Ball for ball-point pen

Details Ball for ball-point pen Ball for ball-point pen

1999-12-03

2001-12-25

Walczak, David J. (Department: 3751)

Coating implements with material supply

Including ball, roller or endless-belt tool

Ball

Reexamination Certificate

active

06332728

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to balls for a ball-point pen which are to be fitted in a pen tip of the ball-point pen.
2. Description of the Related Art
A pen tip of a gel-ink ball-point pen typically has a construction as shown in FIG.
7
. In
FIG. 7
, a pen tip body
10
has a hollow inside portion and a tapered tip portion provided at a front end thereof, and a writing ball (hereinafter referred to simply as “ball”)
11
is rotatably fitted in the tip portion. An ink reservoir tube (not shown) is connected to a rear end of the ball tip body
10
, so that ink is supplied to the hollow inside portion from the ink reservoir tube and then to the ball
11
through an ink flow path
12
.
More specifically, the tip portion of the pen tip has a ball socket
13
communicating with the ink flow path
12
, and the ball
11
is rotatably retained in the ball socket
13
by a crimped rim
14
provided at an opening of the ball socket
13
as shown in FIG.
8
. The ball socket
13
has a concavely tapered innermost surface
15
, on which five ink channels
16
are radially provided as shown in
FIG. 9
to ensure a sufficient ink flow.
When a line is to be written on a paper surface
22
with the ball-point pen having the above pen tip, the ball
11
provided at the pen tip is pressed against the paper surface
22
with the pen tip tilted with respect to the paper surface
22
as shown in FIG.
10
. At this time, the ball
11
is displaced diagonally upward (in an arrow direction B as seen in
FIG. 10
) within the ball socket
13
. The ink is introduced into the ball socket
13
from the hollow inside portion of the pen tip body
10
through the ink flow path
12
and the ink channels
16
, and flows out through a gap between a wall surface of the ball socket
13
and the ball
11
(in an arrow direction C as seen in
FIG. 10
) by gravity. While the ball
11
is rolled across the paper surface
22
, the ink flows through the surface of the ball
11
to be laid down on the paper surface
22
for the writing.
Typically used as a material for the ball
11
is a cemented carbide. For formation of the ball
11
, the cemented carbide is shaped into a spherical body, which is then polished. More specifically, a cemented carbide obtained by sintering a mixture of particles
17
of a hard intermetallic compound such as WC and a binder metal
18
such as Co is shaped into a spherical body, and a surface
19
of the spherical body is mirror-finished by polishing.
In the case of the aforesaid conventional ball
11
, however, gaps between the hard intermetallic compound particles
17
are filled with the binder metal
18
, so that minute fragments of the hard intermetallic compound are exposed from binder metal portions
18
on the surface
19
of the ball
11
after the ball surface
19
is mirror-finished. During use of the ball-point pen, the binder metal portions
18
are abraded, and the minute fragments
20
fall off as shown in FIG.
12
. The minute fragments
20
having thus fallen off act as an abrasive thereby to abrade the pen tip body
10
.
As the soft binder metal portions
18
between the hard intermetallic compound particles
17
are abraded, edges
21
of the hard intermetallic compound particles
17
are exposed on the polished ball surface. When the ball
11
having the edges
21
of the hard intermetallic compound particles
17
exposed on its surface is rotated with a writing pressure being applied thereto, the edges
21
have a cutter-like action on the pen tip body
10
, so that the tapered surface
15
of the ball socket
13
of the pen tip body
10
is abraded thereby to cause the ball
11
to sink into the pen tip body
10
as shown in FIG.
13
.
The abrasion of the tapered surface
15
of the pen tip body
10
causes the ink channels
16
to clog, thereby reducing the ink flow. Further, a friction resistance between the ball
11
and the pen tip body
10
is increased with a greater contact surface therebetween, so that the ball
11
cannot smoothly be rotated. Moreover, the sinkage of the ball
11
into the pen tip body
10
causes the crimped rim
14
of the pen tip body
10
to abut against the paper surface unless the pen is oriented at a greater angle with respect to the paper surface. This results in skipping or thinning of written lines. That is, the angle of the pen with respect to the paper surface
22
which ensures smooth writing (writing permissible angle) becomes greater. With a greater writing permissible angle, the displacement of the ball
11
in the writing (movement of the ball
11
in the arrow direction B as seen in
FIG. 10
) is reduced, whereby the gap between the wall surface of the ball socket
13
and the ball
11
through which the ink flows out is narrowed to further reduce the ink flow. With the conventional ball
11
, therefore, the pen tip body is abraded at an early stage of use of the ball-point pen, so that writing irregularities such as skipping or thinning of written lines and deterioration of writing feeling occur earlier.
In view of the foregoing, it is an object of the present invention to provide a ball for a ball-point pen which can alleviate the abrasion of the pen tip body to ensure a satisfactory writing feeling for an extended period.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention to attain the aforesaid object, there is provided a ball for a ball-point pen, which is composed of a sintered material obtained by sintering hard particles, and having an average inter-particle distance of not greater than 0.2 &mgr;m.
In accordance with a second aspect of the present invention, there is provided a ball for a ball-point pen, which is composed of a sintered material obtained by sintering a mixture of hard particles and a binder metal, and having a Vickers hardness of not lower than Hv 1800.
In accordance with a third aspect of the present invention, there is provided a ball for a ball-point pen, which is composed of a sintered material obtained by sintering a mixture of hard particles and a binder metal, wherein the binder metal is present in the sintered material in a proportion of not greater than 10 wt %, based on a total weight of elements in the sintered material each having an atomic weight not smaller than the atomic weight of sodium.
In the case of the ball according to the first aspect of the present invention, the average inter-particle distance is not greater than 0.2 &mgr;m, which is smaller than in the prior art. Therefore, gaps between the hard particles are very small, so that the size and number of minute fragments exposed from binder metal portions on the surface of the ball are correspondingly reduced. Therefore, the number of minute fragments which may fall off to act as an abrasive during use of the ball-point pen can be reduced, whereby the abrasion of the pen tip body and hence the sinkage of the ball into the pen tip body can be prevented.
Even though the ball is composed of the sintered material obtained by sintering the hard particles alone without a binder metal, the average inter-particle distance is small. Therefore, few particle edges which have a cutter-like action on the pen tip body are present on the ball surface, so that the abrasion of the pen tip body and hence the sinkage of the ball into the pen tip body can be prevented.
Thus, the problems associated with the prior art, i.e., the reduction in the ink flow due to the clogging of the ink channels and the increase in the friction resistance between the ball and the pen tip body due to a greater contact surface therebetween, can be prevented. Further, the increase in the writing permissible angle is suppressed. Accordingly, the deterioration of the writing feeling at an early stage of use of the ball-point pen can be prevented, so that a satisfactory writing feeling can be ensured for an extended period. Since the abrasion of the pen tip body can be suppressed, a ball-point pen with a fine point can be provided by reducing the diameter of the ball.
In the case of t

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