WRITING UTENSIL

Abstract

 An equalizing tube having an equalizing passage formed therein is inserted in an ink storage chamber such that the front end of the tube communicates with that portion of the ink storage chamber which is located near a pen tip, and the rear end of the tube communicates with the outside. During non-writing, the equalizing passage is made to serve as a feeder and used to compensate expansion/contraction of, for example, air in the ink storage chamber so as to maintain the pressure therein equal to the atmospheric pressure. During writing, a portion near the pen tip is set, using the equalizing passage, under a pressure equal to the atmospheric pressure to prevent the head pressure of ink from being applied to the pen tip. Thus, the head pressure of ink is compensated during writing, thereby applying a constant pressure substantially equal to the atmospheric pressure to the pen tip. Further, expansion/contraction of air, for example, in the ink storage chamber is compensated to maintain the internal pressure of the chamber equal to the atmospheric pressure.

Description

Technical Field

[0001] This invention relates to a writing instrument of an ink storing type which contains ink in the form of liquid. More particularly, the invention relates to a writing instrument of an ink storing type in which the pressure of ink to be supplied to a pen tip incorporated in the instrument is kept constant.

Background Art

[0002] In general, in light of the type of ink storage, writing instruments are grouped into a so-called cotton insertion type in which its ink chamber is filled with a porous body such as cotton that holds ink in it by its capillary force, and an ink storage type which contains ink in the form of liquid in an ink storage chamber.

[0003] The cotton insertion type has a simple structure. However, it contains a small amount of ink and supplies its pen tip with ink, using a capillary force. Thus, the amount of ink to be supplied to the pen tip is limited. Accordingly, it is possible that the supply amount of ink to the pen tip will not be sufficient and hence writing will be blurred.

[0004] On the other hand, the ink storage type can store a great amount of ink, and the amount of ink to be slides in accordance with the expansion or contraction of ink and the consumption of ink as a result of writing, thereby maintaining the pressure of ink substantially equal to the atmospheric pressure. In addition, to control the supply of ink to the pen tip, means such as a valve mechanism that opens at a slight pressure difference is provided between the ink storage chamber and the pen tip.

[0005] The above-described structures, however, cannot sufficiently compensate a change in head pressure depending upon the position of the writing instrument, although they can compensate expansion, contraction, etc. of air or ink in the ink storage chamber. In other words, since when writing, the writing instrument is used, substantially vertically, if the axial depth between the free surface of ink in the ink storage chamber and the pen tip is, for example, 80 mm, head pressure corresponding to 80 mm will occur. Although such head pressure is a low pressure, it is possible that some types of pen tips will cause a change in handwriting, or cause an ink blob to fall as a result of oozing of ink from the pen tips.

[0006] There are various types of pen tips. A so-called ball tip in which a ball is rotatably held at the tip of a ball holder, and a so-called felt tip consisting of a porous body that is formed by hardening, for example, fiber are widely used as the pen tips. Although these pen tips have respective properties, ink sealing pressure and ink-drawing pressure are exemplified as their common important properties.

[0007] In these pen tips, ink is held by a capillary force that occurs, for example, in a gap between a ball and a ball holder in the ball tip, or in a gap between fibers in the felt tip, thereby realizing an ink-sealing function. A pressure difference between the outside and the inside of the pen tip for maintaining the sealing function is called the ink-sealing supplied to the pen tip is not limited principally. This is advantageous in that characters will not be blurred even if they are written quickly. However, in the ink storage type, it is necessary to employ a mechanism for compensating, for example, expansion or contraction of air or ink contained in the ink storage chamber due to, for example, a change in temperature, or a change in head pressure due to a change in the position of the writing instrument, or to employ a mechanism for controlling the amount of ink to be supplied to the pen tip. Thus, the ink storage type inevitably has a complicated structure. Even if such compensating mechanisms are employed, the amount or pressure of ink to be supplied to the pen tip may be unstable depending upon, for example, changes in temperature, pressure, the position of the writing instrument, etc.

[0008] Writing instruments of the ink storage type have various structures. A bellow-feeder structure employed in a so-called fountain pen can be mentioned as a typical example. This structure holds ink, using a capillary force, in a feeder that consists of a bellow passage of a small cross section. When, for example, air expands in the ink storage chamber, part of the ink is pushed by the expanded air into the feeder and held in it. When, on the other hand, air contracts in the ink storage chamber, ink held in the feeder is sucked and returned into the ink storage chamber. Thus, expansion or contraction of air in the ink storage chamber is compensated to maintain the pressure of ink.

[0009] There is another structure which uses a slide plug. In this structure, the ink storage chamber is made cylindrical and has its tail-end side open to the outside air. In this chamber, an axially slidable slide plug is provided in an airtight and liquid-tight manner, thereby separating ink from air in the ink storage chamber. In this structure, the slide plug pressure. If the pressure difference between the outside and the inside of the pen tip exceeds the ink-sealing pressure, for example, if the internal pressure exceeds the ink-sealing pressure, ink oozes through the gap, thereby causing an ink blob to fall. On the other hand, if the internal pressure is lower than the ink-sealing pressure, ink in the gap is sucked up and air is introduced through the gap into the ink storage chamber.

[0010] Further, when in the pen tips, ink contained in the gap has been consumed as a result of writing, ink is newly introduced from the inside into the gap. The pressure for newly drawing ink is the ink-drawing pressure. When the internal pressure is higher than the ink-drawing pressure, writing cannot be performed. The ink-sealing pressure and the ink-drawing pressure assume different values between different types of pen tips. In pen tips of the same type, the ink-sealing pressure and the ink-drawing pressure assume substantially the same values.

[0011] If ink used in the ball tip is oil ink of a high viscosity, it has an ink-sealing pressure and an ink-drawing pressure corresponding to about 100 mm. Water-color ink of a low viscosity or quick drying ink containing a volatile solvent has an ink-sealing pressure and ink-drawing pressure corresponding to only about 20 mm. On the other hand, the felt tip generally has a high ink-sealing pressure and ink-drawing pressure corresponding to 100 mm to several hundreds mm.

[0012] Since the felt tip has a high ink-sealing pressure, i.e. has a high ink holding force based on its capillary force, it can transfer only a small amount of ink onto a writing surface of a low hygroscopic property, such as a resin film. In general, only "thin" writing is executed on such a writing surface. On the other hand, the ball tip that uses water-color ink or quick drying ink can perform thick writing even on a surface of a low hygroscopic property, such as a resin film, since it has a small ink holding force. In particular, in the case of using quick drying ink, ink transferred onto the resin film instantly dries up. Therefore, writing can be performed even on a surface of a water repellent material such as a polyethylene film, which is impossible in the conventional cases. Moreover, since in the ball tip, ink attached to the surface of the ball is transferred onto a writing surface while the ball rotates, it is advantageous that, for example, the outline of a written character is clear and even a thin line can be written.

[0013] However, the ball tip, using such water-color ink or quick drying ink, has an ink-sealing pressure and ink-drawing pressure corresponding to only about 20 mm, as aforementioned. Accordingly, a writing instrument using the ball tip must adjust, in a reliable manner, the pressure of ink supplied to the ball tip to a value substantially equal to the external or atmospheric pressure.

[0014] Furthermore, the felt tip has a high ink-sealing pressure and ink-drawing pressure as described above. However, when a pressure difference occurs between the outside and the inside, the amount of ink held in the felt tip easily changes, although neither fall of an ink blob nor suction of air occurs. Accordingly, when the internal pressure has increased even only slightly, the amount of ink contained in the felt ball increases to thereby cause a so-called ink rich state, resulting in undesirably thick handwriting. When, on the other hand, the internal pressure has reduced even only slightly, the amount of ink contained in the felt ball reduces to thereby cause a so-called ink poor state, resulting in undesirably thin handwriting. Therefore, even in the case of a writing instrument including the felt tip, it is a matter of course that to reliably control the pressure of supplied ink is preferable.

[0015] The above-described feeder mechanism, however, has basically only a function for compensating expansion or contraction of, for example, air in the ink storage chamber to maintain the pressure in the ink storage chamber substantially equal to the atmospheric pressure. It cannot compensate the above-mentioned head pressure of ink. Also, since this feeder has a complicated passage in the form of a bellow, a disadvantageous phenomenon will easily occur in which ink dries within the passage and blocks it. This disadvantage is conspicuous when, in particular, using quick drying ink.

[0016] In the case of a writing instrument having the aforementioned slide plug, a difference between the head pressure of ink in the ink storage chamber and pressure corresponding to the sliding resistance of the slide plug acts upon the pen tip during writing. Also in this case, the pressure of ink changes in accordance with a change in the head pressure of ink. Accordingly, also in the writing instrument having the slide plug, it is difficult to accurately control the pressure of ink applied to, for example, a water-color-ink ball tip, to a value falling within the range of the ink-sealing pressure.

[0017] As described above, in the ink storage type writing instrument, it is preferable to maintain the pressure in the ink storage chamber constant at all times, to suppress, for example, fluctuation of ink pressure due to, for example, the head pressure of internal ink during writing, and to control the pressure of ink to be supplied to the pen tip to a constant value equal to the atmospheric pressure. The conventional ink pressure compensating mechanism cannot sufficiently satisfy these matters.

Disclosure of Invention

[0018] This invention has been developed in light of the above-described circumstances, and aims to provide a writing instrument of a simple structure, which is operable in a highly reliable manner, can accurately control the pressure of ink applied to a pen tip incorporated therein, to a value almost equal to the atmospheric pressure, and can realize stable writing even if the ink-sealing pressure range of the pen tip is narrow like a ball tip using water-color or quick drying ink.

[0019] To attain the aim, there is provided a writing instrument characterized by comprising: a main body;

a pen tip provided at a front end of the main body; an ink storage chamber formed in the main body and communicating with the pen tip; and an equalizing passage located substantially parallel to an axis of the ink storage chamber, having a front end communicating with a front end portion of the ink storage chamber, which is near to the pen tip, and a rear end communicating with an outside at a rear side of the main body.

[0020] Since the interior of the ink storage chamber always communicates with the outside via the equalizing passage, if air or ink in the ink storage chamber has expanded or contracted due to, for example, a temperature change, ink is pushed into the equalizing passage or ink or air is sucked up via the equalizing passage to thereby always maintain the pressure in the ink storage chamber equal to the atmospheric pressure. When the writing instrument is in the standing position to perform writing, the head pressure of ink in the ink storage chamber is generated. Since, however, the equalizing passage communicates with a front end portion of the ink storage chamber, which is near to the pen tip, the pressure of ink becomes equal to the atmospheric pressure at the communicating position of the equalizing passage. Accordingly, air existing in the ink storage chamber above the ink is under a negative pressure by a value corresponding to the head pressure of the ink. In this state, the pressure balances and stabilizes.

[0021] Thus, the pressure in the communicating portion of the equalizing passage near the pen tip in the ink storage chamber is always equal to the atmospheric pressure even during writing, and a head pressure corresponding to the distance between the communicating portion of the equalizing passage and the pen tip, i.e. only a low head pressure, is applied to the pen tip. This means that even a pen tip having ink sealing pressure falling within a narrow range, such as a ball tip is free from, for example, falling of ink blob and can execute stable writing. Further, the ink pressure control mechanism of this writing instrument basically has no movable portions, no fine orifices or no portions using a capillary force, and hence the instrument operates in an extremely stable and reliable manner and can be produced easily.

[0022] In a preferable embodiment, the equalizing passage is formed in a tubular equalizing tube that is axially inserted in the ink storage section, and has a front end open to the front end portion of the ink storage chamber, which is near to the pen tip, and a rear end communicating with the outside. Accordingly, the instrument has an extremely simple structure and shows high reliability. Moreover, the equalizing tube can be located extremely close to the pen tip by extending its front end, thereby enabling setting, at a value corresponding to about several mm, of the head pressure of ink to be applied to the pen tip during writing.

[0023] In a preferable embodiment, the main body contains an ink storage cylinder in which the ink storage chamber is formed, and a space formed between an inner peripheral surface of the main body and an outer peripheral surface of the ink storage cylinder serves as the equalizing passage, the front end of the equalizing passage communicating with the ink storage cylinder in a position near the pen tip, and the rear end of the equalizing passage communicating with the outside at the rear side of the main body. Accordingly, the instrument has a simple structure. Further, the gap of the equalizing passage is formed between the ink storage chamber and the main body of the writing instrument, thereby preventing, for example, heat of the hand of the user from being transmitted to ink or air in the ink storage chamber, and hence preventing ink or air from expanding due to the heat of the user's hand.

[0024] In a preferred embodiment, the cross section of the equalizing passage is set to a shape and a dimension which permit ink having entered the equalizing passage to have a shape of a liquid column therein because of a surface tension of a free surface of the ink, and which do not permit gas-liquid interchange therein wherein ink and air are interchanged with each other. Accordingly, ink does not flow to the outside through the equalizing passage irrespective of the position of the writing instrument. This requires no particular structure for preventing outflow of ink and hence enables a simple structure.

[0025] In a preferred embodiment, the ink storage chamber is substantially cylindrical, and the equalizing passage has a cross section set at 1/30 - 1/4 a cross section of the ink storage chamber. Accordingly, in a writing instrument of a usual size, the setting of the size of the equalizing passage within the range permits ink to be received in the equalizing passage without gas-liquid interchange when air in the ink storage chamber expands due to a usual temperature change, thereby realizing a sufficient compensating function.

[0026] In a preferred embodiment, the main body includes a drying prevention mechanism for interrupting, during non-writing, connection between the rear end of the equalizing passage and the outside, or connection between the front end of the equalizing passage and the ink storage chamber, thereby preventing drying of ink. In the writing instrument of the invention, only the free surface of a liquid column of ink in the ink storage chamber is used as an ink evaporating surface. Further, there is no gas-gas interchange between the solvent vapor of ink and air in the equalizing passage. Thus, the drying amount of ink is small. However, provision of such a drying prevention mechanism can substantially completely prevent drying of ink, in particular, drying of quick drying ink for a long time.

[0027] In a preferred embodiment, the pen tip is a ball tip, and a distance between the front end of the equalizing passage and the ball tip is 20 mm or less. Accordingly, even in the case of using a pen tip having a small ink sealing pressure range, it is free from oversupply of ink caused by head pressure during writing.

[0028] In a preferred embodiment, the pen tip is a felt tip, and the main body includes an ink interruption mechanism for interrupting, during non-writing, passage of ink between the ink storage chamber and the felt tip. In the writing instrument of the invention, the pressure of ink applied to the felt tip during writing is substantially equal to the atmospheric pressure during writing, and there is no possibility of oversupply of ink in the felt tip. However, during non-writing, oversupply or undersupply of ink in the felt tip may occur due to a fine pressure difference caused when expansion/contraction of air in the ink storage chamber is compensated During non-writing, however, the supply of ink to the felt tip is interrupted, and hence the above disadvantage is avoided.

[0029] In a preferred embodiment, the rear end of the equalizing passage is provided with an ink-mist-escape preventing mechanism having a bent or maze-shaped passage. Accordingly, even when a strong impact has been applied to the writing instrument, thereby causing ink in the equalizing passage to escape in the form of mist, the mist of ink is prevented from diffusing to the reservoir or to the outside, and hence peripheral elements are protected from contamination.

[0030] In a preferred embodiment, the drying prevention mechanism includes a slide chamber formed at a rear side of the ink storage chamber and communicating with the ink storage chamber and also with the outside of the writing instrument, a sealing slide plug axially slidably contained in the slide chamber with a predetermined clearance defined between itself and an inner peripheral surface of the slide chamber, thereby interrupting connection between the ink storage chamber and its outside, and a viscous fluid having a predetermined viscosity and held by a capillary force between the inner peripheral surface of the slide chamber and the sealing slide plug.

[0031] Since a clearance between the outer periphery of the sealing slide plug and the inner periphery of the slide chamber is sealed by the viscous fluid, the slide chamber is defined and connection between the ink storage chamber and its outside is always interrupted, to thereby prevent evaporation and escape of the solvent vapor of ink and hence to reliably prevent the evaporation of ink in the ink storage chamber.

[0032] Further, when air or vapor in the ink storage chamber has expanded or contracted due to a temperature change, or when the atmospheric pressure has changed, the sealing slide plug moves in the slide chamber to compensate the expansion or the contraction in the ink storage chamber or a pressure difference between the inside and the outside of the writing instrument. In this case, the viscous fluid is filled in the clearance between the sealing slide plug and the slide chamber, thereby preventing the sealing slide plug from directly contacting the slide chamber. Accordingly, the sealing slide plug can smoothly move without any resistance, whereby the pressure difference can be completely compensated, and such a pressure difference will not substantially occur between the inside and the outside of the ink storage chamber.

[0033] When a great change has occurred in temperature or atmospheric pressure and the sealing slide plug has moved by a maximum amount to one side of the slide chamber and become to be unable to any further move, a pressure difference occurs and excludes the viscous fluid from the clearance between the sealing slide plug and the slide chamber. As a result, the ink storage chamber communicates with the outside through the clearance to thereby eliminate the pressure difference between the inside and the outside of the ink storage chamber.

[0034] Although the viscous fluid flows in accordance with the movement of the sealing slide plug, almost no resistance is caused by the flow of the viscous fluid, since the rate of change in temperature or atmospheric pressure is low and hence the movement rate of the sealing slide plug is extremely low. On the other hand, when, for example, the writing instrument has fallen on the floor, a great load is applied to the sealing slide plug. However, such a viscous fluid shows a significantly high resistance if its flow velocity is high. When receiving such an impact load, the sealing slide plug scarcely moves and works like a fixed wall that divides the slide chamber. This means that connection between the ink storage chamber and its outside is completely interrupted. Thus, outflow of ink from the ink storage chamber to the slide chamber as a result of the impact can be prevented.

[0035] Furthermore, the invention can easily manufacture a writing instrument of a simple structure at low cost. Moreover, since pressure balance is established by excluding a viscous fluid from the clearance when a great change has occurred in temperature or atmospheric pressure, it suffices if the slide chamber has a small volume necessary to compensate a temperature or pressure change within a usual range. This being so, the writing instrument can be made compact.

Brief Description of Drawings

[0036] 

FIG. 1 is a longitudinal sectional view showing a writing instrument according to a first embodiment;

FIG. 2 is a sectional view taken along lines 2 - 2 of FIG. 1;

FIG. 3 is a longitudinal sectional view showing the first embodiment in a horizontal position;

FIG. 4 is a longitudinal sectional view showing the first embodiment in a reverse standing position;

FIG. 5 is a longitudinal sectional view showing the first embodiment in a standing position;

FIG. 6 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the first embodiment;

FIG. 7 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the first embodiment;

FIG. 8 is a longitudinal sectional view showing a writing instrument according to a second embodiment;

FIG. 9 is a longitudinal sectional view showing the second embodiment in a horizontal position;

FIG. 10 is a longitudinal sectional view showing the second embodiment in a reverse standing position;

FIG. 11 is a longitudinal sectional view showing the second embodiment in a standing position;

FIG. 12 is a longitudinal sectional view showing a drying prevention mechanism incorporated in a third embodiment;

FIG. 13 is a longitudinal sectional view showing a drying prevention mechanism incorporated in a fourth embodiment;

FIG. 14 is a longitudinal sectional view showing a drying prevention mechanism incorporated in a fifth embodiment;

FIG. 15 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the fifth embodiment;

FIG. 16 is a longitudinal sectional view showing a drying prevention mechanism incorporated in a sixth embodiment;

FIG. 17 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the sixth embodiment;

FIG. 18 is a longitudinal sectional view showing a writing instrument according to a seventh embodiment;

FIG. 19 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the seventh embodiment and being in a cap-attached state;

FIG. 20 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the seventh embodiment and being in a cap-detached state;

FIG. 21 is a longitudinal sectional view showing an ink interrupting mechanism incorporated in an eighth embodiment;

FIG. 22 is a longitudinal sectional view showing an ink interrupting mechanism incorporated in the eighth embodiment;

FIG. 23 is a longitudinal sectional view showing an ink interrupting mechanism incorporated in a ninth embodiment;

FIG. 24 is a longitudinal sectional view showing an ink interrupting mechanism incorporated in the ninth embodiment;

FIG. 25 is a longitudinal sectional view showing a writing instrument according to a tenth embodiment;

FIG. 26 is a longitudinal sectional view showing a writing instrument according to an eleventh embodiment;

FIG. 27 is a partially-enlarged longitudinal sectional view showing the writing instrument of the eleventh embodiment;

FIG. 28 is a partially exploded perspective view of the writing instrument of the eleventh embodiment;

FIG. 29 is a longitudinal sectional view showing a writing instrument according to a twelfth embodiment;

FIG. 30 is a sectional view taken along lines 13 - 13 of FIG. 12;

FIG. 31 is a longitudinal sectional view showing the twelfth embodiment in a horizontal position;

FIG. 32 is a longitudinal sectional view showing the twelfth embodiment in a reverse standing position;

FIG. 33 is a longitudinal sectional view showing the twelfth embodiment in a standing position;

FIG. 34 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the twelfth embodiment;

FIG. 35 is a longitudinal sectional view showing a drying prevention mechanism incorporated in the twelfth embodiment;

FIG. 36 is a longitudinal sectional view showing a writing instrument according to a thirteenth embodiment; and

FIG. 37 is a longitudinal sectional view showing a writing instrument according to a fourteenth embodiment.

Best Mode of Carrying Out the Invention

[0037] Referring to the drawings, the embodiments of the invention will be described. FIGS. 1 to 7 show a writing instrument according to a first embodiment of the invention. This writing instrument is a disposable writing instrument that uses quick drying ink containing an alcohol-based solvent, and a ball tip as a pen tip.

[0038] The writing instrument has a substantially cylindrical body 1, a ball tip 2 is provided at the tip of the body 1, and a tail plug 3 is attached to the rear end portion of the body 1. The body 1 and the tail plug 3 are formed by subjecting a synthetic resin to injection molding. Although the figures show no cap for the writing instrument, a cap of any optional shape can be used.

[0039] A substantially cylindrical ink storage chamber 4 is formed in the body 1, and filled with ink 5 as aforementioned. A front end portion of the ink storage chamber 4 is tapered and directly communicates with the ball tip 2. Further, the rear side of the body 1 is partitioned by a partition member 6, and a drying prevention mechanism 20 described later is provided at the rear side of the partition member 6.

[0040] A pressure equalizer 7 is provided in a middle portion of the ink storage chamber 4 along the axis of the ink storage chamber 4, and a pressure equalizing passage 8 is formed through the pressure equalizer 7. A rear end portion of the pressure equalizer 7 is attached to the partition member 6 such that the former passes through the latter and communicates with the outside through holes formed in the drying prevention mechanism 20 and the tail plug 3. The front end of the pressure equalizer 7 extends to a position near the ball tip 2 that is located at the front end of the ink storage chamber 4, in which position the pressure equalizer communicates with the ink storage chamber 4.

[0041] In this embodiment, the distance between a front end portion of the pressure equalizer 7, i.e. a front end portion of the pressure equalizing passage 8, and the ball tip 2 is set at about 10 mm, which is shorter than a pressure head corresponding to the ink-sealing pressure of the ball tip 2. Furthermore, in this embodiment, the inner diameter of the ink storage chamber 4 is set at about 8 mm, the inner diameter of the pressure equalizer 7, i.e. the diameter of the pressure equalizing passage 8, is set at about 2 mm, and the cross section of the pressure equalizing passage 8 is set at about 1/16 of that of the ink storage chamber 4.

[0042] A cylindrical reservoir section 9 is formed at the rear side of the partition member 6, and the rear end of the reservoir section 9 is defined by a partition wall member 11, thereby forming therein a reservoir 10. The reservoir 10 is adapted to hold ink, if it flows from the pressure equalizing passage 8 in the pressure equalizer 7, thereby preventing leakage of the ink to the outside. An outflow preventing tube section 12 projects from a central portion of the partition wall member 11 to a front side. The reservoir 10 communicates with the outside through the outflow preventing tube section 12. Accordingly, where the reservoir 10 is filled with flown ink, even if the writing instrument is placed horizontally or upside down, the ink will not flow to the outside so long as a front end portion of the outflow preventing tube section 12 is covered by the ink.

[0043] The structure of the drying prevention mechanism 20 will be described. The drying prevention mechanism 20 interrupts the flow of air or of the vapor of an ink solvent to thereby substantially completely prevent ink from drying. Basically, the connection between the pressure equalizing passage 8 and the outside is secured, and hence the pressure in the pressure equalizing passage 8 is kept at the atmospheric pressure. A space between the partition wall member 11 and the tail plug 3 is formed as an oil chamber 22, and a defining member 21 is provided in a substantially axially central portion of the oil chamber 22, thereby dividing the oil chamber 22 into two chambers. A plurality of axially extending slits 24 of a fine cross section are formed in the outer peripheral surface of the defining member 21, thereby making the front side and the rear side of the oil chamber 22 communicate with each other.

[0044] The oil chamber 22 is filled with a predetermined amount of non-volatile oil, for example, silicone oil 23 of a predetermined viscosity. Outflow preventing tube sections 25 and 26 similar to the aforementioned one project from the tail plug 3 and the rear end of the partition wall member 11, respectively, thereby allowing connection to the outside, and also preventing outflow of silicone oil 23 from the oil chamber 22 irrespective of the attitude of the writing instrument. The silicone oil 23 is held in the slits 24 of the defining member 21 by virtue of its surface tension, thereby blocking the slits and accordingly preventing the escape of the vapor of a solvent contained in quick drying ink.

[0045] Referring then to FIGS. 3 to 5, a description will be given of the compensation function of ink pressure in the writing instrument of the first embodiment. FIG. 3 shows the writing instrument in a non-writing state and in a horizontal position. If in this case, a large amount of ink 5 is contained, a front end portion of the pressure equalizer 7 is covered by ink as shown in FIG. 3. Since, however, the pressure equalizing passage 8 of the pressure equalizer 7 has a relatively small diameter, ink is held in the passage in the form of a liquid column 5a as a result of its surface tension, and a so-called gas-liquid interchange phenomenon in which ink and air are interchanged with each other will not occur.

[0046] Accordingly, if in this state, air in the ink storage chamber 4 expands because of, for example, temperature increase, ink is pushed into the pressure equalizing passage 8 by the expansion amount of air. As a result, the pressure in the ink storage chamber 4 is kept at a value substantially equal to the atmospheric pressure. If, on the other hand, air in the ink storage chamber 4 contracts, the ink liquid column 5a having been pushed in the pressure equalizing passage 8 is returned into the ink storage chamber 4, whereby the pressure in the ink storage chamber 4 is kept at a value equal to the atmospheric pressure. In this case, ink in the equalizing passage 8 is not subjected to vapor-liquid interchange, but keeps the state of the liquid column 5a and only axially moves in the equalizing passage 8. Accordingly, ink will not flow out of the equalizing passage 8.

[0047] FIG. 4 shows the reverse standing state of the writing instrument assumed when it is not used for writing. Also in this case, the liquid column 5a of ink moves in the equalizing passage 8 in accordance with the expansion or the contraction of the air contained in the ink storage chamber 4 in the same manner as above, thereby compensating the expansion or the contraction and maintaining the pressure in the ink storage chamber 4 at a value equal to the atmospheric pressure.

[0048] FIG. 5 shows the standing state of the writing instrument. Also in this case, the liquid column 5a of ink moves in the equalizing passage 8 in accordance with the expansion or the contraction of the air contained in the ink storage chamber 4 in the same manner as above, thereby compensating the expansion or the contraction and maintaining the pressure in the ink storage chamber 4 at a value equal to the atmospheric pressure.

[0049] If in the above-described cases, air in the ink storage chamber 4 greatly contracts and the liquid column 5a in the equalizing passage 8 moves to the front end of the equalizing passage 8, outside air is introduced into the ink storage chamber 4 through the equalizing passage 8 to thereby compensate the contraction. If, on the other hand, air in the ink storage chamber 4 greatly expands and the liquid column 5a in the equalizing passage 8 moves to the rear end of the equalizing passage 8, the ink flows into the reservoir 10. However, since the outflow preventing tube 12 is provided in the reservoir 10, the ink is prevented from flowing to the outside and is kept in the reservoir 10.

[0050] Further, if, for example, the writing instrument falls to the floor, it is possible that ink in the equalizing passage 8 will leak in the form of mist from the rear end of the equalizing passage 8. Even in this case, the leaked ink is received in the reservoir 10 and prevented from escaping to the outside.

[0051] As described above, at the time of non-writing, the equalizing passage 8 functions as a kind of feeder for compensating expansion or contraction of air or ink in the ink storage chamber 4. Appropriately setting the relationship between the cross sections of the equalizing passage 8 and the ink storage chamber 4, and the diameter of the equalizing passage 8 enables setting of the instrument such that ink will be rarely pushed into the reservoir 10, or outside air will be rarely introduced into the ink storage chamber 4 through the equalizing passage 8.

[0052] Specifically, the expansion or contraction ratio of air when the temperature has varied from T1°C to T2°C is

. Accordingly, within the usual temperature range, the expansion or contraction ratio of air is about 0.3 % for a change of 1°C in temperature. Supposing that the temperature change range is set at ±30°C, the expansion or contraction ratio of air in the ink storage chamber 4 is about 9%. Since in this embodiment, the ink storage chamber 4 is a cylindrical member whose cross section is axially substantially constant, air in the ink storage chamber 4 axially expands or contracts by about 9%.

[0053] Suppose that the entire ink storage chamber is substantially filled with air, i.e. that the ink storage chamber is empty. Since the length of the equalizing passage 8 is substantially equal to that of the ink storage chamber 4, if the cross section of the equalizing passage 8 is set at 9% that of the cross section of the ink storage chamber, the liquid column 5a of ink in the equalizing passage 8 is (9/100) × (100/9) = 1 where air in the ink storage chamber 4 axially expands by, for example, 9%. Accordingly, the liquid column 4a of ink moves to the rear end of the equalizing passage 8, but does not flow into the reservoir 22. Further, if air in the ink storage chamber 4 contracts, air flows into the ink storage chamber 4 from the equalizing passage 8 to thereby compensate the contraction of air.

[0054] While the writing instrument is used or stored, the temperature change scarcely exceeds ±30°C. Further, in general, the ink storage chamber 4 contains some ink. Accordingly, the volume of the air is less than the supposed one. This being so, in general, the possibility of ink flowing into the reservoir 10 from the equalizing passage 8 can be eliminated reliably if the cross section of the equalizing passage 8 is set at about 1/10 that of the cross section of the ink storage chamber 4.

[0055] Also, to maintain ink in the form of the liquid column 5a in the equalizing passage 8 as described above, it suffices if the equalizing passage 8 is made to have a small diameter. If the diameter of the equalizing passage 8 is about 6 mm or less, usual ink can be kept in the form of a liquid column, although the diameter is determined depending upon the properties, such as viscosity, of ink. However, it is preferable to set the inner diameter of the equalizing passage 8 at about 3 mm or less, in order to reduce the possibility of escape, in the form of mist, of the liquid column 5a in the equalizing passage 8, which may occur when the writing instrument has fallen to, for example, the floor and received a shock, as is described above.

[0056] Although a description has been given of the case where the equalizing passage 8 functions as a feeder at the time of non-writing, the equalizing passage 8 is almost empty at the time of writing, and only a short liquid column 5a of ink exists at a front end portion of the passage. In other words, in this writing instrument, ink is filled at a temperature during writing, i.e. at a room temperature, whereas during manufacturing, only a short liquid column 5a of ink exists in the equalizing passage 8. The aforementioned temperature change is periodical, which means that the temperature always returns to the original room temperature after it increases or decreases. Moreover, ink for use in such a writing instrument is sufficiently degassed during manufacturing, and will not discharge gas in the ink storage chamber 4 after it is filled therein. In addition, the volume of ink will necessarily decrease after writing. Accordingly, usually, the equalizing passage 8 is almost empty at the time of writing such that only a short liquid column 5a of ink exists at its front end portion.

[0057] Also, the equalizing passage 8 has a function for preventing ink 5, especially quick drying ink, from drying. Specifically, since the equalizing passage 8 has a small cross section and the free surface of the liquid column 5a of ink in the passage also has a small cross section, the evaporation amount of the solvent of ink from the free surface is small. Furthermore, the equalizing passage 8 has a small diameter and is axially long, the speed of air flow in the passage is extremely slow, the Reynolds number of the air flow in the passage is extremely low, and complete laminar flow of air occurs in the passage.

[0058] This being so, neither the aforementioned gas-liquid interchange nor gas-gas interchange will occur. Therefore, gas-gas interchange will scarcely occur, in which a solvent evaporated from the free surface of the liquid column 5a of ink at the front end portion of the equalizing passage 8 and rear-side air are interchanged with each other. Thus, in the equalizing passage 8, solvent vapor spreads to the rear side as a result of molecular diffusion. As a result, a continuous vapor pressure distribution is obtained in which the solvent vapor shows a saturated vapor pressure corresponding to the temperature in the vicinity of the free surface of the liquid column 5a at the front side, and shows a continuously reducing vapor pressure as the rear end of the passage is approached. Accordingly, the vapor pressure of the solvent vapor is low at an opening at the rear end of the equalizing passage 8, and hence the amount of solvent vapor diffusing through the rear end opening is small.

[0059] If, as described above, the equalizing passage 8 is made to have a small cross section and a long length, the free surface of the liquid column 5a of ink in the passage has a small area, and the amount of vapor diffusion is small. However, where the equalizing passage 8 has a small cross section, if air in the ink storage chamber 4 expands, the free surface of the liquid column 5a of ink in the equalizing passage 8 approaches the rear end opening, whereby the amount of vapor diffusion becomes larger. To effectively prevent solvent evaporation due to its diffusion, it is necessary to provide a diffusion preventing length of at least about 25 mm between the free surface of the liquid column 5a of ink in the equalizing passage 8 and the rear-side opening of the equalizing passage 8.

[0060] Accordingly, if the temperature increases by an amount falling within the expected range of a temperature change, thereby moving the liquid column 5a of ink toward the rear end of the equalizing passage 8, it suffices if the cross section, the content volume and the length of the equalizing passage 8 are set so that a diffusion preventing length of about 25 mm or more will be left between the free surface of the liquid column 5a of ink and the rear end of the equalizing passage 8.

[0061] The aforementioned temperature change range of ±30°C is set in light of an extreme case where the writing instrument is brought into a warm room from the cold outside, or where the writing instrument is left on the dashboard of a vehicle parked under the burning sun. When such an exceptional case has occurred, it is sufficient to set the temperature change range at about ±10°C if flow of ink from the equalizing passage 8 to the reservoir 10 is allowed.

[0062] Considering the above-described conditions, the equalizing passage 8 must have an inner diameter of 6 mm or less, preferably 3 mm, and a content volume of 3% or more the content volume of the ink storage chamber 4. Preferably, the remaining portion of the passage obtained by subtracting the content volume has a diffusion preventing length of 25 mm or more.

[0063] Further, if in the case of a general writing instrument, the cross section of the equalizing passage 8 is set at 1/30 - 1/4 that of the cross section of the ink storage chamber 4, the equalizing passage 8 can sufficiently compensate a temperature change, and the diffusion of the solvent vapor of ink in the equalizing passage 8 can be reduced to a practically sufficient extent.

[0064] Moreover, since in the embodiment, the reservoir 10 is formed at the rear side of the equalizing passage 8, and outflow preventing tubes 12 and 26 of a small diameter are provided between the reservoir 10 and the drying prevention mechanism 20, gas-gas interchange can be prevented in the outflow preventing tubes. Since in the tubes, only solvent evaporation due to its diffusion occurs, a better evaporation preventing effect is obtained.

[0065] The operation of the writing instrument during writing will now be described. Writing is performed with the writing instrument kept standing and the ball tip directed downward as shown in FIGS. 1 to 5. In this state, ink 5 gathers in a lower portion of the ink storage chamber 4, while air moves to an upper portion of the ink storage chamber 4. At this time, head pressure corresponding to (H1 + H2) is generally exerted on the ball tip 2. However, the front end of the equalizing tube 7 or the equalizing passage 8 reaches the depth of H1, and the rear end of the equalizing passage 8 communicates with the outside. It should be noted that at the time of writing, usually only an extremely short liquid column 5a of ink exists in the equalizing passage 8 as aforementioned. As a result, pressure at a front end portion of the equalizing passage 8, i.e. at the depth H1 of ink 5, is equal to the atmospheric pressure.

[0066] Accordingly, the level of ink 5 in the ink storage chamber 4 slightly lowers, and air in an upper portion of the ink storage chamber 4 expands to thereby reduce its pressure by head pressure corresponding to the depth H1 of ink 5. This state balances in pressure and stabilizes. At this time, ink of an amount corresponding to a reduction in the level of ink 5 enters the equalizing passage 8, whereby the depth of the liquid column 5a in the equalizing passage 8 becomes H3.

[0067] Supposing that H1 is 50 mm, and the axial length of the air section of the ink storage chamber 4 is 50 mm, the air therein reduces in pressure by a value corresponding to a pressure head of 50 mm, and hence increases in volume. Supposing that one atmospheric pressure corresponds to a pressure head of 10000 mm, the axial amount of expansion of the air is about 50 × 50/10000 = 0.25 mm, and the reduction amount of the level of ink 5 is also 0.25 mm.

[0068] Further, in this embodiment, the cross section of the equalizing passage 8 is 1/16 that of the ink storage chamber 4. Accordingly, the increase of the liquid column 5a in the equalizing passage 8 as a result of a reduction in the level of ink 5 in the ink storage chamber 4 is 0.25 × 16 = 4 mm. Thus, the pressure at the front end of the equalizing passage 8, i.e. at the depth of H1, actually becomes higher than the atmospheric pressure by a value corresponding to a pressure head of H3 = 4 mm. Since this is an extremely low pressure, it can be ignored actually.

[0069] Thus, the pressure corresponding to a pressure head of H2 + 4 mm is applied to the ball tip 2. Since in this embodiment, H2 is set at about 10 mm as aforementioned, only the pressure corresponding to a pressure head of 14 mm is applied to the ball tip 2, ink is prevented from oozing through the ball tip even when the ink sealing pressure of the ball tip 2 is as low as a value corresponding to about 20 mm.

[0070] In the writing instrument of this embodiment, the front end of the equalizing tube 7 can be located very near the ball tip 2, and the length of H2 in FIG. 5 is principally unlimited. Where, for example, the front end of the equalizing tube 7 has a small diameter, the ball holder of the ball tip 2 has a large inner diameter, and the front end of the equalizing tube 7 is inserted in the ball holder, the front end of the equalizing tube 7, i.e. the front end of the equalizing passage 8, can be located, for example, as close as 1 mm to the ball of the ball tip 2.

[0071] Since as described above, the pressure applied to the ball tip 2 is low and a substantially constant pressure that is always substantially corresponding to H2, stable writing can be realized. When ink has been consumed during writing, the levels of ink in the ink storage chamber 4 and in the equalizing passage 8 reduce. However, the amount of ink consumed at one time of writing is extremely small, and hence a change in the level of ink during writing can also be ignored.

[0072] Furthermore, it is possible that air in the ink storage chamber 4 will expand during writing because of, for example, the heat of the hand of a writer. At this time, however, the increase in temperature is only about several degrees. Even if, for example, the temperature increases by 3°C, the expansion of air is 0.3% × 3 = 0.9%. Accordingly, if the axial length of the air section is 50 mm, the air axially expands by only 50 × 0.9/100 = 0.45 mm, and hence a reduction in the level of ink in the ink storage chamber 4 is 0.45 mm, and the increase of the liquid column 5a H3 in the equalizing passage 8 is about 0.45 × 16 = 7.2 mm. This scarcely influences writing. To minimize the influence of temperature increase upon writing, it is necessary to set the cross section of the equalizing passage 8 at a high value within a range in which the other conditions are satisfied.

[0073] As described above, the pressure compensating function of the writing instrument of this embodiment during non-writing, and the pressure adjusting function of the instrument during writing are reliably controlled by simply balancing the pressures in various sections. Therefore, there is no section which is influenced by a movable section or by the accuracy of a dimension such as a fine orifice, or which uses a variable element such as a capillary force. This enables realization of a highly reliable instrument, which has a simple structure and can be manufactured easily.

[0074] Referring then to FIGS. 6 and 7, the operation of the aforementioned drying prevention mechanism 20 will be described. FIG. 6 shows a case where the writing instrument is in a horizontal position. Usually, silicone oil 23 contained in the oil chamber 22 is held by its capillary force within the slits 24 of the defining member 21, thereby sealing the slits 24. In this case, the oil chamber 22 is completely sealed by the defining member 21 and oil 23, thereby completely preventing escape of the solvent vapor of ink contained therein and hence preventing the ink from drying.

[0075] If air, for example, contained in the ink storage chamber 4 expands or contracts due to, for example, a temperature change, a pressure difference occurs at the both opposite sides of the defining member 21. This pressure difference moves oil 23 from one side to the other side of the defining member 21 through the slits 24, thereby compensating the change in pressure and maintaining the pressure in the equalizing passage 8 and the ink storage chamber 4 at a value equal to the atmospheric pressure.

[0076] When the amount of expansion or contraction of air in the ink storage chamber 4 is large, oil is removed from the slits 24 after oil 23 completely moves from the one side to the other side of the defining member 21. As a result, air or the solvent vapor moves, in the form of bubbles as shown in FIG. 7, from the one side to the other side of the defining member 21, thereby executing pressure compensation. Although in this case, slight leakage of the solvent vapor may occur, its possibility is very low and the amount of leakage is very small. Accordingly, the drying prevention mechanism 20 can substantially completely prevent ink from drying, even if the ink is quick drying ink.

[0077] Oil 23 has a viscosity and hence a flow resistance. Since, however, the expansion or contraction of air in the ink storage chamber 4 occurs very slowly, and accordingly the drift velocity of oil 23 is extremely low, the flow resistance is low and a pressure difference caused between the inside and the outside of the instrument by the drying prevention mechanism 20 constructed as above is as small as can be ignored.

[0078] As described above, the flow preventing tubes 12 and 26 of the equalizing passage 8 and the reservoir 10, for example, have the effect of preventing leakage of solvent vapor of ink. Addition of the above-described drying prevention mechanism 20 to the flow preventing tubes enables substantial complete prevention of the leakage of the solvent vapor of ink. This structure can prevent even quick drying ink of a very quick evaporation speed from drying for a long time.

[0079] The invention is not limited to the above-described first embodiment. FIGS. 8 to 11 shows a writing instrument according to a second embodiment of the invention. In this instrument, an ink storage cylinder 30 is provided in a main body 1. An ink storage chamber 4 for containing ink 5 is defined in the cylinder. A nozzle section 32 is formed at a front end portion of the ink storage cylinder 30, and an opening formed at the front end of the nozzle section 32 opens near a pen tip, a felt tip 2a in this embodiment. Annular clearances 31 and 35 are defined between the inner peripheral surface of the main body 1 and the respective outer peripheral surfaces of the ink storage cylinder 30 and the nozzle section 32. The clearances 31 and 35 serve as equalizing passages.

[0080] Front end portions of the equalizing passages 31 and 35 communicate with the front-end opening of the nozzle section 32 of the ink storage cylinder 30 as described above, while rear end portions of the equalizing passages 31 and 35 communicate with the outside via a reservoir 10 and a drying prevention mechanism 20 similar to the above-described ones. In this embodiment, the width of the equalizing passage 35 is relatively wide, while that of the equalizing passage 31 is relatively narrow. The equalizing passage 31 is constructed such that a liquid column 5a of ink will be held therein as in the first embodiment. To keep a liquid column of ink in the annular equalizing passage 31, it is preferable that the width should be set at about 2 mm or less, although the width is determined on the basis of the properties of the ink.

[0081] Annular projections are provided on the outer peripheral surface of the ink storage cylinder 30, thereby holding the cylinder on the inner peripheral surface of the main body 1. Slits 33 and 34 are each formed in a corresponding one of the projections, thereby making the equalizing passages 31 and 35 communicate with each other and also with the outside. Other than the above elements, the second embodiment has a similar structure to the first embodiment. In FIGS. 8 to 11, elements similar to those in the first embodiment are denoted by corresponding reference numerals, and no description will be given thereof.

[0082] The second embodiment operates in the same manner as the first embodiment. FIG. 9 shows a non-writing state in which the writing instrument is in a substantially horizontal position. In this state, the level of ink 5 appears in the nozzle section 32 of the ink storage cylinder 30, and air exists above ink. The air section communicates with the outside via the equalizing passages 35 and 31, thereby compensating expansion/contraction of the internal air due to, for example, a temperature change and maintaining the internal pressure at the atmospheric pressure.

[0083] FIG. 10 shows the reverse standing position of the writing instrument assumed in the non-writing state. In this case, part of ink is left in a rear-side portion of the equalizing passage 35. FIG. 11 shows a state in which the felt tip 2a of the writing instrument is directed downward. In this case, part of ink is left in a front-side portion of the equalizing passage 35. In both of the above cases, part of ink exists in the form of a liquid column in the slit 33 or in the equalizing passage 31, thereby sealing the inside of the instrument. Further, the liquid column has a free surface of a small area, and hence only a small amount of the ink solvent evaporates therefrom. In addition, the equalizing passage 31 as a narrow annular clearance, for example, interrupts interchange of the solvent vapor of ink with air. Thus, the second embodiment has a function for preventing escape of the solvent vapor of ink, like the first embodiment.

[0084] When performing writing using the writing instrument of the second embodiment, the felt tip 2a is directed downward as shown in FIGS. 8 and 11. In this case, air is expanded by the head pressure H1 of ink in the ink storage chamber 30, thereby slightly reducing the level of ink contained in the ink storage cylinder 30 and increasing, by an amount corresponding thereto, the height H3 of the liquid column 5a of ink in the equalizing passage 35. Since pressure at the front end of the nozzle section 32 of the ink storage cylinder 30, i.e. at the front end of the equalizing passage 35, is substantially equal to the atmospheric pressure, only the pressure corresponding to a pressure head of H2, more strictly, only the pressure corresponding to a pressure head of H2 + H3 is applied to the felt tip 2a. This means that a constant pressure close to the atmospheric pressure is applied to the felt tip 2a, thereby enabling stable writing as in the first embodiment.

[0085] In the second embodiment, an annular clearance, i.e. the equalizing passage 31, is formed between the main body 1 and the ink storage cylinder 30 as the ink storage chamber, and serves as an adiabatic structure. Accordingly, it is advantageous that outside heat, for example, the heat of the writer's hand, is hard to transmit to the ink storage cylinder 30, thereby minimizing the expansion of air in the ink storage cylinder 30. Furthermore, in this embodiment, the nozzle section 32 is formed at the front end of the ink storage cylinder 30, which enables forming of the equalizing passages 31 and 35 of different widths. By virtue of this structure, the equalizing passage 31 can be made to have a cross section and a width so that a liquid column of ink can be held, and the cross section of the equalizing passage 35 can be formed larger than that of the equalizing passage 31. As a result, in the writing state shown in FIG. 11, the increase in H3 of the liquid column 5a of ink in the equalizing passage 35, caused by a reduction in the level of ink 5 in the ink storage cylinder 30, and the increase in H3 due to the expansion of air in the ink storage cylinder 30 during writing can be minimized.

[0086] In addition, the drying prevention mechanism can have various structures other than the above-described one. For example, FIG. 12 shows a drying prevention mechanism 20a employed in a third embodiment of the invention. In this embodiment, a plurality of slits 24 are formed in the periphery of a defining member 21, which has a simple disk shape, and the oil chamber 22 of the drying prevention mechanism also serves as a reservoir as aforementioned.

[0087] This mechanism has the same function as the above-described one, but has a simpler structure and can be manufactured more easily. It should be noted that silicone oil 23 does not mix with ink, and therefore that even if they are contained together in the oil chamber 22 or in the equalizing passage 8, no problem will be raised during writing.

[0088] FIG. 13 shows a drying prevention mechanism 20b employed in a fourth embodiment. In this embodiment, a porous defining member 40 made of a porous material such as a foaming substance as an open cell, fiber filaments, etc. is used as the defining member. In this mechanism, silicone oil 23 is held in pores in the porous defining member 40 by a capillary force, thereby sealing the member to prevent escape of the solvent vapor of ink. When a pressure difference has occurred due to expansion or contraction of the internal air, silicone oil 23 moves from one side to the other side of the oil chamber 22 through the porous defining member 40, thereby compensating the pressure difference. When the internal air expands or contracts by an amount larger than the amount of the moving silicone oil 23, oil filled in the pores of the porous defining member 40 is excluded therefrom and air passes therethrough, thereby compensating the expansion/contraction of the air and maintaining the pressure in the ink storage chamber 4 at a value equal to the atmospheric pressure.

[0089] FIGS. 14 and 15 show a drying prevention mechanism 20c employed in a fifth embodiment. In this mechanism, a weight chamber 41 that communicates with the equalizing passage 8 is formed in a rear end portion of the main body 1 of the writing instrument, and a valve member 42 formed of an elastic material such as a rubber material is provided such that the weight chamber 41 is defined. A valve hole 43 is formed through a central portion of the valve member 42. A substantially cylindrical weight 45 is provided in the weight chamber 41 so that it can move axially and radially. The weight 45 has a conical valve section 46 at its rear side, and an axial section 44 projecting therefrom and movably inserted through the valve hole 43. A conical tapered surface 47 is provided at a front end portion of the weight chamber 41, and disposed to be engaged with a front end portion of the weight 45. The tapered surface 47 has a radially extending slit 47a for securing passage of air.

[0090] Where the writing instrument is in a horizontal position at the time of non-writing as shown in FIG. 14, in the drying prevention mechanism 20c, the front end of the weight 45 radially slips down the tapered surface 47 and moves to the rear side. Accordingly, the rear-side valve section 46 of the weight 45 is pushed into the valve hole 43 to thereby close the valve hole 43. Thus, at the time of non-writing, the equalizing passage 8 of the writing instrument is disconnected from the outside, and hence evaporation of the ink solvent is prevented. When the writing instrument is in a reverse standing position at the time of non-writing, the weight 45 moves to the rear side because of its weight to thereby close the valve hole 43 in the same manner as above.

[0091] At the time of writing, the writing instrument is in a standing position with its pen tip directed downward, as is shown in FIG. 15. In this case, the front end of the weight 45 slips down the tapered surface 47 toward its center and advances. As a result, the valve section 46 of the weight 45 separates from the valve hole 43 to thereby open the valve hole 43 and connect the equalizing passage 8 to the outside. In this writing instrument, the equalizing passage 8 is disconnected from the outside during non-writing. However, if the writing instrument is moved even during non-writing, the weight 45 moves and opens the valve hole 43 instantly. Accordingly, actually, this operation performs compensation of the expansion/contraction of air even during non-writing. Moreover, when the writing instrument is moved or made to assume the standing position before writing, the weight 45 moves and opens the valve hole 43, thereby making the internal pressure of the writing instrument equal to the atmospheric pressure before writing.

[0092] FIGS. 16 and 17 show a drying prevention mechanism 20d employed in a sixth embodiment. In this embodiment, a weight chamber 51 that communicates with the equalizing passage 8 is formed at the rear side of the main body 1 as in the case of the fifth embodiment, and a weight 52 is provided in the weight chamber 51 so that it can move axially and radially. The weight 52 has, at a substantially central portion thereof, a projecting skirt-shaped valve section 53 provided with a tapered surface at its front side. The rear end surface of a partition wall member 11, which defines the weight chamber 51, is formed as a conical tapered surface. A slit 55 is formed in a portion of the tapered surface 54, and serves as a passage when the valve section 53 contacts the tapered surface. The front end surface of a tail plug 3 employed in the writing instrument is formed as a valve seat surface to be brought into contact with a side surface of a rear end portion of the valve section 53.

[0093] When the writing instrument of this embodiment is in a horizontal position during non-writing as shown in FIG. 16, the tapered surface of the valve section 53 of the weight 52 radially slips down the tapered surface 54 and axially moves to the rear side, whereby the valve section 53 tightly contacts the valve seat surface as the front end surface of the tail plug 3, thereby disconnecting the equalizing passage 8 from the outside. Where the writing instrument is in a reverse standing position, the weight 52 moves to the rear side because of its weight and then tightly contacts the valve seat surface provided at the front end of the tail plug 3 in the same way as above, thereby disconnecting the equalizing passage 8 from the outside. When the writing instrument is shifted to an uptight position in which the pen tip is directed downward as shown in FIG. 17, so as to perform writing, the valve section 53 of the weight 52 slips toward a central portion of the tapered surface 54 and axially moves toward the front side. As a result, the valve section 53 separates from the valve seat surface provided at the front end of the tail plug 3, thereby making the equalizing passage 8 communicate with the outside.

[0094] FIGS. 18 to 20 show a drying prevention mechanism 20e employed in a seventh embodiment. In this mechanism, the ink storage chamber 4 is connected to and disconnected from the equalizing passage 8 in accordance with operations for attaching and detaching a cap 60, thereby preventing the instrument from drying.

[0095] In this mechanism, a holder member 61 for a pen tip is slidably provided at a front end portion of the main body 1 of the writing instrument. The pen tip consisting of, for example, a ball chip 2 is attached to a front end portion of the holder member 61. A seal skirt section 62 is provided at the rear side of the holder member 61 such that it slidably contacts the inner peripheral surface of the main body 1 to maintain the liquid-tight state. Furthermore, a conical valve seat surface 63 is provided at the front end of the holder member 62. When the holder member 61 retreats as shown in FIG. 19, the front end surface of the equalizing tube 7 tightly contacts the valve seat surface 63, thereby disconnecting the ink storage chamber 4 from the front end of the equalizing tube 7, i.e. the front end of the equalizing passage 8. As a result, the connection of the ink storage chamber 4 to the outside via the equalizing passage 8 is interrupted, and escape of the ink solvent is prevented.

[0096] An annular groove 64 is formed in the outer peripheral surface of a front end portion of the holder member 61, while an annular projection 65 to be elastically engaged with the groove 64 is formed on the inner peripheral surface of the cap 60. An annular seal section 66 is provided on the inner surface of a front end portion of the cap 60, so that it can be fitted on a front end portion of the ball tip 2 to thereby prevent the tip from drying. Also, an air hole 67 is formed in the cap 60 in order to prevent the air therein from being compressed and pressure-injected into the writing instrument through the ball tip 2 when attaching the cap 60 to the instrument.

[0097] When in the above-described drying prevention mechanism 20e, the cap 60 is attached at the time of non-writing as shown in FIG. 19, the projection 65 is elastically engaged with the groove 64. When the cap 60 has been further pushed to the rear side of the instrument, the holder member 60 retreats and the valve seat surface 63 tightly receives the front end of the equalizing tube 7, thereby disconnecting the ink storage chamber 4 from the equalizing tube 7, i.e. the equalizing passage 8. Thus, in the non-writing state, ink is completely sealed in the ink storage chamber 4, thereby preventing its solvent from evaporating and escaping.

[0098] When detaching the cap 60 as shown in FIG. 20 to perform writing, the holder member 61 advances together with the cap 60, thereby separating the front end of the equalizing tube 7 from the valve seat surface of the holder member 61 and connecting the equalizing passage 8 to the ink storage chamber 4. As a result, a pressure adjusting operation and a head pressure adjusting operation are executed as described above, which enables stable writing. At this time, the holder member 61 is slightly eccentric with respect to the main body 1, and a shoulder section 66 provided at the outer periphery of a front end portion of the holder member 61 is engaged with the edge of the front end of the main body 1, thereby preventing the holder member 61 from being retreated by pressure applied to the pen tip during writing.

[0099] The drying prevention mechanism in the writing instrument can have various structures for achieving the same object as above, other than the above-described one.

[0100] In addition, in the case where the pen tip is a felt tip, it is possible, as described above, that the amount of ink contained in the felt tip will increase or decrease in accordance with a change in the internal pressure of the ink storage chamber, thereby making handwriting too dark or too light, although the ink seal pressure is high. Specifically, when a temperature change has occurred during non-writing and air in the ink storage chamber has expanded, the amount of ink contained in the felt tip may become excessive due to a fine pressure change, i.e. a so-called ink-rich state may occur, thereby making handwriting too dark, although a pressure compensating function is executed using the equalizing passage. To avoid such a disadvantage, an ink interrupting mechanism 70a is incorporated in a writing instrument according to an eighth embodiment shown in FIGS. 21 and 22.

[0101] In this mechanism, a defining member 71 is provided in a front end portion of the ink storage chamber 4 and defines the front end portion, and an interruption chamber 73 is formed between the defining member 71 and a felt tip 2a. Further, an orifice 72 of a small cross section is formed in a central portion of the defining member 71, through which the ink storage chamber 4 communicates with the interruption chamber 73. The interruption chamber 73 is filled with air.

[0102] If, for example, the writing instrument is in a horizontal position during non-writing, a small amount of ink 5b contained in the interruption chamber 73 in the ink interruption mechanism of the eighth embodiment gathers in a lower portion of the interruption chamber 73. A rear-side portion of the felt tip 2a does not contact ink 5b but contacts air. Accordingly, ink in the ink storage chamber 4 is not guided to the felt tip 2a in the form of liquid, but interrupted by the air. Even when a fine pressure difference has occurred when executing a pressure compensating operation to compensate expansion or contraction of air in the ink storage chamber 4, ink will not be pushed into the interruption chamber 73, or air or ink will not be sucked from the interruption chamber 73 into the ink storage chamber 4, since ink is held by a capillary force in the orifice 72 of the defining member 71. Thus, such a pressure difference is interrupted by the interruption chamber 73, thereby preventing the amount of ink contained in the felt tip 2a from excessively increasing or decreasing because of the pressure difference. As a result, the amount of ink contained in the felt tip 2a is maintained constant.

[0103] Further, if the writing instrument is stood during writing with the felt tip 2a directed downward as shown in FIG. 22, a small amount of ink 5b in the interruption chamber 73 is brought into contact with the rear end of the felt tip 2a, thereby supplying the felt tip 2a with ink to be consumed during writing. When ink 5b in the interruption chamber 73 has been consumed, the pressure in the interruption chamber 73 becomes low. This pressure difference causes ink to be supplied into the interruption chamber 73 through the orifice 72, to thereby keep the amount of ink 5b in the interruption chamber 73 constant. Thus, stable supply of ink is realized.

[0104] FIGS. 23 and 24 show an ink interruption mechanism 70b employed in a ninth embodiment. This mechanism is constructed such that a disk-shaped diaphragm member 81 formed of a flexible material such as a synthetic rubber is provided in a front end portion of the main body 1 to interrupt the connection of the ink storage chamber 4 to the felt tip 2a. A valve hole 82 is formed through a central portion of the diaphragm member 81. A holder member 83 is held in a front end portion of the main body 1 so that it can axially slide, and the felt tip 2a is held in a front end portion of the holder member. A valve axial section 85 projects at the rear side of the holder member 83 and is elastically and tightly inserted in the valve hole 82 of the diaphragm member 81. An ink passage 84 is connected to the felt tip 2a and also to an opening 86 formed in a peripheral surface portion of the valve axial section 85.

[0105] In the ink interruption mechanism 70b in this embodiment, during non-writing, the valve hole 82 of the diaphragm member 81 elastically contacts the outer peripheral surface of the valve axial section 85 as shown in FIG. 23, thereby closing the opening 86 and hence disconnecting the ink storage chamber 4 from the felt tip 2a. Accordingly, even if in this state, a fine pressure difference occurs in the ink storage chamber when executing a pressure compensating operation, it does not act upon the felt tip 2a, and hence the amount of ink contained in the felt tip 2a is prevented from excessively increasing or decreasing.

[0106] When the felt tip 2a has been pushed against a writing surface W as shown in FIG. 24 to execute writing, the holder member 83 is axially retreated by the pressure put on the writing instrument, whereby the diaphragm member 81 deforms toward the rear side of the instrument. As a result, the valve hole 82 of the diaphragm member 81 deforms and enlarges to thereby form a clearance between itself and the periphery of the valve axial section 85, i.e. to open the opening 86. Through the opening 86, the ink storage chamber 4 communicates with the felt tip 4a and ink is supplied.

[0107] Although in each of the embodiments, a description has been given of a disposable writing instrument, the writing instrument of the present invention is not limited to this. For example, a writing instrument according to a tenth embodiment shown in FIG. 25 is of a so-called refill type. This type includes an assembly of an ink storage chamber and a pen tip, which is exchangeably inserted in a writing instrument main body, or which can protrude from and retreat into the writing instrument main body by means of, for example, a knocking mechanism.

[0108] The refill 90 has substantially the same structure as the above-described first embodiment, and comprises a main body 1, a ball tip 2, an equalizing tube 7 and a reservoir 10. In FIG. 25, similar elements to those in the first embodiment are denoted by corresponding reference numerals, and no description will be given thereof. Although the writing instrument of this refill type does not have a drying prevention mechanism as described above so as to be made compact, but has a drying preventing function sufficient to use quick drying ink.

[0109] Specifically, the writing instrument of the refill type has a small diameter so that it can be contained in the writing instrument main body. Accordingly, the cross section of the ink storage chamber 4 and hence that of the equalizing passage 8 in the equalizing tube 7 are also small. This means that the length of the equalizing passage 8 is rather long with respect to its cross section. Therefore, as described above, the equalizing passage 8 is excellent in preventing the solvent of ink from evaporating and escaping therefrom, which means that it has a sufficient drying preventing function. Moreover, as described above, even the outflow preventing tube 25 of the tail plug 3 projecting in the reservoir 10 also has the effect of preventing the solvent of ink from evaporating and escaping. These effects enables the use of quick drying ink.

[0110] FIGS. 26 to 28 show an eleventh embodiment of the invention. This embodiment can prevent a liquid column of ink in the equalizing passage from diffusing in the form of mist as a result of, for example, a certain shock, and can also prevent the solvent of ink from evaporating and escaping. Accordingly, the aforementioned various solvent-evaporation-preventing mechanisms can be omitted.

[0111] The eleventh embodiment is similar to the tenth embodiment, and has a reservoir 10 defined by a partition member 6 at the rear side of the main body 1 and communicating with the equalizing passage 8 of the equalizing tube 7. The rear end of the equalizing tube 7, i.e. the end communicating with the reservoir 10, has a scatter prevention mechanism.

[0112] In the figure, reference numeral 101 denotes a scatter preventing member incorporated in the scatter prevention mechanism. The scatter preventing member 101 includes a head section 102 and a neck section 103. The neck section 103 is fitted in a rear end portion of the equalizing tube 7. Further, the outer diameter of the head section 102 is slightly smaller than the inner diameter of the reservoir 10, and an annular clearance is defined between the outer peripheral surface of the head section 102 and the inner peripheral surface of the reservoir 10.

[0113] A radial communicating groove 104, for example, is formed in a front end surface of the head section 102, i.e. a surface facing the partition member 6. An axial communicating groove 105 is also formed in the peripheral surface of the neck section 103. These communicating grooves 104 and 105 communicate with each other. In this embodiment, the communicating groove 105 of the neck section 103 has a shape obtained by cutting a peripheral portion of the neck section 103 to show a flat surface. When the neck section 103 is fitted in the equalizing tube 7, a clearance or passage of an arcuate cross section is formed between the neck section 103 and the inner peripheral surface of the equalizing tube 7.

[0114] A plurality of projections 106 are provided on the surface of the head section 102 opposed to the partition member 6, and disposed to be brought into contact with the partition member 6 to form a clearance 107 therebetween.

[0115] Since in the eleventh embodiment, the equalizing passage 8 of the equalizing tube 7 communicates with the reservoir 10 through communicating grooves 104 and 105 of the scatter prevention mechanism 102, expansion/contraction of air in the ink storage chamber 4 of the writing instrument is compensated to thereby always maintain the pressure in the ink storage chamber 4 at the atmospheric pressure, and also to eliminate the head pressure of ink when the writing instrument is stood to execute writing.

[0116] The communicating groove 104 is formed radially, and a communicating passage constituted of the communicating grooves 104 and 105 is bent halfway or has a shape like a maze. Therefore, ink does not diffuse into the reservoir 10 even if a strong shock is exerted upon the writing instrument as in the case where the writing instrument drops on the floor from a height, thereby diffusing the liquid column 5a of ink in the form of mist. Accordingly, the mist of ink is reliably prevented from diffusing from the reservoir 10 to the outside through the outflow preventing tube 25.

[0117] Also, since in this embodiment, the rear end of the equalizing passage 8 communicates with the reservoir 10 through a narrow passage consisting of the communicating grooves 104 and 105, the amount of diffusion is minimized and the escape of the solvent vapor can be sufficiently prevented. This is because there is no gas interchange between air and the solvent vapor of ink in the communicating grooves 104 and 105, and these grooves form a narrow passage. Moreover, in this embodiment, the axial length of the reservoir 10 is relatively long, and the length of the outflow preventing tube 25 formed in the tail plug 3 is also relatively long. This long outflow preventing tube 25 is also sufficient in preventing the solvent vapor from escaping. The embodiment can sufficiently prevent evaporation of quick drying ink without any ink evaporation preventing mechanism.

[0118] Furthermore, even if in the embodiment, air excessively expands in the ink storage chamber 4 to thereby cause ink to flow into the reservoir 10 as described above, the ink having flown into the reservoir 10 can be efficiently returned into the ink storage chamber 4 when the air in the ink storage chamber 4 has again contracted.

[0119] More specifically, a clearance 107 is defined between the head section 102 of the scatter preventing member 101 and the partition member 6, and the ink having flown into the reservoir is held by a capillary force in the clearance 107 and in the communicating grooves 104 and 105. Therefore, when air in the ink storage chamber 4 has expanded and again contracted in a state in which the writing instrument is in a horizontal position or is held with the pin tip pointing downward, the entire ink in the reservoir 10 is sucked up into the equalizing passage 8 via the clearance 107 and the communicating groove 104 and 105 and returned into the ink storage chamber 4. When, on the other hand, air in the ink storage chamber 4 has expanded and contracted in a state in which the writing instrument is in a reverse standing position with the pin tip pointing upward, no ink flows into the reservoir 10 via the equaling passage 8 since a front end portion of the equalizing tube 7 protrudes from the level of ink. Accordingly, no ink remains in the reservoir 10.

[0120] In addition, in the eleventh embodiment, the passage formed in the scatter preventing member 101 is not limited to the above one, but may have any shape that is bent or shaped like a maze and can prevent diffusion of mist of ink.

[0121] FIGS. 29 to 35 show a twelfth embodiment equipped with a drying prevention mechanism 20f for drying different inks.

[0122] As described above, the partition member 6 is provided in a rear end portion of the ink storage chamber 4, and a cylindrical slide chamber 110 is formed in the main body 1 between the partition member 6 and the tail plug 3. The front side of the slide chamber 110 communicates with the equalizing passage 8 of the equalizing tube 7 via a communication hole 111 formed in a central portion of the partition member 6.

[0123] An outflow preventing tube 12 is provided at a central portion of the tail plug 3 such that it extends along the axis of the slide chamber and projects inwardly, i.e. toward the radial center of the slide chamber 110. The rear side of the slide chamber 110 communicates with the outside via the outflow preventing tube 112. Since a front end portion of the outflow preventing tube 112 is situated in a central portion away from the inner peripheral surface of the slide chamber 110, liquid in the slide chamber 110 is prevented from leaking to the outside irrespective of which position the writing instrument is in.

[0124] A sealing slide plug 113 is axially slidably provided in the slide chamber 110. The sealing slide plug 113 is cylindrical and has a bottom formed by closing its front end. A predetermined clearance is formed between the outer peripheral surface of the plug and the inner peripheral surface of the slide chamber 110. In this embodiment, the width of the clearance is set at a value falling within the range of 0.05 - 0.1 mm in the case of a usual writing instrument, although it is determined on the basis of the inner diameter of the slide chamber 110 or the properties of a viscous fluid.

[0125] The slide chamber 110 is filed with a small amount of a viscous fluid. Silicone oil having a predetermined viscosity is appropriate as the viscous fluid. Silicone oil 115 is held by a capillary force between the outer peripheral surface of the sealing slide plug 113 and the inner peripheral surface of the slide chamber 110. Thus, silicone oil 115 is interposed in the form of an oil film between the outer peripheral surface of the sealing slide plug 113 and the inner peripheral surface of the slide chamber 110. This means that these surfaces do not directly contact each other.

[0126] As is shown in FIG. 30, axial groove sections 114 are formed in the outer peripheral surface of the sealing slide plug 13. At the groove sections 114, the clearance between the outer peripheral surface of the sealing slide plug 113 and the inner peripheral surface of the slide chanter 110 has a larger cross section. Accordingly, silicone oil 115 held by a capillary force between the outer peripheral surface of the sealing slide plug 113 and the inner peripheral surface of the slide chamber 110 has a smaller capillary force at the groove sections 114 than at the other portions.

[0127] A plurality of projections 116 are formed on the front end surface of the sealing slide plug 113 having a cylindrical body and a bottom. When the sealing slide plug 113 has moved by its maximum amount to the front side of the instrument, the projections 116 are brought into contact with the partition member 6, thereby forming a clearance between the front end surface of the sealing slide plug 113 and the partition member 6. Thus, the communicating hole 111 formed in the partition member 6 is not blocked. Further, the front end of the outflow preventing tube 112 has a shape obtained by obliquely cutting the tube so that the front end opening of the outflow preventing tube 112 will not be blocked even when the sealing slide plug 113 has moved by the maximum amount to the rear side of the instrument, and contacted the front end of the outflow preventing tube.

[0128] The writing instrument of the twelfth embodiment has the same ink pressure compensating function as mentioned above. Specifically, FIG. 31 shows the writing instrument that is in a horizontal position during non-writing, FIG. 32 the writing instrument that is in a reverse standing position during non-writing, and FIG. 33 the writing instrument in a standing position. In these states, the head pressure of ink is compensated in the same manner as described above.

[0129] Referring then to FIGS. 34 and 35, the operation of the ink drying prevention mechanism will be described. As described above, the ink supply mechanism employed in this embodiment requires as a precondition that the pressure in the equalizing passage 8 of the equalizing tube 7 is kept at a value equal to the atmospheric pressure. However, if the rear side of the equalizing passage 8 is made to directly communicate with the outside, the solvent vapor of ink in the ink storage chamber 4 escapes to the outside through the equalizing passage 8, thereby drying the ink. In particular, when using quick drying ink, the escape amount of the vapor is significant, and it is possible, for example, that ink in the ink storage chamber 4 will dry before being consumed, which disables writing.

[0130] Although in this embodiment, the equalizing passage 8 is connected to the outside via the slide chamber 110, the slide chamber 110 is sealed by the sealing slide plug 113. Further, the clearance between the outer peripheral surface of the plug and the inner peripheral surface of the slide chamber 110 is filled with silicone oil 115 and hence sealed. Accordingly, the solvent vapor of ink having diffused to the slide chamber 110 through the equalizing passage 8 is disconnected from the outside by the sealing slide plug 113 and hence prevented from escaping to the outside. As a result, ink in the ink storage chamber 4 is prevented from drying.

[0131] When a change occurs in temperature or atmospheric pressure, air or vapor in the ink storage chamber expands or contracts, and a pressure difference occurs between the ink storage chamber 4 and the outside air. In this case, the sealing slide plug 113 moves in the slide chamber 110 to thereby compensate the expansion/contraction or the pressure difference and maintain the pressure in the equalizing passage 8 and in the ink storage chamber 4 at a value equal to the atmospheric pressure at all times. Accordingly, no pressure difference occurs between the ink storage chamber 4 and the outside, and no problem occurs in the aforementioned ink supply adjusting function, thereby enabling stable ink supply.

[0132] Usually, the sealing slide plug 113 is in a middle position in the slide chamber 110 as shown in FIG. 34, and axially moves therein to execute the above-described pressure compensation. As aforementioned, the outer peripheral surface of the sealing slide plug 113 does not directly contact the inner peripheral surface of the slide chamber 110, but silicone oil 115 is interposed in the form of an oil film in the clearance therebetween. Therefore, when the sealing slide plug 113 moves, silicone oil 115 flows and functions as a lubricant, whereby the sealing slide plug 113 slides smoothly at an extremely low resistance. As a result, almost no pressure difference occurs between the inside and the outside of the ink storage chamber 4, and the pressure in the ink storage chamber 4 is kept at a value equal to the atmospheric pressure.

[0133] Silicon oil 115 has a relatively high viscosity and hence causes a flow resistance during flowing. However, a temperature change or an outside pressure change occurs at a long cycle, for example, at a cycle of one day, and thus the change rate is low. Accordingly, the drift velocity of the sealing slide plug 113 corresponding thereto is extremely low, Since the resistance of a viscous fluid such as silicone oil 115 is proportional to its drift velocity, the flow resistance of silicone oil 115 is extremely low and approaches almost zero during the aforementioned slow movement of the sealing slide plug 113.

[0134] On the other hand, when the writing instrument has erroneously fallen on, for example, the floor, it receives a great impact, thereby applying a great load to the sealing slide plug 113. However, as described above, a viscous fluid such as silicone oil 115 shows a significantly high resistance if its drift velocity is high. When receiving such an instant impact load, silicone oil 115 shows a high resistance, and the sealing slide plug 113 scarcely moves. Thus, when such an impact is applied, the sealing slide plug 113 operates like a fixed wall, whereby no air flow or no pressure change occurs in the slide chamber 110 or the equalizing passage 8, thereby preventing outflow of ink, escape of diffused ink, etc.

[0135] The degree of expansion/contraction of air is about 10% for a temperature change of 30°C. Accordingly, if the volume of the slide chamber 10 is set at 10% or more the content volume of the ink storage chamber 4, the expansion/contraction of air in the ink storage chamber 4 can be compensated even at a temperature change of 30°C or more. Since in a usual environment for writing instruments, a temperature change of more than 30°C seldom occurs, it suffices if the content volume of the slide chamber 110 is set at about 10% that of the ink storage chamber 4.

[0136] However, it is possible that the writing instrument will be exposed to a temperature change of 30°C or more, where a temperature difference is great between the inside and the outside of a room in a cold district, or where the writing instrument is left in, for example, a dashboard of a vehicle parked in a hot weather. In such a case, the sealing slide plug 113 moves by a maximum amount to one side of the slide chamber 10, for example, to the front side of the slide chamber 110 as shown in FIG. 35, and cannot move any more.

[0137] At this time, a certain pressure difference occurs between opposite sides of the sealing slide plug 113. This pressure difference excludes silicone oil 115 from a clearance between the outer periphery of the sealing slide plug 113 and the inner periphery of the slide chamber 110. Then, air flows into the clearance from which silicone oil 115 is excluded, thereby eliminating the pressure difference between the inside and the outside of the ink storage chamber 4. Since the projections 116 are provided on the front end surface of the sealing slide plug 113, a clearance is defined between the front end surface of the sealing slide plug 113 and the partition member 6 when the projections 116 have been brought into contact with the partition member 6. Accordingly, there is no possibility of the closure of the communicating hole 111 of the partition member 6.

[0138] Furthermore, where air in the ink storage chamber 4 has greatly expanded, the sealing slide plug 113 moves by a maximum amount to the rear side of the slide chamber 110 and contacts the front end of the outflow preventing tube 12 of the tail plug 3, thereby disabling any more movement thereof. As in the aforementioned case, silicone oil 115 is excluded from the clearance, thereby establishing connection. Since the front end portion of the outflow preventing tube 112 has an obliquely-cut shape, the front end opening of the outflow preventing tube 12 is not closed even when the sealing slide plug 113 contacts it.

[0139] In the above state, the solvent vapor of ink in the ink storage chamber 4 flows to the outside or air flows from the outside into the ink storage chamber 4. Thus, the solvent vapor of ink escapes in accordance with such air passage. However, such a great temperature change seldom occurs, and the amount of escaped vapor during the process is extremely small, which means that drying of ink, which is considered as a substantially serious problem, does not occur.

[0140] In this embodiment, the groove sections 114 are formed in the outer peripheral surface of the sealing slide plug 113 as shown in FIG. 30, and the capillary force that holds silicone oil 115 is relatively small at the groove sections 114. Accordingly, when a pressure difference as described above has occurred, silicone oil 115 in the groove sections 114 is excluded and air passes therethrough. This means that a smaller pressure difference enables exclusion of the silicone oil and establishment of connection.

[0141] In actual products, the capillary force of silicone oil 115 differs due to the influence of gravity and for other reasons between different portions. Therefore, without the groove sections 114, silicone oil is excluded beginning from a portion of a smallest capillary force, and connection is established before the entire silicone oil is excluded. This being so, it is not always necessary to form groove sections 114 as above.

[0142] Referring now to FIG. 36, a thirteenth embodiment of the invention will be described. This embodiment includes an ink supply mechanism provided with a dividing slide plug 120 in the ink storage chamber 4, and also includes another ink drying prevention mechanism 20g.

[0143] The dividing slide plug 120 is slidably fitted in the ink storage chamber 4 in a liquid tight manner. Ink 5 is filled in a front side portion with respect to the dividing slide plug 120, and a rear side portion is formed as an air section 121 for containing air. After ink is consumed during writing, the dividing slide plug 120 moves to the front side.

[0144] Also, in this embodiment, an inflow preventing tube 127 protruding toward the slide chamber 110 is provided at a central portion of a partition member 126 interposed between the ink storage chamber 4 and the slide chamber 110, thereby preventing, for example, silicone oil from in the slide chamber 110 from flowing into the ink storage chamber 4.

[0145] An outflow preventing tube 128 protruding toward the ink storage chamber 4 is provided in a central portion of the partition member 126. Even when ink has flown into the air section 121, it is prevented from flowing further into the slide chamber 110.

[0146] The inflow preventing tube 127 and the outflow preventing tube 128 have their respective front end openings of an obliquely-cut shape, so that these openings will not be closed when the sealing slide plug 113 contacts them. In this embodiment, the inflow preventing tube 127 and the outflow preventing tube 128 have the same shape so that the writing instrument can be constructed without discriminating the major and minor surfaces of the partition member 126.

[0147] Since this embodiment is similar to the eleventh embodiment except for the above-mentioned points, similar elements in FIG. 36 to those of the twelfth embodiment are denoted by corresponding reference numerals, and no description will be given thereof.

[0148] In this embodiment, ink is separated from air in the ink storage chamber 4 by the dividing slide plug 120, and accordingly, the outflow of ink into the slide chamber 110 is effectively prevented. Further, the ink supply mechanism in the shape of the dividing slide plug is advantageous in that it has a simple structure and can contain a large amount of ink. However, this type mechanism is disadvantageous in that if ink is dried and attached to a sliding surface between the dividing slide plug 120 and the ink storage chamber 4, the smooth sliding of the dividing slide plug 120 is interrupted. However, as described above, the ink drying prevention mechanism can substantially completely prevent drying of ink, and hence the above-mentioned drawback of the ink supply mechanism of the dividing slide plug type can be reliably eliminated.

[0149] FIG. 37 shows a drying prevention mechanism 20h employed in a fourteenth embodiment of the invention. This embodiment incorporates an ink supply mechanism of a so-called "cotton-filled type", in which the ink storage chamber 4 is filled with a porous body 130 consisting of cotton fiber, felt, etc.

[0150] The ink storage chamber 4 contains the above-mentioned porous body 130 that holds ink by a capillary force. In this embodiment, a larger amount of ink than usual is contained in the porous body 130, i.e. as a large amount of ink as oozes from the porous body 130 is contained therein. A relay core 131 formed of, for example, felt and having a larger capillary force than the porous body 130 is provided in a front end portion of the porous body 130 for relaying the supply of ink to the pen tip 2.

[0151] A space is defined as an air chamber 132 at the rear end of the porous body 130. An inflow preventing tube 137 and an outflow preventing tube 138 protrude, as in the above-described case, from a partition 136 that separates the ink storage chamber 4 and the slide chamber 110 from each other. In this embodiment, the outflow preventing tube 138 protruding in the ink storage chamber 4 is made longer.

[0152] Since this embodiment is similar to the thirteenth embodiment except for the above-mentioned points, similar elements in FIG. 37 to those of the thirteenth embodiment are denoted by corresponding reference numerals, and no description will be given thereof.

[0153] In this embodiment, ink is held by a capillary force in the porous body 130 in the ink storage chamber 4, and supplied to the pen tip 2 in units of a predetermined amount. Accordingly, the embodiment is characterized in that it has a simple structure and can be used in a reliable manner. However, the ink supply mechanism of this type is disadvantageous in that the amount of ink held in the porous body 130 is small. If ink held in the porous body 130 is too much, part of ink oozes from the porous body 130 and escapes to the outside through a passage communicating with the outside. If, on the other hand, only a small amount of ink is held, the handwriting may be blurred. To avoid these disadvantages, it is necessary to accurately control the amount of ink held in the porous body 130 at the manufacturing stage.

[0154] In this embodiment, an air chamber 132 is defined in the ink storage chamber 4, and contains an outflow preventing tube 138 protruding from the partition member 136. Accordingly, even if ink oozes from the porous body 130, it remains in the air chamber 132 and is prevented from flowing into the slide chamber 110. This can compensate the disadvantages of the ink supply mechanism of the cotton-filled type, i.e. a large amount of ink can be held in the porous body 130, it is not necessary to accurately control the amount of ink held in the porous body 130 at the manufacturing stage, and the writing instrument can be manufactured easily.

[0155] Moreover, as described above, the ink drying prevention mechanism can substantially completely prevent drying of ink. Where a large amount of ink is held in the porous body 130, if this writing instrument, for example, has fallen on the floor and received an impact, ink therein is liable to escape therefrom in the form of mist. Since, however, in this embodiment, a sealing slide plug 113 is interposed between the inflow preventing tube 37 and the outflow preventing tube 112 located at the rear side and opposed thereto, mist of ink can be reliably prevented from escaping to the outside through the inflow preventing tube 137 and the outflow preventing tube 112.

[0156] The invention is not limited to the above-described embodiments. The type of the pen tip or any other structure is not limited to that employed in the embodiments, either. In addition, in the case where no quick drying ink is used, a drying prevention mechanism or a reservoir as described above is not always necessary, but the equalizing passage may be made to directly communicate with the outside.

Industrial Applicability

[0157] As described above, in the invention, the pressure in a front end portion of an ink storage chamber is adjusted substantially equal to the atmospheric pressure during writing by means of an equalizing passage, thereby maintaining the head pressure applied to a pen tip at any desired low constant value, and hence enabling stable supply of ink and stable writing. Moreover, at the time of non-writing, the equalizing passage can compensate the expansion/contraction of air in the ink storage chamber to thereby maintain the pressure in the ink storage chamber substantially equal to the atmospheric pressure. In addition, the writing instrument of the invention does not include any movable section such as a subtle valve mechanism, or any section using a capillary force such as a fine orifice, but operates simply using the balance of pressure in various sections. Accordingly, the operation is extremely reliable, and the pressure of ink can be controlled in a stable manner. This being so, the invention can provide a cheap writing instrument of a simple structure, which has excellent writing characteristics and can be produced easily at low cost.

Claims

1. A writing instrument characterized by comprising:

a writing instrument main body;

a pen tip provided at a front end of the main body;

an ink storage chamber formed in the main body and communicating with the pen tip; and

an equalizing passage located substantially parallel to an axis of the ink storage chamber, having a front end communicating with a front end portion of the ink storage chamber, which is near to the pen tip, and a rear end communicating with an outside at a rear side of the main body.

2. A writing instrument according to claim 1, characterized in that the equalizing passage is formed in a tubular equalizing tube that is axially inserted in the ink storage section, and has a front end open to the front end portion of the ink storage chamber, which is near to the pen tip, and a rear end communicating with the outside.

3. A writing instrument according to claim 1, characterized in that the main body contains an ink storage cylinder in which the ink storage chamber is formed, and a space formed between an inner peripheral surface of the main body and an outer peripheral surface of the ink storage cylinder serves as the equalizing passage, the front end of the equalizing passage communicating with the ink storage cylinder in a position near the pen tip, and the rear end of the equalizing passage communicating with the outside at the rear side of the main body.

4. A writing instrument according to claim 1, characterized in that a cross section of the equalizing passage is set to a shape and a dimension which permit ink having entered the equalizing passage to have a shape of a liquid column therein because of a surface tension of a free surface of the ink, and which do not permit gas-liquid interchange therein wherein ink and air are interchanged with each other.

5. A writing instrument according to claim 1, characterized in that the ink storage chamber is substantially cylindrical, and the equalizing passage has a cross section set at 1/30 - 1/4 a cross section of the ink storage chamber.

6. A writing instrument according to claim 1, characterized in that the main body includes a drying prevention mechanism for interrupting, during non-writing, connection between the rear end of the equalizing passage and the outside, or connection between the front end of the equalizing passage and the ink storage chamber, thereby preventing drying of ink.

7. A writing instrument according to claim 1, characterized in that the pen tip is a ball tip, and a distance between the front end of the equalizing passage and the ball tip is 20 mm or less.

8. A writing instrument according to claim 1, characterized in that the pen tip is a felt tip, and the main body includes an ink interruption mechanism for interrupting, during non-writing, passage of ink between the ink storage chamber and the felt tip.

9. A writing instrument according to claim 1, characterized in that the rear end of the equalizing passage is provided with an ink-mist-escape preventing mechanism having a bent or maze-shaped passage.

10. A writing instrument according to claim 1, characterized in that the drying prevention mechanism includes a slide chamber formed at a rear side of the ink storage chamber and communicating with the ink storage chamber and also with the outside of the writing instrument, a sealing slide plug axially slidably contained in the slide chamber with a predetermined clearance defined between itself and an inner peripheral surface of the slide chamber, thereby interrupting connection between the ink storage chamber and its outside, and a viscous fluid having a predetermined viscosity and held by a capillary force between the inner peripheral surface of the slide chamber and the sealing slide plug.

Drawing