Gas-pressurized writing instrument and writing instrument refill Number:7,325,992 from the United States Patent and Trademark Office (PTO) owispatent

Title: Gas-pressurized writing instrument and writing instrument refill

Abstract: A gas-pressurized writing instrument simply constructed so that a compressed gas will not escape to the outside by providing a writing point assembly (10) at the front end (14a) of a tube member (14), storing an ink (12) to be fed to the writing point assembly (10) in the tube member (14), encasing at least part of the tube member (10) by a casing cylinder (18) formed of a material that presents low gas permeability or gas impermeability so as to form a space (16) communicating with the rear opening of tube member (14), sealing a compressed gas inside the space (16) so that the compressed gas will push the ink out to writing point assembly (10) to secure the writing performance, and covering the outer periphery of the casing cylinder (18) with an exterior member having thermal resistance or/and moisture resistance greater than that of the casing cylinder so that the casing cylinder can present low gas permeability or gas impermeability.

Patent Number: 7,325,992 Issued on 02/05/2008 to Furukawa,   et al.

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Inventors:	Furukawa; Kazuhiko (Kouza-gun, JP), Fujisawa; Kiyoshi (Takasaki, JP)
Assignee:	Mitsubishi Pencil Kabushiki Kaisha (Tokyo, JP)
Appl. No.:	10/502,742
Filed:	January 30, 2003
PCT Filed:	January 30, 2003
PCT No.:	PCT/JP03/00927
371(c)(1),(2),(4) Date:	July 28, 2004
PCT Pub. No.:	WO03/064177
PCT Pub. Date:	August 07, 2003

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Foreign Application Priority Data

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Jan 30, 2002 [JP]			2002-021787
Jan 30, 2002 [JP]			2002-021790
Jan 30, 2002 [JP]			2002-021791

Current U.S. Class:	401/190 ; 401/192; 401/222
Current International Class:	A46B 11/02 (20060101)
Field of Search:	401/190,209,222,141,142,192,213

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References Cited [Referenced By]

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U.S. Patent Documents

5336007	August 1994	Jozat
6945726	September 2005	Ichikawa et al.
7037019	May 2006	Miyamoto et al.
7071245	July 2006	Ichikawa
2004/0228673	November 2004	Kirita et al.

Foreign Patent Documents

	08-164692		Jun., 1966		JP
	50-122325		Sep., 1975		JP
	52-15859		Apr., 1977		JP
	53-45694		Nov., 1978		JP
	55-159166		Nov., 1980		JP
	58-120084		Aug., 1983		JP
	61-12122		Apr., 1986		JP
	02-135281		Nov., 1990		JP
	4-10076		Mar., 1992		JP
	2000-085290		Mar., 2000		JP
	2001-341492		Dec., 2001		JP

Other References

English translation of International Preliminary Examination Report issued in International Application No. PCT/JP2003/000927. cited by other.

Primary Examiner: Huynh; Khoa D.
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney PC

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Claims

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The invention claimed is:

1. A gas-pressurized writing instrument comprising: a writing point assembly at the front end of the writing instrument, a tube member that stores ink to be fed to the writing point assembly, a casing that surrounds the tube member is connected to the writing assembly, and is closed at the rear end and formed of a material that presents low gas permeability or gas impermeability; and a compressed gas sealed in the casing, an exterior member covers at least part of the tube member and the exterior of the casing, other than the front end of the writing point assembly, and the exterior member constructs a confined structure that isolates an interior thereof from the outside air.

2. The gas-pressurized writing instrument according to claim 1, wherein the exterior member has greater thermal resistance or/and moisture resistance than that of the tube member.

3. The gas-pressurized writing instrument according to claim 1, wherein a clearance is formed between the exterior member and the tube member while a vent hole that communicates with the outside is formed in the exterior member, so that the clearance communicates with the outside by way of the vent hole.

4. The gas-pressurized writing instrument according to claim 3, wherein the vent hole is provided near the rear end of the exterior member.

5. The gas-pressurized writing instrument according to claim 1, wherein the wall thickness of the grip portion of the exterior member at which the user holds is made greater than that of the other part of the exterior member.

6. A gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly and opens at the rear end; and a casing cylinder which creates a space communicating with the rear opening of the tube member and encases at least part of the tube member, wherein the casing cylinder is formed of a material that presents low gas permeability or gas impermeability, and a compressed gas is in fluid communication with the ink, wherein the compressed gas is sealed in the space formed between the tube member and the casing cylinder, characterized in that an exterior member that covers at least part of the casing cylinder except the front end of the writing point assembly is provided.

7. The gas-pressurized writing instrument according to claim 6, wherein the exterior member has greater thermal resistance or/and moisture resistance than that of the casing cylinder.

8. The gas-pressurized writing instrument according to claim 6, wherein the exterior member provides a confined structure that isolates the interior thereof from the outside air.

9. The gas-pressurized writing instrument according to claim 6, wherein a clearance is formed between the exterior member and the casing cylinder while a vent hole that communicates with the outside is formed in the exterior member, so that the clearance communicates with the outside by way of the vent hole.

10. The gas-pressurized writing instrument according to claim 9, wherein the vent hole is provided near the rear end of the exterior member.

11. The gas-pressurized writing instrument according to claim 6, wherein the wall thickness of the grip portion of the exterior member at which the user holds is made greater than that of the other part of the exterior member.

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Description

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TECHNICAL FIELD

The present invention relates to a gas-pressurized writing instrument and a writing instrument refill.

BACKGROUND ART

Conventionally, there have been known various types of gas-pressurized writing instruments,which, with a compressed gas sealed in the barrel cylinder, force out ink therefrom by making use of the pressure of the gas. This gas-pressurized writing instrument enables smooth writing, and writing in an upward position, (with an ordinary ball-point pen, air is sucked from the writing point, as a result, ink flows backwards) because a force for pushing the ink out is exerted by the compressed gas therein.

Various types of the gas-pressurized writing instruments have been proposed.

For example, Japanese Utility Model Application Laid-open Sho 58 No. 120084 discloses a double-fold structure, as shown in FIG. 2, in which a pressure check cylinder is arranged outside an ink storage tube and a compressed gas is sealed in the tube. In writing, the compressed gas provides the function of pushing out the ink, producing smooth writing sensation and enabling writing in an upward position, writing in water, or in a weightless state or under other conditions (conventional example 1).

In the conventional example 1, however, the ink storage tube is arranged to stick out from the plug and be in contact with the outside air. Since the compressed gas also permeates through the ink storage tube to the outside, there is a fear that the compressed gas will escape to the outside via the ink storage tube. Therefore, it is necessary to select a material through which the compressed gas hardly permeates, for that of the ink storage tube.

Further, the ink storage tube should have resistance to ink for storage of ink therein.

Though provision of a transparent ink storage tube makes it possible to monitor the remaining amount of ink from the outside, selection of a material under the above conditions for prevention against permeation of the compressed gas and possession of resistance to ink, generally entails difficulties such that the ink storage tube becomes large in wall thickness. Further, the selection becomes extremely difficult if formability is considered and also clear drain performance or the property of causing ink not to adhere to the inner wall of the ink storage tube is wanted, so as to maintaining the ink storage tube clear after ink consumption. When clear drain performance needs to be kept, polypropylene (PP) that presents high permeability to gas has been used.

Japanese Utility Model Application Laid-open Sho 57 No. 121575 also discloses a gas pressurized ball-point pen having a similar double-folded tube, producing smooth writing sensation and enabling writing in an upward position (conventional example 2).

However, also in this conventional example 2, the ink storage tube is arranged so as to stick out of the barrel cylinder, and ink is stored in the ink storage tube. In the conventional example 2, the projected ink storage tube is covered with a holder, but this holder merely covers the front end of the ink storage tube. Further, in consideration of the use of a thread for fixture, ambient air is allowed to easily permeate, which practically means that the ink storage tube is put in direct contact with the outside air. There is a method of sealing by using a sealing material, but is it markedly difficult to select a material which is greasy and has high gas permeability.

Accordingly, in the conventional example 2, selection of a material that meets the above same conditions as in the conventional example 1, i.e., prevention against permeation of the compressed gas and possession of resistance to ink, generally entails difficulties. Further, the selection becomes extremely difficult if clear drain performance, formability and transparency are considered.

The basic configuration of a gas-pressurized ball-point pen as one kind of the gas-pressurized writing instruments is composed of a point assembly for a writing point, an ink storage tube that is connected to the point assembly and stores ink and compressed gas therein, and a tail plug disposed at the rear end of the ink storage tube. For the ink storage tube, several techniques using transparent resin so as to permit the remaining amount of ink therein to be monitored have been disclosed. However, some cases depending on the used resin suffer the gas leakage problem. Specifically, there occurs the problem in that the compressed gas permeates through the resin and leaks out from the interior of the ink storage tube to the outside.

In view of the problems in the conventional art, it is therefore an object of the present invention to provide a gas-pressurized writing instrument and a writing instrument refill, which can prevent gas leakage with a simple configuration and which is advantageous in appearance. It is also an object of the present invention to provide a gas-pressurized writing instrument and a writing instrument refill, which can prevent gas leakage with a simple structure of a fewer number of parts.

DISCLOSURE OF INVENTION

In order to achieve the above objects, the first aspect of the invention is a gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly, is closed at the rear end and formed of a material that presents low gas permeability or gas impermeability; and a compressed gas sealed in the tube member, characterized in that an exterior member that covers at least part of the tube member other than the front end of the writing point assembly is provided.

The second aspect of the present invention is that defined in the first aspect, wherein the exterior member has greater thermal resistance or/and moisture resistance than that of the tube member.

The third aspect of the present invention is that defined in the first or second aspect, wherein the exterior member constructs a confined structure that isolates the interior thereof from the outside air.

The fourth aspect of the present invention is that defined in the first or second, wherein a clearance is formed between the exterior member and the tube member while a vent hole that communicates with the outside is formed in the exterior member, so that the clearance communicates with the outside by way of the vent hole.

The fifth aspect of the present invention is that defined in the fourth aspect, wherein the vent hole is provided near the rear end of the exterior member.

The sixth aspect of the present invention is that defined in any of the first to fifth aspects, wherein the wall thickness of the grip portion of the exterior member at which the user holds is made greater than that of the other part of the exterior member.

The seventh aspect of the present invention is a gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly and opens at the rear end; and a casing cylinder which creates a space communicating with the rear opening of the tube member and encases at least part of the tube member, wherein the casing cylinder is formed of a material that presents low gas permeability or gas impermeability, and a compressed gas is sealed in the space formed between the tube member and the casing cylinder, characterized in that an exterior member that covers at least part of the casing cylinder except the front end of the writing point assembly is provided.

The eighth aspect of the present invention is that defined in the seventh aspect, wherein the exterior member has greater thermal resistance or/and moisture resistance than that of the casing cylinder.

The ninth aspect of the present invention is that defined in the seventh or eighth aspect, wherein the exterior member provides a confined structure that isolates the interior thereof from the outside air.

The tenth aspect of the present invention is that defined in the seventh or eighth aspect, wherein a clearance is formed between the exterior member and the casing cylinder while a vent hole that communicates with the outside is formed in the exterior member, so that the clearance communicates with the outside by way of the vent hole.

The eleventh aspect of the present invention is that defined in the tenth aspect, wherein the vent hole is provided near the rear end of the exterior member.

The twelfth aspect of the present invention is that defined in any of the seventh to eleventh aspects, wherein the wall thickness of the grip portion of the exterior member at which the user holds is made greater than that of the other part of the exterior member.

The thirteenth aspect of the present invention is a gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly, is closed at the rear end and formed of a material that presents low gas permeability or gas impermeability; and a compressed gas sealed in the tube member, characterized in that a moisture-proof layer is formed by transfer, printing, coating or vapor deposition, on at least part of the outer surface of the tube member.

The fourteenth aspect of the present invention is a gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly and opens at the rear end; and a casing cylinder which creates a space communicating with the rear opening of the tube member, encases at least part of the tube member and is closed at the rear end, characterized in that the casing cylinder is formed of a material that presents low gas permeability or gas impermeability, a compressed gas is sealed in the space formed between the tube member and the casing cylinder, and a moisture-proof layer is formed on, at least, part of the outer surface of the casing cylinder, by transfer, printing, coating or vapor deposition.

The fifteenth aspect of the present invention is that defined in fourteenth aspect, wherein a joint which is formed of a material that presents low gas permeability or gas impermeability and keeps the space between the tube member and the casing cylinder airtight is provided between the tube member and the casing cylinder.

The sixteenth aspect of the present invention is that defined in fourteenth aspect, wherein a joint which is formed of a material that presents low gas permeability or gas impermeability and keeps the space between the tube member and the casing cylinder airtight is provided between the casing cylinder and the writing point assembly, so as to encase the tube member in the casing cylinder, keeping the tube member out of contact with the outside air.

The seventeenth aspect of the present invention is that defined in the fifteenth or sixteenth aspect, wherein a moisture-proof layer is formed on, at least, part of the outer surface of the joint, by transfer, printing, coating or vapor deposition.

The eighteenth aspect of the present invention is that defined in the thirteenth, fourteenth or seventeenth aspect, wherein the material for the moisture-proof layer is principally composed of wax.

The nineteenth aspect of the present invention is a writing instrument refill characterized in that the refill is integrally formed of the writing point assembly and tube member defined in the thirteenth or eighteenth aspect and can be removably fitted to the barrel cylinder of a writing instrument.

The twentieth aspect of the present invention is a writing instrument refill characterized in that the refill is integrally formed of the writing point assembly, tube member and casing cylinder defined in the fourteenth to eighteenth aspects and can be removably fitted to the barrel cylinder of a writing instrument.

The twenty-first aspect of the present invention is a gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly, is closed at the rear end and formed of a material that presents low gas permeability or gas impermeability; and a compressed gas sealed in the tube member, characterized in that a moisture-proof layer is integrally formed by two-color molding on, at least part of the outer surface of the tube member.

The twenty-second aspect of the present invention is that defined in the twenty-first aspect, wherein the material for the tube member is ethylene vinyl alcohol copolymer (EVOH).

The twenty-third aspect of the present invention is that defined in the twenty-second aspect, wherein the material for the moisture-proof layer is polypropylene (PP) or polyethylene (PE).

The twenty-fourth aspect of the present invention is a gas-pressurized writing instrument comprising: a tube member which has a writing point assembly at the front end thereof, stores ink therein to be fed to the writing point assembly and opens at the rear end; and a casing cylinder which creates a space communicating with the rear opening of the tube member, encases at least part of the tube member and is closed at the rear end, characterized in that the casing cylinder is formed of a material that presents low gas permeability or gas impermeability, a compressed gas is sealed in the space formed between the tube member and the casing cylinder, and a moisture-proof layer is formed on, at least, part of the outer surface of the casing cylinder, by two-color molding.

The twenty-fifth aspect of the present invention is that defined in the twenty-fourth aspect, wherein the material for the casing cylinder is ethylene vinyl alcohol copolymer (EVOH).

The twenty-sixth aspect of the present invention is that defined in the twenty-fifth aspect, wherein the material for the moisture-proof layer is polypropylene (PP) or polyethylene (PE).

The twenty-seventh aspect of the present invention is that defined in any of the twenty-fourth to twenty-sixth aspects, wherein a joint which is formed of a material that presents low gas permeability or gas impermeability and keeps the space between the tube member and the casing cylinder airtight is provided between the tube member and the casing cylinder.

The twenty-eighth aspect of the present invention is that defined in any of the twenty-fourth to twenty-sixth aspects, wherein a joint which is formed of a material that presents low gas permeability or gas impermeability and keeps the space between the tube member and the casing cylinder airtight is provided between the casing cylinder and the writing point assembly, so as to encase the tube member in the casing cylinder, keeping the tube member out of contact with the outside air.

The twenty-ninth aspect of the present invention is that defined in the twenty-seventh or twenty-eighth aspect, wherein a moisture-proof layer is formed on, at least, part of the outer surface of the joint, by two-color molding.

The thirtieth aspect of the present invention is that defined in any of the twenty-seventh or twenty-ninth aspects, wherein the material for the joint is ethylene vinyl alcohol copolymer (EVOH).

The thirty-first aspect of the present invention is that defined in the thirtieth aspect, wherein the material for the moisture-proof layer is polypropylene (PP) or polyethylene (PE).

The thirty-second aspect of the present invention is a writing instrument refill characterized in that the refill is integrally formed of the writing point assembly and tube member defined in any of the twenty-first to twenty-third aspects and can be removably fitted to the barrel cylinder of a writing instrument.

The thirty-third aspect of the present invention is a writing instrument refill characterized in that the refill is integrally formed of the writing point assembly, tube member and casing cylinder defined in any of the twenty-fourth to thirty-first aspects and can be removably fitted to the barrel cylinder of a writing instrument.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 1 of the present invention is applied.

FIG. 2 is a vertical half-sectional illustrative view for explaining a joint member and thereabout in FIG. 1.

FIG. 3 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 2 of the present invention is applied.

FIG. 4 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 3 of the present invention is applied.

FIG. 5 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 4 of the present invention is applied.

FIG. 6 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 5 of the present invention is applied.

FIG. 7 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 6 of the present invention is applied.

FIG. 8 is a vertical sectional illustrative view of a gas-pressurized writing instrument, depicting the writing instrument of embodiment 1 of the present invention, in a more specific manner.

FIG. 9(a) is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 7 of the present invention is applied, FIG. 9(b) a gas-pressurized writing instrument to which an embodiment 8 of the present invention is applied, and FIG. 9(c) a gas-pressurized writing instrument to which an embodiment 9 of the present invention is applied.

FIG. 10 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 10 of the present invention is applied.

FIG. 11 is a vertical sectional illustrative view for explaining the essential part of a joint member and thereabout of the gas-pressurized writing instrument of FIG. 10.

FIG. 12 is a vertical sectional illustrative view showing a gas-pressurized writing instrument to which an embodiment 11 of the present invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of the present invention will be detailed with reference to the drawings.

Embodiment 1

As shown in FIG. 1, the embodiment 1 is a gas-pressurized writing instrument including: an elongate, cylindrical resin tube member 14, which has a writing point assembly 10, made of metal or preferably a gas impermeable or low-permeable resin, holding a writing ball at the front end thereof and disposed at a front end 14a of the tube member, opens to the rear (at the rear end) and stores therein an ink 12, selectable from various types such as oil-based ink, water-based ink, thixotropic ink and the like, to be supplied to the writing point assembly 10 (a follower may be provided at the ink rear end); a casing cylinder 18 which is closed at the rear and encases the tube member 14, forming a space 16 that communicates with a rear end opening 14b of the tube member 14, wherein the casing cylinder 18 is formed of a material that presents low gas permeability or gas impermeability; and a compressed gas (dry air or nitrogen gas) charged and sealed in the space 16 formed between the tube member 14 and the casing cylinder 18. In this gas-pressurized writing instrument, as will be detailed later, a joint member 20 is provided, which holds the tube member 14 and writing point assembly 10 with the rear end of writing point assembly 10 being fitted to the front end of tube member 14, at around their fitted portion, within a passage-hole 30 formed therein. A point assembly holder 24 is provided covering the periphery of the joint member 20 and writing point assembly 10. Further, an exterior member 22 as a constituent of a barrel cylinder 28 of the gas-pressurized writing instrument is provided covering the point assembly holder 24 and the casing cylinder 18.

In this gas-pressurized writing instrument, joint member 20 for keeping the space 16 between the tube member 14 and the casing cylinder 18 airtight (in this embodiment, the joint member 20 is joined to writing point assembly 10 and casing cylinder 18) is provided. This joint member 20 is formed of a material that presents low gas permeability or gas impermeability. Here, the concept of `joining` includes fitting, bonding, welding and the like.

Joint member 20 has a hollow, approximately cylindrical configuration (having passage hole 30 penetrating therethrough) having a front end portion 20a enlarged flange-like, and most part of it other than the front end portion 20a sinks into the interior from the front end of casing cylinder 18. The flange-like front end portion 20a abuts the front end of casing cylinder 18 so that it will not sink into casing cylinder 18 more deeply.

Joint member 20 that keeps the space between tube member 14 and the casing cylinder 18 airtight and is formed of a material having low gas permeability or gas impermeability, is disposed between casing cylinder 18 and writing point assembly 10 while writing point assembly 10 is fitted into insertion hole 30 formed in joint member 20 and the tube member 14 joined to the rear end of writing point assembly 10 is enclosed in casing cylinder 18 so that the tube member 14 will not be in contact with the external air. This arrangement makes it possible to broaden the variation of material choice of tube member 14, so that the tube member 14 can be formed of a resin material other than that presenting low gas permeability or gas impermeability. As a result, a material that is excellent in oil resistance, liquid resistance, transparency, formability and clear drain performance, for example, can be used. Specifically, polypropylene (PP), polyethylene (PE) and the like can be used. It should be added that joint member 20 may be colored so as to enable distinction of ink color.

Now, joint member 20 and its vicinity will be described in detail. As shown in FIG. 2, in the vicinity of joint member 20, the front peripheral surface that is tapered toward the end of point assembly holder 24 faces the tapered inner peripheral surface of the front part 22f of exterior member 22. A step, namely, point assembly abutment 10b is formed in writing point assembly 10. Point assembly holder 24 having a stopper portion 24a that can abut the point assembly abutment 10b to limit forward movement of writing point assembly 10, is arranged at the front side of barrel cylinder 28 (on the writing point assembly 10 side) so as to allow the front end 10a of writing point assembly 10 to front to the outside. More detailedly, writing point assembly 24 is engaged with casing cylinder 18 while it covers the joint between writing point assembly 10 and joint member 20 and the joint between casing cylinder 18 and joint member 20 so as to allow the front end 10a of writing point assembly 10 to front to the outside. Here, point assembly holder 24 may be engaged with joint member 20. In the case where point assembly holder 24 is engaged with joint member 20, it is preferred that the joined portion between writing point assembly 10 and joint member 20 is covered by point assembly holder 24. If casing cylinder 18 is joined to writing point assembly 10 without provision of joint member 20, it is preferred that the joined area is covered by point assembly holder 24. Provision of such a point assembly holder 24 makes it possible to prevent the writing point assembly from rushing out as a result of compressed gas.

Further, a reduced diametric portion 10d having a smaller diameter is formed in the rear of writing point assembly 10. This reduced diametric portion 10d borders on a large-diametric portion 10e located in front at a step 10c and has a smaller diameter than the large-diametric portion 10e. Reduced diametric portion 10d is not limited to being formed step-wise from the step 10c, but can be formed so as to taper or so that the diameter gradually becomes smaller.

The rear end of this reduced diametric portion 10d is inserted into and fixed in tube member 14. Of the reduced diametric portion 10d, the portion between step 10c and the fixed portion of tube member 14 and reduced diametric portion 10d, is welded by heating to the front interior periphery (inner periphery of passage hole 30) of joint member 20, so as to keep airtightness. Joining in this way also prevents writing point assembly 10 from dislodging from tube member 14. In a case where no joint member 20 is provided, casing cylinder 18 may be directly jointed to the reduced diametric portion 10d.

Joining of joint member 20 or casing cylinder 18 to reduced diametric portion 10d provides the following effect.

Generally, it is preferred for a writing instrument that the size of the parts disposed around writing point assembly 10 is smaller (it is preferred that the parts become smaller as they approach the writing point). If a large-diametric part is arranged, the part interferes with the field of view, so that the user cannot have clear vision of the writing point (low visibility) when writing. It is also unpreferable in view of appearance because of the loss of stylishness.

When joint member 20 or casing cylinder 18 is joined, it may be joined to large-diametric portion 10e. However, large-diametric portion 10e is located closer to the writing point and is also greater in diameter. Therefore, if joined to the large-diametric portion 10e, joint member 20 or casing cylinder 18 is positioned closer to the writing point, so that these parts may obstruct the visibility of the writing point when writing. It is also unpreferable in view of appearance because of the loss of stylishness.

Provision of reduced diametric portion 10d having a smaller diameter at the rear of writing point assembly 10, fixture of the rear end of the reduced diametric portion 10d to tube member 14 and joining of joint member 20 or casing cylinder 18 to the reduced diametric portion 10d make the writing point visible and also provide stylishness in appearance.

Further, a metallic ring 25 is provided between joint member 20 and casing cylinder 18, so that the ring 25 is heated by induction heating (electromagnetically) to thereby fuse joint member 20 and casing cylinder 18 and cool them down to achieve joining (welding) to establish airtightness.

A clearance d is provided between engaging portion 24a of point assembly holder 24 and point assembly abutment 10b. In this embodiment, if joint member 20 and others swell or expand due to moisture absorption, the step or point assembly abutment 10b abuts engaging portion 24a of point assembly holder 24, causing a risk of point assembly holder 24 coming off. In this case, it is difficult to prevent an accidental rushing of writing point assembly 10 due to compressed gas. To deal with this, in the present embodiment, clearance d is provided aiming at prevention against the above problem resulting from the action of the step or point assembly abutment 10b abutting against engaging portion 24a of point assembly holder 24. Here, in point assembly holder 24 and casing cylinder 18, point assembly holder rear coupling 27b and casing cylinder rear coupling 27a are formed respectively, so that these couplings ride and pass over each other to complete engagement.

Though, in the present embodiment joint member 20 and casing cylinder 18 are joined by welding with heat, the rear couplings 27 are disposed at a different position away from the joint (explicitly, at a position to the front of the joint). Here, rear couplings 27 indicate the structures formed on the casing cylinder and joint member for engagement of the point assembly holder, such as point assembly holder rear coupling 27b and casing cylinder rear coupling 27a. Specifically, these are formed of engaging projections and indentations.

When joint member 20 and casing cylinder 18 are joined together by heat welding, there is a high risk of casing cylinder 18 etc., being thermally deformed. If point assembly holder 24 is engaged at such a place, there are cases where a sufficient strength of engagement cannot be obtained. Arrangement of rear couplings 27 at a position other than the joint provides a high enough coupling strength of point assembly holder 24.

Airtight closure joint sites 31 for keeping the space between the tube member 14 and the casing cylinder 18 airtight are disposed locally around writing point assembly 10.

Here, an `airtight closure joint site` indicates a place where parts are joined to each other to isolate a space keeping compressed gas from the outside air, such as a place where writing point assembly 10 and casing cylinder 18 joins, a place where writing point assembly 10 and joint member 20 joins, a place where casing cylinder 18 and joint member 20 joins, a place where casing cylinder 18 and a tail plug 26 joins when tail plug 26 is provided at the rear end of casing cylinder 18 as shown in FIG. 4., and the like.

For example, if tail plug 26 or the like is provided at the rear end of casing cylinder 18, an anti-removal measure is needed in order to prevent the tail plug 26 from coming off due to compressed gas. Formation of such joints at multiple places needs respective anti-removal measures, resulting in hindrance against efficient design and increase in cost.

Since writing point assembly 10 is usually formed separately, it necessarily needs to be coupled to another part. This means that the writing point assembly should have at least one joint site. Therefore, if other joint sites are localized around the writing point assembly, provision of the safety means such as anti-removal measures and the like can be also be disposed locally around the writing point assembly only, making it possible to reduce the number of places where anti-removal measures are formed. For example, in the configuration shown in FIG. 1, the part needed for anti-removal measures is point assembly holder 24 while casing cylinder 18 is formed of a one-piece cup-shaped figure to realize anti-removal measures.

Here, point assembly holder 24 may not only be transparent but also be colored to be opaque or translucent. This enables ink smudges inside the writing instrument (the rear part of writing point assembly 10 is principally prone to smudge during assembly) not to be seen from the outside, producing improvement in beauty and appearance quality. Further, opaque or translucent coloring enables color indication. In this case, the color is preferably made to correspond to the color of ink.

It should be noted that casing cylinder 18 may be disposed inside joint member 20. Fixture of joint member 20 as well as fixture between other parts is not limited to fixture by welding, but fitting, bonding and other fixing means can be considered. Also, the joint member may be formed using two-color molding. As an adhesive for bonding, those having sealing performance are preferred, and examples include polyvinyl alcohol solution, two-part epoxy, hot melt and others. When bonding is used, in order to secure the necessary gas barrier performance, bonding is made in combination with undercut sealing (fitting). It should be noted that it is very difficult to select an adhesive that has both sealing performance and adhesiveness. Therefore, it is preferred that joining be done by welding.

Covered around the periphery of casing cylinder 18 and point assembly holder 24 is a moisture-proof exterior member 22. This exterior member 22 is formed of front and rear parts (front part 22f and rear part 22r). These parts encloses casing cylinder 18 and are integrated by screw fitting, crimping or bonding at the joint 22b. It is advantageous, if possible, that the joint 22b is sealed.

Production of gas-pressurized writing instruments can be made by forming casing cylinder 18 and others with a material presenting low gas permeability or gas impermeability. However, most of such materials that present low gas permeability or gas impermeability (e.g., ethylene vinyl alcohol copolymer (EVOH), polyvinyl alcohol (PVA), polyacryl nitrile (PAN), nylon) tend to increase gas permeability or permit gas to permeate therethrough as the ambient relative humidity increases. For example, ethylene vinyl alcohol copolymer (EVOH) presents a very high barrier performance when dried. However, as the relative humidity increases, the barrier performance lowers. Covering the periphery of the tube member or/and casing cylinder with moisture-proof exterior member 22 can prevent reduction in barrier performance. Concerning the extent the exterior member 22 covers, it is most preferred that the whole of the material that presents low gas permeability or gas impermeability is covered, but part of the material may be covered. If partially covered, preferably the area the user's hand comes into touch with, most preferably the holding portion (grip portion 32) should be covered.

Here, the exterior member 22 may be formed in a hermetic structure so as to isolate the interior from ambient air. This makes it possible to improve thermal resistance and moisture resistance. The hermetic structure can be formed by joining (by fitting, bonding, welding or other methods) exterior member 22 with casing cylinder 18, point assembly holder 24, joint member 20, tail plug 26 and the like.

Exterior member 22 should have greater thermal resistance or/and moisture resistance than that of casing cylinder 18. In making choice of a low gas permeable or gas impermeable resin to be used for casing cylinder 18 from various resin materials, it is necessary to consider the influence of user's handsweat on the barrel when the user holds the writing instrument and writes with it. It is also necessary to consider a situation in which the writing instrument heats up as it is left on the top of the dashboard of an automobile. However, it is difficult to make choice of a resin material which meets the requirements of both low gas permeability and thermal resistance and moisture resistance. It is not so necessary to consider thermal resistance and moisture resistance when making choice of a material for casing cylinder 18 into which gas will be sealed, from various resin materials presenting low gas permeability or gas impermeability, if exterior member 22 presents the necessary thermal resistance or moisture resistance. Thereby, the range of selection of the resin can be made wider and the functionality can be improved. Preferred examples of the resin to be used for exterior member 22 include polypropylene (PP), polyethylene (PE), polyolefin, cyclic polyolefin, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), vinylidene chloride. Particularly, when the casing cylinder is formed of ethylene vinyl alcohol copolymer (EVOH), polypropylene (PP) and polyethylene (PE) resins are preferably used because these are excellent in thermal resistance, rigidity and adhesiveness. Further, it is also possible to enhance the moisture resistance and the interior visibility (light transmittance) for permitting easy monitoring of the remaining amount of ink therein while keeping up the gas barrier effect.

Though the exterior member 22 has a barrel cylinder structure, separated from casing cylinder 18 (when exterior member 22 is given as a constituent of barrel cylinder 28), the exterior member 22 is not necessarily separated from casing cylinder 18, but exterior member 22 can be formed (by two-color molding, vapor deposition, laminating or other methods) so that it integrally covers the casing cylinder 18 only or the whole part other than the front end 10a of writing point assembly 10.

Further, the wall of grip portion 32 of exterior member 22 at which the user holds, is made thicker than the other part of exterior member 22. The grip portion 32 that the user holds is most affected by handsweat of the user. If the wall thickness of this part is made greater than the other part of the exterior member, it functions to lessen the influence on the casing cylinder 18 inside the exterior member. Enlargement of the wall thickness can be performed by not only merely increasing the wall thickness but also by attaching a grip 33 as a separate part as in the embodiment shown in FIG. 1.

Further, when the writing instrument is heated for incineration or the like, the casing cylinder 18 and exterior member 22 break up first (casing cylinder 18 and exterior member 22 break up before writing point assembly 10 displaces from the joint portion), so that the sealed gas will be released to the outside of the aforementioned space. The term "breakup" in this description indicates fusion, generation of breakage and cracks, formation of a hole, disconnection of a joint if any. Since a breakup occurs first to discharge out the compressed gas, the pressure acting on writing point assembly 10 can be reduced, thus making it possible to reduce the risk of writing point assembly 10 bursting (rushing out).

In this case, point assembly holder 24 is preferably formed of a material having greater thermal resistance than casing cylinder 18. Preferred examples include polypropylene (PP), polyethylene (PE), polybutylene terephthalate (PBT), cyclic polyolefin, polyethylene terephthalate (PET), polyoxymethylene (POM), polyethylene naphthalate (PEN) and polyvinyl chloride.

As the material for the casing cylinder 18 and joint member 20, materials that present low gas permeability or gas impermeability, for example, ethylene vinyl alcohol copolymer (EVOH), nylon, transparent nylon and polyethylene terephthalate (PET) can be used. In particular, ethylene vinyl alcohol copolymer (EVOH) is preferred. The reason will be described later.

Because point assembly holder 24 serving as anti-removal for the writing point assembly 10 is provided and because the rigidity of casing cylinder 18 drops at a predetermined temperature even under incineration after its life, so that gas leak occurs to release gas pressure inside space 16, there is no risk of writing point assembly 10 rushing out from the front of the writing instrument or the refill.

The compressed gas to be sealed in the space 16 may employ nitrogen (N.sub.2) gas or air. Dry nitrogen gas or dry air having a humidity of 60% (at 25 deg. C.) or lower is preferably used.

The volume of space 16 provided between tube member 14 and casing cylinder 18 is adjusted to be 2 to 10 times the volume of ink initially stored in tube member 14, and the pressure inside the space 16 when almost all ink has been consumed at just before the end of writing life is adjusted to be 0.15 MPa to 0.6 MPa.

The reason the compressed gas volume relative to the ink volume is specified to be 2 to 10 times is that, if the volume of the compressed gas is lower than 2 times of the ink volume, it is impossible to obtain a sufficient pressure that forces ink out due to reduction of the ink volume when ink is used up by writing, and that the difference of the pressure at the life end from the initial pressure is too large, or the change in pressure is too large. On the contrary, if the ratio is set to be greater than 10 times, wasteful space is needed, resulting in increase in cost and giving rise to an appearance problem that the amount of ink is perceived to be relatively low.

The reason the pressure inside the space 16 at the ink end when almost all ink has been used up is specified to be 0.15 MPa to 0.6 MPa is that, with a pressure lower than 0.15 MPa, it is difficult to obtain a smooth write feeling for lack of pressure to drive ink out, water is prone to enter into writing point assembly 10 when writing is performed on a wet sheet of paper or the like, and water is prone to penetrate into writing point assembly 10 when the writing instrument drops into water. On the other hand, with a pressure greater than 0.6 MPa, it is difficult to prevent ink leakage from the writing point.

It is preferred that ink will not touch the casing cylinder 18 or/and joint member 20. In this case, it is possible to make the choice of a material without consideration of the ink resistance of the casing cylinder or/and joint member 20. Here, the above mentioned condition "ink will not touch casing cylinder 18 or/and joint member 20" not only means that ink will never touch casing cylinder 18 or/and joint member 20, but also includes the case where a small amount of ink adheres thereto. For example, there are cases where ink adheres to casing cylinder 18 and joint member 20 in the manufacture of a writing instrument. Such a state of adherence should also be considered as a case of "ink will not touch casing cylinder 18 or/and joint member 20".

It is also preferred that at least part of the tube member 14 and casing cylinder 18 is formed of a transparent or translucent resin, in view of easy monitoring of the remaining ink. Further, for the same reason, at least part of exterior member 22 and point assembly holder 24 may also be formed to be transparent or translucent.

Writing point assembly 10, tube member 14, casing cylinder 18 may be integrated so as to provide a refill which is detachably fitted into barrel cylinder 28 of a writing instrument.

Further, writing point assembly 10, tube member 14, casing cylinder 18 and exterior member 22 may be integrated into a refill.

Embodiment 2

FIG. 3 shows an embodiment 2 of a variational example in which the shape of joint member 20 is modified. In embodiment 2, joint member 20 is joined to tube member 14 and casing cylinder 18 so that most of tube member 14 is included in casing cylinder 18.

When a resin material other than that presenting low gas permeability or gas impermeability is used for tube member 14, it is preferred that the front end of tube member 14 is covered by a point assembly holder 24 that is formed of a low gas permeable or gas impermeable resin material, in order to prevent gas permeation from casing cylinder 18 through tube member 14. Detailedly, point assembly holder 24 is joined to writing point assembly 10 and casing cylinder 18 (heat welding, ultrasonic welding, bonding, etc., can be used as the joining method) to thereby prevent compressed gas leakage. When a resin material that presents low gas permeability or gas impermeability is used for tube 14, point assembly holder 24 does not necessarily employ resin material having low gas permeability or gas impermeability and does not necessarily need joining such as welding and the like. In this case, a configuration in which a moisture-proof layer is formed on the inner peripheral surface of tube member 14 as shown in FIG. 11 is preferred. The other configuration is basically the same as embodiment 1 of FIG. 1.

Embodiment 3

FIG. 4 shows an embodiment 3 in which a joint member 20 is extended to the rear and integrally formed with a casing cylinder 18 while a tail plug 26 is joined (fitted) to casing cylinder 18 and exterior member 22. Casing cylinder 18 and joint member 20 may be combined with another part such as tail plug 26 etc., or may be partially interposed with another part. Tail plug 26 in this case, however, needs to have low gas permeability or gas impermeability (gas barrier property) except the case where an aftermentioned gas barrier layer or the like is provided. Further, it is preferred that welding or any other anti-burst (rushing) measure is adopted.

In this embodiment, the casing cylinder 18 and writing point assembly 10 are joined so as to enclose the whole of tube member 14 within casing cylinder 18 and hence keep tube member 14 out of contact with the external air. Because tube member 14 is kept out of contact with the external air, it may use a material that is permeable by compressed gas. Therefore, it is possible to broaden the variation of material choice of tube member 14, so that various types of materials such as materials that are highly transparent, are easy to form and have high clear drain performance and others can be used.

While integral forming of joint member 20 and casing cylinder 18 as stated above reduces the number of parts, provision of tail plug 26 at the rear end of casing cylinder 18 to allow insertion of tube member 14 from the rear negates the reduction of the number of parts. Nevertheless, this arrangement enables choice and design of easily formable parts hence reduces the total cost as well as minimizing the size and improving the transparency.

Casing cylinder 18 shown herein is configured of two parts being joined together, in such a manner that the joint is formed with a lower joining strength than that of a joint with writing point assembly 10. Examples of the joints with writing point assembly 10 may include that between writing point assembly 10 and tube member 14, that between writing point assembly 10 and point assembly holder 24 and that between writing point assembly 10 and casing cylinder 18. In this embodiment, joints having a joining strength smaller than these joints are formed. Such a joint may be one where tail plug 26 is provided for casing cylinder 18 or tube member 14, one where casing cylinder 18 is formed of two parts, or one where a hole is formed in casing cylinder 18 and is joined with a part that fills that hole. It is also possible to consider a configuration where a hole of casing cylinder 18 is filled up with an adhesive or resin. As a method of making difference in joining strength, for example, changing the amount of adhesive, changing the deformed amount when fitting, differentiating the size of the joining area and other methods can be considered. The present embodiment 3 shows a configuration where tail plug 26 is provided at the rear of casing cylinder 18. Joining strength between tail plug 26 and casing cylinder 18 is set to be smaller than the joining strength at the joint between writing point assembly 10 and casing cylinder 18. Thus, this setting causes any other joint than that with writing point assembly 10 to break away so as to discharge the compressed gas outside even if the gas-pressurized writing instrument is heated. As a result, it is possible to reduce the pressure acting on writing point assembly 10 and reduce the risk of writing point assembly 10 bursting and/or ink 12 surging out due to pressure. Here, the joining strength is measured by applying a tensile force in the axial direction to the joint.

Here, for example, in a case, as in embodiment 1 shown with FIG. 1, where joint member 20 is provided between casing cylinder 18 and writing point assembly 10, a joint formed with a joining force smaller than the minor strength of the joining strength at the joint between writing point assembly 10 and joint member 20 and the joining strength at the joint between casing cylinder 18 and joint member 20 may be formed.

Examples of "the joint formed with a smaller joining strength" include, as stated above, one where tail plug 26 is provided for casing cylinder 18 or tube member 14, one where casing cylinder 18 is formed of two parts, or one where a hole is formed in casing cylinder 18 and is joined with a part that fills that hole. It is also possible to consider a configuration where a hole of casing cylinder 18 is filled up with an adhesive or resin. As the method of making difference in joining strength, for example, changing the amount of adhesive, changing the deformed amount when fitting, differentiating the size of the joining area and other methods can be considered. It is further possible that casing cylinder 18 is formed of two parts. For that method, one whereby tail plug 26 is provided for casing cylinder 18 or tube member 14, one whereby casing cylinder 18 is formed of two parts and these two parts are joined together, or one whereby a hole is formed in casing cylinder 18 and is joined with a part that fills that hole, can be considered.

Provision of a joint formed with a joining force smaller than the minor strength of the joining strength at the joint between writing point assembly 10 and joint member 20 and the joining strength at the joint between casing cylinder 18 and joint member 20, makes it possible to cause any other joint than that with the writing point assembly to break away so as to discharge the compressed gas outside even if the gas-pressurized writing instrument is heated. Therefore, it is possible to reduce the pressure acting on the writing point assembly and reduce the risk of writing point assembly 10 bursting and/or ink 12 surging out due to pressure.

When there are multiple joints, it is preferred that the joining strength at the joint with writing point assembly 10 (for example, the joint between the writing point assembly 10 and joint member 20 or the joint between the writing point assembly 10 and casing cylinder 18) is set at the greatest. This is because the joint with writing point assembly 10 is prone to weaken due to the constant load from writing and hence prone to burst out (rush out).

As stated above, when the casing cylinder 18 is adapted to break up first, when a joint with a smaller joining strength than that at the joint with the writing point assembly is provided, and when a joint formed with a joining force smaller than the minor strength of the joining strength at the joint between the writing point assembly and the joint member and the joining strength at the joint between the casing cylinder and the joint member is formed, the material for the casing cylinder (including a tail plug etc.) is preferably ethylene vinyl alcohol copolymer (EVOH).

In some cases, the temperature in storehouses for storage of writing instruments may reach 50 deg. C. to 70 deg. C. If the casing cylinder or other parts will break away in this temperature range, such an article is unmarketable. Ethylene vinyl alcohol copolymer (EVOH) will not decompose in the above temperature range, and starts decomposing at a predetermined temperature above 90 deg. C., which is in excess of the above temperature range. Therefore, this copolymer enables easy storage and will easily decompose if put under incineration providing the effect of discharging the compressed gas outside. The copolymer also has a low gas permeability, providing the function of hardly permitting a gas to permeate therethrough to the outside in an ordinary state. Other material examples are, nylon, transparent nylon, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT) and polyacryl nitrile (PAN).

Alternatively, a thin-wall portion 36 may be formed at a part (the outer periphery in the drawing) of casing cylinder 18. Also, a thin-wall portion 36 may be formed at the bottom of casing cylinder 18, as will be shown in embodiment 4 with FIG. 5. All these configurations enable the thin-wall portion 36 to break first so that the compressed gas will be smoothly discharged out when heated under incineration or the like. The other configuration is basically the same as embodiment 1.

Embodiment 4 and Embodiment 7

FIG. 5 shows an embodiment 4 of a gas-pressurized writing instrument in which a moisture-proof layer 18a is integrally formed on the outer surface of casing cylinder 18 and the outer surface of joint member 20 by fusion bonding using two-color molding. In this embodiment, moisture-proof layer 18a is formed on the entire outer surface of these. In this case, since moisture-proof layer 18a provides part of the function of exterior member 22, exterior member 22 becomes an optional component.

Moisture-proof layer 18a does not need to be formed on the whole surface, but is preferably formed in, at least, the areas exposed and in contact with the external air. When partially formed, moisture-proof layer 18a is formed in a grip portion 32 which is held by the hand and fingers.

As the material for moisture-proof layer 18a formed on the outer surface of the casing cylinder 18, polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), modified polyphenylene ether (m.PPE), cyclic polyolefin, vinylidene chloride, paraffin and the like can be used for improvement of moisture-proof performance. Polypropylene (PP) and polyethylene (PE) are particularly preferred for two-color molding. When the casing cylinder is formed of ethylene vinyl alcohol copolymer (EVOH), polypropylene (PP) and polyethylene (PE) resin are preferably used. This is because it is possible to enhance the moisture resistance and the interior visibility (light transmittance) for permitting easy monitoring of the remaining amount of ink therein while keeping up the gas barrier effect. Further, it is because these are also excellent in thermal resistance, rigidity and adhesiveness.

Concerning two-color molding of moisture-proof layer 18a, when a separate joint member 20 is fitted to or joined to casing cylinder 18, it is necessary to form a moisture-proof layer by two-color molding for each of elements 18 and 20, except the case where point assem