US3082740A - Writing instrument - Google Patents

Description

WRITING INSTRUMENT Filed July 10, 1961 I 31/ IZ4 /26 FIG. ,1

FRANK $365??? 4 m5 ATTORNEYS United States Patent 3,082,740 "WRITING INSTRUMENT Frank A. Eckerle, Tenafly, Ni, assignor to Northern Industrial Products Company, Hachensack, NJ. Filed July 10, 1961, Ser. No. 122,884 4 (Zlaims. (ill. Hit-42.4)

This invention relates to ball point pens of the type provided with a relatively large diameter ink cartridge and, more particularly, to a new and improved ball point pen having a large diameter ink cartridge which cannot leak.

This application is a continuation-impart of my copending United States application Serial Number 83 6,107, filed August 26, 1959, for Writing Instrument, now abandoned.

Customarily, ink cartridges for ball point pens carry a ball tip at one end and are open to the atmosphere at the other end to permit air to enter the cartridge as the ink is dispensed through the ball tip by rotation of the ball during writing. 'If the inner diameter of the ink cartridge is small enough so that it acts as a capillary, ink is normally retained within the cartridge regardless of its orientation. In order to provide a cartridge of reasonable length having a larger ink capacity, however, the diameter must be increased beyond the maximum value at which the cartridge acts as a capillary, and in such cartridges, a seal must be provided to prevent ink from leaking out of the open end of the cartridge.

Conventional seals for larger-than-capillary cartridges are of either of two types, each of which has certain disadvantages. One type of conventional seal, such as that described in the Henriksen Patent No. 2,678,634, for example, comprises a non-rigid plug located at the rear of the ink column consisting of a pasty mass of grease, parafiin or wax. This form of plug tends to mingle with the ink in the reservoir until eventually it becomes ineffective to prevent leakage. Moreover, the plug material is apt to contaminate the ink. The other type of conventional seal utilizes a rigid piston follower, such as the one shown in the Cofield, In, et al. Patent No. 2,777,422 for example, which necessarily requires that a clearance be provided between the piston and the inner cartridge wall in order to permit the piston to move within the cartridge as the ink supply is depleted. This clearance is usually filled with a thin flowable liquid sealing material, such as the thixotropic liquid described in the Cofield, Jr., et al. patent for example, inasmuch as a certain amount of the sealing material is deposited on the cartridge wall as the piston moves within the cartridge, a substantial supply of the material must be provided.

Heretofore, the supply of sealing material for a rigid piston follower of this type has been retained in place by inserting it between two separated pistons or through a transverse bore in the piston into an annular space or cavity formed in the periphery of the piston, both of which constructions are illustrated in the Cofield, J r., et. al. patent. In the latter case, because a thin, flowable sealing material is used, there is not-hing to prevent it from flowing back through the bore and running out of the piston after it has been inserted. Furthermore, the rigid piston follower arrangements not only require complex fabricating and assembly operations but also, because the supply of sealing material is relatively free to flow, is unenclosed, and is separated from the ink by only a short distance along the clearance space between the piston and the cartridge wall, such pistons frequently permit ink to invade and mingle with the supply of sealing material, thereby degrading it. Moreover, when ink does invade the annular space surrounding the piston, which is almost inevitable as the piston moves forwardly in the cartridge,

known type.

BhfiSZfl ill Patented Mar. 26, I953 ice 2 the entire supply of sealing material becomes contaminated and theeffectiveness of the seal is soon lost. In addition, pistons of'this type also allow substantial quantities of sealing material to rise through the column of ink'to obstruct the writing point when the penis inverted.

Accordingly, it is an object of the present invention to provide a new and improved ball point pen which effectively overcomes the above-mentioned disadvantages of the prior art constructions referred to above.

Another object of the invention is to provide a sealing arrangement for a ballpoint-pen cartridge of greater-thancapillary diameter which is of simple construction and continuously r'enews the "seal during use ofthe pen.

A further object of the invention is to provide a new and improved piston follower'for ink cartridges.

An additional object of the invention is to provide "a single piston sealing arrangement for ball point pe'n ink cartridges which is simple to manufacture, is of rugged construction, is inexpensive, and is generally superior to prior art sealing arrangements.

These :and other objects of the invention are accomplished by providing a single cup-shaped rigid follower piston having an interior cavity within the piston and a plurality of openings inthe wall of the piston providing communication between the interior cavity and the outer surfiace thereof. In order to provide a seal within the ink cartridge of a ball point pen, the internal cavity in the piston is filled with a sealing material having the consistency of a paste, as opposed to the prior art free-flowing type of material, and the annular clearance space between the piston and the inner cartridge wall, along with the openings leading thereto, are also filled with the same sealing material.

In a preferred embodiment, the piston has two spaced shallow circumferential grooves which are partly cut through to form slots which communicate with the interior cavity. The provision of the grooves and slots results in the formationo f external piston rings of sealant which piston rings seal against the ink tube wall. The embodiment assures uniform distribution of the sealant about the piston exterior, thus providing a particularly effective seal.

Further objects and advantages of the invention will be apparent from a reading of the following description in-conjunction with the accompanying drawings inwhich: I FIG. 1 is a view in elevation, partly broken away, illustrating a typical ball point pen ink cartridge having a single piston seal arranged according to the invention;

FIG. 2 is a perspective front elevation view of the sealing piston utilized in the cartridge of FIG. 1; and

FIG. 3 is a view in longitudinal section of another piston arranged according to the invention.

Referring now to the drawings, and in particular to FIGS. 1 and 2, reference numeral 10 generally indicates a typical ball point pen ink cartridge having a seal arranged according to the present invention. The cartridge comprises a tube of the conventional type generally referred to by numeral 2 having a narrow neck portion 3 and a Wider reservoir portion 5. The neck portion 3 carries at its forward end a ball tip portion generally indicated by reference numeral 11. The ball tip portion includes a ball proper 4, rotatably mounted in the tube tip 6 in conventional manner. The tip tube 6 has an enlarged rear portion 8 which is press fitted into the forward end of the neck portion 3 of the cartridge.

The diameter of the reservoir 5 of the tube 2 is larger than the maximum diameter capable of acting as a capillary and is filled with ink or similar writing fluid 12. Preferably the fluid 12 is the usual relatively thick and viscous ink customarily used in ball point pens, but of course if desired, the writing fluid may be of any other The ink or writing fluid is dispensed during writing by the rotation of the ball 4 as is well known in the art.

The rear end 14 of the tube 2 is open and in order to prevent the ink from flowing out through the opening 14 a piston member generally referred to by reference numeral 30 is placed on top of the ink. Details of the construction of the piston 30 as used in the embodiment of FIG. 1 can be seen from FIG. 2. It will be noted that the piston is substantially cylindrical and cup-shaped, having a hollow interior forming a storage space 34. The piston 30 is provided with two spaced circumferential grooves 20 and 22, respectively, of relatively shallow depth. Groove 20 is cut through along a portion of its circumference so as to form a slot 24 while groove 22 is correspondingly cut through along a different portion of its circumference so as to form a slot 26. The slots 24 and 26 thus communicate with the storage space 34. It will be noted that the slots 24 and 26 occupy more than half of the groove circumference and that they are partly overlapping. The grooves 20 and 22 are thus the extension of slots 24 and 26, respectively. The piston also has a tapering lower portion 28 as seen in FIGS. 1 and 2. The outer diameter of the piston 30 is only slightly smaller than the inner diameter of the tube 2 so that the piston, with very little play, fits coaxially into the space defined by the tube 2 to form a gap 40 having a width of 0.0020.020". In order to keep the piston member 34 in position at the upper surface of the ink when the pen is in the writing position, the member is formed of a material having a specific gravity slightly less than that of the ink 12 and which is not soluble in or miscible with the ink. Typically, the specific gravity of the material used for the piston 34 is about 1.06, while that of the ink is about 1.14. Inasmuch as the seal effectively prevents any ink from passing to the other side of the piston member, it will be apparent that the piston remains as a barrier between the ink and the air in the cartridge regardless of the orientation of the writing instrument. The preferred material for the piston member 34 is an acrylonitrile butadiene styrene copolymer, such as the material commercially known as Kralastic MM. Other lightweight plastic materials are also suitable for use in fabricating the piston member.

A sealing material 32 (FIG. 1) is inserted into the hollow interior or storage space 34 of the piston. When the cartridge is originally assembled, the piston 30 is placed on top of the ink column 12 whereaf-ter the sealing material 32 is injected into the piston, whereby a small amount of the sealing material will be urged through the openings or slots 24 and 26.

Inaccordance with the invention, the sealing material 32 has plastic characteristics and is thus displaceable under the action of a moving force in any direction and without rupture, is non'thioxtropic and has a pasty consistency. Obviously, if the sealing material were thixotropic, it could not have the desired paste-like consistency under all conditions. Further, the sealant is temperature stable within a range of approximately to 200 F. The temperature stability of the sealant is important because ball point pen cartridges are subjected to varying temperatures within wide ranges. Thus, the ball point pen may be exposed to winter temperature, on the one hand, and to direct sunlight in a show case or display window, on the other hand, while the user will expect proper functioning under all these conditions. The sealant also should have a worked penetration of approximately 300-385 mm./10 in accordance with A.S.T.M. test D2l7-52T. Penetration is a measure of the consistency of a material and is expressed as the distance in tenths of a millimeter that a standard cone passes vertically into the material at a temperature of 77 F. during a period of seconds. Also the specific gravity of the sealant has to be less than that of the piston and of the ink. This is so because the assembled cartridge is normally subjected to centrifugation to expel trapped air. If the specific gravity of the sealant were greater than that of the ink, the sealant would be urged towards the ball tip during the centrifugation. In addition, the sealing material should have a minimum tendency to bleed or form oils or other liquids which could flow freely into the ink supply and, for this reason, materials containing highly effective thickening agents are preferred. Extensive experiments have shown that particularly useful in this regard is the material known commercially as Rykon No. 0 which is a petroleum grease containing an organic thickening agent. Rykon is manufactured by Superla Products, Inc., of Chicago, Illinois.

A sealant of the kind defined which is injected into the interior cavity 34 of the piston will exit through the discharge openings or slots 24 and 26 and into the narrow gap 40 between the ink tube wall and the piston to fill the latter and to form a thin but effective seal between these two elements, thus preventing ink from reaching the open rear end of the cartridge.

In operation, as ink from the reservoir is drawn through the ball tip by use of the pen, the buoyant effect of the ink on the piston is reduced and the piston moves toward the forward end of, the cartridge. Inasmuch as the sealant has the properties and characteristics set forth above, it permits the piston to slide forwardly easily in the cartridge while at the same time maintaining its shape and providing an effective seal. Moreover, as a deposit of sealing material is left behind by the forward motion of the piston, a corresponding amount of fresh sealing ma terial is drawn through the slots 24-, 26 from the supply within the cavity 34, thus renewing the sealing material in the gap at a point close to the ink supply. This is due to the suction action produced by the rotating ball. In this way, any sealing material which has been contaminated by invasion of ink from the tube is displaced rearwardly and replaced by uncontaminated material adjacent to the ink supply, the contaminated material eventually being left behind on the cartridge wall. As a result, an effective seal is maintained throughout the life of the cartridge.

During this process, the sealing material which emeregs through the slots 24 and 26 will enter the narrow gap 40 formed between the inner face of tube 2 and the outer piston surface to form two sealing piston rings at the level of the grooves and slots. The formation of the rings of sealing material is facilitated by the construction of the piston. As the grooves 20 and 22 extend circumferentially they will be entirely filled with the sealant emerging through the slots. The piston rings act very much like the piston rings in motor car engines. When the ink is dispensed from the cartridge, the piston 30, due to its own gravity or weight and due to air pressure and the suction action caused by the rotation of the ball 4, will move downwardly with the ink column so as to be constantly on top thereof. In doing so, the sealant in the gap 40 will be distributed to fill substantially the entire space between the piston and the wall of the tube 2.

Thus, contrary to prior art constructions wherein the entire or at least the major amount of the sealant is, from the very outset, lodged between the piston and the tube, the present construction allows for storage of the bulk of the sealant protected from ink contact while the supply of sealant between the piston and the tube is continuously replenished from this storage supply.

Moreover, if any ink moves to the annular space 40 surrounding the piston member 30 and mingles with the sealing material, the unique construction of the piston in the present invention prevents permanent degradation of the seal. This results from the fact that, as the piston moves forwardly in the cartridge leaving behind a deposit of material on the cartridge wall, fresh and uncontaminated material from the supply within the cavity 34 is drawn through slots 24, 26 as described above to provide a renewed seal. Furthermore, with substantially all of the sealing material effectively isolated from the ink and only a very small quantity immediately adjacent thereto, the amount of sealing material which could move into and mingle with the ink supply 12 in the cartridge is effectively restricted to an absolute minimum as contrasted with conventional piston seals wherein substantially all of the sealing material is in close proximity to the ink supply so that the ink can become contaminated with relatively large quantities of, sealing material.

In the embodiment of the piston shown in FIG. 3, a cup-shaped piston member 130 having an internal cavity is provided with wall openings in the form of peripheral slits 124- and 120 to provide communication between the internal cavity and the external surface of the piston whereby sealant may be supplied from the internal cavity to the outside of the piston. Thus, except for the absence of the peripheral grooves 20 and 22 the structure and operation of a ball point pen utilizing this piston member is the same as that described above with respect to the piston member 3-0 of FIGS. 1 and 2.

In a typical ball point pen cartridge having an internal diameter of 0.175 inch, the piston member of the type shown in FIGS. 1 and 2 had an outside diameter of 0.170 inch, and an internal cavity of 0.134 inch diameter, the depth of the internal cavity being 0.218 inch and the grooves and slots in the walls having a width of 0.025 inch. The peripheral grooves had a depth of from 0.006 to 0.018 inch. With this arrangement, over 80 percent of the total initial quantity of sealing material is contained within the cavity in the piston and thereby preserved from contamination so that fresh sealing material is available even when the piston approaches the forward end of the cartridge.

Although the invention has been described herein with reference to specific embodiments, many modifications and variations therein will readily occur to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the invention as defined by the following claims.

I claim:

1. A cartridge for a writing instrument comprising a tubular reservoir containing writing fluid having a diameter larger than the diameter necessary to form a capillary for the writing fluid and having one end open to the atmosphere, a narrow neck portion at the other end of the reservoir to supply writing fluid to a writing tip, a piston member within the reservoir between the writing fluid and the open end comprising a cup-shaped piston member having an outside diameter slightly smaller than the inside diameter of the reservoir, the piston member being formed with an internal cavity which is open to the atmosphere, a substantial reserve supply of temperaturestable sealing material having a paste-like consistency within the cavity of the piston, said piston member being provided with outwardly open, circumferentialiy extending slot means in communication with said reserve supply of said sealing material in the cavity of the piston, said slot means extending circumferentially around the piston member for supplying sealing material over the em tire inner wall of said tubular reservoir and comprising a plurality of circumferentially extending slots positioned at diflerent levels lengthwise of the piston member, and an annular ring of the same sealing material which is substantially smaller in quantity than the reserve supply forming a seal between the piston member and the wall of the reservoir and communicating with the supply in the internal cavity through said slot means, whereby there is a substantially greater quantity in the piston cavity so that the reserve supply of sealing material in the cavity is isolated from the writing fluid to preserve it from contamination thereby and as the piston moves in the reservoir uncontaminated sealing material from the reserve supply passes through said slot means to replace the material in the ring.

2. A cartridge according to claim 1, wherein said slot means extend for substantially 360 circumferentially around the piston member.

3. A cartridge according to claim 1, including groove means formed in the outer surface of the piston member comprising at least one groove extending circumferentially around the piston member and communicating with one of the slots of the slot means.

4. A cartridge according to claim 1, wherein the volume of the internal piston cavity is equal to at least about percent of the total volume of the cavity and the space between the piston member and the wall of the reservoir.

References Cited in the file of this patent UNITED STATES PATENTS 551,540 Fowler Dec. 17, 1895 2,777,422 Cofield et al Jan. 15, 1957 FOREIGN PATENTS 1,028,325 France Feb. 25, 1953 1,097,511 France Feb. 16, 1955

Claims (1)

1. A CARTRIDGE FOR A WRITING INSTRUMENT COMPRISING A TUBULAR RESERVOIR CONTAINING WRITING FLUID HAVING A DIAMETER LARGER THAN THE DIAMETER NECESSARY TO FORM A CAPILLARY FOR THE WRITING FLUID AND HAVING ONE END OPEN TO THE ATMOSPHERE, A NARROW NECK PORTION AT THE OTHER END OF THE RESERVOIR TO SUPPLY WRITING FLUID TO A WRITING TIP, A PISTON MEMBER WITHIN THE RESERVOIR BETWEEN THE WRITING FLUID AND THE OPEN END COMPRISING A CUP-SHAPED PISTON MEMBER HAVING AN OUTSIDE DIAMETER SLIGHTLY SMALLER THAN THE INSIDE DIAMETER OF THE RESERVOIR, THE PISTON MEMBER BEING FORMED WITH AN INTERNAL CAVITY WHICH IS OPEN TO THE ATMOSPHERE, A SUBSTANTIAL RESERVE SUPPLY OF TEMPERATURESTABLE SEALING MATERIAL HAVING A PASTE-LIKE CONSISTENCY WITHIN THE CAVITY OF THE PISTON, SAID PISTON MEMBER BEING PROVIDED WITH OUTWARDLY OPEN, CIRCUMFERENTIALLY EXTENDING SLOT MEANS IN COMMUNICATION WITH SAID RESERVE SUPPLY OF SAID SEALING MATERIAL IN THE CAVITY OF THE PISTON, SAID SLOT MEANS EXTENDING CIRCUMFERENTIALLY AROUND THE PISTON MEMBER FOR SUPPLYING SEALING MATERIAL OVER THE ENTIRE INNER WALL OF SAID TUBULAR RESERVOIR AND COMPRISING A PLURALITY OF CIRCUMFERENTIALLY EXTENDING SLOTS POSITIONED AT DIFFERENT LEVELS LENGTHWISE OF THE PISTON MEMBER, AND AN ANNULAR RING OF THE SAME SEALING MATERIAL WHICH IS SUBSTANTIALLY SMALLER IN QUANTITY THAN THE RESERVE SUPPLY FORMING A SEAL BETWEEN THE PISTON MEMBER AND THE WALL OF THE RESERVOIR AND COMMUNICATING WITH THE SUPPLY IN THE INTERNAL CAVITY THROUGH SAID SLOT MEANS, WHEREBY THERE IS A SUBSTANTIALLY GREATER QUANTITY IN THE PISTON CAVITY SO THAT THE RESERVE SUPPLY OF SEALING MATERIAL IN THE CAVITY IS ISOLATED FROM THE WRITING FLUID TO PRESERVE IT FROM CONTAMINATION THEREBY AND AS THE PISTON MOVES IN THE RESERVOIR UNCONTAMINATED SEALING MATERIAL FROM THE RESERVE SUPPLY PASSES THROUGH SAID SLOT MEANS TO REPLACE THE MATERIAL IN THE RING.

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