TECHNICAL FIELD
The present invention relates to a push-button writing
instrument according to the first part of claim 1 (JP-A-6 328 891).
A generally known push-button writing instrument is provided
with a refill operating mechanism having a spring biasing a refill slidably inserted
in a barrel toward the back of the barrel, and a push-button which is operated to
project a writing tip attached to the front end of the refill from an open front
end of the barrel and to retract the same behind the open front end of the barrel.
When the push-button writing instrument is held in place
in a pocket, it sometimes occurs that the push-button is pushed unintentionally
by hand and so on and the writing tip is projected accidentally from the front end
part of the barrel. If the writing instrument uses an ink, such as a water-based
ink of a low viscosity or an oil-based ink of a viscosity not higher than 3,000mPa
· s at 25 °C, the ink will exude from the writing instrument and the pocket
will be stained with the ink.
Recently, there have been provided various writing instruments
including push-button writing instruments and using a thixotropic ink generally
called a gel ink having a high viscosity when left standing and have a low viscosity
when stirred e.g. by a rolling ball for writing. The thixotropic ink is contained
in a refill without using any ink absorbing wadding which is used for holding a
water-based ink. Therefore, if the writing tip part of the push-button writing instrument
provided with a refill containing a thixotropic ink is projected accidentally from
the front end part of the barrel, and a ball held on the writing tip part is rolled
by being rubbed with the fabric of a pocket, the viscosity of the thixotropic ink
decreases, and a large amount of the thixotropic ink infiltrates the fabric or is
absorbed by the fabric by the capillary action of the fabric.
Accordingly, a push-button writing instrument provided
with a refill containing a low-viscosity ink or a thixotropic ink is provided with
a safety mechanism capable of preventing the writing tip part of the refill from
projecting out of the open front end of the barrel even if the push-button is operated
accidentally at least when the push-button writing instrument is inserted and held
in a pocket.
However, the push-button writing instrument provided with
such a safety mechanism in addition to the refill operating mechanism has a complicated
mechanism, and needs additional parts. Therefore, it is difficult to employ such
a safety mechanism in a low-price push-button writing instrument in view of problems
in manufacture.
In view of such problems, the inventors of the present
invention made studies to provide a push-button writing instrument provided with
a refill operating mechanism analogous to the conventional refill operating mechanism,
and capable of preventing a writing tip part of the refill from being projected
out of the open front end of a barrel when a force on a touching level is applied
to the push-button. The inventors found through the studies that the pressure necessary
for operating the refill operating mechanisms of the conventional push-button writing
instruments is in the range of 200 to 300 grams and the accidental projection of
the writing tip part of the refill from the open front end of the barrel by an inadvertent
touch to the push-button can be avoided by increasing the pressure necessary for
operating the refill to project the writing tip part of the refill from the open
front end of the barrel, and have made the present invention.
DISCLOSURE OF THE INVENTION
To achieve the foregoing object, the present invention
provides a push-button writing instrument comprising the features of claim 1. Thus,
the writing instrument has a push-button operating pressure for pushing the push-button
against the biasing force of the spring in a range of 500 to 800 grams.
Typically, the writing ink is a thixotropic ink.
According to the present invention , the distance between
the open front end of the barrel and the tip of the writing tip part when the writing
tip part is retracted into the barrel is in a range of 2 to 5 mm, whereas the distance
in the conventional push-button writing instrument is on the order of 1 mm. Therefore,
the writing tip part of the refill of the push-button writing instrument of the
present invention cannot inadvertently and easily be projected from the open front
end of the barrel because of the above distance of 2 to 5 mm, even if a relatively
high pressure is applied to the push-button with the hand. The distance greater
than 5 mm is not desirable in view of operability.
According to the present invention, the term, push-button
operating pressure, signifies a pressure to be applied with a finger to the push-button
necessary for holding the writing tip part of the refill projected from the open
front end of the barrel and is the sum of a pressure necessary for compressing the
spring biasing the refill having the writing tip part toward the back end of the
barrel, and frictional forces acting between the parts of the refill operating mechanism
when the push-button is pushed. Since the push-button operating pressure is greatly
dependent on the resilience of the spring, practically, the push-button operating
pressure may be determined by selectively determining the resilience of the spring.
The push-button operating pressure is measured by a push-pull scale. The push-button
operating pressure is a maximum pressure required to hold the writing tip part projected
from the barrel when the push-button is pressed by an attachment having a flat tip
and attached to an end of a pressing rod of the push-pull scale.
There is the possibility that the writing tip part is projected
when the push-button is touched with the hand if the push-button operating pressure
is lower than 500 grams. The push-button operating pressure exceeding 800 grams
is excessively high, makes the operation of the push-button difficult and tends
to scatter the ink by shocks that may be caused by the spring when the writing tip
part is retracted into the barrel. Therefore, it is important that the push-button
operating pressure is in the range of 500 to 800 grams.
Refill operating mechanisms employed in conventional push-button
writing instruments include those of a rotating cam type, those of a projection-and-hole
type and those of a heart grooved cam type. The present invention may employ a refill
operating mechanism of any one of those types. and there is no particular restriction
on the type of the refill operating mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
- Fig. 1 is a longitudinal sectional view of a push-button writing instrument
in a preferred embodiment of the present invention in a state where a writing tip
part is retracted into a barrel;
- Fig. 2 is a longitudinal sectional view of the push-button writing instrument
shown in Fig. 1 in a state where the writing tip part is projected from the front
end of the barrel;
- Fig. 3 is a sectional view taken on line III-III in Fig. 1; and
- Figs. 4 to 6 are diagrammatic views of assistance in explaining sequential operations
of a cam when a push-button is operated.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to Fig. 1, a push-button writing instrument 1
has a barrel 2, and a refill 5 slidably inserted in the barrel 2. The refill 5 contains
a thixotropic ink, not shown. The thixotropic ink is filled directly in the refill
5. The refill 5 has a writing tip part 4 having a ball-point tip 3. The refill 5
is biased toward the back end of the barrel 2 by a coil spring 6. A known refill
operating mechanism 10 is disposed behind the refill 5. A clip 9 is formed in a
back end part of the barrel 2.
The refill operating mechanism 10 of a known construction
comprises a push-button 7 inserted through an open rear end in the barrel 2 and
partly projecting outside from the back end of the barrel 2, an annular cam portion
7a formed in a front end part of the push-button 7, a rotating cam 8 to be turned
by the action of the cam 7a, and a grooved cam 11 formed in the inner surface of
the barrel 2.
Figs. 3 to 6 shows the relation between the rotating cam
8 and the grooved cam 11. The rotating cam 8 is provided on its outer surface with
a plurality of longitudinal ridges 8a. Normally, the longitudinal ridges 8a are
slidably inserted in longitudinal grooves 11a of the grooved cam 11. A sawtooth
cam 11b is formed in the front end of the grooved cam 11. The annular cam 7a of
the push-button 7 is formed by arranging a plurality of triangular projections in
a circle.
As is generally known, the rotating cam 8 advances when
the push-button 7 is pushed forward with the thumb in a state wherein the writing
tip part 4 is retracted behind the open front end 2a of the barrel 2 as shown in
Fig. 1, and the ridges 8a fitted in the grooves 11a of the grooved cam 11 as shown
in Fig. 4 are moved forward out of the grooves 11a as shown in Fig. 5. Because the
annular cam portion 7a exerts a force on the rotating cam 8 in a circumferential
direction, the ridges 8a are displaced in the same circumferential direction. When
the pressure is removed from the push-button 7, the ridges 8a come into engagement
with the sawtooth cam 11b formed in the front end of the grooved cam 11 as shown
in Fig. 6. Consequently, the writing tip part 4 is projected from the open front
end 2a of the barrel 2 as shown in Fig. 2 by the pushing action of the rotating
cam 8 and is held at the projected position. The ridges 8a are moved forward away
from the sawtooth cam 11b and is displaced in the circumferential direction when
the push-button 7 is pushed again with the writing tip part 4 projected forward,
the ridges 8a engage with the next grooves 11a, respectively, when the pressure
is then removed from the push-button 7, and the ridges 8a are caused to slide backward
along the grooves 11a to a position shown in Fig. 1 by the resilience of the coil
spring 6.
The refill 5 is inserted in the barrel 2 so that the distance
H between the open front end 2a of the barrel and the tip of the writing tip part
4 is in the range of 2 to 5 mm, preferably, about 3 millimeters (mm), when the writing
tip part 4 of the refill 5 is retracted into the barrel 2. The coil spring 6 is
designed and inserted so that the push-button operating pressure for operating the
push-button 7 as measured by a push-pull scale is in the range of 500 to 800 grams,
preferably, about 600 grams. The term, "push-button operating pressure" for operating
the push-button 7 signifies a pressure needed to advance the ridges 8a of the rotating
cam 8 from the position shown in Fig. 4 to a position where the ridges 8a are advanced
beyond the grooves 11a of the grooved cam 11 when the refill operating mechanism
10 as shown is employed. Such requirements may be met, for example, when the coil
spring 6 has a spring constant of 0.036 kg/mm and a compression by which the coil
spring 6 is compressed from its free length to a length in the writing state is
about 13 mm. The rest of the push-button operating pressure is frictional force
acting between the parts of the push-button operating mechanism.
In the push-button writing instrument 1 in accordance with
the present invention, the refill operating mechanism 10 including the rotating
cam 8 operates to advance the refill 5 against the resilience of the coil spring
6 when an set pressure in the range of 500 to 800 grams, such as 600 grams, is applied
to the push-button 7. Consequently, the writing tip part 4 is projected from the
open front end 2a of the barrel as shown in Fig. 2 and is held in the projected
state for writing.
Since the push-button writing instrument in accordance
with the present invention is configured as above, the coil spring will not be compressed
even if a hand touches the push-button inadvertently when the push-button writing
instrument is inserted in a pocket because a pressure that may be exerted on the
push-button by the simple touch of a hand on the push-button is less than 500 grams
in most cases. Consequently, the writing tip part will not be projected inadvertently
from the open front end of the barrel and the fabric forming the pocket will not
be stained. A push-button operating pressure exceeding 800 grams is excessively
high and makes the operation of the push-button difficult. Such a difficulty does
not occur in the push-button writing instrument of the present invention.
The push-button writing instrument in accordance with the
present invention is able to employ a conventional push-button operating mechanism
and does not need any additional safety mechanism which makes the construction of
the push-button writing instrument complicated and needs additional parts. Thus
the present invention is applicable to low-price push-button writing instruments.
