Patent ID: 12187068

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. However, it should be noted that the technical scope of the present disclosure is not limited to each of the embodiments detailed below, and extends to the inventions described in the claims and equivalents thereof.

The fiber-bundled part for writing instruments of the present disclosure is composed of long fiber multifilaments having fibers with different melting points (in the present disclosure, even when the fibers do not have a melting point but have a softening point, this shall be deemed as a melting point), and the multifilaments contain at least crimped fibers.FIG.1(a)is a schematic perspective view showing an embodied example of a fiber-bundled part for writing instruments having a rectangular cross-section.

Fibers generally include filaments (monofilaments, multifilaments) and sliver. Monofilaments and multifilaments are used to obtain a fiber-bundled part having uniform density in the longitudinal direction. The fiber-bundled part for writing instruments in the present disclosure is formed of multifilament fibers of long types having different melting points, and part of the multifilament fibers of long types contains crimped fibers.

In the present disclosure, the multifilaments having different melting points include those composed of a combination of two or more polymers having different chemical structures, such as a combination of polymers having different melting points, selected from polyester, acrylic, polypropylene, wholly aromatic polyester, wholly aromatic polyesteramide, polyamide, semi-aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyether, wholly aromatic polycarbonate, polyimide, polyamideimide (PAI), polyether ether ketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBG), polybenzimidazole (PBI), polytetrafluoroethylene (PTFE), ethylene-vinyl alcohol copolymer, etc. Further, a combination of polymers which have a common chemical structure at least in part but different melting points from one another by introduction of a copolymer involving another structural unit; for example, a combination of polyethylene terephthalate and a copolymerized polyethylene terephthalate copolymer having a lower melting point than the former, and the like can be preferably mentioned.

For example, as shown inFIGS.2(a) and2(b), it is possible to use either a core-sheath type, or a side-by-side type, formed of a low-melting-point fiber and a high-melting-point fiber. As a core-sheath type multifilament a single yarn is composed of a core component and a sheath component. As a side-by-side type multifilament a single yarn is a side-by-side type composite of two or more types of polymers. Among these, the core-sheath type multifilament is preferable, and it is more preferable that the sheath component in the core-sheath type has a melting point lower than that of the core component.

In the present disclosure, the melting point difference (high melting point temperature−low melting point temperature) may and should be at least 30° C., preferably 50° C. or more. The melting point difference of 30° C. or more makes it possible to thermally fuse only the sheath of the core-sheath type multifilaments so as to form point-bonding at the entangled points between the fibers whose mutual parallelism is disturbed by crimping, thereby create three-dimensional reticulate structures and solidify the fibers together. The upper limit of the melting point difference is not particularly limited as long as the fibers are heat-fusible composite fibers available on the market and can be crimped. But the realistic temperature is 100° C. In the present disclosure, the melting point is the value measured conforming to JIS K 7121:2012.

In the present disclosure, the multifilament of long fibers having fibers with different melting points contains at least crimped fibers. The crimped fibers to be used are obtained by imparting two-dimensional or three-dimensional crimps and distortions to the multifilament of long fibers with different melting points, fixing the distortions by an appropriate method so as to disturb the parallelism between the fibers, thereby giving bulkiness and stretchability to the fibers.

In terms of achievement of bonding and solidifying by point-bonding the fibers at the entangled points between the fibers to create three-dimensional reticulate structures, and in terms of formation of a fiber bundle core of high porosity by entanglement between highly bulky fibers, the crimped fibers used in the present disclosure preferably have a crimp ratio of 1 to 50%, more preferably 1 to 20%, as defined in the following formula (1) and shown inFIG.1(b).
Crimp Ratio=(Crimp Width/Crimp Length)×100  (I)

[In the above formula (I), the distance between a wave crest to a next wave crest in the fiber is defined as the “crimp length”, and the distance between the crest (peak) and the trough (valley) of the wave in the direction perpendicular to the crimp length is defined as the “crimp width”.]

In the crimped fibers in the fiber-bundled part for writing instruments of the present disclosure, the crimp shape is not limited to a wavy form. As shown inFIG.1(d), when the crimped fibers have loop shapes, the crimp ratio can be calculated by defining the distance from the crest of the loop to the trough (valley) of the fiber as the “crimp width”, similarly to the wavy fiber.

Specifying the crimp ratio to be 1% or more makes it possible to bond and solidify the fibers by point-bonding the fibers at the entangled points between the fibers to create three-dimensional reticulate structures, and form a fiber bundle core of a high porosity by entanglement between highly bulky fibers. On the other hand, by specifying it equal to or lower than 50%, it is possible to create an optimal flow path for ink delivery without losing the parallelism between the fibers.

From the above points, the content ratio of the crimped fibers is preferably 10 to 100% by mass relative to the total amount of the fiber-bundled part for writing instruments.

The fineness of the multifilament of long fibers with different melting points and that of the crimped fibers are preferably 1 to 20 deniers from the viewpoint of ink retention and tactile sensation when used as a pen tip.

The fiber-bundled part for writing instruments of the present disclosure is produced in such a manner that the multifilaments of long fibers with different melting points and the above-described crimped fibers are put together at the aforementioned specific ratio, stretched and aligned as a bundle, then the bundle of fibers is heated and pressed to be solid without using any short fibers or a solvent as a binder resin for bonding the fibers, namely as a fiber bundled part of bound and solidified fibers. For example, as shown inFIG.4, the multifilaments of long fibers with different melting points and the above-described crimped fibers are put together at the aforementioned specific ratio in a thermoforming machine10while being pulled and aligned longitudinally by tension rollers11arranged ahead, whereby the fibers are bundled and heated, pressed and solidified without use of a binder resin or a solvent, thus forming a fiber-bundled part having a specific shape such as a sheet-like part having a rectangular cross-section, a cylindrical part, a polygonal column, star-shaped polygonal column, and the like.

It is important that the way of heating at this production is implemented within a range in which complete fusion of the fibers does not occur. Further, the heating temperature and time aiming at this thermal molding may vary depending on the type of fibers and the size of the fiber-bundled part to be produced, but may and should be specified within ranges in which the fibers can be bound and solidified by heat and pressure so as to produce a fiber bundle having a binding strength superior to the pull-out resistance from the die. That is, the fibers are bound and solidified into a fiber bundle by heating at a temperature that is equal to or higher than the melting point of the lower-melting point fiber of the two types of fibers having different melting points and equal to or higher than the heat shrinkage completion temperature for crimping. For example, when a PET-based fiber having a heat shrinkage completion temperature of 150° C. is used as the thermoplastic resin crimping fiber, the fibers can be bound and solidified by heating at a temperature that is 150° C. or higher and is equal to or higher than the melting point of the lower-melting point fiber and is lower than the melting point of the higher-melting point fiber.

In addition, as to the strength of the fiber-bundled part, it is possible to control the degree of fusion bonding of the low-melting-point fiber by adjusting the fiber loaded amount (basis weight volume), heating temperature and heating time.

The shape, dimensions, etc. of the fiber-bundled part for writing instruments obtained by the above method can be specified in accordance with its utility such as for sliver, for a pen core, for an ink feed core, for a relay core and the like, so as to have an arbitrary shape (rectangular in cross-section, sheet-like shape, cylindrical shape, polygonal column, star-shaped polygonal column), arbitrary dimensions, arbitrary thickness and the like.

Depending on the utility for the fiber-bundled part such as for a pen core, for an ink feed core, for a relay core and like, the fiber-bundled part obtained by the above method may be cut to an arbitrary length and then shaped and processed for each purpose, as required, to provide a desired fiber-bundled part for writing instruments.

FIG.1(a)shows an embodied example of a sheet-like fiber-bundled part for writing instruments having a rectangular cross-section obtained above, andFIG.3is a schematic perspective view of a cylindrical fiber-bundled part for writing instruments.

In the obtained fiber-bundled part for writing instruments, it is preferable that the fiber bundle has a substantially uniform density. Making the fiber bundle have the substantially uniform density can be achieved by forming the fiber bundle having a yarn density of 2,000 to 7,000 d/mm2.

Further, in this manufacturing method, satisfactory fiber-bundled parts can be manufactured by having a fiber density of 2,000 d/mm 2 or more and specifying the thickness to be 0.1 to 10 mm for those having a rectangular cross-section; and by having a fiber density of 2,000 d/mm 2 or more and specifying the outside diameter to be 0.1 mm or more for those having a circular cross-section.

In addition, the porosity, hardness, etc. of the fiber-bundled part for writing instruments vary depending on the type of ink, the type of writing instrument and the like. For example, the porosity can be adjusted to 30 to 80% by controlling the fiber bundle density, the forming temperature, heating time and the like during the above manufacturing. In the present disclosure, “porosity” is calculated as follows. First, the fiber-bundled part for writing instruments having a known mass and apparent volume is dipped in water, and saturated with water, and then the mass is measured in a state of being taken out from the water. From the measured mass, the volume of water soaked up in the writing core is derived. Assuming the volume of water as the pore volume of the fiber-bundled part for writing instrument, the porosity can be calculated from the following formula:—
Porosity (unit: %)=(water volume)/(apparent volume of the fiber-bundled part for writing instruments)×100.

The thus configured fiber-bundled part for writing instruments according to the present disclosure can offer a fiber-bundled part which, even if it is applied to a fiber bundle core particularly small in diameter such as a core having a rectangular cross-section or an irregular cross-section, can be manufactured simply and effectively at low cost so as not to vary in yarn density in the longitudinal direction of the core, still be excellent in strength and durability without impairing the ink or other liquid supply performance as a fiber-bundled part, and is suitable for writing instruments and applicators for cosmetics and others.

Next, the pen tip and writing instrument of the present disclosure will be explained.

The pen tip of the present disclosure is characterized by: 1) a pen tip having a writing pen core which is composed of the fiber-bundled part for writing instruments having the above configuration; and 2) a pen tip having an ink feed core for feeding ink to the writing part of the pen tip, in which the ink feed core is composed of the above fiber-bundled part for writing instruments.

The writing instrument of the present disclosure is characterized by including a pen tip having the writing pen core configured as described above and/or a pen tip having an ink feed core for feeding ink to the writing part configured as above.

FIGS.6to11are drawings showing examples of an embodiment of a pen tip to which the fiber-bundled part for writing instruments of the present disclosure obtained above is applied, as well as an embodiment of a writing instrument to which the pen tip is applied.FIGS.6and7show a twin-type writing instrument having pen tips at both ends, one having a writing pen core and the other having an ink feed core, depicting a state with its caps on and another state with its caps off, respectively.FIGS.8and9include an enlarged drawing of the pen tip having a writing pen core, and drawings of a holder for holding the writing pen core.FIGS.10and11include an enlarged drawing of the pen tip having an ink feed core, and drawings of a holder for holding the ink feed core.

As shown inFIGS.6and7, a writing instrument X of this embodiment includes a barrel member10serving as a writing instrument main body, ink retainers20and21housed in the barrel member10to store ink, pen tips30and50arranged via front barrels15and16that are fixed at both ends of the barrel member10, respectively, and removable caps70and71covering the pen tips30and50, respectively.

The barrel member10serving as the main body of the writing instrument is formed in a cylindrical shape and is made of thermoplastic resin, thermosetting resin or the like such as polyacetal-based resin, polyethylene-based resin, acrylic-based resin, polyester-based resin, polyamide-based resin, polyurethane-based resin, polyolefin-based resin, polyvinyl-based resin, polycarbonate-based resin, polyether-based resin, polyphenylene-based resin, etc., (hereinbelow, the resins are simply referred to as “each resin”). The barrel member has openings at both ends to which front barrels15and16for holding pen tips30and50are attached, respectively. Housed in the barrel member10are ink retainers20and21for storing ink. The ink retainers20and21are separated by a central partition23and configured to supply ink held therein to respective pen tips30and50.

The ink retainers20and21are impregnated with an ink composition for writing instruments such as water-based ink, oil-based ink, and thermochromic ink, and their examples include a fiber bundle formed of one or a combination of two or more substances, selected from natural fibers, animal hair fibers, polyacetal-based resin, acrylic-based resin, polyester-based resin, polyamide-based resin, polyurethane-based resin, polyolefin-based resin, polyvinyl-based resin, polycarbonate-based resin, polyether-based resin, polyphenylene-based resin, etc., a processed material of fiber bundles of felt etc., and porous materials such as sponges, resin particles, and sintered bodies.

The composition of the ink for writing instruments to be occluded in the ink retainers20and21is not particularly limited, and may be suitably formulated as a compound of a water-based ink, an oil-based ink, or a thermochromic ink, depending on the application of the writing instrument (felt-tip pen, marking pen, felt pen). For example, for underliner pens and the like, fluorescent dyes such as Basic Violet11, Basic Yellow40can be used as ink, or thermochromic microcapsule pigments and the like can be formulated as content.

The ink retainers20and21of this embodiment occlude the same ink composition therein. The ink retainers20and21may occlude different ink compositions from each other.

As shown inFIGS.6to8, the pen tip30has a writing pen core31and a holder40for mounting the writing pen core31. The writing pen core31is formed of a fiber-bundled part for writing instruments described above. The writing pen core31of this embodiment is 1.0 mm thick×2.0 mm wide×16 mm long. The front part of the writing pen core31serves as a writing part32while the rear end is inserted into the front-end side of the ink retainer20so that ink occluded in the ink retainer20is supplied to the writing part32in the front part of the writing pen core31.

As shown inFIGS.6to9, the holder40fixes the writing pen core31serving as a writing core by fitting, and is fixed to the front-end opening of the front barrel15of the barrel member10, and includes a bulging attachment body41, and a flange42and a see-through window frame portion43having a trapezoidal section, on the front side of the attachment body41. Formed inside the attachment body41and on the front-end side of the window frame portion43are mounting holes44and45for receiving the writing pend core31so as to catch and hold the writing pen core31.

The holder40comprised of the above elements has a concave fitting portion46aformed in the width direction on the peripheral surface of the attachment body portion41and liner air circulation grooves46band46cformed on both sides in the longitudinal direction on the peripheral surface thereof. The thus configured holder40is formed of, for example, a synthetic resin, metal, glass and the like.

As shown inFIGS.6,7and10, the pen tip50has an ink feed core51, a writing part52made of a porous material on the front-end side of the ink feed core51and a holder60to which the ink feed core51and the writing part52are attached. The ink feed core51is composed of the above-described fiber-bundled part for writing instruments. The ink feed core51of the present embodiment efficiently feeds (supplies) the ink stored in the ink retainer21to the writing section52, and is 0.8 mm thick×1.6 mm wide×16 mm long.

As shown inFIGS.6,7,10and11, the holder60is composed of a plate-shaped holding part61, a flange part62integrally formed at the rear end of the plate-shaped holding part61so as to protrude radially outward, and a bulging attachment body63integrally formed in the rear of the flange part62.

The plate-shaped holding part61is composed of two plate surfaces61aand61band a thick-plate surface portion61cthat is formed in the plate thickness direction and is surrounded by the front faces of the place surfaces61aand61band one side face of each of plate surfaces61aand61b. The writing part52made of a writing core is held on the thick-plate surface portion61cof the plate-shaped holding part61. The plate surfaces61aand61bare arranged on both sides so as to sandwich the thick-plate surface portion61c. Each of the plate surfaces61aand61bis formed by a plane substantially perpendicular to the thick-plate portion61c(that is, the plane substantially orthogonal to the plate thickness direction). In addition, triangular jagged faces64,64are formed on both outer surfaces of the plate surfaces61a,61b, so that the plate-shaped holding part61is given appropriate flexibility in the plate thickness direction.

A holding groove65in which the writing part52is held is formed in the thick-plate surface portion61c. Further, a holding groove66is defined by the upper parts of the plate surfaces61aand61bso that the ink feed core51is fitted in the holding groove66.

A concave fitting portion63ais formed in the width direction on the outer peripheral surface of the attachment body part63of the thus configured holder60while linier air circulation grooves63band63care formed on both side of the outer peripheral surfaces and extended in the longitudinal direction on the outer peripheral surface.

The holder60thus configured can be, as whole, formed of a relatively hard synthetic resin such as polypropylene, polyethylene, polystyrene, polycarbonate, polyethylene terephthalate, polyacetal, acrylic, nylon, acrylonitrile-styrene copolymer resin (AS resin), acrylonitrile-butadiene-styrene copolymer resin (ABS resin) and others. On the other hand, the material for the holder43may use a synthetic resin having elasticity. Examples of the synthetic resin having elasticity include soft polyethylene, soft polypropylene, nylon, rubber elastic materials (e.g., thermoplastic elastomers such as styrene-based elastomers, olefin-based elastomers, polyester-based elastomers). The synthetic resin forming the holder60may be a resin having transparency, whereby the contact state between the writing part52consisting of the writing core and the paper surface can be visually recognized during writing.

In the pen tip30of the above embodiment, the writing pen core31is composed of a fiber-bundled part for writing instruments having the above configuration with a rectangular cross-section, being 1.0 mm thick×2.0 mm wide×16 mm long. Even if the thickness of the pen tip is thus thin, the fiber-bundled part can offer a writing pen core that is excellent in strength and durability against the writing loads and is free from variation in yarn density with respect to the longitudinal direction of the core without losing ink supply performance and other properties as a fiber-bundled part.

The pen tip50of the present embodiment has the ink feed core51that feeds ink to the writing part. The ink feed core51is composed of a fiber-bundled part for writing instruments having the above configuration, and is excellent in strength and durability and is free from variation in yarn density with respect to the longitudinal direction of the core without losing ink supply performance and other properties as a fiber-bundled part when it is given in a sheet-like form.

Further, since, in the pen tip50of the present embodiment, the plate-shaped holding part61is formed with jagged faces64,64having a depth in the plate-thickness direction, the plate-shaped holding part61can produce suitable flexibility in the plate thickness direction. Further, since the plate-shaped holding part61is made of elastic synthetic resin, the plate-shaped holding part61can reliably obtain flexibility in the plate thickness direction.

According to the writing instrument of the present disclosure having the pen tip30and the pen tip50at both ends as described above, the fiber-bundled part will not lose ink supply performance or writing performance and is free from variation in yarn density with respect to the longitudinal direction of the core while the writing pen core or the ink feed core is excellent in strength and durability.

The writing instrument of the present disclosure is not limited to the above-described embodiment and the like, and can be variously modified without departing from the scope of the technical idea of the present disclosure.

Though in the description of the writing instrument of the above embodiment, the writing instrument of a twin-type writing instrument having the pen tip30with the writing pen core31and the pen tip with the ink feed core51for feeding ink to the writing portion52, at both ends of the barrel member10, was detailed, each of the pen tip30with the writing pen core31and the pen tip50with the ink feed core51for feeding ink to the writing portion52may be individually used to provide a single-type writing instrument.

Though each of the above-described embodiments was described with inks for writing implements (water-based ink, oil-based ink, thermochromic ink), liquid materials such as liquid cosmetics, liquid medicines, coating liquids, and correction liquids may be used.

EXAMPLES

Next, the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples and the like.

Example 1

A fiber-bundled part for writing instruments was obtained by the method shown below using fibers made of the following thermoplastic resins.

(Multifilament of Long Fibers Having Fibers with Different Melting Points: Core-Sheath Type Composite Fiber)

Core-Sheath Type Composite Fiber: composite fiber (5 denier of thickness) consisting of polyethylene terephthalate copolymer having a low melting point (melting point: 160° C.) as the sheath and polyethylene terephthalate having a high melting point (melting point: 250° C.) as the core.

(Crimped Fiber)

The core-sheath type composite fiber was false twisted to be crimped.

The crimp ratios of the crimped fibers were calculated to be 5% and 15%. Also, the content ratio of the crimped fibers to the total amount of the fiber-bundled part was 100% by mass, for both of the two types.

(Manufacturing Method of Fiber-Bundled Part)

As shown inFIG.4, a fiber-bundled part was formed by aligning and pulling the thermoplastic resin fibers in the longitudinal direction to solidify and bind them with the thermoforming machine10. In this process, the temperature for solidifying and binding was 160° C., and the time for the fibers to pass through the die was 30 seconds. The obtained fiber bundle was, specifically a sheet-like fiber-bundled part having a thickness of 1.0 mm and a width of 2.0 mm. In this forming, the fiber with a crimp ratio of 5% was adjusted to have a fiber density of 5,000 d/mm2with a porosity of 50%. The other fiber with a crimp ratio of 15% was adjusted to have a fiber density of 3,000 d/mm2with a porosity of 65%.

When this fiber-bundled part was observed with an electron microscope (SEM), it was confirmed that a homogeneous cross-sectional structure was formed as shown inFIG.5(a)without substantially differential density distributions between the central part of the core and the outer skin part.

This fiber-bundled part was cut into a piece of 16 mm long to form the writing pen core31of the pen tip30, shown inFIG.6.

Example 2

A fiber-bundled part for writing instruments was obtained by the method shown below using fibers made of the following thermoplastic resins.

(Multifilament of Long Fibers Having Fibers with Different Melting Points: Core-Sheath Type Composite Fiber)

Core-Sheath Type Composite Fiber: composite fiber (5 denier of thickness) consisting of polyethylene terephthalate copolymer having a low melting point (melting point: 160° C.) as the sheath and polyethylene terephthalate having a high melting point (melting point: 250° C.) as the core.

(Crimped Fiber)

The core-sheath type composite fiber was false twisted to be crimped.

The crimp ratio of the crimped fiber was calculated to be 5%. Also, the content ratio of the crimped fiber to the total amount of the fiber-bundled part was 100% by mass.

(Manufacturing Method of Fiber-Bundled Part)

As shown inFIG.4, a fiber-bundled part was formed by aligning and pulling the thermoplastic resin fibers in the longitudinal direction to solidify and bind them with the thermoforming machine10. In this process, the temperature for solidifying and binding was 160° C., and the time for the fibers to pass through the die was 30 seconds. The obtained fiber bundle was specifically a sheet-like fiber-bundled part having a thickness of 0.8 mm and a width of 1.6 mm with a fiber density of 4,000 d/mm2and a porosity of 60%.

When this fiber-bundled part was observed with an electron microscope (SEM), it was confirmed that a homogeneous cross-sectional structure was formed without substantially differential density distributions between the central part of the core and the outer part, similarly to that as shown inFIG.5(a).

This fiber-bundled part was cut into a piece of 16 mm long to form the ink feed core51of the pen tip50, shown inFIG.6.

Example 3

A fiber-bundled part for writing instruments was obtained by the method shown below using fibers made of the following thermoplastic resins.

(Multifilament of Long Fibers Having Fibers with Different Melting Points: Side-by-Side Composite Fiber)

Side-by-side composite fiber: Composite fiber (5 denier of thickness) with a mass ratio of 1:1 for 66 nylon (melting point: 265° C.) on one side and 6 nylon (melting point: 225° C.) on the other side.

(Crimped Fiber)

The above side-by-side composite fiber was crimped by push-in-type (gear type) crimping.

The crimp ratio of the crimped fiber was calculated to be 8%. The content ratio of the crimped fiber to the total amount of the fiber-bundled part was 100% by mass.

(Manufacturing Method of Fiber-Bundled Part)

As shown inFIG.4, a fiber-bundled part was formed by aligning and pulling the thermoplastic resin fibers in the longitudinal direction to solidify and bind them with the thermoforming machine10. In this process, the temperature for solidifying and binding was 225° C., and the time for the fibers to pass through the die was 30 seconds. The obtained fiber bundle was specifically a sheet-like fiber-bundled part having a thickness of 1.0 mm and a width of 2.0 mm with a fiber density of 5,000 d/mm2and a porosity of 50%.

When this fiber-bundled part was observed with an electron microscope (SEM), it was confirmed that a homogeneous cross-sectional structure was formed as shown inFIG.5(a)without substantially differential density distributions between the central part of the core and the outer skin part.

This fiber-bundled part was cut into a piece of 16 mm long to form the ink feed core31of the pen tip30, shown inFIG.6.

Comparative Example 1

Instead of using core-sheath type multifilament crimped fibers with different melting points in Example 1 above, a conventional single-component polyester multifilament was molded as crimped fibers, then impregnated with a polyurethane binder resin, and the binder was solidified in a heating furnace in the same manner as in Example 1.

The obtained fiber-bundled part was, specifically, a sheet-like fiber-bundled part having a thickness of 1.0 mm and a width of 2.0 mm with a fiber density of 5,000 d/mm2. The crimp ratio of the crimped fibers was 13%. Also, the content ratio of the crimped fibers to the total amount of the fiber-bundled part was 100% by mass. The porosity of the fiber-bundled port was 50%.

This fiber-bundled part was observed with an electron microscope (SEM). Due to the influence of evaporation of the solvent, the polyurethane binder resin concentrated onto the outer skin part of the core, so that the product presented an inhomogeneous cross-sectional structure with a large difference in the density distribution between the central part of the core and the outer skin part, as shown inFIG.5(b).

This fiber-bundled body was cut into a piece of 16 mm long to form the writing pen core31of the pen tip30shown inFIG.6.

The fiber-bundled parts obtained in Examples 1 to 3 and Comparative Example 1 were assembled into the pen body shown inFIG.6, and the writing performance of each was evaluated. As a result, it was confirmed that the fiber-bundled parts of the examples were superior in the following points to that using the conventional binder in Comparative Example 1:(1) Without use of a binder, sufficient strength and durability for writing were obtained by adjusting the loading amount (basis weight volume) of fibers, heating temperature, and heating time.(2) Since the pen core was free from binder imbalance, hence had no unevenness in hardness, there was no uncomfortable sensation during writing, attributed to the writing direction.(3) The ink holding capacity was improved by 10% or more.(4) Ink fluidity and diffusibility became uniform.
(Examples of Pen Tip and Writing Instrument)

The fiber-bundled parts obtained in Examples 1 and 2 above were used for the writing pen core31and the ink feed core51to produce a writing instrument conforming toFIGS.6to11. The dimensions of the writing instrument, the writing pen core31, the ink feed core51and others were specified as above. In addition, an ink for writing instruments having the following composition was used.

(Writing Instrument Configuration)

Barrel member10: made of polypropylene, 100 mm long with an inner diameter of 8 mm in the middle portion; an outside diameter of 10 mmInk retainers20,21: made of PET fiber, a porosity of 85%, dimensions of {acute over (ø)}6×45 mmHolder40: made of acrylic resin, a transparent window frame of 5×4×11.5 mmWriting part52: a polyethylene sintered core, a porosity of dimensions of 4×3×6 mmHolder60: made of acrylic resin, a transparent window frame of 5×2.5×12 mm
(Ink Composition for Writing Instruments, Ink Color: Black)

An ink of the following composition (100° by mass in total) was used as the ink for writing instruments.Activator: Megafac F410 (fluorine-based anionic surfactant, perfluoroalkyl group-containing carboxylate, manufactured by DIC Corporation) 1% by massAntifungal agent: benzisothiazolin-3-one 0.2% by massGlyceryl glucoside aqueous solution: αGG (high-concentration α-glyceryl glucoside aqueous solution, α-glyceryl glucoside 60% aqueous solution, manufactured by JTS Co., Ltd.) 3% by massPigment aqueous dispersion: FUJI SP BLACK 8041 (black pigment aqueous dispersion, solid content 20%, manufactured by Fuji Pigment Co., Ltd.) 20% by massWater-soluble organic solvent: glycerin 5% by massWater-soluble organic solvent: ethylene glycol 5% by mass

Water (solvent): ion-exchanged water 65.8% by massViscosity (25° C.): 3.6 mPa·s (Cone-plate type viscometer TV-20, manufactured by TOKIMEC Co., Ltd.)Surface tension (25° C.): 40 mN/m (automatic surface tens ion meter DY-300 manufactured by Kyowa Interface Science Co., Ltd.)

It was confirmed that a writing instrument X equipped with the pen tips30and50, respectively using the writing pen core31and the ink feed core51, which both were formed of the fiber-bundled parts obtained in Examples 1 and 2 above could offer excellent strength and durability and be free from variation in yarn density with respect to the longitudinal direction of the core without losing ink supply performance and the like of the ink for writing instruments.

INDUSTRIAL APPLICABILITY

Fiber-bundled parts for writing instruments that are suitably used for ink feed cores and writing pen cores as pen tips of writing instruments, as well as the pen tips and writing instruments using the fiber-bundled part, can be obtained.

DESCRIPTION OF SYMBOLS

X writing instrumentA fiber-bundled part for writing instrumentsB fiber-bundled part for writing instruments30pen tip31writing pen core50pen tip51ink feed core