Knock-type writing instrument

A knock-type writing instrument is provided, which allows an easy refill exchange with a simple operation while inhibiting deformation of slits, breakage of a shaft tube, etc., during the refill exchange.

CROSS REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 USC §371, this application is a National Stage of International Application No. PCT/JP2009/062660, filed Jul. 13, 2009, which claims priority to Japanese Patent Application No. 2008-191227, filed Jul. 24, 2008 under applicable paragraphs of 35 USC §119, wherein the entire contents of each above-noted document is herein incorporated by reference.

TECHNICAL FIELD

The present invention relates to a knock-type writing instrument in which a refill is inserted into a shaft tube from the back end of the shaft tube.

BACKGROUND ART

This kind of knock-type writing instrument includes a knock-type instrument as disclosed in JP Utility Model Registration No. 3139755 by the applicant. This knock-type writing instrument comprises: a shaft tube having a long hole extending axially on its back peripheral wall; a refill having a writing part at its front end and inserted into the shaft tube from the back end of the shaft tube; a return spring biasing the refill backward; a knock member inserted into a back part of the shaft tube to allow its front end to abut the back end of the refill and allow its back part to protrude from the back end of the shaft tube; a resilient piece connected to the front end of the knock member to extend backward and capable of resiliently deforming in a radial direction of the shaft tube; a clip having a clip leg that is connected substantially orthogonally to a surface of the resilient piece and is slidably fitted in the long hole, the clip having a front part compressed into contact with or approaching an outer circumferential surface of the shaft tube; and a lock protrusion formed at the back end of the resilient piece and having a front surface inclined toward an interior of the shaft tube in a direction of the front end of the shaft tube.

In a knock-type writing instrument such as JP 3139755, a lock hole connected to the back end of the long hole via a middle slit as well as a back slit extending from the back end of the lock hole to the back end of the shaft tube are provided on the back peripheral wall of the shaft tube. The clip leg is fitted in the long hole via the lock hole and middle slit from the back slit. When the writing part of the refill is withdrawn within the shaft tube by a bias force of the return spring, the lock protrusion of the resilient piece is locked to the lock hole to maintain this withdrawn state of the writing part. When the back end of the knock member is knocked in such a withdrawn state of the writing part, the clip integral with the knock member and the refill advance, at which point the inclined front surface of the lock protrusion slidingly comes into contact with the inner wall surface of the middle slit, and the resilient piece resiliently deforms inwardly in the radial direction of the shaft tube. This causes the lock protrusion to pass through the middle slit to the long hole. When the lock protrusion moves to the long hole in this way, a resilient restoring force of the resilient piece causes the lock protrusion to be fitted in the long hole to lock the back end of the lock protrusion to the back end wall of the long hole. Thus, the writing part at the front end of the refill is maintained in a writable state in which it protrudes from the front end of the shaft tube.

In this writable state, when a surface of the clip is pressed (knocked), the resilient piece resiliently deforms inwardly in the radial direction of the shaft tube to release the lock of the back end of the lock protrusion to the back end of the long hole, and the refill and knock member are retracted by the bias force of the return spring. Then, when the lock protrusion moves to the lock hole, the resilient restoring force of the resilient piece causes the lock protrusion to fit in the lock hole to lock the back end of the lock protrusion to the back end of the lock hole, thereby maintaining the writing part in the withdrawn state within the shaft tube.

A knock-type writing instrument, such as JP 3139755, is intended to stably keep the writing part protruding from the front end of the shaft tube while increasing a resilient force of the clip, without increasing the number of components. In particular, the knock-type writing instrument of JP 3139755 is characterized in that, in order to stably keep the writing part protruding from the front end of the shaft tube, the lock protrusion, which is locked to the back end of the long hole while the writing part protrudes from the front end of the shaft tube, is formed at the back end of the resilient piece outwardly in the radial direction of the shaft tube. The long hole of the shaft tube is formed into a plane rectangular shape. The clip leg is formed to have a rectangular cross sectional shape as a surface shape in a direction in which its front and back ends are orthogonal to the shaft tube. With the writing part being withdrawn within the shaft tube, the bias force of the return spring causes the back end face of the clip leg to abut the back end face of the long hole in a surface contact state, such that the clip leg does not easily exit the long hole outwardly toward the back end of the shaft tube.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The knock-type writing instrument of JP 3139755 is configured as above. In particular, the entire clip leg is formed to have a rectangular cross-sectional shape as a surface shape in a direction in which its front and back ends are orthogonal to the shaft tube. By fitting the clip leg in the long hole with the plane rectangular shape, the clip leg cannot easily exit the long hole outwardly toward the back end of the shaft tube. Such a configuration is not intended to exchange refills. Thus, there has been a problem that, in order to exchange refills, the knock member must be forcedly moved with a considerable separation force in a direction in which the clip leg fitted in the long hole passes through the back slit via the lock hole from the middle slit so as to remove the knock member from the shaft tube. In such a knock member removal, because the middle and back slits are forcedly widened by the clip leg, there has been a problem that deformation of each of the slits, breakage of the shaft tube due to the forced widening of the slits, etc., are prone to occur. Therefore, there has been a problem that the knock-type writing instrument of Patent Document 1 cannot be easily implemented.

As a knock-type writing instrument other than that of JP 3139755, a common refillable ballpoint is well known, which has a configuration allowing an exchange of refills by removing a tip at the front end of a shaft tube or a tail crown at the back end of the shaft tube. However, since the exchange of refills needs repeated attachment and detachment of the tip or tail crown with respect to the shaft tube as mentioned above, there has been a problem that the refill exchange operation takes a lot of time and work.

The present invention was made to solve the above problems, and is intended to provide a knock-type writing instrument allowing an easy refill exchange with a simple operation while inhibiting the slit deformation, shaft tube breakage, etc., during the refill exchange.

Means for Solving the Problems

A knock-type writing instrument according to the invention comprises: a shaft tube having a long hole extending axially on its back peripheral wall; a refill having a writing part at its front end and inserted into the shaft tube from the back end of the shaft tube; a biasing member biasing the refill backward; a knock member inserted into a back part of the shaft tube to allow its front end to abut the back end of the refill and allow its back part to protrude from the back end of the shaft tube; a resilient piece connected to the front end of the knock member to extend backward and capable of resiliently deforming in a radial direction of the shaft tube; a lock protrusion formed at the back end of the resilient piece; and a clip having a clip leg connected to the resilient piece to be slidably fitted in the long hole, the clip having a front part compressed into contact with or approaching an outer circumference of the shaft tube; wherein a lock hole connected to the back end of the long hole via a middle slit as well as a back slit connected to the back end of the lock hole to reach the back end of the shaft tube are continuously formed on the back peripheral wall of the shaft tube in an extension direction of the back end of the long hole; and wherein the knock-type writing instrument is characterized in that the back end ridge is formed at the back end of the clip leg, the back end ridge sequentially widening the middle slit and back slit in their width directions by pushing out the clip toward the back end of the shaft tube with a pressure greater than a bias force of the biasing member.

The knock-type writing instrument according to the invention is characterized in that the front end ridge is formed at the front end of the clip leg, the front end ridge sequentially widening the back slit, lock hole, and middle slit of the shaft tube in their width directions when the knock member is inserted into the back part of the shaft tube in order to cause the clip leg to fit in the long hole of the shaft tube.

The knock-type writing instrument according to the invention is characterized in that a watering can-shaped notch is formed at the back end of the back slit.

The knock-type writing instrument according to the invention is characterized in that a fitting convex part, which is fitted in the back end of the refill inserted into the shaft tube, is formed at the front end of the knock member.

The knock-type writing instrument according to the invention is characterized in that a press control part having an anti-slip function operating during pressing the clip is provided on a surface of the clip.

Effects of the Invention

According to the knock-type writing instrument of the invention, the back end ridge is formed at the back end of the clip leg connecting the resilient piece of the knock member and the clip, so that, when the refills are exchanged, the middle and back slits of the shaft tube may be sequentially and smoothly widened in their width directions by a simple operation in which the clip is pushed out toward the back end of the shaft tube with the pressure greater than the bias force of the biasing member. This causes the clip leg to pass through the middle and back slits, so that the knock member may be easily removed from the back end of the shaft tube. This brings about an effect that the refills may be exchanged easily and effectively. In this manner, the back end ridge of the clip leg may easily widen the middle and back slits in their width directions during the refill exchange, such that the knock member does not need to be forcedly moved in a direction of removal from the back end of the shaft tube. This brings about an effect that the deformation of each of the slits, breakage of the shaft tube, etc., may be inhibited.

According to the knock-type writing instrument of the invention, the front end ridge is formed at the front end of the clip leg, so that the back and middle slits of the shaft tube may be sequentially and smoothly widened in their width directions also during insertion of the knock member into the back part of the shaft tube. This brings about an effect that the clip leg may be easily incorporated in the long hole.

According to the knock-type writing instrument of the invention, the watering can-shaped notch is formed at the back end of the back slit of the shaft tube, such that the clip leg may be smoothly pushed into the long hole. This brings about an effect that the knock member may be easily incorporated.

According to the knock-type writing instrument of the invention, the fitting convex part formed at the front end of the knock member is fitted in the back end of the refill in the shaft tube, such that the refill and knock member may be removed as one, thereby bringing about an effect that the refills may be more easily exchanged.

According to the knock-type writing instrument of the invention, the press control part provided on the surface of the clip has the anti-slip function, such that an operational force by a user pressing and moving the clip in the knock member removal direction during the knock member removal is easily transmitted to the clip and knock member. This improves operability for pressing and moving the clip, thereby bringing about an effect that the knock member may be more easily removed.

DETAILED DESCRIPTION

FIG. 1is a cross-sectional view showing the knock-type writing instrument according to Embodiment 1 of the invention;FIG. 2is a plan view showing the shaft tube ofFIG. 1;FIG. 3is an enlarged plan view of the back part of the shaft tube ofFIG. 2; andFIG. 4is a cross-sectional view of the entire shaft tube ofFIG. 2.

As shown inFIGS. 1 and 2, the knock-type writing instrument according to Embodiment 1 comprises: a shaft tube1having a port1aprovided at a front end thereof and an axially extending long hole1bformed in a peripheral wall of a back part thereof; a ballpoint refill having a writing part2aat a front end thereof, the refill being slidably inserted into the shaft tube from the back end of the shaft tube1ain such a manner that the writing part2acan be retractably projected from the front end of the shaft tube1via the port1a; a return spring (biasing member)3provided in the shaft tube1for biasing the refill2in a retraction direction; a knock member inserted into the back part of the shaft1with a front end thereof being abutted on the back end of the refill2and with the back part thereof being protruded backward from the back end of the shaft tube1; and a clip5connected to the knock member4and having a front part compressedly contracted with an outer circumferential surface of the shaft tube1.

A more detailed configuration will be explained. As shown inFIGS. 2 and 3, the peripheral wall of the back part of the shaft tube1is formed with a lock hole1dcontinuously connected to a back end of the long hole1bvia a middle slit1c, and a back slit1econtinuously extending to an edge of a back end of the shaft tube1from a back and of the lock tube1dand opened backward. Incidentally, the long hole1bhas a first width, the lock hole1dhas a second width substantially equal to the first width, the middle slit1chas a third width smaller than each of the first and second widths, and the back slit1ehas a fourth width substantially equal to the third width. As best shown inFIGS. 9(a) and9(b), a clip leg5aof the clip5which will be discussed hereinafter has a thickness smaller then each of the first and second widths and larger than the third and fourth widths.

The long hole1bis formed into a plane rectangular shape. The front end of the lock hole1dis tapered, gradually narrowing toward the back end side of the middle slit1c. A watering can-shaped notch1fwidening in a width direction is formed at the back end of the back slit1e.

FIG. 5is a perspective view showing the clip5integral with the knock member4;FIG. 6is a side view ofFIG. 5;FIG. 7is a cross-sectional view ofFIG. 6; andFIG. 8is a cross-sectional view taken along line A-A inFIG. 6.

As shown in these drawings, the knock member4is comprised of a cylindrical back end knock part4a; a front extension4bextending forward along an inner circumferential surface of the shaft tube1from the back end knock part4a; the front end head4ccontinuously formed at the front end of the front extension4bto abut the back end of the refill2within the shaft tube1; a fitting convex part4dprovided at a center of the front end face of the front end head4cin a protruding manner to be fitted within the back end of the refill2; a resilient piece4econnected to the back end of the front end head4cto extend backward in a direction substantially parallel to the front extension4b, the resilient piece4ecapable of resiliently deforming in a radial direction of the shaft tube1and having the back end spaced apart from the front end of the back end knock part4a; and a lock protrusion4fintegrally formed at the back end of the resilient piece4eand facing outwardly in the radial direction of the shaft tube1. A front surface of the lock protrusion4fis formed as an inclined front surface4gthat is inclined from a tip of the lock protrusion4fin an inner diameter direction of the shaft tube1. An inclined and recurved surface4his formed at the back end of the lock protrusion4fas shown inFIGS. 6 and 7. This inclined and recurved surface4hacts as a lock surface with respect to the back ends of the long hole1band lock hole1d, and is inclined in a direction of holding down (covering) outer edges at the back ends of the long hole1band lock hole1dtoward the inner diameter direction of the shaft tube1.

At a substantially middle portion of the resilient piece4eof the knock member4having such a configuration, the clip5is integrally formed via a clip leg orthogonal to the resilient piece4e. The front end of the clip5is configured to be compressively contacted with the outer circumferential surface of the shaft tube1by a resilient force of the resilient piece4e. As shown inFIGS. 6-8, a front end ridge5bis formed at the front end of the clip leg5aintegrally connecting the resilient piece4eof the knock member4and the clip5, and a back end ridge5cis formed at the back end of the clip leg5a. The front end ridge5bserves as a means to facilitate widening of the back slit1eand middle slit1cin this order in their respective width directions during incorporating the knock member4into the shaft tube1from behind. The back end ridge5cserves to facilitate the widening of the middle slit1cand back slit1ein this order in their respective width directions during removal of the knock member4. As best shown inFIGS. 8,9(a) and9(b), each of the front and back end ridges5b,5cis formed in a wedge-shape in cross-section.

The front end of the clip5is configured to be compressed into contact with or approach the outer circumferential surface of the shaft tube1by the resilient force of the resilient piece4e. A press control part5dforming a concave curved surface is formed on a surface at the back end of the clip5, while a gripper6(seeFIG. 1) comprising a resilient material such as rubber is fitted in a grip part of the shaft tube1.

Next, the assembly and operation of the knock-type writing instrument according to this embodiment will now be described.FIGS. 9(a) and (b) are operation diagrams showing principal parts of the knock-type writing instrument.

First, the return spring3is fitted in the front end side of the refill2, and then the refill2in this state is inserted into the shaft tube1from the back end of the shaft tube1. When the front end ridge5bof the clip leg5ais then pushed into the back slit1efrom the notch1fat the back end of the shaft tube1while inserting a side of the front end head4cof the knock member4into the back part of the shaft tube1, the front end ridge5bintervenes in the back slit1e, thereby widening the back slit1e, lock hole1d, and middle slit1cin their respective width directions. This allows the clip leg5ato pass through the back slit1e, lock hole1d, and middle slit1cin this order to be fitted in the long hole1b, such that the knock member4is incorporated in the back part of the shaft tube1.

In such a process of incorporating the knock member4, when the clip leg5ais advanced along the back slit1e, the inclined front surface4gof the lock protrusion4fat the back end of the resilient piece4eof the knock member4slidingly comes into contact with an inner edge of the back slit1e, thereby resiliently deforming the resilient piece4ein the inner diameter direction of the shaft tube1. Then, the lock protrusion4freaches the lock hole1dthrough an underside region of the back slit1e. At this point, the lock protrusion4frushes into the lock hole1dby the resilient restoring force of the resilient piece4e, and the back end of the lock protrusion4fis locked to the back end of the lock hole1dby a backward bias force of the return spring3(seeFIG. 9(b)), such that the writing part2aat the front end of the refill2is maintained in a withdrawn state within the shaft tube1(a nonuse state of the writing instrument). In this state, the fitting convex part4dat the front end of the knock member4continues to be press fitted within the back end of the refill2.

When the back end of the knock member4is knocked while the writing part2aat the front end of the refill2is withdrawn within the shaft tube1, the inclined front surface4gof the lock protrusion4fslidingly comes into contact with an inner edge of the middle slit1c, such that the resilient piece4eagain resiliently deforms in the inner diameter direction of the shaft tube1to advance the lock protrusion4f. When the lock protrusion4fthen passes through an underside region of the middle slit1cin a direction of forward movement, the writing part2aat the front end of the refill2protrudes from the front end of the shaft tube1, and at the same time the lock protrusion4frushes into the long hole1bby the resilient restoring force of the resilient piece4e. Therefore, when knocking the back end of the knock member4is stopped at this point, the back end of the lock protrusion4fis locked to the back end of the long hole1bdue to the backward bias force of the return spring3(seeFIG. 9(a)). This maintains the refill2in a writable state with the writing part2aat its front end protruding from the front end of the shaft tube1.

When a back surface of the clip5is pressed toward the shaft tube1from such a writable state, the resilient piece4eresiliently deforms via the clip leg5ain the inner diameter direction of the shaft tube1. Thus, the lock protrusion4fat the back end of the resilient piece4emoves away from a position in which it is locked to the back end wall of the long hole1b, in the inner diameter direction of the shaft tube1, releasing the lock of the back end of the lock protrusion4fto the long hole1b, and retracting the refill2and knock member4together by the backward bias force of the return spring3to withdraw the writing part2awithin the shaft tube1. At the same time, the lock protrusion4fmoves to the lock hole1dto lock the back end of the lock protrusion4fto the back end of the lock hole1d. Thus, the writing part2ais maintained in the withdrawn state within the shaft tube1.

The exchange of the refill2will now be explained.

If the press control part5dat the back end of the clip5is pressed to push the clip5toward the back end of the shaft tube1when the refill2is exchanged while the writing part2aat the front end of the refill2protrudes from the front end of the shaft tube1, i.e., the back end of the lock protrusion4fis locked to the back end of the long hole1b, the lock of the back end of the lock protrusion4fto the back end of the long hole1bis released. At the same time, the back end ridge5cof the clip leg5asequentially intervenes in the middle slit1cand back slit1eto widen these middle and back slits1c,1ein their respective width directions while sequentially passing the clip leg5athrough the middle slit1cand back slit1e. This allows the clip leg5ato exit the back slit1ebackward to remove the knock member4. Since the fitting convex part4dof the knock member4is press fitted within the back end of the refill2, the refill2as well as the knock member4is drawn from the shaft tube1backward.

After the refill2drawn from within the shaft tube2in this way is replaced with a new refill and the new refill2is inserted into the shaft tube1from the back end of the shaft tube, the knock member4is inserted into the shaft tube1from the back end of the shaft tube, thereby incorporating the knock member4in the back part of the shaft tube1.

The above explains the exchange of the refill2while the writing part2aprotrudes from the front end of the shaft tube1and is kept in such a state. However, the refill2may be exchanged in a manner similar to the above even if the writing part2ais withdrawn within the shaft tube1and kept in such a state.

According to this embodiment described above, the front and back end ridges5band5care formed at the respective front and back ends of the clip leg5aintegrally connecting the resilient piece4eof the knock member4and the clip5, and the clip leg5ais configured to be slidably incorporated in the long hole1bvia the back slit1e, lock hole1d, and middle slit1cin sequence from the back end of the shaft tube1. Therefore, when the knock member4is inserted and incorporated in the back part of the shaft tube1, the front end ridge5bof the clip leg5asequentially widens the back slit1eand middle slit1cin their respective width directions, such that the clip leg5amay easily pass through the back slit1eand middle slit1c. This allows the clip leg5ato be easily incorporated in the long hole1b. This brings about an effect that the assembly of the knock member4to the back part of the shaft tube1may be easy.

A watering can-shaped notch if wider than a width of the back slit1eis formed at the back end of the back slit1e. Further, an inclined hole1gnarrowing gradually toward the back end of the middle slit1cis formed at the front end of the lock hole1d. The inclined hole1gconnects the front end of the lock hole1dand the back end of the middle slit1c. This brings about an effect that the front end ridge5bof the clip leg5amay be more easily pushed into the back slit1eand middle slit1c, respectively.

During insertion of the knock member4into the back part of the shaft tube1, the fitting convex part4dprovided at the center of the front end of the knock member4in a protruding manner is press fitted within the back end of the refill2inserted into the shaft tube1. This brings about an effect that the refill2follows the knock member4during the removal of the knock member4for exchanging the refill2, such that both of them may be removed integrally with a one-touch operation.

When the press control part5dat the back end of the clip5is pressed to move toward the back end of the shaft tube1during the removal of the knock member4, the lock of the lock protrusion4fto the back end of the long hole1bor lock hole1dis released, and at the same time the back end ridge5cof the clip leg5amay easily widen the middle slit1cand back slit1ein their respective width directions. This brings about an effect that the removal of the knock member4may be also easily performed.

The press control part5dhas a concave curved surface to have an anti-slip function operating during a pressing operation. This brings about an effect that, during the removal of the knock member4, the knock member4as well as the clip5may be easily pushed and moved toward the back end of the shaft tube1to be removed.

As described above, the widened watering can-shaped notch1fis formed at the back end of the back slit1e; the inclined hole1gconnects the front end of the lock hole1dand the back end of the long hole1b; and the front and back end ridges5band5care formed at the respective front and back ends of the clip leg5a. This allows the front and back end ridges5band5cof the clip leg5ato easily widen the back slit1eand middle slit1cin their width directions with a slight operational force. This brings about an effect that the deformation of the back slit1eor middle slit1c, breakage of the shaft tube1, etc., due to forced widening of the back slit1eor middle slit1cmay be prevented.

When the back end of the knock member4is knocked, the inclined front surface4gof the lock protrusion4fslidingly comes into contact with the inner edge of the middle slit1c. This brings about an effect that the lock protrusion4fmay be passed under the middle slit1cto smoothly pass through the middle slit1c. Further, the inclined and recurved surface4hformed at the back end of the lock protrusion4fbrings about an effect that the lock protrusion4funder the bias force of the return spring3may surely engage the back end of the lock hole1dor long hole1b, and the engaging force is increased such that the refill2may be certainly held in a knocked position and in a withdrawn position within the shaft tube1.

FIG. 10is a plan view showing the clip of the knock-type writing instrument according to Embodiment 2 of the invention; andFIG. 11is a side view ofFIG. 10.

In this embodiment, an anti-slip rib5eorthogonal to a longitudinal direction of the clip5is formed on a surface of the press control part5don the surface of the back end of the clip5in Embodiment 1 mentioned above. The rib5eallows the press control part5dto be easily pressed to move toward the back end of the shaft tube1during the removal of the knock member4, bringing about an effect of improving its operability.

In the above Embodiment 1, the front and back end ridges5band5cformed at the respective front and back ends of the clip leg5aare explained. In the knock-type writing instrument according to the invention, the back end ridge5cmay be formed at only the back end of the clip leg5a. Again, during the exchange of the refill2, the back end ridge5cmay sequentially and smoothly widen the middle slit1cand back slit1eof the shaft tube1in their width directions by a simple operation in which the clip5is pushed out toward the back end of the shaft tube1with a pressure greater than the bias force of the return spring3. This allows the clip leg5ato pass through the middle slit1cand back slit1eto easily remove the knock member4from the back end of the shaft tube1. This brings about an effect that the refill2may be easily and effectively exchanged. In this way, during the exchange of the refill2, the back end ridge5cmay easily widen the middle slit1cand back slit1ein their width directions. Thus, the knock member4does not need to be forcedly moved in a direction of removal from the back end of the shaft tube1. This brings about an effect of inhibiting the deformation of each of the slits1c,1e, breakage of the shaft tube1, etc.

FIG. 12is a side view of the knock member and clip according to Embodiment 4 of the invention;FIG. 13is a view on arrow ofFIG. 12;FIG. 14is a cross-sectional view taken along line A-A inFIG. 12; andFIG. 15is a cross-sectional view taken along line B-B inFIG. 12.

As with the above Embodiment 1, the front end ridge5bis formed at the front end of the clip leg5aas shown inFIGS. 12-15. However, Embodiment 4 differs from the above Embodiment 1 in the configuration of the back end ridge5cformed at the back end of the clip leg5a.

That is, the back end of the clip leg5ahas the back end ridge5cformed in only its upper region, while its lower region has a planar wall5fwithout the back end ridge5c.

According to this embodiment, when the writing instrument is not used (seeFIG. 9(b)), the back end of the lock protrusion4fis locked to the back end of the lock hole1dby the backward bias force of the return spring3, such that the writing part2aat the front end of the refill2is maintained in the withdrawn state within the shaft tube1. Even if the lock of the back end of the lock protrusion4fto the back end of the lock hole1dis released by some unnecessary external force acting in this state, the lower region at the back end of the clip leg5aformed into the planar wall5fwithout the back end ridge5cdoes not easily widen the middle slit1cand back slit1ein the respective width directions. This brings about an effect of preventing the knock member4from moving backward and being separated.

In the refill exchange, when the press control part5dat the back end of the clip leg5ais pressed to move toward the back end of the shaft tube1, the lock of the lock protrusion4fto the back end of the lock hole1dis released, and at the same time the back end ridge5cformed in only the upper region of the clip leg5amay easily widen the middle slit1cand back slit1ein respective width directions. This may be securely and smoothly performed only during the refill exchange.

Accordingly, the back end ridge5cof the clip leg5afunctions only during the refill exchange, while the rest of the time, the function of the planer wall5fof the clip leg5abrings about an effect of preventing the knock member4from being separated carelessly.

PARTS LIST

A knock-type writing instrument is described comprising: a shaft tube1having a long hole1b; a refill2inserted into the shaft tube1; a biasing member3biasing the refill2backward; a knock member4inserted into a back part of the shaft tube1; a resilient piece4econnected to the front end of the knock member4to extend backward and capable of resiliently deforming in a radial direction of the shaft tube1; a lock protrusion4fformed at the back end of the resilient piece4e; and a clip5having a clip leg5aconnected to the resilient piece4eto be slidably fitted in the long hole1b, the clip having a front part compressed into contact with or approaching an outer circumference of the shaft tube1, wherein a lock hole1dconnected to the back end of the long hole1bvia a middle slit1cas well as a back slit1econnected to the back end of the lock hole1dto reach the back end of the shaft tube1are continuously formed on a back peripheral wall of the shaft tube1in an extension direction of the back end of the long hole1b; and wherein the back end ridge5cis formed at the back end of the clip leg5a, the back end ridge sequentially widening the middle slit1cand back slit1ein their width directions by pushing out the clip5toward the back end of the shaft tube1with a pressure greater than a bias force of the biasing member3.

It will be readily apparent, however, that other variations and modifications are possible within the intended ambits of the following claims: