JP2001071676A - Member for writing utensil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve moldability of members, their transparencies, color matching of fitting members and the dimensional control of the members by a method wherein the members for writing utensil such as a cap or the like are molded by employing a resin mixture of a polypropylene and a polyethylene polymerized by using a metallocene catalyst or a polyethylene-based copolymer. SOLUTION: A writing utensil A consists of a barrel 2, in which an ink occlusal body 22 is housed, a pen point 21, which is held at the tip of the barrel so as to be connected with the ink occlusion body 22, a tail plug 23, which is forced in the opening of the rear end of the barrel 2, and a cap 1, which is detachably fittingly mounted to the pen point 21 side of the barrel 2 and on the surface of which a clip 11 is formed. In this case, the cap 1, the barrel 2 and the tail plug 23 are molded out of a resin mixture of the recycling material made of a polypropylene and a polyethylene polymerized by using a metallocene catalyst or a polyethylene-based copolymer. Thus, the development of sink marks at the injection molding of the members is checked, their moldabilities are raised and, at the same time, the transparency of the members, their color matching and the dimensional management of the fitting parts are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member for a writing instrument (for example, a cap, a barrel, a tail plug, etc.).

[0002]

2. Description of the Related Art (Transparency and flexibility) Conventionally, a member for a writing instrument such as a cap or a barrel is formed of a transparent resin molded body.
2. Description of the Related Art There is known an apparatus that allows visualization of an internal structure and ink filled therein.

[0003] Further, when the writing instrument member has a fitting portion on its outer surface or inner surface, if the molding material is hard, an appropriate fitting action cannot be obtained due to variations in dimensions of the fitting portion. If an excessively large press-fitting force is applied due to the variation, cracks may occur in the fitting portion. As a result, in order to avoid this, high dimensional accuracy is required in the fitting part, and dimensional control of the fitting part becomes difficult. Therefore, in the writing instrument member having the fitting portion, the dimensional variation of the fitting portion is absorbed, and particularly in the case of the detachable fitting portion (that is, when the writing instrument member is a cap, a barrel, or the like), it is soft. In order to obtain a feeling of fitting, appropriate flexibility is required.

Heretofore, as a writing instrument member made of a polypropylene resin molded body, for example, a molded body such as a homopolymer of polypropylene, a random copolymer of polypropylene, a block copolymer of polypropylene, and the like can be mentioned. In general, a random copolymer or homopolymer of polypropylene is insufficient in flexibility as compared with polyethylene, even if it has excellent transparency. In addition, block copolymers of polypropylene are relatively soft but have insufficient transparency.

[0005] In addition, it has been conventionally known to blend a polyethylene resin with a polypropylene resin in order to obtain flexibility. In general, polyethylene is not sufficiently transparent, even though it can secure softness, so that sufficient transparency cannot be obtained by blending polyethylene with polypropylene. Therefore, a writing instrument member having both sufficient transparency and sufficient flexibility could not be obtained easily.

(Moldability) In the past, when a writing instrument member was merely formed by injection molding of a polypropylene resin, sink marks often occurred depending on the shape of the writing instrument member. When the sink occurs in the fitting portion, an appropriate fitting action cannot be obtained. In particular, when the sink occurs in the seal fitting portion, there is a risk of ink evaporation or ink leakage, and a sufficient amount of a writing instrument member can be obtained. No function is obtained.

(Recycled material) In general, members to be fitted to each other, such as a barrel and a cap, or a barrel and a tail plug, are made of different materials. For example, the barrel is formed of polypropylene resin and Molding the cap and tail plug fitted and mounted on the cylinder with polyethylene resin,
Widely known. It is also known that members that fit together are colored in the same color (for example, the cap and the barrel, or the tail plug and the barrel are colored in the same color) to maintain a unified unified appearance. ing.

However, in recent years, writing implement members have been molded from recycled materials. If one of the writing implement members to be fitted with each other is molded from recycled polypropylene resin, the other is made from polyethylene resin. When molding with recycled materials, it is difficult to control the dimensions of the fitting portions due to variations in the physical properties of the recycled materials depending on the production lot.

In addition, in the case where both of the writing instrument members to be fitted with each other are formed of different materials of polypropylene resin and polyethylene resin, and both are colored in the same color,
If both the polypropylene resin and the polyethylene resin are obtained from a recycled material, the color of the resin of the recycled material tends to vary depending on the production lot. For this reason, it is difficult to match the colors of the members fitted to each other (for example, the cap and the barrel, or the tail plug and the barrel), and the appearance is impaired.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and in the case of injection molding,
Sinking is suppressed, moldability is improved, and when a transparent member is used, sufficient flexibility and sufficient transparency are satisfied at the same time. An object of the present invention is to provide a writing instrument member that facilitates color matching between members to be fitted and dimensional control of a fitted portion.

[0011]

Means for Solving the Problems [1] The present invention relates to a polypropylene (a) and a polyethylene or a polyethylene copolymer (b) polymerized using a metallocene catalyst.
A writing instrument member (Claim 1) molded from a resin mixture comprising:

[Polypropylene (a)] In the present invention, as the polypropylene (a), known polypropylenes can be used without any limitation. For example, a homopolymer of polypropylene, a random copolymer of polypropylene,
Examples include a block copolymer of polypropylene or the like, or a recycled material of the polypropylene.

The flowability of the polypropylene (a) is not particularly limited. However, in consideration of moldability, rigidity and impact resistance as a member for a writing instrument, the MFR (melt flow rate) is as follows. It is preferably 1 to 100 g / 10 min. The MF of the polypropylene (a)
R is a value measured at 230 ° C. according to JIS K7210.

The polypropylene (a) may be produced by any method, for example, a Ziegler-Natta type stereospecific catalyst, specifically a magnesium chloride-supported titanium-containing catalyst or a titanium trichloride-modified stereospecific catalyst. Propylene or a mixture of propylene and an α-olefin may be polymerized in the presence of a neutral catalyst or the like and a cocatalyst such as triethylaluminum or diethylaluminum chloride. Further, the polymerization method is not limited to gas phase or liquid phase. Also,
Known nucleating agents and additives can be applied to the polypropylene (a).

[Polyethylene or polyethylene copolymer (b) polymerized using a metallocene catalyst] The polyethylene or polyethylene copolymer (b) polymerized using a metallocene catalyst used in the present invention is, for example, JP-A-58-19309 and JP-A-59-9529.
No. 2, JP-A-60-35005, JP-A-60-350
No. 06, JP-A-60-35007, JP-A-60-35
008, JP-A-60-35009, JP-A-61-1
No. 30314, Japanese Patent Application Laid-Open No. 62-121707, Japanese Patent Application Laid-Open
3-61010, JP-A-63-152608, JP-A-63-264606, JP-A-64-6003, JP-A-1-95110, JP-A-1-121407, JP-A-1-301704, JP-A-1-259004, JP-A-1-319489, JP-A-2-41303, JP-A-2-131488, JP-A-3-56508, JP-A-3-62806, JP-A-3-70708, JP-A-3-70709, JP-A-3-74412 and JP-A-3-1630088, European Patent Application Publication No. 420436, U.S. Pat. No. 5,055,43.
8, the method described in WO 91/04257, etc., that is, disclosed in metallocene catalysts, particularly metallocene-alumoxane catalysts, or in, for example, WO 92/01723 and the like. Such a metallocene compound, using a catalyst consisting of a compound that reacts with the metallocene compound to become a stable anion, by polymerizing ethylene, or by copolymerizing ethylene as the main component and α-olefin as the auxiliary component Manufactured.

(Density) In the present invention, the density of polyethylene or polyethylene copolymer (b) polymerized using a metallocene catalyst is 0.84 to 0.92 g / c.
m ³ is preferred, and more preferably 0.86 to 0.91 g
/ Cm ³ , particularly preferably 0.87 to 0.90 g / cm ^3
3 is valid. If the density is less than 0.84 g / cm ^3, stickiness increases molding becomes difficult, whereas, the density is higher than 0.92 g / cm ^3, it can not be ensured sufficient transparency. In addition, the density is JIS K7112.
It is a value measured according to.

(MFR) In the present invention, the MFR (melt flow rate) of the polyethylene or the polyethylene copolymer (b) polymerized using a metallocene catalyst is preferably from 0.1 to 100 g / 10 min. More preferably, 1 to 80 g / 10 min, particularly preferably 5 to 60 g / 10 min is effective. The MFR is:
If it is less than 0.1 g / 10 min, the mixing property with polypropylene is insufficient, while if it exceeds 100 g / 10 min, the moldability, rigidity and impact resistance as a writing instrument member are inferior. still,
The MFR of (b) is 19 according to JIS K7210.
This is a value measured at 0 ° C.

(Blend ratio) In the present invention, the blend ratio of polypropylene (a) to polyethylene or polyethylene copolymer (b) polymerized using a metallocene catalyst is 100 parts by weight of polypropylene (a). (B) is used in an amount of 0.1 to 100 parts by weight, more preferably 1 to 50 parts by weight, particularly preferably 5 to 30 parts by weight.
It is effective to mix in parts by weight. When the blending ratio of (b) is less than 0.1 part by weight per 100 parts by weight of polypropylene (a), the improvement effect of the present invention is not recognized, while the blending ratio of (b) is If the amount exceeds 100 parts by weight with respect to 100 parts by weight of the polypropylene (a), the production cost increases and is not practical. In addition, the above resin mixture of (a) and (b) is added to another polymer,
Pigments, fillers and various additives can be added as long as they do not impair the invention.

[2] The writing implement member of the first aspect is preferably a cylindrical body having a fitting portion on an inner surface or an outer surface (claim 2).

Since the writing instrument member is a cylindrical body having a fitting portion on the inner surface or the outer surface, the directivity in the circumferential direction at the time of fitting the writing instrument member is lost, and the fitting and mounting property is improved. . Further, when the writing instrument member is a cylindrical body, a seal fitting is made at the fitting portion (for example,
In the case of seal fitting between the cap and the barrel, fitting between the barrel and the pen tip holder, or sealing fitting between the barrel and the tail plug),
Sufficient sealing properties can be obtained.

[0021] The fitting portion may be, for example, a riding-over fitting portion between projections or a press-fitting fitting portion between annular smooth surfaces or between annular smooth surfaces and projections.

(Example of Writing Tool Member) As the writing tool member of the present invention, for example, a cap (Claim 3) attached to the pen tip side of the barrel, ink is contained inside, and the ink is placed at the tip. A barrel having a pen tip from which can be derived (claim 4);
A tail plug fitted to a rear end of the barrel, a nib holder attached to a tip of the barrel and holding a nib;
Alternatively, an ink container or the like can be used.

(Molding method) The molding method of the present invention includes:
Injection molding is preferred, but various molding methods such as extrusion molding and hollow molding are also applicable.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
4) will be described.

[FIG. 1] A writing instrument A shown in FIG. 1 comprises a shaft cylinder 2 containing an ink occluding body 22 impregnated with ink therein, and an ink occluding body 22 held at the tip of the shaft cylinder 2 and contained therein.
Pen tip 21 made of a fiber bundle resin processed body connected to
A tail plug 23 press-fitted and fixed to the rear end opening of the barrel 2,
The cap 1 is detachably fitted to the pen tip 21 side of the barrel 2 and has a clip 11 integrally formed on the outer surface.

On the inner surface of the cap 1 and the outer surface of the front part of the barrel 2, a press-fitting portion 9b composed of annular smooth surfaces is formed. Then, the press-fitting portion 9b (that is, the seal fitting portion) between the cap 1 and the barrel 2 maintains the airtightness of the cap 1, and the pen tip side is sealed by attaching the cap.

Similarly, a press-fitting portion 9b composed of annular smooth surfaces is formed on the inner surface of the rear end of the barrel 2 and the outer surface of the tail plug 23. Then, at the press fitting portion 9b (seal fitting portion) between the barrel 2 and the tail plug 23, the barrel 1
The airtightness inside is maintained. Incidentally, the cap 1, the barrel 2 and the tail plug 23 are cylindrical injection-molded articles of synthetic resin.

In the writing implement A shown in FIG. 1, examples (Examples 1 and 2) of molding materials for the cap 1, the barrel 2 and the tail plug 23 are shown below.

Example 1: The barrel 2 is made of a recycled polypropylene material (colored in the same color as the ink filled inside), and the cap 1 and the tail plug 23 are made of a recycled polypropylene material (the same as the barrel 2). The resin mixture of the present invention (colored in the same color as the internally-filled ink) obtained by mixing a polypropylene made of a recycled material) with polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst.

Example 2: The cap 1 and the tail plug 23 are made of a recycled polypropylene material (colored in the same color as the internal filling ink), and the barrel 2 is made of a recycled polypropylene material (the same as the cap 1 and the tail plug 23). It is a resin mixture of the present invention (colored in the same color as the internally filled ink) in which a polypropylene made of the same recycled material) and polyethylene or a polyethylene copolymer polymerized using a metallocene catalyst are mixed.

Effects In the first and second examples, since the barrel 2 or the cap 1 and the tail plug 23 are made of the same recycled material of polypropylene resin, the members (the barrel 2 and the cap 1, the shaft, Color mismatch between the cylinder 2 and the tail plug 23) is suppressed.
In addition, at the same time as the occurrence of sink marks is suppressed, the variation in the physical properties of the recycled material is also suppressed, and the dimensional control of the fitting portion 9b is facilitated.

[FIG. 2] The writing instrument B shown in FIG. 2 is mainly composed of a bottomed cylinder having a pen tip 51 and an ink holding member 55 at the front and an ink tank 53 for directly storing ink 54 at the rear. And a cap 4 removably fitted to the outer surface of the shaft cylinder 5 on the pen tip 51 side and integrally formed with a clip 41 on the outer surface.

The ink holding member 55 temporarily holds overflowing ink in accordance with an increase in the internal pressure of the ink tank 53. The ink holding member 55 is provided with a pen point holder 52 holding a ballpoint pen point 51 at the tip thereof. A plurality of disc-shaped comb teeth for holding ink. A first ink guide member 56, a second ink guide member 57, and a third ink guide member 58 are provided at the axis of the ink storage member 55.

On the inner surface of the cap 4 and the outer surface of the front part of the barrel 5, a press-fitting portion 9b formed of an annular projection and an annular smooth surface is provided.
And the overriding fitting portion 9a comprising the dispersed projections and the annular projections
Are formed before and after. The press-fitting fitting portion 9b (that is, the sealing fitting portion) between the cap 4 and the shaft cylinder 5 maintains the airtightness of the cap 4, and seals the pen tip 51 side when the cap is mounted. The cap 4 and the shaft cylinder 5 are cylindrical injection molded bodies of synthetic resin.

In the writing implement B of FIG. 2, examples (Examples 3 and 4) of molding materials for the cap 4 and the barrel 5 are shown below.

Example 3: The barrel 5 is a transparent polypropylene resin (for example, a homopolymer or a random copolymer of polypropylene) colored in a color representing the internally filled ink, and the cap 4 is a color representing the internally filled ink. A transparent resin mixture of the present invention obtained by mixing a colored polypropylene resin (for example, a homopolymer or random copolymer of polypropylene) with a polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst. is there.

Example 4: The cap 4 is a transparent polypropylene resin (for example, a homopolymer or a random copolymer of polypropylene) colored in a color representing the internally filled ink, and the barrel 5 is a color representing the internally filled ink. Colored transparent polypropylene resin (for example,
This is a transparent resin mixture of the present invention obtained by mixing a homopolymer or a random copolymer of polypropylene) with a polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst.

Effect In Examples 3 and 4, the cap 4 or the shaft cylinder 5 is
Because it consists of a resin mixture of polyethylene and a polyethylene-based copolymer polymerized using a metallocene catalyst in polypropylene, the occurrence of sink marks is suppressed, and without impairing the original transparency of the polypropylene resin, sufficient Flexibility can be obtained. Thereby,
Variations in dimensions of the fitting portions 9a and 9b are absorbed, and proper fitting and fitting between the cap 4 and the shaft cylinder 5 is maintained. Also,
Since the barrel 5 has transparency, the ink retaining member 55 having a plurality of comb teeth inside the barrel 5 can be visually recognized from the outside of the barrel 5.

[FIG. 3] The writing implement C shown in FIG. 3 mainly includes a writing implement cartridge composed of an ink storage cylinder 74, a shaft cylinder 7 for accommodating the writing implement cartridge therein, and a pen tip 71 side of the shaft cylinder 7. The cap 6 is detachably fitted to the outer surface and integrally formed with the clip 61 on the outer surface.

The ink container 74 is a cylindrical body having both ends opened.
1 is press-fitted and fixed, and the inside thereof is filled with ink 75 and a grease-like follower 76 which advances with consumption of the ink 75, thereby constituting a writing instrument cartridge. I have.

The shaft cylinder 7 is a cylindrical body having both ends opened, accommodates the writing implement cartridge therein, has a base 73 screwed to a front end thereof, and a tail plug 77 is press-fitted and fixed to a rear end. In addition, the tip of the pen 73
Is projected, and the tail plug 77 causes the ink container 7
4 is supported at the rear end.

On the inner surface of the cap 6 and the outer surface of the front part of the barrel 7, there are provided a fitting portion 9a comprising a plurality of dispersed projections and an annular projection, and a press-fitting fitting portion 9b comprising an annular projection and an annular smooth surface. Formed before and after. A press-fitting portion 9b formed of an annular smooth surface and an annular projection is formed on the inner surface of the rear end of the barrel 7 and the outer surface of the tail plug 77. The press-fit fitting portion 9b (that is, the seal fitting portion) between the cap 6 and the barrel 7 keeps the airtightness in the cap 6 and the press-fit fitting portion between the tail plug 77 and the barrel 7. The airtightness in the barrel is maintained by 9b (that is, the seal fitting portion). The cap 6, the shaft cylinder 7, and the tail plug 77 are cylindrical injection-molded articles made of synthetic resin.

In the writing instrument C shown in FIG. 3, examples (Examples 5 and 6) of molding materials for the cap 6, the barrel 7, and the tail plug 77 are shown below.

Example 5: The barrel 7 is a transparent polypropylene resin (for example, a homopolymer or random copolymer of polypropylene), and the cap 6 is a transparent polypropylene resin (for example, a homopolymer or random copolymer of polypropylene). Is a transparent resin mixture of the present invention obtained by mixing polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst, and the tail plug 77 is formed of an opaque resin mixture of the present invention (with the internal filling ink 75 and Colored in the same color).

Effect In Example 5, since the cap 6 is made of an injection-molded product of a transparent resin mixture obtained by mixing polypropylene or polyethylene-based copolymer obtained by polymerizing polypropylene with a metallocene catalyst, And the flexibility can be obtained without impairing the original transparency of the polypropylene resin. Thereby, the dimensional variation of the fitting portion is absorbed, and the proper fitting and fitting of the cap 6 and the shaft cylinder 7 is maintained. In addition, tail plug 77,
Since the injection molding of the resin mixture of the present invention is used, appropriate flexibility is obtained, and at the same time, the occurrence of sink is suppressed, so that a stable seal fitting with the shaft cylinder 7 can be obtained.

Example 6: The barrel 7 is an opaque resin mixture of the present invention obtained by mixing polypropylene and polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst, and comprises a cap 6 and a tail plug. Reference numeral 77 denotes a polypropylene resin (colored in the same color as the internal filling ink 75).

Effect In Example 6, since the barrel 7 is an injection-molded article made of the resin mixture of the present invention, appropriate flexibility can be obtained, and at the same time, the occurrence of sink marks can be suppressed. A stable seal fit with the stopper 77 is obtained.

[FIG. 4] The writing instrument D shown in FIG. 4 mainly includes a pen point 82 (ballpoint pen point), a pen point holder 83 into which the pen point 82 is pressed and held, and a pen point holder 83 having a tip. The shaft cylinder 8 is press-fitted and fixed in the mounting hole, and an exterior body 81 (tail plug) covering the rear end opening of the shaft cylinder 8. The exterior body 81 is fitted to the rear outer surface of the barrel 8,
The space behind the inner follower 85 communicates with the outside through an air hole 86 via a gap between the inner surface of the outer casing 81 and the outer surface of the rear end of the barrel 8.

An aqueous gel ink 8 is provided inside the barrel 8.
4 and a grease-like follower 85 that advances with consumption of the ink 84 is directly filled. A press-fit fitting portion 9b (that is, a seal fitting portion) is formed on the inner surface of the mounting hole at the tip of the barrel 8 and the outer surface of the rear portion of the holder 83. Further, on the outer surface of the rear part of the barrel 8 and the inner surface of the exterior body 81, a fitting part 9a including a plurality of dispersed projections and annular projections, and a press fitting part 9b including an annular smooth surface and a plurality of vertical ribs. Are formed before and after. The barrel 8, the exterior body 81, and the nib holder 83 are cylindrical injection molded bodies.

In the writing implement D of FIG. 4, examples (Examples 7 and 8) of molding materials for the barrel 8 and the exterior body 81 are shown below.

Example 7: The barrel 8 is made of a mixture of a transparent polypropylene resin (for example, a homopolymer or a random copolymer of polypropylene) and polyethylene or a polyethylene copolymer polymerized using a metallocene catalyst. It is a resin mixture of the present invention, and the nib holder 83 and the exterior body 81 are made of polypropylene resin (for example,
(A homopolymer, a random copolymer or a block copolymer of polypropylene).

Effect In the above-mentioned Example 7, since the barrel 8 is an injection-molded article made of the resin mixture of the present invention, the inner surface of the mounting hole at the tip of the barrel 8 into which the outer surface of the nib holder 83 is press-fitted (press-fit). Fitting part 9
The occurrence of sink marks in b) is suppressed. As a result, proper seal fitting with the nib holder 83 without cracking or ink leakage can be obtained. In the case of the conventional barrel 8 made of an injection molded article of polypropylene resin, sink marks are apt to occur on the inner surface of the mounting hole, and cracks may occur at the tip of the barrel 8 due to the ink 84 entering the sink marks. , And ink leakage occurred.

Example 8: The barrel 8 is a homopolymer of polypropylene, the pen point holder 83 is a block copolymer of polypropylene, and the exterior body 81 is polyethylene or polyethylene polymerized using a polypropylene resin and a metallocene catalyst. It is a resin mixture of the present invention mixed with a system copolymer.

Effect In the above Example 8, since the exterior body 81 is the resin mixture of the present invention, the occurrence of sink marks is suppressed, and the stable fitting and attachment with the shaft cylinder 8 is maintained.

[0055]

The member for a writing instrument of the present invention is molded from a resin mixture of polypropylene and polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst. Sinking is suppressed, moldability is improved, and when a transparent member is used, sufficient flexibility and sufficient transparency are satisfied at the same time. The color matching of the members and the dimensional control of the fitting portion are facilitated.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a writing instrument A to which a writing instrument member of the present invention is applied.

FIG. 2 is a longitudinal sectional view showing a writing instrument B to which the writing instrument member of the present invention is applied.

FIG. 3 is a longitudinal sectional view showing a writing instrument C to which the writing instrument member of the present invention is applied.

FIG. 4 is a longitudinal sectional view showing a writing instrument D to which the writing instrument member of the present invention is applied.

[Explanation of symbols]

 A Writing implement 1 Cap 11 Clip 2 Shaft barrel 21 Pen tip 22 Ink occlusion body 23 Tail plug B Writing implement 4 Cap 41 Clip 5 Shaft barrel 51 Nib 52 Pen tip holder 53 Ink tank 54 Ink 55 Ink retaining member 56 First ink guide Member 57 Second ink guide member 58 Third ink guide member C Writing implement 6 Cap 61 Clip 62 Nib seal member 7 Shaft cylinder 71 Nib 72 Nib holder 73 Base 74 Ink cylinder 75 Ink 76 Follower 77 Tail plug D Writing implement 8 Shaft barrel 81 Exterior body 82 Nib 83 Nib holder 84 Ink 85 Follower 86 Air hole 9a Overpass fitting section 9b Press-fit fitting section

Claims (5)

[Claims] 1. A writing instrument member molded from a resin mixture of polypropylene and polyethylene or a polyethylene-based copolymer polymerized using a metallocene catalyst. 2. The writing instrument member according to claim 1, wherein the writing instrument member is a cylindrical body having a fitting portion on an inner surface or an outer surface. 3. The writing instrument member according to claim 1, wherein the writing instrument member is a cap attached to a pen tip side of the writing instrument body. 4. The writing implement member according to claim 1, wherein the writing implement member is a shaft cylinder that stores ink therein and has a pen tip at a tip thereof from which the ink can be led out. 5. The writing implement member according to claim 1, wherein the writing implement member is a tail plug fitted to a rear end of the writing implement main body having a pen tip at a tip.