Writing tool

Abstract

This writing tool includes: an ink accommodation part capable of accommodating oil-based ink; and a tip part capable of guiding the oil-based ink from the ink accommodation part to a surface to be written to by bringing the tip part into contact with the surface to be written to. The ink accommodation part includes polypropylene and a β-crystal nucleating agent.

Description

writing implements

[0001] The present disclosure relates to writing instruments, and more particularly to writing instruments that use oil-based inks.

[0002] Writing instruments using oil-based ink have advantages such as quick drying and excellent durability of written marks, etc. Examples of such writing instruments include ballpoint pens, ballpoint pen refills, and marking pens.

[0003] In such writing instruments, the oil-based ink is generally stored in a storage portion made of polypropylene from the viewpoint of chemical resistance, as disclosed in Patent Document 1, for example.

[0004] JP 2001-139866 A

[0005] Writing instruments using oil-based ink are widely used in hot and humid countries such as Southeast Asia. However, it has been found that writing instruments using oil-based ink tend to have poor writing quality when stored for long periods in hot and humid countries.

[0006] The present disclosure has been made in view of the above circumstances, and one of its objectives is to provide a writing instrument that can suppress poor writing performance that occurs after storage under high temperature and humidity conditions.

[0007] A first aspect of the present invention is a writing instrument comprising an ink reservoir capable of storing oil-based ink and a tip portion capable of directing the oil-based ink from the ink reservoir onto a surface to be written on by contacting the tip portion with the surface to be written on, wherein the ink reservoir contains polypropylene and a β-crystal nucleating agent.

[0008] In a second aspect of the present invention, the β-crystal nucleating agent is represented by the following formula A: ２ (-CONHR ３ ) ｎ (A) wherein n is an integer from 2 to 6, and R ２ is a saturated or unsaturated aliphatic polycarboxylic acid residue having 2 to 18 carbon atoms, an alicyclic polycarboxylic acid residue having 3 to 18 carbon atoms, or an aromatic polycarboxylic acid residue having 6 to 18 carbon atoms, and each R ３are the same or different and are a saturated or unsaturated aliphatic amine residue having 5 to 30 carbon atoms, an alicyclic amine residue having 5 to 30 carbon atoms, or an aromatic amine residue having 6 to 30 carbon atoms.

[0009] A third aspect of the present invention is the writing instrument according to the first or second aspect, wherein the content of the β-crystal nucleating agent is 0.01 to 3% by mass with respect to the total amount of the polypropylene and the β-crystal nucleating agent.

[0010] A fourth aspect of the present invention is the writing instrument according to any one of the first to third aspects, wherein the polypropylene is a homopolypropylene.

[0011] Aspect 5 of the present invention is the writing instrument according to any one of Aspects 1 to 4, wherein the oil-based ink contains at least a colorant and an organic solvent, and 50% by mass or more of the organic solvent has a vapor pressure of 600 Pa or more at 20°C.

[0012] A sixth aspect of the present invention is the writing instrument according to the fifth aspect, wherein the organic solvent is at least one selected from the group consisting of alcohols and glycol ethers.

[0013] A seventh aspect of the present invention is the writing implement according to the fifth or sixth aspect, wherein the oil-based ink further contains a release agent and a resin represented by the following formula (1): In the formula, p, q, r, and s represent composition ratios (mol %) when the sum of p, q, r, and s is 100%, and p≧0, q≧0, r>0, and s>0.

[0014] According to an embodiment of the present invention, it is possible to provide a writing instrument that can suppress writing defects that occur after storage under high temperature and humidity conditions.

[0015] FIG. 1A is an example of a transmission polarized light microscope image of a cross section perpendicular to the longitudinal direction of an ink reservoir according to an embodiment of the present invention. FIG. 1B is an example of a transmission polarized light microscope image of a cross section perpendicular to the longitudinal direction of a conventional ink reservoir according to an embodiment of the present invention. FIG. 2 is an example of a TEM image of a cross section perpendicular to the longitudinal direction of an ink reservoir according to an embodiment of the present invention. FIG. 3 is an example of an image of handwriting in a writing test of an example. FIG. 4A is an optical microscope image of oil-based ink collected from Sample No. 1 after 30 days of storage at 50°C and 100% RH. FIG. 4B is an optical microscope image of oil-based ink collected from Sample No. 1 after 60 days of storage at 50°C and 100% RH. FIG. 4C is an optical microscope image of oil-based ink collected from Sample No. 1 after 90 days of storage at 50°C and 100% RH. FIG. 5A is an optical microscope image of oil-based ink collected from Sample No. 1 after 90 days of storage at 50°C and 100% RH. Figure 5B is an optical microscope image of oil-based ink sample No. 3 taken after 30 days of storage at 50°C and 100% RH. Figure 5B is an optical microscope image of oil-based ink sample No. 3 taken after 60 days of storage at 50°C and 100% RH. Figure 5C is an optical microscope image of oil-based ink sample No. 3 taken after 90 days of storage at 50°C and 100% RH.

[0016] The inventors conducted extensive research to develop a writing instrument capable of suppressing writing defects that occur after storage under high temperature and humidity conditions. As a result, they discovered that using an ink reservoir containing a β-crystal nucleating agent in addition to conventionally used polypropylene can suppress writing defects that occur after storage under high temperature and humidity conditions. This is believed to be due to the following mechanism: Under high temperature and humidity, water vapor can permeate the ink reservoir and be mixed into the oil-based ink. When water is mixed into the oil-based ink, the ink cannot maintain its uniformity due to the immiscibility of oil and water, resulting in writing defects. The inventors discovered that using an ink reservoir containing a β-crystal nucleating agent in addition to the polypropylene typically used can achieve an ink reservoir containing a high density of fine spherulites. It is believed that these spherulites suppress the intrusion of water vapor, thereby suppressing writing defects. The above mechanism does not limit the technical scope of the present invention. Details of each requirement defined in the embodiments of the present invention are provided below.

[0017] A writing instrument according to an embodiment of the present invention includes an ink reservoir capable of storing oil-based ink and a tip portion capable of delivering the oil-based ink from the ink reservoir onto a surface to be written on by contacting the tip portion with the ink reservoir, the ink reservoir containing polypropylene and a β-crystal nucleating agent. This makes it possible to suppress writing defects that occur after storage under high temperature and humidity. Each component will be described in detail below.

[0018] (Ink reservoir) In an embodiment of the present invention, the ink reservoir is capable of storing oil-based ink and contains polypropylene and a β-crystal nucleating agent. The shape of the ink reservoir is not particularly limited as long as it can store oil-based ink, and may be, for example, cylindrical, as long as it is configured to cover at least the sides of the oil-based ink. In addition to being cylindrical, the ink reservoir may also be in the form of a member that stores ink for a known writing instrument. Specific examples include those in which the barrel itself serves as the ink reservoir, those with a built-in ink reservoir (ink occlusion body) that holds the ink, and those that are detachable, such as a refill with a connected nib or a replaceable cartridge. Note that the tip portion, described below, can also store oil-based ink, but the ink reservoir is a concept that excludes this tip portion.

[0019] The polypropylene contained in the ink reservoir may be a copolymer in which propylene units account for at least 50% by mass, preferably 70 to 100% by mass, and more preferably 80 to 100% by mass. The polypropylene contained in the ink reservoir may be either a homopolymer or a copolymer. The copolymer may be either a block copolymer or a random copolymer. The block copolymer may be a copolymer having a polymer block of propylene and a polymer block of an α-olefin other than propylene. The random copolymer may be a random copolymer containing propylene and an α-olefin other than propylene. The polypropylene contained in the ink reservoir may be any of the above, or two or more of these may be used in combination. In one embodiment of the present invention, the polypropylene contained in the ink reservoir is preferably a homopolymer, i.e., homopolypropylene. This more easily prevents water vapor from passing through the ink reservoir. In other words, it more easily prevents water vapor from penetrating into oil-based inks in writing instruments.

[0020] The β-crystal nucleating agent contained in the ink reservoir is not particularly limited as long as it is a crystallization nucleating agent that selectively forms β-crystals when added to polypropylene, but various pigment-based compounds (such as quinacridone) and / or amide-based compounds can be preferably used.

[0021] The presence of a β-crystal nucleating agent in the ink reservoir can be confirmed, for example, by extracting additives other than polypropylene from the ink reservoir using a polar solvent and analyzing the extract by liquid chromatography. The polar solvent is preferably a solvent that does not dissolve polypropylene but can penetrate into polypropylene, such as 1,3-dimethyl-2-imidazolidinone (DMI), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP). The dissolution may be performed by heating (for example, to 100°C or higher) as needed.

[0022] Furthermore, as described above, since the ink reservoir contains a β-crystal nucleating agent in addition to polypropylene, fine spherulites are formed at a high density, and the presence or absence of the β-crystal nucleating agent can be confirmed by observing the morphology using a microscope, etc. An example will be explained below.

[0023] Observation Example 1: FIG. 1A is a transmission polarized light microscope image of an ink reservoir according to an embodiment of the present invention (corresponding to the ink reservoirs of Samples 1 and 4 described below) that was observed by freezing microtoming to expose the central portion between the outer and inner surfaces (i.e., the surface that can come into contact with oil-based ink) in a cross section perpendicular to the longitudinal direction (axial direction) at the center of the longitudinal direction (axial direction). The transmission polarized light microscope images of FIG. 1A and FIG. 1B described below were obtained using a polarizing microscope (LV100POL, manufactured by Nikon Corporation). As shown in FIG. 1A, multiple fine white dots are observed due to the fine, densely formed spherulites. FIG. 1B is a transmission polarized light microscope image of a conventional ink reservoir containing polypropylene but not a β-crystal nucleating agent (corresponding to the ink reservoir of Sample 2 described below) that was observed by freezing microtoming to expose the central portion between the outer and inner surfaces in a cross section perpendicular to the longitudinal direction at the center of the longitudinal direction. As shown in Figure 1B, several white regions with a maximum length of 20 μm or more, which are due to coarse spherulites and the like, which are not observed in Figure 1A, are observed. In this way, by observing multiple fine white dots (all with a maximum length of less than 20 μm) in the above-mentioned transmission polarized light microscope image (magnification: 200x), it can be determined that the ink reservoir contains a β-crystal nucleating agent in addition to polypropylene.

[0024] Observation Example 2: Figure 2 shows a TEM image of an ink reservoir according to an embodiment of the present invention (corresponding to the ink reservoirs of Samples 1 and 4 described below), taken by freezing microtoming to expose the central portion between the outer and inner surfaces in a cross section perpendicular to the longitudinal direction at the center of the longitudinal direction. The TEM image in Figure 2 was obtained using a transmission electron microscope H-7650 (Hitachi High-Tech Corporation). As shown in Figure 2, spherulites are observed to be formed over the entire surface, overlapping in a complex manner. For example, the equivalent circle diameters of spherulites 1 to 4 shown in the hatched areas are 7.5 μm, 7.3 μm, 5.7 μm, and 6.0 μm, respectively, and all other spherulites may be less than 20 μm. The lower limit of the equivalent circle diameter of the spherulite is not particularly limited, but may be, for example, 0.1 μm or greater. Thus, by observing the formation of spherulites with a circle equivalent diameter of less than 20 μm over the entire surface in the above TEM image (magnification: 3000x), it can be determined that the ink reservoir contains a β-crystal nucleating agent in addition to polypropylene.

[0025] The β-crystal nucleating agent contained in the ink reservoir preferably contains an amide compound represented by the following formula A, and more preferably consists of an amide compound represented by the following formula A. This effectively prevents water vapor in the outside air from passing through the ink reservoir in the writing instrument, making it easier to prevent water vapor from entering the oil-based ink. ２ (-CONHR ３ ) ｎ (A) wherein n is an integer from 2 to 6, and R ２ is a saturated or unsaturated aliphatic polycarboxylic acid residue having 2 to 18 carbon atoms, an alicyclic polycarboxylic acid residue having 3 to 18 carbon atoms, or an aromatic polycarboxylic acid residue having 6 to 18 carbon atoms, and each R ３ are the same or different and are a saturated or unsaturated aliphatic amine residue having 5 to 30 carbon atoms, an alicyclic amine residue having 5 to 30 carbon atoms, or an aromatic amine residue having 6 to 30 carbon atoms.]

[0026] Preferred specific examples of the amide compound represented by the general formula A include N,N'-diphenylhexanediamide, N,N'-dicyclohexylterephthalamide, and N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide.

[0027] The content of the β-crystal nucleating agent in the ink reservoir is preferably 0.01 to 3% by mass relative to the total amount of polypropylene and the β-crystal nucleating agent. By adding 0.01% by mass or more of the β-crystal nucleating agent, it becomes easier to form a sufficient amount of spherulites. On the other hand, since the effect of the β-crystal nucleating agent is saturated even if the content exceeds 3% by mass, it is preferable to keep the content at 3% by mass or less.

[0028] In an embodiment of the present invention, the ink reservoir may contain materials other than polypropylene and a β-crystal nucleating agent, such as colorants, heat stabilizers, light stabilizers, UV absorbers, antioxidants, antiblocking agents, release agents, and lubricants, and the total amount of these materials contained in the ink reservoir may be 5% by mass or less.

[0029] In an embodiment of the present invention, when the ink reservoir has a double structure, such as a ballpoint pen containing a ballpoint pen refill (for example, the inner portion is the ink reservoir of the ballpoint pen refill (also referred to as the "inner ink reservoir"), and the outer portion is a barrel that covers the ballpoint pen refill (also referred to as the "outer ink reservoir")), it is sufficient that at least one of the inner ink reservoir and the outer ink reservoir contains polypropylene and a β-crystal nucleating agent as described above. Preferably, both the inner ink reservoir and the outer ink reservoir contain polypropylene and a β-crystal nucleating agent as described above.

[0030] The oil-based ink contained in the ink reservoir is not particularly limited, and for example, a known oil-based ink for writing instruments may be used. When the oil-based ink contains at least a colorant and an organic solvent, and the vapor pressure at 20°C of 50% by mass or more of the organic solvent is 600 Pa or more, the ink is prone to volatilization and is susceptible to the effects of water vapor. However, even in such cases, satisfying the specified requirements of the present invention can suppress writing defects. In other words, the effects of the present invention are particularly pronounced in such cases. Furthermore, when the organic solvent is one or more selected from the group consisting of alcohols and glycol ethers, water vapor dissolves in the ink, causing the blended components to easily precipitate. However, even in such cases, satisfying the specified requirements of the present invention can suppress writing defects. In other words, the effects of the present invention are particularly pronounced in such cases. The content of the organic solvent in the oil-based ink may be, for example, 40 to 95% by mass.

[0031] The colorant contained in the oil-based ink is not particularly limited and may be, for example, a dye or a pigment. The colorant may be one type or two or more types. The content of the colorant in the oil-based ink may be 3 to 40 mass %.

[0032] The oil-based ink may contain other materials in addition to the organic solvent and colorant, such as resins, rust inhibitors, viscosity modifiers, color stabilizers, plasticizers, chelating agents, lubricants, shear thinning agents, and release agents, and the oil-based ink may contain up to 50% by mass of these other materials in total.

[0033] In one embodiment of the present invention, in addition to the organic solvent and the colorant, the oil-based ink preferably further contains a release agent and a resin represented by the following formula (1): In the formula, p, q, r, and s represent the composition ratio (mol %) when the sum of p, q, r, and s is 100%, and p≧0, q≧0, r>0, and s>0. As a result, the ink is suitable for use in writing instruments such as marking pens for writing boards. Examples of the resin include polyvinyl acetal resin (p>0, q>0, r>0, and s>0), polyvinyl butyral resin (p>0, q=0, r>0, and s>0), and polyvinyl acetoacetal resin (p=0, q>0, r>0, and s>0). One or more resins may be used in combination. The resin content in the oil-based ink may be 0.1 to 5% by mass.

[0034] In particular, the glass transition temperature of the resin represented by general formula (1) is preferably 60°C or higher, more preferably 65°C or higher, since this provides better erasability. The upper limit of the glass transition temperature of the resin is preferably 120°C or lower, more preferably 110°C or lower. Generally, handwriting coating films formed on writing surfaces are prone to changes in their physical properties due to external factors such as temperature and sunlight. In particular, handwriting coating films formed over long periods of time are prone to a decrease in erasability due to these changes in physical properties. This is because, if the resin has a low glass transition temperature, when the handwriting coating film rises above the glass transition temperature due to temperature or sunlight, the resin in the handwriting coating film changes its physical properties, causing part of the handwriting to remain on the writing surface. By setting the resin's glass transition temperature to 60°C or higher, changes in physical properties due to external factors are less likely to occur, and excellent erasability can be maintained even over long periods of time.

[0035] As the release agent, known ones can be used. For example, the release agent may contain one or more selected from the group consisting of a compound represented by the following formula (2) and a compound represented by the following formula (3) described in WO2019 / 208603: R in the formula １ ~R ４are either an alkyl group having 6 to 18 carbon atoms or an alkoxypolyglycol group having 2 to 18 carbon atoms and 2 to 10 oxygen atoms. In addition to the above compounds, carboxylic acid esters, silicone surfactants, nonionic surfactants, etc. can also be used as the release agent. For example, compounds such as polyoxyalkylene alkyl ether sulfate esters, polyoxyalkylene alkylaryl ether sulfate esters, polyoxyethylene alkyl ether phosphate esters or salts thereof, dibasic acid esters, monobasic acid esters, and polyalkylene glycol esters can also be used. The release agent may be used alone or in combination of two or more compounds. The content of the release agent in the oil-based ink may be 1 to 15% by mass.

[0036] (Tip Portion) In an embodiment of the present invention, the tip portion (also referred to as the writing tip portion) is not particularly limited as long as it is configured to be able to deliver oil-based ink from the ink reservoir onto the surface to be written on by contacting it with the surface. The tip portion may be located, for example, at either end of the ink reservoir in the longitudinal direction. For example, if the writing instrument is a ballpoint pen or ballpoint pen refill, the tip portion may be a known ballpoint pen tip. If the writing instrument is a marking pen, the tip portion may be any of various known marking pen tips, such as a fiber tip, a felt tip, or a plastic tip. The surface to be written on is not particularly limited, and paper such as writing paper A conforming to JIS P3201 can be used. Examples of marking pens include marking pens for writing boards, whose writing surface is made of an impermeable material.

[0037] In an embodiment of the present invention, the tip is preferably covered with a cap containing polypropylene or is a ballpoint pen tip. This makes it easier to prevent water vapor from entering from the tip. It is more preferable that the cap further contains a β-crystal nucleating agent. When the tip is a marking pen tip, it is preferable that the tip is covered with a cap containing polypropylene, and it is more preferable that the cap contains a β-crystal nucleating agent.

[0038] The polypropylene contained in the cap may be the same as or different from the polypropylene contained in the container, and the β-crystal nucleating agent contained in the cap may be the same as or different from the β-crystal nucleating agent contained in the container.

[0039] The content of the β-crystal nucleating agent in the cap is preferably 0.01 to 3% by mass based on the total amount of polypropylene and β-crystal nucleating agent in the cap. By adding 0.01% by mass or more of the β-crystal nucleating agent, it becomes easier to form a sufficient amount of spherulites. On the other hand, since the effect of the β-crystal nucleating agent is saturated even if it is added in excess of 3% by mass, it is preferable to keep it at 3% by mass or less.

[0040] In an embodiment of the present invention, the cap may contain materials other than polypropylene and a β-crystal nucleating agent, such as colorants, heat stabilizers, light stabilizers, UV absorbers, antioxidants, antiblocking agents, mold release agents, and lubricants, and the total amount of these materials contained in the cap may be 5% by mass or less.

[0041] (Writing Instrument) A writing instrument according to an embodiment of the present invention includes the ink reservoir and the tip portion. The type of writing instrument is not particularly limited, and examples include ballpoint pens, ballpoint pen refills, and marking pens (including marking pens for writing boards). The structure of the writing instrument according to an embodiment of the present invention is not particularly limited as long as it includes the ink reservoir and the tip portion, and may be the structure of a known ballpoint pen, ballpoint pen refill, or marking pen.

[0042] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0043] The compositions of the oil-based inks (black ink and red ink) used are shown in the following Tables 1 and 2. The values ​​in the tables indicate parts by mass.

[0044]

[0045]

[0046] The contents of the raw materials are shown below according to the note numbers in the table. (1) Synthetic alcohol, manufactured by Japan Synthetic Alcohol Co., Ltd., trade name: Synthetic Alcohol 99%, vapor pressure at 20°C: 5850 Pa (2) Propylene glycol methyl ether, manufactured by The Dow Chemical Company, trade name: Dowanol (registered trademark) PM (3) Benzyl alcohol, manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name: Benzyl Alcohol U (4) Black dye, manufactured by Orient Chemical Industry Co., Ltd., trade name: Nigrosine Base EX (5) Yellow dye, manufactured by Hodogaya Chemical Co., Ltd., trade name: Spiron (registered trademark) Yellow C-GNH (6) Resin, manufactured by Arakawa Chemical Industries, Ltd., trade name: Marquid (registered trademark) 33 (7) Resin, manufactured by Evonik, trade name: Tego (registered trademark) Valiplus SK (8) Phosphate ester surfactant, manufactured by Toho Chemical Industry Co., Ltd., trade name: Phosphanol (registered trademark) RA600 (9) Glycerin fatty acid ester, manufactured by Sakamoto Pharmaceutical Co., Ltd., trade name: SY Glyster (registered trademark) TS-5S (10) Polyether-modified silicone, manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF615A (11) Propylene glycol monomethyl ether, manufactured by Nippon Nyukazai Co., Ltd., trade name: methylpropylene glycol (MFG), vapor pressure at 20 ° C.: 893 Pa (12) Methyl lactate, manufactured by Musashino Chemical Research Institute Co., Ltd. (13) 3-methoxy-3-methylbutanol, manufactured by Kuraray Co., Ltd., trade name: Solfit (registered trademark) (14) Red dye, manufactured by Orient Chemical Industry Co., Ltd., trade name: Varifast (registered trademark) Red 1308 (15) Resin, manufactured by Hitachi Chemical Co., Ltd., trade name: Hitanol (registered trademark) 1501 (16) Rust inhibitor, manufactured by Yamato Kasei Co., Ltd., trade name: Belzon (registered trademark) Crystal 120

[0047] (Preparation of Ink) Each raw material was mixed in the amounts shown in Tables 1 and 2 above, and dissolved by stirring at 20° C. for 3 hours to obtain each oil-based ink (black ink and red ink).

[0048] (Preparation of Marking Pens) Cylindrical ink reservoirs having the compositions shown in Table 3 below were prepared (molded). An ink reservoir made of a polyester fiber bundle was placed inside the ink reservoir, and a predetermined amount of each oil-based ink was filled into the ink reservoir. Furthermore, a tip portion was obtained by binding an acrylic fiber bundle with a melamine resin. The tip portion was attached to the ink reservoir with the rear end in contact with the ink reservoir, and the tip portion was then covered with a polypropylene cap (containing no β-crystal nucleating agent), thereby obtaining marking pens Nos. 1 to 4. Samples Nos. 1 to 4 were similar in shape to a commercially available marking pen (Permanent Marker 400, manufactured by Pilot Corporation, maximum diameter: φ16.4 mm, total length: 145.8 mm) (however, no transfer film was provided), except that a β-crystal nucleating agent was contained in a portion of the ink reservoir.

[0049]

[0050] The contents of the raw materials are shown below according to the note numbers in the table. Note that the "β-crystal nucleating agent content" in the table is the content of β-crystal nucleating agent relative to the total amount of polypropylene and β-crystal nucleating agent in the ink reservoir. (17) Polypropylene (homopolymer), manufactured by SunAllomer Co., Ltd., trade name: PM801A (18) Polypropylene (random polymer), manufactured by Japan Polypropylene Corporation, trade name: Novatec (registered trademark) PP MG2TA (19) N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, manufactured by New Japan Chemical Co., Ltd., trade name: NU-100 (20) Black masterbatch, manufactured by Towa Chemical Co., Ltd., trade name: 4003, pigment content in the ink reservoir: 1.0 mass%

[0051] (Writability Test) The marking pen obtained as described above was left in a horizontal position in a constant temperature and humidity room adjusted to conditions of 50°C (humidity uncontrolled) or 50°C 100% RH for 30, 60, or 90 days. After leaving it, the writing condition and the state of the handwriting when handwritten in a spiral shape on writing paper A conforming to JIS P3201 were visually confirmed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 4 below. A grade of "B" or higher was considered to be acceptable. Figure 3 shows example images of handwriting graded "AA," "A," "B," and "C." Evaluation Criteria AA: Good handwriting was possible. A: Some smearing of the handwriting was observed. B: Some smearing of the handwriting was observed. C: The handwriting was very faint or writing was impossible.

[0052]

[0053] The following can be seen from Table 4. Samples No. 1 and 4 both satisfied the requirements defined in the embodiments of the present invention, and the results of the writability test after 90 days at 50°C and 100% RH were pass (B to AA), indicating that poor writing performance after storage under high temperature and humidity was suppressed. On the other hand, Samples No. 2 and 3 did not satisfy the requirements defined in the embodiments of the present invention, and poor writability was observed after 90 days at 50°C and 100% RH.

[0054] Furthermore, for Samples 1 to 4, oil-based ink samples collected from the tip after storage under high temperature and humidity conditions were observed under an optical microscope. Figures 4A to 4C show optical microscope images of oil-based ink samples collected from Sample 1 after storage at 50°C and 100% RH for 30 days (Figure 4A), 60 days (Figure 4B), or 90 days (Figure 4C) (all scale bars in the figures indicate 100 μm). As can be seen from Figures 4A to 4C, Sample 1, which satisfies the requirements defined in the present embodiment, showed almost no change in the oil-based ink even when the storage period at 50°C and 100% RH was increased from 30 to 60 days. Even when the storage period was increased from 60 to 90 days, there was almost no change, or only a slight decrease in uniformity. Figures 5A to 5C show the results of Sample 1. 5A to 5C show optical microscope images of oil-based ink samples No. 3 collected after storage at 50°C and 100% RH for 30 days (FIG. 5A), 60 days (FIG. 5B), or 90 days (FIG. 5C) (all scale bars in the figures indicate 100 μm). As can be seen from FIGS. 5A to 5C, Sample No. 3, which does not satisfy the requirements specified in the embodiment of the present invention, saw a significant decrease in the uniformity of the oil-based ink when the storage period at 50°C and 100% RH was increased from 30 to 60 and 90 days.

[0055] The composition of the oil-based ink (oil-based ink for writing boards) used is shown in Table 5 below. The values ​​in the table indicate parts by mass. The vapor pressure of ethyl alcohol at 20°C was 5580 Pa, that of isopropyl alcohol was 4400 Pa, and that of n-propyl alcohol was 2000 Pa. All of the organic solvents used had a vapor pressure of 600 Pa or higher.

[0056]

[0057] The contents of the raw materials are shown below according to the note numbers in the table: (21) Mitsubishi Chemical Corporation, trade name: MA100 (22) DIC Corporation, trade name: FASTOGEN SUPER RED 254 (23) C.I. A processed pigment consisting of 50% by mass of Mitsubishi Chemical Pigment Black 7 (trade name: MA100, manufactured by Mitsubishi Chemical Corporation) and 50% by mass of polyvinyl butyral (trade name: S-LEC BL-1, manufactured by Sekisui Chemical Co., Ltd.) (24) Sekisui Chemical Co., Ltd., trade name: S-LEC BL-1, glass transition temperature: 66°C (25) Sekisui Chemical Co., Ltd., trade name: S-LEC KS-10, glass transition temperature: 105°C (26) Kuraray Co., Ltd., trade name: Mowital BA20S, glass transition temperature: 84°C (27) Diisononyl cyclohexane-1,2-dicarboxylate (28) Diglyceryl monoisostearate

[0058] (Ink Preparation) For writing board oil-based inks 1 and 2, the organic solvent, colorant, and resin were placed in a mixing vessel in the amounts shown in Table 5 above, and stirred with 70 g of 2 mm glass beads in a high-speed blade mixer at 20°C for 4 hours, after which a release agent was added and stirred for another hour. The mixture was filtered through a mesh to remove the glass beads, thereby obtaining each oil-based ink. For writing board oil-based ink 3, the raw materials were mixed in the amounts shown in Table 5 above, and the oil-based ink was obtained by stirring and dissolving for 3 hours at 20°C.

[0059] (Preparation of Marking Pens) Cylindrical ink reservoirs having the compositions shown in Table 6 below were prepared (molded) in the same manner as in Example 1, and other procedures were repeated to obtain marking pens (marking pens for writing boards) of Samples No. 5 to 9.

[0060]

[0061] The contents of the raw materials indicated by the reference numbers in the table are the same as those in Example 1.

[0062] (Writability Test) The marking pen for writing board obtained as described above was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 7 below.

[0063]

[0064] The following can be seen from Table 7. Samples Nos. 5, 8, and 9 all satisfied the requirements defined in the embodiments of the present invention, and the results of the writability test after 90 days at 50°C and 100% RH were pass (A to AA), indicating that poor writing performance after storage under high temperature and humidity was suppressed. On the other hand, Samples Nos. 6 and 7 did not satisfy the requirements defined in the embodiments of the present invention, and poor writability was observed after 90 days at 50°C and 100% RH.

[0065] This application claims priority from Japanese Patent Application No. 2023-158920, filed September 22, 2023. Japanese Patent Application No. 2023-158920 is incorporated herein by reference.

Claims

1. A writing instrument comprising an ink reservoir capable of holding oil-based ink, and a tip portion capable of directing the oil-based ink from the ink reservoir onto a surface to be written on by contacting the tip portion with the surface to be written on, the ink reservoir containing polypropylene and a beta crystal nucleating agent.

2. The β crystal nucleating agent is represented by the following formula A: ２ (-CONHR ３ ) ｎ (A) wherein n is an integer from 2 to 6, R ２ is a saturated or unsaturated aliphatic polycarboxylic acid residue having 2 to 18 carbon atoms, an alicyclic polycarboxylic acid residue having 3 to 18 carbon atoms, or an aromatic polycarboxylic acid residue having 6 to 18 carbon atoms, and each R ３ are the same or different and are a saturated or unsaturated aliphatic amine residue having 5 to 30 carbon atoms, an alicyclic amine residue having 5 to 30 carbon atoms, or an aromatic amine residue having 6 to 30 carbon atoms.

3. The writing instrument according to claim 1 or 2, wherein the content of the β-crystal nucleating agent is 0.01 to 3 mass % based on the total amount of the polypropylene and the β-crystal nucleating agent.

4. The writing instrument according to any one of claims 1 to 3, wherein the polypropylene is a homopolypropylene.

5. A writing instrument according to any one of claims 1 to 4, wherein the oil-based ink contains at least a colorant and an organic solvent, and 50 mass % or more of the organic solvent has a vapor pressure of 600 Pa or more at 20°C.

6. The writing implement according to claim 5, wherein the organic solvent is at least one selected from the group consisting of alcohols and glycol ethers.

7. The writing implement according to claim 5 or 6, wherein the oil-based ink further contains a release agent and a resin represented by the following formula (1): In the formula, p, q, r and s represent composition ratios (mol %) when the sum of p, q, r and s is 100%, and p≧0, q≧0, r>0, and s>0.

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