqueous ink ballpoint pen is shown in FIG. 11, which 
includes the joint member 8 made of synthetic resin having a front end to 
which the ballpoint pen tip 1 of the present invention is fixed, an ink 
holding member 9 having a front end to which the joint member 8 is fixed, 
and the penholder 7 having a front portion to which the ink holding member 
9 is mounted and forming an ink tank 73 for storing a raw ink (low 
viscosity aqueous ink) at the rear portion thereof. 
The ink holding member 9 temporarily holds an overflowed ink corresponding 
to the pressure change in the ink tank 73. The ink holding member 9 
includes comb teeth 92, slit-shaped ink groove 93, an air exchange concave 
groove 94 and a center hole 95 which are formed integrally by synthetic 
resin (e.g. ABS resin). The plurality of comb teeth form a plurality of 
ink holding grooves 91 at the periphery surface of the ink holding member 
9. The slit-shaped ink groove 93 is provided at the comb teeth in the 
axial direction and communicates with the ink holding groove 91. The air 
exchange concave groove 94 is provided at the comb teeth 92 opposing the 
slit-shaped ink groove 93. 
An ink guide core 96 formed by the extrusion molded body made of synthetic 
resin is inserted and fixed in the center hole 95. The ink guide core 96 
includes an ink introduce path having the capillary force in the axial 
direction at the outer or inner periphery surface itself. The front end of 
the ink guide core 96 is stuck into an ink relaying member 86 which is 
accommodated in the rear portion of the joint member 8. The ink relaying 
member is made of a porous material body or a fiber worked body. In 
addition, a stick-shaped body 87 connected to the front end of the ink 
relaying member 86 for supplying the ink to the back of the ball 5 is 
provided in the pipe 2 of the ballpoint pen tip 1. The gap having the 
capillary force is formed between the stickshaped body 87 and the inner 
periphery surface of the pipe 2. Accordingly, the aqueous ink is smoothly 
guided to the back of the ball 5. It may be preferable that a slit having 
the capillary force for introducing the ink is provided on the outer 
periphery of the stick-shaped body 8. 
FIG. 12 shows a sixth embodiment of the ballpoint pen of the present 
invention. 
An aqueous ink ballpoint pen is shown in FIG. 12, in which the joint member 
8 made of synthetic resin having the ballpoint pen tip 1 of the present 
invention at the front end thereof is inserted into and fixed to the front 
end of the penholder 7. An ink impregnation body 74 made of the porous 
material body or the fiber worked body, with which the low viscosity 
aqueous ink is impregnated, is accommodated in the penholder 7. The ink 
impregnation body 74 is put between an attaching rib 76 provided on the 
inner wall of the penholder 7 and the tail plug 72 engaged with the 
opening portion of the rear end of the penholder 7, and held and fixed by 
them. 
In addition, the ink relaying member 86 connected to the ink impregnation 
body 74 is mounted in the inside of the joint member 8. The ink relay 
member 86 is made of the porous material body or the fiber worked body. 
The stick-shaped body 87 made of synthetic resin is provided in the pipe 2 
of the ballpoint pen tip 1, which is connected to the front end of the ink 
relaying member 86 to supply the ink to the back of the ball 5. The 
stick-shaped body 87 is a synthetic resin molded body having an ink 
introducing slit at the outer periphery thereof, a fiber collected worked 
body or the like. An air hole 75 for communicating the inside of the 
penholder 7 with the outside is provided in the front of the penholder 7. 
Further, in addition to the low viscosity ink, or the low or medium 
viscosity oil ink, the ballpoint pen tip of the present invention can be 
applied to a high viscosity painting or applying material such as an 
adhesive, a cosmetic liquid, an ink erasing liquid or the like.