A barrel and a writing instrument equipped with a barrel.

Abstract

To provide a barrel and writing instrument equipped with a barrel that reduce material usage while ensuring strength and rigidity. [Solution] The shaft 10 is a resin molded product having a non-cylindrical outer surface 11 and a cylindrical inner surface 12, the thickness of the shaft 10 is uneven, and a plurality of through holes 13 are provided on the side surface 11b of the shaft 10.

Description

Technical Field

[0001] The present invention relates to a shaft cylinder and a writing instrument provided with the shaft cylinder.

Background Art

[0002] In recent years, while product development with reduced environmental impact is desired, reduction of the amount of material used has been demanded in the shaft cylinder of writing instruments. To reduce the amount of plastic commonly used in the shaft cylinder of writing instruments, a method of relatively reducing the blending ratio of virgin plastic by using recycled materials and natural materials is common. On the other hand, if more consideration is given to environmental impact, it is desirable to reduce the volume of the shaft cylinder itself to reduce the total amount of material used.

[0003] Patent Document 1 and Patent Document 2 disclose a shaft cylinder and a writing instrument provided with the shaft cylinder in which the amount of material used is reduced by forming through holes on the side surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the shaft cylinder described in Patent Document 1, while the amount of material used can be reduced by forming through holes on the side surface, the strength and rigidity of the shaft cylinder are impaired as the number and size of the through holes increase. Therefore, it is difficult to significantly reduce the amount of material used. Since the shaft cylinder described in Patent Document 2 is manufactured from a non-resin material such as metal, the technology described in Patent Document 2 cannot be directly applied when manufacturing a shaft cylinder using a resin material.

[0006] The present invention aims to provide a barrel and a writing instrument equipped with a barrel that reduce the amount of material used while ensuring strength and rigidity. [Means for solving the problem]

[0007] According to one aspect of the present invention, a shaft cylinder for a resin molded product is provided, comprising a non-cylindrical outer surface and a cylindrical inner surface, wherein the thickness of the shaft cylinder is non-uniform, and a plurality of through holes are provided on the side surface of the shaft cylinder.

[0008] Furthermore, the non-cylindrical shape is preferably a polygonal tube.

[0009] It is preferable that each of the plurality of through holes is a polygonal through hole, and that the polygonal through holes are arranged in an aligned manner.

[0010] It is preferable that the polygonal shape is triangular and that the triangular through-holes are arranged in a truss-like configuration.

[0011] It is preferable that the polygonal shape is hexagonal and that the hexagonal through-holes are arranged in a honeycomb pattern.

[0012] Preferably, the device further comprises a clip member extending from the side surface of the shaft cylinder, and each of the two sides of the clip member is provided with a groove along the direction of extension of the clip member.

[0013] According to another aspect of the present invention, a writing instrument having the barrel described above is provided. [Effects of the Invention]

[0014] According to aspects of the present invention, a common effect is to provide a barrel and a writing instrument equipped with a barrel that reduce the amount of material used while ensuring strength and rigidity. [Brief explanation of the drawing]

[0015] [Figure 1]FIG. 1 is a perspective view of a writing instrument and a shaft cylinder according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of the shaft cylinder shown in FIG. 1. [Figure 3] FIG. 3 is a side view of the shaft cylinder shown in FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view of the shaft cylinder taken along line A-A of FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view of the clip member taken along line B-B of FIG. 3. [Figure 6] FIG. 15 is a cross-sectional view of a mold in the molding of the shaft cylinder shown in FIG. 1. [Figure 7] FIG. 18 is a cross-sectional view of a mold in the molding of the clip member shown in FIG. 1. [Figure 8] FIG. 21 is a perspective view of a writing instrument and a shaft cylinder according to the second embodiment of the present invention. [Figure 9] FIG. 24 is a perspective view of the shaft cylinder shown in FIG. 21. [Figure 10] ] FIG. 27 is a side view of the shaft cylinder shown in FIG. 21. [Figure 11] FIG. 30 is a cross-sectional view of the shaft cylinder taken along line C-C of FIG. 27. [Figure 12] FIG. 33 is a cross-sectional view of a mold in the molding of the shaft cylinder shown in FIG. 21. [Figure 13] FIG. 36 is a perspective view of a writing instrument and a shaft cylinder according to the third embodiment of the present invention. [Figure 14] FIG. 39 is an exploded perspective view of the shaft cylinder shown in FIG. 36. [Figure 15] FIG. 42 is a side view of the shaft cylinder shown in FIG. S36. [Figure 16] FIG. 45 is a cross-sectional view of the shaft cylinder taken along line D-D of FIG. 42. [Figure 17] FIG. 48 is a cross-sectional view of a mold in the molding of the shaft cylinder shown in FIG, 36. [Figure 18] FIG. 51 is a perspective view of a writing instrument and a shaft cylinder according to the fourth embodiment of the present invention. [Figure 19] FIG. 54 is an exploded perspective view of the shaft cylinder shown in FIG. 51. [Figure 20] Figure 20 is a side view of the shaft shown in Figure 18. [Figure 21] Figure 21 is a cross-sectional view of the shaft cylinder along line EE in Figure 20. [Figure 22] Figure 22 is a cross-sectional view of the mold used in the molding of the shaft shown in Figure 18. [Figure 23] Figure 23 is a perspective view of a writing instrument and barrel according to a fifth embodiment of the present invention. [Figure 24] Figure 24 is an enlarged view of section M in Figure 23. [Figure 25] Figure 25 is a perspective view of the shaft shown in Figure 23. [Figure 26] Figure 26 is a front view of the shaft shown in Figure 23. [Figure 27] Figure 27 is a rear view of the shaft shown in Figure 23. [Figure 28] Figure 28 is a right side view of the shaft shown in Figure 23. [Figure 29] Figure 29 is a left side view of the shaft shown in Figure 23. [Figure 30] Figure 30 is a bottom view of the shaft shown in Figure 23. [Figure 31] Figure 31 is a plan view of the shaft shown in Figure 23. [Figure 32] Figure 32 is a cross-sectional view of the shaft cylinder along line FF in Figure 26. [Figure 33] Figure 33 is a cross-sectional view of the shaft cylinder along line GG in Figure 28. [Figure 34] Figure 34 is a cross-sectional view of the shaft cylinder along line HH in Figure 28. [Figure 35] Figure 35 is a cross-sectional view of the shaft cylinder along line II in Figure 28. [Figure 36] Figure 36 is a cross-sectional view of the shaft cylinder along line JJ in Figure 28. [Figure 37] Figure 37 is a cross-sectional view of the shaft cylinder along line KK in Figure 28. [Figure 38] Figure 38 is a cross-sectional view of the shaft cylinder along line LL in Figure 28. [Figure 39] Figure 39 is a cross-sectional view of the mold used in the molding of the shaft shown in Figure 23. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described in detail below with reference to the drawings. Throughout all drawings, corresponding components are denoted by the same reference numerals.

[0017] Figure 1 is a perspective view of the writing instrument 1 and barrel 10 according to the first embodiment of the present invention. Figure 2 is a perspective view of the barrel 10 shown in Figure 1, Figure 3 is a side view of the barrel 10 shown in Figure 1, Figure 4 is a cross-sectional view of the barrel 10 along line AA in Figure 3, and Figure 5 is a cross-sectional view of the clip member 20 along line B-B in Figure 3.

[0018] The writing instrument 1 comprises a barrel 10, a clip member 20 extending from the side near the rear end of the barrel 10, and a writing section 30 provided at the tip of a refill, which is a cursive writing instrument (not shown), placed inside the barrel 10. The refill is, for example, a ballpoint pen refill. Therefore, the writing instrument 1 is a ballpoint pen. In this specification, in the axial direction of the writing instrument 1, the side with the writing section 30 is defined as the "front" side, and the side opposite to the writing section 30 is defined as the "rear" side.

[0019] The barrel 10 is a resin molded product formed by injection molding. A knock member 31 is provided at the rear end of the barrel 10. A release member 32 is provided on the rear side of the barrel 10 through a rectangular opening 15. The refill, which has a writing section 30, is always biased backward by a spring (not shown) inside the barrel 10. The writing instrument 1 is configured such that by performing a knock operation to press the knock member 31 forward, the refill is locked in a state where the writing section 30 protrudes from the opening 10a (Figure 4) of the barrel 10 (writing state), and then by pressing the release member 32, the lock on the refill is released, and the writing section 30 is retracted into the barrel 10 (non-writing state).

[0020] As shown in Figure 4, which is a cross-sectional view, the shaft cylinder 10 is a cylindrical member having an outer surface 11 defined as a roughly triangular cylinder and an inner surface 12 defined as a cylindrical shape. Specifically, the outer surface 11 is a roughly triangular cylinder with a roughly isosceles triangular cross-section consisting of a top surface 11a on which the clip member 20 is provided and two side surfaces 11b. The two side surfaces 11b are connected by corners 11c, and the top surface 11a and each of the two side surfaces 11b are connected by two corners 11d. The cross-sectional shape of the outer surface 11 is a rounded triangle, but because the corners 11c are wide, it can also be seen as roughly square.

[0021] Each side surface 11b of the shaft cylinder 10 is provided with a plurality of roughly triangular, specifically roughly isosceles triangular through holes 13. A slope 13a is provided along the edges of the through holes 13 on the side surface 11b. The plurality of through holes 13 are aligned along the longitudinal direction of the shaft cylinder 10. Specifically, the bases of the plurality of roughly triangular shapes are arranged to extend along the longitudinal direction of the shaft cylinder 10, and adjacent through holes 13 are arranged continuously in an orientation rotated 180 degrees. Therefore, adjacent through holes 13 define beams 14 that are positioned diagonally with respect to the central axis. The plurality of through holes 13 and the plurality of beams 14 form a truss shape on the side surface 11b. In other words, the plurality of roughly triangular through holes 13 are aligned in a truss shape.

[0022] Because the side surface 11b is formed in a truss shape, the shaft cylinder 10 has stable and high strength and rigidity against forces perpendicular to the axial direction, i.e., forces that cause the shaft cylinder 10 to bend. In addition, because the multiple through holes 13 in the shaft cylinder 10 are arranged in a truss shape, the amount of material used to form the shaft cylinder 10 can be efficiently reduced. Furthermore, solid portions defined between the outer surface 11 and the inner surface 12 are provided along the axial direction at positions spaced apart from the central axis of the shaft cylinder 10, in other words, from the central axis of the cylindrical inner surface 12, near the corner 11c and the two corners 11d. In other words, the wall thickness of the shaft cylinder 10 is uneven. The presence of these large volume portions consisting of solid portions near the corner 11c and the two corners 11d, which extend along the axial direction, can ensure even greater strength and rigidity.

[0023] The clip member 20 is integrally formed with the barrel 10. On both sides of the clip member 20, that is, on each of the two sides facing circumferentially around the central axis of the writing instrument 1, a groove 21 is provided along the extending direction of the clip member 20. As shown in Figure 5, the clip member 20 defined by the groove 21 has two wide, thickened portions 23 defined in the circumferential direction (up and down direction in the figure). Each of the thickened portions 23 is formed such that the thickness decreases towards the outside in the circumferential direction. That is, the thickened portions 23 are defined by tapered surfaces 23a that are provided to be closer together towards the outside. The two thickened portions 23 are connected by a connecting portion 24 which corresponds to the bottom of the groove 21 and extends along the extending direction of the clip member 20. A projection 25 is provided on the inside near the tip of the clip member 20, that is, on the surface facing the barrel 10. An object can be held between the shaft 10 and the projection 25 by utilizing the elastic force of the clip member 20.

[0024] The clip member 20 has an I-shaped or H-shaped cross-section due to two thickened sections 23 and a connecting section 24. For example, the solid sections, which are the two thickened sections 23, are positioned spaced apart from the axis of the connecting section 24 and are aligned along the axis. The presence of this large volume consisting of solid sections extending in the axial direction ensures the strength and rigidity of the clip member 20. In particular, it has high strength and rigidity against forces perpendicular to the extending direction of the clip member 20, that is, forces that bend the clip member 20 when gripping an article, etc. Furthermore, the provision of two grooves 21 in the clip member 20 reduces the amount of material used to form the clip member 20.

[0025] Figure 6 is a cross-sectional view of the mold 50 used in the molding of the shaft cylinder 10 shown in Figure 1, and Figure 7 is a cross-sectional view of the mold 50 used in the molding of the clip member 20 shown in Figure 1.

[0026] The mold 50 includes a first movable mold 51 and a second movable mold 52 that define the outer surface 11 of the shaft cylinder 10 and the outer surface of the clip member 20, and a core pin 55 that defines the inner surface 12 of the shaft cylinder 10. The mating surfaces 56 of the first movable mold 51 and the second movable mold 52 are provided symmetrically with respect to the shaft cylinder 10 including the clip member 20.

[0027] During injection molding of the shaft cylinder 10, the first movable mold 51 and the second movable mold 52 approach each other to sandwich the core pin 55, closing the mold 50 (movement in the direction of the arrows in Figures 6 and 7), and defining the cavity 60. Resin is injected from the opening of a gate (not shown) and flows into the cavity 60. After the cavity 60 is filled with resin, the first movable mold 51 and the second movable mold 52 are opened (movement in the opposite direction to the arrows in Figures 6 and 7). Next, the resin molded product is demolded to obtain the shaft cylinder 10. During demolding, the inclined surface 13a of the shaft cylinder 10 and the tapered surface 23a of the clip member 20 function as draft angles, enabling smooth demolding. The material used for molding is a synthetic resin, preferably polycarbonate or ABS, which have excellent strength and rigidity. Furthermore, to ensure the fluidity of the resin, it is preferable that the melt flow rate (MFR: JIS K6922-1:1997 Annex (190℃, 21.18N load)) is 15 [g / 10min] or higher.

[0028] The mold 50 has a simple structure because it consists of a first movable mold 51 and a second movable mold 52 that move in two directions relative to the core pin 55. Therefore, the size of the mold 50 can be reduced, while the number of products that can be placed in one mold 50 can be increased, making it possible to reduce production costs. In addition, stable molding is possible.

[0029] As described above, the shaft 10 and clip member 20 have large volume portions consisting of solid parts, namely the corner portion 11c, the two corner portions 11d, and the thickened portion 23, which ensures good resin flow during injection molding of the shaft 10 and clip member 20. In other words, the resin can be reliably distributed throughout the entire cavity 60 of the mold 50 for the shaft 10 and clip member 20. Furthermore, by setting the gate position in the mold 50 to the corner portion 11c or the top surface 11a in the central part of the longitudinal direction of the shaft 10, the pressure during resin flow can be suppressed, thereby preventing damage to the mold 50 and preventing burrs caused by resin overflowing from the gap in the mating surface 56 of the mold 50. As a result, more stable mass production is possible. Moreover, by setting the gate position to the corner portion 11c or the top surface 11a in the central part of the longitudinal direction of the shaft 10, it is possible to control the weld during injection molding so that it occurs in the large volume portion of the corner portion 11c or the top surface 11a. This enhances the adhesive strength of the weld and minimizes the reduction in strength and rigidity of the shaft 10 caused by the weld.

[0030] The following describes writing instruments and barrels according to other embodiments of the present invention.

[0031] Figure 8 is a perspective view of the writing instrument 100 and barrel 110 according to a second embodiment of the present invention. Figure 9 is a perspective view of the barrel 110 shown in Figure 8, Figure 10 is a side view of the barrel 110 shown in Figure 8, and Figure 11 is a cross-sectional view of the barrel 110 along line CC in Figure 10.

[0032] The writing instrument 100 differs from the writing instrument 1 according to the first embodiment only in the configuration of the barrel 110; the other components, including the clip member 20, are the same as those of the writing instrument 1.

[0033] The shaft cylinder 110 is a resin molded product formed by injection molding. As shown in Figure 11, a cross-sectional view, the shaft cylinder 110 is a cylindrical member having an outer surface 111 defined as a roughly square tube and an inner surface 112 defined as a cylindrical shape. Specifically, the outer surface 111 is a roughly square tube with a roughly square cross-sectional shape consisting of four sides 111a of roughly the same shape. The four sides 111a are connected by four corners 111d. A release member 32 is provided on the rear side of the shaft cylinder 110 via a rectangular opening 115.

[0034] Each side surface 111a of the shaft cylinder 110 is provided with a plurality of roughly triangular, specifically roughly isosceles triangular through holes 113. A slope 113a is provided along the edges of the through holes 113 on the side surface 111a. The plurality of through holes 113 are aligned along the longitudinal direction of the shaft cylinder 110. Specifically, the bases of the plurality of roughly triangular shapes are arranged to extend along the longitudinal direction of the shaft cylinder 110, and adjacent through holes 113 are arranged continuously in an orientation rotated 180 degrees. Therefore, adjacent through holes 113 define beams 114 that are positioned diagonally with respect to the central axis. The plurality of through holes 113 and the plurality of beams 114 form a truss shape on the side surface 111a. In other words, the plurality of roughly triangular through holes 113 are aligned in a truss shape.

[0035] Because the side surface 111a is formed in a truss shape, the shaft cylinder 110 has stable and high strength and rigidity against forces perpendicular to the axial direction, that is, forces that cause the shaft cylinder 110 to bend. In addition, because multiple through holes 113 are arranged in a truss shape in the shaft cylinder 110, the amount of material used to form the shaft cylinder 110 can be efficiently reduced. Furthermore, a solid portion defined between the outer surface 111 and the inner surface 112 is provided along the axial direction at a position spaced apart from the central axis of the shaft cylinder 110, in other words, from the central axis of the cylindrical inner surface 112, near the corner 111d. In other words, the wall thickness of the shaft cylinder 110 is uneven. The presence of this large volume portion consisting of the solid portion near the corner 111d extending along the axial direction ensures even greater strength and rigidity.

[0036] Figure 12 is a cross-sectional view of the mold 150 used in the molding of the shaft cylinder 110 shown in Figure 8.

[0037] The mold 150 includes a first movable mold 151 and a second movable mold 152 that define the outer surface 111 of the shaft cylinder 110 and the outer surface of the clip member 20, and a core pin 155 that defines the inner surface 112 of the shaft cylinder 110. The mold for the clip member 20 is as shown in Figure 7. The mating surfaces 156 of the first movable mold 151 and the second movable mold 152 are provided symmetrically with respect to the shaft cylinder 110 including the clip member 20.

[0038] During injection molding of the shaft cylinder 110, the first movable mold 151 and the second movable mold 152 approach each other to sandwich the core pin 155, closing the mold 150 (movement in the direction of the arrow in Figure 12), and defining the cavity 160. Resin is injected from the gate opening (not shown) and flows into the cavity 160. After the cavity 160 is filled with resin, the first movable mold 151 and the second movable mold 152 are opened (movement in the opposite direction to the arrow in Figure 12). Next, the resin molded product is demolded to obtain the shaft cylinder 110. During demolding, the inclined surface 113a of the shaft cylinder 110 functions as a draft angle, enabling smooth demolding.

[0039] In particular, in the cross-section of the mold 150 shown in Figure 12, that is, the cross-section of the shaft cylinder 110, the through-hole 113 and the bevel 113a are formed such that the angle θ1 shown in Figure 12 is greater than 45 degrees. The angle θ1 is the angle between the bevel 113a in the solid portion near the corner 111d furthest from the mating surface 156 and the median line L that passes through the center of the core pin 155 and divides the through-hole 113 equally. In other words, the through-hole 113 and the bevel 113a are formed such that the angle θ2 between the bevel 113a and the mating surface 156 is greater than 90 degrees. This makes it possible to mold a shaft cylinder 110 with through-holes 113 on all sides 111a while ensuring release properties, using two molds, the first movable mold 151 and the second movable mold 152.

[0040] The mold 150 has a simple structure because it consists of a first movable mold 151 and a second movable mold 152 that move in two directions relative to the core pin 155. Therefore, the size of the mold 150 can be reduced, while the number of products that can be placed in a single mold 150 can be increased, making it possible to reduce production costs. In addition, stable molding is possible.

[0041] As described above, the shaft 110 has four corners 111d, which are large solid sections, ensuring good resin flow during injection molding of the shaft 110. In other words, the resin can be reliably distributed throughout the entire cavity 160 of the mold 150 for the shaft 110. Furthermore, by positioning the gate in the mold 150 at the corners 111d in the central longitudinal section of the shaft 110, the pressure during resin flow can be suppressed, thereby preventing damage to the mold 150 and preventing burrs caused by resin overflowing from the gaps in the mating surfaces 156 of the mold 150. As a result, more stable mass production is possible. Moreover, by positioning the gate at the corners 111d in the central longitudinal section of the shaft 110, the weld during injection molding can be controlled to occur in the large volume section of the corners 111d. This increases the adhesive strength of the weld and minimizes the reduction in strength and rigidity of the shaft 110 caused by the weld.

[0042] Figure 13 is a perspective view of the writing instrument 200 and barrel 210 according to a third embodiment of the present invention. Figure 14 is an exploded perspective view of the barrel 210 shown in Figure 13, Figure 15 is a side view of the barrel 210 shown in Figure 13, and Figure 16 is a cross-sectional view of the barrel 210 along line DD in Figure 15.

[0043] The writing instruments 1 and 100 described above are writing instruments having two operating members: a knocking member and a release member. On the other hand, the writing instrument 200 according to this embodiment is a knock-type writing instrument having a knock mechanism that allows switching between a writing state and a non-writing state by knocking on a single operating member, namely the knocking member 231. The writing instrument 200 has a barrel 210, a rear barrel 216 that is detachably fitted to the rear end of the barrel 210, and a clip member 20 similar to that of the writing instrument 1 that extends from the side of the rear barrel 216.

[0044] The shaft cylinder 210 is a resin molded product formed by injection molding. As shown in Figure 16, which is a cross-sectional view, the shaft cylinder 210 is a cylindrical member having an outer surface 211 defined as a roughly triangular tube and an inner surface 212 defined as a cylindrical shape. Specifically, the outer surface 211 is a roughly triangular tube with a roughly equilateral triangular cross-section consisting of three sides 211a of roughly the same shape. The three sides 211a are connected by three corners 211d.

[0045] Each side surface 211a of the shaft cylinder 210 is provided with a plurality of roughly triangular, specifically equilateral triangular through-holes 213. The plurality of through-holes 213 are aligned along the longitudinal direction of the shaft cylinder 210. Specifically, the bases of the plurality of roughly triangular shapes are arranged to extend along the longitudinal direction of the shaft cylinder 210, and adjacent through-holes 213 are arranged continuously in an orientation rotated 180 degrees. Thus, adjacent through-holes 213 define beams 214 that are positioned diagonally with respect to the central axis. The plurality of through-holes 213 and the plurality of beams 214 form a truss-like structure on the side surface 211a. In other words, the plurality of roughly triangular through-holes 213 are aligned in a truss-like structure.

[0046] Because the side surface 211a is formed in a truss shape, the shaft cylinder 210 has stable and high strength and rigidity against forces perpendicular to the axial direction, i.e., forces that cause the shaft cylinder 210 to bend. In addition, because multiple through holes 213 are arranged in a truss shape in the shaft cylinder 210, the amount of material used to form the shaft cylinder 210 can be efficiently reduced. Furthermore, a solid portion defined between the outer surface 211 and the inner surface 212 is provided along the axial direction at a position spaced apart from the central axis of the shaft cylinder 210, in other words, from the central axis of the cylindrical inner surface 212, near the corner 211d. In other words, the wall thickness of the shaft cylinder 210 is uneven. The presence of this large volume portion consisting of the solid portion near the corner 211d extending along the axial direction ensures even greater strength and rigidity.

[0047] Figure 17 is a cross-sectional view of the mold 250 used in the molding of the shaft shown in Figure 13.

[0048] The mold 250 includes a first movable mold 251, a second movable mold 252, and a third movable mold 253 that define the outer surface 211 of the shaft cylinder 210 and the outer surface of the clip member 20, and a core pin 255 that defines the inner surface 212 of the shaft cylinder 210. The mating surfaces 256 of the first movable mold 251, the second movable mold 252, and the third movable mold 253 are provided so as to divide each of the corners 211d equally at the center of the core pin 255.

[0049] During injection molding of the shaft cylinder 210, the first movable mold 251, the second movable mold 252, and the third movable mold 253 approach each other to sandwich the core pin 255, closing the mold 250 (movement in the direction of the arrow in Figure 17), and defining the cavity 260. Resin is injected from the gate opening (not shown) and flows into the cavity 260. After the cavity 260 is filled with resin, the first movable mold 251, the second movable mold 252, and the third movable mold 253 are opened (movement in the opposite direction to the arrow in Figure 17). Next, the resin molded product is demolded to obtain the shaft cylinder 210.

[0050] Since the mold 250 consists of a first movable mold 251, a second movable mold 252, and a third movable mold 253 that move in three directions relative to the core pin 255, there is no need to provide a slope or the like as a draft angle in the through hole 213. Therefore, it is possible to improve the efficiency of reducing the amount of material used to form the shaft cylinder 210 and the degree of design freedom.

[0051] As described above, the shaft cylinder 210 has three large solid sections, namely the corners 211d, which ensure good resin flow during injection molding of the shaft cylinder 210. In other words, the resin can be reliably distributed throughout the entire cavity 260 of the mold 250 for the shaft cylinder 210. Furthermore, by positioning the gate in the mold 250 at the corners 211d in the longitudinal center of the shaft cylinder 210, the pressure during resin flow can be suppressed, thereby preventing damage to the mold 250 and preventing burrs caused by resin overflowing from the gaps in the mating surfaces 256 of the mold 250. As a result, more stable mass production becomes possible.

[0052] Figure 18 is a perspective view of the writing instrument 300 and barrel 310 according to a fourth embodiment of the present invention. Figure 19 is an exploded perspective view of the barrel 310 shown in Figure 18, Figure 20 is a side view of the barrel 310 shown in Figure 18, and Figure 21 is a cross-sectional view of the barrel 310 along line EE in Figure 20.

[0053] The writing instrument 300 is a retractable writing instrument having a retractable mechanism equipped with a retractable member 231 similar to that of the writing instrument 200. The writing instrument 300 has a barrel 310, a rear barrel 316 that is detachably fitted to the rear end of the barrel 310, and a clip member 20 similar to that of the writing instrument 1 that extends from the side of the rear barrel 316.

[0054] The shaft cylinder 310 is a resin molded product formed by injection molding. As shown in Figure 21, a cross-sectional view, the shaft cylinder 310 is a cylindrical member having an outer surface 311 defined as a roughly square tube and an inner surface 312 defined as a cylindrical shape. Specifically, the outer surface 311 is a roughly square tube with a roughly square cross-sectional shape consisting of four sides 311a of roughly the same shape. The four sides 311a are connected by four corners 311d.

[0055] Each side surface 311a of the shaft cylinder 310 is provided with multiple substantially hexagonal through-holes 313, specifically hexagonal through-holes 313, including half-shapes of regular hexagons. The multiple through-holes 313 are aligned along the longitudinal direction of the shaft cylinder 310. Specifically, one side of each substantially hexagon extends along the longitudinal direction of the shaft cylinder 310. Thus, adjacent through-holes 313 define beams 314 that are positioned diagonally with respect to the central axis. The multiple through-holes 313 and the multiple beams 314 form a honeycomb pattern on the side surface 311a. In other words, the multiple substantially hexagonal through-holes 313 are aligned in a honeycomb pattern.

[0056] Because the side surface 311a is formed in a honeycomb pattern, the shaft cylinder 310 has stable and high strength and rigidity against forces perpendicular to the axial direction, i.e., forces that cause the shaft cylinder 310 to bend. In addition, because multiple through holes 313 are arranged in a honeycomb pattern in the shaft cylinder 310, the amount of material used to form the shaft cylinder 310 can be efficiently reduced. Furthermore, a solid portion defined between the outer surface 311 and the inner surface 312 is provided along the axial direction at a position spaced apart from the central axis of the shaft cylinder 310, in other words, from the central axis of the cylindrical inner surface 312, near the corner portion 311d. In other words, the wall thickness of the shaft cylinder 310 is uneven. The presence of this large volume portion consisting of the solid portion near the corner portion 311d extending along the axial direction ensures even greater strength and rigidity.

[0057] Figure 22 is a cross-sectional view of the mold 350 used in the molding of the shaft shown in Figure 18.

[0058] The mold 350 includes a first movable mold 351, a second movable mold 352, a third movable mold 353, and a fourth movable mold 354 that define the outer surface 311 of the shaft cylinder 310 and the outer surface of the clip member 20, and a core pin 355 that defines the inner surface 312 of the shaft cylinder 310. The mating surfaces 356 of the first movable mold 351, the second movable mold 352, the third movable mold 353, and the fourth movable mold 354 are provided so as to divide each of the corners 211d equally at the center of the core pin 355.

[0059] During injection molding of the shaft cylinder 310, the first movable mold 351, the second movable mold 352, the third movable mold 353, and the fourth movable mold 354 approach each other to sandwich the core pin 355, closing the mold 350 (movement in the direction of the arrow in Figure 22), and defining the cavity 360. Resin is injected from the gate opening (not shown) and flows into the cavity 360. After the cavity 360 is filled with resin, the first movable mold 351, the second movable mold 352, the third movable mold 353, and the fourth movable mold 354 are opened (movement in the opposite direction to the arrow in Figure 22). Next, the resin molded product is demolded to obtain the shaft cylinder 310.

[0060] Since the mold 350 consists of a first movable mold 351, a second movable mold 352, a third movable mold 353, and a fourth movable mold 354 that move in four directions relative to the core pin 355, there is no need to provide a slope or the like as a draft angle in the through hole 313. Therefore, it is possible to reduce the amount of material used to form the shaft cylinder 310 and improve the design freedom.

[0061] As described above, the shaft cylinder 310 has four large solid sections, namely the corners 311d, which ensure good resin flow during injection molding of the shaft cylinder 310. In other words, the resin can be reliably distributed throughout the entire cavity 360 of the mold 350 for the shaft cylinder 310. Furthermore, by positioning the gate in the mold 350 at the corners 311d in the central longitudinal part of the shaft cylinder 310, the pressure during resin flow can be suppressed, thereby preventing damage to the mold 350 and preventing burrs caused by resin overflowing from the gaps in the mating surfaces 356 of the mold 350. As a result, more stable mass production is possible. Moreover, by positioning the gate at the corners 311d in the central longitudinal part of the shaft cylinder 310, the weld during injection molding can be controlled to occur in the large volume section of the corners 311d. This increases the adhesive strength of the weld and minimizes the reduction in strength and rigidity of the shaft cylinder 310 caused by the weld.

[0062] The shaft according to the above-described embodiment has an outer surface defined as a roughly triangular or roughly square shape and an inner surface defined as a cylindrical shape, but the shape of the outer surface can be arbitrarily adopted as long as it is not defined as cylindrical. The shaft may have an outer surface defined as a polygonal cylinder, for example, a roughly pentagonal or roughly hexagonal cylinder, or an elliptical cylinder. Note that a polygonal cylinder is not limited to a cross-sectional shape that consists of vertices and straight line segments connecting the vertices in a geometrically precise manner. That is, the vertices may be round, and the line segments may be arc-shaped. In other words, a polygonal cylinder is defined as a shape whose cross-sectional shape can be recognized as a polygon in its external appearance.

[0063] The shape of the multiple through-holes provided on the side of the barrel is not limited to equilateral triangles or regular hexagons, but can be any polygonal shape. The shape of the multiple through-holes may be a soccer ball shape, a combination of regular pentagons and regular hexagons. In addition, the shape of the multiple through-holes may be a non-circular shape such as an ellipse, other than a polygon. In short, the barrel is a resin molded product having a non-cylindrical outer surface and a cylindrical inner surface, with uneven wall thickness, and multiple through-holes provided on the side of the barrel.

[0064] Figure 23 is a perspective view of the writing instrument 400 and barrel 410 according to the fifth embodiment of the present invention, and Figure 24 is an enlarged view of section M in Figure 23. Figure 25 is a perspective view of the barrel 410 shown in Figure 23, Figure 26 is a front view of the barrel 410 shown in Figure 23, Figure 27 is a rear view of the barrel 410 shown in Figure 23, Figure 28 is a right side view of the barrel 410 shown in Figure 23, Figure 29 is a left side view of the barrel 410 shown in Figure 23, Figure 30 is a bottom view of the barrel 410 shown in Figure 23, and Figure 31 is a plan view of the barrel 410 shown in Figure 23. Furthermore, Figure 32 is a cross-sectional view of the shaft cylinder 410 along line FF in Figure 26, Figure 33 is a cross-sectional view of the shaft cylinder 410 along line GG in Figure 28, Figure 34 is a cross-sectional view of the shaft cylinder 410 along line HH in Figure 28, Figure 35 is a cross-sectional view of the shaft cylinder 410 along line II in Figure 28, Figure 36 is a cross-sectional view of the shaft cylinder 410 along line JJ in Figure 28, Figure 37 is a cross-sectional view of the shaft cylinder 410 along line KK in Figure 28, and Figure 38 is a cross-sectional view of the shaft cylinder 410 along line LL in Figure 28.

[0065] The writing instrument 400 differs from the writing instrument 1 according to the first embodiment only in the configuration of the barrel 410; all other configurations are the same as those of the writing instrument 1.

[0066] The barrel 410 is a resin molded product formed by injection molding. As shown in the bottom view of Figure 30, the barrel 410 is a cylindrical member having an outer surface 411 defined in a hexagonal shape and an inner surface 412 defined in a cylindrical shape. Specifically, the outer surface 411 is a hexagonal cylinder with a regular hexagonal cross-section consisting of two perforated sides 411a and four non-perforated sides 411b. Therefore, the writing instrument 400 as a whole has a shape similar to a pencil.

[0067] The two perforated sides 411a are located opposite each other on the outer surface 411. Therefore, the two perforated sides 411a are arranged parallel to each other. The four non-perforated sides 411b constitute the other surfaces of the hexagonal cylindrical outer surface 411. Two adjacent perforated sides 411a and four non-perforated sides 411b are connected to each other by six corners 411d. Therefore, one perforated side 411a is connected to two adjacent non-perforated sides 411b, and one non-perforated side 411b is connected to one adjacent perforated side 411a and one non-perforated side 411b. A release member 32 is provided on the rear side of the shaft cylinder 410 through a rectangular opening 415.

[0068] Each of the two perforated sides 411a is provided with a plurality of triangular, specifically equilateral triangular through holes 413 and a plurality of triangular, specifically equilateral triangular patterned portions 418. On the other hand, the four non-perforated sides 411b are not provided with through holes. Each of the four non-perforated sides 411b is provided with a plurality of triangular, specifically equilateral triangular recesses 417 and the plurality of patterned portions 418 described above. The through holes 413, recesses 417 and patterned portions 418 are triangular in shape and size. The through holes 413, recesses 417 and patterned portions 418 do not have to be equilateral triangles, as long as they are triangular in shape and size, they may be isosceles triangles or other polygonal shapes, etc.

[0069] Multiple beams 414 are defined at the boundaries of adjacent through-holes 413, recesses 417, and patterned sections 418, positioned diagonally with respect to the central axis. Specifically, the multiple beams 414 are provided along the sides of the through-holes 413, recesses 417, and patterned sections 418, each arranged in a triangular shape. The multiple beams 414 form a truss-like structure on the perforated side surface 411a and the non-perforated side surface 411b.

[0070] Because the perforated side surface 411a and the non-perforated side surface 411b are each formed in a truss shape, the shaft cylinder 410 has stable and high strength and rigidity against forces perpendicular to the axial direction, i.e., forces that cause the shaft cylinder 410 to bend. In addition, because the multiple through holes 413 in the shaft cylinder 410 are arranged in a truss shape, the amount of material used to form the shaft cylinder 410 can be efficiently reduced. Furthermore, a solid portion defined between the outer surface 411 and the inner surface 412 is provided along the axial direction at a position spaced apart from the central axis of the shaft cylinder 410, in other words, from the central axis of the cylindrical inner surface 412, near the corner 411d. In other words, the wall thickness of the shaft cylinder 410 is uneven. The presence of this large volume portion consisting of the solid portion near the corner 411d that extends along the axial direction ensures even greater strength and rigidity.

[0071] As shown in Figure 24, a bevel 413a is provided along the edge of the through hole 413. Part of the internal structure of the writing instrument 400, such as the refill 33, is visible through the through hole 413. A bevel 417a is provided along the edge of the recess 417. The bottom surface 417b of the recess 417 is provided flat, but may be provided in the shape of a convex or concave curved surface.

[0072] The patterned portion 418 is provided with three small recesses 418a. The three small recesses 418a are defined by three straight lines 418b formed to connect the center of the equilateral triangle that constitutes the outer shape of the patterned portion 418 to each of its three vertices. Therefore, each of the three small recesses 418a is isosceles triangular in shape. A slope 418c is provided along the edge of the small recess 418a. The bottom surface 418d of the small recess 418a is provided flat, but may be provided in the shape of a convex or concave curved surface.

[0073] The flat surface of the beam 414 is formed to be flush with the surface of the perforated side 411a and the surface of the non-perforated side 411b. The surface of the straight section 418b is formed to be flush with the surface of the perforated side 411a. Therefore, the outer surface 411, which is composed of the surface of the perforated side 411a and the non-perforated side 411b, has no protrusions as a whole, allowing the user to grip the writing instrument 400 without discomfort. In addition, the multiple through holes 413, multiple recesses 417 and multiple patterned sections 418 serve as anti-slip features for the user's hand and fingers.

[0074] As shown in Figures 26 and 27, the perforated side surface 411a has multiple through holes 413 and multiple patterned sections 418, which are aligned along the longitudinal direction of the shaft cylinder 410. Specifically, the bases of the multiple equilateral triangles in the multiple through holes 413 and multiple patterned sections 418 are arranged to extend along the longitudinal direction of the shaft cylinder 410, specifically along the corners 411d. The height of the triangles in the through holes 413 and patterned sections 418 is set to be approximately equal to the width of the perforated side surface 411a. The multiple through holes 413 and multiple patterned sections 418 are arranged continuously in an orientation rotated 180 degrees relative to adjacent through holes 413 or patterned sections 418. Therefore, the multiple through holes 413 and multiple patterned sections 418 are aligned in a line along the longitudinal direction of the shaft cylinder 410.

[0075] As shown in Figures 26 and 27, on the front side of the perforated side surface 411a, four patterned sections 418 are arranged in a row behind a patterned section 418 that is provided in half, and behind that, four through holes 413 are arranged in a row. Further behind that, three patterned sections 418 are arranged in a row, and further behind that, four through holes 413, three patterned sections 418, and four through holes 413 are arranged in a row in that order. Behind that, the patterned sections 418 are provided all the way to the rear, and finally, the patterned section 418 that is provided in half is provided.

[0076] The arrangement of the multiple through holes 413 and multiple patterned sections 418 on the perforated side surface 411a is not limited to this arrangement and may be adopted arbitrarily. The through holes 413 and patterned sections 418 may be arranged alternately, or two consecutive through holes 413 and two consecutive patterned sections 418 may be arranged alternately.

[0077] As shown in Figures 28 and 29, the non-perforated side surface 411b has a plurality of recesses 417 and a plurality of patterned areas 418, which are aligned along the longitudinal direction of the shaft 410. Specifically, the bases of the multiple equilateral triangles in the plurality of recesses 417 and the plurality of patterned areas 418 are arranged to extend along the longitudinal direction of the shaft 410, specifically along the corners 411d. The height of the triangles in the recesses 417 and the patterned areas 418 is set to be approximately equal to the width of the non-perforated side surface 411b. The plurality of recesses 417 and the plurality of patterned areas 418 are arranged continuously in an orientation rotated 180 degrees relative to adjacent recesses 417 or patterned areas 418. Therefore, the plurality of recesses 417 and the plurality of patterned areas 418 are aligned in a line along the longitudinal direction of the shaft 410.

[0078] For example, as shown in Figure 28, on the front side of the non-perforated side surface 411b, five patterned sections 418 are arranged in a row behind a patterned section 418 that is provided in half, and behind that, three recessed sections 417 are arranged in a row. Further behind that, three patterned sections 418 are arranged in a row, and further behind that, two recessed sections 417, one patterned section 418, three recessed sections 417, three patterned sections 418 and two recessed sections 417 are arranged in a row in that order. Behind that, patterned sections 418 are provided all the way to the rear, and finally, a patterned section 418 that is provided in half is provided.

[0079] The arrangement of the multiple recesses 417 and multiple patterned portions 418 on the non-perforated side surface 411b is not limited to this arrangement and may be adopted arbitrarily. The recesses 417 and patterned portions 418 may be arranged alternately, or two consecutive recesses 417 and two consecutive patterned portions 418 may be arranged alternately.

[0080] Several patterned areas 418 are arranged to be continuously adjacent on the outer surface 411 and recognized as a single unit. As a result, multiple continuously adjacent patterned areas 418 are recognized as a single pattern as a whole, thereby evoking an aesthetic sense in the user. For example, near the center of Figure 27 and near the top center of Figure 28, six patterned areas 418 are arranged integrally to form a single regular hexagon. This also evoks an aesthetic sense in the user.

[0081] Figure 39 is a cross-sectional view of the mold 450 used in the molding of the shaft cylinder 410 shown in Figure 23.

[0082] The mold 450 includes a first movable mold 451 and a second movable mold 452 that define the outer surface 411 of the shaft cylinder 410, and a core pin 455 that defines the inner surface 412 of the shaft cylinder 410. The mating surface 456 of the first movable mold 451 and the second movable mold 452 is provided to divide the shaft cylinder 410 into two equal parts.

[0083] During injection molding of the shaft cylinder 410, the first movable mold 451 and the second movable mold 452 approach each other to sandwich the core pin 455, closing the mold 450 (movement in the direction of the arrow in Figure 39), and defining the cavity 460. Resin is injected from the opening of a gate (not shown) and flows into the cavity 460. After the cavity 460 is filled with resin, the first movable mold 451 and the second movable mold 452 are opened (movement in the opposite direction to the arrow in Figure 39). Next, the resin molded product is demolded to obtain the shaft cylinder 410. During demolding, the inclined surfaces 413a, 417a, and 418c of the shaft cylinder 410 function as draft angles, enabling smooth demolding.

[0084] The mold 450 has a simple structure because it consists of a first movable mold 451 and a second movable mold 452 that move in two directions relative to the core pin 455. Therefore, the size of the mold 450 can be reduced, while the number of products that can be placed in a single mold 450 can be increased, making it possible to reduce production costs. In addition, stable molding is possible.

[0085] The barrel configuration described above may also be applied to the barrels of writing instruments other than retractable writing instruments, such as capped writing instruments. Furthermore, the barrel configuration described above may also be applied to the barrels of applicators other than writing instruments, such as cosmetic applicators like eyeliners, eyebrow pencils, and hair dye containers.

[0086] The refill described above may be a ballpoint pen, or other type of writing instrument such as a marking pen, stylus, or eraser. Furthermore, part or all of the knocking mechanism 31 may be an erasing section for erasing writing marks. The refill may contain thermochromic ink containing a thermochromic colorant. In this case, the writing instrument is a thermochromic writing instrument, and the writing marks can be thermochromic due to the frictional heat generated when rubbed with a friction material acting as an erasing element.

[0087] Here, thermochromic ink refers to ink that maintains a predetermined color (first color) at room temperature (e.g., 25°C), changes to a different color (second color) when heated to a predetermined temperature (e.g., 60°C), and then returns to its original color (first color) when cooled to a predetermined temperature (e.g., -5°C). In writing instruments using thermochromic ink, the second color is made colorless, and the process of heating the line written with the first color (e.g., red) to make it colorless is referred to here as "erasing." Therefore, friction heat is generated by rubbing the writing surface on which the line is written with a friction material, thereby changing the line to colorless, i.e., erasing it. Of course, the second color may be a color other than colorless. [Explanation of symbols]

[0088] 1 writing implements 10 shaft cylinder 11 Exterior 11a Top surface 11b Side 11c Corner 11d Corner 12. Inner self 13 Through hole 13a Slope 14 Beam 20 Clip component 21 Groove 30 Writing section 31 Knock Member 32 Release Member

Claims

1. A resin molded shaft having a non-cylindrical outer surface and a cylindrical inner surface, A shaft characterized by having an uneven wall thickness and having multiple through holes on its side surface.

2. The shaft cylinder according to claim 1, wherein each of the plurality of through holes is a polygonal through hole, and the polygonal through holes are arranged in an aligned manner.

3. The shaft cylinder according to claim 2, wherein the polygonal shape is triangular, and the triangular through holes are arranged in a truss-like configuration.

4. The shaft cylinder according to claim 2, wherein the polygonal shape is hexagonal, and the hexagonal through holes are arranged in a honeycomb pattern.

5. The shaft according to claim 1, further comprising a clip member extending from the side surface of the shaft, wherein each of the two side surfaces of the clip member is provided with a groove along the direction of extension of the clip member.

6. A writing instrument comprising a barrel according to any one of claims 1 to 5.

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