WO2025063187A1 - Writing tool - Google Patents

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

This disclosure relates to writing instruments, particularly writing instruments that use oil-based ink.

Writing instruments that use oil-based ink have the advantage of quick drying and excellent durability of the writing. Examples of such writing instruments include ballpoint pens, ballpoint pen refills, and marking pens.

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

JP 2001-139866 A

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 are prone to writing defects when stored for long periods in hot and humid countries.

This disclosure has been made in light of these circumstances, and one of its objectives is to provide a writing instrument that can suppress writing defects that occur after storage under high temperature and humidity conditions.

Aspect 1 of the present invention is
The ink pen includes an ink storage section capable of storing oil-based ink, and a tip section capable of directing the oil-based ink from the ink storage section onto a surface to be written on by contacting the tip section with the surface to be written on,
The ink reservoir is a writing implement comprising polypropylene and a β crystal nucleating agent.

Aspect 2 of the present invention is
The β-crystal nucleating agent is represented by the following formula A:
R ² (-CONHR ³ ) _n (A)
[In the formula, n is an integer of 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 is the same or different and is 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.]
The writing instrument according to embodiment 1, further comprising a compound represented by the formula:

Aspect 3 of the present invention is
A content of the β-crystal nucleating agent is 0.01 to 3% by mass based on the total amount of the polypropylene and the β-crystal nucleating agent.

Aspect 4 of the present invention is
Aspect 4. The writing instrument according to any one of Aspects 1 to 3, wherein the polypropylene is a homopolypropylene.

Aspect 5 of the present invention is
A 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.

Aspect 6 of the present invention is
Aspect 6. The writing instrument according to aspect 5, wherein the organic solvent is at least one selected from the group consisting of alcohols and glycol ethers.

　式中、ｐ、ｑ、ｒ及びｓは、ｐ、ｑ、ｒ及びｓの総和を１００％としたときの組成比（モル％）を表し、ｐ≧０、ｑ≧０、ｒ＞０、ｓ＞０である。 Aspect 7 of the present invention is
A writing instrument according to Aspect 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.

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 high humidity conditions.

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. 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 the embodiment. 4A is an optical microscope image of the oil-based ink sample No. 1 after storage at 50° C. and 100% RH for 30 days. 4B is an optical microscope image of the oil-based ink sample No. 1 after storage at 50° C. and 100% RH for 60 days. 4C is an optical microscope image of the oil-based ink sample No. 1 after storage at 50° C. and 100% RH for 90 days. 5A is an optical microscope image of the oil-based ink sample No. 3 after storage at 50° C. and 100% RH for 30 days. 5B is an optical microscope image of the oil-based ink sample No. 3 after storage at 50° C. and 100% RH for 60 days. Fig. 5C is an optical microscope image of the oil-based ink sample No. 3 after storage at 50°C and 100% RH for 90 days.

The present inventors have conducted research from various angles in order to realize a writing instrument capable of suppressing writing defects that occur after storage under high temperature and high humidity. As a result, they have found that by using an ink reservoir that further contains a β crystal nucleating agent in addition to the conventionally used polypropylene, writing defects that occur after storage under high temperature and high humidity can be suppressed. 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, which is believed to result in poor writing. The present inventors have found that by using an ink reservoir that further contains a β-crystal nucleating agent in addition to the polypropylene that is normally contained, it is possible to realize an ink reservoir in which fine spherulites are formed at a high density, and it is believed that the spherulites suppress the intrusion of water vapor, thereby suppressing poor writing.
However, the technical scope of the present invention is not limited by the above mechanism.
The following provides details of each requirement stipulated by the embodiment of the present invention.

A writing instrument according to an embodiment of the present invention includes an ink reservoir capable of storing an 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 ink reservoir with the surface to be written on, the ink reservoir containing polypropylene and a β-crystal nucleating agent, thereby making it possible to suppress writing defects that occur after storage under high temperature and high humidity conditions.
Each component will be described in detail below.

(Ink storage section)
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, so long as it is configured to cover at least the sides of the oil-based ink. The ink reservoir may be cylindrical or may be a member that stores ink of a known writing instrument. Specifically, examples of the ink reservoir include those in which the barrel itself is the ink reservoir, those in which a filler (ink occluder) that holds the ink is built in, those in which the pen tip is connected to a refill or a replaceable cartridge, and those in which the ink reservoir is removable. Note that the tip portion, which will be described later, can also store oil-based ink, but the ink reservoir is a concept that excludes the tip portion.

The polypropylene contained in the ink reservoir may have a propylene unit content of at least 50% by mass in the copolymer, 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 made of propylene and a polymer block made 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 alone or in combination of two or more kinds.
In one embodiment of the present invention, the polypropylene contained in the ink reservoir is preferably a homopolymer, i.e., homopolypropylene, which makes it easier to suppress the permeation of water vapor in the ink reservoir, i.e., makes it easier to suppress the intrusion of water vapor into the oil-based ink in the writing instrument.

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.

The fact that the ink reservoir contains a β-crystal nucleating agent 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). When dissolving, the mixture may be heated (for example, to 100°C or higher) if necessary.

Also, as mentioned above, the ink reservoir contains a β crystal nucleating agent in addition to polypropylene, which results in the formation of fine spherulites at high density, and the presence or absence of a β crystal nucleating agent can be confirmed by observing the morphology under a microscope, etc. An example is given below.

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 reservoir of Samples No. 1 and 4 described later) in a cross section perpendicular to the longitudinal direction at the center in the longitudinal direction (axial direction), exposing the central portion between the outer surface and the inner surface (i.e., the surface that can come into contact with oil-based ink) by a freeze microtome method. The transmission polarized light microscope images of Fig. 1A and Fig. 1B described later were obtained using a polarizing microscope (LV100POL, manufactured by Nikon Corporation). As shown in Fig. 1A, multiple fine white dots are observed due to fine, densely formed spherulites.
Fig. 1B is a transmission polarized light microscope image of a conventional ink reservoir (corresponding to the ink reservoir of sample No. 2 described later) containing polypropylene but not a β-crystal nucleating agent, in which the central portion between the outer and inner surfaces of a cross section perpendicular to the longitudinal direction at the longitudinal center portion was exposed by a freezing microtome method and observed. As shown in Fig. 1B, several white regions caused by coarse spherulites and the like with a maximum length of 20 μm or more are observed, which are not observed in Fig. 1A.
Thus, by observing multiple fine white dots (all with a maximum length of less than 20 μm) in the above transmission polarized light microscope image (magnification: 200 times), it can be determined that the ink reservoir contains a β-crystal nucleating agent in addition to polypropylene.

Observation example 2
FIG. 2 is a TEM image of an ink reservoir according to an embodiment of the present invention (corresponding to the ink reservoirs of Samples No. 1 and 4 described below), in a cross section perpendicular to the longitudinal direction at the longitudinal center, in a central portion between the outer surface and the inner surface, which was exposed by a freeze microtome method. The TEM image in FIG. 2 was obtained using a transmission electron microscope H-7650 (manufactured by Hitachi High-Tech Corporation). As shown in FIG. 2, it is observed that spherulites are formed over the entire surface by overlapping in a complex manner. As for the circle-equivalent diameter of the spherulites, for example, the circle-equivalent 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 circle-equivalent diameter of the spherulites is not particularly limited, but may be, for example, 0.1 μm or more.
In this way, by observing the state in which spherulites with a circular equivalent diameter of less than 20 μm are formed all over the surface in the above TEM image (magnification: 3000 times), it can be determined that the ink reservoir contains a β-crystal nucleating agent in addition to polypropylene.

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.

R ² (-CONHR ³ ) _n (A)

[In the formula, n is an integer of 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 is the same or different and is 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.]

Specific examples of preferred amide compounds represented by the above general formula A include N,N'-diphenylhexanediamide, N,N'-dicyclohexylterephthalamide, and N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide.

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 including 0.01% or more by mass of the β-crystal nucleating agent, it becomes easier to form a sufficient amount of spherulites. On the other hand, since the effect of including the β-crystal nucleating agent in an amount of more than 3% by mass is saturated, it is preferable to include the β-crystal nucleating agent in an amount of 3% by mass or less.

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

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")), at least one of the inner ink reservoir and the outer ink reservoir may contain 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.

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 organic solvent is 50% by mass or more and has a vapor pressure of 600 Pa or more at 20° C., the ink is prone to volatilization and is susceptible to the effects of water vapor, but even in such cases, by satisfying the specific requirements of the embodiment of the present invention, writing defects can be suppressed. In other words, the effect of the embodiment of the present invention becomes prominent in such cases.
Furthermore, when the organic solvent is at least one selected from the group consisting of alcohols and glycol ethers, water vapor dissolves in the ink, and the blended components tend to precipitate, but even in such a case, by satisfying the specific requirements of the embodiment of the present invention, writing defects can be suppressed. In other words, in such a case, the effect of the embodiment of the present invention becomes remarkable.
The content of the organic solvent in the oil-based ink may be, for example, 40 to 95% by mass.

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 %.

In addition to the organic solvent and colorant, the oil-based ink may contain other materials. Examples of other materials include resins, rust inhibitors, viscosity modifiers, color stabilizers, plasticizers, chelating agents, lubricants, shear thinning agents, and release agents, and may be contained in the oil-based ink in a total amount of 50% by mass or less.

　式中、ｐ、ｑ、ｒ及びｓは、ｐ、ｑ、ｒ及びｓの総和を１００％としたときの組成比（モル％）を表し、ｐ≧０、ｑ≧０、ｒ＞０、ｓ＞０である。
　上記により、筆記板用マーキングペンなどの筆記具に好適に用いることができる。上記樹脂としては、ポリビニルアセタール樹脂（ｐ＞０、ｑ＞０、ｒ＞０およびｓ＞０）、ポリビニルブチラール樹脂（ｐ＞０、ｑ＝０、ｒ＞０およびｓ＞０）、ポリビニルアセトアセタール樹脂（ｐ＝０、ｑ＞０、ｒ＞０およびｓ＞０）などが挙げられる。樹脂は一種又は二種以上を混合して用いてもよい。油性インキにおける樹脂の含有量は、０．１～５質量％であってもよい。 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 composition ratios (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 can be suitably used 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). The resin may be used alone or in combination of two or more kinds. The content of the resin in the oil-based ink may be 0.1 to 5% by mass.

In particular, the glass transition temperature of the resin represented by the general formula (1) is preferably 60° C. or higher, more preferably 65° C. or higher, since better erasability can be obtained. The upper limit of the glass transition temperature of the resin is preferably 120° C. or lower, more preferably 110° C. or lower.
Generally, the physical properties of the handwriting coating film formed on the writing surface are easily changed due to external factors such as temperature and sunlight, and in particular, handwriting coating films that have been aged for a long period of time are easily prone to a decrease in erasability due to changes in physical properties.
This is because, if the glass transition temperature of the resin is low, when the temperature of the handwriting coating film rises above its glass transition temperature due to air temperature or sunlight, the physical properties of the resin in the handwriting coating film change, and part of the handwriting remains on the writing surface.
By setting the glass transition temperature of the resin 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 after long-term aging.

　式中のＲ^１～Ｒ^４は、それぞれ炭素数６～１８のアルキル基、炭素数２～１８及び酸素数２～１０のアルコキシポリグリコール基のいずれかである。
　剥離剤としては、上記化合物の他、カルボン酸エステル類、シリコーン系界面活性剤、ノニオン系界面活性剤等を用いることもでき、例えば、ポリオキシアルキレンアルキルエーテルの硫酸エステル、ポリオキシアルキレンアルキルアリールエーテルの硫酸エステル、ポリオキシエチレンアルキルエーテルリン酸エステル又はこれらの塩、二塩基酸エステル、一塩基酸エステル、ポリアルキレングリコールエステル等の化合物を用いることもできる。
　剥離剤は一種又は二種以上の化合物を混合して用いてもよい。油性インキにおける剥離剤の含有量は、１～１５質量％であってもよい。 As the release agent, a known one can be used. For example, the release agent may contain at least one 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.

In the formula, R ¹ to R ⁴ are each 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, the release agent may also be a carboxylic acid ester, a silicone surfactant, a nonionic surfactant, or the like. For example, compounds such as a polyoxyalkylene alkyl ether sulfate, a polyoxyalkylene alkylaryl ether sulfate, a polyoxyethylene alkyl ether phosphate, or salts thereof, a dibasic acid ester, a monobasic acid ester, or a polyalkylene glycol ester may 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.

(Tip)
In the 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 lead the oil-based ink from the ink storage portion onto the writing surface by contacting it with the writing surface. The tip portion can be disposed, for example, at either end of the ink storage portion in the longitudinal direction. For example, if the writing instrument is a ballpoint pen or a ballpoint pen refill, the tip portion may be a known ballpoint pen tip, and 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 writing surface is not particularly limited, but paper such as writing paper A conforming to JIS P3201 can be used. Examples of marking pens include marking pens for writing boards, in which the writing surface is made of a non-permeable material.

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. More preferably, the cap further contains a β-crystal nucleating agent.
When the tip is a marking pen tip, the tip is preferably covered with a cap containing polypropylene, and the cap more preferably contains a β crystal nucleating agent.

The polypropylene contained in the cap may be the same as the polypropylene contained in the container, or it may be different. Also, the β crystal nucleating agent contained in the cap may be the same as the β crystal nucleating agent contained in the container, or it may be different.

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% or more by mass of 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 at more than 3% by mass, it is preferable to keep it at 3% by mass or less.

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

(Writing implements)
The writing instrument according to the embodiment of the present invention includes the ink reservoir and the tip portion. The type of the writing instrument is not particularly limited, and examples thereof include a ballpoint pen, a ballpoint pen refill, a marking pen (including a marking pen for a writing board), and the like.
The structure of the writing instrument according to the embodiment of the present invention is not particularly limited as long as it includes the ink reservoir and tip portion, and may be the structure of a known ballpoint pen, ballpoint pen refill, or marking pen.

The following provides a more detailed explanation of the embodiments of the present invention, using examples. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the intent described above and below, and all such modifications are within the technical scope of the embodiments of the present invention.

The compositions of the oil-based inks (black ink and red ink) used are shown in Tables 1 and 2 below. The values in the tables indicate parts by weight.

The ingredients are listed below according to the note numbers in the table.
(1) Synthetic alcohol, manufactured by Japan Synthetic Alcohol Co., Ltd., product 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: Malquid (registered trademark) 33
(7) Resin, manufactured by Evonik, product name: Tego (registered trademark) Variplus SK
(8) Phosphate ester surfactant, manufactured by Toho Chemical Industry Co., Ltd., trade name: Phosphanol (registered trademark) RA600
(9) Glycerol fatty acid ester, manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., trade name: SY Glister (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: methyl propylene glycol (MFG), vapor pressure at 20° C.: 893 Pa
(12) Methyl lactate, manufactured by Musashino Chemical Laboratory 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 Daiwa Kasei Co., Ltd., product name: Belzon (registered trademark) Crystal 120

(Ink Preparation)
The raw materials were 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).

(Making a marking pen)
A cylindrical ink reservoir having the composition shown in Table 3 below was prepared (molded). An ink reservoir made of a polyester fiber bundle was contained in the ink reservoir, and a predetermined amount of each oil-based ink was filled in the ink reservoir. The acrylic fiber bundle was bound with melamine resin to obtain a tip. The tip was attached to the ink reservoir with the rear end of the tip in contact with the ink reservoir, and the tip was covered with a polypropylene cap (without β-crystal nucleating agent) to obtain marking pens of Samples No. 1 to 4. Samples No. 1 to 4 were formed in the same manner as a commercially available marking pen (Permanent Marker 400, Pilot Co., Ltd., maximum diameter: φ16.4 mm, total length: 145.8 mm) except that a part of the ink reservoir contained a β-crystal nucleating agent (however, no transfer film was provided).

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 the 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., product name: 4003, pigment content in ink reservoir: 1.0% by mass

(Written test)
The marking pen obtained as described above was left lying down 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 handwriting was done 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. Note that "B" or higher was considered to be acceptable. Note that FIG. 3 shows example images of handwriting that are "AA", "A", "B" and "C".
Evaluation Criteria AA: Writing with good handwriting was possible.
A: Some smudges were observed in the handwriting.
B: There was some smudged handwriting.
C: The handwriting was very faint or impossible to write.

The following can be seen from Table 4. Both Samples No. 1 and No. 4 satisfied the requirements stipulated in the embodiment 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), and writing defects occurring after storage under high temperature and high humidity were suppressed.
On the other hand, Samples Nos. 2 and 3 did not satisfy the requirements defined in the embodiment of the present invention, and the writability was poor after 90 days at 50° C. and 100% RH.

Furthermore, for Samples Nos. 1 to 4, the oil-based ink sampled from the tip after storage under high temperature and high humidity was observed under an optical microscope.
4A to 4C are optical microscope images of the oil-based inks of Sample No. 1 after storage for 30 days (FIG. 4A), 60 days (FIG. 4B), or 90 days (FIG. 4C) under conditions of 50° C. and 100% RH (all scale bars in the figures indicate 100 μm). As can be seen from FIG. 4A to FIG. 4C, Sample No. 1, which satisfies the requirements stipulated in the embodiment of the present invention, 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, and when the storage period was increased from 60 to 90 days, there was almost no change or only a slight decrease in uniformity.
5A to 5C are optical microscope images of the oil-based inks of sample No. 3 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 FIG. 5A to FIG. 5C, sample No. 3, which does not satisfy the requirements stipulated in the embodiment of the present invention, showed 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.

Table 5 below shows the composition of the oil-based ink (oil-based ink for writing boards) used. The values in the table indicate parts by mass. The vapor pressure of ethyl alcohol at 20°C is 5,580 Pa, that of isopropyl alcohol is 4,400 Pa, and that of n-propyl alcohol is 2,000 Pa. All of the organic solvents used had a vapor pressure of 600 Pa or higher.

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

(Ink Preparation)
For writing board oil-based inks 1 and 2, organic solvent, colorant and resin were added to a mixing vessel in the amounts shown in Table 5 above, and mixed 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 mixed 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 mixed and dissolved at 20°C for 3 hours to obtain an oil-based ink.

(Making a marking pen)
A cylindrical ink reservoir having the composition shown in Table 6 was prepared (molded) and the rest of the process was the same as in Example 1 to obtain marking pens (marking pens for writing boards) of Samples No. 5 to 9.

The ingredients listed in the table are the same as those in Example 1.

(Written Test)
The writing board marking pen thus obtained was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 7 below.

The following can be seen from Table 7. Samples Nos. 5, 8, and 9 all satisfied the requirements stipulated in the embodiment 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), and writing defects occurring after storage under high temperature and high humidity were suppressed.
On the other hand, Samples Nos. 6 and 7 did not satisfy the requirements defined in the embodiment of the present invention, and the writability after 90 days at 50° C. and 100% RH was poor.

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

Claims (7)

The ink pen includes an ink storage section capable of storing oil-based ink, and a tip section capable of directing the oil-based ink from the ink storage section onto a surface to be written on by contacting the tip section with the surface to be written on,
The ink reservoir contains polypropylene and a β-crystal nucleating agent.
Writing implements. The β-crystal nucleating agent is represented by the following formula A:
R ² (-CONHR ³ ) _n (A)
[In the formula, n is an integer of 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 is the same or different and is 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.]
The writing instrument of claim 1 , comprising a compound represented by the formula: 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. The writing instrument according to any one of claims 1 to 3, wherein the polypropylene is homopolypropylene. The 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% by mass or more of the organic solvent has a vapor pressure of 600 Pa or more at 20°C. The writing instrument 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 instrument according to claim 5, wherein the oil-based ink further comprises 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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