JP2026016068A - Resin parts for writing instruments and writing instruments equipped with them - Google Patents

Abstract

The present invention aims to provide resin parts for writing instruments that have certain physical properties and are made using recycled polyolefin resin as a raw material.
[Solution] A resin part for a writing instrument, comprising a recycled polyolefin resin composition, the recycled polyolefin resin composition comprising recycled polyolefin resin and a sliding property-imparting additive, the sliding property-imparting additive comprising silicone and/or a silicone-containing copolymer, and the total content of silicone-derived structural units in the silicone and the silicone-containing copolymer is 1.0 to 4.0 parts by mass per 100 parts by mass of the recycled polyolefin resin.
[Selected Figure] Figure 1

Description

The present invention relates to resin parts for writing instruments and writing instruments equipped with them.

In recent years, as an environmental measure, attention has been focused on the use of post-consumer materials, which are recycled resources from used products collected on the market. Recycled polyolefin resin is widely used as this post-consumer material. Writing instruments are one type of resin product that contains many resin parts, and the following writing instruments are known to use polyolefin resin:

For example, Patent Document 1 discloses a felt-tip pen whose entire components are made of block-type polypropylene resin to ensure the strength of the press-fit and mating parts and the hardness of the entire shaft.

Furthermore, the rotor of a knock-type writing instrument requires good sliding properties to advance the writing lead. Patent Document 2 discloses a writing instrument moving part in which a sliding agent is mixed into a resin. The moving part is made by molding a polycarbonate composition whose essential components are 100 parts by weight of polycarbonate resin (A), 1 to 20 parts by weight of sliding agent (B), and 0.1 to 0.8 parts by weight of sliding agent (C), and the moving part is characterized by a light transmittance of 80% or more in accordance with JIS K7361 for a 3 mm-thick molded edge injection molded from the composition.

Japanese Patent Application Laid-Open No. 2000-025381 Japanese Patent Application Laid-Open No. 2015-217646

Recycled polyolefin resin, a post-consumer material, can contain a variety of polyolefin resins, and its physical properties are often not consistent. Therefore, when using recycled polyolefin resin as a raw material, it is difficult to obtain resin parts for writing instruments with consistent physical properties.

The present invention aims to provide resin parts for writing instruments that have consistent physical properties using recycled polyolefin resin as a raw material.

In this invention, we focused on improving the surface properties of recycled polyolefin resin, particularly its sliding properties, in order to obtain resin parts for writing instruments made from recycled polyolefin resin.

The present invention achieves the above objectives by the following means:

<Aspect 1>
Contains a recycled polyolefin resin composition,
The recycled polyolefin resin composition contains a recycled polyolefin resin and a sliding property-imparting additive,
The sliding property-imparting additive contains silicone and/or a silicone-containing copolymer, and the total content of the silicone and the silicone-derived structural units in the silicone-containing copolymer is 1.0 to 4.0 parts by mass per 100 parts by mass of the recycled polyolefin resin.
Resin parts for writing instruments.
<Aspect 2>
The resin part for a writing instrument according to aspect 1, wherein the recycled polyolefin resin composition has a dynamic friction coefficient of 0.10 to 0.40.
<Aspect 3>
The resin part for a writing instrument according to aspect 1 or 2, wherein the content of the recycled polyolefin resin composition is 60 parts by mass or more, based on 100 parts by mass of the entire resin part for a writing instrument.
<Aspect 4>
A writing instrument comprising the resin part for a writing instrument according to any one of aspects 1 to 3.

This invention makes it possible to provide resin parts for writing instruments with consistent physical properties using recycled polyolefin resin as a raw material.

FIG. 1 is a schematic diagram illustrating the resin part for a writing instrument and the writing instrument of the present invention (FIG. 1(A): schematic diagram of the appearance of the writing instrument, FIG. 1(B): schematic diagram of the cross section of the writing instrument shown in FIG. 1(A)).

Embodiments of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention. Furthermore, in the description of the drawings, identical elements are designated by the same reference numerals, and redundant explanations will be omitted.

Resin parts for writing instruments
The resin part for a writing instrument of the present invention comprises:
Contains a recycled polyolefin resin composition,
The recycled polyolefin resin composition contains a recycled polyolefin resin and a sliding property-imparting additive,
The sliding property-imparting additive contains silicone and/or a silicone-containing copolymer, and the total content of silicone-derived structural units in the silicone and the silicone-containing copolymer is 1.0 to 4.0 parts by mass per 100 parts by mass of the recycled polyolefin resin.

This invention makes it possible to provide resin parts for writing instruments with consistent physical properties using recycled polyolefin resin as a raw material.

Unlike fillers and bulking agents that impart functional properties, which act on the bulk of resin parts, slideability-imparting additives containing silicone-derived structural units, such as silicone or silicone-containing copolymers, impart slideability (reducing the coefficient of friction) to the silicone portions exposed on the surface of resin parts, so slideability is determined by the surface slideability-imparting additive. Therefore, even when slideability-imparting additives are added to recycled polypropylene resin, which often has inconsistent physical properties, the resulting slideability does not depend largely on the type of recycled polyolefin resin, and variation in slideability can be reduced. This makes them suitable for use in writing instrument resin parts, especially components that require slideability.

Figure 1 is a schematic diagram showing one embodiment of a writing instrument equipped with a resin part for a writing instrument of the present invention, but the present invention is not limited to this example. Figure 1(A) is a schematic diagram of the appearance of the writing instrument, and Figure 1(B) is a schematic diagram of a cross section of Figure 1(A).

The writing instrument 10 includes resin parts such as a knock bar 11, a clip inner tube 12, a shaft 13, a mouth 14, and a rotor 15. For example, the knock bar 11, which is a resin part for a writing instrument, contains a recycled polyolefin resin composition, and the recycled polyolefin resin composition may have an average dynamic friction coefficient of 0.10 to 0.40. The resin parts for a writing instrument of the present invention are not particularly limited, but can be used as resin parts for the writing instrument 10, and may be, for example, the knock bar 11, the clip inner tube 12, the shaft 13, the mouth 14, the rotor 15, etc., with the knock bar 11, the clip inner tube 12, the rotor 15, or a combination thereof being preferred.

<Configuration of recycled polyolefin resin composition>
In the resin part for a writing instrument of the present invention, the recycled polyolefin resin composition contains a recycled polyolefin resin and a sliding property-imparting additive, and may contain other additives as necessary.

In the resin parts for writing instruments of the present disclosure, the content of the recycled polyolefin resin composition may be, for example, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more, or 100 parts by mass or less, 99 parts by mass or less, 95 parts by mass or less, or 90 parts by mass or less, based on 100 parts by mass of the entire resin part for writing instruments.

<Recycled polyolefin resin>
The recycled polyolefin resin is not particularly limited, but may include polypropylene resin and/or polyethylene resin.

In the present invention, the recycled polyolefin resin is not particularly limited, but from the perspective of realizing sustainable development, it is preferable to use polyolefin resin recovered from waste.

Polyolefin resins recovered from waste are preferably derived from, for example, post-consumer or pre-consumer materials. Post-consumer materials are defined in JIS Q14021:2000 as materials discarded from households or from commercial, industrial, and other end-user facilities that produce products that can no longer be used for their intended purposes. Pre-consumer materials are defined in JIS Q14021:2000 as materials removed from the waste stream during manufacturing processes.

(Polypropylene resin)
The polypropylene resin is not particularly limited, but examples thereof include homopolypropylene, random polypropylene, block polypropylene, etc. The polypropylene resin is not particularly limited, but one type may be used alone, or two or more types may be used in combination. When two or more types of polypropylene resins are used in combination, the content of the polypropylene resins is the sum of the contents of the respective types.

Homopolypropylene can be, for example, a polymer made solely of propylene monomer.

Examples of random polypropylene include random copolymers of propylene and ethylene, or random copolymers of propylene and an α-olefin having 4 to 20 carbon atoms.

Examples of the α-olefins include 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. Among these, α-olefins having 4 to 8 carbon atoms are preferred, and specifically, 1-butene, 3-methyl-1-butene, 1-hexene, and 4-methyl-1-pentene are preferred. One type of α-olefin may be used alone, or two or more types may be used in combination.

Block polypropylene may be, for example, a polypropylene in which polyethylene is dispersed in homopolypropylene, forming an island-in-a-sea morphology, but is not limited to this. Block polypropylene may also be, but is not limited to, a mixture of propylene homopolymer and propylene-ethylene copolymer.

(Polyethylene resin)
Examples of polyethylene resins include, but are not limited to, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-high molecular weight polyethylene. Furthermore, the polyethylene resin may include, but is not limited to, both an ethylene homopolymer and a copolymer of ethylene and another monomer copolymerizable with ethylene (e.g., a binary or tertiary copolymer). The bonding form of the copolymer is also not limited to, but may be random or block. The polyethylene resin is also not limited to, but may be used alone or in combination of two or more types. When two or more types of polyethylene resins are used in combination, the content of the polyethylene resins is the sum of the respective contents.

Other monomers copolymerizable with ethylene include, but are not limited to, α-olefin compounds, vinyl compounds, non-conjugated polyene compounds, etc. These other monomers may be used singly or in combination of two or more. Examples of the α-olefin compounds include α-olefin compounds having 3 to 20 carbon atoms, such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, and 1-tetradecene. Examples of the vinyl compounds include vinylcyclohexene, styrene, and derivatives thereof. Examples of the non-conjugated polyene compounds include 1,5-hexadiene and 1,7-octadiene.

(Composition of recycled polyolefin resin)
The total content of polypropylene resin and polyethylene resin in the recycled polyolefin resin may be, for example, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more, or 100 parts by mass or less, 99 parts by mass or less, 95 parts by mass or less, or 90 parts by mass or less, based on 100 parts by mass of the entire recycled polyolefin resin.

The amount of polypropylene resin is not particularly limited, but may be 50 parts by mass or more, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more, or 100 parts by mass or less, 90 parts by mass or less, or 80 parts by mass or less, based on 100 parts by mass of the total recycled polyolefin resin.

The amount of polyethylene resin is not particularly limited, but may be 1 part by mass or more, 5 parts by mass or more, or 10 parts by mass or more, or 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less, based on 100 parts by mass of the total recycled polyolefin resin.

Recycled polyolefin resin, particularly recycled polyolefin resin recovered from waste, may contain other resins and impurities in addition to the main components, polypropylene resin and polyethylene resin. The total content of other resins and impurities other than the main components may be 0 parts by mass or more, 1 part by mass or more, or 5 parts by mass or more, or 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less, based on 100 parts by mass of the total recycled polyolefin resin. There are no particular limitations on the other resins and impurities other than the main components, but it is preferable that they are not included.

Other resins that may be contained in recycled polyolefin resin other than the main component include, but are not limited to, general-purpose resins other than polypropylene resin and polyethylene resin, engineering plastics, super engineering plastics, etc.

<Sliding property imparting additive>
In the resin part for a writing instrument of the present invention, the additive for imparting sliding property contains silicone and/or a silicone-containing copolymer.

(silicone)
The silicone is not particularly limited, but includes polysiloxane, etc., more specifically, silicone oil, silicone gum (or silicone rubber), etc. Here, polysiloxane is a polymer compound containing siloxane bonds, and among silicones, oily ones are called silicone oil, and rubbery ones are called silicone gum (silicone rubber). The silicone is not particularly limited, but one type may be used alone, or two or more types may be used in combination. When two or more types of silicone are used in combination, the content of the silicone is the sum of the respective contents.

Examples of polysiloxanes include, but are not limited to, dimethylpolysiloxane, diphenylpolysiloxane, methylphenylpolysiloxane, and modified products thereof. Examples of modified products include, but are not limited to, vinyl-modified silicones in which some of the methyl and/or phenyl groups of the polysiloxane are substituted with vinyl groups; hydrogenpolysiloxanes in which some of the methyl and/or phenyl groups are substituted with hydrogen atoms; alkyl-modified silicones in which some of the methyl and/or phenyl groups of the polysiloxane are substituted with alkyl groups; fluorine-modified silicones in which some of the methyl and/or phenyl groups are substituted with fluorine atoms or fluorinated alkyl groups; polyether-modified silicones in which some of the methyl and/or phenyl groups are substituted with polyether groups; amino-modified silicones in which some of the methyl and/or phenyl groups are substituted with amino groups; carbinol-modified silicones in which some of the methyl and/or phenyl groups are substituted with hydroxyalkyl groups; epoxy-modified silicones in which some of the methyl and/or phenyl groups are substituted with oxirane ring-containing groups; and carboxy-modified silicones in which some of the methyl and/or phenyl groups are substituted with carboxyl groups.

For example, pellets of silicone masterbatched with other resins can be used as silicone. Specific examples of masterbatches containing silicone include, but are not limited to, silicone master pellets X-22-2101 and X-22-2147 manufactured by Shin-Etsu Chemical Co., Ltd., and EverGlide (trademark) manufactured by West One Co., Ltd.

(Silicone-containing copolymer)
The silicone-containing copolymer is not particularly limited, but may be a copolymer of the above silicone and another polymerizable monomer. Examples of the other polymerizable monomer include, but are not limited to, (meth)acrylic acid esters, (meth)acrylic acid esters having other functional groups such as epoxy groups or hydroxyl groups, and olefins. Here, "(meth)acrylic acid esters" refers to either or both of "acrylic acid esters" and "methacrylic acid esters."

Silicon-containing copolymers include, but are not limited to, silicone/acrylic copolymers and silicone/olefin copolymers. Specific examples of silicone/acrylic copolymers include Chaline R-170S, R-175S, and R-200 manufactured by Nissin Chemical Industry Co., Ltd., and Cymac (trademark) US-450 and US-480 manufactured by Toagosei Co., Ltd. Furthermore, examples of silicone/olefin copolymers include Exfora (trademark) PP2000 manufactured by Mitsui Fine Chemicals, and BY27-001 and BY27-201 manufactured by DuPont Toray Specialty Materials.

The silicone-containing copolymer is not particularly limited, but one type may be used alone, or two or more types may be used in combination. When two or more types of silicone-containing copolymers are used in combination, the content of the silicone-containing copolymer is the sum of the contents of each type.

(Amount of Sliding Property-Providing Additive)
In the resin parts for writing instruments of the present disclosure, the total content of silicone and silicone-derived structural units in the silicone-containing copolymer is 1.0 to 4.0 parts by mass, and may be 1.5 parts by mass or more, 2.0 parts by mass or more, or 2.5 parts by mass or more, or may be 4.0 parts by mass or less, 3.8 parts by mass or less, or 3.6 parts by mass or less, relative to 100 parts by mass of the recycled polyolefin resin.

<Other additives>
The recycled polyolefin resin composition may contain known additives such as antioxidants, slip agents, neutralizing agents, light stabilizers, antistatic agents, and pigments, as needed.

(antioxidant)
The antioxidant is not particularly limited, but examples thereof include phenol-based antioxidants, phenol-phosphorus-based antioxidants, and phosphorus-based antioxidants.

Examples of phenolic antioxidants include, but are not limited to, 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, and tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane.

Examples of phenol-phosphorus antioxidants include, but are not limited to, 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepine.

Examples of phosphorus-based antioxidants include, but are not limited to, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene-di-phosphonite, tris(2,4-di-t-butylphenyl)phosphite, and cyclic neopentanetetraylbis(2,4-t-butylphenylphosphite).

(slip agent, neutralizer)
Examples of slip agents or neutralizing agents include, but are not limited to, aliphatic hydrocarbons, higher fatty acids, higher fatty acid metal salts, fatty acid esters of alcohols, waxes, higher fatty acid amides, silicone oils, rosin, etc. Examples of slip agents or neutralizing agents include, but are not limited to, stearates, specifically calcium stearate, magnesium stearate, zinc stearate, etc.

(Light resistance stabilizer)
The light resistance stabilizer is not particularly limited, but examples thereof include benzotriazole-based light resistance stabilizers and hindered amine-based light resistance stabilizers.

Examples of benzotriazole-based light stabilizers include, but are not limited to, 2-(5-methyl-2-hydroxyphenyl)benzotriazole and 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole.

Examples of hindered amine light stabilizers include, but are not limited to, bis(2,2,6,6-tetramethyl-4-piperidine) sebacate and poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}].

(Antistatic Agent)
The antistatic agent is not particularly limited, but examples thereof include aluminosilicates, kaolin, clay, natural silica, synthetic silica, silicates, talc, diatomaceous earth, and glycerin fatty acid esters.

(Pigment)
The pigment is not particularly limited, but examples thereof include inorganic pigments, organic pigments, etc. Examples of inorganic pigments include, but are not limited to, titanium oxide, carbon black, iron oxide pigments, etc. Examples of organic pigments include, but are not limited to, azo pigments, phthalocyanine pigments, condensed polycyclic pigments, etc.

Recycled polyolefin resin compositions can be produced by applying known methods (e.g., dry blending, masterbatch, extrusion kneading, melt kneading, etc.). For example, recycled polyolefin resin compositions can be easily produced by melt kneading raw materials containing the various components listed above.

<Physical properties of recycled polyolefin resin composition>
The recycled polyolefin resin composition may have a dynamic friction coefficient of 0.10 to 0.40. The dynamic friction coefficient may be 0.15 or more, 0.17 or more, 0.19 or more, or 0.21 or more, and may be 0.40 or less, 0.38 or less, or 0.36 or less.

The dynamic friction coefficient of recycled polyolefin resin compositions can be determined in accordance with JIS K7125:1999. Specifically, two test samples (80 mm x 200 mm x 1 mm thick: JIS K7154-2:2002, small square plate type D1) are prepared, stacked together, and placed in an automatic load testing machine (manufactured by Nippon Keisoku Systems, model number: MAX-1KN-H-1). The test samples are then rubbed against each other under a load of 200 g ± 2 g (1.96 N ± 0.02 N) and a friction speed of 100 mm/min, and the dynamic friction coefficient is measured.

<Molding of resin parts for writing instruments>
Resin parts for writing instruments can be molded from recycled polyolefin resin compositions by applying known methods. For example, resin parts for writing instruments can be easily molded by injection molding recycled polyolefin resin compositions.

《Writing implements》
The writing instrument of the present invention includes the above-described resin part for a writing instrument.

The writing instrument of the present invention can be made from recycled polyolefin resin.

In the aforementioned FIG. 1, the writing instrument 10 may include the aforementioned resin parts for writing instruments in the knock bar portion 11, clip inner cylinder portion 12, shaft portion 13, mouth portion 14, rotor portion 15, etc. In particular, it is preferable that at least one of the knock bar portion 11, clip inner cylinder portion 12, and rotor portion 15 include the resin parts.

The writing instrument of the present invention is not particularly limited, but may be a ballpoint pen or a marking pen.

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

The recycled polyolefin resins and sliding property-imparting additives used in the examples and comparative examples are as follows:

(recycled polyolefin resin)
1-1. Recycled colored PP: Polypropylene resin as a post-consumer material, which is colored polypropylene resin.
1-2. Recycled PP: Polypropylene resin as a post-consumer material.

(Slidability-imparting additive)
2-1. R-170S: Chaline R-170S (manufactured by Nissin Chemical Industry Co., Ltd., silicone/acrylic copolymer, 70% by mass of structural units derived from silicone).
2-2. X-22-2101: Silicone master pellets X-22-2101 (manufactured by Shin-Etsu Chemical Co., Ltd., polypropylene resin silicone master pellets, silicone-derived structural units 50% by mass).
PP2000: Exfora PP2000 (manufactured by Mitsui Chemicals Fine Chemicals, silicone/ethylene copolymer, 30% by mass of structural units derived from silicone).
2-4. P-10: Alflow P-10 (manufactured by NOF Corp., fatty acid amide).
2-5. L5000: LUBMER L5000 (manufactured by Mitsui Chemicals, ultra-high molecular weight polyethylene).

Example 1
<Preparation of recycled polyolefin resin composition>
A recycled polyolefin resin composition was prepared by extrusion molding (melting temperature 200°C) of recycled colored PP as a recycled polyolefin resin and R-170S as a sliding property-imparting additive. The content of silicone-derived structural units in R-170S was 1.0 part by mass per 100 parts by mass of recycled colored PP.

<Measurement of dynamic friction coefficient of recycled polyolefin resin composition>
Two test samples (80 mm x 200 mm x 1 mm thick: JIS K7154-2:2002, small square plate type D1) were prepared using the resulting recycled polyolefin resin composition. The two test samples were stacked and placed on an automatic load testing machine (manufactured by Nippon Keisoku Systems, model number: MAX-1KN-H-1). The test samples were then rubbed against each other under conditions of a load of 200 g ± 2 g (1.96 N ± 0.02 N) and a friction speed of 100 mm/min, and the dynamic friction coefficient was measured. The dynamic friction coefficient was measured five times, and the average of the five measurements is shown in Table 1.

<Production of resin parts for writing instruments and evaluation of knock operation>
The recycled polyolefin resin composition was injection molded (melt temperature 200°C, mold temperature 30°C, filling speed 50 mm/s) to produce resin parts for writing instruments, such as the knock bar 11, clip inner tube 12, and rotor 15 of a knock-type ballpoint pen as shown in Figures 1(A) and 1(B). These were then assembled to produce the feeding mechanism 17. The feeding mechanism 17 was subjected to 3,000 retraction and extension operations, and its operability was then confirmed and knock operability was evaluated. Here, the knock load during the retraction and extension operation (the pressure load required for the retraction and extension of the writing refill) was 3 N. The knock operability test was conducted five times and evaluated according to the following criteria.
A: Smooth sliding properties were maintained in all samples.
B: The sliding resistance was large, and some samples were difficult to unwind.

Examples 2 to 4 and Comparative Examples 1 to 5
<Preparation of recycled polyolefin resin composition and measurement of dynamic friction coefficient of recycled polyolefin resin composition>
Recycled polyolefin resin compositions were prepared in the same manner as in Example 1, except that the materials shown in Table 1 were used. The dynamic friction coefficient of each recycled polyolefin resin composition was measured in the same manner as in Example 1. The dynamic friction coefficients of each recycled polyolefin resin composition were as shown in Table 1.

<Production of resin parts for writing instruments and evaluation of knock operation>
Resin parts for writing instruments were produced in the same manner as in Example 1, except that the recycled polyolefin resin compositions produced in Examples 2 to 4 and Comparative Examples 1 to 5 were used. The knock operability of each resin part for a writing instrument was evaluated in the same manner as in Example 1. The knock operability of each resin part for a writing instrument was as shown in Table 1.

It was confirmed that by incorporating a specified amount of silicone (Example 3) or silicone-containing copolymer (Examples 1, 2, and 4) as a sliding property-imparting additive into recycled polyolefin resin, the resin parts for writing instruments and writing instruments possess certain physical properties, specifically, a specific dynamic friction coefficient, and therefore good knock operability. On the other hand, polyolefin resin compositions that did not contain a sliding property-imparting additive (Comparative Examples 1 and 2) or that contained a sliding property-imparting additive other than silicone or a silicone-containing copolymer (Comparative Examples 4 and 5) did not exhibit good knock operability. Furthermore, when the total content of silicone-derived structural units in the sliding property-imparting additive was lower than the specified range, resulting in the dynamic friction coefficient of the polyolefin resin composition not being within the specified range (Comparative Example 3), good knock operability was not exhibited.

While preferred embodiments of the resin parts for writing instruments and writing instruments of the present invention have been described, modifications are possible without departing from the scope of the claims.

10 Writing implement 11 Knock bar portion 12 Clip inner cylinder portion 13 Shaft portion 14 Mouth portion 15 Rotor portion 16 Writing lead 17 Feeding mechanism portion

Claims (4)

Contains a recycled polyolefin resin composition,
The recycled polyolefin resin composition contains a recycled polyolefin resin and a sliding property-imparting additive,
The sliding property-imparting additive contains silicone and/or a silicone-containing copolymer, and the total content of the silicone and silicone-derived structural units in the silicone-containing copolymer is 1.0 to 4.0 parts by mass per 100 parts by mass of the recycled polyolefin resin.
Resin parts for writing instruments. The resin part for a writing instrument according to claim 1, wherein the recycled polyolefin resin composition has a dynamic friction coefficient of 0.10 to 0.40. The resin part for a writing instrument according to claim 1, wherein the content of the recycled polyolefin resin composition is 60 parts by mass or more, based on 100 parts by mass of the entire resin part for a writing instrument. A writing instrument comprising the resin part for a writing instrument described in any one of claims 1 to 3.