Water-based ink composition for writing implements, water-based ink product using the same, and writing implement

Abstract

To provide: an aqueous ink composition for writing utensils, which has little influence on the human body and the environment, in which microorganisms hardly propagate, which can be used for a writing utensil in which an ink frequently comes into contact with the outside air and a writing utensil using various ink supply mechanisms, and which is excellent in safety and storage stability; an aqueous ink product and a writing utensil using the same.SOLUTION: The water-based ink composition for writing utensils contains water, a coloring agent, an alkanediol with 5 or more carbon atoms, and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition for a writing instrument, and a water-based ink product and a writing instrument using the same. [Background technology]

[0002] Because aqueous ink compositions contain water as the main solvent, they are susceptible to the proliferation of microorganisms such as bacteria, mold, and yeast. The proliferation of microorganisms can cause the ink composition to spoil, resulting in changes in the ink composition's physical properties such as viscosity, the formation of foreign matter such as precipitates and aggregates in the ink composition, and discoloration of the ink composition, thereby impairing the functionality of the aqueous ink composition. Therefore, the addition of antibacterial substances to aqueous ink compositions to suppress the proliferation of microorganisms and the like has been widely practiced (see Patent Documents 1 to 3).

[0003] However, if the same antibacterial substance is continuously used in an ink composition, there is a possibility that microorganisms resistant to the antibacterial substance (hereinafter referred to as "resistant bacteria") will emerge and multiply, and there is room for improvement in storage stability.

[0004] Furthermore, although antibacterial effects can be obtained depending on the antibacterial substance used, various problems remain, such as difficulty in appropriately adjusting the surface tension and viscosity of the ink composition, which can result in bleeding, strike-through, and smearing, and when the ink composition is stored for a long period of time, the physical properties of the ink composition change, causing problems with stability over time and writability.

[0005] Furthermore, in recent years, importance has been placed on the safety of ink compositions for writing instruments with respect to the human body and the environment. Although antibacterial substances have antibacterial effects, many of them have strong skin irritation and skin sensitization properties, posing safety issues. In particular, when an aqueous ink composition for a writing instrument is contained in an ink storage container and dispensed from the ink storage container and filled into a writing instrument for use, or when an aqueous ink composition for a writing instrument is contained in a cartridge and the cartridge is replaced to refill the ink for use, there is a high possibility that the ink composition will come into direct contact with parts of the user's body, such as the skin. For this reason, it is particularly necessary to achieve both antibacterial performance and safety in ink compositions used in such writing instruments.

[0006] Furthermore, depending on the conditions of use of the ink and the type and amount of the antibacterial substance added, the antibacterial effect may not be fully exerted, resulting in a problem of impairing the functionality of the aqueous ink composition for a writing instrument. For example, when an ink composition is stored in an ink storage container with an opening and closing, and the ink composition is repeatedly dispensed and filled into a writing instrument, the ink is frequently exposed to the outside air. Therefore, if the antibacterial performance is insufficient, foreign matter such as precipitates and aggregates caused by the proliferation of microorganisms is likely to occur in the ink. As a result, the resulting foreign matter accumulates in the ink supply mechanism, reducing the amount of ink supplied and resulting in faint writing. Furthermore, the generated foreign matter may clog the ink supply channel, preventing the ink from being supplied and making writing impossible. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-48929 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-175851 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-280762 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to solve the above-mentioned problems and to provide a water-based ink composition for a writing instrument that has excellent storage stability due to high antibacterial performance and excellent safety while fully maintaining good writing performance, as well as a writing instrument and a water-based ink product using the same. [Means for solving the problem]

[0009] The aqueous ink composition for writing instruments according to the present invention is characterized by comprising water, a colorant, an alkanediol having 5 or more carbon atoms, and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol.

[0010] The water-based ink product according to the present invention is characterized in that it comprises the above-mentioned water-based ink composition for a writing instrument housed in an ink storage container.

[0011] Furthermore, the writing instrument according to the present invention is characterized by containing the above-mentioned water-based ink composition for a writing instrument. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an ink composition, a writing instrument using the same, and a water-based ink product, which exhibit high antibacterial performance and excellent storage stability while maintaining good writing performance, such as producing handwriting with little smearing, and which also exhibits reduced skin sensitization and skin irritation and is therefore excellent in safety. DETAILED DESCRIPTION OF THE INVENTION

[0013]

[0023] In the present specification, the terms "parts," "%," "ratio," and the like, which indicate the composition, are based on mass unless otherwise specified, and the content, content amount, and added amount are expressed as % by mass of the constituent components based on the mass of the aqueous ink composition.

[0014] <Water-based ink composition for writing instruments> The aqueous ink composition for a writing instrument according to the present invention (hereinafter sometimes referred to as "ink composition") is characterized by comprising water, a colorant, an alkanediol having 5 or more carbon atoms, and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol. It is important that the ink composition of the present invention uses an alkanediol having 5 or more carbon atoms in combination with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol. The combined use of an alkanediol having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol provides excellent antibacterial effects and the ink composition has excellent storage stability. Furthermore, the combined use of an alkanediol having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol also ensures high safety. Therefore, the ink composition of the present invention can achieve both excellent storage stability due to its excellent antibacterial properties and excellent safety. Furthermore, by using an alkanediol having 5 or more carbon atoms in combination with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol, it is possible to maintain the surface tension and viscosity of the ink composition appropriately while still maintaining sufficient antibacterial properties, resulting in good handwriting with little smearing and maintaining excellent writing performance.

[0015] Furthermore, if the ink composition continues to use the same compound with antibacterial properties, microorganisms resistant to the compound with antibacterial properties (hereinafter referred to as "resistant bacteria") may emerge and grow. However, the ink composition of the present invention uses an alkanediol having 5 or more carbon atoms in combination with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol. Therefore, even if microorganisms develop resistance to one of the compounds, the growth of the microorganisms can be suppressed by the other compound used in combination. Therefore, the ink composition of the present invention is also effective against resistant bacteria.

[0016] For the above reasons, the ink composition of the present invention is suitable for use in various writing instruments. In particular, the ink composition of the present invention can be effectively used in writing instruments in which ink is likely to come into contact with the user's skin, etc., and special consideration must be given to safety, such as writing instruments that are stored in an ink storage container and in which ink is dispensed from the container and filled into the writing instrument, and writing instruments that are stored in cartridges and in which the ink is replenished by replacing the cartridges.

[0017] Furthermore, when an ink composition is stored in an ink storage container with an opening and the ink composition is dispensed and repeatedly filled into a writing instrument for use, the ink is frequently exposed to the outside air, which makes it easy for foreign matter such as precipitates and aggregates caused by microbial growth to form in the ink. However, the ink composition of the present invention has excellent antibacterial properties and can therefore suppress the formation of such foreign matter, thereby sufficiently preventing the resulting foreign matter from accumulating in the ink supply mechanism, reducing the amount of ink supplied and resulting in faint handwriting, or even blocking the ink supply flow path due to the generated foreign matter, preventing ink from being supplied and making writing impossible. Therefore, from this perspective as well, the ink composition can be effectively used in the above-mentioned writing instrument.

[0018] The ink composition of the present invention can also be suitably used in writing instruments equipped with a pen tip. The pen tip has grooves that temporarily store ink, ink flow passages, and air passages. When the internal pressure of the ink reservoir changes, excess ink can flow into and be retained between the grooves of the pen tip, preventing ink from dripping from the pen tip and adjusting the ink's ejection properties, resulting in a good writing style. As described above, the ink composition of the present invention has excellent antibacterial properties and can suppress the generation of foreign matter derived from microorganisms, thereby preventing the ink from becoming difficult to flow into the gaps between the comb grooves due to foreign matter, and furthermore, can maintain the ink's surface tension and viscosity at an appropriate level, thereby maintaining good wettability to the pen core. Therefore, the ink composition of the present invention can maintain good ink flowability and ink retention between the comb grooves of the pen core, suppressing dripping from the pen tip, and producing good handwriting.

[0019] Each component constituting the ink composition according to the present invention will be described below.

[0020] <Alkanediols with 5 or more carbon atoms> The ink composition according to the present invention comprises an alkanediol having 5 or more carbon atoms. The alkanediol having 5 or more carbon atoms may have either a straight-chain or branched alkyl group, and the carbon atoms substituted with the two hydroxyl groups may be located at any positions.

[0021] Examples of alkanediols having 5 or more carbon atoms include 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-heptanediol, 2-ethyl-1,3-hexanediol, 2,2-dimethyl-1,3-propanediol, 2,2-dimethyl-1,3-hexanediol, and 3-methyl-1,5-pentanediol.

[0022] Although alkanediols having 5 or more carbon atoms exhibit antibacterial effects by themselves, the antibacterial effects can be enhanced by using them in combination with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol. Although alkanediols having 5 or more carbon atoms have excellent antibacterial effects, if used in amounts exceeding a certain level, they may cause skin irritation. However, by using 3-[2-(ethylhexyl)oxyl]-1,2-propanediol in combination, it is possible to obtain sufficient antibacterial effects while keeping the amount of alkanediol having 5 or more carbon atoms added within a range that maintains safety. Therefore, the ink composition of the present invention, which uses 3-[2-(ethylhexyl)oxyl]-1,2-propanediol in combination with an alkanediol having 5 or more carbon atoms, can achieve both excellent storage stability due to its high antibacterial performance and excellent safety.

[0023] Taking into consideration both antibacterial performance and safety, an alkanediol having 5 to 10 carbon atoms is more preferable, an alkanediol having 5 to 8 carbon atoms is even more preferable, and an alkanediol having 5 carbon atoms or an alkanediol having 6 carbon atoms is particularly preferable. In addition to the antibacterial effect, in consideration of solubility, stability, and improved synergistic effect with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol, the alkanediol having 5 or more carbon atoms is preferably 1,2-alkanediol. In addition, the alkanediol having 5 or more carbon atoms preferably has a linear alkyl group. Therefore, in the present invention, it is preferable to use 1,2-pentanediol or 1,2-hexanediol. Furthermore, when further consideration is given to achieving both antibacterial performance and safety, it is particularly preferable to use two or more different alkanediols each having 5 or more carbon atoms in combination.

[0024] In the present invention, the content of the alkanediol having 5 or more carbon atoms is preferably 0.01% by mass to 10% by mass based on the total mass of the ink composition. This is because a content of 0.01% by mass or more can provide a sufficient antibacterial effect, and a content of 10% by mass or less can reduce the possibility of skin irritation and can prevent smearing and the like, making it easier to obtain excellent handwriting. Furthermore, in consideration of achieving both antibacterial effect and safety, the concentration is more preferably 0.01% by mass to 5% by mass, and even more preferably 0.01% by mass to 3% by mass. When 1,2-pentanediol is used, the amount of 1,2-pentanediol added is preferably 2.5% by mass or less, and when 1,2-hexanediol is used, the amount is more preferably 1.5% by mass or less.

[0025] <3-[2-(ethylhexyl)oxyl]-1,2-propanediol> The ink composition according to the present invention comprises 3-[2-(ethylhexyl)oxyl]-1,2-propanediol. 3-[2-(ethylhexyl)oxyl]-1,2-propanediol is a glyceryl alkyl ether in which 2-ethylhexanol is bonded to the hydroxyl group of glycerin, and is a compound represented by the following formula.

[0026] [ka]

[0027] 3-[2-(ethylhexyl)oxyl]-1,2-propanediol is a highly safe ingredient with low skin sensitization and irritation. 3-[2-(ethylhexyl)oxyl]-1,2-propanediol alone has antibacterial activity, but the effect is small. However, it has the effect of enhancing the antibacterial activity of alkanediols with 5 or more carbon atoms. Therefore, the ink composition of the present invention, which uses 3-[2-(ethylhexyl)oxyl]-1,2-propanediol and an alkanediol having 5 or more carbon atoms, exhibits high antibacterial performance. Furthermore, since sufficient antibacterial effect can be obtained even while reducing the amount of alkanediol having 5 or more carbon atoms added, it also has a high level of safety. Furthermore, 3-[2-(ethylhexyl)oxyl]-1,2-propanediol is structurally stable and is not easily affected by changes in pH, temperature, etc., and therefore, the antibacterial effect is easily maintained. Furthermore, 3-[2-(ethylhexyl)oxyl]-1,2-propanediol also has a moisturizing effect, and therefore, the ink composition of the present invention can also achieve good resistance to drying up.

[0028] In the present invention, the content of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol is preferably 0.01% by mass to 1% by mass, and more preferably 0.01% by mass to 0.5% by mass, based on the total mass of the ink composition. Furthermore, when suppression of skin irritation is particularly taken into consideration, the content is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.08% by mass or less. Therefore, in order to obtain a sufficient antibacterial effect while ensuring excellent safety, the concentration is more preferably 0.01% by mass to 0.2% by mass, even more preferably 0.01% by mass to 0.15% by mass, even more preferably 0.01% by mass to 0.1% by mass, and even more preferably 0.02% by mass to 0.08% by mass.

[0029] In the present invention, the content ratio of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol to alkanediol having 5 or more carbon atoms (3-[2-(ethylhexyl)oxyl]-1,2-propanediol / alkanediol having 5 or more carbon atoms) is preferably less than 1 by mass. Furthermore, it is preferably 0.005 to 0.5, more preferably 0.01 to 0.3, even more preferably 0.01 to 0.2, and still more preferably 0.02 to 0.2. When the content ratio is within the above range, the enhancing effect of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol can be obtained, and sufficient antibacterial effect and safety can be obtained. Furthermore, the surface tension and viscosity of the ink composition can be easily maintained at an appropriate level, dripping from the pen tip can be sufficiently suppressed, good ink ejection properties can be easily obtained, and good handwriting can be obtained with suppressed smearing.

[0030] The ink composition of the present invention preferably further contains an isothiazolinone compound. Examples of isothiazoline compounds include 2-(n-octyl)-4-isothiazolin-3-one (hereinafter sometimes referred to as OIT), 2-methyl-4-isothiazolin-3-one (hereinafter sometimes referred to as MIT), 1,2-benzisothiazolin-3-one (hereinafter sometimes referred to as BIT), 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, and N-(n-butyl)-1,2-benzisothiazolin-3-one. By further comprising an isothiazolinone compound, the growth of a wide variety of microorganisms can be significantly suppressed. Writing instrument ink compositions are likely to be used under a variety of conditions and are likely to be exposed to a wide variety of microorganisms. Therefore, further comprising an isothiazolinone compound is effective. Furthermore, by using an isothiazolinone compound in combination, even if a microorganism has resistance to an alkanediol having 5 or more carbon atoms or 3-[2-(ethylhexyl)oxyl]-1,2-propanediol, the isothiazolinone compound can inhibit the growth of the microorganism. Therefore, further containing an isothiazolinone compound is effective against resistant bacteria.

[0031] On the other hand, isothiazolinone compounds are antibacterial substances that have extremely high antibacterial effects, but can also cause skin sensitization or skin irritation depending on the amount added. By using an isothiazolinone compound in combination with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol, the amount of the isothiazolinone compound added can be kept at a level that ensures sufficient safety, while still achieving excellent antibacterial effects. Furthermore, the combined effect of the isothiazolinone compound and an alkanediol having 5 or more carbon atoms can further improve the antibacterial effects. Therefore, the amount of the isothiazolinone compound added can be kept at a level that ensures sufficient safety, while still achieving excellent antibacterial effects. Therefore, by further containing an isothiazolinone compound in the ink composition of the present invention, it is possible to further improve the antibacterial performance and storage stability while sufficiently maintaining safety, and therefore the ink composition is extremely effective as a water-based ink composition for writing instruments.

[0032] Among the isothiazolinone compounds, OIT, MIT, and BIT are preferred because they are resistant to decomposition even in alkaline conditions, have good heat resistance, and can be used to obtain an odorless ink composition. The content of OIT is preferably 1 ppm to 500 ppm, more preferably 1 ppm to 480 ppm, more preferably 1 ppm to 100 ppm, more preferably 1 ppm to 50 ppm, even more preferably 1 ppm to 15 ppm, and most preferably 1 ppm to 1.5 ppm, based on the total mass of the ink composition. Furthermore, the MIT content is preferably 1 ppm to 500 ppm, more preferably 1 ppm to 480 ppm, even more preferably 1 ppm to 100 ppm, still more preferably 1 ppm to 15 ppm, and most preferably 1 ppm to 1.5 ppm, based on the total mass of the ink composition. Furthermore, the content of BIT is preferably 1 ppm to 500 ppm, more preferably 1 ppm to 480 ppm, even more preferably 1 ppm to 360 ppm, still more preferably 1 ppm to 50 ppm, and most preferably 1 ppm to 15 ppm, based on the total mass of the ink composition. If the content of the isothiazoline compound is within the above range, a sufficient antibacterial effect can be obtained, and the safety of the ink composition can be sufficiently ensured.

[0033] Furthermore, in the present invention, when a plurality of isothiazolinone compounds are used in combination, not only the antibacterial activity of each compound against resistant bacteria but also the antibacterial activity of the other compound against resistant bacteria is strengthened, and the total amount of isothiazolinone compounds added can be reduced, thereby improving both the antibacterial effect and safety, which is more effective.

[0034] In the present invention, the ratio of the content of isothiazolinone compounds to the total content of alkanediols having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol (isothiazoline compounds / (total content of alkanediols having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol)) is preferably 0.0001 to 0.01 by mass, and more preferably 0.00015 to 0.005. When the content ratio is within the above range, sufficient antibacterial effect can be obtained while ensuring sufficient safety. Furthermore, the surface tension and viscosity of the ink composition can be easily maintained at an appropriate level, preventing blurring of handwriting and also preventing dripping from the pen tip.

[0035] The ink composition according to the present invention may further contain any antibacterial substance within the range that does not impair the effects of the present invention. Specific examples of the antibacterial substance include iodopropynyl butylcabamate, sodium benzoate, 2-phenoxyethanol, 2-(sodiothio)pyridine-1-oxide, zinc bis[1,2-dihydro-2-thioxopyridin-1-olate], benzotriazole, and phenol.

[0036] <Coloring agent> The colorant used in the ink composition of the present invention is not particularly limited and may be a dye, pigment, or the like, and may be appropriately selected and used.

[0037] Examples of dyes include various dyes such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes, and food dyes.

[0038] Examples of acid dyes include CI Acid Red 18, CI Acid Orange 10, CI Acid Yellow 3, CI Acid Yellow 7, CI Acid Yellow 23 (Tartrazine), CI Acid Yellow 42, CI Acid Green 3, CI Acid Green 16, CI Acid Blue 1, CI Acid Blue 9, CI Acid Blue 22, CI Acid Blue 90, CI Acid Blue 239, CI Acid Blue 248, CI Acid Violet 15, CI Acid Violet 49, CI Acid Black 1, CI Acid Black 2, CI Acid Red 52, CI Acid Red 289, CI Acid Red 388, CI Acid Red 87 (Eosin), CI Acid Red 92 ( Phloxine), CI Acid Red 97, CI Acid Red 51 (Erythrosine), CI Acid Red 94 (Rose Bengal), Acridine Red (CI 45000), Rhodamine 110, Rhodamine 123, Rhodamine 6G (CI Basic Red 1), Rhodamine 6G Extra, Rhodamine 116, Rhodamine B (CI 45170), Tetramethylrhodamine perchlorate, Rhodamine 3B, Rhodamine 19, Sulforhodamine, Pyronine G (CI 45005), Rhodamine S (CI 45050), Rhodamine G (CI 45150), Ethylrhodamine B (CI 45175), Rhodamine 4G (CI 45166), Rhodamine 3GO (CI 45215), Sulforhodamine G, etc.

[0039] Examples of basic dyes include CI Basic Orange 2, CI Basic Orange 14, CI Basic Green 4, CI Basic Blue 9, CI Basic Blue 26, CI Basic Violet 1, CI Basic Violet 3, CI Basic Violet 10, chrysoidine (CI 11270), methyl violet FN (CI 42535), crystal violet (CI 42555), malachite green (CI 42000), Victoria blue FB (CI 44045), acridine orange NS (CI 46005), and methylene blue B (CI 52015).

[0040] Examples of direct dyes include CI Direct Red 28, CI Direct Yellow 44, CI Direct Blue 86, CI Direct Blue 87, CI Direct Violet 51, and CI Direct Black 19.

[0041] Examples of food dyes include CI Food Yellow 3, CI Food Black 2, Congo Red (CI 22120), Direct Sky Blue 5B (CI 24400), Violet BB (CI 27905), Direct Deep Black EX (CI 30235), Kayalas Black G Conc (CI 35225), Direct Fast Black G (CI 35255), and Phthalocyanine Blue (CI 74180).

[0042] Examples of pigments include inorganic, organic, and processed pigments. Specific examples of pigments include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, quinophthalone-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, and complementary color pigments. Microencapsulated pigments may also be used. Microencapsulated pigments are pigments in which a colored body formed by dispersing a pigment in a medium is encapsulated or solid-dissolved in a shell made of a resin wall-forming substance using a known microencapsulation method. Furthermore, colored resin particles in which a pigment is coated with a transparent or translucent resin, or colorless resin particles colored with a pigment or dye, can also be used. Self-dispersing pigments can also be used.

[0043] Some dyes can serve as nutrients for microorganisms, causing them to grow. However, the ink composition of the present invention, which contains an alkanediol having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol, can inhibit their growth. In particular, when dyes such as CI Acid Blue 90 and CI Direct Blue 87 are used, they tend to serve as nutrients for microorganisms, causing them to grow. However, the combined use of an alkanediol having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol can inhibit their growth. Thus, the aqueous ink composition for writing instruments of the present invention allows the use of dyes that have traditionally been restricted for use, thereby broadening the range of materials available for use in aqueous ink compositions for writing instruments.

[0044] <Water> The ink composition according to the present invention contains water. The water to be used is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water.

[0045] <Other additives> The ink composition of the present invention may contain any additives as needed. The additives that can be used are described below.

[0046] <Water-soluble organic solvent> In the present invention, it is preferable that the ink composition further contains a water-soluble organic solvent. As the water-soluble organic solvent, those used in conventional aqueous ink compositions for writing instruments can be used.

[0047] Examples include (i) glycols such as ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and glycerin, (ii) alcohols such as methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols, and (iii) glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol. Mixtures of two or more of these can also be used.

[0048] When a water-soluble organic solvent is used in the ink composition of the present invention, it is preferable to use a polyhydric alcohol solvent. By using a polyhydric alcohol solvent, the hygroscopic effect of the polyhydric alcohol solvent can be imparted to the ink composition, effectively suppressing evaporation of water in the ink from the pen tip and improving the pen tip's dry-up resistance. Furthermore, as mentioned above, 3-[2-(ethylhexyl)oxyl]-1,2-propanediol also has a moisturizing effect, and its use in combination with a polyhydric alcohol can further improve dry-up resistance. This allows the ink to be smoothly ejected from the start of writing, leaving a uniform handwriting with little smearing, even when the pen tip is exposed to the atmosphere for a long period of time, even in a particularly dry environment. The ink composition can also be suitably used in writing instruments, such as retractable writing instruments, which are particularly susceptible to the pen tip drying out.

[0049] Furthermore, since 3-[2-(ethylhexyl)oxyl]-1,2-propanediol exhibits good solubility in polyhydric alcohol solvents, 3-[2-(ethylhexyl)oxyl]-1,2-propanediol tends to be present stably in the ink composition, and from this point of view as well, it is effective for the present invention to include a polyhydric alcohol solvent.

[0050] Among the polyhydric alcohol solvents, ethylene glycol, diethylene glycol, butylene glycol, or glycerin is preferred, ethylene glycol, diethylene glycol, or glycerin is more preferred, and ethylene glycol or diethylene glycol is particularly preferred.

[0051] When the water-soluble organic solvent is used, its content is preferably 0.1% to 40% by mass based on the total mass of the ink composition. In order to achieve a good balance between dry-up resistance, water resistance of handwriting, and fixability of handwriting, the content is preferably 0.5% to 40% by mass, more preferably 0.5% to 10% by mass, and even more preferably 1% to 5% by mass.

[0052] <pH Adjusting Agent> The ink composition according to the present invention can contain a pH adjusting agent. Examples of the pH adjusting agent include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide; basic organic compounds such as alkanolamines such as sodium acetate, triethanolamine, and diethanolamine; lactic acid, citric acid, and the like. Considering the stability of the ink composition over time, it is preferable to use a basic organic compound. Further, it is preferable to use an alkanolamine because the effects of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol and an alkanediol having 5 or more carbon atoms can be easily obtained, and it is difficult to affect the permeability to the paper surface and the wettability of the pen core. These pH adjusting agents can also be used as a mixture of two or more kinds.

[0053] In addition, since 3-[2-(ethylhexyl)oxyl]-1,2-propanediol shows good solubility in alkanolamine, 3-[2-(ethylhexyl)oxyl]-1,2-propanediol tends to be stably present in the ink composition. From this point of view as well, in the present invention, it is effective to contain an alkanolamine.

[0054] In addition, the pH value of the ink composition of the present invention is preferably 11 or less. This is because if the pH value is 11 or less, the effects of an alkanediol having 5 or more carbon atoms and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol can be easily obtained sufficiently, and high antibacterial performance can be easily obtained. Also, from the viewpoints of the stability of the ink composition over time and the prevention of corrosion of the metal members in contact with the ink composition, the pH value is preferably 6 or more. Therefore, the pH value of the ink composition is more preferably 6 to 11, and even more preferably 8 to 11. In the present invention, the pH value indicates the value measured at 20°C using an HM-30R type pH meter.

[0055] <Rust Preventive Agent> The ink composition according to the present invention may contain a rust inhibitor, such as benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, or dialkylthiourea.

[0056] <Chelating agent> The ink composition according to the present invention may contain a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycoletherdiaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), salts thereof such as alkali metal salts, ammonium salts, or amine salts, or acids such as phytic acid, citric acid, and lactic acid.

[0057] In addition, since metal salts promote the growth of microorganisms, the storage stability can be further improved by using a chelating agent capable of capturing metal salts, and therefore, in the present invention, it is more effective to further use a chelating agent. Among these, ethylenediaminetetraacetic acid (EDTA) and its salts, or phytic acid are effective.

[0058] Furthermore, since the ink composition of the present invention has excellent antibacterial properties and safety, as described above, the ink composition can be suitably used as an ink composition that is stored in an ink storage container having an opening such as an ink bottle, and that is dispensed and repeatedly filled into writing instruments for use. Glass bottles are often used as ink storage containers because they are inexpensive, easy to mold, and can easily achieve the desired strength. However, on the other hand, when an ink composition is stored in a glass bottle, particularly if it is made of soda-lime glass, which is inexpensive and highly versatile, alkaline components in the glass are likely to leach into the ink composition if the ink composition is stored therein for a long period of time. This leachable alkaline component may react with components of the water-based ink composition to form a precipitate. Therefore, the ink composition used in the present invention preferably contains the chelating agent described above, which can capture alkaline components leached from a glass ink storage container, prevent the alkaline components from reacting with components of the ink composition to form water-insoluble precipitates, and prevent the generated precipitates from clogging the ink flow path, resulting in faint handwriting or the inability to write. Among the above chelating agents, aminocarboxylic acids and salts thereof are preferred, taking into consideration their ability to sufficiently capture alkaline components, their tendency to cause little change in the physical properties and performance of the ink composition before and after the incorporation of the chelating agent, their compatibility with 3-[2-(ethylhexyl)oxyl]-1,2-propanediol and alkanediols having 5 or more carbon atoms, and, as mentioned above, their ability to improve the inhibition of microbial growth. Taking these factors into consideration, the use of aminocarboxylic acids and salts thereof is particularly preferred.

[0059] <Moisturizer> The ink composition according to the present invention may contain a humectant, such as the polyhydric alcohols described above, urea, sorbitol, N,N,N-trialkylamino acid, or hyaluronic acid.

[0060] <Surfactant> The ink composition according to the present invention may further contain a surfactant. Examples of such surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, surfactants having an acetylene bond in their structure, silicone surfactants, phosphate ester surfactants, and fluorine-based surfactants. These surfactants have the effect of adjusting the surface tension of the ink composition within an appropriate range and maintaining good wettability of the ink with respect to the pen core. This improves ink blobbing resistance, facilitates good ink ejection, and produces good handwriting with reduced smearing.

[0061] It is preferable to use a nonionic surfactant as such a surfactant. This is because the nonionic surfactant does not inhibit the antibacterial effect of the alkanediol having 5 or more carbon atoms or 3-[2-(ethylhexyl)oxyl]-1,2-propanediol, and the effect of the surfactant can be fully obtained. Furthermore, among nonionic surfactants, those having a polyoxyalkylene structure, such as polyetheramine and polyoxyalkylene glycol, are particularly effective in the present invention because they are more likely to achieve the above-mentioned effect. Furthermore, among those having a polyoxyalkylene structure, surfactants having a polyoxyethylene structure are preferred. This is because they have excellent solubility stability in water and are more likely to achieve the effect.

[0062] In addition, lubricants such as fatty acids and various resins such as acrylic resins, urethane resins, styrene-butadiene resins, polyester resins, and vinyl acetate resins can also be added to improve the physical properties and functions of the ink.

[0063] <Physical properties of ink composition> The ink composition according to the present invention can maintain an appropriate surface tension of the ink by using 3-[2-(ethylhexyl)oxyl]-1,2-propanediol and an alkanediol having 5 or more carbon atoms. The surface tension of the ink composition is preferably 30 mN / m to 65 mN / m in a 20°C environment. If the surface tension of the ink composition is within the above range, when used in a writing instrument equipped with a pen tip, it can maintain appropriate wettability with the pen tip. As a result, even when the internal pressure of the ink reservoir increases, the overflowing ink smoothly enters the ink reservoir inside the pen tip, making it possible to effectively prevent ink dripping from the writing tip. Furthermore, since the ink discharge properties are well adjusted, good handwriting can be obtained with little smearing. Furthermore, in consideration of improving the above effects, a surface tension of 35 mN / m to 65 mN / m is more preferable, 40 mN / m to 60 mN / m is even more preferable, and 45 mN / m to 55 mN / m is particularly preferable. The ink composition of the present invention can adjust the surface tension as described above while maintaining antibacterial properties and safety, and therefore can be suitably used in writing instruments equipped with a pen core. The surface tension of the ink composition can be measured using a surface tension meter (model: DY-200, manufactured by Kyowa Interface Science Co., Ltd., 20° C., platinum plate, vertical plate method).

[0064] Furthermore, 3-[2-(ethylhexyl)oxyl]-1,2-propanediol and alkanediols having 5 or more carbon atoms hardly affect the ink viscosity even when added in the amounts required to obtain sufficient antibacterial effect, and therefore it is also possible to suppress the ink viscosity. Therefore, the ink viscosity measured using a B-type rotational viscometer at 60 rpm and 20°C can be adjusted to 50 mPa·s or less, and even to 10 mPa·s or less. In particular, in writing instruments that have a pen core and a fountain pen-shaped nib, it is necessary to fully utilize the performance of the pen core, suppress dripping, and ensure good ink discharge from the nib, so it is preferable to adjust the viscosity to 5 mPa·s or less, and even 2 mPa·s or less. The ink composition of the present invention can be adjusted to such a low viscosity while maintaining antibacterial properties and safety. For this reason, the ink composition of the present invention is particularly suitable for use in writing instruments that have a pen core and a fountain pen-shaped nib. The viscosity can be measured using a B-type rotational viscometer (model: BLII, rotor: BL adapter, manufactured by Toki Sangyo Co., Ltd.).

[0065] <Method for producing ink composition> The ink composition according to the present invention can be produced by any conventionally known method, specifically by blending the required amounts of the above-mentioned components and mixing them using various stirrers such as a magnetic stirrer, a propeller stirrer, a homogenizer stirrer, a homodisper, a homomixer, or a planetary stirrer, or various dispersers such as a bead mill.

[0066] <Writing instruments> The aqueous ink composition for writing instruments of the present invention can be used in writing instruments such as marking pens and ballpoint pens with a fiber tip, felt tip, plastic tip, or ballpoint pen tip, and fountain pens with a metal fountain pen-shaped tip.

[0067] The writing instrument according to the present invention may also be configured such that the interior of the writing instrument body serves as an ink reservoir and is directly filled with the ink composition. Alternatively, the writing instrument may be configured such that the interior of the writing instrument body is provided with an ink reservoir filled with the ink composition.

[0068] Examples of ink reservoirs include cartridge types that can be easily attached to or detached from the writing instrument body or pen tip and are pre-filled with an ink composition, and ink suction types that are equipped with an suction mechanism that allows the ink composition to be filled from an ink storage container such as an ink bottle.

[0069] The suction mechanism may be provided directly inside the writing instrument body, or may be removably attached to the writing instrument body or pen tip like a converter.

[0070] In writing instruments with cartridge-type ink reservoirs that are detachably replaceable on the writing instrument body or pen tip and that are pre-filled with an ink composition, or ink-filling writing instruments equipped with an ink-filling mechanism that allows the ink composition to be filled from an ink storage container, users repeatedly refill the writing instrument with ink, which can lead to the introduction of microorganisms, and the resulting foreign matter, such as precipitates and aggregates, is likely to adversely affect writing. Therefore, it is necessary to use an ink composition with excellent antibacterial properties. However, on the other hand, there is a high possibility that users will come into direct contact with the ink, so the ink composition must also be excellent in safety. The ink composition of the present invention has sufficiently excellent antibacterial properties and is also excellent in safety, making it particularly suitable for use in such writing instruments.

[0071] The pen tip extension / retraction mechanism of the writing instrument of the present invention is not particularly limited, and examples include a cap type with a cap that covers the pen tip, a knock type, a rotation type, and a slide type.It may also be a retractable type in which the pen tip can be stored inside the barrel.

[0072] Furthermore, the ink supply mechanism in the writing implement is not particularly limited, and may be, for example, the following mechanisms 1 to 4.

[0073] (Mechanism 1) A mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow rate adjusting member and supplies the water-based ink composition to the pen tip. (Mechanism 2) A mechanism that supplies the water-based ink composition to the pen tip through a pen core having a comb groove that temporarily stores ink, an ink flow passage, and an air passage. (Mechanism 3) A mechanism equipped with an ink flow rate adjusting member using a valve mechanism, which supplies the water-based ink composition to the pen tip. (Mechanism 4) A mechanism for supplying the water-based ink composition directly to the pen tip from an ink reservoir or barrel equipped with the pen tip.

[0074] As described above, the ink composition of the present invention can be easily prepared into a low viscosity ink composition, and therefore can be suitably used in writing instruments equipped with the ink supply mechanisms (1), (2), and (3). In particular, writing instruments equipped with the ink supply mechanism (2) may be affected by foreign matter such as precipitates and aggregates caused by the growth of microorganisms, which may prevent the pen tip from functioning properly. Therefore, the ink composition of the present invention, which has sufficiently excellent antibacterial properties, can be suitably used, particularly as a water-based ink composition for writing instruments equipped with the ink supply mechanism (2).

[0075] Specific examples of the writing implement include fountain pens, ballpoint pens, calligraphy pens, etc., and the ink composition of the present invention can be particularly suitably used as an ink composition for fountain pens.

[0076] In other embodiments, the writing instrument is a marking pen, and the pen tip is not particularly limited and may be, for example, a fiber tip, a felt tip, or a plastic tip, and further, the shape may be a bullet type, a chisel type, or a brush pen type.

[0077] In another embodiment, the writing instrument is a ballpoint pen, and can be used in a ballpoint pen equipped with the ink supply mechanism (4) or a ballpoint pen equipped with an ink backflow prevention member.

[0078] <Water-based ink products> The ink composition of the present invention can be used in aqueous ink products in which the ink composition is contained in an ink storage container. Since ink contained in a storage container is dispensed from the storage container for use, the ink is exposed to ambient air more frequently, which increases the possibility of microbial proliferation and may make it difficult to maintain storage stability. Furthermore, when ink contained in a storage container with an opening is dispensed for use, the ink may come into contact with the user's skin. Therefore, the ink composition of the present invention, which has excellent antibacterial properties and safety, can be suitably used in aqueous ink products in which the ink composition is contained in an ink storage container. Furthermore, the present invention is particularly effective for water-based ink products in which the ink storage container has an opening and closing port for dispensing ink, and the ink composition dispensed from the ink storage container is filled into a writing instrument equipped with a pen core as an ink flow regulator. As mentioned above, such water-based ink products have an opening for dispensing the ink, and there is a high possibility that microorganisms will be mixed into the ink composition and multiply. In addition, because the ink is filled into a writing instrument equipped with a pen refill and used, there is a high possibility that the pen refill will not function properly due to foreign matter such as precipitates and aggregates caused by the inclusion of microorganisms, as mentioned above, and there is also a high possibility that the user will come into direct contact with the ink.

[0079] The ink storage container used in the present invention may be any ink storage container used for storing ordinary ink or for refill ink, such as a glass ink bottle or a container made of a resin such as polyethylene, polypropylene, or polyethylene terephthalate. [Example]

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] Example 1 0.05% by mass of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol 1,2-Pentanediol 2.0% by mass Colorant (CI Direct Blue 87: blue dye) 2.0% by mass Water-soluble organic solvent (ethylene glycol) 2.0% by mass pH adjuster (triethanolamine) 2.0% by mass Chelating agent (sodium ethylenediaminetetraacetate) 0.1% by mass Surfactant (surfactant with polyoxyethylene structure) 0.1% by mass Remaining ion-exchanged water A base liquid was prepared by adding 3-[2-(ethylhexyl)oxyl]-1,2-propanediol dissolved in a pH adjuster, an alkanediol having 5 or more carbon atoms, a water-soluble organic solvent, a chelating agent, and a surfactant to ion-exchanged water and mixing with a propeller. A colorant was then added to the base liquid and mixed with a propeller to obtain an aqueous ink composition for writing instruments. The viscosity of the resulting aqueous ink composition for writing instruments was measured using a B-type rotational viscometer (model: BLII, rotor: BL adapter, manufactured by Toki Sangyo Co., Ltd., sample volume: 20 ml) in accordance with JIS Z 8803:2011. Specifically, the ink viscosity at 20°C and a rotation speed of 60 rpm was 1.40 mPa·s. The surface tension of the resulting aqueous ink composition for writing instruments was measured using a surface tension meter (model: DY-200, manufactured by Kyowa Interface Science Co., Ltd., in a 20°C environment, platinum plate, vertical plate method), and was found to be 38.6 mN / m. Furthermore, the pH of the aqueous ink composition was measured at 20°C using an IM-40S pH meter (manufactured by DKK-TOA Corporation), and was found to be 9.27.

[0082] (Examples 2 to 9, Comparative Examples 1 to 4) By changing the types and amounts of raw materials, ink compositions of Examples and Comparative Examples were obtained in the same manner as in Example 1. The compositions of the prepared ink compositions are as shown in Tables 1 and 2. The ink viscosity, surface tension, and pH of the aqueous ink composition for a writing instrument of Example 2 were measured in the same manner as for the ink composition of Example 1. The ink viscosity was 1.40 mPa·s, the surface tension was 35.5 mN / m, and the pH was 9.27.

[0083] [Table 1]

[0084] [Table 2]

[0085] <Testing and Evaluation> The ink compositions obtained in the Examples and Comparative Examples were evaluated by the following methods, and the results are shown in the Table.

[0086] <Antibacterial performance test> In the ink compositions of the Examples and Comparative Examples, Escherichia coli (bacteria), Saccharomyces cerevisiae (yeast), and Aspergillus sp. (mold: BIT-resistant bacteria) were added at approximately 1.0 × 10 per ml of ink composition. 6 Each ink composition was left for 3 days and used as a test ink. Each test ink was cultured at 28°C for 7 days using a potato dextrose agar medium by the pour plate method, and the antibacterial performance was evaluated based on the number of bacteria detected. ◎: The number of bacteria detected is 1 x 10 0 less than cfu / ml. ○: The number of bacteria detected is 1 x 10 0 cfu / ml or more 1×10 2 less than cfu / ml. △: The number of bacteria detected is 1 x 10 2 cfu / ml or more 1×10 6 less than cfu / ml. ×: The number of bacteria detected is 1×10 6 cfu / ml or more.

[0087] <Safety evaluation> The safety of the ink compositions of the Examples and Comparative Examples was evaluated according to the following evaluation criteria. ◎: The 1,2-pentanediol content is 2.5% by mass or less, based on the total mass of the ink composition; the 1,2-hexanediol content is 1.5% by mass or less, based on the total mass of the ink composition; and the 3-[2-(ethylhexyl)oxyl]-1,2-propanediol content is 0.1% by mass or less, based on the total mass of the ink composition. ○: Either two of the following is satisfied: the content of 1,2-pentanediol is 2.5% by mass or less, based on the total mass of the ink composition; the content of 1,2-hexanediol is 1.5% by mass or less, based on the total mass of the ink composition; or the content of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol is 0.1% by mass or less, based on the total mass of the ink composition. △: Satisfies only one of the following: the content of 1,2-pentanediol is 2.5% by mass or less, based on the total mass of the ink composition; the content of 1,2-hexanediol is 1.5% by mass or less, based on the total mass of the ink composition; and the content of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol is 0.1% by mass or less, based on the total mass of the ink composition. ×: The 1,2-pentanediol content is 2.5% by mass or less, based on the total mass of the ink composition; the 1,2-hexanediol content is 1.5% by mass or less, based on the total mass of the ink composition; and the 3-[2-(ethylhexyl)oxyl]-1,2-propanediol content is 0.1% by mass or less, based on the total mass of the ink composition.

[0088] <Written test> The ink compositions of the Examples and Comparative Examples were poured into polyethylene ink cartridges, which were then attached to a fountain pen manufactured by Pilot Corporation (product name: Custom 74 (FKKN-12SR), pen type M), and writing was carried out on writing paper A. The handwriting was visually observed and evaluated according to the following evaluation criteria. ◯: Good handwriting was obtained without smearing. △: The handwriting was smudged. ×: The handwriting was severely blurred.

[0089] <Drip resistance test> The ink compositions of the Examples and Comparative Examples were poured into polyethylene ink cartridges and attached to a fountain pen manufactured by Pilot Corporation (product name: Capless (FCN-1MR), pen type M). The fountain pen was then left to stand under reduced pressure (70 mmHg) for 1 minute, and leakage of ink from the nib was observed and evaluated according to the following evaluation criteria. ◯: No dripping of the ink composition from the pen tip occurred. ×: Dripping of the ink composition from the pen tip occurred.

[0090] Furthermore, when the ink composition of the example contained in an ink storage container (a glass bottle with an opening and closing opening) was repeatedly filled into a fountain pen and used for writing, good handwriting with little smudges was obtained.

[0091] From the above, it has been found that an aqueous ink composition for a writing instrument comprising water, a colorant, an alkanediol having 5 or more carbon atoms, and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol exhibits excellent storage stability due to its high antibacterial properties while fully maintaining good writing performance, and is also highly safe.

[0092] As described above, the first embodiment of the present invention is The aqueous ink composition for writing instruments comprises water, a colorant, an alkanediol having 5 or more carbon atoms, and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol.

[0093] A second embodiment of the present invention is the aqueous ink composition for a writing instrument according to the first embodiment, wherein the content ratio of 3-[2-(ethylhexyl)oxyl]-1,2-propanediol to the alkanediol having 5 or more carbon atoms is less than 1 by mass.

[0094] A third embodiment of the present invention is the aqueous ink composition for a writing instrument according to the first or second embodiment, further comprising an isothiazolinone compound.

[0095] A fourth embodiment of the present invention is a water-based ink product comprising an ink storage container containing the water-based ink composition for a writing instrument according to any one of the first to third embodiments.

[0096] A fifth embodiment of the present invention is a writing instrument containing the aqueous ink composition for a writing instrument according to any one of the first to third embodiments. [Industrial Applicability]

[0097] The aqueous ink composition for writing instruments of the present invention can be used for various writing instruments such as fountain pens, ballpoint pens, brush pens, calligraphy pens, various markers, etc. In particular, since the aqueous ink composition for writing instruments has improved storage stability and safety, it can be suitably used as an ink composition for writing instruments that are often exposed to the outside air, such as fountain pens and dip pens.

Claims

1. A water-based ink composition for a writing instrument, comprising water, a colorant, an alkanediol having 5 or more carbon atoms, and 3-[2-(ethylhexyl)oxyl]-1,2-propanediol.

2. 2. The aqueous ink composition for a writing instrument according to claim 1, wherein the content ratio of the 3-[2-(ethylhexyl)oxyl]-1,2-propanediol to the alkanediol having 5 or more carbon atoms is less than 1 by mass.

3. 3. The aqueous ink composition for a writing instrument according to claim 1, further comprising an isothiazolinone compound.

4. 10. A water-based ink product comprising the water-based ink composition for a writing instrument according to claim 1 housed in an ink storage container.

5. A writing instrument containing the water-based ink composition for a writing instrument according to claim 1.

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